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Silicone products production processes and features

Source:未知 Sentiment:Published time:2018-01-24

First, the silicone material characteristics
 
A. Silicone raw materials are generally gelatinous, somewhat similar to plasticine, colorless and translucent, odorless.
 
B. Its main features are both high temperature (up to 300 ℃) and low temperature (down to -100 ℃), is the best cold, high temperature rubber; excellent electrical insulation, high thermal oxidation and ozone stability Very chemically inert. The disadvantage is the lower mechanical strength, oil, solvent and acid and alkali poor, more difficult to sulfide, the price is more expensive. Operating temperature: -60 ℃ ~ +200 ℃. The above is a description of the silicone rubber in the manual.
 
C. Operating temperature: As mentioned above, the general setting is -40 ℃ - 200 ℃, the role of up to 230 ℃ in a short time.
 
D. Aging problems:
 
Oil, acid and alkali poor, and the force has little to do.
 
E. Bonding problems: Before the surface treatment, in addition to using silicone products as adhesives and silicone parts bonding, and other parts must be fully bonded after the surface of the adhesive, adhesive surface vulcanization can be glued. Anything that can be vulcanized or crosslinked with rubber is referred to as a vulcanizing agent, also known as a cross-linking agent. There are many kinds of vulcanizing agents, and they are still increasing. The vulcanizing agents that have been used are sulfur, selenium, tellurium, sulfur compounds, metal oxides, peroxides, resins, quinones and amines.
 
F. Material hardness: Shaw hardness of plastic parts in the domestic market can theoretically choose between 10 degrees to 80 degrees. Can easily find the general in 20 degrees to 70 degrees, the most commonly used is 40 to 50 degrees.
 
Second, silicone products production process
 
A raw material shape and color
 
B after color mixing after milky white silicone gel shift of various colors of the material C mixing plastic, the raw material into a bar, cut into pieces of a material.
 
D vulcanization molding
 
E trimming, demolition, inspection, packaging.
 
F. Finished figure
 
Third, the product size and characteristics
 
A, the limit size: the thickest can be done 15 ~ 20MM, if the ball can be done diameter 30MM. The recommended thickness of the general thickness of not more than 3MM, when more than 3MM, will spend more curing time and increased costs. The thinnest on the theory of up to 0.2MM, but the design generally take the thinnest 0.3MM, recommended 0.4MM.
 
B, the relative size: the difference in thickness, the thinnest and the thickest recommended not to exceed 3 times. Such problems mainly depend on the temperature and pressure requirements of the material vulcanization.
 
C, shrinkage. Silicone material shrinkage and the hardness of the material, silicone products manufacturers to provide more than 1.022 to 1.042 in the sub-materials, for 40 to 50 degrees of material, generally take 1.03 shrinkage. Compared with plastic, silicone products will not shrink due to similar obvious surface defects.
 
D, dimensional accuracy: Because silicone products are mostly multi-cavity, relative to the plastic products, the number of holes is very large. So there is no plastic products in the size control as convenient. The general accuracy of positive and negative 0.1, high-precision products for the positive and negative 0.05. When used in conjunction with the holes and keys on the plastic part, the clearance should be taken as 0.1 for one side and 0.2 for one side as the recommended value.
 
E, Shape design: For rubber sleeve parts, the general appearance of the product to the factory to provide the original map can be, with the problem to explain the decision by the mold factory. Under normal circumstances, depending on product size, rubber sleeve and the product with the general unilateral small 0.2 ~ 0.5 negative deviation.
 
Fourth, the mold structure
 
A. Mold thickness limit, tentatively 250mm, size up to 500X500, the product can be done in the mold area up to 400X400. Mold structure is generally divided into upper mold, lower mold, floor, roof, ram, mold core, hinges and other auxiliary parts. Silicone product design should pay attention to the mold and the characteristics of the production process:
 
B. Stripping: Silicone products stripping can be directly off. For products without design flaws off the size requirements mainly depends on the maximum mold core and mold release the minimum percussion at the circumference of the ratio of less than 55 ° can be done 2-3 times the area to be forced demoulding There may be sharp edges and openings. Due to vulcanization requirements at a temperature of 180 degrees Celsius, demoulding work apart from the mold itself up and down separately, almost all manual. Therefore, in the design of parts should be taken off easy and fast. To avoid the demoulding time is too long and affect the quality of parts and curing efficiency and production. Due to the demolition of silicone mainly for manual mode, the action of its roof stroke is very small, so the silicone mold and plastic mold compared with no oblique top. Generally do not set the core.
 
C. Mold core fixation:
 
Unlike plastic molds, the mold core of a silicone mold is typically removed with the product part when the mold is opened. Therefore, the mold core fixed and accurate positioning of the plastic mold is difficult to handle, the higher the degree of mold core steel. Usually the core together, once all the core fixed. Or the core through the auxiliary equipment, so that it can quickly locate. Because there is a lot of pressure in the mold clamping process, so to prevent mold movement.
 
D. Core pulling: the general can not automatically take the line, but strong off, the core is only used for small size structure. The setting of the core pulling is similar to the plastic mold, but it is manually removed when the mold is opened. In addition, the core-pulling to occupy a larger space within the mold, which is more than a mold in the mold not only complex processing, and low utilization of mold space. So do not use the core as much as possible.
 
E. Shape: Silicone products have great toughness when the surface is intact, but cracks will expand rapidly under the external force once the cracks exist. In other words, silicone products are very sensitive to cracks. In consideration of these problems, attention should be paid in the design of silicone parts: no sharp corners can be provided in all positions to avoid stress concentration cracks. Opening R angle can not be less than 0.5F. Self-demolition side: The main role of self-demolition side: to accommodate excess rubber; easy mold exhaust; easy to trim flash. Self-demolition edge is generally at the parting surface at the circle of thin edge and the corresponding more substantial tear edge. Thin side of the thickness of the general take 0.1 ~ 0.2, torn part of the thickness of the general take 0.8, width generally take 1 ~ 2MM.
 
G. Insert: Silicone products can be placed in various types of inserts, but should pay attention to several issues: First, the embedded parts surface should be pre-treatment, mainly surface or surface activation of vulcanization. Otherwise, the insert and the glue will be hard to connect firmly. Second, the fixed positioning of the insert, one-way fixed in the vertical direction, but the other directions must be fully fixed. So as not to move the insert during the full mold. Third, the plastic thickness around the insert. For the full package plastic (all surfaces are plastic, so the positioning of the insert can not be) parts, insert the surrounding thickness of at least 0.5MM. For the positioning of the insert, the thickness of the surrounding adhesive layer should be 0.4MM or more.