METAL SLEEVE FOR CARRYING THE ABRASIVE LAYER OF A SAW BEAD IN A SAW CORD

Abstract

Saw cords made of saw beads threaded on a steel cord, where the saw beads are separated by polymer spacers. The saw beads have a metal sleeve of which the outer surface is covered with an abrasive layer. The inner surface of the sleeve has with two sets of parallel grooves in a first and second axial part of the sleeve. The two sets of parallel grooves differ in at least one of the groove angle, the groove offset or the groove spacing, thereby preventing axial movement of the sleeve and blocking the rotation of the saw bead.

Claims

1-15. (canceled)

16. A metal sleeve for use as a carrier for the abrasive layer of a saw bead in a saw cord, said metal sleeve having a radial outer surface and a radial inner surface wherein said inner surface is provided with a first set of parallel grooves in the axial first part of said metal sleeve and a second set of parallel grooves in the axial second part of said metal sleeve, said first and second set meeting at a meeting plane, said first and second set of parallel grooves each having a groove angle relative to the axis of said metal sleeve, a groove offset at said meeting plane and a groove spacing perpendicular to the grooves, said first set and said second set of parallel grooves differing in at least one of the groove angle, groove offset and groove spacing.

17. The metal sleeve of claim 16, wherein said meeting plane is in the axial middle of said sleeve.

18. The metal sleeve according to claim 16, wherein said groove angle of said first set has an opposite sign to that of said second set.

19. The metal sleeve according to claim 18, wherein the magnitude of said groove angle is equal.

20. The metal sleeve according to claim 16, wherein one of the groove angles of said first or second set is zero.

21. The metal sleeve according to claim 16, wherein said groove spacing and said groove angle of said first and second set is equal and said offset is about half of said groove spacing.

22. The metal sleeve according to claim 16, said metal sleeve further having an axial middle section of said inner surface comprising said meeting plane, said axial middle section being substantially cylindrical over a length of between 0.25 to 0.75 times the axial length of said sleeve and wherein the sections axially outside of said middle section have chamfered openings.

23. The metal sleeve according to claim 16 wherein said outer surface is substantially cylindrical with one or more axially oriented flat faces.

24. A saw bead comprising a metal sleeve and an abrasive layer wherein said metal sleeve is according to claim 16.

25. The saw bead of claim 24, wherein said abrasive layer shows a dendritic metallographic microstructure obtained by laser cladding.

26. A saw cord comprising a steel cord and saw beads threaded thereon, wherein said beads are separated by polymer spacers, wherein said saw beads comprise sleeves according to claim 16.

27. The saw cord according claim 26, wherein said steel cord comprises strands twisted together according a lay length and direction, where said first and second set of grooves represent an arrow direction, said arrow direction being opposite to the twist direction that shortens said lay length.

28. A method to produce a metal sleeve according to claim 16 comprising the steps of: providing a mixture of metal powder and binder providing a mould having a mould cavity, formed by an outer shell having an interior surface and a first and second pin enterable and retractable from the opposite ends of said outer shell, said first and second pin meeting one another at a meeting plane, said pins being tapered towards said meeting plane; injecting said mixture into said mould cavity thereby forming a green sleeve; ejecting said green sleeve from said mould by retracting said first and second pin, and removing the green sleeve out of the outer shell; freeing said green sleeve from said binder thereby forming a brown sleeve; sintering said brown sleeve to final shape; wherein said first pin has a first protruding screw thread with a first screw angle and first screw spacing, said second pin has a second protruding screw thread with a second screw angle and second screw spacing, said first and second screw thread meeting one another at said meeting plane with a screw phase, wherein said first and second screw thread are different from one another in at least one of the screw angle, the screw spacing, and the screw phase.

29. The method of claim 28, wherein said first and second screw thread have an opposite handedness.

30. The method of claim 28, wherein said first and second screw thread have equal screw angle and screw spacing and differ in screw phase angle at said meeting plane.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0064] FIG. 1a: bead and sleeve according JPH0259273A

[0065] FIG. 1b: view of bead and sleeve according JPH07156134A

[0066] FIG. 1c: bead and sleeve in perspective as in KR0128010Y1

[0067] FIG. 1d: bead and sleeve as depicted in JP2000176737A

[0068] FIG. 1e: bead and sleeve as JP2009023041A

[0069] FIG. 1f: bead and sleeve on cord KR20120115799A.

[0070] FIG. 2: bead and sleeve according a first embodiment of the invention

[0071] FIG. 3: bead and sleeve according a second embodiment of the invention.

[0072] FIG. 4: overview of the different possible parameter combinations

[0073] FIGS. 5a and 5b: saw cord with saw bead having sleeve with a groove direction relative to the lay direction of the steel cord.

MODE(S) FOR CARRYING OUT THE INVENTION

[0074] In FIG. 2 an exemplary saw bead 200 according the invention is depicted. The bead is cut in half and the inner surface of the sleeve is visible. At the outside the abrasive layer 202 is indicated. The sleeve 204 is made out of a single piece of metal. There is an axial first part 206 and an axial second part 208. In each part a set of parallel helical grooves 212 has been made. Each groove 212 has a crest 214 (indicated hatched) and a valley 215. The spacing of the first set is indicated with d.sub.1, the spacing of the second set with d.sub.2. The spacing is measured perpendicular to the groove helix. The grooves of the first and second set meet at a meeting plane 216. In this example the meeting plane 216 is about at the middle. In the Example, d.sub.1=1.10 mm while d.sub.2=0.95 mm.

[0075] Both sets of grooves have a groove angle indicated with and . According the convention taken in this application, the angle has a positive sign (the turning over the smallest angle is in the anti-clockwise direction), while has a negative sign (the turning over the smallest angle is in the clockwise direction). The handedness of both groove sets is opposite. The first part 206 has a right hand screw direction (Z) while the second part 208 has al left hand screw direction (S). It is to be remembered that the grooves are seen from the inside. In this particular example =45 while =80.

[0076] The groove offset, indicated with , is in this case differing from zero as the number of grooves in both parts is differing. In case the number of grooves is differing, the groove offset can never be zero (as at least one groove will not have a counterpart in the other set).

[0077] The metal sleeve shows a substantially cylindrical middle section 210. The length of this middle section is about half of the total length of the metal sleeve. The end sections outside the middle sections are chamfered.

[0078] Another embodiment is depicted in FIG. 3. The main difference with the previous example is that the first groove angle a is now zero. All other parameters are identical.

[0079] FIG. 4 depicts the different combinations that are possible. In combination 1, the only difference between the parameters is that the groove offset is different i.e. not zero between both groove sets. Groove angle and distance are equal. Combination 2 cannot be realised as the number of grooves in each set will be different, hence the groove offset can never be equal i.e. the difference in groove offset cannot be zero. In combination 3 = i.e. the angles have the reverse sign. The graphs of Combinations 4 to 6 show embodiments where only one parameter is equal. The inventors find combinations 3, 4, 5 and 7 the best. Graph 1 is easiest to realise in practice.

[0080] The metal sleeves can easily be made in a mould similar to the one described in PCT/EP2013/073905 of the same applicant, more particularly paragraphs [70] to [73], in conjunction with FIGS. 3a, 3b, 4a and 4b. These paragraphs and figures are hereby introduced by reference. The difference between the prior art mould and the current mould is that the first and second pins that are enterable into the outer shell have a different screw angle and/or screw spacing. The screw angle and spacing of the first and second enterable or insertable pin imprint into the green sleeve thereby forming the grooves of the first and second set with the corresponding groove angle and spacing as the negative of the screw.

[0081] Typically, the following ingredients can be used to make a metal sleeve according the invention by means of metal injection moulding:

[0082] A first type of feedstock is available from PolyMIM and [0083] MIM 2200 FN02 Nominal alloy composition: [0084] Ni (1.5 to 2.5 wt %), Mo (0.5 wt % max), Si (1.0 wt % max), C (0.1 wt % max), Fe (the balance). [0085] MIM 2200 FN08 Nominal alloy composition: [0086] Ni (6.5 to 8.5 wt %), Mo (0.5 wt % max), Si (1.0 wt % max), C (0.4-0.6 wt %), Fe (the balance). [0087] MIM 17-4 PH Nominal alloy composition: [0088] Cr (15-17.5 wt %), Ni (3.0-5.0 wt %), Mn (1.0% max), Si (1.0 wt % max), Cu (3.0 to 5.0 wt %), C (0.07% max), Fe (the balance).

[0089] The PolyMIM system allows for water based debinding of the green sleeve (demin water at 40-60 C. for about 5 hours, plus 2 hours drying). In the PolyMIM system the mold is kept at 40 to 60 C., the temperature of the feedstock at the nozzle at 190 C. while an injection pressure of between 750 to 950 MPa is needed. Feed rate is between 3 to 25 cm.sup.3/s.

[0090] A second feedstock is according the Catamold system of BASF (see e.g. U.S. Pat. No. 5,802,437): [0091] Stainless steel 316L Nominal alloy composition: [0092] Cr (16-18 wt %), Ni (10-14 wt %), Mo (2-3 wt %), Mn (2.0% max), Si (1.0% max), C (0.03% min), Fe (the balance).

[0093] The Catamold system is based on catalytic debinding at 110 C. in a HNO.sub.3 environment (afterburn required).

[0094] Sintering cycles are prescribed by the feedstock supplier. Typically they include a hold step for about 1 to 2 hours at 600 C. and a 2 to 3 hour hold step at final temperature (1290 C. to 1380 C. depending on the alloy). The sintered sleeves showed a good density of over 95% of the theoretically possible density. In an metallographic cross section micron sized (1 to 5 m) pores remain visible. This is evidence that sleeves have been made by metal injection moulding.

[0095] After the abrasive layer has been applied on the sleeve either by laser cladding or by brazing a ring of sintered metal powder with diamond onto the sleeve, the sleeve must be correctly mounted on the saw cord. This is illustrated in FIGS. 5a and 5b for respectively an S and Z handed steel cord 522 and 522. For a left hand S cord the closing direction is indicated by arrow 520. Turning the cord end in that direction will tend to shorten the lay length of the steel cord 522. This is also the direction of the torque exerted on the saw bead during sawing, in order to make the bead and rope rotate. The cord is coated with a polymer 524 that also fills the gap between the metal sleeve 526 and the steel cords 522.

[0096] In the semi-transparent metal sleeve the grooves are indicated with lines 528. Only the grooves in the nearer half of the sleeve are indicated and the form is as an arrow indicating a direction that is opposite of the closing direction of the cord 520. FIG. 5b is actually just the mirror image of FIG. 5a and illustrates the orientation of the arrows in the case of a Z type cord. The inventors found that in this way the bead does not start to rotate relative to the steel cord, thereby solving the problem of saw bead rotation.