FORMING MOULD OR ARTICLE

Abstract: A relatively large reflector (10) or curved mould is constructed from rib members (11, 12) interleaved with each other so as to form a multiple cell or egg-box like structure. The rib members are pre-shaped on one edge (14) to conform approximately to the required curvature and a pre-cut panel is fitted to each cell to form a backing for a curved surface comprising a coating of surface material extending over the panels and the pre-shaped edges of the rib members.

Description: FORMING MOULD OR ARTICLE. This invention relates to a relatively large assembly for use either as a mould in forming an article such as a reflector antenna having a curved main surface which has to be formed to a high degree of accuracy. Objects of the invention are to provide an assembly of this kind having good mechanical stiffness to combat gravity and thermal effects, a high accuracy profile, low creep distortion with time and flexibility in choice of the generating profile. A further object of the invent¬ ion is to provide an improved method of constructing such an assembly. One example of such an assembly would be a reflector antenna of parabolic shape such as might be used in a compact test range for radar equipment. According to one feature of the invention the assembly comprises, in combination, a plurality of rib members interleaved with each other to form a multiple cell or egg-box like structure, the rib members being pre-shaped on one edge so that when assembled the edges approximate lines on the curved surface, a panel member secured to each cell to form a backing for surface material, and a coating of surface material extending over the face of the structure formed by the rib members and the panel members. - 2 - Preferably the surface material is a loaded resin and preferably the curved surface is formed by a blade member shaped to the required generating curve and used as a strickle template. Further features of the invention will appear from the following description with reference to the accompanying drawing where Figs. 1 & 2 show a side and front elevation respectively of a parabolic reflector antenna according to the invention. Fig. 3 shows in more detail the egg-box like structure. Fig. 4 shows a section through the structure and Fig. 5 the preferred method of assembly. Refering now to Figs 1, 2, & 3 the reflector, generally indicated at 10, is constructed from a numbe of pre-rcut horizontal and vertical rib members 11 & 12 with a plane surface 13 as the rear surface and a pro¬ filed form approximating to the desired parabolic shap on the front surface 14. The rib members are formed from fibre glass skinned honeycomb sandwich material a the members are bonded together to form a relatively lightweight rigid structure. The rear face of the structure is inclined to the plane containing the foca axis of the parabolic, the angle approximating to the mean slope of a generating curve. As shown-in Fig. 5, assembly of the structure is carried out in the horizontal attitude on a wedge shaped steel frame 15, the rib members 11 '& 12 being structurally connected to the frame at selected points. The number and position of these points are selected such that deviation in profile for a reflector manufactured in the horizontal attitude is still acceptable when the reflector is mounted in the vertical attitude. The space frame 15 also provides a number of surfaces which act as location for the assembly process, and the widge shape of the frame permits the plane rear surface 16 to lie in a horizontal plane when the focal axis of the structure lies vertical• The front openings of the individual cells are each filled with a flat fibre glass skinned honeycomb panel 17, each panel being individually cut to fit thfe specific opening. On assembly the panels are set tangent to the required surface and bonded to the rib members 11 & 12. When so set the projected shape of the panels relative to the axis of the structure is square. On completion of the assembly, all exposed honeycomb material is filled in and the joints at the front surface are fibre glassed over. The whole surface is then screeded with a loaded resin 18, a blade 19, shaped to the required generating curve and rotatable about a pedestal 20, being used as a strickle template. The loaded resin is - 4 - then, if necessary, surface ground to produce a surface with the necessary finish and profile accuracy, and finally the surface is sprayed with silver loaded paint in order to produce a surface reflector to microwave energy. Erection of the reflector may be achieved by securing trunnions (not shown) on the support frame 15 to corresponding trunnions on a steel pedestal frame and then adding steel ties which hold the upper end of the support frame relative to the pedestal frame. All lifting, transportation, etc., is' preferably effected by interfacing the support frame.

Claims: CLAIMS CLAIM 1. An assembly for use either as a mould in forming an article having a large curved main surface or an article itself, characterised by the combination of a plurality of rib members interleaved with ' each other to form a multiple cell or egg-box like structure, the rib members being pre-shaped on one edge so that when assembled the edges approximate lines on the curved main surface, a panel member secured to each cell to form a backing for surface material, and a coating of surface material extending over the face of the structure formed by the rib members and the panel members. CLAIM 2. An assembly according to claim 1 wherein the rib members and the panel members are formed from fibre glass skinned honeycomb material, the rib-members and the panel members being bonded together. CLAIM 3. An assembly according to claim 1 or claim 2 wherein the structure is attached to a supporting frame, the curved main surface of the structure being offset parabolic shape and the supporting frame being provided with a supporting surface which when disposed horizon¬ tally allows the surface to be machined to the offset parabolic shape by rotating a template of appropriate form round a vertical axis. CLAIM 4. An assembly according to any preceeding claim wherein the surface material is a loaded resin. CLAIM 5. An assembly according to claim 4 wherein the surface material is coated with silver loaded paint. O

Inventors: GARDNER N, SEATON P, TAYLOR M, THOMAS G
Applicants: BRITISH AEROSPACE, GARDNER N, SEATON P, TAYLOR M, THOMAS G
Application year: 1979
Main classification: H01Q15
IPC codes: B32B3, H01Q15