This invention relates to a method of rolling a ring from a metal blank according to the preamble of claim 1. An example of such a method is disclosed by GB 1 329 251 A.

The blanks are typically of standard steels such as wrought steels, but could comprise other metals or alloys. They can be rolled to form rings having many uses, particularly bearing components. The invention may also be applied to powder metal blanks.

In rolling processes of the kind described above, the metal blank is mounted on a mandrel located between two forming rolls either side of the mandrel axis. Growth control rolls are disposed above and below the mandrel axis to engage the blank as it turns between the forming rolls. Four growth roll controls are used; one directly above another between the mandrel axis and each forming roll. This process has produced good results with very good quality roundness in the final product. However, the process does generate lobes. The present invention seeks to further reduce the generation of lobes, and thereby further improve the roundness of the ring rolled product.

This is achieved by the features of claim 1. Preferred embodiments are described in the dependent claims. According to the invention, the growth control rolls are arranged above, below and on either side of the mandrel axis to generate a less symmetric pattern of forces acting on the ring blank with more of the horizontal forces being resolved between the upper or the lower growth control rolls and the forming rolls. The preferred arrangement has the pair of upper growth control rolls with their axes parallel to but closer than those of the lower rolls. However, for some applications of the invention the lower pair of growth control rolls can be closer together than the upper pair.

In the method of the invention the upper and lower growth control rolls will normally be arranged with their axes equidistant on either side of the vertical plane containing the mandrel axis. In one variant of the invention, the two upper growth controls can be replaced by a single growth control with its axis disposed directly over the mandrel axis. In this variant, the upper growth control does of course apply only vertical forces to the ring blank with all the horizontal forces being resolved between the lower growth control rolls and the forming rolls. The disposition of the growth control rolls is preferably selected to minimise the length of unsupported blank between peripherally adjacent rolls (forming rolls and growth control rolls).

In the methods of the invention, the mandrel axis and the forming rolls are in the same horizontal plane. However, in some applications of the invention there can be some benefit in locating the mandrel axis below the axes of the forming rolls so that there is a vertical component of the forces between the forming rolls and the ring blank.

The invention will now be described by way of example and with reference to the accompanying schematic drawings in which:

• Figure 1 shows a cross-section through ring rolling apparatus adapted to practice the method of the invention; and
• Figure 2 shows an alternative apparatus to that of Figure 1 in which the upper growth controls,are replaced by a single roll.

As shown in Figure 1 a metal blank (2) is mounted on a mandrel (4) disposed between two forming rolls (6). The axis (8) of the mandrel (4) is located below the horizontal plane containing the axes (10) of the forming rolls, the line between the axis (8) and each forming roll axis (10) subtending an angle β with the horizontal. Angle β is normally no more than 10°, and typically will be no more than 5°. Effective performance has been achieved with angle β at around 1°.

Two lower growth control rolls (12) are disposed beneath the mandrel (4) to engage the metal blank (2) from below. The rolls (12) are arranged symmetrically on either side of the vertical plane containing the mandrel axis (8); equally spaced from that vertical plane. The rolls (12) are mounted on a framework (14) enabling their spacing to be adjusted. It will be appreciated that the diameter of the lower growth control rolls may need to vary depending upon the spacing between them, to avoid interference with either each other or the forming rolls. The critical factor is of course the line of engagement with the blank on the mandrel, and the angle θ subtended between the line of engagement and the mandrel axis and the horizontal. This angle θ is typically in the range of 50° to 70°, and normally at least 60°.

Two upper growth control rolls (16) are mounted in a framework (18) over the mandrel axis for engaging the blank (2) from above. These rolls (16) are located closer to each other than are the lower growth control (12) but once again their spacing can be altered by movement of their axes in the framework (18). The rolls (16) are also arranged symmetrically on either side of the vertical plane containing the mandrel axis, and the angle θ' subtended by the line of engagement of the roll (16) and the blank (2) and the mandrel axis relative to the horizontal will of course be greater than the angle θ defined in the location of the lower growth controls. The angle θ' is typically in the range of 50° to 80°, normally in the range 65° to 70°.

As noted above different sized growth control rolls can be used depending upon the geometry of the desired roll arrangement and of course the size of the ring to be rolled on the forming rolls. Because of the forces involved, the diameter of the growth control rolls should be as much as the geometry allows. The location of the growth control rolls relative to the blank is normally selected such that the spacing between the lines of engagement of the upper rolls (16) is substantially equal to the spacing between each upper roll and the line of engagement of the adjacent forming roll (6). The lower growth control rolls (12) are located in a similarly symmetric arrangement.

Figure 2 shows a modification of the arrangement in Figure 1 in which the upper growth control rolls (16) are replaced by a single roll (20). In other respects the arrangement of forming and growth control rolls is the same as in Figure 1.