GB1569462A

GB1569462A - Brazing presses

Info

Publication number: GB1569462A
Application number: GB4150277A
Authority: GB
Original assignee: TOCCO STEL
Current assignee: TOCCO STEL
Priority date: 1976-10-05
Filing date: 1977-10-05
Publication date: 1980-06-18
Also published as: FR2366907B1; CH622729A5; FR2366907A1; NL7710791A; ES462869A1; JPS5353548A; CA1077576A; DE2744861A1; IT1087559B

Abstract

High-frequency induction-heating brazing press for joining a deep-drawn (dish-shaped) workpiece (2), which workpiece comprises a flat bottom and raised edges, to a heat-distributing covering (3) which matches the shapes of the bottom and of at least part of the raised edges. The press comprises a main inductor (1) contained in a rigid block, a mandrel (4, 5) carrying the deep-drawn (dish-shaped) workpiece and an intermediate heater element (100, 101) made of ferromagnetic material in two separate parts, namely a plane central part (100) and a peripheral part (101) of a particular shape enabling the raised edges of the distributing covering to be pressed against the corresponding parts of the deep-drawn (dish-shaped) workpiece. It also includes an additional inductor (110) surrounding this annular peripheral part so as to heat it and springs (16) for mounting the peripheral part (101) in order to exert a pressure on the periphery of the distributing covering (3) independently of that which is exerted on its central part. Such a brazing press enable the heat-distributing bottoms to be brazed onto cooking vessels (saucepans or frying pans). <IMAGE>

Description

(54) BRAZING PRESSES (71) We, TOCCO-STEL, a French Body Corporate, of 173, Boulevard Haussmann, 75008 Paris, France, 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: The present invention relates to brazing presses for brazing together two or more metal plates to obtain a laminated metal structure; more particularly it relates to presses for brazing together a first part having a plane central portion and a peripheral curved portion, and a second part which covers the central portion and at least part of the peripheral portion of the first part.

Such brazing presses are generally used in the manufacture of cooking vessels where it is advantageous to join together a pressing or stamping made, for example, of stainless steel and having a flat bottom and curvedover and raised side walls, and a part called a heat-diffusing bottom consisting of a metal which is a good conductor of heat such as copper, aluminium or alloys thereof.

United States Patent No. 3,609,277 discloses and illustrates in Figure 1 a brazing press for connecting together a pressing having raised edges, and a preformed heatdiffusing cladding whose surface facing the pressing also has raised edges matched to the shape of the pressing. In this case brazing is effected by means of a single intermediate heating member of ferromagnetic material termed a "susceptor" which is of a special form, i.e., it has a slightly concave thin central portion and thick raised edges whose surface facing the heat-diffusing cladding matches the final external configuration which the cladding will assume after being brazed to the pressing. The pressure exerted by the press on the edges of the susceptor causes the edges to pivot slightly, owing to the fact that the susceptor is concave, with respect to its centre, and thus pushes the raised edges of the heat-diffusing bottom hard against the facing portions of the pressing.

The press disclosed in the patent referred to above also includes an auxiliary inductor which surrounds the edges of the susceptor, in order to make it possible to braze the curved peripheral portions.

Experience has shown that after a certain number of pressing and heating operations, a susceptor arranged in this way loses its concavity of its central part and it is necessary to remove the susceptor from the press and to restore it to its proper shape by applying, for example, pressure against its centre, which results in production being interrupted during the time required for replacing the susceptor with a new one.

Furthermore, French Patent No.

2,105,660, discloses a press for pressing a first cladding, which is positioned on a pressing having a flat bottom and raised edges, so that the cladding covers both the bottom and the edges, and for brazing them together. This press has a mandrel carrying the pressing, two coaxial rams the first of which carries at its lower end a rigid block incorporating the main inductor and the central flat part of the ferromagnetic susceptor. The first ram is operated first and presses the fiat cladding against the fiat bottom of the pressing. The second ram carries at its lower end a cylindrical rigid sleeve or case which surrounds the inductor block. The sleeve carries at its lower end the peripheral annular portion of the susceptor, which portion is separate from its central portion and is designed both to press the periphery of the heat diffusing cladding to a shape which conforms to the raised edges of the pressing, and to braze them together by means of an auxiliary inductor which surrounds the peripheral portion of the susceptor on the outside.

Moreover, United States Patent No.

3,754,109 also discloses a brazing press for joining a preformed heat-diffusing cladding to a pressing or stamping in order to cover the flat bottom and the raised edges of the pressing or stamping, in which in order to obtain close contact between the raised edges of the pressing and the periphery of the heat-diffusing cladding, supplementary pressure is exerted from below on the edges of the sidewall of the pressing so as to slightly deform it. This is achieved either by resilient means such as springs, or by means of a double-acting press (a press with two rams). The supplementary pressure exerted on the sidewall must be carefully adjusted to the elastic limit because it is necessary to avoid both permanent deformation of the pressing and insufficient deformation, or a total lack thereof, due, for example, to weakening of the springs, the pressing or stamping being generally very stiff. This results in an increase in the cost of the installation.

According to the invention there is pro vided a brazing press for assembling receptacles having a layered bottom portion obtained by joining a pressing or stamping having a flat bottom, a sidewall symmetrical about an axis normal to said bottom and a curved portion linking said bottom to said sidewall, to a preformed cladding having a central portion for covering said bottom and a peripheral portion for covering at least part of said curved portion, said press comprising a fixed supporting frame, a press ram carried by said frame, a mandrel reciprocable by means of said ram for supporting said pressing, a block containing a main inductor situated opposite, above and coaxially with said mandrel and coupled to said frame, intermediate heating means of a ferromagnetic metal including a flat central part associated with the bottom face of said inductor block and magnetically coupled to said main inductor for applying pressure to and heating the central portion of said cladding, when in use, and an annular, peripheral part having an inner face matching in shape the outer face of the peripheral portion of said cladding which covers the curved portion of said pressing or stamping, an auxiliary inductor surrounding and magnetically coupled to said annular peripheral part for heating it, a cylindrical sleeve member at least a portion of which is made of a non-deformable insulating material, surrounding said block co axially and having its upper end coupled to said frame for carrying at its lower end said annular peripheral part and said auxiliary inductor, wherein one of said central and peripheral parts of said intermediate heating means is coupled to said frame by means of calibrated resilient coupling means and is guided by guide means to be displaceable axially, whereas the other part is fixed to said frame, so as to obtain an auxiliary pressure exerted on said peripheral cladding portion which is independent of the that acting on said central portion when said single ram compresses the cladding and pressing between said mandrel and said block.

The invention will now be further described, by way of example, with reference to the accompanying drawings illustrating two preferred embodiments of the invention, and in which: Figure 1 is an elevational cross-sectional view of a portion of a first embodiment of a brazing press according to the invention; Figure 2 is an elevational cross-sectional view of a portion of a first version of a second embodiment of the brazing press; Figure 3 is a sectional view of a second version of the second embodiment, and, Figure 4 is an elevation view, partly in axial section, of a portion of a preferred version of the second embodiment of brazing press according to the invention.

Referring to the drawings, Figure 1 shows a main inductor 1 of the brazing press, which makes it possible to join together two plates the first of which is formed by the bottom of a stamped workpiece or pressing 2 which is usually of stainless steel, and the second of which is a plate made of a good heat-conducting material intended to form a heat-diffusing cladding or covering 3, which consists for example, of aluminium or copper, which are to be joined together by the fusion of a brazing composition generally consisting of a flux and a metal alloy generally having a melting point slightly lower (i.e. 30 to 400C lower) than that of one of the two metals which has the lower melting point (ire. aluminium or one of its alloys) inserted between the two plates 2 and 3.

The pressing 2 is supported by a mandrel comprising a first and a second member.

The first member 4 is fixed to the rod 14 of a ram (not shown) mounted on the frame of the press and consists of metal, whereas the second member 5, which is designed to come into contact with the bottom of the pressing 2 which is to receive the heatdiffusing cladding 3 secured thereto by brazing, is made of heat-insulating material, e.g..

an asbestos-cement compound. The second member 5 of the mandrel is supported by the first member 4 and its upper end matches the shape of the inside of the pressing 2.

The heat-diffusing cladding, lining or cover 3 is preformed, i.e., its surface facing the pressing 2 is shaped so as to match the shape of pressing 2. The main inductor 1 is embedded in a plastics or a refractory material based on cement to form a rigid block 6. The block 6 is carried by a metal plate 7 secured to a limb of the frame of the press, (the press being formed in a known manner and not being shown) so as to be disposed opposite to and coaxial with the mandrel 4, 5. The inductor block 6 may be protected against overheating (when it is not made of refractory material) by means of a cold screen and a heat-insulating plate (not shown) of asbestos-cement both placed, in a conventional manner, between the lower face of the block 6 and an intermediate heating element consisting of ferromagnetic material which has been denoted as a susceptor in the above-mentioned patents of the present Assignee.

The dimensions of the main inductor 1 substantially correspond to those of the flat portion of the bottom of the pressing 2, the inductor 1 substantially covering this flat bottom portion.

The main inductor 1 is of a conventional type usually utilized for heating as uniformly as possible a plane surface, such as a flat spiral or "pancake" type inductor having a uniform or non-uniform pitch, or a conical or frustoconical spiral. It is also possible to use advantageously an inductor derived from the flat spiral, as disclosed in the United States patent No. 3,632,948, wherein there is disclosed an inductor having a plurality of concentric turns connected in series and respectively located at different distances from the heating susceptor so as to obtain an essentially uniform heat distribution in the interface between the bottom of the pressing 2 and the heat-diffusing cladding 3. Since the heat-diffusing cladding 3 has raised edges which are also to be brazed to the workpiece 2, in the present instance the press has two separate intermediate heating elements one of which, the element 100, is plane and forms the central part of the susceptor located below the main inductor 1, whereas the other, the element 101, is annular in shape and constitutes the peripheral part of the susceptor and surrounds the central part 100 and the curved periphery of the heat-diffusing cladding 3 as described in French Patent No. 2,105,660 and United States patent No. 3,754,109 referred to above.

In particular, the central part 100 of the susceptor is formed in the present case by a flat plate having approximately the same dimensions as the flat portion of the bottom of the pressing 2, and thus as those of the inductor block 6. The lower face of this plate 100 is intended to come directly into contact with the upper face of the central flat portion of the heat-diffusing cladding or cover 3 and to be heated by the main inductor 1.

The peripheral part 101 of the susceptor is of annular shape and in the present case has a lower face which is curved or inclined so as to follow the shape of the outer face of the raised edges of the heat-diffusing cladding 3, an upper flat face and a lateral outer face which is substantially cylindrical (or possibly frustoconical). The two parts 100, 101 of the susceptor are made of substantially indeformable and slightly magnetic steel.

Since the main inductor 1, as disclosed in the patents referred to above, is provided only for brazing the flat portion of the heatdiffusing cladding 3 to the pressing 2, it is necessary to provide an auxiliary inductor 110 to heat the peripheral annular part 101 of the susceptor, and thus to braze the raised edges of the heat-diffusing cladding 3 to the curved portion of the workpiece 2 connecting the bottom to the side-walls of the latter. The additional inductor 110 includes a single turn or a plurality of turns arranged in helical (solenoid) form and is constituted, for example, by a tube of circular or rectangular cross section, which may consist of copper, through which a cooling fluid flows. The tube is held in place by members 12, e.g. moulded members made of a heat-insulating, preferably refractory, material by means of which the tube is fixed by means of screws 13 to an element 15 secured to the peripheral susceptor part 101. The additional inductor 110 must be disposed around and close to the outer circumferential face of the peripheral part 101 of the susceptor, thus being closely coupled to the susceptor by surrounding it. The number of turns and the shape of the auxiliary inductor 110 and the amperage of the high frequency current flowing through it are calculated to obtain uniform heat distribution throughout the interface between the heat-diffusing cladding 3 and the pressing 2. This can be done either by experiment, i.e., by brazing up some samples and then taking them apart for examination, or by measuring the temperatures in this interface by means of thermocouples according to a method disclosed in United States patent specification No. 3,632,948 mentioned above.

Further, the pressing shown in Figure 1 has a flat central portion forming its bottom and a frustoconical side-wall which is connected to the bottom via curved portions which, together with the bottom, are to be joined by brazing to the heat-diffusing cladding 3. To replace the pressure exerted on the" heat-diffusing cladding or cover 3 by the pivoting movement of the edges of the single susceptor described in the Assignee's first mentioned United States Patent, which would make it possible to press the cladding 3 against the corresponding parts of the pressing, it is the periphery, of the heat diffusing cladding 3 which is acted on, by exerting an auxiliary pressure on the raised edges thereof by means of the annular part 101 of the susceptor. The auxiliary pressure must be independent of that acting on the flat bottom portions of both the pressing 2 and the heat-diffusing cladding 3 in order to act independently on the periphery, while this periphery is softened by the heating.

To this end, the peripheral annular part 101 of the susceptor is rigidly mounted on the lower end of a cylindrical hollow sleeve (or jacket) 15 which is made of an indeformable insulating material and which surrounds the inductor block 6, the sleeve 15 being mounted at its upper end on the supporting plate 7 by means of resilient compression means such as compensation springs 16. The resilient means 16 when compressed by the ascending movement of the ram and the mandrel 4, 5, generate the desired auxiliary pressure. The sleeve 15 may be made of ceramic material or in a more economical manner it may consist of resin-impregnated fibres, e.g., wood fibres embedded in a phenol formaldehyde resin or asbestos fibres embedded in a silicon resin.

It will be noted that the resilient means may comprise a plurality of calibrated helical springs of "coil" form symmetrically disposed with respect to the axis of the inductor block 6 in a circle surrounding the block 6 and having one of their ends resting against the support plate 7 and the other against the sleeve 15.

The total height of the sleeve 15 including the annular part 101 of the susceptor attached to it is chosen in such a way that when the springs 16 are fully compressed, the inner periphery of the lower face of the annular part 101 is situated above the lower face of the central plate 100 of the susceptor.

Thus, an auxiliary pressure, due to the compression force of the calibrated springs 16, is exerted on the curved or raised periphery of the heat-diffusing cladding 3 independently of the pressure exerted on its flat central portion.

Owing to the resilient suspension, the sleeve 15 is displaceable and in order to obtain correct operation in combination with the press assembly, the movement of the sleeve 15 must be confined by guiding means to directions parallel to its axis, that is to say, from below upwards and from above downwards.

The guide means can be produced, for example, by adjusting the inner dimensions of the sleeve 15 to the outer dimensions of the inductor block 6 and by letting the contiguous surfaces slide one with respect to the other. Another way of providing the guide means is to make use of a plurality of vertical rods 17 rigidly mounted in the fixed support plate 7 fixed to the frame of the press, the rods 17 fitting into calibrated vertical holes or bores 18 formed in the sleeve 15 or in a member secured thereto.

The rods 17 and the bores or holes 18 cooperate with one another and must be symmetrically disposed with respect to the axis of the sleeve 15.

It is possible to advantageously combine the guide means with the resilient suspen sion means in the manner illustrated in Figure 1.

Such - a combined assembly comprises rigid guide and retaining rods 17 formed with a screw thread at their two ends, one of which is screwed into screw-threaded holes in the fixed support plate 7 so that the rods 17 extend vertically and are arranged symmetrically about the axis of the block 6. The wall of the sleeve 15 is formed with holes 18 from its upper end, the holes 18 being situated and dimensioned so as to permit the rods 17 to be inserted in them and having sufficient length to provide correct guide action in the vertical direction. The lower ends of the holes 18 open into recesses 19 which have dimen sions sufficient to allow a check nut 21 to be screwed onto the screw-threaded lower end and to permit full vertical movement of the sleeve 15 under the prompting of the ram pushing the rod 14. The check nuts 21 determine the lower position of the sleeve 15 and thus the position of the annular part 101 of the susceptor when no pressure is exerted.

The springs 16, which could be coil springs, are inserted on the rods 17 before their insertion in the holes 18 of the sleeve 15 so as to be disposed between the plate 7 and the upper end thereof.

Experience has shown that it is expedient to utilize springs 16 each comprising a stack or pile of resilient elements or individual springs 22 each of which may comprise a resilient washer of frustoconical shape (termed "Belleville" washers in the trade) since their utilization makes it possible to vary the resilience and stiffness of the composite spring 16 by changing the orientation and/or the number of stacked elements 22.

Figure 1 shows the elements 22 stacked alternately in opposite directions, thereby obtaining maximum elasticity and minimum stiffness. The elements 22 can also be piled up one inside the other or it is possible to combine or to alternate the two ways of assembling to obtain the desired parameters.

It will be noted that it is also possible and perfectly equivalent to place the springs 16 between the lower end of the sleeve 15, which is then inverted and fixed to the sup port plate 7, and the annular part 101 of the susceptor which then rigidly carries, for example, one of the ends of the rods 17.

The operation of the brazing press of Figure 1 is as follows: -when the ram of the press is actuated, the rod 14 carrying the mandrel 4, 5 and the assembly of the elements 2, 3 to be brazed are displaced upwards; since the springs 16 are expanded, the peripheral part 101 of the susceptor is well below the central part 100 of the susceptor and first comes into contact with the curved periphery of the heat-diffusing cladding 3 of aluminium; --continuation of the ascending movement of the ram results in the springs 16 being compressed until the top face of the plane central portion of the cladding is pressed against the bottom face of the central plate lO of the susceptor fixed to the block 6, thereby stopping the ascending movement of the ram. Then the pressure force exerted on the flat bottom portions of an article having a diameter of about 200 mm may be of the order of 4 tons.

The auxiliary pressure on the periphery of the cladding 3 is then exerted, independently of the pressure exerted on its central portion, by the suitably calibrated compensation springs 16 and may reach several 100 kg, which is sufficient for intimately applying the periphery of the cladding 3 against the adjacent parts of the stamping 2 when the aluminium reaches a temperature of about 5800C and becomes easily deformable after a generator supplying the main inductor 1 and the auxiliary inductor 110 has been put in operation.

The stamping 2 shown in Figure 1 has a frustoconical side-wall (a frying pan) and thus there is no difficulty in separating the periphery of the heat-diffusing cladding 3 from the annular part 101 of the susceptor immediately after brazing. The same does not apply when the side-wall is cylindrical (a saucepan) and when the cladding 3 has to cover the beginning of the side-wall. In that case, however, by taking advantage of the higher expansion coefficient of aluminium and of the poor thermal conductivity of the upper part 5 of the mandrel, the annular part 101 of the susceptor positively engages the periphery of the cladding 3 after brazing onto the workpiece and releases it only when the workpiece has cooled sufficiently. This means that when the mandrel 4, 5 has been moved downwards after brazing, the workpiece remains attached to the peripheral part 101 of the susceptor and this slows down the production rate. It would be possible to blow cool air from below into the workpiece from the mandrel 4, 5 or from above onto the cladding 3 via a cylindrical space provided for this purpose between the inductor block 6 and the sleeve 15 to accelerate cooling, but although it is contemplated to do this, the time thus saved is not sufficient.

Accordingly, there is proposed a second embodiment of the brazing press according to the invention in which pressure is exerted on the periphery of the Darts to be brazed independently of the pressure exerted on their central portion, and when the mandrel is withdrawn after brazing, a thrust is exerted on the central portion in order to push the brazed workpieces towards the mandrel notwithstanding the clamping action thereon by the annular part of the susceptor.

Figure 2 shows a partial cross-sectional view in elevation of the second embodiment of the brazing press according to the invention. Parts similar to those shown and described in Figure 1 will have the same numerals used in Figure 2 and all new elements will bear different numerals.

In Figure 2, the mandrel 4, 5 matches the shape of the inside of the pressing 20, which has a cylindrical side-wall (saucepan) and an inductor block 6 and the central susceptor plate 100 joined to the bottom of the block 6 cover only respective flat portions of the bottom of the pressing 20 and of the heat-diffusing cladding 3, whose curved periphery reaches the beginning of the cylindrical side-wall of the pressing 20 and because of this is liable to remain in the grip of the annular part 101 of the susceptor after brazing.

To eliminate this disadvantage, use is made here of a solution derived from that illustrated in Figure 2 of the first mentioned United States Patent No. 3,609,277 where the inductor block 6 can be made movable with respect to the fixed sleeve which surrounds the block and rests on the periphery of the susceptor, in order to effect bending of the periphery of the cladding 3 by means of the raised periphery of the one-piece susceptor. Such mobility was achieved in the abovementioned prior patent by means of a spring which rests against the upper face of the inductor block.

In the second embodiment of the invention illustrated in Figure 2, a sleeve 150 is fixed, at its upper end, to a support plate 7 (e.g. by means of screws) and carries, at its lower end, the peripheral annular part 101 of the susceptor and the auxiliary inductor 110 is designed to heat by induction this annular part. The inductor block 6 is mounted on the same support plate 7 by resilient means so as to be displaceable parallel to its axis of symmetry, so that the auxiliary pressure exerted on the respective flat central portions of the two workpieces 20, 3 to be brazed together is independent of the pressure exerted on the raised or curved periphery.

The resilient means comprises in this case a set of helical springs 160 in the form of a "coil" which are symmetrically arranged with respect to the axis of the inductor block 6 between the inner face of the support plate 7 and the upper face of the block 6.

There are also provided guide means for the axial displacement of the inductor block, the guide means comprising rigid guide and retaining rods 170 having two screwthreaded ends one of which is screwed into the inductor block 6 and the other of which passes through guide holes or bores 180 formed in recesses or cavities 190 provided in the support plate 7, where they carry a check nut 210 which define the lower position of the inductor block 6 when the mandrel 4, 5 is withdrawn. The springs 160 are arranged to encircle each of the rods 170. The springs 160 can be replaced by frustoconical washers of "Belleville" type utilized in the first embodiment shown in Figure 1 or by any other known type of spring.

The operation of the press according to the second embodiment of the invention is as follows: -when the ram is operated, the mandrel 4, 5 which carries the pressing 20 and the cladding 3 starts its ascending movement; during this ascending movement the upper flat face of the heat-diffusing cladding 3 is first brought into contact with the lower face of the central part 100 of the susceptor whose lowered position, which is determined by the check nuts 210, is below the lower face of the adjacent periphery of the annular part 101 of the susceptor; -while the mandrel continues its ascending movement, the springs 160 are compressed and apply pressure on the plane central parts of the two elements 20, 3 to be brazed; -the mandrel 4, 5 then comes into abutting engagement with the fixed annular part 101 through the curved periphery of the bottom of the workpiece 20 and the periphery of the heat-diffusing cladding 3; when, after a high frequency generator (not shown) coupled to both the main inductor 1 and the auxiliary winding 110 has been put into operation and the periphery of the cladding 3 has reached a temperature of about 580"C, the pressure exerted by the ram causes deformation of this periphery so as to press it intimately against the adjacent parts of the pressing 20 during brazing.

As soon as heating has been terminated, the mandrel 4, 5 starts its descending movement and pressure exerted by the springs 160 on the flat central portion of the cladding 3 enables the pressing 20 to be pushed downwards and released from the clamping action of the substantially vertical surfaces of the annular part 101 of the susceptor without the need to wait until it is cooled.

The two embodiments of the invention described above are equivalent because they both allow two mutually independent pressures to be obtained from a single-ram press, one of which acts on-the flat central portion and the other of which acts on the curved edges of the assembly comprising the elements to be brazed 2 (20) and 3.

Figure 3 shows a partial axial crosssectional view in elevation of a preferred variant of the second embodiment illustrated in Figure 2, with the jaws (block 6, mandrel 4, 5) of the press spaced from each other.

Parts similar to those shown and described in Figures 1 and 2 will have the same numerals used in Figure 3 and all new elements will bear different numerals.

In Figure 3, the resilient coupling means 161 between the inductor block 6 and the support plate 7 comprise a single assembly of frustoconical washers ("Belleville") which are stacked or piled up in pairs of alternately reversed washers so as to obtain an assembly calibrated to suit requirements.

The single assembly 161 is coaxially arranged with respect to the inductor block 6 and is inserted on guide means which comprise a hollow sleeve 181 having its upper end screwed in a screw-threaded hole 182 formed in the bottom of a recess 191 in the support plate 7 and a guide and retaining rod 171 disposed along the axis, and fixed to the upper end of, the block 6. The rod 171 is a matched fit in the cavity 183 of the sleeve 181 and its upper end is screwthreaded so as to carry a check nut 21 comprises a single coil in the form of a solid conductive ring 111 which is open and surrounds at a short distance the side wall of the peripheral part 101 of the susceptor.

The ring 111 carries a tube 112 of the same material (copper) which is attached thereto by brazing and through which a cooling fluid flows.

The principal advantage of this preferred variant is the readiness with which the stroke of the inductor block 6 is adjusted by means of a single screw 211 as well as the adjustment of the auxiliary pressure by different arrangements of the stack of washers 22 which form a single spring 161.

It is also possible to improve the operation of a brazing press by making the temperature distribution more uniform between the bottom of the pressing or stamping (2 or 20) and the heat-diffusing cladding while they are being brazed.

One of the possible ways of making such an improvement is disclosed in British patent No. 1,064,903, where the use was proposed, in a brazing press for brazing together two or more flat circular plates of different diameters, of an inductor in the form of a flat spiral (termed a "pancake coil") of large diameter, and of a set of interchangeable windings consisting of single short-circuited turns of different diameters one of which is arranged around the plates to be brazed in the same plane as, and co-axially with, the plates, so as to form a screen by masking those turns of the inductor whose dimensions exceed those of the plates and in this way to ensure uniform distribution of the heat generated by the alternating magnetic flux which passes through them.

Experience has shown that the annular peripheral part of the susceptor to some degree performs the same function as the short-circuited loop in relation to the main inductor, but since when cold it offers by no means negligible resistance to the induced current and because it is arranged below the main inductor, the temperature equalising effect at its edges is inadequate.

Figure 4 is an elevation view, partly in section, of a preferred version of the second embodiment of the invention which enables the uniformity of temperature at the periphery of the plates to be brazed to be improved, by using a metal support-piece of cylindrical shape surrounding the main inductor to carry the annular peripheral part of the susceptor.

The preferred embodiment of brazing press according to the invention which is shown in Figure 4 will thus be chiefly characterised by the fact that it also includes, inserted between the said insulating sleeve and the said annular peripheral part of the susceptor, to each of which it is attached, a cylindrical support-piece made of a metal alloy of low thermal conductivity which surrounds the main inductor block, in order to make more uniform the alternating magnetic flux which is generated by the main inductor in the plane central part of the susceptor.

In the preferred embodiment of Figure 4, the resilient connecting means 164 between the inductor block 6 and the support plate 7 are formed by at least three sets of stacked frustoconical washers 22 (Belleville washers) which are symmetrically arranged relative to the axis of the inductor block 6.

The spring washers 22 are threaded onto mounting means formed by rods 172 which are threaded at both ends, the upper ends 173 being screwed into tapped holes in the support plate 7 and the lower ends 174 being inserted in suitable holes in Ushaped coupling brackets 60 attached to the upper face of the inductor block 6, being retained therein by check nuts 212 whose position determines the travel of the block 6. At the top, the stacked springs 22 bear against a collar 175 secured to rod 172 and at the bottom they bear against a hollow cylindrical block 165 which surrounds rod 172 and whose height is selected in accordance with the number of stacked washers 22 and the manner in which they are stacked so that the required pressure can be obtained.

Means for guiding the axial movements of the inductor block 6 are formed in the present case by a single assembly situated on the axis of the block which comprises a hollow sleeve 184 whose upper end is screwed into a tapped hole 185 formed in the bottom of a recess 191 in the support plate 7, and a guide rod 61 arranged on the axis of the block 6 which is secured to the end thereof. The rod 61 is a matched fit in the bore 186 in sleeve 184.

In the present case the sleeve 15, which is attached at the top to the support plate 7 and surrounds the inductor block 6 and carries the annular peripheral part of the susceptor 101 at the bottom, is in three parts which are secured together. The upper oile 151 of these parts is made of a nonrefractory insulating material (resinimpregnated wood for example) and the lower one 155 adjoining the annular part 101 of the susceptor is made of a refractory metal alloy of low thermal conductivity and high mechtanical strength, such as an alloy of nickel and other metals such as chrome, iron and/or molybdenum for example.

An alloy of this nature consisting of nickel (70 to 80%), chrome (17 to 14%) and iron (10 to 5%) is widely marketed under the name "INCONEL" (registered trade mark of The International Nickel Co.

Inc.) and it has a relative magnetic perme ability close to that of brass (1.003 to 1.007) and a thermal conductivity of around substantially a thirtieth that of copper, thus restricting heat losses by thermal leakage.

These losses are also restricted by the fact that the alloy is of good mechanical strength, which enables the thickness of the lower part 155 of the sleeve to be reduced, this portion being in the shape of a thin but virtually undeformable metal ring or girdle.

The metal girdle 155 is attached at the top to an intermediate part 154 which forms a flange (or directly to the upper part 151), and, when part 154 must not be exposed to heat (being bakelized wood for example), the top of the girdle 155 has brazed to it a metal tube 156 (of copper for example) through which a cooling fluid flows.

At the bottom, the Inconel girdle 155 carries the annular part 101 of the susceptor, which is either attached to it directly by means of screws or rivets for example, or else is detachably connected by means of U-shaped clips 157 or lugs made of a nonrusting refractory metal which are secured at one end to the girdle 155 and whose other ends are free and are passed through cut-outs 105 into an annular groove 104 formed in the cylindrical outer wall of the peripheral part 101 of the susceptor. The fact of the peripheral part 101 of the susceptor being detachably mounted on the lower part 155 of the sleeve 15 of the support has the advantage that it enables stampings 20 of various shapes (saucepans or frying - pans) to be brazed to heatdiffusing claddings 3 which are likewise of various shapes and thicknesses but of closely related diameters, using one and the same inductor assembly, and the annular part 101 easily to be replaced in the event of breakage or wear.

Because, in relation to the main inductor 1 which it surrounds and the auxiliary inductor 110 which surrounds it, the closed girdle 155 constitutes a short-circuited coil carrying an induced current, whose effect is to form a screen and to reduce the intensity of heating at the periphery of the central flat portions of the bottoms of members 3 and 20 and thus to cause the temperature distribution to be more uniform, the path for the induced current needs to be concentrated at certain points. It is therefore sometimes advantageous to form in the girdle oblong vertical slots 158, whose number, length and position are determined by experiment when the reduction in temperature at the periphery is found to be too great with a solid girdle 155 (in the case of articles of small diameter for example).

Between the upper insulating part 151 and the lower conductive part 155 of the sleeve, is inserted an intermediate part 154 which forms a radially projecting flange which is intended to carry the auxiliary inductor 110 by means of threaded rods 134, nuts 131 and 133, and parts made of insulating material which come into contact with the metal parts of the auxiliary inductor. These insulating parts comprise a sleeve 135 provided with a collar 136, which is threaded onto the threaded rod 134, and two washers 137, 138 of which the first 137 is rigid to set the spacing between the coils of the auxiliary inductor 110 and of which the second, 138, together with the collar 136 on sleeve 135, serves to insulate the inductor 110 from the nut 131. The thread 139 at the top of rod 134 is screwed into a tapped hole in the central portion of the sleeve 15 which forms the flange 154, which is preferably likewise made of a non-refractory insulating material (a plastics material or a composite material formed from polymerising resins and glass, textile or wood fibres for instance).

It should be noted that the insulating upper part 151 and the insulating intermediate part 154 (the flange) of the sleeve 15 may be all in one piece, with a considerable amount of material being lost during machining.

In the preferred embodiment of Figure 4, the auxiliary inductor 110 which is coupled to the annular peripheral part 101 of the susceptor is formed by two superimposed coils consisting of two solid conductive rings 111 which enclose the lateral wall of the peripheral part 101 of the susceptor at a short distance from it. At its periphery, and brazed to it, each ring 111 carries a tube 112 of the same material (copper) through which a cooling fluid flows.

From a single-ram press, it is possible in accordance with the present invention to obtain two mutually independent pressures which act in the one case against the flat central portions of the members 20 and 3 to be brazed, and on the other against their curved edges.

It should also be noted that the metal supporting girdle 155 for the annular peripheral part of the susceptor 101 may also be used in the first embodiment of the invention shown in Figure 1, where it is the sleeve 15 which is coupled to the frame of t-he press by resilient means 16 and the inductor block 6 is fixed.

The invention is applicable in particular to the brazing of heat diffusing claddings made of a good heat conducting material such as aluminium or copper, to stamped cooking vessels of stainless steel (saucepans, frying-pans or pressure-cookers). It is also possible to braze two or more claddings to the same workpiece to obtain a multilayer structure (stainless steel, aluminium or copper, and steel).

The brazing presses described herein make it possible to avoid the risk of permanent or insufficient deformation by exerting additional pressure not on the sidewalls but on the curved edges of the cladding without the need to use a double-acting press as in the French patent No. 2105660 referred to above.

WHAT WE CLAIM IS: 1. A brazing press for assembling receptacles having a layered bottom portion obtained by joining a pressing or stamping having a flat bottom, a sidewall symmetrical about an axis normal to said bottom and a curved portion linking said bottom to said sidewall, to a preformed cladding having a central portion for covering said bottom and a peripheral portion for covering at least part of said curved portion, said press comprising a fixed supporting frame, a press ram carried by said frame, a mandrel reciprocable by means of said ram for supporting said pressing, a block containing a main inductor situated opposite, above and coaxially with said mandrel and coupled to said frame, intermediate heating means of a ferromagnetic metal including a flat central part associated with the bottom face of said inductor block and magnetically coupled to said main inductor for applying pressure to and heating the central portion of said cladding when in use, and an annular, peripheral part having an inner face matching in shape the outer face of the peripheral portion of said cladding which covers the curved portion of said pressing or stamping, an auxiliary inductor surrounding and magnetically coupled to said annular peripheral part for heating it, a cylindrical sleeve member, at least a portion of which is made of a non-deformable insulating material surrounding said block coaxially and having its upper end coupled to said frame for carrying at its lower end said annular peripheral part and said auxiliary inductor, wherein one of said central and peripheral parts of said intermediate heating means is coupled to said frame by means of calibrated resilient coupling means and is guided by guide means to be displaceable axially, whereas the other part is fixed to said frame, so as to obtain an auxiliary pressure exerted on said peripheral cladding portion which is independent of the that acting on said central portion when said single ram compresses the cladding and pressing between said mandrel and said block.

2. A press according to claim 1, further comprising retaining means for determining the axially most distant position of the mobile part relatively to the fixed one of said intermediate heating means.

3. A press according to either of claims 1 or 2, wherein the said resilient means are formed by calibrated springs disposed around the inductor block symmetrically to its axis.

4. A press according to claim 3, wherein said springs are formed by assemblies of individual resilient or spring members, such as frustoconical washers.

5. A press according to any one of claims 1, 2, 3 or 4, wherein the resilient means and the guide means are fitted in a combined fashion.

6. A press according to any one of claims 2, 3, 4 or 5, wherein said guide means are made up from at least one sleeve and at least one rod slidably inserted inside said sleeve, each having one end respectively secured to the supporting frame and the mobile part of said intermediate heating means and parallel to the common axis of said mandrel, sleeve member and block, wherein said retaining means is formed by a radial projection secured to the free end of said at least one rod which emerges from said sleeve.

7. A press according to any one of claims 1 to 6, wherein said resilient coupling means comprise more than two calibrated springs disposed symmetrically relatively to the common axis of said mandrel, block and sleeve member, between the top end of said sleeve member surrounding said block which is fixed to the frame and said supporting frame, the bottom end of said sleeve member being secured to said annular peripheral part of said intermediate heating means.

8. A press according to any one of claims 1 to 6, wherein said resilient coupling means comprise more than two calibrated springs disposed symmetrically relatively to the common axis of said block, said mandrel and said sleeve member, between the bottom end of said sleeve member surrounding said block which is fixed to the frame and said annular peripheral part of said intermediate heating means, the top end of said sleeve member being secured to said frame.

9. A press according to any one of claims 1 to 6, wherein said resilient coupling means comprise at least one calibrated spring disposed symmetrically relatively to the common axis of said mandrel, block and sleeve member, between said block and said supporting frame, the top end said sleeve member being secured to said frame and said annular peripheral part of said intermediate heating means being secured to the bottom end of said sleeve member, so as to allow the ejection of the stamping on pressing from the annular peripheral part of the intermediate heating means which grips the peripheral cladding portion, by the downwards motion of the block urged by said at least one spring to follow the withdrawal of the mandrel after brazing.

10. A press according to claim 9, wherein said guide means comprise a single guide

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. make it possible to avoid the risk of permanent or insufficient deformation by exerting additional pressure not on the sidewalls but on the curved edges of the cladding without the need to use a double-acting press as in the French patent No. 2105660 referred to above. WHAT WE CLAIM IS:

1. A brazing press for assembling receptacles having a layered bottom portion obtained by joining a pressing or stamping having a flat bottom, a sidewall symmetrical about an axis normal to said bottom and a curved portion linking said bottom to said sidewall, to a preformed cladding having a central portion for covering said bottom and a peripheral portion for covering at least part of said curved portion, said press comprising a fixed supporting frame, a press ram carried by said frame, a mandrel reciprocable by means of said ram for supporting said pressing, a block containing a main inductor situated opposite, above and coaxially with said mandrel and coupled to said frame, intermediate heating means of a ferromagnetic metal including a flat central part associated with the bottom face of said inductor block and magnetically coupled to said main inductor for applying pressure to and heating the central portion of said cladding when in use, and an annular, peripheral part having an inner face matching in shape the outer face of the peripheral portion of said cladding which covers the curved portion of said pressing or stamping, an auxiliary inductor surrounding and magnetically coupled to said annular peripheral part for heating it, a cylindrical sleeve member, at least a portion of which is made of a non-deformable insulating material surrounding said block coaxially and having its upper end coupled to said frame for carrying at its lower end said annular peripheral part and said auxiliary inductor, wherein one of said central and peripheral parts of said intermediate heating means is coupled to said frame by means of calibrated resilient coupling means and is guided by guide means to be displaceable axially, whereas the other part is fixed to said frame, so as to obtain an auxiliary pressure exerted on said peripheral cladding portion which is independent of the that acting on said central portion when said single ram compresses the cladding and pressing between said mandrel and said block.

rod and a single hollow guide sleeve slideably surrounding said rod and respectively fixed to said block on its axis and to said frame.

11. A press according to claim 10, wherein said resilient coupling means comprise a single spring assembly encircling said hollow guide sleeve.

12. A press according to claim 10, wherein said resilient coupling means are formed by at least three assemblies of individual springs in the form of washers, which are arranged symmetrically in relation to the axis of said block.

13. A brazing press according to any one of claims 9, 10, 11 and 12, wherein the said sleeve member has an upper insulating part which is attached at the top to the frame of the press and a lower part made of a metal alloy of low thermal conductivity which carries the peripheral part of the intermediate heating means, the two parts of the sleeve being fixed to one another. the said lower metal part forming a closed short-circuited girdle around the main inductor which enables the temperature distribution in the flat central part of the intermediate heating means to be made substantially uniform.

14. A press according to claim 13, wherein the said alloy is an alloy of nickel and at least one other metal selected from the group comprising chrome, iron and molybdenum.

15. A press according to claim 14, wherein the said alloy consists of nickel, chrome and iron, being such as the alloy which is marketed under the name "Inconel" (registered trade mark).

16. A press according to any of claims 13, 14 and 15, wherein the said girdle contains vertically orientated oblong cut-outs which enable the paths of the induced currents to be restricted to desired areas so as to achieve optimum uniformity of temperature.

17. A press according to any of claims 13 to 16, wherein, when the upper insulating part of the sleeve is non-refractory, the lower metal part carries, brazed to it in the region of its contact with the bottom of the upper part, a metal tube conveying a cooling fluid.

18. Brazing presses substantially as hereinbefore described with reference to Figure 1, or Figure 2, or Figure 3 or Figure 4 of the accompanying drawings.