Precision Silicone Extrusion: Solving Tolerances in Tubing and Custom Profiles

While compression and injection molding are perfect for discrete, individual parts, many industries require continuous lengths of silicone. From FDA-grade fluid transfer tubing in commercial coffee machines to weather-resistant architectural window seals, Silicone Extrusion is the process that creates these continuous profiles.

However, continuous extrusion is notoriously difficult to control. Unlike a closed mold where the steel dictates the final shape, extruded silicone is pushed through a die into thin air before it is cured. This introduces unique physical challenges. At Reemane, we have mastered the art and science of custom silicone extrusion. Here is how we overcome the biggest engineering hurdles to deliver precision tubing and profiles for our B2B partners.

1. The Physics of “Die Swell”

The most common mistake inexperienced buyers make is assuming that the hole in the extrusion die matches the final dimensions of the silicone tube. It rarely does.

When highly pressurized, unvulcanized silicone is forced through the die, the polymer chains compress. As soon as the material exits the die, those chains instantly relax and expand—a phenomenon known as “Die Swell.” If a factory cuts a 5mm circular die, the resulting tube might swell to 5.5mm or more.

Our tooling engineers use advanced flow-simulation and decades of empirical data to calculate exact die-swell compensation. We machine our extrusion dies in-house, systematically adjusting the geometry so that after the silicone expands and cures, it settles perfectly into your specified 2D tolerances.

2. Wall Thickness and Concentricity in Tubing

For medical catheters, peristaltic pumps, or high-pressure fluid lines, the inner diameter (ID) and outer diameter (OD) must be perfectly aligned. If the inner hole is slightly off-center, the tubing will have a thick wall on one side and a thin wall on the other (poor concentricity). A thin wall creates a weak point that will burst under pressure.

To guarantee precision, Reemane utilizes Inline Laser Micrometers. As the continuous silicone tube exits the curing oven, laser sensors measure the OD and wall thickness in real-time across multiple axes. If the dimensions drift by even a fraction of a millimeter, the extrusion speed and die pressure are automatically adjusted. This closed-loop feedback ensures that spool number 100 is identical to spool number 1.

3. HAV (Hot Air Vulcanization) vs. Platinum Curing

Once the silicone is extruded, it must be cured instantly to hold its shape.
Traditionally, factories use long Hot Air Vulcanization (HAV) tunnels, often combined with peroxide-cured silicone. While cheap, this leaves behind acidic residues and a white “bloom” on the surface.

For premium industrial, food, and medical applications, we employ Platinum-Cured Silicone Systems combined with precision infrared (IR) or specialized thermal curing ovens. Platinum-cured extruded tubing is crystal clear, exhibits superior tear strength, will never turn yellow over time, and is 100% free of toxic byproducts.

4. Co-Extrusion: Radiopaque Lines and Multi-Durometer Profiles

Modern product design often requires more than a simple tube. Reemane is equipped for complex Co-Extrusion, which involves feeding two different types of silicone through the same die simultaneously.

• Medical Applications: We can co-extrude a solid Barium Sulfate (radiopaque) stripe down the length of a transparent catheter, allowing it to be visible under X-ray.
• Industrial Applications: We can co-extrude a highly conductive carbon-silicone strip alongside standard insulating silicone for EMI shielding, or combine a rigid silicone base (70 Shore A) for mounting with a soft silicone sponge lip (20 Shore A) for sealing.