The process that connects
The stator and rotor cores of electrical machinery are manufactured using thin sheets stacked together in order to minimize eddy current losses. The laminations must be joined in order to create a stable core. A general distinction is made between techniques integrated into the punching process (interlocking, spot bonding or face bonding) and those downstream from the punching process (welding, clamping, conventional bonding). Using Backlack as a bonding medium minimizes processing effects, especially the effects on magnetic properties.
Face bonding is a technique used in the production of stator and rotor cores
Fully processed and Backlack-coated electrical steel is used as the basis for adhesive-bonded electrical steel cores. After the laminations have been punched, they are subjected to temperature and pressure to initiate the bonding reaction of the Backlack varnish. Homogeneous pressure distribution within the stack is crucial to ensure uniform contact between the laminations and to minimize the risk of varnish leakage caused local pressure increase. The curing reaction of the Backlack varnish is achieved by heating to curing temperature. Homogeneous temperature distribution is essential because the entire stack must achieve bonding temperature.
The processing windows for processing the Backlack varnish in the voestalpine portfolio can be found in the Backlack Varnish Processing Guidelines.Backlack Processing Guidelines PDF4.19 MBeng-GB
In as-delivered condition, the varnish supplied by voestalpine is in the so-called B state. The varnish is applied to the steel strip in the desired layer thickness and is physically dried but remains chemically reactive. This reactivity is important for bondability at the customer.
Additional requirements are mandatory to ensure bondability during storage and transport. More detailed information can be found in the Backlack Varnish Processing Guidelines.Backlack Processing Guidelines PDF4.19 MBeng-GB
Key factors in the transport and storage of Backlack varnish-coated electrical steel strip are as follows:
- A limit temperature of +40 °C must not be exceeded. This limit temperature may be reached for a maximum of one month. The recommended storage temperature is +23 °C.
- The period of maximum storage is six months, beginning at the time the material is supplied by voestalpine.
- Dry storage must be ensured, and condensation must be avoided.
Storage in delivery condition
The following diagram illustrates adhesive strength as a function of storage duration in the B state.