GB1565521A - Method of continuous transfer of work through a sealed chamber - Google Patents

Description

(54) A METHOD OF CONTINUOUS TRANSFER OF WORK THROUGH A SEALED CHAMBER (71) We, WENTGATE ENGINEERS (1976) LIMITED, a Bristol Company, of Industrial Estate, St. Ives, Huntingdon, Cambridgeshire PE17 4LU, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to apparatus for providing continuous feeding of workpieces through a region of reduced pressure, i.e. a sealed chamber in which the pressure is below atmospheric pressure and in which some operation is to be performed on each work piece.The construction of the chamber is not critical, since an existing vacuum chamber or pressure chamber may be used without necessitating any radical modification to its pumping or valving arrangements, and in this aspect, the invention is of particular use in the electron beam welding of small work pieces but is also applicable to any other operation requiring a low pressure or vacuum such as, for example, brazing, metallising and evaporation, freeze drying, leak detection, sample charging in electron microscopy or impregnation.

In some previously proposed arrangements for pressure or vacuum chamber operations, the workpieces are inserted either singly or in batches on an indexing machanism in a vacuum chamber by opening a door therein.

Such an arrangement is time-consuming when the finished workpiece or workpieces are to be removed and replaced with un finished workpieces, and frequently requires the use of elaborate sealing devices, or re ducing the pressure inside the chamber to atmospheric pressure for each batch.

According to the invention there is pro vided apparatus for transferring workpieces through a region of reduced pressure for the performance of an operation thereon, said apparatus comprising a sealed chamber; first pressure reducing means for reducing the pressure within the sealed chamber below atmospheric pressure; means defining a passageway extending through the sealed chamber; a plurality of workholders each shaped for insertion into an input end of said passageway for movement therealong towards an output end thereof, each end of each workholder including an annular portion disposed for sealing engagement of the wall of the passageway when the workholder is located therein, so that when the workholders are disposed end to end in said passageway they define a series of compartments within the passageway which move therealong as the workholders are moved along the passageway, the workholders including means for supporting a workpiece within each compartment, there being an opening in the part of the passageway which is located within the sealed chamber whereby the interior of a compartment as it reaches an operating station in the passageway adjacent said opening is exposed to the interior of the sealed chamber for the performance of an operation on a workpiece supported in said compartment; and second pressure reducing means for reducing the pressure in each compartment in turn to a level between atmospheric pressure and the reduced pressure in the sealed chamber as the workholders are moved along the passageway towards said operating station, said second pressure reducing means being in communication with the interior of said passageway via a port in the wall of said passageway located upstream of said sealed chamber with regard to the direction of movement of the workholders along said passageway, the dimension along the passageway of said port being greater than the dimension along the passageway between the forward edge, with regard to the direction of movement of the workholders along said passageway, of said annular portion of the rearward end of one workholder and th2 rearward edge of the said annular portion of the adjacent forward end of the workholder which immediately succeeds said one workholder in the passageway, so that, whilst one compartment downstream of said port is disposed at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein, the rearward annular end portion of a workholder upstream of said operating station and the adjacent forward annular end portion of the immediately succeeding workholder are both disposed adjacent the port between the sides of said port.

In a preferred embodiment of the invention, indexing means are provided for moving the workholders along said passageway in stepwise fashion so that at the end of each stepwise movement the rearward annular end portion of each workholder in turn and the adjacent forward annular end portion of the immediately succeeding workholder are halted adjacent said port between the sides of said port, and a respective compartment downstream of said port is halted at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein.

Means may also be provided for raising the pressure in each compartment in turn to a level between the reduced pressure in the sealed chamber and atmospheric pressure as the compartments pass a location downstream of the operating station, said means preferably comprising a conduit of which one end opens out into the passageway at said location downstream of said opening in the passageway and the other end opens out into the passageway at a location upstream of said port.

Conveniently, the dimension of the opening along the passageway is greater than the length of each compartment so that the interior of more than one compartment can be exposed to the interior of the sealed chamber at the same time.

Means may also be provided for moving a workpiece supported within a compartment once that compartment reaches said location within the passageway adjacent said aperture.

Preferably the means defining a passageway comprises a tubular member which pierces the walls of the sealed compartment, there being sealing means between the tubular member and the walls of the chamber. Conveniently, the passageway is cylindrical and each end of each workholder is formed as a disc of which the diameter corresponds substantially to the internal diameter of the passageway; there being an 4;0"-ring or a sealing ring of rectangular cross section embedded in the periphery of each disc which sealingly engages the walls of the passageway as the associated workholders moves therealong.

According to another aspect of the invention, there is provided a method using apparatus according to the invention as described above, for transferring workpieces through said sealed chamber which constitutes a region of reduced pressure, the method comprising the steps of reducing the pressure in said sealed chamber; locating the workholders in series at said input end of said passageway to form said compartments; loading a workpiece in each compartment; moving the workholders along said passage way so as to bring the rearward annular end portion of each workholder in turn and the adjacent forward annular end portion of the immediately succeeding workholder into registration with said port so that pressure in the respective compartments can be reduced via said port whilst simultaneously bringing a compartment downstream of said port to said operating station; performing an operation on a workpiece in said compartment at the operating station; removing a finished workpiece from each compartment as it reaches the output end of the passageway; and removing the unloaded workholders from said output end and returning them to said input end of the passageway for reloading of the compartments there formed with fresh workpieces.

Reference will now be made to the accompanying drawing, of which the sole Figure illustrates diagrammatically, and by way of example only, one embodiment of the invention where the pressure in the sealed chamber is to be reduced to a value at which workpieces in each compartment can be electron beam welded.

The apparatus illustrated in the drawing comprises a sealed housing 1 which defines a sealed chamber 2, the housing 1 being capable of withstanding reduced pressures in chamber 2. An electron gun 3 of suitable design is mounted on the housing 1 so that it can direct a beam 4 of electrons through an aperture 4a in the housing 1 and into the chamber 1. A port 5 is provided in the housing to which a suitable pump (not shown) is connected for the purpose of evacuating the chamber 2. An open-ended tube 6 pierces the walls of the housing so as to pass through the chamber 2, there being suitable "O"-ring seals 6a between the tube and said walls. The tube 6 has an opening 7 in an intermediate section which is located within the chamber 2, so that workpieces moved along the tube in a manner described below can be exposed through opening 7 to the reduced pressure or vacuum within the chamber 2 and to the electron beam 4 for welding.

A plurality of workholders 8 are positioned end-to-end at the input end 9 of tube 6 and are moved along within the tube by a slider 10 which engages the rearmost workholder 9 disposed in position A. Each workholder 8 is substantially cylindrical, having disc-like end walls 11. In the periphery of each end wall 11 is an "O"-ring 13 or a sealing ring of rtangular cross section which sealingly engages the internal walls of the tube 6 when the workholder is located within the tube. Thus between the end walls 11 of each workholder and the wall of the tube 6 is formed a res pective substantially cylindrical compartment which moves along the tube as the workholder moves therealong.Between its end walls 11, each workholder includes an intermediate portion 12 which is adapted to support a workpiece with the compartment defined between the end walls during movenent of the workholder along the tube 6 and dumg the welding operation. Preferably, the sll:icr 10 moves the line of workholders in stepwise fashion, the length of each stepwise rnovemen,t being equal to the pitch along the tube of the workpiece joints to be welded, i.e.

in this embodiment the length of each workholder, so that each time the workholders move, the joints in the workpieces respectively supported in the compartments are brought in turn into alignment with the electron beam 4 for the welding operation; the drawing illustrates the positions of the workholders at the end of a stepwise movement.

As the workholders are pushed along the tXe 6, the compartments pass in turn through potions B, C and D, the pressure inside each compartment formed as described above being at this stage equal to atmospheric pressure.

When each compartment reaches position E, the foremost end wall of its respective workholder is adjacent a port 14 in the tube 6 leating wia a conduit 15 to a further pump which reduces the pressure in the compartment to about 0.1 Torr. The compartment remains exposed to the port 14 when it is moved to the next position F, but further moved to the next position F, but further off the compartment briefly.It should be noted that the dimension of port 14 along the tube is such that although the pressure in the cospartment leaving position F is 0-1 Torr, tbe rearmost end wall of that workholder sealingly engages the wall of the tube im mediately downstream of port 14 before the foremost end wall of the workholder next but one in succession, moving between positions D and E, encounters the edge of port 14 so that at most two compartments are exposed to the port 14 at any one time.That is to say, the dimension of port 14 along the tube 6 is greater than the dimension along the tube between the forward edge of the rearward end wall of one workholder and the rearward edge of the forward end wall of the workhol der which immediately succeeds said one sPrkholNer.

When each çompartment reaches position G, the foremost end wall of its respective workholder encounters the opening 7 so that the compartment is exposed to the interior of the sealed chamber and the reduction of the pressure in the compartment to a level of about 10-2 Torr can commence. The time interval between each stepwise movement of the workholder is that taken to perform a welding operation, in this instance between about 1 and 10 seconds, so that each compartment is first evacuated via port 14 and then via opening 7 for this welding time interval.

Should this time interval prove to be too short for the pressure in the compartment to be reduced to about 10-2 Torr by the time it is indexed forward into the welding position H, then additional pumps may be provided to produce further preliminary pressure reduction via ports such as that indicated in dotted lines at 16. Additionally or alternatively the dimension of opening 7 along tube 6 may be increased to expose more than two compartments at a time to the pumping action of the pump connected to port 5, thereby giving each compartment additional time for its internal pressure to be reduced to the desired value before position H is reached.

At position H, a workpiece such as the shaft and roller attachment 17 supported within the respective compartment is welded by the electron beam 4. This is done either by deflecting the beam 4 to describe the desired weld profile whilst the workpiece remains stationary, or, as in the illustrated embodiment, the workpiece is rotated or moved linearly relative to a stationary electron beam which remains switched on for an appropriate time for a weld to be completed. Rotation of the workpiece is achieved by means of a right angle gear 18 engaged by a gear 19 on a rotatable shaft 20 which is raised into an operating position during welding and then lowered to permit further rightward movement of the workholder, as viewed in the drawing, towards position J.

As the compartment containing a welded workpiece moves to position J, the end walls of its respective workholder re-engage the walls of tube 6, sealing off the compartment of which the internal pressure is still 10-2 Torr. Once this occurs, the foremost end wall of the next but one workholder in succession leaving position F for position G encounters the opening 7.Further rightward movement of the workholder from position J to position K results in the internal pressure of the respective compartment being raised via a port 21 either by venting to atmosphere, or as illustrated by cross connecting port 21 to a second port 22, upstream of port 14, via a conduit 23 thereby raising the pressure in the compartment in position K to a level intermediate 10-2 Torr and atmospheric pressure and lowering the pressure in the compartment in position D adjacent port 22 from atmospheric pressure to approximately the same intermediate level by effectively doubling the volume to be occupied by the air in the compartment at position D. This cross connection provides for useful preliminary pressure reduction in compartments before port 14 and opening 7 are encountered.

Finally, the compartment moves from position K to position L at the output end 24 of tube 6; the workholders may be removed from the output end 24, and the welded workpieces recovered.

It should be noted that at each end of tube 6, the pressure exerted on the outermost workpieces is one atmosphere, whereas the pressure inside the tube between positions E and K at least is less than one atmosphere, so that the workholders in the tube are held in contact with each other as they progress along the tube.

Since the workholders are not otherwise physically interconnected, and can be easily removed, any heat generated during welding, which would tend to result in a possibly detrimental temperature rise in a fixed workholder, is easily removed from the welding station and dissipated, for example by fan cooling, before the workholder is reloaded.

The use of "O"-ring seals or sealing rings of rectangular cross section on the workholders and the fact that the workholders can be readily removed from the tube means that replacement of the seals in the event of any wear presents little problem. Usually sliding seals for work transfer through high vacuum are of the face seal type, which are inherently more complicated than circular "O"-ring seals or sealing rings of rectangular cross section, and the use of the latter in this embodiment of the present invention has the advantage that the apparatus is self valving and may be readily used with an existing vacuum chamber.

WHAT WE CLAIM IS:- 1. Apparatus for transferring workpieces through a region of reduced pressure for the performance of an operation thereon, said apparatus comprising: a sealed chamber; first pressure reducing means for reducing the pressure within the sealed chamber below atmospheric pressure; means defining a passageway extending through the sealed chamber;; a plurality of workholders each shaped for insertion into an input end of said passageway for movement therealong towards an output end thereof, each end of each workholder including an annular portion disposed for sealing engagement of the wall of the passageway when the workholder is located therein, so that when the workholders are disposed end to end in said passageway they define a series of compartments within the passageway which move therealong as the workholders are moved along the passageway, the workholders including means for supporting a workpiece within each compartment, there being an opening in the part of the passageway which is located within the sealed chamber whereby the interior of a compartment as it reaches an operating station in the passageway adjacent said opening is exposed to the interior of the sealed chamber for the performance of an operation on a workpiece supported in said compartment; and second pressure reducing means for reducing the pressure in each compartment in turn to a level between atmospheric pressure and the reduced pressure in the sealed chamber as the workholders are moved along the passageway towards said operating station, said second pressure reducing means being in communication with the interior of said passageway via a port in the wall of said passageway located upstream of said sealed chamber with regard to the direction of movement of the workholders along said passageway, the dimension along the passageway of said port being greater than the dimension along the passageway between the forward edge, with regard to the direction of movement of the workholders along said passageway, of said annular portion of the rearward end of one workholder and the rearward edge of the said annular portion of the adjacent forward end of the workholder which immediately succeeds said one workholder in the passageway, so that, whilst one compartment downstream of said port is disposed at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein the rearward annular end portion of a work holder upstream of said operating station and the adjacent forward annular end portion of the immediately succeeding workholder are both disposed adjacent the port between the sides of said port.

2. Apparatus as claimed in claim 1, comprising indexing means for moving the workholders along said passageway in stepwise fashion so that at the end of each stepwise movement the rearward annular end portion of each workholder in turn and the adjacent forward annular end portion of the immediately succeeding workholder are halted adjacent said port between the sides of said port, and a respective compartment downstream of said port is halted at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein.

3. Apparatus as claimed in claim 2, in which the duration of each stepwise movement is determined by the time taken to perform said operation on a workpiece brought to the operation station.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (20)

**WARNING** start of CLMS field may overlap end of DESC **. pressure to approximately the same intermediate level by effectively doubling the volume to be occupied by the air in the compartment at position D. This cross connection provides for useful preliminary pressure reduction in compartments before port 14 and opening 7 are encountered. Finally, the compartment moves from position K to position L at the output end 24 of tube 6; the workholders may be removed from the output end 24, and the welded workpieces recovered. It should be noted that at each end of tube 6, the pressure exerted on the outermost workpieces is one atmosphere, whereas the pressure inside the tube between positions E and K at least is less than one atmosphere, so that the workholders in the tube are held in contact with each other as they progress along the tube. Since the workholders are not otherwise physically interconnected, and can be easily removed, any heat generated during welding, which would tend to result in a possibly detrimental temperature rise in a fixed workholder, is easily removed from the welding station and dissipated, for example by fan cooling, before the workholder is reloaded. The use of "O"-ring seals or sealing rings of rectangular cross section on the workholders and the fact that the workholders can be readily removed from the tube means that replacement of the seals in the event of any wear presents little problem. Usually sliding seals for work transfer through high vacuum are of the face seal type, which are inherently more complicated than circular "O"-ring seals or sealing rings of rectangular cross section, and the use of the latter in this embodiment of the present invention has the advantage that the apparatus is self valving and may be readily used with an existing vacuum chamber. WHAT WE CLAIM IS:-

1. Apparatus for transferring workpieces through a region of reduced pressure for the performance of an operation thereon, said apparatus comprising: a sealed chamber; first pressure reducing means for reducing the pressure within the sealed chamber below atmospheric pressure; means defining a passageway extending through the sealed chamber;; a plurality of workholders each shaped for insertion into an input end of said passageway for movement therealong towards an output end thereof, each end of each workholder including an annular portion disposed for sealing engagement of the wall of the passageway when the workholder is located therein, so that when the workholders are disposed end to end in said passageway they define a series of compartments within the passageway which move therealong as the workholders are moved along the passageway, the workholders including means for supporting a workpiece within each compartment, there being an opening in the part of the passageway which is located within the sealed chamber whereby the interior of a compartment as it reaches an operating station in the passageway adjacent said opening is exposed to the interior of the sealed chamber for the performance of an operation on a workpiece supported in said compartment; and second pressure reducing means for reducing the pressure in each compartment in turn to a level between atmospheric pressure and the reduced pressure in the sealed chamber as the workholders are moved along the passageway towards said operating station, said second pressure reducing means being in communication with the interior of said passageway via a port in the wall of said passageway located upstream of said sealed chamber with regard to the direction of movement of the workholders along said passageway, the dimension along the passageway of said port being greater than the dimension along the passageway between the forward edge, with regard to the direction of movement of the workholders along said passageway, of said annular portion of the rearward end of one workholder and the rearward edge of the said annular portion of the adjacent forward end of the workholder which immediately succeeds said one workholder in the passageway, so that, whilst one compartment downstream of said port is disposed at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein the rearward annular end portion of a work holder upstream of said operating station and the adjacent forward annular end portion of the immediately succeeding workholder are both disposed adjacent the port between the sides of said port.

2. Apparatus as claimed in claim 1, comprising indexing means for moving the workholders along said passageway in stepwise fashion so that at the end of each stepwise movement the rearward annular end portion of each workholder in turn and the adjacent forward annular end portion of the immediately succeeding workholder are halted adjacent said port between the sides of said port, and a respective compartment downstream of said port is halted at said operating station adjacent said opening for the performance of an operation on a workpiece supported therein.

3. Apparatus as claimed in claim 2, in which the duration of each stepwise movement is determined by the time taken to perform said operation on a workpiece brought to the operation station.

4. Apparatus as claimed in claim 2 or

claim 3, in which said indexing means comprises a reciprocating slider disposed to push the workholders along the passageway in said stepwise fashion.

5. Apparatus as claimed in any of claims 1 to 4, in which said annular portion of each end of each workholder is constituted by a respective pliable sealing member which surrounds the respective workholder end.

6. Apparatus as claimed in any of claims 1 to 5, in which means are provided for raising the pressure in each compartment in turn to a level between the reduced pressure in the sealed chamber and atmospheric pressure as the compartments pass a location downstream of the operating station.

7. Apparatus as claimed in claim 6, in which said means for raising the pressure in each compartment in turn comprises a conduit of which one end opens out into the passageway at said location downstream of said opening in the passageway and the other end opens out into the passageway at a location upstream of said port.

8. Apparatus as claimed in any of claims 1 to 7, in which the dimension of the opening along the passageway is greater than the length of each compartment so that the interior of more than one compartment can be exposed to the interior of the sealed chamber at the same time.

9. Apparatus as claimed in any of claims 1 to 8, in which means are provided for moving a workpiece supported within a compartment relative to the workholders once that compartment reaches said operating station.

10. Apparatus as claimed in any of claims 1 to 9, in which the means defining a pasageway comprise a tubular member which pierces the walls of the sealed compartment, there being sealing means between the tubular member and the walls of the chamber.

11. Apparatus as claimed in any of claims 1 to 10, in which the passageway is cylindrical and each end of each workholder is formed as a disc of which the diameter corresponds substantially to the internal diameter of the passageway, there being an "O"-ring or a sealing ring of rectangular cross section embedded in the periphery of each disc which sealingly engages the walls of the passageway as the associated workholder moves therealong.

12. Apparatus substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

13. Apparatus as claimed in any of claims 1 to 12, adapted for electron beam welding, the apparatus further comprising means for directing a beam of electrons through said sealed chamber into each compartment in turn when said compartment is at said operating station adjacent said opening so as to perform a welding operation on a workpiece supported therein.

14. Apparatus as claimed in claim 13, in which the first pressure reducing means is arranged to reduce the pressure in said sealed chamber to about 10-2 Torr and the second pressure reducing means is arranged to reduce the pressure in each compartment as it reaches the port to about 0.1 Torr.

15. A method using apparatus as claimed in any of claims 1 to 12, for transferring workpieces through said sealed chamber which constitutes a region of reduced pressure, the method comprising the steps of: reducing the pressure in said sealed chamber; locating the workholders in series at said input end of said passageway to form said compartments; loading a workpiece in each compartment; moving the workholders along said passageway so as to bring the rearward annular end portion of each workholder in turn and the adjacent forward annular end portion of the immediately succeeding workholders into registration with said port so that pressure in the respective compartments can be reduced via said port whilst simultaneously bringing a compartment downstream of said port to said operating station; performing an operation on a workpiece in said compartment at the operating station;; removing a finished workpiece from each compartment as it reaches the output end of the passageway; and removing the unloaded workholders from said output end and returning them to said input end of the passageway for reloading of the compartments there formed with fresh workpieces.

16. A method as claimed in claim 15, in which the workholders are indexed along the passageway so as to halt each compartment in turn adjacent said opening at the operating station.

17. A method of transferring workpieces through a region of reduced pressure substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.

18. A method of electron beam welding using apparatus according to claim 13, the method comprising a method of transferring workpieces through the sealed chamber as claimed in any of claims 15 to 17, and including the further steps of directing a beam of electrons through said sealed chamber at each workpiece in turn as the compartment within which that workpiece is supported arrives at the operating station.

19. A method as claimed in claim 18, in which the pressure in said sealed chamber is reduced to about 10-2 Torr and the pressure in each compartment is reduced via said port to about 0.1 Torr.

20. A method of electron beam welding substantially as hereinbefore described with reference to and as illustrated in the accompanying drawing.