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Silicone Technology

As the vulcanization of rubber products require heat treatment. Liquid technology is more advanced. So it’s widely used in electronic appliances, household chemical products, and textiles, mold manufacturing and other industries.

As silicone waterproof and dustproof, it can improve the power transmission and distribution system in the harsh environment of the anti flashover performance. It is generally used for hollow tube, high voltage insulation coating, and the lightning arrester and other products.

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Silicones That Work

Our vision is to put silicone technology to work for our customers. We manufacture, package, and supply a variety of silicone products including: PTFE/Silicone Septa, silicone sealing mats, custom silicone compounds, conductive silicone elastomers, and thin silicone membranes. Our customers typically find us because they need a much shorter lead time, cannot get the product delivered to meet their packaging requirements, or have been unable to develop a custom silicone that works for their application.

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History

The first silicone elastomers were developed in the search for better insulating materials for electric motors and generators. Resin-impregnated glass fibers were the state-of-the art materials at the time. The glass was very heat resistant, but the phenolic resins would not withstand the higher temperatures that were being encountered in new smaller electric motors. Chemists at Corning Glass and General Electric were investigating heat resistant materials for use as resinous binders when they synthesized the first silicone polymers, demonstrated that they worked well and found a route to produce polydimethylsiloxane commercially.

Properties

Silicone rubber offers good resistance to extreme temperatures, being able to operate normally from -55°C to +300°C. At the extreme temperatures, the tensile strength, elongation, tear strength and compression set can be far superior to conventional rubbers although still low relative to other materials. Organic rubber has a carbon to carbon backbone which can leave them susceptible to ozone, UV, heat and other ageing factors that silicone rubber can withstand well. This makes it one of the elastomers of choice in many extreme environments.

Compared to organic rubbers, however, silicone rubber has a very low tensile strength For this reason; care is needed in designing products to withstand even low imposed loads. Silicone rubber is a highly inert material and does not react with most chemicals. Due to its inertness, it is used in many medical applications and in medical implants Structure.

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Silicone rubber chain

Polysiloxanes differ from other polymers in that their backbones consist of Si-O Si units unlike many other polymers that contain carbon backbones. One interesting characteristic is an extremely low glass transition temperature of about -127? C ( Fitzpatrick 1999:428). Polysiloxane is very flexible due to large bond angles and bond lengths when compared to those found in more basic polymers such as polyethylene. For example, a C-C backbone unit has a bond length of 1.54? And a bond angle of 112? And a bond angle of 130?

Repeat unit of silicone rubber

The siloxane backbone differs greatly from the basic polyethylene backbone, yielding a much more flexible polymer. Because the bond lengths are longer, they can move further and change conformation easily, making for a flexible material. Another advantage of polysiloxanes is in their stability. Silicon is in the same group (IV) on the periodic table as carbon, but the properties of these elements are quite different. Silicon has the same oxidation state as carbon, but has the ability to use 3d orbitals for bonding by expanding its valence shell. Si-Si bonds have far less energy than C-C bonds and so are more stable, though in practice Si-Si-bonds are very hard to create.

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Mechanical properties  

Hardness, shore A: 10–90

Tensile strength: 11 N/mm2

Elongation at break: 100–1100%

Maximum temperature: +300°C

Minimum temperature: -120°C

Special grades

There are also many special grades and forms of silicone rubber, including: steam resistant, metal detectable, electrically conductive, chemical/oil/acid/gas resistant, low smoke emitting, and flame-retardant. A variety of fillers can be used in silicone rubber, although most are non-reinforcing and lower the tensile strength.

Liquid Silicone

Liquid silicone rubber is a high purity platinum-cure silicone.

Medical device manufacturers favour liquid silicone because of its biocompatibility and excellent part quality. Medical grade silicone combined with a lack of human contact reduces risk of contamination, especially when manufactured in a clean room environment. However, failures of medical implants have occurred due to poor manufacture or poor design.

It is typically supplied in two parts with one of the parts containing the platinum catalyst. These are then automatically mixed with any colors and ingredients which may be required. The mixing produces a very homogeneous material that leads to products that are not only very consistent throughout the part, but also from part to part.

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Applications

Once milled and colored, silicone rubber can be extruded into tubes, strips, solid cord or custom profiles according the size restrictions of the manufacturer. Cord can be joined to make O-rings and extruded profiles can be joined to make seals. Silicone rubber can be molded into custom shapes and designs.
Becoming more and more common at the consumer level, silicone rubber products can be found in every room of a typical home. From automotive applications; to a large variety of cooking, baking, and food storage products; to apparel, undergarments, sportswear, and footwear; to electronics; to home repair and hardware, and a host of unseen applications.
Non-dyed silicone rubber tape with an iron-oxide additive (making the tape a red-orange color) is used extensively in aviation and aerospace wiring applications as a splice or wrapping tape due to its non-flammable nature. The iron-oxide additive adds high thermal conductivity but does not change the high electrical insulation property of the silicone rubber. This type of tape self-fuses or amalgamates without any added adhesive.

Injection molding of liquid silicone rubber (LSR) is a process to produce pliable, durable parts in high volume.
Liquid silicone rubber is a high purity platinum cured silicone with low compression set, great stability and ability to resist extreme temperatures of heat and cold ideally suitable for production of parts, where high quality is a must. Due to the thermosetting nature of the material, liquid silicone injection molding requires special treatment, such as intensive distributive mixing, while maintaining the material at a low temperature before it is pushed into the heated cavity and vulcanized.
Chemically, silicone rubber is a family of thermoses elastomers that have a backbone of alternating silicone and oxygen atoms and methyl or vinyl side groups. Silicone rubbers constitute about 30% of the silicone family, making them the largest group of that family. Silicone rubbers maintain their mechanical properties over a wide range of temperatures and the presence of methyl-groups in silicone rubbers makes these materials extremely hydrophobic.
Typical applications for liquid silicone rubber are products that require high precision such as seals, sealing membranes, electric connectors, multi-pin connectors; infant products where smooth surfaces are desired, such as bottle nipples, medical applications as well as kitchen goods such as baking pans, spatulas, etc. Often, silicone rubber is overmolded onto other parts made of different plastics. For example, a silicone button face might be overmolded onto a Nylon 6, 6 housing.

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Equipment

In order for the liquid injection molding process to fully occur, several mechanical components must be in place. Typically, a molding machine requires a metered pumping device in conjunction with an injection unit—a dynamic or static mixer is attached. An integrated system can aid in precision and process efficiency. The critical components of a liquid injection molding machine include: [1]

Injectors. An injecting device is responsible for pressurizing the liquid silicone to aid in the injection of the material into the pumping section of the machine. Pressure and injection rate can be adjusted at the operator’s discretion.

Metering Units. Metering units pump the two primary liquid materials, the catalyst and the base forming silicone, ensuring that the two materials maintain a constant ratio while being simultaneously released.

Supply Drums. Supply drums, also called plungers, serve as the primary containers for mixing materials. Both the supply drums and a container of pigment connect to the main pumping system.

Mixers. A static or dynamic mixer combines materials after they exit the metering units. Once combined, pressure is used to drive the mixture into a designated mold.

Nozzle. To facilitate the deposition of the mixture into the mold, a nozzle is used. Often, the nozzle features an automatic shut-off valve to help prevent leaking and overfilling the mold.

Mold Clamp. A mold clamp secures the mold during the injection molding process, and opens the mold upon completion.

Injection molding process

Liquid silicone rubbers are supplied in barrels or hob bocks. Because of their low viscosity, these rubbers can be pumped through pipelines and tubes to the vulcanization equipment. The two components are pumped through a static mixer by a metering pump. One of the components contains the catalyst, typically platinum based. A coloring paste as well as other additives can also be added before the material enters the static mixer section. In the static mixer the components are well mixed and are transferred to the cooled metering section of the injection molding machine. The static mixer renders a very homogeneous material that result in products that are not only very consistent throughout the part, but also from part to part. This is in contrast to solid silicone rubber materials that are purchased pre-mixed and partially vulcanized. In contrast, hard silicone rubbers are processed by transfer molding and result in less material consistency and control, leading to higher part variability. Additionally, solid silicone rubber materials are processed at higher temperatures and require longer vulcanization times.

From the metering section of the injection molding machine, the compound is pushed through cooled sprue and runner systems into a heated cavity where the vulcanization takes place. The cooling allows production of LSR parts with nearly zero material waste, eliminating trimming operations and yielding significant savings in material cost.

Our factory also supply all kinds of silicone rubber tube.If you have any needs,Please contact us!

Shenzhen LYA silicone rubber products CO.,Ltd.

+86-755-28107078

Email:sale16@lyasilicone.com

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