CYLINDER SHOULDERS DESCRIPTION

The present invention relates to a method for machining a workpiece i n order to obtain a cage for bearings for lamination cylinder shoulders. In a further aspect, the present invention also relates to a bearing for lamination cylinder shoulders and to a method for manufacturing it. Some methods are known for manufacturing a bearing cage which include the following phases:

execution of a single turning to generates a ring having the same thickness and width as the final cage;

execution in the cage of pockets by means of an end milling machine. Such pockets serve as the housing of the cylindrical rollers of the bearing.

The execution of pockets in the cage includes the milling of said ring by means of an end milling machine. The pockets are milled first on one side and then on the opposite side of the ring; during the milling the ring is kept in its place by means of a dedicated jig.

The cage subsequently undergoes a tumbling or sanding treatment to remove the machining burrs.

If necessary, a burnishing or phosphate coating treatment can be performed to reduce friction. An inconvenience of this manufacturing method is that the execution of said single turning on the workpiece brings about the generation of internal tensions, which, during the subsequent milling of the pockets, may considerably deform the piece and therefore increase the risk of malfunctioning and consequently breaking the cage during the use. This problem is particularly significant if the bearings are employed in lamination cylinder shoulders, as these are machines for which extraordinary maintenance interventions are absolutely to be avoided in consideration of the high costs connected to plant stopping in steel production.

An example of prior art methods for manufacturing cages of bearings is described in the US Patent Application US 2008/260313.

In this context, the technical tasks of the present invention is to propose a method for manufacturing a cage for bearings of shoulders of rolling mill cylinders that overcomes the above mentioned inconveniences of the known technique.

Particularly, the aim of this invention is to provide a method for manufacturing a cage for bearings of shoulders of rolling mill cylinders that allows the production of reliable and sturdy cages and bearings.

Furthermore, the invention aims at proposing a method for manufacturing a cage for bearings of shoulders of rolling mill cylinders that enables the production of bearings suitable for bearing high loads.

A further object of the present invention is to provide a method for manufacturing a cage for bearings of shoulders of rolling mill cylinders in which tensions and stresses on the starting workpiece during its machining are avoided or reduced.

The above mentioned technical task and purposes are achieved by a method for manufacturing a cage for bearings of shoulders of rolling mil l cyl inders which is characterized in that it comprises machining a starting workpiece according to the following steps:

performing a preliminary turning on said workpiece to obtain a ring having an extra thickness relative to the nominal dimensions of the cage;

forming pockets in the obtained ring, said pockets being intended to receive rollers of said bearing;

performing a boring of said pockets;

performing an additional turning operation to eliminate said extra thickness and bring the cage to its nominal dimensions.

In a further aspect, the present invention also relates to a method for manufacturing a roller bearing for shoulders of rolling mill cylinders which is characterized in that it comprises the following steps:

preparing a cage for said roller bearing by using the above-described method;

preparing an external ring for said roller;

preparing an internal ring for said roller;

positioning logarithmic profile rollers in the pockets of said cage;

positioning said cage and said rollers between an outer ring and an inner ring of said bearing.

Moreover, the present invention also relates to a roller bearing for lamination cylinder shoulders which is characterized in that it comprises:

an internal ring for said roller bearing;

an external ring for said roller bearing, said external ring having a circumferential central rim and two lateral circumferential rims obtained on the internal surface of said external ring;

a cage with a double-comb structure comprising a central track, a plurality of separators branching off in opposite directions from said central track to define a plurality of pockets on both sides of said central track, said pockets housing rollers of said bearing;

said cage and said rollers being positioned between said external ring and said internal ring of

1 said bearing, the central track of said cage facing the circumferential central rim of said external ring.

Further features and advantages of the present invention will be more clear from the description of preferred but not exclusive embodiments of a method for manufacturing a cage for bearings according to the invention, as well as of a bearing, in particular a bearing of shoulders of rolling mi l l cylinders shown by way of examples in the accompanying drawings, wherein:

figure 1 shows an exploded view of a bearing including a cage produced with the method of the present invention;

figure 2 shows a section view of the bearing of figure 1.

In details, the method for manufacturing a cage 2 for bearings 1 of shoulders of rolling mill cylinders according to the present invention, comprises machining a starting workpiece according to a well-defined sequence of steps. The cage 2 is suitably made in a single -block piece, i.e., it is made of a single piece and not assembled from more pieces. Preferably, the material of said cage 2 is brass. The cage 2 is inteded to house and keep in place the rollers 6 that allow the bearing I to minimize friction.

In particular, the machining of the starting workpiece includes a first phase of performing a preliminary tu ning of the starting workpiece piece to obtain a ring having an overthickness compared to the nominal size of cage 2.

The phase of the preliminary turning is suitably carried out so as to obtain an overthickness of, e.g., less than 4 millimeters, preferably less than 2 mil limeters. This overthickness is important as it allows a limited deformation of cage 2 during the execution of the subsequent machining phases on the workpiece.

In the subsequent phase, pockets 3 are formed in the workpiece, such pockets 3 being intended to house the rollers 6 of the bearing 1.

During the machining operation to form the pockets 3, separators 9 are generated which separate a pocket 3 from the ones immediately adjoining. These separators 9 are shaped l ike teeth which, because of the tensions that are released during the execution of the pockets 3, may be deformed, thus compromising the shape of the pockets 3 and therefore the correct functioning of the bearing 1.

The overthickness left during the preliminary turning operation allows the minimizing of this deformation, thus offering a larger resistant section. Furthermore, any deformation that may possibly occur is completely recovered in the subsequent boring operation.

The forming phase of the pockets 3 includes the execution phase of a milling of the piece, preferably by means of a disc mill. Preferably pockets 3 are formed on both sides of the ring obtained in the previous phase, so as to obtain a cage 2 with a double-comb structure. In this case, the cage 2 includes a central circumferential portion 91 from which the separators 9 extend to form the various pockets 3 on both sides of the ring, as clearly shown in the attached figures.

During the execution phase of the milling of the cage 2 the workpiece to be machined is positioned on the worktop of the milling machine, with the axis of the cage 2 (which will coincide with the rotation axis of the bearing 1) orthogonal to the worktop.

The next step of the machining operation consists of performing a boring of said pockets 3. The boring of the pockets 3 in the workpiece allows to obtain the correct clearance between the pocket 3 and the roller 6 contained in it, the radial retaining of the rollers 6, and the above mentioned correction of the shape of the pocket 3 in case of residual deformation, with the subsequent correction of the rotation axis of the rollers 6. Any possible formation of machining burrs can be easily removed.

After the formation and shaping of the pockets 3 is completed, the method of the present invention foresees an additional turning operation on the cage 2 to eliminate the overthickness left during the preliminary turning operation.

The execution phase of an additional turning of the cage 2 can include the phase of gripping a side of said piece by means of a jig. Thanks to this additional turning phase it is possible to remove the overthickness, therefore giving the cage 2 its final size.

Thus, the present invention allows to obtain a sturdy cage 2 w ith substantially no deformations and w ith the correct clearance between the pockets 3 and the rollers 6. Consequently, the risk of malfunctioning and possible breaking of the cage during the use is considerably reduced with respect to prior art bearings.

Preferably, the method according to the present invention suitably includes also a silver- plating phase of the cage 2, which is conveniently carried out after said additional turning. The silver-plating phase includes a surface treatment of electrolytic silver-plating. The silver- plating phase is suitably carried out by applying on the cage a layer of coating of less than 0.05 millimeters thick, preferably between 0.01 and 0.03 millimeters thick.

Such treatment will allow the reduction of the superficial roughness and therefore decrease the friction between the pocket 3 and the bearing roller inserted in this pocket 3. This causes a reduction of the bearing temperature at a given rotation speed.

Before applying the silver layer on the cage 2, its external surface in correspondence of the central circumferential portion 1 (i.e. the surface that will face the internal face of the external ring 5 of the bearing 1) may be grinded so as to perfectly fit with the interior surface of the external ring 5 of the bearing 1, as better explained hereinafter

As previously said, the present invention also relates to a method for manufacturing a roller bearing 1 for lamination cylinder shoulders that includes the following phases:

preparing a cage 2 for said roller bearing 1 by using the above-described method;

preparing an external ring 5 for said roller 1;

preparing an internal ring 4 for said roller 1;

positioning logarithmic profile rollers 6 in the pockets 3 of said cage 2;

positioning said cage 2 and said rollers 6 between an outer ring 5 and an inner ring 4 of said bearing 1.

The internal and external rings 4 and 5 are suitably produced in compliance with the P6 (DIN 620) size tolerance and the P5 (DIN 620) shape tolerance.

The method therefore includes the execution phase of said external ring 5. The thickness of the external ring 5 is preferably as low as possible. In particular, it has been seen that the ratio between the thickness of the external ring 5 and the external diameter of said ring 5 can conveniently be lower than 0.05. Such reduced thickness allows the insertion of rollers of higher diameters than the rollers that can normally be placed in the unified bearings having the same diameter.

Consequently, the bearing 1 manufactured with the method of the present invention can bear higher loads with respect to conventional roller bearings having the same diameter.

The external ring 5 is made in steel preferably 100Cr6. The same material is used for the internal ring 4 too.

The manufacturing method of the roller bearing 1 of the present invention preferably also includes the following steps:

a grinding phase of a circumferential rim 92 obtained on the internal surface of said external ring 5;

a grinding phase of a circumferential track 91 obtained on the surface of the cage 2 that, after the assembling of the bearing 1, opposes said external ring 5, said circumferential track 91 facing said circumferential rim 92.

When the bearing 1 is assembled, the distance between the circumferential rim 92 of the external ring 5 and the track 91 of said cage 2 is as low as possible, e.g. in the range of 0.05- 0.07 millimeters or lower. This allows the more precise and stable positioning of the cage 2. Preferably, the circumferential rim 92 of the external rin 5 is suitably equidistant as regards the two end bases of the external ring 5. Therefore, the circumferential rim 92 can be defined as a central circumferential rim.

A largely preferred method for manufacturing a roller bearing 1 for lamination cylinder shoulders according to the present invention comprises therefore the following phases:

manufacturing a cage 2 with a double-comb structure by machining a starting workpiece according to the following steps:

performing a preliminary turning on said workpiece to obtain a ring having an extra thickness relative to the nominal dimensions of the cage 2;

forming pockets 3 on both sides of said ring thereby resulting in the formation of a cage 2 with a double-comb structure comprising a central track 91, a plurality of separators 9 branching off in opposite directions from said central track 91 to define a plurality of pockets 3 on both sides of said central track 91, said pockets 3 being intended to receive rollers 6 of said bearing 1 ;

performing a boring of said pockets 3;

performing an additional turning operation to eliminate said extra thickness and bring the cage 2 to its nominal dimensions;

grinding said central track 91 ;

preparing an external ring 5 for said roller bearing 1, said external ring 5 having a circumferential central rim 92 and two lateral circumferential rims 93 and 94 obtained on the internal surface of said external ring 5;

grinding said a circumferential central rim 92;

preparing an internal ring 4 for said roller bearing 1 ;

positioning logarithmic profile rollers 6 in the pockets 3 of said cage 2;

positioning said cage 2 and said rollers 6 between said outer ring 5 and said inner ring 4 of said bearing 1, the central track 91 of said cage 2 facing the circumferential central rim 92 of said external ring 5.

Said central circumferential rim 92 is suitably interposed between two lateral circumferential rims 93 and 94 obtained on the internal surface of the external ring 5. At the same time, the circumferential track 91 obtained on the cage 2 is symmetrically disposed between the separators 9 developing therefrom, and, as a result, once the bearing 1 is assembled the cage 2 is perfectly centered with respect to the external ring 5 of the roller bearing 1.

The method suitably provides for the execution of the rollers 6. This phase suitably provides for the execution of the rollers 6 having circularity (or, more generally, shape) size tolerances lower than 1 micrometer.

As a consequence, all the rollers of a bearing 1 work at their best in the respective work areas, and simultaneously (thus reducing the risk that, because of the lack of diameter and tolerance uniformity, only some rollers work).

Roller bearings having the above-described set of features and the corresponding advantages over the prior art bearings are not known at present. Thus, the roller bearings I for lamination cylinder shoulders according to the present invention comprise, in their more general definition:

an internal ring 4 for said roller bearing 1 ;

an external ring 5 for said roller bearing 1, said external ring 5 having a circumferential central rim 92 and two lateral circumferential rims 93 and 94 obtained on the internal surface of said external ring 5;

a cage 2 with a double-comb structure comprising a central track 91, a plurality of separators 9 branching off in opposite directions from said central track 91 to define a plurality of pockets 3 on both sides of said central track 91, said pockets 3 housing rollers 6 of said bearing 1 ;

said cage 2 and said rollers 6 being positioned between said external ring 5 and said internal ring 4 of said bearing 1, the central track 91 of said cage 2 facing the circumferential central rim 92 of said external ring 5.

This invention shows numerous advantages. Particularly, it allows the availability of a method to execute an extremely sturdy cage, so as to minimize the risk of executing extraordinary maintenance interventions in lamination plants due to the breaking of bearings.

The invention as it is conceived is susceptible of several modifications and variants, ail of which fall within the invention concept that characterize it. Furthermore, all the details can be replaced by other elements that are technically equivalent. In practice, all the employed materials, as well as the sizes, can vary based on the particular needs.