The present invention relates to a method for heat treatment, e.g. quenching of annular metal blanks, such as bearing rings bearing cups or the like, with high demands on inner and/or outer roundness, whereby the heat treatment is carried out with the blank secured in a fixture, incorporating at least one press member adapted to subject the inner and/or outer surface/surfaces of the blank to an axial and/or radial pressure. The invention also relates to such a fixture.

BACKGROUND OF THE INVENTION

During heat treatment of bearing rings and similar annular blanks, where the demands for ring roundness are high, it is necessary to secure the blank in such a manner that the roundness can be maintained and even be improved. Hitherto this securing has been accomplished in different manners, which all have had their advantages and drawbacks.

According to the so called chuck method the blank is secured in a chuck, whereby the following positive and negative aspects can be mentioned. EXTERNAL CHUCK METHOD

Distortion correction

+ Radial chucking around the entire circumference.

+ Several contact points.

+ Good engagement contact/support. - No flatness correction.

Technical aspects

+ Easy to obtain nominal roundness.

+ Flexible and large range with reference to ring sizes.

+ Standard components can be used. - Difficult to achive sensitive force control.

- Rather complicated equipment.

- Parallel contact surface is preferred.

SUBSTITUTE SHEET

INTERNAL CHUCK METHOD Distortion correction

+ Radial chucking along the entire circumference. + Several contact points. + Good engagement cont ct/support.

- No flatness correction. Technical aspects

+ Easy to obtain nominal roundness.

+ Flexible and large range with reference to ring sizes. + Standard components can be used.

- Difficult to achive a sensitive force control.

- Rather complicated equipment.

- Parallel contact surface is preferred.

- Limited bore diameter.

According to the so called axial press method, whereby the blank is secured by one of its end surfaces being pressed against a die, the following positive and negative aspects can be mentioned. Distortion correction

+ Good flatness control.

+ Good contact against the end surface.

- No roundness control.

- Radial friction forces prevent natural volume change. Technical aspects.

+ Simple force control.

+ Flexible and large range with reference to ring sizes.

+ Simple equipment.

According to the so called cone/die etod, where a cone is inserted in the ring, which cone presses the ring against a counterstay or die, the following aspects can be mentioned. CONE/DIE METHOD - ONE CONE Distortion correction + Good properties of maintaining roundness. + Several contact points. + Properties of maintaining flatness.

- Very limited engagement contact/support.

- Ability of rounding is dependent of the rigidity/stability of the structure, and of the perpendicularity of the cone relative to the engagement plane of the component. - Impossible to compensate for both 00R rings and rings having non-parallel faces.

- Axially slender rings may deflect. Technical aspects

+ Easy to obtain nominal roundness. + Flexible and large range with reference to ring sizes. + Simple structure. + Can be applied both as OD or ID.

CONE/DIE METHOD - DOUBLE CONES FACING EACH OTHER Distortion correction

+ Good properties of maintaining roundness.

+ Several contact points.

+ Properties of maintaining flatness.

- Limited engagement contact/support. - Ability of rounding is dependent on the rigidity/stability of the structure, and on the perpendicularity of the cone relative to the engagement plane of the component.

- Impossible to compensate for both OOR rings and rings having non-parallel faces. Technical aspects

+ Easy to obtain nominal roundness.

+ Flexible and large range with reference to ring sizes.

+ Simple structure.

+ Can be applied both as OD or ID. - Thin or narrow rings will limit the flexibilty and the range of variation.

- The double cones will make the handling substantially more complicated.

- Very difficult to optimize both flatness and roundness.

PURPOSE AND MOST ESSENTIAL FEATURES OF THE INVENTION

The purpose of the invention is to provide both a method for heat treatment of annular metal blanks and a fixture for performing the method, which minimizes distortion and out-of- roundness, as well as set-up time, maintenance and production costs, and which maximizes the product quality. These tasks have been solved by the features defined in the claims.

DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a section through an annular blank having parallel end faces, which blank is secured by means of a partly spherical fixture according to the invention, and where the longitudinal axis of the fixture coincides with the axis of the annular blank or ring.

Fig. 2 is a section analogue with Fig. 1, wherein the end faces of the ring are not parallel to each other. For the sake of understanding the non-parallelity is much exaggerated in the example illustrated in this figure.

Fig. 3 shows a section also analogue with Fig. 1, but where the base surface is arranged at an angle to the ground plane. The misalignment is much exaggerated in this example.

DESCRIPTION OF PREFERRED EMBODIMENTS

All three embodiments show an annual metal blank 11, which can be a bearing ring, a bearing cup, but also a thooted ring or the like. A fixture 12 incorporates on one hand a convex press member 13 and a counter-stay or die 14. The fixture also incorporates an actuator (not shown) , by means of which the press member can be displaced to and from the blank 11, and which can press the press member to engagement with the die. In the embodiments shown the press member 13 has a part- spherical form, whereby the part-spherical surface has such an extension, that it, independent on the position of the ring 11, will engage the inner peripheral end edge of the

ring along a circular engagement line in contrast to a tapering press member, which, in unfavourable circumstances, corresponding to what is shown in Fig. 2 and Fig. 3, will engage along an oval contact line.

The spherical form of the press member gives very good round¬ ness maintaining properties, it provides a large number of contact points (line contact) , it provides good properties for maintaining the plane shape, it makes it easy to obtain nominal roundness, it gives flexibility and a large range of ring size variations, it has a simple construction and can be applied both as OD and ID, and it has limited requirements for rigidity and alignment.

The invention is not limited to use of a spherical press member, but operates with the same advantages with double spherical press members, one at each side of the ring, where¬ by one of the press members corresponds to the die 14.

It is also possible to design the press member with a concave press surface 15, such as shown in Fig. 4. Also combinations of convex and concave sperical press members can be appro¬ priate for certain applications.

The invention is not limited to the embodiments shown in the drawings and described in connection thereto but variations and modifications are possible within the scope of the appended claims.