posted April 30, 2002 01:35 AM               

My apologies if I've posted this in the wrong space. I must admit to being confused by the various techniques being discussed. I find myself in a bit of bind, however, and I'm hoping someone here can help.

I'm here because I'm working with a web research service, and I've got a tough client. He posted the following question to our service (copied and pasted from our site, so any spelling errors are intact):

"In a foamong extrusion process that I try, I get breakage in corners of the profile, probably resulting from excess melt sheer forces inside the die, how can this be avoided?"

This isn't enough information for any of our researchers to go on. I did give him the URL for this site, and the suggestion that he pose his question to the pros here, but he was not satisfied with that answer and demanded further research. When asked for more information, he replied (again copied and pasted):

"We assume that the reason for the breakage is excess foaming that occurs in high shear forces along the die's land (current die lend is 1.6", we need this relativelly long land, as we want the bubles to be nucliated inside the land). The shear forcess stimulate buble nucliation at certain locations of the profile, resulting in a very thin, foamy wall, which causes the breakage."

Which still doesn't help me.

Fellas, I'm no plastics professional. I'm a mom with a web research job - a job which entails pointing clients to the information they need to get their problems solved, not solving their problems for them. This client doesn't seem to grasp that, and keeps asking for more data than I can provide.

Can any of you make heads or tails of what this client means and direct me to a resource I can point him to? Or a cluster of resources?

I would be grateful for any assistance you could provide, and would gladly repay you with a plate of homemade baklava.

Thanks in advance,

Missy

posted April 30, 2002 03:45 PM               

You, or your client could try doing a search at www.knovel.com They have electronic versions of a number of plastics texts, and all the papers presented at the last four Annual Technical Confrences of the Society of
Plastics Engineers. To access the full text, you must be a subscriber, but your chap could use the returns on his search as a request list from his nearest library.

posted April 30, 2002 09:00 PM               

Foam is not my thing, but it seems as if the client has asked and answered his own question. If shearing causes the problem, reduce the shearing. Some remedies common to all plastic processes are:

1) Lower the shear rate by slowing down the process.

2) Lower the shear stress by lowering the apparent viscosity.

2a) Pick a lower viscosity resin.

2b) Pick a resin that shear thins more.

2c) Raise the resin melt temperature.

2d) Lubricate the resin.

3) Redesign the die to lower the high shear.

All of this is basic plastic engineering, not an R&D project. The question your client asks is like "My resin gets hot when I run it in an extruder. How can this be avoided?"

Perhaps he should stay away from extruders and engineering problems.

Tom C

posted April 30, 2002 11:35 PM               

Thank you so much for your help. I'm laughing at the suggestion that the client stay away from extruders and engineering problems, because that was my reaction after his second demand for more data! He was a real pain in the keister, and I'm glad to be done with him.

I appreciate your help immensely.

I was serious about the baklava, BTW. E-mail your snail addy to me, and I'll send it priority mail!

Gratefully,