cd 74 problem

[peterh]

hi guys,

got a big problem on the cd 74 5 colour and nobody seems to be able to solve,i have had electricians,engineers,demonstrators but no luck,problem we got is that on a very random basis,maybe 1 every stack of paper we get 1 sheet really really badly setoff,like you have stood all over it,the sheets above and below are all perfect,we have had the spray unit serviced ,although i have been told that it cannot be that as 1 sheets cannot set off which makes sense,we have had chemists in to check ink,water,we have tried a few different makes of ink,including heidelbergs own,
i personally think we must be getting a massive build up of static and then boom,on one sheet it just gives it all to it,the press is fitted with static eliminators from and back and we have tried with them on and off,as i said i had an engineer here last week with a sparky for 3 days and they cannot solve it,they just said it should not be happening,all cams on gripper bars have been checked,we run ksl spray,so dont know what to do next,everything in the delivery has been checked,the press is printing perfectly and runs very comfortably within iso12647-2 colour so again i know we are not getting a bad ink water balance as both this and the chemists results prove that.
any thoughts would be appreciated

 

[FSA]

peterh
I've seen that, it turn out to be one of the operators were pulling out the sheet. Had a big fight about his habit, he would flick the sheet when pulling it out and he kept preselecting the vacuum when the gate would open, therefore the sheet on top would get a bad jog. Some times people will never beleive that it is something so simple. Check it out and don't say anything to the guys, just watch, maybe it could be that simple for you.
FSA

 

[peterh]

hi,
thanks for that quick reply ,will ask the lads,although i`m a bit sceptical on that as i have been there when it happens and we used to have a sm 74 will no such issues,
when you say preselecting the vacumn when the gate is open can you elaborate with what you mean

 

[mrheidelberg]

I think 1 sheet per stack that has setoff, would eliminate any operator error checking the sheets during the run ?? (I hope a printer would check the sheets more than just once during running a stack of paper !!)
You can select a suction device which holds the top sheet (on the fingers) on certain Heidelberg press models.
Personally i think that there is an issue with the powder spray device shutting off momentarily during the run because that is the one thing on the machine that stops setoff.

Regards.

 

[peterh]

hi,
thanks for the offering,i have talked to heidelberg tecnical and they say that the spray cannot switch off for one sheet and even if it could there would be enough spray in the vicinity not to set off 1 sheetsee the pic for how bad it is
http://i25.photobucket.com/albums/c96/peterh7036/pic2.jpg

 

[peterh]

http://i25.photobucket.com/albums/c96/peterh7036/pic1.jpg
another picture

 

[FSA]

peterh
That is serious offset, it looks like the just on the outside edge, if so then there is too much air being used from the fans and tubes. When the press is shuting down the spray maybe shuting down too early and what spray hits the sheet is being blown off. Had one operator he felt that full on the fans worked best, the folder operator could tell when he ran jobs because his piles were messy and lots of setoff here and there. There is a special light you can get to see the flow of spray. Also a flat beam of light can be used to see the spray that is on the sheet, that will tell you if your spray unit is making it to all areas of the sheet. If the tech can't find anything then it is most likely something simple that is being overlooked because it is so simple nobody would look at that to be the problem, good luck.
FSA

 

[peterh]

hi thanks for quick response,we have sort of ruled out standard set off as it only happens every x amount of sheets as i said it will print maybe 10 inches and you will get 1 sheet then 10 inches of perfect sheets,i have placed an led lamp across the sheet in a dark room and you can see the spray on it,i have thought about the sparay beinf blown off and we have set our air blasts to minimum and have had photos from others where they run their air,this press has the xl 75 delivery so its the latest model of cd 74,we bought it off a printer in belgium and it has been under warranty with plantin(heidelberg belgium)all of its life,and an easy life that is as it has only done 30 million imps

 

[turbotom1052]

peterh i too go with the idea of a huge static discharge. But fsa also touched on a good point. Im a firm believer of minimum air in the delivery. I tend to run blow down fans down really low then i use a combination of slower speeds on the slowdown wheels and a late sheet release to kinda "s t r e t c h" out the sheet before its gently dropped down on the pile. I also try to run the pile up high so that the drop to the top of the pile isnt a long one. Good luck in solving this mystery of presswork!!! As perplexing as this kinda thing can be its mysteries like this that still keep the job interesting after over 30 years running presses.

 

[Steve Arndt]

peterh,

One quick question for you...

Are the peripheral systems connected to the CAN Open bus (pretty purple cables) or are they serial devices? If they are connected to the CAN Open bus, I would be curious if anything is shown in the CAN History for the power spray device or dryer. The CAN History can capture gliches that happen very quickly and may not even register on the operating console.

...just curious.

Steve

 

[peterh]

hi steve
not really sure where to look for what you mention,there are no dryers as its a 4/1 press,is it iin the electrical cabinet.?

 

[Waqas_zahid]

Hello peterh,

Has this problem been resolved? I am curious to know that cause.

 

[Steve Arndt]

peterh,

It is unlikely my question has anything to do with your problem, but I did see a case where data collisions on the CAN Open bus would interrupt communication between a peripheral device and the main control cabinet intermittently.

If you would still like to check it out, look for a purple connecting cable coming out of the bottom of your powder spray device. This would only be true if you have a Weko or Grafix sprayer. If you don't see the purple cable, you have a device with serial communication. With a serial device, the diagnostic capabilities are not as elaborate.

If you find that it IS connected to the CAN Open system, you will need to have a Heidelberg technician look at the CAN History. This can be done through an onsite visit or remotely via a modem or ethernet if you have purchased that Heidelberg service.

No matter what the problem and solution, I would like to know what is done to finally resolve your issue. Please post the solution once it is found.

Steve

 

[peterh]

had a good look today and noticed that if you view the bacl of the pile then the pile is wobblin by about 4-5mm,at this point the front of the press at the gate is not tight just normal,i asked the printer and he told me he showed this to the engineer and he said thats normal,i cannot believe its normal for the stack to move like this,the top 1/4 to half inch is moving back and fore quite a lot in the same direction as the set off mark,also if you look at this video i took on my phone(sorry about quality)one sheet is droping differently to the rest,even though the engineers supposeidly adjusted all sheet arrival about a month ago.
the engineers used were a london based company called quatrotech,anybody have any dealings with these guys,
we bought the machine off whire horse machinery and the enginners are the ones theyused,we are not out of warranty so will be using our usual engineers from now on.
any thoughts on video heres the link
http://s25.photobucket.com/albums/c96/peterh7036/?action=view&current=IMG_3533.mp4

 

[FSA]

peterh
Use wedges and move them up as the pike grows in size, also the sheets are not floating down , release the sheet earlier and it looks like it's been blown down hard, too much air, therefore you will always get setoff on the top of the pile. Then when the motor lowers the pile , bam , mega setoff. One solution is to make smaller piles. The video was fine, it shows the problem very clear.
FSA

 

[peterh]

hi steve,

appreciate the answer but i dont think its as simple as wedges as we have run heidelberg for last 20 years and not had this problem,our last press was a sm 74 and in 8 years this never happened once,so same printers same tactics and bang,as i have mentioned this only happens a couple of times per stack,my theory is that in the video one sheet looks like it falls different o others and with the sheets moving it just makes the odd one rub like hell.
anybody elses cd 74 wobble like this at the back of the stack.?like stock was 130 gsm gloss so not even a heavy card to make it wobble.we have check the table and that is sqaure as we thought it may have been leaning backwards.

 

[William Taylor]

Without trying to make you look a fool and I know its obvious, but when you checked the sheet under the lamp in the dark room, was it the sheet before the bad sheet or was it the bad sheet? It would have been the sheet before that didn't have any powder on it and not the sheet with set off.
I think the problem is with the powder unit or a sensor somewhere. If the press still has warranty then get Heidelberg in to change a few parts to eliminate this and that.
Does it have the same problem on different stocks? This would eliminate static if it did.

 

[turbotom1052]

after viewing your video im quite surprised that ALL the sheets didnt have offset. Im guessing that the only thing that prevented the entire job from offsetting is that youve probably got coating on the sheet and its pretty set by the time it reaches the pile. That front to back rocking of the pile is not normal!!! Two things come to mind worth checking. The first is to be sure your delivery platform is level from front to back. You mentioned that you checked squarness but what about level when the load builds up a bit? The second is to be sure that your rear jogger is set correctly to the sheet size your running. Too tight of a rear jogger can cause a tall load to rock back and forth like that when the front joggers move fore and aft as they do. Lastly i would recommend that you try delivering the sheet with a bit less blowdown air and use a combination of a slower speed on your slowdown wheels and an advanced sheet release to sorta stretch the sheet out so it can be deposited on the top of the pile with a little more finesse.

 

[NZ Printer]

anybody elses cd 74 wobble like this at the back of the stack.?like stock was 130 gsm gloss so not even a heavy card to make it wobble.we have check the table and that is sqaure as we thought it may have been leaning backwards.

Hi PeterH, The delivery pile in our 74 wobbles like that also; only when the pile is high, like over half of the delivery full. I solve this by means of wedges on the front edge. The back gauge is not set too tight and everything is square. Only seems to happen on lighter stocks from 74 GSM to 200 GSM. Basically if the stack is level it won't do it. If this was causing set off, it would be your entire job set off, not just one sheet !!! Is the air supply to the slow down wheels consistent ? sometimes this can cause problems; i.e a small air leak in a hose.

 

[peterh]

hi guys,

problem still here,sent video to heidelberg and they say thats not correct,waiting for a downtime slot to get an engineer in,here`s hoping this resolves the problem