WO1996019404A1

WO1996019404A1 - Submicron particle feeder

Info

Publication number: WO1996019404A1
Application number: PCT/US1995/016934
Authority: WO
Inventors: Michael E. Everett
Original assignee: Crystal Mark, Inc.
Priority date: 1994-12-21
Filing date: 1995-12-20
Publication date: 1996-06-27
Also published as: AU4609596A

Abstract

An apparatus (140) for feeding a powder (106) of submicron particles in a pressurized gas comprises an upper feed chamber (104), a lower mixing chamber (108), a first gas inlet conduit (142) for introducing a first pressurized gas into the feed chamber (104) at a first pressure, a second gas inlet conduit (146) for introducing a second pressurized gas into the mixing chamber (108) at a second pressure, a delivery conduit (162) in communication with the lower mixing chamber (108) for transporting a flow of powder (106) and pressurized gas from the mixing chamber (108), and a regulator (174) for maintaining a pressure differential between the first pressure and the second pressure so that the first pressure is lower than the second pressure by between at least about 5 psi to about 30 psi. The apparatus (140) can be used to alter a target (200) such as by cutting or polishing, or can be used to coat a target (200) with fine particles.

Description

SϋBMICRON PARTICLE FEEDER Background The delivery of fine powder and pressurized gas through a nozzle has a variety of uses including cutting, abrading, deburring, polishing and texturing materials. Some specific industrial uses include contouring and cutting semiconductor wafer edges, conformal coating removal from electronics, ceramic cleaning, and plastic deflashing. Medical uses include porcelain crown preparation for adhesion and tooth detail carving. Other uses include the cleaning of fossils and gemstones, and glass engraving.

In conventional apparatus for delivering mixtures of fine powder and pressurized gas, one or more gas inlet conduits serves to deliver pressurized gas to the top of a feed chamber equalizing the pressure gradient between the feed chamber and a lower mixing chamber. This conventional arrangement facilitates movement of the particles and gas towards the lower mixing chamber and is effective in supplying a mixture of powder and pressurized gas for many uses. An example of such a system is the SWAM-BLASTER® (micro-abrasive sandblaster) Model MV-1 available from Crystal Mark, Inc. Glendale, CA. However, the conventional arrangement has difficulty in delivering a mixture of powder and pressurized gas when the diameter of the particles in the powder is less than about 5 microns. The limitation on the ability of conventional systems to deliver a mixture of powder having very small particle sizes and pressurized gas has led to the use of buffing wheels, chemical/mechanical polishing equipment or lapping equipment as alternatives. Mechanical wheels, however, generate heat making them inappropriate for many uses involving semiconductors and the like, and can not be used on some types of fragile material.

For the foregoing reasons, there is a need for an apparatus and method for creating a mixture of powder having a very small particle size and pressurized gas for delivery through a conduit. 1 Summary The present invention is directed to an apparatus that satisfies this need. The apparatus can create a mixture of powder having a very small particle size, such as 0.25 microns, and pressurized gas for delivery through a conduit. The apparatus comprises an upper feed chamber for the fine powder and a lower mixing chamber for receiving the powder from the feed chamber. A first gas inlet conduit introduces a first pressurized gas into the feed chamber at a first pressure and a second gas inlet conduit introduces a second pressurized entrainment gas into the mixing chamber at a second pressure. A delivery conduit communicates with the lower mixing chamber for transporting a flow of powder and pressurized gas from the mixing chamber. A regulator maintains a pressure differential between the first pressure and the second pressure so that the first pressure is lower than the second pressure by at least about 5 psi.

The apparatus can be used to deliver a mixture of powder having particles with a diameter of less than about 5 microns, and even submicron particles with a diameter of 0.25 microns. This is effected by placing the powder in the feed chamber, and causing the first gas to flow into the feed chamber and the second gas to flow into the mixing chamber. The first gas and the second gas can be the same gas from the same source, or different gases from different sources. Vibration agitates the feed chamber and mixing chamber, facilitating transfer of powder from the feed chamber to the mixing chamber. Once in the mixing chamber, the powder mixes with and is entrained by the second gas, and the mixture is transported to the delivery conduit through the discharge port connecting the mixing chamber with the delivery conduit.

The mixture of fine powder and gas is discharged from the delivery conduit to a target material such as semiconductor wafers, ceramic, plastic, porcelain, tooth, fossil, stone or glass, where the powder can cut, abrade, debur, polish or texture the material, among other uses. The fine powder can also be used to coat a target, thus creating a new surface.

Drawings These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings where:

Figure 1 is a vertical cross section through a feed chamber and mixing chamber of an apparatus for mixing powder and pressurized gas as is known in the prior art;

Figure 2 is a vertical cross section through the feed chamber and mixing chamber of an apparatus for mixing powder and pressurized gas according to the present invention; and Figure 3 is a schematic diagram of a system for delivering a controlled flow of a mixture of powder and pressurized gas through a delivery conduit according to one version of the present invention, showing the relation of the feed chamber and mixing chamber illustrated in Figure 2 to other parts of the system. Description

Referring now to Figure 1, there is illustrated a vertical cross section through a portion of a prior art apparatus for mixing powder and pressurized gas as is known in the prior art. The apparatus 100 comprises a housing 102 having therein an upper feed chamber 104 for the powder 106 and a lower mixing chamber 108 for receiving powder 106 from the feed chamber 104. The apparatus 100 further comprises a base 110 for securing the housing 102 to a vibrator, not illustrated, and a cap 112 having a door 114 and an "O" ring 116 therein. The cap 112 is affixed to the housing 102 by a cap nut 118 threadingly engaged onto the housing 102 by threads 120.

The apparatus 100 has a single gas inlet conduit 122 affixed to the housing 102 by a fitting 124. The single gas inlet conduit 122 communicates with an internal conduit 126 which passes from the mixing chamber 108 into the feed chamber 104, communicating with the upper portion of the feed chamber 104 by an opening 128.

Pressurized gas from the gas inlet conduit 122 passes into the internal conduit 126 and thereby to the top of the feed chamber 104. Powder 106 and pressurized gas then pass to the lower mixing chamber 108 through apertures 130 in a plate 132 separating the upper feed chamber 104 from the lower mixing chamber 108. Movement of the pressurized gas and the powder 106 from the feed chamber 104 to the mixing chamber 108 is down a pressure gradient created by the introduction of pressurized gas at the top of the feed chamber 104. The mixture of powder 106 and pressurized gas passes from the lower mixing chamber 108 into a delivery conduit (not shown) by a discharge port 134 and thereby to a nozzle (not shown) for delivery to a material.

In contrast to conventional systems, I have unexpectedly discovered how to uniformly and continuously produce a mixture of powder and pressurized gas where the diameter of the particles in the powder is less than about 5 microns, thereby overcoming the particle size limitation inherent in the prior art. This is effected by supplying separate pressurized gas inlet conduits into a feed chamber and a mixing chamber, and by utilizing a regulator on the pressurized gas inlet conduit into the feed chamber. This configuration allows me to maintain the pressure in the mixing chamber higher than the pressure in the feed chamber with the surprising result that very fine particles, including submicron particles, can be fed. The ability to create a mixture of powder having a very small particle size and pressurized gas for delivery through a conduit advantageously permits uses where the delivery of larger particles is inappropriate. For example, this apparatus can be used to polish very fine grooves and can be used on fragile material where the use of powders having larger particle sizes would not be possible. Further, the apparatus can be used to deliver a stream of fine particles for coating materials.

Referring now to Figure 2, there is illustrated an apparatus 140 embodying features of the present invention.

The same reference numbers are used to describe the apparatus 140 for similar items shown in Figure 1.

The apparatus 140 comprises a housing 102 having an upper feed chamber 104 and a lower mixing chamber 108 therein. The apparatus 140 further comprises a base 110 for securing the housing 102 to a vibrator 164, illustrated in Figure 3, and a cap 112 having a door 114 and "O" ring 116 therein. The cap 112 is affixed to the housing 102 by a cap nut 118 which is threadingly engaged onto the housing 102 by threads 120. The upper feed chamber 104 communicates with the lower mixing chamber 108 by apertures 152 in a screen 150. The apertures 152 can be formed by discrete holes in a solid plate or by using a mesh as the screen 150. The screen size is from about 40 mesh to about 320 mesh. The screen 150 can also be a plurality of multiple screens, having the same or differing sizes of mesh. Passing the powder through a plurality of screens can advantageously assist in breaking down clumps of powder into individual particles, thereby improving powder flow. In a preferred embodiment, the screen 150 comprises at least three screens having decreasing aperture size toward the lower mixing chamber.

Referring to Figures 2 and 3, a first gas inlet conduit 142 is connected to the upper feed chamber 104 by a first fitting 144. A second gas inlet conduit 146 is connected to the mixing chamber by a second fitting 148.

To use the apparatus 140, a first gas is introduced through the first gas inlet conduit 142 and into the top of the upper feed chamber 104. A second entrained gas is introduced through the second gas inlet conduit 146 into the lower mixing chamber 108.

A vibrator 164 agitates the housing 102, thereby causing the powder 106 to pass from the upper feed chamber 104 through the screen 150. Other techniques known in the art, such as suction blasting can be used to cause particles to flow into the mixing chamber 152 into the lower mixing chamber 108. The powder 106 then mixes with the second pressurized gas and passes from the lower mixing chamber 108 through a delivery conduit 162, illustrated in Figure 3, by a discharge port 134. Regulator means, such as a controllable pressure regulation 174 controls the pressure of pressurized gases through the first gas inlet conduit 142 such that a pressure differential is set up where the first pressure at the top of the feed chamber 104 is lower than a second pressure in the lower mixing chamber 108. This pressure differential is preferably between about 5 psi and about 30 psi during operation of the apparatus. A pressure differential less than 5 psi is not conducive to the uniform and continuous delivery of a fine powder having a particle size of about 5 microns or less to the lower mixing chamber 104. A pressure differential greater than about 30 psi tends to cause inconsistent delivery of fine powder from the upper feed chamber 104 into the lower mixing chamber 108. Therefore, using a differential pressure between about 5 psi and about 30 psi allows the fine powder to be fed through the delivery conduit at a substantially uniform rate for a period of time at least about 10 seconds to about an hour or more depending on the capacity of the feed chamber.

As used herein, "powder having a particle size of about 5 microns or less" or "powder having a particle size of about 0.25 microns or less" or a similar phrase refers to a powder in which the diameter of at least half of the particles making up the powder have a maximum diameter of about 5 microns or less, or about 0.25 microns or less, respectively. While the apparatus 140 can be used to deliver powder and pressurized gas where the powder has particles with a diameter greater than 5 microns, one advantage of the present invention is that it can be used to deliver very small particles.

Preferably, a single gas source is used for both gas streams. A source of pressurized gas 168 delivers gas to a main gas conduit 170. The main gas conduit 170 divides into the first gas inlet conduit 142, which enters the upper feed chamber 104, and the second gas inlet conduit 146, which enters the lower mixing chamber 108. A main gas conduit, variable, pressure regulator 172 on the main gas conduit 170 controls the pressure of gas from the pressurized gas source 168 to the first gas inlet conduit 142 and the second gas inlet conduit 146. The first gas inlet conduit regulator 174 in the first gas inlet conduit 142 serves to establish the pressure differential between the top of the upper feed chamber 104 and the lower mixing chamber 108. A filter 176 prevents back flow of powder 106 into the first gas inlet conduit 142.

The means for maintaining the pressure differential can also include different cross-sectional areas of the first gas inlet conduit 142 and the second gas inlet conduit 146. In a preferred version of the present invention, the cross- sectional area of the first gas inlet conduit 142 is smaller than the cross-sectional area of the second gas inlet conduit 146 by at least about 15%. In a particularly preferred version of the present invention, the pressure differential is maintain by using a first gas inlet conduit 142 which is smaller than the cross-sectional area than the second gas inlet conduit 146 by at least about 50%, as well as a first gas inlet conduit regulator 174 on the first gas inlet conduit 142.

A delivery conduit 162 transports pressurized gas and fine powder 106 from the lower mixing chamber 108. A hand piece 178 connects the delivery conduit 162 proximally with an optional nozzle 180 distally. The entrained powder 190 is impinged onto a target 200 for cutting, abrading, deburring, polishing, texturing or coating the target.

A second gas inlet conduit valve 182 in the second gas inlet conduit 146 serves to stop and start gas flow into the lower mixing chamber 108. A delivery conduit valve 184 in the delivery conduit 162 serves to stop and start the flow of powder 106 and pressurized gas from the lower mixing chamber 108 into delivery conduit 162. A control 188 opens and closes the two valves 182 and 184. Preferably, the control 188 is a footswitch which can be operated by an operator.

A variety of substances can be used as the powder in the apparatus 140. Examples of such substances include powderized aluminum oxide, walnut shell, dolomite, soda bicarbonate, silicon carbide, glass bead, crushed glass, tungsten disulfide, diamond dust, cerium oxide and plastic media.

The apparatus 140 can be used as follows. A selected powder or mixture of powder is added to the feed chamber 104 by unscrewing the cap nut 118 and opening the door 114 in the cap 112. After the powder 106 is added to the feed chamber 104 the cap nut 118 is secured to the housing 102. Next, gas flow from the source of pressurized gas 168 is begun through the main gas conduit 170. Preferably, the flow is between about 1 to about 5 standard cubic feet per minute. In a particularly preferred version, the flow rate is about 3 standard cubic feet per minute. The flow is then divided between the first gas inlet conduit 142 and the second gas inlet conduit 146.

Gas through the first gas inlet conduit 142 enters the top of the upper feed chamber 104. Gas through the second gas inlet conduit 146 enters the lower mixing chamber 108. A pressure differential between the top of the upper feed chamber 104 and the lower mixing chamber 108 is established with a first gas inlet conduit regulator 174 on the first gas inlet conduit 142, with or without using a first gas inlet conduit 142 having a smaller cross-sectional area than the second gas inlet conduit 146. The pressure differential is such that the pressure at the top of the feed chamber 104 is lower than the pressure in the mixing chamber at least about 5 psi. Preferably, the pressure differential is between about 5 psi and 30 psi.

The vibrator 164 connected to the housing 102 is actuated, thereby agitating the feed chamber 104 and the mixing chamber 108. This facilitates transfer of the powder 106 from the feed chamber 104 to the mixing chamber 108 through the apertures 152 in the screen 150.

Flow through the delivery conduit 162 is begun by actuating the control 188 thereby opening up the second gas inlet conduit valve 182 in the second gas inlet conduit 146 and the delivery conduit valve 184 in the delivery conduit 162. Fine powder 106 is entrained in the pressurized gas and flows through the delivery conduit 162 and out the nozzle 180. The nozzle 180 directs the stream for delivery to a material, thereby cutting, abrading, deburring, polishing, texturing, coating or otherwise altering as desired. Then, the control 188 is shut off, stopping the flow of powder 106 and gas through the delivery conduit 162. The vibrator 164 is then shut off and the flow of gas through the main gas conduit 170 stoppe .

Although the present invention has been described in considerable detail with reference to certain preferred versions thereof, other versions are possible. For example, instead of a single source of pressurized gas 168, multiple sources can be where one source supplies the first gas inlet conduit 142 and another supplies the second gas inlet conduit 146. When multiple gas sources are used, the composition of the gas supplied by the sources can be substantially the same or can be substantially dissimilar. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

Claims

WHAT IS CLAIMED IS;

1. An apparatus suitable for delivering a flow of an entrained powder of particles with a diameter less than about 5 microns, the apparatus comprising: (a) an upper feed chamber for a powder of particles with a diameter less than about 5 microns;

(b) a lower mixing chamber for receiving the powder from the feed chamber;

(c) a first gas inlet conduit for introducing a first pressurized gas into the feed chamber at a first pressure;

(d) a second gas inlet conduit for introducing a second pressurized gas into the mixing chamber at a second pressure for entraining the powder therein, thereby producing a flow of entrained powder;

(e) a delivery conduit in communication with the lower mixing chamber for transporting the flow of entrained powder from the mixing chamber; and

(f) means for maintaining a pressure differential between the first pressure and the second pressure so that the first pressure is lower than the second pressure by at least about 5 psi so that entrained powder flows from the mixing chamber into the delivery conduit.

2. The apparatus of claim 1 further comprising a powder of particles with a diameter less than about 5 microns in the feed chamber.

3. The apparatus of claim 2 where the powder is selected from the group consisting of aluminum oxide, walnut shell, dolimite, soda bicarbonate, silicon carbide, glass bead, crushed glass, tungsten disulfide, diamond, cerium oxide, and plastic media.

4. The apparatus of claim 1 where the means for maintaining maintains the pressure differential of no more than about 30 psi.

5. The apparatus of claim 1 where the first gas inlet conduit has a smaller cross-sectional area than the second gas inlet conduit.

6. The apparatus of claim 1 further comprising a vibrator for agitating at least the feed chamber, thereby facilitating transfer of the powder from the feed chamber to the mixing chamber.

7. The apparatus of claim 1 further comprising a nozzle in communication with the delivery conduit.

8. The apparatus of claim 1 further comprising a valve in the second gas inlet conduit for controlling flow of the second gas into the mixing chamber.

9. The apparatus of claim 8, where at least one of the first gas and the second gas is selected from the group consisting of air, carbon dioxide, and nitrogen.

10. The apparatus of claim 9, where the first gas has substantially a same composition as the second gas.

11. The apparatus of claim 1 further comprising a single source of pressurized gas in communication with both the first gas inlet conduit and the second gas inlet conduit, the single source of pressurized gas supplying both the first pressurized gas and the second pressurized gas.

12. The apparatus of claim 1 where the means for maintaining comprises a pressure regulator.

13. An apparatus suitable for delivering a flow of an entrained powder of particles with a diameter less than about

5 microns, the apparatus comprising:

(a) an upper feed chamber for a powder of particles with a diameter less than about 5 microns; (b) a lower mixing chamber for receiving the powder from the feed chamber;

(c) a first gas inlet conduit for introducing a first pressurized gas into the feed chamber at a first pressure; (d) a second gas inlet conduit for introducing a second pressurized gas into the mixing chamber at a second pressure for entraining the powder therein, thereby producing a flow of entrained powder; (e) a delivery conduit in communication with the lower mixing chamber for transporting the flow of entrained powder from the mixing chamber; and

(f) means for maintaining a pressure differential between the first pressure and the second pressure so that the first pressure is lower than the second pressure by at least about 5 psi so that entrained powder flows from the mixing chamber into the delivery conduit; and

(g) at least one screen disposed between the upper feed chamber and the lower mixing chamber, the screen having a plurality of openings therethrough which allows the powder in the feed chamber to pass into the mixing chamber.

14. The apparatus of claim 13 wherein the at least one screen is one screen.

15. The apparatus of claim 14 wherein the one screen is from about 40 mesh to about 320 mesh.

16. A method for feeding a powder into an entrain ent gas comprising the steps of:

(a) placing the powder into an upper feed zone located above a lower mixing zone; (b) introducing a first pressurized gas into the upper feed zone;

(c) introducing the pressurized entrainment gas into the lower mixing zone; and

(d) maintaining a pressure differential between the upper feed zone and the lower mixing zone, such that the pressure in the upper feed zone is at least 5 psi less than the pressure in the lower mixing zone causing the powder to flow from the upper feed zone into the lower mixing zone for entrainment by the entrainment gas, thereby producing a flow of entrained powder.

17. The method of claim 16 where the mixing zone and the feed zone are in a housing, the method further including the step of vibrating the housing to vibrate the powder.

18. The method of claim 16 where the powder in step (a) has a particle size of less than about 5 microns.

19. The method of claim 16 where the powder in step (a) is a submicron powder.

20. The method of claim 16 where the pressure differential between the two zones is no more than about 30 psi.

21. The method of claim 16 further including the step of feeding the entrained powder through a delivery conduit from the mixing zone.

22. The method of claim 21 where the entrained powder is fed through the delivery conduit at a substantially uniform rate for at least about 60 seconds.

23. The method of claim 21 where the entrained powder is impinged onto a target for cutting, abrading, deburring, polishing, texturing, or coating the target.

24. A method for feeding a powder into a gas stream comprising the steps of:

(a) placing the powder into an upper feed zone located above a lower mixing zone;

(b) providing a pressurized gas, introducing a first portion of the pressurized gas into the mixing zone at a first pressure, reducing the pressure of a second portion of the pressurized gas, and introducing the second portion of the pressurized gas having reduced pressure into the feed chamber at a second pressure; and (c) maintaining the pressures of the first portion of the pressurized gas and the second portion of the pressurized gas so that the second pressure is at least about 5 psi less than the pressure in the lower mixing zone to cause the powder to flow from the upper feed zone into the lower mixing zone for entrainment by the first portion of the pressurized gas.

25. The method of claim 24 where the step of maintaining comprises causing the first portion of the pressurized gas to flow through a first conduit prior to being introduced into the mixing zone, and the second portion of the pressurized gas to flow through a second conduit prior to being introduced into the feed zone, where the second conduit has a smaller cross-sectional area than a cross-sectional area of the first conduit.

26. The method of claim 24 wherein the step of maintaining comprises actuating a regulator valve through which the second portion of the pressurized gas flows prior to being introduced into the feed zone.

27. The method of claim 26 wherein the step of maintaining additionally comprises causing the first portion of the pressurized gas to flow through a first conduit prior to being introduced into the mixing zone, and the second portion of the pressurized gas to flow through a second conduit prior to being introduced into the feed zone, where the second conduit has a smaller cross-sectional area than a cross-sectional area of the first conduit.

28. A method of delivering a controlled flow of a mixture of powder and pressurized gas to a target comprising the steps of:

(a) providing an apparatus comprising an upper feed chamber for receiving the powder, a lower mixing chamber for receiving the powder from the feed chamber, a first gas inlet conduit for introducing a first pressurized gas into the feed chamber at a first pressure, a second gas inlet conduit for introducing the second pressurized gas into the mixing chamber at a second pressure, a delivery conduit for transporting the mixture of the powder and the pressurized gas from the mixing chamber by a discharge port, and a regulator for maintaining a pressure differential between the first pressure and the second pressure so that the first pressure is lower than the second pressure by at least about 5 psi;

(b) supplying a target for delivery of the mixture of the powder and the pressurized gas thereto; (c) actuating the apparatus, thereby causing the first gas to flow into the feed chamber and the second gas to flow into the mixing chamber;

(d) maintaining the pressure differential between the feed chamber and the mixing chamber such that the pressure in the feed chamber is lower than the pressure in the mixing chamber by at least about 5 psi;

(e) causing the powder to transfer from the feed chamber to the mixing chamber thereby mixing with the second gas in the mixing chamber, and the mixture of the powder and second gas to flow into the delivery conduit; and

(f) delivering the mixture of the powder and second gas through the delivery conduit to the target.