First, large-size, large-size O-ring production process
1, the selection of large-size O-rings should pay attention to the following technical details
(1) To calculate the pre-stretch rate (piston seal) or pre-compression rate (piston rod seal), the area shrinkage;
(2) Pay attention to the compatibility of the seal and the sealed liquid, taking into account the swelling of the seal;
(3) Also consider the thermal expansion of the seal.
For example, the piston seal: if the diameter of the seal groove is 780, then the inner diameter (including the tolerance) of the seal you order is at least 780 or less; if the piston rod seal: if the diameter of the groove is 780, then you ordered The outer diameter of the seal (including tolerances) must be at least 780.
2. Processing method of large size O-type sealing ring
Large size non-standard O-ring processing method, mold design, using Dongguan rubber mold processing upper and lower mold design long strip multi-cavity mold, the mold is closed at both ends of the removable, to ensure high-pressure curing, the upper and lower mold are installed at a temperature of 30 to 250 °C adjustable heating device, the upper and lower mold installed at both ends of the temperature of 30 to 250 °C adjustable cooling device; assuming that the upper and lower mold temperature is between 150 to 220 °C, the upper and lower mold detection dust removal after the mold and adjust the temperature According to the processing of non-standard O-ring wire diameter requirements to prepare a width and height of the rubber strip, the rubber strip into the upper and lower mold cavity after the mold, the upper and lower mold two closed pressurized curing; The vulcanized rubber strip is taken out of the upper and lower molds and vulcanization is continued. After the length of the strip reaches the total length, the strips are butted together until the entire O-ring is butt-joined and then trimmed to detect the large-scale non-standard O-ring.
Second, NBR rubber O-ring oil resistance
NBR rubber O-rings are resistant to most oils, especially alkane oils. Oils are classified into two types: paraffinic oils and aromatic oils. Paraffinic oils are molecular structures that are chain-shaped. Aromatic oils are molecules that contain benzene rings. Ring-shaped oils, such as common gasoline, engine oil, diesel oil, peanut oil, soybean oil, etc., belong to paraffinic oils; Dongguan rubber mold processing and pine tar and coal tar oils are aromatic oils. This is still relatively easy to understand, NBR rubber chain contains -CN (cyano) group, is a polar rubber, and the paraffin oil chain is a straight chain, there is no prepolar group, non-polar structure, Aromatic oils contain ring structures such as benzene rings and also exhibit very strong polarity, which is the so-called "similar compatibility" principle.
NBR rubber O-ring referred to as NBR. A synthetic rubber made from a copolymer of butadiene and propylene. NBR rubber O-rings are known for their excellent oil resistance, their oil resistance is second only to polysulfide rubber, acrylic rubber and fluorine rubber, and NBR rubber O-rings also have good wear resistance and aging resistance. Sex and airtightness, but ozone resistance, electrical insulation and cold resistance are relatively poor, and conductive properties are better.
NBR rubber O-ring production process has the following characteristics:
1. The monomer is relatively strong in polarity, resulting in a less stable latex during the polymerization process. The greater the amount of acrylonitrile, the poorer the stability of the latex.
2. The alkali or acidity of the medium is too strong or the polymerization temperature is too high can cause the hydrolysis of the cyano group, that is: the generated acid will destroy the emulsifier, which is also one of the reasons leading to instability of the latex. 3. The amide group in the intermediate product of the hydrolysis reaction and the cyano group in the polymer chain may undergo cross-linking reaction at a relatively high temperature, resulting in deterioration of product quality.
4. The reactivity ratio between butadiene and acrylonitrile is quite far apart (0.3 and 0.02 at 40°C, respectively). Therefore, the composition and distribution of monomers in the copolymer are more dependent on the conversion rate. The addition of acrylonitrile in batches can improve the cyano distribution. NBR rubber due to the strong interaction between the molecular chains, hardness is greater, so the processing is more difficult, in which the polymerization temperature of 30 °C prepared hard rubber is the most difficult to process, need to be pre-plasticized in the cold roller before operation. Industrially, it is often used to more effectively adjust the molecular weight and reduce the polymerization temperature to 5°C to reduce side reactions to improve its processability. On the other hand, NBR can also be blended with various rubbers such as neoprene rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, and synthetic resins such as polyvinyl chloride, phenolic resins, etc. (see Polymer Blends.) (material) to improve performance. Third, how to identify the specific material of rubber products
Our O-rings are available in a variety of materials, including NBR, O-rings, silicone O-rings, EPDM O-rings, neoprene O-rings, etc. Identify these materials? 1, resistance to medium weight gain test
Samples can be taken from purchased O-rings. After the temperature is determined, they are immersed in a selected medium or media. After a certain period of time, they are weighed. Dongguan rubber mold processing infers materials based on the weight change rate and hardness change rate. kind of. For example, immersed in 100-degree oil for 24 hours, butadiene, fluorine rubber, neoprene quality and hardness change rate is very small, and natural rubber, EPDM more than double the weight and hardness changes, volume expansion is obvious.
2, combustion method
Take a sample and burn it in the air. Observe the phenomenon. In general, fluorine rubber, natural rubber will be extinguished after leaving the fire, even if the burning flame is much smaller than the EPDM. Of course, if you look closely, burning conditions, colors, and odors will provide us with a lot of information. Such as NBR / PVC and glue, there is fire when the flames of the chaotic splash, it seems like water, away from the fire self-extinguishing, strong smoke and sour. It should be noted that sometimes the addition of flame retardant but halogen-free glue will also extinguish itself from the fire, which has to be further inferred by other means.
3, hot air aging test
Samples were taken and placed in an aging box for one day of aging to observe the phenomenon after aging. In order to grade aging, you can gradually warm up. For example, neoprene at 150 degrees, natural rubber, SBR will be brittle, Dingqing, EPDM is still flexible. Rising to 180 degrees, ordinary nitrile will be brittle; and 230 degrees, hydrogenated nitrile will be brittle fracture, fluorine rubber and silicone are still very good flexibility. 4, low temperature method
Samples are taken and dry ice and alcohol are used to create a suitable low temperature environment. The sample was soaked in a low temperature environment for 2-5 minutes and the softness of the O-ring was felt at the selected temperature. For example, at -40 °C, the same high temperature and oil resistance of silica gel and fluorine rubber, silica gel will be relatively soft.
5, the proportion of measurement
With precision electronic scales, plus a cup of water, a hair can be. In general, the proportion of fluoroelastomer is the largest, more than 1.8, CR, ECO is also more than 1.3, the proportion of significantly larger can be considered these glue.
The above methods can only be used to simply test the composition of rubber. If you want a specific test report, you need to send a special testing agency to test it.