GB1592423A - Moulding components of thermosetting materials using a resilient sheath - Google Patents

Description

(54) MOULDING COMPONENTS OF THERMOSETTING MATERIALS, USING A RESILIENT SHEATH (71) We, HYDROTROLE LIMITED, a British rompany of Rooth Street, Georges Road Industrial Estate, Stockport, SK4 lBP, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention concerns the moulding of components from thermosetting materials, using a resilient sheath.

In the moulding of tubular components, such as containers, reservoirs and bladders used in the containment of fluids, problems are encountered with increase in the size of the product required to be moulded, especially where the wall of the component is required to be of predetermined thickness and, perhaps, to differ in thickness from location to location, and is required to have accurately predetermined shapes at its ends, for example for attachment, alignment and/ or suspension purposes. Traditionally, use has been made in the past of mould assemblies which comprise a mould body into which fits an internal axially-extending core, so that the body and core between them define a mould space corresponding to the desired component shape. In one way of using such a mould assembly the mould is used hot. A desired amount of moulding material is introduced into the body, whereafter the core is forced into the body, by means of a press, so as to compress the moulding material and cause it to flow and eventually take up a configuration such as to occupy the mould space. This compression moulding technique can result in products having wall thicknesses deviating from their designed dimensions, in the event of any tilting of the core, or relative inaccuracy of its location in the mould body which can arise, for instance, if slightly more moulding material is put in at one side of the cavity than the other.

In another way of using such a mould assembly, the core interfits from the outset with the body and is provided with a separate chamber for receiving the moulding material, and an externally-protruding piston fits into the chamber. Upon pressure being applied to the piston in a press, the moulding material is transferred, through transfer passages in a head of the core, from the chamber and into the mould space.

The capital investment in such mould assemblies is particularly high and, of course, an individual mould assembly is needed for each size and shape of component required to be moulded. With increase in the size of the components, space difficulties have to be overcome in extracting the core from the mould body and thereafter removing the product from within the mould body or from the outside of the core, and consequently very long stroking largearea pressure-applying arrangements have to be employed, with consequential increase in the capital cost of the equipment involved.

Moreover, with increase in size and/or length of the product, considerable pressures are involved to make the material flow the necessary long distances to fill the mould space, with consequential need for the equipment to be correspondingly massive and expensive.

An object of this invention is to provide a moulding method, for thermocuring or thermosetting materials, which can be employed for producing large moulded components and which does not need the use of massive mould bodies and consequently i1 ìvolves considerably less capital expenditure than the hitherto known traditional moulding techniques.

With this object in view, the present invention provides a method of producing a moulded component from a thermosetting material which comprises forming a resilient sheath around a metal mandrel whose external shape corresponds to the desired interior component shape, removing the sheath, applying moulding material around the mandrel, drawing the sheath over the mandrel so as to hold the moulding material thereto and subjecting the resultant sheathed assemblage to heat to cause fusion and curing or setting of the moulding material whilst held in shape around and pressed resiliently against the mandrel by the sheath.

In a preferred method of carrying the invention into effect, the resilient sheath is formed externally on the metal mandrel by laying up the mandrel with layers of thermo setting material and subjecting the resulting assemblage to heat, to cure the material of the sheath, and the moulding material is applied to the mandrel by laying-up the mandrel with layers of thennosetting moulding material. it will readily be understood that the method of the invention, which employs the flexible sheath to define the mould cavity, can be used for producing tubular components of any desired practical length and diameter, without the need for providing a mould body in the traditional sense.

In making the sheath, the assemblage, consisting of the mandrel with the layers for forming the sheath, is preferably wound, prior to it being subjected to heat, with overlapping windings of a tape or band not adversely affected by the heat to which the assemblage is subjected to cure the material of the sheath.

Where the component being moulded is required to have portions of different thickncsscs, this can be achieved, of course, by providing greater or smaller numbers of layers of the moulding material over corresponding portions of the mandrel, as dictated by the desired thickness variations.

Thus, for example, with a component re quired to be of increasing thickness from one end to the other, the mandrel may, for instance, be laid-up with a first layer of the moulding material over substantially its entire length, with a second layer extending only over about two-thirds of its length from one end, and with a third layer extending over about one-third of its length from the same end.

The method of the invention can be used, for instance, for moulding simple slightlytapered tubular components using thermo- setting moulding material which achieves a substantially rigid product, since, of course, such a product can readily be separated from the mandrel (after removal of the sheath) by withdrawing the mandrel therefrom.

With a thermocuring moulding material which achieves a resilient or deformable product, the component can, of course, be caused (e.g. by supplying compressed air thereto, for instance through the interior of the mandrel or by way of passages through the pattern) to expand for remov- ing it from the mandrel. In this instance, of course, there is no need for the component and mandrel to be tapered for component removal, and shaped, contoured and/or stepped components can be produced, provided the contouring, shaping or stepping is such that component removal can be achieved by appropriate expansion of the product.

It will readily be understood that if demandrel one or both of the ends of the mandrel may be adapted for further moulding material to be moulded-on onto the moulding material layers, by compression moulding and/or transfer moulding tech- niques.

Thus, for example, where it is required for the moulded tubular component to have an accurately moulded with cylindrical mouth on one end, if desired with circumferential ribs, and/or beads and/or grooves, pas- sages may be provided in the mandrel for moulding material to be transfer moulded into a mould space defined around the respective end of the mandrel by an appro- priate surrounding mould cap. Then, the transfer moulded material becomes integral with the layer material, of course, during subsequent heat treatment of the mandrel with the moulding material applied thereto.

Snmarly, for example, where it is required for the other end of the moulded component to have a centrally-apertured or domed end, the respective end of the pattern may be correspondingly domed and auapted mternany, for pressure moulding of the said domed end of the compenent.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which:- Fig. 1 is a cross-sectional side elevation masuaung a mandrel titted with transfer moulding means at one end and with compression moulding means at the other end, this assembly being suitable for use in moulding a component, in the form of a substantially cylindrical flexible bladder having an accurately-moulded cylindrical and ribbed mouth at one end and a cen- trally-apertured domed end at the other end, by the method of the invention; Fig. 2 illustrates the mandrel of Fig. 1 laid-up with layers of an appropriate the mocuring material wound with a surrounding band or tape for producing a sheath as a step in producing the bladder aforesaid; Fig. 3 illustrates the pattern of Figs. 1 and 2 after removal of the sheath and laid up with layers of moulding material ready for producing the bladder, with the latter naving graduated wall thickness form one end to the other: Fig. 4 is a view similar to Fig. 3 but illustrating the assembly with the end sheath drawn thereover, and with the end moulding means in position; Fig. 5 is a view similar to Figs. 3 and 4 but showing moulding material pressure moulded and transfer moulded onto the enus on cne mandre to join with the laidon material; and Fig. 6 is a perspective view illustrating the resultant product.

Referring firstly to Fig. 1 of the drawings, a mandrel indicated generally by the reference numeral 10, for use in producing a component in the form of a long resilient tubular container (indicated by numeral 11 in Fig. 6) which may be, for instance, some two or three metres in length or even longer, comprises a relatively thin-walled tubular body 12, tapering slightly from one end to the other. At its narrow end, the body 12 is closed by a relatively thicker-walled closure dome 13 having a central screwthreaded aperture 14, this forming part of compression moulding means which further includes a compression moulding cap 15 locatable by a rod 16 engageable into the aperture 14, this rod being a piston rod of a compression moulding ram 17, a compression moulding space 18 being defined around the dome 13 by the cap 15.

At its wide end, the body 12 is closed by a substantial end plug 19 in which is formed an axial cylinder 20 accommodating a piston 21 whose rod 22 projects out of the cylinder 20 and extends through a mounting plate 23 fixed relative to the end plug 19 by columns 24 engaged in respective bores (not visible) in the end plug 19. This arrangement forms part of transfer moulding means which further includes a surrounding transfer moulding cap 124 which surrounds the plug 19 and defines, around the latter and the adjacent end of the body 12, a respective transfer moulding space 25 which communicates with the cylinder 20 by passages 26, as well as a transfer moulding ram 42 by which the piston 21 can be withdrawn from the cylinder 20 to enable it to be loaded with moulding material and forced into the cylinder 20 for transfer moulding said material as will later be described.

Fig. 2 illustrates a first stage in carrying the method of the invention into effect. In this, initially the mandrel 10 is laid up with a plurality of layers of thermosetting material which, after curing, yields a resilient product, being, for instance, an acrylonitrile butadiene synthetic rubber. In the illustrated case, there are three layers, indicated by the numerals 27, 28 and 29, of this thermocuring material, but it is to be understood that the number of such layers may be varied according to practical circumstances, for example according to the thickness of the layers and the desired finished wall thickness of a sheath (to be described shortly) which will be produced from the said layers. The layers 27, 28, 29 having been applied, overlapping windings of a tape or band 30 are wound therearound so as to grip the layers 27, 28, 29 tightly against the outer surface of the mandrel 10. The material of the tape or band 30 is selected such that it will not be adversely affected (i.e. caused to deteriorate or change its physical characteristics and/ or properties) when subjected to an elevated temperature sufficient to cause curing, and fusion together, of the layers 27, 28 and 29.

To facilitate the laying up of the layers 27, 28 and 29 and/or the winding of the tape or band 30, the mandrel 10 may be mounted, using the aperture 14 and the cylinder 20, between centres (not shown) so as to be rotatable about its longitudinal axis.

The laid-up and wound assemblage of Fig. 2 having been achieved, this assemblage is then subjected to heat, e.g. in an oven (not shown sufficient to cause curing of the layers 27, 28 and 29, causing these to fuse together and cure, to result in a resilient sheath, the form of which is illustrated at 31 in Figs. 4 and 5 which will be described later.

Upon completion of the curing, the mandrel with the sheath 31 formed thereon is removed from the oven and allowed to cool, after which the tape or band 30 is unwound and the sheath 31 is removed to make the mandrel 10 available for use in the next stages of the process.

Turning now to Fig. 3, the mandrel 10 is now laid up with layers of a thermosetting material selected according to the desired properties of the eventual product.

In the practical example under consideration the eventual product, which is illustrated in perspective in Fig. 6, is required to be a resilient tubular reservoir or container 32 having a thickened tubular mouth end 33 with a circumferential bead 34 and a domed end 35 with a central aperture which is not visible in Fig. 6. Adjacent the thickened mouth end 33, the main tubular part 36 of the reservoir or container 32 is of thinnest wall thickness, the wall thickness gradually increasing up to where it merges into the domed end 35. To provide for this, in laying up the mandrel 10, as shown in, Fig. 3 a first layer 37 is provided so as to extend substantially the entire length of the body 12 of the mandrel 10, a second layer 38 is provided to extend over approximately two thirds of the length of the first layer 37 from the closure dome 13, and a third layer 39 is provided to extend over approximately one third of the length of the first layer 37 from the same end. It will be understood, however, that dependent upon the degree of graduation of the thick ness increase of the main wall portion of the reservoir or container 32, a greater or lesser number of the layers 37, 38, 39 may be provided, and the arrangement and posi tioning of the layers can be selected as de sired as to number, thickness, position and areas covered, according to variations in wall thickness in the finished product.

The mandrel 10 having been laid up as described and shown in Fig. 3, the sheath 31 is now drawn thereover, this being effected, for example, by use of compressed air to inflate the sheath to increase the diameter thereof just sufficiently to slide into place. In one way of doing this, a socket may be inscrted into one end of the sheath 31 and supplied with compressed air, whilst the other end of the sheath is offered to the closure dome 13 so that the latter tends to close said other end. Then, the pressure of the air tends to expand the said other end, so as to escape between the sheath 31 and the closure dome 13, with the result that the sheath 31 can be caused to move onto the mandrel 10.

Upon the sheath 31 being fully drawn onto the mandrel 10, the compression moulding cap 15 is brought into its pre viously-described disposition with its rod 16 screwed into the aperture 14, tapered annular lip 40 of the cap 15 entering between the respective end of the sheath 31 and the corrcsponding ends of the layers 37, 38, 39 which project very sliehtl into the compression moulding space 1 8, it being understood that an appropriate amount of compression moulding material (for example of the same material as the layers 37, 38, 39 and being for instance of an acrylonitrile butadiene synthetic rubber, also) is introduced into said space 18 as the cap 15 is brought into place.

Also. the transfer moulding cap 124 is fitted into place around the end plug 19 so that a tapered annular lip 41 Thereof similarly enters between the respective end of the sheath 31 and the layer 37, with the latter projecting into the transfer moulding space 25. An amount of transfer moulding material (gain conveniently the same as that of the layers 37, 38, 39) is filled into the cylinder 20 and the piston 21, rod 22 and thrust plate 23 are fitted in place. This condition is illustrated in Fig. 4, but with the moulding material omitted from the mould space 18 and the cylinder 20, and the assemblage so achieved is heated. Whilst being brought up to an appropriate elevated temperature sufficient to cause curing or setting the material of the layers 37, 38, 39, pressure is applied by the transfer moulding material from the cylinder 20 to the transfer moulding space 25, thereby to form the thickened tubular mouth end 33 in the transfer moulding space 25. Additionally. pressure fluid is supplied to the compression moulding ram 17 to cause relative move ment of the cap 15 towards the domed end 13 thereby to cause the moulding material in the mould space 18 to flow and occupy the whole of the space 18 which, as can be understood from Fig. 4 may be formed with concentric grooves 43 (Fig. 5) to form surrounding sealing and /or rcinforcing beads 44 around the aperture which will be present in the resulting product as a result of the presence of the rod 16.

Accordingly, one achieves simultaneous transfer moulding at one end of the mandrel 10 and compression moulding at the other end of the mandrel 10 whilst the layers 37, 38, 39 and the transfer and compression moulding materials are all being subjected to heat. As a result one achieves simultaneous fusion and curing or setting of the materials being moulded to achieve an integral or homogenous product 32 which is shown in position still on the mandrel 10 in Fig. 5 and is shown subsequently removed in Fig. 6.

It will thus be appreciated that the method and apparatus of the invention enables containers and other moulded products to be produced to substantial lengths, with differences in length involving only differences in the cost of the different lengths of the body part 12 of the mandrel 10, which is relatively inexpensive. Obviously, once the sheath 31 has been produced, it can be used again and again in the series production of the products. The function of the sheath 31 is, of course, to ensure that the material being moulded is held and gripped tightly to the mandrel during the heat treatment to effect the curing or setting, so that the eventual shape of the resultant product is properly dictated by the outer surface shape of the mandrel 10.

It will readily be understood that the invention is not confined to the precise details of the foregoing example and variations may be made thereto. Thus, in the described case, the product is of a resilient nature and can. therefore, readily be stripped from the mandrel. It is, of course, possible to use the method of the invention to produce articles of thermosetting materials, which set to a substantially rigid or non-yielding form, provided the shape of the mandrel is such (e.g. by being slightly tapered) to permit removal of the product.

Also, one can use the method of the invention to produce simple tubular products, such as plain tubes, in which case the transfer moulding means and compression moulding means may be omitted; it can also be applied in instances where transfer moulding and/or compression moulding is required to be effected at one end only.

WHAT WE CLATM IS: 1. A method of producing a moulded component from a thermosetting material which comprises forming a resilient sheath around a metal mandrel whose external shape corresponds to the desired interior

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (12)

**WARNING** start of CLMS field may overlap end of DESC **. sired as to number, thickness, position and areas covered, according to variations in wall thickness in the finished product. The mandrel 10 having been laid up as described and shown in Fig. 3, the sheath 31 is now drawn thereover, this being effected, for example, by use of compressed air to inflate the sheath to increase the diameter thereof just sufficiently to slide into place. In one way of doing this, a socket may be inscrted into one end of the sheath 31 and supplied with compressed air, whilst the other end of the sheath is offered to the closure dome 13 so that the latter tends to close said other end. Then, the pressure of the air tends to expand the said other end, so as to escape between the sheath 31 and the closure dome 13, with the result that the sheath 31 can be caused to move onto the mandrel 10. Upon the sheath 31 being fully drawn onto the mandrel 10, the compression moulding cap 15 is brought into its pre viously-described disposition with its rod 16 screwed into the aperture 14, tapered annular lip 40 of the cap 15 entering between the respective end of the sheath 31 and the corrcsponding ends of the layers 37, 38, 39 which project very sliehtl into the compression moulding space 1 8, it being understood that an appropriate amount of compression moulding material (for example of the same material as the layers 37, 38, 39 and being for instance of an acrylonitrile butadiene synthetic rubber, also) is introduced into said space 18 as the cap 15 is brought into place. Also. the transfer moulding cap 124 is fitted into place around the end plug 19 so that a tapered annular lip 41 Thereof similarly enters between the respective end of the sheath 31 and the layer 37, with the latter projecting into the transfer moulding space 25. An amount of transfer moulding material (gain conveniently the same as that of the layers 37, 38, 39) is filled into the cylinder 20 and the piston 21, rod 22 and thrust plate 23 are fitted in place. This condition is illustrated in Fig. 4, but with the moulding material omitted from the mould space 18 and the cylinder 20, and the assemblage so achieved is heated. Whilst being brought up to an appropriate elevated temperature sufficient to cause curing or setting the material of the layers 37, 38, 39, pressure is applied by the transfer moulding material from the cylinder 20 to the transfer moulding space 25, thereby to form the thickened tubular mouth end 33 in the transfer moulding space 25. Additionally. pressure fluid is supplied to the compression moulding ram 17 to cause relative move ment of the cap 15 towards the domed end 13 thereby to cause the moulding material in the mould space 18 to flow and occupy the whole of the space 18 which, as can be understood from Fig. 4 may be formed with concentric grooves 43 (Fig. 5) to form surrounding sealing and /or rcinforcing beads 44 around the aperture which will be present in the resulting product as a result of the presence of the rod 16. Accordingly, one achieves simultaneous transfer moulding at one end of the mandrel 10 and compression moulding at the other end of the mandrel 10 whilst the layers 37, 38, 39 and the transfer and compression moulding materials are all being subjected to heat. As a result one achieves simultaneous fusion and curing or setting of the materials being moulded to achieve an integral or homogenous product 32 which is shown in position still on the mandrel 10 in Fig. 5 and is shown subsequently removed in Fig. 6. It will thus be appreciated that the method and apparatus of the invention enables containers and other moulded products to be produced to substantial lengths, with differences in length involving only differences in the cost of the different lengths of the body part 12 of the mandrel 10, which is relatively inexpensive. Obviously, once the sheath 31 has been produced, it can be used again and again in the series production of the products. The function of the sheath 31 is, of course, to ensure that the material being moulded is held and gripped tightly to the mandrel during the heat treatment to effect the curing or setting, so that the eventual shape of the resultant product is properly dictated by the outer surface shape of the mandrel 10. It will readily be understood that the invention is not confined to the precise details of the foregoing example and variations may be made thereto. Thus, in the described case, the product is of a resilient nature and can. therefore, readily be stripped from the mandrel. It is, of course, possible to use the method of the invention to produce articles of thermosetting materials, which set to a substantially rigid or non-yielding form, provided the shape of the mandrel is such (e.g. by being slightly tapered) to permit removal of the product. Also, one can use the method of the invention to produce simple tubular products, such as plain tubes, in which case the transfer moulding means and compression moulding means may be omitted; it can also be applied in instances where transfer moulding and/or compression moulding is required to be effected at one end only. WHAT WE CLATM IS:

1. A method of producing a moulded component from a thermosetting material which comprises forming a resilient sheath around a metal mandrel whose external shape corresponds to the desired interior component shape, removing the sheath, applying moulding material around the mandrel, drawing the sheath over the mandrel so as to hold the moulding material thereto and subjecting the resultant sheathed assemblage to heat to cause fusion and curing or setting of the moulding material whilst held in shape around and pressed resiliently against the mandrel by the sheath.

2. A method as claimed in Claim 1 wherein the resilient sheath is formed externally on the metal mandrel by laying up the mandrel with layers of thermosetting material and subjecting the resulting assemblage to heat, to cure the material of the sheath, and the moulding material is applied to the mandrel by laying-up the mandrel with layers of thermosetting moulding material.

3. A method as claimed in Claim 2 wherein the assemblage, consisting of the mandrel, with the layers for forming the sheath, is wound, prior to it being subjected to heat, with overlapping windings of a tape or band not adversely affected by the heat to which the assemblage is subjected to cure the material of the sheath.

4. A method as claimed in Claim 2 or 3 wherein different numbers of layers of the moulding material are provided over different portions of the mandrel, as dictated by desired thickness variations in the finished component.

5. A method as claimed in Claim 4 wherein the mandrel is laid-up with a first layer of the moulding material over substantially its entire length, with successive layers each extending only progressively shorter portions of its length from one end.

6. A method as claimed in any preceding claim wherein the moulding material is a thermosetting moulding material which achieves a resilient or deformable product, the component being caused to expand for removing it from the mandrel.

7. A method as claimed in any preceding claim wherein use is made of a mandrel which is adapted for further moulding material to be moulded-on onto the moulding material layers, by compression moulding and/or transfer moulding techniques.

8. A method as claimed in Claim 7 for moulding a tubular component having an accurately moulded cylindrical mouth on an end thereof, wherein passages are provided in the pattern to extend to said one end, and moulding material is transfer moulded into a mould space defined around the re spective end of the mandrel by an appropriate surrounding mould cap.

9. A method as claimed in Claim 7 or 8 for moulding a tubular component which has a centrally-apertured or domed end, wherein the respective end of the mandrel is correspondingly domed and is adatped internally, for pressure moulding of the said domed end of the component, and moulding material is pressure moulded onto said domed end.

10. A method of producing a moulded component from a thermosetting material, substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

11. A moulded component produced by the method of any preceding claim.

12. A moulded component substantially as hereinbefore described with reference to and as illustrated in Fig. 6 of the accompanying drawings.