Most spring applied brakes are designed for operation in dry conditions. Brakes should be protected from water, and particularly grease and oil which can cause a large drop in torque. Ambient temperature range is -20°C to +40°C. Below zero care should be taken to protect the rotor and armature plate from freezing. Cold Climate Version (CCV) brakes are available for outdoor and extreme conditions down to -40°C as may be encountered in cold stores and wind turbines.
Brakes can be used in potentially explosive atmospheres to ATEX Zone 11 in holding duties, explosion group 11 and temperature class T4.
Brakes can be protected from severe environments by adding a seal on the outside diameter and a shaft seal. When shielded from water jets this approaches IP65 protection. Alternatively, a metal sealed enclosure can be used to achieve IP65 or higher. Spring applied brakes with protection to IP69 are available for the marine environment.
Lifetime and Wear
Spring applied brakes require regular inspection and maintenance by qualified personnel. Qualified personnel are defined as persons who, because of their education, experience, training and knowledge including the corresponding standards and regulations, are authorised by the persons responsible for the safety of the plant to perform the required actions. They should be able to recognise potential hazards.
In applications with dynamic braking, spring applied brakes will exhibit wear on the rotor. This can easily measured at the working air gap between the stator body and the armature plate when the brake is engaged. As new, air gaps range from 0.1 to 0.5mm depending on brake size and they can be allowed to increase by a factor of up to 150% due to wear. At that point the brake is required to be reset back to the initial air gap. This adjustment can be done up to 5 times before the rotor has to be replaced.
The wear rate depends on the operating conditions, particularly the frequency on engagement, rotational speed and the loads. It is not possible to accurately predict the required frequency of inspection and maintenance although in some cases an estimate can be made. It is recommended that initially inspection be done after short periods and a long term schedule be based on actual experience.
Safety sensitive applications
Spring applied brakes are not truly failsafe although they are highly dependable. Lack of maintenance, incorrect sizing, overload or long-life fatigue can cause unpredictable failures in extreme circumstances. In safety sensitive applications spring applied brakes should be selected with a suitable service factor, usually 2.0 of higher. For machine safety evaluation to DIN EN ISO 13849-1, there are B10 and B10d values available for INTORQ brakes available from Lenze. A data sheet can be downloaded from the website www.techdrives.co.uk.
Brake safety can be enhanced by choosing optional micro-switch monitoring of status. This can be used to detect a wear limit or operational malfunction.