Today’s guide explains what liquid silicone rubber is, chemical composition, manufacturing process, benefits and injection molding process, among other vital processes.
So, if you want to learn more about this important liquid silicone, read this guide.
What Is Liquid Silicone Rubber?
Liquid silicone rubber is thermoset polymer know for low viscosity. Unlike other silicone rubbers, LSR is platinum cured.
In most cases, it exists as liquid silicone and platinum.
Chemical Composition Of LSR
First, LSR is a type of silicone. The main elements in silicone are:
- Silicon
- Hydrogen
- Oxygen, and
- Carbon
Where silicone and oxygen bonds are the main chemical chain. We refer to the chemical chain as siloxane.
However, during the curing process, manufacturers add platinum. A reason, LSR is also called platinum-cured plastic rubber.
This produces a high performance rubber with high tear and tensile strength. Additionally, the silicone rubber is clear and consistent.
It is worth noting that siloxane bonds and platinum are responsible for the versatile properties of LSR.
Additionally, depending on the specific applications, LSR may have additional fillers and additives.
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How To Manufacture Liquid Silicone Rubber
Silicones do not exist naturally. You must process the raw material – silicates.
Below is a brief summary of the entire process:
i. Get raw material, which is mainly rocks or sand with silica
ii. Mix silica with carbon source then heat to get silicon and carbon monoxide
iii. Add methyl chloride to silicon then heat to produce Dimethyldichlorosilane
iv. Subject the compound to distillation then add water to produce disilanol and hydrochloric acid
v. To produce polydimethylsiloxane, you should condense disilanol
vi. From here, you will subject polydimethylsiloxane to various chemical processes producing a range of rubber formulations such as:
- Liquid silicone rubber (LSR)
- Heat cured rubber (HCR), just to mention a few
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Benefits Of LSR
There are many reasons why you can choose LSR for some applications:
LSR Performs Well Within A Wide Range Of Temperature
At high temperature (250°C), LSR maintains desirable properties without melting. It will remain stable even at extremely high temperatures.
On the other hand, at -100°C, LSR will neither cracks nor become brittle. They will remain flexible.
Exhibit Excellent Resistance To Aging
LSR has excellent resistance to weathering or UV rays. As a result, they are perfect for most outdoor applications.
Ability To Retain Elasticity
LSR compression set ranges from 15% to 20%. Therefore, even when you subject liquid silicon rubber to prolonged compression, it will resist deformation.
Therefore, LSR can maintain elasticity for a long period of time.
Excellent Resistance to Chemical And Most Solvents
LSR resists degradation by most chemicals. However, resistance may be limited to specific temperatures depending on the rubber formulation.
Ideally, they will remain stable on exposure to oxidation, UV rays, water, or ozone.
LSR Is Non-toxic With Virtually No Allergic Reactions
The popular grade of LSR is hypoallergenic. In fact, even for sensitive skins, this silicone rubber is the best material.
Closely related to this is the biocompatibility. A reason LSR is a popular choice for most baby products.
It Offers Better Electrical Resistance
Silicone rubber has the best insulation properties. It can resist electrical stress and corona discharge. Actually, it is the main reason the material is perfect for most high voltage applications.
Other benefits include:
- It has an exceptionally smooth surface
- Available in a range of colors
- It is odorless and tasteless
- Resistance to corrosion
- Absorbs vibrations
From the benefits, you can see why this liquid silicone is popular for many applications
Limitations Of Liquid Silicone Rubber
Although LSR has many benefits, there are some limitations you should know. They include:
i. LSR is a thermoset – it is not recyclable
ii. There are few grades of LSR to choose from
iii. Production cost is relatively high
iv. You should treat it to prevent the sticky feel, which may attract dust
v. Materials such as sulfur may inhibit proper curing
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Injection Molding Liquid Silicone Rubber
Injection molding LSR is popular in making a range of products. It is due to:
- Ability to achieve high volume production
- Parts are high quality, with consistent dimensions
Like injection molding plastics, LSR injection molding is a straight forward process. It entails the following key steps:
i. Design tooling for injection molding LSR
ii. LSR injection molding machine has two containers. One container will have liquid silicone while the second container will have platinum. Platinum is a catalyst in the injection molding process
iii. The metering unit will release the liquid silicone and platinum in a ratio of 1:1. Of course, the machine will add any necessary pigments which will improve quality of the final product.
iv. Injectors will pressurize liquid. As a result, the liquid will flow into metering pumps.
v. A mixer will move to the heated mold cavity. At this point, vulcanization occurs thereby creating parts. It is the nozzle, which delivers the mixture into the mold.
vi. Once the parts cool, you will remove the mold clamps to access the product.
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Let’s look at another molding technique:
Liquid Silicone Rubber Clean Room Injection Molding
In LSR clean room injection molding, the entire production process takes place in a controlled environment. May be you can refer to it as a “sterile environment”.
As a result, the liquid silicone rubber parts are free from any form of contamination.
Normally, the clean room injection molding process eliminates possible contamination by;
- Microbes
- Dust
- Tiny airborne particles
In liquid silicone rubber clean room injection molding, everything must comply with the ISO 14644 standards. Depending on the types of LSR products you want, the ISO 14644 Classes range between ISO Class 1 and ISO Class 9.
LSR clean room injection molding is suitable for making silicone parts in laboratory, health and medical industries.
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Unlike other silicone injection molding process, here you will mold LSR in three different options:
i. Over a substrate
ii. Under a substrate or,
iii. Through a substrate
By doing so, you will have complete parts with exceptional designs and aesthetic appeal.
However LSR Overmolding is a challenging process for most product designers. Therefore, only companies with expertise can handle the process.
When it comes to liquid silicone rubber Overmolding, you can try any of the following techniques:
- Multi-shot injection molding liquid silicone – In this technique, the first shot will form your substrate. Then your second shot of LSR will form the overmold.
- Insert molding silicone – For insert molding, you will start by placing your substrate in the mold. Then you will cover the substrate either partially or fully with LSR.
In short, SLR offers a range of flexibility when it comes to design and molding silicone parts.
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Liquid Silicone Rubber Uses
Some examples of liquid silicone rubber products are:
- Gasket and sealing systems in automatic and aerospace industries
- Insulation systems in electrical and electronics industry
- Consumer products hardware products
- Keyboards and touch pads
- Health care products such as hearing aids, respirators, wearable devices, masks, catheter tubing, etc.
- Hand instruments
- Valve parts and component, just to mention a few
In short, LSR is a perfect material for many applications in virtually all industries.
Industries such as life sciences, consumer products, aerospace, automotive, healthcare, agriculture, food processing, oil and gas use LSR parts.
Of course, this is due to the many benefits the silicone rubber material offers.
Conclusion
LSR plays an integral role in manufacturing a range of rubber parts. It is a high performance thermoset rubber with unmatched physical, and chemical properties.
In fact, molding LSR is a popular technique for most fabricators.
At LegenDay, we offer perfect solution for all your silicone rubber products – contact us now.