US2700951A

US2700951A - Apparatus for internal coating of containers

Info

Publication number: US2700951A
Application number: US271235A
Authority: US
Inventors: Smith Lee Thornton
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1952-02-12
Filing date: 1952-02-12
Publication date: 1955-02-01
Anticipated expiration: 1972-02-01

Description

Feb. 1, 1955 T. SMITH 2,700,951 APPARATUS FOR INTERNAL COATING OF CONTAINERS Filed Feb. 12, 1952 4 Sheefis-Sheet l INVENTOR F 1 L5; 275mm Feb. 1, 1955 T. SMITH APPARATUS FOR INTERNAL COATING OF CONTAINERS Filed Feb. 12, 1952 4 Sheets-Sheet 2 COH77/V6 Mmwa 007' INVENTOR Lee 7. 5111171] BY W A RNEY Feb. 1, 1955 L. T. S MITH 2,700,951

APPARATUS FOR INTERNAL COATING OF CONTAINERS Filed Feb. 12, 1952 4 Sheets-Sheet 3 INVENTOR j" 3 Leg 1." 51111'111 j 4% Feb. 1, 1955 L. T. SMITH 2,700,951

APPARATUS FOR INTERNAL COATING OF CONTAINERS Filed Feb. 12, 1952 4 Sheets-Sheet 4 2?- 5 Le OR ISE Y United States Patent APPARATUS FOR INTERNAL COATING OF CONTAINERS Lee Thornton Smith, Marion, Ind.,

assignor to Radio Corporation of America,

My invention pertains to an apparatus for applying a coating to the inner surface of a closed vessel for example an envelope of an electron discharge device and particularly for applying a coating of an electrically conductive material to the inner surface of an envelope or bulb of a cathode ray tube.

In electrical circuits wherein cathode ray tubes are used and the phosphor screen is energized by means of a high velocity electron beam, secondary electrons are emitted by such screen. For best operation and to prolong the life of the screen of the tube, the secondary electrons must be collected as quickly as they are produced and removed from the vicinity of the screen. If such secondary electrons are not carried away, the phosphor screen is bombarded by them with the result that the phosphor material is burned and the life span of the tube is thereby decreased. One solution to this problem is the provision of a conductive coating on the inner surface of the envelope or bulb of a cathode ray tube. Such conductive coating is suitably biased to collect and draw oif the secondary electrons.

During the period when round and comparatively small (on the order of 14 to 17 inches) cathode ray tubes were in use, the industry developed a satisfactory method of applying the internal conductive coating. According to this method, an operator inserts a hinged brush into the tube envelope, and while the tube is rotated, the conductive coating is painted on the inner surface by the brush.

As rectangular cathode ray tubes were introduced into use, and larger envelopes were developed, such a method of coating the interior of the tube became less satisfactory. It developed that the corners of the surface near the face plate were so inaccessible that the bulb could not be coated unless the operator hand-painted them at a very slow rate. Furthermore, it was found that the quality of such a coating was low and that the coating had a tendency to peel and blister.

A further difficulty was the poor appearance of the edge of the coating in the vicinity of the screen. Because of the method of deposition, the coating edge, necessarily, was uneven and jagged in appearance. The physical arrangement of the coating which produced this poor appearance also reduced the operative life of the tube because the coating was furthest away from the screen in the corners where it should have been as close as possible to receive the secondary screen electrons. It was found that the uneven edge of the coating in the vicinity of the screen produced X burn, which is the name I apply to a localized reduction in phosphor efliciency which takes the form of a letter X spread across the face of the screen with its origins in the corners of the screen. The solution to this problem was to move the coating closer to the screen and provide a smooth and even edge on the coating in the vicinity of the screen. Attempts to provide this solution by means of the above described brush method of applying the internal conductive coating have proved unsatisfactory.

Electron discharge devices other than cathode ray tubes may present a problem with respect to the collection of secondary electrons. In addition other containers than envelopes of electron discharge devices may require internal coatings. These other devices may also be coated internally by the apparatus of my invention.

Accordingly, the principal object of my invention is to provide an improved method and apparatus for applying a coating to the inside surface of a closed receptacle having a small opening.

Another more specific object of my invention is to provide an improved method and apparatus for applying a conductive coating to the inside surface of an electron discharge device.

A further object of my invention is to provide a method and apparatus for applying to the inner surface of a cathode ray tube a conductive coating which lies close to the phosphor screen and has a smooth and even edge in that vicinity.

A further object of my invention is to provide a method and apparatus for applying a conductive coating to an electron discharge device by coating the conductive fluid rapidly and evenly over such surface and without foaming and spattering of the fluid material.

Another object of my invention is to provide a method and apparatus for applying a conductive coating to the internal surface of a cathode ray bulb in which the level of the coating in the vicinity of the screen is automatically controlled.

In general, I accomplishthe purposes and objects of my invention by positioning the envelope or bulb of an electron discharge device in a vertical direction with its open end down. I then fill the envelope with a liquid suspension of the conductive material through the open end. I feed the fluid into the tube until it has reached the desired level and then I remove the fluid from the tube. In the most satisfactory embodiment of my invention, which is particularly suited for mass production coating, I control the filling of the bulb and all other steps of the process automatically by a sequentially operating electrical control system.

The invention is described in detail below with reference to the drawings wherein:

Fig. 1 is a schematic representation of one embodiment of my invention;

Fig. 2 is a side view, partly in section, of the flow coating and vent rod assembly as positioned within the neck of a tube envelope;

Fig. 3 is a schematic diagram of the electrical control system of my invention;

Fig. 4 is a side view of an alternative control arrangement for use in coating metal tubes; and,

Fig. 5 is a schematic diagram of the electrical control system modified to accommodate the alternative arrangement shown in Fig. 4.

The detailed description of my invention is subdivided according to the various components of the apparatus as follows.

Tube and flow coating rod assembly Referring to Figures 1 and 2, a glass or metal envelope or bulb 30 of a cathode ray tube having a phosphor screen 32 deposited therein is mounted on a flow coating rod assembly 34 which acts, among other things, as a support for the bulb or envelope. The envelope is arranged vertically with its neck 36 and open end 38 down so that the conductive fluid may be fed into it from below. The flow coating rod assembly comprises a hollow coating draw pipe 40 which, in this case, is a metallic member and is provided with a threaded orifice 42 through which it is intended to pass the conductive fluid into and out of the tube. The draw pipe 40 is inserted at one end into a neck seal hose 44 with which it forms a liquid-tight seal. A hose clamp 46 is fastened around the hose and draw pipe to secure their liquidtight engagement. The other end of the draw pipe is provided with a stopper 48 which forms a liquid-tight seal therewith. A circular flange 52 is welded to the draw pipe 40 and a stopper clamping device comprising a clamping bar 54 is connected thereto by means of two bolts 55. The clamping bar 54 engages the stopper and forces it into liquid-tight engagement with the draw pipe 40.

The stopper 48 is provided with an opening through which a vent pipe 50 is adjustably inserted. The vent pipe 50 has an opening at each end and the upper opening is intended to be maintained above the fluid level in the envelope 30. The vent pipe 50 is provided at this inner end with a cap 56 and a plurality of slots 58 just below the cap for allowing the passage of air into and out of the tube. The vent pipe is vertically adjusted before the tube envelope is slipped over it. The other end of the vent pipe is connected by means of a hose 60 and a safety device 61 to an air manifold pipe 62 which is provided with connections to a source of atmospheric pressure, and exhaust apparatus (not shown), and a source of low pressure air (not shown). The last mentioned group of apparatus is described further below.

The vent pipe 50 has soldered to it a conical baffle or skirt 66 which is in the shape of a frustum of a cone. The baffle is mounted on the vent pipe with its larger base 68 down. When the envelope 30 is positioned on the flow coating rod assembly 34 the baffle is located where the neck 36 of the envelope begins to bell out to a larger diameter. The neck seal hose member 44 tits in liquid tight engagement with the neck 36 of the envelope.

The purpose of the baffle is to control the turbulence of the liquid as it enters the draw pipe and rises into the expanded bulb of the tube. Without such a baffle the entering fluid would boil and foam and ricochet off the walls of the draw pipe hose and neck and spatter onto the phosphor screen, thus ruining the tube. However, as can be seen from the drawing, the baifle slows the incoming fluid and intercepts any ricocheting droplets which might otherwise strike the screen. The baffle also minimizes the turbulence of the fluid so that it does not boil in but enters smoothly with little turbulence in the center of the widening pool inside the bulb. This reduction of center turbulence or boiling is the factor which sharply reduces the introduction of air into the coating which gives the effect of foaming of the fluid.

The flow coating rod assembly is mounted on a suitable support member 70 by means of the circular flange 52 which is bolted thereto.

The threaded opening 42 in the draw pipe 40 is provided with a suitable plumbing assembly which comprises an elbow 72 joined to a T member 74 which has an inlet orifice 76 and an outlet orifice 78.

Air flow system The vent pipe or rod 50 is joined to a hose 60 which is connected to a safety device 61. the top of which is higher than the level of liquid in the fluid reservoir. The device 61 is connected to the air manifold 62 which has connections to three solenoid operated valves 64, 80 and 82. These comprise solenoids which move plunger armatures to operate the valve mechanism. The valve 64 is designed to be opened to the atmosphere through an orifice 63. The valve 80 is connected to an air exhaust device (not shown) and the valve 82 is connected to a source of low pressure air (not shown). All of the solenoids are embodied in an electrical circuit which allows them to be controlled automatically and sequentially. The electrical circuit will be described further below.

Fluid circulation apparatus The particular embodiment herein described utilizes gravity feed of the conductive fluid for filling the cathode ray bulb. However, any other feed system which provides suitable control of the fluid entering the tube could be used.

The conductive fluid 83, which may comprise an aqueous suspension of graphite in a silica binder, is stored in an upper tank 84. The tank is connected to a coating fluid manifold 86 which conducts the coating fluid to the various coating positions, one of which is shown in detail in Fig. l. The manifold, in turn, is joined by means of a hose or tube 88 to the inlet orifice 76 of the T member 74. The hose 88 passes through an inlet pinch clamp 90 which is normally closed at the end of a cycle of operation. The outlet orifice 78 of the T is linked through a tube or pipe 92 to a trombone antioverflow device 94 and finally to a lower storage tank 96. The tube 92 passes between the operative members of. an outlet pinch clamp 98 which is normally open at the end of a cycle of operation. The inlet and outlet pinch clamps 90 and 98 respectively comprise

stationary base members

100 and 101 and

movable clamping members

102 and 103 which are controlled by air operated pistons. The cylinders 104 and 105 in which the pinch clamp pistons operate are connected by means of hoses 106 and .107 to a solenoid operated double-acting pinch clamp valve 108 which in turn is connected to a source of high pressure air (not shown) through a line 110. The high pressure air is the operating medium for the pinch clamps and passses from the line 110 through the valve 108 and into the pinch clamp cylinders 104 and 105 by way of the hoses 106 and 107. The function of the trombone anti-overflow device 94 will be described below.

A motor operated pump 112 is connected through suitable plumbing 114 between the lower tank 96 and the upper tank 84. A conventional float switch (not shown) is provided within the lower tank and whenever the fluid therein reaches the proper level for operating the switch, the pump motor is automatically switched on. The pump is thus designed to operate intermittently and in such a manner that some fluid is always retained in the lower tank. The reason for this is that the particular pump used in this embodiment is a high capacity device. and would soon lose its prime if it were not stopped before the lower tank was completely empty. Also. air would be mixed with the conductive fluid it the pump operated continuously (especially if the lower tank went dry periodically). However, other pumping arrangements may be employed.

A by-pass line 116 is provided between the upper and lower tanks for circulation of the conductive fluid in case of inactivity of the bulb-filling portion of the circulation system. It is desirable to keep the fluid in continuous circulation in order to maintain the graphite particles in the proper state of suspension.

The trombone anti-overflow device 94 is a safety feature provided in case of failure of the circulating pump. Consider the bulb-filling apparatus idle and no bulb in position. Assume the pump to be circulating the fluid through the by-pass line 116 into the lower tank 96 and back to the upper tank 84. If the pump were not functioning, all the coating in the upper tank would soon be in the lower tank, filling it to the brim. Since the liquid level in the lower tank would be higher than the top of the bulb neck seal 44, gravity flow of coating would occur from the lower tank, through the outlet hose 92 and the neck seal, to the floor. This is possible because the exit pinch clamp is normally open when the apparatus is idle. The trombone anti-overflow device is thus inserted in the line between the tank and the neck seal with the top of the bend of the trombone higher than the top of the lower tank. Thus, an extremely high level of coating in the lower tank cannot cause an overflow through the neck seal.

The air flow system also performs a safety function for the fluid flow equipment in case the automatic electric control system, to be described below, fails to operate.

The open air solenoid valve 64, the low air pressure solenoid valve 82, and the air exhaust solenoid valve 80 may all be positioned at a level which is higher than the coating in the upper tank. However, as shown, it is sufficient to provide a safety device such as 61 which extends above the fluid level in the upper tank. Thus, if the fluid continues to rise in the bulb due to failure of the electrical control system, it enters the slots 58 in the vent pipe, travels down inside the pipe to the connecting hose 60, and then upward through the safety device 61 until it can rise no further. since it has reached its own level in the upper tank. If this protective arrangement were not provided. the conductive fluid would enter the vent line manifold 62 to which all three solenoid valves are connected, and foul it in addition to impairing the operation of these valves. With such a protective arrangement provided, after the operator notices that an overflow has occurred, he is able to stop the apparatus by means of an emergency switch.

The electrical control system and operation The electrical system and the operation of the entire apparatus will be described at one time. Referring, in addition, to Figure 3, to prepare the assembly for operation, a main switch 118 is closed. To initiate the operating cycle, a starting switch 120 is closed by the operator, whereupon current flow energizes a relay havin a sole noid 122 and four

armatures

124, 126, 128 and 130. The armature 124 which is normally closed is moved to the o en position and a cycling light 131 is thereby turned off. The li ht had been turned on at the end of the previous operating cycle when the armature 124 was moved to the closed position due to interruption of current flow through the solenoid 122. The cycling light is thus turned off to indicate the beginning of another cycle of operation. The normally open holding contact armature 126 is also closed and the armature 130 is moved to the closed position. The armature 130 forms part of the circuit of a solenoid operated relay associated with a photocell arrangement which is described in detail below. The armature 128 is also closed and the resulting current flow energizes a solenoid 132 in the open air valve 64. The solenoid 132 operates a plunger armature 133 which is normally in the open valve position.

When the solenoid 132 is energized the armature 133 is moved to the closed valve position and the vent pipe 50 access to the atmosphere through the opening 63 (Figure l) is thereby closed. The same current flow which energizes the solenoid 132 also energizes a solenoid operated pinch clamp valve 108 which comprises a fill solenoid 134, an empty solenoid 136 and a common plunger armature 138. The armature 138 controls openings in the pinch clamp valve 108 which admit air from the high pressure air source (not shown) and transmit it to the fill or inlet and empty or outlet pinch clamps 90 and 98. At the end of a cycle of operation, the armature 138 is in such position that the valve opening 140 to the outlet pinch clamp 98 is open and the opening 141 to the inlet pinch clamp 90 is closed. Thus the high pressure air source (not shown) is connected to the pinch clamp 98 whereby that clamp is maintained open and the inlet pinch clamp is maintained closed. With the apparatus thus arranged, the outlet fluid flow line 92 is open and the inlet flow line 88 is closed. Thus when the operative cycle of the apparatus is initiated and the fill clamp solenoid 134 is energized, the plunger armature 138 is moved to open the fill pinch clamp and close the empty pinch clamp. At this time, fluid flows from the upper tank 84, through the coating manifold 86 and the inlet pipe or hose 88 and into the flow rod assembly 34. The fluid then passes into the hollow draw pipe 40 and the neck seal 44, past the conical baflie 66 and into the envelope 30.

The same current flow which energizes the valve solenoid 132 and fill solenoid 134 also initiates the operation of a conventional timer 142 which comprises a motor having a commutator which is designed to close a contact 144. After the predetermined period of time has elapsed and the timer closes the contact 144, the resulting current flow therethrough energizes the air exhaust valve solenoid 146 which moves a plunger armature 148 to open the valve 80 and thereby connects the exhaust apparatus (not shown) to the vent pipe 50. Air is thus exhausted from the tube envelope through the vent pipe. This arrangement speeds the flow of fluid into the tube by reducing the air pressure above the level of the liquid entering therein.

An electric eye arrangement comprising a light source 150 and a photocell or phototube 152 is positioned adjacent to the tube envelope at the level to which it is desired to raise the conductive coating. When the liquid reaches the predetermined level, light is cut off from the photocell 152 and current flow through an electric eye solenoid 154 is discontinued. When this happens a normally closed armature 156 is opened and current flow to the solenoid 134 through the conductor 157 is discontinued.

At the same time an armature 158 is closed and current flow therethrough and through the armature 130 energizes the solenoid 136 which, in turn, moves the plunger 138. Thereby, the double acting armature 138 is operated to open the air flow path between the high pressure air source and the inlet pinch clamp 90 and close the air path to the outlet pinch clamp 98. Thus, the inlet pinch clamp is closed, the outlet pinch clamp is opened and the inlet path 88 to the envelope is closed and the outlet path 92 is opened. With the apparatus thus arranged fluid flow into the tube is discontinued and flow out of the tube through the hose 92 is begun. The current which energizes the empty solenoid 136 also energizes a low pressure air valve solenoid 137. The solenoid 137 moves a plunger armature 139 to open the valve 82 and a source of low pressure air (not shown) is thereby connected to the vent pipe 50. Thus a stream of air pours into the tube envelope and aids the removal of the conductive fluid. The same current which energizes the empty solenoid 136 also energizes another conventional timer 160 of the same type as the timer 142. After the predetermined time for which the timer is arranged has passed, a contact switch 162 is closed and current flows through another circuit breaker solenoid 164 which opens a normally closed armature 166. This action cuts olf current flow through the solenoid 122 and ends the cycle of operation. This results in returning the armature 124 to the closed position whereby the cycling light 131 is turned on to indicate the end of the operating cycle.

A manually operated switch 168 is provided for opening the circuit through the solenoid 122 and thus stopping the apparatus in case of an emergency.

The armatures and 158 are arranged to perform a joint function which will now be described. Assuming, for example, that the armature 130 were omitted from the apparatus, then, after timer had counted out the time to drain the bulb and had energized the solenoid 164 to end the operation of the cycle. The armature 158 would still be closed and the empty solenoid and low pressure air solenoid would still have voltage applied to them. In this condition, low pressure air would continue to pour through the vent pipe and the envelope. Thus the dripping bulb would have to be removed with air blowing through it and there would be danger of splashing the screen during the removal. Since the electric eye beam remains broken with no bulb in position due to the fact that the beam is focused through the refractive walls of the glass envelope, this condition continues until a second bulb is loaded. The situation could be remedied by throwing the safety or emergency switch, however, it is desirable to have the apparatus shut off automatically. To fulfill this need the armature 130 is inserted in the circuit so that only when the solenoid 122 is energized can air blow into the tube through the vent pipe. Thus when the solenoid 164 is energized and the circuit to the solenoid 122 is broken, the armature 130 is moved to the open position and all units become inoperative except the cycling light and the photoelectric eye arrangement. The latter is maintained in an energized condition so that there is no need for warm-up for each cycle of operation and the apparatus may thus function continuously and smoothly.

In case of failure of the electric eye arrangement to operate as described, the apparatus is designed to function as follows. Conductive fluid continues to flow into the envelope until it overflows through the slots in the vent pipe and rises in the tube 60 until it reaches its own level in the safety pipe 61. At this time, the operator of the apparatus closes the starting switch, however, since the electric eye beam is broken by the coating in the envelope, the tube filling apparatus will not operate. However, a current path through the line 153 and

armatures

158 and 130 provides for energization of the low pressure air valve solenoid 137. Thus the air stream will blow all of the fluid in the tube 61, hose 60 and vent pipe 50 back into the bulb and out into the lower tank. Timer 160 eventually shuts off the apparatus, but the operator presses the start button again and again, to operate the low pressure air source and air dry any coating adhering to the walls. At the end of this operation, the ruined bulb is removed, placed on a truck which will take it to be washed clean, and the offending position is again ready for operation. In the meantime, the operator has been operating the other positions unaffected by the accident.

The arrangement of the electric eye, above described, is suitable for a glass cathode ray envelope. If it is desired to apply the principles of my invention to a metal tube, a side arm 169 (Figure 4) may be attached to a draw pipe of a flow coating rod assembly 172.

A suitable fluid inlet and outlet pipe 170 is provided near one end of the assembly 172. The top opening 171 of the side arm has a rubber or other similar stopper 173 inserted therein. The stopper 173 is provided with an opening 175 to permit air to escape as the conductive fluid rises in the side arm.

A probe 177 is inserted through the stopper 173 to the level of coating in the side arm corresponding to the desired level in the tube envelope.

The probe may be substituted in the electrical control system by a few simple changes as shown in Figure 5. The electric eye is removed and the probe is inserted in cooperative relationship with the solenoid 154. When the probe contacts the coating, a circuit is completed from the probe through the coating and through the various tanks, pumps, and piping to ground. Thus an instantaneous electrical circuit is completed from the positive side of the power line through the armature 128, the

conductor 183, the solenoid 154, conductor 185, the probe and conductive coating to ground. The current through the solenoid 154 moves an armature 181 to the closed position which results in a short circuit across the probe 170. Thus, the solenoid 154 is maintained energized when the conductive fluid recedes in the side arm 169.

The energized solenoid also opens the armature 156 and closes the armature 158 which sets the remainder of the electrical system into operation as described above.

Having fully described my invention what I claim is:

1. Apparatus for applying a conductive coating to the inner surface of an electron tube envelope having a neck portion and a flared portion, said neck portion having an open end, said open end being the sole opening into said envelope, said apparatus comprising a support for holding said envelope in a vertical position with neck portion open end down; a fluid tight assembly for positioning said apparatus in said open end of said envelope, said assembly comprising a hollow tubular means for passing fluid, an inlet tube and outlet tube connected to said tubular means for conducting fluid into and out of said envelope, and an air flow pipe passing through said assembly with one portion disposed within said envelope and another portion extending outside of said envelope and beyond the open end thereof, a conical skirt positioned on said pipe for controlling the turbulence of said fluid, the flared end of said conical skirt being so positioned on said pipe that when the assembly is mounted in operative position in the neck, the flared end of the conical skirt is positioned substantially at the junction between said neck portion and said flared portion, the opening of the portion within said tube being positioned above a predetermined level within said tube; a source of conductive coating fluid connected to said inlet and outlet tubes; flow control means associated with said inlet and outlet tubes for controlling the flow of fluid therethrough; a source of air pressure, an air exhaust means, and a connection open to the atmosphere arranged to be selectively switched into oper ative relationship with said pipe; a light source and a photocell arranged in cooperative relationship at a predetermined position for operation at said predetermined level on said envelope and arranged to produce an electrical control signal when the fluid has reached said predetermined level; and electrical means for sequentially controlling the operation of said flow control means and for connecting said source of air pressure, said exhaust means and said connection to the atmosphere with said air flow pipe in response to the signal developed by said photocell.

2. Apparatus according to claim 1, wherein means are provided to act in cooperation with said envelope for focusing light from said light source onto said photocell, whereby said flow control means is rendered inoperative except when said envelope is properly indexed with respect to said apparatus.

References Cited in the file of this patent UNITED STATES PATENTS 2,303,290 Michael Nov. 24, 1942 2,444,572 Leet et a1 July 6, 1948 2,449,783 Laidig et al Sept. 21, 1948 2,538,562 Gustin et al Jan. 16, 1951 2,582,822 Evans Jan. 15, 1952 FOREIGN PATENTS 532,886 Great Britain Feb. 3, 1941