A. general silicone material is gelatinous, somewhat similar to the rubber mud, colorless and tasteless translucent.
B. was characterized by both high temperature (up to 300 DEG C) and low temperature (minimum -100 C), is currently the best cold resistant, high temperature resistant rubber; at the same time, excellent electrical insulation, stability of thermal oxidation and ozone high chemical inertness.
The disadvantage is low mechanical strength, oil resistance, solvent resistance and corrosion resistance is poor, difficult to cure, the price is more expensive. The service temperature is -60 ~ +200 centigrade. These are the instructions for silicone rubber in the manual.
C. use temperature: as mentioned above, generally set to -40 - 200 degrees, in a short period of time can reach 230 degrees.
D. the problem of aging: oil resistant, acid and alkali resistance is poor, and stress has little relationship.
E. problem: in the absence of bonding surface treatment, besides using silicone products as adhesive and adhesive silicone parts, and other parts must stick full after surface activation, rubber vulcanization treatment to cement. Who can occur with rubber vulcanization or material to crosslinked collectively as vulcanizing agent, also known as crosslinking agent. Many kinds of curing agents, and growing, curing agent has been used with sulfur, selenium, tellurium, sulfur compounds, metal oxides, peroxides, resin, quinone and amine etc..
F.: plastic material hardness according to the hardness in the domestic market theory can choose from 10 degrees to 80 degrees. Can find in 20 degrees to 70 degrees, the most commonly used is 40 to 50 degrees.
Two. Production process of silica gel products:
Production process of general silica gel products:
A, material shape and color.
Sheet B, after color mixing by the opaline silica displacement of various colors.
C, mixing, shaping, raw materials will be pressed into strips, cut into strips of material.
D, vulcanization molding.
E, trimming, trimming, inspection, packing.
F and finished product drawing
Three, product size and characteristics:
A, ultimate size: the thickness of 15~20MM can be achieved, if is a sphere, can be 30MM in diameter. Generally recommended thickness is not greater than 3MM, when more than 3MM, will spend more time to increase the cost of vulcanization. The thinnest of 0.2MM in theory, but in general the design of thin 0.3MM, 0.4MM.
B, the relative size in thickness difference, the thinnest and thickest suggest not more than 3 times. This problem mainly depends on the material requirements of curing temperature and pressure.
C, shrinkage: the shrinkage of silica gel material is related to the hardness of the material, the secondary materials provided by the manufacturer are mostly between 1.022~1.042, for 40 to 50 degrees of material, generally take 1.03 shrinkage. Compared with plastic, silicone products have obvious surface defects similar because of shrinkage.
D, precision: because the silicone products for the first mock exam multiple points, the number of points relative to the plastic products very much. So the size control not as convenient plastic products. The general accuracy of plus or minus 0.1 plus or minus 0.05, high precision products. When used to match the hole and button of the plastic parts, the gap is minimum to take one side 0.1, and the recommended value is unilateral 0.2.
E, shape design: for the rubber sleeve parts, according to the general appearance of the product to the mold factory to provide the original map, the problem of cooperation to explain, decided by the mold factory. Under normal circumstances, depending on the product size, with the rubber sleeve and the product is generally negative deviation of unilateral small 0.2~0.5.
Four. Die structure:
A, the thickness of the mold cap, temporary 250mm, size of 500X500, the largest in the product mold area can be 400X400. The die structure is generally divided into the upper die, the lower die, the bottom plate, the top plate, the mandril, the die core, the hinge and other auxiliary parts.
B, release: silicone products can be directly stripping off strong. For the design defect of the products off strong size requirements mainly lies in the core position of maximum and minimum perimeter edge stripping ratio for 55 degrees below the product can be 2-3 times, be forced demolding part can not exist and the opening angle. Because of curing at the temperature of 180 degrees Celsius, demoulding work except the mold itself up and down, almost all manual.
So the parts should be considered during the design and convenient and fast. Because the release time is too long and affect the curing quality and production efficiency of parts. Because the silica gel demoulding method is mainly manual, its roof movement stroke is also very small, so the silica gel mold and plastic mold has no inclined roof. Generally, no core pulling is adopted.
Fixing of C and die core:
Different from the plastic mold, the mold core of the silica gel mold is usually taken out with the product parts when the mold is opened and the parts are taken out. So in the fixed and accurate positioning is the core of plastic mold is difficult to handle, high degree of steel core. The general will die together, once all the fixed core. Or will die by the auxiliary tool, which can quickly locate. Because there are a lot of pressure in the mold process, so to prevent mobile core.
D, core: general can not automatically running, but strong core pulling off, only for small size structure. Set and plastic mold about core pulling is similar, but in the mold is manually removed. In addition, the core pulling to occupy a larger space in the mold, the mold not only in the first mock exam more complex processing, and use of the mold space rate is low. So don't pull the core as much as possible.
E, shape: silica gel products in the integrity of the surface when the toughness is great, but there are cracks, cracks under the action of external force will rapidly expand.
That is to say, silicone products are very sensitive to the crack. In consideration of these problems, attention should be paid to the design of silica gel parts: all positions should not have sharp corners, so as to avoid stress concentration cracks. The R angle at the opening shall not be less than 0.5.
F, remove the edge: since the main function: remove the edge.