WO2019097036A1

WO2019097036A1 - Vent element and mould

Info

Publication number: WO2019097036A1
Application number: PCT/EP2018/081657
Authority: WO
Inventors: Anton Nachtmann; Peter KROKER; Anton Killer; Guenter Treffert
Original assignee: W.L. Gore & Associates Gmbh
Priority date: 2017-11-20
Filing date: 2018-11-16
Publication date: 2019-05-23
Also published as: WO2019096419A1

Abstract

Disclosed is a vent element configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould, and methods of moulding therewith. The vent element has an elastically deformable member with an inflow end and an outflow end and at least one vent passage extending therebetween. During moulding, the vent passage allows gas to vent until pressure applied by mouldable material compresses the elastically deformable member and closes the vent passage. A vent element may also comprise a film over the inflow end or a porous support, to which a film may be attached directly, or to an intermediate elastically deformable member.

Description

Vent Element and Mould

Field of the Invention

The invention relates to a vent element configured to be arranged within a vent hole of a mould cavity, and to a mould comprising such vent element.

Background to the Invention

In the moulding of articles, for example compression moulding of tyres, venting is required to allow pockets of gas which may become trapped between the moulding material and the mould surface to escape, thereby ensuring a good impression of the mould pattern. In moulding applications using a closed mould cavity, such as injection moulding, the moulding material displaces gas already present in the mould cavity, which must also be vented.

Mould vents commonly take the form of small diameter vent holes through the mould wall, from the mould surface. The vent holes may extend to a still smaller diameter vent, or may vent themselves to the outside. Commonly, so-called“insert vents” (or simply“inserts”) are used. Insert vents are small plugs inserted in the vent hole, which allow gas to be vented but which block the flow of the moulding material. A problem may occur when a portion of the moulded material breaks off during demoulding and blocks the vent hole. Moreover, this may leave undesired spikes or runners on the outer surface of the moulded article. Such a blocked vent may not be immediately apparent and can cause subsequent poor quality mouldings because trapped gas cannot be vented. Another problem may be that the plug inserts get contaminated with rubber and, after the moulding process, cannot be sufficiently cleaned before the moulding of a new article. This will result in either blocked vents, or the plug inserts will have to be replaced with new plug inserts, which may be quite cost intensive. US 4 740 145 A describes a tyre mould having venting holes provided with synthetic resin plugs mounted in enlarged bore portions of the vent holes adjacent the inner forming surface of the mould. The plugs are axially compressible and project a slight distance beyond the inner surface of the mould, becoming generally flush with the mould surface under the pressure applied by the moulding material. Such plugs require a substantial amount of material and, thus, are quite costly to produce.

DE 28 08 474 A1 describes an air-permeable mould component made of a microporous PTFE material. The air-permeable component sits within a comparatively large aeration nozzle. The large amount of material required is therefore also quite costly to produce. It would thus be beneficial to address some or all of the above mentioned drawbacks.

Summary of the Invention

A first aspect of the invention relates to a vent element configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould, the vent element having an inflow surface and an outflow surface and an elastically deformable member disposed therebetween;

the elastically deformable member having an inflow end and an outflow end and at least one vent passage extending through the elastically deformable member from the inflow to the outflow end;

wherein the vent passage is configured to permit a flow of gas through the vent element and to close along at least a part of its length, under the action of pressure applied to the inflow surface by mouldable material so as to substantially prevent flow of mouldable material through the passage to the outflow surface.

During moulding gas is able to flow through the vent passage. When pressure is applied to the inflow surface by the mouldable material, (for example during injection or compression moulding) the elastically deformable member deforms and constricts the vent passage, before mouldable material flows out of the outflow end. A mould typically includes a plurality of vent elements and a flow front of mouldable material may reach vent elements in different part of a mould at different times, particularly for large moulds or complicated geometries. The invention provides for vent elements which individually respond to the flow front as and when it arrives at each part of a mould. The pressure required to close the vent passage may be selected for a particular application (based for example on the properties of the moulding material, the pressure applied thereto - including a motive gas pressure or the physical pressure applied during compression moulding - the temperature at which moulding is conducted, etc.).

For example, an elastomeric material having a Shore A hardness of between around 5 to 100, or between around 10 to 70, or between around 15-60, at least in the region of the elastically deformable member around the vent passage, may be suitable for compression moulding, including of tyres.

Similarly, the diameter of the vent passage may be selected according to a particular application. For example, wider vent passages may be required for applications under higher moulding pressures, or where fewer vent elements are present, to allow for higher flow rates from a mould cavity. Typically however, a vent passage has a diameter of about 1 mm, for example in the range from 0.1 - 3 mm, 0.1-1.0mm, 0.3 - 1.0 mm, or 0.1-0.5mm.

The elastically deformable member may comprise a single elastically deformable material, or multiple materials. The elastically deformable member may be generally homogeneous or may include different regions having different degrees of elastic deformability. The elastically deformable member may for example comprise more than one layer, the more than one layer being concentric around and/or normal to the vent passage. The elastically deformable member may include any suitable type of plastics or elastomeric material. One or more materials may be selected independently from a natural rubber, a butyl rubber, a polyurethane, a silicone, a fluoroelastomer such as a fluorinated or polyfluorinated polyvinylidene (FKM, FFKM, Viton etc), a polyethylene (such as polyethylene propylene diene, EPDM), or a nitrile rubber (e.g. hydrogenated nitrile butadiene rubber, HNBR, carboxylated nitrile butadiene rubber, XNBR) or the like.

By elastically deformable, or elastic, we refer to a property whereby a material or article is capable of being physically deformed (whether by compression, tension, shear forces or the like) and recovering to its original dimensions on removal of the cause of the deformation. An elastically deformable member may accordingly be compressible, for example under the action of pressure during moulding, in use. The invention is not limited to any particular composition of the elastically deformable member, nor degree of elasticity, but at least a portion of the elastically deformable member maybe capable of reversibly changing a dimension by between around 5%-200%, or 5%-100%, or 5% or 50% of that particular dimension.

The inflow surface may be defined by the inflow end of the elastically deformable member. The inflow surface may be defined by a film layer attached to the elastically deformable member.

The film layer may be formed from a polymeric material. Use of a relatively strong polymeric material is desirable, for example a film layer having a matrix tensile strength greater than 10,000 psi in orthogonal directions.

The film layer may comprise a metallic foil.

The film layer may be porous. One or both faces of the film layer may be porous. The film layer may comprise a material having a porous microstructure.

The film layer may be gas permeable.

The film layer may be gas permeable as a result of its porosity. For example, the pores of a film having a porous microstructure may permit gas to permeate therethrough.

The film layer may comprise a porous polymeric material, such as an expanded polymer. A suitable expanded polymer is expanded polytetrafluoroethylene (ePTFE). The film layer (which may be referred to herein as a membrane) may be sintered and/or densified ePTFE. Sintered, or“amorphously locked” ePTFE has been heated to above its crystalline melt temperature (around 325°C) without changing its dimensions. Densified ePTFE is a layer or membrane that has been at least partially compressed, so as to reduce its thickness. Densification may occur during manufacture, for example when ePTFE layers are laminated or calendared together, or when an ePTFE layer is moulded to the elastically deformable member (cf., for example, the process as described in US 7,521 ,010 which is incorporated herein by reference in its entirety). In some circumstances, a densified ePTFE layer, particularly in the region of the inflow surface can have a lower roughness than a non-densified ePTFE layer, which can improve resistance to the conditions during moulding and mitigate against adherence of moulded material during demoulding. Pore size or porosity in a densified region, typically of a surface, may be reduced, for example to an average of below around 1 micron. A determination whether the membrane material has any pores can be made, according to an embodiment, with a scanning electron microscope (SEM), e.g. with a magnification of 3000. If a SEM with magnification of 3000 does not show any pores, this shall be understood herein as a membrane material densified to an extent that it does not have pores any more.

Other polymeric film materials may also be used, such as polypropylene (PP) or polyethylene (PE), which may also form a porous microstructure. The film layer may be a woven or non-woven fabric layer, formed for example of an above mentioned polymeric material. The film layer may be an extruded (non-expanded) or skived (sliced) layer of a polymeric material.

The skilled person will appreciate that by varying commonly known parameters for forming such film layers or membranes, advantageous properties for gas permeability, thickness, density and/or pressure and temperature resistance, as disclosed herein, may be achieved. The film layer may have one or more of the following properties which may be achieved by the skilled person by common routine methods: In some embodiments, the film layer is configured to withstand a pressure of 24 bar at a temperature of 150°C for a minimum of 40 min.

In some embodiments, the film layer is configured to withstand a pressure of 16 bar at a temperature of 170°C for a minimum of 18 min. In some embodiments, the at least one film layer has a maximum pore size of smaller than approx. 6 pm. In some embodiments, the film layer is configured to provide an airflow through it of greater than approx. 0.2 l/h, preferably between 0.2 and 3 l/h, at a pressure of 70 mBar. In other embodiments the film layer or membrane is configured to provide an airflow through it of greater than approx. 4 l/h, preferably between 10 and 200 l/h, at a pressure of 70 mbar. The gas permeability referred to herein are given in terms of air flow, as measured with a D 570 airflow tester, manufactured by ATEQ Corp, Ml, USA on test vent samples having a diameter of 4mm.

In some embodiments, the film layer has an average thickness in a range of approx. 10- 200pm, 30 - 150 pm or 30-80 pm, and/or an average density in a range of approx. 0.5 - 8, or 1 - 2.5 g/cm³.

In some embodiments, the film layer is formed by a laminate comprising at least one thermoplastic layer. For example, a thermoplastic layer can be used for bonding the at least one film layer to the elastically deformable material and/or to any other element, such as a housing element used for housing the film layer and/or elastically deformable material. For example, the thermoplastic layer is perforated at least in a region thereof configured for venting the gaseous fluid therethrough. A film layer may be perforated (e.g. perforations formed by etching, e.g. laser or chemical etching). By“perforated” herein we refer to a plurality of holes, typically sized in the 1-100 micron range, extending through a said film. Such perforations are distinct from any apertures through the film layer of larger size, such as in the range of 0.1 -1.0 mm. The vent passage may extend through the film layer. That is to say, the film layer may comprise an aperture aligned with the vent passage through the elastically deformable member.

The film layer may comprise more than one, or a plurality of, apertures. Each of the apertures may be aligned to a vent passage, as discussed below, or only one or a subset may be so aligned.

The film layer may be attached to the elastically deformable member (or, as disclosed below, the porous support element) by any suitable method. Strong bonding of the film layer is desirable to reduce or eliminate infiltration of moulding material between the film layer and the underlying part of the vent element in use, and to resist delamination of the film layer during demoulding for example. In some embodiments, the film layer is attached by adhesive (whether by chemical or physical bonding). A silicone material may be used as an adhesive. Thermal welding may also be used to attach the film layer to the elastically deformable body. The film layer may be attached at least in part by infiltration of an adhesive, or by the material of the elastically deformable body, into pores or perforations.

Attachment by adhesive or otherwise may be across the entire surface, or at one or a plurality of discrete points, lines or regions.

The film layer may be surface treated (e.g. by etching) to provide a roughened surface to promote attachment to the elastically deformable member.

The outflow surface may be defined by the outflow end of the elastically deformable member. In some embodiments, the vent element further comprises a porous support element attached to the outflow end of the elastically deformable member, the porous support element defining the outflow surface of the vent element.

The porous support element may comprise any suitable porous material or materials. For example, the porous support element may comprise a sintered particulate material, such as a sintered plastics, metal or ceramic material. A porous structural foam may be used, such as a metallic or ceramic foam. The porous support element may itself be perforated.

The vent passage may in some embodiments extend through the porous support element to the outflow surface.

Where both a film layer and a porous support layer is present, the elastically deformable member can be considered as an elastically deformable intermediate member disposed between the porous support member and the film layer.

The film layer may extend around other surfaces of the vent element. This may provide for more secure attachment of the film layer. The film layer may entirely surround the vent element. The film layer may define the inflow surface and sides of the vent element, wherein at least a portion of the outflow surface is defined by the elastically deformable member or the porous support element, as the case may be. The vent element may be any suitable shape, but may conveniently be generally cylindrical around an axis extending from the inflow to the outflow surfaces. The vent element may be circularly cylindrical, or may have another cross sectional shape, such as elliptical, square or polygonal. The vent element may by tapered, for example conical or frustoconical, in shape.

The vent element may be generally symmetrical around an axis, for example along which the vent passage extends. The vent element may comprise two or more layers (for example formed by each of the film layer, elastically deformable member or porous support element), oriented generally normal to an axis extending from the inflow to the outflow surfaces.

Various embodiments of the vent element may comprise more than one of each of the components disclosed herein. For example, more than one film layer may be provided. A film layer may for example be laminated, and formed from more than one layer, of one or more type. The elastically deformable member may itself include more than one layer.

Indeed, more than one porous support element, or a said element having more than one layer may be provided. The vent element may also comprise more than one vent passage.

The vent element may comprise a housing element enclosing at least a part of a periphery of the vent element.

The housing element may include a lip extending around the vent element, over a peripheral region of the inflow surface and/or the outflow surface. The or each lip may in effect form an inwardly extending flange.

The housing element may for example comprise a metallic tubular structure, crimped at one or both ends, or at an intermediate portion thereof, to form a lip.

A housing element may assist in securing the vent element within a vent hole of a mould. For example, a housing element, or a part thereof, may be placed in compression when inserted in a vent hole, to exert a retaining biasing force against the walls of the vent hole and resist removal of the vent element during demoulding.

A housing element may alternatively a moulded or cast structure, such as an injection moulded plastics element. The porous support element may be integrally formed therewith. For example, a perforated portion of a housing element may function as a porous support element.

The vent elements disclosed herein may in some embodiments lack an elastically deformable member. That is to say, the invention extends in a second aspect to a vent element configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould, the vent element having an inflow surface and an outflow surface and comprising:

a porous support element having an inflow end and an outflow end, and the outflow end of the porous support element defining the outflow surface; and

a film layer attached to the porous support element at its inflow end, the film layer defining the inflow surface; and having at least one gas flow pathway therethrough.

The film layer may be porous. The porous support member may have at least one vent passage extending therethrough. The film layer may in some embodiment have an aperture aligned with the or each vent passage, such that the vent passage extends between the inflow and outflow surfaces.

The porous support member may comprise at least one porous support material. The porous support member being configured for venting a gaseous fluid received at a first side of the support material to an outer environment of the mould at a second side of the support material opposite the first side, at least one film layer being arranged above the at least one porous support material at the first side and configured to be exposed to the interior cavity of the mould and to permit passage of the gaseous fluid therethrough, wherein the at least one film layer is formed from a polymeric material with matrix tensile strength greater than 10,000 psi in machine and transverse directions. A housing element may enclose the at least one porous support material, wherein the at least one porous support material is formed by at least one support element integrally formed with the housing element.

According to a third aspect of the invention, there is provided a moveable or fixed mould half for injection or compression moulding, comprising at least one forming surface and a vent hole extending from the at least one forming surface, and a vent element according to the first or second aspect in the vent hole.

In a fourth aspect the invention extends to a mould for injection or compression moulding, comprising an interior cavity having at least one forming surface, a vent hole in the at least one forming surface and a vent element according to the first or second aspect in the vent hole.

The mould or mould half may comprise a plurality of vent holes and a plurality of vent elements therein.

In a fifth aspect, the invention relates to the use of the vent element, mould or mould half according to the other aspects, in a moulding process; such as an injection or compression moulding process. In a sixth aspect of the invention there is provided a method of compression moulding, comprising:

providing a first forming surface; the first forming surface having at least one vent hole and at least one vent element in the vent hole; wherein the vent element is in accordance with the first aspect;

providing a second forming surface

providing a mouldable material between the first and second forming surfaces;

compressing the mouldable material into a mould cavity defined between the first and the second forming surfaces;

venting gas from the interior cavity through the vent passage of the vent element; and compressing the elastically deformable member under the action of the flow of mouldable material against the inflow surface of the vent element; and thereby closing the vent passage.

The second forming surface may comprise at least one vent hole and at least one vent element.

The first and second forming surfaces may from parts of a mould half in accordance with other aspects of the invention disclosed herein.

Compressing the mouldable material may comprising moving the first and second forming surfaces together. Venting may comprise venting gas from between the mouldable material and the first and/or second forming surface.

The method may comprise curing or drying the mouldable material, for example by heating the mouldable material when in the cavity.

The method may further comprise venting gas generated during the moulding process, for example during curing or drying of the mouldable material.

The method may comprise reducing or preventing flow of gas vented through the vent passage by at least partially blocking or filling the vent passage with mouldable material, and then closing the vent passage by compressing the elastically deformable member.

The method may comprise closing the vent passage before mouldable material flows through the passage to the outflow surface.

The method may comprise opening the mould cavity and removing the moulded material therefrom. The vent elements may remain in situ during this process. Advantageously, the film (for example a metal or an ePTFE film) may facilitate removal of the moulded material without residue sticking to the vent element. This may provide for a better surface finish of the moulded article, or may reduce the amount of excess material which needs to be removed from the moulded material after removal. Moreover, clean demoulding may prolong the working lifetime of each vent element.

The mouldable material may be flowable or pliable. The mouldable material may be a plastics or polymeric material, or precursor thereof, including natural or synthetic rubbers in uncured or partially cured form. The mouldable material may be a foam material, such as a polyurethane (PUR) foam, or a thermoplastic material, including thermoplastic elastomers, such as a thermoplastic polyurethane (TPU), a thermoplastic polyester (TPE) or the like.

The method may be a method of moulding a tyre.

In a seventh aspect of the invention there is provided a method of injection moulding, comprising;

providing a comprising an interior cavity having at least one forming surface, a vent hole in the at least one forming surface and a vent element in the vent hole; wherein the vent element is in accordance with the first aspect;

flowing mouldable material into the interior cavity;

venting gas from the interior cavity through the vent passage of the vent element;

compressing the elastically deformable member under the action of the flow of mouldable material against the inflow surface of the vent element; and thereby closing the vent passage. Further features are as disclosed in relation to the sixth aspect.

The invention also relates to a vent element as described below. In an embodiment a vent element is configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould. The vent element comprises at least one porous support material which is configured for venting a gaseous fluid received at a first side of the support material to an outer environment of the mould at a second side of the support material opposite the first side; at least one film layer arranged above the at least one porous support material at the first side and configured to be exposed to the interior cavity of the mould and to permit passage of the gaseous fluid therethrough. The at least one film layer is formed from a polymeric material with matrix tensile strength greater than 10,000 psi in machine and transverse directions. The at least one film layer may be formed from a densified expanded porous membrane material. The at least one film layer may be formed from a fluoropolymer material, preferably polytetrafluorethylene material, more preferably densified expanded polytetrafluorethylene material. The at least one film layer may comprise at least one of polytetrafluorethylene, polypropylene and polyethylene. The at least one film layer may be formed by a laminate comprising at least one thermoplastic layer.

The thermoplastic layer is optionally perforated at least in a region thereof configured for venting the gaseous fluid therethrough. The at least one porous support material may comprise a sintered metal material or a perforated plastic support.

The vent element may further comprise a housing element enclosing the at least one porous support material, wherein the housing element is made of at least one of a metal material and solid plastic material.

The at least one porous support material may be formed by at least one support element integrally formed with the housing element. The at least one film layer is in some embodiments bonded to at least a portion of the at least one support material, for example by thermal welding.

The at least one film layer may be wrapped around at least a portion of the at least one support material, for example such that the at least one film layer is positioned on top of the support material and bonded thereto to be exposed to the interior cavity of the mould and in at least a peripheral region of the support material between a mould wall and the support material. The at least one film layer has in some embodiments a maximum pore size of smaller than approx. 6 pm. The at least one film layer may be configured to provide an airflow through it of greater than approx. 0.2 I/hr, preferably between 0.2 and 3 I/hr, at a pressure of 70 mbar and/or have an average thickness in a range of 20-60 pm and/or an average density in a range of approx. 0.6 - 1.5 g/cm³.

At least one compressible intermediate material may be disposed between the at least one porous support material and the at least one film layer, wherein the at least one film layer is positioned on top of the intermediate material to be exposed to the interior cavity of the mould, optionally wherein the at least one film layer is bonded to the at least one

compressible intermediate material.

The at least one film layer may be formed by a laminate comprising at least one first membrane formed from a polymeric material with matrix tensile strength greater than 10,000 psi in machine and transverse directions and at least one second membrane of porous material, wherein the at least one second membrane is bonded to the at least one compressible intermediate material. The at least one second membrane may have a pore size of greater than approx. 2 pm and/or be formed from an expanded polytetraflourethylene membrane material. The at least one first membrane in some embodiments has no pores or a pore size, if any, of less than approx. 1 pm. The at least one first membrane may be configured to provide an airflow through it of greater than approx. 4 l/h, preferably between 10 and 200 l/h, at a pressure of 70 mbar, and/or have an average thickness in a range of 30-80 pm and/or an average density in a range of approx. 1 - 3 g/cm³. The at least one compressible intermediate material may be formed of thermoplastic elastomers (TPE), preferably of at least one of silicone, PU, and NBR material. The at least one compressible intermediate material may comprise at least one through hole within an area in which the gaseous fluid is vented, wherein the at least one through hole is configured to vent at least portions of the gaseous fluid through it, the through hole optionally being configured to close, at least within portions of the intermediate material along the at least one through hole, by material deformation upon pressure on the at least one film layer exerted from the interior cavity of the mould. Further optionally the at least one film layer comprises at least one hole aligned with the at least one through hole and configured to vent at least portions of the gaseous fluid into the at least one through hole.

The at least one film layer may be configured to withstand a pressure of 24 bar at a temperature of 150°C for a minimum of 40 min, or a pressure of 16 bar at a temperature of 170°C for a minimum of 18 min.

The vent element may be configured to be arranged within a vent hole of a mould for vulcanization of rubber. A mould comprising a mould cavity with a forming surface for forming at least one article and at least one vent hole extending from the forming surface to an outer environment of the mould comprises at least one vent element as disclosed herein mounted in one or more vent holes for venting a gaseous fluid from the mould cavity to the outer environment, the mould being optionally configured for forming the at least one article by means of vulcanization of rubber in the mould cavity, and further optionally configured for forming at least one tyre.

The term“approximately” used herein shall mean that a number slightly exceeding or falling below the respective cited numbers (such as 0.1 pm or 0.9 pm maximum pore size in the above embodiment) shall still be encompassed, since no“hard” structural or physical border for any number of pore size, gas permeability, layer thickness, density, and/or weight etc. exists. In this regard, for example, a range of +/- 10% shall be encompassed with the term “approximately”.

It should be appreciated that selected options and features disclosed in relation to one aspect of the invention may also correspond to selected options and features of any other aspect of the invention.

Description of the Drawings

Non-limiting example embodiments will now be described with respect to the accompanying drawings, in which:

Fig. 1 shows a schematic perspective cross-sectional view of a vent element positioned in a mould;

Fig. 2 shows a cross-sectional view of another vent element positioned in a mould;

Fig. 3 shows in two cross-sectional views a further vent element positioned in a mould according in different situations during a moulding process;

Fig. 4 shows a schematic view of a film layer for a vent element;

Fig. 5 shows a cross-sectional view of another example of a vent element positioned in a mould;

Fig. 6 shows a schematic view of a further example of a film layer for a vent element; Fig. 7 shows a cross-sectional view of a still further vent element;

Fig. 8 shows a cross-sectional view of an exemplary embodiment of a densified

expanded porous membrane material;

Fig. 9 shows a diagram of venting performance of exemplary film layer prototypes after a respective vulcanization cycle;

Figs. 10-13 show cross-sectional views of further examples of vent elements positioned in a mould. Detailed Description of Example Embodiments

In Fig. 1 , there is shown a schematic perspective cross-sectional view of a vent element 10. The vent element 10 is adapted to be positioned in a mould 50. Generally, any type of mould can be used in connection with the present invention, or in other words, the vent element 10 according to the invention can be used, in principle, in any type of mould 50. Basically, the mould 50 comprises a mould cavity 53, schematically shown in Figs. 2 and 3, with at least one forming surface 51 for forming at least one moulded article. Generally, a mould for forming any type of article may be used, including for forming an article by means of vulcanization of rubber in the mould cavity 53. The mould 50 may for example be configured for forming a tyre in the mould cavity 53.

In the moulding of articles, particularly rubber articles such as tyres, typically venting is required to allow pockets of gas, such as air, which may become trapped between the article and the hot mould surface, to escape so that every part of the curing article surface contacts the mould 50 and its forming surface 51. To this end, the mould 50 comprises at least one vent hole 52 (in practice, a mould 50 used in the field of tyre manufacturing typically comprises a plurality of such vent holes) extending from the forming surface 51 to an outer environment of the mould 50, so that the trapped gas may escape to the outer environment of the mould 50. Such mould vent holes 52 commonly take the form of small diameter holes bored through the mould wall 54 normal to the forming surface 51.

In order to prevent the mouldable material (e.g. rubber) from flowing out of the interior mould cavity 53 to the outer environment of the mould 50, a vent element 10 is mounted in the vent hole 52. Where a mould comprises a plurality of vent holes 52, a vent element 10 is placed in each of the vent holes 52. Typically, each vent element is sized to fit in the vent hole, but in some cases a vent hole can accommodate more than one vent element.

In a typical tyre mould, there is provided a high number of vent holes 52, so that the equipment costs for the vent elements 10 to be used scale up with the number of vent holes 52 and can achieve a significant amount when hundreds of vent elements 10 are to be used for the manufacturing of a typical tyre.

A basic function of a vent element 10 is to vent a gas 1 1 , typically trapped gas, from the mould cavity 53 of from between a mouldable (e.g. pliable) material and the forming surface 51 to the outer environment of the mould 50, preferably at a high gas flow rate, while preventing the mouldable material from flowing through the vent hole 52. It is also desirable to limit the amount of penetration of the mouldable material into the vent hole, which would otherwise leave undesirably large spikes or protrusions on the surface of the resulting moulded article, such as the tyre. Such protrusions may require additional post-treatment of the surface of the moulded article to remove them and may also lead to blockages of the vent hole and subsequent poor quality mouldings. Further, a mouldable material should be releasable from the vent element 10 without damage to the final moulded article, such as a tyre. In addition, such vent element 10 should provide a high durability so that it can be reused multiple times, thus decreasing

manufacturing costs. As further shown in Fig. 1 , the vent element 10 has an inflow surface 40 facing the mould cavity 53 and an outflow surface 42 adjacent to a duct 6 to the outside of the mould 50. The vent element 10 includes a porous support element 3, in the embodiment shown being formed from a porous material. The porous support element 3 is gas permeable and so capable of venting the gas 1 1 therethrough. The porous support element 3 has an inflow end (or first side) 41 and an outflow end 42 (second side). For example, the porous support material 3 comprises a sintered metal material or a perforated plastic support.

The porous support element 3 may have a pore size selected for any particular application and may for example be microporous or where higher venting rates are required (e.g. for higher pressure injection moulding methods), macroporous. The porous support element 3 may alternatively or additionally be perforated by through holes (e.g., having small or large diameter, or a mixture thereof), such as in a perforated plate, or any other gas permeable structure (such as the“canal” structure schematically shown in Fig. 2, having a vent passage 30, which is discussed in further detail below).

The vent element further comprises a film layer 1 attached to the support element 3 and defining the inflow surface 40. The support element 3 supports the film layer 1 against the pressures and temperatures exerted from the mould cavity 53 in use of the vent element 10. The vent element 10 further comprises a housing element 54, for example formed from a moulded plastics material such as PEEK. The film layer 1 and porous support element 3 are mounted in the housing element 54. The housing element 54 is sized so that the vent element can be press-fit (i.e. cooperatively received) in the vent hole.

The film layer 1 is, in the embodiment shown, a gas permeable polymeric film with a matrix tensile strength greater than 10,000 psi in orthogonal directions. In the example shown, the film is a densified expanded PTFE membrane material, but other fluoropolymers and other polymeric materials may also be used such as polypropylene or polyethylene. Such densified expanded porous membrane is distinguishable from any structure which has micropores, but has not been densified, since the densification or compression alters the structure of the micropores and/or their arrangement within the layer which is significant for the densification or compression and different from an expanded porous membrane material which has not been densified or compressed.

In alternative embodiments, the film layer 1 alternatively or in addition be perforated, i.e. wherein the porosity is established at least in part by one or more holes, such as formed by a laser beam. The film may also be provided with one or more larger apertures 23, which may be aligned with a vent passage 30 as shown in Figure 2.

In the embodiments of Figs. 1 and 2, the film layer 1 is positioned on top (in the orientation shown in the figures) of the support material 3 on the first, inflow end 41 thereof to be exposed to the interior cavity 53 of the mould.

Preferably, the film layer 1 is bonded to at least a portion of the support material 3 to avoid any interspaces between film layer 1 and support material 3 and ensure a proper functioning of the gas passage through the components. For example, the film layer 1 may be bonded the support material 3 by thermal welding or an adhesive.

In the vent element 10 of Figure 1 , the film layer 1 is wrapped around the sides 43 of the support element 3, and when the vent element in inserted snugly in the vent hole 52, the film is trapped between the inner wall of the vent hole and the support element (or, in other embodiments disclosed herein, alternatively or additionally an elastically deformable member for example as shown in Figure 5), which assists in maintaining the attachment of the film layer 1. Wrapping of the film layer 1 in this way may also assist in sealing, thereby reducing or preventing mouldable material from flowing around the inflow surface 40, during moulding.

It is not essential that the film layer 1 be wrapped around the sides 43 of the porous support element 3, however, and as shown in the embodiment of Figure 2 a press fit may be established directly between the porous support element 3 and the vent hole 52 and wherein the film layer 1 is bonded to the inflow end 41 of the porous support element.

Fig. 4 shows a schematic view of a film layer 1 according to an embodiment of the invention which may be used in connection with bonding the film layer 1 to the support material 3, or to an elastically deformable member, as the case may be. As schematically shown, the film layer 1 is formed by a laminate comprising a membrane layer 21 formed with membrane material as described above with respect to the film layer 1 (having preferably the properties as set out above) and at least one thermoplastic layer 22. The film layer 1 may be bonded (e.g. to the support material 3) with the thermoplastic layer 22 having appropriate bonding properties, so that the properties as set out above with respect to the moulding process involving high temperature and pressure resistance and durability and robustness may be decoupled from the bonding properties to a material layer arranged on the opposite side. The thermoplastic layer 22 may be perforated at least in a region thereof configured for venting the gaseous fluid 1 1 therethrough, in order to not negatively influence the gas permeability of the film layer 1 as a whole.

For certain applications, for example rubber moulding of tyres, the membrane material in the film layer 1 has a maximum pore size of smaller than approx. 6 pm. This provides a good compromise between gas permeability on the one hand and durability and robustness on the other hand. For example, the film layer 1 is configured to provide an airflow through it of greater than approx. 0.2 l/h, preferably between 0.2 and 3 l/h, at a pressure of 70 mbar.

According to various embodiments, the film layer 1 may have the following properties alone or in combination: an average thickness in a range of 20-60 pm and/or an average density in a range of approx. 0.6 - 1.5 g/cm³. According to an embodiment, the combination of support material 3 and film layer 1 may have a total thickness of approx. 1.5 mm. Such thickness of approx. 1.5 mm may also be employed for a combination of support material 3, intermediate material 2 (as described in more detail below) and film layer 1. The thickness of a vent element will generally depend on the diameter of the corresponding vent hole. For example, were a vent hole has a diameter of around 4mm, a vent element may have a thickness (i.e. in a dimension normal to the forming surface) of around or in some case more than, 2 mm. Whereas for smaller diameter vent holes, for example around 2.5 mm diameter, the total thickness of the vent element may be around or even less than 2mm.

Fig. 3 shows in two cross-sectional views another vent element 10 positioned in a mould vent hole 52 according to a further embodiment of the invention. In particular, Fig. 3A shows a situation during a compression moulding process before pressure is exerted onto the film layer 1 by a pliable rubber material 5 (an example of a mouldable material) placed over the forming surface 51 of the mould. Fig. 3B shows a situation during the moulding process when pressure is exerted onto the film layer 1 by the rubber material 5.

Fig. 3A shows a vent element 10 having an inflow end 40 and an outlflow end 42. The vent element has a porous support element 3 which defines the outflow end.

Attached to the support element 3 at the first, inflow end side 41 thereof, is an intermediate elastically deformable member 2. A film layer 1 is attached to the elastically deformable member 2 and defines the inflow surface 40 of the vent element 10. The film layer 1 may be formed, as disclosed herein, from a densified expanded porous membrane material.

The intermediate elastically deformable member 2 may be formed from a variety of elastically deformable materials, for example a silicone material, PU (polyurethane), NBR (Nitrile butadiene rubber) are possible or other thermoplastic elastomers (TPE). The film layer 1 may be bonded to the compressible intermediate (an intermediate, elastically deformable member) 2, for example by lamination, adhesive or thermal welding. In case of adhesive, the bonding may be established either in regions without airflow through it, or by using a discontinuous pattern or gas permeable adhesive.

In some embodiments, bonding can be achieved by positioning the porous film layer 1 on the elastically deformable member 2 (e.g. silicone material) not yet fully cured, and with curing the material of the intermediate elastically deformable member 2 thereafter, the film layer 1 gets bonded thereto. For this embodiment the elastically deformable member 2 needs to have low Shore A values (in the range of 50) - at least during manufacture of the vent element and when not yet fully cured - such that the material can penetrate into the pores of the film layer 1.

The vent element can also be manufactured from a relatively fluid precursor of the elastically deformable material, by placing the film over a container or a ring constraining the precursor and then curing once the porous film has been infiltrated in a region adjacent to the precursor material. The container or ring may then be removed.

Another example of a laminated film layer 1 for use with a vent element is shown in Fig. 6. The laminate comprises at least one first membrane 21 , in this embodiment of densified expanded porous membrane material, and at least one second membrane 25 of porous material. The structure, function and properties of the membrane 21 are preferably the same or similar to those as described above with respect to the film layer 1 of the previous embodiments. By virtue of its porosity, the second membrane 25 adapted to be bonded to an elastically deformable member.

In turn, the first membrane 21 can be designed such that it has increased stability and/or durability when exposed to conditions of high temperature and/or pressure during moulding. This can be achieved with a densified expanded porous membrane material.

The properties of the two membranes 21 , 25 may be“tuned” for the particular purpose they are required to perform. For example, the second membrane 25 may have a relatively large pore size, e.g. of greater than approx. 2 pm and the first membrane a relatively small pore size, e.g. of less than approx. 1 pm (or may be non-porous in some surface regions or across the entire inflow surface). The relatively low pore size may result from partial densification. The second membrane 25 (and optionally also the first membrane) may be formed from an expanded polytetraflourethylene (ePTFE) membrane material.

In this regard, Fig. 8 shows a cross-sectional view of an exemplary embodiment of a densified expanded porous membrane material (such as an ODF disclosed below) in a film layer 1 , which is still open, i.e. has micropores not greater than approx. 6 pm.

Referring again to Fig. 3A, in order for the vent element 10 further includes a vent passage 30 extending from the inflow surface 40, and through an aperture 23 in the film 1 aligned therewith, and through the elastically deformable member 2. In other embodiments (not shown) multiple such vent passaged may be provided.

During moulding, gas 1 1 is vented through the vent passage 30 (e.g. from a closed cavity such as in injection moulding, or as a mouldable material such as the rubber material 5 is compressed during compression moulding), through the porous support element 3 and out of the duct 6.

Fig. 3B shows the vent element 10 of Figure 3A at a later stage of the moulding process, when pressure is exerted by the rubber material 5 onto the film layer 1. As a result of the pressure onto the film layer 1 , the intermediate elastically deformable member 2 is compressed or“squeezed” which results in a material deformation of the elastically deformable member 2 upon pressure on the film layer 1. The elastically deformable member 2, upon the pressure and the resulting material deformation, closes the vent passage 30 at least along a part of its length, preventing further advance of the mouldable material 5 towards the outflow end 42 of the vent element.

Fig. 5 shows a cross-sectional view of another embodiment of a vent element 10 positioned in a mould 50. The vent element 10 is similar in structure and properties to the vent element as described with reference to Figs. 3A, 3B, but the film 1 is wrapped around the sides 43 of the vent element 10. A portion of the outflow end 42 is not covered by the film, and so allows for venting of gas in use. The intermediate elastically deformable member 2 has a vent passage 30 therethrough. The gas permeable film 1 extends over the upper end (in the orientation shown in the figure) of the vent passage. Fig. 7 shows a cross-sectional view of another embodiment of a vent element 10. In this embodiment, the vent element 10 further comprises a housing element 54 which encloses the porous support element 3 and, in some embodiments, also the film layer 1 and an elastically deformable member 2, as in the shown in the figure.

The housing element 54 may be made from a cast or machined metal material or a moulded or machined plastic. The porous support element 3 may be integrally formed with the housing 54 or sized to fit across the end of the duct 6. In the embodiment shown, the porous support element 3 is porous by virtue of channels 24, which extend from the inflow to the outflow end of the vent element and form vent passages.

In other embodiments, the housing 54 and integrally formed porous support element 3 may be used with a member 2 and film 1 in which the film is wrapped around the sides and at least part of the outflow end of the elastically deformable member, generally as described above.

Exemplary parameters of membrane layers which can be used for the film layer for the embodiments disclosed herein are as follows: 1. A densified membrane material with pores (so-called“Open Densified Film (ODF)”), particularly for embodiments without intermediate elastically deformable material (c.f. Fig. 1 ) or embodiments without through hole(s):

Thickness: 30 pm

Density: 0,89 g/cm³

Pore size: max. 5 pm

2. A more densified membrane material with no pores or very small pores (so-called “Densified Film (DF)”), particularly for embodiments with an elastically deformable member and through hole(s) (cf. embodiments according to Figs. 3A, 3B, 5). For example, a multilayer structure of a densified film laminated with a FEP (fluorinated ethylene propylene) layer to a porous ePTFE film

Laminate parameters: Thickness: 78 pm

Density: 1 ,9 g/cm³

Pore size of the outer densified membrane layer (cf. first membrane‘2T in Fig. 6) is too small to be measured with a SEM at magnification of 3000. Densified outer layer has thickness of around 50pm.

Inner porous ePTFE membrane layer (cf. second membrane‘25’ in Fig. 6) to realize bond to an elastically deformable member has pore size of 2 pm.

Examples:

1. Production of Densified Film (DF) structure: A densified ePTFE sheet was prepared according to the general teachings of US 7 521 010 to Kennedy et al., with the exception that the final stretch above the crystalline melt temperature of PTFE was omitted (i.e., an unsintered product). The preparation procedure was performed to result in a densified sheet of ePTFE having a thickness of 16,76 pm, a mass/area of 36.3 g/m², a calculated standard specific gravity (SSG) of 2.15 g/cc, an average matrix tensile strength (MTS) in the machine direction of 19,300 psi (approximately 133.1 MPa) and an average MTS in the transverse direction of 14,700 psi (approximately 101.4 MPa).

Finally, a lamination step was performed as follows:

For the lamination step a metal mandrel with an outside diameter of about 90 mm and a length of about 300 mm was used with film layers having a width in the order of 400 mm. 3 densified layers (as described above) were wrapped first, followed by a FEP layer and then a porous ePTFE film having a pore size of 3 pm. Clamps were used to fix the material at the ends of the mandrel to prevent the film from shrinking back. The sintering conditions were 370 °C for 30 minutes. 2. Production of Open Densified Film (ODF) structure:

The open densified ePTFE layer was also prepared according to general knowledge of densifying PTFE as described above. Here the preparation procedure was performed to result in a less densified sheet of ePTFE having a thickness of 30 pm, a calculated standard specific gravity (SSG) of 0.89 g/cc and a pore size of 5 pm as determined via bubble point measurement (determined using a Coulter Porometer (pore size distribution analysis).

3. Prototype of vent element with DF

The vent housing element is produced with PEEK (Victrex PEEK 150G903 BLACK). The design is adapted to the press fit column in the mould cavity (see example 5) and contains space for a porous support element, for example made from a permeable material (e.g. sintered metal disc, 1.4404 SIKA-R20, GKN Sinter Metals Filters GmbH). The vent housing element has a cut-out to receive the venting construction in a way that prevents sintered metal disc moving when the moulding pressure is applied.

The DF (see example 1 ) with a diameter of 11 mm is shaped to a cup form by a drawing process at 250°C. The cup diameter is 4.2 mm with a height of 3.5mm. This cup is filled with a silicon elastomer (Wacker RT601 ) which penetrates into the bottom layer of the DF film. The resulting silicon thickness is 1.50 mm.

After curing, the silicone has a hardness of“Shore 50A”. Then, the silicon filled cup is provided with a through hole of 0.30mm in diameter by laser cutting. Finally, the sinter metal disc is positioned on the silicone and the overlapping DF film is wrapped around sinter metal disc.

This resulting unit is pressed into the vent housing element. This construction offers a venting performance of 13 l/h at 70 mbar air pressure.

4. Prototype of vent housing element with ODF:

The vent housing element is produced with PEEK (Victrex PEEK 150G903 BLACK). The design is adapted to the press fit column in the mould cavity (analogous to the housing shown in Fig. 1 ) and contains space for a porous support element (e.g. sintered metal disc,

1.4404 SIKA-R20, GKN Sinter Metals Filters GmbH). The vent housing element has a cut- out to receive the venting construction in a way that prevents sintered metal disc moving when the moulding pressure is applied.

The ODF (see example 2) with typical diameter 11 mm is wrapped around the sinter metal disc. This resulting unit is pressed in the vent housing, so the ODF film is facing to the moulding material (NBR) during the process.

This construction offers a venting performance of 1 l/h at 70 mbar air pressure.

5. Moulding of plastic parts with vent prototypes To test the prototypes, a stainless steel mould with a plurality of cavities was created, whereas each cavity was equipped with a vent prototype at the bottom of the cavity. For the moulding process the cavities were filed with elastomer (NBR-70 Shore, Kani, Art. Nr.: PP7AHZ) at a pressure of 24 bar at +170°C and cured for 20 minutes. During the moulding process, the remaining gas was able to exit the cavity via the venting construction.

After the moulding process the cured elastomer was released by hand and the system was filled with new uncured rubber for the next moulding process. Even after 35 cycles no significant decrease of venting performance was measured (see Figure 9).

Fig. 9 shows a diagram of venting performance of exemplary prototype vent elements after a respective vulcanization cycle. In each vulcanization cycle, gas is vented out through the respective vent element from the moulding cavity after the respective vulcanization cycle.

For each of the vent elements with membrane materials ODF and DF, three exemplary samples (DF-1 , DF-2, DF-3, ODF-1 , ODF-2, ODF-3) were tested. Although manufactured from the same or similar basic material having in principle the same structure, the respective samples are not identical in venting performance, but slightly deviate in venting performance from each other within a certain range as depicted in Fig. 9. This may result from, e.g., a slightly varying pore size among the samples. Prototypes“DF-1” and“DF-2” use film layers from the same basic material (e.g. from the same roll of basic material) with hole diameter of 0.40 mm of the central hole (cf. hole‘23’ in Fig. 3). Prototype“DF-3” uses an alternative film layer with hole diameter of 0.30 mm. All ODF samples use film layers from the same basic material (e.g. from the same roll of basic material).

Fig. 10 shows a still further embodiment of a vent element 10, arranged in a vent hole 52 of a mould 50 (or mould half). The mould hole 52 is provided with an annular lip 60, to assist in retaining the vent element therein.

The vent element has an inflow surface 40, defined by the inflow end 41 of the elastically deformable member 2, which faces the interior cavity 53, and an outflow surface 42 at its opposite end, adjacent to the duct 6. The vent element includes an elastically deformable member 2, having an inflow end 41 and an outflow end 44 (which, in the embodiment shown defines the outflow surface 42 of the vent element 10). The elastically deformable member 2 has a vent passage 24 extending from the inflow end 41 to the outflow end 44.

As described generally in relation to Figs 3A and 3B, the vent passage 30 permits a flow of gas therethrough, but is configured (for example by virtue of its dimensions, and in relation to the compressibility / hardness of the elastically deformable member, moulding conditions etc) to close along at least a part of its length in use, under the action of pressure applied to the inflow surface 40 by mouldable material. Figure 11 shows another vent element 10, which is similar to that shown in Figure 10, and further comprises a film layer 1 attached to the elastically deformable member 2, the film layer 1 defining the inflow surface 40.

The film layer in the embodiment shown is a metallic foil (e.g. stainless steel), but may alternatively be a polymeric material as described herein. In general terms a film layer 1 may be selected to reduce the adherence of mouldable material to the vent element 10 which may assist when demoulding a moulded article.

The film layer 1 may be gas permeable and, to this end, may be provided with an aperture 23 therethrough, aligned with the vent passage 30. As such, the vent passage may extend entirely from the inflow surface 40 to the outflow surface 42.

In alternative embodiments, the film is porous, and the aperture may not be required.

Fig. 12 shows another embodiment of a vent element 10, having an elastically deformable member 2 with an inflow end 41 which defines an inflow surface 40 facing the cavity 53, and an outflow end 42. Coupled to the outflow end 44 of the elastically deformable member 2 is a porous support element 3, which defines the outflow surface 42 of the vent element 10. The vent element has a vent passage 30 which extends from the inflow surface 40 to the outflow surface 42, through both the elastically deformable member 2 and an aperture 26 in the porous support element 3, and communicates with the duct 6.

As described above, the vent passage permits a flow of gas therethrough, but is configured to close along at least a part of its length in use, under the action of pressure applied to the inflow surface by mouldable material. Thus, flow of mouldable material past the outflow surface and into the duct 6 is prevented.

The vent element 10 of Fig. 12 also includes a tubular support element 54 (in this instance steel). The support element 54 has an annular lip or flange 61 at its upper end, and at a midpoint, an annular shoulder 62. The porous support element 3 and the elastically deformable member 2 are retained between the lip 61 and shoulder 62, optionally slightly under compression. The support element 54 may thereby assist at least in part to retaining the layers 2, 3 of the vent element together, and resist forces which might otherwise pull them apart, in particular during demoulding.

In addition, the support element 54 assists in retaining the vent element 10 in the vent hole 52. The support element has a lower portion 54a below the shoulder 62 may be configured to exert an outwardly biasing force against the call of the vent hole 52, to resist removal of the vent element during demoulding and also prevent the vent element from being forced further down into the vent hole in use. A lower portion of the support element may also enable the use of thinner (in the vertical direction of the figures) elastically deformable member, support element or film (as the case may be) within a given size of vent hole, which can save material costs - particularly for moulds with a large number of vent holes.

Figure 13 shows another vent element 10, which is similar to that shown in Figure 12, but further includes a film layer 1.

Table shows examples of vent elements according to embodiments of this invention

In examples 1 to 4 of table 1 , the vent element also comprises a stainless steel disc as support element with a thickness of 0.3mm, commercially available under the brand “Futureblech” (a trade mark) by the company Futronika AG, Germany.

The film layer may, in alternative embodiments extend around the sides of the elastically deformable member and, where present, the porous support element, within a support element. Alternative support elements are envisaged which lack the lower part 54a, or terminate in a lower lip; for use for example in a vent hole generally as depicted in Fig. 10. A support element may be used in embodiments lacking an elastically deformable member, or lacking a porous support element. Indeed, whilst various exemplary embodiments have been disclosed, it shall be understood that variations, modifications and combinations of the vent elements, moulds and methods disclosed herein may be made without departing from the scope of the appended claims.

Claims

1. A vent element configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould, the vent element having an inflow surface and an outflow surface and elastically deformable member disposed therebetween;

2. The vent element according to claim 1 , wherein the elastically deformable member has a ShoreA hardness of between around 15 to 60.

3. The vent element according to claim 1 or 2, wherein the inflow surface is defined by the inflow end of the elastically deformable member.

4. The vent element of claim 1 or 2, wherein the inflow surface is defined by a film layer attached to the elastically deformable member.

5. The vent element of claim 4, wherein the film layer comprises a polymeric material.

6. The vent element of claim 5, wherein the film layer is formed from a polymeric material with matrix tensile strength greater than 10,000 psi in orthogonal directions.

7. The vent element of claim 4 or 5, wherein the film layer comprises ePTFE.

8. The vent element of claim 4, wherein the film layer comprises a metallic foil.

9. The vent element of any one of claims 4 to 8, wherein the film layer is porous.

10. The vent element of any one of claims 4 to 9, wherein the vent passage extends through the film layer.

1 1. The vent element of any preceding claim, wherein the outflow surface is defined by the outflow end of the elastically deformable member.

12. The vent element of any one of claims 1 to 10, further comprising a porous support element attached to the outflow end of the elastically deformable member, the porous support element defining the outflow surface of the vent element.

13. The vent element of claim 12, wherein the porous support element comprises a sintered metal or plastics material, or a perforated plastics material, or a ceramic material.

14. The vent element of claim 12 or 13, wherein the vent passage extends through the porous support element to the outflow surface.

15. The vent element of any one of claims 12 to 14, when dependent on any one of claims 4 to 10, wherein the elastically deformable member is an elastically deformable intermediate member disposed between the porous support member and the film layer.

16. The vent element of any preceding claim, wherein the vent element is generally cylindrical around an axis extending from the inflow to the outflow surfaces.

17. The vent element of any preceding claim, comprising two or more layers oriented generally normal to an axis extending from the inflow to the outflow surfaces.

18. The vent element of any preceding claim, comprising a housing element enclosing at least a part of a periphery of the vent element.

19. The vent element of claim 18, wherein the vent element comprises a said porous support element, wherein the at least one porous support element is integrally formed with the housing element.

20. A vent element configured to be arranged within a vent hole of a mould extending from a forming surface of an interior cavity of the mould, the vent element having an inflow surface and an outflow surface and comprising:

21. The vent element of claim 20, wherein the film layer is porous.

22. The vent element of claim 20 or 21 , wherein the porous support element has at least one vent passage extending therethrough.

23. The vent element of claim 22, wherein the film layer has an aperture aligned with the or each vent passage, such that the vent passage extends between the inflow and outflow surfaces.

24. The vent element of any one of claims 21 to 23, comprising:

at least one porous support material which is configured for venting a gaseous fluid received at a first side of the support material to an outer environment of the mould at a second side of the support material opposite the first side;

at least one film layer arranged above the at least one porous support material at the first side and configured to be exposed to the interior cavity of the mould and to permit passage of the gaseous fluid therethrough, wherein the at least one film layer is formed from a polymeric material with matrix tensile strength greater than 10,000 psi in machine and transverse directions.

25. The vent element according to any one of claims 21 to 24, comprising a housing element enclosing the at least one porous support material, wherein the at least one porous support material is formed by at least one support element integrally formed with the housing element.

26. A moveable or fixed mould half for injection or compression moulding, comprising at least one forming surface and a vent hole extending from the at least one forming surface, and a vent element according to any preceding claim in the vent hole.

27. A mould for injection or compression moulding, comprising an interior cavity having at least one forming surface, a vent hole in the at least one forming surface and a vent element according to any one of claims 1 to 25 in the vent hole.

28. The mould half of claim 26 or the mould of claim 27, comprising a plurality of vent holes and a plurality of vent elements therein.

29. Use of the vent element of any one of claim 1 to 25, in a compression moulding process.

30. A method of compression moulding, comprising:

providing a second forming surface

providing a mouldable material between the first and second forming surfaces;

31. The method of claim 30, wherein compressing the mouldable material comprises moving the first and second forming surfaces together.

32. The method of claims 30 or 31 , wherein venting comprises venting gas from between the mouldable material and the first and/or second forming surface.

33. The method of any one of claims 30 to 32, comprising reducing or preventing flow of gas vented through the vent passage by at least partially blocking or filling the vent passage with mouldable material, and then closing the vent passage by compressing the elastically deformable member.

34. The method of any one of claims 30 to 33, comprising closing the vent passage before mouldable material flows through the passage to the outflow surface.

35. The method of any one of claims 30 to 34, comprising opening the mould cavity and removing the moulded material therefrom, wherein the vent elements may remain in situ during this process.

36. The method of any one of claims 30 to 35, comprising moulding a tyre.

37. A method of injection moulding, comprising;

flowing mouldable material into the interior cavity;

compressing the elastically deformable member under the action of the flow of mouldable material against the inflow surface of the vent element; and thereby closing the vent passage.