posted August 25, 2005 09:43 PM               

I don't like running regind because todays solution often will not run on tomorrows material.

A good process for wet nylon usually involves 2 or 3 vents. Get the water out as soon as possible.

Starting with a clean slate I would set up the screw to initially grind and heat the rsin, but not melt it, then I would atmospherically vent. Then vacuum vent the hot solids, then melt the resin and vacuum vent again before discharging. This setup is likely to preserve the nylon's viscosity.

Setting up the design to melt/not melt on a mega while getting a good rate is tricky. Also since the residence time on a mega is so low, you will need a design to the described in order to get any water out.

If your company is willing to spend a few bucks for some design work, send me an email.

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Best Regards,

Tom Cunningham

Extrusion Technical Services

posted August 26, 2005 09:49 AM            

I agree with your remark about transient solutions; we have conducted several DOE's to find that either the problem has magically disappeared or the resin being profiled is no longer available. We currently run one atmospheric vent and one vacuum vent and are in the process of looking at a second atmospheric. Do you feel that second vacuum vent would be superior to a second atmospheric vent?

posted August 26, 2005 10:44 AM               

I think your within spitting distance of the most you will ever get out of the machine. You should be proud because most don't get this much out of their megas.

As you have seen by pushing the machine this hard you are getting unmelted materials. This has the effect of keeping the melt cool, which may be saving you from degradation due to the presence of water. It is kind of a trick.

When I run a simulation using your rate I get a residence time of 7 seconds. Devolitilization of a melt is a time dependent process. You don't have a lot of time under the vent to work with. Degradation is also a time dependent process, so in the balance things may work out.

As I said, this whole process can be tricky. You need to balance melting, devolitilization, production rate and degradation. The optimum can be hard to find or not exist at all.

Trying to get the moisture out before melting is a good strategy and is used in a number of unique process for reclaim. For your process at mega speeds, I think you are exploring new territory.

I have some technical resources such as Twin Screw Process Simulation which I offer on a professional basis. Sample process below

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Best Regards,

Tom Cunningham

Extrusion Technical Services

posted August 26, 2005 11:47 AM            

Again, I thank you for your help and support. I will be in touch if I can get a go ahead from the uppers.