MOISTURE AND IMPRESSION
We are working with a Windmill. We are located in Southern California. Lately, we had an issue getting a good deep hit on some 20pt Lettra. It has been cold ( CA cold 45-60 ) and rainy leaving humidity around 70-90%. Our unit has no heat or climate control only a beer fridge and Netflicks. I have read about spritzing a sheet with water to help get a better hit. I figured the weather related moisture in the sheet would help give a better hit. I ended using a lot of packing and impression to get the job done. Can moisture in a paper cause the problem we had. I felt like I was trying to print on a wet sponge. The normal hit kind of deflected away leaving no good impression. Is there some way the cold and rain could have effected the Windmill?
Your inclination is correct, high humidity generally will soften the paper to allow for deeper impression and better ink coverage. I don’t think the cool temps would have much effect on things, although cold air actually holds less humidity than warmer. Lettra generally does not require dampening to get a deep impression, so you might look to something else which has changed in your press setup. Have you noticed recently a change to needing more impression gradually?
In the Windmill press there is a shear collar which is designed to fracture if the press binds. That collar can get a crack which will require progressively greater impression setting to be used.
I’ve personally had no experience with the shear collar, but there may be some on the list who have had similar difficulty and could suggest what to look for.
John Henry
Cedar Creek Press
We have not had a noticeable change in pressure but then we bought the press used and in 5 years have never had a shear collar fail. Thanks for the feed back. I will check the collar to see if there are any cracks and let you know.
Need to raise the humidity?, strips of old blanket dangling down into a bucket of water, or two or three. Mind you its amazing how often you forget they are there and kick them over!. An SRA1 sheet can vary over a weekend by about a sixteenth of an inch in its width, so if you have no air-con
and two colour offset presses doing four colour work in two passes, then expect to make replacement plates on Monday! Or plan the work days better, and/or fire the works manager!
Mind you I’m talking litho here.
Are you using photopolymer plates? I use copper engravings with good results, but photopolymer works just as good.
Back in the day I’ve used wood mounted cuts where the wood compresses. I use sterling base now.
I agree with the shear collar problem, I check mine annually and keep a spare just in case. You really don’t notice it till the impression backs off.
bppayn, thanks for the feedback about the collar I have already ordered a new shear collar. I would have never thought about the shear collar but it does explain a lot. We work with photopolymer for printing and had just added a new larger base. We now wonder if the combination of the base, cold wet weather and compression has pushed the collar past the breaking point and caused it to crack, or crack more than it was. I will pull it once the new one arrives and let you know. Again thanks to all for pointing me in a direction I never would have thought of.
Do you have a copy of the manual? It goes over the process of replacing the shear collar properly. 106-108, “Safety overload device”
Just in case, here’s an online one:
https://d1mkprg9bp64fp.cloudfront.net/wp-content/blogs.dir/2/files/2012/...
I believe this was a part meant to be kept on hand and replaced over long periods of time, with spares kept on hand to help mitigate catastrophe, so if you wind up needing to replace it- I’d suggest ordering another spare so you’ll have one on hand in the event something falls into the works etc etc.
We pulled the old shear collar today. The old collar showed signs of age and had signs of abrasion but was still it tact and had no cracks. We will keep it as the backup. I have a manual which was a big help. The collar and the other piece popped out so easy I did not see how they went back together, which went in first. The pic the manual answered my question. The process took 15 minutes to do. I spent more item finding a 24mm and a 28mm socket plus buying a breaker bar than I did fixing the collar.
Man, those efficient germans! Engineering/Making it easy to replace wear items!
I thought for sure the collar might be adding to our impression issue. I knew if it was busted it would not work, but wondered if it was cracked or fatigued if it could still function but at the reduced or unpredictable capacity somehow. I had read blogs about how difficult it was to replace so expected the worst. I removed the cover and saw the collar. I reached in to see what I would need to do to get it out and gave a little tug and it popped out and went rolling across the floor. I am back to wondering if high content of moisture in the paper and damp cold weather was more of a problem than I first thought. I had thought the weather would be a good thing, now I am not so sure. I at least know that there is no mechanical, base, plate or press related issue. That leaves only paper and human. It’s the papers fault.
“When you hear hoofbeats, think of horses not zebras”.
We replaced the shear collar and have noticed a difference. The packing math now works like I would expect and or impression is much more controlled. We do feel the collar was at least part of the problem. When we are talking about a distance or factor of 3-4 sheets of copy paper - 15-20 pts - it is not a lot but can change how things function. Our most recent job was packed to a 47pt with printed sheet and packing combined. The pressure was at the first ring past zero. I had a useable sheet on the first pull with a kiss impression like the days of old.
That’s great! Just shows how important that little collar is, and that it doesn’t have to have visible cracks to need replacing.