What is heat shrink tubing crosslinking?

The Raychem Corporation pioneered the development of heat shrinkable products back in the 1960’s. Raychem developed new types of plastics and elastomeric materials that were engineered to possess unique properties. This was achieved by modifying the raw material using radiation technology – a process that is now known as crosslinking (or cross-linking, x-linking).

The original crosslinking process worked by bombarding the raw material of the plastics with high energy electron beam radiation. The radiation caused the long chains of polymers to link together, altering the chemical structure of the material and increasing the molecular mass. Although the materials are usually crosslinked through the use of electron beams, it can also be achieved chemically using butperoxides, or moisture.

The process for making heat-shrink tubing is as follows:

1. The raw material is chosen based on its properties. The material is often compounded with other additives (such as colorants, stabilizers, etc.) depending on the application. A starting tube is extruded from the raw material.
2. The extruded tube is then taken to a separate process where it is cross-linked, usually through radiation. The cross-linking creates a memory in the tube.
3. The tube is heated to just above the polymer’s crystalline melting point and expanded in diameter, often by placing it in a vacuum chamber.  Whilst in this expanded state it is rapidly cooled.
4. Later, when heated (above the crystalline melting point of the material) by the end user, the tubing shrinks back to its original extruded size.

As previously mentioned many of the material properties can be improved by crosslinking, for example:

• Mechanical properties, such as tensile strength
• Scratch resistance
• Performance at higher temperatures, often with an increase in the melting temperature
• Resistance to chemicals because of lowered solubility in organic solvents
• Gas permeation reduction
• Shape memory retention. Certain plasyic types (elastomers etc) may be crosslinked to a slight degree to give them “memory” – they will return to their original shape after being expanded.

Typical advantages of crosslinked materials include:

• High Flexibility
• Flame Resistance
• High Dielectric Strength
• Cold Flow Resistance
• High Temperature Stability
• High Mechanical Strength
• Chemical Resistance
• Abrasion Resistance

The most commonly used product categories for these enhanced wonder plastics are Single Wall Tubing’s, Raychem’s RNF-100 and RNF-3000 being the quality standard bearer.

Dual Wall Tubing’s with ATUM, HTAT and SCL leading the way in this category, and Elastomeric Tubing’s with RW-200 and DR-25 key products to the aerospace and defence markets.

This technology was originally developed in the 1950’s since then these basic product categories have been refined, enhanced and developed. Careful synthesis of materials provided products which could perform selective and very specific purposes. The addition of adhesives, shielding facilities, fibre and fabric materials ensures that the products are capable of performing in the most sophisticated installations.

Typical uses include:

• Identification via colour coding
• Strain relief
• Primary electrical insulation
• Cable jacketing and repair
• Component encapsulation
• Waterproofing
• Mechanical protection
• Corrosion protection
• Packaging
• Environmental protection

PMG Company are uniquely placed, we can offer all the Single and Dual Wall products manufactured by Raychem/TE Connectivity either supplied TE Branded or where commercial constraints are paramount PMG can offer our own Plastronic brand equivalent.