This guide will provide you with all the basic and crucial information on High Consistency Rubber (HCR). So, if you want to learn more about high consistency silicone rubber, read this guide.
What is HCR?
High Consistency Rubber (HCR) is a unique material possessing both elastic and viscid properties. It is made up of reactive silicone gums. HCR can also be referred to as Heat Cured Rubber or High Temperature Vulcanizing silicone rubber (HTV).
Compounds in High Consistency Rubber
High Consistency Rubber is made up of the following ingredients:
- Polymers-these form the bulk of the HCR formula, the most common one being the Vinyl Methyl Silicone.
- Fillers-they are used to increase the durometer, tear and tensile strength of the elastomer.
- Peroxide-this is a curing agent.
- Heat stabilizer– is meant to shield the polymer from being weakened by excessive heat. Magnesium Oxide is a good heat stabilizer in this case.
- Pigment-this gives the material color. Red Iron Oxide is the most common pigment used in this process. However, you can blend different pigments to produce custom colors.
High Consistency Rubber Fabrication Process
Fabrication of HCR involves six main steps:
Step 1: Mill Softening and Catalyzation
Use a two- roll mill to blend the ingredients/raw materials hence forming a homogenous product. It is also at this step that you can add peroxide catalysts to speed up the curing process. At this stage, the hardness the material might have acquired during storage is reversed.
Step 2: Preparation of a Preform
Cut the elastomer sheet obtained at step 1 into strips. Note that this process is labor intensive.
Step 3: Extrusion
Feed the preformed strips into a single-screw extruder. The material extrudes in desired shapes.
Step 4: Molding
Load the preforms into the molding equipment. You may obtain molds with a big number of cavities due to HCR slow cure cycles.
Step 5: Vulcanization
You will achieve this by passing the extruded product through hot-air vulcanizing (HAV) ovens. This process ensures that the material is hardened thus making it stronger and more durable.
Step 6: Finishing
Here, the material is ready for inspection. Check it out for any possible errors and if satisfied then have it cut as desired. In addition to that, elimination of peroxide by-products can be done at this stage through a post- cured process.
Properties of High Consistency Rubber
This material has a number of desirable properties which include:
- Chemical inertness
- Hardness 30-80 ShA
- Non-reactive to alkali and chemicals
- Elongation 200-800%
- High tear strength 15-40 N/mm
These properties make the material attractive to manufacturers in the construction, automotive, aerospace and many other sectors.
Applications of High Consistency Rubber
HCR has of a wide range of applications:
- Automotive industry- to make cables, hoses and gaskets
- Medical sector- to make implants, tubes, connectors and cables
- Electrical sector-to make insulators and safety cables
- Building and construction sector-used for sealing and piping.
- Used in the manufacture of kitchenware and other appliances
Advantages of High Consistency Rubber
High Consistency rubber is known for its unique ability to regain its original size and shape when force causing stretching, bending, compressing and twisting is withdrawn. This increases the demand for the material.
Besides, the material is highly resistant to extreme weather conditions and can also withstand very low and high temperatures (-50-300OC).
Comparison between High Consistency Rubber and Liquid Silicone Rubber
- HCR has a higher viscosity than LSR
- HCR manufacturing wastes material unlike LSR manufacturing.
- The cost of labor in HCR manufacturing is higher than in LSR.
- Unlike LSR, HCR manufacturing requires additional equipment and manual labor thus making its cost of production higher.
- LSR is a newer technology as opposed to HCR.
It is quite evident that HCR has outstanding features which make it a versatile material for most manufacturing industries.
Liquid Silicone Rubber – Source: LegenDay
LSR Vs HCR – Source: Simtec
High Consistency Rubber – Source: Medical Design