Crown height is the difference between the diameter of the roller center and the diameter of near the roller end (Generally 50 mm from the end)
The purposes of giving crown to rollers are:
a. Correction of the roller deflection during operation. (Uniform contact)
b. Making the most appropriate flow of the substrate such as cloth, plate and paper. (To avoid meandering)
It is better to give crown especially to the following rollers.
- The value of L/D (roller length / roller diameter) is relatively big.
- The pressure of the roller is relatively big.
Crown precision is influenced by factors such as the roller length, the roller diameter, the rubber type, the rubber thickness, the finish condition, the crown volume and the rubber hardness. The crown precision of Katsura is within 5/100 mm (the tolerance between the diameters of 2 symmetrical points of the roller.)
Depending on the applications, various rubber hardness is used, from very hard one like metal to very soft one like sponge.
You can predict the compression strain of the rubber by the hardness.
The rubber hardness determines the nip width and the contact time between the substrate and the roller.
Durometer A (Shore-A) is generally used for soft rubbers. Asker C is used for sponge materials. Durometer D is used for extremely hard materials.
1.How to read the scale
Keep the tester vertical and press the needle vertically to the surface of test piece and read the scale immediately.
2.Thickness of the test piece:
Use the test piece with thickness of more than 12 mm for A type and more than 6 mm for C type. In case the thickness is less than that, correct the measured values by referring to the table below.
Hardness Correction Values Depends on the Thickness of the Test Piece