EP0163776A2

EP0163776A2 - Highly concentrated supersonic flame spray method and apparatus with improved material feed

Info

Publication number: EP0163776A2
Application number: EP84116416A
Authority: EP
Inventors: James A. Browning
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-01-18
Filing date: 1984-12-28
Publication date: 1985-12-11
Also published as: EP0163776A3; JPS60169555A

Abstract

A supersonic flame spray apparatus (1, 1') utilizing an internal burner continuously feeds oxy-fuel products of combustion through an extended length nozzle (7, 37) of diminished throat area (14, 35), supersonic expansion duct (15, 44) and an extended length nozzle passage (16, 36). The expansion from the throat (14, 35) to the end of the expanding duct provides a gas velocity of well in excess of supersonic velocity. Solid material in rod or particle form is introduced axially or radially into the supersonic gas flow at the end of the expanding duct (15, 44). This permits the extended length nozzle passage (16, 36) to have a relatively large diameter which prevents the solid material (4, 29) introduced to the flow to melt, reach the nozzle passage wall, and adhere thereto or abrade the nozzle wall, while permitting low pressure material injection into the gas flow stream (G).

Description

FIELD OF THE INVENTION

This invention relates to supersonic molten metal or ceramic spraying systems or sand blast systems, and more particularly, to an improved low pressure material feed to the products of combustion from an internal burner after substantial expansion at the upstream end of a nozzle of extended length for concentrated stream spraying onto a substrate downstream of the nozzle.

BACKGROUND OF THE INVENTION

Internal burners have supplied by continuous combustion of an oxy-fuel mixtures, products of combustion under high pressure which exit from the combustion chamber into a spray nozzle of extended length. Internal burner type supersonic flame spray apparatus have evolved over the years. My earlier U.S. patents 2,990,653 entitled "METHOD AND APPARATUS FOR IMPACTING A STREAM OF HIGH VELOCITY AGAINST THE SURFACE TO BE TREATED" issuing July 4, 1961; and U. S. patent 4,370,538 entitled "METHOD AND APPARATUS FOR ULTRA HIGH VELOCITY DUAL STREAM METAL FLAME SPRAYING" issuing January 25, 1983, were the forerunners of a further recently issued U. S. patent 4,416,421 entitled "HIGHLY CONCENTRATED SUPERSONIC LIQUIFIED MATERIAL FLAME SPRAY METHOD AND APPARATUS" issuing November 22, 1983. By the utilization of an expansion nozzle of extended length, the products of combuation from the internal burner to which an oxy-fuel mixture is continuously fed and combusted with combustion effected under substantially high pressure and with the products of combustion directed through a flow expansion nozzle, permits the creation of a flame spray stream of supersonic velocity. By means of improved mode of introduction of the solid material in either rod form or particle form into the flame spray, there is insured a concentrated and highly focussed core of flame spray material for material spray coating downstream of the nozzle at supersonic velocity.
In U. S. patent 4,416,421, the material is introduced to the gas flow at a point ahead of the maximum nozzle restriction or throat of the venturi type nozzle, rather than, as in the past, by the introduction of the material to be flame sprayed within the combustion chamber itself. By the utilization of a path length desirably more than ten times in excess of the nozzle restriction diameter, maximum particle velocity is achieved under conditions in which the metal or ceramic particles are intensely heated and lignified" prior to discharge from the extended length nozzle, but are prevented from coating the internal wall of the nozzle and clogging the nozzle passage. Particularly, the combustion products are directed as a converging stream into the converging portion and upstream of the throat of the extended length nozzle and the solid rod or solid particle material is introduced axially into the converging stream at or upstream of the converging inlet leading to the restricted diameter throat of of the nozzle bore itself.
Under such arrangements, the major gas expansion through the nozzle to the atmosphere takes place after introducing the spray material to the hot combustion product gases. The solid material is introduced at the point where the pressure of the products of combustion is at a maximum. This in turn, requires particularly for solid particle form material, the necessity to employ relatively high pressures to force a stream of such particles into the flow stream of the products of combustion passing through the nozzle. Further, under such an arrangement, the diameter of the nozzle of extended length is required to be maintained relatively small and this restriction in the nozzle diameter increases the possibility of liquified spray material contaminating the nozzle wall and ultimately blocking the nozzle passage.
Flame spray apparatus of this type have also evolved for the specific purpose of causing solid particles such as sand, grit and the like to reach supersonic velocities without melting as a confined, small diameter stream, thereby permitting the particle stream to function as a sand blast stream and abrade the surface of an object placed in the path of the high velocity particles. However, it is difficult to produce such a stream without in turn abrading the flame spray nozzle wall through which the particles pass prior to discharge at ultrasonic velocity against the surface to be abraded.
It is, therefore, a primary object of the present invention to improve such high-velocity flame spray and sand blast systems by permitting the reactive gases to expand by a considerable magnitude prior to the introduction of the spray material into the extended length nozzle, thereby allowing the solid material to be introduced to the products of combustion under simplified feed conditions and via a low feed pressure carrier gas when the solid material is in particulate form.
It is a further object of the present invention to provide an improved high-velocity flame spray or sand blast system wherein the extended length nozzle may have a relatively large bore without adversely affecting the supersonic velocity of the particle carrying stream impacting against the substrate downstream of the extended length nozzle with substantially less likelihood of particle melting and deposition on bore wall of the extended length nozzle and elimination of nozzle blockage where the particles are molten as a result thereof or without abrading the nozzle bore wall where the particles are solid and form a "sand blast" stream.

SUMMARY OF THE INVENTION

In one aspect, the present invention constitutes a flame spraying method involving the steps of:

combusting under pressure a continuous flow of an oxy-fuel mixture comfined within an essentially closed internal burner combustion chamber,
discharging the hot combustion product gases from the combustion chamber to a flow expansion nozzle as a high velocity hot gas stream,
feeding material to the hot gas stream for high temperature heat softening or liquefaction or forming a solid particle abrasion stream, and
spraying the material at high velocity onto a surface positioned in the path of the stream at the discharge end of the nozzle,
the improvement wherein the step of feeding the material comprises:
introducing the material in solid form outside of the combustion chamber into a supersonic flow stream of the combustion product gases downstream of a diminished throat area of the nozzle and at the upstream end of an expansion nozzle bore of extended length to allow material passage through a relatively large diameter nozzle bore and insuring the prevention of build-up of melted particle material on the nozzle bore wall or solid particle abrasion of the nozzle bore wall while maintaining flow of the hot combustion product gases and material intrained thereby at supersonic flow velocity prior to particle impact -ainst the surface.

Combustion is effected under sufficiently high pressure such that expansion well above the critical expansion is provided within an expansion duct prior to the introduction of the material to the gaseous flow. Preferably, the material is introduced radially or axially to the high velocity combustion product hot gas stream at the intersection of the nozzle expansion duct and the extended length nozzle bore.
Additionally, the invention is directed to a highly concentrated supersonic material flame spray apparatus which comprises a spray gun body having a high pressure, essentially closed, internal burner combustion chamber and involving means for continuously flowing an oxy-fuel mixture under high pressure through the combustion chamber for ignition within the chamber. An extended length nozzle opens to one end of the combustion chamber for permitting the products of combustion to discharge therethrough with the nozzle including a converging inlet leading to a reduced diameter throat, an expanding duct downstream of the throat, and an extended length outlet bore portion, with the bore portion having a length which is at least five times the diameter of the nozzle throat. Means are required for introducing material in solid form outside of the combustion chamber into the hot combustion gases for subsequent heat softening or melting and acceleration. The improvement resides in such means introducing the material within the expansion duct at a point where greater than critical pressure drop exists for the flow of the products of combustion to facilitate such introduction of the material and permit use of a relatively large nozzle outlet bore diameter to assure against particle build up of material introduced to the flow of the products of combustion on the surface of the bore and possible clogging of the nozzle prior to particle impact on a substrate downstream of the discharge end of the nozzle bore or abrasion of the nozzle bore wall during passage therethrough. Such introducing means may take the form of at least one radial passage within the nozzle in the vicinity of the junction between the expansion duct and the extended length nozzle outlet bore portion downstream thereof. Alternatively, the combustion chamber terminates in a plug having a conical projection positioned within the bore of the nozzle, with the periphery of the conical projection spaced from the nozzle bore to define with the upstream end of the nozzle bore the throat and the expansion duct, and wherein the plug includes an axial bore therein opening to the outlet bore portion. Means are provided for supplying a metal or ceramic powder or abrasion particles under relatively low pressure to the axial bore within the conical projection for discharge into the nozzle outlet bore portion.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a longitudinal, sectional view of one embodiment of the highly concentrated supersonic flame spray apparatus of the present invention.
Figure 2 is a longitudinal sectional view of a second embodiment of the present invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring first to Figure 1, there is illustrated in longitudinal, sectional form, and somewhat schematically, the main elements of the improved flame spraying apparatus 1 forming one embodiment of the present invention. The apparatus 1 which may constitute a flame spray "gun" for spraying liquified metal or ceramic, is comprised of a spray torch body 10 defining an internal burner combustion chamber 11 formed by opposed end walls lOa, lOb at opposite ends of a cylindrical center section lOc and integrated thereto. End wall lOb carries a extended length venturi type nozzle indicated generally at 7, including a diminished throat area 14 and supersonic expansion duct or passage 15 leading to an extended length nozzle passage or bore 16, also defined as a nozzle outlet bore portion of constant and relatively large diameter. Fuel and oxidizer (oxygen or air) are supplied to the combustion chamber 11 as indicated by arrows 8 and 9 respectively via fuel supply tube 13 and oxygen supply tube 12. The tubes 12 and 13 terminate at end wall lOa, and the fuel and oxygen enters the combustion chamber 11 via small diameter drilled passages 5 and 6, respectively which are angled with respect to each other so that the flows intersect. The fuel and oxygen as at 8 and 9 are supplied under relatively high pressure. The fuel, which may be in liquid or gaseous form, forms with the oxygen a fuel/air mixture. Continuous burning of a continuous flowing oxy-fuel mixture to the combustion chamber 11 is effected within the combustion chamber by ignition means such as a spark plug (not shown) with burning being initiated at the point of delivery of the fuel and air, that is, near end wall lOa and proceeding towards the opposite end wall lOb. Thus, combusting of a continuous flowing fuel/air mixture is confined within an essentially closed internal burner combustion chamber 11.
The hot products of combustion reach sonic velocity in dicharging through the narrow throat section 14 of the venturi form nozzle 7, provided a greater than critical pressure drop exists. Further expansion of the products of combustion occurs in expansion duct or passage 15, creating a supersonic flow of the products of combustion at this point within the extended length nozzle 7. The velocity of this flow at the entrance 16a to the extended length nozzle passage or bore 16 is determined by the remaining pressure drop available and the degree of expansion provided by the expanding duct 15. For example, for a chamber 11 pressure of 250 psig, the throat pressure of the hot gas flow is about 130 psig. A pressure ratio of over 9 to 1 still remains prior to discharge to the atmosphere at the discharge or exit end 16b of the extended length nozzle bore 16.
Expanding the cross-sectional area from the throat 14, to the end of the expanding duct 15 by a factor of four, provides a gas velocity of near Mach 2.5 into the entrance 16a of the nozzle passage or bore 16. There is a further increase in this velocity within the extended length nozzle bore 16 as the gases pass to the atmosphere. The overall expansion ratios are determined by the combustion chamber pressures used and the desired exit diameter of the flame jet from the nozzle extended length passage defined by bore 16.
The present invention is directed to the introduction of powder, in this embodiment, radially into the supersonic gas flow after considerable gas expansion and after reaching the gas flow supersonic velocity at a point where powder (or solid material in rod form) is heated, melted and accelerated by the gas passing through the extended length bore 16 and extending to the workpiece or substrate 20 upon which a deposite of particles 19 is formed. In the embodiment of Figure 1, a metallic powder or ceramic powder 4, or a mass of abrasion particles such as sand is supplied via tube 17 to nozzle 7 at the end of the expansion duct 15 where the constant diameter bore 16 initiates. In that respect, a small diameter radial hole 3 in the nozzle 7 is aligned with the end of the tube 17 so that the powder particles 18 are introduced into the gas stream G emanating from the venturi portion of the extended length nozzle 7. The particles 18 are aspirated into the stream G, and are carried thereby at supersonic velocity for melting prior to impact directly against the substrate or workpiece 20 to form deposit 19.
A major advantage of adding the spray material 18 within the supersonic section of the nozzle 7 is that this extended length section 16 has a diameter much greater than that achieved in the past, as exemplified by my prior U. S. patent 4,416,421 for the same flow rates and pressure of the reactants. For example, under typical gun dimensions and operating parameters for the apparatus exemplified by U. S. patent 4,416,421, where solid material in particulate powder form is added before or at the nozzle throat, the nozzle throat diameter was commonly 5/16 inch. With this diameter, the powder is spaced from the wall (upon entry) less than 1/8 of an inch from a 1/6 inch injector hole. For the equivalent spray apparatus (torch 1) of the present invention with a selected expansion ratio of 9 to 1, the diameter of the nozzle bore 16 increases threefold and with the powder spacing from the wall increasing to 3/8 of an inch. As may be appreciated, it is much more difficult for the powder to reach the wall of the extended length bore 16, melt and interfere with proper operation of unit, and under the most adverse conditions, accumulate if molten or near molten on the bore wall to the degree where the bore is completely clogged.
A second advantage of creating a major expansion of the hot gases exhausting from the internal burner, prior to injecting the spray material into the hot gas flow stream, is that the region into which the material is injected is at a much reduced pressure. As such, conventional low-pressure powder hoppers (not shown) may be employed for supplying powder 4 via tube 17 to the extended length nozzle portion 16. As an example, the prior apparatus exemplified by U. S. patent 4,416,421 with powder injection into the throat area for a combustion pressure of 250 psig, requires a gas feed pressure of well over 125 psig. Currently, within the apparatus illustrated in Figure 1, using the same combustion pressure of 250 psig within combustion chamber 11, the carrier gas pressure required to supply the powder as at 4 can be as low as 50 psig allowing the use of readily available powder feed systems.
Where the powder or rod form solid material is introduced radially to the hot products of combustion rather than axially into the stream, during their radial expansion the ability to concentrate the particles and to prevent them from adhering to the bore of the extended length nozzle is significantly reduced over an arrangement where the solid rod material or particulate material is introduced axially into the stream of gases at its center.
Reference to Figure 2 illustrates an internal burner type supersonic flame spray apparatus wherein the same metal or ceramic powder as employed in the Figure 1 embodiment is introduced axially to the extended length nozzle passage or bore 36 of the flame spray apparatus indicated generally at 1'. In this embodiment, a main burner body indicated generally at 30 is comprised of an elongated cylindrical portion 30c having integrally formed therewith at one end, an upstream end wall 30a bearing respectively small diameter bores or holes 32, 33 for the supply of oxygen and fuel, respectively, as indicated by arrows 49 and 48.
In like manner to the embodiment of Figure 1, an oxy-fuel mixture formed by the fuel 48 and oxygen 49 provided to passages or bores 33, 32, respectively, under relatively high pressure, burn within combustion chamber 31 of the internal burner. The combustion products exit as a high pressure stream through four longitudinally parallel holes 34 within formed by a cylindrical plug 21 sealably welded, or integrated, to body 30 at the downstream end of the combustion chamber 31. The cylindrical body portion 30c is provided with threads 27 on its outer periphery, at the downstream end thereof. Further, an extended length nozzle indicated generally at 37 is provided with a radially enlarged head 37a, which head is recessed at its outer periphery at 37c so as to fit onto the end of the cylindrical section 30c of body 30. Nozzle 37 comprises an extended length nozzle outlet bore portion or bore 36. A clamping ring 26 which is threaded on its inner periphery as at 28 threads to the body 30 so as to clamp nozzle 37 in position. The longitudinal extent of the recess 37c is such that there is a formed manifold ring volume 42, i. e. an annular space between the head 37a of nozzle 37 and block 21. Further, the block 21 is extended at its downstream end face 21a by a conical projection 43 which is of an axial length so as to project partially within nozzle bore 36. A nozzle throat 35 is thus formed between corner 37d of the extended length nozzle 37 and conical projection 43 at the inlet of the nozzle passage bore 36.
As may be appreciated, the annular area at throat 35 may be equal to the area of throat 14 of the embodiment of Figure 1 and functions as the equivalent thereto. Bore 36 may be of the same diameter throughout its length, or alternatively, it may comprise a constant diameter portion as at 36c leading to a diverging section 36d approaching the nozzle outlet 36b. A large expansion of gas flow of the products of combustion takes place within an expanding annular passage 44 from throat 35 to the end of the conical projection 43.
In this embodiment, a ceramic or metal powder as indicated by arrow 29 is supplied under fairly low pressure carrier gas via powder supply tube 22 which fits to the cylindrical portion 30c of body 30 within a radial hole 23. A radial passage 24 of somewhat smaller diameter extends from bore 23 to the center of plug 21 and a right angle axial bore 25 of relatively small diameter extends therefrom to the end of the conical projection 43 opening to the extended length nozzle bore portion 36c downstream of the expanding annular passage 44 defined by projection 43 and that bore portion 36c. Powder is thus injected into a region where the gas flow velocity is well above Mach 1 and at point of substantially reduced pressure relative to the pressure generated within combustion chamber 31. The presence of the particles at the center of the gas flow stream, which converges towards the introduced stream of particles, cause concentration of the particle stream and at the same time due to the relatively large size of extended length nozzle bore 36, melting of the particles is assured within the bore 36 without the possibility of contact with and accumulation or deposit on the nozzle bore wall. An advantage of the embodiment of Figure 2 is that the hot gas flow entering the bore 36 from the passage 44 defined by the bore 36 and plug projection 43 envelopes the powder flow symmetrically around a full 360 degrees eliminating areas of recirculation which can carry the powder to the walls of the nozzle passage or bore 36.
In the illustrated embodiment nozzle passage 36 comprises a constant diameter straight section 36c and an additional diverging expansion passage section 36d, although the complete extended length bore 36 may be of constant, relatively large diameter.
As may be appreciated, in the process and apparatus of the present invention, the use of solid rods or wires in place of powders 4 and 29 may provide the same advantageous result and such substitution therefor may be readily made in the manner exemplified by my prior patent 4,416,421.
As may be further appreciated, the essence of the invention is in its particular applicability to high pressure combustion. The invention is premised on the requirement that an expansion well above critical expansion be provided within the apparatus prior to the introduction of the spray material to the flow. Further, the combustion product gas flow must be in the supersonic range, and the combined hot gases, spray material are then required to be directed through an extended nozzle passage length, throughout which the gas flow velocity remains supersonic.

Claims

1. In a flame spray method comprising the steps of:

combusting under pressure, a continuous flow of an oxy-fuel mixture confined within an essentially closed internal burner combustion chamber (11, 31),

discharging the hot combustion product gases from the combustion chamber (11, 31) to a flow expansion nozzle (7, 37) as a high velocity hot gas stream,

feeding material (4, 29) to said stream for high temperature heat softening or liquefaction or for forming a solid particle abrasion stream, and

spraying said material (4, 29) at high velocity onto a surface (20) positioned in the path of the stream at the discharge end of the nozzle,

the improvement wherein the step of feeding said material comprises:

introducing said material in solid form outside of said combustion chamber (11, 31) into a supersonic flow stream of said combustion product gases downstream of a diminished throat area (14, 35) of said nozzle (7, 37) and at the upstream end of an expansion nozzle bore (16, 36) of extended length, to allow material passage through a relatively large diameter nozzle bore (16, 36) insuring the prevention of build up of melted particle material (18) on the nozzle bore wall or solid particle abrasion of the nozzle bore wall, while maintaining flow of the hot combustion product gases and the material extended thereby at supersonic flow velocity prior to discharge from the end (16b, 36b) of said bore.

2. The method of claim 1, wherein combustion is effected under sufficiently high pressure that expansion well above the critical expansion is provided within an expansion duct (15, 44) of said nozzle (7, 37) prior to introduction of the material to the gaseous flow.

3. The method as claimed in claim 2, wherein said material (4, 29) is added radially to the high velocity combustion product hot gas stream (G) at the intersection of the nozzle expansion duct (15, 44) and said extended length nozzle bore (16, 36).

4. The method as claimed in claim 2, wherein the material (4) fed to the stream is introduced into the stream axially at the intersection of the expansion duct (15) and the nozzle bore (16) of extended length downstream thereof.

5. A highly concentrated supersonic material flame spray apparatus (1, 1') comprising:

a spray gun body (10, 30),

a high pressure, essentially closed internal burner combustion chamber (11, 31) within said body (10, 30),

means (5, 6, 32, 33) for continuously flowing an oxy-fuel mixture under high pressure through said combustion chamber (11, 31) for ignition within said chamber,

an extended length nozzle (7, 37) opening to one end of said combustion chamber (11, 31) for permitting the products of combustion of said oxy-fuel mixture to discharge therethrough; said nozzle (7, 37) including a converging inlet leading to a reduced diameter throat (14, 35), an expanding duct (15, 44) downstream of said throat (14, 35), and an extended length outlet bore portion (16, 36) with said outlet bore portion (16, 36) having a length which is at least five times the diameter of the nozzle throat (14, 35), and

means (17, 3, 22, 24, 25) for introducing material (4, 29) in solid form outside of said combustion chamber into the hot combustion gases for subsequent heat softening or melting and acceleration,

the improvement wherein said means (17, 3, 22, 24, 25) for introducing said material (4, 29) in solid form into the hot combustion gases comprises means for introducing said material within said expansion duct (15, 44) at a point where greater than critical pressure drop exists for the flow of the products of combustion to facilitate the introduction of said material (4, 29) , permit a relatively large nozzle outlet bore portion (16, 36) diameter to insure against particle build up of the material (4, 29) introduced to the flow of the products of combustion on the surface of the bore and possible clogging of the nozzle (7, 37) or solid particle abrasion of the nozzle bore wall prior to particle impact on a substrate (20) downstream of the discharge end (16b, 36b) of the nozzle bore (16, 36).

6. The apparatus as claimed in claim 5, wherein said means (17, 3) for introducing material in solid form into the hot combustion gases comprises at least one radial passage (3) within said nozzle (7) in the vicinity of the juncture between the expansion duct (15) and the extended length nozzle outlet bore portion (16) and means (17) for supplying solid material (4) in particle form under pressure to said radial passage.

7. The apparatus as claimed in claim 5, wherein said means for introducing material (29) in solid form into the hot combustion gases comprises a plug (21) within said body (30) at one end of said combustion chamber (31), said plug (21) terminating in a conical projection (43) within the bore (36c) of said nozzle (37) with the periphery of the conical projection (43) spaced therefrom and defining with the upstream end of said nozzle bore said throat (35) and said expansion duct (44), and said plug (21) including an axial passage (25) therein opening to said outlet bore portion (36c), and means (22, 24) for supplying a metal or ceramic powder (29) or solid abrasive particles under relatively low pressure to said axial passage (25) for discharge into said nozzle outlet bore portion (36c).