You may be looking for a highly reliable, durable, and safe material to solve design and production problems, and HCR meets all three of those needs. And it is used in several important areas. But it is a new composite material, and you may not fully understand what HCR silicone is. In this article, we’re going to present you with a comprehensive, practical guide to HCR silicone. From a variety of aspects of the introduction to help you quickly understand the advantages of HCR silicone, applicable scenarios,s and selection reference. Help you make scientific and efficient decisions.
Chemical Structure and Composition
The basic structure of HCR silicone is a polysiloxane skeleton. It consists of alternating Si and O atoms. The silicon atoms are often attached to -CH₃, -CH=CH₂, or other functional organic groups for cross-linking or improved properties. It is this backbone that gives HCR silicones their flexibility, heat resistance, and chemical resistance.
In addition to the main polysiloxane backbone, it consists of fillers, additives, and catalysts. Fillers are silica gel and reinforcing agents used to adjust viscosity and improve strength. The additives and catalysts are used to control curing, colour, and durability. This combination of components results in HCR silicones with high viscosity, high mechanical properties,s and good heat resistance.
Key Properties of HCR Silicone
Excellent tensile strength
The main chain of HCR silicone consists of a silicone-oxygen (Si-O) backbone. This chemical bond is both strong and tough. Fillers complement it, giving the material a significant boost in mechanical strength. This is why HCR does not break easily when stretched. It is able to maintain its integrity when subjected to prolonged or high-stress environments. This property makes it especially suitable for use in seals, gaskets, and pipe joints that are subjected to stretching.
Good flexibility and elasticity
The low rotational energy of the silicone main chain and the organic side groups, such as methyl and vinyl. This makes the molecular chain highly flexible. Uniformly distributed fillers do not affect the elasticity of the rubber. Therefore, HCR can maintain its shape even after repeated bending or compression. This property can be fully used in situations where high flexibility is required, such as electronic component coverings, automotive seals, and medical device hoses.
Low compression set
HCR has a high cross-link density and a uniform filler network structure. This allows the material to diffuse stresses when compressed, thus reducing permanent deformation. The shape remains stable under long-term compression with minimal deformation. It is suitable for long-term pressure components such as seals, cushions, and shock absorbers.
Biocompatibility
HCR silicone does not contain volatile organic compounds, heavy metals or other harmful by-products. Stable chemical structure. It does not easily decompose into small irritating molecules. So it is safe for contact with the skin or human body and generally does not trigger allergic reactions. This makes HCR the material of choice for medical devices, food contact materials, and baby products.
High durability and ageing resistance
Silicone skeletons are chemically stable. It has low reactivity to oxidation, UV rays, and high and low temperature environments. Fillers and antioxidants further enhance the material’s weathering resistance. As a result, HCR is resistant to ageing, UV rays, and ozone over long periods of time. It maintains its performance even in harsh environments such as outdoor, automotive, or industrial equipment.
Stable electrical insulation properties
Silicone oxygen chains are themselves electrical insulators. There are no free electrons or conductive groups in the molecular structure. The dielectric properties can be enhanced by selecting suitable fillers.HCR has good insulating ability and voltage resistance properties. It is suitable for use in electronic component coverings, wire sheathing, and electrical seals where electrical safety is required.
Advantages of HCR Silicone
Outstanding high-temperature resistance
During moulding and actual use, HCR silicone needs to withstand constant heating or hot and cold changes. If the material’s performance is unstable at high temperatures, problems such as hardening and cracking can easily occur. Silicone main chain structure is stable and with suitable addition system. So it has strong resistance to heat breakdown and structural damage. It can be used in the range of -60℃ to 250℃ for a long time. So it is often used in high-temperature seals, engine peripheral parts, and electronic components for heat protection.
Good chemical resistance
Many silicone products come into contact with cleaning agents, oils, acids, and alkali media during use. If the material is sensitive to chemical media, surface ageing, or properties decline quickly.HCR Silicone gel by virtue of a stable silicone-oxygen skeleton and low reactive organic side groups. It has good resistance to most acids, alkalis, salts, oxidising agents, and common organic solvents. The support of the filler system helps the material to maintain structural and performance stability over long periods of use. It is suitable for use in making industrial seals, chemical piping, and laboratory-related products.
Very low volatile organic compound (VOC) content
HCR silicones are typically made from high-purity polysiloxane raw materials. It is processed through a controlled manufacturing process. It contains no or very small amounts of volatile organic compounds (VOCs). This characteristic makes the material less reactive to allergic reactions in humans and less likely to cause environmental irritation. This low VOC characteristic makes it easier for HCR to meet the needs of applications with strict safety and health requirements. It is also more suitable for environmentally and personnel-friendly production scenarios. Examples include medical devices, food contact products, and baby products.
Comparison Between HCR and Other Types of Silicone
When choosing silicone materials, you may not be able to distinguish the specific characteristics of the difference between HCR, LSR, and RTV, but only feel roughly the same. These three materials have different focuses, actually. There are obvious differences between the three materials in terms of form, processing methods, production efficiency and application scenarios. In the following, we will compare the differences between HCR and LSR, and HCR and RTV in the form of a table.
HCR vs. LSR & RTV (Liquid Silicone Rubber)
| Comparison Item | HCR Silicone (High Consistency Rubber) | LSR (Liquid Silicone Rubber) | RTV (Room Temperature Vulcanizing Silicone) |
| Material form | High-viscosity solid rubber | Low-viscosity liquid | Paste or liquid |
| Curing method | Heat curing | Heat curing | Room-temperature curing |
| Main processing methods | Compression moulding, transfer moulding, and extrusion | Liquid injection moulding (LIM) | Pouring, coating, dispensing |
| Equipment and tooling requirements | Flexible equipment; tooling cost is relatively controllable | Requires dedicated metering systems and high-precision moulds | Little to no tooling required |
| Production efficiency | Suitable for batch production with flexible adjustments | Highly automated; ideal for large-volume production | Relatively low efficiency |
| Suitability for part complexity | Suitable for thick-walled parts, profiles, and structural components | Suitable for thin-walled, small, high-precision parts | Not suitable for complex moulded parts |
| Dimensional and performance consistency | Good | Excellent | More affected by environmental conditions |
| Typical applications | Seals, gaskets, hoses, profiles, cable insulation | Medical disposables, precision electronic components | Bonding, sealing, potting, repair |
| Best-fit use case | Manufacturing molded products | High-precision, standardized mass production | On-site application or auxiliary processes |
HCR silicone is balanced in terms of consistent performance, processing flexibility, and cost control. It is commonly used for moulded, transfer, and extruded products. LSR is more dependent on automated equipment, especially in medium to large volume production. It is more suitable for mass production scenarios that require high-dimensional accuracy and consistency. Usually used for parts with more complex structures or smaller sizes. RTV silicone adhesives are more often used for bonding, sealing, or on-site construction. They are mainly used to solve installation and repair problems. It is not mainly used for batch moulding per se.
Manufacturing Processes of HCR Silicone
Mixing and homogenization
HCR needs to be mixed first in a two-roll refiner or open kneader. The fillers and additives are allowed to distribute evenly in the silicone matrix to form a stable rubber. Temperature control is important; overheating may affect material properties. Homogeneous mixing ensures subsequent moulding and vulcanisation.
Moulding
HCR can be processed by compression moulding, transfer moulding or extrusion moulding. Compression moulding involves placing a mixture into a heated mould and forming it under pressure. It applies to thick parts or mass production. In transfer moulding, the rubber is first heated and then injected into the mould. It is applied for making complex structures. The extrusion moulding process is suitable for long products such as seals, which can be processed continuously.
Vulcanisation
Vulcanisation is an important step in making HCR. It is done in a heated mould. By controlling the temperature and time, the product can achieve the desired hardness, tensile strength and dimensional stability. Good or bad vulcanisation affects the mechanical properties and service life of the finished product. It needs to be strictly controlled.
Post-treatment and inspection
After demoulding, the products are usually deburred and trimmed to ensure a clean surface. Next, tests for dimensions, hardness, temperature and chemical resistance are conducted to confirm that the design requirements are met. For medical or food-grade products, they are also cleaned or sterilised to ensure safety and hygiene. The whole process ensures that each finished product is reliable in terms of performance and quality.
HCR Silicone Applications
HCR silicone is used in industrial seals such as O-rings, gaskets, seals and tubing connections. It is resistant to high temperatures and chemicals. It has good resilience to compression. It is not easily damaged by long periods of compression. So it is widely used in automobiles and mechanical equipment.
In electronic and electrical equipment, it is mostly used for wire sheathing, cable sealing or component wrapping. Silicone skeleton itself has good insulating properties. Resistant to high temperature and ageing. It can also remain flexible. Installed in electrical industrial control equipment, it is not easy to break or crack due to heat or time. The overall reliability is higher.
HCR is also widely used in the automotive field, such as engine seals, hoses, vibration-damping pads, and some exhaust system components. It is resistant to oil and ageing, and its performance is stable under a high-temperature environment. And it can withstand long-term engine vibration. So these parts are not easy to fail under complex working conditions, and the service life is also longer.
In the field of medical devices and food contact, HCR is often used to make catheters, hoses, baby products and food-grade moulds. It has low volatiles and low risk of toxicity and allergenicity. It is also stable and does not react easily with external media. It is therefore easier to pass the relevant health and safety requirements. It can come into direct contact with the human body or food.
In industrial equipment, HCR is often used as shock absorbers, cushions, elastic washers and some wear parts. The main reason is that it has stable elasticity and is not easily fatigued in long-term use. Customised requirements can be met, such as transparent or coloured electronic housings, or products used for sealing and potting. HCR also maintains a rather reliable performance, both in terms of look and performance.
FAQ
How to choose the right HCR silicone grade for your project?
The first step is to look at the conditions of use, such as operating temperatures, stresses, and whether or not they are exposed to oils or chemical media, which is the basis for material selection. This is followed by matching the required mechanical properties and moulding process, as different formulations and filler ratios will have a direct impact on performance and will determine the appropriate processing method. The vulcanisation system is also important as it relates to heat resistance and odour residue. If the product is to be used in a high safety scenario, such as food or medical, it will also be necessary to compare it with the relevant regulations. Finally, cost and production volumes are taken into account.
How long does it take for HCR silicone to cure under normal conditions?
The curing time of HCR silicone is variable and usually ranges from a few minutes to several tens of minutes. It depends mainly on the temperature, thickness and formulation. The higher the temperature and humidity, the shorter the curing time will be. Thin-walled parts are heated evenly and tend to cure in 5-20 minutes. Thicker parts are slower to transfer heat and take longer to fully cure.
Is HCR silicone recyclable or eco-friendly?
HCR silicone cures to form an irreversible three-dimensional cross-linked structure. So they are generally not recyclable and cannot be heat remoulded like thermoplastics. Uncured rubber can be remixed or processed, while cured trimmings can be crushed for fillers or secondary uses.HCR Raw materials are low in volatility, free of heavy metals, resistant to ageing and have a long life. It is also environmentally friendly and reduces the waste resulting from frequent replacement.
How does humidity or storage temperature impact HCR silicone performance?
High temperatures and humidity accelerate the pre-curing of HCR silicone rubber, making the material hard and affecting processability. Low-temperature and low-humidity storage can slow down this ageing process, but temperatures that are too low can make the rubber hard and even difficult to handle during compounding. Therefore, a balance needs to be found when storing, keeping the environment dry and the temperature moderate. This allows the material to remain stable and easy to process.
Can HCR silicone be bonded to metals or plastics?
Yes. However, HCR silicone is a chemically inert thermoset elastomer. It is not easy to bond directly to metal or most plastic surfaces. Specialised silicone adhesives or surface preparation techniques are required to provide secure bonding.
What certifications or standards are relevant for HCR silicone?
Different applications in different fields refer roughly to the following standards or certifications.
Medical / Biocompatibility: ISO 10993, USP Class VI, ISO 13485
Food Contact: FDA 21 CFR 177.2600, LFGB, EU 10/2011
Material Performance: ASTM D412/D2240/D395, ISO 37/48, UL 94
Environmental / Industrial Compliance: RoHS, REACH
Final Thoughts
HCR Silicone has many advantages, so it is widely used in various industries. It is resistant to high temperature, chemical corrosion and has good elasticity. It is also not easily deformed after compression and has stable insulating properties. When selecting the material, it mainly depends on the working temperature, force and contact medium, and some products have to meet food or medical safety standards.
In this respect, Legensilicone’s technology is well established. Our formulations and production processes are reliable. Legensilicone can provide consistent, customised HCR products. Whether it’s high-temperature seals, electronic parts, or medical and food contact items, we offer a complete service from material selection to series production. Consistent performance and compliance with standards are guaranteed. You can contact us anytime.
