CA1065203A - Thermal spraying using cool plasma stream - Google Patents
Thermal spraying using cool plasma streamInfo
- Publication number
- CA1065203A CA1065203A CA237,226A CA237226A CA1065203A CA 1065203 A CA1065203 A CA 1065203A CA 237226 A CA237226 A CA 237226A CA 1065203 A CA1065203 A CA 1065203A
- Authority
- CA
- Canada
- Prior art keywords
- plasma
- powder
- nozzle
- passageway
- gas stream
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
- B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
- B05B7/22—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc
- B05B7/222—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc using an arc
- B05B7/226—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed electrically, magnetically or electromagnetically, e.g. by arc using an arc the material being originally a particulate material
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
- B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
- B05B7/1606—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air
- B05B7/1613—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed
- B05B7/162—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed and heat being transferred from the atomising fluid to the material to be sprayed
- B05B7/1626—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed the spraying of the material involving the use of an atomising fluid, e.g. air comprising means for heating the atomising fluid before mixing with the material to be sprayed and heat being transferred from the atomising fluid to the material to be sprayed at the moment of mixing
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B05—SPRAYING OR ATOMISING IN GENERAL; APPLYING FLUENT MATERIALS TO SURFACES, IN GENERAL
- B05B—SPRAYING APPARATUS; ATOMISING APPARATUS; NOZZLES
- B05B7/00—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas
- B05B7/16—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed
- B05B7/168—Spraying apparatus for discharge of liquids or other fluent materials from two or more sources, e.g. of liquid and air, of powder and gas incorporating means for heating or cooling the material to be sprayed with means for heating or cooling after mixing
-
- H—ELECTRICITY
- H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
- H05H—PLASMA TECHNIQUE; PRODUCTION OF ACCELERATED ELECTRICALLY-CHARGED PARTICLES OR OF NEUTRONS; PRODUCTION OR ACCELERATION OF NEUTRAL MOLECULAR OR ATOMIC BEAMS
- H05H1/00—Generating plasma; Handling plasma
- H05H1/24—Generating plasma
- H05H1/26—Plasma torches
- H05H1/32—Plasma torches using an arc
Landscapes
- Physics & Mathematics (AREA)
- Engineering & Computer Science (AREA)
- Plasma & Fusion (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Electromagnetism (AREA)
- Nozzles (AREA)
- Coating By Spraying Or Casting (AREA)
- Plasma Technology (AREA)
- Application Of Or Painting With Fluid Materials (AREA)
- Physical Or Chemical Processes And Apparatus (AREA)
- Manufacture Of Metal Powder And Suspensions Thereof (AREA)
Abstract
ABSTRACT OF THE DISCLOSURE
Thermal spray apparatus incorporating a cooled nozzle extension features high particle velocities and a precise particle temperature control capability produces high quality coatings in a simple and economical manner.
Thermal spray apparatus incorporating a cooled nozzle extension features high particle velocities and a precise particle temperature control capability produces high quality coatings in a simple and economical manner.
Description
52~3 BACKGROUND OF THE INVENTION
The present invention relates in general to the coating arts and, more particularly, to the production of coatings by thermal spray techniques.
Three thermal spray techniques are utilized at the present time in the production of coatings, viz., flame, plasma and detonation spray processes. These processes all depend upon the generation of a hot stream of gases which are used to heat and propel a finely-divided coating material to a surface to be coated. ;~
In the flame spray process the combustion of a gas mixture such as oxygen and acetylene provides the necessary heat. The plasma spray technique does not depend upon a combustion process. Instead an inert gas, usually argon, is electrically excited resulting in a high temperature plasma. In the detonation spray process a controlled ex-plosion of gases, such as a mixture of oxygen, acetylene and nitrogen takes place within the detonation gun, the powders being driven therefrom on a shock wave, Flame gun gas temperatures are, of course, determined and limited by those attainable in the process of combus-tion. In the detonation spray processes, temperatures of about 6000F. and exit gas velocities on the order of 2500 feet per second are typical. Plasma gas temperatures, however, are extremely high, reaching 20a000F. and very high gas velocities are attainable.
Because of the significant differences in the respec-tive process parameters, particularly temperature and gas .. ..
Z~
velocity, significant differences may be seen in the de-posited coatings depending upon the process utilized and despite the fact that powders of the same composition are - being sprayed. The higher temperatures in the plasma spray gun results, in some coating systems, in a deposited coating of different phase structure than that achieved with the detonation gun. This difference in phase structure results in a difference in the physical properties of the coating, the difference in many instances being sufficient to result in acceptability or unacceptability of the coating for the purpose intended.
One coating composition adapted to deposition by spray techniques, usually plasma or detonation spray, is a nickel/
aluminum material. This is utilized to provide fretting and gall resistance to certain titanium alloy gas turbine engine parts. Experience has shown that many coatings deposited by ~ -conventional plasma spray techniques are of good theoretical density but are highly stressed and, hence, prone to cracking and spalling, particularly under conditions involving thermal shock. Those resultant from a detonation spray with lower formation temperatures are more satisfactory from a cracking and spalling viewpoint, but are less than optimum, particu-larly in tenms of masking requirements and economy.
With existing processes and apparatus it is impossible, in many, many circumstances at leasta to generate spray coatings having not only the requisite composition and metallurgical structure but also the desired coating adher-ence and density. It is also desirable to minimize some of ; - 3 -~6~
the production problems incident to the conventional spray-ing operations. Detonation processes, for example, are for safety reasons usually conducted with the operator situated in a position remote from the coating operation itself, re-quiring careful prepositioning of the part to be coated and/or remote control. Conventional plasma spray techniques require careful surface preparation and masking and may pose some danger in overheating the substrate.
SUMMARY OF THE INVENTION
The present invention is directed to improvements in thermal spray coating apparatus and methods These improve-ments not only eliminate the majority of the drawbacks associated with existing apparatus and methods, but also provide a number of ancillary benefits as well A major advantage of the invention results from an ~-ability to generate optimum coating structures, in a variety of coating systems if desired, with excellent adherence and density. This advantage is, moreover, achieved with con-current improvements in process economy and safety.
The invention contemplates the provision of an elongated passageway for defining the hot gas stream in thermal spray apparatus and into which the powders to be sprayed may be injected into a cooled gas stream at a predetermined location or locations, the residence time of the coating particles being such as to provide the desired heating and velocity to such particles.
In one embodiment of the invention, a cooled nozzle extension assembly adapted to mate with conventional plasma - ' - lO~SZQ3 spray equipment is fabricated with an aerodynamically efficient passageway through which the hot plasma may be passed and into which the coating powders may be introduced at a selected loc-: ation or locations along the passageway. In operation thereof, helium is utilized as the plasma gas.
In accordance with an embodiment, a thermal powderspray apparatus comprises: means for providing a gas at high temperature; an elongated nozzle forming an exit for the gas and through which the gas may be passed as a high velocity stream; means for cooling the gas to provide a colled gas stream in at least a portion of the nozzle: and means for inject-ing powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location pro-viding sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
In accordance with a further embodiment, a plasma powder spray apparatus comprises: means for generating a plasma:
an elongated nozzle forming an exit form the plasma generating means and through which the plasma may be passed as a high velocity stream, means for cooling the plasma to provide a cooled gas stream in at least a portion of the nozzle, and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
In accordance with a still further embodiment, a plasma powder spray apparatus comprises: a plasma gun having a plasma generating chamber, a nozzle having an elongated passageway there-through communicating with the chamber: means for cooling the nozzle: and access means through which powder to be sprayed may be injected into the passageway intermediate its ends at an B ~ _5_ iO~;SZ~;~
injection location selected to impart a desired level of heating and a high velocity to the powder.
From a different aspect, there is provided, in accordance with the invention a plasma powder spray apparatus including a plasma generating chamber, the improvement which comprises:
a nozzle having an elongated passageway therethrough communicating with and forming an exit for the plasma generating chamber, means for cooling a plasma traversing the passageway, and access means for injecting powder to be sprayed into the passageway intermediate its ends and downstream of the initial source of plasma cooling.
In accordance with a still further aspect, an embodi-ment of the invention comprises, a nozzle extension assembly for a plasma spray gun comprising: an inner member having an elong-ated passageway extending therethrough, one end of the inner -member being adapted to mate with gas exit opening of the plasma gun, the passageway being aligned with said port' coolant jacket surrounding the inner member, the coolant jacket cooperating with the inner member to form a coolant chamber therebetween, means for admitting a coolant to the coolant chamber, access means communicating with the passageway intermediate its ends for admitting a powder to the passageway; and means for connecting the nozzle extension assembly to the plasrna gun in position.
From a still further aspect, a plasma powder spray method comprises: generating a plasma, passing the plasma at high velocity through an elongated nozzle, cooling the plasma, forming a cooled plasma gas stream' admitting coating powder to the cooled gas stream in the nozzle, providing sufficient powder residence time in the cooled gas stream to plasticize the powder and impart a high velocity thereto, and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
In accordance with a still further embodiment, a plasma ~ -5a-1~6SZ~
powder spray method comprises: generating a helium plasma athigh temperature, passing the plasma at high velocity through an elongated nozzle, cooling the nozzle and the plasma passing therethrough formlng a cooled plasma gas stream, admitting coating powder to the cooled gas stream in the nozzle, plasticizing the powder and imparting a high velocity thereto, and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
BRIEF DESCRIPTION OF THE DRAWING
The drawing depicts plasma spray apparatus according to the teachings of this invention.
DESCRIPTION OF THE_PREFERRED EMBODIMENTS
The plasma spray apparatus shown in the drawing corres-ponds to that which has been actually used in the deposition of coatings according to the present invention.
A spray nozzle extension assembly 2 is adapted to fit around the nozzle 4 of a standard plasma spray gun 6, such as the METCO 3MB Plasma Gun with GP Nozzle. The nozzle extension assembly comprises a tubular finned mernber 8 having a passageway 10 extending therethrough. As shown, the finned member is formed of a material of high therrnal conductivity, such as copper and is surrounded by a steel water jacket 14 having a cooling water inlet 16 and outlet 1~. The cooling fluid passing through the water chamber 19 cools the finned member preventing melting or other heat damage due to the hot plasma flowing through the passageway 10 during operation of the apparatus. In its traverse through the passageway in the cooled finned member, the hot plasma itself undergoes substantial cooling.
In this apparatus in the interest of maintaining a -5b-tB
..... . ,,,. ~, ,, high gas velocity the passageway 10 has been shaped for aerodynamic efficiency, utilizing an inlet portion 20, a nozzle portion 22 and an outlet portion 24. The particular assembly shown is 6.3 inches in length with an inlet por-tion 4 x 0.215 inches, a nozzle portion about 0.25 inch long having a throat diameter of 0 14 inch, and an outlet portion having a diameter of 0.15 inch. Thus, the nozzle is convergent/slightly divergent.
Typically, it is desirable to provide the powders to the surface to be coated, not only at high velocity and , heated, but in a plastic rather than molten condition. As the plasma gas traverses the passageway it is cooled and, accordingly, introduction of the powders at a downstream location will generally result in a reduced heating of the powders because the temperature is lower than the upstream temperature. Accordingly, the nozzle is fabricated to pro-vide sufficient length to substantially reduce the plasma temperature in the nozzle. Thus, as the word "elongated"
is used herein, it will be understood to mean sufficient length to provide substantial cooling of the plasma. From the foregoing, it will be seen that in the present invention the coating powders are exposed in a relatively low temper-ature/long time cycle as contrasted with a high temperature/
short time cycle in conventional plasma spray operations.
The nozzle extension assembly is provided with an access port or ports, 40 and 42 in the drawing, through which powder may be introduced into the plasma gas stream.
The location of these powder access ports will depend upon .
~ 3 the powders being sprayed and the particular process para-meters and apparatus being utilized. Basically, however, the location is selected to provide the correct heating of the powders.
In the spraying of nickel/aluminum in the apparatus described, the powders are admitted in an inert carrier gas through access port 42 which is a 1/16 inch hole located about 3.5 inches downstream from the nozzle extension inlet or just upstream of the nozzle portion.
One or more access ports can be utilized for the intro-duction of differing powder compositions where such powders are to be sprayed concurrently or sequentially, or for the introduction of powders of the same composition where the processing parameters are to be changed. The formation of graded coatings by gradually phasing in one composition while phasing out another thereby eliminating a planar interface between the compositions is readily achieved.
As has been previously discussed, powder temperature can be readily controlled in a given system by careful selection of the axial location along the passageway where the powders are admitted to the hot gas stream. The apparatus is also readily adaptable to other means of powder tempera-ture control. Access port 40 or some other port can, for example, be utilized for the admission of a temperature-modifying gas to the plasma stream. This temperature-modifying gas may simply be a cold gas stream of the plasma gas composition or may be one which alters the heat transfer characteristics or some other property of the plasma.
- ~ ~
:10~ 5~ ~ ~
As shown, the nozzle extension assembly comprises apparatus distinct from the plasma gun itselfO This parti-cular construction was selected for reasons of practicality to permit utilization of the present invention with existing plasma equipment. There is, of course, no reason why the extended nozzle cannot be integral with the gun itself.
Also although the finned member 8 is shown formed as a single piece, various portions thereof may preferably be formed as separate members either to permit adaption of the assembly to alternative coating operations or equipment, or simply to facilitate repairs or replacement of parts as they wear in use.
Usually to develop the optimum phase structure in the applied coating it is advantageous to have the powder parti~
cles impacting the surface to be coated in a plastic condi-tion, but at as low a temperature as possible. However, the cooler the particles the higher the impact velocity must be to generate the maximum density and adherence.
Thus, there is a considerable advantage to be gained through the provision of a capability of providing a high coating particle velocity.
Particle velocities are inherently limited by the gas velocity in the particular system being employed. In de-tonation spray processes, the particles are typically limited to shock wave velocities on the order of 2500 feet per second. Plasma spray guns, using argon as recommended by the manufacturers, may reach gas velocities up to 4000 feet per second. In the preferred embodiments of the ~6S~
present invention gas velocities of up to 12,000 feet per second or higher are possible.
Contrary to the usual industry practice, the use of helium as the plasma gas is preferred in the present inven-tion. Although helium is known to have possible use in - plasma spray operations, its light weight and poor heat transfer characteristics have resulted in industry dis-couraging its use in conventional plasma spray equipment.
In the present invention its use is not only possible but advantageous.
In conventional equipment the gases exiting the plasma gun quickly disperse. Powders injected into such a stream - reside therein for only a very short period of time. In these short residence times, the use of helium with its poor heat transfer capabilities, rather than argon, would increase the difficulty of imparting proper heat to the powders. This same short residence time and rapidly dis-persing gas also aggravate the problem of providing the velocity component to the powders.
The preferred use of helium in the present invention provides controlled heating and a high velocity capability.
In addition there are other advantages. With every coating process, it is essential to consider not only the effect of coating components and process parameters on the coating per se, but also their effect on the substrate being coated.
Often the character of the substrate is such that certain ;~ temperatures of the substrate not be exceeded. The rela-tively poor heat transfer qualities of helium, as compared _ 9 _ ; .
l~S~
to argon for example, inherently result in a reduced heat transfer to the substrate ` In the conventional plasma spray operations, the dis-persion of the heated gases results in a fairly large sub-- ~ strate area receiving h~at, particularly areas where no coating is desired and which may be masked. In the present invention, there is a much greater degree of focus in the stream. Thus, smaller areas of the substrate are usually exposed at any one time to the hot gases and, hence, with a greater heat sink substrates remain cooler. As an addi-tional benefit, it has been found that because of greater deposition area control the necessity and extent of masking is minimized; variations in coating structure and thickness are more controlled; and there is less powder waste, pro-moting economy.
Coating operations are also facilitated in another way through use of this invention. In use of a detonation gun operations are usually conducted with the operator posi-tioned remote from the coat~ng operation for safety reasons.
With conventional plasma spray guns the exiting gas is at such a high temperature that eye damage from ultra-violet radiation can quickly occur and suitable eye protection is required. In the present invention, exit gas temperatures are reduced and the possibility of eye damage is lessened -although, of course, suitable safety measures should be ob-sér~ed in any event.
In a conventional process, a part is typically prepared for coating by, first, masking to leave exposed only the - . . - .: .
~ .
S;~Q~
areas to be coated; second, grit blasting; third, a cleanup to remove the effects of the grit blasting; and finally, a remasking. The present invention eliminates the need for many of these conventional steps in many cases Since focusing is vastly improved the extent of masking is much reduced. Further, because particle velocities are very high, it has been found possible to eliminate the grit blasting operation and the masking and cleanup associated therewith. A simple surface wipe for degreasing with Freon has been found to be sufficient.
Example Apparatus ..
Plasma Gun - METC0 3MB with GP Nozzle Power Supply - PLASMADYNE
350 D.C. arc amps 50-56 D.C. arc volts Powder Feeder - S.S. AIRABRASIVE unit - (miniature grit blaster) powder feed rate .357 lbs./hr.
Nozzle Extension Assembly - per drawing Powder ~METC0 450) Composition (wt.%)-95 percent nickel 5 percent aluminum Particle size -170 + 325 mesh (ASTM B214) ~;s~
Process Parameters Plasma Gas - helium Gas Rate - 275 ft.3/min.
~un to Substrate Distance - 2-3 inches Size of Focus - 3/8 inch Substrate - titanium alloy Coating area - flat washer Deposition Using the hand held coating gun with attached nozzle extension assembly, a coating .008-.010 inch in thickness was applied for galling and fretting resistance to one surface of the flat washer.
Results A coating density of well over 99 percent of theoretical density was achieved. This is in excess of that attainable in any conventional plasma processO
Adherence was excellent. Repeated thermal shocking from high temperature resulted in no evidence whatsoever of cracking or flaking.
Although this invention has been described in detail with reference to certain examples and preferred embodiments for the sake of illustration, the invention in its broader aspects is not limited to such specific details but departures may be made from such details without departing from the principles of the invention and without - . .
.. . ,:
s~
:
:
sacr;ficing its chief advantages.
The present invention relates in general to the coating arts and, more particularly, to the production of coatings by thermal spray techniques.
Three thermal spray techniques are utilized at the present time in the production of coatings, viz., flame, plasma and detonation spray processes. These processes all depend upon the generation of a hot stream of gases which are used to heat and propel a finely-divided coating material to a surface to be coated. ;~
In the flame spray process the combustion of a gas mixture such as oxygen and acetylene provides the necessary heat. The plasma spray technique does not depend upon a combustion process. Instead an inert gas, usually argon, is electrically excited resulting in a high temperature plasma. In the detonation spray process a controlled ex-plosion of gases, such as a mixture of oxygen, acetylene and nitrogen takes place within the detonation gun, the powders being driven therefrom on a shock wave, Flame gun gas temperatures are, of course, determined and limited by those attainable in the process of combus-tion. In the detonation spray processes, temperatures of about 6000F. and exit gas velocities on the order of 2500 feet per second are typical. Plasma gas temperatures, however, are extremely high, reaching 20a000F. and very high gas velocities are attainable.
Because of the significant differences in the respec-tive process parameters, particularly temperature and gas .. ..
Z~
velocity, significant differences may be seen in the de-posited coatings depending upon the process utilized and despite the fact that powders of the same composition are - being sprayed. The higher temperatures in the plasma spray gun results, in some coating systems, in a deposited coating of different phase structure than that achieved with the detonation gun. This difference in phase structure results in a difference in the physical properties of the coating, the difference in many instances being sufficient to result in acceptability or unacceptability of the coating for the purpose intended.
One coating composition adapted to deposition by spray techniques, usually plasma or detonation spray, is a nickel/
aluminum material. This is utilized to provide fretting and gall resistance to certain titanium alloy gas turbine engine parts. Experience has shown that many coatings deposited by ~ -conventional plasma spray techniques are of good theoretical density but are highly stressed and, hence, prone to cracking and spalling, particularly under conditions involving thermal shock. Those resultant from a detonation spray with lower formation temperatures are more satisfactory from a cracking and spalling viewpoint, but are less than optimum, particu-larly in tenms of masking requirements and economy.
With existing processes and apparatus it is impossible, in many, many circumstances at leasta to generate spray coatings having not only the requisite composition and metallurgical structure but also the desired coating adher-ence and density. It is also desirable to minimize some of ; - 3 -~6~
the production problems incident to the conventional spray-ing operations. Detonation processes, for example, are for safety reasons usually conducted with the operator situated in a position remote from the coating operation itself, re-quiring careful prepositioning of the part to be coated and/or remote control. Conventional plasma spray techniques require careful surface preparation and masking and may pose some danger in overheating the substrate.
SUMMARY OF THE INVENTION
The present invention is directed to improvements in thermal spray coating apparatus and methods These improve-ments not only eliminate the majority of the drawbacks associated with existing apparatus and methods, but also provide a number of ancillary benefits as well A major advantage of the invention results from an ~-ability to generate optimum coating structures, in a variety of coating systems if desired, with excellent adherence and density. This advantage is, moreover, achieved with con-current improvements in process economy and safety.
The invention contemplates the provision of an elongated passageway for defining the hot gas stream in thermal spray apparatus and into which the powders to be sprayed may be injected into a cooled gas stream at a predetermined location or locations, the residence time of the coating particles being such as to provide the desired heating and velocity to such particles.
In one embodiment of the invention, a cooled nozzle extension assembly adapted to mate with conventional plasma - ' - lO~SZQ3 spray equipment is fabricated with an aerodynamically efficient passageway through which the hot plasma may be passed and into which the coating powders may be introduced at a selected loc-: ation or locations along the passageway. In operation thereof, helium is utilized as the plasma gas.
In accordance with an embodiment, a thermal powderspray apparatus comprises: means for providing a gas at high temperature; an elongated nozzle forming an exit for the gas and through which the gas may be passed as a high velocity stream; means for cooling the gas to provide a colled gas stream in at least a portion of the nozzle: and means for inject-ing powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location pro-viding sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
In accordance with a further embodiment, a plasma powder spray apparatus comprises: means for generating a plasma:
an elongated nozzle forming an exit form the plasma generating means and through which the plasma may be passed as a high velocity stream, means for cooling the plasma to provide a cooled gas stream in at least a portion of the nozzle, and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
In accordance with a still further embodiment, a plasma powder spray apparatus comprises: a plasma gun having a plasma generating chamber, a nozzle having an elongated passageway there-through communicating with the chamber: means for cooling the nozzle: and access means through which powder to be sprayed may be injected into the passageway intermediate its ends at an B ~ _5_ iO~;SZ~;~
injection location selected to impart a desired level of heating and a high velocity to the powder.
From a different aspect, there is provided, in accordance with the invention a plasma powder spray apparatus including a plasma generating chamber, the improvement which comprises:
a nozzle having an elongated passageway therethrough communicating with and forming an exit for the plasma generating chamber, means for cooling a plasma traversing the passageway, and access means for injecting powder to be sprayed into the passageway intermediate its ends and downstream of the initial source of plasma cooling.
In accordance with a still further aspect, an embodi-ment of the invention comprises, a nozzle extension assembly for a plasma spray gun comprising: an inner member having an elong-ated passageway extending therethrough, one end of the inner -member being adapted to mate with gas exit opening of the plasma gun, the passageway being aligned with said port' coolant jacket surrounding the inner member, the coolant jacket cooperating with the inner member to form a coolant chamber therebetween, means for admitting a coolant to the coolant chamber, access means communicating with the passageway intermediate its ends for admitting a powder to the passageway; and means for connecting the nozzle extension assembly to the plasrna gun in position.
From a still further aspect, a plasma powder spray method comprises: generating a plasma, passing the plasma at high velocity through an elongated nozzle, cooling the plasma, forming a cooled plasma gas stream' admitting coating powder to the cooled gas stream in the nozzle, providing sufficient powder residence time in the cooled gas stream to plasticize the powder and impart a high velocity thereto, and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
In accordance with a still further embodiment, a plasma ~ -5a-1~6SZ~
powder spray method comprises: generating a helium plasma athigh temperature, passing the plasma at high velocity through an elongated nozzle, cooling the nozzle and the plasma passing therethrough formlng a cooled plasma gas stream, admitting coating powder to the cooled gas stream in the nozzle, plasticizing the powder and imparting a high velocity thereto, and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
BRIEF DESCRIPTION OF THE DRAWING
The drawing depicts plasma spray apparatus according to the teachings of this invention.
DESCRIPTION OF THE_PREFERRED EMBODIMENTS
The plasma spray apparatus shown in the drawing corres-ponds to that which has been actually used in the deposition of coatings according to the present invention.
A spray nozzle extension assembly 2 is adapted to fit around the nozzle 4 of a standard plasma spray gun 6, such as the METCO 3MB Plasma Gun with GP Nozzle. The nozzle extension assembly comprises a tubular finned mernber 8 having a passageway 10 extending therethrough. As shown, the finned member is formed of a material of high therrnal conductivity, such as copper and is surrounded by a steel water jacket 14 having a cooling water inlet 16 and outlet 1~. The cooling fluid passing through the water chamber 19 cools the finned member preventing melting or other heat damage due to the hot plasma flowing through the passageway 10 during operation of the apparatus. In its traverse through the passageway in the cooled finned member, the hot plasma itself undergoes substantial cooling.
In this apparatus in the interest of maintaining a -5b-tB
..... . ,,,. ~, ,, high gas velocity the passageway 10 has been shaped for aerodynamic efficiency, utilizing an inlet portion 20, a nozzle portion 22 and an outlet portion 24. The particular assembly shown is 6.3 inches in length with an inlet por-tion 4 x 0.215 inches, a nozzle portion about 0.25 inch long having a throat diameter of 0 14 inch, and an outlet portion having a diameter of 0.15 inch. Thus, the nozzle is convergent/slightly divergent.
Typically, it is desirable to provide the powders to the surface to be coated, not only at high velocity and , heated, but in a plastic rather than molten condition. As the plasma gas traverses the passageway it is cooled and, accordingly, introduction of the powders at a downstream location will generally result in a reduced heating of the powders because the temperature is lower than the upstream temperature. Accordingly, the nozzle is fabricated to pro-vide sufficient length to substantially reduce the plasma temperature in the nozzle. Thus, as the word "elongated"
is used herein, it will be understood to mean sufficient length to provide substantial cooling of the plasma. From the foregoing, it will be seen that in the present invention the coating powders are exposed in a relatively low temper-ature/long time cycle as contrasted with a high temperature/
short time cycle in conventional plasma spray operations.
The nozzle extension assembly is provided with an access port or ports, 40 and 42 in the drawing, through which powder may be introduced into the plasma gas stream.
The location of these powder access ports will depend upon .
~ 3 the powders being sprayed and the particular process para-meters and apparatus being utilized. Basically, however, the location is selected to provide the correct heating of the powders.
In the spraying of nickel/aluminum in the apparatus described, the powders are admitted in an inert carrier gas through access port 42 which is a 1/16 inch hole located about 3.5 inches downstream from the nozzle extension inlet or just upstream of the nozzle portion.
One or more access ports can be utilized for the intro-duction of differing powder compositions where such powders are to be sprayed concurrently or sequentially, or for the introduction of powders of the same composition where the processing parameters are to be changed. The formation of graded coatings by gradually phasing in one composition while phasing out another thereby eliminating a planar interface between the compositions is readily achieved.
As has been previously discussed, powder temperature can be readily controlled in a given system by careful selection of the axial location along the passageway where the powders are admitted to the hot gas stream. The apparatus is also readily adaptable to other means of powder tempera-ture control. Access port 40 or some other port can, for example, be utilized for the admission of a temperature-modifying gas to the plasma stream. This temperature-modifying gas may simply be a cold gas stream of the plasma gas composition or may be one which alters the heat transfer characteristics or some other property of the plasma.
- ~ ~
:10~ 5~ ~ ~
As shown, the nozzle extension assembly comprises apparatus distinct from the plasma gun itselfO This parti-cular construction was selected for reasons of practicality to permit utilization of the present invention with existing plasma equipment. There is, of course, no reason why the extended nozzle cannot be integral with the gun itself.
Also although the finned member 8 is shown formed as a single piece, various portions thereof may preferably be formed as separate members either to permit adaption of the assembly to alternative coating operations or equipment, or simply to facilitate repairs or replacement of parts as they wear in use.
Usually to develop the optimum phase structure in the applied coating it is advantageous to have the powder parti~
cles impacting the surface to be coated in a plastic condi-tion, but at as low a temperature as possible. However, the cooler the particles the higher the impact velocity must be to generate the maximum density and adherence.
Thus, there is a considerable advantage to be gained through the provision of a capability of providing a high coating particle velocity.
Particle velocities are inherently limited by the gas velocity in the particular system being employed. In de-tonation spray processes, the particles are typically limited to shock wave velocities on the order of 2500 feet per second. Plasma spray guns, using argon as recommended by the manufacturers, may reach gas velocities up to 4000 feet per second. In the preferred embodiments of the ~6S~
present invention gas velocities of up to 12,000 feet per second or higher are possible.
Contrary to the usual industry practice, the use of helium as the plasma gas is preferred in the present inven-tion. Although helium is known to have possible use in - plasma spray operations, its light weight and poor heat transfer characteristics have resulted in industry dis-couraging its use in conventional plasma spray equipment.
In the present invention its use is not only possible but advantageous.
In conventional equipment the gases exiting the plasma gun quickly disperse. Powders injected into such a stream - reside therein for only a very short period of time. In these short residence times, the use of helium with its poor heat transfer capabilities, rather than argon, would increase the difficulty of imparting proper heat to the powders. This same short residence time and rapidly dis-persing gas also aggravate the problem of providing the velocity component to the powders.
The preferred use of helium in the present invention provides controlled heating and a high velocity capability.
In addition there are other advantages. With every coating process, it is essential to consider not only the effect of coating components and process parameters on the coating per se, but also their effect on the substrate being coated.
Often the character of the substrate is such that certain ;~ temperatures of the substrate not be exceeded. The rela-tively poor heat transfer qualities of helium, as compared _ 9 _ ; .
l~S~
to argon for example, inherently result in a reduced heat transfer to the substrate ` In the conventional plasma spray operations, the dis-persion of the heated gases results in a fairly large sub-- ~ strate area receiving h~at, particularly areas where no coating is desired and which may be masked. In the present invention, there is a much greater degree of focus in the stream. Thus, smaller areas of the substrate are usually exposed at any one time to the hot gases and, hence, with a greater heat sink substrates remain cooler. As an addi-tional benefit, it has been found that because of greater deposition area control the necessity and extent of masking is minimized; variations in coating structure and thickness are more controlled; and there is less powder waste, pro-moting economy.
Coating operations are also facilitated in another way through use of this invention. In use of a detonation gun operations are usually conducted with the operator posi-tioned remote from the coat~ng operation for safety reasons.
With conventional plasma spray guns the exiting gas is at such a high temperature that eye damage from ultra-violet radiation can quickly occur and suitable eye protection is required. In the present invention, exit gas temperatures are reduced and the possibility of eye damage is lessened -although, of course, suitable safety measures should be ob-sér~ed in any event.
In a conventional process, a part is typically prepared for coating by, first, masking to leave exposed only the - . . - .: .
~ .
S;~Q~
areas to be coated; second, grit blasting; third, a cleanup to remove the effects of the grit blasting; and finally, a remasking. The present invention eliminates the need for many of these conventional steps in many cases Since focusing is vastly improved the extent of masking is much reduced. Further, because particle velocities are very high, it has been found possible to eliminate the grit blasting operation and the masking and cleanup associated therewith. A simple surface wipe for degreasing with Freon has been found to be sufficient.
Example Apparatus ..
Plasma Gun - METC0 3MB with GP Nozzle Power Supply - PLASMADYNE
350 D.C. arc amps 50-56 D.C. arc volts Powder Feeder - S.S. AIRABRASIVE unit - (miniature grit blaster) powder feed rate .357 lbs./hr.
Nozzle Extension Assembly - per drawing Powder ~METC0 450) Composition (wt.%)-95 percent nickel 5 percent aluminum Particle size -170 + 325 mesh (ASTM B214) ~;s~
Process Parameters Plasma Gas - helium Gas Rate - 275 ft.3/min.
~un to Substrate Distance - 2-3 inches Size of Focus - 3/8 inch Substrate - titanium alloy Coating area - flat washer Deposition Using the hand held coating gun with attached nozzle extension assembly, a coating .008-.010 inch in thickness was applied for galling and fretting resistance to one surface of the flat washer.
Results A coating density of well over 99 percent of theoretical density was achieved. This is in excess of that attainable in any conventional plasma processO
Adherence was excellent. Repeated thermal shocking from high temperature resulted in no evidence whatsoever of cracking or flaking.
Although this invention has been described in detail with reference to certain examples and preferred embodiments for the sake of illustration, the invention in its broader aspects is not limited to such specific details but departures may be made from such details without departing from the principles of the invention and without - . .
.. . ,:
s~
:
:
sacr;ficing its chief advantages.
Claims (12)
1. Thermal powder spray apparatus which comprises:
means for providing a gas at high temperature;
an elongated nozzle forming an exit for the gas and through which the gas may be passed as a high velocity stream;
means for cooling the gas to provide a cooled gas stream in at least a portion of the nozzle; and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
means for providing a gas at high temperature;
an elongated nozzle forming an exit for the gas and through which the gas may be passed as a high velocity stream;
means for cooling the gas to provide a cooled gas stream in at least a portion of the nozzle; and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
2. Plasma powder spray apparatus which comprises:
means for generating a plasma;
an elongated nozzle forming an exit from the plasma generating means and through which the plasma may be passed as a high velocity stream;
means for cooling the plasma to provide a cooled gas stream in at least a portion of the nozzle; and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
means for generating a plasma;
an elongated nozzle forming an exit from the plasma generating means and through which the plasma may be passed as a high velocity stream;
means for cooling the plasma to provide a cooled gas stream in at least a portion of the nozzle; and means for injecting powder to be sprayed into the cooled gas stream upstream of the downstream end of the nozzle at an injection location providing sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
3. Plasma powder spray apparatus which comprises:
a plasma gun having a plasma generating chamber;
a nozzle having an elongated passageway there-through communicating with the chamber;
means for cooling the nozzle; and access means through which powder to be sprayed may be injected into the passageway intermediate its ends at an injection location selected to impart a desired level of heating and a high velocity to the powder.
a plasma gun having a plasma generating chamber;
a nozzle having an elongated passageway there-through communicating with the chamber;
means for cooling the nozzle; and access means through which powder to be sprayed may be injected into the passageway intermediate its ends at an injection location selected to impart a desired level of heating and a high velocity to the powder.
4. Apparatus according to claim 3 wherein:
the access means is located downstream of a cooled portion of the nozzle whereby the plasma traversing the passageway is cooled before reaching the powder injec-tion location thereby limiting the temperature to which the powder is exposed.
the access means is located downstream of a cooled portion of the nozzle whereby the plasma traversing the passageway is cooled before reaching the powder injec-tion location thereby limiting the temperature to which the powder is exposed.
5. In plasma powder spray apparatus including a plasma generating chamber, the improvement which comprises:
a nozzle having an elongated passageway there-through communicating with and forming an exit for the plasma generating chamber;
means for cooling a plasma traversing the passageway; and access means for injecting powder to be sprayed into the passageway intermediate its ends and downstream of the initial source of plasma cooling.
a nozzle having an elongated passageway there-through communicating with and forming an exit for the plasma generating chamber;
means for cooling a plasma traversing the passageway; and access means for injecting powder to be sprayed into the passageway intermediate its ends and downstream of the initial source of plasma cooling.
6. The improvement according to claim 5 wherein:
the means for cooling a plasma traversing the passageway comprises means for cooling the walls of the passageway.
the means for cooling a plasma traversing the passageway comprises means for cooling the walls of the passageway.
7. The improvement according to claim 5 wherein:
the means for cooling a plasma traversing the passageway comprises access means communicating with the passageway for injecting a cooling gas thereinto.
the means for cooling a plasma traversing the passageway comprises access means communicating with the passageway for injecting a cooling gas thereinto.
8. The improvement according to claim 5 wherein:
the access means for injecting powder into the passageway is selected to provide sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
the access means for injecting powder into the passageway is selected to provide sufficient powder residence time in the cooled gas stream to impart a desired level of heating and a high velocity to the powder.
9. A nozzle extension assembly for a plasma spray gun which comprises:
an inner member having an elongated passageway extending therethrough, one end of the inner member being adapted to mate with gas exit opening of the plasma gun, the passageway being aligned with said port;
coolant jacket surrounding the inner member, the coolant jacket cooperating with the inner member to form a coolant chamber therebetween;
means for admitting a coolant to the coolant chamber;
access means communicating with the passageway intermediate its ends for admitting a powder to the passageway; and means for connecting the nozzle extension assembly to the plasma gun in position.
an inner member having an elongated passageway extending therethrough, one end of the inner member being adapted to mate with gas exit opening of the plasma gun, the passageway being aligned with said port;
coolant jacket surrounding the inner member, the coolant jacket cooperating with the inner member to form a coolant chamber therebetween;
means for admitting a coolant to the coolant chamber;
access means communicating with the passageway intermediate its ends for admitting a powder to the passageway; and means for connecting the nozzle extension assembly to the plasma gun in position.
10. A plasma powder spray method which comprises:
generating a plasma;
passing the plasma at high velocity through an elongated nozzle;
cooling the plasma, forming a cooled plasma gas stream;
admitting coating powder to the cooled gas stream in the nozzle, providing sufficient powder residence time in the cooled gas stream to plasticize the powder and impart a high velocity thereto; and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
generating a plasma;
passing the plasma at high velocity through an elongated nozzle;
cooling the plasma, forming a cooled plasma gas stream;
admitting coating powder to the cooled gas stream in the nozzle, providing sufficient powder residence time in the cooled gas stream to plasticize the powder and impart a high velocity thereto; and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
11. A method according to claim 10 wherein:
the plasma is a helium plasma.
the plasma is a helium plasma.
12. A plasma powder spray method which comprises:
generating a helium plasma at high temperature;
passing the plasma at high velocity through an elongated nozzle;
cooling the nozzle and the plasma passing therethrough forming a cooled plasma gas stream;
admitting coating powder to the cooled gas stream in the nozzle, plasticizing the powder and imparting a high velocity thereto; and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
generating a helium plasma at high temperature;
passing the plasma at high velocity through an elongated nozzle;
cooling the nozzle and the plasma passing therethrough forming a cooled plasma gas stream;
admitting coating powder to the cooled gas stream in the nozzle, plasticizing the powder and imparting a high velocity thereto; and directing the plasticized powder to a surface to be coated and effecting a coating buildup thereon to the desired thickness.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US51258574A | 1974-10-07 | 1974-10-07 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1065203A true CA1065203A (en) | 1979-10-30 |
Family
ID=24039722
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA237,226A Expired CA1065203A (en) | 1974-10-07 | 1975-10-07 | Thermal spraying using cool plasma stream |
Country Status (15)
| Country | Link |
|---|---|
| JP (2) | JPS5632031B2 (en) |
| AU (1) | AU503161B2 (en) |
| BE (1) | BE834234A (en) |
| BR (1) | BR7506565A (en) |
| CA (1) | CA1065203A (en) |
| CH (1) | CH604914A5 (en) |
| DE (1) | DE2544847C2 (en) |
| FR (1) | FR2287276A1 (en) |
| GB (1) | GB1529455A (en) |
| IL (1) | IL48254A (en) |
| IT (1) | IT1043176B (en) |
| NL (1) | NL177286C (en) |
| NO (1) | NO148113C (en) |
| SE (1) | SE427804B (en) |
| ZA (1) | ZA756342B (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5858469A (en) * | 1995-11-30 | 1999-01-12 | Sermatech International, Inc. | Method and apparatus for applying coatings using a nozzle assembly having passageways of differing diameter |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS5941214U (en) * | 1982-09-08 | 1984-03-16 | 株式会社大食美術 | paper container |
| JPS623418U (en) * | 1985-06-24 | 1987-01-10 | ||
| JPH0251898A (en) * | 1988-08-13 | 1990-02-21 | Nippon Steel Corp | Plasma spray gun |
| CH693083A5 (en) * | 1998-12-21 | 2003-02-14 | Sulzer Metco Ag | Nozzle and nozzle assembly for a burner head of a plasma spray device. |
| JP5185641B2 (en) * | 2008-01-30 | 2013-04-17 | 日鉄住金ハード株式会社 | High-speed gas spraying device, plasma spraying device, and injection port member |
| JP2012193431A (en) * | 2011-03-17 | 2012-10-11 | Hiroyuki Shimada | Plasma spraying device |
| US10612122B2 (en) * | 2017-08-25 | 2020-04-07 | Vladimir E. Belashchenko | Plasma device and method for delivery of plasma and spray material at extended locations from an anode arc root attachment |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE1571153A1 (en) * | 1962-08-25 | 1970-08-13 | Siemens Ag | Plasma spray gun |
| JPS432978Y1 (en) * | 1965-11-09 | 1968-02-07 | ||
| DE1281769B (en) * | 1966-12-30 | 1968-10-31 | Messer Griesheim Gmbh | Method and device for feeding a powder into the plasma jet during plasma spraying |
| US3627204A (en) * | 1969-06-18 | 1971-12-14 | Sealectro Corp | Spray nozzle for plasma guns |
-
1975
- 1975-10-03 FR FR7530300A patent/FR2287276A1/en active Granted
- 1975-10-04 CH CH1284975A patent/CH604914A5/xx not_active IP Right Cessation
- 1975-10-06 SE SE7511150A patent/SE427804B/en not_active IP Right Cessation
- 1975-10-06 NO NO753361A patent/NO148113C/en unknown
- 1975-10-06 BE BE160726A patent/BE834234A/en not_active IP Right Cessation
- 1975-10-06 NL NLAANVRAGE7511712,A patent/NL177286C/en not_active IP Right Cessation
- 1975-10-07 DE DE2544847A patent/DE2544847C2/en not_active Expired
- 1975-10-07 IT IT28037/75A patent/IT1043176B/en active
- 1975-10-07 ZA ZA00756342A patent/ZA756342B/en unknown
- 1975-10-07 CA CA237,226A patent/CA1065203A/en not_active Expired
- 1975-10-07 BR BR7506565*A patent/BR7506565A/en unknown
- 1975-10-07 AU AU85494/75A patent/AU503161B2/en not_active Expired
- 1975-10-07 IL IL48254A patent/IL48254A/en unknown
- 1975-10-07 JP JP12117675A patent/JPS5632031B2/ja not_active Expired
- 1975-10-07 GB GB41015/75A patent/GB1529455A/en not_active Expired
-
1983
- 1983-02-28 JP JP58033710A patent/JPS6029542B2/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5858469A (en) * | 1995-11-30 | 1999-01-12 | Sermatech International, Inc. | Method and apparatus for applying coatings using a nozzle assembly having passageways of differing diameter |
Also Published As
| Publication number | Publication date |
|---|---|
| NO148113B (en) | 1983-05-02 |
| SE7511150L (en) | 1976-04-08 |
| DE2544847C2 (en) | 1986-05-15 |
| IL48254A0 (en) | 1975-12-31 |
| CH604914A5 (en) | 1978-09-15 |
| JPS5163324A (en) | 1976-06-01 |
| NO753361L (en) | 1976-04-08 |
| NL177286C (en) | 1985-09-02 |
| FR2287276B1 (en) | 1983-04-15 |
| JPS5632031B2 (en) | 1981-07-24 |
| BE834234A (en) | 1976-02-02 |
| IT1043176B (en) | 1980-02-20 |
| JPS6029542B2 (en) | 1985-07-11 |
| AU8549475A (en) | 1977-04-21 |
| GB1529455A (en) | 1978-10-18 |
| NL177286B (en) | 1985-04-01 |
| ZA756342B (en) | 1976-09-29 |
| FR2287276A1 (en) | 1976-05-07 |
| AU503161B2 (en) | 1979-08-23 |
| NL7511712A (en) | 1976-04-09 |
| BR7506565A (en) | 1976-08-10 |
| DE2544847A1 (en) | 1976-04-15 |
| SE427804B (en) | 1983-05-09 |
| NO148113C (en) | 1983-08-10 |
| JPS58202062A (en) | 1983-11-25 |
| IL48254A (en) | 1978-07-31 |
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