WO2019011145A1

WO2019011145A1 - Shaped sawing wire

Info

Publication number: WO2019011145A1
Application number: PCT/CN2018/094068
Authority: WO
Inventors: Wenxian HUANG; Kurt VAN RYSSELBERGE
Original assignee: Bekaert Binjiang Steel Cord Co., Ltd.
Priority date: 2017-07-11
Filing date: 2018-07-02
Publication date: 2019-01-17
Also published as: JP3227718U; CN207127339U

Abstract

A shaped sawing wire having a specific shape is described. The shaped sawing wire is made of steel wire that is provided with two crimps in mutual perpendicular directions that are on their turn perpendicular to the shaped sawing wire axis. The applied waveform is equal in both mutual perpendicular directions and only differs by a phase that is introduced between both crimps. The shaped wire is characterised by its projection along its axis that forms a convex trace with corners connected by sides, wherein the number of corners is three or four. In other words the sawing wire has the shape of a tetragonal or trigonal helix i.e. a helix of which the projection along its axis shows a trigonal or tetragonal trace with three or four corners. The shaped sawing wire is cheap to make and shows no preferential direction during sawing due to its helix form.

Description

SHAPED SAWING WIRE

Description Technical Field

The invention relates to a shaped sawing wire that is used for cutting hard and brittle materials such a silicon, sapphire, galliumarsenide, quartz and the like.

Background Art

Sawing wires are used on sawing machines for cutting hard and brittle materials. In the sawing machine a sawing wire is spirally wound over two or more grooved capstans thereby forming a web. The sawing wire is moved back and/or forth while a viscous liquid comprising abrasive particles -called slurry -is poured over the web. The abrasive particles caught between the work piece and the sawing wire abrade the brittle material and thereby progressively cut through the work piece.

Sawing wires are round and thin steel wires with a high tensile strength. When the cutting length becomes long -e.g. longer than 200 mm -there is the possibility that at the exit of the cut no more abrasive particles are present and the cutting efficiency is locally reduced. This hampers the overall cutting speed of the process. In order to overcome this it has been suggested to provide the straight wire with small local bends with in between straight segments that connect the bends resulting in a ‘shaped sawing wire’ . Due to the bends the slurry is better dragged into the cut and the depletion of abrasive material towards the end of the cut is reduced.

Various suggestions have been made in order to implement such bends. Initially a single, zig-zag crimp implemented on a steel wire has been suggested (JP19880117836) . However, such embodiment suffers from the fact that the zig-zag plane does not align with the cut resulting in non-straight cutting. This problem was resolved partly by WO 2006 067062. Therein a monofilament saw wire is described that is provided with two crimps, each crimp having a pitch length and an amplitude, the crimps being arranged in at least two different planes. However, when one of the crimps prevails, the cutting will only be done by that crimp. In addition, two pairs of crimper wheels are needed to implement the crimps which makes it an expensive operation.

In order to provide a shaped sawing wire that does not have a preferred plane of sawing and that is efficient in making, the inventor suggests what follows.

Disclosure of Invention

The object of the invention is to provide a sawing wire of double crimp that does not form a preferred cutting plane during use.

The problem is solved by providing a shaped sawing wire according claim 1. The shaped sawing wire comprises a steel wire. The steel wire has small bends with substantially straight segments in between the bends thereby connecting the bends. The shaped sawing wire extends along a shaped sawing wire axis for example by keeping it taut under a small tension along the vertical. In each perpendicular cross section of the steel wire a centre point can be defined. Connecting these centre points results in a central line of the steel wire.

A projection of the central line on a plane that is perpendicular to the shaped sawing wire axis shows a convex trace with corners. In other words the trace is the curve in the plane perpendicular to the shaped sawing wire axis formed by the intersection of that plane with lines parallel to the axis through any point of the central line. A convex trace is a trace wherein all points on lines connecting any pair of points on the trace remain inside the trace. The corners are connected by sides. The corners have an increased curvature compared to the curvature of the sides. The curvature is the inverse of the radius of curvature. The radius of curvature at any point of the trace is the radius of an osculating circle to the trace at that point. In three dimensional space one can identify the axis of the shaped sawing wire with the Z-axis, while the plane of projection then becomes the XY plane perpendicular to the Z-axis.

In a preferred embodiment the number of corners is three or four. Most preferred is four.

The steel wire is a round, far drawn, high tensile, high carbon steel wire with a diameter ‘d’ between 40 and 300 μm. Most preferred are between 100 and 120 μm such as 115μm. Inroads are being made to use wire of even finer gauge such as 110, 100 or even 90 to 80 μm. As the wire must be tensioned during sawing, the tensile strength must also increase accordingly. Tensile strengths of above 4000 N/mm ² are now customary for 120 μm wires.

Preferably, the shaped sawing wire has a circumscribed diameter ‘D’ and the ratio D/d is between 1.04 and 1.40. More preferably, the ratio D/d is between 1.05 and 1.20, e.g. 1.10. The ratio D/d is a convenient measure to use as a production control. It is the ratio of the optical diameter of the wire (corresponding to the diameter of the circumscribed cylinder) to the steel wire diameter. Large D/d values such as above 2.0 are less preferred as then the shaped wire obtains a too large elongation at low load which is detrimental for the bow formation in the cutting.

Preferably, the average distance along the axis of the shaped sawing wire between bends is between 5 and 50 times the diameter ‘d’ of said sawing wire itself. The average distance is the ratio of a measuring length ‘L’ along the shaped sawing wire axis and the number of bends in three dimensional space counted over that length ‘L’ . The measuring length ‘L’ should at least comprise ten bends.

If the average distance along the axis between bends of the shaped sawing wire is more than 50 times the diameter ‘d’ of the steel wire, the recesses are too distant leading to insufficient drag of abrasive material into the cut. Otherwise, if the average distance along the axis between bends of the shaped sawing wire is less than 5 times the diameter ‘d’ of the steel wire, there are too many bends per unit length and the wire will elongate too much during use. More preferably, the average distance along the axis of the shaped sawing wire between bends is between 15 to 25 times the diameter ‘d’ of said sawing wire itself, e.g. 20 times the diameter ‘d’ of said sawing wire.

The centreline of the wire has a length ‘S’ when measured over an axial length ‘L’ taken along the shaped sawing wire axis, and preferably (S-L) /L is between 0.006 and 0.6 per cent. This (S-L) /L is the ‘extra length’ that is build-in to the wire due to the shape of the wire. If this ‘extra length’ is below 0.006%there is insufficient deformation of the wire to entrain particles in the bends of the wire resulting in insufficient drag of abrasive. If this ‘extra length’ is above 0.6%the wire will elongate much too much during use, which would cause the saw wire to slacken during the sawing process.

Brief Description of Figures in the Drawings

Figure 1 shows a three dimensional representation of the inventive shaped sawing wire with indication of the axis of the sawing wire.

Figure 2 shows a first embodiment together with the generating function of the shaped sawing wire.

Figure 3 shows a second embodiment together with the generating function of the shaped sawing wire.

Mode (s) for Carrying Out the Invention

The shaped sawing wire is made by crimping. Crimping is the action whereby a straight steel wire is guided in between a pair of intermeshing toothed wheels. The teeth of the wheels are rounded in order not to damage the wire. This is much like a pair of gear wheels except that the gear wheels are spaced apart to let the steel wire pass. As the teeth on the toothed wheel are regularly spaced apart the steel wire will receive a periodic deformation.

This periodic deformation can be described by a waveform ‘f (z) ’ wherein ‘z’ is the argument of the function that corresponds to the distance along the axis of the shaped sawing wire. The value of the function ‘f’ corresponds to the deviation from the Z-axis in for example the X-direction. The value of f (z) varies beween X=-a and X=+a wherein ‘a’ is the amplitude of the function. The waveform ‘f (z) ’ has the property that f (z+W) =f (z) for every argument ‘z’ of the function. ‘W’ is then the wavelength of the waveform. Consequently ‘f (z) ’ must become zero for a value ‘z ₀’ that is chosen as the origin of the Z axis. By that choice f (0) becomes 0 and likewise f (W) must be zero. The waveform f (z) has one minimum at ‘w ₁’ (f (w ₁) =-a) and one maximum at ‘w ₂’ (f (w ₂) =+a and w ₁ ＜ w ₂) within each range 0 to W and so there must be another Z coordinate ‘w ₀’ between 0 and W for which f (w ₀) =0. If w ₁=W/4 and w ₂=W-w ₁ the waveform is symmetric and ‘w ₀’ is situated w ₀=W/2. If w ₁ is different from W/4 and w ₂ = W-w ₁ the waveform will be called ‘skewed’ . All other waveforms lead to non-convex projection traces.

The inventive sawing wire is now generated by one waveform f (z) wherein first a deformation in the X-direction is given (i.e. the steel wire obtains a crimp that is laying in the XZ plane) . Thereafter this single flat crimp obtains a second crimp in the Y-direction perpendicular to the plane of the already crimped wire with exactly the same waveform f (z) . However, the second crimp is shifted to the first crimp with a forward phase difference ‘F’ where F is between W/8 and 3W/8 for example W/4. Hence the waveform given in the Y-direction is f (z+F) .

In this way the shaped steel wire will take a roughly helicoidal shape of which the projection of the central line of the steel wire on a plane perpendicular to the axis will show a convex trace with corners connected by sides and wherein the corners have an increased curvature. The period of the helix corresponds to the wavelength of the crimpers.

Figure 1 gives a perspective view of such a shaped sawing wire 100. It comprises a steel wire that has obtained a helicoidal squared deformation by first deforming the steel wire into a single crimp wire in the X direction according a certain waveform f (z) . The crimped wire then lays in plane XZ. The wire is subsequently deformed in the Y direction by the same waveform but shifted W/4. In this way a helical space curve is obtained of which the projection forms a tetragonal trace on the XY plane. Note that the scale in the X and Y direction is equal but these scales are different in the Z direction.

Figure 2 shows the three projections of the central line of the steel wire. The generating deformation f (z) is a triangular function as depicted the upper right figure. It has a wavelength of 4 mm. The amplitude ‘a’ of the deformation is 0.008 mm or 8 μm. The phase difference ‘F’ between the two deformations has been set to 0.78 mm or 0.19×W. The wire itself has a diameter ‘d’ of 120 μm. The circumscribed diameter D is 135 μm. The ratio D/d is thus 1.125. The difference between the actual length of the central line ‘S’ compared to the axial length ‘L’ over which this length is determined is (S-L) /L is equal to 0.0061%. On average the distance between bends is 1 mm or 9.2 times the diameter ‘d’ .

Figure 3 shows the projection of the central line of the steel wire of a shaped sawing wire according another embodiment. Here the deformation function f (z) is a skewed triangular waveform as shown in the lower left figure. The maximum of the triangle is not reached at the quarter of the 4 mm i.e. 1 mm wavelength but at 1.2 mm. The phase difference ‘F’ was set to 1 mm i.e. W/4. Again the central line shows in projection on the XY plane a convex tetragon with varying curvature at the corners and at the sides. The diameter of the steel wire is 120 μm. The circumscribed circle diameter of the shaped sawing wire is 136 μm. Hence D/d is 1.13. The extra length (S-L) /L is 0.0067 %. The average distance between bends is 9.2×d.

The shaped sawing wire with the described shape has the advantage that it provides for gaps between the sawing wire and the circumscribed cylinder in which abrasive particles can get trapped. This leads to a better sawing efficiency. Due to the helical shape the sawing wire will not start to saw according a preferred crimping direction. Moreover the wire can be made at high speed as only two phase shifted crimps need to be made in order to obtain a helix structure.

Claims

A shaped sawing wire comprising a steel wire having bends with segments in between, said shaped sawing wire extending along the shaped sawing wire axis, said steel wire having a central line

characterised in that

the projection parallel to said shaped sawing wire axis of said central line on a plane perpendicular to said shaped sawing wire axis has a convex trace having corners connected by sides, said corners having a larger curvature compared to the curvature of said sides.
The shaped sawing wire according to claim 1 wherein said number of corners is three or four.
The shaped sawing wire according to claim 1 or 2 wherein said steel wire has a diameter ‘d’ , said diameter being between 40 and 300 μm.
The shaped sawing wire according to any one of claims 1 to 3 wherein said steel wire has a diameter ‘d’ and said shaped sawing wire has a circumscribed diameter ‘D’ and wherein the ratio D/d is between 1.04 and 1.40.
The shaped sawing wire according to any one of claims 1 to 4 wherein said steel wire has a diameter ‘d’ and wherein the average distance between bends along said shaped sawing wire axis is between 5 and 50 times said diameter ‘d’ .
The shaped sawing wire according claim 1 wherein the length ‘S’ of said central line when measured over an axial length ‘L’ is larger than said axial length ‘L’ by an amount of 0.006%to 0.6 %of said axial length ‘L’ , said axial length being measured along said shaped sawing wire axis.