The majority have been searching for an understanding of HCR silicone. Some think it’s solid, others think it’s liquid. Meanwhile, HCR silicone is a solid silicone. However, to fully understand what HCR silicone is about, you need to read this guide to the end.
What Is HCR Silicone
HCR silicone is a silicone elastomer with a solid gum-like material that uses heat as the curing agent. Its main formula is (Gum+Silica+Plasticizer+Additives). These types of silicone feature very high molecular weight, excellent aging resistance, residual strain in high temperatures, good mechanical properties after vulcanization, and long dangling chains as one of its chemical structure materials.
In addition, HCR silicone has polydimethylsiloxane. Polydimethylsiloxane is a type of silicone polymer you can include in the production process of HCR silicone for high flexibility and cold resistance. You can cure HCR silicone by formulating chemical additives (platinum complexes), they are usually cured at high temperatures with either organic peroxides or a platinum catalyst.
Lastly, you’ll find HCR silicone in wire and cable, office equipment parts, and automotive parts. Their application usually determines whether you need to add more or fewer crosslinks when you’re producing them. You can formulate HCR silicone in different colors, effects, and performance. However, HCR silicone has a lower elongation break and higher tensile strength to the point of failure.
Properties Of HCR Silicone
Excellent Tensile Strength
HCR silicone comes with up to 800 to 1500 psi (pounds per square inch) tensile strength to withstand pulling force, making them a perfect match for instances where your applications need durability under stress.
Good Flexibility
HCR silicone includes Polydimethylsiloxane. The purpose of polydimethylsiloxane is to give stretching and compressing ability to hoses and gaskets for versatile design in applications.
Minimal Compressibility
HCR silicone does not break, shrink, or burst when you use it in high-pressure applications due to its minimal compressibility.
Biocompatibility
HCR silicone does not have an adverse effect on your skin, meaning you can use it in medical applications like prosthetics, medical tubing, etc and you can use it in food processing industries.
Durability
This type of silicone has the mechanical strength to maintain its shape irrespective of how much you expose it to higher thermal stress, UV, heat, and other aging factors.
Electrical Properties
They have excellent insulating properties. This means that you can use HCR silicone in electronics and other electrical applications.
Advantages Of HCR Silicone
Here are some of the advantages that distinguish HCR silicone from other types of silicone:
Temperature Resistance
You can use HCR silicone even for applications with fluctuating weather due to its ability to withstand temperatures from -50 °C to +300 °C. Some special types of this silicone could work from -120 ℃ or above 300 °C.
Chemical Resistance
HCR silicone has good resistance to chemicals like oil, solvents, and other industrial lab chemicals like hydrochloric acid, ammonia, potassium hydroxide, acetic acids, etc. They also resist weathering and aging, and they are flexible in a wide range of conditions where exposure to harsh substances is mandatory.
Minimal Volatile Organic Compounds
Volatile organic compounds (VOCs) are released due to the heat-curing process HCR silicone passes through. This helps the silicone to reduce emissions and gives it deep curing in thick silicone components for durability and reliability in industrial applications.
Chemical Structure Of HCR Silicone
HCR silicone is also called High-temperature vulcanizing silicone rubber (HTV). They are made up of silicone polymers that have methyl groups joined to the silicon atoms rather than hydrogen atoms.
Because of their size, which keeps the chains from crowding closely together and permits unrestricted movement, methyl groups give your silicone its flexibility.
The curing process creates cross-links between polymer chains. By acting as connecting points, these cross-links enable polymer chains to form a coherent, three-dimensional network.
HCR’s elasticity, heat, chemical, and compression resistance are all attributed to the cross-linking, which limits chain movement. In the absence of cross-links, the substance would always be a liquid.
Comparison Of HCR Silicone and Other Types Of Silicone
HCR and LSR are the same types of silicone elastomer, but there are some key differences you should take note of.
HCR Silicone vs LSR Silicone
The first thing you should be aware of is that HCR silicone generates condensation reactions between its polymer chain through the aid of heat. This means that you need to bake them in an oven after they have been shaped, you can achieve this by transfer or compression molds.
On the other hand, you can cure LSR silicone with injection molds for complex fabrications using a platinum-catalyzed addition reaction. However, you need to initiate it at room temperature.
In addition, HCR silicone has a lower elongation break compared to LSR silicone. This tells you that when you apply both HCR and LSR silicone under a high tensile load, LSR silicone will stretch much more than HCR silicone.
When you think of compression sets, HCR and LSR have the best compression set. However, LSR silicone has a much lower viscosity compared to HCR silicone. Lastly, HCR silicone hardness and temperature resistance are higher than LSR silicone. Although LSR silicone gives room for more intricate and precise parts, HCR has minimal mold fouling that enables its mold to last longer.
HCR Silicone vs RTV Silicone
You will find HCR and RTV silicone in industrial and consumer applications because they both belong to silicone polymers and methyl groups. But there are some key differences you need to know.
HCR silicone uses Peroxide/Platinum catalyzed as their curing system for density and durability while RTV silicone makes use of a condensation cure system. This means that RTV silicone cures at room temperature without additional heat, making it suitable for applications where heating isn’t feasible.
When you require higher tensile strength and durability, HCR silicone is a perfect match due to its ability to withstand tear and significant wear irrespective of how harsh the environment is. However, when you think of flexibility over strength, RTV silicone is a good choice.
Compared to HCR silicone which has a temperature resistance between -50 °C to +300 °C, RTV silicone has a lower temperature range. This means that you can only use RTV silicone for short-term application.
Process of Manufacturing HCR
The processes of manufacturing HCR silicone rubber are compression molding and Injection molding.
Compression Molding: In the process of compression molding, you need to first mix, and degas the silicone. The purpose of this is to remove the air bubbles. After which you need to pour it into a preheated mold cavity. Then compress the mold and fill the cavity with a press. When compressing you will notice plenty of materials flowing out, this enables the silicone to intricate mold features.
NOTE: If you want to recover the finished HCR component, allow the mold to cool before you
open it.
Injection Molding: In this process, you need to utilize high-pressure injections of HCR silicone to fill a mold. Then, you put the mold through a post-cure bake cycle after shaping to finish the cross-linking.
NOTE: The injection method is most suitable for producing HCR silicone in bulk.
How To Cure HRC Silicone
As you know heat is the main factor when you’re curing HCR silicone. Active sites are created on the polymer chains when the prepolymer’s chemical groups are disintegrated by heat. Then you need to join nearby active sites through the condensation process.
As a result of this, there will be the creation of crosslinks between polymer chains. This means that an interwoven rubber network is formed when individual polymer chains are joined chemically, thus allowing the crosslinking to move through the HCR material.
After the heat is induced, the liquid HCR compound is transformed into a solid elastomer with durability and flexibility. The curing temperature is usually determined by the actual formulation, although it is always between 140°C – 205°C. Although some newer equipment has a reduced curing cycle.
For consistent final qualities, big industrial batches are guaranteed to cure uniformly thanks to precise temperature control.
Applications Of HCR Silicone
HCR silicone is widely used in most industries due to its durability and versatility. Here are some examples:
- Automotive and Transportation: You’ll find HCR silicone in automotive gaskets, seals, hoses, and O-rings due to their chemical and heat resistance.
- Medical and Healthcare: They are used for tubing, catheters, and medical seals due to flexibility and sterilization resistance.
- Aerospace and Defense: You’ll find HCR silicone in aerospace gaskets, dampers, seals, and insulators due to their high-temperature resistance and stability in a stressful environment.
- Consumer Electronics: You’ll find HCR silicone in electronic keypads, grommets, and connector seals of electronics due to their mechanical wear resistance and insulation properties.
- Food and Beverages: They are used for baking molds, seals, and gaskets due to their chemical cleaning agent.
- Construction and Architecture: You’ll find them in windows, doors, and facades due to their durability and UV-resistance properties.
- Industrial Manufacturing: They are good for creating molds, rollers, and conveyor belts due to abrasion resistance and flexibility.
Conclusion
In conclusion, HCR silicone is a versatile type of silicone with exceptional properties like chemical resistance and excellent temperature resistance. Based on its high versatility, you’ll find them in almost all industries.
More Resources:
Silicone Rubber: Comprehensive Guide For You – Source: TOGOHK
What Is Fluorosilicone? – Source: TOGOHK
Electric outlook: Is silicone conductive material? – Source: TOGOHK
Understanding UL94V-0 Silicone Rubber for Safety Standards – Source: TOGOHK
Silicone vs Rubber: Which Material is Right for You? – Source: TOGOHK