To meet the demand for arrangements to have magnetic yokes correctly welded, the background art has proposed that the press distortion be minimized by using frames which are made as rigid as possible and driven by a large number of hydraulic cylinders placed at short intervals from one another. As an example, a prior press for welding yokes with the above-specified dimensions has 13 hydraulic cylinders which are arranged to act on the pressers with the interposition of respective metal blocks effective to spread the pressing load over the relevant pressure area of the corresponding cylinders.
Thus, the design trend is toward "segmenting" the press into sections of reduced length which can be more easily handled versus induced deformations.
In practice, this prior press operates as if the pressers acting on the half-yokes were split into contiguous sections correspondingly with the areas affected by the respective cylinders, thereby achieving decreased deformation of a yoke being pressed by virtue of a smaller spacing of the cylinders.
Each cylinder, moreover, is suspended above the yoke by means of a portal-type frame the pillars whereof extend upright from the press bed.
A first drawback of this prior press design is that the uniformity of the half-yoke pressing is directly dependent on the machining accuracy of the various press components as well as, of course, on its overall rigidity, particularly as concerns the pressure surfaces and pressers, and on the various hydraulic cylinders applying an even pressure force. In view of the considerable length dimension of a yoke, it is evident that it is quite difficult to ensure uniform pressing conditions over the entire length of the half-yokes.
Further, since welding along the two opposed generatrix lines of the yoke is a time-consuming operation, it becomes necessary to ensure that the pressure inside the hydraulic cylinders be kept throughout its duration within very narrow limits of variation, possibly by providing pressure accumulators, automatically driven manostat-regulated control units, or some like ancillary equipment.
But not even by providing such items of equipment can an initiated processing step be discontinued, such as at the end of the workday, because no provision is made to ensure that the hydraulic cylinders will keep the necessary pressure on the yoke throughout the break. In addition, such items of ancillary equipment are themselves a source of problems on account of their requiring adjustment and maintenance, and being liable to failure, not to mention the problems of operational continuity brought about by possible power outages.
A further drawback is that the hydraulic cylinders are mounted directly above the yoke being processed, thereby any loss or leakout of hydraulic fluid is apt to foul the yoke to be welded and cause welding problems.
Another problem that accompanies this prior press comes from the dense presence of the pillars which support the cylinders on either sides of the frames. Such pillars greatly hinder access to the yoke under the press, and to the welder heads.
Furthermore, the pillars are in the way of the operators checking that the weld has been correctly made.
The problem underlying this invention is to provide a press for welding magnetic yokes, which is so constructed as to be free of the drawbacks affecting the above-discussed background art.