A very slight angle may be normal for your machine, but a glue strip which is not straight indicates the carton is getting skewed before it enters the nip roller and belts. This would include Carton Picking, Moon Nip Rollers, Side Seam Rollers, and Nip Belts/Bogie Wheels.

 

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Is the side seam glue strip not parallel to the edge of the carton?

 

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Possible causes might be one of the following:

 

Warped Cartons

Incorrect Magazine Changeover Location Values

Incorrect Carton Picker Position

Vacuum Cups Wear or Damage

Incorrect Moon Nip Roller Pressure

Incorrect Nip/Metal Roller Gap

Nip Belts and Bogie Wheels Bind or Jam

Bogie Wheel Tension Against Nip Belt