How To Resolve Gear Streaks On Your Press

Gear streaks correspond to # of gear teeth.

Gear streaks in offset printing occur due to the teeth that drive the printing cylinder.  Bearers are meant to smooth this out, but that is not always the case.  Hence gear streaks.  Whenever we have seen them on our presses, they occur parallel to the cylinder and correspond exactly to the distance between the teeth of the gear that drives the cylinder.  When this happens, we know that either a setting is out or something is worn.  I would like to share a couple of remedies for this problem.

Below I list possible causes and solutions according to the order that I would troubleshoot them.  It makes sense to start troubleshooting with the simpler things before getting deep into the problem.

1.  Improper Packing

It is quite possible that one of the two cylinders (blanket or plate) is trying to drive the other.  For example, when a blanket is over packed, the circumference of it increases.  This increases the surface speed of the blanket cylinder and causes it to drive the other.  

Solution: Get out the manual and pack both the blanket and plate cylinders according to the manufacturers specifications.  You no doubt have some indications  that will tell you how much to pack them over bearer.

2.  Wrong Bearer Pressure

If your cylinder bearer pressure is too light, the paper will push the cylinders apart enough to cause a bounce when the blanket and plate gaps meet.  The result is gear streaks.

Solution:  Have a machinist or a very experienced pressman set the cylinder bearer pressures.  Ensure new blankets are on the press for this test.  There are different three ways that I have heard of doing this. 

• The tin foil method.  A thin strip of tin foil is used similar to a stripe gauge.  The impression between the bearers will create a strip that when magnified, can serve as a reliable reading to gauge other printing units.
• Prussian blue.  This method is used by our preventative maintenance team.  It is much like the previous method except that a stripe is made on the bearer using a special blue grease.
• The light method.  Using various thicknesses of packing between the blankets, the impression is turned on.  A bright light behind where the bearers meet will reveal either a thin crack of light or nothing at all.

3.  Worn Gears

Depending on the age of your press, this could be the problem.  Generally though these gears are well lubricated and should last the life of the press.  We have one Hantscho web press from 1987 and we have never changed these gears.  However this is an easy inspection so I recommend this as the third point to check.

4.  Worn Bearings

I have seen this a few times.  The cylinder bearings in the side frames can start to go.  Instruments exist that can read any unusual heat or noise coming from them.  Your preventative maintenance personnel should be equipped with these kind of tools.  Have them make an inspection.  If one is going, make a schedule to have all cylinder bearings in the press replaced.

In conclusion though, I must say that these should rarely if ever have to be adjusted.  On one half web we have, the bearer settings came “sealed” from the press manufacturer.  In other words, if we started getting gear streaks, they wanted us to look elsewhere first as these settings should not change.  So my recommendation would be to check older web presses periodically for any variation.  

Related posts:

Web Press Troubleshooting Guide

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