To understand the production process of medical silicone rubber products, you need to first understand the raw materials of silicone.
1. Characteristics of silicone material
A. Silicone rubber raw materials are generally gel-like, somewhat similar to plasticine, colorless, translucent, and odorless.
B. Its main features are both high temperature resistance (up to 300 ℃) and low temperature resistance (minimum -100 ℃), which is the best cold-resistant and high-temperature resistant rubber at present; at the same time, it has excellent electrical insulation and high stability to thermal oxidation and ozone. , chemically inert. The disadvantage is that the mechanical strength is low, the oil resistance, solvent resistance and acid and alkali resistance are poor, it is difficult to vulcanize, and the price is more expensive. Operating temperature: – 60 ℃ ~ + 200 ℃. The above is the description of silicone rubber in the manual.
C. Use temperature: As mentioned above, it is generally set to -40 ℃ – 200 ℃, and it can reach 230 ℃ in a short time.
D. Aging problem: oil resistance, acid and alkali resistance are poor, and it has little to do with the stress.
E. Adhesion problem: Before surface treatment, in addition to using medical silicone rubber products as adhesives to bond with silicone parts, the adhesion to other parts must be surface activated, and the glue surface can be cured by vulcanization. All substances that can react with rubber or make it cross-link are collectively referred to as vulcanizing agents, also known as cross-linking agents.
F. Material hardness: According to Shore hardness, the plastic parts can theoretically be selected between 10 degrees and 80 degrees in the domestic market. The ones that can be easily found are generally 20 degrees to 70 degrees, and the most common ones are 40 to 50 degrees.
2. the production process of medical silicone rubber products
A: Shape and color of raw materials
B: After color matching and kneading, the flakes of various colors are transformed from milky white silicone rubber
C: After kneading and shaping, the raw materials are pressed into strips and cut into strips.
D: Vulcanization molding
E: Trimming, edge removal, inspection, packaging.
F: finished product
3. Product size and characteristics
A. Limit size: the thickest part can be 15~20MM, if it is a sphere, the diameter can be 30MM. Generally, the recommended thickness is no more than 3MM. When it is larger than 3MM, it will take more vulcanization time and increase the cost. The thinnest part can theoretically be up to 0.2MM, but the thinnest 0.3MM is generally taken in the design, and 0.4MM is recommended.
B. Relative size: In terms of thickness difference, it is recommended not to exceed 3 times the thinnest part and the thickest part. Such problems mainly depend on the temperature and pressure requirements when the material is vulcanized.
C. Shrinkage rate. The shrinkage rate of the silicone material is related to the hardness of the material. Most of the secondary materials provided by the manufacturer are between 1.022 and 1.042. For materials with a temperature of 40 to 50 degrees, the shrinkage rate is generally 1.03. Compared to plastic, medical silicone products do not suffer from similar apparent surface defects due to shrinkage.
D. Dimensional accuracy: Because most of medical silicone rubber products are one mold with multiple cavities, the number of cavities is very large compared to the plastic products. Therefore, it is not as convenient as plastic products in size control. The general accuracy is plus or minus 0.1, and the high-precision product is plus or minus 0.05. When it is used for matching the hole of the plastic part and the button, the minimum clearance is 0.1 per side, and the recommended value is 0.2 per side.
E. Shape design: For rubber sleeve parts, it is generally enough to provide the original drawing to the mold factory according to the product shape drawing, and explain the matching problem, which is decided by the mold factory. Under normal circumstances, depending on the size of the product, the coordination between the rubber sleeve and the product is generally a negative deviation of 0.2~0.5 on one side.