TECHNOLOGY FOR MANUFACTURING THE MAGNETIC CORE OF A SMALL-SIZED STEREOBETATRON FROM THIN STEEL STRIP

V. I. Kudryavchenko

(Presented by the scientific seminar of the Research Institute of Nuclear Physics.)

At the Research Institute of Nuclear Physics at TPI, a small-sized 3-MeV stereobetatron operating at an increased frequency has been built. Its magnetic core is made of E310 electrical steel strip 0.08 mm thick, which substantially changed the technology for manufacturing the accelerator magnetic core [1].

The general view of the stereobetatron magnetic core is shown in Fig. 1. It has the form of a toroid and consists of two semitoroidal yokes 1, two pairs of profiled pole pieces 2, and two plate blocks 3.

The yokes consist of five semicircular sections of different diameters, glued together and forming, in cross section, a stepped shape approximating a circle. To manufacture the rings that form the yokes, a machine for winding the cores of large pulsed transformers, developed at TPI [2], was used.

Fig. 1.

The main attention in constructing the stereobetatron magnetic core was devoted to the question of coating the strip steel with an insulating varnish layer, since an excessively thick film considerably reduces the coefficient of filling of the magnetic core with steel. Therefore, the thickness of the insulating film was monitored continuously during the winding of the steel rings.

The technological scheme for winding the rings for the yokes of the stereobetatron magnetic core is shown in Fig. 2 and represents a continuous cycle from mechanical cleaning of the steel strip to obtaining a finished—

part. From reel 1 the strip is unwound through rubber clamp 2, which cleans it of powder and oil with which it is treated at the factory. After mechanical cleaning, the strip enters tank 3, filled with a 10% solution of calcined soda heated to (70–80)°C, and is rinsed in tank 4, containing clean hot water at (85–90)°C. To prevent carryover of the soda solution from tank 3 into tank 4, a removable block 5 with felt strips pressed into it is installed between them. The same block is provided at the outlet

Fig. 2.

from tank 4 and serves to remove water from the surface of the strip. Final drying of the strip is achieved by passing it over heating element 6. The degreased, washed, and dried steel strip enters tray 7 with a varnishing device, filled with Bakelite varnish. The consistency of the varnish is selected so that the coating thickness does not exceed 0.01 mm on both sides. After being coated with varnish, the strip is dried in heating device 8 and, passing through brake 9, which creates strip tension during winding, is wound onto special mandrels 10. To ensure that the finished cores could be easily removed from the mandrels, the latter were first wrapped with several layers of oiled cable paper.

The steel rings obtained were baked in a furnace at a temperature of 130–150°C for 2–3 hours and cut along the diameter on a milling machine. The half-ring sections were glued together with Bakelite varnish, with a layer of calico impregnated with varnish placed between them beforehand, protecting them from short-circuiting. Subsequently, the glued yokes at the joints of the half-rings were coated with epoxy resin, and the end faces were tightened with bandage rings made of textolite. As a result, a compact monolithic yoke structure was obtained without tie rods or bolts.

In manufacturing the profiled poles, an involute method was used for making the poles from plates of identical length [3]. For this purpose, strips 192 mm long were cut from steel strip 32 mm wide. Since the length of the strips is many times greater than their width, the pole assembly technology consisted of two stages: first, preliminary assembly of the poles was carried out on a special mandrel with subsequent tightening by a bandage, and then the pole was pressed through a conical mandrel to the required size into a special bandage.

Before assembly began, the steel strip was washed with gasoline, dried, and a thin film of Bakelite varnish 0.01 mm thick was applied to its surface. Assembly of the pole was carried out as follows: in a special casing, the plates coated with an insulating layer were placed around a toothed mandrel. The grooves in it are necessary for

so that the plates would not spread apart during tightening; therefore some of the plates were made 3 mm longer than the others. After the plates had been assembled in the mandrel, a banding tightening ring was slipped over them. The plates, tightened by the banding ring, were inserted into a conical mandrel whose outlet opening has the size of the pole, and through it they were pressed first into a steel band and then into a textolite one. The internal toothed mandrel was knocked out of the finished pole, after which the pole was baked at a temperature of 118–120° for 4–5 hours. After baking, the central toothed opening in the pole was bored on a lathe and filled with a central insert assembled from parallel plates (Fig. 3).

Fig. 3.

The central inserts and the “biscuits”—central liners—were made according to the following technology: pre-cut, ground, and varnished plates were assembled in a special fixture—a faceplate—and baked in a furnace. The well-tightened rectangular packs were machined on a lathe to the required dimensions. The central inserts thus obtained were pressed into the central openings of the poles, and on the finished pole blocks a profiled surface corresponding to that selected on the flat model was turned on a lathe.

The surface of the “biscuits” was ground to the required dimensions on a surface-grinding machine, after which holes needed for tightening the biscuit block were drilled in their centers.

The proposed method for manufacturing the parts of the magnetic core does not require the making of dies individual for each installation, and the winding machine can be used repeatedly for constructing yokes of stereobetatron magnetic cores with different geometric dimensions. Winding the yokes on the machine and the evolvent method of manufacturing the poles made it possible to make them from steel 0.08 mm thick, with a high steel filling factor equal to 0.85, and to simplify the manufacturing technology.

REFERENCES

1. V. I. Kudryavchenko, V. A. Moskalev. Development of a small-sized stereobetatron for high frequency (present collection).
2. N. I. Vorob'ev. A machine for winding cores of large dimensions. Proceedings of the III Interuniversity Conference, Tomsk, 1961.
3. Šipik. Czechoslovak patent, class 21, item 36—(H—05), No. 106478. Filed 9/VI-1961, published 15/II-1963.