In the rubber processing industry, the scaling problem of rubber mold is a common phenomenon. During the vulcanization process, a layer of sediment is formed on the die wall and gradually accumulated in the subsequent production cycle.

Causes and substances of scaling in rubber mould

The sulfur-containing compounds separated from the compound are spot like solid substances.

The water contained in the rubber compound combines with the mold metal surface during vulcanization to form Brown corrosion.

The residue left on the surface of the mold cavity after vulcanization of solid release agent (such as talc powder and stearate).

Mechanism of scaling in rubber mould

It is learned that zinc sulfide is the most annoying reaction by-product causing scaling in the vulcanization process for various sulfides (and zinc oxide) contained in polymer rubber mixture. No semi permanent release agent or permanent (metal) coating can avoid this deposition.

Scaling is initially caused by zinc sulfide (inorganic deposit) attached to the mold and forms a gray deposit. As a function of temperature, the low molecular weight components of the mixture adhere to the microcrystals of zinc sulfide and cause the second stage of deposition (organic deposition). Oxidation products are formed within a certain time and cause carbon deposition.

By understanding the causes of rubber mold scaling and the internal mechanism of zinc sulfide micro crystal formation on the metal surface of the mold, it is possible to produce a method suitable for the current processing process to reduce the formation of zinc sulfide, so as to prevent rubber mold scaling. Through the study of the causes of scaling, it is possible to reduce this phenomenon.

Prevention of scaling in rubber mould

There are two possible solutions to prevent or reduce the formation of dirt: changing the composition of the mixture or coating (improving the surface of the mold).

1. Rubber mixture

Reducing the level of zinc oxide in rubber mixture can reduce the scaling of rubber mold; Using nano-sized ZnO can eliminate or reduce mold scaling. However, more research must be carried out in order to achieve optimal mechanical and dynamic performance; Other metal oxide catalysts can not solve the problem of mold scaling; Alternative catalysts, such as amine or MFAs, can also reduce mold fouling. However, those catalysts / accelerators have a bad smell and some are toxic. In addition, in order to obtain a considerable vulcanization rate, another zinc catalyst (zbec) must be used.

Change the composition of the mixture to reduce mold scale

Mold scale caused by zinc oxide or vulcanization must be reduced or eliminated. Most deposits are associated with high levels of sulfide and zinc oxide, which are usually used in tire rubber products. In terms of volume, tires are the largest type of rubber products in the world (up to 75%). Therefore, most experiments are carried out with the mixture of NR / BR compounds and SBR compounds commonly used in tire production. In the aspect of reducing mold scale by changing the composition of the mixture, the effects of zinc sulfide, short-term vulcanization experiment and compound composition were investigated.

2. Coating reduces mold scale

Electrochemical reaction is not involved in the solution of mold scaling problem; Metal coating is not helpful to reduce mold scaling, and a closed barrier must be formed on the mold surface; Plastic coating, such as PTFE, can solve scaling. However, due to the problem of manual laying and spatial instability, these coatings can not be applied to tire molds; Magnetite (Fe 3O 4) coating is a possible candidate. The results should be very promising, but in order to confirm the ability of magnetite (Fe 3O 4) coating to prevent scaling, experiments must be carried out on tire molds.

Cleaning treatment method of rubber mould after scaling

Reasons for cleaning rubber mold:

The rubber is crosslinked and shaped by heating in the closed mold cavity. Dirt is inevitably generated on the mold surface for a long time, and the amount of dirt increases with time, which will not only affect the product appearance, but also affect the dimensional accuracy of the outer edge of the product with the increase of dirt thickness. Therefore, in order to ensure the normal use of the die, it must be cleaned regularly.

Mold cleaning method:

Manual descaling, metal brushing, abrasive skin surface force friction

Mechanical descaling, sand blasting, water grinding, etc

Chemical descaling, special mold washing water cleaning

In the alkaline electrolytic cell, water is spot decomposed into hydrogen and oxygen, bubbles are formed on the metal surface, and die scale is washed away

Ultrasonic descaling makes use of the principle of frequency and wavelength to shake off the dirt in the mold cavity. The effect is better when combined with mold washing water

In situ cleaning, mold cleaning with mold glue, mold glue can be covered on the mold surface during vulcanization, and mold scale can be removed