Technologies

Non-metallic squeeze gaskets |General-purpose seal technology | Technologies | NOK CORPORATION

Non-metallic squeeze gaskets |General-purpose seal technology | Technologies | NOK CORPORATION

Description

Characteristics of non-metallic squeeze gaskets

Non-metallic type squeeze packing (rubber gasket) requires material selection at high and low temperatures, but because it is softer than other materials, it can be assembled with relatively little force and has good sealing properties. Types of non-metallic squeeze packings include seat gaskets, liquid adhesive gaskets, and O-rings. Similar to O-rings, there are D-rings and square rings for twist prevention and proper seating on the groove. The O-ring, which is the simplest representative of the squeeze packings, is introduced here to explain how to select and use it. There are many applications and types of fixed O-rings, and they have long been used in all fields, from household products to automobiles, industrial equipment and aircraft.

Properties required for O-ring materials

Since the sealing function of an O-ring is achieved by the stress generated by the crushing of the O-ring, it is basically required to have appropriate stress within the range that does not cause abnormal deformation. In addition, this property must not be lost during use. Synthetic rubber is the best material with such characteristics. However, it is difficult to cover all of these properties with one material, so it is necessary to use suitable materials for different applications. NOK offers a variety of materials to suit all conditions of use.

Types of NOK’s O-ring materials

The sizes of NOK-O-Rings (standardized products) are based on JIS, ISO, JASO, AS and NOK standards.

Classification and applications For general equipment
O-Rings Standards JIS B 2401 ISO (General industrial use) NOK Iron Rubber P and G standards (JIS B2401 compliant) NOK S Standards NOK SS Standards
By material JIS symbol (application) Symbols of materials Symbols of materials Symbols of materials
Class 1A (mineral oil resistant) Class 1B (mineral oil resistant) Class 2 (gasoline resistant) Class 3 (animal and vegetable oil resistant) Class 4C (heat resistant) Class 4D (heat resistant) A305 U565 U801 A305 F201
By applications ・P series (for motion and stationary applications) ・G series (for stationary applications) ・V series (for vacuum flanges) For stationary applications ・P series (for motion and stationary applications) ・G series (for stationary applications) ・S series* (for low pressure stationary applications) – SS series* (for low pressure stationary applications)
O rings—Mounting groove dimensions and sizes ・JISB2406 (for motion and stationary applications) ・JISB2290 (for vacuum flanges) ・JISB2406 (for motion and stationary applications) NOK S Standards NOK SS Standards
Back-up rings ・JIS B 2407
T1 (Spiral) T2 (Bias cut) T3 (Endless)
Classification and applications For automobiles For aircraft
O-Rings Standards JISO F404 AS568 (former ARP568)
By material JASO symbols (applications) Symbols of materials
Class 1A (mineral oil resistant) Class 2 (gasoline resistant) Class 3 (vegetable oil resistant ) Class 4C (heat resistant) Class 4D (heat resistant) Class 4E (heat resistant) Class 5 (coolant resistant) H * (wear resistant) A305 A105 F201
By applications Wire diameter 1.9 series (former 1000 series) ・Wire diameter 2.4 series (former 2000 series) ・Wire diameter 3.1 series ・Wire diameter 3.5 series (former 3000 series)  (All of them are for motion and stationary applications) For stationary applications (former AN6227 is for motion applications)
O rings—Mounting groove dimensions and sizes JASOF404
Back-up rings

Types and characteristics of NOK’s O-ring materials

NOK prepares materials equivalent to JIS and JASO standards as standard materials, and a variety of special materials are available to meet a wide range of usage conditions. Typical examples are shown below. For other materials prepared for special applications, please contact the nearest sales office.

Category NOK’s symbols of materials Types of rubber Characteristics Japanese Industrial Standards

B2401 symbols
Standard materials A305 Nitrile rubber Nitrile rubber is the most representative material with excellent oil and wear resistance as well as stable heat resistance. It is also a standard material for NOK’s pneumatic O-rings. Class 1A
A105 Nitrile rubber A material with almost the same properties as A305, but with higher hardness and better pressure resistance than A305. Class 1B
A122 Nitrile rubber Nitrile rubber is a material for general fuel oil with excellent resistance to kerosene, diesel oil and other fuel oils. Class 2
R189 Styrene-butadiene copolymerized rubber (SBR) SBR is a material with the best resistance to animal and vegetable oils such as ethylene glycol and brake oil. Class 3
S503 Silicone rubber Silicone rubber has excellent oil and cold resistance and can be used in the widest range of temperatures among synthetic rubbers. Class 4C
F201 Fluororubber Fluororubber is a versatile material with the best oil, chemical and heat resistance among synthetic rubbers. Class 4D
T767 Acrylic rubber Acrylic rubber has higher heat resistance than nitrile rubber, especially for engine oil, gear oil, and torque converter oil. Class 4E*
E116 Ethylene propylene rubber Ethylene propylene rubber is resistant to coolant oil, steam, vegetable oil, brake oil, and flame-retardant vegetable oil. However, it cannot be used for mineral oil. Class 5*
G607 Hydrogenated nitrile rubber Hydrogenated nitrile rubber is superior to nitrile rubber in terms of heat resistance, oil resistance, weather resistance, high strength, and abrasion resistance. H *
U565 NOK’s Iron Rubber (urethane rubber) The material has excellent wear and oil resistance. However, it may degrade against chemically active oils.  
U801 NOK’s Iron Rubber (urethane rubber) A material with almost the same properties as U565, but with higher hardness and better pressure and wear resistance than U565  
Other

Recommended materials
A980 Nitrile rubber This material has almost the same oil resistance as A305, and has particularly good cold resistance.  
A746 Nitrile rubber This material has excellent gas and weather resistance among nitrile rubbers, and has cleared the standard of the Japan L.P. Gas Instrument Inspection Association.  
S740 Silicone rubber This material has particularly good heat and steam resistance among silicone rubbers. The material also has excellent compression and permanent strain resistance.  
FL68 Fluororubber The material has the same oil, chemical and heat resistance as F201, and has excellent cold resistance among fluororubbers. Fluororubber is widely used for gasoline.  
FP29 Fluororubber This material has excellent resistance to hot water, water vapor and LLC. It also has excellent resistance to high-temperature and high-concentration chlorinated water, which is required for cogeneration systems such as electric and gas water heaters.  

*Class 4E and Class 5 are standard materials for JASOF 404. * Material ‘H’ is NOK’s material symbol.

The squeeze and groove dimensions of O-rings

The squeeze is set at a minimum value of approximately 8% for sealing purposes, and a maximum value of approximately 30% for the compression set limit of the rubber material. For the dimensions of the grooves, please refer to the catalog.

Surface roughness of grooves

The table below shows the surface roughness of the parts of the O-rings that come into contact.

Parts of equipment Applications How pressure is applied Surface roughness
Ra Rz
Side and bottom of the grooves For stationary applications No pulsation Level surface 3.2 12.5
Cylindrical surface 1.6 6.3
With pulsation 1.6 6.3
For motion applications When using a backup ring 1.6 6.3
When not using a backup ring 0.8 3.2
Contact surface of the O-ring seal For stationary applications No pulsation 1.6 6.3
With pulsation 0.8 3.2
For motion applications 0.4 1.6
Chamfered part of the O-ring for installation 3.2 12.5

Use at high pressure (clearance and protrusion)

The O-ring exerts a sealing function due to the compressive stress of the material, and also exerts a self-sealing effect due to the pressure of the sealed fluid. Therefore, in principle, the limit of pressure may not be considered; however, in practice, there is always a gap between the O-ring and the fluid to be sealed, which may cause the O-ring to become incapable of functioning due to the pressure of the sealed fluid. When the groove clearance is expected to exceed a limit, it is recommended to use a backup ring. For the groove design and use of a backup ring, contact our sales office nearest to you. Back-up rings should be installed on both sides of the O-ring when pressure is applied from both directions, and one ring should be installed on the opposite side of the O-ring when pressure is applied from one direction. There are three types of backup rings: endless, bias cut and spiral. Endless is the most effective; however, bias cut and spiral are more convenient in terms of installation.

Chamfering holes and shafts

To prevent damage to the O-ring during installation, make sure to taper the corners of the cylinder and piston rod as shown in the table below. In addition, it is recommended to set the L dimension to (G + b) or more to prevent the O-ring from galling due to bent shafts at the time of installation.

O-ring nominal number a minimum b
JIS JASO At 15 degrees At 30 degrees
P 3 ~P 10 P 10A~P 22 P 22A~P 50 P 48A~P150 P150A~P500 1003~1035 2010~2071 3022~3150 0.9 0.9 1.1 1.3 1.5 3.4 3.4 4.1 4.9 5.6 1.6 1.6 1.9 2.3 2.6
G 25~G145 G150~G500 3025S~3145S 1.1 1.3 4.1 4.9 1.9 2.3
NOK S Standards S  3~S150         SS22~SS12 0.9 3.4 1.6

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