This invention relates to magnetic transducing heads and in particular to a method of manufacturing magnetic cores for magnetic transducing heads.
The cores of magnetic transducing heads are often formed of ferrite magnetic elements which are bonded together by a non-magnetic material, such as glass, in such a manner that there is a non-magnetic gap between the ferrite elements. The gap is usually filled by the non-magnetic bonding material in order to reinforce the edges of the ferrite members and to prevent the ingress of foreign matter into the gap. In use of the magnetic head, the gap co-operates with a magnetic record medium for recording data onto the medium and/or for reading data recorded on the medium.
In the manufacture of such cores, two magnetic members, both of which may be of channel section or one of channel section and the other of rectangular section, are lapped to provide planar polished gap defining surfaces. Spacers are deposited on the gap defining surface or surfaces of one of the members and the members are assembled with their respective gap defining surfaces in confronting relationship and spaced apart by the spacers. Pressure is applied to the members to maintain them in this position so that the gap between the gap defining surfaces is determined by the spacers. Glass in the form of powder is applied as a slurry adjacent the gap and the assembly is heated to a temperature sufficiently high to cause the glass to flow and to enter and fill the gap between the gap defining surfaces. When the assembly has cooled, the glass bonds the magnetic members together. Generally the magnetic members are larger than the thickness of the required cores and therefore the assembly is cut into a number of slices to provide a plurality of cores, those slices containing the spacers being discarded.
The operating characteristics and performance of a magnetic transducing head depends upon the dimensions of the non-magnetic gap in the magnetic core and particularly upon the length of the gap. In the case of magnetic heads intended for operation with very high frequency signals the length of the gap may be of the order of 0.00005 inches and hence very small variations in the length of the gap can represent a large percentage change and hence result in a change in the characteristics of the head incorporating the core such that the head characteristics are outside the acceptable tolerance limits.
Generally the spacers for setting the length of the non-magnetic gap have been formed of metal such as copper or gold deposited at each end of the gap defining faces of one of the magnetic members. This has been satisfactory when using a relatively soft glass for bonding and filling the gap between the members because such glass flows at a relatively low temperature. However it is desirable to use a glass, for filling the gap, which has a resistance to wear which is more nearly comparable with the resistance to wear of the ferrite of which the magnetic members are formed. Therefore it is required to use a harder glass and such glasses require a much higher temperature to cause their viscosity to be reduced to a value at which the glass will flow into and fill the gap without the formation of voids in the glass filling. It has been found that at the higher temperatures necessitated by the glass, the conventional spacers tend to deform with the result that the length of the gap cannot be determined with sufficient accuracy by the spacers of metal.