Plate cracking is a very annoying and difficult problem to find in some cases. Then when you think the problem is fixed it may crop up again. The problem may be random or isolated to one unit. Sometimes the problem may come and then go as fast as it came. The following is a guide to solving plate cracking problems.

If the bend on the plate is uneven by as much as a few degrees it can be difficult to mount the plate properly, causing a slight buckle on one side of the plate when it is mounted on the press. The plate can also be bent out of square, which will cause the pressmen to try to modify the trail edge of the plate, causing the plate to have a slight buckle on one side of the mounted plate.

The grain of the plate is also very important. If grain of the plate runs in the machine direction the plate will be very strong. However, if the plate grain runs in the same direction of the bend on the plate it will be much more likely to crack.

The length of plate from bend to bend can be very critical. If the distance is too far apart, the form rollers and blanket cylinder will try to form a new bend in the plate causing the plate to flex and the plate to break prematurely. If the bend is too short, the plate will flex the bend in the plate and it will crack prematurely.

If I have a plate movement problem while the press is running I will use double-sided tape to ensure that a printing plate remains firmly against the plate cylinder. If this stops the cracking, I will then try to use chain bar oil applied to the cylinder to create suction so that the plate will not move while the press is running. If the chain bar oil stops the cracking I will use it on a regular basis until I find out why the plates are moving while the press is running.

Look at the back of the plate after the plate has run on the press for a while. I look for obvious marks that may be caused by manufacturing defects or by raised metal on the plate cylinder such as a scratch. If you suspect that this is a problem, use ruby lithe tape over the scratch to prevent the scratch from damaging the printing plate. If applying the tape to the scratch resolves the problem, then hone the scratch.

If ink form rollers are too tight or too hard it can cause plate cracking. It can also be a combination of both. Ink form rollers should only be set for a strip width of 1/16 of an inch per roller diameter to the plate and the hardness of the form roller should not be any harder than 45 shore hardness. Instead of just turning the form rollers on to the plate, back off to view the stripe made when the form roller contacted the plate. I sometimes turn the form rollers on to the plate and leave them on while revolving the printing unit several revolutions. I will then stop the press unit, let it set for a few seconds and then move the unit just far enough ahead to see the stripe that was made by the form roller. This technique is the same method used to set ink transfer rollers. The reason I do this is because sometimes the ink form roller brackets will move too sluggishly to get an acceptable stripe reading by just turning the ink form roller on and then back off again.

Loose blankets will cause plates to crack and should probably be one of the first things that you check. If the blankets are too long, plate cracking will occur because the blanket will not be pulled tightly enough to the blanket cylinder, increasing the pressure that the blankets apply to the bends on the plates. The blanket bolts can be too long, which will leave the blankets loose causing the same problem as the blankets being too long. The blanket bolts should be checked to ensure that the threads are smooth and will not bind, since a torque wrench is used to ensure that the blankets are not installed too tight, causing the blanket bars to pull loose. The depth of the bolt holes should also be checked for debris or to ensure that the manufacturer has drilled and tapped the holes deep enough to allow the blankets to be pulled down firmly. In any case the blanket height on both sides of the blanket slot should be checked to see if this is causing the problem.

The distance between the blanket and plate cylinder can be too tight creating excessive pressure against the printing plates. Always check to make sure the iron-to-iron settings are correct or that the bearer pressure is set correctly.

Blanket heights are also very important. The blanket may be too thick or the blanket and packing thickness may be excessive. A Caddy gauge or micrometer should be used to verify blanket thickness. The blanket thickness should be checked every time a blanket is installed. Manufacturers have been known to send blankets that are the wrong thickness or those that have a manufacturing problem. The same scenario applies to the blanket or plate packing materials if used. Some newspapers also use packing under the printing plates, which, if the wrong thickness is used, will cause plate cracking to occur.

Plate lockups will cause the plates to crack if they are mounted too high or if the locks don’t move freely. The locks will also crack plates if certain components are loose depending on the type of lockup you have on your press. The pin register blocks may not be in line with each other on two-plate around presses, causing the plate to buckle slightly on one side. The best way to verify that the lockups are correctly installed is to use a magnetic base with a 25 power or better lope attached to it. The lope should have a scale etched in the glass so that when the plate cylinder is rotated a person can view to see if both register pins lineup accurately.

If the plate or blanket cylinder has been replaced and plate cracking starts to occur the problem could be that the cylinder was resurfaced to the wrong size. Normally, the cylinder can be checked with a pi tape and then checked against the unit specifications to ensure that the proper size cylinder was installed.

Repositioning the blanket and plate cylinder slots may help elevate plate cracking, but should not be used as a permanent fix for the problem. If the cylinders are offset for a test to reduce the plate cracking, the cylinders should be reset as soon as the real cause of the problem is located. A block gauge should be purchased or made, then used to ensure that the alignment between the plate and blanket cylinder is accurately maintained.

The best way to solve any problem, especially plate cracking, is through accurate record keeping. The records should include the date, unit, position on the unit, blanket height, plate thickness plus any packing, the plate to blanket distances, number of impressions made and any comments that may help resolve the problem.

Remember that whatever contacts the printing plate can cause it to crack. Always check to ensure that the plates rest firmly against the plate cylinder on both sides and all the way around the plate cylinder. Just remember, plate cracking is generally caused by excessive pressure coming from somewhere, or the plates are loose on the plate cylinder in some way will cause the plate cracking — that is if the problem is press-related.

Plate cracking problems can be very difficult to correct, but not impossible. The more serious you are about resolving the problem the more likely you will be able to achieve your goal.

Frank Bourlon, executive and training director for the Newspaper Production & Research Center, has over 30 years’ experience in the industry. He can be reached at 405.524.7774 or via e-mail at fbourlon@np-rc.org.