Frequently Asked Questions - Please choose a question:
How do I stop cracking?
Follow the guidelines for choosing the correct matrix size.
Use “Reduced Bead Creasing”. Reduced bead creasing is a method that has been used for many years. Originally reduced bead required lowering and tightening the matrix and replacing the score rule with the next wider size. What this did was it trapped more material in tighter space, causing more delamination and a better fold. Over time we have broadened our thinking to include any method of creating more delamination by tightening the matrix channel to be considered reduced bead creasing. We have found that keeping the channel tight is a good everyday practice to stop cracking before it starts. Refer to the “Determing Matrix Size” section.
The goal is to create as much internal delamination or the substrate as possible. Basically, the more air and space you can create when scoring the better your score will fold and the less memory your score will have. We always recommend keeping your channel tight and trapping the matrix at the points of critical distance, sometimes increasing the height will help achieve this as well. This will cause the substrate to stretch and lead to greater delamination and less memory in the substrate. Don’t get too tight! If the matrix edge is cutting through, the channel is too tight.
Check your score rule heights. A lack of score rule will often times lead to cracking. An easy way to determine if your score rule is to low is to look at your score right off the press. When you hand fold the score the bead should look solid. If the score looks “ropey” or like it is “falling” your score rule could be too low. For choosing the correct score rule height refer to the “Determining Score Rule Height” section.
If cracking is occurring on press before the score is folded you could have too much score rule height. This often occurs when the job in question has capacity scores, or when the job has many scores on a multiple cavity die. It is beneficial to lower your score heights .005” in these situations to help eliminate lateral draw and on press cracking.
A common problem we run into with cylinder presses are the scores running through the cylinder want to blow out the first quarter to half inch off of the gripper. Many attribute this to matrix problems, but in reality it is more than likely a bearer problem. Obviously, most cylinder presses that are being used today have been around the block once or twice. Bearers compress about .003” when the press is on impression. Over time the edges where the chase bearers meet the cylinder bearers wear down and begin to dip at that point of contact, causing more impression and gripper edge scores to crack or blowout. How do you solve the problem? The quick fix is to file down the first quarter to half inch of one’s creasing rule. The long-term fix is to contact someone with experience working on these types of presses and have it fixed.
Cylinder presses require a different set-up than a high speed platen or clamshell. One major aspect of a die for a cylinder press that is often overlooked is crease rule. The crease rule that runs through the cylinder should always be .003” - .005” lower than the crease rule that runs across the cylinder. This is due to the constant pressure applied to the crease rule running through the cylinder. Often times we get calls from companies that complain about their scores through the cylinder cracking or blowing out. In most cases this is a result of the die being set-up with one height of creasing rule instead of the two it should have. By specing out a lower score through the cylinder companies should be able to save themselves some headaches on press.