What are HTV silicones?HTV silicones (High Temperature Vulcanizing) are silicone rubbers that only cure at high temperature, in a heated mould or press. That makes them fundamentally different from casting silicones (RTV), which cure at room temperature.Within HTV there are two families, distinguished mainly by consistency and processing method:LSR, Liquid...
HTV Silicones – LSR (liquid) and HCR (high consistency rubber) (3)
What are HTV silicones?
HTV silicones (High Temperature Vulcanizing) are silicone rubbers that only cure at high temperature, in a heated mould or press. That makes them fundamentally different from casting silicones (RTV), which cure at room temperature.
Within HTV there are two families, distinguished mainly by consistency and processing method:
LSR, Liquid Silicone Rubber
Liquid to paste-like two-component silicone, processed on an injection moulding machine. For high volume precision parts.
HCR, High Consistency Rubber
Solid, kneadable silicone rubber, processed with conventional rubber technology such as compression moulding and extrusion. For profiles, tubing and robust moulded parts.
A note on terminology: in the rubber industry HTV is often used as a synonym for solid silicone (HCR). Technically LSR also vulcanizes at high temperature, so it falls under HTV as well. When requesting a quote, always state LSR or HCR so we know exactly which material you mean.
LSR and HCR at a glance
| LSR | HCR | |
|---|---|---|
| Consistency | Liquid to paste-like, pumpable | Solid and kneadable, similar to raw rubber |
| Components | A and B, usually 1:1, machine metered | Base compound plus curing agent or catalyst, mixed on a two-roll mill |
| Cure system | Almost always platinum (addition) | Peroxide or platinum |
| Processing | Injection moulding with metering unit and cold runner | Compression and transfer moulding, extrusion, calendering, also injection moulding |
| Cycle time | Short, often seconds to a few minutes | Longer, typically several to over ten minutes per press cycle |
| Investment | High, LSR machine and precision mould | Lower, a heated press and a simple mould are sufficient |
| Best for | High volumes, small and complex parts, little finishing | Profiles and tubing, smaller runs, high tear strength |
LSR, liquid silicone rubber
LSR is pumped from drums or pails through a metering unit, mixed in the correct ratio and injected into a hot mould, typically between 150 and 200 °C. It fills thin walls and fine details and cures within a short time.
- ✓High repeatability and dimensional accuracy
- ✓Automated, with little waste and finishing
- ✓Closed process, clean and easy to validate
Typical applications: teats, seals and membranes, watch straps, diving masks, medical and electronic components.
HCR, solid silicone rubber
HCR is mixed with curing agent and optional colour on a two-roll mill, then moulded under pressure and heat in a press, or extruded into a profile or tube and vulcanized in an oven or hot air tunnel.
- ✓High tensile and tear strength
- ✓Suitable for extruding continuous profiles and tubing
- ✓Cost effective for smaller runs thanks to lower tooling costs
Typical applications: gaskets and O-rings, tubing, door seals and profiles, bakeware, keypads, cable insulation.
→ Semsil HTV platinum silicone (HCR), order directly from 1 kg
Which one fits your process?
- →You run an LSR injection moulding machine and produce large numbers of small or complex parts, choose LSR
- →You extrude profiles, cords or tubing, choose HCR
- →You have a heated press and produce small to medium runs, choose HCR
- →You have no heated press or injection moulding machine, choose platinum casting silicones (RTV-2) that cure at room temperature
⚠️ HTV silicones are not casting rubber. Without a heated mould, pressure and the right equipment they will not cure properly. They are not suitable for mould making, prototyping or hand casting.
Processing and post-curing
Platinum or peroxide
Platinum cures without by-products, gives a clean, odourless end product and is the standard for food and medical use. Peroxide is robust, insensitive to the substances that inhibit platinum, and widely used in extrusion and technical HCR applications.
Post-curing
After moulding, parts are often post-cured for several hours, for example 4 hours at 200 °C. This removes volatiles and stabilises the properties. For food contact and medical applications it is almost always required, always follow the datasheet.
Avoiding inhibition
Platinum cure is inhibited by sulphur, tin and amines, among others. Keep moulds, mixing equipment and gloves free from residues of peroxide or condensation cure systems.
Colouring
HCR is coloured with a colour masterbatch on the two-roll mill, LSR with a colour paste dosed by the metering unit. Only use pigments compatible with the cure system, see our silicone pigments.
What we do for you
- ✓Grade selection based on your process, hardness, colour and food or skin contact requirements
- ✓Grades from renowned brands and custom variants on request
- ✓Trial quantities to test before you scale up
- ✓Documentation such as TDS and SDS, and declarations of conformity where available
LSR and custom HCR grades are supplied to business customers only, on quotation.
Frequently asked questions
Is LSR also an HTV silicone?
Technically yes, LSR vulcanizes at high temperature. In practice, however, many suppliers and processors use HTV to mean solid silicone only, in other words HCR. So always state LSR or HCR in your enquiry.
Can I cast HTV silicones like casting rubber?
No. HCR is not pourable and LSR only cures at high temperature in a closed mould. If you want to cast at room temperature, choose platinum or condensation cure casting silicones (RTV-2).
Are HTV silicones food safe?
There are grades that comply with FDA 21 CFR 177.2600 or BfR XV. Our Semsil HTV platinum silicone complies with FDA 21 CFR 177.2600. Food safety applies to the end product and also depends on your process and post-curing. The manufacturer of the end product is responsible for certification.
Which hardnesses are available?
Semsil HTV platinum silicone (HCR) is available from stock in Shore A 40, 60 and 80. Other hardnesses, in both LSR and HCR, are available on request.
Can I order small quantities?
Semsil HTV platinum silicone can be ordered directly in the webshop from 1 kg. For LSR and custom HCR grades we prepare a tailored quotation, including trial quantities.
Related categories
→ Platinum silicones (RTV-2)
→ Silicone pigments
→ Primers for silicones
Need advice or a quote?
Tell us which process you use, which hardness you need and which requirements the end product must meet. You will receive a reply within 1 working day.