GB2157208A - Apparatus for explosive-abrasive surfacing and spraying - Google Patents

Abstract

The proposed invention relates generally to means for applying coatings by high-temperature spraying and, more particularly, to apparatus for explosive-abrasive treatment of and application of coatings to the working surface of machines and mechanisms. The apparatus comprises: a barrel (1) connected to a unit (2) for dosing a powdered material to be sprayed, a gas mixer (3) connected on the one hand by way of a coil pipe (4) to the barrel (1) and on the other hand through solenoid-operated valves (5, 6, 7) to gas feed sources (8, 9, 10); a spark plug (11) disposed in a location where a gas mixture is supplied to the barrel (1) and intended to initiate explosion of this gas mixture; and a control system (14) for actuating the solenoid-operated valves (5, 6, 7) and powdered material dosing unit (2) and energizing the spark plug (11). The apparatus is further provided with a unit (12) for dosing a powdered abrasive material to a second barrel (13) arranged concentrically relative to the first barrel (1). <IMAGE>

Description

SPECIFICATION Apparatus for explosive-abrasive surfacing and spraying This invention relates generally to means for applying coatings by high-temperature spraying, and more particularly to devices for explosive-abrasive treatment of and application of coatings to the working surfaces of machines and mechanisms.

The invention can find application in machine construction, shipbuilding, aviation engineering and light industry.

Wide industrial use of a variety of protective and special-purpose coatings is a most effective way to extend serviceability of machines and parts, as well as to reduce the amount of metal consumed for their fabrication and lower the manufacturing costs involved.

Application of coatings may be necessitated by the need to: protect structural parts from the damaging effect of hot gases, vaporized metals, melts, acidic and alkaline solutions, and other corrosive media; protect materials against overheating and loss of strength under the action of high temperatures; impart to materials predetermined electrical, magnetic or optical properties; and make materials more stable to the influence of ionizing radiation.

At present, there are well known and widely used the following methods for obtaining metallic and non-metallic coatings: diffusion coating processes, flame and gas-flame plating, deflagration coating, supersonic gas-jet and electric arc spraying, vapour deposited coating, chemical plating methods, and hard-facing.

However, when service conditions require that coatings must posess a variety of properties (such as excellent bonding, minimized porosity, and invariable physical and mechanical properties of a workpiece being coated), most preferable is the use of explosive spraying.

This method resides in that a gun barrel is filled with a gas (generally oxy-acetylene) mixture and a batch of powdered material is fed thereto for an explosion of this mixture to be initiated by means of a spark plug.

A high-temperature gas flow generated by the explosion escapes from the barrel at a supersonic speed to thereby heat and accelerate the particles of the material being sprayed for these particles to be impacted against the workpiece surface, imbed therein upon contact and form a coating.

Thereafter, subsequent to blowing-through of the barrel by a neutral gas (normally nitrogen) the process is recommenced in the same sequence until a required thickness of the coating is attained.

Such intermittent spraying is effected by means of an automated detonation assembly, which includes a detonation device or gun, a control unit, and means for feeding the explosive gas mixture components and the neutral gas.

There is known an apparatus for explosive spraying comprising a barrel with a spark plug, a dispenser of a powdered material to be sprayed, a gas mixer connected to the barrel by means of a safety coil pipe and to gas feed sources by way of solenoid-operated valves disposed in feeding lines (cf. USSR Inventor's Certificate No. 605,361, IPC B 05 B 7/20, published 1976).

Thanks to the provision of a control unit, the barrel is periodically filled with the working gases (oxygen and acetylene) by opening the corresponding solenoid-operated valves, portions of the powdered material are periodically fed to the barrel, and explosions are initiated in the barrel by the spark plug. As a result of detonation,particles of the powdered material are hurled against the workpiece surface to form a layer of coating.

The gun is provided with a feedback circuit which comprises a pickup for detecting the presence of the powdered material in the products of explosion, and a transducer unit for transducing signals received from the pickup. In the case of absence of the powdered material in the products of explosion, the apparatus automatically terminates its operation thus preventing idling.

However, the thus obtained coating very often fails to meet the specified service requirements, since the strength of adhesion of the coating to the base metal of the workpiece may not be sufficient due to the lack of required surface roughness.

In order to improve the quality of coatings obtained by apparatus of the aforedescribed construction (i.e., a single - barrel gun apparatus) it is very often necessary to carry out abrasive surface treatment of the workpiece to be coated. However, the combination of abrasive surfacing of and spraying powdered materials to the workpiece sometimes fails to result in a desired effect, since the particles of the powdered abrasive are mixed in the same barrel with the powdered material to be sprayed, which affects the quality of coating or even may result in a complete failure to obtain a coating.

One more apparatus is known for explosive-abrasive treatment of and application of coating to workpieces which bears the closest resemblance to the herein proposed construction. It comprises a barrel connected to a dispenser of a powdered material to be sprayed, a gas mixing chamber connected on one side by way of a coil pipe to the barrel and on the other side through solenoid-operated valves to gas feed sources, a spark plug arranged in the zone where the explosive gas mixture is supplied to the barrel and intended for initiating detonation of this mixture, and a control unit for actuating the solenoid-operated valves and energizing the spark plug (cf., USSR Inventor's Certificate No. 438,215, IPC B 05 B 17/00, published 1973).

Inherent in the above apparatus is a disadvantage residing in that the provision of a single barrel fails to assure a combination of abrasive surfacing of and applying a coating to the workpiece, because the particles of the abrasive powder tend to mix with the particles of the powdered material being sprayed to thereby prevent sufficient bonding between these particles of the material being sprayed and the surface of the workpiece.

In addition, when applying a coating of easily oxidizable materials, partial oxidation of the particles of the material being sprayed occurs due to the presence of some amount of oxygen in the products of explosion, this effect being especially pronounced with a multitude of fine particles having considerably larger overall surface area. These particles are carried away toward the periphery of the spray cone escaping from the gun barrel to imbed in the workpiece surface around the spray spot and form a halo or film of oxides or other compounds of the material being sprayed on the workpiece surface. These compounds affect bonding of subsequently sprayed coating layers.

The present invention is therefore directed toward the provision of an apparatus for explosive spraying in which, thanks to a specific structural arrangement of its barrel and the provision of an additional unit for dispensing or dosing an abrasive material, a greater efficiency of the process of explosive spraying and improved quality of coating would be attained.

In accordance with the invention, there is provided an apparatus for explosive-abrisive surfacing and spraying, comprising a barrel connected to a unit for dosing a powdered material to be sprayed; a gas mixer connected on the one hand to the barrel and on the other hand through solenoid-operated valves to a plurality of gas feed sources; a spark plug for initiating explosions of gas mixture in the barrel, and a control system for actuating the solenoid-operated valves and powdered material dosing unit and for energizing the spark plug, the apparatus being additionally provided with a second barrel arranged concentrically relative to the first barrel and connected to a unit for dosing a powdered abrasive material and to which the explosive gas mixture is also supplied.

This arrangement of the apparatus for explosive spraying renders the process of applying a coating to a workpiece more efficient by combining the operations of abrasive treatment of the surface of the workpiece and spraying a coating thereon. It also makes it possible to improve the quality of coating by obviating a halo formed during spraying by the particles of the abrasive powder.

In addition, the barrel connected to the unit for dosing the powdered material to be sprayed is provided with radial holes to communicate with the barrel connected to the unit for dosing the powdered abrasive material.

This provides for the admission of the explosive gas mixture and neutral gas to the barrel connected to the unit for dosing the abrasive material and for propagation therein of the gases produced by the explosion initiated by the spark plug in the barrel connected to the unit for dosing the powdered material being sprayed.

The invention will now be described in greater detail with reference to a preferred embodiment thereof as illustrated in the sole Figure of the accompanying drawings, which is a schematic view of an apparatus for explosive spraying according to the invention.

Apparatus for explosive-abrasive surfacing and spraying comprises a barrel 1 connected to a unit 2 for dosing a powdered material to be sprayed, a gas mixer 3 connected on the one hand through a coil pipe 4 to the barrel 1, and on the other hand through solenoid-operated valves 5, 6 and 7 to feed sources 8, 9 and 10 of a neutral gas, oxygen and acetylene, respectively. The apparatus is also provided with a spark plug 11, arranged at a location close to where the gas mixture is fed to the barrel 1, intended for initiating explosion of this mixture; a unit 12 for dosing an abrasive material and connected to a second barrel 13 mounted concentrically relative to the barrel 1; and a control system 14 for actuating the solenoid-operated valves 5, 6 and 7 of the gas mixer 3 and for energizing the spark plug 11.The first barrel 1 has radially extending holes 15 communicating with the second barrel 13.

To ensure intermittent supply of the neutral carrier gas from the source 8 to the dosing units 2 and 12, there are provided solenoid-operated valves 16 and 17 actuated, like the valves 5, 6 and 7, by the control system 14 which also energizes the spark plug 11.

A workpiece 18 to be sprayed is moved in a direction indicated by the arrow A by means of a manipulator (not shown) in front of the ends of the barrels 1 and 13.

The apparatus according to the invention operates as follows.

A signal generated by the control system 14 causes the valves 6 and 7 to open, whereby acetylene and oxygen are delivered from the respective feed sources 9 and 10 to form in the mixer 3 an explosive mixture which is fed through the coil pipe 4 to the barrel 1 and is conveyed also to the barrel 13 through the holes 15. As the barrels 1 and 13 are filled with the explosive gas mixture, the powdered material to be sprayed is supplied to the barrel 1 and the abrasive material is fed to the barrel 13. For this purpose, the valves 16 and 17 of the dosing units 2 and 12 are made to open for a certain duration for the neutral gas to be admitted to their interior and thereby convey the powdered material to be sprayed and the abrasive material to the respective barrels 1 and 13.Subsequent to occupation of these barrels with the explosive mixture the valves 6 and 7 are closed, while the valve 5 is opened for the interiors of the mixer 3 and the coil pipe 4 to be vented by the neutral gas. Then, an explosion is initiated in the barrels 1 and 13 by a signal from the control system 14 which energizes the spark plug 11, and the thus formed products of explosion hurl the powdered material and abrasive powder from their respective barrels 1 and 13 against the surface of the workpiece 18.

Thereafter, the neutral gas is fed through the open valve 5 to the interiors of the barrels 1 and 13 for venting, which is followed by closing of the valve 5 for the aforedescribed cycle to recommence.

During first bursts a spray spot appears on the workpiece surface in the zone of the barrel 1, while preliminary abrasive treatment of the portion of the workpiece confronting the zone of action of the barrel 13 is effected. In the course of progressive displacement of the workpiece 18 by the manipulator a coating is applied to this workpiece as a result of impact of the powdered material escaping from the barrel 1. The absence of a halo around the spray spot (this halo being erased by the particies of the abrasive material) results in improved bonding and therefore higher quality of the coating thus obtained. Also, the process becomes more efficient -due to the simultaneous abrasive treatment and explosive spraying.

Claims (3)

1. An apparatus for explosive-abrasive surfacing and spraying, comprising a barrel connected to a unit for dosing a powdered material to be sprayed; a gas mixer connected on the one hand to the barrel and on the other hand through solenoid-operated valves to a plurality of gas feed sources; a spark plug for initiating explosions of gas mixture in the barrel, and a control system for actuating the solenoid-operated valves and powdered material dosing unit and for energizing the spark plug, the apparatus being additionally provided with a second barrel arranged concentrically relative to the first barrel and connected to a unit for dosing a powdered abrasive material and to which the explosive gas mixture is also supplied.

2. An apparatus as claimed in claim 1 in which the first said barrel is provided with radial holes to communicate with the second said barrel for the passage of explosive gas mixture.

3. An apparatus substantially as herein described with reference to the accompanying drawings.