GB2182886A - Moulding a thermoplastics pipe coupling incorporating a pre-formed elastomeric sealing ring - Google Patents

Abstract

The molten thermoplastics material is injected to flow longitudinally along the mould cavity, so that it moves across and cleanses a tail portion (22) of the sealing ring (20), which projects into the mould cavity to become embedded in the wall of the coupling. The wall cavity is defined between a pair of exterior mould blocks (e.g. 30), and separable mould core parts (42, 36) and (38, 44), between which are clamped a sealing ring at either end of the cavity. The mould blocks define the sprue (34), and a main runner (35) which discharges into the cavity, at the central cavity location (40) of an abutment (14, Figure 1) projecting inwardly from the coupling wall. Diametrical and branch auxiliary runners (60, 62, Figure 5) also discharge into the cavity at circumferentially spaced locations around the abutment, to ensure that the longitudinal flow is circumferentially uniform. Displacement of the tail (22) by the flow is restrained by mould pins (58), comprising a castellated part of mould end rings (52). <IMAGE>

Description

SPECIFICATION Moulding method The invention relates to an injection moulding method for producing pipe couplings ofthe kind comprising a substantiallytubularsynthetic plastics member provided at least one end with an inward facing annularsealing ring previously manufactured from a crosslinked thermosetting material. re- suiting pipe coupling, which may be ofthe sleeve typeorofthesocketandspigottypeaccordingto whether it is provided with an annular sealing ring at each end or only at a socketed end, may be intended for plastics piping or piping of clayware of other mat erials such as are usedforsewers, drains, cableconduitorthe like.Particularly when connecting sewer pipes it is importantthatthe coupling forms awater tightflexiblemechanicaljointsothatthe pipeline does not leak and sothatthejoint is compliantto a certain amount of movement ofthe adjacent lengths of pipe resulting for example from ground settle- mentafterthe pipe line has been laid.

In a previous attempt to produce such a pipe coupling it has been proposed to perform a two-stage or composite moulding ofatubularthermoplastics member and an annular elastomeric sealing member in a common mould.The annularelastome ricsealing member has been injection moulded in a first moulding stage and thetubularthermoplastics member has then been injection moulded onto the preformed sealing member in a second injection moulding stage. It has been proposed to use chemically compatible materialsforthetwo membersofthe coupling with a view to obtaining the optimum chemical bond between them. It was also stated that a bond of limited strength could be formed with incompatible materials.We believe that this result was dependent on the first material being freshly moulded. However, even though such a bond of limited strength could possibly be formed it was nevertheless deemed necessary to recommend that, in addition, a tail portion ofthe annular sealing member should be so shaped thatin thefinished productit becomes embedded in the wall ofthetubular thermoplastics memberto form an interlocking type mechanical bond.

The object of the invention isto provide a moulding method for producing pipecouplingsthetubular plastics members and pre-manufactured annular sealing members of which can be made of certain materials previously thoughtto be incompatible, that isto say a thermoplastics material and of a crosslinked (vulcanised) elastomericthermosetting material respectively in which at least a tail portion of the sealing memberwill be securely bonded tothe material ofthe sleeve.

According to one aspect of the invention, there is provided a method of moulding a pipe coupling in which at least a tail portion of a previously manufactu red elastomeric sealing ring is securely bonded to the thermoplastics material of a sleeve portion of the coupling, the method includingthesteps of mounting the pre-manufactured sealing ring between adjacent elements of a multi-part core assembly so thatthetail portion of said sealing ring projects intothe generally cylindrical mould cavity, and of admitting molten thermoplastics material to the mould in a manner such that the flow of said material as itfillsthe mould cavity at least in the region of the tail portion of the sealing ring, is predominantly longitudinal ofthe mould cavity so that it flows across and cleanses and/or scours the surface of said tail portion and thus produces a chemical and/or physical cohesive bond between the materials.

According to another aspect of the invention, there is provided injection moulding apparatus for moulding a pipe coupling in which at least a tail portion of a pre-manufactured elastomeric sealing ring is securely bonded to the thermoplastics material of a sleeve portion of the coupling, the apparatus including a pairof mould blocks which can cometogether to define the outer periphery of the mould cavity and to define also the sprue and main runner, that isto say the passages by way of which the molten thermoplastics material is to enter the mould cavity at a first entry point and including also a multi-part core assembly comprising a pair of core elements between which a portion ofthe sealing ring can be tightly clamped so that its tail portion projects into the generally cylindrical mould cavity, there being at least one auxiliary runner provided in the apparatus to admitthermoplastics material to the mould cavity at an additional entry point, to promote a flow of molten thermoplastics material, as itfillsthe mould cavity, which at least in the region of the tail portion ofthesealing ring is predominantlylongitudinal of the mould cavity so that it flows across and cleanses and/orscoursthesurfaceofsaidtail portionofthe sealing ring and thus produces a chemical and/or physical bond between the materials.In addition to a main auxiliary runner extending diametrically across the multi-part core assembly the apparatus may in dude also a pairofdiverging auxiliary runners which extent outwards from the main auxiliary runnerto break into the annular mould cavityatspaced re gionsaround its circumference to bring aboutasub- stantiallyuniform cross flow of molten thermoplastics material impinging againstthetail portion of the pre-manufactured elastomeric sealing ring.The apparatus will preferably include a plurality of equ ally spaced support pins projecting into the mould cavitytosupportthetail portion of the elastomeric sealing ring againstthe inrush ofthermoplastics material into the mould.

The pipe coupling to be moulded in the apparatus may be ofthe double ended type, that is to say comprising a thermo plastics sleeve element with an elas tomericsealing ring at each end, and in this case may have an abutmentflangewithinthesleeveelement midway of its length to limit the extent by which a pipe can be entered into the sleeve from either end. If so, the auxiliary runner or runners may extend across the abutting faces of core elements which define said abutmentflange.

Throughoutthis specification the term "promanufactured sealing ring" is intended to mean a sealing ring which has been formed, priorto the moulding of the sleeve portion of the coupling, in apparatus otherthan that in which the thermo plastics sleeve portion is formed. Consequently, the pre-manufactured sealing ring may well be (but need not necessarily be) a "bought outfinished" compo nent.

In orderthatthe invention may be fully understood and readily carried into effect, embodiments thereof will now be described, by way of example on ly, with reference to the accompanying drawings, of which: - Figure 1 is a part sectional plan view of a pipe coupling sleeve which has been produced by the in ventive moulding method, Figure2 is an end view ofthe coupling sleeve, Figure 3 is a sectional view of a multi-impression mould in which the coupling sleeve has been prod uced, Figure4is a detail viewofa partofthe mould, drawntoasomewhatlargerscalethan Figure3, Figure 5is a view on the line 5-5 in Figure 3, and Figure 6is a detail sectional view on line 6-6 in Figure 5.

Referring now to Figures 1 and 2 of the drawings, the pipe coupling there illustrated has been prod uced by the inventive moulding method and is ofthe sleeve type comprising a double-ended sleeve el- ement 10 moulded inthermoplasticwhich in this em bodiment is polypropylene. Another polyolefin, not ably polyethylene, can be used alternatively. Each end of the sleeve element is adapted to receive the end of a clayware pipe 12 as shown in the right hand half of Figure 1. An abutmentflange is shown to be provided within the sleeve element and midway of its length to limit the extent by which a clayware pipe can be entered into the sleeve from either end.

Each end ofthe moulded plastics sleeve has a por tion 16 of enlarged wall thickness within which has been moulded a relatively narrow and flexible tail portion 22 of a pre-manufactured captive annular sealing ring 20 made of a thermo-setting ethylene propylene elastomer. The flexible tail portion ofthe pre-manufactured sealing ring has become securely bonded to the material of the sleeve element despite the fact that heretofore these materials haveinvari- ably been regarded by experts in the art as being in compatible. This bond is so strong that the elastome ricsealing ring will tear under a sufficiently great stress, without the bond to the tail portion breaking.

The bond is not dependent on the sealing ring being freshly manufactured. The sealing rings can be sto redforsometimebetweentheirmanufactureand their moulding into a sleeve. The bond is notdepen dent on mechanical retention. In fact, if the elastome rio sealing ring is pre-manufactured from a com pletelyincompatible material which will not bond to the polyolefin underthese moulding conditions, the mechanical retention is so insignificant that the pro ductoannotbedemoulded intact, and the sealing ring is completely displaced in the demoulding pro cess.

Suitable combinations of elastomer and thermoplastics can be established by experimental trial to determinewhetherthe materials will bond underthe moulding conditions ofthis invention. We believe that the elastomer and thermoplastics should have a monomer in common.

We have found that a cause of the excellent bond obtained in this invention is that during the injection of the thermoplastics material into the mould, the flow of the molten material is such that it impinges against and flows across the flexible tail portion 22, thereby cleansing and/or scouring the surface area of said tail portion. We have found that a bond to at least part of the surface 24 is frequently obtained, as well as the bond to the tail portion 22. This is found to be especially so if the inrush of molten thermoplastics material is caused to impinge against a slightly upstanding leading edge ofthe sealing ring as shown in the illustrated example.

The way in which the required flow of molten thermoplastics material is brought about to promote the essential cleansing and/or scouring action is illustrated in Figures 3 to 6 which are views which il lustratetheinjection moulding apparatus inwhich the coupling sleeve has been produced.The mould isa multi-impression mould butitwill be understood that the numberofimpressions is not important; the following description relates to a single one ofthe impressions.

Referring in particularto Figures 3 and 5, the outer periphery of the mould cavity is defined by generally semi-cylindrical cavities in respective upper and lower blocks 30, 32 which can cometogetherto define also the sprue 34and runner35, that isto saythe passages by way of which the molten thermoplastics material is to enter the mould cavity. The inner per- iphery ofthe mould cavity on the other hand is defined by a multi-part core assembly including a pair of core elements 36,38 which abut together substanti- ally midway of the overall length of the generally cylindrical mould cavity. An annular space 40 which is formed by a peripheral step in the face of the core element 36 forms the abutmentflange 14 of the moulded pipe coupling illustrated in Figures 1 and 2.

The core elements 36, 38 are slidably mounted on respective radially inner core elements 42, 44these each being provided with annularflange portions 46, 48. Spring means, illustrated diagrammatically at45 in Figure 3, are provided for urging the core elements 36, 38through a limited distanceawayfromthere- spective inner core elements 42, 44 on which they are mounted, but as the apparatus is drawn in Figure 3 the force of said spring means has been overcome in orderto bring the elements ofthe mould to the closed condition, securely clamping the sealing ring in readiness, for the injection ofthethermoplastics material into the mould cavity. Securelyclamping the radially inner part ofthe sealing ring in this way ensures that the molten thermoplastics material cannot penetrate to said inner part ofthe ring. The annularflange portions of the inner core elements, together with peripheral portions of respective end rings 50, 52 and radially inner portions of respective ejector rings 54, 56, define the shape of the opposite end portions of the plastics sleeve which is to be produced in the mould.

Referring now in particularto Figure 4, which illustrates in greater detail the relationship between the mould parts which definetheshape ofthe end portions of the plastics sleeve, it will be seen that before the mould elements have been broughttogetherfor the thermoplastics material to be injected into the mould cavity, that part of the previously manufactured annular sealing ring which isvisible in thefin ished product has been tightly clamped between the core element concerned and the adjacent annular flange portion ofthe radially inner core element.The flexible tail portion ofthe sealing ring extends, as shown, into the mould cavity and rests against tor can rest against during the injection of moulding material) the ends of a plurality of closely spaced support pins 58 which are formed at the periphery of the adjacent end ring and themselves project into the mould cavity. (In Figure 4the support pins appear in section as a narrow skirt portion of each end ring, but as shown at49 by the chain-dotted lines in Figure3 this has been castellated to form the plurality of closely spaced support pins).

Also indicated in Figure4 bythe series of arrows is the flow of molten thermoplastics material which must take place ifat leasttheflexibletail portion of the pre-manufactured annular sealing ring isto be securely bonded to the thermoplastics material of the sleeve. The arrows indicate how the molten material flows across and cleanses and/orscoursthe opposing surfaces ofthe tail portion ofthesealing ring, this creating the condition in which a chemical and/ or physical cohesive bond between the materials is effected.Since it is imperative that an effective bond is achieved around the entire circumference of the tail portion ofthe sealing ring and notonlythatregion nearestthe runner 35 (from where it will be seen the molten material can very easily "flash" outwards towardstheoppositeendsofthegenerallycylindri- cal mould cavity), further runners are provided to ensure that atthe instant of molten material injection intothemould,theflowofmaterial isoutwardsfrom the plane in which the annular space 40 is located, towards the opposite ends of the generally cylindrical mould cavity, as equally as possible around the entire circumference of the mould cavity.As shown in Figure 5 these comprise a main auxiliary runner60 extending diametricallyacrossthefaceofthecore element38to join diametrically opposite portions of the annular space 40, and diverging auxiliary runners 62, 62 which extend outwardsfromthe main auxiliary runner as shown to break into the annular space 40 at other regions around its circumference. It will be understood that the precise regions in which the auxiliary runners break into the annularspace have been determined by trial and experiment to bring aboutthe substantially uniform cross flow of molten material impingingagainstthetail portions ofthe pre-manufactured sealing rings.

The required cross sectional dimensions ofthe auxiliary runners have also been determined by trial and experiment to bring about the substantially uniform cross flow of molten material impinging against the tail portions ofthe pre-manufactured sealing rings. As shown in Figure 6, the cross sectional areas ofthe main auxiliary runner and ofthe diverging auxiliary runners in the illustrated moulding apparatus are very much greaterthan would normally be required in the moulding of a synthetic plastics article ofthis general kind (but without pre-manufactured sealing rings moulded in it).It will also be observed that the auxiliary runners are fairly thick in relation to theirwidth, that is to say being of very nearly square cross section, th is being so that the molten material can be conveyed through them with negligible heat loss (which could be a problem if the runners were of relatively thinner section). The "gates" that is to say the relatively narrow flow pas- sages, which areformedwheretheendsoftheauxil- iary runners break into the annularspace40, are not a problem in this respect because heat loss overthe relativelyshortdistances involved is negligble.It will be understood that the auxiliary runners are trimmed from the finished moulded pipe couplings by being severed through atthethinner portions resulting from the "gates", in line with the inner peripheral surfaces ofthe abutment flanges.

When the moulding apparatus is opened to release the moulded coupling sleeve, the upper and lower blocks 30, 32 first begin to move apart and the core elements 42, 44 then move away from each other. The initial movement of the core elements 42, 44 away from each other underthe action of spring means 45 results in relative sliding movements of the respective core elements 36,38 of only very limited extent but sufficient to release the parts ofthe pre-manufactured annularsealing rings previously tightly clamped between the core elements concerned so that they are free to deform as necessaryto accommodate the "jumping-out" of the core elements as they are withdrawn from the moulded coupling sleeve.Movement of the ejector rings 5A 56 relative to the respective core elements and end rings asthe mould is opened causes the moulded sleeve to be stripped from the support pins 58 and from the respective core elements.

Thus there is provided a method of and apparatus for producing pipe couplings each having at least at one end a pre-manufactured annular sealing ring, thethermoplasticsmaterial ofthesleeveandthepremanufactured thermosetting material of the sealing ring having previously been though to be incompatible. Various modifications may however be made.

Various modifications may however be made. For example, the pipe coupling need not necessarily be ofthe sleeve type; it could be of the socket and spigot type and comprise a socket and bonded-in elastome ricsealing ring at only one end. Such a socketand spigotmembercould befusion welded to an el- ongate plastics pipe after being moulded by the method described above.

Claims (7)

1. A method of moulding a pipe coupling in which at least a tail portion of a previously manufactured elastomeric sealing ring is securely bonded to the thermoplastics material of a sleeve portion of the coupling, the method including the steps of mounting the pre-manufactured sealing ring be tween adjacent elements of a multi-part core assembly so that the tail portion of said sealing ring projects into the generally cylindrical mould cavity, and of admitting molten thermoplastics material to the mould in a manner such that the flow of said material as it fills the mould cavity at least in the region of thetail portion of the sealing ring, is predominantly longitudinal ofthe mould cavity so that it flows across and cleanses and/or scours the surface of said tail portion and thus produces a chemical and/or physical cohesive bond between the materials.

2. Injection moulding apparatus for moulding a pipe coupling in which at least a tail portion of a premanufactured elastomeric sealing ring is securely bonded to the thermoplastics material of a sleeve portion ofthe coupling, the apparatus including a pairofmould blocks which can cometogetherto define the outer periphery ofthe mould cavity and to define also the sprue and main runner, that isto say the passages by way of which the molten thermoplastics material is to enterthe mould cavity at a first entry point, and including also a multi-coreassembly comprising a pair of core elements between which a portion ofthe sealing ring can be tightly clamped so that its tail portion projects into the generally cylindrical mould cavity, there being at least one auxiliary runner provided in the apparatus to admit thermo- plastics material tothe mould cavity at an additional entry point, to promote a flow of molten thermoplastics material, as itfillsthe mould cavity,which at least in the region ofthetail portion ofthesealing ring is predominantly longitudinal ofthe mould cavity so that itflows across and cleanses and/or scours the surface of said tail portion of the sealing ring and thus produces a chemical and/or physical bond between the materials.

3. injection moulding apparatus according to claim 2, in which in addition to a main auxiliary runner extending diametrically across the multi-part core assembly, there is included also a pair of diverg ing auxiliary runners which extend outwards from the main auxiliary runnerto break into the annular mould cavity at spaced regions around its circumferenceto bring aboutasubstantiallyuniform cross flow of molten thermoplastics material during a moulding operation, the cross flow of molten material impinging againstthetail portion ofthe premanufactured elastomeric sealing ring.

4. Injection moulding apparatus according to either one of claims 2 and 3, including a plurality of equally spaced support pins projecting into the mouldcavitytosupportthetail portionoftheelas- tomeriosealing ring againsttheinrush ofthermo- plastics material into the mould.

5. Injection moulding apparatus according to any one of claims 2to4, in which the or each auxiliary runner extends across the abutting faces of core el ements which define an abutment flange which is to be formed midway of the length ofthesleeveel- ement so that, in use of the sleeve element, the extent by which a pipe can be entered into the sleeve from either end is limited.

6. A method of moulding a pipe coupling, substantially as hereinbefore described with reference to and as illustrated by the accompanying drawings.

7. Injection moulding apparatus for moulding a pipe coupling in which at least a tail portion of a premanufactured elastomeric sealing ring is to be securely bonded to the thermoplastics material of a sleeve portion ofthe coupling, the apparatus being constructed, arranged and adapted to be used substantially as hereinbefore described with reference to and as illustrated by Figures 3 to 6 of the accompanying drawings.