WO1992004171A1

WO1992004171A1 - Method and apparatus for the curing of fusible materials and use hereof

Info

Publication number: WO1992004171A1
Application number: PCT/DK1991/000257
Authority: WO
Inventors: Ole Riis Olsen
Original assignee: Gn Danavox A/S
Priority date: 1990-09-11
Filing date: 1991-09-06
Publication date: 1992-03-19
Also published as: AU8611991A; DK217790A; DK217790D0

Abstract

An apparatus for use in the curing of fusible materials comprises a mould (6) with a mould cavity (16), into which is poured the moulding material. The mould is suspended pivotally and can be rotated around its own longitudinal axis (17) by a motor (19). The apparatus moreover comprises a substantially closed vessel (5), from which the atmospheric air can be displaced by leading in CO2 (9, 10, 11) and bleeding the vessel (21, 22, 23). The apparatus additionally comprises lighting members (13, 14) and a control keyboard with a display (3) for controlling and operating the apparatus. The application also relates to a method for the curing of fusible materials with ultra-violet rays, and the application of the invention for producing housings for all-in-the-ear hearing aids.

Description

METHOD AND APPARATUS FOR THE CURING OF FUSIBLE MATERIALS AND USE HEREOF

The invention relates to a method and an apparatus for use in the curing of fusible materials which after being filled into a mould are cured by means of radiation.

Several different types of fluent materials, for example different kinds of acrylic plastic, which are fluent by ordinary room temperature, may be cured by means of radia¬ tion, in that radiation, for example with ultra-violet rays, makes the material polymerize. Such materials have many different applications, both within the industry and for more individual tasks, such as for example dental coat- ing materials which are cured by radiation with ultra¬ violet rays.

It is a disadvantage by many radiation reactive types of plastic, as for example acrylic plastic, that the plastic does not cure in areas with oxygen occurrence, i.e. in those areas where the fluent plastic is in direct contact with atmospheric air. In such areas the external molecular layers do not cure, the result being that the surface of the cured product must be cleaned, for example with alcohol or a similar purifying agent. In many cases it is thus necessary to completely cover an item before the radiation in order to prevent air from percolating, which can give rise to many difficulties.

It is the object of the invention to present a new method and a new apparatus, by which air or oxygen is in a simple manner prevented from percolating into the area where the moulding material is to cure.

This is achieved by proceeding as presented and character¬ ized in claim 1, for example by applying an apparatus as presented and characterized in claim 6.

The moulding material is placed in a closed vessel from which the atmospheric air, and thus the oxygen, is removed by letting an air displacing gas, for example CO,,, into the vessel. A substantially closed vessel could for example be a vessel with a cover, which vessel is filled with the air displacing gas during simultaneous bleeding at or in the cover in order to allow the confined atmospheric air to escape as the vessel is filled with the air displacing gas.

By proceeding as presented and characterized in claim 2, for example by applying an apparatus as presented and char¬ acterized in claim 7, a substantially vertical streamline flow is achieved in the vessel during the filling-in of the air displacing gas, the result being that all atmospheric air, and thus all oxygen, is displaced from the vessel, or in any case from that part of the vessel where the mould is. In this manner the mould is comparatively quickly and for certain completely surrounded by the air displacing gas, so that the curing can commence without air percolat¬ ing into the still uncured moulding material.

By proceeding as presented and characterized in claim 3, for example by applying an apparatus as presented and char¬ acterized in claim 8, it is achieved that the surface of the fluent material is not exposed to radiation and thus does not cure, which is a great advantage if the products to be produced are hollow items or shells. The covering of the surface in some way or another from the ultra-violet rays is thus avoided. If the radiation lasts sufficiently long, and if, instead of a non-reflecting ceiling, a re¬ flecting ceiling is applied, for example by inserting a re¬ flecting plate, the possibility is provided of producing completely solid items, such as for example earplugs for use in connection with behind-the-ear hearing aids. By proceeding as presented and characterized in claim 4, for example by applying an apparatus as presented and char¬ acterized in claim 9, the possibility is provided of pro¬ ducing thin-walled items, such as for example ear shells for all-in-the-ear hearing aids. By controlling the radia¬ tion and the pouring in respect of time, the possibility is provided of producing shells of any desired wall-thickness, as for example a wall-thickness in the range 0.5-1.5 mm.

By proceeding as presented and characterized in claim 5, for example by applying an apparatus as presented and char¬ acterized in claim 10, it is ensured that the inside of the shell structure cures completely, even in structures having a narrow or very irregular cavity. The special cover design prevents the formation of whirls in the gasses in the vessel during the bleeding; the bleeding moreover has the particular advantage that all the gasses which appear during the curing of the moulding material are sucked away from the apparatus, the result being that immediately after termination of the curing process, the apparatus may be opened and the finished items removed.

The invention is developed particularly for use in the pro- duction of thin-walled, individually adapted housings, so- called shells, for all-in-the-ear hearing aids, and as pre¬ sented and characterized in claim 11. It will, however, be obvious to a person skilled in the art that the apparatus may be applied for any kind of moulding of items of fusible materials to be cured by radiation, for example solid ear¬ plugs, items for dentures, models etc. Compared to the known methods for the production of ear shells for all-in- the-ear hearing aids, minimum shrinking is achieved in addition to the fact that the shells become completely uni- form with a uniformly smooth surface on both sides; the production time is considerably reduced, while at the same time the production becomes independent of the ambient temperature; the apparatus according to the invention automates the otherwise difficult production of individual ear shells, so that less is required of the operating staff, whereby the training time is considerably reduced. All of this reduces the costs of the production of ear shells for all-in-the-ear hearing aids considerably. The method and the apparatus may also be applied in connection with further processing, for example for different kinds of refinishing of housings for all-in-the-ear hearing aids, such as embedment of type and number or the like, embedment of a tube which constitutes the ventilating duct in the hearing aid, etc.

As air displacing gas is used CO,,, since this type of gas is both well suited for the purpose and absolutely harmless to the operating staff as long as the CO.-, concentration in the room is low. It is obvious to a person skilled in the art that other gasses are applicable without deviating from the basic idea of the invention, if the gas is capable of displacing the oxygen from the moulding material during the curing process.

The invention will hereafter be explained in more detail with reference to the drawing, in that

fig. 1 shows an apparatus according to the invention seen from above from an inclined angle, and

figs. 2-5 show section II-V in the apparatus in fig. 1, which section illustrates the method and the function of the apparatus.

In fig. 1 is seen an apparatus 1 for use in the production of shells for all-in-the-ear hearing aids, which are mould¬ ed in acrylic plastic which can be polymerized by radiation with ultra-violet rays having a wavelength in the range 3-

-Q 500 nm (10 m).

The apparatus 1 comprises a closed vessel to which access is gained via a cover 2. For controlling the process, the apparatus comprises an electronic control member which is operated and programmed via a display control keyboard 3 comprising among other things three adjustable timing cir¬ cuits 26, 27, 28, as well as various control buttons 29. The apparatus may of course be provided with other signal¬ ling devices, for example acoustic or optical, which signal when a curing-moulding process is terminated and the cover and the finished items may be removed. The cover 2 is more¬ over preferably designed in such a manner that it cannot be opened during the curing-moulding process, if the process is not stopped or interrupted in due form via the control keyboard.

Figs. 2-5 show cross sections of the inside of the appar- atus. A vessel 5 is closed at the top by a tight cover 2 by means of an annular packing 24 between the vessel wall and the cover.

In the following the invention will be explained in connec- tion with the moulding of shells for all-in-the-ear hearing aids; it will, however, be obvious to a person skilled in the art that many other items could be moulded in the apparatus without substantially deviating from the follow¬ ing method.

In the vessel 5 is placed a mould (French: cuvette) 6 com¬ prising a hardened or stiffened duplicate gel, in which is formed a number of cavities 16. Each cavity 16 constitutes a mould for an individual ear shell, and the cavities appear because a number of ear prints have been placed in the mould, after which it has been filled up with gel; when the gel has stiffened or hardened the ear prints are remov¬ ed. Both the gel and the mould, which are made of plastic, are fully translucent to ultra-violet rays.

Each cavity 16' is thus an individual mould for an indivi¬ dual ear shell for an all-in-the-ear hearing aid. In prac¬ tice one or more ear prints could be placed in the mould depending on the length of the mould, and with that the size of the apparatus, the result being that a comparative- ly large number of individual shells are moulded at a time.

Before the mould 6 is placed in the apparatus, all cavities 16' are filled with acrylic plastic 16, which will cure by ultra-violet radiation. The mould 6 is placed in the vessel 5 mounted in suspension members (not shown), so that the mould is rotatable around a longitudinal axis 7. The sus¬ pension members may at the one end be manoeuvred by an electric motor 19, for example a step motor, controlled by the electronic control circuit.

When the mould 6 has been placed as shown in fig. 2 in the vessel 5, the cover 2 is closed and the process is started by opening of the valve 9, so that C0₂ is led into the vessel 5 through the tube 10 and the distributing pipe 11 with openings 12. The C0₂ gas is led in at comparatively low pressure and at a low velocity of flow, so that the vessel 5 is slowly filled from the bottom without the gas getting mixed with the atmospheric air in the vessel. The atmospheric air in the vessel is, as described, displaced from below because the density of C0₂ is approx. 50% higher than that of atmospheric air, and because C0₂ is not miscible with atmospheric air.

While the C0₂ gas is filled in, the content of atmospheric air in the vessel is removed through the cover 2, which comprises an inner cover 20 constituting a flow filter, for example a plate with small holes, and the air is sucked out through the tube 21 from the vessel-like area in the cover behind the inner cover 20. By opening of the valve 22 the vessel is bleeded through the tube 21, and the atmospheric air and other gasses from the vessel 5 are led through an exhaust pipe 23, for example to a suction device. The filter-shaped inner cover prevents too heavy bleeding of the vessel, so that the atmospheric air is not mixed with the C0₂ gas. To be certain that no quantities of air, and thus oxygen, remain in the vessel 5 until a level a distance above the mould 6, both the mould and the vessel are designed with inclined walls, so that any accumulation of air may easily escape and ascend up through the C0₂ gas and escape through the cover.

The mould inserted, the cover closed and the vessel filled with C0₂ gas, the three timing circuits 26, 27 and 28 are set, after which the curing process may commence. The first of the timing circuits 26 is set for the number of seconds in which the two light sources consisting of lamps 13, which emit ultra-violet rays and have reflectors 14, are to be on. The lamps may for example be of the type DULUX S9/78, arranged to be able to switch on and off by means of a switch circuit, so that the illumination is not con- tinuous, but produced by a number of flashes in quick suc¬ cession. The lighting members are separated from the vessel 5 by means of an inclined glass plate 15, and are moreover arranged in such a manner that the mould 6 is exposed from below from an inclined angle and from the sides. The under- side of the inner cover 20 is designed in a non-reflecting manner, for example with a dead black coating, which pre¬ vents the moulding material 16 in the cavities 16' from being exposed from above, whereby the surface does not cure at all. The timing circuit 26 is for example set for 450 seconds of illumination, after which the light will automatically switch off. The illumination is illustrated in fig. 3.

Depending on the time of illumination the moulding material 16 cures in the cavities 16', the result being a shell of a desired thickness, which is still filled with fluent uncur- ed moulding material.

The electronic control circuit hereafter starts the mould motor 19 and turns the mould upside down, see fig. 4, so that the uncured moulding material 17 drips out and ends up as superfluous moulding material 18 on a drip plate at the bottom of the vessel under the mould. The timing circuit 27 decides for how long the mould must stay in the position shown in fig. 4. Tests have established that a period of about 50 seconds is suitable for emptying the mould com¬ pletely for fluent uncured moulding material. During the whole process, i.e. from the moment when the turning of the mould is started, the lighting members 13 are off, and they stay off during the whole pouring process.

The mould motor 19 hereafter turns the mould with the mould openings towards one of the light sources 13, see fig. 5. The relevant light source is activated again, and now the final curing of the moulded shell is taking place, and in such a manner that the inside of the shell is cured by radiation from one of the light sources. During this curing process, which is controlled by the third timing circuit 28, the mould makes a seesaw motion in front of the lighting member, as illustrated by the arrows 30, so that the ultra-violet rays are certain to reach every corner of the shell. The mould is moved about 30 to each side in relation to normal position opposite the lamp; the seesaw motion is repeated continuously during the whole of the final curing process, which lasts for example 60 seconds. The curing process is hereafter terminated, and the mould motor turns the mould to its original position. The electronic control system will hereafter signal that the process is terminated, and the mould may be removed.

During the lighting phases and during the pouring phase, C0₂ is led in continuously, and the valve 22 is opened at intervals for bleeding in order to ensure that no air, and thus no oxygen, reaches the mould.

After refinishing the individual shells slightly, like for example trimming the edges, they will be ready for the mounting of cover and electronic equipment, the result being a finished all-in-the-ear hearing aid. Any refinish- ing or cleaning of the outside or the inside of the moulded shell has been found unnecessary.

Claims

C L A I M S

1. Method for the curing of fusible materials, which after being filled into a mould are cured by means of radiation, c h a r a c t e r i z e d in that the mould filled with moulding material is placed in a substantially closed vessel, after which the vessel is filled with an air dis¬ placing gas which is heavier than atmospheric air, for example C0₂, and the radiation is carried out, for example with ultra-violet rays.

2. Method according to claim 1, c h a r a c t e r i z e d in that the vessel is filled by leading in gas, for example C0₂, into the bottom area of the vessel, and in that the leading in of gas takes place in such a manner that the vessel is filled from the bottom.

3. Method according to claim 2, c h a r a c t e r i z e d in that the radiation is carried out in such a manner that the top surface of the filled mould is not exposed to radiation.

4. Method according to claim 1, 2 or 3, c h a r a c ¬ t e r i z e d in that the mould is hereafter turned inside the vessel in order that any uncured moulding material drips out, after which the radiation is repeated.

5. Method according to any one of the claims 1-4, c h a r a c t e r i z e d in that during the lighting the mould is turned around its own axis inside the vessel.

6. Apparatus for use in the curing of fusible materials, which after being filled into a mould are cured by means of radiation, c h a r a c t e r i z e d in that it comprises a substantially closed vessel (5) for the mould (6) filled with moulding material (16); that the vessel comprises means (9, 10, 11) for the leading in of an air displacing gas which is heavier than atmospheric air, for example C0_?; and at least one lighting member (13, 14) for the radiation of the moulding material with, for example, ultra-violet rays.

7. Apparatus according to claim 6, c h a r a c t e r ¬ i z e d in that the means (11) for leading in the air dis¬ placing gas are arranged in such a manner that the gas is distributed all over the bottom area of the vessel, so that the vessel is filled up from the bottom.

8. Apparatus according to claim 6 or 7, c h a r a c ¬ t e r i z e d in that the vessel comprises a cover (2) which can be opened, the inside of which consists of a radiation absorbing material (20); and that the lighting member(s) (13, 14) are placed in such a manner that the mould (6) is only exposed from below or from below and from an inclined angle.

9. Apparatus according to claim 6, 7 or 8, c h a r a c ¬ t e r i z e d in that the mould (6) is mounted pivotally in suspension members (7, 19) allowing the mould to be rotated, preferably all the way round, without being re- moved from the vessel.

10. Apparatus according to any one of the claims 6-9, c h a r a c t e r i z e d in that the vessel comprises means (20, 21, 22, 23) for the leading out of air and/or gas from an area in the vessel above the position of the mould, preferably through the cover (2), which may comprise a flow restraining filter (20).

11. Application of the method or the apparatus according to any one of the claims 1-10 for the moulding of thin-walled, individually designed housings (shells) for all-in-the-ear hearing aids on the basis of individual ear prints