How to Maintain Rubber Rollers in Offset Printing

To maintain rubber rollers on your offset printing press, you need to have a good system for checking and storing them.  Here I will outline the maintenance system we have in place, the tools you need, and how we deal with problems that happen.  

First of all, here are the reasons why maintenance is needed.

• Bad settings on the press.  I have covered this before in another article.  Settings must be done right.  Too hard and the roller will wear out prematurely.  There will be more heat leading to other problems.  

• Improper storage. For example, not being covered or suspended. When the rollers come from the supplier, they should have a certain hardness and be of the proper diameter.  To maintain this they cannot be sitting on their side. They must be suspended on a rack in order to not get flat spots. They should also have a wrapping that prevents them from being exposed to light.  If not, it will cause them to become hard prematurely.

• Age. Rollers will lose their properties over time, though protective wrappings can keep them good for years.

• Poor manufacturing.  Each roller in the printing press has a specific hardness that is designated by the manufacturer.  If it is too hard, it will effect other rollers that it touches. 

• Bad bearings. If a bearing is bad, it will cause the roller to slip against the plate or other rollers.  It will heat up.  This will cause premature wear.

Proper storage

One of the best systems is to have them mounted to a wall.  They must be suspended so that the rubber is not in contact with any surface.  Contact would create flat spots.  A rack can be easily built near the printing press.  

Advantages of storing printing press rollers this way:

1. It's economical to build.

2. Saves space.

3. Suspends the rollers.

Another setup I have seen that works is when there are multiple offset printing presses and the rollers are shared between them.  All the rubber rollers are stored on a portable rack with wheels. The only problem is that it is not as economical for saving space.  Storing them in this way has advantages and disadvantages.

Advantages

1. All rollers in one place

2. Portable.  Can be easily moved to the printing press.

3. Suspends the rollers. No points of contact causing flat spots.

Disadvantages

1. More expensive to build.

2. Takes up more space.

3. Protect the rolls while they are on a rack.

 

Special paper that acts as a light barrier should be wrapped around the rolls.  They come from the company resurfacing the roller and the same should be done when storing them. Even if they have already been used.

As a side point, NOBODY should use a knife to remove this paper cover from the roller.  It only takes one nick and the roll is no good  Take the extra minute and just peel it off by hand.  

The rollers should also be wrapped in an additional layer of bubble wrap.  Just one layer is fine. This is what we do in our shop. The reason is that one hard bump can cause the roller to have a flat spot and then it's no good. 

Lastly, every 6 months or so the rollers should be rotated. This prevents the roller from stress towards any one side, resulting in an oval shape.  

Tools and equipment needed:

There are two essential tools required for your roller maintenance program.  Both are worth the investment as they save a lot of money and are quite cheap.  Here they are.

An infrared sensor is perfect for maintaining rubber rollers while on press.

The tool is cheap and provides live feedback of two things:

1. If a roller setting is too hard.  This will generate heat and quickly wear out the roller.  All you need to do is save one roller and the tool pays for itself.  Here is the one we use.  They are relatively cheap. 

2.  If the bearing on the end is starting to wear.  You need early feedback when this starts to happen and it's easy to do.  Just walk along the press after it has been running for a while and point it toward the ends of the roller.  The heat generated by a wearing bearing will give it away.

A Shore A Durometer

When the rollers come from the supplier, it should be checked for hardness. The specs from the printing press manufacturer should be the same as the reading.  This is the tool that you need.  

It must read Shore A hardness.  For example, there are durometers that read "D" hardness.  You do not want this one for offset printing.  Type A reads softer materials and this is the proper scale you want.  Here is one here.

From time to time, the hardness should be checked while on press. If the rollers starts to get hard, it is time to rejuvenate or replace it.

Three reasons why roller hardness is so important.

1. To transfer properly.  Once a roller starts to reach a certain hardness, it will act more like a squeegee. It will not transfer properly. Just the right squish will allow the ink to pass through. Too much and it will not pass.  Not enough and the ink film thickness will not be sufficient for the printed product. 

Water rollers tend to be softer so as to transfer water properly. Ink rollers can be a little harder.  Once they get hard, they lose their transferring properties.

2. To prevent heat.  This is an enemy in offset printing.  Hot rollers change the properties of the ink.  It causes more dot gain and is difficult to control the ink and water balance. 

3. To prevent wear.  When rollers become hard, they wear faster.  Pitting will occur.  If the rollers are touching the plate, like form rollers, they will wear the plate out faster.  For that reason, rollers that touch the printing plate must be kept soft

Mantain Rubber Rollers with Rejuvenator

To get longer life out of your rollers, you should use a chemical provided by most ink companies called a 'rubber rejuvenator'.  Here is an example of one provided by Flint Ink.  You simply spray it in the printing unit and let it run for 15 minutes.  Do this twice. 

Here are the advantages of using it:

• performs a deep cleaning of the rollers
• the return is significant for how cheap it is
• it extends the life of the rollers
• It restores the ability to transfer ink
• the surface is restored to the original texture

With time, gum arabic and paper form a thin coating on the rollers. Rubber rejuvenator deglazes and cleans the rubber, restoring it's soft properties. It is good to use on blankets as well.

Resurfacing rubber rollers

There is no need to buy new rollers as there are many companies that will resurface the old rubber. Each resurfacing company brags about having the best and longest lasting rollers. This is a hard one to test as it can take years to get the results of a test done on press.

The best quality control program we have found is simply checking rollers for consistency when they arrive.  We measure each roller for the proper diameter and hardness.  You would be surprised how many rollers do not have the proper diameter or hardness. 

Conclusion

I simply talk about the things we do for our offset printing presses.  Please leave a note in the comment if I miss something.  Thanks in advance for your feedback.

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