GB1583191A

GB1583191A - Housing for an electrical appliance

Info

Publication number: GB1583191A
Application number: GB1721677A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1976-04-24
Filing date: 1977-04-25
Publication date: 1981-01-21
Also published as: FR2349257B1; FR2349257A1; DE2617965A1; YU104677A; DE2617965B2

Description

(54) A HOUSING FOR AN ELECTRICAL APPLIANCE (71) We, BROWN, BOVERI & CIE, AKTIENGESSELLSCHAFT, of D 6800 Mannheim-Käfertal, Kallstadter Strasse 1, Federal Republic of Germany 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 invention relates to a housing for an electrical appliance, the housing being of the type comprising two parts having interengaging edges defining a gap which is filled with cast resin. Explosion-proof housings are required for electrical and/or electronic appliances in explosion-endangered areas for the control and/or regulation of motors and/or complete plants. Such explosion-endangered areas may be present in chemical process technology, where the accumulation of explosive mixtures has to be reckoned with. An example of the use of such a housing is the safe encapsulation of an electromagnetic contactor for the purpose of controlling a motor.

Most commercially available explosionproof housings of the aforementioned type are too specific to the appliance in regard to configuration.

Explosion-proof housings of the aforementioned type are usually manufactured from grey cast iron and also have besides an explosion-proof switch chamber space, a connecting space, adapted to the cross-section of the wire or cable to be connected, for increased safety. Certain electrical and/or electronic functional units, for example, a contactor, must be metal clad in an explosion-proof way, but do not always require a connecting space for increased safety.

Some disadvantages of this explosionproof encapsulation are The housings are usually of comparatively large volume, in comparison with the volume of the appliance which is to be accepted and metal clad. As the housings are conceived to be large-volumed, i.e. have to be usable as multilaterally as possible, the wall thickness, for this reason, must necessarily be in relation to the volume of the switch chamber. Caused by this dependence between the volumes, this entails, because of the accumulation of material, a noticeable increase in cost and increase in the weight of the end product.

An increase in the weight of the housing however, requires once again in the plant a specially stable and therefore materialintensive costly construction in order to fasten the device which is composed of a functional unit which may be very small.

As the housing combines in itself not only the switch chamber but also the connecting space for increased safety, but separates them spatially one from the other by suitable ballast, from a manufacturing and technological point of view a high degree of accuracy is demanded, and consequently further increases in cost caused by labourintensive processing result.

If the housing, however, is to be maximally armed with electrical and/or electronic functional units, the switch chamber space of the same has a gap area and gap length correspondingly adapted to the operating zone and the medium, for encapsulation which is impenetrable by fire, before a unit thus metal clad can be put into operation.

If an explosion-proof housing which is armed to the maximum with electrical and/ or electronic appliances has to have a gap of predetermined length and breadth, it is therefore necessary that the two parts which form the switch chamber space be either face-ground, cylindrically precision-finished or provided with a thread, i.e. in both cases a cylindrical collar with or without a thread must be able to be inserted with play into a cylindrical aperture either with or without a thread.

In the event of construction of the housing members without a thread, means such as, for example, threaded bolts, nuts, screws and chuck jaws for holding together the parts forming the switch chamber space are therefore necessary.

Furthermore, a housing with an explosion proof switch chamber space has become known in a special type of protection, in which grooves are provided in the faceground surfaces - fitting surfaces -, the exposed sides of which face each other congruently and enclose the switch chamber all round with one partial area, i.e. the grooves form inside the housing body a closed passage system - in communication which is represented at least on one outer side, - top edge - as a groove which is open on one side. The holding-together of the housing members occurs purely and simply by cast resin which is poured via the groove into the passage system. This means, however, that the face-ground surfaces have to possess a small peak-to-valley roughness, so that the cast resin cannot penetrate from the passage system into the switch chamber space or outside the housing. This type of construction of an explosion proof housing necessitates in the manufacture of an explosion-proof encapsulation precise auxiliary means and casting equipment and a high degree of skill if filling takes place manually, which once again results in an increase in costs.

Furthermore, it should also be noted at this point, that in contrast to the peak-tovalley roughness of the fitting surfaces, the peak-to-valley roughness of the grooves must be very great, so that a decided connection between the housing members is guaranteed for a long period.

The task which underlay the present invention was to limit to a minimum the not inconsiderable manufacturing and technological but also use-technological disadantages of known explosion-proof housings.

According to the present invention there is provided a housing for an electrical appliance, comprising: a first part and a second part, the first part having an annular peripheral wall and the second part having an annular groove formed therein and into which the annular peripheral wall of the first part projects, the housing containing line bushings or terminals for connection to the electrical appliance. an annular gap being defined between the annular peripheral wall of the first part and the second part, the gap being filled with cast resin which extends across the gap between the second part and the annular peripheral wall of the first part, securing elements locking the two parts together, assembly of the housing having comprised inserting the annular peripheral wall of the first part into the annular gap of the second part, the securing elements thereupon locking the first and second parts together.

The first and second parts may be circular in cross section, the cross-sectional area of the second part decreasing in the direction away from the first part. This allows the two parts to be made with large manufacturing tolerance and production of an unusable switch chamber space is avoided or hindered.

The circular shape, which is ideal from a manufacturing technology point of view, does not, however, preclude the first and second parts being square or rectangular in cross-section, the cross-sectional area of the second part decreasing in the direction away from the first part. The corners and edges at the surface transitions are preferably constructed as radii for ease of manufacture.

The first and second parts can be constructed not only as plastics parts, the first part being provided with integrated line bushings or terminals, but also as a cast aluminium or aluminium injection-moulded parts, the line bushings or terminals being insulated. Such an aluminium part can have an oxide film, which brings two noteworthy and important properties with it; namely, a toughening of the surface - hardness - on the one hand, and an increase in peak-to-valley roughness, on the other hand. As a result of the great peak-to-valley roughness produced by the oxide film, a further outstanding property is produced, that is to say, that of a partial brake, i.e. the hot copper particles which are set free by the electrical appliance during switching in the switch chamber space cannot dislodge any aluminium particles from part which is brought into use, because of the hardening of the surface. Furthermore, the hot particles are decelerated by the superficial peak-to-valley roughness, so that the danger of escape of ignitable particles - which may occur through gaps between actuating elements which are brought out - is very strongly hindered, as gaps between the first and second parts do not exist because they are filled up with cast resin.

Preferably the line bushings or terminals are disposed adjacent the peripheral wall of the first part and secondary walls are disposed between the bushings, on the interior and on the exterior of the first part, to increase air and creep gaps between adjacent bushings. Preferably the peripheral wall of the first part projects beyond the secondary walls on the interior of the first part. At least some of the secondary walls on the exterior of the first part may have respective noses engaging a cap surrounding the first part of the housing.

Consequently. in a simple manner, a further and not inconsiderable double protection can be produced, as the cap may simultaneously be used as a blind shape for the cast resin after wiring has taken place and the tail of the cable has been brought out, whereby the cap is so located on the base part that adequate protection - leakage distances and air gaps - is also ensured without a grouting compound.

The invention is further described below by way of example with reference to the accompanying drawings, in which: Figure 1 is a partial section through a housing according to the present invention; Figure 2 is an inverted plan view of the housing shown in Figure 1; Figure 3 is a section through the top of the upper portion of one form of the top part of the housing; Figure 3a is a plan view of the upper portion of Figure 3, Figure 3 being a section along the section line shown in Figure 3a; Figure 4 is a section through the upper portion of another form of the top part of the housing.

In the drawings like reference numerals indicate like parts. Referring to Figure 1, a housing 30 comprises a first or bottom part 31, a second or top part 32, a resilient gasket 33 interposed between the parts 31 and 32, flexible resilient parts 34 holding the parts 31 and 32 together, and grouting compound 35. The bottom part 31 comprises a base having upper and lower surfaces 36 and 36a respectively and an upstanding peripheral wall. In the housing 30, an electrical switching appliance 37 is firmly located on the base of the part 31. Mains supply and connecting wires 38 are connected to line bushings or terminals 39, which penetrate the base of the part 3. Furthermore, stays or secondary walls 40 are located not only on the upper side 36 of the base but also on the lower side of the base between the line bushings 39, in order to increase air and creep gaps between adjacent line bushings. The stays 40 on the upper side of the base 36 are connected not only to the base but also to an annular edge 41 of the peripheral wall of the part 31. The stays 40 on the surface 36a are connected only to the base. The annular edge 41 of the part 31 terminates upwardly and inwardly in a rebate 42. The outlying stays 40 have noses 43 approximately in a base area 40a.

The noses 43 accept a cap 44 which is detachable by means of a snapping technique and surrounds the bottom part 31. The cap 44 is flush with the top part 32 along a line 45, i.e. the bottom part 31 with the cap 44 does not extend laterally beyond the top part 32. A cable tail 47, which is connected by soldering to the line bushings 39, is brought out of an "increased safety" connecting space 46 formed by the bottom part 31 and the cap 44. The "increased safety" connecting space 46, which is formed from the cap 44 which is snapped onto the bottom part 31, is filled up with further grouting compound 35 via a filling aperture which is provided in the cap 44, as a result of which the formation of leakage distances is impossible or is at least substantially eliminated, and at the same time, tension relief as a fixture and also protection against buckling can be achieved. An annular edge 49 of the cap 44 has a narrow sealing lip 49a, which is formed from inside to outside by a bevel, whereby gap and space grouting can take place in one operation, i.e. the sealing lip 49a of the cap 44 rests tightly against the edge 50 of the top part 32 and one operation can be saved. The top part 32.with a square cross-section area which tapers upwardly, has an inner annular groove 53 which is adjacent an inner edge 52 of the top part 32 and by which the switch chamber space 55 is formed as a result of the gasket 33 and the annular edge 41 of the peripheral wall of the bottom part 31 and also the flexible moulded part 34 which engage projections 41a and 54 of the bottom part 31 and top part 32 respectively, and as a result of the grouting compound 35. The projections 54, as support surfaces for the flexible moulded parts 34, can have various shapes. The groove 53 is of substantially trapezoidal section.

Each of the resilient flexible moulded parts 34 is flat in section and comprises a first portion 34b, the free end of which engages underneath the projection 41a of the peripheral wall of the bottom part 31, a second end portion 34a' and a third portion 34a". The first and second portions are at an obtuse angle to each other and the second and third portions are at right angles to each other.

Whilst the projection 41a is located running round the edge 41 of the bottom part 31 for reasons of efficiency, the radially outlying projections 54 on the edge 52 of the top part 32 are so designed that they are in material communication via suitable apertures 56 with recesses 57 located alternately to the projections 54 and with an edge wall 58, so that the projections 41a and 54 and also the edge wall 58 acts as an abutment for the flexible moulded parts 34 for the connection of top and bottom part 32 and 31, i.e. to produce an explosion-proof switch chamber space 55.

Referring to Figure 2, the flexible moulded parts 34 are located as security elements and are mutually spaced over the periphery 6 of the bottom and top parts 31 and 32 between rims - projection 41a and projection 54, aperture 56, set-back 57 and also one wall 58 of the top part 32 - for the purpose of self-closure and forced closure.

In this state of assembly, the switch chamber space 55 is formed by the rubberlike gasket 33 which is inserted between the bottom and top parts 31 and 32, and is hermetically sealed from the outside atmosphere, so that essentially only the grouting compound 35 has to be cast in a gap 59 which forms between the bottom and top parts 31 and 32.

Hereafter, the assembly of the compression-proof housing 30 will be described by way of example. As stated previously, the electrical switching appliance 37 is installed on the upper surface 36 of the base of the bottom part 31, so that the latter only has to be inserted manually or mechanically with a clearance width X formed from the edge 52 of the top part 32 and the free portions 34b of the flexible moulded parts 34, into the top part 32, which has already been prepared placing the rubberlike gasket 33 into the groove 53 and positioning portions 34a' of the flexible moulded parts 34 in the apertures 56. The clearance width X decreases towards the groove 53, so that a frustoconical or truncated pyramid-shaped aperture is formed, depending upon the cross-section of the parts 31 and 32.

For reasons of casting technology, and in order to avoid flaw points in the gap grouting of the groove 53, the flexible moulded parts 34 have bores 34d in the free arms 34c which are in the groove 53. The bores 34d are so dimensioned that weakening does not occur as a result of aging.

During the assembly procedure, that is to say, the insertion of the bottom part 31 into the top part 32, an outer surface 41b, which is tapered towards the free edge 41, slides over the portions 34b of the parts 34 as a result of a force P, which acts in a certain way on the bottom part 31, into the top part 32, using the dead weight of the bottom part and using respective slide-pairing of the materials e.g. steel-plastics or steelaluminium.

The edge 41 of the bottom part 31 deforms and compresses the rubberlike gasket 33, when encountering it positioned in the groove 53, to an extent such as permits the free arm ends 34a, using a spring action enlargement of the clearance width X - to slide from the outer surface 41b onto a projection 41a, expanding the deformed rubberlike gasket 33, there to remain in a final position, so that a hermetically encapsulated switch chamber space 55 is formed between the bottom part 31 and the top part 32. The switch chamber space 55. i.e. the parts 31 and 32. are converted in this way by gap grouting in the form of grouting compound 35, into an undetachable compression-proof encapsulation. The grouting compound 35 is resin which is cast into the gap 59 and the space 46.

There exists the possibility of repeated opening of the switch chamber space 55, but this can only occur by means of a suitable tool which is suited to the parts 31, 32 and 34, and offers the manufacturer the chance of repeated use of the parts 31 and 32 forming the compression-proof housing, if a suitable grouting compound 35 which can be dissolved out is used.

In Figures 3 and 3a there is represented, a detachable plate 61 which is located in the upper portion 51 of the top part 32, and which permits a multitude of potentialities of use of the compression-proof housing 30.

Thus, the plate 61 can be provided as a metal and/or plastics with breaches 62, which may be desirable, depending upon requirements. The plate can here be inserted as a threaded or perforated flange (gland) 64 into the portion 51 from outside or inside, or an inspection glass 65 can be integrated in the plate 61 or occupy an entire area and have actuating elements such as elements 63 shown in Figure 4.

Obviously, any other conceivable arrangement and sequence of the elements being used is possible, so that by this means, high-power electrical and or electronic switching appliances 37 can be inserted and operated from outside in a comparatively small, attractive and handy compressionproof housing 30, without the housing wall thickness of the parts 31 and 32 having to be greater on account of possible high internal pressure occurring and because of corresponding heat generation by the high-power electrical and/or electronic appliances 37, and the gap grouting between the bottom part 31 and top part 32 having to be correspondingly thicker in dimensions, or without making a larger housing necessary.

A valve can be located in the portion 51 because of the high-power electrical switching appliance 37 which is in the switch chamber 55, which valve, for the purpose of effective pressure reduction in the switch chamber space 55, has available the gap area which is particularly necessary for it, and is provided with a particle brake. as through the selection of the connecting elements in the form of flexible moulded parts 34, the gap 59 between the top and bottom part 31 and 32 basically has to be filled up with grouting compound 35.

The range of use of the housing 30 of the invention can consequently be enlarged for an imposing number of electrical and/or electronic appliances.

Figure 4 shows an upper portion 51 of the top part 32, the upper position having a plate 61 with actuating elements 63 inserted therein, and fastening elements 67 which secure the latter in the portion 51 or in a straight wall 66. All the actuating elements 63 project, according to their function, by a definite amount from the plate 61 on one operating side 61a, and can be actuatable rotationally and also translationally. The fastening elements 67, in contrast to the actuating elements 63, are located countersunk in the plate 61, so that the latter can be secured with grouting compound 35. On the other side, the actuating elements 63 can naturally also be so located in the plate 61, that the latter do not project and also not cause trouble, and consequently unintentional actuation of the actuating elements 63 is precluded from the outset.

The entire concept underlying the invention is, however, not limited to the use of only a very specific plate 61 or inspection glass 65 in a portion 51 or a straight wall 66 of an explosion-proof housing 30, which is constructed so as to be specially protected.

An explosion-proof housing can be operated in areas exposed to explosion or fire, for functional units (safety switch of a motor, thermal relays, motor protection, line safety switches and power switches), the gap 59 which is formed between the bottom part 31 with brought-out line bushings 39 and functional units, and the top part 32, being sealed with cast resin 35.

The special advantage of the housing of the invention as herein described with reference to and as shown in the drawings, can be seen in that firstly, the parts which form the housing and therefore the switch chamber space are configuratively so shaped that a permanent connection, as a result of the use of flexible moulded parts 34 and a gasket 33 which is unexposed to the outside atmosphere and is between the free edge of the bottom part and the base of a groove in the top part, requires no material for screws and like fixing devices. Furthermore, penetration of moisture - for example, because of a difference in temperature - between the gap grouting is substantially completely prevented by the rubberlike gasket which is inserted between the parts and therefore underneath the gap grouting during pressure-testing when the parts are tested.

WHAT WE CLAIM IS: 1. A housing for an electrical appliance, comprising: a first part and a second part, the first part having an annular peripheral wall and the second part having an annular groove formed therein and into which the annular peripheral wall of the first part projects, the housing containing line bushings or terminals for connection to the electrical appliance, an annular gap being defined between the annular peripheral wall of the first part and the second part, the gap being filled with cast resin which extends across the gap between the second part and the annular peripheral wall of the first part, securing elements locking the two parts together, assembly of the housing having comprised inserting the annular peripheral wall of the first part into the annular gap of the second part, the securing elements thereupon locking the first and second parts together.

2. A housing according to claim 1, wherein upon assembly of the housing the securing elements were resiliently urged to positions in which they locked the first and second parts together.

3. A housing according to claim 1 or claim 2, wherein the first and second parts are circular in cross section and the crosssectional area of second part decreases in the direction away from the first part.

4. A housing according to claim 1 or 2, wherein the first and second parts are square or rectangular in cross section and the cross sectional area of second part decreases in the direction away from the first part.

5. A housing according to any preceding claim, wherein the groove formed in the second part is substantially trapezoidal in cross-section.

6. A housing according to any preceding claim, wherein the line bushings or terminals are disposed adjacent the peripheral wall of the first part and secondary walls are disposed between the bushings, on the interior and on the exterior of the first part.

7. A housing according to claim 6, wherein at least some of the secondary walls on the exterior of the first part have respective noses engaging a cap surrounding the first part of the housing.

8. A housing according to claim 5 or 7, wherein the peripheral wall of the first part projects beyond the secondary walls on the interior of the first part.

9. A housing according to any preceding claim, wherein the peripheral wall comprises a projection with which the securing elements engage to lock the first and second parts together.

10. A housing according to any preceding claim, wherein the electrical appliance is fastened to the interior surface of the first part.

11. A housing according to any preceding claim, wherein the second part is provided with openings in a peripheral wall thereof, the recesses receiving the securing elements.

12. A housing according to claim 11, wherein each securing element is flat in section and comprises a first portion having a free end engaging the first part of the housing, a second portion received in a respective one of said openings in the peripheral wall of the second part and a third portion engaging the internal surface of the peripheral wall of the second part.

13. A housing according to claim 12, wherein the first and second portions are at an obtuse angle to each other and the

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

Claims

**WARNING** start of CLMS field may overlap end of DESC **. operating side 61a, and can be actuatable rotationally and also translationally. The fastening elements 67, in contrast to the actuating elements 63, are located countersunk in the plate 61, so that the latter can be secured with grouting compound 35. On the other side, the actuating elements 63 can naturally also be so located in the plate 61, that the latter do not project and also not cause trouble, and consequently unintentional actuation of the actuating elements 63 is precluded from the outset. The entire concept underlying the invention is, however, not limited to the use of only a very specific plate 61 or inspection glass 65 in a portion 51 or a straight wall 66 of an explosion-proof housing 30, which is constructed so as to be specially protected. An explosion-proof housing can be operated in areas exposed to explosion or fire, for functional units (safety switch of a motor, thermal relays, motor protection, line safety switches and power switches), the gap 59 which is formed between the bottom part 31 with brought-out line bushings 39 and functional units, and the top part 32, being sealed with cast resin 35. The special advantage of the housing of the invention as herein described with reference to and as shown in the drawings, can be seen in that firstly, the parts which form the housing and therefore the switch chamber space are configuratively so shaped that a permanent connection, as a result of the use of flexible moulded parts 34 and a gasket 33 which is unexposed to the outside atmosphere and is between the free edge of the bottom part and the base of a groove in the top part, requires no material for screws and like fixing devices. Furthermore, penetration of moisture - for example, because of a difference in temperature - between the gap grouting is substantially completely prevented by the rubberlike gasket which is inserted between the parts and therefore underneath the gap grouting during pressure-testing when the parts are tested. WHAT WE CLAIM IS:

1. A housing for an electrical appliance, comprising: a first part and a second part, the first part having an annular peripheral wall and the second part having an annular groove formed therein and into which the annular peripheral wall of the first part projects, the housing containing line bushings or terminals for connection to the electrical appliance, an annular gap being defined between the annular peripheral wall of the first part and the second part, the gap being filled with cast resin which extends across the gap between the second part and the annular peripheral wall of the first part, securing elements locking the two parts together, assembly of the housing having comprised inserting the annular peripheral wall of the first part into the annular gap of the second part, the securing elements thereupon locking the first and second parts together.

second and third portions are at right angles to each other.

14. A housing according to any preceding claim, wherein the first part and/or the second part of the housing are made of synthetic plastics material.

15. A housing according to any preceding claim, wherein the first part of the housing and/or the second part of the housing are made of aluminium.

16. A housing according to any preceding claim, wherein a resilient sealing member is disposed in the groove and compressed between the free edge of the peripheral wall of the first part and the base of the groove.

17. A housing according to claim 1, substantially as described herein with reference to and as illustrated in Figures 1 and 2 of the accompanying drawings.

18. A housing according to claim 17, substantially as described herein with reference to and as illustrated in Figures 3 and 3a or Figure 4 of the accompanying drawings.