U.S. patent number 3,574,400 [Application Number 04/751,507] was granted by the patent office on 1971-04-13 for polypropylene armchair.
This patent grant is currently assigned to S. Hille and Company Limited. Invention is credited to Robin Henry Day.
United States Patent |
3,574,400 |
Day |
April 13, 1971 |
POLYPROPYLENE ARMCHAIR
Abstract
A unitary moulded chair shell forming the seat, back and arms of
a chair, provided with a continuous integral rolled flange forming
a channel extending along the under or rear side of at least the
front edges of the arm and seal portions of the shell, and having
integral webs extending across said channel in the regions where
the arms merge with the seat.
Inventors: |
Day; Robin Henry (Chelsea,
London, EN) |
Assignee: |
S. Hille and Company Limited
(Watford, Hertfordshire, EN)
|
Family
ID: |
10401978 |
Appl.
No.: |
04/751,507 |
Filed: |
August 9, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Aug 18, 1967 [GB] |
|
|
38,211/67 |
|
Current U.S.
Class: |
297/452.14 |
Current CPC
Class: |
A47C
3/12 (20130101); A47C 5/12 (20130101) |
Current International
Class: |
A47C
5/12 (20060101); A47C 5/00 (20060101); A47c
003/12 (); A47c 007/16 () |
Field of
Search: |
;297/(Molded Digest)/
;297/457 (Foam/ Digest)/ ;297/454 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Machado; Reinaldo P.
Claims
I claim:
1. A unitary injection molded chair shell forming a seat, back and
arms of a chair, said chair shell being provided with a continuous
open angularly disposed flange forming a channel extending along
the outside of at least front edges of the arm and the underside of
a front edge of said seat, characterized by the provision of a
plurality of integral injection molded webs extending across said
channel from a location beneath said seat to a location along said
arms and across a juncture of said arms and said seat thereby
preventing distortion of the chairback and of the chairback
relative to the arms due to a user's applying with his back either
rearward or combined rearward and sideways forces to the back or
both the back and either arm of the chair.
2. The chair shell as defined in claim 1, wherein said plurality of
integral injection molded webs are positioned only at the two front
points of merger between said arms and said seat.
Description
This invention relates to shells for chairs of the type comprising
a unitary shell forming the seat, arms and back of the chair
supported by a frame attached to the underside of the seat portion
of the shell.
A major problem in the design of shells for such chairs is the
provision of sufficient rigidity, especially in response to
loadings due to a user leaning against the back of the chair, and
particularly in the case of chairs having arms lounging sideways in
the chair.
Earlier chairs of this type usually had shells of fibre reinforced
synthetic resin, and local reinforcement of the shell could fairly
readily be incorporated during manufacture, for example by local
variation of the thickness of the shell; however the material as
well as the manufacturing techniques involved were relatively
costly. It is desirable to be able to use cheaper materials and
moulding processes, in particular injection moulding of
unreinforced synthetic resins, for example polypropylene.
Unfortunately, practical limitations in injection moulding
technique restrict the reinforcement techniques available and it is
a practical requirement that the shell be of substantially constant
thickness throughout, whilst the absence of fibrous reinforcement
reduces the inherent rigidity of the material.
A limited degree of local deformability in certain parts of the
chair shell is desirable since it enhances the comfort of a user,
but it is necessary to avoid any substantial distortion of the
shape of the shell as a whole, and in particular distortions likely
to cause fatigue failure of the shell material. Two main expedients
are known for this purpose. Firstly, a rolled section or flange can
be provided along at least selected parts of the edge of the chair
shell. Secondly, if the shell is designed to include integral arms,
these help relieve the bending stresses that would otherwise be
applied at the junction of the seat and the back. In neither case
is any variation in the thickness of the shell required, but even
in combination these expedients do not overcome the liability of
the shell to certain types of distortion, in particular those
caused by the forms of user behavior outlined above. One solution
to this problem would be to extend the rolled section of flange to
form a completed tubular section around the edge of the chair, but
such sections cannot be formed by injection moulding.
Surprisingly, we have found that the problem can be solved, where a
continuous roll or flange along the front edges of the seat and
arms of the chair is provided, by moulding webs across the channel
formed by the roll or flange in the regions where the arms merge
into the seat, this modification being found to largely prevent
distortion of the shell due to rearward or sideways forces applied
by the user to the back of the chair.
Thus, according to the invention, a unitary moulded chair shell
forming the seat, arms and back of a chair, provided with a
continuous rolled flange forming a channel extending along the
under or rear side of the front edges of the arm and seat portions
of the shell, also comprises integral webs extending across said
channel in the regions where the arms merge with the seat.
The advantage of this construction is that the provision of such
webs provides the desired stiffening of the chair shell with the
minimum of additional material and without altering the general
appearance of the shell, the webs being inconspicuous due to their
location, whilst they are readily produced by injection moulding
techniques; moreover alteration of the number and exact location of
the webs can be carried out without major modification of the mould
used. The invention is particularly useful in the moulding of chair
shells from thermoplastic materials such as polypropylene or
polyethylene, and overcomes the liability to excessive distortion
which has hitherto been a serious disadvantage of moulded
thermoplastic chair shells.
The invention is described further with reference to the
accompanying drawings in which:
FIG. 1 shows a perspective view of a chair shell in accordance with
the invention, partially broken away in order to clarify the
construction,
FIG. 2 shows an underneath plan of the same shell, and
FIG. 3 shows on an enlarged scale, a part section of the shell on
the line III-III in FIG. 2.
Referring to the drawings, only the chair shell 1 comprising a seat
portion 2, a back portion 3 and arm portions 4 has been shown, the
frame being omitted: this may take a number of forms, and is
attached by screws to bosses 5 formed integrally on the lower
surface of the seat portion 2. The edges of the shell are turned
downwardly and/or rearwardly to form a rolled flange 6 around the
periphery of the shell, the extent of this roll along at least the
front edges of the arms and seat, and in the example shown also the
top edges of the arms, being sufficient to form a channel 7. In
each of the regions where the arm portions merge with the seat
portion, this channel is spanned by a number of webs 8. In the
example shown, five webs are used in each such region, spaced
throughout the transitional region of the channel between the arm
portion and the seat portion: however, the number and spacing of
the webs can be varied experimentally to suit differing designs of
shell: it will normally be possible to modify an existing mould in
order to add additional webs if necessary. Conveniently, the webs
are approximately the same thickness as the main shell.
* * * * *