1. Field of the Invention

THIS INVENTION relates adjustable reusable ceramic inserts. The invention is particularly suitable for, but not limited to, ceramic inserts for rubbing dies of the type used in rotating spinner straightening and cutting machines.

Throughout the specification, the term "ceramic" shall be used to include partially stabilized zirconia (PSZ) and like ceramic materials.

2. Prior Art

For the efficient manufacture of concrete reinforcing fabric (e.g. mesh), it is necessary to straighten the ribbed wire, drawn from, e.g. a supply coil, before the fabric is assembled and then welded on an automatic resistance line.

Hitherto, the rubbing dies have used tungsten carbide inserts, as the inserts are subject to high abrasion, and sometimes high lateral forces. It is known that ceramics such as PSZ have a very low co¬ efficient of friction and an extremely low heat transfer, both ideal characteristics for die inserts. However, PSZ has a very low resistance to tensional forces, being easily cracked or chipped, and this characteristic has precluded its adoption as a practical substitute for tungsten carbide in replaceable inserts for rubbing dies.

Early attempts to produce PSZ inserts failed due to problems with the design of the rubbing die support holders, in which the inserts are mounted. In the early holder designs, e.g. where the ceramic inserts were glued or shrink-fitted into the holders, the inserts failed due to lack of support and uneven support due to the surface finishes of the mating parts.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide an adjustable reusable ceramic insert, suitable for use in rubbing dies, which is an economically- acceptable consumable for straightening ribbed wire, round wire for reinforcement mesh production, and the like.

It is a preferred object to provide a die insert where the straightened wire has a smooth surface, which will increase production rates in the welding line.

It is a further preferred object to provide a die which generates less heat in the straightening operation, with a consequent reduction in input energy, and decreased heat transfer to the machines.

It is a still further preferred object to provide a die enabling increased production rates, without defect or loss in quality, and with fewer adjustments to the dies. Other preferred objects of the present invention will become apparent from the following description.

In one aspect, the present invention resides in a rubbing die assembly including: a holder having a bore or recess to receive a die insert; and a ceramic die insert receivable in the bore or recess, wherein: the respective mating faces of the bore or recess in the holder, and of the die insert, are finished to a smooth finish; and the external dimension(s) of the die insert are equal to, or just greater than, the internal dimensions of the bore or recess of the holder. Preferably, the die insert has a small

interference fit in the holder. For example, for an annular die insert, the external diameter of the die insert is preferably not more than 0.1%, more preferably not more than 0.06%, greater than the diameter of the bore in the holder.

The die inserts may be of annular or split- annular (ie. half) construction and be received in complementary support holders.

Preferably, the support holders are of medium tensile steel - this will provide the necessary support strength, while the "elasticity" of the steel will at least partially absorb the shocks to the inserts without allowing physical failure of the latter.

Preferably, the inserts are adjustably mounted in the holders to enable compensation for wear.

In a second aspect, the present invention resides in an adjustable reusable ceramic insert (e.g. for rubbing dies) as hereinbefore described.

BRIEF DESCRIPTION OF THE DRAWINGS To enable the invention to be fully understood, a number of preferred embodiments will now be described with reference to the accompanying drawings, in which:

FIGS. 1 and 1A are top plan and side elevational views, respectively, of an annular support holder;

FIGS. 2 and 2A are similar views of a ceramic die insert for use with the holder of FIGS. 1 and 1A;

FIGS. 3 and 3A are similar views of an alternative ceramic die insert for the holder;

FIGS. 4, 4A and 4B are top plan, side elevational, and end elevational views, respectively, of a half support holder;

FIGS. 5 and 5A are top plan and side elevational views, respectively, of a die insert for the

holder of FIGS. 4 to 4B;

FIGS. 6, 7 and 8 are sectional side elevational views showing one embodiment for adjustment of the die insert for wear; and FIGS. 9 to 15 show the steps of grinding and adjusting the die insert for wear according to the one embodiment;

FIG. 16 is a sectional side view showing a second embodiment for adjustment of the die insert; and FIG. 17 is a similar view of a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIGS. 1 and 1A, the support holder 10, of medium tensile steel, has a body 11, with plain main bore 12 and frusto-conical end bore 13, and the body 11 provided with a peripheral flange 14 at the end adjacent the bore 13. A circlip groove 15 is provided about the main bore 12 adjacent the opposite end of the body 11 to the flange 14. The ceramic die inserts 20, 30 (see FIGS. 2 and 2A; 3 and 3A) have bodies 21, 31 machined from cylinders of PSZ, with waisted bores 22, 32 therethrough. The walls of the bores 22, 32 are machined on a constant radius (e.g.. of 60.0mm). The external diameter of the insert bodies 21, 31 is just greater than the internal diameter of the bore 12 in the holder 10. For example, where the diameter of the bore 12 of the holder 10 is 55.0 + 0.00/-0.01mm, the external diameter of the die inserts 20, 30 may be 55.025 + 0.00/-0.005mm, and where the diameter of bore 12 is 31.98 ± 0.00, the die insert diameter may be 32.0 ± 0.00. It will be noted that the external diameter of the die inserts 20, 30 exceeds the internal diameter of the bore 12 by less than 0.1%, preferably 0.05-0.06%. Both the internal bore 12 of the holder 10 and

the external faces 23, 33 of the die inserts 20, 30 are machined, e.g. by grinding, to a very smooth finish to ensure even support of the die inserts 20, 30 in the holders 10. Referring now to FIGS. 4, 4A and 4B, one of a pair of split- or half-rubbing die holders 40 is shown, where the holder 40 has a body 41 of medium tensile steel, with curved, convergent grooves 42, 43 leading to a transverse bore 44 to receive the half insert 50 (see FIGS. 5 and 5A) .

The half die insert 50 is circular in plan view and has a waisted groove 51, which is curved in both plan and side views with respective constant radii.

The diameter relationships of the body 52 of the die insert 50 and the bore 44 of the holder 40 are as hereinbefore described, with the outer face 53 of the die insert 50 and the wall of the bore 44 machined smoothly.

A circlip groove 45 is provided around the bore 44 to receive a circlip 46 for the purpose to be hereinafter described.

Referring now to FIGS. 6 to 8, these Figures show how the die inserts 50 are adjusted to compensate for wear, it being preferred that such adjustment be effected where the grooves 51 have worn down approximately 2mm.

In FIG. 6, the die insert 50 is located against a circlip 46 (in groove 45). After the first 2mm of wear, a steel adjustment spacer 47 is inserted between the die insert 50 and the circlip 46 to raise the die insert in the holder 40. After further wear, a thicker adjustment spacer 48 is provided between the die insert 50 and the circlip 46.

Depending on the load applied to the die inserts by the wire, further adjustments may be

possible, using thicker spacers, until the die insert is replaced.

The adjustment steps will now be described with reference to FIGS. 9 to 15. The circlip 46 is removed from the back of the holder 40 with internal circlip pliers (not shown) (see

FIG. 9).

The support/insert assembly is placed upside down on an adjustment plate 60 (see FIG. 10) and a pressing mandrel 61 is placed on the back of the insert

50. This assembly is placed in a broaching press 62.

The die insert 50 is then pushed down through the support 40 until it passes through the hole 63 in the adjustment plate 60 to engage the anvil face 64 of the press 64. The die insert 50 is now positioned relative to the holder 40 as shown in FIG. 11.

The die holder 40 is placed on the magnetic table of a surface grinder (not shown) and the protruding face 54 of the insert 50 is ground flush with the top face 49 of the holder 40 - see FIG. 12. The adjustment spacer 47 is inserted in the bore 44 and the circlip 46 is refitted - see FIG. 13.

The assembly is returned to the broaching press 62, resting on the anvil face 64 and a pressing mandrel 65 presses the insert down in the holder 49 (see

FIG. 14) until it contacts the spacer 47 and circlip 46. The rubbing die is now ready for service. In an alternative embodiment (see FIG. 16), the outer end of the bore 44 may be screw-threaded (at 44A) and an adjustment screw 70 screw-threadedly engaged therewith, the inner end of the screw 70 bearing against the die insert 50 to enable the die insert 50 to be selectively advanced in the holder 40 as the wearing surface is worn down by the passage of the ribbed wire. In a further alternative embodiment (see FIG.

17), the insert 50 may be selectively advanced hydraulically by a ram 80 in a hydraulic cylinder 81 of a ram 82 mounted on the holder 40 behind the die insert 50. In a still further embodiment not shown, the insert 50 is of frusto-conical shape and is received in a complementary conical bore 44 in the holder 40. In this embodiment, the holder 40 is periodically machined back, the pair of holders 40 advanced towards each other to compensate for the wear in their respective inserts 50. This arrangement has the advantage that a greater bearing area is provided between each holder 40/insert 50 combination.

Under test, the following advantages of ceramic (PSZ) dies over tungsten carbide dies have been achieved:

(a) approximately 25% increased production rate;

(b) higher quality surface finish on the wire (with an 11% increased production rate at the next operation of resistance welding the wire due to the smoother wire surface) ;

(c) die life increased by 300%;

(d) lower heat build-up and lower heat transfer to the machines;

(e) lower energy input; and

(f) reduced dust particles and steel splinters.

It will be readily apparent to the skilled addressee that these advantages are significant and provide a sound basis for the adoption of the adjustable die inserts of the present invention.

Various changes and modifications may be made to the embodiments described and illustrated without departing from the scope of the present invention defined in the appended claims.