Need Help Agfa 1600 mv banding at beginning of print

[Ronald_]

Hope someone can help me a bit with a problem we're having. Since a couple of weeks our Agfa is banding. Almost every time at the beginning of the print. Banding usually starts at around 5% into the print and ends at around 20%, rest of the output is fine. The affected area seems to be scaling with print size. Not all prints are affected. Usually first 1-2 prints after startup are perfect. After that the banding begins, but not on all prints. Size of the banding is equal to the belt advancement per pass.

Some prints are affected, some are not. Last week we printed 150 pvc foam boards 140x120 cm. All boards had the same image. 32 boards had the banding issue.

Banding is dark lines, like the passes are overlapping. All tests, including the belt advancement, are perfectly fine. Nozzles are fine.

Banding occures in all print modes, 4p or 8p, uni- or bidirectional. In 8p mode the banding is twice as small.
Banding occures on different ink densities or colors. Even in light blues or in dense built-up blacks. Tested with different mediaprofiles, same results.
Banding occures on different substrates. Tested on dibond alu-panel, forex PVC foam, foambord, acryclic glass. Same results.

Printer, heads and baseplate are cleaned every day machine is used.

2 months ago the output fan of the left UV assembly was replaced. The fan was damaged and stopped working. Printer was banding bad. After the replace banding was gone. I guess it must be 2 weeks after this the printer started this banding issue. Fans are still fine on visual inspection.

Any ideas?

 

[Hamster]

perhaps it is necessary to check the system vacuum pressure

 

[Terry01]

Check media compensation..your passes are overlapping.

 

[Ronald_]

Check media compensation..your passes are overlapping.

I've changed the feed adjustment to a higher value and it appears the banding has disappeared.
The feed adjustment test print from the printer panel looked good, but appaerently is not accurate enough to judge uppon.

thnx for the help!!

 

[Ronald_]

So, as it turned out the problem is still here. This is a solid gray background. Printing at the beginning of print with very faint banding. The banding becomes more intense 30 cm/1ft into the print. Then the heavy banding apears for approx. 10 cm and then disappears. After that the print is just perfect. Same results 3 different times.

This was printed on rigid PVC foam. Printed the same solid gray on hard solvent paper and there is no banding whatsoever.

Any ideas?

 

[Andy_warp]

Does your machine use a bulk ink system? Are there inline filters? Also the lines could be scummy...maybe give them a flush?

Doh! just saw that it didn't band on paper.

Maybe your board stock is getting moisture?