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Basic knowledge of Rubber Rollers（5,6）

5.Crown processing

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.

1.Crown types

2.Crown Precision

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.)

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6.Rubber hardness

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.

1.Hardness tester

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.

2.Durometer Spring type hardness tester

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

Hardness
Test Piece		 Shore-A
15 20 25 30 35 40 45 50 55 60 65 70 75 80
Thickness of the piece / mm 3 8 7 6 5 5 4 4 3 3 2 2 1 1 0
6 4 3 3 2 2 1 1 1 1 0 0 0 0 0
9 2 2 2 1 1 1 1 0 0 0 0 0 0 0
12 1 1 1 0 0 0 0 0 0 0 0 0 0 0
18 0 0 0 0 0 0 0 0 0 0 0 0 0 0

Note: Subtract the figure in the table from the measured value.

3.Influence of Temperature on Rubber Hardness
An increase in the temperature usually results in a decrease in the hardness of common types of rubber. Hardness should be compared at the same temperature, accordingly.
The environmental temperature standard under JIS is 23 ± 2 degrees.

The temperature dependency of the hardness of Katsura's representative materials is shown in the table below.

Grade / Temp (°C) -20 -10 0 10 20 30 40 50 100
white270 / NBR 96 90 81 76 73 72 72 72 72
White370 ／ CR 80 78 75 73 72 71 70 69 66
White770 / EPT 82 78 74 73 73 73 73 72 70
White970 / Silicone 71 70 70 70 70 70 70 70 70
White1370 / SBR 85 80 76 73 73 73 73 73 71
White3370 / CSM 94 88 75 72 72 70 69 69 68
#6040 / Special NBR 86 54 46 42 41 38 36 36 31
#7040 / IIR 52 46 43 41 40 39 38 38 35

4.Measurement Variations
There are the differences in the measured values because of individual variations such as the pressure strength, the pressure speed, the pressure angle the instrumental time, etc...
Because of these factors, Katsura gives ±3 for measurement allowance as the internal standard

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