GM · CONVERTING UNIT
34
A series of tests has been done on standard label material.
Tool: 25” Gerhard cylinder.
Plates: 304.8 mm plate distorted for a 25” (200Z) die. Three different dispro factors tested.
The gab size between the labels was 2.8 mm giving a distance of 304.8 mm – 2.8mm = 302 mm between
the first and last cutting line.
Dispro factor
Length
Difference in millimetres
Test plate A
99,5874 301,61 mm
-0,39
Gab to big.
Test plate B
99,6504 301,81 mm
-0,19
Gab to big.
Test plate C
99,71339 302,07 mm
0,07
Gab to small.
Ideal length (304.8mm - 2.8mm gab)
302 mm
Ideal dispro factor for 25" die
99,69626
(calculated using the results from the test plates)
Conclusion:
Remember that this factor can be altered by web stretching (thick/special web curving around rollers),
and mechanical factors (plate manufacture tolerances / die cylinder mechanical tolerances).
Keep in mind that if the dispro factor is a bit off, the error will become large as the plate size increases.
Keep the plates small to minimize distortion problems and lower costs.
Example:
Difficult long die plate. 10 labels in the length direction. High demands on the print lenght, registration and
plate dispro factor.
.
Good die plate. Two labels, short length. Short distance between registration marks, no dispro factor
problems.
