Technical
Resources

Costing


Quick selection guide on cost of rubber and basic properties
 
  Price Grade Max Int Temp
(°C)		 Max Cont Temp
(°C)		 Lowest Temp
(°C)		 Oil/Fuel Resistance Weather Resistance Hardness Range
Natural 1 105 75 -60 Poor Poor 40-90
SBR 1 115 85 -55 Poor Poor 40-90
EPDM 1 150 130 -50 Poor Excellent 30-90
CR 2 125 95 -40 Good Very Good 30-90
NBR 1 130 100 -40 Very Good Fair 30-90
Silicone 4 300 205 -60 Good Excellent 30-80
HNBR 12 160 125 -30 Very Good Fair 50-90
FKM 10 300 205 -20 Excellent Excellent 60-90
FluoroSilicone 16 200 180 -60 Good Very Good 40-80
PU 9 90 70 -20 Very Good Excellent 30-80

Colour


Rubber gains much of its strength and its resistance to heat and light from the addition of carbon black, thus the vast majority of rubber is black.

Silicone rubbers are the most suitable for achieving reliable and clean coloured mouldings, even with pale colours and translucent. Differing textures on the same product may give visual differences on the colour.

   

Texture/Surface Finish


The finish of rubber can range from semi-gloss to extremely matt using the same mould, not comparable to plastic surface. Depending on the machining processes to achieve the part design, this has impact on cost of tool.

Differing textures on the same product may give visual differences on the colour.
 
VDI 3400 ISO, VDI, ASA ISO/TC 213
Char Milles Ra=CLA=AA Rz  
CH um uinch um
  0.025 1   N1
0.05 2 N2
0 0.1 4 N3
1 0.11 4
2 0.12 5
3 0.14 6
4 0.16 6
5 0.18 7
6 0.2 8 N4
7 0.22 9
8 0.25 10
9 0.28 11
10 0.32 13
11 0.35 14
12 0.4 16 1.5 N5
13 0.45 18  
14 0.5 20
15 0.56 22 2.4
16 0.63 25  
17 0.7 28  
18 0.8 32   N6
19 0.9 36  
20 1 40  
21 1.12 45 4.7
22 1.26 50  
23 1.4 56  
24 1.62 63 6.5 N7
25 1.8 72  
26 2 80  
27 2.2 88 10.5
28 2.5 100  
29 2.8 112  
30 3.2 125 12.5 N8
31 3.5 140  
32 4 160  
33 4.5 180 17.5
34 5 200  
35 5.6 224  
36 6.3 250 24 N9
37 7 280  
38 8 320  
39 9 360 34
40 10 400  
41 11.2 448  
42 12.6 500 48 N10
43 14 560  
44 16 640  
45 18 760 69

Tolerance


Rubber has a higher shrinkage value than plastic, please refer to ISO 3302-1 tolerance table for rubber parts.
 
Tolerances For Moulded Parts - Rubber
Acc. To ISO 3302-1
Nominal dimension
(mm) 		Tolerance Class M1 Tolerance Class M2
Mould dependant dimensions Dimension with Overflow Mould dependant dimensions Dimension with Overflow
Tolerances – in mm Tolerances – in mm
> 0 - 4.0 ± 0.08 ± 0.10 ± 0.10 ± 0.15
> 4.0 - 6.3 ± 0.10 ± 0.12 ± 0.15 ± 0.20
> 6.3 - 10 ± 0.10 ± 0.15 ±0.20 ± 0.20
> 10 - 16 ± 0.15 ± 0.20 ± 0.20 ± 0.25
> 16 - 25 ± 0.20 ± 0.20 ± 0.25 ± 0.35
> 25 - 40 ± 0.20 ± 0.25 ± 0.35 ± 0.40
> 40 - 63 ± 0.25 ± 0.35 ± 0.40 ± 0.50
> 63 - 100 ± 0.35 ± 0.40 ± 0.50 ± 0.70
> 100 - 160 ± 0.40 ± 0.50 ± 0.70 ± 0.80
        Tolerances – in % Tolerances – in %
>   160   ± 0.30 ± 0.40 ± 0.50 ± 0.70

Table classes M1 (Precision) and M2 (Commercial)
* To achieve M1 class, lesser cavities are required, resulting in higher part cost

Hardness


Hardness is measured in degrees usually on the Shore "A" scale and are normally based on a nominal value e.g. 50±5° or 50-60°.
 
Very Soft 30-40°
Soft 40-50°
Soft-Medium 50-60°
Medium 60-70°
Firm 70-80°
Hard 80-90°

Tensile Strength


Tensile strength is the maximum tensile stress reached in stretching a test piece.

Tensile tests are used for controlling product quality and for determining the effect of chemical or thermal exposure or an elastomer. In the latter case, it is the retention of these physical properties, rather than the absolute values of the tensile stress, elongation or modulus, that is significant.
 
Grade Typical Range
Natural 10 to 15 Mpa
SBR 9 to 12 Mpa
EPDM 7 to 15 Mpa
CR 9 to 14 Mpa
NBR 7 to 20 Mpa
Silicone 4 to 10 Mpa
HNBR 7 to 10 Mpa
FKM 5 to 9 Mpa
FluoroSilicone 6 to 12 Mpa
PU 9 to 15 Mpa

Compression Set


The permanent deformation remaining after release of a compressive stress.

Compression set is expressed as the percentage of the original specimen thickness for Method A (constant force) or the percentage of the original deflection for Method B (constant deflection).

Compression set is an important property for elastomers and cushioning materials.
 
24 hours @ 70°C
Grade Typical Value Tight Value
Natural 30% 20%
SBR 30% 20%
EPDM 30% 15%
CR 40% 20%
NBR 30% 20%
Silicone 20% 10%
HNBR 30% 20%
FKM 35% 20%
FluoroSilicone 20% 10%
PU 35% 20%

Electrical Properties


Rubber is often used as an electrically insulating material, when formulated; it can offer outstanding electrical properties. Electrical properties are dependent on the materials used in compounding and requirements should be clearly defined.

Surface resistivity is the resistance to leakage current along the surface of an insulating material. Surface Resistivity is expressed in ohms (per square) and a practice to measure on compounding sheet level.
 
Ohms Per Square Resistivity
103 - 104 Conductive
106 - 1011 Static
> 1012 Insulative