| next newest topic | next oldest topic |
| Author | Topic: Gas injection into extruders |
|
irish Member Posts: 4 |
posted March 08, 2007 07:46 AM
  
hello I’m looking for any information about equipment/suppliers to inject gas into an extruder at high pressure. The gas is inert and can be held under high pressure easily. Any help would be appreciated. IP: Logged |
|
Stephen J. Derezinski Senior Member Posts: 63 |
posted March 11, 2007 06:47 PM
Irish-- A two-stage extruder screw can be used to inject gas into polymer through the barrel port. However, the screw must be designed such that the second stage will hold the gas pressure(instead of a vacuum as would be the normal case for devol.) This means a shallower second stage metering section. Of course, the first stage must also have the ability to develop the gas injection pressure. Any good screw designer can desgin such a screw. ------------------ IP: Logged |
|
irish Member Posts: 4 |
posted March 12, 2007 06:54 AM
Thank you for your reply, i was thinking along those lines. Now what i need is information on the equipment to inject gas under high pressures and what nozzles/injectors to use. IP: Logged |
|
Bob Cunningham Senior Member Posts: 124 |
posted March 12, 2007 12:00 PM
This can be done with a single-stage screw. You might need a relief near the injection point. I assume you will get a commercially-available gas in bottles, perhaps at 900 PSI. Most importantly, you'll probably need some sort of pressure booster to get the pressure to extrusion pressure (5000 PSI?). Then you'll probably want an accumulation bottle downstream of the pressure booster pump. And you'll need a set of switching to control when the pump comes on and off (perhaps on at 4500 PSI and off at 5000 PSI). And you'll need a check valve to keep the high-pressure gas from flowing backwards. On the output of the accumulator bottle you will want a high-pressure regulator to eliminate pressure variation caused by the booster- perhaps set for 4000 PSI (in my example). Actual pressures etc. will vary depending on your process. Many of these components (except the booster) are available from a company named APtech - www.aptech-online.com . I think a company named Brooks can supply the pressure booster itself. -Bob Cunningham [This message has been edited by Bob Cunningham (edited March 12, 2007).] IP: Logged |
|
Steve H Moderator Posts: 400 |
posted March 12, 2007 03:08 PM
G'day Irish Welcome to the single screw forum, here's some links that might assist you with your project: These companies all supply the kind of equipment, I think you are looking for ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Stephen J. Derezinski Senior Member Posts: 63 |
posted March 12, 2007 03:10 PM
Irish-- I never tried a single screw to inject gas, but it sounds interesting. I am not sure if the added equipment would offset the cost of a two-stage screw. I think you might find the two-stage screw to have the advantage that there would be allot more free surface area for the gas to be absosbed. This might be needed if the diffusion of the gas into the polymer is relatively slow. A barrier screw might be a good single stage screw to use as it will tend to have some free surface in the melt deliver channel side. There is a patent on a single stage barrier extraction screw that would be if similar ilk to what you would need. US #6,293,690, Sept 25, 2001. This may help. However, trying the single stage may be a good place to start if you already have a suitable screw for that purpose. Try it. If it works, good. If not, you will learn something to help you. Also good.
------------------ IP: Logged |
|
chris baldwin Member Posts: 2 |
posted March 13, 2007 07:19 AM
For a retrofit on an unmodified extruder you can inject the gas after the end of the barrel and use a static mixer to blend. IP: Logged |
|
irish Member Posts: 4 |
posted March 13, 2007 07:44 AM
hello/G'day all Many thanks to all of you for your help. At the moment i think we will retrofit our existing barrel and be using pressures around 2000-3000psi. The website have been helpful but the nozzle/injector is my only problem, i cant find much info on this on the web. IP: Logged |
|
Stephen J. Derezinski Senior Member Posts: 63 |
posted March 13, 2007 09:15 AM
Irish-- In the two-stage system that I am familiar with, no special nozzle was used. Care was needed in getting started so as not to force polymer up into the gas line. Keeping the gas line hot would allow it to be purged by the gas, however, in the event that some polymer did get in there. I think that a valve, close to the input to the extruder would serve the purpose of keeping out the polymer unil the gas pressure was turned up. Keep everthing warm so that any polymer won't freeze. Good Luck! Happy St. Pat's Day ------------------ IP: Logged |
|
Tom C Moderator Posts: 830 |
posted March 13, 2007 10:13 AM
This company makes a gas valvee for extruders which stays closed until sufficient injection pressure is reached. It prevents polymer backflow and clogging of the valve and pipes. Please mention my name and FeedScrewDesigns if you do business with them. C+H Engineers, Incorportated ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
irish Member Posts: 4 |
posted March 15, 2007 04:11 AM
Thanks again for everybodys help, it has given plenty of ideas to get this project running. If anybody else has something to add please do so. Happy St Patricks day to everyone (in 2 days) ;-) IP: Logged |
All times are ET (US) | next newest topic | next oldest topic |
  |
|
Contact Us | Feed Screw Designs
Powered by Infopop www.infopop.com © 2000
Ultimate Bulletin Board 5.45a
