LSR Injection Molding

Liquid silicone rubber injection molding works by forcing low-viscosity LSR into a mold cavity, where it quickly cures into the final part shape. Here is the complete process step-by-step:

Step 1: Create LSR Molding Tool
Initially, a molding tool for liquid silicone rubber is fabricated using CNC machining. For the purpose to withstand the LSR injection molding process, this tool must possess high-temperature resistance. Also, the tool can be polished to meet different finish options. The finished molding tool is then put into an LSR-specific injection molding press.

Step 2: Prepare Material
You can prepare uncured liquid silicone in two containers connected to the pumping system. One container holds the base-forming material, whereas another container houses the catalyst, typically platinum based. Both two materials are pumped through a static mixer by a metering pump. Before the material enters the static mixer section, an additional color pigment and other additives can be added. The two compounds must be mixed in a 1 to 1 ratio.

Step 3: Inject the Material into Mold
The material is heated and injected into the mold cavity under high pressure through a nozzle. After filling the mold cavities, the material takes the shape of the molds. The mold decides the shape of the liquid silicon rubber products. Injecting the LSR mixture into the mold cavity under high pressure can ensure it fills the needed details and features.

Step 4: Curing Process
After filling the mold, it is heated to begin the curing process. This converts the liquid silicone rubber substance into a solid silicone rubber part. The size and complexity of the parts or products determine the curing time.

Step 5: Cooling and Demolding
After the LSR products have undergone sufficient cooling, they should be removed and separated from the molds. This is commonly accomplished through the utilization of automated systems. However, a worker is responsible for removing the parts in manual molding operations characterized by less sophistication and smaller production volumes. The occurrence of flashing in LSR molding is quite infrequent, mostly because of the inherent properties of LSR.

Step 6: Post-molding Secondary Operations
Post-molding secondary operations may be necessary following the demolding and parts removal process. In general, post-molding secondary operations are conducted after the completion of the molding process. Secondary operations encompass a range of jobs such as slitting, printing, marking, assembling, post-curing, etc.

Injection molding of Liquid Silicone Rubber (LSR) is a process used to produce pliable, durable parts in high volumes. During the process, several components are necessary: an injector, a metering unit, a supply drum, a mixer, a nozzle, and a mold clamp, among others.

Injection molding of Liquid Silicone Rubber (LSR) is a common technology used for the production of different products for medical and electrical applications, among others. In addition to the innate properties of the material, the parameters of the process are critical too.

The first step is the preparation of the mixture. LSR usually consists of two components, pigment, and additives (fillers for example), depending on the desired properties of the final product. In this step, the ingredients of the mixture are homogenized and can be combined with the temperature stabilization system for a better control of silicone temperature (ambient temperature or silicone preheating).

The internal part of the product, called inserts, which are embedded in the silicone coating after the injection process, are placed in the mold. These inserts can be kept in ambient conditions prior to injection or preheating.

Liquid Silicone Rubbers are normally supplied in barrels. Because of their low viscosity, the material can be pumped through pipelines and tubes to vulcanization equipment.
The mold is usually heated by water flowing inside the mold or by electrical heaters. Additionally, a cold runner system can be used to prevent the premature curing of the flowing silicone in the runners or its vicinity.

In the second step, the mold is closed by a clamping machine, the injection process starts.
The injection can be made either under atmospheric pressure (an efficient ventilation system is required) or in vacuum conditions. The injection time depends on the injection pressure determined by the product to be manufactured and the silicone properties, such as viscosity. The latter depends on both the shear rate, increasing during the flow, and the temperature.

Once the mold is filled with silicone, the mold temperature is increased to accelerate the crosslinking process of the silicone rubber, resulting in the material transformation from a liquid to solid state; this step is called the curing stage. The time of the curing stage is specific for a given silicone grade and, of course, product. This is another critical step in the processing, because the material overheating and significant pressure increase inside the mold can be observed as a result of the exothermic effect of a curing reaction and high thermal expansion of silicone.

The final step of the injection molding process of silicone rubber is the cooling of the product inside the mold, followed by a product demolding and final cooling in ambient conditions.

All parameters mentioned above strongly affect the course of silicone molding. In consequence, all these aspects can be subjected to optimization to ensure the shortest production cycle time while simultaneously keeping the highest final product quality.

In liquid silicone injection molding, the mould adheres to the product, often known as the mould sticking, or the demoulding is particularly difficult and requires the use of a release agent and other physical means to help demoulding. This LSR silicone injection molding process will lead directly to low production efficiency of liquid silicone injection molding, damaging equipment and products. The silicone injection molding process quality also affects a lot on the final quality silicone products. Silicone products are stretched and deformed, and physical means are used to remove the silicone particles when they stick the mould, causing the mold to damage and damage, etc. The silicone injeciton mold lifespan will be shorten if it needs mold maintanence often.

The original traditional method:
Cleaning and sticking the mold or removing it with potion, and using potion or brush to remove the flash on the parting surface.

However, for transparent products at that time, the mold was polished to a mirror surface, and the traditional function was to scrub it bit by bit with cotton pads. , and a professional polishing master is required, otherwise the mold will be directly disassembled, and the flash on the parting surface can only be picked out bit by bit with a toothpick. The efficiency can be imagined, even if it is ordinary silicone The efficiency of product cleaning with chemicals is also low, generally taking about 30 minutes.

The use of a new fluorine nano-coating process can effectively reduce the occurrence of mold sticking:
Coating features: Anti-fingerprint, stain-resistant, easy to clean, smooth, release, wear-resistant

Uncoated mold: It is difficult to take off during molding, cannot be taken off, and is easy to get stuck. The product scrap rate is high due to mucous membrane, erosion, and corrosion during the die-casting process. Or during stamping and forming processing, the mold is often damaged due to wear. , sticking, bite, fatigue fracture and other factors lead to low production efficiency.

Coated mold: Easy to clean, smooth, good release property, completely solves the problem of mucous membrane in the die-casting process in hydrophobic and oleophobic state, does not get stuck, and improves production yield rate.

For the touch: Rubber mold, liquid silicone mold, self-adhesive silicone, the mold is made of stainless steel.
Processing process: The processing speed is fast and the efficiency is high. The full coating process can be completed within 1-3 days.