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 Extrusion, Single Screw
 POM-C heavy section solid profile extrusion
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| Author | Topic: POM-C heavy section solid profile extrusion |
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peters_a Senior Member Posts: 9 |
posted May 16, 2007 03:49 PM
  
Looking for some advice regarding processing of thick section POM profiles to avoid 'coring' and/or cracking of product. There is a balance between the two but processing pressures seem to be excessive to eliminate porosity - any thoughts? IP: Logged |
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Tom C Moderator Posts: 852 |
posted May 17, 2007 06:23 PM
Are you having problems with shrinkage voids or small foamy bubbles? By your description it seems that you may be overheating the material. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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peters_a Senior Member Posts: 9 |
posted May 18, 2007 06:05 AM
Combination of different variables. Having to apply high melt pressures to overcome microporosity although this can compromise the ability to apply 'back pressure' through the downstream. IP: Logged |
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Tom C Moderator Posts: 852 |
posted May 20, 2007 07:42 AM
Normally there is no relationshp between backpressure and porosity in melt extrusion unless you are overheating the melt. I'm not quite sure what you are describing. Do you know what your melt temperatrue is by insertion melt probe or IR gun? POM is very sensitive to melt temperature. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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peters_a Senior Member Posts: 9 |
posted May 21, 2007 02:16 PM
Tom Using the combined Melt temperature/pressure sensor a value of 185°C is seen at the adaptor plate. This is as per recommendation from BASF and Ticona. linear through put is circa 1mm per minute although with screw barrel pressures upto 60bar this can lead to slippage through the haul off. IP: Logged |
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Tom C Moderator Posts: 852 |
posted May 22, 2007 02:31 PM
The melt tmeperature measuring unit that you have primarily reads the temperature of the metal that it is installed in. By far the biggest issue with POM is temperature related. I recommend a insertion probe or IR gun measurement as before. I don't follow the remainder of your statement. Tom Cunningham [This message has been edited by Tom C (edited May 22, 2007).] IP: Logged |
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peters_a Senior Member Posts: 9 |
posted May 22, 2007 05:30 PM
Tom Apologies, I was refering to the linear output speed of the rod profile being manufactured. The kg output being observed is roughly 12kg per hour with two strands being produced per this particular manufacturing line. Do you have experiance of this type of large cross section extrusion process? IP: Logged |
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Tom C Moderator Posts: 852 |
posted May 22, 2007 07:59 PM
All extrusion processes follow the same ground rules. What I would look at in your case is; 1) Real melt temperature These items will determine porosity or voids in the melt. The whole process needs to be looked at as a system. Those items which seem outside of normal operation at dealt with first. Often these items are checked on computer simulation programs so we can see into the process. Then all of the parameters are checked to see if they are helping to make a good quality product. Usually I find if all parameters are driven to what would be considered normal, the process runs without problems. Rod profiles are amoung the easiest to check out, but I think your problem is in the extruder.
------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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peters_a Senior Member Posts: 9 |
posted May 23, 2007 12:32 PM
Tom The project we are looking at involves processing rods upto 12" diameter in copolymer acetal and this has proved to be a troublesome scaleup from smaller diameters. Difficult to get access to clear direction specific to this as raw material suppliers cannot give hard and fast parameters to apply. I will investigate the areas suggested and look at the process model. Thanks for the suggestions! IP: Logged |
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Tom C Moderator Posts: 852 |
posted May 23, 2007 12:42 PM
Large diameters like that would seem very difficult. Product cooling time could likely be measured in days, and that in itself might be enough to cause degradation. With very large cross sections like this I believe you would need a heavy stabilizer package. Also these types of sections are often made using intrusion molding. This is where a very large metal form is filled quickly by extrusion and cooled over a period of times in a large water tank, or by air. Certianly there is nothing easy about it. A special screw design which produces a very cool melt and has low residence time might be helpful. Contact me if you would like to explore those possibilities. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
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louis33 Senior Member Posts: 166 |
posted May 30, 2007 09:52 AM
Pipe Die? IP: Logged |
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