Plate Cracking and Benders
Plate cracking is one of the most costly and most difficult problems to solve. As a rule-of-thumb, the cause is from a variety of things being done at the same time. Throughout the rest of these pages, you will read of different things that can cause a plate to
crack. The reason for bringing up the subject here is that most people think of a cracked plate as being a bender problem.
One of the reasons for cracked plates is the use of plates with wrong grain direction (see page 9). A simple test can be performed to prove the point. Take a plate and cut two strips of the same size (two inches by four inches); one cut with the four inch dimension going with the grain, and the other with the four inches against the grain. With
each plate bend the plates back and forth (the two inch direction) until they break, and at the same time keep track of the number of times you have bent the plates. You will find that the plate bent across the grain will outlast the plate bent with the grain, proving
the importance of the grain of the plate.
A variety of things happen with plates grained incorrectly. In bending these plates, fine cracks will form in the bonding that is between the strands of aluminum. These fine cracks can open up into major cracks caused by the pounding of the plate cylinder or
by ink build-up on the blanket while running narrow webs.
A cocked image can lead to a cracked plate, caused by the operator twisting plates on the cylinder. The same thing can happen by bending a plate inaccurately. Let’s look at bender pin systems. The following information covers two of three types of pin systems. In short, any mechanical type of system is only as good as the operator.
Let´s look at bender pin systems. The remaining part of the page
covers two of three types of pin systems. In short, any mechanical
type of system is only as good as the operator.
The one system not covered is the butting of the plate to a guide. As a rule of thumb, the system is as good as the faults of the bender. Another problem is positioning of the plate on the bender by the operator. There is one system that does not fall in line with this general rule - this system has an electronic activated system that works.
The illustration entitled “Manual Bender Checks” shows some simple methods of checking out your manual bender. Some of these things can be applied to the automatic bender also, such as the tramming rod.
Two things are not covered with an illustration in this section on the use of a manual bender. The first may be one of the most important parts of bender knowledge: in bending a plate, each bend should only be bent once. The reason is that these are a braker
bender. This type of bender stretches the metal as you bend it, creating fine cracks in the bend. This problem can be reduced to a workable minimum by proper maintenance. The second largest problem is not using vacuum.
Two things are not covered in this section with an illustration, the
use of a manual bender. The first may be one of the most important
parts of bender knowledge; in bending a plate, each bend
should only be bent once. The reason that these are a braker
bender. This type of bender stretches the metal as you bend it creating
fine cracks in the bend. This problem can be reduced to a
workable minimum by proper maintenance.”The second “largest
problem is not using vacuum.
There is a solution to these problems. First, there are two basic
types of benders; Braker and Forming. As far as we know the
forming type of bender only comes in automatic. An automatic
forming bender will solve many of your bending problems. The
cost of these benders can save money in improperly registered
plates.
In many plants we go into, we find unidentified problems that could
be caused by the bender. As with any other mechanical piece of
equipment, it should be checked regularly. No one disagrees with
this idea, but most bender manufacturers do not tell you how to check
out their benders. We feel that with the importance a bender
plays in your scheme of registration, you should know how to
check a bender out. The illustrations entitled “Manual Bender
Checks,” “Two of the most Accurate Tools for measuring Lead
Pinned Plates,” and “The Method of Checking the Squareness of
Tail Pinning to Lead Bend” give you the means to check them.
The illustration entitled “Two of the Most Accurate Tools for Measuring
Lead Pinned Plates” covers the method of checking out
the placement of the register holes in relation to the lead bend. To
date, we have seen scales, business cards, pieces of paper, and
dial calipers used to do this. The only method that comes close to
working, is the dial calipers method. This method will give you a
different reading, depending upon the person using it and the
angle the dial caliper is held at.
To solve this problem, there are the indicators illustrated. These indicators
will give you a consistent reading, no matter who is using the calipers. In addition to checking out a bender,
the indicators can also be used to check for plates that have been mounted
wrong.
TTo date, there is no accurate method of checking out a tail Register
System. The illustration entitled “The Method of Checking the
Squareness of Tail Pinning to Lead Bend“, comes the closest to
giving you an idea.
We can’t and won’t argue that a bender shouldn’t bend square,
because it should. The point is, if your registration problem is
greater than the bender error, your problem may lie elsewhere.
Too often a problem is blamed on something other than the real
cause, such as bad masters or the way the plates were mounted.
