Why choosing liquid silicone injection molding is the future trend of silicone rubber products?
LSR injection mold is also known as liquid injection mold (LIM), silicone injection molding, LSR mold, liquid silicone mold, liquid silicone injection mold, which is an advanced mold processing, compared with the traditional rubber compression molding method, is an ideal process for many silicone parts with complex geometry, high precision dimensional requirements and high safety material requirements. Liquid injection molds have significant advantages in mold design flexibility, excellent performance of liquid silicone rubber, high production efficiency, closed and safe production environment, high tolerance / precision, and liquid silicone injection secondary molding (also known as LSR secondary molding).
Liquid silicone rubber injection molding is much more expensive than the compress molding, but why do we recommend customers to choose liquid silicone rubber injection molding production? Let’s take a closer look at the specifications.
First of all, what is the difference between liquid silicone and solid silicone rubber?
The difference between liquid silicone and solid silicone can be seen from their appearance, one is solid and another is liquid. Liquid silicone is a liquid state with fluidity, it is a highly transparent and safe food-grade material, no vulcanizing agent and other auxiliary materials are added when molding, and the material is sealed and molded. Liquid silicone is generally used in babyware products and kitchen supplies and medical supplies, it is a high transparent and safe food grade material that can directly contact with food and human body, no vulcanizing agent and other auxiliary materials are added in the production, and the material is sealed and cast; solid silicone is generally used in household products and industrial miscellaneous parts and auto parts, it is a transparent material, and vulcanizing agent is needed to speed up the vulcanizing time when molding, and high temperature Vulcanization molding.
For industries with higher raw materials safety requirements, such as medical grade CPAP full face mask, CPAP nasal placements, medical grade approval is required for medical accessories such as baby care products, such as FDA10993, UPS Class VI, BFR XV, FDA 21 CFR 177.2600, etc. Liquid silicone rubber would be considered as the material, by using the liquid injection molds, liquid silicone rubber is a high purity, non-toxic It is a high purity, non-toxic material with advantages like low compression, less air bubble defection, high heat resistance (working temperature -40℃～230℃), good tensile strength and tear resistance, etc.
LSR is a clean, plasticizer-free, tasteless, odorless, water-resistant, oxidation-resistant, acid- and alkali-resistant chemical.
Properties
Next, what is the choice of liquid silicone injection molding?
Liquid silicone is injection-molded liquid silicone rubber (LSR): the full name is injection-molded liquid silicone rubber, and the vulcanization equipment is injection molding machine.
Injection molding machine has many advantages, such as simple process (no need the mixing ingredients, refining rubber material, cutting materials, placing material onto the mould and other manpower processes, only need a worker to take the product out), high product accuracy (all manual procedures before molding are replaced by the automatic machine), high yield (A/B rubber mixed in a certain temperature in a few seconds to form), save manpower and electric energy, save raw materials etc. It can produce all the silicone rubber products that needs high temperature, as the mainstream of the silicone rubber materials these years.
The advantages of silicone products are obvious: high fabricability and good elasticity, therefore, the demand for injection molded silicone products is increasing day by day, as most of the products in the market need good elasticity, so silicone is widely used in many different industries, from automobile production to home appliance and household products, and also for the medical industry. The increasing demand for “silicone” (LSR) is the new generation of “silicone rubber”, replacing the previously outdated HCR (High Strength Rubber) with increasing momentu. LSR tends to expand in the hot and shrink slightly in the cold, so that their products do not always stay in the convex side of the mold as expected, but stay in the larger surface area of the mould cavity.
For example, one of our customers required a liquid silicone bellow product, which is used for self-adhesive labels on fruits. The side holes and notches on the top is an important structure of the bellow, as the air outlet of the pneumatic system, used for labeling on fruits . If there are some burrs in the hole, the air cannot pass smoothly, which will affect the suction and the sticker cannot be successfully attached to the fruit. The silicone bellow formed by liquid silicone injection molding can achieve no burrs in the holes, and the holes can be directly removed. For compress molded parts, the holes are difficult to demould, and need to be cut with a die-cutter, and the position of the holes cannot be positioned well, and there will be some burrs on the holes that are difficult to remove.
One of the complex designs of this liquid injection mold is the undercut edge structure.
The chamfering of silicone bellows, especially the inversion inside the product, is a tricky point in manufacturing and molding.In the design evaluation, the engineers must take this technical difficulty into consideration, in order to achieve feasibility and the easiest edge removal in production. The liquid silicone rubber material for silicone injection has excellent physical properties, such as high tensile strength, high elongation, etc. Therefore, in order to reduce the indentation, we can directly take out the part from the mold without any special mold structure. Many products have a lot of material, usually it is not necessary to consider the extension angle, generally using a middle mould plate or the sliding block split structure can have an easy demoulding.
The following design is compression molded production,the customer’s version is not easy to get outshaped. There will be small burrs on the hole. Our engineer would recommend to update the structure of the hole and add a die cutter. If such update is not accepted by customer, we can only use liquid silicone injection molding.
For products with small wall thickness, when the wall thickness is less than 0.5mm, compression molding is not suitable for production, and the minimum wall thickness for the removable mould core can usually achieve is 0.5mm.
Liquid silicone rubber injection molding has its own material feeding system, which can automatically fill the cavity without feeding by hand. Therefore, for bellows/suction cups with small thickness and strict wall thickness requirements, LSR injection molding is a better choice, and the wall thickness will be consistent. There is no misalignment, and the tolerance can reach ±0.05mm. If use compression molding, the wall thickness might be uneven and offset, especially when the worker does not place the silicone material well, and for products with small wall thickness, the mold core is not easy to demold, and is easily damaged during demolding.
During liquid silicone injection molding, the mold core is usually heat treated by S136 steel, so that the mold has a longer service life.
Even some high-precision LSR seals, silicone gaskets and seals require tight tolerances (±0.01mm to ±0.03mm), and liquid silicone injection molding is the only option. The liquid silicone rubber injection mold has better clamping force, and the clamping of the upper and lower molds is better than that of compression molded production. Plus the material feeding system and the needle valve flow channel, the accurate material control makes the liquid silicone injection parts a tighter tolerance.
Liquid silicone injection molding is suitable for large volume, semi-automatic production, and the cold runner system for automatic production liquid injection molding plays the same role as the hot runner system. The cold runner system of the liquid injection mold keeps the liquid silicone cool until the liquid silicone rubber material is injected into the hot cavity of the mold. Therefore, the cold runner system can reduce waste and save a lot of material. Liquid silicone injection molding is a closed-loop system, and it’s the repeatable pressure molded production technology that controlled by computer, with high efficiency and manpower saving. Liquid silicone injection molds are highly productive, no longer require workers to feed the materials, and have shorter production cycle time.
Silicone Pro Co., Ltd. is committed to producing high precision silicone rubber products, liquid silicone rubber products for all customers.
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