US20050037697A1

US20050037697A1 - Abrasive media blast nozzle

Info

Publication number: US20050037697A1
Application number: US10/641,359
Authority: US
Inventors: Lance Nord; Gary Thompson
Original assignee: Media Blast and Abrasives Inc
Current assignee: Media Blast and Abrasives Inc
Priority date: 2003-08-14
Filing date: 2003-08-14
Publication date: 2005-02-17

Abstract

A nozzle used in an abrasive blast cleaning apparatus through which a plurality of abrasive particles is propelled. The nozzle has a first bore with a constant first diameter, a radially converging section, a throat section with a constant second diameter, a radially diverging section, a second bore, and a second bore having a constant third diameter. The first bore defines a first end for receiving the abrasive particles and a second end. The radially converging section defines a third end connected to the second end and a fourth end. The throat section defines a fifth end and a sixth end, wherein the fifth end is connected to the fourth end of the converging section. The radially diverging section defines a seventh end and an eighth end, wherein the seventh end is connected to the sixth end of the throat section. The second bore defines a ninth end and an exit, wherein the ninth end is connected to the eighth end. The constant first and third diameters are larger than the constant second diameter.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT RE: FEDERALLY SPONSORED RESEARCH/DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The following generally relates to nozzles and, more specifically, to an improved abrasive media blast nozzle suitable for delivering abrasive medium for removing unwanted materials from a substrate.
Abrasive blasting processes are widely used to remove unwanted materials from a substrate surface. In most cases, compressed air or other fluid is applied to propel abrasive particles such as sand, ceramic alumina, tungsten carbide, boron carbide, or silicon nitride through a conduit, against the substrate surface. Through a nozzle, the abrasive materials are accelerated to a high speed and collide with a target surface. The collisions force removes unwanted dirt or other materials away from the target surface.
For example, paint or dirt is often removed by propelling abrasive particles against building exterior surfaces. Likewise, in another example, ridges of material are sometimes removed from machined parts by abrasive blasting to thereby improve the surface finish of the part. Advantageously, the speed and efficiency of these abrasive blast processes can save significant amounts of money.
Conventional abrasive blasting is not appropriate for all applications. Abrasives used to remove unwanted materials from a substrate can abrade and otherwise damage a relatively soft substrate. For example, users often experience this problem when removing graffiti, when cleaning pool liners, or when cleaning printing components through abrasive blasting processes. In response to this concern, sodium bicarbonate (commonly referred to as “baking soda”) has been recently used in abrasive blasting processes. Sodium bicarbonate has a heavier specific gravity, but is less hard than most other abrasives, and as such, sodium bicarbonate effectively cleans unwanted dirt and debris from a surface, but normally does not damage the underlying abrasives.
For most kinds of abrasives, the blast nozzle is a major element determining the blasting effectiveness in the blasting operation. The nozzles used in abrasive blasting include an entrance bore through which compressed air/fluid carrying abrasive particles passes. The entrance bore of the nozzle converges over a relatively short distance into a smaller-diameter exit bore. The quickly decreasing cross sectional area of the converging section of the nozzle accelerates the abrasive particles. Such acceleration allows the abrasive materials to exit the nozzle and bombard the target surface at elevated speeds for more efficient cleaning.
A more recent and improved nozzle is disclosed in British Patent 722,464, and issued to Mead. As disclosed, the nozzle comprises an entrance bore that converges into a smaller-diameter throat section and then diverges into a larger-diameter exit bore. As fluid-borne abrasive particles move from the entrance bore into the converging section, the pressure increases, causing the fluid and particles to accelerate. The fluid travels faster than the abrasives due to the mass of the abrasive, but when traveling through the throat section, prolonged exposure to the high-velocity fluid accelerates the abrasive particles further. Finally, the progressively increasing cross sectional area of the diverging section decreases the fluid pressure substantially to atmospheric pressure. The abrasives continue to accelerate, and the reduction of fluid pressure allows the abrasives to exit the nozzle without creating a shock wave that might otherwise disturb the flow of the grit. Thus, the abrasive particles retain their kinetic energy to work more effectively on the target surface.
Another nozzle design is disclosed in U.S. Pat. No. 5,975,996, issued to Settles. Similar to the Mead nozzle, the Settles nozzle comprises an entrance bore, a converging section, a throat section, and a first diverging section; however, the Settles nozzle further includes a second diverging section. From a cross sectional viewpoint, the wall of the first diverging section has a steeper slope (relative to the axis) than the wall of the second diverging section. The converging section, the throat section, and the first diverging section cause similar accelerations of the fluid and particles as described above; however, the profile of the second diverging section helps to further accelerate the abrasive particles for even more effective cleaning.
The aforementioned nozzles are designed with structures to increase the speed of the abrasive media. However, the blasting effectiveness, particularly the blasting of bicarbonate soda, depends on a number of operating parameters including nozzle pressure, standoff distance, angle of impingement, media flow rate, water pressure, and traverse speed. The aforementioned nozzles, though increases the speed of the abrasive media, does not provide the required control of angle of impingement and traverse speed of the abrasive media against the target surface. There is thus a substantial need to provide an improved nozzle that does not only deliver an abrasive media with an increased speed, but also adequately control the impingement angle and traverse speed of the abrasive media while being impinged upon the target surface to be blasted.

BRIEF SUMMARY OF THE INVENTION

The aforementioned needs are addressed by the nozzle provided by the present invention. The nozzle is used in an abrasive blast cleaning apparatus through which a plurality of abrasive particles is propelled. The nozzle comprises a first bore with a constant first diameter, a radially converging section, a throat section with a constant second diameter, a radially diverging section, a second bore, and a second bore having a constant third diameter. The first bore defines a first end for receiving the abrasive particles and a second end. The radially converging section defines a third end connected to the second end and a fourth end. The second diameter is smaller than the first diameter, and the throat section defines a fifth end and a sixth end, wherein the fifth end is connected to the fourth end of the converging section. The radially diverging section defines a seventh end and an eighth end, wherein the seventh end is connected to the sixth end of the throat section. The third diameter is larger than the second diameter, and the second bore defines a ninth end and an exit, wherein the ninth end is connected to the eighth end.
Preferably, the first bore, the radially converging section, the throat section, the radially diverging section, the second bore are made of boron carbide. To protect the bores and sections made of boron carbide, the nozzle comprises a malleable or compressive exterior jacket member. The jacket member is made of aluminum, steel, or polyurethane.
The present invention further provides a nozzle for use in an abrasive blast apparatus through which a plurality of abrasive particles is propelled by a compressed fluid. The nozzle comprises a continuous inner member which defines a converging bore, a first straight bore extending from the converging bore, a diverging bore extending from the first straight bore, and a second straight bore extending from the diverging bore. Preferably, the diameter of the first straight bore is smaller than that of the second straight bore.
To improve the resistance against abrasion, the inner member is made of boron carbide, and the nozzle comprises a jacket member surrounding the inner member. The jacket member is made of malleable or compressive material such as steel, aluminum or polyurethane to provide protection of the inner member made of boron carbide. The inner member may further define an additional straight bore having a first end from which the compressed fluid and abrasive particles enter the nozzle and a second end from which the converging bore extends.

BRIEF DESCRIPTION OF THE DRAWINGS

These as well as other features of the present invention will become more apparent upon reference to the drawings wherein:
FIG. 1 is a cross sectional view of a nozzle suitable for delivering sodium bicarbonate as an abrasive medium in abrasive blast processes.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings wherein the showings are for purposes of illustrating preferred embodiments of the present invention only, and not for purposes of limiting the same. FIG. 1 illustrates one embodiment of an improved nozzle 152 suitable for delivering abrasive medium in abrasive blast processes. In this embodiment, the abrasive medium includes sodium bicarbonate, silica sand, aluminum oxide, plastic medium, and other materials suitable for surface cleaning, finishing, or paint removal.
As shown in FIG. 1, the nozzle 152 comprises a tubular inner member 154. The inner member is hollow so as to define a passage 156. The passage 156 defines an inner surface 122 and an axis 120 that is generally straight. As will be discussed in greater detail below, the inner member 154 directs a compressed fluid (e.g., air, water) through the passage 156, and the fluid carries the abrasive medium through the passage 156 and accelerates the same for use in abrasive blasting processes.
The passage 156 includes an entrance bore 158. The entrance bore 158 defines an end point 157. The entrance bore 158 is able to receive the compressed fluid and particles of the abrasive medium from a source (not shown) and direct the same through the remaining portions of the passage 156.
As shown in FIG. 1, the passage 156 also includes a converging section 160 which begins at the end point 157 of the entrance bore 158 and has an end point 162. In the converging section 160, the inner surface 122 converges toward the axis 120 until an end point 162. Consequently, the cross sectional area of the converging section 160 is gradually decreasing towards the end point 162. As the abrasive medium enters the converging section 160, the decreasing cross sectional area of the passage 156 causes the fluid pressure to increase. As a result, the fluid and the particles of abrasive medium contained therein accelerate. This initial acceleration of the particles of abrasive medium advantageously increases the kinetic energy of the particles to ultimately increase the kinetic energy thereof to increase the effectiveness of the blasting process. Also, the decreasing cross sectional area of the converging section 160 causes the abrasive particles to move radially towards the axis 120.
However, as the fluid flows through the converging section 160, accompanied turbulence of the fluid flow bunches the particles of abrasive medium together, and hinders the progress of the fluid and the abrasive medium. Therefore, depending on the bore size of the nozzle, the axial length of the converging section 160 is adjusted to avoid turbulence of the fluid which disturbs the flow of the abrasive medium. Consequently, the abrasive particles attain a higher speed when traveling through the adjusted axial length of the converging section 160 for more effective blasting.
A common problem associated with the converging section 160 of the nozzle is the insufficient energy transfer from the fluid to the abrasive medium. As shown in FIG. 1, connected to the end point 162 is a throat section 170 characterized by a generally constant diameter smaller than that of the entrance bore 158. The throat section 170 ends at an end point 172. The straight bore of the throat section 170 allows the fluid retains its high speed therein, and provides a more efficient energy transfer from the fluid to the abrasive medium. Advantageously, the throat section 170 moves the particles to higher speeds, thereby increasing the effectiveness of the blasting process.
The passage 156 further includes a gradually diverging section 180, which begins at the end point 172 of the throat section 170. In the diverging section 180, the inner surface 122 diverges away from the axis 120 and continues to diverge until an end point 182. As the fluid-borne particles move through the diverging section 180, the abrasive particles continue to accelerate because the fluid still moves faster than the particles, and thus the fluid continues to impart kinetic energy to the particles. Moreover, because the cross sectional area of the passage 156 continually increases, the fluid pressure decreases. In one embodiment, the fluid pressure decreases to atmospheric pressure to thereby prevent a shock wave that could otherwise disturb the flow of abrasive as it exits the nozzle 152.
The passage 156 also includes an exit bore 159, which begins at the end point 182. The exit bore 159 has a generally constant diameter, and the exit bore 159 directs the fluid and abrasive material out of the nozzle 152 and onto a target surface. Due to the profiles of the diverging section 180, the particles of abrasive medium flowing through the end point 182 are dispersed to a large area. Although a high speed of the particles of abrasive medium is obtained, the impingement angle and traverse velocity against the substrate surface cannot be properly controlled. The straight bore of the exit bore 159 connecting the end point 182 of the diverging section 180 directs the dispersed particles of abrasive medium traveling substantially parallel to the axis 120. Therefore, the nozzle provided by the present invention provides the advantages of both venturi type nozzle and straight bore nozzle.
As shown in FIG. 1, the passage 156 comprises a plurality of transitional portions 140, which are located at the end points 157, 162, 172. The transitional portions 140 create smooth transitions between the entrance bore 158 and the converging section 160, between the converging section 160 and the throat section 170, between the throat section and the diverging section 180, and between the diverging section 180 and the exit bore 159. The transitional sections 140 provide the fluid and particles with a smooth contoured inner surface 122 over which to flow, to thereby inhibit eddies from forming and disturbing the flow of abrasive particles.
As the particles of abrasive medium flow through the nozzle 152, the inner member 154 wears away and the blasting effectiveness is reduced. Materials such as ceramic, cast iron, boron carbide, silicon carbide and tungsten carbide have been available for fabricating the inner member 154. Ceramic and cast iron are considered short-life nozzles, while boron carbide provides best resistance against abrasion and provides the longest lifetime of the nozzle among the above materials. However, boron carbide is brittle and will not survive being bumped and flexed frequently. Therefore, in the embodiment shown, the nozzle 152 further comprises a jacket member 150. The jacket member 150 is preferably a relatively malleable or compressive material surrounding the inner member 154. In one embodiment, the jacket member 150 is made out of aluminum, steel, and polyurethane. The malleability or compressive characteristics of the jacket member 150 counteracts the brittleness of the inner member 154 to thereby protect the inner member 154 from fracture. Advantageously, the jacket member 150 increases the longevity of the nozzle 152.
This disclosure provides exemplary embodiments of a nozzle useful for delivering sodium bicarbonate as an abrasive blast medium. The scope of this disclosure is not limited by these exemplary embodiments. Numerous variations, whether explicitly provided for by the specification or implied by the specification, such as variations in shape, structure, dimension, type of material or manufacturing process may be implemented by one of skill in the art in view of this disclosure.

Claims

1. A nozzle for use in an abrasive blast cleaning apparatus through which a plurality of abrasive particles is propelled, the nozzle comprising:

a first bore having a constant first diameter and defining a first end and a second end, wherein the first bores receives the abrasive particles;

a radially converging section defining a third end and a fourth end, wherein the third end is connected to the second end of the first bore;

a throat section having a constant second diameter that is smaller than the first diameter, further defining a fifth end and a sixth end, wherein the fifth end is connected to the fourth end of the converging section;

a radially diverging section defining a seventh end and an eighth end, wherein the seventh end is connected to the sixth end of the throat section; and

a second bore having a constant third diameter and defining a ninth end and an exit from which the abrasive particles are propelled away from the nozzle, wherein the ninth end is connected to the eighth end.

2. The nozzle of claim 1, wherein the first bore, the radially converging section, the throat section, the radially diverging section and the second bore are made of boron carbide.

3. The nozzle of claim 1, wherein the nozzle comprises a malleable or compressive jacket member surrounding the first bore, the radially converging section, the throat section, the radially diverging section and the second bore are made of boron carbide.

4. The nozzle of claim 3, wherein the jacket member is made of aluminum, steel, or polyurethane.

5. The nozzle of claim 1, whereint eh third constant diameter is larger than the constant second diameter.

6. A nozzle for use in an abrasive blast apparatus from which a plurality of abrasive particles is propelled by a compressed fluid flowing therethrough, the nozzle comprising a continuous inner member which defines a converging bore, a first straight bore extending from the converging bore, a diverging bore extending from the first straight bore, and a second straight bore extending from the diverging bore.

7. The nozzle of claim 6, wherein the first straight bore has a diameter smaller than that of the second straight bore.

8. The nozzle of claim 6, wherein the inner member is made of boron carbide.

9. The nozzle of claim 6, further comprising a jacket member surrounding the inner member.

10. The nozzle of claim 9, wherein the jacket member is made of steel, aluminum or polyurethane.

11. The nozzle of claim 6, wherein the inner member further defines an additional straight bore having a first end for receiving the compressed fluid and abrasive particles and a second end from which the converging bore extends.