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The Mechanical Properties of Buna N Oil Seal

Views:15     Author:Cindy     Publish Time: 2018-01-31      Origin:Site

The Mechanical Properties of Buna N Oil Seal

Buna N Oil Seal is the co-polymer obtained from the two monomers of butadiene and acrylonitrile through emulsion polymerization. 



With good oil resistance, heat resistance,  and excellent physical and mechanical properties, Nitrile Rubber Seal is widely used in aerospace, chemical industry, automobile, electric wire and cable, printing, food packaging and textile, etc. 



All kinds of additives in the synthesis of NBR gasket process have great influence on the performance of NBR.

 





Buna N Oil Seal Physical Properties


The wear resistance of nitrile rubber gasket is higher 30% to 45% than natural rubber, the high temperature resistance of NBR O Ring is superior than Natural rubber (NR) , Neoprene (CR) and styrene butadiene rubber (SBR). However, there are some defects in the aspects of elasticity, heat generation and deformation, cracking resistance, electrical insulation and oxygen resistance.


 NBR-O-ring.jpg

 

Mechanical properties


Compared with natural rubber, nitrile rubber mechanical properties are lower. Increasing the content of acrylonitrile rubber helps to improve the strength and abrasion resistance, but the resilience deteriorates. NBR washer is non-crystalline amorphous polymer, which must be filled with fortifier (such as carbon black), the strength can up to 25MPa.


The relationship between Tensile properties, permanent deformation, and resilience content with acrylonitrile are shown in Tables 10-1 and Table 10-2.

Table 10-1 Relationship Between Content with Acrylonitrile and Rebound Elasticity

Content with Acrylonitrile / %

Rebound Elasticity / %

19

40

28

34

34

24

39

12

49

7

 

Table 10-2 The dependence of tensile strength, elongation and tear strength on tensile rate

NBR

tensile rate / (mm/s)

tensile strength / Mpa

Elongation     /     %

tear strength / (kN/m)

High  Acrylonitrile

8.3~5000

19.11~21.85

310~330

47.04~95.06

Medium &High Acrylonitrile

8.3~5000

18.52~19.6

410~420

54.88~86.24

Medium Acrylonitrile

8.3~5000

15.97~20.58

300~390

46.06~71.54

Low  Acrylonitrile

8.3~5000

17.74~20.19

400~490

49~64.68

Note: Formula: NBR 100;  ZnO  5;  Stearic acid  1.0; Sulphur 1.5; HAF 50; Accelerator DM 1.5; Anti ager PBNA 1.0.

 

The abrasive resistance of NBR shaft oil seal is 30%~50% higher than natural rubber, which is better than natural rubber in high temperature. Impoving the content of  acrylonitrile can improve its wear resistance.

 

NBR sealingj gasket. jpg


Heat resistance and cold resistance

 

The heat resistance of nitrile rubber gasket is better than natural rubber, styrene butadiene rubber and butadiene rubber. Under the 100 ℃, 120 ℃ can be continuous work 40 days while in 150 ℃ can only work 3 days.

Compared with other rubber, vulcanizates of nitrile rubber have a wide temperature range, such as continuous working at 120 ℃ for a long time, soaking at 191 ℃ oil 70h NBR oil seal still has flexing performance.

In general-purpose rubber, nitrile rubber seal has inferior resistance to low temperature  (see Table 10-3).

Table 10-3 Comparison of brittle temperature of general purpose rubber

General purpose rubber

Brittle temperature / ℃

Natural Rubber (NR)

-50 ~ -70

Polyisoprene rubber (IR)

-50 ~ -70

Styrene butadiene rubber (SBR)

-30 ~ -60

Butadiene rubber (BR)

-73

Neoprene (CR)

-35~ -55

Butyl Rubber (IIR)

-30 ~ -55

Ethylene propylene rubber (EPDM)

-40 ~ -60

Nitrile rubber (NBR)

-10 ~ -20

 

The cold resistance of nitrile rubber sealing gasket is worse than natural rubber, styrene butadiene rubber and butadiene rubber. The low temperature resistance is related to the content of acrylonitrile. With the increasing of acrylonitrile content , the glass transition temperature and brittle temperature also increased (see Table 10-4). After proper coordination, nitrile rubber can reduce the glass temperature to improve the low temperature property. The cold resistance of NBR seals increased with the decrease of acrylonitrile content.

Increasing the content of acrylonitrile can improve the heat resistance, but reduce the cold resistance.

Table 10-4  Comparison of acrylonitrile content with glass transition temperature and brittle temperature

Acrylonitrile content /  %

glass transition temperature /℃

brittle temperature / ℃

0

--

-80

20

-56

-55

22

-52

-49.5

26

-52

-47

29

-46

-46

30

-41

-38

31

-43

--

33

-37 ~ -39

-33

37

-34

-26.5

39

-26 ~- 23

-23

40

-22

--

52

-16

-16.5

 

The use of nitrile rubber in high temperature has the tendency of increasing hardness and  tensile strength,  and also decreasing elongation. In order to improve the cold resistance and not reduce the oil resistance, the acrylonitrile can be taken into polymerization in batches, adding low temperature plasticizer or Combining a rubber with excellent low temperature properties.

 

NBR Gaskets.jpg


Electrical and breathable properties


Nitrile rubber seal has good antistatic properties, and its volume resistivity is about 109-1010Ω·cm, which is equal to or lower than the critical limit of 1010Ω·cm of the volume resistivity of semiconductor materials. Therefore, nitrile rubber gasket is a semiconductor material. In general rubber , the NBR  ia a rubber only can be made for antistatic rubber products.


Because of the polarity, so the electrical insulation property of NBR is not good, which belongs semi-conductive rubber,so it unsuited for being made for insulating material. Various electrical properties of nitrile rubber parameters in Table 10-5. 

Table 10-5 Electrical properties of nitrile rubber

Volume resistivity / Ω·cm

Dielectric strength / (MV/m)

Dielectric constant

Power factor

3.5X107

9.88

13.0

3.0

 

The breathability of NBR seal is only second only to butyl rubber. The breathability is related to the content of acrylonitrile, which will decrease with the increasing of acrylonitrile content. When the ACN content up to 39%, the breathability of both are proportionable. 

NBR Oil Seal.jpgNBR mold tool.jpg


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