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Crushed cores on paper rolls can happen at the mill, in transportation to the press room, or at the press itself. This paper defect concerns web press offset printers. There are two main causes:
1. The roll was dropped.2. The clamps were too tight at some point during transportation.3. The inserted roll shaft at the press was done improperly.
How to fix crushed cores.
There are several companies that specialize in repairing this problem such as this one. Or the core can be fixed right in the press room. It really depends on the extent of the damage.
There are different tools to accomplish this yourself.
The first one every web offset printer should have. It's simply called a 'paper core restorer'. Here is what it looks like:
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| Paper core restorer. |
Of course this type can only restore the ends of the roll. Deeper core damage requires better equipment. Notice the video below. This is the approach take with better machinery.
Below is a core repair done by a company that specializes in this work. Before and after.
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| Paper core repair. |
How to prevent crushed cores.
1. Clamp pressure set properly. This is a calculation and has a number of variables in it. The following is taken into account:
- Contact pad friction of the clamps.
- Wrapping/packaging.
- Weight of the roll.
- Dimensions/size
- Paper grade
The calculations are best taken from the user manual of the clamp truck that is used. The paper mill will also be able to provide the proper clamp truck setting.
2. Competent handling personnel.
Personnel that accidentally hit the wrong levers on the clamp truck are expensive. Every roll that drops can represent a lot of lost money. Choose personnel that are careful and do not race around like it's a super mario cart race.
3. Proper inspection at point of delivery. Crushing of the core can happen when loading the truck at the paper mill. Each core can be inspected upon arrival if this is a reoccurring problem.
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