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Articles from 1997 In October


Scientific Molding, Part II: Cooling


This is the second in a three-part series on scientific molding. THe first part, which appeared int October 1997 issue of IMM, discussed the filling stage of molding and included some background and history on the scientfic molding process. This month, we focus on the cooling stage of the process, and how to optimize it to help presses and parts run more efficiently.

Sidebars:

As much attention as one might like to give the filling stage of the molding cycle, the fact is that it is only a fraction of the overall process. Most of the cycle, usually about 90 percent, is spent packing, holding, and cooling the part or parts. Optimizing cooling provides parts of consistent quality and consistent weight.

The tendency, says John Bozzelli, one of the molding industry's leading advocates of scientific molding, is to overfill the part during injection. "If the part is filled on first stage (boost) you waste energy, cannot control velocity, even on closed loop machines, and will produce flashed and short parts as lots change," he says. This leads to molded-in stress and other structural defects. Bozzelli, the principal of IM Solutions, his Midland, MI-based consulting business, often works with Ashland Chemical Co.'s General Polymers Div. The two are among several in the industry trying to make molders more efficient and competitive by using scientific molding, also known as systematic molding or Decoupled molding.

As discussed last month in IMM, the goal during the filling stage using scientific molding is to leave the part about 1 percent short (99 percent full). This gives the second stage the "wiggle" room it needs to properly fill out a part. As with the filling stage, the goal with cooling is to derive a set of parameters specific to the mold and material that can be transferred to any other capable machine. These "universal" parameters for cooling include pack and hold time, pack and hold melt pressure, and mold temperature.

Note: The process of leaving a part 99 percent full involves optimization of injection velocity, injection pressure, and transfer position. Please see the October issue for details.

Cases in Point Revisited

Last month we examined the filling stage optimization of two presses at two different molders. The first molder is in South Carolina, molding a 4-by-4-inch gun shot primer tray in an eight-cavity hot runner mold. The tray has 100 evenly spaced holes, each about .25 inch deep. The material is a precolored black polypropylene. Intrusion had been used on this gun shot primer tray during the cooling stage to eliminate a sink that developed at the center of the part. Bozzelli and McDonnell turned off intrusion, increased pack and hold presure, and ran a agate seal test.

When we last left the tray, Bozzelli and General Polymers (GP) technical service representative John McDonnell had built an on-machine melt rheology curve for the material, selected a fill time based on the curve, and determined the transfer position to provide a part about 99 percent full. Cooling then begins on second stage.

This particular part had been using intrusion during the cooling stage to eliminate a sink that developed at the center of the part, a sink exacerbated by the suction cups on the part takeout robot. To start, Bozzelli and McDonnell turned off intrusion and increased pack and hold pressure in 200-psi increments until the part looked full. Next, they performed a gate seal test to determine the optimum pack and hold time.

The gate seal test tells at what point the plastic in the gate cools enough to provide a seal against plastic backflowing out of the part and into the runner or sprue. If parts are run without the gate freezing, the process is less robust. Plastic is compressible and acts as a compressed spring to push plastic back into the runner if the gate is not frozen when second stage pressure ends or drops off. Says Bozzelli, "Parts may have inconsistent dimensions, quality, and/ or weight. Many molders are running multicavity tools with some parts seeing gate seal and others not. Then folks wonder why identical steel cavities produce nonidentical parts."

Sealing the gate also means that melt in the mold will not back into the gate before it has hardened; such an action can produce parts of inconsistent weight and quality if other processes are not tightly controlled. While some molders may wish to mold with gate seal, there are instances when it is not preferable. Either way, a molder should at the very least know at what point the gates seal for each mold for each material used. Although the gun shot primer tray mold uses hot runners that theoretically never actually seal, the melt will reach a point where it is cold enough to prevent the material from backing out.

To do the gate seal test, Bozzelli left the pack and hold pressure constant and incrementally reduced the pack and hold time during a series of cycles, careful to make sure cycle time remained consistent throughout. He started at 6 seconds and reduced the time in 1-second increments to a 1-second pack and hold time. All eight parts from the mold were collected after each cycle and weighed together. Results are presented here.

Results of the gate seal test
performed on the gun shot primer tray.
Pack and hold time
(seconds)
Weight
(grams)
1 136.73
2 139.31
3 140.52
4 141.05
5 141.46(gate sealed)
6 141.46

Gate seal is achieved when the total weight stops increasing - that is, no unmelted material is backflowing through the gate. In this case, gate seal occurred at 5 seconds. Bozzelli and GP like to set the pack and hold time a little bit longer than the gate seal time - about 10 percent longer (or more) in most cases - to accommodate any variables that might cause the gate to seal later than usual. In this case, they chose 6 seconds. This pack and hold time also eliminated the sink at the center of the parts.

Because these parts must comply with quality control standards, Bozzelli and McDonnell then produced parts with the pack and hold time set at 6 seconds, with lower and higher pack and hold pressures. These samples were marked and sent to the quality control department in the mold shop to determine which pressure setting produced the most acceptable parts.

The goal of Bozzelli's analysis of the mold and part was to reduce the cycle from the original 21.3 seconds to the quoted cycle of 19 seconds. By optimizing the filling and cooling, he reduced the cycle to 18.3 seconds, saving the molder about $25,000 in machine time, given a 4500 hour/year schedule and a $40/hour machine recharge rate. Says Bozzelli in the end, "Now, we've taken some time (about 2 hours) and wasted a little material, but it will more than make up for itself in the time and energy saved."

Thermal Consistency

At the molder in Wisconsin, Bozzelli and GP senior technical service representative Alan Larsen demonstrated how providing thermal consistency to the material can save money. Like many molders, this shop was dominated by manual labor. On one press molding a pump housing with six manually placed inserts, Bozzelli noticed that the mold closed as soon as the operator situated the inserts and closed the safety gate.

One of the variables that affects material viscosity is residence time. The way the job was configured, the next cycle didn't start until the gate was closed. If the operator took more or less time than usual placing the inserts, material viscosity would change, causing the press to produce parts of varying quality. The rule is simple: the higher the viscosity, the slower the material moves; the slower it moves, the higher the viscosity gets. If you can stabilize viscosity you can stabilize part quality

Bozzelli and Larsen set the mold open time to just higher than average for the operator. Then, after the operator placed the inserts and closed the gate, the clamp did not close until the set time was reached, about 2 seconds after the gate was shut. Although it flustered the operator at first to close the gate and not see the mold close, Bozzelli's adjustment brought consistency to the cycle, providing the same residence time for each shot. "Total part count will probably decrease because of what I did, which annoys the bean counters," says Bozzelli, "But consistent viscosity of material produces better parts and reduces the scrap rate. In the long run, they save money. It's like making toast to the same brownness - consistent time is critical."

Mold Cooling

One other check commonly performed by Bozzelli and GP is of water flow through molds. Checking water lines is simple and sometimes wet, but again often ignored by many molders. All it requires is a flow meter. At the Wisconsin molder, water flow in most lines was good - more than 2 gal/minute - but Bozzelli and Larsen did encounter one water line that was completely blocked. Actually, the channel in the mold to which the blocked line ran was an old one, like a dead end road. The line was blocked because it went nowhere. This wasn't detected until Bozzelli checked it with the flow meter.

Other cooling water characteristics to watch are pressure loss between inlet and outlet, temperature differential, and water quality. Generally you need to see a pressure differential between inlet and outlet of the tool of 30 to 35 psi to drive the right amount of water through the channel. Lots of water must flow through the channel to obtain turbulent flow, which will optimize heat removal. "Temperature is not as critical as driving the maximum volume through the channel. Slow flow due to a plugged line can kill a process," Bozzelli notes. Plugging can be caused by Teflon tape, rust, sand, or scale buildup.

Bozzelli reports that scale buildup of as little as .0625 inch can reduce cooling efficiency by as much as 40 percent. Make sure your cooling water is properly filtered to remove rust, dirt, and other buildup. The temperature differential between inlet and outlet water should be at or below 4 deg F for best cooling.

All of these factors, if not properly maintained, can lead to inefficient and insufficient cooling of parts. One good way to monitor mold temperature is by use of an infrared camera. It picks up a lot of the subtle temperature variations from cavity to cavity and core to core to highlight hot spots in the mold. This is a favorite Bozzelli tool, and will be the topic of next month's final installment on scientific molding.

The Universal Setup Card

In his effort to make molding a process that is machine independent and less subject to injection machine variables, John Bozzelli has constructed the universal setup card, a list of data and parameters that focus on the material and the mold, not the press. These are parameters that can be derived using the scientific molding method (also known as systematic or decoupled molding). They allow you to transfer the mold and material to another machine, without loss of part quality. They focus on plastic variables, not machine variables. The universal data include:
  1. Mold number, number of shots to date, part name, customer, date, molder's name, and any other information your plant may require.
  2. Fill time for a part 95 to 99 percent full.
  3. Weight and picture of part 95 to 99 percent full.
  4. Transfer volume, transfer position, or cavity pressure (time and hydraulic pressure transfer modes are not recommended).
  5. Nozzle melt pressure range for different lots at transfer volume, position, or cavity pressure.
  6. First stage set melt pressure (nozzle); this is first stage set pressure times the intensification ratio.
  7. Cycle time.
  8. Quoted cycle time(s).
  9. Gate seal time.
  10. Pack and hold time.
  11. Pack and hold melt pressure.
  12. Shot size in volume.
  13. Mold temperature, cooling channel map.
  14. Water flow diagram, with gallons/minute of each channel, temperature of water in and out, and water pressure in and out.
  15. Screw run time (average).
  16. Mold open and closed time, cure time, or cooling times.
  17. Melt temperature via hot probe.
  18. Nozzle tip length, diameter, land length, radius, and type.
  19. Hydraulic pressure vs. time response curve.
  20. Cavity pressure integral at the gate and end of fill.

The Load Compensation Test

There is an easy test you can perform on your machine to see just how repeatable it is, and how well it controls pressure in the mold. The theory behind the load compensation test says that once you set a fill time, the machine should be able to control itself to meet that time whether shooting into a mold or shooting into the air (no resistance). By John Bozzelli's standards, that time shouldn't vary by more than .04 second.

At the Wisconsin molder, Bozzelli demonstrated the load compensation test on a late-1960s model 125-ton press molding a spring housing from ABS. After optimization of the fill stage, a standard shot was made into the mold, with a fill time of 2.19 seconds. Then, the mold was opened and a shot was performed into the air. This one took 2.12 seconds. Although the .07 differential was significant by Bozzelli's standards, he says "the difference is good for a machine of this age."

At the South Carolina molder, a shot into the mold took 1.03 seconds at 1420 psi of hydraulic pressure. Into the air it took .99 second at 474 psi. If you record the hydraulic pressure each time, there's a formula (developed by RJG's Rod Groleau) you can use with this data that gives you the actual load differential per 1000 psi of hydraulic pressure.

Bozzelli says he likes the load differential to be less than 5 percent/1000 psi. Anything between 5 and 10 percent can be lived with but will have to be addressed eventually. Anything above 10 percent, he says, "you must do something to fix it right away."

Top 10 questions that send Bozzelli over the edge

Last month we described in some detail the passion, exuberance, and enthusiasm with which John Bozzelli carries the message of scientific molding. Never one to embrace "shortcuts" or "quick fixes" in a molding shop, Bozzelli is easily agitated, antagonized, and driven to animation by questions that suggest a molding machine should or could be operated in a manner that is less than efficient or even logical.

Kendall Healthcare Products, based in Ocala, FL, is a molder that has benefited from Bozzelli's expertise; it is also a molder that has apparently caught glimpses of Bozzelli's impatience with inefficiency, impracticality, and sloth. Matt Lofgren is a molding supervisor at Kendall and wrote this list of 10 questions likely to make John Bozzelli blow.

10. When our Brody Ring wears out, is it possible to grind a groove in it to fit a smaller Brody Ring, or should we just replace it?

9. How many flights on our screw can be broken off before we should consider trading it out for a screw with fewer missing flights?

8. How fast should we turn the screw to gain shear heat to compensate for bad heater bands?

7. Most of our molds need negative pressure units to stop all of the leaks in the cores/cavities, but we still have some that leak badly. Is it possible to tie two negative pressure units together to solve this problem?

6. What's the highest injection pressure to which we can safely go to compensate for a clogged filter nozzle?

5.When running a mold in a press that has too little clamp tonnage, what is the best kind of knife to use to trim the flash?

4. Our presses will only allow nine eject strokes. Would it be better to put a full-time operator on the press, or call the factory to have them retrofit our machine to add another digit for ejection?

3. Is kitty litter a better alternative to "floor dry" around our machines? When sucking up all the oil from the floor and sump to put back in our machines, the "floor dry" tends to float on top of the reservoir, whereas the kitty litter tends to sink. Which one is better?

2. Our machine has one broken tiebar. How do we estimate how many and what thickness of shims to install under the corner of the mold base to keep it from flashing? Or, how much should we loosen the opposite tiebar to compensate?

1. When molding with the scientific or decoupled method, is it better to use balsa wood and super glue when plugging off cavities, or just solder and super glue?

The Troubleshooter, Part 18: Dimples in overmolded TPR

This article continues our series of troubleshooting reports from one of the leading on-the-spot problem solvers in the molding industry. Bob Hatch is manager of technical service and customer support for Prime Alliance, the Des Moines-based resin distributor. Before his present assignment, Bob managed a molding oeration for 25 years.


Figure 1. Dimples mysteriously began to form on the overmolded tread portion at the gates of this part. Nothing had changed on the molds, the nozzle checked out, sprue bushings hadn't changed, runners and gates were the same, vents were still self-cleaning, and the material was the same. What happended?

A customer called with a complaint about dimples at the gates of a glass-filled polypropylene roller overmolded with a thermoplastic rubber material. The problem was with the gates on the overmolded part. I knew the part well. I had helped the company with the design of the two molds several years ago. We had used a glass-filled polypropylene to mold the hub and a 40 shore A TPR to mold a tread on the circumference of the hub in a second mold. Both molds were eight cavities and each had a balanced runner feeding material into the cavities (Figures 2 and 3).

Figure 2. The roller's humb is molded from a glass-filled polypropylene, then overmolded with the TRP tread. A ring gate is used on the hub mold to keep the parts a round as possible.
Figure 3. Horseshoe runners for tread overmold gate into the hub from two points that are opposite each other. The single subgate of .125 inch was changed to two subgates, side by side, of .090 inch each.

We had used a ring gate on the hub mold to keep the parts as round as possible, and it worked well. For the tread we used a horseshoe runner to go around the outside of the hub and gate into the hub from two points that were opposite each other.

Everything worked well except for the gates for the TPR part of the molding. The size of the subgate we had to use for volume considerations was causing a chunk of the material to be pulled out with the gate when the part ejected. So we changed the single subgate of .125 inch to two subgates, side by side, of .090 inch each.

It turned out to be a blessing in disguise for us after all, because the two side-by-side subgates actually did a better job of filling and packing than the single subgate, plus the smaller gates didn't pull a chunk of the material out with them.

What Had Changed?

We had two molds that have been running well for four or five years, and now the customer says he is getting a sink hole or dimple at the gate areas in the tread portion of the part. I reviewed both molds to see if anything had changed since I last worked with them. I looked to see if the company was using a nozzle with an orifice that was smaller than it should be, which would change the machine's ability to fill and pack the parts correctly. But the molder had drilled out a nozzle to use for each mold, which were still being used, so that ruled out the nozzle as a problem.

Next I looked to see if the sprue bushings had been changed and they had not. I looked to see if the gates and runners were different than before and they were still like we left them. I also wanted to be sure some overzealous toolmaker hadn't tried to reduce the size of the runners or gates to keep from generating extra regrind or to keep from slowing down the cycle. Nothing had been changed. Then I looked at the runner and part venting to see if the vents had been hobbed shut or were full of material residue. Nope, we had made the vents self-cleaning originally and they were still working great.

What was left to look at, the material? The molder was still using the same original materials, and since we had optimized the tooling, we could pretty much be assured the slight differences in lot-to-lot variations of the material would not cause us much of a problem in filling and packing either part.

All that was left now was to look at the setup sheets to double check the processing conditions to see if any changes had been made. The heats, speeds, pressures, mold temps, backpressure, and screw rpm were all pretty close to what they should have been.

Next I went out to the molding machine and watched the mold that puts the TPR treads on the hub insert. I like to watch the screw go forward and visualize the material being injected into the mold and see what is going on with the cushion and whether or not it holds properly.

The Slipping Cushion

I like to use a medium to medium/slow injection speed for thermoplastic rubbers, even urethanes for that matter, and this was still a slow injection speed, which is good. The cushion was about .25 inch, which was what we wanted, but during the hold pressure portion of the injection sequence, I noticed the cushion slipped to about .125 inch. Something was wrong there. Either the check valve was leaking or extra material was being pushed through the gate after the inject, pack, and hold pressure sequence was finished.

I like to use the hold pressure in this manner to fill voids as they form on thick-walled parts, but this wasn't a thick-walled part. It had some thick to thin transitions but not the traditional thick walls and definitely not at the gate.

I turned the hold pressure down from 400 psi to 200 psi, and the dimples at the gates went away. We watched several cycles and the problem did not return. I went back to the setup sheet to see why I had not noticed the problem there. Then it hit me; we are used to seeing the hold pressure being about half of the inject pressure. But in this case the hold pressure was originally set at about a quarter of the inject pressure.

No doubt one of the molding technicians had accidentally raised the hold pressure, thinking it was too low, and caused the dimples to form at the gates. The dimples probably didn't show up until the next full shot and by then he had walked away to get a cup of coffee. The operator probably didn't notice the problem until the quality control person spotted the dimples, so the molding technician did not relate the dimples to his change in the hold pressure.

It is pretty easy to miss a problem like this by just looking at the setup sheet. You have to watch the machine run to get a feel for the plastic injecting into the mold, check the cushion and see what it does, watch the screw recover, and then watch it all over again.

From what I've seen, this problem pretty much shows up only on the soft materials, such as flexible PVC, thermoplastic rubbers, thermoplastic elastomers, and the softer polyurethanes. The customer made the changes to his setup sheet, threw the old ones away, and vowed to use only master copies of the setup sheets so this kind of problem would not bother him again.

The Business of Molding #19

It is important to understand how your customers view you and what kinds of games they can play. It's equally important to know how you'll respond. Bill Tobin of WJT Assoc. talks about these relationships in a third installment, part of his ongoing series on business relationships of custom molders. The first part appeared in IMM's August 1997 issue; the second part in September 1997.

OEMs today are seeking a small but highly loyal group of suppliers. Hitching your wagon to a large client may seem like an invitation to abuse, and there are many examples of this out there. But the buyer's job is to get the best deal he can with the least amount of trouble. Your job is to maximize your profit and minimize your losses. These two philosophies are not necessarily in conflict with each other.

Most vendor evaluations are an in-depth look to see if a fit exists. Today, the auto and computer industries are demanding more of their suppliers (both in terms of using electronic technologies and statistical reporting) than they themselves are capable of doing in-house. While this may seem hypocritical, there is a logic to it. They are simply preparing for a massive downsizing.

In the future, most big- name product producers will be designers and marketers. They will do little, if any, manufacturing. This capability allows them to easily upgrade their systems to work with suppliers, and they will abandon obsolete systems that related to their own in-house divisions and plants. Some clients require molders and moldmakers to have systems like their own MRP and CAD systems. Of course, another equally large client with a different system, different languages, or custom configurations can require that you use its systems and equipment.

Small businesses are now the targets for big business. Why? Because they let themselves be targets. Too many small companies do business with those listed in the Fortune 500 and feel powerless. Partially this is our own fault. We think because they have the money, clients can make whatever rules they want and we must abide by them. By giving them this power we become the willing victims of being squeezed out of fair profits.

Many custom molders are highly intimidated by the customer's threat of pulling jobs to have someone else mold the parts. However, there is a simple truth to be considered: In today's mentality of low inventories and JIT deliveries, the pain and agony of relocating any custom job can only be justified if it offsets the pain and agony of leaving it where it is. If a customer is going to pull a job, he'll do it, and there is little to be done to stop it. If you fall for the bluff that the tools will be pulled if you do not lower the price, you are only showing the customer he can blackmail you into further concessions in the future. If you go out of business, your customers will just take their tooling elsewhere. Here are two more games that are played.

Vendor Evaluation

The Scenario: The client's buyer and his engineering team come to you to do their evaluation. They are very impressed with your operation, your quality, and your delivery performance record. The buyer takes you aside and tells you he will very shortly be going to electronic purchase orders, releases, and payments, and he will also be releasing dimensionless databases as part designs. While you have some computer equipment, he says in order to stay an approved supplier (or become one) you will have to do some significant upgrading of your systems as well as training your personnel. He also states his company is instituting a program called "Q/A-SPC 2000." (This is CorpSpeak for "Quality Assurance, Statistical Process Control for the next century because we don't know how to do it.") He dumps a 50-page pamphlet on your desk that looks a lot like a combination of the International Standards Organization (ISO 9000) requirements and a certification program for your company in SPC.

The Response Your Client Anticipates: You look at this program (with which you know the company itself couldn't comply), the business, and the profit you have had (or anticipate) from this customer, and ponder your decision. The buyer expects that you will pony up for the cost of equipment, training, and all other secondary costs to meet these requirements to get the job.

Your Counter: If your IQ is higher than your shoe size, you will quickly figure out you are being asked to invest a major sum of working capital for something that has a convenience factor payback for your client. However, he also knows this will allow him to get better deliveries and lower prices down the road. Agree totally with the buyer about the program. Perhaps you should purchase new computer equipment. Ask to be "paid to play," to make sure you are completely familiar with his required MRP system, CAD systems, and other electronic documentation transfer systems.

Require the client to provide the software, secondary firmware (dedicated telephone lines, encrypted modems, etc.), training of your personnel, upgrade training, and new releases of the programs as they come out and as your personnel turns over. If possible, get into his master purchasing program so that you can buy computer equipment at the prices he is buying, instead of having to pay street price. This should only be done with the understanding that it is tied, in writing, to more business (and more profit) for you both.

Your Last Move: Show how linkage to more business, better engineering, tooling modifications, and new jobs could substantially impact the cost of parts. Do not make the concession to absorbing the entire cost, because your investment has a payback only if it works with his system and is tied to a guarantee of work.

Make Dust or Eat it

This is a variation of the vendor evaluation game. It has two scenarios:

The First Scenario: You are trying to become a new supplier to the client. Assume that you have played the vendor evaluation game. You now have the systems in place, the folks trained, and all is operating with a good degree of success. Now is the time to leverage this new-found capability to new customers.

A normal plant visit follows your initial sales call. Here you take the opportunity to point out that you have electronic capability, and many other vendors do not. Show him the advantages of immediate data transfer on releases of orders, or your ability to look at his market projections so that your response time can be quicker. Also show that through data transfer and e-mail you can assist/analyze his designer's CAD drawings and offer added value by eliminating problems early in the design phase. With all these capabilities in place, it will be difficult for him to turn you down.

The Second Scenario: You are trying the leveraging game with another division of your existing client's company. Since most companies use corporate systems, another division's system will be almost identical to the one for which you are approved. This leverage allows you to become a preferred supplier with a minimum of work.

The Response Your Client Anticipates: There are two kinds of suppliers: those who make dust and those who eat it. Anything that makes the job of the buyer easier will enhance his status and allow you to make more profit. Other secondary costs to meet these requirements are a good investment for the buyer to make in you. There should be very little work necessary to become approved if you are "world class."

Your Counter: Present your credentials, show off the plant, buy lunch. The last question you should ask is, "If I am equal or better than your existing suppliers, what does it take to become a preferred supplier and quote on some jobs?"

Your Last Move: Shut up and listen. Some folks are so in love with their existing supplier base they will stall their own management by making excuses why their buddies will not or cannot upgrade. If this is the case, you are kicking a dead horse. If the buyer is truly interested, you'll get the business. There have been many cases in which a molder came to a large potential client and said, "Let us make your manufacturing problems on this product go away," when the client's original thinking was to ship it off to China or Malaysia. However, being electronically linked and nearby is usually much more tempting than dealing with 11 different time zones, multiple languages, and a completely different culture.

Business survival is a game. There are rules, tactics, players, strategies, and goals. As anyone knows who has stepped up to a roulette table or craps game in a casino, not knowing the rules is a quick way to separate you from your money.Assoc.

Bill Tobin will conduct a three-day seminar in January that revolves around game strategy and other issues related to the business side of injection molding. This article is adapted from his new book, "Survival Techniques for the Small Manufacturer."

Ford has a larger-yet-thinner idea

How did Ford reduce bumper fascia weight by 5 lb, wall thickness by 1.1 mm, and still meet the company's own 5-mph impact standard? "In a word, teamwork," says Jim Krebs, product development engineer for Visteon Automotive Systems (formerly Ford APO). Together with material suplier Montell, moldmaker Paragon Tool and Die, and molder Polycon Industries, Ford designers produced the 2.4-mm fascia for this 1998 Windstar van, meeting cost, performance, and safety goals.

Thin-wall designs have long been the status quo for portable electronic device housings, parts that rarely exceed the size of a notebook computer. On the opposite end of the dimension spectrum, automotive manufacturers wouldn't mind taking out weight, cost, and cycle time by employing the same concept. Large parts in particular show significant reductions in all three of these categories, even when wall thickness is reduced by a mere 10 percent. And where are there more large molded parts than on a vehicle?

Although safety-critical automotive fascias hardly seem likely candidates for wall thickness reduction, a concerted effort of the Visteon design department, its Tier One molder, resin supplier, and toolmaker produced results that underscore the benefits of thin-wall molding for large parts. (In case the name Visteon doesn't ring a bell, see "What's in a name?" below.) Their collaboration reduced weight of the TPO fascia for Ford's 1998 Windstar by 5 lb, making it the lightest bumper in the minivan class, and produced a system that passes a 5-mph impact test. This group endeavor exemplifies a current truth: making technological leaps in molding today requires simultaneous input from all parties involved.

Jim Krebs, product development engineer for Visteon and leader of the project, explains that Ford selected the Windstar platform for its initial thin-wall design attempt for a very good reason. "Ford felt Windstar had become synonymous with safety, a key issue for minivan buyers," says Krebs. "We wanted to carry that tradition forward, creating a thinner walled fascia with no safety compromise."

In addition to lighter weight and equivalent safety, the team also aimed for Class A surface quality, high stiffness, paintability, and a more cost-effective solution. By reducing the amount of material per bumper by 25 percent, raw material cost savings contribute to this latter goal. Less material also means shorter cycle times. According to Bill Ferris, product engineer for molder Polycon, the cycle time reduction is significant. "And the high-flow TPO allowed us to use 40 percent lower injection pressure and 30 percent lower hold pressure," Ferris adds.

Table: Material for a Thin-wall Fascia
Melt flow, 10 g/minute 15
Specific gravity .97
Flexural moduls, psi 195,000
Tensile Strength at yield, psi 200
Notched izod impact at 23C, kJ/sq m 25
Heat deflection temperature at 66 psi, deg F 203
CLTE x 10-5, deg F 2.9
Mold shrinkage, tool mils/inch 7.0
Mold shrinkage, afterbake mils/inch 9.0

Speaking of material, those issues were handled by Mike Barrera of Montell Polyolefins, who suggested Hifax HSBMF762, a high-strength TPO created with Catalloy technology. Highlights from the property table below include a low coefficient of linear thermal expansion for dimensional stability, a melt flow index of 15 for filling thin walls, and a 40 percent higher tensile strength than material used for the previous thicker fascia. The new TPO also features a flexural modulus of roughly 200,000 psi to provide sufficient stiffness at the reduced thickness. "Mathematically speaking, stiffness depends on thickness in plastic part design," says Krebs, "so we needed to compensate for the lack of thickness with this material."

Polycon currently molds the fascias on four Klockner-Windsor presses - two 2000-ton machines for rear fascias, and two 3000-ton machines for front fascias. Tools for the parts contain sequential valve gates with six drops and employ a hot runner. Ken Crawford, Paragon Tool & Die, estimates that adding sequential gating increased tool cost by about $30,000, but Ferris confirms this cost was more than offset by the ability to control knit line locations.

"In the past, we had to employ a cut-and-weld process until gate locations were correct," says Ferris, "which added six weeks to the production schedule. With sequential valves, we can change process parameters in 1 or 2 hours at the press to adjust knit line locations." - Michelle Maniscalco

What's in a Name?

Several months ago, when this project was completed at Ford's Engineering Test Facility in Dearborn, MI, the components divisions were known as Ford Automotive Products Operations. But at the Frankfurt Motor Show in mid-September, Ford announced that it was changing the name of this group to Visteon Automotive Systems. Charlie Szuluk, president of Visteon, confirms that the newly named enterprise will be a separate Ford company, with each of 24 strategic business units accountable for its own profit and loss. Like its closest competitor, Delphi (owed by GM), Visteon will solicit non-Ford business; in fact, the global marketing plan aims to expand this segment to 20 percent of sales.

Visteon, a name derived from Latin and meaning both visionary and timeless, will contain seven major divisions focused on design, development, and delivery of fully integrated systems. These include chassis, climate control, electronics, exterior, interior, glass, and powertrain control. Product lines consist of 27 systems, 10 modules, and 64 components.

Market Focus: Medical Products

You know a trend is here to stay when it gets its own acronym. Take the medical market, for instance. A year ago, we were hearing rumblings of demand and designs for surgical instruments that got in and out of the body with as little physical damage as possible. You can't call it noninvasive surgery because surgery by definition is invasive - and the medical technology commonly seen on Star Trek is not yet with us. Instead, you can call it minimally invasive surgery. But, if you're in a rush, just use MIS. It shows you're on the cutting edge.

Ticona's marketing manager for healthcare, Barb Canale, says MIS demands product miniaturization without sacrificing material strength or durability. The ultimate goal, she says, is to get people back on their feet faster and out of the hospital sooner. This not only makes patients happy, but insurance companies as well, where an extended hospital stay is the bane of medical managers everywhere. Miniature here means walls as thin as .004 inch, and diameters of 5 to 8 mm (formerly 12 mm) over distances of 5 to 14 inches.

Canale says there's a concurrent demand in the surgical market (dental as well) for plastic products that can be reused. Such products must be molded from materials that can withstand some of the standard sterilization procedures, used not only in the U.S., but throughout the world. Canale lists such sterilization procedures as steam, gamma radiation, EtO, and, in France, a 1-hour bath in a 275F sodium hydroxide solution. "All of the rules are changing," Canale says.

The implication here is that staying nationally competitive is becoming blasZ; products must be able to pass muster around the world, putting greater demands on your products and materials. Canale reports Ticona's had a fair amount of success in this arena with its Vectra liquid crystal polymer, which she says, "flows like water," maintains its dimensions at thicknesses down to .004 inch, and reportedly does not degrade under a variety of sterilization systems.

If you are going global, Canale also says to watch for regional variation, where instruments designed for one country may not be suitable for another. "Instruments are being refined and customized to a specific region," she says. "What works in the U.S. may not work in Korea."

No surprise here. As is the trend in most markets (except building and construction), polypropylene is the most used material. In a relatively uncommon second place is polystyrene. Data is courtesy of the Plastic Buyer Profiles database, compiled by Phillip Townsend and Assoc. (Houston).

Latch lock works from inside

At Cycles Inc. in Sterling, MA, 23 presses, all less than 150 tons, make a variety of pharmacological disposables, cosmetics parts, automotive products, and some computer and business equipment parts. Recently, says vice president Augie Bates, he had to mold a poly-propylene insert for a metal shell for a perfume container. At .875 inch in diameter and 1.5 inches long, it has internal ribs that must be accurate to within plus or minus.002 inch.

Because of the way the mold is configured, says Bates, he couldn't hang any latches or stripping mechanisms off the side of the tool. Looking for a latch to fit in the mold, Bates gave the Precision Latch Lock a try, a simple latch and lock system designed for use in stripper, three-plate, and double ejection/collapsible core molds. "The nice thing," says Bates, "is that the latch lock is completely internal. Nothing hangs outside the mold."

This latch lock, currently manufactured by Precision Plastic Tool in South Windsor, CT, is a three-piece tool that consists of a latch of spring steel, a lock that fits in and is held by the latch, and a pin that runs through both and releases the lock from the latch when the third plate opens. The latch lock installs internally in the mold, and cavities for the device can be machined simply, either when the tool is constructed, or later. Pulling action on the latch lock is inline, with no side loads or side actions; neither the latch nor the lock extends beyond the parting line.

The latch is typically installed in the B side of the mold; the lock is installed in the stripper plate; the pin is installed in the A half of the mold. When the mold is closed, the latch holds the tip of the lock in its spring-loaded fingers; the release pin runs through both. The length of the pin determines the distance the mold opens before the stripper, or third, plate opens. The end of the pin is tapered and when it reaches the spring-steel fingers of the latch, it opens the latch, releasing the lock (see diagrams).

In these three views of a stripper plate mold, the figure above shows the mold closed position, the figure above right shows the mold open position, and figure right shows the stripper open position.

Bates has been using the Precision Latch Lock for four years in molds that average about 50,000 shots per year. He reports no problems to date and says the only maintenance he performs is an occasional oiling of the components. Of his 400 molds, Bates says about 10 have such latches.

At Innovative Mold and Machine in Chicopee, MA, president Steve Young echoes similar sentiments, but for different reasons. "It was a nice alternative," he says. "It was internal, which means we didn't have anything hanging off the side." Young says he likes to use Master Unit Die frames in the mold; the internal latch lock system allows him to change out MUD units at will without worrying about the latch system. "It's a good alternative to allow us to use a different style of mold frame," he reports.

Of the 25 or 30 molds he built in the last year, Young estimates he used the latch lock in about half. He's also gotten creative, in several instances telescoping the pin, or modifying it to move the stripper plate and for transferring parts. Like Bates', his molds average about 50,000 shots. He does note that the latch lock is more expensive than external latching systems he's used, but that "the internal convenience outweighs any cost difference."

The Precision Latch Lock is currently manufactured and sold by Precision Plastic Tool. Roehr Tool (Hudson, MA) is involved in marketing the latch lock for Precision Plastic Tool. Paul Catalanotti, president of Roehr, says you can look for an externally mounted version of the Precision Latch Lock by early 1998.

Ceramic feedstocks simplify design, molding problems

Thanks to a chemical gel, one of the barriers to widespread ceramic injection molding recently became a thing of the past. While the basic molding technology has been in place for more than 30 years, feedstock materials haven't exactly been easy to use. For one, removing the polymer or wax binders can be time consuming. For another, this debinding step produces a brittle as-molded part.


Parts molded from ceramics with Allied Signal's new binder system span a broad range of markets, from fine porcelain cups to zirconia oxygen sensors.

Instead, imagine molding ceramic parts that gingerly drop into a bin as they are ejected from the mold, stiff but elastic enough to hold their own before firing. Then envision reducing costs by as much as 40 percent over traditional ceramic processing. When Allied-Signal Engineered Materials created a new binder, made from water and agar (a seaweed-derived polysaccharide not unlike Jell-O), these visions became reality.

How real? At the company's Autolite plant (Fostoria, OH), a 22-ton production molding machine pumps out 1 million parts annually using the water-based feedstock. During a visit, IMM spoke with Cliff Ballard, director of powder injection molding ventures for AlliedSignal, about the potential for this technology.

"Compared to the traditional shape forming ceramic processes, molding offers to reduce the number of steps required and, thus, take out cost," says Ballard. "But polymer and wax binders have held back growth. Parts have 40 to 50 percent binder content by volume. Removing it generates toxic effluent and may take days. The end result is a brittle part that must be carefully handled. In addition, part thicknesses are limited to less than .25 inch."

By comparison, Allied-Signal's water-based system requires no separate debinding step - the water simply evaporates after molding, leaving intergranular pores open. Of course, concerns over toxicity are also eliminated. As for the agar binder, it adds only 2 to 3 percent by weight to the feedstock. According to Ballard, there are no part thickness limitations, although thickness does determine drying time. And like polymer/ wax systems, tolerances can be controlled to ±.3 percent.

What really sets this new feedstock apart, from a designer's point of view, is the greater freedom it allows. "We're producing parts that were formerly impossible to mold," says Richard Schultze, manager of ceramic applications. At the plant, workers are able to mold spark plugs with a 7-mm wall thickness, vs. 12 to 14 mm for standard processing. Parts with combined thick and thin cross sections, undercuts, and complex geometries all benefit from the moldability of the feedstock. As an example, he cites a turbine blade produced via traditional methods at a cost of $1300. "Our customers are now molding prototypes of that part, and the price could drop to between $50 and $150."

Savings are a big driver for ceramic molding. Last year, a vendor told Autolite it could no longer supply an intricate component, formed traditionally in two half shells, because the cost was prohibitive. Jason Hogan and David Lyons, part of the CIM team at Autolite, had a prototype mold running parts within eight days after the announcement. This year, Lyons estimates the company has saved more than $250,000 on these parts. "In fact, because of the freedom this process allows, we were able to add features that the vendor could not produce ," says Lyons.

Differential shrinkage rates for the new molding compound are greater than those for most thermoplastics, ranging from 16 to 20 percent (depending on the material). However, notes Ballard, these are the same rates found in traditional ceramic forming. This has a lot to do with the composition of the new ceramic molding compound - by volume, 53 percent ceramic powder (alumina, zirconia, or silicon nitride), 47 percent polymer dissolved in water. It is this latter component that makes the mixture act like a thermoplastic.

Processing is another area where the Allied system saves money. Cycle times are similar to those for thermoplastic parts. But because injection pressures don't exceed a 500-psi maximum, and temperatures rarely go above 185F, prototype parts can be molded using aluminum- filled epoxy or even SLA masters. There is no mixing in the barrel; instead, material is moved along by a screw with no compression, then injected through the nozzle at a consistency similar to toothpaste. Parts bounce out of the mold, with strengths after drying about four times higher than those of conventional green ceramics. Molding machinery need not be modified for the process. At the production facility in Fostoria, technicians use three 22-ton Boy machines and a 27-ton Arburg.

Melt flow rates for the ceramic are difficult to measure using traditional thermoplastic equipment. However, spiral flow tests confirm that the material will fill complex geometries at low pressure. A turbine vane test part, 7 inches long with a feathered edge, had no problem filling. When it comes to wear, the compound acts like a 30 percent glass-filled nylon. Total wear for production molds, in stainless 440C, rarely exceeds .004 inch for 500,000 shots.

Material properties for the first commercial Allied compound--AS194 alumina--are equivalent to traditional 94 percent Al2O3 materials. With an initial raw-material cost of $5.50/lb, the gel-based material can be easily recycled in-plant, either by grinding parts and adding water, or by adding still-wet scrap directly to the hopper.

The gel technology developed for this first ceramic compound is also being applied to metal injection molding materials with similar benefits, Ballard adds. He shares a product development roadmap, which targets commercial release for additional ceramics as well as stainless steel products within the next 12 months. Stay tuned.

Opportunity knocks in unlikely places

Going global among U.S. manufacturers has become tantamount to a divine directive. Dutifully, if not enthusiastically, American companies have opened new plants overseas and begun to address a world market. Wouldn't the picture change if the concept of expanding your business to another country not only meant serving market demands better but improving your financial picture significantly? Emerging nations in the Caribbean are offering just such enticements, and one country in particular believes it is well suited for plastics processing.

At 166 sq miles, Barbados, a small island in the West Indies, is roughly the size of JFK International Airport. And indeed, the Concorde lands here once a week bringing European travelers seeking sand and sun. Before you write it off as a tropical vacation paradise rather than a productive manufacturing environment, however, consider some eye-opening statistics. You'll find that its small size belies some very real business possibilities for molders.

First and foremost, Barbados has an ideal location for shipping to the U.S., South America, and Europe. And thanks to several trade agreements, Barbadian-made products can enter the U.S., Europe, Canada, Venezuela, and other Caribbean nations free of duty. Secondly, export-oriented manufacturing concerns are exempt from taxes on corporate profits for 10 years. After that time, they receive a special tax rate of 2.5 percent. Also, any raw materials, machinery, and other purchased components are also exempt from import duties.

Manufacturers receive assistance through the Barbados Investment Development Corp. (BIDC), an agency of the Barbados government. For example, the agency helps manufacturers by securing government subsidized factory space that can be rented for roughly $3/sq ft/year.

IMM spoke with BIDC's Peggy Griffith, director international business, and Donville Inniss, business development officer. Griffith explains, "BIDC also offers a range of free services, and administers several programs, including a Training Grant Scheme to help companies offset training costs during start-up and expansion phases." When it comes to training, Barbados has a potential workforce of 126,000 out of 257,000 residents with an overall literacy rate of 98 percent. A British schooling system, recognized by the U.N. as one of the best in the world, is free to all residents and includes a campus of the West Indies university system, numerous secondary schools, and a variety of primary schools.


One of only two molding operations on the island of Barbados, CPM Ltd. and its five employees provide the domestic market with a variety of products - disposable utensils and plates, combs, ice trays, soap dishes, and pharmacy vials - molded in HDPE, LDPE, PP, PS, and HIPS. Director Shiu Shun Yeung, who relocated here from Hong Kong, tells IMM that his biggest challenge is maintaining molds. "We have no toolmakers locally, so I must rely on periodic mold maintenance from Hip Wo Co., an overseas partner," he explains. Yeung's immediate plans include expanding to a larger facitly. And like the current 2400-sq-ft space, it will be subsidized by the Barbadian government.
Various initiatives across the West Indies and abroad are designed to boost trade. For example, the Caricom (Caribbean Community Common Market) agreement allows products made in Barbados to be exported free of customs duties to 12 other islands within the West Indies, including Jamaica and Trinidad. The Caribbean Basin Initiative allows Barbadian-made products duty-free entry into the U.S. For Canada, a similar agreement is known as Caribcan. Legislation known as the Lome Convention allows companies manufacturing in Barbados to ship to the European Union countries without paying duties.

Concerned about infrastructure? Barbados is self-sufficient in natural gas. Its crude oil production supplies 30 percent of the country's electrical needs, while the other 70 percent is imported. A pilot wind power plant financed by the government seeks to make use of another natural resource - powerful sea breezes. Roads are relatively narrow by U.S. standards, but adequately handle the smaller-sized vehicles prevalent on the island. Phone, fax, and shipping capabilities are equivalent to most industrialized countries. You can even choose from several overnight courier services, including FedEx and UPS.

Molding Opportunities

Timing is everything when making a business decision, and conditions in Barbados today are fertile ground for investment. Here is the condensed version of current available opportunities:
  • Many of the products made here require molded plastic components, which are currently purchased abroad by necessity. For instance, lack of domestic molders forces a large state dairy to purchase its HDPE yogurt and ice cream containers from a Canadian processor. Electronics manufacturers buy housings from the U.S., then assemble products here. If manufactured on the island, these same components would be much less expensive, according to Andrew Applewhaite, a former director of electronics firm Bel-tronics. He believes that not only would ocean freight costs be eliminated, but the 10-year tax abatement may allow a molding operation more leeway in its pricing.
  • According to a 1994 United Nations seminar, environmental sustainability for a small island means successfully recycling solid waste such as PET and HDPE containers. One company, Envirotech Inc. (St. Michael, Barbados), is in the preliminary stages of building such an operation. Andrew Simpson, director of the firm, currently has 1 million lb of PET bottles shredded, baled, and stored as a result of a government "bottle bill" inducing consumers to return the containers for a 10-cent return. But rather than selling the bales on the open market, where prices have fallen considerably, Simpson hopes to utilize new technology that would allow him to mix PET and HDPE flake without separating them. The end result: a roofing and tile product suited to the conditions in the sunny Caribbean.
  • As chief environmental engineer, Jeffrey Headley tells IMM that Barbados wants to attract industries that generate little or no waste. "Because of our limited land space, we stress technology rather than waste-producing industry," he says. "Plastics processing fits well into this scheme, because in-plant scrap can be reground and used again or sold."

    In a similar vein, any environmental endeavors are supported by government incentives: "There are several such initiatives now that illustrate the level of public and private sector cooperation."

  • The island contains its own bottling operations for Coca-Cola. To produce the PET bottles, this concern must buy the injection molded parisons for use in the stretch-blow process. A local supplier could consolidate both processes at considerable savings, according to potential investor Boney Mathew of Mathson Industries (Clarkston, MI).
  • Another potential - moldmaking shops. There are currently a few molding operations, but they must rely on outside toolmaking and maintenance because there are no moldmakers in the country.
  • While the Barbadian government is seeking to diversify its country's economy, the fact remains that tourism is one of the three largest industries, next to sugar and rum. As such, molded wares in demand include disposable service items, recreation goods, and souvenir items. Again, most of these products are purchased abroad at a relative premium.

Investor's Snapshot of Barbados

It's not a typical postcard, but the following facts definitely beat "wish you were here" for investors:
Electric rates 30 cents/kwh
Currency Bds$ 2 to US$ 1 (only Caribbean nation that has not devalued its currency)
Banking system 34 offshore banks with total assets of US$ 4.8 billion
Population 257,000
Labor force 126,000
Literacy rate 98 percent
Language English
Health care government-sponsored system, free to all residents
Education free public schooling through university level, rated by U.N. as one of the best in the world.

Automotive winners and losers

Injection molders serving the lucrative automotive market will need to carefully pick their targets in the coming years, according to Jim Best of Market Search Inc. (Toledo). In his just-published report, "Automotive Plastics Report-1997," Best claims that usage of injection molded thermoplastics in passenger cars and light trucks assembled in the United States and Canada will grow from 1.74 billion lb this year to 2.28 billion lb in 2007 (see table). However, Best cautions, this growth will not be uniform.

Areas of growth and decline for injection molded components in the automotive market.
Market Area Million lb.
TPO bumper covers 105.5
Nylon intake manifolds 51.2
Injection molded body panels 11.2
Clutch/accelerator pedals 2.4
PVC steering wheels -6.6
Polyolefin egg-crate bumper energy absorbers -9

U.S. and Canadian injection molding material consumption for automotive applications.
Year Million lb.
1992 1223
1997 1742
2002 2049
2007 2284

Opportunities

Injection molded nylon intake manifolds will see a new competition between fusible-core vs. welded processing, says Best, and between nylon 6/6 vs. nylon 6. Usage of injection molded intake manifolds is forecast to grow a spectacular sixfold, to reach 65.6 million lb per year by 2007. This application, according to Best, is just the start of a new generation of underhood engineering plastics components from water pump impellers to throttle bodies.

Bumper covers are converting from RIM to injection molded TPO and ionomer in one application after another and are forecast by Best to grow to 284 million lb per year by 2007. Also, injection molded clutch and accelerator pedals are forecast to see 20-fold growth to reach 2.7 million lb per year by 2007.

Model changes from specific automotive OEMs are fueling some big opportunities for molders of exterior body panels. Saturn, for instance, is working on a larger model for 1999 that will essentially double the number of vehicles with injection molded bodies. Chrysler is developing its injection molded Composite Concept Vehicle (CCV), and in Europe, Mercedes is preparing to introduce its Smart car, which features an injection molded body. Owing to all of this, Best estimates total growth of injection molded exterior body panels to increase 19.5 percent to reach 45.9 million lb per year by 2007.

On the instrument panel (IP) side of things, Best sees the trend going toward injection molded integral structural ducts. A recent example he cites is the Jeep Cherokee. But the 1997 Jeep Wrangler goes the other direction, saving money with an unpainted polypropylene IP. And Chrysler's 1997 minivan instrument panels start a new trend to unpainted TPO. Because of the nearly 100 percent penetration of injection molding for interior applications, says Best, there will be no significant growth in IPs.

Areas to Avoid

On the negative side, bumper energy absorbers injection molded into an egg crate design will continue to give way to foamed polypropylene. Best projects this transition to cost injection molders more than 9 million lb of business per year by 2007. Also, steering wheels injection molded from PVC are being replaced by RIM urethane. This will cost molders more than 6.6 million lb of business per year by 2007.

About the Report

Best analyzes a total of 238 specific injection molded applications and materials systems in his 1076-page report. Current usage, historical usage, and five- and 10-year forecasts are provided for each application. Specific new applications and developmental programs, based on interviews with automotive OEM engineers, are described as well. "Automotive Plastics Report-1997" costs $3100; copies and sample pages are available from Market Search by calling (419) 535-7899.

Dissecting sides on the PVC issue

Welcome to the great vinyl debate - not unlike a recent heavyweight title bout, minus the biting. In this corner, wearing green and weighing in with a genuine concern for Mother Earth, we have environmental watchdog groups such as Greenpeace who contend that polyvinyl chloride is a big contributor to dioxin production. In the opposite corner, wearing a different shade of green, are manufacturers and industry groups such as the Vinyl Institue, presenting evidence of PVC's recyclability and environmental friendliness. Ready to rumble?

Marketing campaigns don't always attempt to sell products. Sometimes, the target is perception. Following in the advertising industry's "perception-is-reality" footsteps, environmental groups such as Greenpeace use the familiar symbol for poison as a logo for PVC. And to the general public, skull-and-crossbones images married to vinyl might actually wash. Tactics such as these play on awareness of and concern for the environment. But selling this image to an audience of plastics industry insiders is a different story. Here, the group can knowledgeably digest the facts required to fully understand all of PVC's facets, including its environmental impact.

With that premise in mind, IMM set out to uncover both sides of the controversy over PVC's alleged role in releasing dioxin to the environment. As with most issues in life, we found that there are quite a few gray - make that light green - areas in the fracas surrounding vinyl.

Forest Green Defined

Defining the controversy over PVC's environmental impact is relatively simple, especially compared to resolving it. Essentially, environmentalists contend that the significant amount of chlorine inherent in vinyl's manufacture and released upon its combustion is a primary contributor to dioxin in the soil and air. Chemically speaking, during the combustion process, chlorine can combine with organic matter to form dioxin. Dioxins, according to the Chlorine Chemistry Council, are a family of 75 solid chemical compounds, both colorless and odorless, based on chlorine, hydrogen, and oxygen. These compounds do not dissolve readily in water, but are highly soluble in fatty substances and organic matter.

An EPA study of laboratory animals given high doses of the most toxic form of dioxin - 2,3,7,8-TCDD - concluded that this form may cause cancer in humans. But the carcinogenic properties of this and other forms of dioxin are still under debate among scientists. For example, the EPA currently lists an ADI (allowable daily intake) for TCDD as .01 picograms (pg) (1 x 10-14g) per kg of body weight per day. At this dosage, the calculated cancer risk would be 1 in 1 million. By comparison, the World Health Organization sets that level at 10 pg (1 x 10-11g).

Black-and-White World?

Just as there are shades of gray in life, so there are shades of green in the PVC controversy. D'Lane Wisner, manager of environmental solutions for PVC manufacturer Geon (Avon Lake, OH) states that vinyl is half chlorine, and points out that nearly all plastics use chlorine in some way. "Remember also that 60 percent of all chemistry involves chlorine, including products used in water purification systems," he says. During a recent Geon seminar, Wisner cited an example: "The government of Peru decided to stop chlorinating the water supply several years ago in an attempt to prevent chlorine exposure. The result was 20,000 deaths from cholera, malaria, and other diseases before Peruvian officials did a quick about-face, returning chlorine to the country's water.
Uses for PVC range from computer housings to appliances to toys. It is recyclable, offering up to eight heat histories without property loss. Although it has been maligned recently by environmental advocates, PVC supporters and manufacturers contend that vinyl provides us with both function and environmental friendliness.

Whether or not dioxin is carcinogenic, a 1996 study points to the fact that environmental dioxin is on the decline. At the same time, PVC usage and manufacture is climbing. Researchers from both Europe and the U.S. measured dioxin in lake sediments, going layer by layer to determine the age of the deposit. They determined that around 1960, dioxin deposits (measured in pg/sq cm/year) peaked at about 35. Sediments from 1996 show dioxin at about 10. In comparison, vinyl production measured 2.5 billion lb annually in 1960 while reaching almost 13 billion lb last year. Groups such as the Vinyl Institute and Chlorine Chemistry Council assert that if PVC was directly responsible for dioxin in the environment, the study would have shown a direct correlation.

On the flip side, Greenpeace cites a study from 1984 that found an abrupt increase in dioxin concentrations in lake sediment after 1940. This study found agreement between the production of chloro-organic compounds and the level of deposited dioxin.

Study Wars

As you may have already surmised, each side in the vinyl debate fortifies its opinions by performing scientific research, compiling the results into massive studies. On the environmental side, Greenpeace most recently published "PVC The Poison Plastic." Trade organizations point to the 1995 study conducted by the American Society of Mechanical Engineers and authored by scientists Rigo, Chandler, and Lanier.

Briefly, the Greenpeace study concluded with recommendations to decrease chlorine-containing vinyl as the primary method of reducing dioxin. In the ASME study, researchers found that the production of dioxin had no correlation to the amount of PVC or chlorine in the feedstream. Rather, they concluded, the presence of dioxin in stack gases depended upon combustion temperature and incinerator design and operation.

While Greenpeace acknowledged that facility design, operating conditions, and catalysts also contribute to dioxin formation, the group attempted to discredit Rigo et al in the report, "Chlorine and Dioxin." But again, related research failed to find positive correlation between chlorine in the feed and dioxin in the stack gases in more than 80 percent of the municipal incinerators examined.

The Burning Question

These and other studies point to the central issue in the PVC controversy: what really happens when it is burned in an incinerator? In summary, environmentalists contend that dioxin is formed due to the heavy concentration of chlorine from PVC in the waste stream. Trade organizations point out that any incinerator, whether it contains a high concentration of PVC or not, will emit dioxins if the temperature of incineration is below 2000F and if the design and operation are shoddy. Another problem, these groups say, is that chlorine can be introduced from many sources, both natural and synthetic.

Now a word from the neutral corner: The Environmental Protection Agency considers incineration one of the viable alternatives for handling solid waste. In a report entitled "An Agenda for Action," the EPA's Municipal Solid Waste Task Force advocates developing environmentally safe incineration facilities as part of an overall plan to reduce solid waste that also includes recycling, reuse, and reduction. Now for the burning question - where are these incinerators going to be located? One of the problems facing implementation of this option is the Nimby syndrome, a.k.a. "not in my back yard." It is difficult to convince communities of environmental safety when visions of dioxin-emitting incinerators still exist. Currently, less than 10 percent of unrecycled waste in the U.S. is incinerated; the remainder goes to landfills.

Other countries offer a contrasting perspective on this issue. Sweden, for example, one of the only countries with specific dioxin regulations, sends 55 percent of all solid waste to incinerators, where it becomes fuel for energy plants. Twelve years ago, the country conducted a one-year study of air emissions, concluding that modern incinerator technologies such as electrostatic precipitators, lime scrubbers, and fabric filters could reduce harmful emissions by more than 95 percent. Solid waste-to-energy conversion also runs successfully in Japan (46 percent) and Germany (35 percent).

Environment Canada, a government agency, also offered input on this question. It conducted a study in which two pilot air-pollution control systems were connected to a mass-burning incinerator in Quebec City that contained a significant amount of plastic in the feedstream. Testing showed that higher flue gas temperatures - 1800 to 2200F - removed 95 percent of all pollutants.

A rebuttal to these findings from environmentalists comes from the EPA in Denmark. A 1993 Danish study found that "doubling the PVC content of an incinerator's wastefeed increases dioxin emissions by 32 percent," according to Greenpeace's Thornton. He also reports that the German EPA found that combustion of chlorinated wastes containing plastics and other chemicals produced higher dioxin concentrations in ash residues than combustion of chloride-containing but chlorine-free paper, wood, cotton, or wool.

Recycling: Just Say Yes

Recycling could represent a mutually agreeable solution to the PVC controversy. Unfortunately, recycling vinyl and other plastic products generally remains yet another solid-waste alternative that causes government, industry, and environmental advocacy groups to differ. That's because efforts to create viable recycling infrastructures have stalled. Government involvement is nil at present, and while a few notable companies are operating profitably, there are almost no economic incentives to set up the collection, cleaning, and separating systems necessary to generate revenue. Without a thriving industry, the hope of successfully and economically recycling PVC or any thermoplastic remains dim.

Compare this to the bright outlook on PVC's ability to be recycled. Geon's Wisner explains: "Vinyl retains its properties upon remelting - on average, it can see eight heat histories before significant property losses occur. Also, the end-use applications for recycled PVC are numerous. When recycling becomes widespread, vinyl will be one of its star performers." - Michelle Maniscalco