Throwing press plates

[hubber]

I work on a Goss Community 13 unit web press. Starting in early June we started throwing plates. They will either come off entirely or simply release one edge and end up completely reversed but still attached. The kicker is it has only happened on our three high and our stacked unit, both run process color. None of our single units have thrown any. Any suggestions?

 

[Deleted member 16349]

I work on a Goss Community 13 unit web press. Starting in early June we started throwing plates. They will either come off entirely or simply release one edge and end up completely reversed but still attached. The kicker is it has only happened on our three high and our stacked unit, both run process color. None of our single units have thrown any. Any suggestions?

Hi Hubber,

I have seen something similar a bit over twenty years ago and maybe it is related to your problem.

This was with aluminum plates on a web press. Normally there was no problem but then suddenly the plate's leading edge was working out of the gap. As it did this, the leading edge of the plate was being deforming. In about a 1000 meters this would show up and the plate would almost be totally out of the gap.

What it turned out to be was that the way the packing was placed under the plate changed. Instead of having the packing go right up to the edge of the plate bend, operators were placing it short, maybe about a 4 millimeters back of the leading edge.

What seemed to be happening is that there was no support under the plate at the leading edge. The plate would sit up a bit off the plate cylinder and each time the form rollers hit it, it would deform the leading edge bend. Then the plate would lift up again and again get hit by the form rollers on the next impression.

As I remember it, if the packing edge was back from the leading edge more than a certain amount there was no problem and if the packing was at the leading edge there was no problem but if the packing was at some critical distance from the leading edge, the plate would work out of the gap.

It was the strangest thing to see after so few impressions. Anyhow going back to the original packing placement sorted this problem out.

At least that is how I remember it.

 

[HachiZenki]

We had this problem with our new 4-HI. All of a sudden we started throwing plates and could not figure out why. We checked the plate thicknesses and they were the same, we checked the blanket and packing thicknesses with a cobra mike and they were withing spec. We were considering pulling the blankets and packing to check iron to iron when I decided to check our mylar packing on the plate cylinders. Turns out that rather than being .006", which they should have been, they were measuring .0065". I changed to the correct .006" mylar packing and the problem went away.

 

[Dan Roll]

Remember, the plate and blanket surface speeds depends on their diameter. The higher a surface is packed, the faster it will be moving. The lower, the slower. If there is too much of a difference between the plate and blanket speeds you will see plate wear, streaking, tail cracking, and even throwing plates.

 

[HachiZenki]

Remember, the plate and blanket surface speeds depends on their diameter. The higher a surface is packed, the faster it will be moving. The lower, the slower. If there is too much of a difference between the plate and blanket speeds you will see plate wear, streaking, tail cracking, and even throwing plates.

Which is why when using compressible blankets (almost industry standard on web offsets) you normally underpack a little.

 

[HecTiK]

So if it's wearing too quick and cracking a lot you would go to a smaller packing then?

 

[Alois Senefelder]

Compressible Blankets

Compressible Blankets

Gentlemen,


All compressible blankets SHOULD be overpacked by - .05 mm - .10 mm


Regards, Alois

 

[rathishvm1]

Blanket height above bearer should be 0.05 to 0.10?

Blanket height above bearer should be 0.05 to 0.10?

Gentlemen,


All compressible blankets SHOULD be overpacked by - .05 mm - .10 mm


Regards, Alois

Dear Mr.Alois Senefelder,

Do you mean the compressible blankets must be packed till the blanket is above the bearer by 0.05 mm (or) Plate cylinder dia+ plate + plate underpacking +0.05mm = Blanket cylinder diameter+blanket thickness+blanket packing.

I think GOSS COMMUNITY is a bearerless cylinder? Can Mr.Paul Feeney step in?

 

[maynardsayswhat]

I'm not sure if this helps at all but here's 2 pennies:

A long way back when I was operating a King web (5-unit) we had a similar-sounding issue late in long runs. Turns out we had packing material wrapping around the turn where the blanket ends are secured making it "thicker" at that point by a few extra microns. This caused a hard impact at where the plate and blanket met which caused wear on the edge of the tightly tensioned plate where it met the gap of the blanket. Running top speed and after a long-ish run (for that press) the plates would sometimes break at that impact point.

Again, I'm not sure that helps (Goss and King secure blankets slightly differently) but thought I should mention it just for another possible thing to check.

Good luck and until it gets fixed, wear a helmet!

 

[Alois Senefelder]

Compressible Blankets # 2

Compressible Blankets # 2

Hello fellow Lithographers,

The Goss Community also Suburban Presses are " Bearer Clearence "

for more enlightenment read -- PDFs


Regards, Alois