Production of rubber suction cups using microwave vulcanization

Microwave is an electromagnetic wave with a frequency in the range of 300~3000MHz (megahertz). Because of its high frequency, it is also called ultra-high frequency (high frequency is not less than 0.5MHZ), and its wavelength is 12.5Cm and the length of radio waves. (1~103m) is relatively short and micro, so it is also called microwave. The biggest feature of microwave is that it can penetrate objects with poor conductivity and generate heat inside. It can be used for preheating, vulcanization and waste rubber desulfurization in the field of suction cups manufacturing.

The rubber suction cup manufacturing industry typically uses two ultra-high frequency currents with a frequency of 915 MHz per second or 2450 MHz with a wavelength of 12.5 Crn. The rubber generates heat in an ultra-high frequency electric field and is therefore suitable for thick-walled or geometrically shaped suction cups. Microwave heating is characterized by rapid heating and heating of the rubber from room temperature to 200 ° C within 30 s.

According to this mechanism, a microwave channel device has been designed to rapidly heat up to the vulcanization temperature as the suction cup semi-product passes. The microwave channel is equipped with two circular waveguides (power 25kW) and a magnetron. The rubber can generate intense rotational vibration in the electric field to obtain heat.

The characteristic of microwave heating is that heating starts from the inside, and microwave vulcanization can avoid the difference in the degree of vulcanization of the inner and outer layers. Due to its temperature up to 200 ° C, it is particularly suitable for production lines with short vulcanization processes. Such continuous production lines used to use a low melting point alloy bath, a common molten salt bath, steam, and glass beads as a heating medium. However, these methods often have disadvantages such as large deformation and surface contamination (cleaning). In contrast, the microwave heating cycle can be shortened by 1/3, the equipment footprint is small (due to the shortened equipment length), and the manufacturing cost is also reduced. It has been determined that a microwave continuous vulcanization unit capable of producing 350 kg of rubber suction cups per hour consumes an average of 50 kW, while an equivalent productivity salt bath vulcanizer consumes 180 kW.

The greater the polarity of the compound for microwave vulcanization, the better the heating effect. For this reason, polar rubber species (such as NBR, CR, etc.) are generally selected as the host material. Polarized auxiliaries, such as carbon black (which contains polar groups on the surface), help to increase the polarity of the compound and are therefore suitable for use.

Microwave heating can also be used for desulfurization of waste rubber. Its biggest feature is that the temperature can be adjusted to 250~350 °C, and the desulfurization can be completed in 5 minutes.

In 1987, Goodyear developed the first microwave desulfurization unit, which has been 17 years. The frequency used for microwave desulfurization is the same as that of the microwave continuous vulcanization unit, ie 915MHZ or 2450MHk to the energy consumption level (0.17~0.22kW∙h∕kg) depending on the type of waste rubber.

The advantages of microwave desulfurization are as follows:

1) Energy saving has low requirements on the fineness of the waste rubber particles (6~8mm), while the traditional method requires the fineness of the waste rubber to reach 28-240 mesh.
2) Recycled rubber with high quality and desulfurization by microwave method can achieve more than 80% performance before desulfurization, and high viscosity and plasticity.
3) It is only 500,000 yuan to invest in a complete microwave desulfurization unit.
4) It is not necessary to use softeners, active agents and other raw materials that are easy to pollute the environment, and there is no need to install boilers and smokeless dust.
5) Suitable for a wide range of special synthetic rubbers such as IIR, EPDM.NBR.CR, which are difficult to desulfurize.