Note: Descriptions are shown in the official language in which they were submitted.
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DESCR I PTION
SCREENED RACK
The invention relatès to a screened rack, and in
particular, but not exclusively,to a rack for holding a
plurality of card frames in which a plurality of printed
circuit boards may be releasably held, the rack being
screened against raclio Erequency interference.
A rack for holding card frames basically comprises
a metal framework of four vertical metal posts which are
interconnected by four cross pieces at their upper ends
and four cross pieces at their lower ends, forming a
cuboidal framework. The six "faces" of the framework
are each provided with a closure which may either be
removable, e.g. a door, to allow access to the interior
of the rack, or may be permanently connected, e.g.
a panel, to the framework where access is not required,
e.g. the base and the top.
The contact between the doors and the framework
must be continuous around the whole of the perimeters
of the doors, in order to achieve effective screening
of the interior of the rack and to avoid unwanted effects,
such as earth loops which may form in a gap between a
closure and the frame. The required con-tac-t is normally provided
by using a radio frequency interference gasket comprising
wire mesh in the form of a tube, with a thin rubber tube
inside.
When a door is closed against the gasket, the gasket
deforms to provide a continuous seal around -the perimeter
of the door. The wire mesh is provided with a flange
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running along its leng-th. The gasket is secured to the
frame by attaching L-shaped brackets to the flange by
means of a screw passing through one arm of~ the bracket
and the flange and passing into the frame. Brackets
must be secured approximately every 150mm to hold the
gasket in place and also to provide a stop for the door
with the end of the o-ther arm of the bracket. The
securing of the gaske-t every 150mm is labour intensive
and also expensive over the total length of frame in a
rack which may amount to several metres.
It is an object of -the present invention to
provide a screened rack which will have substantially
continuous contact around the whole perimeter of the
frame of the rack but which is constructed in a much
simpler and less labour intensive manner than
heretofore.
In accordance with the present invention, there
is provided a gasket arrangement for forming an electrical
connection between two relatively displaceable metal
members when the two members are brought into abutment,
wherein one of said metal members is provided with an
elongate groove which receives longitudinally therewithin
a tubular, resilient, electrically conductive gasket, the
groove having a cro-ss-sectional configuration such tha-t,
when said metal members are in a separated state, the
gasket is held in said groove in a substantially
undistorted condition by means of opposed projections
at or adjacent the mouth of the groove and with a
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longitudinal peripheral portion of the gasket projecting
out of the groove, and such that, when the metal members
are brought into abutment with the gasket resiliently
compressed therebetween, the gasket can be accommodated
further within the groove.
Preferably, the groove is at least partially
defined by -two side walls which are inclined relative
to one another and which serve to support the gasket so
that it projects partially out of the groove when in
said undistorted condition.
Preferably, the base of the groove is provided with
a recess intermediate said two relatively inclined side
- walls for accommodating part of the gasket when -the two
metal members are in abutment with the gaske-t compressed
therebetween.
Advantageously, the projections at or adjacent the
mouth of the groove comprise integral, knife-edged lips
disposed at the outer ends of said inclined side walls.
Preferably, said knife-edged lips extend along the
whole length of the groove.
Preferably, said inclined side walls are mutually
perpendicular.
By way of example only, a specific embodiment of the
invention will now be described, with reference to the
accompanying drawings, in which:-
Fig. 1 is an exploded perspec-tive view of a
corner of a rack, formed with a gasket arrangement in
accordance with the invention;
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Fig. 2 is a cross-section through an uprigh~ member
of a rack embodying the invention, with two doors fitted;
Figs. 2a and 2b are details of Fig.2 showing the
section of the retaining grooves to a larger scale; and
Fig. 3 is a cross section through a hori~ontal
member of a rack embodying the invention.
Referring to the figures, a post 10 of a rack frame
is secured to two base portions 12, 14 of the frame. Only
one corner of the frame is illustrated, but it will be
appreciated that four posts 10 and eight portions 12, 14 are
provided, and that the other seven corners are similar.
The post 10 is extruded from aluminium and comprises
an exterior wall 16 and a parallel interior wall 18. A wall
20 extends normally from one edge of the wall 16 and meets a
wall 22 extending parallel to wall 18. In turn, the wall 22
meets a wall 24 extending normally to, and joining, ~he wall
18. Extending normally from the other edge of wall 16 is a
wall 26 which joins a wall 28 at right angles thereto. Wall
28 joins wall 30 which joins, and is normal to, the wall 18.
The walls 24 and 28 are each provided with a long-
itudinal retaining groove 32, which are used for retaining
a metal mesh sealing strip, as will be explained. The walls
18 and 30 are each provided with a groove 34, 36 respectively
which assist in defining the shape of the retaining grooves
32. The wall 18 is also provided with two brackets, one 38
extending normally to the wall 18 and the 40 being an
extension of the wall 18. The brackets are provided with a
plurality of apertures 42 so that they may be used as mountings.
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The post 10 is substantially hollow, but within
the post are extruded four near-circular grooves 44.
These are shaped to receive self-tapping screws (not
shown) which may be passed through holes in the base
portions 12, 14 and screwed into the grooves 44 to secure
the frame together, as will be explained.
ReEerring to the retaining grooves 32 in more
detail, these comprise a flat base 46, parallel to the wall
24 or 28, two parallel opposed faces 48, perpendicular to
the base 46, two faces 50 inclined at about 45 degrees
to the faces 48, and two faces 52, inclined substantially
- perpendicularly to the faces 50. The edges of the faces
52 define two opposed, longitudinal, inwardly-facing, knife-
edged lips along the two sides of the retaining groove. In --
use, the retaining grooves hold a flexible wire mesh tube
54 comprising a wire mesh tube with a rubber tube inside,
which affords a flexible, resiliently deformable conductor.
In use, the wire mesh tube is pressed into the retaining
grooves 32 and is held in the grooves by the lips 52 of the
groove 32, and abuts the faces 50 of the groove 32. When
inserted, the wire mesh tube 54 is substantial]y circular
in cross~section, as in the upper groove illustrated in
Fig. 2, but when deformed e.g. by a door 56 as illustrated
in the lower groove illustrated in Fig. 2, the portion of the
tube extending out of the groove is flattened, and the tube
is deformed to fill the groove more fully, and in particular
to occupy the portion of the groove between the base 46 and
the two opposed faces 48.
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Referring now ~o Figs. 1 and 3, the base port,ions
12 and 14 comprise a horizontal portion 58, two portions
60, 62 perpendicular to the horizontal portion 58 and two
flanges 64, 66, one being an extension of the horizontal
5 portion and the other being an extension of the portion 62,
parallel to the flange 64. The surface of approximately
half the horizontal porti.on 58, indicated at 68, is at a
lower level than the rest oE the horizontal portion.
Provided on the slightly lower surface 58 is a flange 70,
forming another retaining groove 32 identical to those
previously described. As before, in use, a flexible wire
mesh tube 54 is held in the groove. Also provided on
the surface 68 are two elongate pro~ections 72 on either
side of the flange 70, which are triangular in cross-
section. The apex of each' of the projections is at the
same level as the higher surface of the horizontal portion
58 and the faces are inclined at 45 degrees to the surface
68. The eight portions 12, 14 are all identical.
Referring to Fig. 1, the ends of the two base
portions 12, 14 are mitred at an angle of 45 degrees to
form a right-angle between the two base por-tions. Four
holes 74 are provided in the base portions 12, 14 and
screws passing through these holes and into the grooves
44 secure the post to the base portions 12, 14, with the
pos-t 10 occupying the position marked with dotted lines.
Since there are four posts 10, eight corners are created
in this way, with the portions 12, 14 at the top oE the
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posts 10 being inverted. In this way, a cuboidal frame is
created, into the open faces of which doors may be fitted.
When the frame is complete, a retaining groove 32
extends around the whole of the periphery of the framework fo~ing
the open faces. A fIexible wire mesh tube 54 is pressed
into the groove 32 in each section of the frame and is
held in the grooves by the lips 52 extending along
substantially the whole length of the grooves. The wire
mesh tube may pass into different straight sections of
framework via a portion 76 which is cut out of the face
24 of the post 10. In this way, a continuous conductive
connection is maintained around the whole periphery of the
` open face of the framework.
Referring to Fig. 2, two metal doors 56 are
illustrated, one in the open position and one in the
closed position. The doors illustrated are hinged, but
the doors may be replaced with panels which are permanently
connected to the framework of the rack. When the door is
open, as the upper door in Fig. 2, the wire mesh tube
is held in place by the lips 52 of the groove 32, and
the tube assumes substantially its original shape within
the groove due to the resilience of the inner rubber tube.
When the door is closed, as the lower door in Fig. 2, the
wire mesh tube is deformed as previously described, pressing
the tube into the groove 32, and a conductive contact is
provided around the whole periphery of the door. The face
24 forms a stop which the door abuts when in the closed
position.
The door may be opened and closed frequently, and
the wire mesh tube will still provide a continuous
peripheral contact because of its resilience. However,
installing the wire-mesh tube is a simple matter of
pressing into a groove and requires no screwdriver and
no fittings in order to secure it.
The invention is not res-tricted to the details of
the foregoing embodiment, for example, the lips 52 of the
groove 32 need not be continuous, but may comprise one or
more projections extending into the groove.
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