I. production process of large size O-ring
1. Pay attention to the following technical details when selecting large-scale O-ring
(1) the pre stretching rate (piston seal) or pre compression rate (piston rod seal) and the reduction of area shall be calculated;
(2) pay attention to the compatibility of the seal and the sealed liquid, and consider the swelling of the seal ring;
(3) also consider the thermal expansion of the seal.
For example, piston seal: if the diameter of the seal groove is 780, the inner diameter (including tolerance) of the seal you ordered should be at least 780; if it is piston rod seal: if the diameter of the groove is 780, the outer diameter (including tolerance) of the seal you ordered should be at least 780.
2. Processing method of large O-ring
The processing method and mold design of large non-standard O-ring are adopted. The upper and lower molds are used to design long strip multi cavity molds. The two ends of the molds are closed and removable to ensure high-pressure vulcanization. The upper and lower molds are respectively equipped with adjustable heating devices with a temperature of 30 to 250 ℃, and the upper and lower molds are equipped with adjustable cooling devices with a temperature of 30 to 250 ℃. Assuming the temperature of the upper and lower molds is between 150 to 220 ℃, the upper and lower molds will be The mold is closed after dust removal and temperature rise is regulated; the rubber strip determined by width and height is prepared according to the requirements of the processed non-standard O-ring diameter, and the rubber strip is put into the cavity of the upper and lower mold to close the mold, and the two ends of the upper and lower mold are sealed and pressurized for vulcanization; the vulcanized rubber strip is taken out of the upper and lower mold and continues to be vulcanized, and after the length of the rubber strip reaches the total length, it is butted in turn and straight To complete the whole O-ring butt joint after trimming detection, in order to achieve large-scale non-standard O-ring preparation.
II. Oil resistance of NBR O-ring
NBR O-ring can withstand most oils, especially alkane oil. There are two kinds of oils, alkane oil and aromatic oil. Alkane oil refers to the oil with chain structure. Aromatic oil refers to the oil with ring structure such as benzene ring in the molecular chain, such as common gasoline, engine oil, diesel oil, peanut oil, soybean oil, etc. all belong to alkane oil; pine tar and coal tar belong to aromatic oil This is easy to understand. NBR molecular chain contains - CN (cyano) group, which belongs to polar rubber, while alkane oil molecular chain is straight chain, without pre polar group, non-polar structure. Aromatic oil contains benzene ring and other ring structure, which also shows strong polarity, that is, the so-called "similar compatibility" principle.
NBR is short for O-ring. A synthetic rubber made by copolymerization of butadiene and acrylonitrile. NBR O-ring is known for its excellent oil resistance, which is next to polysulfide rubber, acrylate rubber and fluororubber. In addition, NBR O-ring also has good wear resistance, aging resistance and air tightness, but its ozone resistance, electrical insulation and cold resistance are poor, and its conductivity is better.
The production process of NBR O-ring has the following characteristics:
1. The polarity of monomer acrylonitrile is strong, so the latex is not very stable in the polymerization process. The larger the amount of acrylonitrile is, the worse the stability of the latex is.
2. The hydrolysis of cyano group can be caused by too strong alkalinity or acidity of the medium or too high polymerization temperature, that is to say, the generated acid will destroy the emulsifier, which is also one of the reasons for the instability of the emulsion.
3. Amido, the intermediate product of hydrolysis, and cyano group in polymer chain may be cross-linked at higher temperature, which will lead to the deterioration of product quality.
4. The reactivity ratios of butadiene and acrylonitrile are quite different (0.3 and 0.02 respectively at 40 ℃). Therefore, the composition and distribution of monomers in copolymers are highly dependent on conversion. The cyanogen distribution can be improved by adding acrylonitrile in batches. NBR is difficult to be processed due to its strong intermolecular force and high hardness. The hard rubber prepared at polymerization temperature of 30 ℃ is the most difficult to be processed and can only be operated after pre plasticization on the cold roll. In order to improve its processability, the method of adjusting molecular weight more effectively and reducing polymerization temperature to 5 ℃ are often used in industry. On the other hand, NBR can be blended with a variety of rubbers such as neoprene, isoprene, cis-1,4-polybutadiene, styrene butadiene rubber and synthetic resins such as PVC, phenolic resin (see polymer blends) to improve its performance.
III. how to distinguish the specific materials of rubber products
The O-ring produced by our company has a variety of materials, including Dingqing O-ring, fluororubber O-ring, silica gel O-ring, EPDM O-ring, neoprene O-ring, etc., so how to identify these materials?
1. Medium resistant weight increase test
Samples can be taken from the purchased O-ring, soaked in one or several selected media after determining the temperature, weighed after a certain period of time, and the type of material can be inferred according to the change rate of weight and hardness. For example, soaking in 100 ℃ engine oil for 24 hours, the change rate of quality and hardness of NBR, fluororubber and neoprene is very small, while that of natural rubber and EPDM has more than doubled weight gain and changed greatly in hardness, with obvious volume expansion.
2. Combustion method
Take samples and burn them in the air. Observe the phenomenon. Generally speaking, fluoro rubber and natural rubber will be extinguished after leaving the fire. Even if the fire is burning, it is much smaller than EPDM. Of course, if carefully observed, the burning state, color and smell will also provide us with a lot of information. For example, NBR / PVC is mixed with glue. When there is a fire source, the fire will splash. It seems that there is
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