Ceramic-Coated Silicone Rubber Cable Manufacturing Process: Reference Parameters for The Entire Process—Vulcanization, Extrusion, And Curing

Notes:

1. During vulcanization, the open mill must be supplied with cooling water, and the temperature must not exceed 50°C;

2. Do not over-knead, as this may cause the compound to stick to the rollers, making it difficult to unroll;

3. Compound without vulcanizing agent can be stored in a cool, shaded place for 1–2 years;

4. Compounds to which vulcanizing agents have been added can be stored in a cool, shaded place for 7–30 days in summer and no more than 60 days in winter;

5. Compounds stored for too long may harden due to structural changes; this is a characteristic of silicone rubber and does not indicate a quality issue. Simply place the compound in the open mill, re-knead it until it coats the rollers, then unroll it for continued use.

II. Extrusion

Equipment: Silicone rubber wire and cable extruder. It is recommended to select an extruder with appropriate extrusion pressure; choose a die suitable for the specifications of the wire and cable being extruded, and install and commission the die properly. It is recommended that the sizing section of the extrusion die be approximately half the size of that of a standard rubber extruder. Additionally, the mandrel and die opening should be mirror-polished. Reference: Cold extrusion must be used; the temperatures of the extruder’s screw, die head, and machine body must be kept below 30°C and must not exceed 50°C. The lower the cooling water temperature, the better. This is particularly important for vulcanized (rubber-insulated) wire and cable production lines, where the die head must be kept at a very low temperature; otherwise, the rubber compound is prone to melting and clogging the die head. The length of the die sleeve (orifice) sizing section is shorter than that of standard rubber or silicone rubber wire and cable extrusion die sleeves (orifices). The recommended sizing section lengths are 1.5–3 mm for small-cross-section wires and 2–5 mm for large-cross-section cables; these can be adjusted based on actual conditions. If the extruded surface appears rough or uneven, adjust the distance between the die sleeve (or die orifice) and the die core. At the same time, ensure that the extruded compound is slightly larger than the diameter of the finished wire, and that the die sleeve (or die orifice) is slightly smaller than that used for standard silicone rubber wires and cables. Final adjustments should be based on on-site commissioning during actual production, and the die sleeve (or die orifice), die core, conductor, and designed wire diameter must be properly matched.

Note: The extruder must not be heated and must be equipped with a cooling system; extrusion machines cannot be used for silicone rubber production because they lack cooling systems and vulcanization equipment, and there is a significant difference in extrusion pressure between plastic and rubber extruders.

III. Vulcanization

Equipment: Hot-air vulcanization oven or warm-water vulcanization. For warm-water vulcanization, a water tank with a temperature of 95°C or higher and a length of at least 12 meters is recommended. For hot-air vulcanization ovens, an oven with at least 12 zones is recommended, with a vulcanization temperature of 160°C to 230°C; specific settings should be determined based on the extrusion speed and cable specifications. It is recommended to increase the temperature gradually.

Reference:

1.Set up an electrically heated drying tunnel (or oven) with the following temperature zones: Zone 1 at 140–170°C, Zone 2 at 155–185°C, Zone 3 at 170–175°C, Zone 4 at 175–180°C, and the final section at 240–280°C. Alternatively, vulcanization temperatures for each section may be set based on the specific equipment model and cable structure. The principle is to ensure that the product cross-section has no micro-pores and that no bubbles form along the length of the wire or cable. If bubbles do form, first lower the temperatures of the first and second sections by 5–10°C, then reduce the temperature of each subsequent section by 5–10°C until no bubbles appear;

2.Turn on the extruder cooling water, clean the feed inlet, screw, and die head, and confirm that there are no foreign objects or rubber particles inside before beginning to feed the material. Feed the material evenly to ensure uniform extrusion; it is best to use a forced feeding device, also known as a side pressure roller. Adjust the eccentricity and start extrusion; begin at a slow speed and gradually increase the speed; 

3.If the extruded surface is rough, adjust the specifications of the die core and die sleeve, as well as the distance between them. Also, adjust the extrusion pressure, the corresponding take-up speed, and the extrusion speed.

Beyond the manufacturing process, material selection is equally critical.

The flame-retardant performance of ceramicized silicone rubber depends not only on the precise control of formulations and process parameters but is also closely related to the flame-retardant-ceramicization system used. YinSu Flame Retardant provides tailored ceramicization and flame-retardant solutions for different substrate systems:

YS-TCG5 for silicone rubber systems: Offers excellent compatibility with HTV matrices and uniform dispersion; 2mm test strips achieve UL94 V-0 self-extinguishing upon removal from the flame; withstands 30 minutes of flame erosion at 1000°C+ without burn-through; provides thermal insulation performance >600°C; suitable for high-end fire-resistant sealing applications in aviation, defense, rail transit, and nuclear power; recommended base rubber: Flame retardant = 1:0.55–0.7 ratio.

95-TC7 for polyolefin cables: Compounded masterbatch made by coating red phosphorus with a ceramicized ablation-resistant agent; upon exposure to fire, the red phosphorus first provides gas-phase flame retardancy, while the ceramicized component simultaneously sintered into a dense ceramic shell that does not melt or drip, meeting fire resistance ratings such as BS 6387 CWZ. The masterbatch can be directly dry-blended without altering existing extrusion processes