Silicone Rubber Tubing and Extruded Profiles: Process, Tolerances and Material Grade Selection
Specifying silicone rubber tubing sounds simple until the production samples arrive: the inner diameter drifts out of tolerance, the tube kinks at the fitting, the peristaltic pump life is half what the brochure promised, or the biocompatibility file is rejected because the tubing was peroxide-cured instead of platinum-cured. This guide gives medical device engineers, food and beverage equipment buyers, pharma bioprocess engineers, industrial distributors and automotive hose buyers a single reference for extrusion, tolerances and grade selection so your RFQ lands on the right compound the first time. For a deeper dive into material families, see our silicone material selection guide.
1. How Silicone Tubing Is Extruded and Vulcanized
The silicone rubber compounding process follows a defined sequence from raw gum to a continuous, vulcanized profile. Understanding the steps helps you judge supplier capability and lead time.
- Compound preparation: HTV/HCR silicone gum (VMQ) is mixed with peroxide or platinum cure system, fillers, pigments and process aids on a two-roll mill or internal mixer.
- Extrusion: The compound is fed cold into an extruder barrel and forced through a die that defines the ID and wall. For LSR, a two-part liquid is metered cold through a static mixer and die.
- Continuous vulcanization: The green profile passes through a hot-air tunnel (typ. 200–500 °C, several meters long) or a steam-autoclave for thick walls; LSR cures in-line in the heated tunnel.
- Post-cure (medical/food): Platinum-cured stock is post-cured 4 h at 200 °C to drive off residual volatiles and extractables.
- Cutting and packaging: Profile is spooled onto reels or cut to length, 100%-dimensionally inspected, and packaged clean for medical or food lines.
| Wall thickness | Hot-air tunnel temp | Line speed | Line length |
|---|---|---|---|
| 0.5–1.5 mm (thin) | 250–350 °C | 20–60 m/min | 6–12 m |
| 1.5–3 mm (standard) | 200–300 °C | 10–25 m/min | 8–15 m |
| 3–10 mm (thick / pressure) | Steam vulcanizer 140–180 °C | 5–10 m/min | 20–40 m autoclave |
| LSR tubing | 180–230 °C tunnel | 10–30 m/min | 6–12 m |
2. Sizes, Tolerances and Mechanical Specs to Put on Your RFQ
The most common root cause of a returned batch is not bad material — it is an unspecified tolerance. ISO 3302-1 defines E1/E2/E3 tolerance classes for rubber extrusions, and the difference between E1 and E3 can be the difference between a seal that snaps into a groove and one that falls out. Always agree the class on the drawing before tooling.
| Parameter | Typical range | Tolerance option |
|---|---|---|
| Inner diameter (tubing) | 0.5 mm to 100+ mm (custom dies) | E1 ≈ ±0.1–0.25 mm (small IDs) |
| Wall thickness | 0.5–10 mm | E2 ≈ ±0.2–0.5 mm (production default) |
| Profile cross-section | Any continuous shape | E3 looser — sponge, large gaskets |
| Hardness, Shore A | 30–80 (40–60 most common for tubing) | ASTM D2240, ±5 typical |
| Property | Test method | Value |
|---|---|---|
| Tensile strength | ASTM D412 | 7–12 MPa |
| Elongation at break | ASTM D412 | 200–700 % |
| Tear strength | ASTM D624 Die B | 10–40 kN/m |
| Continuous service temperature | — | −60 °C to +200 °C (peaks +250–300 °C) |
Note that silicone is low-tear compared with EPDM or natural rubber: avoid sharp-edge routing, barbed fittings with sharp teeth, and abrasive clamp positions. RFQ checklist: ID × OD (or ID × wall), ISO 3302 tolerance class, Shore A, cure system (peroxide vs platinum), color, required certifications, packaging (cut lengths vs reels), and annual volume.
3. Choosing the Grade by Application
Cure system and additive package determine whether a silicone tube is suitable for a body, a brewery, a bioreactor or a turbo inlet. The wrong choice is rarely caught at goods-in — it shows up in the regulatory file, the extractables test, or the field-failure report.
| Application | Recommended grade | Hardness | Required certifications |
|---|---|---|---|
| Medical (drainage, feeding, breathing circuits) | Platinum-cured VMQ or LSR, post-cured 4 h @ 200 °C | Shore A 50–70 | USP Class VI (USP <88>), ISO 10993-5/-10 |
| Food & beverage (dairy, brewery, coffee machine) | Platinum-cured VMQ, food-grade pigments | Shore A 50–70 | FDA 21 CFR 177.2600, EU 1935/2004 |
| Pharma bioprocess / peristaltic filling | Platinum-cured VMQ or LSR, post-cured | Shore A 50–65 | USP Class VI, ISO 10993, FDA 177.2600; pump life 200–1000+ h |
| Industrial / coolant / oven seals | Peroxide-cured VMQ (acceptable) | Shore A 40–70 | — |
| Automotive coolant / turbo hose | Reinforced VMQ (polyester or aramid braid) | Shore A 60–80 | OEM specs; 5–20 bar WP by ID |
Key rules: peroxide-cured tubing is not acceptable for medical or food contact. For peristaltic pumps, target Shore A 50–65 and confirm pump-life hours at your rotor speed and fluid — generic “pharma-grade” claims without a tested life curve are not enough. For pressure service, specify working pressure by ID; bigger ID means lower working pressure for the same braid. Browse our standard silicone rubber tubing and reinforced hose range.
4. Profiles, Framed Seals and Co-Extrusion
Beyond tubing, silicone extrudes into continuous profiles: glazing beads, oven-door seals, enclosure gaskets and HVAC strips. The same extrusion line handles solid and sponge (closed-cell 0.3–0.9 g/cm³) compounds and can co-extrude a solid carrier with a sponge bulb or a conductive stripe for EMI or static-dissipative seals.
| Profile type | Construction | Corner / joint method | Compression set (ASTM D395 B, 22 h @ 175 °C) |
|---|---|---|---|
| Solid framed seal | Solid VMQ, custom cross-section | 45° scarf joint, vulcanized in corner mold | ≤ 20–35 % peroxide VMQ |
| Sponge bulb seal | Closed-cell sponge 0.3–0.9 g/cm³ | Mitered + vulcanized corner | ≤ 15–25 % post-cured |
| Co-extruded seal | Solid carrier + sponge bulb, or + conductive stripe | Vulcanized corner joint on both materials | Per component grade |
| Gasket-on-a-roll | Continuous profile, cut to length | — (no joint) | Per compound datasheet |
Tooling for extruded profiles is inexpensive compared with injection molds — typically a few hundred dollars and 1–2 weeks lead time — which makes custom cross-sections economical from a few hundred meters upward. Specify compression set as well as hardness: a low-set compound keeps the corner radius under load after years of door cycling.
Frequently Asked Questions
What tolerance class should I specify for silicone rubber tubing?
Default to ISO 3302-1 E2 (±0.2–0.5 mm) for production tubing, drop to E1 (±0.1–0.25 mm on small IDs) for tight medical or peristaltic-pump fittings, and use E3 only for sponge profiles. Always mark the tolerance class on the drawing so the extruder can quote against the same datum.
Platinum-cured vs peroxide-cured silicone tubing — when does it matter?
Platinum-cured VMQ or LSR, post-cured 4 h at 200 °C, is required for medical (USP Class VI, ISO 10993-5/-10), food contact (FDA 21 CFR 177.2600, EU 1935/2004) and pharma bioprocess. Peroxide-cured tubing is acceptable for industrial and many automotive uses and costs less, but will fail biocompatibility review.
How long does platinum-cured silicone peristaltic pump tubing last?
Typical pump life is 200–1000+ hours depending on rotor speed, number of rollers, Shore A hardness (50–65 is the sweet spot) and the fluid being pumped. Always request a curve from the supplier at your specific RPM rather than a generic brochure number.
Conclusion
Tubing that kinks, IDs that drift, peristaltic pumps that fail early and rejected biocompatibility files are almost always specification problems, not manufacturing problems. Lock down cure system, ISO 3302 tolerance class, hardness, post-cure, certifications and packaging in the RFQ, and you will receive a silicone rubber tubing or extruded profile that drops into your assembly, your regulatory file and your service environment on the first attempt. Send your drawing and target annual volume to our engineering team for a same-week feasibility and quote.
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