GB2280400A - Production of parabolic aerial reflectors - Google Patents

Description

2280400 PRODUCTION OF PARABOLIC AERIAL REFLECTORS The present invention

relates to a method of producing a negative mould for a parabolic aerial reflector, to a mould produced by such method, to a method of producing a -parabolic aerial reflector produced by that method, to a method of producing a compound body for a parabolic reflector, and to a compound body produced by and equipment for use in that method.

In order to achieve a highly smooth, for example optically reflecting surface, in the case of fibre compound components one of the main difficulties is that of producing a mould surface with minimum waviness and roughness. Metal moulds, for example of steel, are generally used as negative moulds. A liquid or pasty parting compound is applied to the mould surface in order to prevent adhesion between the metal surface and the fibre compound. The metal surface itself is polished (see DE 30 00 216 A1). Due to the crystalline structure of metal such as steel, and due to alloying phenomena and fine crack formation at the surface, the achievable depth of roughness and waviness lies far abov the limit values required for aerials in the case of use of fibre compounds with an optically high grade surface.

It is also known from DE 30 00 216 A1 to use a glass (ceramic) as a negative mould material, the surface of which by far surpasses that of metal, for example steel. The surface of such a glass mould is thinly coated uniformly with a detachable, closed separating layer, which is applied by, for example, cathode atomisation and consists of gold or a similar noble material.

The surface of a mould made of glass (ceramic) has a high abrasion resistance, is chemically highly resistant and does not corrode in air. These very good surface properties of glass ceramic moulds are, however, counterbalanced by their difficult, time consuming and cost-intensive treatment due to the high abrasion resistance of this material.

Because of the easy workability of aluminium by comparison with steel and 91 ass ceramic, moulds of this material are occasionally used for prototypes and for experimental purposes.

Basically, however, aluminium is not suitable a a material for the production of highly accurate moulds for parabolic aerials, as a] uminium i S so sensitive to scratching that scratching is noticeable even on application of the separating means and during is subsequent polishing. In addition, an aluminium surface polished to high gloss corrodes in the course of time and thus appears to be matt and becomes rougher. Furthermore, the ability of aluminium to resist chemical attack is too low. Aluminium is therefore frequently anodised to increase abrasion resistance and the ability to resist chemical attack.

Moreover, an aluminium mould can deform in an uncontrolled manner if milled at one side. Consequently, in the case of aluminium it is merely its good working properties that cause it to be used for prototypes or for one-off production when a lower standard of accuracy may be acceptable.

1 1 Also available is an organic mould material on a polyurethane (PU) base, which is distributed by the company Ciba Geigy under the trade mark CIBATOOL. This material can be worked very well and can be processed with high feed and high cutting reduction. Furthermore, with a density of 1.1 grams per cubic centimetre, it is particularly light and therefore can be conveniently handled.

However, it is a disadvantage of the material CIBATOOL (trade mark) that it has a microporous and non-polishable surface property 1 and a thermal co-efficient of expansion of 30. 10-6 millimetres per degree K, whereas glass ceramic and steel have thermal co-efficients of expansion of 5.10- 6 and 12.10-6 millimetres per degree K. Because of hygroscopic behaviour, moulds of CIBATOOL (trade mark) material which are to be accurately manufactured should, as far as possible, be processed and stored in air-conditioned rooms.

However, even with accurately produced moulds, only an average result is usually achieved, since - due to shrinkage of laminating resin during setting - a lattice-like structure of the web laminate always appears at the surface of compound parts. For this reason, so-called coupling layers, which consist of fleece impregnated by synthetic resin or of glass and carbon fibre sections, which are mixed with thixotropic, thermosetting resin mass, are applied between the gel coat (fine layer) and the web laminate. Since the paste must be brushed onto the gel coat, this material is not suitable for aerial reflectors intended to have a high degree of accuracy; the non-uniform application of the paste and the air inclusions would later show through the metallised surface polished to high gloss and result in a disrupted image.

In the case of use of fleece enriched by resin, a more uniform application results in case of use of fibre cuttings paste; a more disrupted image results due to the non-homogeneous fibre cuttings. Moreover, due to the application of such coupling layers, the weight of, for example, an aerial reflector would be increased unnecessarily.

Epoxy and polyester resins which, due to capillary effect, completely fill out a preset minimum gap between a compound component and a mould are used in a method for the formation of a coating with a surface of high quality and accuracy in dimension and shape (cf DE 36 14 191 C2). In addition, a foil of organic substances and metal or of a compound of metal andorganic substances can be laid against the mould by vacuum effect and/or with the aid of a mechanical device. The gap between the foil and the compound component is filled by the highly fluid synthetic material in capillary manner, whereby the parts are connected together. After removal from the mould, the foil surface reproduces the mould very well, which means that a coating of the desired outline is obtained in one operating step and the previously tempered compound component is corrected at the same time. However, a reflecting surface cannot be achieved at the fibre compound parts, because dust grains embedded between the mould and the foil show up as small craters on the surface of the compound parts.

Since the resin matrix has a different moisture absorption as well as a different shrinkage behaviour by comparison with the reinforcing fibres, a grating-like structure of the web laminate used as underlay results, so that this structure appears at the surface of the compound parts under normal climatic conditions a few days after the removal of the parabolic aerial from the mould. It is not possible to prevent, by the afore-described coating, the appearance of the grating-like structure at the surface, even if in less pronounced form.

A method for production of reflectors for directional radio aerials and the like in supporting core mode of construction, in which a parting compound and thereupon a passivation layer and subsequently an electrically conductive metal layer are applied onto a master body, which corresponds to the shape of the reflector to be produced, is disclosed in DD-PS 116 353.

A manufacturing method for microwave aerials is known from DE 37 14 882 A2, in which a coating of a protective pigmenting resin is applied to a casting mould, and on that a metallising layer by spraying of very small particles of molten metal. One or more re inforcing layers, which are impregnated with a thermosetting resin, are then applied to the metallising layer.

It is furthermore known to produce a basic mould of brick and concrete, the surface of which is strengthened by a glass-fibre synthetic material layer. The last profile-determining layer consists of a mixture of synthetic epoxy resin and slate powder (see RICHARDS, C. J.: Parabolantennen in Kunstharz-Glasfaserkonstruktion in Rundfunktechnische Mitteilungen, Volume 10, 1966, Issue 5, pages 262 to 267). Finally, it is known from US-PS 3 150 030 to initially coat a mould with a resin-impregnated glass-fibre fabric.

There remains a need for a method, which can be performed with relatively low cost, for the production of a negative mould for a parabolic aerial reflector and a method for the production of such a reflector, the surface of which has a property meeting optical requirements, as well as a method and equipment for the production of a compound body for a reflector.

According to a first aspect of the present invention there is provided a method of producing a negative mould for a parabolic aerial reflector, comprising the steps of pouring a multicomponent synthetic material in liquid state onto a horizontal and laterally bounded sheet of flexible material to form a layer thereon, securing the layer, when the material thereof has attained a pliable gel state, under pressure to a homogeneous and isotropic mould carrier processed to define an end contour for such a reflector, and processing the layer to form a polished mould surface having a quality meeting a predetermined optical requirement.

By means of such a method, a surface meeting requirement in the visible and higher wave region may be able to be achieved at a negative mould for a parabolic aerial reflector, and consequently at the reflector itself, without the time-consuming and cost-intensive constraints of the previously used methods.

Preferably, the mould carrier is processed by numericallycontrolled machining and the layer by numerically-controlled machining and subsequent surface polishing. The layer can be secured to the mould carrier by gluing, and the pressure provided by clamping means.

1 For preference, the mould carrier comprises one of foamed synthetic material, metal, foamed material, ceramic material and casting resin, while the material of the Tayer can be thermosetting or thermoplastic synthetic material.

The method can comprise the further step of applying a firmly adhering abrasion-resistant coating to the polished mould surface; such as by evaporation or sputtering.

According to a second aspect of the invention there is provided a method of producing a parabolic aerial reflector with use of a mould produced according to the first aspect of the invention, comprising the steps of applying a poorly adhering electrically conductive metal layer to the mould surface of such mould by chemical metallisation, galvanically strengthening the metal layer, applying a layer of homogeneous, stiff and dimensionally stable material to the metal layer by way of an adhesive agent, disposing a compound body over the material layer, introducing an elastomer under pressure into a space between the material layer and the compound body thereby to firmly interconnect the layer and body, and removing the mould through detaching the metal layer from the mould surface so that the metal layer remains attached to the compound body and defines a reflector surface corresponding to the contour of the mould surface.

Preferably, the metal layer is etched.prior to application of the material layer.

The step -of introducing the elastomer can be carried out by way of a bore disposed in the compound body centrally thereof.

For preference, the compound body is prepared sandwich or solid laminate body, while the material of the material layer comprises a thermosetting synthetic material and the elastomer comprises a polyadded silicone or polyurethane.

The method may comprise the preliminary step of applying a gel coat to the mould surface, applying a low shrinkage, highly fluid laminating resin to the gel coat after setting thereof so as to form a coupling layer, spraying particulate material at low pressure onto the resin of the coupling layer and connecting the coupling layer with the compound body. The resin can be applied to the gel coat by rolling, and the particulate material can comprise micropearls or sand.

m According to a third aspect of the invention there is provided a method of press-moulding a compound body for a parabolic aerial reflector with use of a mould produced according to the first aspect of the invention, comprising the steps of tensioning a sheet of flexible material over a plate having an opening corresponding in outline shape to but larger in size than the rim outline of the mould surface of such mould, applying a laminating resin and at least one fibre layer to the sheet, causing the plate together with the sheet to be placed over the mould surface of the mould, urging the plate towards a base member supporting the mould so that the sheet portion extending across the opening is pressed against the mould surface, removing excess resin and allowing the resin to set.

Expediently, the step of removing excess resin comprises applying lubricant to the sheet and moving a wiper over the sheet outwardly from the centre thereof.

1 According to a fourth aspect of the invention there is provided pressmoulding equipment adapted for use in carrying out the method of the third aspect of the invention, comprising a base member for mounting of such mould thereon, a plate having an opening corresponding in outline shape to but larger in size than the rim outline of the mould surface of the mould, and clamping means for urging the plate towards the base member so that, in use, a portion of a sheet of flexible material tensioned over the plate and coated with a laminating resin and at least one fibre layer is pressed against the mould surface.

The base member can be provided with means for securing the mould to the member centrally thereof from the underside of the member.

According to a fifth aspect of the invention there is provided press-moulding equipment for use in press-moulding a compound body for a parabolic aerial reflector by way of the mould produced according to the first aspect of the invention, comprising a base member for mounting of such mould thereon, a plate having an opening smaller in size than the rim outline of the mould surface of the mould and provided with a counterprofile which forms a fixed component of the plate and corresponds to the contour of the mould surface, and three-dimensional spacer webs which are disposed between the counterprofile and the mould and are pressable against the mould by clamping means so that upper and lower covering layers at the rim of a three-dimensional ly constructed spacer web frame are firmly connected together whilst the frame remains in the region of the opening, assumes the shape of the mould surface and maintains the shape after setting of the laminating resin.

Methods exemplifying and moulds, equipment and reflectors embodying the invention will now be more particularly described with reference to the accompanying drawings in which:

Fig. 1 is a schematic sectional view of a negative mould produced by a method exemplifying the invention; is a sectional view, to an enlarged scale, of part of the negative mould prior to final processing; is a schematic plan view of equipment for press moulding a parabolic aerial reflector with use of the mould; is a schematic sectional view of the equipment along the ine IV-IV in Fig. 4; and is a sectional view to enlarged scale, of part of a parabolic aerial reflector produced with use of the mould.

Referring now to the drawings, there is shown in Fig. 1 a negative mould 2a comprising a mould carrier 2 which has been brought to a final outline and consists of a dimensionally stable material, such as foamed synthetic material, for example CIBATOOL (trade mark), foamed metal, metal such as steel, aluminium and the like, or ceramic material. The mould carrier 2 is coated with al synthetic or plastics material layer 1 of thermosetting or', thermoplastic material. As will be later described in detail, a surface meeting requirements in the visible and higher wave range is Fig. 2 Fig. 3 Fig. 4 Fig. 5 to be achieved for the applied layer 1 by an intensive finishing treatment, in particular by a concluding CNC-controlled polishing.

In addition, a very thin and abrasion-resistant layer 3 can be applied to the layer 1 by, for example, a sputtering process or by evaporation.

Fig. 2 shows a part of a paraboloid negative mould 2a which comprises the mould carrier 2 milled to final outline and of the same material as mentioned above in conjunction with Fig. 1. The layer 1, which is applied by way of a carrier foil 4, consists of a hardened thermosetting multicomponent resin secured to the mould carrier 2 by means of an adhesive resin 5.

In Figs. 3 and 4, simple press equipment for the press moulding of a parabolic aerial reflector in sandwich mode of construction is illustrated in, respectively, plan view and sectional view along the line IV-IV in Fig. 3. For simplification, the parabolic aerial reflector is not illustrated in these two figures. The equipment comprises an upper plate 113, for example an MN (medium density fibreboard) fibre plate, which has in its central region a cut-out of elliptical shape, as can be seen from Fig. 3. A transparent tensioning foil 50 is glued to the plate 113 and extends over the cut-out therein. The equipment further comprises a rigid inflexible base plate 132, which can be made of multiveneer plates or the like and on which a support plate 126, preferably made of MW fibre plate material, is mounted. Provided at the support plate 126 is a fastening and support plate 125, by which the produced negative mould 2a is attached and thereby fixed relative to the base plate 132.

In the case of small or very small scale mass production, a negative mould 2a of the kind shown in Fig. 1 is produced in the following manner. Threaded inserts 1251 (see Fig. 4), the flanges of which serve as the bearing surface 125 for fastening elements during use of the mould in the afore-described press-moulding equipment, are glued into the centre of a mould carrier blank, for example of CIBATOOL (trade mark). The blank is CNC-milled with a certain excess dimension into a shape which is elliptical in plan view and receives a final parabolic contour by MCshape-milling.

For flow limitation of a synthetic material mass (to form the layer 1) to be applied in liquid state, for example material with an epoxy resin base, a flexible round rubber hose of about 1.5 millimetres diameter is glued, according to a planned elliptical aerial reflector shape, onto the foil 4, which is horizontally oriented and glued under tension to the plate 113.

After the gel point of the epoxy resin synthetic material mass applied in liquid state has been exceeded, the plate 113 together with the coated foil 4 is turned over and into an arrangement similar to that shown in Fig. 4. The epoxy resin layer 1 is then glued to the mould carrier 2, which has been milled to shape, by means of the adhesive resin 5.

In order to impart to the resulting raw negative mould 2a a surface property meeting requirements in the visible and higher wave range, the compound layer of foil 4 and synthetic material 1 is CNC- fine-milled after setting of the epoxy resin of the layer, whereby the foil 4 and a part of the thickness of the layer 1 are removed. In this case, about 300 micrometres can be milled away from a layer t 1 having a thickness of, for example, 600 to 1500 micrometres.

Subsequently, the layer 1 is treated mechanically, inclusive of polishing, to achieve a mould surface 10 (indicated by dashed lines in Fig. 2) which meets the stated requirements. Instead of a thermosetting resin, a thermoplastic resin can be used. if required, a hard layer 3 (Fig. 1) can be evaporated onto the mould surface 10 of the negative mould 2a.

Any excess size of the negative mould 2a is now milled away.

As a final step, a marking is scratched into the mould at the rim of the major elliptical axis by means of a CNC-milling machine. This serves for the later adjustment of an aerial reflector at an aerial support device to which it is later fastened. The negative mould or matrix 2a is thus finished.

A prerequisite for the aforedescribed example of producing the compound of foil 4 and synthetic material layer 1 is bubble-free epoxy resin hardness mixture. The epoxy resin used can contain a filler substance, but must remain liquid.

The setting behaviour of epoxy resins is exploited in the described method. The course of the degree of hardening of epoxy resin is practically linear to 98%. The gel point is passed through at a hardening degree of about 55%; the epoxy resin is no longer liquid, but flexible for a short time before becoming completely hard. This short term state can be utilised for coating mould carriers which are not too complicated, since the mass can be processed like a thick, tough sheet for a short time.

For the production of a parabolic aerial reflector,an electrically conductive weakly adhering metal layer 46 (Fig. 5) is first applied onto the mould surface 10 - defined by the synthetic materi a] 1 ayer 1 - of the negative mould 2a, preferably by metallisation through chemical gilding or copper-plating.

Practically any desired layer thickness with at the same time high quality, can be achieved by a subsequent galvanic reinforcement such as electroplating.

A chemical copper-plating of the surface, polished to a gloss,.

of the thermosetting or thermoplastic resin layer of the negative mould 2a will adhere with sufficient strength to withstand the next operating steps without damage, but can be later removed without problems, so that a separating agent can be dispensed with. The depth of roughness, or peak-to-valley height, of the metal layer in this case corresponds to that of the negative mould. Moreover, the metal layer corresponds exactly to the required parabolic structure of the negative mould.

Subsequently, a low-shrinkage epoxy or polyester resin 48, which sets well at room temperature, is applied by, for example, being rolled or sprayed on repeatedly. A prerequisite for a selfsupporting homogeneous synthetic material body that is not reinforced is, however, a highest possible stiffness and dimensional stability as well as a low water absorption and cupping of the synthetic material used.

1 Appropriate known operating steps are performed to effect construction and surface preparation of a compound body 40 to 44 to complete the reflector. An opening in the form of a bore of a diameter of about 3 millimetres is introduced at the highest point and in the centre of the body, which has been previously tempered and has a sandwich or solid laminate mode of construction.

The thus prepared compound body 40 to 44 is now positioned at a preset spacing with respect to the negative mould 2a, provided with the metal layer 46 and the epoxy or polyester resin layer 48, by means of adjustable retain'lng elements of a press device (not illustrated). A connection, which is coupled by way of a hose with a pressure container, is provided in the bore at the rear side of the compound body. Silicone wetted by polyaddition is now carefully admixed and evacuated in the pressure container.

After the ventilation, silicone 47 is filled into the intermediate space between the compound body 40 to 44 and the synthetic resin layer.48 applied by a carefully effected air supply.

In this case, the vertically adjustable retaining elements of the press device prevent the compound body from 'being urged away upwardly.

The feed is switched off as soon as the intermediate space is completely filled by the silicone 47, which can be ascertained by silicone oozing out at the outer rim of the compound body. The retaining elements of the press device are then removed so that the compound body lies completely without tension on the negative mould 2a. Lateral slipping of the com pound body from the mould can be prevented by appropriate locating means.

By comparison with other rubber-like materials, for example polyurethane, the silicone used here has more suitable characteristics. Moreover, silicone can be processed very easily. The breaking elongation of silicone lies at about 60% and its viscosity amounts to about 15,000 centipoises. Moreover, by way of applied adhesion-promoting agents, separation of the silicone 47 from the adjoining areas can be prevented.

The parabolic surface of a reflector is corrected in the afore-described manner and has a roughness which completely corresponds with that of a polished glass ceramic mould, i.e. the surface of the reflector produced in the afore-described manner has a property meeting the requirements in the visible or higher wave range. The thickness, which is-dependent on the size of a parabolic reflector, of the silicone layer absorbs any microsurface change of the compound parts, such as the grating-like structure of the surface of such a part, and does not pass it on to the surface of the finished reflector. Thus, the surface property, which meets the optical requirements, of the negative mould 2a is transmitted in its entirety to the finished reflector.

In the following, a method of producing a compound body for a parabolic aerial reflector by means of the simple press equipment illustrated in Figs. 3 and 4, is described. In this method, light high-grade laminates are achieved, which is desirable for,:o-r example, the production of accurate reflectors from carbon fibre, i since the fibre volume reaches nearly 70% by volume. The pressing takes place by means of the foil 50, which adapts itself to the parabolic outline of a negative mould 2a. The press equipment in Figs. 3 and 4 is usably only in connection with negative moulds with a convex surface.

A coarsely cut, multi-layer carbon fibre web is laid onto the surface of the foil 50 and impregnated with laminating resin.

Subsequently, the base plate 132 with the negative mould 2a is fastened thereon is turned over and positioned on the impregnated carbon fibre web. The upper plate 113 is retained lightly at the base plate 132 by clamping elements 114, for example screws and wing nuts.

After then turning over the unit of the base plate 132, upper plate 113 and carbon fibre web applied over the negative mould 2a, the cla mping elements 114 are tightened until the pinch-edge or rim of the mould surface shows through-the foil 50. Excess resin is pressed out by way of a flexible hard rubber wiper (not shown) which slides outwardly from the centre across the transparent foil. In order to avoid excessive stressing.of the foil 5, it is sprayed with a silicone lubricant. This operation is continued until no more resin comes out. After setting of the resin, the upper plate 113 is carefully removed.

Next, PMI-foam substances are shaped-glued. For this purpose, a highly liquid two-component adhesive substance is applied at one side on multilayer, large precut PMI-parts. The individual PMIparts are laid onto the foil 50 at the upper plate 113 and shape- pressed analogously to the laminate layers by tightening of the clamping elements. After setting of the adhesive substance and removal of the upper plate 113, the negative mould 2a is taken off the base plate 132.

4 In the case of use of three-dimensional reinforcing materials in place of foam substances, three-dimensional fibre materials are applied to excess size in a single layer or several layers onto a set or not set carbon fibre web or directly onto a set gel-coat fine 1 ayer 44. Fibres in the web laminate after the impregnation with laminating resin automatically orient themselves perpendicularly to the surface and form a three-dimensional frame.

Subsequently, a compression is effected at the rim of the negative mould 2a. For this purpose, the negative mould 2a is fastened to the upper side of the rigid base plate 132 centrally from the underside thereof and the upper plate arranged thereover has a cut-out, which is small with regard to the size of the negative mould 2a, and a counterprofile which corresponds to the surface outline of the mould 2a (this is not illustrated in detail in Figs. 3 and 4).

The three-dimensional spacer webs, which are provided between the counterprofile and the mould 2a, are pressed by means of the clamping means 114 against the mould. Thereby, the upper and the lower cover layer as well as the vertically extending fibre strands are compressed at the rim of the three-dimensional web frame and firmly connected ogether. Thethree-dimensional web remains maintained loosely in the region of the cut-out, assumes the shape of the negative mould and retains it during the setting of the laminating resin.

During the trimming of the protruding rim parts of the compound of carbon fibre laminate or PMI-foam substances or three dimensional fibre webs, the rim is subsequently so worked down that the mould 2a is not damaged. In order that the laminate at the rear side can be glued firmly with the front laminate of the sandwich construction, a trough is formed mechanically at the rim of the foam substance and subsequently filled by an epoxy filler mass. The open hollow spaces of the PMI-foam substance surface should be sealed in the same operating step in order to avoid that air bubbles from the foam substance surface penetrate into the laminate.

After setting, the rear laminate can be applied in the same manner as described previously for the front laminate and the excess resin is removed with the aid of the hard rubber wiper. After complete setting of the compound at room temperature or in a heated cabinet, the mould 2a is detached from the base plate 13 2 and, as described previously, the protruding rim of the rear laminate is removed. The compound body is then removed from the mould. The compound body obtained in this manner is produced relatively easily and rapidly so that a good cost/output ratio is achieved for small scale or very small scale production.

When the weight of the negative mould does not play a large part, as for example in the case of small moulds, aluminium steel, foam metal or ceramic material can be used in place of the organic material CIBATOOL (trade mark). When synthetic materials of greater resistance to heat are used as the synthetic material coating, the negative mould can also be used for preimpregnated systems setting at 18WC. The initially described disadvantage is then prevented by the applied synthetic material coating.

A part of a parabolic aerial reflector, which is produced in sandwich mode of construction, with a compound body is shown in Fig.

5. Such a compound body comprises a rear laminate 40 of fibre compound materials, a core 41, for example of polymethacrylimide foam material or threedimensional fibre webs, and a front laminate 42 of fibre compound materials. In order to prevent the grating like structure of the fibre laminate showing through at its surface, a coupling layer 43 is applied to reduce the waviness or roughness of the surface and to create the prerequisites for the use of aerials in the millimetre wave band.

For the formation of the coupling layer 43, a gel-coat layer 44 is applied onto the surface of the mould 2a and, after setting of this layer, a low-shrinkage, highly fluid laminating resin is applied by rolling. After brief ventilati.or!, micropearls of glass are sprayed on at a low pressure of about 0.5 bar by way of a sand blasting gun. Intermediate spaces are completely 'filled out by resin due to capillary forces. After setting, a uniform surface similar to sandpaper arises with a thickness of about 200 micrometres. The afore-described operation can be repeated as often as desired, in which case a thickness of about 600 micrometres can be achieved on the second application. In order to achieve a higher compression of the micropearls of glass, the treated substrate can be set into a micro-oscillation, for example with the aid of an electrically operated shaking table or the like. The coupling layer 1 43 is connected with the front laminate 42 of the compound body.

In the case of the parabolic aerial in compound mode of construction as illustrated in Fig. 5, a layer 47, which is created in the aforedescribed manner, of a polyadded silicone or of another appropriate material with a breaking elongation of about 60% is provided between the epoxy or polyester layer 44 and the thermosetting layer 48. The galvanically reinforced metal layer 46 is connected with the thermosetting layer 48 by way of the adhesionpromoting agent 45.

The surface property of the parabolic aerial reflector described by reference to Fig. 5 is suitable for use in the infrared or imaging waveband.

Claims (28)

1. A method of producing a negative mould for a parabolic aerial reflector, comprising the steps of pouring a multicomponent synthetic material in liquid tate onto a horizontal and laterally bounded sheet of flexible material to form a layer thereon, securing the layer, when the material thereof has attained a pliable gel state, under pressure to a homogeneous and isotropic mould carrier processed to define an end contour for such a reflector, and processing the layer to form a polished mould surface having a quality meeting a predetermined optical requirement.

2. A method as claimed in claim 1, wherein the mould carrier is processed by nuffierically-controlled machining.

3. A method as claimed in claim 1 or claim 2, wherein the layer is processed by numerically-controlled machining and subsequent surface polishing.

4. A method as claimed in any one of the preceding claims, wherein the layer is secured to the mould carrier by gluing.

5. A method as claimed in any one of the preceding claims, wherein the pressure is provided by clamping mean-,.

6. A method as claimed in any one of the preceding claims, wherein the mould carrier comprises one of foamed synthetic material, metal, foamed metal, ceramic material and casting resin.

1 i

7. A method as claimed in any one of the preceding claims, wherein the material of the layer is thermosetting or thermoplastic synthetic material.

8. A method as claimed in any one of the preceding claims, comprising the step of applying a firmly adhering abr as ion -resistant coating to the polished mould surface.

9. A method as claimed in claim 8, wherein the coating is applied by evaporation or sputtering.

10. A method as cl aimed in cl aim 1 and substantially as hereinbefore described with reference to the accompanying-drawings.

11. A mould produced by a method as claimed in any one of the preceding claims.

12. A method of producing a parabolic aerial reflector with use of a mould as claimed in claim 11, comprising the steps of applying a poorly adhering electrically conductive metal layer to the mould surface of such mould by chemical metallisation, galvanically strengthening the metal layer, applying a layer of a homogeneous, stiff and dimensionally stable material to the metal layer by way of an adhesive agent, disposing a compound body over the material layer, introducing an elastomer under pressure into a space between the material layer and the compound body thereby to firmly interconnect the layer and body, and removing the mould through detaching the metal layer from the mould surface so that the metal layer remains attached to the compound body and defines a reflector surface corresponding to the contour of the mould surface.

13. A method as claimed in claim 12, comprising the steps of etching the metal layer prior to application of the material layer.

14. A method as claimed in claim 12 or claim 13, wherein the step of introducing the elastomer is carried out by way of a bore disposed in the compound body centrally thereof.

15. A method as claimed in any one of claims 12 to 14, wherein the compound body is a prepared sandwich or solid laminate body.

16. A method as claimed in any one of claims 12 to 15, wherein the material of the material layer comprises a thermosetting synthetic material.

17. A method as claimed in any one of claims 12 to 16, wherein the elastomer comprises a polyadded silicone or polyurethane.

18. A method as claimed in any one of claims 12 to 17, comprising the preliminary step of applying a gel coat to the mould surface, applying a low-shrinkage, highly fluid laminating resin to the gel coat after setting thereof so as to form a coupling layer, spraying particulate material at low pressure onto the resin of the coupling layer and connecting the coupling layer with the compound body.

-.25 -

19. A method as claimed in claim 18, wherein the resin is applied 1 to the gel coat by rolling.

20. A method as claimed in claim 18 or claim 12, wherein the particulate material comprises micropearls or sand.

21. A parabolic aerial reflector produced by a method as claimed in any one of claims 12 to 20.

22. A method of press-moulding a compound body for a parabolic aerial reflector with use of a mould as claimed in claim 11, comprising the steps of tensioning a sheet of flexible material over a plate having an opening corresponding in outline shape to but larger in size than the rim outline of the mould surface of such mould, applying a laminating resin and at least one fibre layer to the sheet, causing the plate together with the sheet to be placed over the mould surface of the mould,.urging the plate towards a base member supporting the mould so that the sheet por tion extending across the opening is pressed against the mould surface, removing excess resin and allowing the resin to set.

23. A method as claimed in claim 22, wherein the step of removing excess resin comprises applying lubricant to the sheet and moving a wiper over the sheet outwardly from the centre thereof.

24. A compound body produced by a method as claimed in claim 22 or claim 23.

25. Press-moulding equipment adapted for use in carrying out the method claimed in claim 22, comprising a base member for mounting of such mould thereon, a plate having an opening corresponding in outline shape to but larger in size than the rim outline of the mould surface of the mould, and clamping means for urging the plate towards the base member so that, in use, a portion of a sheet of flexible material tensioned over the plate and coated with a laminating resin and at least one fibre layer is pressed against the mould surface.

26. Equipment as claimed in claim 25, wherein the base member is provided with means for securing the mould to the member centrally thereof from the underside of the member.

27. Equipment substanti a] ly as hereinbefore described with reference to Figs. 3 and 4 of the accompanying drawings.

28. Press-moulding equipment for use' in press-moulding a compound body for a parabolic aerial reflector by way of the mould claimed in claim 11, comprising a base member for mounting of such mould thereon, a plate having an opening smaller in size than the rim outline of the mould surface of the mould and provided with a counterprofile which forms a fixed component of the plate and corresponds to the contour of the mould surface, and three dimensional spacer webs which are disposed between the counterprofile and the mould and are pressable against the mould by clamping means so that upper and lower covering layers at the rim of i a three-dimensionally constructed spacer web frame are firmly connected together whilst the frame remains in the region of the opening, assumes the shape of the mould surface and maintains the shape after setting of the laminating resin.