Incorrect Thickness Discussion

[d0ugd0ug]

Dear all, this is my first post in the forum since I haven't been using this account in years so please go easy on me. I know this is one of the place where printing professionals gather around so I would be super grateful if anyone could give some advice on this difficult situation of mine.

I have been purchasing plates from a Chinese supplier through a third-party company in my country but last year's April I was able to secure the supplier's information and worked with them directly for the first order in June. Our printers are the 8-page, 10-page, 12-page and 16-page Komori & Mitsubishi printers that have been used to printing plates with thickness from 0.27mm to 0.30mm, and the June order was an experiment with 0.25mm plates. Surprisingly it worked pretty well and I was ready to order the same order's thickness last November.

For some reasons, the plates we received from this provider on the second order was 0.22mm-0.23mm, which is already different from what we initially agreed, and it is my first time working with such plates in such a bad timing in our region (we will be having Lunar Holiday soon so everything must be done before the holiday begins) so I'm very stressed out at the moment. The supplier said that a lot of printers around the world can manage to print with this thickness, so please enlighten me if anyone is experienced in dealing with this type of plates with the similar printers like ours.

It is super, super appreciated for your guidance as I have more than tens of thousands of square meters of plates with this thickness to deal with, and these plates are close to impossible to sell in our country.

 

[Alois Senefelder]

Hello DzungDH,

1) Are your Presses - Sheet-fed or Web-Offset ?????

Regards, Alois

 

[turbotom1052]

The reduced thickness of plates brings to mind a few different unsettling possibilities. First off it is NOT consistent with what you agreed upon. Years ago this wouldn't be as much a problem as it is today because you could just make up caliper difference with paper packing. Most modern sheetfed presses (assuming we are talking sheetfed) run either bare cylinders or polyester permapac adhered to the plate cylinder. If your press is equipped with auto plate, adding sheets of packing may not work well with auto plate. Then there is the issue of the plate clamps perhaps needing to be re set to accommodate the thinner plates. Then you've got the needed recalibration of your presses either pressure gauges or potentiometers so that when you enter sheet thickness into the press you're getting correct pressures. So for your plate rep to tell you that guys are adjusting, im sure other printers are doing just that. The question becomes WHY should you have to adjust??? And who should incur the costs of the adjustment???

 

[Magnus59]

This problem can be rectified by simply adding the necessary packing under the blanket cylinders of your sheetfed Komori and Mitsubishi to make up for the thinner plate. You’ll need to do it on all the printing units and also keep that number in mind so you can subtract it when setting the usual paper thickness for impression on every job. If it’s a significant enough plate thickness change you may also need to readjust all of the form roller pressures, as well. Not exactly an ideal prospect to look forward to, but once done, it will solve the issue once and for all.

*Lunar Holidays are really just a reason to go outside and Bark at the Moon!

That approach is fine as long as print length is not critical.

 

[d0ugd0ug]

Hello DzungDH,

1) Are your Presses - Sheet-fed or Web-Offset ?????

Regards, Alois

Hi Alois, we do Web-Offset.

Regards, DzungDH

 

[d0ugd0ug]

The reduced thickness of plates brings to mind a few different unsettling possibilities. First off it is NOT consistent with what you agreed upon. Years ago this wouldn't be as much a problem as it is today because you could just make up caliper difference with paper packing. Most modern sheetfed presses (assuming we are talking sheetfed) run either bare cylinders or polyester permapac adhered to the plate cylinder. If your press is equipped with auto plate, adding sheets of packing may not work well with auto plate. Then there is the issue of the plate clamps perhaps needing to be re set to accommodate the thinner plates. Then you've got the needed recalibration of your presses either pressure gauges or potentiometers so that when you enter sheet thickness into the press you're getting correct pressures. So for your plate rep to tell you that guys are adjusting, im sure other printers are doing just that.

What if the presses are web-offset in another situation?

The question becomes WHY should you have to adjust??? And who should incur the costs of the adjustment???

This is something I have discussed with the rep repeatedly during our discussion and is consistently ignored by them. I have no idea how they operate like this.

 

[jshawy]

Hello DzungDH,
1. Your press manufacture would recommend 0.3mm +0.01/-0.03 plate so why change it?
2. A web offset press usually runs bearers on the cylinders so pressure adjustment is not possible.

This problem can be rectified by simply adding the necessary packing under the blanket cylinders of your sheetfed Komori and Mitsubishi to make up for the thinner plate. You’ll need to do it on all the printing units and also keep that number in mind so you can subtract it when setting the usual paper thickness for impression on every job. If it’s a significant enough plate thickness change you may also need to readjust all of the form roller pressures, as well. Not exactly an ideal prospect to look forward to, but once done, it will solve the issue once and for all.

3. Not recommended for web offset. Increasing the blanket packing will change the surface speeds between plate/blanket cylinders, causing plate wear or at worst force the plate to move on the cylinder and fly off. The plate staying on the cylinder will depend on your plate bend size and clamping mechanism. Doing this will also increase the printing pressure between blanket to blanket. Plate cracking could also be an issue on long runs.
4. Do your presses run packing on the plate cylinder or not? If they run packing increase thickness to accommodate new plate. If not add packing like turbotom suggested.

The supplier said that a lot of printers around the world can manage to print with this thickness

5. I am calling bullshit on this one. I have never seen a plate this thin running on any web offset press I have worked on. For 0.3mm plate they are always supplied at the bare minimum of 0.27mm. They could manage it by adding packing to plate cylinder.

Regards,
J
If it ain't broken don't f@$k with it

 

[jshawy]

3) Packing the different cylinders in offset printing is as old as printing itself. Other than possibly increasing or decreasing the print length marginally, if there was a significant enough difference to create a surface speed issue and possibly cause the plate to fly off, you would certainly see that issue in the clarity of the printed dot. Also, adding packing to the blanket cylinder to make up for the loss in plate thickness does not increase the printing pressure, it simply compensates for it.
4) If there was a surface speed issue with packing the blanket cylinder, that same issue would certainly be there if you were to pack the plate cylinder.

Might work on Sheetfed but not the blanket to blanket cylinders of a web offset press. Cylinder bearer pressures are fixed on web offset not adjustable. Yes you would see issues with the dot. Printing pressure blanket to blanket should be around 0.1-0.15mm, increasing the packing on both blanket cylinders by 0.08mm to accommodate the plate loss would double it.
A 0.16mm(2 x 0.08mm of plate) loss of diameter on plate cylinder and a increase of 0.16mm diameter on blanket cylinder with the increased packing creates a surface speed difference of 0.1%. That is a lot force on the plate if you running a web offset press at 30,000 impression per hour or more.

I saw a web offset press with random plates flying off. It was caused by blankets swelling with an extra 0.1mm over bearer height. The lazy operators would wash the blankets with a solvent soaked sponge, instead of scrubbing the ink pile off with a rag. As their blankets where not sealed on the edges, the excessive amount of solvent would penetrate into the fabric of the blanket and cause swelling. They would not change their bad habit of washing with a sponge. To resolve the issue the blanket packing was reduced. Recommended plate 0.3mm. Their plates were 0.25-0.27mm.

The biggest issue here is that the bean counters tried to save some money on aluminum and never asked about the consequences on the press.

 

[d0ugd0ug]

Hello DzungDH,
1. Your press manufacture would recommend 0.3mm +0.01/-0.03 plate so why change it?
2. A web offset press usually runs bearers on the cylinders so pressure adjustment is not possible.

1. Our offset press manufacture markets do indeed print with 0.3mm thickness, but they have accepted to print with 0.27mm and 0.25mm with minimal to no adjustments. This helps us reduce our import costs while still maintaining the quality of our plates.
2. I am not very used to this field and was told that the customers use said offset machines on the top post, so I am not certain if your statement is applicable in this case.

Can you elaborate further for 3 & 4?

5. I totally get it and wholeheartedly believe you since our market does nothing of sort. As I mentioned that the supplier claimed their customers can print with these plates with said thickness, I discovered that the customers are told to be from Peru, Ukraine, India, Pakistan and some undisclosed Chinese locations and checked their company's background. It's unbelievable that this supplier used their mediocre customers to back up their excuses.

 

[jshawy]

1. Our offset press manufacture markets do indeed print with 0.3mm thickness, but they have accepted to print with 0.27mm and 0.25mm with minimal to no adjustments. This helps us reduce our import costs while still maintaining the quality of our plates.
2. I am not very used to this field and was told that the customers use said offset machines on the top post, so I am not certain if your statement is applicable in this case.

Can you elaborate further for 3 & 4?

5. I totally get it and wholeheartedly believe you since our market does nothing of sort. As I mentioned that the supplier claimed their customers can print with these plates with said thickness, I discovered that the customers are told to be from Peru, Ukraine, India, Pakistan and some undisclosed Chinese locations and checked their company's background. It's unbelievable that this supplier used their mediocre customers to back up their excuses.

Anyone who knows web offset printing machines will understand what I have written. Talk to your operators.

 

[d0ugd0ug]

Thank you all for the information, it was very helpful!

 

[turbotom1052]

That approach is fine as long as print length is not critical.

Print length should not be an issue as the packing Alibryan suggests is under the blanket. To have an effect on print length the packing change would need to be under the plate on a sheetfed press. Even if there was a change in print length, it would be minor. An additional .004"of packing on a 28x40 sized press, would equate roughly to a row or two of dots at the tail of a 28"x40" sheet. The only time that would create a problem would be if some offline imprinting, perforating, or varnishing was needed to be done on another press, and even then it wouldn't even be worth a second thought.

 

[turbotom1052]

What if the presses are web-offset in another situation?

This is something I have discussed with the rep repeatedly during our discussion and is consistently ignored by them. I have no idea how they operate like this.

They manage to "operate" like this because you and others are still buying their product!!!