The structure of thermosetting liquid silica gel (LSR) injection mold, liquid silica gel manufacturers are generally similar to the mold structure of thermoplastic rubber material, but there are many significant differences. For example, LSR adhesives tend to have a low viscosity and thus have a very short filling time, even at very low injection pressures. In order to avoid air retention, setting up an outstanding exhaust device in the mold is crucial to what silicone is.

In addition, LSR adhesives do not shorten in the mold as thermoplastic adhesives do; they tend to expand in response to heat and shorten slightly in response to cold. Thus, the product does not always remain on the convex surface of the die as expected, but in a cavity with a large surface area.

1 shortening rate

Although The LSRS do not shorten in the mold, they often shorten by 2.5 to 3 percent after stripping and cooling. How much is shortened depends in part on the formulation of the compound. However, from the mold's point of view, the shortening rate may be affected by several factors, including the temperature of the mold, the temperature at which the glue is released, and the pressure in the mold cavity and subsequent shrinkage of the glue.

The orientation of the injection point is also worth considering, because the shortening rate of the flow direction of the glue is generally larger than that of the straight flow direction of the glue. The size of the product also has an effect on its shortening rate, the shortening rate of thicker products is generally smaller than thin ones. If secondary vulcanization is required, an additional 0.5-0.7% reduction may be possible.

2 the parting line

Determining the orientation of parting line is one of the first several processes in the planning of silicone rubber injection molding. Exhaust is mainly through the groove located on the parting line to achieve, such groove must be in the final area after the injection of rubber material. This helps to avoid internal bubbles and reduce the loss of strength at the adhesive joints.

Due to the low viscosity of LSR, it is necessary to be accurate in parting line to avoid forming glue overflow. Even so, parting lines are often seen on molded pieces. Demoulding is affected by the size of the product and the direction of the parting surface. Planning the product to be slightly chamfered helps to ensure that the product has a common affinity for the desired other half of the cavity.

3 the vent

With the injection of the LSR, the air remaining in the cavity is compressed when the die is closed and then discharged through the ventilation groove as the die is filled. If the air can not be discharged completely, it will stay in the rubber material (which often constitutes part of the product exposed white edge). Ventilation grooves are generally lmm-3mm wide and 0.004mm-0.005mm deep.

Vacuum in the die to create a very good exhaust action. This is achieved by planning a gasket on the parting line and rapidly vacuuming all the cavities with a vacuum pump. Once the vacuum reaches an additional degree, the mold is completely closed and the injection begins.

Some injection molding equipment allows operation with variable closing force, which enables the processor to close the mold at low pressure until 90-95% of the cavity is filled with the LSR (making it easier to expel air) and then switch to a higher closing force to avoid silicone rubber swelling and overflow.

4 injection point

Cold runner system is used for molding LSR. The advantages of this kind of glue can be brought into full play to a great extent, and the production efficiency can be improved to a great extent. In this way to process products, it is not necessary to remove the glue injection, thus avoiding increasing the labor intensity of the operation, and sometimes can avoid a lot of waste of data. In many cases, the glue-free structure also reduces operating time.

The injection nozzle is controlled by a needle valve for forward flow. Now many manufacturers can provide the injection nozzle with a pneumatic switch as standard equipment, and can set it in various parts of the mold. Some die makers have developed an open cold runner system that is so small that multiple injection points (thus filling the cavity) can be placed in a very limited mold space. This skill makes it possible to produce a large number of good silicone rubber products without the need to separate the rubber injection port.

If a cold runner system is chosen, it is important to create a useful temperature interval between the hot mold cavity and the cold runner. If the runner is too hot, the glue may begin to vulcanize before the injection. However, if it is cooled too quickly, it will absorb too much heat from the gate area of the mold and cannot be completely cured.

For the products with conventional injection sprue (such as diving sprue and conical sprue), it is appropriate to choose small diameter injection mouth feeding (feeding mouth diameter is generally 0.2mm-0.5mm) to pour. With low viscosity LSR adhesives, as with thermoplastic adhesives, it is important to balance the flow channel system so that all cavities are evenly filled with the adhesives. The application of simulation software for planning flow channel system can greatly simplify the mold development process, and its usefulness has been proved by mold filling test.

5 release

The vulcanized liquid silicone rubber simply sticks to the metal surface, and the flexibility of the product makes it difficult to demoulder. The high temperature tear strength of the LSR allows the mold to be released under normal conditions, even large parts will not be damaged. Very common demoulding skills include demoulding of templates, demoulding of pins, and demoulding of forces. Other common skills are roller scraping, plate stripping, and automatic stamping.

When using the demoulding system, it is necessary to keep it in a high precision range. If the gap between the top selling and the guide pin sleeve is too large, perhaps the parts because of long-term wear and tear and the gap becomes larger, it may constitute glue overflow. Inverted cone or mushroom top selling effect is very good because it allows the selection of larger contact pressure, easy to improve the tightness of the content.

6 Mold Information

Mould trays are usually made of non-alloy tool steel (No.1.1730,DIN Code C45W). For mould trays which need to be subjected to high temperatures of 170℃-210℃, pre-tempered steel (No.1.2312,DINcode 40 CRMN-M oS 8 6) should be used in consideration of impact resistance. The supporting plate of the mold cavity should be made of b steel after nitriding or tempering heat treatment to ensure its high temperature resistance.

For high fill LSRS, such as oil resistant LSRS, it is recommended to use a higher hardness material for the mold, such as bright chrome steel or powder metal specially developed for this purpose (No.1.2379,DINcode X 155 CrVMo121). When planning high wear data molds, those parts that receive high friction should be planned as replaceable components so that the entire mold does not have to be replaced.

The surface of the cavity has a great influence on the finish of the products. It is remarkable that the mold will match the cavity surface exactly. Moulds for transparent products should be made of polished steel. Surface treated Chin/nickel steel has very high wear resistance, while PTFE/nickel makes demoulding easier.

7 Temperature control

Generally speaking, it is advisable to choose electric heating method for LSR molding, which is generally belt electric heater, cylindrical heater or heating plate heating. It is critical to evenly distribute the temperature field throughout the die to promote uniform solidification of the LSR. On large molds, it is an economical and useful heating method when pushing oil temperature control heating.

Covering the die with an insulating plate helps to reduce heat loss. Any improper part of the hot mold may cause it to suffer from large temperature fluctuations between operating procedures, or constitute gas leakage. If the surface temperature is too low, the curing speed of the glue will slow down, which often makes the products can not be demoulded, causing quality problems. A certain distance should be kept between the heater and the parting line to avoid bending and deformation of the template and forming overspill burr edge on the product.

If you plan a mold for the cold runner system, it is necessary to separate the hot end from the cold end. Can choose special Chin alloy (such as 3.7165[TiA16V4]) production, this is because compared with other steel, its thermal conductivity is much lower. For an overall die heating system, the heat shield shall be placed between the die and the die support plate to minimize heat loss.

Proper planning and design ensure that LSR injection molding is very important in this mold. The above mold planning criteria are aimed at filling the mold cavity with rubber material, shortening curing time, high quality products and high output, so as to enable silicone rubber processors to obtain outstanding economic benefits.

The convenient deployment and wearing beauty of silicone invisible bra let the majority of women get rid of the root bra marks and shoulder strap slip embarrassment, but faced with different materials of silicone invisible bra, many women do not know, blindly follow the trend, choose to wear silicone bra, constitute irreparable body damage! Here's the secret to the silicone bra.

What is a silicone bra?

Silicone bra underwear literally means bra built-in sandwich made of silicone breast pads.

What are the dangers of silicone bras?

1, side effects

China's invisible bra market is not mature, resulting in price disorder, and some small manufacturers to make huge profits, the use of defective silicone products, shovel-quality. The residual silica gel has great side effects on the body and skin.

2. Raw materials

Silicone bra raw materials throughout the airtight, continuous use of more than 6 hours, may cause skin discomfort, allergy, itching, redness; And its viscose type planning, simple let a person produce discomfort.

Silicone bra breathable skin is too sensitive to simple allergies. To remind you, the invisible bra with silicone gel has side effects. Silicone gel will decompose and enter the body from the nipple, so it is not easy to wear for a long time. As for breast enlargement, it's not possible. The invisible bra is designed to visually magnify breasts by drawing them together, so it won't work.

3. Reaction

Traditional bra uses shoulder straps to hold the chest, while silicone bra does not use shoulder straps, so it cannot really improve the chest position, but can only adjust the height of the two pieces to change the chest shape visually. However, such adjustment will squeeze and damage the original chest shape, making the chest in an unnatural state for a long time. The result may be to sow seeds.

4, not exercise

Silicone bra is designed with two cup buckles as the common selling point, and there is no other fixed method. Therefore, it can not fix the chest, and the product itself has a certain weight, in the process of intense exercise, intangible aggravates the burden of the chest muscles, chest ups and downs in the process of exercise and left and right shaking ups and downs than wearing traditional bra ups and downs, so it is not suitable for use in sports.

5. Low repetition

Silica gel bra adopts front buckle buckle, buckle is posted on the inside of the silica gel cup, when the force is uneven or pulled, simple damage, so as to reduce the reuse of the bra.

6, more requirements for the environment

Although the silicone bra can be reused 100 times, the viscosity is greatly affected by the outside world, such as towels, paper towels, dust and fine hair suspended in the air, which may shorten the service life of the invisible bra; Not only to the cleaning of the drying environment requirements are high, and is not easy to store.

7. No risk is guaranteed

After 6 hours of continuous use of silicone bra, the cup will lose viscosity due to a lot of sweating, and simple slide constitutes embarrassment.

8, chest load is large

Too heavy. The weight of silicone invisible bra is generally about 100g, and some can weigh more than 400g. Many mm bras with silicone raw materials feel large pressure on the chest.

Love beautiful you must not be on the silicone bra when, pay an unnecessary price! Choose your underwear correctly and wear it correctly.