Question of the Month: Screw and barrel wear (June issue)

Hi. My name is Ruth Stricklen. I was born and raised in Tecumseh Mi. I have Living relatives that still live in the city. T&D Machine is my brother and sister inlaw.
I have Lived in the Cookeville/Sparta Tn area for the past 18 years. And I have only been in the injection molding industry for 6yrs. I have been recently promoted to an "A" Operator, which essentially means I'm fairly new to the processing part.
but i ran a machine last night that was said to have a bad screw. I watched as the cushion bounced between .02 and .27. would not hold cushion, and would time out the cycle time. the parts were both short filled and flashy. the plastic if it did form a passable part was a bit on the grainy side.
oh and the doggone thing drooled all night lone...(3rd) I will give you my personal e mail because i am very interested in anything you have to tell me that I may learn from...you see I want to be the best I can be...I am Eat up with it. I have a real Hunger for the knowledge of injection molding. Thank You!
ruthstricklen@yahoo.com

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Email: james-zhuo@pbmould.com
Web Site: www.pbmould.com
James

How do you monitor screw and barrel wear? How often do you do it, and does it catch problems before they become major? I have spent countless hours over the last thirty plus years answering these three questions. They are paramount to our industry. If all of us had a better understanding of the answers to these three questions, our cost per part ratio could drop considerably.

First, we should monitor screw and barrel wear by watching recovery time, shot consistency, part quality, barrel temp set points, screw drive torque requirements to name a few. All of these and more are indications of something less than desirable going on with our equipment.

Second, we should be monitoring our screw and barrel wear constantly. By observing all of the above, when a processing problem comes to our attention, we can address it. If we can do a screw pull, there is so much to learn by measuring the screw flight diameter and barrel ID. When we measure the screw flight diameter, we need to pay special attention to where along the flighted length we see the most wear. This will give us important information we can us to dial in the temperature profiles, screw design, or screw material we have been using. The same goes with measuring the barrel ID. Where do we see the most wear? Is it towards the rear of the barrel, or near the discharge end? We would like to see the barrel ID wear evenly throughout its length. If this isn't the case, and it usually isn't, we can take a close look at the temperature profiles we have been running, screw profile, or maybe the barrel lining material.

Thirdly, if we can monitor the screw and barrel wear, we will eliminate most, if not all, the problems before they become major. If we can log the data we gain from a screw and barrel inspection, we will soon be able to see how much time it takes to wear the screw and barrel before it adversely affects our processing. We should know in advance when we will need to refit the machine. This would eliminate any problem before they become major and by dialing in the aforementioned items, give us a better cost per part ratio.

Randy Conner
President
Concor Tool & Machine, Inc.

I am bored to pull the screw out but it needs to be done at least once a year. If you can calculate with these datas/information , please tell me more.
It will be convenient to analyse our problem in each month also.
This is my e-mail.

rhuthaichanok-p@saraya.co.th

Thank
Beer..

MY EMAIL IS
ELIUE12345@AOL.COM

DO YOU REALLY HAVE MORE INFORMATION ABOUT THIS SUBJECT? I WILL REALLY APPRECIATE IF YOU CAN GIVE ME THAT INFORMATION.

THANK YOU VERY MUCH.
ELIU ESCOBAR

I have initiated a simple to use test that allows me to measure average wear in a screw and barrel while the machine is running. With the number of Injection presses in our facility it is not feasable to pull screws without reason. This test gives me an output efficiency and allows me to accuratly estimate output for a given RPM, wear between barrel and screw and maximum output the machine can plasticize. I have used this method of estimating screw wear to help schedule downtime for replacement of the screw and barrel and also to help diagnose problems such as heaters out of calibration or obstructions in the screw. Plasticizing limits for scheduling can also be taken from this test to help place the molds in the best possible presses. The data I collect for this test includes:
Cycle time
Total shot weight
Screw run time
Screw RPM
Maximum RPM
Rated output at Maximum RPM
Screw and barrel wear after removal

Back pressure and heats are considered after the calculations are done and are taken in consideration before replacing components. If you would like more information on this subject please write to me at,
Phil.Deloge@wna.biz.

The cushion test for a bad check ring or barrel wear should be done monthly: When you first start up a machine, under low pressure put a LARGE cushion (such as 4 inches). Also turn up the packing time to a few MINUTES. Note the position when under pressure. Go and get coffee. Note the position when you come back. If it hasn’t changed your check valve / barrel wear is minimal. If it has moved several inches, you have a leak and usually the valve needs to be replaced.

Pulling screws, changing the check valve, and inspecting the barrel should be done at least on an annual basis. If you notice the screw turning during injection and you are not doing intrusion molding it is another sign of worn components.

Checking the valves, screw wear/deplating, and barrel wear is as important as changing your tires on your car. While you don’t have to do it until something breaks, if you want top performance, you have to take care. Said Differently: If you’ve got the money to make scrap, you’ve got the money to do maintenance.

Think about it.

Bill Tobin

Please send us the quotation. if it can help me to recognise the screw wear i will save so much of time.

rajendra
rrecherla@hotmail.com

Screw and Barrel wear over time, will reduce screw recovery, increase scrap rates and increase energy consumption. While molders may recognize the costs of wear, they usually accept it as a necessary part of their business.

Glycon Corp. (Tecumseh, MI) has developed and patented two slick methods of measuring screw and barrel wear WITHOUT DISASSEMBLING THE MACHINE! This allows molders to determine wear rate and to plan changeovers BEFORE wear affects production rates and part quality. Savings can be quite significant.

Jeff Kuhman
President
Glycon Corp
Tecumseh, Michigan

Glycon actually has a product to measure this without having to pull the screw.

We pull the screw and check visually and dimensionally at least once a year for benign resins and every 6 months for abrasive and/or corrosive resins.
Barrels are checked at this time, as is clearance between barrel and screw. Barrel ID and screw OD are logged so as to determine where wear is occurring.
When clearance exceeds tolerance, replacement is in order. Small, medium,and large units have increasing tolerances for clearance,the manufacturer can help. Generally small units, have a tolerance of 0.015", medium,0.017" and so on.
Monitoring of cushion. recovery time,extrusion rpms and pressure can help spot problems without bothersome screw pulling at more frequent intervals.
The NRV valve (though not in the question) is an important part of the screw/barrel combination. Here also monitoring of cushion spots problems before they get big. Clearance is checked when screws and barrels are physically checked
I have welded shut nozzle tips, which I install every six months, and with HDPE in the barrel, try to inject slowly forward at reduced pressure to quanitfy the ability of the press to hold cushion. Again, you can spot a problem before it becomes serious.
The quality of a molded part can only be as good as the quality of the injection unit combination.

Brent