Tips

In the past few weeks we have talked about the causes of web wrinkles. Machine characteristics can also cause wrinkles. Here are a few examples:

Idler roll buckling or deflection causes wrinkles because the web will actually deflect out of its normal running plane at different intervals across the web width. This out of plane condition will occur wherever the greatest amount of deflection (usually the center) is in the idler roll. When roll deflection occurs, webs will wrinkle because they will compress toward the deflection point.

Air entrainment in webs as they flow over rolls will cause wrinkles. Air entrainment will create slippage between the web and the roll face. If this slippage occurs, then the web is not in traction with the roll. Air entrainment problems can be detected by viewing idler rolls that stop rotating during the converting process. Also, if wear spots are seen across idler roll faces, air entrainment is probably the problem. Machinists’ bluing dye can be applied to idler rolls where air entrainment is suspect to detect wear spots.

Material roll buckling or deflection. If the parent roll deflects on its support mechanism (air shaft, mechanical chucks or core cones mounted on a steel through shaft) then compressive forces will cause the material roll to buckle and wrinkle before the web enters the converting process.

Varying tension through several different types of processes in one converting line will cause wrinkles. A good example of this is tension through a coating section, printing process, drying section and slitting section. Tension through the coating section may be high, then through the printing process may be lower, then through the drying process lower yet, then through the slitting section may be high again. Wrinkles will occur under these conditions because the web will stretch and contract creating compressive and decompressive forces.