GB2025927A

GB2025927A - Apparatus for and method of dividing gas-filled glass tubing

Info

Publication number: GB2025927A
Application number: GB7922115A
Authority: GB
Original assignee: SELF POWERED LIGHTING Ltd
Current assignee: SELF POWERED LIGHTING Ltd
Priority date: 1978-07-21
Filing date: 1979-06-26
Publication date: 1980-01-30

Abstract

In an apparatus for and method of dividing gas-filled glass tubing, particularly where the tubing is filled with a radioactive gas, division is effected by drawing the glass tubing (6) through opposing laser beams (19, 20) at a rate low enough so that at least opposing faces of said glass tubing are each divided and each sealed to the other in a single pass through said laser beam. The glass tubing is contained within a pressurized chamber (1), the pressure in said chamber being greater than that within the tubing, even when the tubing is heated by the laser beam. Where the side walls of the tubing are not completely divided in a single pass, the glass tubing is taken through the laser beam for a second pass, complete division being effected in no more than two passes. A plurality of tubes (6) can be held in a single holder (5) and cut in a single pass, or, at most, in two passes, so that the production rate achievable by the apparatus and method is high. <IMAGE>

Description

SPECIFICATION Apparatus for and method of dividing gas-filled glass tubing The invention relates to the division of gas-filled glass tubing.

The cutting of glass tubing where the tubing has sealed ends and contains a valuable gas gives rise to the obvious problem of retaining the gas during the cutting operation. Apparatus for cutting such tubing by the use of a laser beam or a pair of laser beams where the tubing contains a radioactive gas is already known. In general, a laser beam is focussed upon the glass tubing under conditions such that the pressure exterior to the tubing exceeds that within the tubing, even allowing for the pressure rise attendant upon heating the tubing during the act of dividing same, so that the tubing collapses when heated to diffusion temperature forming a pair of segments both ends of which are hermetically sealed.

While conventional methods have achieved the desired objective of dividing the tubing without loss of gas, except for that which penetrates the glass during the fusion operation, the apparatus and methods disclosed thus far have been relatively expensive, primarily because the rate at which the cutting operation takes place is low. In general, the methods have relied upon a scanning technique in which a zone completely surrounding the tubing is gradually raised to diffusion temperature so that the entire zone collapses essentially simultaneously to form a pair of sealed ends. Since the major portion of the zone to be collapsed is outside of the laser beam during the heating operation, that portion of the zone is subject to cooling while the minor portion of the zone in the path of the beam is being heated.

Accordingly, the scanning technique involves a serious loss of heat during the dividing step so that the process is, of necessity, slow. Of course, the rate at which the division is carried out can be increased by increasing the energy output of the laser providing the beam. However, an extra expense would be incurred.

An additional problem arises from the fact that scanning requires that the workpiece and the laser beam be moved relative to each other at a relatively high rate since, as aforenoted, cooling takes place at those areas of the zone not immediately under the laser beam. This high rate motion generates problems of stability such as oscillation and increased oscillation at resonance frequencies.

As is evident, then, an apparatus and a method for dividing gas-filled glass tubes into segments at an increased rate is to be desired.

The present invention provides apparatus for dividing gas-filled glass tubing, comprising: holder means for holding at least one gas-filled tube; chamber means surrounding said holder means, said chamber having a pair of opposing faces and a window in each of said faces disposed for permitting a laser beam to pass therethrough and fall upon said tube; pressurizatior means for raising the pressure within said chamber means to a level greater than that reached within said tube during division thereof; transport means for moving said holder and said tube in directions both parallel to and transverse to the length of said tube; and stationary laser means disposed for transmitting a laser beam through each of said windows for impinging on opposite faces of said tube for cutting same at a desired region.

in another aspect the invention provides a method of dividing a gas-filled glass tube comprising the steps of: mounting said glass tube in a tube holder; placing said glass tube in said tube holder on a table in a pressurizable chamber, said table being movable both lengthwise of and transverse to said tube holder and said glass tube, said chamber having windows through which laser beams can be transmitted for heating opposed faces of said glass tube; pressurizing said chamber to a level greater than that which may be reached within said tube during division thereof; introducing a laser beam through said windows; and moving said tube through said laser beam in a direction transverse to the length of said tube, said tube being moved at a rate such that at least the faces of said tube opposed to said beam are divided in two and sealed to each other to form tube ends, said opposed faces being each divided and sealed to each other in a single traverse of said tube through said laser beam.

Where the side walls of the tube are heavy relative to the power of the beam, bridges between the tube segments may remain after a single traverse. However, said bridges are readily removed and the tube segments are completely divided from each other in a second traverse of the tube through the beam.

Preferably, a single laser source is used, a beacon splitter being provided for splitting the beam into two beams, the separate beams being directed through windows in opposite faces of the pressure chamber. Lenses in the path of the beam provide for focussing of the beam against opposing walls of the tube.

Preferably, a plurality of tubes are held in a single tube holder so that each of said plurality of tubes may be cut in a single traverse of the tube holder through the laser beam.

A preferred procedure for dividing a glass tube is to cut into approximately equal halves, then quarters, then into eighths, etc, until the final length of the segments is that desired.

A microprocessor is preferably used for positioning the tube holder lengthwise and for carrying out the traverse operation at a rate such that each division of the tube is effected in, at most, two traverses.

An embodiment of glass tube cutting apparatus and method, in accordance with the invention, will now be described by way of example only, with reference to the accompanying drawings of which: Fig. 1 is an elevational view of an apparatus for cutting glass tubes; Fig. 2 is another side elevational view of the same apparatus taken at an angle of 900 to that of Fig. 1; Fig. 3 is a plan view of a tube holder with several gas-filled glass tubes mounted therein; Fig. 4 is a view taken along line 4-4 of Fig. 3; and Fig. 5 is a sectional view of a gas-filled glass tube.

Apparatus in accordance with the present invention is shown in Fig. 1 in which a pressure chamber 1 has therein an X-Y table that is movable in the X and in the Y directions, the Y direction being parallel to the length of the glass tubes, and the X direction being transverse to the length of the tube. The X-Y table has the reference numeral 2. Movement of the table in the X direction is effected by X-drive motor 3 and in the Y direction by Y-drive motor 4.

Tube holder 5 for holding glass tubes 6 is mounted on table 2 by clamping means such as screws 7.

Pressure chamber 1 is pressurized by introducing gas through valve 8 from a source (not shown).

Division of the tube is effected by a beam from a laser source. Preferably, the beam is of the CO2 type and has an output of at least 100 watts continuous wave. The beam from laser source 9 is directed to beam splitter 11 which splits it into two beams of essentially equal intensity. One of the beams reaches mirror 12 through window 13 in pressure chamber 1. The other half-beam is reflected from mirror 14, enters pressure chamber 1 through window 16 and is reflected towards the glass tube from mirror 17. Both half-beams 19 and 20 are focussed by lenses 18; to insure precise focussing of the opposed beams on opposite faces of glass tubes 6, a rigid mount 22 is provided.

Preferably, several glass tubes are held in tube holder 5 for cutting, five tubes 6 being held in the tube holder of Figs. 3 and 4. In a preferred form, the tube holder comprises a pair of opposed plates 23 and 24 at least one of'which is faced with an elastic sheet 26. A suitable material for sheet 26 is rubber. The purpose of the rubber is to provide a firm grip on the glass tubes and to allow for variations in the thickness and straightness of the glass tubes. The tube-holder plates 23 and 24 and elastic sheets 26 have slots therethrough to provide access of the laser beams to the glass tubes.

In the preferred cutting sequence, the tubes are cut into essentially equal halves by traversing the tube holder 5 and the glass tubes mounted thereon through the laser beam in the direction indicated by the arrow M in Fig. 3. As indicated in said Fig. 3, a first cut has been made through slot A. Four of the tubes have been completely separated. However, one of the tubes has been sealed off only so far as the two walls facing the laser beam are concerned. In this case, complete separation has not been achieved so far as the side walls are concerned. In general, complete separation of the tube into two segments is achieved in a single traverse of the laser beam by the movable tube holder.However, where the walls of the glass tube are heavy, then the heating requirement necessary to bring the entire side walls up to the fusion temperature may be greater than the laser beam can supply at the particular traverse rate being employed. The reason for this increased requirement can be seen from Fig. 5 which makes it evident that the heating requirement for the fusion of the portion of the major faces 34 and 36 of the tubes between the lines spanned by the double arrow N is less than for the portion of the faces outside these lines. In any event, it has been found that the bridge 27 which, on occasion, remain after a single traverse, can invariably be removed by a second traverse of the laser beam by the tubes in question. As is evident, the same effect can be achieved by carrying out the traverse at a lower rate or by increasing the power of the beam.However, it is generally more cost-effective and the production rate is increased by providing for a second traverse.

As aforenoted, it is preferred to carry out each division so that the tube is cut into approximately equal halves, the reason being that the pressure of the remaining gas in each of the halves, after division, will be approximately the same. If the tubes are to be further subdivided, then, each segment is preferably divided into approximately equal halves. Accordingly, a desired sequence of division and successive subdivisions would be to traverse the laser beam so that the beam first penetrates through slot A and then through slots B, C, D, E, Fand G.

It has been found that the pressure within the chamber is critical with respect to causing collapse of the tube and fusing to form sealed ends during the heating step. Preferably, where the thickness of the glass is about 0.010 inches and the diameter of the laser beam is about 0.010--0.015 inches as it strikes the tube walls, the pressure in the chamber is about 2 Ibs. greater than that within the tubes. The pressure is read on gauge 18.

A microprocessor 33 controls the operation, interlocks (not shown) preventing the turning on of the laser source 9 until one or more tubes are mounted in the tube holder 6, the tube holder is clamped to X-Y table 2 and pressure chamber 1 is pressurized to the desired value. The microprocessor, then, through electrical connections 29 activates the laser source 9 and drive motors 3 and 4 to sequence the table 2 through the desired series of steps to divide glass tubes 6 into as many segments as desired. Drive motors 3 and 4 are preferably of the stepping type and position table 2 by means of threaded shafts 31 and 32.

Generally, the glass tubes hold tritium, however, they may be filled with another gas or the radioactive gas krypton. Where the gas is tritium, a small quantity of same will penetrate the glass during the fusion step and may form water on the surface of the segments. Accordingly, it is desirable that the segments be washed before being handled.

The apparatus disclosed herein provides for an extremely rapid process, it being possible to make a single cut in each of as many as five tubes in a few seconds. Moreover, the entire process insofar as positioning the tubes with respect to the laser beam and carrying out the traverses is effected completely automatically so that a minimum of operator attention is necessary and the operator encounters no hazards. In addition, should breakage of a tube containing a radioactive gas occur an alarm (not shown) can be provided to signal any significant amount of radioactivity within the pressure chamber. The end seals resulting from the apparatus and method of the present invention are not only hermetic but rugged so that the segments can be handled without danger of breakage of the seals.

It will thus be seen that the objects set forth above, among those made apparent from the preceding description, are efficiently attained and, since certain changes may be made in carrying out the above method and in the constructions set forth without departing from the spirit and scope of the invention, it is intended that all matter contained in the above description and shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Claims

1. Apparatus for dividing gas-filled glass tubing, comprising: holder means for holding at least one gas-filled tube; chamber means surrounding said holder means, said chamber having a pair of opposing faces and a window in each of said faces disposed for permitting a laser beam to pass therethrough and fall upon said tube; pressurizationqneans for raising the pressure within said chamber means to a level greater than that reached within said tube during division thereof; transport means for moving said holder and said tube in directions both parallel to and transverse to the length of said tube; and stationary laser means disposed for transmitting a laser beam through each of said windows for impinging on opposite faces of said tube for cutting same at a desired region.

2. An apparatus for dividing gas-filled glass tubing, as defined in claim 1, wherein said transport means is arranged and constructed for moving said tube in said transverse direction during said division of said tube at a rate such that said region on each of said opposite faces is brought to the fusion temperature in a single traverse of said laser beam by said tube.

3. An apparatus for dividing gas-filled glass tubing, as defined in claim 2, wherein said rate is such that when said apparatus is used for dividing a tube having two opposed major faces disposed for impingement of said laser beams on same and two side faces, each major face is divided and joined in the opposite face, thereby forming two tube end seals in said single traverse.

4. An apparatus for dividing gas-filled glass tubing, as defined in claim 3, wherein said rate is such that each of said side faces is also divided in said single traverse.

5. An apparatus for dividing gas-filled glass tubing, as defined in claim 3, wherein said rate is such that said major faces are divided in a single pass and said side faces are divided in a second traverse.

6. An apparatus for dividing gas-filled glass tubing, as defined in any of claims 1 to 5, wherein said holder means includes a pair of opposed plates for holding said tube therebetween and clamp means for holding said plates together, each of said plates having transverse slots therein through which said laser beams can pass for impingement on said tube.

7. An apparatus for dividing gas-filled glass tubing, as defined in claim 6, wherein said holder means includes a sheet of an elastic material between at least one of said opposed plates, said sheet having transverse slots therein corresponding to said slots in said plates.

8. An apparatus for dividing gas-filled glass tubing, as defined in claim 7, wherein said sheet is of rubber.

9. An apparatus for dividing gas-filled glass tubing, as defined in any of claims 6 to 8, wherein each of said plates has slots therein disposed for sequentially cutting said tube into two essentially equal segments and each segment into smaller equal segments, the number of slots provided being at least that corresponding to the vnitial length of said tube and the desired degree of subdivision.

10. An apparatus for dividing gas-filled glass tubing, as defined in any of claims 6 to 9s wherein said holder means is wide enough to hold a plurality of said tubes parallel to and spaced apart from each other, and said transport means is arranged and constructed for moving all of said tubes successively through said laser beams.

1 1. An apparatus for dividing gas-filled glass tubing, as defined in any of claims 1 to 10, further comprising microprocessor means for controlling said transport means for positioning said holder means in the lengthwise direction of said tube and for moving said holder means in said transverse direction through said laser beams.

12. An apparatus for dividing gas-filled glass tubing, as defined in any of claims 1 to 1 1, wherein said laser means is a single laser source and includes a beam splitter for forming two beams, mirror means for directing said beams through said windows into said chamber means and focussing means for focussing said beams on the faces of the tube held in said holder means.

13. A method of dividing a gas-filled glass tube comprising the steps of: mounting said glass tube in a tube holder; placing said glass tube in said tube holder on a table in a pressurizable chamber, said table being movable both lengthwise of and transverse to said tube holder and said glass tube, said chamber having windows through which laser beams can be transmitted for heating opposed faces of said glass tube; pressurizing said chamber to a level greater than that which may be reached within said tube during division thereof; introducing a laser beam through said windows; and moving said tube through said laser beam in a direction transverse to the length of said tube, said tube being moved at a rate such that at least the faces of said tube opposed to said beam are divided in two and sealed to each other to form tube ends, said opposed faces being each divided and sealed to each other in a single traverse of said tube through said laser beam.

14. A method of dividing a gas-filled glass tube, as defined in claim 13, wherein side faces of said tube are each divided in a second traverse of said tube through said laser beam.

1 5. A method of dividing a gas-filled glass tube, as defined in claim 13 or claim 14, wherein said tube is divided into two essentially equal segments.

16. A method of dividing a gas-filled glass tube, as defined in claim 15, wherein each segment is successively divided into two equal segments, the process being continued until a desired state of division is reached.

17. A method of dividing a gas-filled tube, as defined in any of claims 13 to 1 6, wherein a plurality of tubes are placed in parallel in spacedapart relationship and at least said faces of said plurality of tubes opposed to said beam are each divided in two and sealed to each other to form tube ends in a single traverse of said holder means and tubes through said laser beam.

1 8. A method of dividing a gas-filled glass tube, as defined in claim 17, wherein side faces of each of said tubes are each divided in a second traverse of said tubes through said laser beam.

19. A method of dividing a gas-filled glass tube, as defined in any of claims 13 to 18, wherein said tube, subsequent to said division, is washed to remove any traces of contaminants reaching the surfaces of same from the interior thereof during said division.

20. A method of dividing a gas-filled glass tube, as defined in claim 13, wherein said chamber is pressurized to a pressure of between 1.5 and 2.5 p.s.i. preferably substantially 2 p.s.i. greater than that within said tube prior to heating same by said laser beam.

21. A method of dividing a gas-filled glass tube according to claim 13 and substantially as described herein.

22. Apparatus for dividing a gas-filled glass tube substantially as described herein with reference to or as illustrated in the accompanying drawings.