Posts: 5
From:Cadillac, MI, USA
Registered: Oct 2003

posted October 23, 2003 08:29 AM               

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Does anyone have problems with air creating a linear void on multi cavities? We run ECO and have issues where the cavities come together in the center air somehow gets trapped. Some think it is the result of the tooling. As the rubber passes over the bridge of the die a void is created. Some think it is a void that is created as rubber comes off the end of the screw. Does anyone have this similar problem or any suggestions?

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Posts: 243
From:McHenry, IL USA
Registered: Nov 2002

posted October 24, 2003 07:38 AM               

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Could simply be gas being trapped. Are the cavities vented? If so, perhaps the vents are plugged up. If not, you need vent's.

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Posts: 5
From:Cadillac, MI, USA
Registered: Oct 2003

posted October 24, 2003 10:11 AM               

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All cavities are vented. Typically the air is present at every start up. We purge the extruder with out a die or head on and run out 3-4 feet of material. The air is always present in the center of the solid rubber purge. We turn on the vacuum at start up to help aid in the removal, but it doesn't completely remove it. I just want to eliminate it completely so I don't have to rely on the extruder operator to remove it.

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Posts: 242
From:Brodheadsville, PA USA
Registered: Jun 2001

posted October 24, 2003 09:31 PM               

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Does the air look like a lot of small bubbles, or one big void?

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Posts: 5
From:Cadillac, MI, USA
Registered: Oct 2003

posted October 27, 2003 07:51 AM               

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The air is only seen on the outside wall of where the center cavities come together. It looks like a small hole that travels the full length of the tube. When you pinch or collapse the hose the rubber tears the length of the air entrapment. It resembles as if therre were a die cut, but it will not be seen until the hose is expanded or you collapse the hose many times in the same location.

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Posts: 242
From:Brodheadsville, PA USA
Registered: Jun 2001

posted October 27, 2003 08:05 AM               

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I'm not sure exactly what you have, but it sounds like an area in the die where flow is low and the material is not welding together. Then when the material cools and shrinks a void is pulled in that area. The weld line extends to the surface and that is why it splits. Please send information on the extrusion and the die design to my email address and I may be able to check the design by computer simulation.

Tom Cunningham
Extrusion Technical Services

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Posts: 5
From:Cadillac, MI, USA
Registered: Oct 2003

posted October 27, 2003 02:19 PM               

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I am putting together a crude drawing of the die. Our temp profile is 120F, 120F, 120F, 140(exit of extruder) and the screw is 110F. We see the air cut at the time of extrusion it doesn't become visible only after cure. We see it immediatly at the start up. It is present every time we start any job. After the machine is full and builds a little head and back pressure it dissipates, but for this mat'l (ECO)we can only get rid of it by going to a single cavity pin and die set up. I just want to be able to eliminate it at all and not have to convert from a 4 cavity to a 1 cavity.

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