US3516204A

US3516204A - Abrading apparatus

Info

Publication number: US3516204A
Application number: US661861A
Authority: US
Inventors: Walter Kulischenko
Original assignee: Pennwalt Corp
Current assignee: Pennwalt Corp
Priority date: 1967-08-21
Filing date: 1967-08-21
Publication date: 1970-06-23
Anticipated expiration: 1987-06-23
Also published as: FR1577017A; CH516976A; BE719639A; CH543349A; DE1777013A1; NL6811940A; BE719638A; SE344700B; GB1232034A

Description

June 23, 1910 INVENTOR. Walrer KUIISChGflkO ATTORNEY.

United States Patent 3,516,204 ABRADING APPARATUS Walter Kuliscllenko, Staten Island, N.Y., assignor, by

mesne assignments, to Pennwalt Corporation, Philadelphia, Pa, a corporation of Pennsylvania Filed Aug. 21, 1967, Ser. No. 661,861

Int. Cl. B24c 3/ 00 US. Cl. 51-4) Claims ABSTRACT OF THE DISCLOSURE I This invention relates to abrading apparatus of the type employed for carefully controlled removal of material from a workpiece, and more particularly to an improved exhaust system therefor.

Abrading apparatus includes a mixing chamber which combines pressurized air and abrasive material in the desired proportions and issues a uniformly concentrated stream of airborne particles through a supply line to a nozzle. The cutting action of the nozzle is carefully controlled by traversing it with a mechanism which should be kept free of abrasive particles if it is to endure. Also, in order to have control of the nozzles cutting effect, it is desirable to guard against variations in abrasive concentration heretofore caused by starting and stopping of the abrasive stream.

Conventionally, the abrasive stream is pinched off at the outlet of the mixing chamber upon termination of an abrading operation, whereupon the pressure in the supply line decays to atmospheric pressure by slow release through the tiny nozzle orifice and abrasive particles deposit in the supply line. On restarting flow for the next abrading operation the deposited particles from the previous operation are carried off by the leading portion of the new stream, with the result that the first portion of a restarted stream has an abnormally high abrasive concentration; and there is also the problem of afterfiow during the mentioned pressure decay when the supply is again terminated at the mixing chamber.

Relocation of the pinch valve to the nozzle end is not entirely practicable, not only because of structural complications but also because there is still the danger of clogging the nozzle with abrasive residue and the uncertainties of having abrasive material at static pressure within the supply line.

As a solution, the present inevntion proposes to divert the abrasive stream to the exhaust line through a bypass or shunt line upon termination of any one abrading operation, preferably while pinching off the supply line at the outlet of the mixing chamber. As a result, the nozzle is bypassed but may be kept open. The establishment of a connection to a suction line clears the supply line of abrasive material and readies the apparatus for the succeeding abrading operation.

The exhaust line is connected between a suction device and a ducted exhaust hood. The latter may be positioned in closely spaced relationship above a table or holder for a workpiece, with a flared end portion to promote the ingress of air which carries spent abrasive particles from the work site through the exhaust line to collecting container. Further in accordance with the invention, the exhaust hood receives a tubular nozzle holder through an adapter which permits movement of the nozzle holder 3,516,204 Patented June 23, 1970 relative to the hood and provides a seal therebetween to prevent loss of suction by the hood.

In the drawings:

FIG. 1 is a schematic illustration of apparatus constructed according to the invention.

FIG. 2 is a fragmentary sectional view through an exhaust hood for practicing the invention.

The illustrated abrading apparatus will now be described as applied to the trimming of a thick-film resistor or other workpiece designated by the numeral 10, utilizing an abrasive stream issuing from a nozzle 12. The latter is supplied through a supply conduit 14 by a mixing chamber 16 where pressurized air from a compressor 18 is uniformly mixed in the desired proportions with abrasive powder from a reservoir 20. By means of a unique arrangement more fully described in the present inventors application Ser. No. 365,123, filed May 5, 1964, now US. Pat. No. 3,344,524, granted Oct. 3, 1967, a vibrator 22 is employed to produce an automatically replenished trickle of about 3 to 5 grams per minute of abrasive powder, such as aluminum oxide with an average particle size of 27 microns, from the reservoir 20 to the mixing chamber 16 for combining with air at about 40 to pounds per square inch pressure.

The flow of airborne abrasive particles is initiated by the energization of a solenoid operated pinch valve 24 in the upstream end of the supply conduit 14, that is, at the outlet of the mixing chamber 16. With the nozzle 12 having a restricted (.018 inch diameter) orifice of much smaller cross-sectional flow area than the .093 inch diameter supply conduit 14, the entire system is pressurized. As previously noted, uniform cutting action depends on a uniform concentration of particles in a constant airstream so that it is desirable, not only to remove spent particles from the work site to prevent damage to wearable parts, but also to c ear the supply conduit 14 of abrasive powder between operations to avoid an unduly heavy concentration of powder on a restarted air stream following pressure decay in the supply conduit.

The supply conduit 14 may be a flexible hose of abrasion resistant material, but it is preferred that at least the terminal or end portion adjacent the nozzle 12 be of rigid tubular construction so that it can serve as nozzle holder 26 capable of having its movements accurately controlled by a traversing mechanism 28 connected thereto by a rigidly constructed arm 30. The nozzle holder 26 is suitably journalled in the extended free end of the arm 3!), in upright position above a holder 32 for the workpiece 10. For the sake of brevity, details of construction of the traversing mechanism 28 are omitted from the present disclosure; and it will suffice to note that the mechanism serves to move the nozzle 12 by its holder 26 transverse to the longitudinal extent of the holder, or into and out of the plane of the drawing illustrating the apparatus, whereby the abrasive stream is traversed along the length of the workpiece to cut or abrade along the line of travel. The traversing mechanism 28 responds to signals received via conductors 34 from a control 36 to move a controlled distance first in one direction and then usually in opposite direction upon completion of an abrading operation. The control 36 also sends energizing current through conductors 38 to the solenoid of pinch valve 24 to effect its closing upon completion of an abrading operation; but otherwise during abrasive trimming the pinch valve 24 is held open.

Having recognized the potential danger of destructive wear to moving parts posed by spent abrasive particles deposited about the abrading site and deflected from the workpiece 10, it has been proposed heretofore to enclose the traversing mechanism 28 and other movable parts in plastic bags. These, however, have not proved entirely 3 successful in practice; and the present invention is therefore directed to an arrangement for effectively removing spent abrasive material by means of a unique exhaust system now to be described.

A suction device 40 utilizing an air translating device or fan (not shown) is employed to apply suction to an exhaust duct or conduit 42 connected to a ducted hood 44 positioned above and in closely spaced relation to the workpiece holder 32, with the encircling wall structure of the hood being formed about the upright nozzle holder 26. The upper, horizontal portion of the hood 44 is apertured to loosely receive the end of the supply conduit 14 or nozzle holder 26, and also the associated portion of the arm 30. The loose fit accommodates the traversing lateral movement of the nozzle holder 26 and therefore permits the hood 44 and exhaust conduit 42 to be stationarily mounted in securely fixed relation to the workpiece holder 32 and other fixed parts of the apparatus.

Provision is also made to maintain the nozzle holder parts extending through the hood aperture in sealing relationship with the hood 44 even though they are movable relative to one another. As shown, a sealing device generally designated by the numeral 46 comprises a felt washer 48 snugly fitting the assembly at its inner surface and resting with a metal washer 49 in the hood aperture between an upper nylon washer 50 which rides on the top surface of the hood and a lower washer 52 of neopreneimpregnated nylon cloth which rides on the underside of the hood, with top and bottom

metal retaining washers

54 and 56 cooperating with vertically disposed screws 58 for holding the assembly together. It is to be noted that there is ample clearance between the edge of the aperture in hood 44 and the outer edges of washers 48 and 49 to permit considerable lateral movement of the assembly 46 while the felt washer 48 maintains a seal with the nozzle holder 26 and associated parts; and the washers 50 and 52 extend horizontally to such an extent that even at the limits of lateral movement of the assembly 46 a seal with the upper and lower surfaces of the hood 44 is maintained by the mutually facing and contacting surfaces. As a result, the ducted hood 44 permits the nozzle 12 to perform all its functions without interference, and yet low pressure is maintained within the hood for drawing in air as well as entrained, spent abrasive particles for disposal via the exhaust conduit 42. The flared lower end configuration of the hood 44 ensures maximum air moving efiiciency. Moreover, the hood 44 is molded from any suitable plastic material which renders this part transparent so that the cutting end of the apparatus may 'be observed abrading a workpiece while the hood is positioned for clearing the work site of spent particles and material removed from the workpiece.

Optionally the control 36 may be employed to adjust the vibrator 22 by transmission through electrical conductors 58.

The invention also contemplates that the exhaust system will be placed in communication with the supply conduit 14 by means of at least one, and preferably two or more,

bypass conduits

60 and 62 connected between the exhaust conduit 42 and the supply conduit 14 at locations adjacent the respective opposite ends thereof. The

bypass conduits

60 and 62 are provided with respective solenoid-operated, normally closed

valves

64 and 66 which move to open position on signal from the control 36 via conductors 68. These bypass conduits 60 and 62 serve as shunt passages for diverting the abrasive stream from the nozzle 12 to the suction device 40 when an abrading operation is terminated, thus keeping the supply conduit 14 clear of deposited abrasive material between abrading operations.

If the pinch valve 24 were to be omitted from the apparatus or was to remain open at the end of an abrading operation it can be seen that the bypass lines would still divert all or most of the abrasive stream into the exhaust system until, on signal from control 36 deenergizing the solenoids of

valves

64 and 66, the

bypass conduits

60 and 62 were reclosed to repressurize the supply conduit 14 and reestablish flow to the nozzle 12. Preferably, however, on termination of an abrading operation simultaneous signals are sent from control 36 through conductors 34, 38 and 68 to reverse the traversing mechanism 28, close the pinch valve 24, and open the

bypass valves

64 and 66. As a result, in a matter of milliseconds the nozzle 12 is moved backwards, the supply of airborne abrasive material from the mixing chamber is stopped, and pressure in the supply conduit 14 is relieved partly through nozzle 12 and partly through communication with the exhaust conduit 42 simultaneously with diversion of the abrasive stream and clearing of the supply conduit 14.

From the foregoing it can be seen that the invention effectively extends the useful life of the apparatus and improves the accuracy and dependability of its performance.

What is claimed is:

1. Abrading apparatus for removing material from a workpiece comprising:

a holder for the workpiece,

means including a supply conduit and a nozzle at one end of the supply conduit for directing a high velocity stream of abrasive particles to a workpiece held by said holder,

exhaust means including a ducted hood in closely spaced relation to said holder, an exhaust conduit having one end connected to said hood, and a suction device connected to the other end of said exhaust conduit for exhausting abrasive particles after they have abraded upon said workpiece, said one end of said supply conduit being in sealing relationship with said hood and mounted for movement relative thereto,

and means for traversing said one end of said supply conduit and the nozzle carried thereby along the length of said holder for abrading along said workplece.

2. Abrading apparatus according to claim 1 wherein said holder includes a generally horizontally disposed, upwardly facing surface for supporting said workpiece, said hood is a downwardly opening and downwardly flaring wall structure disposed above said surface of said holder, and said one end of said supply conduit extends through the wall structure of said hood.

3. Abrading apparatus according to claim 2 wherein said one end of said supply conduit supports said nozzle, being of rigid tubular construction and being relatively movable along said holder for directing a generally upright abrasive stream toward said workpiece.

4. Abrading apparatus according to: claim 1 wherein said hood comprises wall structure made of transparent material to provide a view therethrough of abrading taking place on the surface of said holder.

5. Abrading apparatus according to claim 1 wherein said holder and said hood are stationarily mounted.

6. Abrading apparatus according to claim 4 wherein said wall structure of said hood is provided with an aperture loosely receiving said one end of said supply conduit to permit free movement thereof, and further including washers of flexible and gas impervious material annularly disposed on said one end of said supply conduit, said washers having their edges in overlapping relationship with portions of said hood wall structure at the margin of said aperture to provide a seal between opposite surfaces of said hood wall structure and said supply conduit at said aperture.

7. Abrading apparatus for removing material from a workpiece comprising:

a holder for the workpiece,

first means including a supply conduit and a nozzle at one end of the supply conduit for directing a high velocity stream of abrasive particles to a workpiece held by said holder, wherein said nozzle has an orifice of smaller cross-sectional flow area than said supply conduit, exhaust means including a ducted hood in closely spaced relation to said holder, an exhaust conduit having one end connected to said hood, a suction device connected to said exhaust conduit for exhausting abrasive particles after they have abraded upon said workpiece, a bypass conduit between said supply conduit and said exhaust conduit, and a bypass valve in said bypass conduit normally closed during flow of abrasive particles through said nozzle, and control means for opening said valve when actuated, the flow areas of said exhaust conduit, said bypass conduit and said valve being larger than said nozzle orifice whereby flow is diverted from said nozzle to said exhaust conduit by opening said valve. 8. Abrading apparatus according to claim 7 wherein said means for directing a stream of abrasive particles further includes a mixing chamber supplied with pressuriz/ed air and particulate abrasive material and an outlet for airborne abrasive particles connected to said other end of said supply conduit, and further including a supply valve in said supply conduit at said other end thereof normally open during the flow of abrasive particles through said nozzle and responsive to actuation of said control means for closing said supply conduit to the flow of abrasive particles, whereby residual abrasive material in. said supply conduit is carried into said exhaust conduit.

9. Abrading apparatus according to claim 1 further comprising a supply valve at the other end of said supply conduit normally open to pass said stream of abrasive particles to said nozzle, a bypass conduit including a nor mally closed bypass valve connected between said exhaust conduit and said supply conduit between the ends thereof, and control means for effecting closing of said supply valve and opening of said bypass valve upon termination of abrading said workpiece.

10. Abrading apparatus according to claim 1 further comprising a bypass conduit including a normally closed bypass valve connected between said exhaust conduit and said supply conduit. and control means for effecting opening of said bypass valve and reversal of said traversing means upon termination of abrading said workpiece.

References Cited UNITED STATES PATENTS 537,160 4/1895 King 51--8 847,269 3/1907 Wise 51-12 955,468 4/1910 Motz 51-8 955,469 4/1910 Motz 51 s 2,455,514 12/1948 Mead 51-8 2,597,434 5/1952 Bishopet a1 51-12 3,075,318 1/1963 Dilliard et al. 51-8 3,344,524 10/1967 Kulischenko 51-12 X LESTER M. SWING LE, Primary Examiner