Note: Descriptions are shown in the official language in which they were submitted.
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MOUNTING FASTENER FOR ELECTRICAL WIRING BOXES`
Back~round of the Invention
The subject invention is directed toward the art of
mechanical connectors and more particularly, to a screw
thread connection of the "push-in" type.
The invention is especially suited for use in
electrical junction and wiring box structures to provide
screw mountings for wiring devices and will be described
with reference thereto; however, as will become apparent,
the invention is capable of broader application and could
be used in many different environments.
Electrical wiring boxes commonly include connections
for facilitating the mounting of various wiring devices
such as switches, electrical outlets and the like. The
connections are typically simple threaded openings for
receiving mounting screws. In certain designs, however,
the openings have included resilient tabs or inserts to
allow for "push-in" insertion of the mounting screws. Such
arrangements are illustrated, for example, in U. S. patents
~- 4,130,335, 4,069,448, 3,955,463 and 4,188,854.
In each of the known prior art arrangements a
separate spring steel insert or multiple independent
components are required. As is apparent, these prior
designs tend to increase the cost of the units. Further,
the use of the separate inserts requires an additional
: assembly step during the box manufacturing process.
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;, Brief Statement of the Invention
The subject invention overcomes the above noted
problems and provides a fastener design which is
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ij3i particularly suited for incorporation in molded plastic
junction boxes. The fastener assembly can be molded
integrally with the box structure so that a separate insert
member or the like is not required. In particular, in
accordance with a preferred embodiment of the invention,
there is provided an electrical outlet box molded of
plastic and having at least one push-in type screw
receiving opening formed therein. The screw receiving
opening is defined by rigid semi-cylindrical first and
second walls having opposed faces mounted in spaced and
' axially aligned relationship to produce a generally
~, 15 cylindrical passage open at an outer end. Threads or
thread forming sections are carried on the opposed faces
inward from the outer end to provide helical screw
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,~ receiving threads about the interior of the cylindrical
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;' passage. At least the first of the semi-cylindrical walls
`~ 20 is supported and carried substantially entirely by a
resilient support wall lying in a plane generally
# perpendicular to the axis of the cylindrical pa6sage. The
~i support wall has opposed ends with one end ~olning the
~' first semi-cylindrical wall ad~acent the outer end of the
cylindrical passage. The other end of the support wall is
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'~ mounted and supported in cantilever fashion at a location
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spaced radially from the axis of the cylindrical passage on
the side opposite the first wall.
The arrangement of the first semi-cylindrical wall
and its support wall is such that when a threaded screw
, 5 member is moved axially into the screw receiving opening
, the first semi-cylindrical wall section is caused to pivot
; away from the second cylindrical wall. The pivoting is
sufficient to allow the threaded screw to enter the
passageway. After entry of the screw into the passageway,
the first cylindrical wall section can move back to its
original parallel relationship with the second cylindrical
^ wall. Thus the first wall moves into engagement with the
screw member. The screw member cannot be simply axially
withdrawn because of the relationship between the
cylindrical walls and the support wall. That is, a camming
closure of the two support walls causes the screw to be
tightly gripped in threaded relationship with the opening.
d, The screw member can, however, be axially withdrawn by a
normal unthreading type operation.
All of the elements which form the fastener opening
` are formed integrally with the body of the molded plastic
outlet box. Thus manufacture and assembly of separate
elements is not required and a highly efficient push-in
type fastener design results.
In accordance with a more limited aspect of the
invention, the support wall is integral with the first
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semi-cylindrical wall and the remainder of the outle~ box.
In addition, the support wall normally maintains the first
semi-cylindrical wall biased to its normal position
1 parallel with the second cylindrical wall. The required
3 5 resiliency in the first wall is preferably provided by
proper selection and shaping of the plastic material from
which the box and its integral fastener assemblies are
molded.
In accordance with a more limited aspect of the
invention, the support wall defines an outer surface of the
assembly adjacent the open outer end of the threaded
, passage way. Preferably, the outer end of the threaded
passageway has a generally conical configuration to assist
in guiding the associated screw into the opening and into
proper biasing relationship with the support wall.
;~ As can be seen from the foregoing, a primary object
of the subject invention is the provision of a push-in type
fastener assembly for use in electrical outlet boxes which
assembly eliminates the need for separate fastener insert
members and the like.
A still further object of the invention is the
provision of fastener assembly of the general type
described wherein all elements of the fastener receiving
opening are molded integrally with the outlet box.
Another object of the invention is the provision of
a push-in fastener assembly which is a simple, one piece
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molding.
The above and other objects and advantages will
become apparent from the following description when read in
conjunction with the accompanying drawings wherein:
Figure 1 is a pictorial view of an electrical outlet
box formed in accordance with a preferred embodiment of the
subject invention;
Figure 2 is a greatly enlarged plan view of one of
q the screw receiving fastener openings of the outlet box of
Figure 1;
Figure 3 is a partial cross-sectional view taken on
line 3-3 of Figure 2; and,
Figure 4 is a cross-sectional view similar to Figure
3 but showing the tilting movement of the fastener
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receiving opening which takes place during installation of
a mounting screw.
Referring more particularly to the drawings wherein
the showings are for the purpose of illustrating a
~ preferred embodiment of the invention only, and not for the:~ 20 purpose of limiting same, Figure 1 shows the general
I overall arrangement of an electrical outlet box assembly
10. The outlet box assembly 10 is of a typical overall
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size and configuration as is used, for example, for
c~ conveniently mounting and supporting electrical wiring
devices such as switches, receptacles, lighting fixtures
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and the like. Typically, the boxes of the type under
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consideration are mounted in wall or ceiling openings' and
- the electrical device and/or cover plates used with the
boxes are mounted to the box through the use of small
diameter screws.
', 5 In the subject embodiment the box lO is illustrated
r~ as being a molded as a one piece structure formed from a
, suitable resinous plastic. Many different thermoplastics
are suitable for use in this type of structure and
environment. Typical of those which could be used are
polyvinylchloride, polyphenylene oxide and polycarbonate
resins. Obviously, many different types of resinous
plastic materials could be used and are known to have the
characteristics desired.
As shown in Figure 1, box assembly lO includes a
lower wall or base 12 with opposed upstanding side walls 14
and 16. Integral with the base and the side walls 14, 16
are a pair of opposed end walls 18 and 20. The box
' assembly lO thus provides a chamber 22 which can house
various wiring connections and/or associated wiring
devices of the type mentioned earlier.
As is typical with electrical boxes of the type
;` under consideration, means are provided to permit the box
.r to be suitably mounted to wall studs or associated support
# structure. As shown in Figure 1, the subject box is
illugtrated ag includlng integrally molded nail braokets or
holding elements 24. Elements 24 are conventional and
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~- provide means for connecting suitable mounting nails or the
like to the box assembly 10.
~ As is customary, the box is illustrated as having
'J screw receiving opening assemblies 26 formed in each of the
end walls generally centrally thereof. The exact locations
of the screw receiving openings, as well as the total
number of such openings provided, can vary widely from that
shown depending upon the size of the box and the particular
wiring devices which are to be mounted. The illustrated
box is typical of those used for the standard switch and
electrical outlet assemblies~ As previously mentioned, and
J as shown in the noted prior art patents, many different
types of screw receiving openings and screw fastening
assemblies have been proposed for use in such electrical
outlet boxes. The more desirable types are those which
j permit the screws to be mounted in the openings by a simple
;~ push-in operation. As discussed, the prior push-in type
screw receiving openings have required the use of separate
~',!,1 spring steel inserts which must be installed in a separate
assembly operation during the manufacture of the boxes.
`. The subject invention provides a highly simplified and
` ef~iclent structure which can be molded directly ln the box
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. during the molding operation.
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::i As best shown in Figures 2 through 4, the screw
receiving assemblies 26 are molded integrally with the end
~ walls 18, 20 of the box assembly 10. Each of the screw
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receiving openings in the sub~ect preferred embodiment are
of identical structure and configuration. Accordingly,
only one will be described in detail and the description
thereof is to be taken as equally applicable to the other.
In particular, the screw receiving ass~mbly 26 carried on
wall 20 is located at the upper end of a concave wall
section 28 which runs the vertical length of the end wall
20. Vertically aligned with the groove or recess 28 is the
screw receiving opening 30. The opening 30 comprises a
vertical passageway defined by rigid first and second walls
32 and 34 respectfully. The walls 32 and 34 have semi-
. cylindrical interior faces. They are positioned with their
semi-cylindrical interior faces mounted and spaced in
~ axially aligned relationship to produce a generally
`, 15 cylindrical screw receiving passage open at the upper end
as illustrated. The interior faces of the walls 32 and 34
are each provided with thread forms which cooperate to
define a helical screw thread about the interior of the
:~ cylindrical passageway. The thread forms are made by a
standard tapping operation; however, it should be
~, understood that the threads could be molded and/or be given
different configurations.
As best illustrated in Figure 2, the walls 34 and 32
`~ are spaced apart a distance "d". It is important to note,
however, that each of these walls is molded as an integral
part of the main structure of the box assembly 10.
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The upper or outer end face 36 is coplanar with the
upper edge of the box assembly lO. In addition, the outer
end of the threaded screw receiving passageway 30 is
preferably chamfered or provided with a frusto-conical
configuration as best illustrated in Figure 3. This
facilitates guiding of the associated mounting screw into
the passageway.
According to the subject invention, at least the
first semi-cylindrical wall 32 is mounted in a manner which
permits it to, in effect, tilt away from the opposed wall
34 when an inwardly directed axial force is applied to the
wall. This, as can be appreciated, allows the wall to move
to the position illustrated in Figure 4 so that the
associated screw 38 can be pushed axially into position in
the passageway 30. It should, of course, be understood
that after the screw 38 has been moved to its located
position in the opening, the wall will reassume its normal
relationship with wall 34 to firmly grip the screw 38.
Similarly, because of the relationship and the method by
which the wall is mounted, a simple axial force cannot be
used to remove the screw 38. That is, an axial withdrawal
force applied to the screw merely causes the wall 32 to
more tightly grip the screw by moving in a direction
~i generally toward the opposed wall 34.
~ 25 As particularly shown in Figure 3, the wall 32 is
t supported adjacent the outer open end of the passage 30 by
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a horizontally extending support wall section 40. Wall
. section 40 is designed so as to be resilient and to
maintain the wall 32 under a continual bias toward the
normal position Figure 3. In the embodiment under
consideration, wall 40 is coextensive with the upper
: surface 36 and lies in a plane which is perpendicular to
I the central axis 42 of the passage 30. As best illustrated
.- in Figure 2, the wall 40 is separated from the remainder of
the top surface of the box assembly by a vertically
, 10 continuous slot 44 on one side and a similar slot 46 on the
other side. In this embodiment, slots 44, 46 extend
parallel and the wall 40 is provided with a fillet at its
`~: junction with wall 32.
The support wall 40 is mounted and supported in
~antilever fashion at a location spaced outwardly from the
' axis 42 and joined along a line generally in the plane of
the top surface 36 and in a plane parallel to the axis 42
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~ but lying on the side opposite the wall 34. ~s
'~,~ illustrated, the wall 40 is supported from a generally
rectangular protuberance 48 (see Figure 1) which extends
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. outwardly from the end wall 20. This protuberance and the
support wall 20 are lntegrally molded wlth the remalnder
of the electrical outlet box assembly 10.
Referring more particularly to Figure 4, the
movement of the first wall 32 during insertion of the
threaded screw is clearly illustrated. In particular, as
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the screw 38 is moved axially into the passageway 30 it
will normally engage with the outer end of the opening and
be prevented from moving axially inward because of
engagement between the external threads on the screw and
the internal threads in the opening 30. As the screw is
pushed axially inward, however, the forces act to cause the
wall section 32 to be tilted in the manner shown because of
the inherent and biasing flexibility built into the support
wall 40. The support wall does, as a consequence, maintain
10 a continual bias on the wall 32 attempting to return it to
its normal Figure 3 position~ As the screw 38 moves
. inwardly to its final located position, its screw threads
are received in the internal screw threads of the opening
30 and when inward movement is complete, the wall 32
returns to its position firmly in engagement with the
exterior of the screw 38.
.~ It should be appreciated that the screw 38 can be
removed by a simple unthreading operation and multiple
connections and disconnections are possible.
The invention has been described with reference to
pre~erred and alternate embodlments. Obviously,
modifications and alterations will occur to others upon the
~ reading and understanding of this speci~ication. It is
~ intended to include all such modifications and alterations
.j 25 insofar as they come within the scope of the appended
claims or the equivalent thereof.
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