Running powder on a GTO

I have an old GTO46 and want to know about using powder.
I think I have mastered all the other aspects of the press and mostly I run uncoated stock doing single colour and 4 colour work. Recently I tried some coated stock. I had some powder around so I tried it. I have used powder one time in the past with a Hamada E47 which I also did 4 colour on coated stock. I worked well but not this time on the GTO. It tended to clump up and get on the blanket and stop ink transferring properly. I ended up shutting it off and finishing the run with out it. I ran the job again and thought it would be ok without powder but the sheets ended up sticking to each other.
Any and all help with using powder on my GTO will be greatly appreciated. What powder do I get? How do I adjust it? How do I know when it is the right amount so it does not ruin the job? etc

 

I feel that for the typical commercial printing applications a known brand of powder in the 25 to 30 micron range should do you fine. As important as the type and size of powder, is that the powdering unit is performing as it should. I can not over emphasize the need for powder unit performance that is consistent, and repeatable. Powder units are often overlooked when there comes time to do press maintenance. Press crews want to first maintain the things on the press that makes the image print well. When you consider that even the very best print images can wind up in the trash bin if they setoff or stick together then you can see the importance of proper powdering unit maintenance. I wouldn't consider it excessive to do a complete cleaning of the powdering unit 4 times a year. Also very important would be to make sure your powder remains dry. I myself like to store powder in a large airtight Tupperware style tub that remains sealed after every refill. Be sure to fluff the powder before filling the hopper and also be sure that the powder filling is without any contaminants that could clog up the lines and nozzles.
As for finding the required amount of powder to lay down on a freshly printed sheet there is no completely painless way other than to keep lowering the powder feed in small increments until the print begins to setoff. Once you reach the point of setoff then just turn it back up a bit. This amount required can vary with the amount of coverage, type of paper, and ink film thickness so beware.
A good tip would be that if you've got a cloud around the delivery of your press when running that your running too much powder. It would be about expected for the pressman to have to blow his nose few times during the course of a shift to know that there is at least some powder being delivered.

 

I've found a 320 grade powder good for many stocks and jobs. Heavy coverage remove sheets in small lifts to help avoid offset. And keep powder to minimum. I don't use powder on any stock that's not coated. But coated, matte sheets yes! Tom has pretty much covered things for you.