Numerous industrial processes have an inherently high risk potential. Special pressure switches support the safety of individuals and the environment. Example: the vulcanisation of tyres for motor vehicles. To monitor this technique, leading manufacturers utilize the model MW switch from WIKA with SIL 2 rating.
Why such a pressure switch is essential for safety in this application is shown by way of a look at the process: In a steam-heated press, the raw tyre is first filled with warm water to adapt it to the inner shape of the press. Then, consuming pressures of around 24 bar and temperatures of 150 �C to 170 �C the vulcanisation itself occurs. In the process, with the addition of sulphur, the tyre is given its elastic and robust final shape. However, if there is no appropriate monitoring, overpressure can occur in the curing press without warning. If this happens, the danger of boiling hot steam escaping is high. To rule out such an occurrence, tyre manufacturers generally use pressure switches to guarantee the safety of the process.
The model MW pressure switch with SIL 2 rating has been developed for safety-relevant applications, such as tyre vulcanisation.
Control of overpressure and interlocking
The instruments fulfil two functions at once: On the main one hand, they intervene in case of overpressure, and on the other hand, they control the internal interlocking of the curing press to avoid it from opening accidentally before vulcanisation is completed. The process is finished as soon as a preset pressure value is reached. Then the pressure switch lifts the lock. This mechanism is continually in motion in high-throughput automatic tyre production. Due to this fact, the switch is continually being loaded. Consequently, it must have an extended service life at this critical point. Premature wear would otherwise lead to an unscheduled shutdown of the plant.
Lowest failure probability
Tyre manufacturers therefore require pressure switches with distinct robustness and safety. Because of this, WIKA is rolling out the model MW pressure switch for safety-relevant applications such as for example vulcanisation. As a mechanical device, the model MW will switch without reliance on any energy supply, a significant safety aspect. A SIL 2 rating relative to the IEC 61508 standard certifies the functional safety of the pressure switch. Its operational safety can be SIL 2 certified. Thus, the expected service life is approximately 90,000 pressure cycles and switching operations. The chance assessment of the model MW relative to EN ISO 13849-1 by an external certification resulted in the best performance level ?PL e? (lowest failure probability).
Microswitches, also with argon filling
All model MW instruments have microswitches that switch electrical loads around 250V AC, 20 A directly. For certain applications, microswitch versions with argon filling offer an additional boost to safety and service life. The gas reduces oxidation, protects against corrosion and prevents sparking. For low switching powers, for example in PLC applications, there exists a variant with gold-plated contacts.
Formula existing plants
The model MW safety pressure switches from WIKA are also suitable for retrofitting. Regarding tyre vulcanisation, they can therefore help to adapt existing installations to the specifications of DIN EN 16474, that was amended in 2015. This standard obliges tyre manufacturers to use all new machines with improved safety technology. The regulation is supposed to prevent risks of danger in the long term.
Note
More info on the model MW pressure switches and their safety features can be found on the WIKA website. In case you have any questions, your contact will gladly assist you to.
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