| next newest topic | next oldest topic |
| Author | Topic: bead breathing or washing |
|
Allan Senior Member Posts: 25 |
posted December 04, 2006 09:20 PM
  
Can someone give the cause and some of the fixes for this problem.And yes I am having this problem. There is no surging in the extruders and there is 6 of them 3 with gear pumps 3 with out. Im thinking that there is hot and cold spots in the chrome rolls but really dont have any way to find out.Point me in the right direction please. IP: Logged |
|
Tom C Moderator Posts: 838 |
posted December 05, 2006 02:50 PM
Need a lot more detail. How about some pictures? What resin? What are the product specs? This problem can be solved. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
Allan Senior Member Posts: 25 |
posted December 06, 2006 07:06 PM
Tom, The resin is clarified P.P, Adhesive and evoh in the middle. but the washing is also present in my Mono job also. As for specs ,the last product on the machine was 1.0 Mil X 560 MM . The chome rolls heats were 14c,90c,45c T M B Tom I could try and get a vid of the bead if that would help. The size of the extruder. Main 90 mill,2 65 mill 3 50 mill. Main runs P.P the 2 65s run P.P 1 of the 50s run P.P and the 2 50s run adhesive and evoh. Regards Allan IP: Logged |
|
Allan Senior Member Posts: 25 |
posted December 12, 2006 03:50 PM
Tom ,I tried to get a camera in there but the bead light is just to bright. I did try to turn it off but then it was to dark and could not see the bead. IP: Logged |
|
Tom C Moderator Posts: 838 |
posted December 13, 2006 09:52 AM
Help me with your terminology; Washing? Is this wavyness in the product? Bead? Have you always had this problem, or is it new? I have a roll cooling simulation program. It shows how fast the rolls cool the product. Since your one roll is 14C the simulation may show something interesting. The only thing I ask is permission to post the result as advertising for the product. It you are interested please email me the geometric details of your roll layout. The result only shows a graphic representation and does not give details of the geometry. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
Allan Senior Member Posts: 25 |
posted December 13, 2006 05:18 PM
Tom. If you are watching the bead between the top and middle rolls it gets bigger and smaller. I have been here going on 7 months and this problem has been here before I took this job. I not sure what you taling about when you say geometric,Im asuming your talking about how the rolls are stacked. Thanks IP: Logged |
|
Tom C Moderator Posts: 838 |
posted December 14, 2006 10:29 AM
Allan, The bead is sometimes called a bank. When you have a bank the material gets heavily processed by the rolls and if the bank is not consistent in size, you will get the wavyness you see. If you are running a coextrusion a heavy rolling bank could also roll the layers of plastic, which is not likely the effect that you want. The desired setting would be a barely perceptable bank of material so that the film is just contacting the top and bottom rolls for a polish. If you have surging in any of the equipment, then the material either will pulsate in bank size, or intermittently contant the top roll. Neither is a desirable consdition. Have you checked the roll RPMs for consistency? Sometime motor drives can be set for too much speed correction and this makes the RPMs unstable. Are you sure the extruders are running a consistent output. The lines with gear pumps should have sufficient pressure on the suction side, >500psi. If that is true and the gear pumps are not worn, and the gear teeth not broken, and the motor drives are running well, then you can rule out the extruders with gear pumps as causing the output flucuation. For the lines without gear pumps, if they are running >300psi head pressure and the pressure is dead flat, and the motor amp draw is dead flat, then you can say they are running without variation. This is not likely the case. If the RPMs are low you are likely to be able to detect a "screw beat". Look at the period of time that the bead surge occurs in. That will be a clue where to look.
------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
Allan Senior Member Posts: 25 |
posted December 14, 2006 04:08 PM
Tom I just completed a tear down of this machine. Pulled all the screws and had all the barrels checked for wear. I replaced 2 of the gear pumps and checked the 3rd for damage. The screws were in bad shape, some of the flight were chewed up and had crackes in them so i had a couple of screws on the shelf so they went in. AS for the surging I graphed all of them and they are very steady. I have graphed all the rolls and they are steady as well. I run a small bank on the hips jobs but it wont work on the p.p cause the bank flips to the top when it washing in and out. Im looking into getting some new Chrome rolls as these are old and not true. Allan IP: Logged |
|
Steve H Moderator Posts: 404 |
posted January 01, 2007 03:49 PM
G'day Allan What roll gaps are you setting, how much "run out" on the chill rolls, are they concentric. Have you checked the RPMs of the drives for screws and gear pumps? From the comment in your last post" the rolls are old and not true" what have you found to be wrong. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 02, 2007 02:49 AM
G'Day Steve I have checked all the RPM's on all the extruders and the gear pumps and they all are fine, no surging. The chrome rolls are down stack and they are chain driven and the rpms are steady. The rolls have been damaged a couple of times and been repaired. I have checked the rolls with a dial indicater and have found one that was 4 thousands out of round and had it sent out for repair. The other 2 that are in now are out also but not that much. I have 2 roll that should be in from repair this week so I will put them in a find out if that was the problem. I will let you know what I find. Thanks IP: Logged |
|
Steve H Moderator Posts: 404 |
posted January 02, 2007 02:29 PM
G'day Allan If your rolls are Chain Driven, have you checked for uneven wear in the chain links and the condition of the drive and idler sprockets, bearings and guides etc. Its amazing the difference a new chain can make (are your chains the "silent" type? ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 03, 2007 04:54 AM
G'day Steve. Im dont know what the silent type of chain is. One of the first things I did to this line when I took on this job was change the chain and replace the middle chrome roll sprocket. I really thought that would fix the problem. Im going to put these repaired rolls in and if that dont fix it, I really dont know what to do. IP: Logged |
|
rawelk Senior Member Posts: 22 |
posted January 04, 2007 08:01 PM
Silent chain is an inverted tooth power transmission chain type. Ramsey Chain is one of the manufacturers, and their website provides a useful primer on how it works. It is more expensive than standard roller chain, but, when lubricated correctly, lasts longer. It is often used in chill roll applications because it has higher power handling capacity at high speeds than roller chain, and transmits the power more smoothly. [This message has been edited by rawelk (edited January 04, 2007).] IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 05, 2007 03:43 AM
Thanks, I have used Ramseys before,and that is what runs this chrome roll stacknow, didnt know they were called the silent type though. IP: Logged |
|
Steve H Moderator Posts: 404 |
posted January 06, 2007 02:36 AM
quote: Nice link Bob, thanks I've bookmarked it  Well looks like you've covered the mechanical posibilities Allan- the problem doesn't occur when you run HIPS but is present with your co-ex PP/tie/EVOH/tie/PP, has the thicknesses of the various layers been checked, and the consistancy of the thickness of each of those layers? If there's some variation, maybe your feed block needs tuning to better match the viscosties of the various layers- some experimentation with extrusion parameters to vary the melt temp of the PP layers might help. Have you experimented with some different roll temps-When I've run PP sheet(mono layer), I found that it worked best with not more than a 5C temp difference between the middle and top roll. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 07, 2007 06:31 AM
quote: Nice link Bob, thanks I've bookmarked it Well looks like you've covered the mechanical posibilities Allan- the problem doesn't occur when you run HIPS but is present with your co-ex PP/tie/EVOH/tie/PP, has the thicknesses of the various layers been checked, and the consistancy of the thickness of each of those layers? If there's some variation, maybe your feed block needs tuning to better match the viscosties of the various layers- some experimentation with extrusion parameters to vary the melt temp of the PP layers might help. Have you experimented with some different roll temps-When I've run PP sheet(mono layer), I found that it worked best with not more than a 5C temp difference between the middle and top roll. [/QUOTE] Hi Steve, IP: Logged |
|
Steve H Moderator Posts: 404 |
posted January 07, 2007 09:15 PM
G'day Allan
quote: Hmmmm, HIPS is really forgiving as far as extrusion goes. A couple more mechanical posibilities- What maintains the nip pressure on your chill rollers, air or hydraulics. Is there any variation in the pressure on the top roller, so that the nip gap is varying? Another posibility could be pull/haul off nip, is there a variation in pressure there, or a variation in haul off tension or speed. Either of these would give you an effect similar to the extruder "surging" without any of the tell tale signals. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 15, 2007 07:45 AM
Steve The chrome roll nip is controled by air,I have some gauges on but have not seen any flucuation in the pressure. As for the tension and speed i have graphed the speed on the computer and it is spot on. I am going to look into the air side of your tip to see if there may be some thing there, as well as the pull roll pressure. Thanks IP: Logged |
|
griffex Senior Member Posts: 42 |
posted January 22, 2007 07:36 PM
Way back when, someone mentioned frequency of the breathing/surging. This is one of my two basic questions; the other is if the surge/breathing is on a regular cycle or irregular, and if regular, what is its cycle time (frequency)? If the frequency matches a roll or even the screw, that's very helpful, and the m,atching device is the likely source. If it's irregular, I look back to the feed -- high scrap content may feed irregularly, for example. PP is especially sensitive to rear barrel temperature -- go up and down there. (That's my "aspirin" to be tried when all else fails.) Next, look at amps to see if there is unusually high "wiggle" (variation). If you can't print out a plot of amps vs time, stare at the ammeter long enough to get an idea of the variation and the period of the cycle if consistent. What I'm looking for is second-zone surge, where the material hits compression zone before it is soft enough to deform -- melt already formed is pushed up between the particles to form globs of melt-particle mix that stick to the screw until they get blown through by the increasing pressure from the rear. Amp cycles here are around 30-90 seconds, cure is maybe a hotter rear barrel temp, or slower rpm. Preheating will help but isn't always an option. A quick frequency (1-3 seconds) may signal draw resonance, but unless you have a very big gap and thin product, you seldom see this in sheet. An even quicker frequency would signal melt fracture, but that's rare for HIPS and for sheet in general. On a separate track, if you have an air knife plastering the melt to the first contact, you may need less or maybe even no pressure from the top roll, hence no bead. I hope this helps. Let us know. Allan Griff Bethesda, MD USA IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 23, 2007 01:53 PM
Allan. I have plotted and graphed all the extruders and all the Chrome rolls and they are all fine. I have been all over with the heats in the feed section and worked with the feed throat cooling to no avail. The the frequency for the breathing is 5 to 6 seconds which leads be to an out around chrome rolls, We will find out this weekend when the new roll goes in. IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted January 25, 2007 08:44 AM
Hi Allan, When the bead gets smaller and bigger does it happen even across the die exit or is it random? What melt pressure do you get at the barrel exit, before the gear pump and in the die? Regards quote: IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 29, 2007 01:34 PM
Welcome Bonzo. The washing is even all the way across and is not random,There are 6 extruders 3 with gear pumps and three with out and all run into a large feed block.The main extruder pressure is 174 Bar before the Gear pump, the 2 65 mm run 137 an 145 the other 3 are 2" extruders and run 204 bar 206 bar and 275 and these run without gear pumps. I dont have anyway to tell you the pressure in the die. Thanks IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted January 30, 2007 08:04 AM
Hi Allan, How are the extruders with gear pump controled? Rgs Rgs quote: IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 30, 2007 10:16 AM
Bonzo They are controled by pressure tranducers, You asked what the pressure was in the die. If you are asking what I run the suction pressure at then that is run at 75 Bar. Thanks Allan IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted January 31, 2007 06:15 AM
Hi Allan, Sorry for the confusion. Do you get any suction pressure variation? If so how much and time frame please that for any of the extruders with a gear pump. Regards
quote: IP: Logged |
|
Allan Senior Member Posts: 25 |
posted January 31, 2007 01:52 PM
Bonzo There is a small variation, maybe a couple of bar either way on all 3 with gear pumps and the time frame on the one with the biggest variation was 4 bar @ 4 min. So says the computer. IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted February 01, 2007 07:01 AM
Hi Allan, If the microprocessor parameters are set up properly a time frame of 4'should well be within the capability of the screw to kick in when the suction pressure drops or back of when there is a pressure increase to maintain a stable pressure in the die. Nevertheless I believe that a stable process should have a suction pressure variation not higher then +/- 1 bar, on a 4' timeframe, if you process the right material with a correct designed screw. What is the size of the bead you are running? What is the thickness of the finished product? How stable is the pressure of the 3 other extruders without a gear pump? Regards quote: IP: Logged |
|
griffex Senior Member Posts: 42 |
posted February 03, 2007 03:12 PM
Looks like we have the whole world on this one, should be able to solve it. 1. If either roll is out of round the breathing cycle should match the roll rpm -- e.g., a 45-cm diameter roll running at 14 m/min will repeat every 6 seconds. That should be a clear proof of what's wrong. If both rolls of the nip are out of round that's harder. What did you find out when you replaced a roll? 2. Draw resonance. I noticed thickness is 1 mil. I had thought it was 1 mm (maybe it is), and in that case draw resonance is unlikely. If it's 1 mil (0.001") DR is definitely a possibility. Move the takeoff closer or further away from the die. If it's DR, the frequency will change. 3. Gear pump inefficiency. We can't assume a gear pump is masking surges, even if it's new. If you know the pump displacement you can figure out the theoretical 100% throughput (remember to use melt density not solid -- PP is around 0.73 g/cc). Compare with the actual throughput of the material in the pump -- the further you are from the 100% figure, the less efficient and the more likely a surge will pass through. A problem with this idea is that I can't think of anything behind the gear pump that will give a regular 6-second cycle. Hope this helps. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 05, 2007 08:30 AM
quote: Allan , The new rolls have not made to me yet, I am getting them this coming weekend they are telling me now. I am really leaning towards the middle roll being the problem though. Thanks to all for their tips and suggestions. I will let you know when I install the roll what the outcome is. [This message has been edited by Allan (edited February 05, 2007).] IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 19, 2007 10:21 PM
G'day guys, The repaired roll made no difference in the bead instability. I am out of Ideas. I may have someone come in that knows a lot more about muti-layerd sheet and co extrusion than I do. Anyone want to come to Melbourne Australia. IP: Logged |
|
Tom C Moderator Posts: 838 |
posted February 20, 2007 08:26 AM
Allan, Sorry the rolls did not work out. You are sure everything is set up right and there is no problem with the rolls drive? Lets try the divide and conquer method of diagnostics. You said that the same problem existed on your mono jobs. Which extruder(s) do you use for the mono jobs? ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted February 20, 2007 08:32 AM
Hi Allan, Do you experience the same problem when running a mono layer? Regards, Bonzo
quote: IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 20, 2007 08:02 PM
quote:Tom, At this point I am starting to dought some of the info Im getting from the computer so no Im not sure the drives are set up right. When we run the mono stuff I run 4 of the 6, the 2 I dont run are 2" extruders with out gear pumps. I have a mate of mine from the states that says that I need more heat in the top chrome roll, and I tend to agree with him, but when I increase the temp I loose clarity in the sheet,and this is clarified sheet so supposed to be clear. IP: Logged |
|
Tom C Moderator Posts: 838 |
posted February 20, 2007 10:11 PM
Allan, Any chance you can run the extruders individually through the rolls to try and identify a problem? If they all wash, then the problem is in the downstream. If some do and some don't then you know where to look. ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
griffex Senior Member Posts: 42 |
posted February 21, 2007 03:53 PM
Some of us doglovers don't give up. Back of Feb 3 I mentyioned roll, darw resonance and gear pump inefficiency as possibles. You've eliminated #1. How about #2 -- what are the product thickness and die gap? As for #3, do you know volume displacement of the pump (maker should know this) and the percentage of this that you're getting? Pump feedback circuit may also be faulty, but you'd see a match-up of the period of screw speed-ups with the period of the breathing. Best regards IP: Logged |
|
Steve H Moderator Posts: 404 |
posted February 21, 2007 05:57 PM
G'day Ain't life and production a bitch Rather than use the computer generated info, try checking everything with an independant tachometer- Follow Allan Griff's advice, better still persuade him to come visit Melbourne again and give you a hand in person. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 21, 2007 09:08 PM
quote:Tom, I have wanted to do that for a while but cant get machine time for the trial. I was down all last week so I need to get caught back up on roll stock.Should have some time in a week or so. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 21, 2007 09:27 PM
quote:Griff are you a dog lover too . The product thickness is 1.3 mm and the die gap is set 20% more ,but the die lip blows out to over 2 mm when running. Now when you start talking about pump feed back circuits and volume displacement you loose me. Im not a process engineer so please bear with me. IP: Logged |
|
Chemeng34 Senior Member Posts: 5 |
posted February 21, 2007 10:55 PM
Allan: Do you have an e-mail address I can correspond with you. I have some information on processing and equipmentthat may help resolve your problem. I have ran into this before at Cryovac here in the US. mine is jgranda@teleflex.com Should you still need the assistance.
quote:Griff are you a dog lover too . The product thickness is 1.3 mm and the die gap is set 20% more ,but the die lip blows out to over 2 mm when running. Now when you start talking about pump feed back circuits and volume displacement you loose me. Im not a process engineer so please bear with me. [/B][/QUOTE] ------------------ IP: Logged |
|
bonzo Senior Member Posts: 6 |
posted February 22, 2007 07:50 AM
quote:Tom, I have wanted to do that for a while but cant get machine time for the trial. I was down all last week so I need to get caught back up on roll stock.Should have some time in a week or so. [/B][/QUOTE] Regards IP: Logged |
|
Allan Senior Member Posts: 25 |
posted February 27, 2007 03:55 PM
quote:Email allan.miller@visy.com.au Thanks [This message has been edited by Allan (edited February 27, 2007).] IP: Logged |
|
Allan Senior Member Posts: 25 |
posted March 19, 2007 09:45 PM
G'day Gents Im sorry I have not updated you on the progress of this fine machine that i have here but I may be closer to solving this problem . I changed over to Hips after a very long run of p.p and one of the extruders started to surge. The Surge has the same frequency as the bead wash so I guess there was a surge after all but it was not showing up on the computer nor could i hear it as I can now. I know from a tear down in Nov that this barrel is in need of replacing but I could not get one so I had to put the screw back in a have go at it. Now I need to order the barrel and the screw right, i cant just put a new barrel on ? IP: Logged |
|
Tom C Moderator Posts: 838 |
posted March 19, 2007 10:19 PM
Allan, Well the rest of the machine should be tip-top by the time you get done. Wear is not the only cause of surging. How much wear did you find? What is the diameter, L ------------------ Tom Cunningham www.ExtrusionTechnicalServices.com IP: Logged |
|
Steve H Moderator Posts: 404 |
posted March 20, 2007 03:45 PM
G'day Allan What grade/make HIPS are you running? what are the temp settings on the troublesome extruder? what temp are you getting (melt temp) When you say you can hear some thing different now with that extruder, what has changed, try and describe what you're now hearing. ------------------ If at first you don't succeed, skydiving is not for you. IP: Logged |
|
Allan Senior Member Posts: 25 |
posted April 15, 2007 11:35 PM
Sorry Guys, I have been ill for almost a month now and have not been on the computer much or at work for that matter. Im still rounding up info on the screws and the barrels and but been giving other duties also. Im not on the extruder as much as I was.I will keep in touch when i find out more. Again thanks for all your help IP: Logged |
, RPMs and output rate of the machine that is surging?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
