GB1578790A

GB1578790A - Method and apparatus for manufacturing moulded objects

Info

Publication number: GB1578790A
Application number: GB40621/77A
Authority: GB
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-10-14
Filing date: 1977-09-29
Publication date: 1980-11-12
Also published as: NO149017B; NO149017C; SE7611400L; NO773518L; DE2745395A1; SE404323B

Description

(54) IMPROVEMENTS IN OR RELATING TO A METHOD AND APPARATUS FOR MANUFACTURING MOULDED OBJECTS (71) I, TORE GEORG PALMABR, a Swedish Citizen, of Smultranvägen 28, S-331 00 Värnamo, Sweden, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: The present invention relates to a method and an apparatus for manufacturing moulded objects of thermoplastics material.

More particularly the present invention relates to a method and an apparatus for moulding articles of thermoplastics material, which articles have a contact surface which feels pleasant to the skin, by means of vacuum moulding a plastics material foil in a moulding tool connected to a vacuum source. An example of such an article is a sealing ring intended for use on ear-defenders or on head phones. Ear-defenders are worn by personnel who operate noisey equipment such as tractors, rivetting machines and the like to reduce the intensity of the noise acting on the ear drums.

The invention will be described in this specification with reference to the manufacture of ear-defenders but it is to be understood that the invention is not limited to this particular application.

A sealing ring for ear-defenders, like many other objects intended to be in continuous or long term contact with the skin under pressure, should be designed in accordance with the following principles: A. The material used should have a dense surface, that is to say, a surface not having any pores, so that it can easily be kept clean. A suitable material for the purpose is a plastics material which feels pleasant to the skin.

B. The material in contact with the skin should be resilient or flexible so that it will readily conform to the shape of the skin against which it is pressed and will also conform to the shape of the skin during movements of the skin.

C. The material in contact with the skin should be patterned so that only parts of the material actually contact the skin to enable the greatest possible ex panse of skin to "breath" but without the protruding parts of the pattern caus ing too great a surface pressure.

D. The patterning of the material should be such that elastomeric stretching of the material is facilitated to enable ad justment to the skin in response to the least possible basic pressure. The pat tern should therefore be ribbed or waffle-like, for example.

E. The parts directed substantially perpen dicularly backwards from the contact surface of the ring with the skin should be made weak to facilitate the forma tion of pleats in these surfaces, thus re ducing the pressure required for uni form adjustment of the contact sur face of the ring against the skin and also enlarging the contact surface upon increased pressure against the skin so that the specific pressure on the skin is reduced.

F. A pressure equalising medium should be provided within the sealing ring to resiliently urge the ring into contact with the skin, this medium being a flexible, solid material such as foam plastics material, liquid such as glycol, gas such as air, or combinations of these.

However, it has hitherto been found to be impossible to manufacture a sealing ring fulfilling all the requirements listed above in an economic manner.

In presently utilised vacuum moulding methods a moulding tool is usually used which has a large number of evacuating channels arranged in the bottom. With complete and permanent moulding of a foil of plastics material, small marks usually occur in the surface of the foil, i.e. the contact surface, that is to say the surface of the ring which is usually subjected to the greatest wear during use, and the ring therefore has a relatively short service life.

The present invention seeks to provide a method and an apparatus for performing the method in which the above described disadvantages and drawbacks are obviated or reduced.

According to one aspect of this invention there is provided a method of manufacturing moulded objects of thermosplastics material having a contact surface which feels pleasant to the skin, by vacuum moulding a plastics material foil in a mould connected to a vacuum source, wherein the foil is caused to abut a diffuser which rests on the bottom surface of a closed mould, and extends to an annular lateral slot located at a distance from the bottom of the mould and formed in the wall of the mould in order to provide the moulded foil with a surface pattern, whereupon the mould is evacuated through the annular lateral slot.

According to another aspect of this invention there is provided an apparatus for manufacturing molded objects of thermoplastics material having a contact surface which feels pleasant to the skin, by means of vacuum moulding a plastics material foil, said apparatus comprising a mould connected to a vacuum source a diffuser resting on the bottom of the mould, and extending to an annular evacuation slot located at a distance from the bottom of the mould provided in the wall of the mould.

According to yet another aspect of this -invention there is provided a soft, flexible -sealing ring for ear-defenders and the like, which is pleasant to the skin, manufactured by a method according to said one aspect of the invention and filled with foam plastics material liquid or some other similar pressure-distributing medium, wherein the surface intended to come into contact with the skin is patterned to produce a large number of recesses between the contact surfaces and the skin and wherein the casing parts of the ring substantially adjacent this contact surface are smooth and provided with folds or identaflons therein.

In a method in accordance with this invention a plastics material foil is caused to abut a diffuser covering the bottom surface of a closed mould, said foil having constant material tension in order to.achieve a surface pattern as well as predetermined distribution of material, whereupon the mould is evacuated through a lateral slot located at a distance from the bottom of the mould.

In order that the invention may be more readily understood and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a sectional view of an earmuff cover with a sealing ring manufactured by a method in accordance with the invention, Figure 2 is a cross-sectional view through the ring shown in Figure 1, Figure 3 is a schematic perspective view of a moulding tool which can be used for performing the method according to the invention, Figure 4 schematically illustrates the movement of the moulding tool past a number of work stations, and Figure 5 is an enlarged sectional view of the lower half of the moulding tool.

For the sake of simplicity the invention will be specifically described, and illustrated with reference to a method for the production of a sealing ring for an ear-defender.

The invention may of course also be used for making many other objects such as sweat-bands for head-gear, sealing edges for gas-masks, ear-plugs, eye-shields, linings for diving suits and so on, and one of the advantages with objects manufactured in accordance with the invention is the ability of skin in contact with such objects to "breath" which prevents or minimises the occurrence of exzema, for instance.

Figures 1 and 2 show a sealing ring for ear-defenders, which sealing ring is made primarily of a foil of thermosplastics material which feels pleasant to the skin. The foil surface 2 in contact with the skin 1 the contact surface -- has a ribbed or waffle pattern which is designed so that the spaces between adjacent ribs pressed against the skin are sufficiently narrow to permit the sealing ring effectively to block noise. However, the skin is still able to "breath" to a certain extent. Furthermore, due to constant small movements of the skin the position of the numerous small pressure surfaces in the waffle pattern is altered. The contact surface 2 is subjected to wear and other strain and should therefore be relatively thick. The ring sections 3 and 4 located substantially perpendicular to the contact surface 2 have an annular section which is thinner and provided with folds or indentations 5 and 6 by a method subsequent to the moulding process herein described so that pleats are formed all the way round when the ring is compressed in use.

This facilitates a uniform compression of the ring without irritating transverse folds forming in the contact surface 2. Thus a large proportion of the- ring which is be tween the bent foil parts 7 is in contact with the skin. A pressure equalising medium is contained in the ring and consists of a foam -plastics material pad 8 which feels soft and maintains a stable resiliency irrespective of the ambient temperature. The air in the foam plastics material pad 8 can be changed or ventilated through the small evacuation apertures 9, 10 and 11 located as far from each other as possible. The apertures 9 and 10 are formed in a part of the ring which is exposed to the atmosphere when the eardefenders are in use, whereas the aperture 11 is formed in part of the ring which is on the inside of the ear-defender, when in use. The apertures 9, 10 and 11, and the foam plastics material 8 co-operate to form noise-suppressing evacuation channels, which act to equalise pressure differences between the interior and exterior of the eardefender, thus equalising pressure differences on the ear drum of the person wearing the ear-defenders. The total area of the apertures 9 and 10 is approximately 2 to 4 times greater than the area of the aperture 11 in order to minimise discomfort when putting on the ear-defenders.

Behind the foam plastics material pad 8 there may be a liquid-filled pad 12, the purpose of which is to equalise pressure around the ear like a communicating receptacle. The liquid is in a special annular member, which is strengthened to prevent puncturing thereof, since such puncturing might lead to unpleasant consequences.

The sealing ring is welded to a rigid pressure ring 13 provided with a peripheral section which provides a seal against the cover 15 and an upstanding snap-on connector which secures the ring to the cover 15 of the ear-defenders, as hereinafter described.

Figure 3 shows a complete moulding tool consisting of a lower plate 21 and an upper plate 22. In the lower plate 21 is a cavity 16 with welding electrodes 17 and in the upper plate is a cavity 23 for the pressure ring 13. The tool shown in Figure 3 is preferably arranged on a circular feed table 24 including a vacuum source 25 with its connections, arranged to co-operatwith the lower plate 21 and its cavity 16. Figure 4 shows the circular feed table 24 arranged to move the tool past a number of work stations in the direction of the arrow A, comprising in turn the following: An inser tion station 26 for the foil, a vacuum furnace 27, a second insertion station 28 for application of the foam plastics material pad 8 and liquid ring 12, if any, a station 29 for the application of the pressure ring 13, a station 30 for maintaining constant temperature, and finally a welding station 31. The two halves of the tool 21, 22 are placed together before the tool reaches sta tion 31. After the welding station 31 the tool returns to station 26 where the finished product is removed and a new foil is applied.

Figure 5 shows a section through the lower plate 21 of the tool illustrated in Figure 3 which is a suitable combination tool for manufacturing the sealing ring partly by means of vacuum moulding a plastic foil and partly by filling the ring thus formed and subsequently welding. The tool can be made fully or semi-automatic. The lower plate 21 of the tool comprises an upper half 17' and a lower half 18 which together define cavity 16 or mould. Between the halves 17', 18 is a gap 19 for evacuation of the mould, the gap 19 being connected via channels 20 to a vacuum source, not shown in Figure 5.

The cavity in the half 18 is covered by a diffuser element 32 to produce a pattern on an article moulded within the tool, this element also serving as equalisation member during evacuation. The diffuser covers the entire surface of the cavity in the lower half 18 and extends to the evacuation gap 19. In its simplest form the diffuser comprises a cloth of relatively thin threads with relatively large spaces therebetween, i.e. an open weave. It may of course equally well consist of metal mesh, filter cloth or a porous ceramic material or similar heatresistant material. The material used for the diffuser is preferably form-retaining, i.e. can tolerate the operating pressure used without being formed.

In contrast to previous manufacturing methods, the use of the diffuser 32 results in even evacuation and the requisite fitting of the foil along the diffuser 32. Furthermore, the foil is reduced in material thickness at the sections close to the evacuation gap, whereas the part which will later constitute the surface in contact with the skin has a uniform thickness and is patterned.

The moulding process is such that the contact surface of the material is moulded with a substantially constant material tension and a predetermined distribution of material.

The invention is of course not limited to the embodiment shown in the drawings but can be varied in many ways within the scope of the following claims. For example the invention has been described with reference to a simple moulding tool but it is possible, within the scope of the invention, to utilise multiple tools for the simultaneous manufacture of many rings or other moulded objects.

WHAT I CLAIM IS: 1. A method of manufacturing moulded objects of thermoplastics material having a contact surface which feels pleasant to the skin by vacuum moulding a plastics material foil in a mould connected to a vacuum source, wherein the foil is caused to abut a diffuser which rests on the bottom surface

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

Claims

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

-plastics material pad 8 which feels soft and maintains a stable resiliency irrespective of the ambient temperature. The air in the foam plastics material pad 8 can be changed or ventilated through the small evacuation apertures 9, 10 and 11 located as far from each other as possible. The apertures 9 and

10 are formed in a part of the ring which is exposed to the atmosphere when the eardefenders are in use, whereas the aperture 11 is formed in part of the ring which is on the inside of the ear-defender, when in use. The apertures 9, 10 and 11, and the foam plastics material 8 co-operate to form noise-suppressing evacuation channels, which act to equalise pressure differences between the interior and exterior of the eardefender, thus equalising pressure differences on the ear drum of the person wearing the ear-defenders. The total area of the apertures 9 and 10 is approximately 2 to 4 times greater than the area of the aperture 11 in order to minimise discomfort when putting on the ear-defenders.

Behind the foam plastics material pad 8 there may be a liquid-filled pad 12, the purpose of which is to equalise pressure around the ear like a communicating receptacle. The liquid is in a special annular member, which is strengthened to prevent puncturing thereof, since such puncturing might lead to unpleasant consequences.

The sealing ring is welded to a rigid pressure ring 13 provided with a peripheral section which provides a seal against the cover

15 and an upstanding snap-on connector which secures the ring to the cover 15 of the ear-defenders, as hereinafter described.

Figure 3 shows a complete moulding tool consisting of a lower plate 21 and an upper plate 22. In the lower plate 21 is a cavity

16 with welding electrodes 17 and in the upper plate is a cavity 23 for the pressure ring 13. The tool shown in Figure 3 is preferably arranged on a circular feed table 24 including a vacuum source 25 with its connections, arranged to co-operatwith the lower plate 21 and its cavity 16. Figure 4 shows the circular feed table 24 arranged to move the tool past a number of work stations in the direction of the arrow A, comprising in turn the following: An inser tion station 26 for the foil, a vacuum furnace 27, a second insertion station 28 for application of the foam plastics material pad 8 and liquid ring 12, if any, a station

29 for the application of the pressure ring 13, a station 30 for maintaining constant temperature, and finally a welding station 31. The two halves of the tool 21, 22 are placed together before the tool reaches sta tion 31. After the welding station 31 the tool returns to station 26 where the finished product is removed and a new foil is applied.

Figure 5 shows a section through the lower plate 21 of the tool illustrated in Figure 3 which is a suitable combination tool for manufacturing the sealing ring partly by means of vacuum moulding a plastic foil and partly by filling the ring thus formed and subsequently welding. The tool can be made fully or semi-automatic. The lower plate 21 of the tool comprises an upper half 17' and a lower half 18 which together define cavity 16 or mould. Between the halves 17', 18 is a gap 19 for evacuation of the mould, the gap 19 being connected via channels 20 to a vacuum source, not shown in Figure 5.

The cavity in the half 18 is covered by a diffuser element 32 to produce a pattern on an article moulded within the tool, this element also serving as equalisation member during evacuation. The diffuser covers the entire surface of the cavity in the lower half 18 and extends to the evacuation gap 19. In its simplest form the diffuser comprises a cloth of relatively thin threads with relatively large spaces therebetween, i.e. an open weave. It may of course equally well consist of metal mesh, filter cloth or a porous ceramic material or similar heatresistant material. The material used for the diffuser is preferably form-retaining, i.e. can tolerate the operating pressure used without being formed.

In contrast to previous manufacturing methods, the use of the diffuser 32 results in even evacuation and the requisite fitting of the foil along the diffuser 32. Furthermore, the foil is reduced in material thickness at the sections close to the evacuation gap, whereas the part which will later constitute the surface in contact with the skin has a uniform thickness and is patterned.

The moulding process is such that the contact surface of the material is moulded with a substantially constant material tension and a predetermined distribution of material.

The invention is of course not limited to the embodiment shown in the drawings but can be varied in many ways within the scope of the following claims. For example the invention has been described with reference to a simple moulding tool but it is possible, within the scope of the invention, to utilise multiple tools for the simultaneous manufacture of many rings or other moulded objects.

WHAT I CLAIM IS: 1. A method of manufacturing moulded objects of thermoplastics material having a contact surface which feels pleasant to the skin by vacuum moulding a plastics material foil in a mould connected to a vacuum source, wherein the foil is caused to abut a diffuser which rests on the bottom surface

of a closed mould, and extends to an annular lateral slot located at a distance from the bottom of the mould and formed in the wall of the mould in order to provide the moulded foil with a surface pattern, whereupon the mould is evacuated through the annular lateral slot.
2. A method according to claim 1, wherein the material is moulded with the portion of the foil which contacts the diffuser having a substantially constant material tension and a predetermined distribution of material.
3. A method according to claim 1 wherein a form-retaining material is used as diffuser.
4. A method according to claim 3 wherein a textile-like material is used as diffuser.
5. A method according to claim 2, wherein a metal mesh, a filter cloth or a porous ceramic material is used as diffuser.
6. An apparatus for manufacturing moulded objects of thermoplastics material having a contact surface which feels pleasant to the skin, by means of vacuum moulding a plastics material foil, said apparatus comprising a mould connected to a vacuum source a diffuser, resting on the bottom of the mould and extending to an annular evacuation slot located at a distance from the bottnm of the mould provided in the wall of the mould.
7. An apparatus according to claim 6, wherein the diffuser consists of a form-retaining material.
8. An apparatus according to claim 6, wherein the diffuser consists of textile, metal mesh, filter cloth or porous ceramic material.
9. A soft, flexible sealing ring for eardefenders and the like, manufactured by a method according to claim 1 and filled with foam plastics material, liquid or some other similar pressure-distributing medium, wherein the surface intended to come into contact with the skin is patterened to produce a large number of recesses between the contact surfaces and the skin and wherein the casing parts of the ring substantially adjacent this contact surface are smooth and provided with folds or indentations therein.
10. A sealing ring according to claim 9, wherein air channels are provided to enable equalisation of air pressure within ear-defenders provided with such a sealing ring.
11. A method of manufacturing a moulded object substantially as herein described with reference to the accompanying drawings.
12. A moulded object whenever manufactured by a method according to any one of claims 1 to 5 or 11.
13. An apparatus for manufacturing moulded objects substantially as herein described, with reference to and as shown in Figures 3 to 5 of the accompanying drawings.
14. A sealing ring for ear-defenders, substantially as herein described with reference to, and as shown in, Figures 1 and 2 of the accompanying drawings.