Silicone Injection

Using transfer molding process to produce silicone medical device components, not only convenient and cost-effective.Transfer molding (transfer molding, also known as transfer molding) is widely used in molding silicone cladding products (ie, the second injection), in particular, handle medical devices and surgical instruments. The process produced durable parts, and because of short production cycle, mold and production process of replacing a small number of flexible and highly acclaimed. In addition, this process for a variety of customized mold structure, is also popular OEM manufacturers.Abstract...Articles section Using transfer molding production of medical equipment for the three major key raw material selection, mold and cavity design, and processing equipment performance. This article will discuss each of these three elements, so that OEM manufacturers can better understand this process, find the right suppliers.
Transfer molding process
Pass to use when molding with a piston / cylinder systems of injection molding equipment, so you can flow through the holes or the silicone material into the mold cavity. This process can be transferred to the mold material, and heating in the case of pressure, to produce cured parts.
The process is divided into 4 steps, step by step operation to produce qualified molded cured product .The following summary describes these four steps:
• the cutting and weighing well over the silicone material into the injection molding equipment delivery slot. Silicone from the trough through a series of flow pressure into the mold cavity.
• material flow through into the cavity. Silicone in the mold cavity to a certain temperature and pressure to stay a certain period of time for curing. Curing process lasted 2-12 minutes, need 260 ° to 300 ° F temperature and pressure of 500 to 1000psi.
• recover the transfer plunger, remove the excess silicone from the mat.
• silicone completely cured, removed the pressure to open the mold. The product removed from the mold cavity, you can start the second process - trimming, removal of excess mold mold line flash.
Transfer molding process is particularly suitable for silicone parts of the injection and insert molding of the cladding. For the best silicone adhesive, it is necessary to ensure a clean injection equipment or apparatus, no excess material or contamination. Used during the insert injection, usually add a clean and insert pre-processing steps.
Injection experts know how to use without excessive surface treatment method, therefore, OEM manufacturers can choose a variety of handle kernel. This method does not need too much spray grit handling or modification, you can get a strong adhesion and can withstand repeated high-pressure steam sterilization cycle.
If you find that bond strength or layered effect is not satisfactory, you will need to adjust the surface treatment or transfer molding process. Silicone primer can greatly improve the adhesion, especially for plastics and other low surface energy materials. Corona or plasma treatment can be most effective oxidation of the surface, thus improving adhesion. Another method is to handle kernel was modified slightly, such as: adding vertical grooves, mechanical locking structure or concave cut.
Injection equipment is another factor affecting the injection molding process. Injection should be used 50 tons delivered automatically transfer molding machine, is particularly suited for customized silicone handle and instrument production. Injection molding machine 50 tons of clamping force in the mold curing process to ensure effective sealing, molded parts specifications to ensure consistency.
Expansion of silicone in the mold, the cavity pressure to 400 bar. The projected area of ​​the cavity and the cavity pressure multiplied, you can calculate the appropriate clamping force. Table I handle the processing parameters for the instrument example.
50 t injection molding machine using the benefits of its size in the general equipment for the processing handle. The size of the machine with the handle while the number of the processing. In addition, 50 tons of injection molding machines are smaller and shorter heating time and stability, and small footprint, suitable for lean production.
Machine settings can be standardized, so the injection molding machine can handle 18 × 18-inch mold. These molds can shuttle between different injection molding machine moves to minimize setup time.
Transfer molding advantages
Equipment manufacturers usually without affecting the quality of research and development under the premise of minimizing development costs. Silicone transfer molding technology for large-scale production of an easy transition method, which enables OEM manufacturers to achieve these goals.
Transfer molding for the biggest advantage of both short-term production, is also suitable for mass production. Compared with other silicone injection technology, the technology cycle is short, fewer replacement mold, injection molding workers because a machine can be used simultaneously on more than one cavity. Die easy to replace, just simple cleaning when switching colors.
Processing time depends on the type of injection. Not the same injection molding process, mold cleaning and replacement of the length of downtime required is not the same. In some cases, may take up to 6 hours. The transfer molding, different colors of silicone replacement within 30 minutes to complete. Die replacement in one and a half hours. Flexible production and short switching time increase production and shorten the delivery time, even customized components, can also play this advantage.
Transfer molding technology is also suitable for processing details and design elements of complex structural components. With this injection technique can process a precise depression, unique texture, trademark or logo. OEM manufacturers often prefer such a complex structure, because of the unique design allows the product in the marketplace, increase brand awareness.
Transfer molding is also suitable for re-forming the package insert. Before the transfer of silicone, the stainless steel, aluminum or high-performance plastic inserts into the cavity, the injection molding process, the silicone will bond on the insert.
Although the transfer molding is a hand-held tools and equipment ideal for processing, but this technology also has drawbacks. By passing the injection, surgical instruments can be easily short-term and high-volume production, but this method is not suitable for mass production of more than 10,000-20,000 pieces. Individual mold cavities and molding machine cycles per day are limited.
In addition, the use of thick silicone injection for delivery of raw materials, the need to separate the silicone rubber, curing catalysts and colorants for pre-mixing or grinding. These ingredients mixed by two-roll rolling mill. Advance materials, mixed materials, hybrid disadvantage is that the shelf life of only about 3 months. Cryopreservation may be extended shelf life, but generally only in small quantities mixed in order to maintain the material fresh.
Transfer can also use liquid silicone injection molding, or even to cast silicone system. This is quite useful for product design, as engineers can choose a wider variety of materials. Some materials can be hand-mixed, degassed, and then pass directly into the tank. Processing systems need to be adjusted when the pressure and temperature, to prevent the occurrence of early curing on the assembly line.
Curing
Silicone resin curing process is very important and delicate steps. Curing refers to heat, pressure and catalyst to change the nature of silicone chemistry. Curing silicone materials can be converted into stable forms that can be used. Heat, pressure, time, thickness of the part and mold design and other parameters can affect the cure.
Silicon resin transfer molding process, commonly used peroxide or platinum curing catalyst, two methods of follow-up steps are similar.
Will be mixed with peroxide or platinum catalyst in the silicone gum. In the injection molding process, the catalyst is heat and pressure activated, causing the cross-linked silicone polymer and curing products.
Compared with platinum cured, peroxide cured more cost-effective. However, the peroxide will lead to the emergence of silicone-products. This residue can cause the surface of silicone from the cream and bleaching. The use of peroxide curing, in order to avoid the adverse effects of residues must be carried out after curing process.
Platinum curing catalyst is a real cure. After the catalyst heated to a temperature activated, and cause silicone curing. The process is very expensive, but there are advantages. Platinum-catalyzed curing faster, shorten the cycle time injection molding process. Curing process, the silicone resin to be heated to 265 ° -300 ° F. Cured without treatment.
The advantages of silicone
Silicone is a material commonly used in medical devices, because the material complies with FDA for medical products and equipment regulations. The material does not support bacterial growth, and compatible with human tissue and body fluids.
Use of silicone medical devices containing silicone polymers to enhance the fillers, coloring agents and catalysts. Silicone is the most stable on the market of a material with a long service life.
Silicone is resistant to acids, alkalis, chemicals, oil and water erosion, and can withstand repeated high-pressure and high temperature steam sterilization. It will not cause staining of other materials, nor corrosion of other materials. The material can withstand extreme environments and long-term large temperature range, -75 ° to 500 ° F can be used between. Silicone has good thermal stability and high melting point and boiling point, it is often not competent for the application of other materials.
Because silicone is very soft, comfortable grip users, so commonly used in the manufacture of handheld medical devices. Silicone can also customize the colors, hardness and texture, so manufacturers can design a unique look and ergonomic surgical instruments package. However, silicone has its limitations.
Long-term use, the silicone will absorb the dust in the surrounding environment. Therefore, the medical silicone products must regularly clean and keep clean. As the silicone easy to attract dust, grinding process must be carried out in the clean room to minimize contamination of materials. And because the pre-grinding of the silicone material shorter shelf life, must be carefully stored in a clean, cool environment, to ensure optimal performance.
Conclusion
Transfer molding with a flexible production, short molding cycle times and less mold change, and each have a number of insert molding mold structure, therefore, can be cost-effective production of silicone handheld medical devices. In considering the use of silicone resin transfer molding process to manufacture medical devices and equipment when parts, OEM manufacturers should choose a transfer molding technique and can custom design special products supplier. If the device or equipment contains complex design elements, or need in stainless steel, aluminum or plastic wrap on the insert molding, then transfer molding is a good choice.

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            Peter  Huang