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How to reduce compression permanent deformation of rubber
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Compression permanent deformation is one of the most important performancesof rubber products, rubber seals and sealing performance are closely related,so the technical personnel in the design formula always want to be as far as possible to reduce compression permanent deformation, in order to achieve the best sealing effect. Vulcanized rubber compression permanent deformation,involves the vulcanized rubber elasticity and recovery. Some people are simply assumed that the elasticity of the rubber, the recovery is rapid, the permanent deformation is small. This kind of understanding is not enough, elasticity andrecovery are two interconnected nature of. But sometimes, rubber essence has not fundamentally changed, the size of the permanent deformation is mainly affected by the change of rubber recovery ability dominated. The capability of recovery factors are molecular ask force, the change of network structure,intermolecular displacement. When the rubber deformation is caused by themolecular chain extension, its recovery (or permanent deformation) is mainlydetermined by the elasticity of the rubber, if the relative slide destruction andmolecular chain of rubber deformation accompanied by network, this can be said to be irreversible, it is irrelevant with elastic. So, what affect rubber elasticity andrecovery factor, are the factors affecting the permanent deformationcompression vulcanized rubber.

Of course, rubber compression test method of deformation will decide the size of the measured values. According to the research of different shapes ofspecimen, the B specimen diameter is small, but it's a larger radius of curvature,the top compression degree is more serious, and in the same volume, B typespecimens in contact with air is 2.2 times as large as A sample, which is in the process of experiment B type specimens, aging opportunity than type Asamples, so the compression of B type specimens of permanent deformation is greater than A, while the hot air aging of rubber is from the outside to the inside,the sample is greater, the greater will be the slow aging, a factor of compressionpermanent deformation of less than B type specimen which is A type specimens.For the 10 × 10mm samples, because is restored at room temperature, rubbermolecular activity at low, difficult to fully recover, so relative to the high temperature compression deformation of A type, B type and large recovery.Therefore, according to GB / T 7759 - 1996 test, compression test specimen type B permanent deformation is greater than that of the A specimen; according to GB / T 7759 - 1996 on the B sample test, according to GB / T 1683 - 1981 to10 × l0mm samples of 10 × l0mm specimens, compression permanent deformation is greater than B sample. But no matter what kind of test method, rubber compression deformation ultimately its composition and structure of the.

This paper selects some commonly used rubber, and the major factors affectingthe compression permanent deformation overview.

Nitrile rubber, nitrile butadiene rubber is a kind of molecular chains with cyanopolymer, polar cyano and force caused by polar nitrile rubber oil resistant resulthas certain and high temperature resistant performance, is widely used as oil resistant sealing ring production. With 26 grades for the nitrile rubber for rubber,adding 65 phr N770, and cooperate with other agents, the test was performed according to GB / T7759 - 1996, the effects of different curing systems on compression deformation, the vulcanized rubber peroxide curing system ofcompression set minimum, compression deformation is only 6%, while in theperoxide curing system when the amount of curing agent, 2.5 copies, 0.3 phr of sulfur, accelerator TMTD or DPG 1.5 phr of vulcanized rubber compression permanent deformation, and other physical properties are better. The maximumcompression permanent deformation of vulcanized rubber general sulphur vulcanization system and CD mg curing system, when the sulfur and accelerator DM dosage was 1.5 phr, compression permanent deformation of 54%, cadmium oxide was 5 phr, magnesium oxide was 15 phr, accelerant DM was 1 phr,accelerant CZ with 2 phr, compression permanent deformation of 57%.Vulcanized rubber semi efficient vulcanization system and efficient compression permanent deformation, when TMTD was 1.5 phr, accelerator DM is 2, the amount of sulfur 0.8 phr, compression permanent deformation of 15%. When TMTD was 3 phr, sulfur 0.3 phr, compression permanent deformation of 14%.Research to improve the Ding Jing rubber hardness and reduced at high temperature rubber compression permanent deformation of the way Ding Jing,found Ding Jing rubber acrylonitrile content in 25% ~ 30% tensile strength high,low compression permanent deformation, comprehensive physical properties,and the addition of magnesium methacrylate (MMg) can effectively improve the heat resistance of Ding Jing compound, reduce compression permanentdeformation, and through the reinforcing system suitable to the Ding Jing rubbertensile strength more than 20MPa, hardness 85shore A, compression permanent deformation is less than 30%.

Fluorine rubber is a kind of side groups are substituted by fluorine atoms of the polymer, fluorine atom atomic radius is smaller, surrounded around the carbonchain, the chain is very stable. The structure characteristics of fluorine rubberdetermines the high temperature and solvent resistance of it, so it is widely used in the production of a variety of sophisticated rubber seal products. With thetraditional two amine curing agent (such as 3 curing agent) cured fluorine rubberprepared, compression permanent deformation in high temperature, hard to playhigh quality elastic sealing material. Since the late 60's early 70's, foreigndeveloped two hydroxy compounds with low compression permanentdeformation of vulcanization system, the high temperature fluorine rubberpermanent compression deformation greatly improved, 200 C × 70hcompression permanent deformation by original 50% (amine curing) down to 25% ~ 30% (hydroquinone and 12% ~ 15% (sulfide) effect of bisphenol AF)level. Study on the effect of different curing systems compression permanent deformation of fluorine rubber, and according to the ASTM D1414

φ 25 × 3.5O ring (compression ratio is 25%) to test, compared the compression permanent deformation difference between 26B type and 246G type two kinds offluorine rubber. Through the test of several curing system, it is considered that the 246G fluorine rubber using hydroquinone vulcanization system is the good performance of the rubber with low compression permanent deformation of fluorine, compared with the 26B type fluorubber using the system, not easy toburn, liquidity and good storage stability. 26B vulcanizate compression permanent deformation is better than No. 3 curing agent. Although thepermanent deformation of compression than bisphenol AF vulcanizator itsvulcanizate, but because of its curing agent and accelerant price is much lower than that of bisphenol AF and the corresponding promoter, which has a goodeconomy and practicality. 246, when the proportion is 30, ethyl acrylate and allylacrylate copolymer 70, 175 ℃ for 72h, compression set minimum can reach 17.4%.

Three rubber manufacturing brake cup, sealing ring, sealing strip and many other products are used for sealing occasions. To achieve long-term reliabilitysealed, generally have strict requirements on rubber compression permanent deformation. Study of three yuan and three yuan of ethylene propylene rubberreclaimed rubber and rubber compression permanent deformation performance,mainly studies three Yuan Yibing rubber / reclaimed EPDM and ratio, curing system, carbon black, antioxidant effect of the type and amount of compressionpermanent deformation of the vulcanizate. According to GB / T 7759 - 1996 test,the results showed that: in the EPDM reclaimed rubber and ethylene propylene rubber amount three yuan (Sheng Jiao), a peroxide curing system. Reduction ofsemi reinforcing carbon black content, can effectively reduce the rubber and thecompression permanent deformation; in the research scope, antioxidant RD andantioxidant content of MB was 1.5 / 2, rubber and thermal aging is better, but adding antioxidant RD and antioxidant MB in compression permanent deformation increased vulcanizate. A.van Meerbeek, 100 EPDM, 5 copies of zinc oxide, 100 N550,1 portions of stearic acid, 70 samples of paraffin oil, at 100 ℃ for 22h, sample thickness 12.5mm measured under the condition ofcompression permanent deformation (similar to the GB / T 7759 - 1996), found that the sulfur 0.4 phr, accelerant CZ was 0.7 phr, accelerator the TMTD was 2.5 phr, EPDM can be used as a low compression permanent deformation of vulcanization system, while both the longest scorch time, fast curing and good physical properties.

Through the study of the three yuan of ethylene propylene rubber found, in the same dosage, different packing compression permanent deformation increasesroughly as follows: FEF<SRF<ISAF< spray carbon black < < < calcium carbonate nano kaolin clay, which only has high structural but also has a certainparticle size of carbon black filled vulcanizates strong, will have a relatively smallpermanent compression deformation.

Chloroprene rubber due to the widespread use of the hose, rubber seal products, compression permanent deformation is an important index. Reportedabroad on the vulcanization system improves the compression permanent deformation chloroprene rafter amine compound is studied, the basic with the use of zinc oxide, magnesium oxide, and three methyl thiourea (TMU) andcatechol borate two adjacent toluene guanidine salt (PR) of the (TMU / PR)curing system compression deformation, can be obtained excellent sulfide.However, the vulcanization system will reduce the storage stability of rubber compounds, and in the process of storage, will also cause the scorch. In order to improve this defect, based on the analysis of the function of PR, found the PR primary body catechol and boric acid ester (CTOB) and with the (TMU/CTOB)curing system with (TMU/PR) curing system, can produce excellent compression set of sulfide, and the glue material storage stability increased. Research on the influence of CR varieties, curing system, filler and plasticizer system and curing process of CR compound compression permanent deformation. According to GB/T 1683 - 1981 test, results show that, the non sulfur modified CR2321, thezinc oxide / magnesium oxide and three methyl thiourea as curing system, room temperature compression when filled with carbon black N774, high temperaturecompression of carbon black filled N330, with about 12 copies of the naphthenic oil at the same time, and prolonging the curing time and improve the curing pressure, are conducive to reducing rubber compression permanent deformation, which added CR2321 45 N774,25 × 48h, deformation is 2.8%; while the CR2321 add 50 copies of the following N330125 ℃× 24h, compression permanent deformation can be controlled within 7%. By testing and found that the N774 black filled compound is less than 45 in the amount of compression permanent deformation is smaller than the compound calcium carbonate and clay filled; clay filling compressed rubber permanent deformation than calcium carbonate filler gum, but less than white carbon black filled rubber.

Conclusion

Rubber compression permanent deformation in addition to the size of thespecies and rubber, other such as the structure and particle size of filler,plasticizer, curing system, curing time, test specimen shape and other factors willaffect the final result size. As the rubber seal products is an important indicator,the system to carry out various factors alone or research both on compression permanent deformation is very important.