Heidelberg Packing

Discussion in 'Heidelberg Printing Presses' started by Alfred33, Apr 26, 2019.

  1. Alfred33

    Alfred33 Member

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    This will probably be an easy one for you Heidelberg guys to answer, but I'm trying to get some clarity on how to pack our GTOs and our SM52. I've been told ideal plate/blanket squeeze is .004, but can print .003-.006. So, I guess first question is, does this sound about right?

    All of these presses have a plate cylinder undercut of .001 and a blanket cylinder undercut of .118. Going by the above numbers, I feel like we're overpacked, but we've done it this way for years. The plates we use are spec'd at .008, but usually MIC around .007-.0075. Given the .001 undercut, we're already at minimum .006 over on the plate. Currently, our blanket cylinders use a .077 blanket with .042-.043 packing under it. That makes us .001-.002 over bearer on the blanket. Add the blanket (.001-.002) and plate (.006), that puts us at .007-.008 squeeze, which by all accounts would be too much.

    Is it okay to be less than bearer height on the blanket cylinder? To get to the "ideal" squeeze, we'd need to be .002-.003 under bearer height on the blanket cylinder. Can we still get the impression we need from the impression cylinder if our blanket isn't over bearer? I think that thought is what has made us pack these presses the way we do.

    Thanks for your help in understanding this.
     
  2. alibryan

    alibryan Senior Member

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    Plate should be approximately .003-.004 over but I don't know how you'll get there with an .008 plate. I remember using plates that were .005, I believe.

    The blanket pack on GTO/SM52s should be .042., and you can adjust that with .040 if necessary, but you may have to compensate a little with your impression settings. So with a blanket that mics at .077 combined with a .040 under-pack, you end up with (approximately) .117 total, or .001 under on the blanket. If everything is correct, you should end up with .004-.005 squeeze, which is actually really good. This combination should also give you an almost perfect 100% print length from your plate.

    I believe the impression settings are also set up for paper thickness when using an even with the bearers blanket/pack combination. But again, you can compensate with the impression if it ends up being too much.
     
  3. Alfred33

    Alfred33 Member

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    Hmmm... I don't know that I can get that changed here. In our GTOs, we're using the Mitsubishi Silver Digiplate (paper) and in our SM52, we're using a metal plate by Fuji (LH-PJ). We're a large company with many shops and these are "standard" products for us. I may just have to do some experimenting, but I thank you for your input and expertise. I thought we were way strong on the plate cylinder -- we use the same metal plates for our Didde web presses, but the plate cylinder undercuts on those presses are greater.
     
  4. junker1984

    junker1984 Senior Member

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    Recalling from my time the with Heidelberg, during the instructional phase of a new press installation and troubleshooting print issues on a machine already in production, the Heidelberg instructors clearly stressed the importance of maintaining factory packing specs. That being, .004"-.006" over on plate (.006" specifically adhered to for compressible blankets, at least until that blanket had been run for a time) and bearer height on blanket.
     
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  5. turbotom1052

    turbotom1052 Senior Member

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    If your permapacking your plate cylinder your pretty much locked into to a plate height over bearer. We always tried to get the plate height as mentioned to .005 inch over the bearer. The blanket height, as mentioned by Steve was run level with the bearer as measured with a packing gauge. When the blanket sunk down below bearer height it was time to add .001 or .002 under the blanket. I never trusted what was stamped on the blanket or blanket packing. I always measured before installing blanket and used a packing gauge to monitor the conditions of blankets.
     
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  6. Alfred33

    Alfred33 Member

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    Thanks for the replies and your insight. We're won't be able to get around running the .008 plates here, but I will pack the blanket at bearer height. We run some pretty light stocks here, so I worry that we won't be able to get enough back cylinder pressure to get good impression if we go any lower. Unfortunately it looks like we're stuck with our squeeze being a little strong.
     
  7. alibryan

    alibryan Senior Member

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    From your OP and subsequent replies, it sounds like you may be a manager with possibly some operator’s experience.

    If so, you might understand that the factory spec’ed targets aren’t always 100% ideal (or even practical, in some instances) for maintaining a day-to-day, high quality production environment. Fortunately, experience will eventually teach (some) operators what ends up working the best for their particular presses, and shop setup.

    A lot of the time that’s pretty close to said factory specs, but definitely not always.
     
    Last edited: May 3, 2019
  8. Alfred33

    Alfred33 Member

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    You'd make a good detective. ;) Yes, I ran presses for many years, some Heidelbergs, some different webs, but now I'm part of the management control environment. The entire company is looking for more standardization and process controls across the sites, and with all of that push, plate/blanket squeeze came up. They want to develop operators to be more than push button factory workers, which is a great initiative, and hasn't always been the case here. The problem is that in the training documentation, etc., they come out standard targets for squeeze that aren't really attainable with the consumables that they provide. I have never ran a blanket lower than bearer height, so I was trying to learn if that was even an option to get us down to that number. It's as simple as just changing our packing and trying it, but I thought I'd check here before wasting the time and materials. We don't seem to have any trouble printing where we're at, which is a squeeze around .007-.008. It's a little more than ideal, and it did raise some questions.
     
  9. turbotom1052

    turbotom1052 Senior Member

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    When you talk about lack of back cylinder pressure or squeeze, are you being limited by your pot readings or is it a mechanical limitation? Potentiometers can be recalibrated if needed!!!
     
  10. Alfred33

    Alfred33 Member

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    I'm going to say mechanical, because I'm not sure. Its quite possible that I've been thinking about this wrong, and if you can straighten me out, I'm open to learning what I don't know. :) Between plate and blanket, the blanket, packing, plate, along with factoring cylinder undercut calculate/create the squeeze, which optimally would equate to .004"-.006". Because we have to use .008" plates here, we would have to pack our blankets at .002"-.003" under bearer height. +.007" (Plate) + -.002 (Blanket) would get us to .005" total squeeze. I've been told, and maybe incorrectly, that you can't get enough impression between the blanket cylinder and the impression cylinder if you don't at least run bearer height on the blanket cylinder. If we do that, the best we can do is .007".

    The impression cylinder is even with the bearer height if I remember correctly, but should have a .118" cylinder jacket. With some of the 20# stocks we run, can we get enough impression if the blanket is under bearer height? I guess the other issue is that on some of our Heidelberg GTOZs, we also number, so instead of a .118 cylinder jacket those press units have a .014" mylar on the impression cylinder. I don't know if I said any of this in a way that makes sense to you, but if it does, feel free to educate me.

    We haven't really been having any issues with the way we have things set up, but if we could do it better and/or do it right, then I feel like we should. If fact, right now, most of our Heidelbergs are .001"-.002" over bearer on the blanket right now, which puts us in the .008".009" squeeze range. This is how we've packed these for years and years and years, but now I've moved into a process control type position and I know by the numbers, we're not right, so I've been questioning it. I've had a few days off recently, so I haven't been able to make any changes to try any different setups as of yet.
     
  11. turbotom1052

    turbotom1052 Senior Member

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    You need to bear in mind a few things... Firstly the impression cylinder is NOT intended to roll on bearers with the blanket cylinder. The belly to belly rolling of the impression cylinder surface, with the blanket cylinder surface, is what allows for adjustment of squeeze between the blanket surface and the impression cylinder surface. There would be no such adjustability if them 2 cylinders were to ride on bearers. In a perfect world it would be great to run all cylinder rolling heights to a factory spec but often does not work out. If you absolutely must have the blanket surface height above bearer, in order to allow for ample squeeze between the blanket and the impression cylinder, then so be it. What would need to happen in this situation is that you might need to lower the height of plate surface so that a plate to blanket squeeze of .004" to .006" is maintained. This .004" to .006" plate to blanket squeeze is something that I would say is a must, to be able to print to any sort of acceptable standard. What needs to be considered should you alter the height of the plate surface, is that you will also be altering the image length. This altered image stretch (should you pull height from the plate cylinder) will be negligible. The only time this would become and issue would be if you were needing to match print length with another press.
    Now that I've hopefully cleared this up for you, there is some good news. You mention impression cylinder jackets. Here is an area where you can make up for some of the print pressure shortcomings you describe. Depending on how your perfector is configured, the heights of impression jackets can be built up with packing. If your perfector configuration allows for this, there lies the potential adjustability. I would caution that this adjustability not exceed app. 004". From what youve described id be willing to bet that an increase in blanket to impression squeeze of .004" should be enough to get you were you want to be. Once you arrive at the required impression, regardless of how you get there the impression cylinder potentiometers can be adjusted to match the pressure.
     
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  12. Alfred33

    Alfred33 Member

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    Thank you Tom for taking the time to make your post. It's helpful. With our standard plate, which we don't have the option to change, we are going to be .006" or .007" over on the plate which means we'll have to be under bearer height on the blanket by a couple thousandths. By all accounts and what you've described here, that shouldn't be an issue with being able to get enough pressure between the blanket and impression cylinder, but if it were, I could possibly add a couple of thousandths under the packing under the cylinder jacket to offset it. That makes sense. Hopefully, I can get a hold of a couple of presses in the next couple of weeks to try this and make them right.
     
  13. turbotom1052

    turbotom1052 Senior Member

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    is there a sheet of polyester perma pack adhered to your plate cylinder or does the plate sit on top of bare metal?
     
  14. Alfred33

    Alfred33 Member

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    Bare metal, there is no perma pack, but we're using .008" thick plates. However, I mic'd some the other day at .007". Either way, that puts us over enough on the plate cylinder that we'd have to go under bearer on the blanket cylinder to achieve the desired .004"-.006" squeeze. Unfortunately, these are the plates we have to use and can't get around that.
     
  15. alibryan

    alibryan Senior Member

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    You can go under a couple thousandths on the blanket cylinder to counter for your extra plate thickness, if necessary. When I ran SM52s some years ago (for whtever reason it was), sometimes I would pack .038" or .039” under the blanket and as far as I can remember, it worked fine.
    If you check with your operators, you may also find out that for their lightest weight substrate right now, even with the blanket packing at bearer height, they're still probably setting their impression to about .08 mm or higher. So there's some wiggle room there, and you can come down with that number on the impression to make up for the under pack on the blanket if you decide to try the .038” or .039”.
     
    Last edited: May 15, 2019
  16. KimHengMechanic

    KimHengMechanic New Member

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    Hi, since you going bare metal (correct me if i am wrong, means in between blanket and/or impression cylinder jacket, there is no additional material in between them), you may want to consider adding full size sheet of paper fit to your cylinder or at least your desired printing area depending on thickness you need to "top up" to print out the ideal effect you want. Meaning to say, you can decrease the blanket pressure first, add in the the sheets of paper depending on your thickness, then re-adjust the pressure accordingly. This way, you may avoid having the 2 cylinders belly to belly or running on the bearers.
    Frankly speaking, as GTOs could be ranged from pretty old from 1970s to 2000s, the earlier generation would have some wear & tear at some point of time, therefore factory setting as per the guide book may not necessary work out the way you want to. Especially you mentioned earlier in your posts. Different machines might have different wear and tear location and it would take some time to get the right feel to calibrate and adjust the pressure for your printing. The old way of trial and error and gut feeling of an experienced operator would be your best bet on getting the print pressure.
     
  17. turbotom1052

    turbotom1052 Senior Member

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    When you describe the cylinder undercuts, are you just reading off of Heidelberg's tags and doing the math, or are you quoting numbers that you've measured with either a dial indicator, or a dedicated packing gauge? Also have you checked just how the cylinders are rolling? Im referring to bearer pressure measured at multiple points, on both the gear side and operator side of the press. This can be checked a couple of different ways. One way would be to use long feeler gauges between plate cylinder bearers and blanket cylinder bearers. The other way would be to thoroughly clean and degrease all bearers, and then tap on a film of ink in multiple locations to see just how the ink transfers from one bearer to another while cylinders rolling under pressure. Pressure should be consistent all around the cylinder bearers and also consistent from one side of the press to the other. If there is a side of the press that has too weak or too strong of a transfer the bearer pressure can be adjusted within reason. At this point my recommendation would be to call in an experienced Heidelberg tech.
     
  18. Alfred33

    Alfred33 Member

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    When I refer to undercuts, I am talking about the stamped Heidelberg numbers. I have also checked those undercut numbers with a packing gauge, and they're real close if not dead on. I don't think we have any mechanical issues... we do check bearer pressure, and we do it in the manner you described with cleaning the bearers and using ink thumbprints around the bearer. I really think you all answered my questions/concerns already. Because of the plates we have to use, we're going to be over bearer on the plate cylinder by 6 or 7 thousandths, depending on how the plate mics. My concern was about whether or not packing a blanket to be under bearer height would allow us to get enough back cylinder pressure to get good impression. Between yours and alibryan's responses, I think I should be fine even on our thinner stocks to go a couple of thousandths under on the blanket to get the squeeze to where it should be. I just need to get out to a press and change it.

    Like I said earlier, for as long as I've worked in this shop, 20+ years, we've packed our GTOs at .001" or .002" over on the blanket height, which gives us a squeeze that could be as high as .009". Moving into this position that I'm in now and learning as much as I have over the last couple of years, I knew that was too much! I just wanted to understand if there was a reason that I didn't know as to why we were doing it this way, and it just sounds like we've just been packing them wrong. It's probably one of those deals where 25 years ago, someone did it and everyone from that point on just put back in what they took out and here we are. Again, it hasn't caused us an issue really, but if we're giving people the tools and training to hopefully do things the right way, then we should do it the right way. I greatly appreciate all the knowledge and help!
     

  19. turbotom1052

    turbotom1052 Senior Member

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    Your last paragraph describes a very real dynamic that occurs in lots of industries. Just doing something, because thats the way we have always done it sez alot about company management. I applaud your efforts to try and initiate a new mindset but be warned.... sometimes upper management will resist some efforts and just view you as rocking the boat. If your company is not one of them companies I mention then I say have at it in ALL areas of pressroom management. You do need to be aware of this however if you aren't already... The sort of adjustments in plate to blanket pressures that your describing here, will most likely require you to adjust pre press curves to compensate for your change in pressures. That is unless of course your quality standards are lax and your just printing hang um and bang um impressions.
     
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