GB2107082A - Apparatus for applying coatings by detonation - Google Patents

Abstract

Apparatus for applying coatings by detonation which includes a detonation chamber (1), a gas mixture supply system (2) and a powder system (3), each of said supply system communicating with the detonation chamber (1). A control unit (15) controls valves (5, 6 and 7) of a mixer (4) in the gas supply system (2), a detonation initiating device (14) disposed in the detonation chamber (1) and a valve (13) of a batch meter (12) in the powder supply system (3). The valve (13) is operated through a time-delay element (20) and a programmer (21) adapted to vary the time lag thereof so as to enable the energetic parameters of the powder particles being deposited to be varied depending on the physical and chemical properties of a layer to which a coating is applied. <IMAGE>

Description

SPECIFICATION Apparatus for applying coatings by detonation The present invention relates to the practice of applying coatings by a high-temperature spraying technique, and more specifically is concerned with apparatus for applying coatings by detonation. The invention may be used in the metallurgical industry, chemical industry, aircraft industry, shipbuilding, aerospace engineering and mechanical engineering in manufacturing articles which when in use take up high loads or are subject to a higher-than-usual mechanical, corrosive, erosive and thermal wear.

Since the initial development of detonation coating there has been little change in the basic apparatus for carrying it out. An apparatus of this type normally includes a detonation chamber made in the form of a barrel closed at one end, a gas mixture supply system and powder supply system for delivering a powdered coating material, both systems communicating with the detonation chamber. The apparatus also has a spark plug mounted in the barrel for initiating detonation. Automated forms of the apparatus are also provided with a control system wherein a control unit which is a setting-device is electrically connected through control circuits to the spark plug, a valve of a batch meter in the powder supply system, and valves of a mixer in the gas mixture supply system.

Improvements relating to individual units and systems of the apparatus have been directed mainly to improve the quality of the resultant coatings by stabilizing one or several coating process parameters which influence this quality.

US Patent No. 3,884,415 describes an apparatus of this type which allows stabilization of the amount of powder being injected into the detonation chamber.

In another known apparatus (disclosed in US Patent No. 3,773,259) the mixer has a construction which provides for the uniform preparation of the gas mixture delivered to the detonation chamber, and its composition is maintained constant. The apparatus includes all the above-mentioned units which operate in a sequence controlled by signals transmitted to these units from a control unit through control circuits.

In this apparatus as in other conventional apparatus of this type, the deposition of the first layer and all the following layers of a coating being formed is effected under similar operating conditions without taking account of the fact that physical and chemical properties of a substrate to which the particles of the powder are bonded during the first shots and those of the coating layer to which the powder particles are bonded by the following shots of the apparatus are not similar. Therefore to obtain a uniform adhesiveness of the particles (no high-quality coating can be produced without observance of this condition), the velocity and temperature of the powder particles must be correspondingly varied depending on powder spraying parameters, in particular on the composition of the explosive mixture used and the position of the powdered coating material within the barrel.

The construction of the above apparatus does not allow these parameters to be varied automatically during operation, which affects both the quality of the resulting coating and the efficiency of the spraying operation, since the energetic parameters of the particles do not allow a coating layer of a sufficient thickness to be formed by one shot.

The present invention is directed to the provision of apparatus for applying coatings by detonation which enables higher quality coatings to be achieved with higher efficiency due to the use of means which enables the position of the powdered coating material within the barrel to be changed automatically at a moment when the detonation is initiated.

The present invention consists in apparatus for applying coatings by detonation, which includes a detonation chamber in communication with a powder supply system having a batch meter and a gas mixture supply having a mixer connected through valves with gas sources, and a control unit electrically connected through control circuits to the batch meter, the valves of the mixer and a detonation initiating device located in the detonation chamber, wherein the control circuit for operating the batch meter includes a timedelay element and a programmer connected thereto for varying the time lag thereof.

During the period beginning from the moment when the powder is injected into the detonation chamber to the moment when the detonation is initiated, the powder is displaced by the gas mixture flow towards the open end of the detonation chamber. The provision of the timedelay element in the control circuit for operating the batch meter, and of the programmer for controlling this time-delay element makes it possible to alter the period of time during which the displacement of the powder takes place by varying the time lag of the control pulse operating the valve of the batch meter. The location of the powder in the detonation chamber at the moment of explosion influences the length of time during which the powder particles are in contact with the detonation products having a high temperature.This time determines the temperature to which the powder particles are heated and their end velocity (at the surface onto which said particles are deposited), and is precisely these parameters which define the strength of the bond between the particles and the surface being coated. The velocity and temperature of the powder particles may be selected by adjusting the time lag in a manner which will provide an optimum strength of bond in accordance with physical and chemical properties of a layer onto which a coating is applied. In addition, under such conditions more powder particles acquire a velocity and temperature sufficient to ensure bonding thereof to a surface being coated than in the known apparatus in which such adjustment is not provided. Therefore the thickness of the coating layer formed by one shot can be increased.

Thus the construction of the apparatus described above enables the quality of the coatings and the efficiency of the coating operation to be enhanced.

In the preferred embodiment of the invention the programmer may be provided with a variable resistor and a drive connected thereto for altering its effective resistance and thus enabling a required time lag to be selected with the desired precision.

For the sake of simplicity and reliability the drive of the variable resistor may be constructed in the form of an electric motor whose shaft is coupled through a clutch to a shaft of the variable resistor.

The time-delay element may be constructed in the form of two multivibrators connected in series with one another through a differential circuit, the variable resistor of the programmer being placed in a time-setting circuit of the first multivibrator.

The invention will now be explained with reference to embodiments thereof in conjunction with the accompanying drawings, wherein: Figure 1 is a diagram of one form of apparatus for applying coatings by detonation; Figure 2 schematically represents a programmer used in the apparatus of the invention; Figure 3 is a basic diagram of a time-delay element used in the apparatus of the invention; Figure 4 shows a possible basic diagram of a control circuit for operating the batch meter in the apparatus of the invention; and Figure 5 is an operation sequence diagram of the proposed apparatus for initial cycles of the coating operation.

Referring now to Figure 1, an apparatus for applying coatings by detonation comprises a detonation chamber 1 made in the form of a barrel closed at one end, a gas mixture supply system 2 and a powder supply system 3, both of the supply system 5 communicating with the detonation chamber 1. The gas mixture supply system 2 includes a mixer 4 which is connected through valves 5, 6 and 7 with gas sources 8, 9 and 10 to supply gases which are used as components to produce an explosive gas mixture.

These gas mixture components are a combustible (for instance acetylene), an oxidizer (for instance oxygen) and an inert gas (for instance nitrogen).

The mixture supply system 2 communicates with the detonation chamber 1 through a coil pipe 11.

The powder supply system 3 includes a batch meter 12 provided with an electromagnetic valve 13.

The detonation chamber 1 is provided with a detonation initiating device 14 mounted therein and constructed in the form of a spark plug.

The control system of the apparatus has a control unit 1 5 electrically connected through a control circuit 16 with the valves 5 and 6 of the mixer, through a control circuit 1 7 with the valve 7 of the mixer, through a control circuit 1 8 with the detonation initiating device 14, and through a control circuit 19 with the valve 13 of the batch meter 12.

The control circuit 19 for operating the batch meter includes a time-delay element 20 and a programmer 21 electrically connected to the time-delay element 20. Triggering the programmer is done with the aid of a circuit 22 which connects said programmer to the control unit 15.

The programmer 21 (Figure 2) incorporates a variable resistor 23 coupled with a drive adapted to vary the active resistance of said resistor, which drive is an electric motor 24 having a controlled speed of rotation. The shaft of the electric motor 24 is connected through a clutch 25 with the shaft of the resistor 23.

The time-delay element 20 includes a first multi-vibrator 26 (Figure 3), a differential circuit 27 and a second multivibrator 28, connected in series.

The first multivibrator 26 includes a timesetting circuit in which is placed the resistor 23.

The differential circuit 27 is adapted to differentiate the trailing edge of the first multivibrator 26 and is made up of either passive RC elements or a capacitor connected in parallel with an amplifier.

The above construction of the control circuit 1 9 is a preferred one because of its simplicity, reliability and the ability to adjust the time lag with a desired precision.

Shown in Figure 4 is another possible modification of the control circuit for operating the batch meter 12, in which the programmer 21 includes an electromagnetic relay 29 having a make contact 30 and a break contact 31 placed respectively in circuits 32 and 33 of capacitors 34 and 35 in a time-delay circuit 36 of the timedelay element 20. To delay the operation of the relay 29 relative to the moment of its being fed with a supply voltage, the programmer 20 is provided with an integrating RC-circuit 40 connected to the coil of the relay 29. The circuit 22 is adapted to apply a supply direct voltage from the control unit 1 5 to the programmer 21.

The time-delay element 20 connected to the control unit 1 5 through the control circuit 19 includes an electro-magnetic relay 37 having a make contact 38 placed in a power supply circuit 39 of the batch meter 12, which power supply circuit 39 is connected to the output of the control unit 15. The relay 37 is connected to the time-delay circuit 36.

The apparatus for applying coatings by detonation operates in the following manner.

When a push-button "START" on the control console (not shown) is pressed, the control unit 1 5 (Figure 1) supplies a direct voltage to the programmer 21 and generates in cycles control signals in accordance with the operation sequence diagram shown in Figure 5. The shaft of the electric motor 24 (Figure 2) starts rotating and the valves 5 and 6 (Figure 1) operate in response to control signals applied through the circuit 1 6 (Figure 5a). The mixer 4 (Figure 1) is filled with acetylene and oxygen, whereafter the mixture thus produced from said gases in the mixer 4 is delivered through the coil pipe 11 to the detonation chamber 1 and the valves 5 and 6 are caused to close.A signal from the control unit 15 is applied through the control circuit 1 7 to the valve (Figure 5b), and in response the valve 7 opens (Figure 1) to let nitrogen pass into the mixer 4 and the coil pipe 11 and thereby force the explosive mixture therefrom to the detonation chamber 1. In this way the mixer 4 and the coil pipe 11 are purged by an inert gas.

Before the purging operation is completed, a powdered coating material is injected from the batch meter 12 into the detonation chamber 1 with the use of an inert gas (in this particular case nitrogen is also used as a carrier gas use). To this end, a control signal is transmitted from the control unit 1 5 through the control circuit 1 9 to the time-delay element 20, which control Signal is a fast electric pulse (Figure 5c) which triggers the first multivibrator 26 (Figure 3). A signal which is generated by this multivibrator has a duration which is determined by the resistance value of the variable resistor 23, which resistance value depends in its turn on the position of the shaft of the resistor 23, coupled with the shaft of the electric motor 24 (Figure 2).The trailing edge K (Figure 5c) of this pulse, selected by the differential circuit 27 (Figure 2) is used to trigger the second multivibrator 28 which produces a pulse (Figure 5d) directly applied to the electromagnetic valve 1 3 (Figure 1) of the batch meter 12. Thus the pulse at the output of the time-delay element 20 (Figures 1, 4) is delayed for a time /(Figures 5c, d) relative the pulse at its input.

After the detonation chamber 1 (Figure 1) is filled with the explosive mixture, the mixer 4 and the coil pipe 11 are purged by an inert gas, and the powdered coating material is delivered from the batch meter 12 to the detonation chamber 1, detonation of said explosive mixture being initiated by a spark ignited in the device 14 in response to a control signal applied thereto from the control unit 1 5 through the control circuit (Figure 5e).

The powder particles having been accelerated and heated by the detonation products pass out from the detonation chamber 1 (Figure 1) and interacting with the surface of a part 41 positioned in their path form a thin layer of a coating thereon. After the detonation products have left the detonation chamber the latter is purged with said inert gas, the valve 7 of the mixer 4 being open. The purging operation completed, the valve 7 is caused to close (Figure 5) and the coating cycle Tis repeated from the beginning.

During the first shot, when the shaft of the electric motor 24 (Figure 2) begins to rotate slowly, the angle of rotation of this shaft and hence the shaft of the variable resistor 23 is a minimum which corresponds to the minimum resistance of the variable resistor and minimum time lag / (Figure 5) of the signal transmitted from the unit 1 5 through the control circuit 1 9 to the batch meter 12 (Figure 1). Therefore, the period m from the moment when the powder is injected to the moment when detonation is initiated in the barrel in the first operating cycle is a maximum so that the coating material powder under the action of the gas mixture filling the detonation chamber is displaced towards the open end of the barrel.

During the following shots of the apparatus as the shaft of the electric motor 24 (Figure 2) is rotated, the angle of rotation of the shaft of the variable resistor 23 increases, thereby increasing the time lag /(Figure 5) and correspondingly decreasing the period m so that the suspension of the powder is not displaced as much towards the outlet of the barrel and at the moment of explosion is located at a greater distance from the surface being coated than during the first shot.

Thus, the path along which the powder particles are carried by the flow of detonation products is ionger, so that particles are heated to higher temperature and their velocity is lower.

Due to this controlled procedure, there are provided optimum conditions for a bond to be formed between the particles and the substrate after the first two or three shots, whereupon by increasing the temperature and decreasing final velocity of the powder particles, optimum conditions are provided for bonding of the particles to the already formed underlayer of the coating, with the physical and chemical properties of said underlayer being different from those of the substrate.Furthermore, in comparison with the process of applying coatings carried out with the use of conventional apparatus, the proposed process allows the thickness of the coating layer formed by one shot to be increased, which is possible due to the longer period during which the powder particles are exposed to the detonation products and hence there are imparted to a greater number of the particles energetic parameters sufficient to bond these particles to the surface being coated.

Stabilizing the time lag /(Figure 5) of the signal controlling the valve 1 3 of the batch meter 1 2 (Figure 1) and hence stabilizing the above-said parameters of the powder particles takes place when the variable resistor 23 is forced by the electric motor 24 (Figure 2) to its end position, in which case a further-rotation of the electric motor 24 shaft does not change the position of the shaft of the resistor 23 and only results in slipping of the clutch 25.

The speed of rotation of the shaft of the electric motor 24 and the maximum angle of rotation of the resistor 23 shaft are determined experimentally depending on what temperature and velocity of the powder particles of the coating material are optimum for the formation of a corresponding layer of the coating.

After the coating of a desired thickness has been formed the apparatus is switched off and the electric motor 24 is reversed to cause the shaft of the resistor 23 to take its initial position.

In the modification of the control circuit for operating the batch meter 12, shown in Figure 4, a control signal delay is effected in the following manner.

A control signal from the control unit 15 is applied through the control circuit 1 9 to the timedelay circuit 36. At the first operation cycles of the apparatus the signal applied to the coil of the relay 29 through the circuit 22 does not attain a value sufficient to operate said relay because of the slow response of the RC-circuit 40 and its contact 30 remains open while the contact 31 remains closed. Therefore the time lag I of the signal (Figure 5) to operate the valve 13 (Figure 1) of the batch meter 12 depends on the capacitance of the capacitor 35 (Figure 4) connected to the relay 37 through the contact 31.

When the relay 37 is energized its contact 38 is caused to close and to thereby let the control signal be applied through the circuit 39 to the valve 13 of the batch meter 12 (Figure 1). In the absence of a pulse at the input of the circuit 36 (Figures 4 and 5c) the relay 37 (Figure 4) is deenergized with a time-delay corresponding to the time of discharging of the capacitor 35.

At the following operational cycles of the apparatus (2 to 3 cycles later if a part onto which a coating is applied is not a movable one) the voltage across the coil of the relay 29 of the programmer 21 attains, due to discharging of the capacitor of the RC-circuit 40, a value which is sufficient for this relay to operate. As a result, the contact 31 opens and the contact 30 closes to connect the capacitor 34 of the time-delay circuit 36 to the coil of the relay 37, in response to which the capacitor 35 is disconnected. Now, when a control signal from the unit 15 is applied to the time-delay circuit 36 the time lag /(Figure 5) decreases since its value is determined by the capacitance of the capacitor 34 (Figure 4), selected greater than that of the capacitor 36.

With the increase of the time lag of the control signal operating the valve 12 (Figure 1) of the batch meter 13 the temperature and final speed of the powder are increased as in the modification of the apparatus described above.

The use of the above-described apparatus for applying coatings by detonation makes it possible to enhance the adhesiveness of a coating to a substrate, with the simultaneous improvement in the properties of the coating and the efficiency of the apparatus.

While particular embodiments of the invention have been shown and described various modifications which will be apparent to those skilled in the art may be made in the invention without departing from the spirit of the invention as defined in the claims.

Claims (5)

Claims

1. Apparatus for applying coatings by detonation, which includes a detonation chamber in communication with a powder supply system having a batch meter and with a gas mixture supply system having a mixer connected through valves with gas sources, and a control unit electrically connected through control circuits to the batch meter, the valves of the mixer and a detonation initiating device located in the detonation chamber, wherein the control circuit for operating the batch meter being provided with a time-delay element and a programmer connected thereto for varying the time lag thereof.

2. Apparatus as claimed in claim 1, wherein the programmer includes a variable resistor and a drive connected thereto for altering its effective resistance.

3. Apparatus as claimed in claim 2, wherein the drive of the variable resistor is constructed in the form of an electric motor whose shaft is coupled through a clutch to the shaft of the variable resistor.

4. Apparatus as claimed in claim 2 or 3, wherein the time-delay element is constructed in the form of two multivibrators connected in series with one another through a differential circuit, the variable resistor of the programmer being placed in a time-setting circuit of the first multivibrator.

5. Apparatus for applying coatings by detonation substantially as described with reference to the accompanying drawings.