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| Author | Topic: Extruder Bridging Up |
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dk1 Member Posts: 4 |
posted October 25, 2002 09:55 AM
  
An adhesive resin we use is bridging up in our extruder feed throat. The extruder is a 1.5" DS. and is running at 108 rpm. the feed throat temp is 330 F Would the extruder be bridging up due to excessive sheer forces creating heat in the feed throat? Or is it that the screw can't feed the required amount and the resin is sitting in the feed throat for to long? IP: Logged |
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Peter P Senior Member Posts: 61 |
posted October 25, 2002 10:37 AM
330°F corresponds to about 165°C, which is very high for the feed throat and is probably about the softening point of your material. You need to cool your feed section more effectively - extruders usually incorporate a water cooled section at the throat with some way of monitoring and controlling the water flow. The heat build-up is probably due to the conduction of heat back along the barrel from the barrel heaters. Regards, Peter P [This message has been edited by Peter P (edited 10-26-2002).] IP: Logged |
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Steve H Moderator Posts: 386 |
posted October 25, 2002 01:54 PM
DK Peter is completely correct, can you cool the feed throat? Ideally you would also bore and cool the screw for about 2 LD's past the feed throat as well, but at 1.5", doing this may weaken your screw- talk to DS about doing this and see what they recommend. Steve Hodgson [This message has been edited by Steve H (edited 10-25-2002).] IP: Logged |
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dk1 Member Posts: 4 |
posted October 25, 2002 02:10 PM
Unfortunately, there is no way to cool the feedthroat without purchasing a cooling system. I don't think my company would go for that. I figured that decreasing the first barrel zone temp. would do the trick. What do you think decrease 10-20 F? I'm fairly new to adhesive resins, is there something I should know about them extrusion wise? Thanks dk1 IP: Logged |
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Steve H Moderator Posts: 386 |
posted October 25, 2002 03:29 PM
When does the bridging problem occur- Start up, after running awhile? Trying various feed zone temps may help- are you drying the adhesive resin before extruding it-Maybe lowering the drying temp a little might help. The cooling system is fairly simple and low cost (so long as your feed throat has a cooling gallery). Even just running a water supply through it and then dumping the water would help. If the casting isn't bored, encasing it in a fabricated box, through which water was circulated would. Setting up a cooling system will certainly cost, but that needs to be balance up against the cost of lost production, off spec material shipped out, non delivery on promised dates etc etc. Suddenly a few dollars dosn't seem so bad Do a search on your material suppliers web site, you should be able to locate a copy of their data sheet and processing instructions. Steve H IP: Logged |
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Tom C Moderator Posts: 737 |
posted October 25, 2002 09:43 PM
A quick, cheap and dirty cooling system can be had by wrapping the lower part of the hopper and throat with soft copper tubing. Run tap water through it, and then perhaps drain into the water bath. This is an easy way to see if the problem is heat control in the throat. Tom C IP: Logged |
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Steve H Moderator Posts: 386 |
posted October 26, 2002 02:09 AM
You could also try playing compressed air round the casting- Just to prove the cause and then make a case for a long term solution. Steve IP: Logged |
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alpertl Senior Member Posts: 49 |
posted November 04, 2002 04:54 PM
quote:
No way to get a chiller on the puppy, eh? IP: Logged |
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alpertl Senior Member Posts: 49 |
posted November 04, 2002 04:57 PM
quote: IP: Logged |
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zabielski Senior Member Posts: 386 |
posted November 05, 2002 07:12 AM
Since you say the Company you'r with won't spend any money, try to simply measure the feed throat with a hand pyrometer carefully taped to the inside of the hopper. Now determine the melting temperature of your adhesive resin (the Vendor should give you this info., or you can run a DSC yourself). Ideally, a way to control the feed temperature bridging is to core your screw out to about two feet and insert a cooling wand with the installation of a rotary union. Then you can cool the shank and feed segment jsut prior, at and around the feed zone. IP: Logged |
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dk1 Member Posts: 4 |
posted November 05, 2002 01:25 PM
Thank you everyone for your input. I have a little update. I can't put my finger on the bridging problem. (resin, extruder speed, etc????) I decreased my BZ1 and BZ2 temps 15 F. This seemed to work. IP: Logged |
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alpertl Senior Member Posts: 49 |
posted November 05, 2002 03:59 PM
quote:
As far as a chiller is concerned, you could set up a cost savings measure (and ISO 1400). We use a closed chiller loop for all of our machines with a mix of glycol, and our savings has been calculated on +150K gallons of water a year for 6 small line (all machines are smaller, the biggest being 1.25"). IP: Logged |
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rvmalik Member Posts: 3 |
posted November 12, 2002 12:09 PM
In India, the overheating problem whould have been solved by spending not more than 20 dollars (INR 1000/-)!!! Immediately after the hopper throat, a hollow pipe jacket with 2 flanges at ends and a hole of nearly barrel OD bored in the side flanges can be slid on the barrel and welded in place with 2 drilled water cooling ports of say 3/8" BSP size. Cool water can be circulated through this jacket to keep down the temperature at feed throat below the softening point of polymer. The cooling jacket length need be approx. 2D long with an annular gap of approx. 3/4" all around the barrel for water to pass. It is cheap!! IP: Logged |
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dk1 Member Posts: 4 |
posted November 12, 2002 12:29 PM
thanks to everyone's help, I solved the bridge up problem. I misspoke about the extruder having a cooling jacket. Upon closer inspection there is a small copper line running to the feed section. This wasn't that big of a deal now that I think about it. I didn't realize it before, but the resin we're using allows me to dump the temp. down to 250 F in the first barrel zone. That seems to have helped a lot. Also, the cooling water line that I thought didn't go to the feed section wasn't turned up all the way. Thanks again IP: Logged |
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