I M P R O V E M E N T OF T H E ROLL D R I V E OF T H E C O L D - R O L L I N G T U B E M I L L S

(UDC 621.771.28-23)

B . M . K t i m k o v s k i i a n d A . S . T k a c h e n k o

Insti tute of Ferrous Metal lurgy, Ukraine A c a d e m y of Sciences

Translated from Metai lurg, No. 4, pp. 36-37, Apri l , 1964

The stands of the co ld - ro l l ing tube mil ls are driven by a paired c rank-gear (Fig. 1).

Since the torsion is appl ied to the paired driving gears from one side, this results in a misa l ignment of the stand during operat ion of the mi l l . The direct ion of misa l ignment is changed depending on the direct ion of forces

ac t ing on the stand. As the gears ro l l along the rack and pinions, the tee th can become wedged, which leads to intense wear of the teeth and even to their breakage. Wearing of the tee th can be reduced if between them and

the racks are set gaps which should be as smal l as possible,since large gaps are also undesirable because they lead to the deve lopment of dynamic forces during mi l l operation.

If the resistance of the stand to mot ion were to change smoothly, then the misa l ignment of the stand would also occur smoothly. However, during rot l ing when the stand is in the front or back positions, the stand resistance to mot ion changes abruptly and the stand begins to vibrate around the ve r t i ca l axis, as result of which great dynamic forces arise in the parts of the main drive and rolI drive. This apprec iab ly lowers the service Iife of the units and parts of the mi l l .

An analysis of the operation of the main drive showed that the more rigid the system and the smal ler the gaps in the e lements of the main d r ive , the less wi l l be the misal ignments of the stand. When the connections are worn, the ampl i tude of vibrations increases and the dynamic load on the gears and rack increases. Since as a result of the stand vibrations the gears do not engage simultaneously with the rack, only one driving gear works constantly.

Therefore, we can consider that one gear is sufficient for the roll drive. On the other hand, an analysis of stand

operat ion showed that the ampl i tude of vibrations of the gears of the roils is greater , the farther they are from the rol l ing axis. Therefore, the closer the gears connect ing with the racks are to the center of the stand, the smal ler wi l l be the impacts of the gears on the rack, and the operat ion of the geared pair , racks and gears, wii1 improve. It is evident that the main drive for new mil ls should be designed so that misal ignments of the stand are reduced to a min imum and the driving gears of the rolls are si tuated as close as possible to the roi l ing axis.

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Fig. i. Kinemat ic d iagram of the main drive of the co ld- ro l l ing tube m i l l

On the presently operat ing co ld - ro l l ing tube mil ls each rol l can be engaged through a gear d i rec t ly with the rack, which makes it possible not only to reduce impacts in the gear couplings, but also to reduce the number of gears of the rol l drive from 6 to 2.

Some reconstruction was needed to ensure the proposed engagement , For example , for the KhPT-Sg-2E mi t l this amounted to cutt ing off one gear seat on the upper rol l and the box with the bearings being covered with a l id. On the other end of the rol l was instal led a gear Z = 24 in place of the gear Z = 26. On the lower rol l the neck on one side was cut off from the seat of two gears, and the homer was covered with a lid.

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Fig. 2. Improved roll drive of the cold-rolling tube mill: 1) Frame; 2) phmger; 3, 4) racks; 5) slide; 6) runner; 7) adapter.

On the other side a gear connecting the rolls with a rack Z = 24 was installed in place of the gear Z = 26, and the gear Z = 26 was removed. The roll neck was shortened,and only one seating place was left.

The design of the racks and their attachment was changed to ensure a normal engagement of the rolls and the proper direction of the rotation (Fig. 2). An adapter was made for engaging the upper roll with the rack. The adapter brings the rack closer to the stand and the rack is fastened on it with teeth upward. On the other side the rack is made wider owing to the stem of the attachments.

The proposed modernization of the engagement of the roils with the racks takes the load off the stand and creates favorable conditions for the engagement of the rolls with the racks. A theoretical analysis has shown that the proposed measures considerably reduce the dynamic forces. This is achieved mainly by modernization, viz., individuality of the roll drive and a decrease in the distance from the rolling axis to the gears. Since this distance is reduced, the impacts are reduced. The individuality of the drive excludes the mutual effect of the roils through the gears. Thus, the proposed measure should appreciably facilitate and make cheaper the operation of the cold-

rolling tube mills.

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