spray powder build up on blanket

Our PM 74 operator has had problems with spray powder building up and causing a line in solids and a heavy coverage when he backs up a job. I suggested he use less spray powder on the first pass but he says it won't help. As he is doing it, he can back up about 300 sheets and has to wash the first to blankets. Any suggestions would be helpful

 

Hi,

Is the gripper / spray bar timing ok.
What grade of powder are you using ?
Do you have a spare unit to dust on.

Regards.

 

Thanks for responding. I'll check the timing. The build up occurs about 2 inches from the gripper. I think our powder is Oxy-dry 744. We have just four units on the PM 74. We run KCMY and the black and cyan units are where the power is giving us a problem. The cyan is really only a problem if there is not much coverage on the black unit.

 

your preesman does not have enough experience. First of all if he can onlt back up 300 sheets before he has to stop, he is runnig 10 times too much powder! He should be able to back upo 3000. If it is a straight line running from gripper to tail, then your problem lies on the in feed. Something at the feeder,perhaps a hold down p[addle is creating the build up on the blanket.
Take a sheet that has the line from the build up and put it on top of the load. Run it down to the head stops real slow and see what lines up with the line.

Lildaddy

 

Hi,

Just ask the operator to turn the spray powder % down and run a few smaller stacks to build his confidence up, so he knows the jobs will not set off.
Also sometimes if the front lay infeed venturi is set too high that can disturb the first couple of inches of the paper if there is too much powder on the sheet.

Regards.

 

Thank's guys. We reprinted a job today and I told him to turn down the powder and run smaller lifts. It turned out alot better. I worry about this pressman sometimes though. Anyway. Thanks again.

 

Running less powder and racking in small lifts does help. If that doesnt help the only alternative is to dust the job first by 'wet plating it ' as it goes through the press for the dusting process.

 

in some jobs you need extra powder and turning it down will be a problem.
if you do have alot of powder , no matter what you do it will come off to the first blankets.
what you can do in this case is run the stock once befor printing or use a pile turner with air to get rid of the free powder - then when you get it in the press you will have less build up.
Sorry , printing technology is only 100's of year old and not perfect yet

 

If it's a problem @ 300 sheets you have a problem with your powder unit or your pressman. Try running a smaller grain powder too.

Good luck

 

I agree with the infeed solution. Most of the 74's have brushwheels at the tail and feather wheels about two inches from the gripper. The feather wheels stop when the sheet does and disturbs the powder in that particular area. The hold downs, flaps, leaders, paddles, or whatever your particular shop calls them can also make a vertical line near the gripper. Raising them up will correct it but if stock is curly then then you can run into feed problems.

 

I agree with the suggestions given to the powder issue. You might also look into the amount of ink film thickness being applied to the sheet. This is where the craftmanship of being a pressman comes to bear.Sounds like the operator has been burnt a few times with jobs sticking together and the natural thing to do is you got it-more powder. Experienced operators have certain keys they look for when running presses. Does the plate look wet when running, does the ink on the rollers have that soft velvety look to them. You should be able to tell whether you are running too much powder by how the sheets come into the delivery. For instance, if you drop a load onto the floor, does the top sheets start sliding everywhere? Noticing little things like this helps the operator see he probably can lower his setting some. I hope this helps

 

powder problems

i noticed that you mentioned you were running an oxy dry powder system. my feelings about oxydry powder systems is that for the most part its an antiquated system that has remained unchanged technologically for the last 30 plus years. ive found them to be unreliable. when a pressman cant have confidence and repeatable results in a powder system then he will tend to run more powder. id suggest looking into upgrading your powder unit to something a little more current and reliable. graphix comes to mind first. weko is an option too but at a higher cost. both of these powder units will give predictable and consistent results

 

I think the OP mentioned the actual spray powder is from oxy dry.........Heidelberg use's Grafix or Weko spay powder units.

 

i stand corrected. upon a closer read i see that he was in fact talkin bout the type of actual powder but it should be noted as long as were correcting each other here that any powder system is an option when delivered from germany. ive worked on heidelberg presses that were equiped with oxy dry units installed by oxy dry as a cheaper alternative to the graphix or weko units

 

Of course I agree with everything that's been said, but I feel I must put my two-cents in.

Do not, arbitrarily , drastically reduce the amount of spray powder put on a coated sheet. I once worked for an idiot who one day walked up to the press and halved the amount of powder I was putting on the sheet. The job stuck and cost him quite a bit of money.

You can always dust a job, but once it sticks it is a worthless pile of crap.

 

Too much spray powder, I had problems with the griper to tail marks before, it was from the sheet brake wheels in the delivery.

 

It sounds as if you have two things going on.
You seem to be using too much anti set-off spray. Set-off occurs within the first minute or so of printing, as ink will usually set in that time. Mishandling of loads could cause set off but gently lowering and moving them should avoid any problems. Dont sit on loads
Reduce your set-off spray and print 100 sheets then inspect them for set-off, as set off usually occurs at the time of delivery.

Run 200 and inspect.

Run 300 and inspect.

If no problem, you may try to reduce it more.

Its worth doing once as you will not have to repeat the process.

If you reduce ink tack at all, use a thixotropic tack reducer.

If my memory serves me right there are more "water dispersable" spray powdwers available, this may reduce the number of blanket washes. Its a few years since I got my hands dirty.

If the spray is an electrostatic dispersal type, check that someone has not cleaned it out with a blade. They will dump spray afterwards.


You are probably cleaning part of the sheet with some part of the sheet transfer system; sheet smoother, run-down wheels, two-sheet trip, transfer cylinders etc. This will show up on the blanket and thus the print.

Hope this helps.

 

First of all find the cause of runing more powder; if your pressroom has lower humidity it causess setoff lower ph cause setoff if you are runing more water it also slowdown drying.Change if paper is acidic & use quick drier, in the end change ink with a good quality drying & anti screatch ink, these kind of inks gives a good result against setoff, beside this also try to use racks for short pile on heavy solids , use decurler to keep straghten the paper,try to keep the sheets in correct order when printing in the delievry,use antistatic rod.

 

Maybe slow the press speed down to give more time for the ink to set before too much weight gets on top.

Anything to use less powder.