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Silicone products production process

Source:未知 Sentiment:Published time:2017-09-11

First, the characteristics of silicone material
 
A. Silicone raw materials are generally gel-like, somewhat similar to the rubber mud, colorless translucent, tasteless.
 
B. Its main feature is high temperature (up to 300 ℃) and low temperature (minimum -100 ℃), is the best cold, high temperature rubber; at the same time excellent electrical insulation, thermal oxidation and ozone stability is high , Chemical inertia. The disadvantage is the mechanical strength is low, oil, solvent and acid and alkali resistance, more difficult to vulcanization, the price is more expensive. Use temperature: -60 ℃ ~ +200 ℃. The above is a description of the silicone rubber in the manual.
 
C. Use temperature: As mentioned above, the general set to -40 ℃ - 200 ℃, in the short term time up to 230 ℃.
 
D. Aging problem:
 
Oil resistance, acid and alkali resistance is poor, and the relationship between the force is not.
 
E. Adhesive problems: in the absence of surface treatment, in addition to the use of silicone products for adhesives and silicone parts, and other parts must be adhered through the surface activation, glue curing can be bonded. Anything that can be vulcanized or rubbed with rubber is collectively referred to as a vulcanizing agent, also known as a crosslinking agent. There are many types of vulcanizing agents, and they are still increasing. The vulcanizing agents which have been used are sulfur, selenium, tellurium, sulfur compounds, metal oxides, peroxides, resins, quinones and amines.
 
F. Material hardness: plastic parts according to Shore hardness in the domestic market can be theoretically between 10 degrees to 80 degrees to choose. Can easily find the general in 20 degrees to 70 degrees, the most commonly used is 40 to 50 degrees.
 
Second, the production of silicone products
 
A raw material shape and color
 
B after color mixing by the milky white silica gel variegated in a variety of colors of the film C after mixing, the raw materials into a strip, cut into a piece of material.
 
D vulcanization molding
 
E dressing, dismantling, inspection, packaging.
 
F. Finished product drawings
 
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. General thickness recommended size is not greater than 3MM, when greater than 3MM, will spend more time and increase the cost of curing. The thinnest on the theory up to 0.2MM, but the design of the general to take the thinnest 0.3MM, recommended 0.4MM.
 
B, the relative size: the thickness of the difference, the thinnest and the thickest recommendations do not exceed 3 times. Such problems mainly depend on the requirements for temperature and pressure when the material is vulcanized.
 
C, shrinkage rate. Silicone material shrinkage ratio and the hardness of the material, manufacturers provide more than the material between 1.022 ~ 1.042 between 40 to 50 degrees for the material, generally take 1.03 shrinkage. Relative to the plastic, silicone products will not shrink due to similar to the obvious surface defects.
 
D, dimensional accuracy: silicone products for the more than a multi-point, relative to the plastic products, the number of their points is very much. 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 positive and negative 0.05. When used with the plastic parts with the hole between the key, the gap to take a minimum of 0.1, the recommended value of unilateral 0.2.
 
E, shape design: for the plastic sleeve parts, generally according to the product outline to the factory to provide the original map can be, with the description of the problem, by the mold factory to decide. Under normal circumstances, depending on the product size, plastic sleeve and the product with the general unilateral small 0.2 to 0.5 negative deviation.
 
Fourth, the mold structure
 
A. Mold thickness limit, tentative 250mm, size up to 500X500, the product can be done in the mold area up to 400X400. The mold structure is generally divided into mold, lower mold, bottom plate, roof, mandrel, core, hinge and other auxiliary parts. In the silicone product design should pay attention to its mold and production process features:
 
B. stripping: silicone products can be directly off the stripping. For the design of defective products, the size of the requirements of the main force is mainly the largest core and mold release when the minimum nozzle at the circumference ratio, for 55 ° below the product can be 2-3 times, forced to stripping the site is not There can be cracks and openings at the sharp corners. Due to the requirements of vulcanization at 180 degrees Celsius temperature, the work of the mold in addition to the mold itself separated from the upper and lower, almost all manual. So the design of the parts should be considered off the convenient and fast. So as to avoid the demoulding time is too long and affect the quality of parts vulcanization and production efficiency. Silicone release mode is mainly for the manual, the roof of the action stroke is also very small, so the silicone mold and plastic mold compared to no sloping roof. Generally do not set the core.
 
C. Fix the core:
 
Unlike plastic molds, the molds of the silicone molds are generally removed from the product parts when the mold is removed. So the fixed and accurate positioning of the core than the plastic mold is difficult to deal with the higher requirements of the core of the steel. Generally the core to do together, once fixed all the core. Or the core through the auxiliary equipment, so that it can quickly locate. Due to the mold in the process there is a lot of pressure, so to prevent the core movement.
 
D. Core: generally can not automatically walk bit, but can be strong off, core is only used for small size structure. The setting of the core is similar to that of the plastic mold, but is manually removed when the mold is opened. In addition, the core to occupy the mold within the larger space, which in a mold more than the silicone mold is not only complex processing, and the mold space utilization is low. So as far as possible without pulling core.
 
E. shape: silicone products in the surface when the toughness of a great, but there is a crack, under the action of external cracks will be rapid expansion. In other words, silicone products are very sensitive to cracks. Taking into account these issues, in the design of silicone parts should be noted: all positions can not have sharp corners, so as not to focus on stress cracks. Opening angle R can not be less than 0.5F. Self-dismantling: self-dismantling the main role: to accommodate the excess rubber; easy mold exhaust; easy to trim the flash. Since the split edge is generally at the part of the parting surface in a circle of thin edge and the corresponding more solid tear. Thin edge part of the general thickness of 0.1 to 0.2, tearing part of the thickness of the general take 0.8, the width of the general take 1 ~ 2MM.
 
G. insert: silicone products can be placed within the various types of inserts, but should pay attention to several issues: First, the embedded parts should be pre-pretreated surface, mainly surface curing or surface activation. Otherwise the insert and the plastic pieces will be difficult to securely connect. Second, the fixed positioning of the embedded problem, in the vertical direction can be fixed in one direction, but the other direction must be fully fixed. In order to avoid moving in the whole process of the insert. Third, the surrounding rubber thickness of the insert. For the full package (all the surface are plastic, so can not position the case of the fixture) parts, insert the surrounding at least 0.5MM thickness. For the positioning of the embedded, the thickness of the surrounding adhesive layer should be more than 0.4MM.
 
H. Other auxiliary processes:
 
Glue (plastic) process:
 
Similar to the injection, the first part of the glue will be fixed, close the first layer of mold to control the injection of raw materials will not pollute the site is not designed injection. And then the second layer of mold, the rubber material molding.
 
Rolling process: the first manual compound preform
 
Into the mold. This process can be used for full encapsulation.
 
Dipped: rubber (rubber) body material for the fluid, the workpiece several times immersed in raw materials. In the inner layer of raw materials after curing again, until the design thickness.
 
Dijiao: raw materials have good mobility, similar to paint, room temperature vulcanization. Mold is relatively simple, the general manual operation, in the first layer of fast curing when painted once
 
L. Multicolor products: A sub-vulcanization 2 sets of mold, B hand color, a vulcanization, part of the separation of parts require a certain height, so as not to mix color conductive adhesive, secondary vulcanized silica gel and silicone (rubber) can not do direct vulcanization Adhesion five, hardness measurement and tools
 
Measuring the hardness of rubber The most commonly used instrument called Shaw (also known as Shore) hardness. Use a spring to press a metal indenter into the surface of the material and measure how deep it can penetrate. The instrument measures a penetration depth of zero to 0.100 inches. A zero reading on the ruler means that the indenter penetrates the limit depth and a reading of 100 means that the penetration depth is zero. There are a variety of different hardness range and degree of automation Shore hardness tester.
 
One of the most common scales is the Shore A scale. Shore A grade hardness meter has a blunt indenter and a spring spring. When the reading is above 90, the Shore A grade hardness meter becomes not very accurate. For such harder materials, a Shore D hardness tester is used. It has a sharp indenter and a very strong spring spring that can penetrate deeper into the depth.
 
When measuring harder plastic, use a pressure gauge that is sharper and more flexible, such as a Rockwell Hardness Tester. At the other extreme, the Shore 00 hardness tester is used to measure the soft gel and foam rubber.
 
Most of the material can withstand the initial pressure, but over time, due to creep and relaxation will yield. The hardness meter readings can be read instantly, or after a certain delay time, usually after 5 to 10 seconds. Instant readings always show higher (or harder) readings than delayed readings. Delayed readings are not only representative of the hardness of the material but also for its elasticity. A weaker, less resilient material is more prone to creep than those that are stronger and more resilient.
 
In order to ensure the validity of the data, accurate testing steps are required. In order to obtain accurate readings, you must have a very smooth surface and thick enough to prevent the indentation of the support surface. The required thickness is usually 0.200 inches, but for smaller deformed hard materials, when the thickness is thin, can also be accurately tested.