U.S. patent number 3,892,882 [Application Number 05/364,171] was granted by the patent office on 1975-07-01 for process for plasma flame spray coating in a sub-atmospheric pressure environment.
This patent grant is currently assigned to Union Carbide Corporation. Invention is credited to Keith Graham Ford, Christopher John Scott Guest.
United States Patent |
3,892,882 |
Guest , et al. |
July 1, 1975 |
Process for plasma flame spray coating in a sub-atmospheric
pressure environment
Abstract
The invention relates to the production of plasma-sprayed
coatings at low surface speeds and long stand off distances e.g.
more than 7.5 cm. A zone of sub-atmospheric pressure is maintained
through which the hot gas effluent and entrained coating powder
produced by a plasma torch is caused to pass on its way to the
substrate being coated. The sub-atmospheric zone preferably extends
over the whole path of hot gas effluent and entrained coating
powder. Apparatus is provided which comprises a plasma torch and a
chamber preferably a tube together with means for maintaining a
zone of sub-atmospheric pressure in the chamber. In the case of the
tube this may be a spiral passage mounted in said tube which
injects a sheath of gas moving along the inner surface of the tube
in a spiral path.
Inventors: |
Guest; Christopher John Scott
(Swindon, EN), Ford; Keith Graham (Swindon,
EN) |
Assignee: |
Union Carbide Corporation (New
York, NY)
|
Family
ID: |
23433362 |
Appl.
No.: |
05/364,171 |
Filed: |
May 25, 1973 |
Current U.S.
Class: |
427/446;
219/121.47; 219/121.51; 219/121.5; 239/81 |
Current CPC
Class: |
B05B
7/226 (20130101); B05B 5/06 (20130101) |
Current International
Class: |
B05B
5/06 (20060101); B05B 7/16 (20060101); B05B
7/22 (20060101); B05b 005/06 () |
Field of
Search: |
;117/93.1PF,22,23
;219/76,121P ;239/81 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Martin; William D.
Assistant Examiner: Newsome; John H.
Attorney, Agent or Firm: Terminello; D. J.
Claims
We claim:
1. A method for producing plasma sprayed coatings comprising
maintaining an arc between a first and second electrode;
passing a gas into said arc to produce a hot gas effluent;
introducing a coating powder into said hot gas effluent;
passing said coating powder entrained hot gas effluent through an
arc constricting nozzle;
surrounding said coating powder entrained hot gas effluent by a
vortical flow of gas moving in the same direction as said hot gas
effluent to provide a zone of sub-atmospheric pressure from said
nozzle substantially to a substrate to be coated;
maintaining said coating powder entrained hot gas effluent within
said zone of sub-atmospheric pressure until it strikes said
substrate.
2. A method according to claim 1 wherein said vortical flow of gas
is established in a nozzle connected in gas tight relationship with
said arc constricting nozzle.
Description
The present invention relates to improvements in plasma arc
spraying and to apparatus for same.
Plasma spraying is a coating process in which particulate coating
material is injected into a plasma stream generated by a plasma
torch in which stream the powder is heated and accelerated towards
a workpiece to be coated. In order to achieve good properties in
the resulting coating it is generally necessary to build up the
coating as a series of discrete layers the thickness of each of
which layers depends on the type of coating to be applied. For a
given coating material however, to achieve a coating of
satisfactory properties, e.g. good hardness, low porosity, no
cracking and high bond strength there is a maximum limit to the
thickness of each of the discrete layers.
The thickness of each discrete layer depends on the deposition flux
on the coating powder and, when the workpiece is moved relative to
the plasma stream as is usually the case, upon the relative speed
of the workpiece to the plasma stream (called the surface speed of
the workpiece).
The deposition flux depends on the feed rate of coating powder into
the plasma stream and because the powder tends to spread out as it
travels towards the workpiece from the point of injection, also on
the distance the injected powder travels before striking the
workpiece.
The lower the feed rate of coating powder, the lower the deposition
flux. The longer the distance travelled by the coating powder
before striking the workpiece the lower will be the deposition
flux.
Plasma torches comprise a first and second electrode between which
is maintained an electric arc, a gas being passed through this arc
and then through an arc restricting nozzle. The gas is heated by
the arc and forms a plasma which is ejected from the nozzle at high
speed. The coating powder may be injected into the plasma either in
the torch itself or outside the torch. Since the powder must reach
the requisite temperature for coating before reaching the surface
to be coated, it must remain in the plasma long enough to reach the
requisite temperature, for the coating powder used.
If the coating powder is injected inside the torch into the arc
itself, very rapid heating of the powder occurs so that the coating
temperature is rapidly attained and the substrate to be coated can
be placed only a short distance, e.g. 1.5 to 3 cm from the torch
nozzle. At such close distances however very high surface speeds
are necessary to achieve good coating properties, and although it
has been found that such coatings exhibit by far the best
properties hitherto obtainable, the economics of working in this
way can prove prohibitively expensive. Also such high surface
speeds sometimes involve potential safety problems which make it
undesireable or impossible to work at such high speeds.
However the powder feed rate does enable some reduction in surface
speed to be obtained but at the same time makes the coating time
longer and therefore more costly thus negating any cost advantage
in lower surface speed. Increasing the torch to substrate distance
(usually called stand-off distance or simply stand-off) also
enables lower surface speeds to be used but the coating produced at
long stand-off have hitherto been found to have substandard
hardness and a tendency to be porous.
If the powder is injected outside the torch proper the rate at
which the powder is heated is lower and therefore a longer dwelling
time in the plasma and consequently a longer stand-off is
unavoidable. Low surface speeds are therefore usual in this type of
method. The coatings produced by such methods however also suffer
from substandard hardness and a tendency to be porous.
Attempts have been made to improve matters by the use of shrouds or
tubes surrounding the plasma stream and by using jets of inert gas
in an attempt to exclude the surrounding atmosphere and improve
coating properties. Such methods have not however met with
significant success at the stand-off distances which are required
for low surface speed at an economic rate of powder feed.
It is an object of the present invention to provide a method of
plasma arc spraying in which improved hardness and a lower tendency
to porosity can be achieved at long stand-off and low surface
speed.
It is a further object to provide apparatus whereby such improved
results can be achieved under conditions of long stand-off and low
surface speed.
According to the present invention the first object achieved by by
providing in a method of producing plasma sprayed coatings in which
an arc is maintained between a first and second electrode, a gas is
passed into said arc to produce a hot gas effluent and said hot gas
effluent passed through an arc constricting nozzle and together
with a coating powder entrained therein is directed at a substrate
to be coated. The length of the path from nozzle to substrate being
such as to provide low deposition flux values and consequently
enable low substrate surface speeds to be used, the improvement
which comprises passing said hot gas effluent and entrained coating
powder through a zone of sub-atmospheric pressure disposed between
said nozzle and said substrate to be coated.
The distance of the substrate from the outlet of the nozzle should
be for example more than 7.5 cm if low surface speeds are to be
achieved at economic powder feed rates. The powder feed rate may be
from 25 to 60 gms per minute depending on the density of the
powder. The surface speed is preferably below 25 cm per second. The
degree of vacuum in the sub-atmospheric pressure zone need not be
very great, significant increases in coating quality being achieved
at vacuum levels of as little as about 4 cm of mercury.
The zone of sub-atmospheric pressure should extend over a major
portion of the path of the entrained coating powder and is
preferably of sufficient diameter to encompass the effluent from
the torch.
In one embodiment the hot gas effluent and entrained coating powder
is passed through a chamber disposed between the nozzle and the
substrate to be coated, the region within the chamber being
maintained at a sub-atmospheric pressure by means for example of a
vacuum pump. The inlet end of the chamber is preferable connected
in gas tight relationship with the nozzle by suitable means. In
general the surface of the substrate should be disposed close to
the outlet of the chamber e.g. within about 1 cm of the outlet.
The zone of sub-atmospheric pressure preferably extends over the
whole path of the effluent from nozzle to substrate. This effect
may be achieved for example by carrying out the coating process
inside a vacuum tank maintained at a sub-atmospheric pressure. This
embodiment does have some drawbacks in terms of e.g. access to the
workpiece during coating etc, nevertheless high quality coatings
can be produced at low surface speeds by this means.
A more preferred method of carrying out this invention however, is
to pass the hot gas effluent and entrained coating powder through a
tube in which a zone of sub-atmospheric pressure is maintained by
the passage of a sheath of gas moving in a helical path along the
tube between the inner surface of the tube and the hot gas effluent
and entrained powder. The sheath of gas preferably passes through
the tube in the same general direction as the effluent, the zone of
sub-atmospheric pressure under these conditions extending a
short-distance (e.g. about 1-2 cms) beyond the mouth of the tube
from which the effluent flows. The area of impingement of powder on
the substrate surface is preferably maintained within this
extension of the sub-atmospheric zone. The inlet end of the tube is
preferably connected in gas tight relationship with the nozzle when
the zone of sub-atmospheric pressure may extend from the nozzle to
the surface of the substrate being coated.
The tube need not be cylindrical and may for example have a taper
in which the diameter of the tube increases with increasing
distance from the nozzle. Other forms of tube are also possible as
described hereinafter.
In the preferred form of the invention the coating powder is also
injected into the arc and passed through the arc restricting
nozzle.
The invention also provides apparatus for carrying out the method
of the invention comprising first and second electrodes, electrical
connection means for impressing on said first electrode a voltage
which is capable of maintaining an arc discharge between said first
and second electrodes, nozzle means for constricting said arc,
means for supplying and directing gas at a controllable rate into
said arc and through said nozzle to provide a hot gas effluent from
said nozzle, means for entraining a coating powder at a
controllable rate in said gas to provide a stream of hot gas
effluent having coating powder entrained therein for direction and
impingement on a substrate to be coated, enclosure means
surrounding at least a portion of the path of said stream and
vacuum producing means for forming and maintaining a zone of
sub-atmospheric pressure in said enclosure means.
In one embodiment the chamber extends from and is connected in gas
tight relationship to the nozzle and has an opening in a wall
thereof remote from said nozzle and disposed to allow passage of
the stream of hot gas effluent and entrained coating powder
therethrough, said chamber being provided with gas out-let passage
means for connection to a vacuum pump.
In a preferred embodiment the enclosure means comprises a tube and
a vortex gas sheath producing means is provided for producing a
sheath of gas moving in a helical path along the inner surface of
the tube whereby to produce a zone of sub-atmospheric pressure in
said tube. Preferably the tube is frusto-conical in shape, the
narrow end of the tube being nearer to the nozzle. For best results
the tube should be connected to the nozzle, preferably in gas tight
relationship. Other shapes of tube may also be used.
The vortex gas sheath producing means may for example comprise gas
injection means communicating with a spiral passage the outlet or
outlets of which are disposed adjacent the inner surface of the
tube preferably at the inlet end of the tube. Alternatively a
plurality of tangentially directed gas inlet ports may be provided
in the tube itself or in a separate attachment which may for
example form the connection between the tube and the nozzle. The
means for producing the vortex gas sheath may also be disposed in
the nozzle or in the torch itself.
Any of the conventional plasma torches may be used in the method of
the invention. Torches in which the coating powder is injected into
the arc are preferred.
The invention will be further described by reference to the
accompanying drawings in which:
FIG. 1 is a perspective view in part cut away section of one form
of apparatus according to the invention.
FIG. 2. is a sectional view of an apparatus similar to FIG. 1 but
having a tube the inner surface of which is of frusto-conical
shape.
FIG. 3 is a sectional view of another form of apparatus according
to the invention.
FIGS. 4 to 6 are sectional views of apparatus of the type of FIG. 1
with variations as to shape and manner of introducing the vortex
gas sheath,
FIG. 7 is a sectional view of an apparatus similar to FIG. 1 but
having a gap between the enclosure means and the nozzle.
Referring to the FIG. 1 of the drawings:
A nozzle 1 disposed within a block 2 forms the anode of a
collimated arc effluent torch the other electrode of which is
provided by a rod 3. The remainder of the torch is not shown. The
nozzle 1 has an orifice 4 terminating in an outlet 5. Extending
from the block 2 is a tube 6 attached to the block 2 by suitable
means (not shown). A gas injection insert 7 disposed within the
tube has a conical passage 8 formed therein and therethrough which
diverges from the outlet 5 of the nozzle 1. A gas inlet conduit 9
communicates with a spiral passage 10 of rectangular cross-section
formed by the abuttment of a rectangular cross-section formed by
the abuttment of a rectangular screw thread 11 cut in the outer
surface of insert 7 against the inner surface 12 of the tube 6.
Whilst only one start on the thread 11 is shown, it may in fact
have a plurality of starts. Again, whilst only one inlet conduit 9
is shown, a plurality of inlet conduits may be provided. Gas
injected into conduit 9 passes into and through the spiral passage
10 whereby it acquires a spiral motion along the inner surface 12
of tube 6. This spiral motion imparted to the gas continues after
it leaves the spiral passage 11 so that the gas tends by the action
of centrifugal force to remain in the vicinity of the inner surface
12 of tube 6 as it passes along the tube.
Referring to FIG. 2, like numbers show like parts. The essential
difference between the embodiment of FIG. 2 and that of FIG. 1 lies
in the frusto-conical shape of the inner surface 12 of the tube 6
beyond the gas injection insert 7. It is believed that this
configuration increases the effective diameter of the low pressure
zone with increasing distance from nozzle thus reducing the
tendency for spray effluent to travel in the high pressure zone
near the inner surface 12 of the tube 6. In FIG. 2 the inlet
conduit 9 feeds into an annular space 13 formed by a groove 14 in a
distance piece 15 and an abutting flange 16 formed in gas injection
insert 7. Gas ports 17 formed in flange 16 allow gas to flow into a
second annular space 18 which in turn communicates with the spiral
passage 10.
Referring to FIG. 3 of the drawing a chamber 19 is attached in gas
tight relationship with block 2. An end wall 20 has an opening 21
to allow passage of effluent and entrained powder out of the
chamber. A conduit 22 extends from the body 23 of the chamber for
connection to a vacuum pump (not shown). In operation the pressure
is maintained below atmospheric by the application of suction to
conduit 22 thus maintaining a zone of sub-atmospheric pressure in
chamber 19. The hot gas affluent emanates from the nozzle, passes
through the chamber and out of opening 21 onto a substrate (not
shown) held close to opening 21.
In the embodiment of FIG. 4 the sheath gas is fed into ports 24
provided in a distance piece 25 attached on the one hand to the
block 2 and on the other to tube 6. Ports 24 communicate with
annular space 26 which in turn communicates with spiral passage
10.
In the embodiment of FIG. 5, a gas port 27 formed in a distance
piece 28 communicates with annular space 29 formed between distance
piece 28 and a flanged annular insert 30 in which are formed a
plurality of tangentially disposed gas ports 31 which extend from
annular space 29 to an annular channel 32. Sheath gas is supplied
to port 27 from which it flows via annular space 29, through gas
ports 31 into the annular channel 32 and thence along the inner
surface of insert 30 and thence along inner surface 12 of tube 6.
The disposition of ports 31 imparts a helical motion to the sheath
gas. FIG. 5A shows a section on the line X--X of FIG. 5 and shows
the angular orientation of ports 31.
In the embodiment of FIG. 6 the tube 6 has a constriction formed in
the interior thereof, the inner surface 12 tapering from its mould
inwardly to a minimum diameter at 33 and then outwardly again to an
annular channel 34 formed in a distance piece 35. A spiral passage
10 is formed between annular channel 34 and gas inlet port 36.
Sheath gas fed into gas inlet port 36 is given a spiral motion by
spiral passage 10 an passes via channel 34 along the inner surface
12 of tube 6.
In the embodiment of FIG. 7 a gap 37 is left between the outlet 5
and the distance piece 38 the two sections of the apparatus being
held rigidly in this position by means not shown. The means for
forming the vortex sheath is similar to that in FIGS. 1 and 4.
The method of the invention will be further illustrated by
reference to the following Examples:
EXAMPLE I
An arc effluent coating torch of the type described and claimed in
U.K. Pat. No. 869,791 was modified by being provided with an
extension as generally illustrated in the accompanying drawings.
The tube had a length of 12.7 cm and an internal diameter of 3.5
cm. The gas injection means had a four start thread of two teeth
per inch of rectangular cross-section the width of cut being 2.38
mm and the depth of cut 1.19 mm, the injection means having an
overall length of 2.54 cm.
This modified torch was used to coat a previously grit-blasted
workpiece, the workpiece being placed 1.3 cm from the mouth of the
tube for a period sufficient to build up an adequate coating (about
3 seconds). The workpiece and torch remained stationary during the
coating. The coating material was a Stellite 31 (a cobalt based
alloy composition 20% Cr 10% Ni 7.5% W and balance Co) in the form
of a-325 mesh powder. A torch gas flow of 162 cubic feet per hour
CFH a powder carrier gas flow of 138 CFH, and an envelope gas flow
of 775 CFH, all of Argon were used, the powder feed rate being 37
gm. per minute. The coating obtained had the folliowing
properties:
Oxide content 0.2%
Porosity 0.2%
Cross-section Micro Hardness 292VPN
Bond Strength greater than 7,960 p.s.i.
No cracking or separation of the coating was observed.
If the unmodified torch had ben used under the above conditions
even 3.8 cm from the workpiece a relative speed of 25,400 cm per
minute as between workpiece and torch would have been necessary to
enable a similar coating to be applied.
EXAMPLE II
In this example two modified torches were used (a) similar to that
described in Example I but having an inner tube diameter of 2.54 cm
and an unthreaded gas injection means providing an annular space
1.19 mm thick between injection means and the tube, and (b) similar
to that of Example I but having a 2.54 cm inner diameter tube and a
gas injection means threaded in the manner of Example I. The
modified torches were operated with a torch gas flow of 162 CFH and
powder carrier gas flow of 162 CFH both of Argon and a powder feed
rate of 25 gms per minute of chromium oxide. Three tests were
carried out as follows, the workpiece being stationary realtive to
the torch in each case and 2.54 cm from the end of the tube:
i. No gas envelope using modified torch A. The coating obtained had
the following properties:
Porosity 5 percent
Cross-sectional Micro Hardness 1204 VPN
ii. A gas envelope of Argon was injected through the annular space
of torch A at a flow rate of 775 CFH to flow in a direction
parallel to the longitudiinal axis of the tube. The coating had the
following properties:
Porosity 4 percent
Cross-sectional Micro Hardness 966 VPN
iii. Using Torch B and two different envelope gases the following
results were achieved:
ENVELOPE GAS GAS COATING COATING CROSS- FLOW POROSITY SECTIONAL
MICRO- HARDNESS ______________________________________ 775 CFH
Argon 2.5% 1300 VPN 675 CFH Nitrogen 3.0% 1261 VPN
______________________________________
The above results should be compared with those obtained in the
following comparative Example:
COMPARATIVE EXAMPLE
i. Using an unmodified torch and the same torch gas feed, powder
carrier gas feed and powder feed rate as in Example II, a stand-off
of 1.9 cm and a relative speed of workpiece to torch of 30,480 cm
per minute coatings were obtained having porosities less than 3
percent usually 1 to 2 percent and cross-sectional micro hardness
in the range 1,150 to 1,400 VPN.
ii. Using a stand-off of 5 inches and the workpiece stationary
relative to the torch of the porosity rose to 5 percent and the
cross-sectional microhardness dropped to 890 VPN.
In the following examples MSI is the volume of coating of 1 mil
thickness by 1 sq. inch area. 1,000 MSI = 1 cubic inch of coating.
Mils/sec is 0.001 inch (or 0.0254 mm) per sec of coating. The
porosity figures quoted were obtained by visual technique using
comparison standards, where numbers 10 or 20 are quoted within
brackets these relate to the average size in microns of the holes
as assessed by visual technique. Hardness figures were obtained
according to ASTM-E-92. When the presence of oxide is quoted the
amount is as assessed by visual techniques.
EXAMPLE III
An apparatus similar to FIG. 2 but having a cylindrical tube of 1
inch (2.54 cm) diameter and overall length of 3 11/16 inches (9.37
cm) was employed to produce coatings under the following conditions
and produced the results shown in Table I.
______________________________________ Torch Conditions Powder
composition: Chrome sesquioxide Powder feedrate: 30 grams per
minute Torch type: Model No. 1101A Arc power: 9.0 kw Total torch
gas flow 300 cfh Gas composition: Argon Stand off 4.5 inches (11.43
cm) Surface speed 100 inches (254 cm) per minute
______________________________________
Table I
__________________________________________________________________________
Vacuum Coating Data Method of Obtaining Vacuum (in. Hg) Hardness
Porosity Deposition Rate VPN % (mils/sec)
__________________________________________________________________________
Torch alone 0 963 4.5 4.8 800 cfh argon sheath gas 2.4 1041 3.5
10.0 1600 cfh argon sheath gas 4.7 1092 3.5 7.5 2000 cfh argon
sheath gas 6.2 1043 5.0 7.5
__________________________________________________________________________
EXAMPLE IV
An apparatus of the type of FIG. 2 of overall tube length 3 3/16
inch (8.1 cm) and tapering from an internal diameter of 1 inch
(2.54 cm) at the point of injection of sheath gas at an angle of
22.degree. over an axial length of 2 inches (5.08 cm) was used
under the following conditions and produced the results set out in
Table II.
______________________________________ Torch Conditions Powder
composition: Chrome sesquioxide Powder feedrate: 30 grams per
minute Torch type: Model No. 1101A Arc power: 9.0 kw Total torch
gas flow: 300 cfh Gas composition: Argon Stand off 4.5 inches
(11.43 cm) Surface speed 100 inches (254 cm) per minute
______________________________________
Table II
__________________________________________________________________________
Vacuum Coating Data Method of Obtaining Vacuum (in. Hg) Hardness
Porosity Deposition Rate VPN % (mils/sec)
__________________________________________________________________________
Torch alone 0 963 4.5 5.3 800 cfh argon sheath gas 1.6 1183 3.5 9.5
1200 cfh argon sheath gas 2.7 1155 3.0 9.7 2000 cfh argon sheath
gas 4.6 1103 2.5 11.2
__________________________________________________________________________
EXAMPLE V
An apparatus of the type shown in FIG. 3 in which the chamber has
an overall length of 3 7/8 inches (9.84 cm) and the outlet is 1 3/8
inches (3.48 cm) in diameter was used to produce coatings under the
following conditions and gave the results set out in Table III.
______________________________________ Torch Conditions Powder
composition: Chrome sesquioxide Powder feedrate: 30 grams per
minute Torch type: Model No. 1101A Arc power: 9.0 kw Total torch
gas flow: 300 cfh Gas composition: Argon Stand off 41/4 inches
(10.8 cm) Surface speed zero
______________________________________
Table III
__________________________________________________________________________
Vacuum Coating Data Method of Obtaining Vacuum (in Hg) Hardness
Porosity Deposition Rate VPN % (mils/sec)
__________________________________________________________________________
Torch alone 0 963 4.5 4.8 22 psig on steam ejector 1.5 8.6 34 psig
on steam ejector 3.0 8.2 51 psig on steam ejector 6.0 8.9 65 psig
on steam ejector 9.0 1353 2.5 10.1 84 psig on steam ejector 14.0
1344 2.5 10.7
__________________________________________________________________________
EXAMPLE VI
A standard torch was used to produce coatings in a substrate, the
torch and substrate being disposed wholly within a vacuum tank
connected to a steam ejector. The conditions of coating were as
follows and produced the results set forth in Table IV.
______________________________________ Torch Conditions Powder
composition: Chrome sesquioxide Powder feedrate: 30 grams per
minute Torch type: Model No. 1101A Arc power: 9.0 kw Total torch
gas flow: 300 cfh. Gas composition: Argon Stand off 4.5 inches
(11.4 cm) Surface speed 100 inches (254 cm) per minute
______________________________________
Table IV
__________________________________________________________________________
Vacuum Coating Data Method of Obtaining Vaccum (in Hg) Hardness
Porosity Deposition Rate VPN % (mils/sec)
__________________________________________________________________________
Coated into atmosphere 0 963 4.5 2.6 34 psig on steam ejector 3.0
1244 2.0 4.5 51 psig on steam ejector 6.0 1306 1.5 4.0 65 psig on
steam ejector 9.0 1257 1.5 5.0 77 psig on steam ejector 12.0 1268
0.75 4.5
__________________________________________________________________________
EXAMPLE VII
Using the methods and apparatus described in Examples IV, V and VI
with three different coating materials the following results were
achieved as set out in Table V.
TABLE V. Material Comparison
__________________________________________________________________________
VACUUM TANK Coating Data Material and Conditions Vacuum Hardness
Porosity Deposition Rate (in. Hg) VPN % (mils/sec)
__________________________________________________________________________
Chrome Sesquioxide 0 963 4.5 4.8 Powder feedrate: 30 gm/min 3.0
1244 2.0 8.2.sup.1 Torch type: 1101A Arc power: 9.0 kw Total torch
gas flow: 300 cfh 6.0 1306 1.5 8.9.sup.1 Gas composition: argon
Tungsten Carbide-Cobalt 0 725 3.0 at 20.mu. 5.7 2.7 9.6.sup.2
Powder Feedrate: 55 gm/min 3.0 727 2.5 at 10.mu. Torch type: 1101A
Arc power: 9.0 kw 4.6 8.6.sup.2 Total torch gas flow: 300 cfh 6.0
738 2.5 at 10.mu. Gas composition: argon Aluminum Bronze 0 104 0.5
4.5 Powder feedrate: 40 gm/min 3.0 206 0.5 5.3 Torch type: 1101E
Arc power: 9.0 kw Total torch gas flow: 300 cfh 6.0 200 0.75 5.3
Gas composition: argon 12.0 8.5
__________________________________________________________________________
1. Apparatus of FIG. 3. 2. Apparatus of FIG. 2.
EXAMPLE VIII
Using the apparatus of FIG. 4 with a tube of overall length 5
inches (12.7 cm ) of cylindrical shape and internal diameter 1 3/8
inches (3.49 cm) the spiral passage is a 4 start thread 2 teeth per
inch (254 cm) and a sheath gas feed rate of 775 cubic feet (21,954
litres) per hour conditions and coating powders set forth below the
following results were obtained.
Table VI
__________________________________________________________________________
Coating Powder Surface Properties of coating Type feed speed
Hardness Bond Porosity Oxide rate per sec. VPN Strength % %
(gm/minute) lb/m.sup.2
__________________________________________________________________________
LA6 36 5 inches 927 9,000+ 4 -- (12.7 cm) LN-2B 40 " 147 8,500+ 0.1
Less than 0.1 52-F 37 " 598 7,000+ 1 to 1.5 -- X-40 35 " 405 8,630+
0.5 1 LT-1 28 1 inch 265 8,800+ 0.5 Less than (2.54 cm) 0.25 LS-31
37 5 inches 254 8,600+ 0.25 3 (12.7 cm)
__________________________________________________________________________
The coating types in Table VI are as follows: LA-6 Aluminium Oxide
(Al.sub.2 O.sub.3) LN-2B Pure Nickel 81.41% Tungsten Carbide 52-F
17.61% Cobalt 56% Cobalt 25% Chromium X-40 10% Nickel 7% Tungsten
0.3% Carbon LT-1 Pure Tantalum 20% Chromium LS-31 10% Nickel
remainder Cobalt 7.5% Tungsten
__________________________________________________________________________
EXAMPLE IX
Using the apparatus of FIG. 5 with a cylindrical tube of overall
length 31/2 inches (8.9 cm) internal diameter 1 3/8 inches (3.49
cm), the spiral passage being a 4 start thread 2 teeth per inch,
chromium oxide (Cr.sub.2 O.sub.3) was used at a powder feed rate of
45 gm per minute and a substrate surface speed of 5 inches (12.7
cm) per second the sheath gas feed rate being 775 cubic feet
(21,945 litres) of argon per hour, a coating of the following
properties was obtained:
Hardness VPN 1006 Bond strength lb/in.sup.2 8000(562.4 Kg/cm.sup.2)
Porosity 4% (10)
EXAMPLE X
Using the apparatus of FIG. 6 with a tube of overall length 31/2
inches (869 cm) minimum diameter 1 inch (2.54cm) maximum diameter
13/8 inches (3.49 cm) and outward taper 8.degree. with a spiral
passage formed by a 4 start 2 teeth per inch thread was used with a
sheath gas feed rate of 775 cubic feet (21,945 litres) per hour of
argon and a powder feed rate of 26 gm per minute of chromium oxide
(Cr.sub.2 O.sub.3) and a surface speed of 5 inches (12.7 cm) per
second and produced the following properties in a coating:
Hardness VPN 1204 Bond strength lb/in.sup.2 11000+ (774 + Kg per
cm.sup.2) Porosity 4% (10)
EXAMPLE XI
The apparatus of FIG. 7 was used with a tube length of 3 inches
(7.62 cm) an internal diameter of 1 inch (2.54 cm), the gap between
nozzle and tube being 3/4 - 1 inch (1.9-2.54 cm), the spiral
passage a 4 start 2 teeth per inch (2.54 cm) thread and a sheath
gas feed rate of 775 cubic feet (21,945 litres) per hour of argon
and a powder feed rate of 26 gm per minute of chromium oxide
(Cr.sub.2 O.sub.3) at a surface speed of 5 inches (12.7 cm) per
second and produced a coating having the following properties.
______________________________________ Hardness VPN 1261 Porosity
3% (10) ______________________________________
* * * * *