GB2102151A - Apparatus for detonation coating - Google Patents

Abstract

Apparatus for the detonation coating of the surfaces of parts, which includes a detonation chamber (1) connected to a powder supply system (4) and a gas mixture supply system (3). A control system incorporates a powder detector (32) adapted to determine the amount of powder in the detonation products and connected with a control unit (22) through a feed-back circuit (33) which includes a coating thickness measuring unit (35) arranged to de- energize the apparatus after the predetermined thickness of the coating being applied is attained. The unit (35) has an A to D converter (37) and an adder (38) which stores the cumulative value from the detector (32) for successive detonations. When the adder (38) has a value substantially identical to a reference value stored by unit (36) the coating process is halted. <IMAGE>

Description

SPECIFICATION Apparatus for detonation coating The present invention relates to apparatus for applying coatings onto surfaces of articles by coating material spraying, and more specifically is concerned with an apparatus for detonation coating.

The invention may be applied in the shipbuilding and aircraft industry, aerospace engineering, mechanical engineering and instrument engineering for manufacturing parts which are subjected under operating conditions to high loads and are also subject to corrosive, erosive or thermal wear.

A number of difficulties are associated with the application of a coating of a desired thickness by using a detonation wave coating technique since in practice it is not possible to achieve accurate batch metering of powder with the aid of batch meters at present used in the known coating apparatus, and direct measurement of the thickness of a coating during its application is very difficult to achieve since the measuring means used are exposed to strong dynamic action and thermal effect produced by the pulsed flow of metal powder particles.

Most of the prior art arrangements for detonation coating, which generally comprise a detonation chamber made in the form of a barrel communicating with a powder supply system and gas mixture supply system, and a detonation initiating device, do not even include means for controlling the amount of coating material powder at the outlet of the detonation chamber (cf. US Patents No 2,950.867 and 3,773,259).

Recently, apparatus has been developed wherein apart from the above-mentioned units and a conventional control unit (not mentioned above) to operate the valve of a batch meter incorporated in the powder supply system, the valves of a mixer incorporated in the gas mixture supply system, and a detonation initiating device, there is also provided a powder detector adapted to indicate the amount of powder in detonation products and connected to the control unit through a feed-back circuit which includes an amplifier unit (powder detector signal converter), which detector together with said units form a control system for monitoring the operation of the apparatus (cf. co-pending Patent application No.

36,799/1979. "Apparatus for detonation coating", field on 28 March, 1979). The powder detector determines the brightness of the detonation products leaving the barrel during operation of the apparatus, and it has been established that this brightness depends on and is proportional to the amount of powdered coating material contained in the detonation products.

A signal from the powder detector is applied through the amplifier unit to the control unit so that when the level of the signal decreases, a command signal is formed to increase the amount of the powder delivered to the detonation chamber from the batch meter of the powder supply system. If said powder is not present (not detected) in the detonation products the control unit de-energizes all the systems of the apparatus.

However, even the presence of a powder detector for indicating the amount of powder in the detonation products does not enable the above apparatus to form a coating of a precise thickness since the said detector detects in principle only the deviation from a predetermined amount in the detonation products resulting from a single shot.

Therefore, the resulting coatings generally have a greater thickness than that required, so that the parts coated in this way need subsequent mechanical treatment. According to another method the coating is applied by short trains of shots and after each such trains of shots the resulting thickness of the coating being formed is measured. In the both cases the use of labour increases while the efficiency of the coating process decreases.

It is an object of the present invention to overcome the above disadvantage.

The present invention consists in an apparatus for detonation coating, comprising a detonation chamber, a powder supply system including a powder batch meter communicating with the detonation chamber, a gas mixture supply system including a mixer communicating at the inlet through valves with gas sources and at the outlet with the detonation chamber, a detonation initiating device connected to the detonation chamber, a control unit electrically connected to the valves of the powder batch meter and of the mixer, and to the detonation initiating device, and a powder detector adapted to determine the amount of the powder in the detonation products for each shot, electrically connected to the control unit, and to a coating thickness monitoring unit for detecting when the coating thickness as represented by the accumulated value of signals from the powder detector from successive shots is equal to or within allowable limits of a pre-set desired coating thickness and thereupon preventing further shots.

The presence of a coating thickness monitoring unit makes it possible to monitor the thickness of the coating during the application thereof and to cease the formation of coating when the desired thickness thereof is achieved. As a result, the resulting coating does not require additional mechanical treatment to bring to the required thickness and the apparatus does not need to be stopped during the operation in order to measure the thickness of the coating being formed, so that the labour consumption of the process is decreased and its efficiency is increased.

The invention will now be explained with reference to an embodiment thereof which is represented in the accompanying drawing which schematically represents a general view of the proposed apparatus.

An apparatus for detonation coating comprises a detonation chamber 1 made in the form of a cylindrical barrel closed at one end, a detonation initiating device 2 which is a spark plug secured inside the barrel, a gas mixture supply system and a powder supply system 4, both said supply systems being connected to the detonation chamber 1.

The gas mixture supply system 3 includes a gas mixer 5 for preparing a gas mixture from a combustion gas (for example, acetylene), an oxidizer (for example, oxygen) and an inert gas (for example, nitrogen). Supplies 6,7 and 8 of these gases communicate with the mixer 5 through pipe lines 9, 10 and 11 on which are mounted valves 12, 13 and 14. The mixer 5 communicates with the detonation chamber through a coil pipe 1 5 adapted to suppress a back surge.

The powder supply system 4 includes a batch meter 1 6 into which a coating material powder is delivered from above. The inlet 1 7 of this batch meter is arranged to receive a carrier gas, and its outlet 1 8 communicates with the detonation chamber 1 through a delivery pipe 1 9. Through a gas supply pipeline 20 connected to the inlet 1 7 the batch meter 1 6 is connected to a source of carrier gas which in this particular case is the supply 8 of the inert gas.

The batch meter 1 6 may be a conventional pulse-type (cf. USSR Author's Certificate No 523,846, Int. Cl. B65C 53/40, 1 976.), although any other suitable feeder may be used.

A valve 21 is mounted in the gas delivery pipe 20 near the inlet 1 7 for controlling the delivery of the carrier gas to the batch meter 1 6.

The apparatus is provided with a control system which includes a control unit 22 having its outputs electrically connected to valves 12, 1 3 and 14 of the gas mixer 5 through control lines 23 and 24, to the valve 21 of the batch meter 16 through a control line 25, and to the detonation initiating device 2 through a control line 26. The control circuit 22 comprises a series circuit including a pulse shaper 27, a binary coded decimal counted 28, a decoder 29, a program set unit 30, and an amplifier unit 31.

The control system further includes a powder detector 32 adapted to determine the amount of powder in the detonation products, which powder detector is electrically connected to the control unit 22 through a feed-back circuit 33. The powder detector 32 is in the form of a photodiode sensitive to radiation produced by the detonation products. Instead of the photodiode use may be made of any other suitable device, for instance, a photoresistor.

The feed-back circuit 32 includes an amplifier unit 34 having its input connected to the powder detector 32, and a coating thickness monitoring unit 35 having its input connected to an output of the unit 34 and its output connected to the control unit 22.

The amplifier unit 34 comprises a series circuit including a voltage amplifier, a first power amplifier, an integrating RC-circuit and a second power amplifier (not shown).

The coating thickness monitoring unit 35 includes a coating thickness set unit 36 and a series circuit made up on an analog-to-digital converter 37, an adder 38, and a comparison unit 39.

The coating thickness set unit 36 is a decimal wafer switch unit including a plurality of separate wafer switches with the aid of which a setting defining a desired thickness of the coating being formed may be established.

The analog-to-digital converter 37 is located at the input of the coating thickness monitoring unit 35 and is adapted to convert an analog signal from the powder detector 32 (amplified by the amplifier unit 34 and applied in the form of an alternating voltage to the input of said analog-todigital converter 37) to a digital code at the moment when the brightness of the powder in the detonation products of a single shot is a maximum.

The adder 38 is intended for adding numbers which determine the thickness of the coating being formed by one single shot, which numbers are fed to this adder in the form of a digital code from the analog-to-digital converter 37. The comparison unit 39 has one input connected to the output of the set unit 36, and the other input connected to the output of the adder 38, and is intended to generate command signals to de energize the apparatus as soon as a - predetermined thickness of the coating being applied is attained. The output of the unit 39 is connected to the control unit 32 through a key 40 constructed in the form of a relay with back break contacts in the circuit 41 through which a supply voltage is applied to the control unit 32.

The apparatus for detonation coating operates as follows.

When a push-button "START" on a control panel (not shown) is pressed a supply voltage is applied through the key 40 of the unit 35 to the control unit 22. The shaper 27 generates rectangular pulses which are applied to the binary coded decimal counter 28, which translates a serial number of each arriving pulse within the apparatus operating cycle into a binary decimal code. In the decoder 29 these pulses are distrubuted in a conventional manner so that potentials are produced at that pair of its outputs which corresponds to the code of each arriving pulse.The program set unit which is made in the form of a decimal switch selects necessary pulses according to the program, which through the amplifier unit 31 are transmitted to the control circuits 23 and 26 so as to operate the valves 12-14 of the gas mixer 5, valve 21 of the powder batch meter 16, and the detonation initiating device 2.

The unit 22 first generates a command signal in response to which the valves 12 and 13 open to let the combustion gas and oxidizing gas be delivered through the pipelines 9 and 10 from the sources to the gas mixer 5, and then a command signal to open the valve 14 is transmitted from the control unit 22 to the circuit 24. The inert gas from the source 8 passes through the pipeline 11 into the mixer 5 wherein all the three ingredients of the gas mixture are mixed together, which gas mixture is delivered through a coil pipe 1 5 to the detonation chamber 1. When the detonation chamber is being filled with said gas mixture a command signal to open the valve 21 is transmitted to the unit 22 output through the circuit 25.The valve 21 remains open for a period of time the length of which is determined by the length of the pulse generated by the pulse shaper 27 so as to provide delivery of the inert gas from the source 8 to the batch meter 1 6 and thus to inject the coating material powder through the delivery pipe 1 9 into the detonation chamber 1. After the detonation chamber 1 is filled with said gas mixture and powder, a command signal to close the valves 12 and 13 on the pipe lines 9 and 10 (for the combustion gas and oxidizing gas respectively) is transmitted from the control unit 22 through the control circuit 23. Since the valve 14 still remains open the inert gas continues to be forced into the mixer 5, thereby purging the cavities of the mixer and the coil pipe 1 5.

Simultaneously with the command signal to shut off the valve 14 the signal transmitted from the unit 22 through the control circuit 26 ignites a spark acros the spark plug 2 to initiate explosion in the detonation chamber 1. The detonation products entrain the coating material powder and carry it out from the detonation chamber 1 to deposit it onto a part 42 positioned in the path of the detonation products.With the other conditions being constant (they are constant during the formation of one and the same coating) the brightness of the detonation product flow depends on the amount of the powdered coating material contained in the detonation products, so that the signal generated by the powder detector 32 dependent upon the maximum brightness of the detonation flow during a shot is proportional to said amount of the powder, which amount varies from shot to shot because due to variations in the metering of the powder by the powder batch meter 16. A signal from the powder detector 32 is transmitted to the amplifier unit 33 wherein it is amplified first in voltage and then in power.The analog-to-digital converter 37 of the coating thickness monitoring unit 35 converts a signal arriving at its input from the output of the unit 36 to a digital code, whereafter said signal is applied to the input of the adder 38 which determines the thickness of the coating being formed by adding signals arriving in succession from the converter 37. A signal from the adder 38 is compared in the comparison unit 39 with the predetermined thickness of the coating to be applied, which thickhess magnitude is stored in the memory of the set unit 36. When the compared values coincide or are within allowable limits after a successive shot in the unit 39 generates a signal in response to which the back contacts of the relay of the key 40 are opened to interrupt the voltage supply to the control unit 22 and thereby stop the apparatus.

The apparatus can be operated again provided the memorized value stored in the memory of the adder 38 is erased.

Thus the coating process in the proposed apparatus is fully automated which ensures its high accuracy, efficiency and safety in operation.

Various modifications may be made within the scope of the present invention.

Claims (3)

1. An apparatus for detonation coating, comprising a detonation chamber,a powder supply system including a powder batch meter communicating with a detonation chamber, a gas mixture supply system including a mixer communicating at the inlet through valves with gas sources and at the outlet with the detonation chamber, a detonation initiating device connected to the detonation chamber, a control unit electrically connected to the valves of the powder batch meter and of the mixer, and to the detonation initiating device, and a powder detector adapted to determine the amount of the powder in the detonation products for each shot, electrically connected to the control unit, and to a coating thickness monitoring unit for detecting when the coating thickness as reprsented by the accumulated value of signals from the powder detector from successive shots is equal to or within allowable limits of a pre-set desired coating thickness and thereupon preventing further shots.

2. An apparatus as claimed in claim 1, wherein the coating thickness monitoring unit includes a coating thickness set unit for pre-setting a desired coating thickness, a converter for converting analog signals from the powder detector into digital signals, an adder for accumulating the digital signals from the converter, and a comparison unit for detecting when the value of the accumulated digital signals is equal to or within allowable limits of a value set by the coating thickness set unit.

3. An apparatus for detonation coating substantially as described with reference to the accompanying drawing.