This invention relates to an apparatus for rotary compression of hollow parts, in particular of hollow axles and stepped shafts. The notion of "hollow part" is to be understood as a tubular product which has a cylindrical or shaped hole located centrally along its axis, while the notion of "hollow axle or stepped shaft" is to be understood as a product which has steps of different diameters in its longitudinal section as well as a cylindrical or shaped hole located centrally along its axis.

JP-A-59120336 discloses a rolling apparatus, in which two lower rolls are stationary and a third upper roll is movable towards the lower rolls.

Devices for producing hollow parts in metal machining methods have already been developed. They include, for example, skew rolling mills, piercing mills, tube-rolling mills as well as pilger mills for producing tubular parts. A detailed description of mills used for producing tubes has been given in the literature (W. Dobrucki "Podstawy konstrukcji i eksploatacji walcowni," Wydawnictwo Slask, Katowice 1973). The machines described therein are predominantly used for producing all types of tubes, including hollow parts which are characterized in that their external and internal diameters are constant and their length is considerably big when compared to other dimensions - long parts.

The Polish patent specification No. 21345 describes a skew rolling mill with skew rolls used for producing thin-walled drawn tubes, where the product forming process is done with mandrel by means of rotating rolls with skew axes. The apparatus is used for producing parts of considerable lengths and of simple geometry - the internal and external diameter is constant along the whole length of the part.

Cross rolling mills which comprise two working rolls, three working rolls, rolls and concave or flat segments have also been known and used. Cross rolling mills have been described in detail in the literature (Z. Pater, W. S. Weroński "Podstawy procesu walcowania poprzeczno-klinowego," Wydawnictwo Politechniki Lubelskiej, Lublin 1996, pp. 177-188).

The essence of the apparatus for rotary compression of hollow parts, especially of hollow axles and stepped shafts, comprising three drive shafts, a chain transmission, a gear-motor, a hydraulic feed and a hydraulic operator consists in that to a frame, mounted on adjustable vibration isolation anti-slip stands, a skid plate is attached, on which a mill stand comprising a pillar plate with two pillars attached is mounted, inside which a vertically movable slide guided by sleeves in four columnar guides mounted in a clamping plate which clamps the two pillars from above, the slide is powered by a hydraulic operator mounted in the plate and fed by a hydraulic feed, and in the central part of the mill stand three drive shafts, which have working rolls -, the tools-, attached to them, are rotatingly placed, and two of those drive shafts - the lower ones, have their bearing placed in two pillars in such a way that that their axis position cannot be changed, and the third drive shaft, the upper one, has its bearing in the slide which is configured to move down driven by four sleeves and columnar guides, and the three drive shafts with the attached working rolls - the tools -, are is configured to be driven by the chain transmission which encircles the three drive shafts and is provided with hydraulic stretchers which are configured to maintain constant chain tension during the shift of the slide with the upper drive shaft, and the chain transmission is powered by the gear-motor via an intermediate chain transmission.

A beneficial effect of the present invention is that it allows for plastic forming of hollow stepped shafts and axles within one operation. The forming tools comprising three rolls attached to the apparatus have a simple construction and are relatively cheap to manufacture. The apparatus has a simple and compact construction which does not require special foundation engineering, owing to which its position can optionally be changed if necessary.

The apparatus allows for hollow parts to be compressed with or without mandrel, owing to which relatively accurate cylindrical and shaped holes can be obtained. Another beneficial effect of the apparatus is its universality, as the present apparatus can be used for compressing hollow parts made from all metals and alloys which are suitable for metal machining.

The apparatus for rotary compression of hollow parts, especially of hollow axles and stepped shafts, has been schematically presented in three figures, where Figure 1 shows an axonometric projection, Figure 2 shows the apparatus front view, and Figure 3 shows section A-A of the apparatus.

The apparatus for rotary compression of hollow parts, particularly of hollow axles and stepped shafts, comprises three drive shafts 7a, 7b and 7c, a chain transmission 15, a gear-motor 13, a hydraulic feed 10 and a hydraulic operator 11. To a frame 1, mounted on adjustable vibration isolation anti-slip stands 12, a skid plate 2 is attached, on which a mill stand comprising a pillar plate 3, with two pillars 4 attached to it, is mounted. Inside the pillars 4 a slide 6 moves vertically guided by sleeves 19 in four columnar guides 18 mounted in a clamping plate 5, which clamps two pillars 4 from above. The slide 6 is powered by the hydraulic operator 11, which is mounted in the plate 5 and fed by the hydraulic feed 10. In the central part of the mill stand, three drive shafts 7a, 7b, 7c are rotationally placed and they have working rolls 8 - the tools attached to them, two drive shafts 7a and 7b - the lower ones, have their bearing placed in two pillars 4 in such a way that their axis position cannot be changed. The third drive shaft 7c, the upper one, has its bearing in the slide 6, which moves down driven by four sleeves 19 and the columnar guides 18. The three drive shafts 7a, 7b, 7c with the attached working rolls 8 - the tools, are powered by the chain transmission 15, which encircles three shafts 7a, 7b, 7c and is provided with hydraulic stretchers 14, which maintain constant chain tension during the vertical shift of the slide 6 and the upper drive shaft 7c. The chain transmission 15 is powered by the gear-motor 13 via an intermediate chain transmission 16.