US3524426A

US3524426A - Apparatus for coating by thermal evaporation

Info

Publication number: US3524426A
Application number: US709376A
Authority: US
Inventors: James C Ogle Jr; Anthony Olszewski
Original assignee: Libbey Owens Ford Glass Co
Current assignee: Pilkington North America Inc
Priority date: 1968-02-29
Filing date: 1968-02-29
Publication date: 1970-08-18
Anticipated expiration: 1987-08-18
Also published as: BE729026A; AT286738B; IE33433L; FR2002902A1; LU58110A1; NL6903181A; CH501064A; SE347024B; GB1250544A; NO123939B; IE33433B1; DE1911198A1; JPS494156B1

Description

United States Patent [72] Inventors .lamesC.Ogle,Jr.

Toledo, Ohio;

Anthony Olszewski, Natrona, Pennsylvania [21] AppLNo. 709,376 [22] Filed Feb.29,l968 [45] Patented Aug.l8, 1970 [73] Assignee Libbey-Owens-Ford Glass Company Toledo, Ohio a Corp. of Ohio [54] APPARATUS FOR COATING BY THERMAL EVAPORATION 7 Claims, 23 Drawing Figs.

[52] U.S.Cl 118/49, 214/1 [51] Int. Cl C23c 11/00 [50] Fieldof Search 118/1 8,

4849.5; l17/Inquiry; 214/1 lRCM; 312/1; 128/1.02

[56] References Cited UNITED STATES PATENTS 2,260,471 10/1941 McLeod 113/49 2,522,272 9/1950 Johnson et al.. 118/49 2,801,607 8/1957 Vodar et al. 118/504X 3,128,205 4/1964 lllsley 118/49 3,197,328 7/1965 Jung et 211.... 117/1072 3,206,322 9/1965 Morgan 118/49X 3,396,696 8/1968 Becker 1 18/49 Primary Examiner- Morris Kaplan Attorney-Collins and Oberlin ABSTRACT: Vapor deposition apparatus including a vacuum chamber containing a source of coating material to be evaporated; a separate vacuum chamber having means supporting a substrate therein; a housing which is intermediate to and integral with said chamber and has a valve member therein which is movable whereby to selectively communicate said chambers with one another; and an annular shield which is movable from within the evaporating chamber to the position intermediate the chambers to confine the vapor path and to shield the valve member.

Pat en ied Aug. 18, 1970 Sheet l of 12 raq on? ATTORNEYS INVENTORS game/L 6. 9c. .dmd (4M4 Patented Aug. 18, 1970 G' of 12 Sheet IINVENTORS 6e, aw? (9&1 @mwjflman ATTORNEYS Patented Aug.- 18, 1970 Sheet ATTORNEYS Patented Aug. 18, 1970 Sheet LZ of 12 175 im "12,-; 164 L INVENTORS W gamed.

ATTORNEYS APPARATUS FOR COATING BY THERMAL EVAPORATION SPECIFICATION The present invention relates to an improved apparatus for coating glass sheets or substrates of other materials in a vacuum system.

In one conventional procedure, the coating of substrates by vacuum deposition of the coating material on the substrates has been carried out in the vacuum chamber of a so-called bell jar connected with a diffusion pump for evacuating the chamber to a desired pressure. The vacuum chamber contains a source or sources of vaporizable coating material and the substrates are positioned in spaced relation to said source or sources, with the surfaces to be coated facing the same for receiving the vaporized coating material thereon.

One of the principal objections to such a procedure is that after a substrate or plurality of substrates in the vacuum chamber have been coated the vacuum in the chamber must be broken and the chamber raised to atmospheric pressure to permit removal of the coated substrates and the introduction of other substrates for coating, after which the chamber must again be pumped down to the desired pressure.

This pumping down of the vacuum chamber between the coating of successive substrates or groups of substrates is time consuming and renders the operation slow and expensive, particularly when only a few or even a single substrate is to be coated. Such a system does not lend itself to the successive coating of individual substrates of different configurations or types of coatings for which separate vacuum operations are required.

It is, therefore, a primary object of this invention to provide improved vacuum coating apparatus which is of particular utility in successively coating individual substrates, and to a procedure by which this can be accomplished more efficiently and economically.

Another object of the invention is the provision of apparatus in which the degree of vacuum required for coating can be attained in a much shorter period of time, with the result that individual substrates can be successively coated much more rapidly than in the past.

Briefly stated, the apparatus of this invention contemplates a main vacuum or evaporation chamber containing a source of coating material to be evaporated and a separate and preferably relatively smaller coating chamber for receiving the substrate to be coated andwhich is alternately placed in communication with and sealed off from said evaporation chamber. Separate means are provided for maintaining a vacuum in the evaporation chamber and in the coating chamber such that the vacuum can be maintained in the evaporation chamber during loading and unloading of the substrates in the coating chamber and with the coating material being evaporated when the coating chamber is placed in communication with the evaporation chamber to thereby expose the substrate in said coating chamber to the source of coating material. In this way, successive substrates or groups of substrates can be coated in the coating chamber without breaking the vacuum in the evaporation chamber.

Other objects and advantages of the invention will become more apparent during the course of the following description when read in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIG. I is a side elevation of the coating apparatus constructed in accordance with the invention;

FIG. 2 is a front elevation of the coating apparatus;

FIG. 3 is a plan view;

FIG. 4 is a section taken on line 4--4 of FIG. 3 showing the system for operating the closure lid for the upper chamber;

FIG. 5 is a longitudinal vertical section taken on line 5--5 of FIG. 3 showing the closure lid in the closed position as in FIG.

FIG. 6 is a transverse vertical section taken on line 6--6 of FIG. 3 with the closure lid in the open position as in FIG. I;

FIG. 7 is a horizontal section taken on line 7--7 of FIG. 6 showing the sealing plate valve between the upper and lower chambers of the apparatus;

FIG. 8 is a detail section taken on line 8--8 of FIG. 7 showing the plate valve and support carriage therefor in the sealing position;

FIG. 9 is a detail section taken on line 9--9 of FIG. 7, with the plate valve in the sealing position;

FIG. 10 is a similar detail view of the plate valve as it is moved toward the open position thereof;

FIG. 1 l is a perspective view of the plate valve and support carriage;

FIG. 12 is a plan view of the apparatus, with the closure lid and plate valve in the respective open positions;

FIG. 13 is a detail section taken on line 13--I3 of FIG. I2 showing the control system of a glow discharge unit;

FIG. 14 is an enlarged view of the coating chamber when the same is opened and sealed from the evaporation chamber for the loading operation;

FIG. 15 is a similar enlarged view of the coating chamber when the same is closed and in communication with the evaporation chamber for coating operation;

FIG. 16 is a fragmentary perspective of one form of glass sheet support;

FIG. 17 is a horizontal section taken on line l7--I7 of FIG. 5 of the evaporation chamber;

FIG. 18 is a detail section taken on line l8--18 of FIG. 17, showing the structure of a supply unit for the coating material;

FIG. 19 is a detail section taken on line l9--19 of FIG. 17 showing the structure of a shutter device arranged above the coating source;

FIG. 20 is an end elevation of the shutter device;

FIG. 21 is a diagrammatic view of the vacuum systems for the coating and evaporation chambers; and

FIG. 22 and FIG. 23 are diagrammatic views of an electrical control system for operation of the apparatus.

Referring now to the drawings, the coating apparatus of this invention comprises generally a relatively large evaporation chamber, generally designated by the letter A; a relatively smaller coating chamber B located above the evaporation chamber for receiving the sheet S to be coated, and a valve compartment C located between the evaporation chamber and coating chamber and in which is mounted a horizontally movable plate valve D. The plate valve D is operable to separate the evaporation chamber A from the coating chamber B when in the closed position and for placing the chambers in communication with one another when moved to the open position. In this connection. it will be noted in FIG. 1 that the apparatus per se is located on a supporting floor, designated by the letter F, and that convenient access to the coating chamber B can be had by working personnel on a platform or upper floor area designated at UF.

THE EVAPORATION CHAMBER The evaporation chamber A is vertically elongated and comprises a housing (FIG. 5) including a horizontal base 101, a horizontal top wall 102 and vertically disposed side wall 103; said wall 103 having a substantially flat forward wall portion 104, on which an access door 105 is mounted and oppositely disposed parallel side wall portions I06 and 107 that merge into or terminate in a continuous semi-circular rear wall portion 108. The housing 100 is supported on the floor F by suitable means, such as the pedestals I09, arranged and connected to the base 101 at the respective corners thereof. The top wall 102 is formed with an annular opening I10 that is axially aligned with similar openings in the respective horizontal walls of the coating chamber B and valve compartment C to permitcommunication therethrough.

As shown in FIGS. 1, 2 and 5, the side wall I03 is provided with a tubular conduit member 111 affixed at its inner end 112 in the said wall and equipped at the outer end thereof with an annular flange I13 sealingly connected to the duct work of the evacuating system for the evaporation chamber A, as will hereinafter be more fully described in connection with FIG. 21. The orifice at the inner end 112 of conduit 111 is protected from the stream of coating material, while the same is being directed upwardly from a source of evaporable material E, by a deflector or baffle 114 disposed across the lower area thereof. The deflector 114 has a substantially flat, upwardly inclined forward wall 115 and curved side wall 116 extending into and thereby interfitting with the inner surface of the conduit 111; said deflector being mounted by brackets 117 on the side wall 108 of the evaporation chamber A. The forward wall 115 of the deflector carries a cooling coil 118 on its inner surface; said coil having

end pipes

119 and 120 connected to suitable sources for conducting a coolant across the wall 115 of the deflector 114.

The source E comprises a crucible 123 for containing the material to be evaporated which is mounted on the base 101 of the housing in offset relation to the vertical axis of the chamber formed in said housing. More particularly, the crucible is mounted on a platform 124 having a top wall 125 and rearwardly extended ledge 126 which is carried by posts 127. The posts 127 are mounted on a base plate 128 secured to the base 101 of the housing 100. In this respect, it will be noted that the base plate 128 also serves to hermetically seal an aperture 129 provided in the base 101 whereby the source E in its entirety can be readily installed in and removed from the evaporation chamber A. V

Preparatory to the actual coating operation and during initial heating of the evaporable material to desired temperature, the open upper end of the crucible 123 is substantially covered by a shutter device generally designated by the numeral 135. As shown in FIGS. 6, l7, l9 and 20, the shutter device comprises a horizontally disposed (in the covering position) panel 136 carried at one or the inwardly disposed end of an arm 137 which is adapted to produce swinging movements of the panel from the full-line position in FIG. 6 to an upwardly inclined position in phantom line when the coating operation is in progress. For this purpose, the arm 137 is secured to the outwardly directed end of a rotary plug 138 located in the casing 139 of a rotary valve member 140 and having a rod extension 141 adapted to be operatively rotated by a fluid motor 142. The valve member 140 and motor 142 are mounted on the housing 100 by a frame structure 143 having a vertically disposed base member 144 sealed in the side wall portion 108.

The direction of pressure to the fluid motor 142 is controlled by a valve arrangement 146 and by way of

pipes

147 and 148; said valve being connected to a source of pressure by pipe 149. The valve arrangement 146 is adapted to make connection between pipes 147-149 or pipes 148-149 when actuated by control switch devices to be hereinafter described in connection with FIGS. 22 and 23.

The shutter panel 136 is insulated from the high heat of the source E of evaporable material by a coolant coil 155 mounted on its upper surface and communicating through

tubular extensions

156 and 157 to the rotary plug 138 and thence by

pipes

158 and 159 to sources ofpressure and sump.

It being advantageous to maintain the evaporation chamber A at the functional low degree of vacuum for substantially long periods of operation, the chamber A is provided with a hermetically sealed annex or secondary chamber 161 in which is mounted a cart for evaporable material, said cart being movable forwardly toward the cFucible 123 when it is desired to replenish the material therein and then rearwardly to its initial position within the chamber 161. This will be hereinafter more fully described in connection with FIGS. 17 and 18.

Generally stated, the chamber 161 is formed by a bottom wall 162.

side walls

163 and 164 and a top wall 165; the inner ends of these walls entering the evaporation chamber A and being hermetically sealed to the circular side wall 108. At their respective outer ends, the

walls

163 and 164 are provided with an integral peripheral flange 166. The outer end of the chamber 161 is closed by a panel 167 that is secured by bolt and nut fastenings 168 to the flange 166, with a suitable sealing gasket 169 being disposed therebetween.

THE COATING CHAMBER The housing 200 of the coating chamber B is mounted on the housing of the valve compartment C which in turn is carried by the top wall 102 of the evaporation chamber A. Thus, the housing 200 of the coating chamber is defined by a horizontal base 201, substantially circular side wall 202 and horizontal top wall 203. As will be more fully described, the base 201 is formed with an annular opening 204 communicating with the evaporation chamber A through the valve compartment C.

The top wall 203 is similarly provided with an axially aligned opening 205 that is adapted to be closed by a lid or cover member 206 during the coating operation. The lid 206 has a centrally disposed, flat panel portion 207, an annular side wall 208 received within the opening 205 in the top wall 203 and a horizontally disposed peripheral flange or lip 209. The undersurface of the flange 209 is formed with a groove in which an O-ring or like gasket member 210 is located to hermetically seal the coating chamber B when the lid 206 is in the closed position.

For movement between the open and closed positions of FIGS. 3 and 4, the lid is equipped with spaced integral arms 211 rising upwardly from the panel 207 and pivotally mounted by axles 212 in the upper ends of vertically disposed posts 213 of a bracket 214 mounted on the base 201 of the housing 200. Medially between the arms 211, and the lid 207 is provided with an upwardly projecting ear 215 which is connected by a pin 216 to a clevis member 218 on the end of piston rod 219 of a cylinder 220. The casing of this cylinder is supported by trunnions 223 on posts 224 spaced equally inward from the closely associated posts 213 on the bracket 214.

The piston 225 within cylinder 220 operates to retract the related rod 219 upon application of pressure by the valve 227 from pipe 228 through pipe 229 to the rod end of the cylinder. This action swings the lid 206 upwardly from the full-line closed position of FIG. 4 to the open position as in FIG. 1 and as indicated in phantom line in FIG. 4. When the lid is to be moved downwardly to the closed position, the valve 227 is actuated by an electrical control, as hereinafter described, to direct pressure from pipe 228 through pipe 230 to the head end of the cylinder 220, thereby producing outward or projected movement of the piston rod 219.

The lip or flange 209 on the lid 206 carries

switch actuating members

233 and 234 that are moved into operable engagement with

switches

235 and 236 respectively when a sealed inter-facial relation is established between the surfaces of the lip 209 and the top wall 203 of the housing 200. The switch 235 completes circuits to operate control devices for valve 227 to discontinue pressure through the pipe 230. In this connection, it should be noted that the valve will not operate to produce opening of the lid 206 unless the coating chamber B is at atmospheric pressure.

Thus, when the plate valve D within the valve compartment C is in closed position to separate the chambers and the chamber 8 is open to the atmosphere, the lid 206 can be raised or lowered between the closed and open positions thereof. Likewise, after the lid has been moved to the closed position to seal the coating chamber B from atmospheric pressure, communication between the evaporation chamber and coating chamber cannot be effected by movement of the plate valve D to the open position until the low pressure obtained in the coating chamber B substantially equals the pressure maintained in the evaporation chamber A. It will be noted in FIG. 3 that the side wall 202 of the coating chamber is provided with a flanged extension 237 which is connected by bolt fastenings 238 to the similarly flanged end of a conduit 239 connecting with the evacuating system for the coating chamber B (see FIG. 21). When the lid is in the closed position, the limit switch 235 completes an electrical circuit to open connection of the evacuating system (FIG. 21 to the coating chamber B through conduit 239.

The sheet S to be coated is supported in the chamber B on a plate 240 removably mounted on a ring-gear 241. As viewed in FIGS. 14 and 15, the ring-gear is carried on a friction-free mounting in which the inner vertical surface of the ring-gear 241 and the opposed outer surface of a stationary ring member 242 of smaller diameter are formed to provide the inner and outer races of a ball-bearing type of mounting and in which a plurality of spherical elements or ball-bearings 243 constitute the actual rotary support for the ring-gear 241. The ring member 242 is fixedly secured, as by bolts 244, to the upper surface of the base 201 of the housing in concentric axial relation with the opening 204 therein.

As shown in FIGS. 12, 14 and 16, the support plate 240 for the sheet S to be coated is carried on the upper surface of the ring-gear 241 and has at least two diametrically opposed holes 245 in which are received locating pins 246 fixed in the body of the ring-gear. This permits ready substitution of the support plate 240 for a like plate having ledge areas adapted to support sheets of larger or smaller dimensions or of varying outline. As shown in FIG. 16, by way of example, support or ledge areas in the body of plate 240 are defined by a substantially rectangular outline 247 and include a shelf 248 on which the sheet is placed and an outwardly inclined surface 249 for convenience of sheet handling. In the exemplary form of support plate, the ledge areas on each side of the rectangular outline are interrupted by notched or recessed areas 250 to permit easy handling of the edges of a sheet when loading or removing the same. These notched areas are partially enclosed by downwardly directed hoods 251 to prevent passage of the stream of coating material, being evaporated from the source E in the chamber A, from beyond the lower surface of the sheet or the support plate 240 thereabout.

During the coating operation, the ring-gear 241 is adapted to be rotated to insure that the layer of coating material is uniformly distributed or laid down on the lower surface of the sheet thereby avoiding the existence of potential pinholes", other objectionable discontinuities or thicker areas in the layer. For this purpose, as in FIGS. 3 and 12, the teeth 252 of ring-gear 241 are in meshed relation with the teeth of a drive pinion 253 located in a chamber defined by a subsidiary wall portion 254 of the side wall 202 of the housing 200. The pinion 253 is keyed to one end and preferably the lower end of a shaft 255, journaled in a bracket 256 on the outer surface of the top wall 203 and equipped with a sprocket 257 on the opposite or upper end thereof. By means of a sprocket chain 258, the shaft 255 and sprocket 257 are adapted to be driven by a related sprocket 259 on the output shaft of a reduction gear unit 260 operated by a motor 261. Operation of the motor 261 is controlled to start at the beginning of the coating operation and to be terminated when a layer of coating material of predetermined thickness has been observed on the sheet, about which more will be said later.

With reference now to the utility of the limit switch 236, when lowering of the pressure in the coating chamber is initiated, this switch originates an electric circuit to a glowdischarge unit generally designated by the numeral 265 and which provides a high alternating current potential which is effective to thoroughly clean the bottom exposed surface of the sheet by ionic bombardment. This unit includes a ring or circular element 266 that is supported by blocks 267 of insulating material on the inner vertical wall of the stationary ring member 242, as in FIG. 12. While in no way restricting the use of similar devices or structures, the element 266 of the unit herein shown is connected to an AC ammeter 268 through a lead cable 269, as shown in FIG. 13, which cable is suitably formed to extend from a support tube 270, beneath the ringgear 241, and thence inwardly through a passage 271, provided in the fixed ring element 242, to the element 266. As herein employed, the ammeter 268 is mounted by bracket 272 on the top wall 203 of the housing 200; said bracket also supporting the tube 270. Through control by the limit switch 236, a circuit to the circular glow-discharge element 266 can be completed while the chamber B is being evacuated and to cease as the air content is reduced. Of course, when the actuator 234 is lifted from engagement with the switch 236 as the lid 206 is swung upwardly, the abovedescribed circuitry is deactivated.

THE VALVE COMPARTMENT The valve compartment C, which is interposed between the evaporation chamber A and coating chamber B, includes a substantially rectangular, horizontally elongated housing 300, clearly shown in FIGS. 1, 5 and 12. The housing 300 is formed with a horizontal base 301, forward wall 302,

side walls

303 and 304, rear wall 305 and horizontal top wall 306. The base 301 of valve compartment C is formed with a circular opening 307 axially aligned with and having a diametric dimension substantially equal to that of the opening in the top wall 102 of the evaporation chamber A. Similarly, the top wall 306 has a communicating circular opening 308 concentrically located with reference to the opening 204 in the base 201 of the coating chamber housing 200.

The relatively open communication between the lower evaporation chamber A and the upper coating chamber B is illustrated in FIG. 12 with the lid 206 in the open position, as in FIG. l, and with the plate valve D in the valve compartment C in the open position, as in FIG. 5. It will be understood that during operation of the apparatus, and when the lid is in the open position, the plate valve will be in closed position, as in FIGS. 6 and 14, since the evaporation chamber A is to be continuously maintained at a relatively low degree of vacuum. It is equally important that the inter-facial surfaces of the chambers and the compartment should be hermetically sealed to one another. To this end, the opposed surfaces of one or the other of base walls 102-301 an 201-306 are formed with annular grooves to receive O-rings or

gasket members

309 and 310, respectively.

Within the housing 300 and secured to the under surface of the top wall 306 is a flat panel 312, having a circular opening 313 concentric with the opening 308 thereabove; said panel constituting the seat" or fixed element of the valve arrangement for sealing the coating chamber B from the valve compartment C and evaporation chamber A. The undersurface 314 of the panel 312 (FIG. 14), therefore, has an exceedingly fine finish and is formed with an annular groove for a sealing gasket 315.

The plate valve, identified by the letter D, comprises a substantially rectangular body 318 and is carried between the closed position of FIG. 14 and the open position of FIG. l5 by a carriage, designated in its entirety by the numeral 319. As seen in FIG. 1 l, the carriage 319 includes front and rear transversely disposed channel members 320-321, respectively, longitudinally disposed channels 322-323, equally spaced from the longitudinal axis of the carriage, and outwardly disposed panels 324-325 arranged in parallel with the outwardly facing webs 326-327 of the channels 322-323 respectively.

The webs 328-329 of the channel members 320-321 support U-shaped brackets 331; the spaced legs of which similarly mount the ends of small axles or pins 332 on which one or the lower end of links 333 are medially journaled. The upper end of each link 333 is connected by a pin 334 to a block-like bracket 335 fixed to the undersurface of the plate valve 318. The arrangement of the brackets 331 and associated brackets 335 relative to one another is best shown in FIGS. 7 and l l. A further supporting relation between the plate valve and carriage is provided by links 337, each supported by a pin 338 on brackets 339 integrally fixed to and located between the channels 322-324 and adjacent panels 323-325, respectively. ln this instance, the upper end of each link 337 is provided with a roller 340 adapted to be received in a cam-shaped notch 341 of a block 342 fixed to the plate valve. As illustrated in FIG. 7, it will be seen that the

several blocks

335 and 342 are arranged in substantially a hexagonal outline or pattern to uniformly support the plate valve on the carriage at a plurality of equally spaced points.

Briefly stated, the carriage 319 is adapted to carry the plate valve D between an open position, as in FIGS. 5 and l5, and a closed position as in FIGS. 6 and 14. During these traversing movements of the carriage, the plate valve is supported at a lowered elevation with reference to the carriage by links 333- 337 being disposed in a forwardly inclined position as in FIG. 1 1. Now, when the plate valve is moved to closed position, the said links are moved to a vertical position whereby the plate valve will be raised and the upper surface thereof placed in interfacial sealing relation with the lower surface 314 of the panel 312. Also, preparatory to removal of the plate valve from its closed position, an initial movement of the carriage causes the links to start return movement to their inclined position thereby lowering the plate valve.

With reference now to FIGS. 6, 7 and 8, there is shown a pair of spaced, parallel horizontally

disposed bars

345 and 346 suitably secured at one end to the panel 312 and at their opposite end to base wall 301 of the valve compartment and equally spaced from the longitudinal axis of the housing 300. Formed in the inwardly facing, vertically disposed surface 347 of each

bar

345 and 346 is a lower, substantially rectangular groove 348 forming a track-like surface 349 and an upper rectangular groove 350 providing a track surface 351. As viewed in FIG. ll, the carriage 319 is provided in its respective corner areas with caster wheels 353 journaled on fixed axles 354 carried by blocks 355 at the ends of the

transverse channel members

320 and 321. The wheels 353 traverse the track surfaces 349 and serve to support the carriage as it is caused to move between open and closed position during the application of pressure to one end or the other end of a cylinder 356 (FIG. 12). Guide rollers 357, suitably mounted on the

carriage panels

324 and 325 by brackets 358, ride along the vertical surfaces 347 of the

bars

345 and 346 to guide the carriage in its movement.

The carriage 319 is moved between the closed and open positions of the plate valve 318 by means of the cylinder 356 mounted on the rear wall 305 of the housing 300. The piston rod 360 of contained piston 361 is connected at its outer end by a tapped block 362 and pin 363 to mounting plates 364 integral with the rear channel member 321 of the carriage 319 (FIGS. ll and l4).

As the carriage approaches the limit of its forward movement, the head ofa bolt 366, adjustably carried by a tapped or internally threaded stud 367 fixedly secured to the forward channel member 320, engages the actuating plunger of a limit switch 369 to bring about stopping of the carriage. As disclosed, the head end of cylinder 356 is connected by pipe 370 to a pressure control valve 371, while the rod end of the cylinder is also connected to said valve by pipe 372; said valve being connected by pipe 373 to a source of supply. The limit switch 369 is instrumental in actuating the valve 371 to discontinue pressure to the head end of the cylinder. When the carriage is moved rearwardly, a bolt 374 adjustably carried by a stud 375, secured to the outwardly directed surface of the web 329 of rear channel 321, is adapted to engage the plunger ofa limit switch 376 mounted on the rear wall 305 ofthe housing 300 to discontinue pressure to the rod end of the cylinder.

The plate valve 318, as in FIG. 1 l, is provided in the corner areas, adjacent its leading end, with rollers 378 supported in brackets 379, said rollers traversing the track surfaces 351 of the upper grooves 350 in bars 345-346. As viewed in FIG. 8, the track surfaces define a substantially horizontal track section 382, a forwardly and upwardly inclined section 383 and a vertical section 384. Thus, when the plate valve is carried forwardly by the carriage 319 in its lowered position, as determined by the

links

333 and 337 in their forwardly inclined positions beneath the opening 313, the rollers 378 will move from the horizontal track sections 382 onto the inclined track sections 383 and into abutting relation with the vertical track sections 384, thereby lifting the plate valve into contact with the plate 312 to close the opening 313. It will be understood that while the plate valve is being carried forwardly by the carriage, the plurality of

links

333 and 337 are disposed in their inclined positions. However, when movement of the plate valve is halted by engagement of the rollers 378 with the vertical track surfaces 384, forward movement of the carriage is continued, whereby the

links

333 and 337 will be swung into vertical position to lift the plate valve into surface-to-surface sealing engagement with the panel 312.

As the

links

333 and 337 reach a substantially vertical or dead-center position, forward motion of the carriage is halted by bolts 385 (FIG. 8), adjustably mounted in a transverse bar 386 secured at its opposite ends to the adjacent ends of the

longitudinal bars

345 and 346. As noted earlier, the bolt 366 at the forward end of the carriage engages the plunger of limit switch 369 to produce closure of the pressure valve 371 to discontinue pressure to the head end of cylinder 356 slightly in advance of engagement of the bolts 385 by the carriage to halt the same. A similar positive stopping of the carriage 319 is also produced upon rearward movement thereof, by bolts 387 supported by brackets 388 on the base 301 of the valve compartment (FIG. 12).

Suitable guide rollers 380, similar to the guide rollers 357 of the carriage, are mounted by brackets 381 at the respective corners of the body of the plate valve. To prevent abrasion of the surfaces of the plate valve body 318 and panel 312 during separation, upon termination of the coating operation, as will be hereinafter described, the carriage is provided with a pair of links 390 carried by pins 391 and located between the channels 322-324 and adjacent panels 323-325 at the rear corners of the carriage (see FIG. 11). These links, proximate their upper ends, are freely swingable within slots 392 provided in the plate valve body. Each link 390 is provided at its upper end with a roller 393 that is adapted to be received in a notch 394 in the undersurface of plate 312 when moved to a vertical position.

As viewed in FIG. 9, the links 390 are vertically disposed when the plate valve is in closed position; however, upon rearward movement of the carriage the rollers 393 will traverse the inclined cam surfaces 395 of blocks 396, thereby operating to swing the links forwardly and force the rollers against the vertical surfaces of the notches 392 whereupon the rear end of the plate valve will be pushed downwardly, as in FIG. ID, to free the surface thereof from sealing engagement with the surface 314 of the panel. As rearward movement of the carriage continues, the plurality of

links

333 and 337 are caused to similarly swing to their inclined positions and lower the plate valve. During such rearward movement, the caster wheels 353 support the carriage as they traverse the track surfaces 349 and the rollers 378 move along into the horizontal track sections 382 of the grooves 350, with the position of the plate valve on the carriage as shown in FIG. 5.

THE ANNULAR SHIELD To protect the inner surfaces of the valve compartment from undesirable deposits of the coating material during evaporation, there is provided an annular metal shield, generally designated by the numeral 400, which in the functional position (FIG. 5) constitutes a substantially tubular passageway between the evaporation chamber A and the coating chamber B. The shield includes an annular vertical wall 402 having a rolled rim 403 at its upper end and a base portion 401 at its lower end. The shield is supported on a vertically disposed rod 404 attached by a block 405 to the base portion 401 as in FIG. 6. Located diametrically from the rod 404, is a vertical rod 406 which serves to guide the shield during its upward and downward movements; said rod 406 being fixed at its upper end to a lug 407 secured to the undersurface of the top wall 102 of the housing and at its lower end in an angle bracket 408 secured to the side wall 103 of said housing. The guide rod 406 is slidingly engaged by a plate 409 attached to the base 401 of the shield.

When the coating chamber B is open to atmosphere and the plate valve 318 is in closed position as in FIG. 6, the shield 400 is in a lowered position as in FIG. 6, with the upper rim 403 substantially at an elevation within the opening in the top wall 102 of the evaporation chamber and the opening 307 in the base 301 of the valve compartment. On the other hand, after the plate valve 318 has been moved to open position preparatory to the coating operation, the shield is raised until the annular wall 402 is disposed within the valve compartment C as in FIG. 5. As best seen in FIG. 12, the base portion 401 of the shield has a circular opening 411 eccentrically located with reference to the vertical axis of the annular wall 402.

The support rod 404 extends downwardly through the base 101 of the evaporation chamber A at which point it is contained within a sealing gland 415. The lower extremity of the rod is connected by a block 416 to the rod 417 of piston 418 in a cylinder 419 mounted by a bracket 420 on an adjacent pedestal 109.

The annular shield, at the limits of its vertical movements, is adapted to alternately engage

switch devices

421 and 422 mounted in vertically spaced relation on a fixed bracket 420 and which are instrumental in controlling certain phases of the automatic coating operation as will be hereinafter explained. For this purpose, the connector block 416 is provided with an outwardly directed finger 423 which, at the lower limit of movement, as viewed in FIG. 6, engages the actuating plunger of the limit switch 421 to stop the downward movement of the shield. Likewise, when the annular shield has been raised to its upper position, the finger 423 will actuate the limit switch 422 to halt such movement. The upward and downward movements of the annular shield are controlled by a cylinder 419 connected by

pipes

425 and 426 through an electrically controlled valve 427 (FIG. I) to the supply pipe 428.

During vertical movement of the rod 404, it is slidably supported and guided within the evaporation chamber A by a bearing block 429 supported on the side wall 107 by mounting plates 430. As seen in FIGS. 6 and 17, the rod 404 between the block 405 and the base 101 of housing 100 is located behind a vertically disposed barrier or shield 431 mounted on said base and having its upper end 432 projecting through the opening 411 to an elevation substantially in a horizontal plane with the top wall 102 of the housing.

SOURCE OF EVAPORATION The source E of evaporable material, which includes a crucible 123, utilizes bombardment by an electron beam to heat the coating material within the crucible to a temperature at which it vaporizes rapidly whereby a steady stream of vapor molecules is produced and directed toward the exposed surface of the glass sheet, in the coating chamber. For this purpose, an electron gun, generally designated by the numeral 435, is disposed beneath the crucible and laterally thereof. Preferably, the electron gun is spaced from the metal being bombarded to reduce the possibility of damage or short circuiting of the gun as a result of contamination by ions of the evaporated material or released gases. With the gun so located, the electron beam projected therefrom is guided from the focusing coil 436 into the open top of the crucible 123 under the influence ofa magnetic field generated between the focusing plates 437-438 of magnets indicated generally by the numeral 439. The electron beam is thus guided by the magnetic field over and down into the open top of the crucible to bombard and vaporize the coating material contained therein. While an electron beam source is preferred other sourcesmay be used without departing from the spirit of the invention. While in no way restricting the number or kinds of materials that may be evaporated in the apparatus of this invention, layers of either aluminum or chromium, of the metallic group of materials, have produced highly efficient mirror surfaces. Also, titanium dioxide, of the oxide group, may be used to provide coatings of high reflectivity while magnesium fluoride of the halogen group will provide antireflective coatings.

THICKNESS MONITOR As best shown in FIGS. 3 and 6, provision is made for monitoring the thickness of the coating applied to the glass sheet. The monitoring system includes a light source 445 and a light beam receiver 446 having a photoelectric cell 447. The light source 445 is contained within a casing 448 supported on the wall of the conduit 111 located in the side wall 108 of the evaporation chamber. A tubular extension 449 of the casing extends upwardly into the conduit and has an open-end orifice 450 through which the light beam L is projected toward the receiver 446. Preferably, the extension and the orifice thereof are disposed behind the shield 114.

The light receiver or thickness monitor 446 is contained within a casing 451 mounted on lid 206, with an aperture 452 being provided in the center panel 207 thereof as shown in FIG. I.

The casing 448 of the light source 445 is mounted on the conduit 111 such that the axis of the light beam L is directed angularly upward within the evaporation chamber A toward the thickness monitor device 446 through the opening 452 in lid 206 when in its closed position. When the coating on the glass sheet reaches a predetermined thickness, it will impede passage of the light beam, whereupon the photoelectric cell 447 will be activated to bring about termination of the coating operation.

COATING MATERIAL LOADING UNIT to again reduce the pressure within the chamber before the coating operation could be resumed. Therefore, to add desired amounts of coating material to the crucible 123 between coating operations and without breaking the vacuum in the evaporation chamber, there is provided a material loading unit, generally designated by the numeral 460, mounted in hermetically sealed relation on the side wall 108 of the evaporation chamber.

The loading unit 460, illustrated in FIGS. 17 through 20, includes a cart 461 located within the annex chamber 161, preferably formed integrally with the housing 100, and an outwardly located source of power 462 for controlling movement of the cart.

The cart 461 has a chassis 464 provided with wheels 465 by which it is adapted to traverse tracks 466 that may be formed of angle members firmly secured at their outer ends to the inner surface of the vertical end panel 167. The receptacle 468 for the coating material is supported on the chassis 464 by means of a vibratory device 469. The receptacle has a conically shaped body 470 and a forwardly projecting trough 471; said body having a rear wall 472 and downwardly convergent side walls 473 that are continued forwardly as at 474 to provide a relatively long narrow trough. A front wall 475 is located at the junctures of side walls 473 and 474 and is interrupted to provide a means of egress, such as the port 476, for passage of the material from the body into the trough.

The vibratory device 469 is preferably an electrically actuated unit that is connected through a flexible cord 47 8, lead-in plug 479 and cable 480 to a suitably controlled source. When the device is energized, vibrations transmitted to the body of the cart cause particles of the coating material to move outwardly along the trough 471 after the cart is moved forwardly from the full line to the phantom line positions in FIG. 18.

The cart 461 is connected to the source of power 462 by a rod 482 which passes through a sealing gland 483 on the panel 167. The outer end of rod 482 is coupled by a connector sleeve 484 to the end of the rod 485 of a piston 486 contained in a cylinder 487. The cylinder is mounted on the web 488 of a U-shaped bracket 489 mounted at the ends of its leg portions 490 on the panel 167. To maintain substantially dust-free, sliding action for the rod 482, said rod is enclosed by a dust bellows 491, or like accordian-type of shield, attached by clamping rings 492 at one end to the gland 483 and at its opposite end to the connector sleeve 484.

The head end of the cylinder 487 is connected to a pressure control valve 494 by pipe 495, while a second pipe 496 similarly connects the rod end of the cylinder to said valve. Suitable switch devices (FIG. 23) cause the valve 494 to direct pressure from supply pipe 498 alternately to the

pipes

495 and 496. Pressure is thus directed by pipe 495 to the head end of cylinder 487 for forward movement of the cart 461. When the trough is located above the crucible and movement of the cart is stopped, operation of the vibratory device is manually started to supply the material to the crucible. Also, operation of the vibratory device is halted in advance of return movement of the cart when pressure is directed by pipe 496 to the rod end of cylinder 487.

To protect the cart and contents during the coating operations, a freely swingable door 501, arranged in front of the trough 471, is supported on a hood member 502 fixed to the side wall 108 of the housing 100. The door 501 is adapted to rest at its lower edge on the ledge 126 forming an extension from the platform 124 for the crucible 123. As the cart 468 is propelled forwardly from the full line position in FIG. 18, the end of trough 471 engages the door and swings the same upwardly until the said trough end is located, as in phantom line, above the crucible 123. When in this position, operation of the vibratory device 469 will cause a desired amount of the coating material to be discharged from the trough 471 to into the crucible. After the supply of coating material has been replenished and the cart is moved rearwardly, the door 501 is permitted to swing downwardly in front ofthe trough.

ELECTRICAL SYSTEM With reference now to FIGS. 21, 22 and 23, there is diagrammatically shown an exemplary form of electrical systems for substantially continuous operation of the vacuum system of the evaporation chamber A and for automatic operation of the coating apparatus.

As herein provided, the evaporation chamber A is connected from the conduit 111 to the vacuum system by

pipes

505 and 506 and a manually operated valve 507 through which pipe 505 and the chamber A can be connected to atmosphere. Preparatory to operation of the apparatus, the valve 507 is actuated to connect pipe 505 through pipe 506 to the vacuum system. A manual (on-off) switch MS510 (FIG. 2] when closed, then completes a circuit from source line 511 to energize the solenoid 513 of a spring-biased relay switch RS514 by line 512 to source line 515 to engage contact pair 516 and make a circuit from source line 511 by line 517 to source line 515 through mechanical pump 519 of the vacuum system for the evaporation chamber A which also includes a blower unit 521 and diffusion pump 522. The pump 519 is connected by pipe 523 through the blower 521 to a control valve 524 and pipe 525 to pipes 505-506 and conduit 111 of the evaporation chamber housing 100. The pressure in the chamber is initially reduced until about 20 microns is obtained, at which time, valve 524 is closed and a valve 526 is opened to connect pipe 523 to the diffusion pump 522. This pump may be of substantially the type disclosed in US. patent 3,203,624 and will be understood to b generate a heated condition therein and in so doing cause further pumping of the chamber A to obtain a pressure of preferably about 4.5 X microns, at which pressure the coating of the glass sheet or other substrate is carried out. This is accomplished by connection of pipe 523 and pipe 527 through a poppet valve 528 to pipe 525 and pipes 505-506 and conduit 111. When the pressure in chamber A is to be raised to atmospheric after completion of a series of coating operations, opening of switch 510 permits disengagement of contacts 516 of RS514 to break the circuit of

source lines

511 and 515 to the mechanical pump 519. The valve 507 can then be operated to connect pipe 505 and the chamber A to atmosphere.

As viewed in FIG. 22, the lid 206 is located in the open position to which it was swung upon completion of the previous coating operation and while the supply pipe 228 was connected through valve 227 and pipe 229 to the rod end of cylinder 220. The plate valve D with the carriage 319 has been moved to the closed position while the supply pipe 373 was connected through valve 371 and pipe 370 to the head end of the cylinder 356. Similarly, the annular shield 400 is in the lowered position to which it was moved during connection of supply pipe 428 through the valve 427 and pipe 426 to the rod end of cylinder 419. After a sheet S to be coated has been loaded on the support member 240 in the coating chamber B, the operator closes manual switch M5530 (FIG. 22) to first complete a circuit from source line 511 to energize the solenoid 533 of relay switch RS534 by line 531 to source line 515; RS534 having opposed solenoid 535 and pair of contacts 536. When contacts 536 are engaged, a circuit is completed from source line 511 to originate a service line 537 to put functioning of the apparatus on an automatic cycle. At the same time, branch line 538 completes a circuit through bleeder valve 539 thereby closing connection of pipe 239 to atmosphere and placing the same in communication with an electrically controlled valve 541 which controls connection of the pipe 239 to the vacuum system (FIG. 21) for the coating chamber B.

Simultaneously, a circuit to energize the solenoid 543 of relay switch RS544 is completed by branch line 542 from line 531 to source line 515; RS544 having opposed solenoid 545 and pair of contacts 546. When solenoid 543 is energized, contacts 546 will be engaged to complete a circuit from service line 537 through engaged contacts 549 of relay switch RS550 to energize solenoid 551 by line 548 to source line 515; RS550 having opposed solenoid 552 and engaged contacts 553. When solenoid 551 is energized, the circuit of line 548 is opened upon disengagement of contacts 549. At the end of a previous operation, the contacts 553 completed the circuit of a line 554 to actuate the end 555 of valve 227. As earlier described, valve 227 connected supply pipe 228 to the rod end of cylinder 220 by pipe 229 to retract the piston rod 219. Now, when disengaged, contacts 553 open the circuit of line 554 through the end 555 of four-way valve 227. Line 548 by branch line 556 also completes a circuit through the end 557 of valve 227 to source line 515. This actuates the valve to direct pressure from pipe 228 through pipe 230 behind piston 225 at the head end of cylinder 220 to swing cover 206 downwardly as piston rod 219 is projected.

When the coating chamber B is closed by the lid 206, actuator member 233 engages switch 1.5235 to complete a circuit from service line 537 through engaged contacts 558 of RS559 to energize solenoid 560 by line 561 to source line 515; RS559 having opposed solenoid 562 and presently open contacts 563. When energized, solenoid 560 acts to disengage contacts 558 to open the circuit ofline 561 and to engage contacts 563 to complete a circuit to energize solenoid 545 of RS544 by line 564 to source line 515. This serves to open the circuits of lines 548-556 and de-energize the end 557 of valve 227 at the limit of downward movement of the lid 206.

When closed, LS235 also causes completion of a circuit from service line 537 to energize the solenoid 565 of relay switch RS566 by line 567 to source line 515; RS566 being equipped with opposed solenoid 568 and pair of contacts 569. When these contacts are engaged, a circuit from line 537 is completed by line 570 through the engaged contacts 571 of relay switch RS572 and line 570'through valve 541 (FIG. 2 l) to source line 515. Valve 541 can thereby be opened to connect the coating chamber 8 through conduit 239 to the mechanical pump 573 of the vacuum system for said chamber, since the valve 539 has been closed to atmosphere. RS572 is equipped with

opposed solenoids

574 and 575, disengaged contacts 576 and engaged contacts 576' in addition to contacts 57].

When manual (on-off) switch M8577 is closed, a circuit is completed to energize the solenoid 578 of spring-biased relay switch RS579 by line 580 to source line 515; RS579 having contacts 581. When engaged, contacts 581 complete the circuit of line 511 through line 582 to the pump 575 to initiate operation of the vacuum system for the coating chamber.

The vacuum system for the coating chamber B includes a small blower unit 583 and large blower unit 584. lnitially, the pump 573 is connected by pipe 585, automatically

operable valves

586 and 587 and valve 541 to the conduit 239 associated with the housing 200 of the chamber B. When a roughing" pressure of about 1000 microns is obtained in the chamber, the pump 573, being connected through pipe 588 to the small blower unit 583, influences low pressure switch LPS589 to start operation of the blower unit 583. At this time, the automatic valve 585 closes and the chamber B is connected to the small blower unit 583 via pipe 590 and valve 587. After a timed delay of about 15 seconds and at a pressure of about 100 microns, the large blower unit 584 is started and the pipe 590 from the small blower 583 is connected with valve 541 through pipe 591; valve 587 then automatically closing. The mechanical pump 573 is thus connected to the coating chamber through both blower units and operated to obtain a pressure of about 10 microns in coating chamber B.

Now, while the coating chamber is being evacuated to a low pressure substantially that established and maintained in the evaporating chamber A, the closure of switch LS236 (FIG. 21) by actuator member 234 on lid 206 completes a circuit from service line 511, line 593 and engaged contacts 594 of spring-biased relay switch RS595, having solenoid 596, to line 597 and engaged contacts 598 of relay switch RS599 thereby energizing related solenoid 600 via line 601 to source line 515', RS599 having opposed solenoid 602 and disengaged contacts 603. When energized, solenoid 600 acts to disengage contacts 598 to open the circuit of lines 597-601 and to engage contacts 603 to complete the circuit of line 604 through a transformer 605 and the AC ammeter 268 to the glow-discharge unit 265. This unit is adapted to cleanse the surface of the sheet by ionic bombardment until a sufficiently low pressure obtained in the coating chamber causes ionic bombardment to cease due to reduction in air content.

When the pressure within coating chamber B is substantially equal to that in evaporation chamber A, a thermocouple 607 in chamber B completes a circuit from service line 537 to energize the solenoid 608 of a spring-biased relay switch RS609 by line 610 to source line 515; RS609 having contacts 611 which, when closed, complete a circuit from service line 537 to line 612 through closed contacts 613 of relay switch RS614; RS614 also having opposed

solenoids

615 and 616. Line 612 is completed by line 618 through engaged contacts 619 to energize solenoid 620 of relay switch RS621 to source line 515. RS621 is equipped with opposed solenoid 622, disengaged contacts 623 and engaged contacts 624 and 625.

A circuit from contacts 619 is also completed by line 626 through engaged contacts 576' of RS572 to energize the associated solenoid 574 by lines 627 to source line 515. While energized, the solenoid causes disengagement of contacts 576' to open the circuit of lines 626-627, disengagement of contacts 571 to open the circuit of lines 570-570 to the valve 541, and engagement of contacts 576 to complete the circuit of line 628 from service line 537 to a thermocouple 629 within the chamber B and activated when the pressure of the chamber reaches atmospheric.

The circuit of line 626 is extended to energize solenoid 630 of RS631 by line 632 to source 515; RS631 having opposed solenoid 633, presently engaged contacts 634 and

disengaged contacts

635 and 636. When energized, solenoid 630 disengages contacts 634 to open the circuit of a line 638 through the end 639 of valve 371 to source line 515 which will close the connection of supply pipe 373 to the head end of the cylinder 356 through pipe 370.

When energized, solenoid 620 acts to disengage

contacts

619, 624 and 625 while engaging contact pair 623 to make a circuit from service line 537 through the end 641 of the fourway valve 371 by line 640 to source line 515. The valve thereby connects pressure via pipes 372-373 to the rod end of cylinder 356. This moves the carriage 319 rearwardly, disengaging LS369, to remove the plate valve D in valve compartment C from sealing relation with the panel 312 and put the coating chamber B in open communication with evaporation chamber A. As the actuator bolt 366 is carried from engagement with LS369, the contacts of side 643 thereof are disengaged while contacts of side 644 are engaged to make a circuit by line 645 to the valve 241 thereby closing communication of pipe 591 to pipe 239. After an interval of about 4 to 8 seconds, operation of the small and

large pumps

583 and 584 is discontinued although the mechanical pump 573 continues to function to hold an evacuated condition in the system.

Automatic valves

586 and 587 are also reopened when the

blowers

583 and 584 are stopped.

When the actuator bolt 374 on the carriage 319 actuates switch LS376, a circuit will be made from service line 537 to energize solenoid 622 of RS621 by line 647 to source line 515. This initially disengages contacts 623 to break the circuit of line 640 to valve end 641 thereby closing connection of pipe 373 to pipe 372 through the valve 371. Re-engaged contacts 624 then make a circuit to energize the solenoid 650 of RS651 by line 648 to source line 515; RS651 having opposed solenoid 652 and contact pair 653. Contacts 653 connect lines 654 and 655 to prepare the making of a circuit through the solenoid 633 of relay switch RS632. Further action of RS632 will produce movement of the carriage 319 to locate the plate valve D in sealing position. At the present time, however, the circuit of line 654 is open at disengaged contacts 657 of spring-biased relay switch RS658 having solenoid 659. As hereinafter described, RS658 is actuated after a coating operation has been completed to produce movement of the plate valve D to the closed position.

Referring again to RS621, presently engaged contacts 624 complete a circuit from service line 537 and by line 661 to a timing relay TR662, in series with source line 515 and service line 537, and also energizes the solenoid 615 of RS614 by line 663 to source line 515. Disengagement of contacts 613 opens the circuit of lines 612-618 which will place RS614 in condition for use in a subsequent operation.

While functioning during the coating operation, TR662 completes a circuit to energize the solenoid 664 of a springbiased relay switch RS665 by line 666 to source line 515; RS665 having disengaged contacts 667. When engaged, contacts 667 are adapted to make a circuit by line 668 through the engaged contacts 669 of relay switch RS670. RS670 is equipped with

opposed solenoids

671 and 672. While contacts 669 are engaged. they complete a circuit from service line 537 and line 668 to energize the solenoid 675 of relay switch RS676 by line 677 to source line 515. RS676 has opposed solenoid 678, presently disengaged contacts 679 and engaged contacts 680 and 681. Contacts 679 then make a circuit from service line 537 through the end 683 of four-way valve 427 by line 682 to source line 515. This causes the valve to direct pressure by pipe 425 to the head end of cylinder 419 to move the rod 404 upwardly, disengaging limit switch LS421, until the annular shield 400 is bodily located within the valve compartment C. At this upper limit of movement, the finger 423 engages limit switch LS422.

LS422 is operable to complete a circuit from service line 537 via line 685 to timing relay TR686, in series with source line 515 and service line 537, which timer functions to open the circuit of lines 668-677 at contacts 669 and to open contacts 679 while reclosing contacts 680 and 681. Thus, TR686 initially makes a circuit to energize solenoid 671 of RS670 by line 687 to source line 515, thereby disengaging contacts 669 and opening the circuit of lines 668-677 to de-energize solenoid 675 of RS676. TR686 then makes a circuit to energize the solenoid 678 of RS676 by line 688 to open contacts 679 and close the connection of pipe 425 to the valve 427 as the end 683 thereof is de-energized. Closed contacts 680 then complete the circuit of service line 537 to energize the solenoid 691 of relay switch RS692 by line 690 to source line 515; RS692 having an opposed solenoid 693 and contacts 694.