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