Patent GB-547249-A (GB)
Title: Improvements in apparatus for depositing reflecting metallic coatings on base members or bodies
IPC: C23C14/56
Filed: 1941-02-14
Abstract: 547,249. Coating with metals. BRITISH THOMSON-HOUSTON CO., Ltd. Feb, 14. 1941. No. 2056. Convention date, Feb. 14, 1940. [Class 82 (ii)] An apparatus for depositing a reflecting metal coating on the inner surfaces of pairs of concave base members comprises a head having an opening therethrough over the opposite ends of which the base members are placed and having a connecting passage for permitting the opening and the space enclosed by the base members to be exhausted, and heating coils mounted on the head in the opening therein for vaporizing coating material so that it condenses on the surfaces of the base members. Heads 15 for carrying vitreous base members 16 are mounted at regular intervals around the periphery of a turret 17 which is driven intermittently to carry the heads through each of the stations A ... Q. Each head is connected through a pipe 44, Fig. 2, pinch valve 47 and pipe 48 to the upper part 42 of a rotary valve on the turret. At station A, portions 22, Fig. 3, of coating material, e.g. aluminimum, are inserted in the heating coils 23, 23<SP>1</SP> carried by the rods 26; and members 16 are' mounted in the head. At station B, the head is connected to a vacuum source by alignment of the passage 50, Fig. 2, in the upper part of the rotary valve with the passage 53 in the lower part thereof. A leak-detecting mechanism, operating at station C, comprises a manometer 56, Fig. 8, connected to the head by alignment of the passage 50 with other passages in the lower part of the rotary valve. Any leak in the assembly of head and members 16 causes movement of mercury in the manometer 56 to close contacts 58, 59 to operate a solenoid 60 to release a latch 69 whereby rotation of the weighted pulley 70 causes turning of the arm 76 which causes an operating lever to close the pinch valve 47, so isolating the leaking head 15 from the vacuum source, and operates the valve 55 to reset the manometer 56: the remainder of the leak-detecting mechanism is reset by rotation of the cam 93, Fig. 1, which, when resetting is necessary, contacts the roller 99 which is positively connected by the linkage 100 ... 102 to the shaft 86 of the lever 76. At stations D and E, the head 15 is successively connected through the passage 50, providing the pinch valve 47 is not closed, to sources of flushing gas, which may be dry air or nitrogen, and to evacuating means. At F, a continuously operating mercury pump 137, Fig. 2. backed up by other exhausting means, is connected to the head 15 through the pipe 138 by the opening of a pinch valve 111 provided there is no leak in the head; if there is a leak, the pin 122 on the operating lever of the pinch valve 47 engages the roller 123, Fig. 1, to close the switch 127 to lower the arm 134 into the path of movement of the arm 113<SP>1</SP> which is thus pivoted upon opening the pinch valve 111. Movement from station F to station G causes closing of the exhaust line 48 by contact of a stationary roller 153 with the cam 78, Fig. 2, of the pinch valve 47. Evacuation continues through stations G and J and during movement from J to K the vacuum is tested by the apparatus of Fig. 9 comprising a Wheatstone bridge circuit, the resistances 154 ... 157 of which are sealed in envelopes 158, 159 the latter of which is connected with the head through the tube 160 ; unbalance of the bridge caused by improper vacuum in the head 15, together with the mechanical contact of the brushes 167, 168 with the bands 170, 171 occurring only during the movement from J to K, actuates, through the amplifying circuit 173, 174 &c., a relay 181 to close the circuit through the solenoid 187 to raise the roller 186 which closes the pinch valve 111: any faulty head is thus cut off from the exhaust system. At each of stations K ... N, the heaters 23, 23<SP>1</SP> are energized ; engagement of contacts 199 with blocks 198, Figs. 1 and 11, first closes the secondary circuit of transformer 202, Fig. 11, after which the primary circuit is closed through a mercury switch 220 operated by contact of cams 222 on the shaft 94 with levers 221 ; if however the head is faulty, the pinch valve 111 will be closed and a pin 227, Fig. 2, extending from the operating lever thereof will open the switch 219, Figs. 1 and 11, and so prevent closing of the primary circuit. At K, the heater is raised to a temperature of 600‹ C. to drive off moisture etc.; at L, M, N, to 2000‹ C. to vaporize the coating metal. Moving from station N, the pinch valve 111 is permanently closed. O is an idle station. At P, the pinch valve 47 is opened and the passage 50 in the rotary valve aligned with a passage through which dry air is admitted to the head. At Q, the members 16 are removed from the turret. Specification 515,091, [Group XI], is referred to.