Contamination in regrind

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It must brought by one people at the first time. And until almost all of them and contaminated.
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I am not convinced that this is the forum for such a large scale discussion. This is the work for research and developers within the industry, not idle comment from a few.

Matt
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Always separate the materials by type to avoid contamination.
Matt Proman
Matthew Proman

Yes please use the advanced methods for grinding, It can avoid a lot of contamination. Seems you are still using the old procedures for the purpose.
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Eliminating contaminated material is an excellent source of profit.

Brent is correct. Grind it right at the machine and recycle it back into the process. LABEL the grinder to keep somebody from seeing white plastic and mistaking PVC for HDPE just because they are the same color.

Part of setup is to clean the grinder and, as Brent says, this means stripping it apart and cleaning everything. While this sounds dumb, when you wipe off the insides with a damp rag (as opposed to blowing everything out all over the plant) make sure you're using a clean rag. While a 'little' detail, there's no sense in contaminating a grinder with a rag that already full of dust.

If you're worried about metal, put a magnet tray in your loader because somebody took it out. Better yet, teach the techs to clean the magnet tray - they do fill up and will eventually drop off what they've picked up.

Clean the INSIDE of the vacuum hose by sucking up a damp NERF ball. A 4" ball will easily compress into the hose, wipe the walls clean then resume its original shape as soon as it exits the tube. Get this 'sponge' and rinse it out to remove all the dust and crud it's picked up before using it again.

When it comes to material changeovers, whether at the press site or in the regrind room; make and hold people accountable. When someone cleans the grinder, have them put their name on it and label it CLEAN. If the setup team does it, they are the ones who are responsible.

While teamwork is essential, screw-ups like you've described are expensive. Since you pay your people, they should be considered professionals. Dirty regrind is an amateur mistake.

As to the 'Save the world with hot runners' bunch, while a delightfully simplistic solution, you still have to do something with the scrap you produce. Hot runners only get rid of the sprue and runner. The reason why people are still making molds with sprues and runners is that a huge amount of molded parts don't justify the $10,000 minimum it takes to use HR. However I'll also agree that I've seen many molds that should have had HR that didn't. For those, I don't get the thinking of the molder or the customer.

Getting rid of contamination and using all your regrind is a simple operation. BUT it will fail miserably if people don't pay attention.

In conclusion I only have three words: Training, Training and Followup.

IF you don't do it, you'll always get what you deserve.

Hope this helps

Bill

When You regrind, You are not only contaminating your material, You also are contaminating our world. Try to start building hot runners molds or isolated runners.
Thanks for stop making last century molds.
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We take a piece of clear packing tape and put a strip on the side of the grinder. We will write in marker the part name, and machine running the part. As well, we will hang a sprue from a wire on the grinder. Usually that will eliminate errors. We also label the driers the same way.
When we clean grinders and driers, will will remove the tape and put a new one with "cleaned" on it. Usually the person doing the cleaning will do that as the last step.
By the way, cleaning a grinder involves removing the screen and cleaning all the plugged holes as well as vacuuming and air blowing all over. Finally running a rag/towel down the side walls. Then when we run the new regrind, we will grind half a dozen sprues and pull out the drawer to check for old regrind. Usually we will just vacuum the drawer lightly and call it good from there. (Unless we are going from Black to clear, then it has to be perfect. Not a fun job)

Best to use regrind RAM as older molders say. RIGHT AT MACHINE. Grind and use right back in the process proportionally if possible.

Also IDENTIFY all regrind, especially left over stuff this includes Lot Numbers

DICKC is also important. This means Discipline In Cleaning and Keeping Clean. This when changing jobs and cleaning grinders.

Where is the metal coming from? Chipped blades? Stuff being tossed into the grinder? I like sprue pickers so only runners go down the hatch (not Bob)

Regrind has been used for as long as thermoplastic molding has existed and it doesn't take but a bit of common sense to use it correctly. It can save money and the environment.

Skip Glatt of GAIM Industries in Bensenville Illinois molds his whole product line from regrind, mostly post consumer. He is an expert on regrind, he won't let virgin in the plant, except for R and D.

Some HDPE and PP actually gain properties after being molded and reground and molded again (and again and again).

I too know a bit about regrind, but not because I make a lot of rejects!

Also you can search the article archive section on regrind usage such as the Cascade System. With the continuous system, over long runs, you are going to get some % of the regrind being used having multiple heat histories. This could be a problem with some resins. Then you would use the Cascade System. I think RJG still teaches this system.

Where I work, very few jobs allow regrind, those that do allow certain percentages. In these, we RAM and proportion. Having the correct weight of sprue and runners simplify proportioning.

I am getting long-winded again.

KEEP MOLDING!

brent

www.matrixtooling.com

Speaking of Bob Hatch, if he had his way, we'd have a lot more regrind to deal with!

Just kidding Bob, I love your articles and I have "On the Road" Will soon buy the new one if you autograph it for me! ( Buy from him at his site and he will autograph every one until he gets writer's cramp)