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O-rings
is one of the most common seals in use today. They can be used in both
static and dynamic applications and offer an economic and effective
sealing solution. By choosing a compound and hardness it is usually
possible to find a suitable O-ring for most applications. Rubber
O-rings can operate in temperatures from -55 deg C to + 320 deg C and
(with backup rings) at pressures of 400 Bar. They are available in a
large range of standard imperial and metric sizes The most common
international standards for O-Ring dimensions, in addition to ISO
3601/1 are:-
- American Standard : AS-568
- Great Britain : BS 1806 - BS 4518,
- Germany: DIN 3771,
- Sweden: SMS 1586,
- France: NF T 47 501,
- Japan: JIS B 2401-77
CROSS SECTIONS :-
- Common metric sections include 1.0mm, 1.5mm, 2.0mm, 2.5mm 3.0mm, 3,5mm, 4.0mm, 4.5mm 5.0mm, 6.0 etc.
- Common Swedish sections include 1.6mm, 2.4mm, 5.7mm, 8.4mm
- Common French sections include 1.8mm
- Common Japanese Sections include 1.9mm, 2.7mm, 3.1mm 3.6mm,
- Common Imperial sections are 1.78mm, 2.62mm, 3.53mm, 5.33mm and 6.99mm
It
can be seen from the above that there is an o ring section to suit
almost any requirement, inside dimensions range from less than 1mm to
over 800 mm with bigger sizes than that available as Customer Specials
".
HARDNESS:-
Common rubber compounds are available in a range of hardness grades,
the most common being 70 shore (Standard Hardness), 80 shore, 90 shore
(Hard) is also available, with 40/50 shore (soft) being the least
popular. Fluoro elastomer (VITON) O'rings to be slightly harder with
75/80 Shore being the norm.
Most Common Materials:-
| FKM |
Viton |
-40
deg C + 230 deg C |
High
Temperature, Synthetic and hydraulic fluids, many acids and alkalis |
| FKM |
Perfluoro
elastomer
(Viton) |
-30
deg + 320 deg C |
Very
high temperature, Best chemical resistance of all Elastomers High
performance material |
| MVQ |
Silicon |
-55
Deg C + 230 Deg C |
High
Temp Air, Water, Oxygen, alkalis and some acids Static applications only |
| NBR |
Nitrile |
-40
deg C + 110 Deg C |
Mineral
based Hydraulic and lubricating oils LPG Gas, Butane, Propane,
Acetylene, Petrol, Diesel |
| EPDM |
Ethylene-propylene |
-55
deg C + 150 deg C |
Fire
resistant hydraulic fluids, Brake fluids, Hot water, Steam Not
resistant to mineral oils |
| PU |
Polyurethane |
-30
deg + 80 deg C |
Good
wear and extrusion resistance Not resistant to glycol based fluids,
acids or alkalis |
| PTFE |
Polytetrafluoroethylene
|
-200
deg +260 deg C |
Very
good chemical resistance except liquid alkaline metals No rubber elastic properties, static applications only |
Above
table is only a guide to the most common Elastomers, performance would
be dependant on the particular variant of elastomer used. Chemical
resistance should also be checked before use.
The correct
functioning of the O-ring
is dependant on both the groove size and the radial clearance. For
higher pressures the o ring hardness can be increased, backup rings can
be used or radial clearance should be decreased.
O-Rings Recessing Arrangement for AS-568 Series (American Standard): -
|
O-Rings Cross Section
|
Static Application
|
|
Radial Compression
|
Axial Compression
|
Recess
Radius
(R)
|
|
Depth 0
(D) -0.05
|
Width +0.2
(W) 0
|
Groove 0
Width -0.05
|
Step +0.1
Depth 0
|
|
1.78
2.62
3.53
5.34
6.99
|
1.31
2.09
2.86
4.38
5.57
|
2.4
3.6
4.8
7.1
9.5
|
2.38
3.57
4.76
7.14
9.52
|
1.2
2.0
2.8
4.2
5.5
|
0.5
0.75
1.0
1.0
1.5
|
|
O-Rings
Cross Section
|
Dynamic Application
|
|
Depth 0
(D) -0.05
|
Width +0.2
(W) 0
|
Recess
Radius
(R)
|
|
1.78
2.62
3.53
5.34
6.99
|
1.43
2.26
3.1
4.75
6.1
|
2.4
3.6
4.8
7.1
9.5
|
0.5
0.75
1.0
1.0
1.5
|
All dimensions in mm.
|
