Arrangement for conveying powder to the barrel of a gas detonation apparatus

The arrangement comprises a housing (1), a hopper (2) containing a powder and communicating with the interior of the housing (1), and a slide valve (11) having a drive (9) mounted inside the housing (1) and provided with a powder-metering cavity in the form of a recess (12). The housing has through passages for feeding compressed gas, and conveying the powder from the hopper (2) to the recess (12) and from the recess to the barrel. The slide valve (11) is arranged at the top part of the housing (1) and resiliently urged thereto in the zone of outlet holes of the passages. The arrangement also has a shut-off unit (18) connected to the slide valve (11) to block the outlet hole (8) of the passage for feeding the powder from the recess (12) to the barrel in one of extreme positions of the slide valve (11), in the other extreme position thereof the powder-metering cavity (12) communicates with the outlet hole (8) of the passage conveying the powder to the barrel.

FIELD OF THE INVENTION 
This invention relates generally to apparatus for applying powder coatings 
to workpieces, and more particularly it concerns an arrangement for 
conveying powder to the barrel of a gas detonation apparatus. 
The invention can be utilized with the utmost advantage for obtaining 
refractory, corrosion- and wear-resistant coatings by gas detonation to 
protect units and parts of machines and mechanisms operating in highly 
corrosive media against intensive abrasive wear. 
BACKGROUND OF THE INVENTION 
The essence of applying coatings by gas detonation rests in the following. 
A barrel open at one end is filled with an explosive gaseous mixture, a 
powder for obtaining a coating is fed, and detonation is initiated at the 
closed end of the barrel. The high-temperature (.about.4000.degree. C.) 
and high-speed (.about.1500 m/s) flow of detonation products heats and 
accelerates the powder particles which are thrown against the surface of a 
workpiece before the open end of the barrel to form a coating. Normally, 
the apparatus for applying coatings by gas detonation are automatically 
controlled, the detonation process being repeated at a frequency of about 
10 shots per second. 
One of the major units of the gas detonation apparatus is an arrangement 
for conveying a powder material to the barrel. This arrangement is 
intended to convey a preset quantity of powder to a preset section of the 
barrel at a preset point in time. The more accurately such conditions are 
conformed to the higher is the quality of coatings, expressed by such 
characteristics as stability of the coating, strong bond between the 
coating and the surface of the workpiece, porosity, and thickness of the 
coating after one shot. 
Among factors complicating normal functioning of such arrangements in 
apparatuses for applying coatings by gas detonation are the following: 
penetration of the products of detonation from the barrel to the housing 
of the powder-feeding arrangement (backfire) and penetration of the 
explosive mixture to the housing of the arrangement as this mixture is fed 
to the barrel of the apparatus. These two factors can lead to failure of 
the apparatus. 
Therefore, the arrangement for conveying powder to the barrel should be so 
constructed as ensure an extra service life, stable cyclical feeding of 
the powder with particle size of 5 to 50 mkm (at a frequency of 1 to 10 
cycles per second), an accurately preset quantity of powder for each 
cycle, reliable protection of the arrangement against backfires, uniform 
distribution of the powder particles in the flow of detonation products, 
fluidity of the powder as it fills the powder-metering recess, amenability 
to automatic remote control over the quantities of powder and carrier gas, 
and provision for minimizing the quantity of powder-carrying gas entering 
the barrel. 
At present, apparatuses for applying coatings by gas detonation use two 
types of powder feeding arrangements, particularly pneumatic and 
mechanical. In the pneumatic arrangements powder is conveyed to the barrel 
of the apparatus by a compressed gas continuously or in a pulse-wise 
manner. In the continuous feeding of the powder to the barrel the quantity 
of powder is spread in the barrel in the form of an elongated mist. In 
this case the difference in the initial position of the powder particles 
axially of the barrel leads to variations in the speed and heating 
temperature of the particles as they are accelerated and heated by 
detonation products in the barrel of the apparatus. Experiments have shown 
that for obtaining high-quality coatings from a preselected powder 
material it is necessary that during the escape of the powder particles 
from the barrel the speed and temperature of all the particles of the 
quantity of powder fed to the barrel be approximately equal. This 
condition cannot be complied with during continuous feeding of the powder 
to the barrel, and therefore continuous feeding of the powder to the 
barrel results in low quality coatings with unstable characteristics. 
During pulsewise feeding of the powder to the barrel in agreement with the 
working cycle of the apparatus the metered quantity of powder is localized 
in a small volume in the zone where the powder is introduced to the 
barrel, whereby a negligeable spread in the speed and temperature of 
powder particles at the outlet from the barrel and near the surface being 
coated is ensured. The pulsewise feeding of powder to the barrel allows to 
control the process of coating application. 
The quantity of powder fed to the barrel is preset in various manners, such 
as by the diameter of pipe carrying the powder, or by the depth to which a 
rod with a powder-metering recess is immersed in a hopper filled with the 
powder. An inherent disadvantage of such powder metering arrangement rests 
in variations (to tens of percent) in the quantity of powder introduced to 
the barrel because of low fluidity of the powder or a change in the volume 
of the powder metering device due to abrasive wear of the metering recess 
eventually resulting in unstanble characteristics of coatings. 
The known powder feeding arrangements lack means for protecting against 
backfires propagating through the powder-conveying gas pipes. In order to 
prevent the action of backfires, the pipes carrying the powder are 
elongated which leads to delays in power supply, i.e., a slower response 
of the arrangement. 
An arrangement bearing the closest resemblance to one to be described in 
the present invention includes a pressure-sealed cylindrical housing 
accomodating a piston valve driven by compressed gas. 
The housing comprises a hopper containing a powder and communicating with 
the interior of the housing, and a slide valve provided with a 
powder-metering recess and a drive, the housing having through passages 
for conveying the powder from the hopper to the powder-metering recess, 
for feeding a compressed gas and for conveying the powder from the 
powder-metering recess to the barrel. The powder-metering recess is 
provided in the slide valve and arranged so that in one of its extreme 
positions it communicates with the hopper where it is charged with the 
powder, whereas in the other extreme position it communicates with holes 
for feeding the powder to the barrel and for feeding the compressed gas 
carrying the powder from the powder-metering recess to the barrel. In this 
construction of the arrangement the quantity of powder fed to the barrel 
is preset by the volume of the powder-metering recess, whereas the piston 
valve protects the powder-metering device against backfires, as the hole 
through which the powder is fed to the barrel is closed by the piston 
valve during detonation. 
However, with this construction of the powder-metering device the clearance 
between the containing surface of the piston valve and housing is 
susceptible to penetration therein of the powder fed to the barrel to 
result in possible jamming of the slide valve and failure of the 
powder-metering device. Also, penetration of the powder to the clearance 
between the slide valve and housing results in fast wear of contacting 
surfaces and reduces the quantity of powder fed to the barrel. For this 
reason, losses of powder can be as high as 30-40% of the powder quantity 
determined by the powder-metering recess resulting in unstable thickness 
of the coating applied by one shot. 
SUMMARY OF THE INVENTION 
The present invention aims at providing such an apparatus for conveying 
powder to the barrel of a gas detonation apparatus which would obviate 
jamming and wear of a slide valve as the powder penetrates into the 
clearance between the engaging surfaces of the slide valve and housing, 
while ensuring accurate and stable meter-feeding of the powder to the 
barrel. 
The aims of the invention are attained by that in an arrangement for 
feeding powder to the barrel of a gas detonation apparatus comprising a 
housing, a hopper containing the powder and communicating with the 
interior of the housing, and a slide valve provided inside the housing and 
having a powder-metering recess and a drive, the housing having passages 
for feeding compressed air and for conveying the powder from the hopper to 
the powder-metering recess and from the powder-metering recess to the 
barrel, according to the invention, the slide valve is positioned at the 
upper part of the housing and resiliently urged thereto in the zone of 
outlet holes of the passages, the powder-metering recess being made at the 
surface of the slide valve in contact with the housing, a shut-off unit 
being further provided which is connected to the slide valve and which 
blocks the outlet hole of the passage for conveying the powder from the 
powder-metering recess to the barrel in one of the extreme positions of 
the slide valve, in the other extreme position of the slide valve the 
powder metering recess communicates with the outlet hole of the passage 
for conveying the powder to the barrel. 
The proposed construction of the powder-metering device has a long service 
life, is reliebly protected against backfires, and ensures feeding a 
quantity of powder to a small volume of the barrel to eventually result in 
obtaining high-quality coatings with stable characteristics. This has been 
attained by arranging the slide valve at the top part of the 
powder-metering device, a substantial part of the surface of the slide 
valve being free from contact with the housing, and pressure of the slide 
valve at the side of the free surface preventing its jamming in the 
housing thereby ensuring operability and long service life of the 
arrangement. When powder penetrates into the clearance between the 
contacting surfaces of the housing and slide valve, the slide valve is 
caused to be displaced along a line normal to the surface of contect, 
whereby the powder leaves the clearance and falls to the bottom of the 
housing. Arranging the powder-metering device in the form of a recess 
ensures accurate metering of the powder and prevents leaks of the powder 
from the metering recess. 
Protection or the powder metering device against backfire is ensured by the 
shut-off unit connected to the slide valve and drive. The shut-off unit 
moves in synchronism with the slide valve to reliably block the outlet 
hole of the passage for conveying the powder from the powder-metering 
recess to the barrel. 
In a preferred embodiment of the invention an additional recess is provided 
at the surface of the slide valve in contact with the housing, the housing 
having a passage communicating the passage for feeding compressed gas 
through the additional recess with the interior of the hopper in one of 
the extreme positions of the slide valve. A quantity of compressed air 
acts to air-lift the powder material from the bottom of the hopper thereby 
preventing bridging of the powder. 
In one alternative embodiment the shut-off unit has the form of a wedged 
connection. 
This construction of the shut-off unit reliably protects the 
powder-metering device against backfire, and facilitates locking of the 
powder-metering recess under the outlet hole of the hopper. 
Preferably, the slide valve has the form of a prism. 
This construction of the slide valve is the simplest.

BEST MODE OF CARRYING OUT THE INVENTION 
The proposed apparatus comprises a pressure-sealed housing 1 (FIGS. 1 and 
2) having mounted thereon a hopper 2 communicating with the interior of 
the housing 1 via a passage 3 made in a cover plate 3' of the housing 1. 
The housing 1 has a passage 4 (FIGS. 3 and 4) for feeding compressed air 
with outlet holes 5 and 6 at the inside surface of the cover plate 3' of 
the housing 1, and a through passage 7 with an outlet hole 8 also made at 
the inside surface of the cover plate 3' of the housing 1. Connected to 
the housing 1 a pneumatic drive 9 (FIGS. 1 and 2) having a pressure cavity 
10 communicating with the passage 7 via passage 4 (FIGS. 1 and 3). 
The interior of the housing 1 accomodates a slide valve 11 positioned so 
that its top edge is continuously in contact with the inside surface of 
the cover plate 3' of the housing having the outlet holes 3, 5, 6 and 8, 
and is in contact with the wall of the housing 1 only by one side edge. 
The slide valve 11 is connected to the drive 9 to execute reciprocations 
along the housing 1. Provided at the upper edge of the slide valve 11 is a 
volume-calibrated powder-metering cavity in the form of a recess 12 and an 
additional recess 13. The slide valve 11 is resiliently urged to the 
housing 1 by a cylindrical helical spring 14. 
The housing 1 has a through passage 15 (FIG. 2) with a hole 16 letting out 
into the passage 3 for conveying the powder from the hopper 2, and a hole 
17 (FIGS. 4 and 5) made at the inside surface of the cover plate 3' of the 
housing 1. The passage 15 connects the passage 4 for feeding compressed 
air through the additional recess 13 with the interior of the hopper 2 in 
one of the extreme positions of the slide valve 11. 
At the side of the outlet hole 8 of the passage 7 the slide valve 11 is 
rigidly connected to a shut-off unit 18 (FIG. 1), whereas the housing 1 
accomodates a wedged ledge 19. The shut-off unit 18 moves together with 
the slide valve 11 so that in the extreme (left-side as seen in FIG. 1) 
position its beveled lower face bears on the ledge 19 to form a wedged 
connection and tightly block the hole 8 (FIG. 3) for feeding the powder to 
a barrel 19'. 
The slide valve 11 can be of any known suitable construction; however, in a 
preferred embodiment it has the form of a prism, as the most simple and 
reliable, since the contact with the surface of the housing 1 runs along 
the top and slide faces of the prism to allow for the travel along the 
common edge of said faces. 
The housing 1 includes a removable tray 20. The passage 7 extends into the 
barrel 19' of the gas detonation apparatus (FIGS. 2 and 3). 
The proposed arrangement operates in the following manner. 
Prior to starting operation a powder is charged into the hopper 2. In the 
initial position the drive 9 acts to set the slide valve 11 to the extreme 
(left side as seen in FIG. 1) position. The spring 14 forces the slide 
valve 11 by its upper and side faces to the housing 1, the upper face of 
the slide 11 blocking the holes 6 and 17, whereas the metering recess 12 
is filled with the powder through the hole 3. In this position the 
shut-off unit 18 bears on the ledge 19 and closes the holes 5 and 8. As 
the compressed air is admitted to the pressure cavity 10 and passage 4, 
the drive 9 moves the slide valve 11 with a quantity of powder in a 
direction from left to right as seen in FIG. 2, and when the slide valve 
11 reaches the extreme right position, the quantity of powder is 
discharged from the recess 12 through the hole 8 and along the passage 7 
to the barrel 19' by compressed gas conveyed through the hole 5 of the 
passage 4 (FIG. 3). At the same time, from the passage 4 via the hole 6 
and additional recess 13 the compressed gas flows to the passages 15 to 
escape at a high velocity through the holes 16 to the interior of the 
hopper 2 at its base and thereby break bridges of powder formed inside the 
hopper 2 for the powder to fall on the top face of the slide valve 11. 
Then the drive 9 returns the slide valve 11 to the initial position which 
is preset by the wedged ledge 19 restricting the travel of the shut-off 
unit 18 and consequently of the slide valve 11, whereas the wedged shape 
of the shut-off unit 18 and the corresponding inclination of the contact 
surface of the wedged ledge 19 ensure that the force of the drive 9 is 
converted into closing force, whereby the shut-off unit 18 reliably blocks 
the hole 8 preventing the breakthrough of the products of detonation from 
the working zone of the barrel 19' along the passage 7 to the interior of 
the housing 1 during detonation. In the course of movement of the slide 
valve 11 the spring 14 ensures reliable pressure and allows displacement 
of the slide valve 11 from the housing 1 as the grains of powder enter the 
space therebetween avoiding jamming of the slide valve 11 during its 
movements. 
The service life of the arrangement is increased and the wear of the slide 
valve 11 is reduced by minimizing the working force of the spring I4. On 
the other hand, this force must be sufficient for providing reliable 
pressure of the slide valve 11 to the housing 1 during the movement of the 
slide valve 11. 
Industrial Applicability 
The invention can be used in gas detonation units for obtaining heat, 
corrosion and wear resistant coatings for machine parts operating under 
conditions of high abrasive wear and in corrosive media.