Liquid Injection Molding (Liquid Silicone Rubber Injection Molding) System utilizes high-quality liquid silicone materials and precise liquid injection molding machines to achieve a new molding method. This highly efficient and precise manufacturing technique is used in the production of various silicone-based products by injecting liquid silicone rubber into a mold cavity under high pressure, allowing it to cure and solidify into the desired shape.
The process starts with preparing the silicone material, i.e., LSR, or liquid silicone rubber, is a two-component liquid material consisting of A and B components.. The A
and B components are mixed in a precise 1:1 ratio using a mixer, and if the products require color, a color pump set and metering part are used.
After thorough mixing of A+B components, additives, and coloring agents, the mixture enters the plasticizing system. The plasticizing screw homogenizes and mixes the mixture before injecting it into the hot mold, where the curing reaction of the silicone occurs at a mold temperature of 120 to 180 Celsius degrees. The LSR is then injected into the mold cavity using a high-pressure injection unit, and the mold is held closed under pressure until the silicone cures, which can take seconds to minutes depending on the material and part geometry. The whole process is automatic, simplifying the work process, shortening the work time, and ensuring high-quality products.
When using a cold runner system, it's important to ensure that the runner is cold enough to avoid glue leakage. A needle valve is mounted on the surface of the mold part to immediately close the nozzle after injection is completed.
Liquid Injection Molding Machine
The structure of the liquid silicone rubber (LSR) injection mold is similar to molds used for thermoplastic compounds, but there are significant differences. LSR compounds have low viscosity, resulting in very short filling times even at low injection pressures. Good exhaust devices are important to avoid air stagnation in the mold due to the low viscosity. Unlike thermoplastic compounds, LSR compounds do not shrink in the mold, but tend to expand when heated and shrink slightly when cooled. The shrinkage rate is affected by factors such as mold temperature, demolding temperature, pressure in the mold cavity, and subsequent compression of the rubber. The location of the injection point is also important, as shrinkage in the flow direction of the compound is usually greater than in the perpendicular direction.
Shrinkage
LSR typically shrinks by 2.5%-3% after demolding and cooling, with the amount of shrinkage depending on the compound formula and the product's external dimensions. Thicker products generally have smaller shrinkage than thinner products, and secondary vulcanization may cause an additional 0.5%-0.7% shrinkage.
Parting Line
Determining the parting line position is crucial in designing a silicone rubber injection mold, with exhaust achieved through grooves on the parting surface. The grooves must be in the area where the injection compound reaches to avoid internal bubbles and reduce strength loss. Due to LSR's low viscosity, precise parting lines are necessary to prevent spillage, although parting lines may still be visible on shaped products.
Demoulding
Demoulding is influenced by the product's geometric dimensions and the parting surface position, and designing the product with a slight chamfer helps ensure consistent affinity for the other half of the cavity.
Liquid Silicone Rubber (LSR) injection molding offers numerous benefits for producing high-quality parts. One key advantage is the ability to create intricate and detailed parts due to the high flowability of the liquid silicone, allowing it to fill even the most complex mold cavities. This process also enables the production of parts with tight tolerances and consistent wall thicknesses.
In addition, LSR injection molding results in parts with excellent mechanical properties, including high tear strength, elongation, and resilience. This makes silicone materials ideal for applications requiring flexibility, durability, and resistance to extreme temperatures.
Furthermore, LSR injection molding is advantageous for producing single-color silicone products with a flexible structure, similar to plastic injection molds with slider or ejector mechanisms. It can also be used for overmolding with plastic and metal, as well as creating two-color products with multiple advantages of silicone overmolded with other materials.
Moreover, the process significantly reduces overall molding time compared to compression molding, as products can be easily removed from one base plate while the other is vulcanized. The base plate's ability to move left or right on the sliding plate adds to the versatility of LSR injection molding, which operates similarly to plastic injection with molding done through the shot area of the upper plate.
Liquid silicone rubber (LSR) has become an irreplaceable material in the production design of various products such as health products, automobiles, baby products, medical supplies, diving equipment, kitchen utensils, and silicone seals. The application of LSR, particularly LIMS (Liquid Injection Molding System), has resulted in increased productivity, decreased human costs, and improved efficiency in the workplace.
For over a decade, YEJIA has been a reputable manufacturer of high-quality silicone products. Our team of experts is experienced in LSR injection molding and has extensive knowledge of silicone rubber materials. We have established long-standing partnerships with numerous Fortune 500 enterprises, including SONY and LG. If you are in search of a reliable LSR injection molding factory, please do not hesitate to contact us.
