Spray powder bombs-40" Komori

[GazKL440]

Ok so we are getting what *appears* to be spray powder bombs when backing up jobs at the moment. On the job we are currently running, it's requiring a blanket wash at least twice per stack, and it shows up pretty badly in the 4 colour screens, but is mainly evident on the first 2 units (black and cyan).

Both the first two units show small blotches of spray powder on the blankets when backing up, and must be getting picked up on the first pass then transferring onto the blankets during the second pass.

The problem is that none of us can find where it's coming from on the first pass. The delivery and gooseneck have been blown down and vacuumed several times this week, we have been under the press and pulled every bit of stray paper out from under it, and have cleaned all the drip trays under the blanket washers, searched high and low for places where powder has settled and cleaned it all... Yet the spots continue.

It's very_****ing_IRRITATING.

With the job we are currently running we can get away with it, and have around 300,000 or so impressions to finish it off. The next job on however, is an agency magazine, so any blotches will be unacceptable. And it's a 300+ pager with all the lovely match-ups of horizonstal bars etc that will be a pain to print: and I DO NOT want to re-print it if it gets knocked back for spray powder bombs.

The press is a 2000 model Komori Lithrone 440... I wish it was a 5 so I could bump it all back a unit and use unit one to despray it..... But it's not.

Any ideas are appreciated

 

[Ajax]

Do the blotches appear in the same spot every time and is this board stock, text weight, gloss or offset?

 

[GazKL440]

The blotches appear in the same area, but are not exactly the same.... Similar patterns and appearance, approximately 1/3 of the distance from each edge of the sheet (where a gutter would be in a standard A4/8up job)

We are running a matte stock called 'high bulk velvet', 80gsm with a sheet size of 890x627mm. It's a Chinese stock that we have used for several year now with 2/3 containers being processed per month, and generally it's a very good stock: it runs well, prints well, dries well... Good paper IMHO.

Having had a few beers now and a think about it, the general area where the splotches are showing up lines up with the lip edge on the exhaust duct, located directly above the top of the gooseneck. This was never set up properly, and I reckon there could be a bit of build up there... Will have a look on Monday...

 

[cheetoh]

Are you sure your Powder box is dispensing properly?

 

[Servicetech]

Electrostatic powder sprayer

Electrostatic powder sprayer

Is the powder sprayer a hopper/ roller type with a static bulb? if so the spray powder may not be sticking to the roller and just dropping off in larger clumps.

Turn the sprayer on in manual, and watch the roller as it turns, the powder should stick to the roller uniformly until it gets to the static bulb. The roller can become dirty, or worn where the powder won't stick to it and it will just drop off in "bombs".

 

[peter61]

sounds to me like you have a build up of powder and grease on your rails or delivery pan,you need to do a though job of cleaning the delivery part of your press.Do you have a extended delivery?

 

[Diddler]

What is the status of the Grill/ Grate above your delivery. Have you blown this down also? “Powder Bombs” always come from above.

 

[Michael Ziemke]

Make certain your blankets are not under packed. Insufficient plate to blanket squeeze becomes obvious when powder seems excessive on the backup. Do not confuse this with impression provided by the back cylinder. Packing is the only thing that governs plate to blanket pressure. Depending on where you are with blanket height (most presses should be even with bearer) try adding .002" (.05mm) under your blankets. With most any compressible blanket made today, this will likely cause no appreciable increase in dot gain, but will assist in moving the powder to the dampening recirculator tank, leaving less powder to collect on the blankets.

 

[GazKL440]

Ok we have sorted this out, and in the end it just came down to comprehensively cleaning out the bottom of the gooseneck. Each week it gets a delivery clean as part of the weekly maintenance, but we usually limit this to an air gun blow down to remove shite from the traveling grippers. Not having an assistant and being limited to 2 hrs maintenance means that this can be a quick once over, as just the critical greasing takes a fair amount of time on it's own, and the result is that (obviously also critical) maintenance cleaning is not done as thoroughly as it should be.

Sometimes I think that saving a few dollars on NOT having an assistant at all on a 26" 5col and a 40" that both run 2 shifts a day is a false economy. Sure, it saves a few bucks in the short run but when you NEED an extra set of hands and don't have them, it costs you time... And time is money. Monday mornings consist of maintenance and a cold press start up: a lot of work on your own, and things like cam followers are damn near impossible with back cyl washers in the way!

Micheal: we run blankets when installed at .005 overpacked, they compress down to around .002/3 pretty much straight away: having said that I haven't miked one up for a while...

 

[John Arneson]

GazKL440,
In the 200 series Komories there is a bar connecting the two sprockets that drive the delivery lowering. The bar is very close the the electostatic sprayer, it builds up powder very fast. When the pile drops down it is not like the smooth movement of a rollex watch the eye sees it and it drops about 3/4 of an inch and the stop is sudden. That is where your "bombs" are from. Wipe it off everyday when you fill your powder.
Hope this helps.
John