Note: Descriptions are shown in the official language in which they were submitted.
1081419
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This invention relates to the manufacture of plastics
pipe couplings either of the sleeve type or of the socket and
spigot type for plastics piping or piping of clayware, pitch-
fibre, asbestos cement or concrete such as is used in sewers,
drains, cable conduit or the like.
According to one aspect of the present invention there
is provided a method of manufacturing a plastics pipe coupling
of the kind comprising a tubular member of stiff plastics
material and a resilient elastomeric annular sealing member
secured therein for engaging a pipe end when inserted into the
coupling, which method comprises preforming a first of the said
members, disposing the preformed member in injection-moulding
apparatus in such a way that the preformed member defines at
least one mould member of said apparatus an annular moulding
cavity, and injection moulding the other said member in the said
cavity thereby forming the other said member bonded to the
first member.
It is preferred to use chemically compatible materials
for the respective annular members with a view to achieving the
optimum chemical bond therebetween when the one member is injection
moulded onto the other member. It is however possible to utilize
incompatible materials which do not tend chemically to unite
when the one member is injection moulded onto the other member
by ensuring that the members are relatively configured to
provide an interlocking type mechanical bond therebetween.
A preferred application would be of compatible
, thermoplastic material for the respective members giving the
best chance of a chemical bond
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~081419
with the members also being designed to achieve a mechanical
(interlocking) bond. For example the preformed member may
comprise the main body member of a cou ling and be formed from
a rigid PVC or polypropylene and the annular m~mber which is
injection moulded onto the preformed member may comprise a
sealing element of the coupling and be formed from a plasticised
PVC suitable particularly for plastics pipes made to close
tolerances.
For clay pipes with wider diameter tolerances and
where resistance to long term shear loads are more important
the preformed member may again be the main body member of the
coupling of polyolethene material (polyethylene, polypropylene)
and the member injection moulded onto the preformed member may
again be a sealing member of the coupling of a thermoplastic
rubber (elastomer) cross-linked to give compression-set resistance
properties.
It is also within the scope of the invention however,
for the preformed member to be a sealing member of the coupling
and this could be of a moulded thermosetting rubber material,
the main body
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1081419
member of the coupling being of a thermoplastic material and
being injection moulded onto the sealing member with the
members being respectively configured to provide a mechanical
(interlocking) bond therebetween.
A major application of the invention is in the two-
stage or composite moulding of a coupling element where the
preformed second annular member is first injection moulded in
a first moulding stage and the first annular member is then
injection moulded onto the preformed member in a second injection
10 moulding stage both of which stages are preferably carried out .
in a common mould using different mould profiles respectively.
. According to another aspect of the invention there
is provided apparatus for two stage moulding of plastics pipe
couplings of the kind comprising a tubular member of stiff .
plastics material and a resilient annular sealing member secured
` therein for engaging a pipe and when inserted into the coupling,
said apparatus comprising a cavity block defining the external
periphery of a cavity, a core assembly disposed in said cavity
;~ with an annular gap between the internal surface of the mould.; 20 block and the peripheral surface of the core assembly, said
core assembly comprising core members mounted for axial relative
movement, said core members having a first position in which the
core assembly in cooperation with the cavity block defines a
''~?~ first moulding cavity, a first injection.moulding nozzle adapted
~i to communicate with said first moulding cavity for injection
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i: moulding a first member of a said pipe coupling, said core
~ members having a second position in which there is defined in
cooperation with the injection-moulded first member of the pipe
coupling a second moulding cavity, and a second injection moulding
~ 30 nozzle adapted to communicate with said second moulding cavity
i for injection moulding the other aforesaid member of the pipe~ `
. coupling in contact with the said first member of the pipe coupling.
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1081419
The invention will now be described by way of an
examp:Le with reference to the accompanying drawings in wr.ich:
Fig. 1 is an axial section through a sleeve-type
coupling element for connecting together plain ended pipes;
Fig. 2 is a view on line A - A of Fig. l;
Fig. 3 is a sectional view of a composite injection
mould for producing the element shown in Figs. 1 and 2, the
mouled being illustrated in the condition for performing a
first injection moulding operation for forming the main body
member of the element and
Fig. 4 is another sectional view of the mould shown in
Fig. 3, the mould in this case being illustrated in the condition
for performing a second injection moulding operation for moulding
the seal member of the coupling element onto the preformed
main body member.
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108~419
~he coupling element ~how~ in Figs. 1 and
2 comprise~ a substantially plain cylindrical main
bod~ member 1 of rigid polypropylene and an inner
~ealing member 2 of a suitable elastomer injection
moulded onto the body member the nature of the
' re~pective materials baing such that durin~
-~ the inJection moulding of the sealing member ontothe body member a chemical bond is to a greater or
les~er extent established between the members.
The body member i8 formed with a central
annular pipe-end locating rib 3, a serie~ of
circumferentially ~paced axially extending ribs 4,
~ and undercuts 5 at the margins, the ribs 4
'~ and undercuts 5 serving to form mechanical
means for interlocking the main bod~ and the
,~ sealing member together 80 that in the completed
coupling element, these members are interconnected
7 with chemical- mechanical bond. ~he sealing memberji .~
~ has an internal wave-li~e formation for ~ealing
;~, 20 against the external surface~ of a pair of plain
, j
'.. `! ended pipes-
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r~r - Manufacture Or the above-described coupling
~'~i element i~ effected in a two-stage in~ection
,i moulding proces~ in apparatu~ a~ ~hown in
~'~ 25 Fig~. 3 and 4.
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108~419
~he moulding apparatua comprise~ a fixed
: platen 6 carrying a fixed inner core 7 and
a moving platen 8 carrying a moving inner core
9 both core~ being pe~ipherally profiled as
: 5 showR to define the wave-like configuration o~ the
: coupling ~ealing member 2. ~he cores operate
: in a main cavity block 10 having a moulding cavit~
the wall of which define~ the outer profile o~ the
main body member 1 of the coupling element and a
! 10 pair of opposed core sleeve~ 11 and 12 ~it over there~pecti~e cores for sliding movement into and out
of tha mould ca~ity. Opposed hydraulically
~ operated pair~ Or side plates 13a, 1~ and 14a, 14b
: are linked together for radially inward and outwardmovement as will be described and the appRratus i8
~ completed by a horizontally movable cyli~der 15 with
3 a~sociated injection ~ozzle and a vertically movable
cylinder 16 also with associated injection nozzle.
~ The core sleeve 11 is mechanically linked to
i 20 the cylinder 15 and the core sleeve 12 is connected. to a ~o~able support plate 17.
:. For the first in~ection mouldiRg ~tage,
;: fox moulding the main body member 1 of the
¢oupling element (Fig. 3) the side plates are
; 25 in their outer or open po~itio~, the core~ are
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1~8:1419
closed together within the mould cavity, the core
~leeve 12 is positio~ed within the cavity b~ advance
of the support plate 17 and the horizontal cylinder
15 ad~anced into a position in which its nozzle
i8 ~ituated in an injection opening 18 in the
~ixed i~ner core, advance of the horizontal
cylinder al~io causing the core sleeve 11 to be
advanced into the moulding cavitg. In this
¢ondition the shape of the main body member 1
of the coupling element i~i defined between the
' wall of the moulding cavity and the outer
surfaceis of the core sleeves, the sleeves a~d cores
having clearance between the respective inner edgss
for the formation of the annular rib 3 of the
.; .
;;~ 15 coupli~g element and for the introduction of the
moulding material from cylinder 15. ~irst stage
., injection mouldi~g is thus effected with material
i from cylinder 15.
i After the firæit ~tage moulaing~ the cylinder
15 retract~ thereby stripping the core ~ileeve 11
` from the mould cavity and support plate 17 also
; retracts the strip of the core slecve 12. The side
plates 13, 14 are then closed to shut off on the
: core~ and it will be seen from ~i.g. 4 that an
~, 25 i~ection inlet 19 is formed between the ~ide plate
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10 8~ 419
13a and the main cavity block with the ~hape Or the
sealing member 2 of the coupling element being
defined between the pre-~ormed main bod~ member 1,
the cores 7 and 9 and the ~ide plates 13, 14. ~he
~ertical cylinder 16 then advances into an injection
ope~ing 20 formed between the side plate 13a and the
cavity block and ~econd stage moulding is ef~ec~ed
; through the inlet 19 ~o that the ~ealing member 2
i~ inJection moulded o~to the pre-formed main body
~ ! , 10 member 1 with the~e member~ becoming con~e¢ted
; together with a chemical/mechanical bond as
i previously described.
fter the seaond stage moulding the vertical
-; cylinder retracts and the press opens stripping the
, j .
~i ' 15 completed moulding from the fi~ed inner core. ~he
~ main ca~ity block and side plates are restrained as
-1 ~ a unit, whil3t the moving in~er core continues to
open, stripping the moulding from this core~ ~he
-i - side plates then open and the ~upport plate 17
closes up to the main cavity block to e~ect the
moulding. ~he apparatuæ is then ready to comme~ce
the next moulding cycle.
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