Our rollers will turn up soon, special order westland 20 duro. Will update when I test the shore A and get them on the machine
why does it have to be a special order when it's a must to have a roller shore A of 18-22 for IPA free printing? I am trying to find an answer as to why this shore A range is not being marketed. Is there anything related to durability? Also what is the crown? half crown? no crown? and for what machine?
Last edited by mazengh; 08-16-2012 at 03:26 AM.
From what I've been told, the 18 - 22 Shore A, is now considered by the roller manufacturers in europe / asia as old technology, and they recommend starting at 25 shore A. This is to give a longer service life from the roller, apparently once the very soft shore A hardness roller starts to age and harden, their service life deteriates rapidly.
Originally Posted by mazengh
Funny part is the USA is still using the 20 - 22 as a starting point then changing them out once they get to the 25 point.
My machine runs zero crown metering roller as it has a cocking adjustment that you can make if needed.
would be interesting to see what US roller manufacturers have to say about this.
Originally Posted by Lukew
We have lost total dampening control with the 20 duro metering more testing will be needed.
"Funny part is the USA is still using the 20 - 22 as a starting point then changing them out once they get to the 25 point."
Those numbers described are a bit low for U.S. durometers. For alcohol free printing, regardless of the machine, water form and metering rollers typically begin at a 25 Shore.
They get changed once they hit about 30 - 32, if running alcohol free. You can print with harder ink forms and distributors but the dampening systems rollers are certainly more critical.
Polyurethane rubber was a great material in it's day for roller manufacturers but with age, they got softer rather than harder; making ink and water control more difficult to balance. For that reason, it's rarely used anymore.
Aaron Sures - Pressroom Technical Specialist
Gans Ink & Supply Company
After 3.7 years in the press it is highly likely that the rollers both inking and dampening are shot. As a rule of thumb, if a newly installed roller or dampener measured 25 shore A hardness then it will be ready for replacement at 35 shore A. Depending on what you do to them, generally speaking they should be changed once a year. You have to be very careful with shore 20 rubber, it can easily be damaged by harsh solvents, bright light and heat. Heat builds up very quickly in the ink train and is anathema to the life of the rollers. Unless you have a very good reason to use the 20 deg rubber then avoid it. When the rollers are out of spec they are next to useless for good printing. You should discuss your roller needs with the supplier and ask them to reccommend a good roller maintenance program for you. This will most likey include a deglazing wash up and a de calcifying wash up. These two items are not the same and are equally important to the life cycle of your rollers.
Store your new rollers vertically in a dully lit place, no sunshine here, IN the wrappers.
The reason we went to 20 duro metering rollers was that we couldn't get a stable damp & the damp feed rates were to high on the dial, especially with PMS colours often maxing out the dials.
I have adjusted the damp/speed compensation graph and so far it's working. Compared to the previous roller @ 26 duro running on the black unit which started at 50 water dial and would get up to 65+ water dial . The 20 duro, is starting at 32 and hasn't gone over 40 yet.
Other metering rollers that ranged from 28 - 30 duro we would see a starting damp feed rate of 60+
This is odd as the majority of literature available states 18 - 22 as a starting point for the metering roller.
Originally Posted by Asures
However I have had to take the 20 duro off the machine, absolutely lost all damp control, scumming one minute, flooding the next and that could be edge of sheet, centre of sheet there was no rime or reason and could not tighten the nip any further. Going to 25 duro now.
Luke, you are right about all the literature available stating the requirement of 18-22 shore A durometer. And this is the reason I was contacting roller vendors inquiring about the shore A and crown since no vendor provides helpful information about this issue.
Originally Posted by Lukew
P.S.: Luke, I've been trying to reply to your private message but it says your inbox is full.... i know it's a pain to keep on deleting messsages... maybe printplanet admins should allow more than 50 messages.