US 3852918 A
An abrasive reservoir is provided with an internal venturi tube arranged to establish a recirculating stream of pressurized gas and abrasive. Provision is made for diverting a portion of the abrasive laden gas, with a controllable valve interposed in the delivery line.
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Description (OCR text may contain errors)
United States Patent [191 Black GAS-ABRASIVE MIXING AND FEEDING DEVICE  Inventor: Robert B. Black, 2450 Morgan St.,
Corpus Christi, Tex. 278405  Filed: Mar. 29, 1972  Appl. No.: 239,211
 U.S. Cl. 51/12  Int. Cl. B24c 7/00  Field of Search 51/8, 12
 References Cited UNITED STATES PATENTS Wytcherley 51/12 UX Dec. 10, 1974 2,553,625 5/1951 Andersen 5l/l2 2,725,684 12/1955 Crowe 51/8 2,759,266 8/1956 Cassani 5l/l2 X Primary ExaminerD0nald G. Kelly Attorney, Agent, or FirmSynnestvedt & Lechner  ABSTRACT An abrasive reservoir is provided with an internal venturi tube arranged to establish a recirculating stream of pressurized gas and abrasive. Provision is made for diverting a portion of the abrasive laden gas, with a controllable valve interposed in the delivery line.
9 Claims, 1 Drawing Figure GAS-ABRASIVE MIXING AND FEEDING DEVICE This invention relates to equipment for mixing or incorporating abrasive particles into a gas stream and for delivery of the mixture to a suitable nozzle from which it escapes as a high velocity jet.
This general type of equipment is known, but the known forms of equipment have limitations, especially with respect to uniformity and accuracy of control over the ratio of abrasive to the pressurized gaseous carrier medium. Moreover, at least most of the prior systems employ a controllable shut-off valve so arranged in the system that the response to the action of the shut-off valve, both when opened as well as when closed, has an undesirable time delay factor.
It is a general objective of the present invention to provide a mixing and feeding system overcoming the disadvantages of prior art systems and also achieving other advantages as will further appear. In consequence the system of the present invention is well adapted to many uses for which other systems are not well suited. This is particularly true in connection with delicate dental operations including abrasive jet etching as described hereinafter, and also in many industrial applications, such as resistor trimming and the heatless, shockless cutting ofa wide variety of hard, brittle materials such as germanium, silicon, mica, glass, fragile crystals, ceramics and the like.
For any of the purposes referred to it is of great importance that the quantity of abrasive particles carried by the gaseous medium be uniform and be capable of accurate regulation. It is therefor an important objective of the present invention to provide for uniformity of feed of the abrasive particles and also for accurate control thereof. These characteristics of the equipment provided by the present invention make possible use of the present equipment for a much broader range of purposes and applications than has been practicable with prior known systems.
It is also an object of the invention to provide a control system which operates to start and stop the delivery of abrasive without any appreciable time delay.
Another objective of the invention is to eliminate the spurting and erratic flow of abrasive into the gaseous carrier medium which has been characteristic of various prior systems, particularly where the prior system depends upon a single, low velocity tube for feeding the abrasive into the gaseous carrier medium.
It is also an object of the invention to eliminate the use of vibrators, selenium rectifiers, rheostats, electric wiring, etc., as used and required by many prior art systems. In contrast, the system of the present invention is simple and reliable and readily adjusted.
How the foregoing and other objects and advantages are attained will appear more clearly from the following description referring to the accompanying drawing in which the single FIGURE is a somewhat diagrammatic view of equipment conforming with the present invention, certain parts being shown in section for convenience of illustration.
In the drawing, a receptacle indicated at l constitutes a reservoir for abrasive particles, the receptacle having a generally conical bottom end having a top wall indicated at 2 with a removable closure 3 threaded on the spout 4, with interposition of a sealing gasket 5. In a typical embodiment, the receptacle 1 may be cylindrical and from about 2 to 6 inches in diameter, and the body or charge of abrasive particles introduced will initially fill the receptacle to a level such as indicated at 6.
Although the system may be operated on any of a variety of pressurized gases, such as air, CO or other chemically inert gases, dry air is most convenient and for most purposes is preferred. A compressed air supply line is indicated in the drawing at 7, this line having a shut-off valve 8 therein which, as will further appear, is normally in the open position during intervals when the equipment is to be employed. The compressed air supply line is provided with 2 branches indicated at 9 and 10, the branch 9 being extended for connection with a pressure chamber 11 in the form of a cup connected with a lower end of the receptacle 1 at the apex of the conical bottom wall.
A venturi tube 12 is positioned within the receptacle 1 and has its lower or inlet end downwardly open for connection with the pressure chamber 11. A nozzle 13 formed centrally of disc 14 is positioned so as to deliver a stream of compressed air into the throat of the venturi tube 12. The nozzle 13 and disc 14 are desirably formed of rubber and the nozzle is preferably automatically collapsable so as to close across the passage from the pressure chamber 11 into the venturi tube at times when the abrasive stream is shut off. This closure of the nozzle 13 prevents undesired downward flow of abrasive particles from the venturi tube into the chamber 11. I
The inlet end of the venturi tube is provided with a series of apertures or ports 15 connecting with the surrounding space within the receptacle 1 and thus communicating with the mass or reservoir of the abrasive particles within the receptacle 1. 1
At its upper or discharge end, the venturi tube 12 is provided with a series of apertures or ports 16 also communicating with the interior of the receptacle 1, for a purpose to be explained more fully hereinafter.
An abrasive delivery connection 17 is connected with the upper end of the venturi tube 12 and is extended exteriorly of the receptacle 1. The connection 17 is adapted to communicate with the flexible tube 18 through the controllable shut-off valve 19. The free end of the tube 18 is provided with a discharge or jet nozzle 20 formed, for example, of tungsten carbide for wear resistance.
The branch 10 of the compressed gas supply line is extended for connection with the upper end of the venturi tube 16 adjacent to the point of connection of the delivery line 17. This branch 10 is provided with a controllable or variable choke valve 21. Each of branch lines 9 and 10 is provided with an automatic check valve 22 oriented to prevent flow from the abrasive reservoir back toward the compressed air supply line.
In a typical operation of the equipment just described, the compressed air supply line 7 delivers air under pressure through the branches 9 and 10 when the valve 8 has been open and this establishes a pressurized condition throughout the system. When the controllable valve 19 is opened, for instance by means ofa foot operated or other remote control device of known kind, an abrasive laden air stream flows from the delivery line 17 through the valve and through the flexible connection 18 to be discharged in the form of a jet from the nozzle 20. The adjustable choke valve 21 serves to deliver more or less abrasive free air from the branch 10 to the delivery connection 17. If this valve 21 is placed in the full open position, the quantity of abrasive particles carried by the air stream will be at a minimum. Complete closure of the adjustable choke valve 21 will shut off the direct flow of air from branch to the delivery connection 17 and all of the air reaching the delivery connection 17 will then flow through the branch 9 and through the venturi tube 12. This will deliver the maximum quantity of abrasive with the air.
Because of the presence of the ports through the wall of the inlet end of the venturi tube, abrasive particles will be drawn into the venturi tube through those ports and will thus be incorporated in the air stream. The presence of the ports 16 through the wall of the outlet end portion of th venturi tube results in flow of both air and abrasive particles from the venturi tube back into the abrasive reservoir. This produces a recirculation of air and abrasive within the receptacle 1. This recirculation occurs only when the controllable delivery valve 19 is open. At times when that valve is closed, the system remains pressurized, but no circulation occurs. The circulation will occur with any adjustment of the choke valve 21, although the volume of the recirculation will increase with decrease in the opening of the choke valve and will decrease with increase in the opening of the choke valve.
The recirculation of the air stream and abrasive above referred to produces a turbulence within the reservoir and this turbulence results in uniformity of the abrasive mixture delivered through the valve 19 to the nozzle. In effect, when the controllable delivery valve 19 is open, a portion of the recirculating abrasive laden air is diverted from the path of recirculation and delivered to the discharge or jet nozzle.
The system of the invention, including the recirculation of abrasive and air within the reservoir, together with the action of the choke valve 21 also provides a wide range of accurate adjustment of the quantity of abrasive delivered with the air stream.
The use of the flexible and collapsable nozzle 13 for delivering the air jet into the throat of the venturi tube 12 is highly effective in preventing undesired falling of abrasive particles downwardly into the pressure chamber 11. Each time the control valve 19 is closed, the nozzle 13 instantly collapses and thus closes the passage between the inlet end of the venturi tube and the pressure chamber 11. This is important in order to avoid an initial spurt of an excess of abrasive particles at the time when the valve 19 is opened.
Although not essential to the operation of the system, it is desirable to include the check valves 22 in the two gas supply branches 9 and 10. In this way under special conditions, such as moving the equipment, abnormal pressure fluctuations, and the like, abrasive particles will not be permitted to travel upstream in the branch connections 9 and 10.
As above mentioned, when the main shut-off valve 8 is open, the entire system is pressurized and ready for use, i.e., ready for delivery of abrasive upon opening of the normal control valve 19. It will be observed that the valve 19 is located in the delivery line at the output side of the reservoir and this is an important feature, because the opening of the valve 19 results in delivery of the desired abrasive jet without any appreciable time delay such as would be involved if the control valve 19 were eliminated and the valve on the input side such as valve 8 was used each time it is desired to deliver the abrasive jet. Reliance upon a valve at the input side of the system would require that the system be pressurized each time the control valve was opened and this would introduce an undesirable time lag in the delivery of the abrasive jet. Moreover the location of the normal control valve 19 on the output side of the system has the further advantage that when the valve is closed, the abrasive jet is virtually instantaneously terminated. In contrast, if the normal control valve was located on the input side of the system, the closure of that valve in an effort to terminate the abrasive jet would result in a time delay, with accompanying drizzle of the abrasive from the jet nozzle 20 during the interval of time required for the system to depressurize.
The system of the invention, especially the recirculation of the air and abrasive is of great importance in providing uniformity of admixture of abrasive particles with the air stream without the necessity for employing any vibrators or mechanical agitators. This is advantageous because of the simplification of the equipment, in addition to the advantages accruing from the greater uniformity of the admixture secured.
The system of the present invention is useable with various abrasive particles, but for many purposes aluminum oxide particles are preferred, advantageously in particular sizes running from about 10 microns to about 30 microns.
The air or other gas pressure employed may also vary over a broad range, for instance from about 20 p.s.i. to about 150 p.s.i., but for most purposes will run from about 40 p.s.i. to about p.s.i.
The passage in the nozzle 20 is desirably much smaller than any of the other passages in the system and should be only a small fraction of the total cross sectional area of the ports 15 in the inlet end of the venturi tube or of the ports 16 in the outlet end of the venturi tube. The nozzle passage will, of course, depend somewhat on the particular purpose for which the equipment is being used. For various of the purposes above referred to, nozzles having a bore in the range from about 0.0l8 to about 0.025 inch is suitable. ln atypical equipment in which the receptacle 1 is about 3 inches in diameter and in which the venturi tube is about 4 inches in length, the ports 15 in the inlet end of the venturi desirably comprise about six evenly spaced holes, each of about 0.065 inch diameter, while at the same time using about twelve equally spaced holes of about 0.055 inch diameter, as ports 16 in the upper or delivery end of the venturi.
As an example ofa typical use of the equipment, reference is made to the trimming of resistors. For this purpose, aluminum oxide particles of about 30 microns are desirably employed, and a jet nozzle having a bore of about 0.018 is used. Air under a pressure of about 80 p.s.i. is suitable for this purpose.
As another example, reference is made to the use of the equipment in applying plastic or resinous coating to teeth. For this purpose aluminum oxide particles of about 10 micron size are appropriate with a supply air pressure of about 80 p.s.i., and with a nozzle having a bore of about 0.018 inch. In the preparation of teeth for resinous coating, the jet is directed to the tooth surface and the action of the abrasive achieves three important results. First, organic matter is completely removed. Second, the surface of the tooth is etched in a manner providing a surface texture which is highly effective from the standpoint of adherence of the resin film to be applied. Third, the cleaning and etching are accomplished while at the same time establishing and maintaining a bone dry condition of the tooth surface. These objectives are achieved much more effectively by this abrasive preparation of the tooth surface, than is possible with other preparation techniques such as the use of phosphoric acid. In consequence, when the resin film is applied much greater life and adherence of the film is secured. This abrasive technique as applied to tooth surface is thus especially advantageous for tooth coating, particularly when the coating material comprises a polermerizable resin, such as that known in the dental professioion as NuvaSeal, made by Caulk Division of Dentsply International, Inc. A resin material of this type when applied to a bone dry, etched surface of the kind produced by the system of the present invention may readily be cured or polermerized in situ as by exposure to ultra-violent light thereby providing an adherent coating without any appreciable elevation in temperature.
Still another use for which the equipment of the invention is especially adapted, is dental prophylaxis. in this case it is preferred to employ a relatively soft abrasive, for instance micron calcium carbonate. The calcium carbonate should be of crystalline form and may be derived, for example, from Iceland Spar or from fresh water clam shells, high grade silicate free white marble. For prophylaxis purposes, a nozzle bore of 0.018 inch is suitable, and an air supply pressure of about p.s.i. The use of the equipment and method for dental prophylaxis is highly effective and will leave the tooth enamel well polished.
- I claim:
1. Equipment for use in mixing abrasive particles with a compressed gas, comprising a reservoir for abrasive particles, a venturi tube in the reservoir, the tube having its inlet end portion apertured to provide communication with the interior of the reservoir, an abrasive delivery connection extended from the discharge end of the venturi tube, the discharge end portion of the venturi tube being apertured to provide communication with the interior of the reservoir, and means for causing abrasive particles to circulate through the venturi tube and the reservoir and to deliver abrasive particles through said delivery connection comprising a compressed gas supply line and a nozzle for delivering a stream of compressed gas from said line into the throat of the venturi tube through the inlet end of the tube.
2. Equipment as defined in claim 1 and further including a conduit interconnecting the compressed gas supply line and the abrasive delivery connection.
3. Equipment as defined in claim 2 and further including an adjustable choke valve in said conduit.
4. Equipment as defined in claim 3 and further including a check valve in said conduit between the choke valve and the abrasive delivery connection.
5. Equipment as defined in claim 1 and further including a controllable shut-off valve in said delivery connection.
6. Equipment for use in mixing abrasive particles with a compressed gas, comprising a reservoir for abrasive particles, a venturi tube in the reservoir, the tube having its inlet end positioned in a lower region of the reservoir and having apertures in communication with the interior of the reservoir, the tube having its discharge end positioned in an upper region of the reservoir and having apertures in communication with the interior of the reservoir, an abrasive delivery connection connected with the discharge end of the venturi tube downstream of the apertures in the discharge end, a compressed gas supply line having one branch connected with the inlet end of the venturi tube arid a second branch connected with said abrasive delivery connection, a nozzle directed into the inlet end of the venturi tube for delivering a stream of compressed gas from said one branch into the throat of the venturi tube, and a controllable shut-off valve in said abrasive delivery connection.
7. Equipment for use in mixing abrasive particles with a compressed gas, comprisinga reservoir for abrasive particles, a venturi tube having a throat and inlet and outlet ends extending in opposite directions from the throat and progressively increasing in cross section as compared with the throat, the inlet end of the venturi tube being presented downwardly adjacent the bottom of the reservoir and having abrasive inlet portage below the venturi throat, the oulet end of the venturi tube being presented upwardly in the reservoir and having abrasive outlet portage through the wall of the outlet end above the venturi throat, a valved delivery line connected with the venturi tube above the outlet portage, a compressed gas supply line connected with the inlet end of the venturi tube, and a nozzle in the connection of the gas supply line with the inlet end of the venturi tube, the nozzle being extended into the inlet end of the venturi tube and serving to deliver a compressed gas jet through the throat of the venturi tube, the abrasive inlet portage providing for inlet of the abrasive in a zone surrounding said nozzle.
8. Equipment for use in mixing abrasive particles with a compressed gas, comprising a reservoir for abrasive particles, a venturi tube having a throat and inlet and outlet ends extending in opposite directions from the throat and progressively increasing in cross section as compared with the throat, the inlet end of the venturi tube being presented downwardly adjacent the bottom of the reservoir and having abrasive inlet portage below the venturi throat, the outlet end of the venturi tube being presented upwardly in the reservoir and having abrasive outlet portage through the wall of the outlet end above the venturi throat, a valved delivery line connected with the venturi tube above the outlet portage, a compressed gas supply line connected with the inlet end of the venturi tube, and a nozzle in the connection of the gas supply line with the inlet end of the venturi tube, the nozzle being positioned to direct a stream of compressed gas into the throat of the venturi tube.
9. Equipment as defined in claim 8 in which the abrasive inlet portage comprises a plurality of apertures through the wall of the inlet end of the venturi tube