Fluoroelastomer has been successfully developed and put into industrial production by DuPont in the mid-1950s for more than 60 years. It has excellent oil resistance, high temperature resistance, concentrated acid resistance, alkali resistance, radiation resistance, corrosion resistance, strong oxidant resistance, strong chemical resistance, good gas tightness, good physical and mechanical properties, and electrical insulation, low compression and permanent deformation. As a special synthetic rubber, it is widely used in chemical industry, aerospace, automobile, petroleum industry, machinery, electronics and other fields. Fluorine rubber has excellent performance and broad application prospects. Independently developed by China's low-temperature fluoroether rubber has been successfully used in the manufacture of Long March series of launch vehicle servo mechanism seals, as well as assembled in fighter jets, new tanks on the oil pipe, electrical circuit sheathing and other accessories. In civil use for automotive parts, increasing day by day, in the industrial field gradually promote the use of fluorine rubber.
Although fluorine rubber has excellent resistance to media and high temperature as mentioned above, there are some abnormalities and difficulties in the process of processing and producing fluorine rubber products, among which the common ones are scorched dead material when mixing, open refining sticky rollers, sometimes small white dots are found when cutting and checking after the film is released, the products are easy to tear, shrink and crack, burn the edges, there are traces at the joints, lack of rubber, product deformation, serious mold staining and other phenomena, which affect the product quality. The quality of products is affected.
In response to the above abnormalities in the production process, the following solutions were made.
Point 1. Mixed fluorine rubber dead material
The reason for the ingredient rubber contact with sulfur yellow or sulfur yellow products, many enterprises do not have a special refining fluorine rubber machine, often refining other sulfur yellow rubber material, cleaning is not in place, or ingredients accidentally tainted with sulfur yellow or water, so that can be combined with the fluorine rubber promoter caused by scorching, or the role of water to make the fluorine rubber surface activation decomposition. Solution, the best special machine, if not, should also be in the conversion of fluorine rubber before the refining, must be completely clean the baffle plate and the material plate, absolutely avoid contact with water and sulfur yellow, ingredients application special tools, a material a spoon, to prevent cross-contamination. Keep calcium hydroxide and magnesium oxide sealed and ready to use.
Point 2. The sticky roller phenomenon
Mainly in the mixing process on the opening machine, the rubber material tightly wrapped in the back roller, or at the same time wrapped before and after the two rollers, resulting in the former rubber material can not turn refining, and the latter with the added agent easily pressed into flakes and fall off, resulting in uneven dispersion. The main reason for the fluorine rubber material sticking to the rollers is the low Menny or low molecular content of fluorine rubber. The solution to this problem is to choose raw rubber with a viscosity of about 70, and to use raw rubber with a narrow molecular weight distribution, and then add a small amount of Brazilian wax or fluorine wax or low molecular weight polyethylene into the formula, which can also solve the sticky roller phenomenon.
Point 3. About the small white spots in the compounding rubber
It is due to some powder dispersion of fluorine rubber compounding agent is not uniform, or due to the powder moisture caking, such as acid absorbers calcium hydroxide, magnesium oxide and diatomaceous earth, barium sulfate, etc., the solution, to prevent the compounding agent moisture and strengthen the thin pass process.
Point 4. The product is easy to tear
The cause, may be too thick burr, trimming when tearing, or mold with too tight, out of the mold burr parts are stuck in the mold, easy from the product and burr before tearing, uneven force when starting the mold, easy to tear the product. Sometimes the mold cavity processing is rough, or the adhesive material sticks to the mold, and when the vulcanization is finished, it causes difficulties to take off the mold and tears the product easily. In addition, the vulcanization temperature is too high, which will also make the products become brittle and easy to tear. For the above abnormality, it can be solved from the following aspects: mold processing precision should be good cavity roughness Ra less than 0.8, the fit gap should not be too large, the vulcanization temperature control left between 170 degrees is good, and the rubber material weighing should be accurate.
Point 5. Shrinkage and cracking problem
It is due to the pressure is removed when the mold is opened, fluorine rubber shrinkage, and the burr part is stuck in the mold with the surface between, so between the product part and the burr produce a tensile force, so that the product and the burr split, when the crack enclosure is expanded to the product part, it causes shrinkage and cracking phenomenon. The solution is to reduce the vulcanization temperature appropriately, choose the Menny viscosity in about 70 [ML1+4] 121 degrees, while the mold fit degree should be appropriate, not too loose and too tight.
Point 6. Edge is like burning
It is the vulcanization temperature is too high, especially thick products, appropriate to reduce the vulcanization temperature can be overcome.
Point 7. There are traces at the joint
It is due to the lap part of the adhesive material is not completely fused together, or due to the adhesive strip has impurities or oil fouling, the solution is to keep the preformed adhesive strip in storage, transportation, loading glue clean, to prevent pollution.
Point 8. Lack of glue
It is related to the structure of the mold and the liquidity of the glue. The closed mold is more likely to produce lack of glue than the open mold. The solution is to adjust the liquidity of the rubber and open the air venting hole in the mold cavity.
Point 9. Product deformation
It is due to the fluorine rubber shrinkage rate is large, after molding the product shrinkage anisotropy, the coefficient of thermal expansion of the rubber in different directions is different, two vulcanization process will form additional cross-linking, especially a section of vulcanization under sulfur, two vulcanization of the product, more obvious deformation, so to give full cross-linking in a period of vulcanization time, to avoid two vulcanization of the product deformation.
Point 10.Mold stain serious phenomenon
We generally use the 26 type fluorine rubber, phenol vulcanization system, in the vulcanization process will be generated HF, it is a very strong acid, has a great corrosive effect on the mold, the formula to add acid absorbent is to absorb the HF generated, to prevent pollution of the mold. The solution is to use sufficient calcium hydroxide and magnesium oxide in accordance with the formula, the dosage is generally 6 parts and 3 parts, and Brazilian wax can be added to the formula, which can migrate to the rubber surface during the vulcanization to form a film to prevent the mold from being contaminated.
The above ten common abnormalities in the production and processing of fluorine rubber can be solved by various measures.
