TWI Industrial Member Report Summary 245/1984
By P J Blakeley and A Sanderson
It is well known that magnetic fields can seriously interfere with welding processes which utilise electric arcs or electron beams. This report deals with the reduction of such residual fields to levels which enable welding to proceed successfully, taking note of the fact that some welding techniques are more tolerant to magnetism than others. Apart from heat treatment above the Curie temperature, the available demagnetisation techniques involve swamping the component in an oscillating or reversing magnetic field. The frequency of the reversing magnetic field used is of vital importance since it determines the depth in the material to which demagnetisation will take place. Three types of commercially available demagnetising units are described and details are given of an iron-cored system which has been constructed to handle a large range of component shapes and sizes. Results of trials involving 16 and 100mm steels are given.