GB2097291A - A coating material atomizing a dispensing apparatus - Google Patents

Abstract

Apparatus (Fig. 1) for atomizing and dispensing a coating material includes a turbine (10) having a housing (12) and a shaft (56) rotatably supporting an atomizing device (11). The turbine includes a turbine wheel (88) having a set of vanes (98) against which jets of air are directed from nozzles (80). The wheel (88) has another set of vanes (230) and a nozzle (224) directs a jet of air against these additional vanes (230) to brake the turbine when the coating material delivery rates or the coating material characteristics require braking, to maximize turbine bearing life, minimize wear, or optimize coating material atomization characteristics. <IMAGE>

Description

SPECIFICATION A coating material atomizing a dispensing apparatus This invention relates to a coating material atomizing and dispensing apparatus, which includes a turbine wheel with a feedback speed control system for driving a rotatable atomizing device.

Various drive mechanisms for a coating material atomizing device are known, see for instance U.S. Patents Nos. 2,759,764; 2,754,226; 3,358,931; 1,853,682; and 3,011,472, and U.S. Reissue Patent No.

24,602. Some devices have been driven by electric motors at the same potential as the target or at a different potential, which promoted transfer of coating material from the atomizing device to the target.

Many coating devices are known which are driven by fluid motors, such as air motors, see for instance U.S. Patents Nos. 3,067,949; 3,121,024; and 2,711,926. The increasing use of such fluid motors is attributable, in part, to the ease with which the rotational speed of an atomizing device driven by such a motor can be varied by varying the fluid pressures to the motor input.

With such devices, rotation speeds of 10,000 rpm to 30,000 rpm have been used.

However, many of the low solvent-content, or so-called "high-solids," coating materials now increasing in popularity require still higher rotation speeds, of 40,000 rpm and more for best atomization. To reach the 40,000 rpm range, air- or other fluid-turbine drives have been employed. The atomizing devices used with such turbine drives have been small diameter devices, e.g., in the 20 mm to 80 mm diameter range. A problem associated with the use of such small devices is that they have small angular momentum. Changes in some characteristics of coating materials being dispensed from an atomizing device can cause significant variations in the rotational speed of the device by changing the loads on the fluid motor. The same is true for such devices when switched from a coating material dispensing mode to an idling mode (e.g., between articles on a coating line).These observations are particularly true of low horsepower (e.g., fractional horsepower) fluid motors. The changing loads represented by changing coating material characteristics, colour change operations on an automated coating line, and switching between coating material dispensing modes and idling modes have detrimental effects on motor loads and therefore on motor-bearing wear and other motor parameters and characteristics. Further, the inability to control atomizing device rotation speeds, both by acceleration and deceleration, results in waste of material and time on a multiplecoating line where, for example, the atomizing device has to "coast down" to the optimum rate to atomize one coating material after dispensing another coating material at a higher rate. The time factor is important in a high-throughput assembly line coating operation.The waste of coating material between jobs is to be avoided for economic and environmental reasons.

Changing characteristics of the coating materials include changes in viscosity, solids content and specific gravity. Unfortunately, in many cases, for example where colour changes are carried out between the finish coating of successive articles on a production line, the very act of changing the colour results in a substantial change in the characteristics. This occurs simply because it is not always possible to match every pertinent characteristic of every different coating material which is being used on the line. This results unavoidably in changes in the load on the fluid motor.

According to this invention, a coating material atomizing and dispensing apparatus includes a rotatable device for atomizing coating material; means for supplying coating material to the device; a fluid motor having a driven wheel; means coupling the driven wheel to the atomizing device to rotate the latter; a driving fluid input for directing driving fluid against the driven wheel tending to accelerate it; a source of driving fluid; means for controlling flow of driving fluid from the driving fluid source to the driven wheel; a braking fluid nozzle; a source of braking fluid; and means for controlling flow of braking fluid from the braking fluid source to the braking fluid noz zle; wherein the driven wheel includes a braking fluid vane or bucket and the braking fluid nozzle directs braking fluid from the braking fluid source to the braking fluid vane or bucket so as to counteract the tendency of the wheel to accelerate in the direction determined by driving fluid flow from the driving fluid input.

The driven wheel may include a periphery providing a series of vanes or buckets against which driving fluid is directed, tending to accelerate the driven wheel, and the surface providing the braking fluid vane or bucket includes an axially facing surface. Also the driven wheel may include a plurality of such braking fluid vanes or buckets oriented about the axis of the wheel and disposed radially between the axis and the periphery of the wheel. Eaxh such braking fluid vane or bucket may include a generally radially extending surface which is substantially flat and oriented at an angle, for example 30 to the axis of the wheel, against which braking fluid is directed.

Further, each braking fluid vane or bucket may also include a somewhat part-cylindrical surface.

The invention will now be described by way of example, with reference to the drawings in which: Figure 1 is a partly block diagrammatic and partly fragmentary longitudinal sectional view of part of a coating material atomizing and dispensing apparatus, including a fluid motor and atomizing device; Figure 2 is a partly fragmentary side elevation of a detail of the fluid motor seen in Fig.

1; Figure 3 is an end elevation of the apparatus of Fig. 2, as seen from plane 3-3 of Fig.

2; Figure 4 is a plan view of a detail of the apparatus of Fig. 1; and Figure 5 is a fragmentary perspective view of the apparatus of Fig. 4.

Referring to Fig. 1, a turbine fluid motor 10 for rotating an atomizing device 11 includes a housing 12 which is, for example, cast aluminum. Housing 1 2 is supported from an insulating post 14 by bolts 1 6 which extend through a collar 1 8 on housing 1 2 and into the reduced lower end portion 20 of post 14.

A lead 22 is attached between a bolt 1 6 and a source 23 of high electrostatic potential 23 (illustrated diagrammatically) to place the fluid motor 10 and atomizing device 11 at high electrostatic potential. The supply of electrostatic potential to device 11 causes the particles of coating material dispensed thereby to be electrostatically charged during the atomization and dispensing process to improve the coating efficiency of the atomized particles in accordance with well-known principles.

Housing 12 is divided into an atomizing device side housing portion 32 and a support means side housing portion 34 joined together by a plurality of cap screws 36 (only one of which is shown). Housing portion 32 includes a central cylinder 44 which extends longitudinally through portion 32 from inside housing 12 to surface 50 of portion 32. A removable cartridge 48 housed within cylinder 44 and captured between housing portions 32, 34 carries the turbine's rotary components.

With specific reference now to cartridge 48, a motor shaft 56 extends longitudinally through a sleeve 49 in cartridge 48. Sleeve 49 includes press-fitted bearing races 52, 54 near its opposite ends. Bearing races 58, 60 are press-fitted onto portions 62, 64, respectively, of shaft 56. Suitable bearings 66 in races 52, 58 and 54, 60 support shaft 56 for rotation in housing 1 2. One end of shaft 56 is located in housing portion 32 by a locating nut 68 which holds outer race 54 in position in housing portion 32. Nut 68 is threaded into the end of sleeve 49.

The motor end of housing portion 32 includes a radially outwardly projecting, axially extending collar 71 providing an outwardly facing annular groove 72. An annular nozzle plate 74 is mounted in groove 72 by a plurality of screws 70 which extend through countersunk bores in nozzle plate 74 and mating threaded bores in grove 72. A sealing ring minimizes leakage of compressed air between collar 71 and cylinder 44. Another sealing ring 77 mounted on sleeve 49 also helps minimize the possibility of air escaping between cylinder 44 and sleeve 49.

Nozzle plate 74 is provided with one or more apertures or nozzles 80 at its periphery.

The nozzle plate 74 also contains an outwardly opening groove 82 in which is located a sealing ring 83 which seals the outer periphery of nozzle plate 74 to the inner side wall 84 of housing portion 32 to prevent leakage of compressed air therebetween.

The inner end 86 of shaft 56 is internally threaded. A driven turbine wheel 88 is placed on the inner end 86 of shaft 56 and held against rotation by a key (not shown). A washer 200 and screw 202 secure turbine wheel 88 against axial movement on shaft 56. Screw 202 tightens turbine wheel 88 against the inner race 58 on shaft 56.

Housing 1 2 is divided into a high-pressure or intake side 92 and a low-pressure or exhaust side 96 by nozzle plate 74. Turbine wheel 88 includes a plurality of generally radially extending vanes 98 about its outer periphery. Vanes 98 are in the path of compressed air flow through nozzle 80 between high-pressure side 92 and low-pressure side 96. As the compressed air expands through nozzle 80 from the high-pressure side 92 to the low-pressure side 96, this air reacts against vanes 98, causing turbine wheel 88 and motor shaft 56 to spin. In the fluid motor 10 of Fig. 1, a high-pressure side 92 pressure of 64.7 psia to 34.7 psia, variable to adjust the wheel 88 rpm, and a low-pressure side 96 pressure of 14.7 psia provide satisfactory results.

An air inlet 102 is provided in lower housing portion 32 to supply air from a source 104 of compressed air (illustrated diagrammatically) to high-pressure side 92 through a speed-control mechanism to be described. The speed-control mechanism controls the air pressure in high-pressure side 92, thereby controlling the pressure differential between highpressure side 92 and low-pressure side 96 and the rpm of turbine wheel 88.

An exhaust port 108 is provided in housing portion 34 to exhaust from low-pressure side 96 air which has already passed through nozzle plate 74 and wheel 88. Air can be exhausted to atmosphere directly, or through a muffler, or through a variable restrictor.

The shaft 56 supports a slinger 1 24 having a central aperture 1 26. Slinger 1 24 prevents coating material, e.g., paint, from migrating along shaft 56 away from atomizing device 11 and fouling the lower bearings 66 of motor 1 0. Slinger 1 24 also cooperates with nut 68 to provide a labyrinth seal 127 which serves to minimize the escape of compressed air from between nozzle plate 94 and turbine wheel 88, between bearing races 52, 58, sleeve 49, and shaft 56, and between bearing races 54, 60. Leakage of compressed air in the direction of device 11 must be minimized to avoid the detrimental effects of such leakage on the pattern of atomized locating material dispensed from device 11.

Device 11 includes a tapered central bore 1 30. The taper of bore 1 30 matches the taper of a portion 118 of shaft 56. These matching tapers facilitate mounting of atomizing device 11 on the shaft 56 and minize the possibility of misalignment of device 11 on the shaft 56, and the resultant imbalance.

These matching tapers 11 8, 1 30 permit device 11 to be replaced quickly and easily by another atomizing device of the same or a different type without the need for critical and time-consuming balancing procedures. Device 11 is held on motor shaft 56 by a bolt 1 50 which is threaded into a bore in portion 11 8 of shaft 56.

Referring now to Fig. 4, the turbine wheel 88 has an axially facing surface 1 52 which includes a black finish portion 1 54 and a smooth-surfaced, reflective, plated and brushed portion 1 56. Light from a light source 1 58 (Fig. 1) is transmitted via an optical fiber conductor 1 60 terminating in a head 1 62 to the surface 1 52. The reflective portion 1 56 of the turbine wheel 88 reflects the light back to head 1 62 where it is transmitted by another fiber optic conductor 164 back to a photoelectric receiver 166.

Potential separation between the relatively high magnitude potential, e.g., + 90KV to 150KV, on housing 1 2 and device 11 and ground is accomplished through electrically insulative fiber optic conductors 160, 1 64.

The head 1 62 and conductors 160, 1 64 are of a type such as the Spectral Dynamics Fiberoptic Cable Model 13134-GPT-1 available from Spectral Dynamics Corporation of San Diego, P. O. Box 671, San Diego, California, 92112.

The light pulses provided to the photoelectric receiver 1 66 through conductor 1 64 are amplified by a flip-flop amplifier, e.g., a Schmitt trigger, and converted in a frequencyto-voltage converter, both of which are included in receiver 1 66. The output of receiver 1 66 is therefore a voltage proportional to the speed of rotation of turbine wheel 88 and permits indication, for instance by means of a digital voltmeter, not shown. Alternatively, a frequency meter, not shown, could be coupled to the output of the pulse amplifier.

The voltage signal proportional to the speed of rotation is coupled to a comparator 1 70 which, contingent on the set value of a manually adjustable set value potentiometer 1 72 or of the set value output signal of a program control device 1 74 (as determined by the position of a switch 173), transmits a control voltage to an amplifier 1 76. The zero point and the limits for a voltage-pressure (V/P) transducer 1 78 are adjusted on amplifier 1 76. V/P transducer 1 78 can be, for example, a Fairchild Model 5109 Transducer from Fairchild Industrial Products Division, 1 501 Fairchild Drive, Winston-Salem, North Carolina, 27105.The output signal of 0.2 to 1 bar of transducer 1 78 is amplified by a pressure amplifier 1 80 to a value of approximately 1 to 6 bars. Amplifier 1 80 can be, for example, a Fairchild Model 20#205103 1:6 Volume Booster, also from Fairchild Industrial Products Division. The air flow to the turbine wheel 88 can be shut off completely by means of a solenoid valve 1 82. Valve 1 82 can be, for example, a Skinner N.C. Solenoid V53 DA2020, 24 VDC Coil, from Skinner Electric Valve Division, Skinner Precision Industries, Incorporated, 95 Edgewood Avenue, New Britain, Connecticut, 06050.

In order to enable a quick rotational speed drop when changing coating materials or going to idle, the turbine is equipped with an additional braking air connection which is supplied by a braking air line 1 84. To reduce turbine wheel 88 speed, a control command "rotational speed reduction" is given by the program control device 1 74. A brief description of the program control device 1 74 will suffice for purposes of explanation. The program control device is programmable to provide an electrical output signal which varies in accordance with the characteristics of the desired coating materials to be dispensed from device 11 as targets to be coated are conveyed along a conveyor (not shown) past device 11.That is, the program which is stored in the program control device 1 74 and which controls the operation of the system illustrated in Fig. 1 includes stored information relative to the characteristics of each of such coating materials, and calls up the stored information relative to the characteristics of a particular coating material as that particular coating material is dispensed.This information relative to characteristics appears as a directcurrent electrical signal on line 1 92. Typically, each of the coating materials to be dispensed has associated with it a different DC voltage level on line 1 92. Typically, these DC voltage levels on line 1 92 are generated by closing of respective switches within the program control device 1 74, in accordance with the program stored therein, to couple different DC voltage supplies within the program control device to line 1 92. In any event, the different DC voltage levels appearing on line 1 92 command respective different pressures in lowpressure air line 40 and different pressures in the compressed air delivered from source 104 through V/P transducer 1 78, pressure amplifier 1 80, and solenoid valve 1 82 to the high pressure side 92 of nozzle plate 74.The program control device 1 74 calls up a new set value for the new coating material to the comparator 1 70. As long as the actual turbine wheel 88 speed exceeds this new set value, a braking valve 1 88 coupled between compressed air source 104 and braking air line 1 84 is opened by a switching amplifier 1 90 and the turbine wheel 88 is slowed by the braking air supplied by braking air line 1 84.

Turning again to Figs. 2-5, upper housing portion 34 is provided with a threaded aperture 220 which is oriented at an angle to the motor 1 2 axis of rotation. A threaded air fitting 222 provided with an air tube 224 is screwed into opening 220. The air tube 224 extends at the angle into close proximity to turbine wheel 88, and is formed with a bevelled end 234. In the assembled motor, the bevelled end 234 is closely spaced to a series of vanes or buckets 230 formed in surface 1 56 of wheel 88. Each bucket 230 includes a substantially flat, generally radially extending surface 236 inclined at an angle to the motor 1 2 axis of rotation and a curved, somewhat part-cylindrical surface 238. As best illustrated in Fig. 1, the braking air line 1 84 is attached to fitting 222. When the braking air valve 1 88 is opened by an electrical input signal from switching amplifier 1 90, braking air under pressure is directed from opening 234 into the braking air vanes, or buckets, 230, causing the wheel 88 to react in a direction opposite the direction in which it moves in response to the directing of air through nozzle 80 against vanes 98, thereby braking wheel 88 to a slower speed. The speed of wheel 88, of course, is continuously output through fiberoptic cable 164, and receiver 1 66 to comparator 1 70 where it is compared with the desired value from potentiometer 1 72 or program control device 174, as determined by the position of switch 1 73.

Claims (10)

1. A coating material atomizing and dispensing apparatus including a rotatable device for atomizing coating material; means for supplying coating material to the device; a fluid motor having a driven wheel; means coupling the driven wheel to the atomizing device to rotate the latter; a driving fluid input for directing driving fluid against the driven wheel tending to accelerate it; a source of driving fluid; means for controlling flow of driving fluid from the driving fluid source to the driven wheel; a braking fluid nozzle; a source of braking fluid; and means for controlling flow of braking fluid from the braking fluid source to the braking fluid nozzle; wherein the driven wheel includes a braking fluid vane or bucket and the braking fluid nozzle directs braking fluid from the braking fluid source to the braking fluid vane or bucket so as to counteract the tendency of the wheel to accelerate in the direction determined by driving fluid flow from the driving fluid input.

2. The apparatus of claim 1 wherein the driven wheel includes a periphery providing a series of vanes or buckets against which driving fluid is directed, tending to accelerate the driven wheel, and the surface providing the braking fluid vane or bucket includes an axially directed surface.

3. The apparatus of claim 2 wherein the driven wheel includes a plurality of braking fluid vanes or buckets disposed about the axis of the wheel and radially between the axis and the periphery of the wheel.

4. The apparatus of claim 3 wherein each braking fluid vane or bucket includes a generally radially extending surface against which braking fluid is directed from the braking fluid nozzle.

5. The apparatus of claim 4 wherein the generally radially extending surface is inclined at an angle not more than 45D to the axis of the driven wheel.

6. The apparatus of claim 5 wherein the generally radially extending surface is inclined at an angle of 30 to the axis of the driven wheel.

7. The apparatus of claim 4 wherein the nozzle is oriented at an angle to the axis of the driven wheel.

8. The apparatus of claim 4 wherein each braking fluid vane or bucket includes a partcylindrical surface.

9. A coating material atomizing and dispensing apparatus including a device for rotation to atomize coating material; means for supplying coating material to the device; a fluid motor having a driven wheel means for coupling the driven wheel to the atomizing device to rotate it; a driving fluid input for directing driving fluid against the driven wheel tending to accelerate it; a source of driving fluid; a valve for controlling the flow of driving fluid from the driving fluid source to the driven wheel; a braking fluid input; a source of braking fluid; a valve for controlling the flow of braking fluid from the braking fluid source to the braking fluid input; and a feedback mechanism for sensing motor speed and for controlling the driving fluid control valve and braking fluid control valve in response to sensed motor speed; and the driven wheel including a surface providing a braking fluid vane or bucket and the motor including a nozzle for directing braking fluid from the source to the braking fluid vane or bucket and means for coupling the nozzle to the braking fluid input, actuation of the braking fluid control valve causing braking fluid to flow from the nozzle and against the braking fluid vane or bucket, counteracting the tendency of the wheel to accelerate in the direction determined by driving fluid flow from the driving fluid input.

10. A coating material atomizing and dispensing apparatus constructed and arranged substantially as herein described and shown in the drawings.