Patent GB-1402906-A (GB)
Title: Reflectors
IPC: F21S8/00
Filed: 1972-09-25
Abstract: 1402906 Electro-forming AMERACE ESNA CORP 25 Sept 1972 [30 Sept 1971] 44254/72 Heading C7B [Also in Divisions F4 and G2] A reflector 190 intended for use in a marine lantern 100 may be made by electro-forming and comprises a curved, substantially rigid, preferably part-spherical, transparent body having a smooth front surface 191 and a plurality of cube-corner reflector elements 211, Figs. 14 and 15, covering the rear surface, the cube diagonal or "cube axis" extending from each cube corner being normal to the imaginary surface defined by the corners. Light emitted by the source 135 and impinging on the reflector is therefore subjected to total internal reflection and is redirected back to the source. The cube corners 211 are arranged in juxtaposed groups of four to form units 210, Fig. 14, each corner 211a-211d being square in plan and having three mutually perpendicular faces 215 inclined from an apex 216. The reflector is constructed from two identical sections 205a, 205b, Fig. 10, moulded in acrylic resin and welded together along end edges 206a, 206b, the outer end edges 194, 195 of the sections being disposed in parallel planes which do not pass through the centre of curvature of the surface 191 and the side edges 192, 193 lying in planes which do pass through the centre of curvature and are not perpendicular to the aforesaid parallel planes so that the reflector is slightly skewed. The angular extent of the reflector between the side edges is about 60 degrees so that two or more reflectors may be arranged side by side depending on the required angular extent of the beam to be emitted by the lantern, the non-vertical disposition of the line of abutment between any two reflectors preventing the formation of a region of decreased light intensity in the beam. A method of making the reflector commences with the step of forming an array of abutting pins 258, Fig. 28, arranged in bundles of four, each pin having a cube-corner projection 259 at its end and each bundle 257 corresponding in shape to the unit 210 shown in Fig. 14. Nickel or another metal is deposited or electro-formed on to the array to form a self-supporting layer and the layer is then prised off the pins and placed in a die 250, Fig. 33, where it becomes the part 253, which is held by the side walls 251 and a bottom wall 252 of the die. The exposed surface of the part 253 is plated with a separating layer of chromium, and nickel or another metal is then deposited or electro-formed on the chromium to form a member 270 about.007 inches thick. The member is given an epoxy backing 275 and then prised off the die, Fig. 35. A block in the form of a rectangular paralelepiped (240), Fig. 23 (not shown), is constructed by bolting together twelve segments 241, Fig. 24, of progressively increasing width and a part-spherical surface 244 is formed on the top of the block, the width of each segment being such that the lateral arc lengths of the spherical zones 246 are equal. Pieces of tape 277 are then placed on each zone 246 and cut precisely to size, after which they are transferred to the surface 272 of the metal member 270, Fig. 35, which is then sprayed with paint. The tapes are removed and the member is cut along the boundaries between the painted and unpainted areas to form pieces 279, Fig. 38, which, after separation from the epoxy backing, are bent on to the zones 246 of the corresponding segments 241 and secured thereto by adhesive. The pieces, being flat, cannot be made to conform exactly to the spherical surface so they are bent in the longitudinal direction only. The segments are then reassembled and the exposed surface is covered with a separating layer of chromium and plated with nickel or another metal to form a member (290), Fig. 41 (not shown), which, when separated from the segments, forms one half of a mould. The other half of the mould has a smooth part-spherical surface, the mould being employed to produce reflector halves such as 205a, 205b, Fig. 10, by injection moulding acrylic resin. In a modified method, Figs. 45-50 (not shown), the die 250 containing the part 253 has acrylic resin moulded on to the surface to form a member (310) about.080 inches thick. The acrylic member is then ground down from the rear, smooth, surface until it is thin enough to be pliable and is cut into strips using the pieces of tape 277, the strips being secured to the segments 241. The exposed surfaces of the strips are metallized, e.g. by vacuum deposition, to render them conductive and are then plated with nickel as in the previous method to form one half of the mould. The rear surface of the reflector made by the methods described is divided into a plurality of zones 207a, Fig. 10, separated by boundary lines 208a disposed in parallel planes which do not pass through the centre of curvature of the front surface 191. These zones occur because the pieces such as 279, Fig. 38, which are secured to the segments 241 are not exactly spherical but are bent in the longitudinal direction only. A cylindrical reflector may be made by a method, Figs. 51-54 (not shown), in which nickel or another metal is electro-formed on to the pins 258, Fig. 28, the nickel layer is backed with epoxy resin to retain its shape whilst it is prised off the pins, and the metal member (345) thus formed is applied to a cylinder (340) with its front surface (347) containing the cube corner cavities in contact with the cylinder. Additional nickel is plated on to the back of the member to form a rigid mould (350) from which the required reflector can be obtained.