I. Characteristics of silica gel raw materials:

A. Silicone rubber material is generally gelatinous, somewhat similar to silly putty, colorless, translucent, tasteless. B. Its main characteristics are both high temperature resistance (300℃) and low temperature resistance (-100℃), is currently very good cold resistance, high temperature resistance rubber; Together with outstanding electrical insulation, thermal oxidation and ozone stability is very high, chemical inertia. Defects are low mechanical strength, oil resistance, solvent resistance and acid and alkali resistance, difficult to vulcanize, the price is more expensive. Operating temperature: -60℃ ~ +200℃.

C. Operating temperature: as mentioned above, generally set to -60℃ - +200℃, up to 230℃ in a short time.

D. aging problem: oil resistance, acid and alkali resistance is poor, and the force condition is not related.

E. Bonding problem: in the absence of surface treatment, in addition to using silica gel products as adhesive and silica gel parts bonding, and other parts bonding is necessary after surface activation, vulcanization treatment can stick. In any vulcanization reaction with rubber or make the crosslinking of the material collectively known as curing agent, also known as crosslinking agent. There are many kinds of vulcanizing agents, and they are still being added. The vulcanizing agents are sulfur, selenium, tellurium, sulfur-containing compounds, metal oxides, peroxides, tree esters, quinones and amines.

F. Data hardness: according to shore hardness, rubber parts can be theoretically selected between 10 degrees and 80 degrees in the domestic market. Easy to find generally in the 20 to 70 degrees, usually 40 to 50 degrees.

Some explanations on the production process of silicone rubber materials and products

Two, liquid silica gel products production process:

The production process of liquid silica gel products of liquid silica gel manufacturers:

A Material shape and color

B After color mixing, the milky silica gel is transformed into a variety of color sheet materials

C after mixing and shaping, the material is pressed into strips and cut into strips.

D curing molding

E Trimming, edge removal, inspection, packaging.

F. products figure

Iii. Product size and characteristics:

A, very large scale: very thick can be 15~20MM, if it is A sphere, can be 30MM in diameter. General thickness recommended size is not greater than 3MM, when greater than 3MM, will cost more curing time and add costs. Very thin theoretically up to 0.2mm, but the planning is generally very thin 0.3mm, recommended 0.4mm.

B. Relative scale: in terms of thickness difference, it should not exceed 3 times for very thin and very thick parts. Such problems primarily depend on the temperature and pressure requirements of vulcanization.

C. Shrinkage rate. The shrinkage rate of silica gel raw materials is related to the hardness of raw materials. The secondary materials provided by the manufacturer are mostly between 1.022 and 1.042. For information about 40 to 50 degrees, the shrinkage rate is generally 1.03. Related to plastic, silicone products do not shrink to produce similar apparent appearance defects.

D, scale accuracy: because silica gel products are mostly one mold and many holes, the number of holes related to plastic products is very large. Therefore, the scale control is not as convenient as plastic products. General accuracy is plus or minus 0.1, high precision products are plus or minus 0.05. When the cooperation is used for the cooperation between the holes and keys of plastic parts, the gap is very small and the recommended value is unilateral 0.1.

E. Shape planning: for rubber sleeve parts, it is generally necessary to provide the original drawing to the mold factory according to the shape drawing of the product, and the cooperation problem is clarified by the mold factory itself. In general, depending on the size of the product, the cooperation between the rubber sleeve and the product is generally a negative error of 0.2~0.5.

Iv. Mold structure:

A. The upper limit of mold thickness is temporarily set at 250mm, and the size can reach 500X500. The product can reach 400X400 in the large mold area. The mould

The structure is generally divided into upper die, lower die, bottom plate, roof, push rod, die core, hinge and other auxiliary parts. In the planning of silica gel products, we should pay attention to the characteristics of the mold and production process:

B. Demoulding: Demoulding of silica gel products can be directly strong. No planning defects of the product strong off the scale requirements of the first is the core is very large and demoulding is very small closure of the perimeter ratio, about 55° below the product can do 2-3 times, to force demoulding parts can not exist cracks and openings of the sharp Angle. Because vulcanization requirements in 180 degrees Celsius temperature, demoulding work in addition to the mold itself up and down apart, it is all manual. Therefore, the convenience and speed of taking off should be considered when planning parts. Avoid too long demoulding time and affect the vulcanization quality and production efficiency of parts. Because the demoulding method of silica gel is mainly manual, the action stroke of its roof is also very small, so the silica gel mold has no inclined top compared with the plastic mold. There is generally no core pulling.

C. Mold core fixation:

Different from plastic moulds, the mold core of silica gel moulds is generally removed together with the product parts when the mold is opened. Therefore, it is more difficult to fix and locate the mold core accurately than the plastic mold, and the steel degree of the mold core is higher. The mold core is generally done together to fix all the mold core at one time. Or the mold core through auxiliary appliances, so that it can be quickly positioned. Because there is a lot of pressure in the mold closing process, it is necessary to prevent the mold core from moving.

D. Core pulling: Generally can not automatically move, but can be forcibly off, core pulling is only used for small-scale 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 large space in the mold, which is not only messy processing in a mold more than the silica gel mold, and the utilization rate of mold space is low. So don't pull the core as much as possible.

E. Shape: Silica gel products have great toughness when their appearance is complete, but once there are cracks, cracks will expand rapidly under the action of external forces

Zhang. That is to say, silicone products are very sensitive to cracks. Considering these problems, in the planning of silica gel parts, attention should be paid to: all directions can not have sharp angles, to avoid stress concentration and crack. The R Angle at the opening cannot be less than 0.5

F. Self-edging: the primary function of self-edging is to contain the remaining rubber material; Easy to die exhaust; Easy to trim flaps. Self - disassembly is generally by

A circle of thin edges and corresponding stronger tearing edges at the parting surface of the part. The thickness of the thin side is generally 0.1~0.2, the thickness of the torn side is generally 0.8, and the width is generally 1~2MM.

G. Inserts: All kinds of inserts can be placed in silicone products, but attention should be paid to the following problems: First, the appearance of the embedded parts should be pre-processed.

The first is external vulcanization or external activation. Otherwise, it will be difficult to firmly connect the inserts and rubber parts. Second, the fixed positioning of the insert, in the vertical direction can be one-way fixed, but it is necessary to fix all the other directions. Avoid insert movement during full mode. Three is the thickness of the glue around the insert. For all the parts covered with glue (all the outer surface is covered with glue, so it is impossible to position the insert), the periphery of the insert should be at least 0.5mm thick. For fixed inserts, the thickness of peripheral rubber layer should be above 0.4mm.

H. Other auxiliary processes:

Glue injection (wrap) process:

Similar to injection molding, the parts of the injection shall be fixed first, and a layer of the mold shall be closed first to control the material during injection so as not to pollute the parts of the injection that are not planned. And then one layer of mold, the rubber material pressing molding.

I. Rubber rolling process: the rubber material is pre-formed into the mold. This process can be used in the case of full coating.

J. Dipping: The rubber (rubber) body material is fluid, and the workpiece is repeatedly immersed in the material. After curing the inner material, dip it again.

Until the planned thickness is reached.

K. Glue drop: the material has good fluidity, similar to paint, vulcanized at room temperature. The mold is relatively simple, the general technical operation, in the first layer of fast curing coating

L. multi-color products: A sub-vulcanization of 2 sets of mold,B technical color matching, A vulcanization, parts separation part must have A certain height,

Avoid mixed color conductive adhesive combination, secondary vulcanization of silica gel and silica gel (rubber) can not do direct vulcanization bonding

Five, hardness measurement and tools:

Measurement of rubber hardness is very commonly used instrument called Shaw (also known as Shore) hardness tester. Use a spring to press a metal indenter into the surface of the data and measure how deep it can penetrate. The instrument measures penetration depths from zero to 0.100 in. A reading of zero on the ruler means that the indenter has penetrated a very large limit of depth, while a reading of 100 means that the penetration depth is zero. There are various scales of hardness and degree of automation shore hardness tester.

One of the most commonly used scales is the Shaw class A scale. Shore A hardness tester has A blunt indenter and A medium spring spring. The Shore A hardness tester becomes less accurate at readings above 90. For such hard data, shore's D hardness tester is used. It has a sharp head and a strong spring spring, can penetrate deep depth.

When measuring harder plastics, a hardness tester with a sharper indenter and greater elasticity, such as rockwell hardness tester, is used. At the opposite end, a Shore 00 hardness tester is used to measure soft gels and foam rubber.

Most data can withstand the initial pressure, but succumb over time due to creep and relaxation. Durometer readings can be read immediately or after a specific delay, typically 5 to 10 seconds. Instant readings always show higher (or harder) readings than delayed readings. The delay reading is more representative not only of the hardness of the data but also of its elasticity. A weaker, less elastic material is more prone to creep than a stronger, more elastic material.

In order to ensure the validity of data, accurate testing procedures are required. In order to obtain accurate readings, it is necessary that you have a flat and thick specimen that does not allow the indenter to be affected by the supporting surface. A thickness of 0.200 in. Is generally required, but hard data with small deformations can be accurately tested when the thickness is thinner.