GB2029928A - Improvements in or relating to pressure mounting assemblies - Google Patents

Abstract

A pressure mounting assembly which is particularly suitable for mounting high power electronic components such as thyristors is provided with an indicator to indicate when a predetermined mounting pressure has been reached. The pressure mounting assembly consists of two pressure rings 3 and 4 which initially are forced by disc washers 5 against internal abutments 6 and 7 formed in the wall of a cylindrical shell 1. When a predetermined mounting pressure is achieved the disc washers 5 are compressed due to loads on collars 9, 10 sufficiently to free the rings 3 and 4 from the abutments band 7 so that the shell 1 is free to rotate under the action of a torsion spring 5 thus providing an indication that the predetermined load has been reached. <IMAGE>

Description

SPECIFICATION Improvements in or relating to pressure mounting assemblies This invention relates to pressure mounting assemblies and is primarily intended for use in mounting high power electronic components on to thermal and/or electrical conductors.

In order to ensure the existence of a sufficiently good thermal and/or electrical path between a conductor and such a component it is usually necessary to provide some means for holding the two in intimate pressure contact, as the alternative of providing a permanent bond between the two. for example by means of soldering or welding, is unacceptable in many instances because of the nature of the component and/or the need to replace easily the component from time to time. In practice it is difficult to ensure that just the right degree of pressure exists between a high power electronic component and a thermal or electrical conductor. If the pressure is too low the poor thermal or electrical contact respectively may impair the satisfactory operation of the component and may even seriously damage it, whilst if the pressure is too high the component may suffer irreparable damage.In fact, for many high power electronic components the correct pressure is rather critical. The difficulty is aggravated by the fact that components are often sold for installation by a customer who, even if he takes the trouble to ascertain the correct mounting pressure, may well have no way of checking that the correct pressure is being applied. The present invention seeks to provide a pressure mounting assembly in which this difficulty is reduced.

According to this invention a pressure mounting assembly for mounting a component to a body includes spaced first and second reaction members with resilient means positioned therebetween, and a housing arranged to surround and locate the first and second reaction members and the resilient means, the housing being held firmly in one position by means of pressure exerted on the reaction members by the resilient means, the arrangement being such that when the assembly is used to pressure mount the component to the body the resilient means are compressed in the mounting operation by means of an elongate pressure member passing through aligned apertures in the housing, first and second reaction members and the resilient means so that when a predetermined mounting pressure is reached the housing is free to rotate about the elongate pressure member.

Preferably resilient bias means are provided to produce rotation of the housing when said predetermined mounting pressure is reached.

Preferably again the resilient bias means urges rotation of the housing to a position at which it is free to move in the direction of the axis of the elongate pressure member. If the elongate pressure member or the component or the body relaxes whilst a component is mounted to a body this freedom of movement prevents reduction or removal of the mounting pressure from the component.

Preferably again the housing is a cylindrical shell and the resilient means comprises one or more dished annular washers mounted co-axially within the cylindrical shell.

Preferably the first and second reaction members are held in position in the cylindrical shell by internal abutments formed in the wall of the shell and against which they are urged by the action of the resilient means. The strength of the resilient means and the distance apart at which the reaction members are held by the abutments determine the predetermined pressure at which the housing becomes free to rotate, and conveniently the reaction members and the resilient means during manufacture of the assembly are compressed by the predetermined pressure, and at least some of the abutments formed whilst the pressure is maintained so as to prevent relative movement of the reaction members away from each other when the pressure is released.

The invention is further described by way of example with reference to the accompanying drawings in which, Figure 1 shows a section view of a pressure mounting assembly in accordance with the present invention, Figure 2 shows a plan view of the assembly shown in Figure 1.

Figure 3 shows a cylindrical shell forming part of the assembly, Figure 4 shows a reaction member, Figure 5 shows a resilient bias means and Figure 6 illustrates the use of a pressure mounting assembly in accordance with the present invention to mount a component to a body.

Referring to Figures 1 and 2, a housing in the form of a cylindrical shell 1 surrounds first and second reaction members in the form of pressure rings 3 and 4, which sandwich between them a number of disc springs 5. The pressure rings 3 and 4 are retained in position by abutments 6 and 7, which constitute deformed portions of the shell 1. As can be seen more clearly from Figure 2, three abutments 6 and three abutments 7 are provided. The collar 8 is bonded to the upper pressure ring 3 and in use the upper surface 9 of the annular 8 receives the head of a mounting bolt which passes through aligned apertures formed in the collar 8, first and second pressure rings 3 and 4 and the disc springs 5. The shell 1 is in the form of an open ended cylinder and at its lower end a further collar 10 is bonded to the lower pressure ring 4.A resilient bias means in the form of a torsion spring 11 is positioned around the outside of the lower collar 10 and at one end the torsion spring 11 is secured to a tab 12 formed in the wall of the shell 1 and at its other end is located in a small aperture 13 formed in the lower pressure ring 4.

The pressure mounting assembly shown in Figures 1 and 2 is in its assembly state and is ready for use for mounting a component to a body. The construction of the pressure mounting assembly can be more clearly seen with reference to Figures 3, 4 and 5, which illustrate parts thereof in greater detail.

The lower pressure ring 4 is a plain washer, having an outer diameter corresponding to the diameter of projections 15 formed on the upper pressure ring 4, which is described subsequently. Its diameter is such that the washer is just able to rotate freely within the cylindrical shell 1. The small aperture 13 is a small circular hole passing through the thickness of the washer.

Referring to these drawings, the shell 1 is initially formed of a short length of cylindical tubing, typically stainless steel, in which three internal abutments 7 are formed by piercing and distorting appropriate portions of the wall of the cylindrical shell 1. The tab 12 is formed at this stage and the torsion spring 11 is subsequently fitted to the shell 1.

Plan and elevation views of the tension spring 11 are shown in Figure 5. The hook 25 of this spring 11 is clipped behind the tab 12 in the manner shown in Figure 2. The lower pressure ring 4 is placed in position resting on the abutments 7, with the free end 26 of the torsion spring 11 inserted into the aperture 13 of the lower pressure ring 4. The lower collar 10 is then inserted through the torsion spring 11 into the pressure ring 4, the ring 4 and the collar 10 being permanently fixed together, for example, by means of a suitable adhesive.

The disc springs 5, which are dished washers of suitable thickness and diameter, are positioned above the lower pressure ring 4 as shown in Figure 1 after which the upper pressure ring 3 is positioned above it. The pressure ring 3 is more clearly illustrated in Figure 4 and it can be seen from drawing b that the upper surface of the ring is provided with three raised lips 27. The circumferential position of the lower pressure ring 4 is adjusted with respect to the shell 1 so that tab 12 that secures the hook 25 of the torsion spring 11 holds the spring under tension.

The upper pressure ring 3 is rotated circumferentially so that the three projections 15 are adjacent the position where the upper abutments 6 are to be formed. The pressure mounting assembly is placed in a suitable press and a predetermined pressure applied between the upper surface of the upper pressure ring 3 and the lower surface of the collar 10 so as to compress the disc springs 5. When the correct predetermined pressure is applied the shell 1 is pierced by a staking tool in three positions equally spaced around the circumference of the shell 1 to form the upper abutments 6, which hold the upper pressure ring 3 captive, thus maintaining the disc springs 5 under permanent compression.

During this operation it is likely that the shell 1 just below the position of the abutments 6 will have been forced against the three projections 15 in the upper pressure ring 3 making it difficult for the shell 1 to rotate. Advantageously before the assembly is removed from the press, a suitable tool is clamped around the shell 1, which is then rotated forecably ani-clockwise so that the abutments lie over the positions X marked on Figure 4 so that in this position any distortion of the shell immediately below the abutments will be clear of the projections 15 and will be free to rotate. The shell 1 is held in this position relative to the abutments 6, whilst it is removed from the press and the disc springs 5 force the two pressure rings 3 and 4 apart against the abutments 6 and 7, which locks the shell 1 firmly in place preventing its rotation.Finally, the upper collar 9 is inserted into the upper pressure ring 3 and bonded into place by means of a suitable adhesive.

When the pressure mounting assembly is to be used to mount a component to a body a threaded rod or bolt 16 is inserted through the central apertures in the manner shown in Figure 6. The lower surface of the collar 10 rests upon a plate 17 and the component 18 is held against a body 19 by the action of the bolt 16, which passes through a small aperture formed in the plate 17 and which is threaded into a tapped hole formed in the upper surface of the body 19. With the arrangement shown in Figure 6, two pressure mounting assemblies would be required, one on either side of the component 18, but if the component 18 is itself apertured, the bolt 16 may pass through it in which case only a single pressure mounting assembly is required.The bolt 16 is tightened down until the springs 5 are compressed to a point where the pressure rings 3 and 4 are no longer firmly held against the abutments 6 and 7 of the shell 1. The shell 1 is then free to rotate and turns anti-clockwise (when viewed from above) under the influence of the torsion springs 11. The shell 1 turns until the three abutments 6 are stopped by the three lips 27 on the upper surface of the pressure ring 3. At this point the abutments 6 and 7 align with the recesses 20 formed in the pressure rings 3 and 4, so that the shell 1 is free to move in a vertfical place with respect to the pressure rings 3 and 4 and the disc springs 5. Thus any relaxation in the bolt 16 or the structure of the equipment in which the component 18 is mounted can be taken up by the deflection of the disc springs 5 without significantly altering the pressure applied to the component 18.

The invention is particularly suitable for mounting a higher power thyristor to a heat sink. By means of the pressure mounting assembly a thyristor can be clamped to a heat sink with an accurately predetermined pressure. Conveniently the shell 1 is provided with visible markings so that it can be ascertained at a glance whether it has been rotated to its correct position by the action of the torsion spring 11. In practice it is expected that the shell 1 will produce an audible click when its rotation is brought to rest by contact of the internal abutments with the raised lips on the upper pressure ring, thereby informing an operatorthatthe correct mounting pressure has now been reached.

Claims (6)

1. A pressure mounting assembly for mounting a component to a body including spaced first and second reaction members with resilient means positioned therebetween, and a housing arranged to surround and locate the first and second reaction members and the resilient means, the housing being held firmly in one position by means of pressure exerted on the reaction members by the resilient means, the arrangement being such that when the assembly is used to pressure mount the component to the body the resilient means are compressed in the mounting operation by means of an elongate pressure member passing through aligned apertures in the housing, first and second reaction members and the resilient means so that when a predetermined mounting pressure is reached the housing is free to rotate about the elongate pressure member.

2. An assembly as claimed in claim 1 and wherein resilient bias means are provided to produce rotation of the housing when said predetermined mounting pressure is reached.

3. An assembly as claimed in claim 2 and wherein the resilient bias means urges rotation of the housing to a position at which it is free to move in the direction of the axis of the elongate pressure member.

4. An assembly as claimed in claim 3 and wherein the housing is a cylindrical shell and the resilient means comprises one or more dished annular washers mounted co-axially within the cylindrical shell.

5. An assembly as claimed in claim 4 and wherein the first and second reaction members are held in position in the cylindrical shell by internal abutments formed in the wall of the shell and against which they are urged by the action of the resilient means.

6. A pressure mounting assembly for mounting a component to a body substantially as illustrated in and described by reference to Figure 1 of the accompanying drawings.