Background to the invention Certain oil-well drilling operations require lengths of wire mesh to serve as a filter to prevent particulate material such as sand from the strata through which the drilling has been made, to enter the bore. Typically referred to as sand screens, these filters essentially comprise elongate strips of woven wirecloth rolled up in the form of a tube so that the longer edges overlap, which are introduced down-hole and then expanded to fill the hole, the longer edges remaining overlapped (albeit to a lesser extent) after expansion. The strips are cut from a wider width of woven wirecloth by a slitting process which can produce accurate width strips but thereafter the strips must be cut accurately to length and the ends finished in a manner which will enable them to be accommodated within the drilling operation and to fit precisely between collars down-hole so as to provide a continuous filter screen over the length of the drilling which is to be protected.

It is an object of the present invention to provide apparatus and a method by which elongate strips of wirecloth can be cut to length and their ends finished so as to maintain the integrity of the weave at both ends of the cut to length strip.

Summary of the invention According to the present invention a method of cutting an elongate strip of wirecloth to a given length and finish the ends so as to maintain the integrity of the weave at both ends comprises the steps of:- (1) clamping one end of a rolled up oversize length of woven wirecloth, and unrolling the wirecloth over a flat surface; (2) clamping the far end of the unrolled length of cloth; (3) tensioning the unrolled length by moving one clamp relative to the other, so that the wirecloth lies flat over the whole of its length between the clamped ends; (4) positioning parallel sided bars across the wirecloth adjacent the two clamped ends so that the desired final length of the strip is defined by the distance measured along the length of the strip from the outer face of one to the outer face of the other of the two bars, the outer face in each case being that face of the bar which is closest to the adjacent clamped end of the wirecloth, and the inner face of each bar being the face thereof parallel to the outer face; (5) clamping the two bars in that position so that they extend at a desired angle across the cloth relative to the length dimension of the cloth; (6) marking the wirecloth with two pairs of parallel lines using the said inner and outer faces of each bar as straight edges to define the positions of the two lines in each said pair, each pair of lines thereby being spaced apart by a distance commensurate with the width of the bar between its inner and outer faces; (7) removing the bars from the wirecloth and binding together the warp and weft wires of the cloth between each pair of parallel lines to form a solid seam across the width of the strip, thereby locking the weave in place between the two seams; and (8) cutting across the wirecloth along the outer of each of the pairs of lines to produce the desired length of cloth, with the seams immediately adjacent each of the two cut ends.

The clamping of one or both of the opposite ends of the length of cloth may be removed before or after the cutting step.

If clamping is removed prior to the cutting step, clamping means may be positioned adjacent the seam to flatten the cloth prior to the cut being made.

In a preferred arrangement the clamping means at one end is fixed relative to the flat surface and the clamping means at the opposite end can be moved in a direction towards and away from the fixed clamping means at the said one end.

The movement of the movable clamping means may be effected manually or more preferably by a powered drive means such as a pneumatic air cylinder.

The parallel sided bars may be positioned before or after tensioning the cloth. If before, a gap is left below each bar to allow the cloth to slip relative to the bars as it is tensioned.

The cutting step is conveniently performed using a guillotine.

Binding the warp and weft wires to form the seams may be performed for example by soldering or welding or by an adhesive, in each case the solder, weld material, or adhesive being applied to the cloth between each pair of parallel lines. A preferred type of welding is resistance welding. If desired, the two seams can be formed simultaneously.

Alternatively portable apparatus is provided for forming each of the seams, which apparatus is positioned first and one and then at the other of the two ends of the cloth, to form the seams one after another.

Where the seam is formed by soldering or adhesive the method may include the step of cleaning the wirecloth between each pair of parallel line before applying the solder.

In addition or alternatively soldering flux may be applied to the wirecloth likewise between each pair of parallel lines before solder is applied.

It is important that the wirecloth is not stretched beyond its length when pulled out straight under the tension applied, the latter merely being applied to ensure that the length of cloth between the clamped ends lies flat and does not contain creases or ridges. To this end additional clamping may be effected at spaced apart positions along the length of the tensioned wirecloth, by which the latter can be flattened against the flat surface over which the wirecloth has been unrolled.

Preferably the clamping steps at opposite ends may differ to the extent that whereas one end of the cloth is firmly clamped between a pair of jaws, and will not normally slide relative to the jaws, even when tensioned, the clamping of the other end may be effected between jaws which do not clamp the cloth so firmly therebetween, thereby permitting slip to occur after a specific tension is achieved in the cloth between the clamped ends thereof.

By selecting the specific tension to be below that at which permanent stretching of the wirecloth could occur, so the tensioning process is limited to merely flattening and straightening out the length of wirecloth, as desired.

The clamping steps may be effected manually and the manual operation may involve operating one or more levers to clamp cloth between jaws or lowering a bar down to overlie the cloth and trap it between the bar and the flat surface. Clamping may be alternatively effected by powered drive means such as an air cylinder or solenoid or electric motor.

Manual operation may simply comprise the step of operating a switch or valve so as to supply power (e. g. air or electricity) to activate a drive to effect clamping.

Likewise soldering or welding or gluing step may be performed manually.

Soldering or welding or gluing may also be effected by a machine having a powered drive.

The drives for the soldering, welding or gluing may for example may be a solenoid or electric motor or a pneumatic air cylinder.

The method may be automated where powered drives are employed in that a programmable computer based control system may be provided to control the supply of operating power to each of the drives in turn after the length of wirecloth has been unrolled and initially clamped in position.

By suitably illuminating the upper surface of the cloth, the presence of any unevenness can be identified either by an operator or by visual inspection means comprising at least one television camera and video signal processing circuit means adapted to identify whether reflection of light from the wirecloth surface is uniform over the length of the cloth, the control system (if provided) being programmed to check the output signals from the signal processing means after tensioning and before continuing with the clamping and marking of the cloth.

Where the process is to be automated powered marking means is required with the drive therefor being activated at the appropriate time in the sequence.

Likewise powered cutting means may be provided, also activated at the appropriate time in the sequence.

Where one or both ends of the finished length of wirecloth is to be shaped in a particular way by additional cuts, or punching to provide holes, the method may include such additional cutting and punching steps as are required to effect this.

Where access to the underside of the cloth is required to perform any step in the process, a discontinuity may be provided in the flat surface over which the cloth is laid, at the point or points along its length where such access is needed. Any such discontinuity may be permanent or formed by temporarily removing a section of the supporting surface.

This is of particular relevance where the seams are to be formed by welding or gluing and where an automatic resistance welding apparatus has electrodes which have to roll over the surface of the cloth above and below the weld line in electrical contact therewith.

The invention also lies in apparatus adapted to perform some or all of the steps of the above-described method.

The invention also lies in elongate cut to length strips of woven wirecloth having secured ends when fabricated in accordance with the method of the invention or as modified by any of the alternative methods herein described.

The invention will now be described by way of example with reference to the accompanying drawings which illustrate a method and apparatus embodying the invention described herein, in which:- Fig 1 is a diagrammatic plan view of an elongate worktable on which the method can be performed, Fig 1A shows in detail the left hand end of the worktable of Fig 1 with the air cylinder with the clamping bar raised, Fig 1B is a similar view with the clamping bar in its clamped position, Fig 1C shows the two guillotines beyond the air cylinder, Fig 1D shows the right hand end of the worktable of Fig 1 with the intermediate clamping bar clamped and the further clamping bar shown raised, Fig 1E shows the three guillotines beyond the right hand worktable end, Fig 2 shows the clamping of one end of an unrolled length of wirecloth, Fig 3 shows the clamping of the opposite end of the wirecloth, Fig 4 shows the strip before tensioning, Fig 5 shows the strip after tensioning, Fig 6 shows the positioning of a bar across the tensioned cloth to allow marking of the cloth using the side faces of the bar as straight edges, Fig 7 shows the application of soldering flux to the cloth after it has been released from the clamps, Fig 8 shows solder being applied to the fluxed region between the pair of parallel lines produced by marking the upper surface of the cloth, Fig 9 shows the guillotining of one end along the outer of the two edges of the soldered seam, Fig 10 shows a further guillotining step to produce an angled cut across one corner of the cut length at one end, Fig 11 shows a punching step to form a hole through the wirecloth, Fig 12 shows the finished product coiled up ready for packing, Fig 13 shows the guillotines, Fig 14 is a flow chart of the steps of the method, and Fig 15 is a perspective view of an automatic electric resistance-welding device which can be used in place of the soldering step, to form a seam at each end of the cloth.

In the drawings the complete worktable assembly is shown in plan view from above in Fig 1. The main worktable is designated 10 and includes an end clamp 12 at one end and a second end clamp 14 at the other end with intermediate clamps at 16 and 18. Beyond the clamp 12 is pneumatic tensioning device 20 and beyond the ends of the table 10 are located guillotine tables 22,24 and 26 and 28 and beyond 28 a hole punch table 30. An air pressure indicator 32 indicates the line pressure of the air available to the pneumatic tensioning device 20.

Fig 1A illustrates the LH end of the table 10 and shows the tensioning device 20 as comprising an end clamp which includes manually operable clamping jaws 34,36 which can be clamped together or moved apart by rotating a lever 38. The clamp body 40 is slidable on an inclined flat support plate 42 and is attached to the outboard end of a piston rod 44 which extends from an air cylinder 46. Air is supplied to 46 via an airline 48 from an air control valve 50 operable by a lever 52, itself supplied with air via an airline 54 from a manifold 56 of the air pressure indicator 32. A pressure-controlling valve 58 is provided to allow the operator to adjust the air pressure to be supplied to the cylinder 46 along line 48 by reference to the indicator 32, thereby to adjust the tension in the cloth when air cylinder 46 is activated.

The clamp 12 comprises a rigid metal bar 60 hinged at 62 to one side edge of the table 10 so that it can be pivoted up through an elevated position and drawn away from the table to allow a length of wirecloth (not shown in Fig 1A) to be laid on the table 10. One end of the wirecloth is then fitted between the jaws 34,36. By lowering the bar 60 in the direction of the arrow 64 to the position shown in Fig 1B, wirecloth laid on the table and gripped between the jaws 34,36 will become trapped between the underside of the bar 60 and the upper surface 66 of the table 10. Once in the lowered position the bar can be secured in place by raising the U-shaped over-centre clamp 68 and lever 70 so that the crown of the clamp rests in the groove 72 of the bar 60 after which the bar can be pulled downwardly by rotating the lever 70 back through the over-centre position, so as to tension the clamp 68 and in turn tension the bar 60.

If the bar 60 is to be lowered onto the cloth before the latter is tensioned using the device 20, it is necessary for the cloth to be capable of sliding beneath the bar 60. In this event the thickness of the bar 60, the height of the hinge point 62 and the slot 74 in which the bar 60 engages when lowered must be chosen so that the gap between the underside of the bar and the table top is such that whilst the cloth is gripped between the bar and the table, it can still slide below the bar when pulled taut as the clamp body 40 is pulled back as the cylinder 46 is pressurised.

If the bar 60 is not to be clamped onto the cloth until after the latter has been tensioned, no gap of significance needs to be provided between the bar and the table top.

By inclining the support plate 42 downwardly relative to the table 10, the cloth will be pulled in a similar direction where it leaves the LH end of the table, so ensuring that the cloth is held in contact with the table.

The bar includes two plates 76,78 which assist in flattening the cloth as it moves under the bar as it is tensioned by the air cylinder 46.

The two guillotining tables 22 and 24 are shown in Fig 1C. The guillotine blade 80 is shown raised but can be lowered past the cutting edge 82 by pulling a lever 84 in the direction of arrow 86. By locating the wirecloth on the support plate 88 with the nearside edge against the guide 90 any cloth extending below the blade 80 will be cut square to the guide 90.

The guillotine blade 92 of 24 is likewise lowered relative to a co-operating cutting edge 94 by pulling on lever 96 in the direction of arrow 98. Guides 100,102 etc. enable the squared end of the cloth to be positioned precisely relative to the edge 94 which as shown is at an acute angle, typically 45°, to the edge guide 100 on support plate 104.

The RH end of the table 10 is shown in Fig 1D and here clamping bar 106 pivotally joined at 108 to the side edge of the table 10 (and forming clamp 14 of Fig 1) is shown in its raised position. Bar 110 of a similar clamp (18 in Fig 1) is shown in its lowered and clamped position, in which the over-centre tensioning device is shown with the crown of the U-shaped clamp 112 engaged in the groove 114 of the bar 110 and the tensioning lever 116 in its fully lowered position.

The clamping device shown at 118 is similar and the when bar 106 is lowered, it too can be clamped under tension in the same way.

The thickness of the bar 106 and the height of the hinge axis in 108 and the slot 120 in which bar 106 rests when lowered across a sheet of wirecloth laid along the table 10 are selected so that when clamped in the lowered position, bar 106 firmly clamps any wirecloth between it and the upper surface 66 of table 10. When so clamped, any pull exerted on the wirecloth by operation of the air cylinder 46 at the LH end of the table, will tension and flatten the cloth against the surface 66 and only after the tension increases beyond a preselected level does any slippage of the cloth below bar 106 occur. The selection of the dimensions associated with bar 106, hinge 108 and slot 120 thereby determine the maximum tension which can be introduced into the wirecloth on operation of the air cylinder 46.

The intermediate clamp 16 is constructed in a similar way to that of clamp 18, and both are designed to firmly clamp wirecloth to the surface 66 when lowered and clamped in place in the same way as does clamp bar 106 of clamp 14. In general only one of the clamps 14,16 and 18 is used to clamp the wirecloth to the table, the choice being determined by the final length of cloth required.

While the guillotine 22 is used to accurately cut square the LH end of the cloth, the guillotine 26 at the RH end of table 10 is used to cut square the RH end of the length of cloth. This is shown in Fig 1D and also in Fig 1E. Guillotines 116,118 of table 28 are also shown in Fig 1E.

The guillotines are all similar in design and operation to guillotine 22, described with reference to Fig 1C, except that as shown in Fig 1, guillotines 116,118 can be angled across the table 28 as required, to enable the RH end of the cloth to be cut at an angle if required, by using one of 116,118 instead of 26.

As shown in Figs 1D and 1E the support plate 120 of guillotine 26 may be joined to the RH end of table 10.

Fig 2 shows clamping bar 110 lowered over wirecloth 122 and the lever 124 being lifted by the operator in the direction of arrow 126 so that the crown of the U-shaped clamp 112 can be positioned over the groove 114 in the bar 110, as described with reference to Fig 1D.

Operation of clamping bar 106 of clamp 14 (of Fig 1) (or the bar of clamp 16 (of Fig 1) (not shown) ), is similar to that shown in Fig 2.

Fig 2A shows the bar 110 clamped in position after lever 124 has been rotated back to its down position, with the U-shaped clamp over the end of the bar.

Fig 3 shows how the end of a length of wirecloth 122 can be clamped between the jaws 34, 36 of the cloth tensioning device 20. Fig 4 shows how a long length of wirecloth 122 can be laid out along the table 10 and shows how it will tend to buckle and curl, and will only lie flat if clamped and tensioned by extending cylinder 46 of tensioning device 20 while clamping the cloth using one or more of the clamps 14,16 or 18.

Fig 5 shows the LH end of the table 10 with the wirecloth 122 clamped at the far end by clamp 14,16 or 18 (not shown) and gripped between the jaws 34,36 of tensioning device 20 and tensioned by the air cylinder 46 (not shown in Fig 5). Here the bar 60 of clamp 12 is shown lying loosely across the wirecloth ready to be clamped in place by clamp 68,70.

Fig 6 shows the wirecloth fully clamped by bar 60 and the operator using a sharp tool to scribe two lines across the wirecloth using the opposite parallel sides of bar 60 as guides.

Fig 7 shows the LH end of the wirecloth 122 released from the clamping jaws 34,36 after scribing and after air cylinder 46 has been de-pressurised, and after release of clamping bar 60, now shown rotated outboard of the table 10 clear of the cloth. The operator is seen applying flux to the cloth between the two scribed lines (not shown in Fig 7).

Fig 8 shows the operator applying solder between the two scribed lines using a hand held heated soldering tool 128 and solder bar 130.

Figs 9 and 10 shown the operator cutting an angled corner using guillotine 24 after cutting a square end using a guillotine such as 22 or 26.

Fig 11 shows the RH end of the cloth 122 being formed with a hole using a punch 132 operated by a lever 134. The cloth is positioned on the punch support platform 136 using guides 138,140 and 142.

Fig 12 shows the length of wirecloth after being cut to length, rolled up for packing and delivery to a customer.

Fig 13 is a further view of the LH end of the table 10 showing the cloth tensioning clamping jaws 34,36 and air cylinder 46, guillotine 22 and guillotine 24.

Fig 14 shows the steps of one method of using the table of Fig 1 to cut a length of wirecloth to length.

Fig 15 shows an automatic electric resistance welding machine which can be moved across the wirecloth if the latter is stretched across a gap as between the RH end of table 10 and the table of guillotine 26 (see Fig 1). The machine is mounted on a stand 144 and comprises an upper driven wheel 146 and a lower anvil wheel 148. Both wheels are carried on telescoping struts 150,152 so as to be capable of being moved transversely across the wirecloth with he wheels in contact with the cloth. To this end upper wheel 146 is mounted on a slideway 154 so that it can be raised or lowered relative to wheel 148.

The telescoping struts 150,152 and raising and lowering of the wheel 146 may use pressurised air or hydraulic oil or electromagnetic linear driver The weld bead formed by the machine can be used to stabilise the cloth instead of a solder bead, and replaces the soldering step previously described.