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| Author | Topic: Single screw Chain drive |
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JInman Senior Member Posts: 9 |
posted October 19, 2003 09:34 PM
   
Has any one ever worked with a chain drive extruder? We bought a used extruder which had the belt drive replaced with a chain drive and its been anightmare trying to eliminate surging. HELP! IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 19, 2003 11:38 PM
Can't see any reason why swapping a belt for a chain would cause a sigle screw extruder to surge. When you say surge, what do you mean? What's happening with the screw motor amps, melt pressure, melt temp, what material are you running, what process etc Have a look at the other postings in this forum that relate to surging [This message has been edited by Steve H (edited October 19, 2003).] IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 20, 2003 01:06 PM
We've tried several temp profiles and have one that runs a stable saleable extrudate,put new thermocouples and temp controls added a new tachometer etc.We're running rigid PVC filament on an xaloy barrel and screw with saxton mixerwith awater cooled screw and feed throat (@70 degrees).There is a repetitive pulse/surge no matter what temp or screw RPM is set.Tried varying water remp and flow rate.Anything else ? IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 20, 2003 02:07 PM
What is the frequency of the "pulse", I assume the pulse is accompanied by a dimension variation. Steve IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 20, 2003 04:05 PM
The pulse surge varies with speed but is regular in nature.It occurs about every 6-8 seconds at 25 Rpm and has a proportional increase until it is virtualy continuous at 50 RPM. IP: Logged |
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Bob Cunningham Senior Member Posts: 65 |
posted October 20, 2003 04:21 PM
Could you have a feeding problem? I would guess that it's not a drive or screw problem. Is this a gravity-fed machine? Maybe material is bridging right above the feedthroat? -Bob Cunningham [This message has been edited by Bob Cunningham (edited October 20, 2003).] IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 20, 2003 05:35 PM
What form is your rigid PVC in, pelletized compound or powder? What screen pack are you running- 40/20 mesh or 60/40/20 in Stainless Steel would be worth trying. What are the channel depths, L/D etc of your machine. What material/s was it running before you brought it. Steve H IP: Logged |
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felix Senior Member Posts: 16 |
posted October 21, 2003 10:05 AM
More often than not surging is a result of low back pressure or the screw design. You say the extruder was used, what was it designed to run PVC? You might have to get a new screw. IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 21, 2003 04:04 PM
I'll try and answer several quetions at once. We're running a gravity fed PVC pellet and have already looked into the bridge question. I haven't seen any evidence of over heating in the feed section and its a circular hopper. It was originally built for floropolymers but has an almost new PVC screw barrel diameter was checked and has some wear but is well w/in acceptable tolerances.Currently I am getting a new breaker plate with different hole pattern and I have looked into stainless screens and want to try them but need a pre cut circular supplier.Extruder is 24 to 1. I working on this reply at home and don't have the specs on the last screw and barrel inspection with me so I'll get to that tommorrow. So far thanks for all the input quite a bit more effort than I'd hoped to get. IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 21, 2003 05:55 PM
Have you experimented with different cooling temps on the screw? I think you may be running the screw temp too low. Screw cooling is mandatory for PVC extrusion. The system should be set up so that the oil flows to the screw tip first to cool Hang in there, we'll tame that beast yet Steve H IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 22, 2003 04:35 PM
Okay new breaker plates will be here on Tues. I'm going to take a shot at the screw cooling recommendation from Steve tomorrow. I'm a novice as far as screw and water jacket cooling so here's another question, can I get away with seperate syststems with water cooling for both or do I really need a oil heat exchanger for the screw and if so what type of oil? IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 22, 2003 09:58 PM
Posibily, if your water cooling system is pressurised, you could take it up to 130-140C. But you'll need seperate systems for the feed throat 45-50C and screw 93-121C. Heat transfer oil is what you're asking your oil company rep for, there are several suppliers advertising on this site. Steve H IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 26, 2003 06:19 PM
The srew cooling idea didn't seem to affect the problem at all. So,I'm still going back to my original question about chain drives,has anybody run one? I checked alot of the new and used equipment sites and have yet to find a single mention of a chain driven extruder. I ran LDPE & HDPE for years and saw alot of extruders but no chains is this really viable drive method? IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 26, 2003 09:13 PM
I've never heard or worked with a chain drive extruder. Eactly what sort of chain is it fitted with. If you believe the that the chain is the cause of your problem, then swap the sprockets and chain for a drive belt and pulleys. Where are you at with screen packs, what are you currently using. Steve H IP: Logged |
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alpertl Senior Member Posts: 34 |
posted October 30, 2003 01:25 PM
quote:
If it happens at 5-6 second intervals at 25 RPM, that is close to being every 2 revolutions of the screw. I would check that the chain and or sprockets are not worn or binding on each other (under load). IP: Logged |
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JInman Senior Member Posts: 9 |
posted October 30, 2003 09:42 PM
Geetings and salutations ! I am up and running. Smaller diameter holes in new breaker plates cured most of the problem lowering screw temperature cured more of it and I'm pretty damn sure I'm getting rid of the chain drive at the first opportunity. Never,never again.Thanks to one and all. (Where should I send the virgins?). IP: Logged |
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Steve H Moderator Posts: 262 |
posted October 30, 2003 10:53 PM
Great to hear that you're in production  . The more restrictive breaker plate will have increased back pressure, which in turn will dampen any size fluctuations. You might want to keep an eye on the breaker plate in case there are any dead spots that could cause your material to degrade though.The advice to run a stethescope over the gear box/thrust bearing assembly is well worth following, dismantling and checking any reduction gears/sprockets (any that are turning once for every two screw revolutions might bear some fruit. You might want to looking at joining SPE, check out www.4spe.org The extrusion division produces an excellent newsletter, and the book store has a number of useful books. Steve H Ps Tie bundles of $20.00 bills to virgins and send to.........(address deleted by wife) IP: Logged |
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