EP0433003A1

EP0433003A1 - Interface assembly for bulkheads in explosive environments

Info

Publication number: EP0433003A1
Application number: EP90313414A
Authority: EP
Inventors: John David Sowerby
Original assignee: C M P (UK) Ltd
Current assignee: C M P (UK) Ltd
Priority date: 1989-12-11
Filing date: 1990-12-11
Publication date: 1991-06-19
Also published as: GB2240668B; GB2240668A; GB8927965D0

Abstract

An electrical connector for mounting in a bulkhead or other boundary, for use in an explosive environment, comprises a plastics material member (10; 10A) which, in use, is inserted into an aperture in the bulkhead. The member (10; 10A) has at least one through bore in which a metal connector pin (12) is received which, in use, protrudes to one side of the bulkhead whilst a cable (14) is connected to the pin from the other side. A flame path (17) is defined in the region between the connector pin (12) and the member (10; 10A) or between the member and the bulkhead. In this region an annular sleeve (18; 18A, 18B) of material resistant to erosion by a propagating flame is received in a recess in the plastics member (10; 10A). The sleeve (18; 18A, 18B) may be of metal or ceramic material or any other wear resistant material.

Description

This invention relates to interface assemblies for components passing through a boundary.
Connectors for potentially explosive environments are known in which the connecting pins are mounted in a plastics moulding. The connector is mounted in a bulkhead or other boundary sealing off the source of ignition. As the pins are designed to be capable of removal and replacement, there is a clearance between the moulding and the pins to enable removal of the pins. This clearance constitutes a flame path by which flame can propagate from one side of the boundary to the other. Therefore, it is important that the dimensions of the flame path are small enough to stifle any flame before it reaches the other side. By making the flame path sufficiently constricting the flame is cooled sufficiently such that it does not constitute a potential source of ignition to a potentially explosive environment on the other side of the boundary.
It is known to mould the plastics body to provide such a clearance for the pin or pins. However, the plastics material is unable to present sufficient resistance to the erosive effects of a propagating flame. This causes the gap between the plastics and the pin to increase eventually to the point where any propagating flame is no longer sufficiently stifled in the flame path.
British Standard BS 5501 sets the test for enclosures of greater than 100 cm³ having at least one face of plastics material, by which the reliability of a flame path therein can be measured. It requires that the flame path through the enclosure is able to withstand at least 50 controlled explosions subjecting the flame path to a propagating flame without experiencing erosion of the flame path sufficient to render the flame path ineffective.
It is an object of the present invention to provide an interface assembly for an element passing from one side of a boundary to another which is more able to withstand the erosive effects of a flame propagating along a flame path through the assembly.
According to the present invention there is provided an interface assembly for at least one element passing through an aperture in a boundary, including a first member mounted in the aperture; the or each element and the first member, and/or the first member and the boundary, defining a flame path or paths across the boundary, at least the first member being provided with a wear resistant insert in at least part of the region or regions defining the or each flame path.
The assembly may be arranged such that the member mounted in the aperture is removable, the element or elements being fixed and sealed in the first member. Alternatively, the element(s) may be removably mounted in the first member. In the first case, the flame path can be arranged to be between the boundary and the first member. In the second case, the flame path can be arranged to be between the first member and the element.
Commonly, the insert is a circular ferrule, or sheath which, together with the adjacent surface of the boundary and/or the adjacent surface of the element, defines an annular flame path from one side of the boundary to the other.
The insert may be either metal or, possibly, made of a ceramic material, or any sufficiently hard wearing material suitable for the purpose. In any event, it should be a material which is able to resist wear significantly better than the plastics material of which the first member mounted in the boundary will commonly be formed. A typical plastics material for the first member is a dough moulding compound (d.m.c.) of polyester or an epoxy.
In one particular form, the present invention is incorporated in a cable connector having metal contact pins which are mounted in a plastics first member and project from the boundary in which the first member is mounted. The flame path is defined between each pin and the surrounding plastics material. Thus, the insert is made in the form of a cylindrical collar or sheath between at least part of the length of each pin and an adjacent portion of the plastics material. Preferably, the insert is received in a radially extending recess in the plastics material in order that it lies flush with it.
The assembly is intended to comply with BS 5501 and it is preferable, in this regard, if the dimensions and wear resistivity of the material of the insert are sufficient for this purpose.
The invention also extends to an enclosure incorporating an assembly according to the invention.
The present invention can be put into practice in various ways some of which will now be described by way of example with reference to the accompanying drawings in which:

Figure 1 is a scrap-section through a connector pin assembly according to the invention; and
Figures 2A & 2B are an end view and a cross-section through a connector body also according to the invention.

Referring to Figure 1, an electrical connector comprises a plastics connector body 10 which is formed with an aperture 11. A brass connector pin 12 protrudes from one end of the aperture 11. Inside the aperture 11 the pin 12 is connected to one end of a cable 14. Generally mid-way between the ends of the aperture 11, the pin 12 is formed with a radially extending brass head portion 16.
The pin 12 may be held in place by, for example, grub screws which are threadedly received in radially extending holes in the plastics body 10 which bite on the shank of the pin to hold it in place. Similarly, the cable 14 may be secured in a recess in the head portion 16 by, for example, a grub screw threadedly received in the head portion 16. Clearly, there are other forms of securement of the pin 12 to the body 10 and of the cable 14 to the pin 12 which will be readily apparent to the skilled person.
The pin 12 is a clearance fit in the aperture 11 which has a smaller bore portion 11a corresponding to the shank of the pin 12 and a larger bore portion 11b corresponding to the head 16 and cable 14. The annular gap between the head 16 and the adjacent surface of the body 10 constitutes a flame path 17 in which flame to one side of the boundary in which the assembly is mounted is stifled before it reaches the other side. The flame path conforms to BS 5501.
A metal insert 18 is moulded into a radially projecting recess in the plastics body 10 adjacent the head portion 16 of the pin 12. The insert 18 is in the form of an annular sheath or collar which lies flush with the larger bore portion of the aperture 11. The insert is made of brass. However, it could equally well be made of any other suitable non-corrosive metal, such as stainless steel.
Figures 2A and 2B illustrate another form of elertical connector body according to the invention in which the body 10A is formed with apertures for four angularly spaced connector pins (not shown) which would protrude out of the body to the right-hand side as depicted in Figure 2B. The body also has a central earth pin 20 and earth screen 22 extending radially between the apertures for the connector pins.
In this embodiment, the flame path 17 is defined betwen the metal pin (not shown) and a metal insert 18A in a similar manner to that in Figure 1. Additionally, the plastics body has a further annular insert 18B extending around the circular section body 10A. The insert 18B lies in a recess in the body 10A such that its radially outer surface is flush with the outer surface of the body 10A. The body is receivable within either a protective metal housing by which it is securable to the bulkhead, or it is receivable directly in the metal bulkhead itself. In either case, the insert 18B defines a wear resistant flame path in conjunction with the adjacent surface of the housing or bulkhead.
In this embodiment, the inserts 18A and 18B are a minimum of about 1 mm thick. The insert 18A is about 16 mm internal diameter and the insert 18B is about 66 mm internal diameter. The length of the flame path is 12.5 mm long and the maximum gap is 0.4 mm. The combinations of path length and gap can, of course, vary. Preferably, they are kept within the limits specified in BS 5501.
In an alternative form the body and the element passing through it or the boundary both require erosion protection, in which case the flame path is completely defined by more than one insert mounted respectively on the body and the adjacent surface of the element or boundary.
It is also the case that the present invention can be used in other forms of assembly providing an interface at the boundary between an enclosure and an outside environment through which a communicating line, for example, an optical fibre or pipe, is required with the ability for it to be removed or shifted. The assembly may constitute a connecting junction or a flame proof seal for the line etc., passing through the bulkhead.

Claims

An interface assembly for at least one element (14) passing through an aperture in a boundary, including a first member (10; 10A) mounted in the aperture; the or each element (14) and the first member (10; 10A), and/or the first member (10; 10A) and the boundary, defining a flame path or paths across the boundary, at least the first member (10; 10A) being provided with a wear resistant insert (18; 18A,18B) in at least part of the region or regions defining the or each flame path (17).
An interface assembly as claimed in claim 1, characterised in that the first member (10; 10A) is adapted to be removably mounted in the aperture and in that the or each element (14) is fixed and sealed in the first member (10; 10A), one flame path (17) being defined between the first member (10; 10A) and the boundary.
An interface assembly as claimed in claim 1 characterised in that the or each element (14) is removably mounted in the first member (10; 10A) one flame path being defined between the first member (10; 10A) and the or each element (14).
An interface assembly as claimed in any preceding claim, characterised in that the or each insert (18, 18A, 18B) is made from metal or ceramic material.
An interface assembly as claimed in any preceding claim characterised in that the insert (18; 18A, 18B) is a cylindrical collar located between at least part of the length of the or each element (14) and an adjacent portion of the first member (10; 10A).
An interface assembly as claimed in any preceding claim characterised in that the insert (18; 18A, 18B) is received in a recess in the first member (10; 10A).
A cable connector including an interface assembly as claimed in any preceding claim characterised in that each element (14) is a metal contact pin.
A cable connector as claimed in claim 7 characterised in that the first member (10; 10A) is of plastics material.
An enclosure incorporating an assembly or connector as claimed in any preceding claim.