GB1572283A - Metal spraying device and method utilizing the same - Google Patents

Description

(54) METAL SPRAYING DEVICE AND METHOD UTILIZING THE SAME (71) We, KAKOHKI COMPANY LIMITED, a Japanese Company of 19-8 Nishi Shinbashi 1 chome, Minato-ku, Tokyo, Japan, do hereby declare the invention for which we pray that a patent may be granted to us and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a metal spraying device and to a method of utilizing the same.

Metal spraying is defined as a method whereby molten droplets of a metal are ejected with a continuous stream of compressed air and deposited on the solid surface of a substrate. Such a substrate may be of metal, ceramic, glass or wood. Metals which are usable for metal spraying include tin, lead, copper, silver, gold, aluminum, iron and alloys thereof.

With metal spraying devices, it has heretofore been customary to use metal wires invariably having a circular cross section, no matter whether the devices are of flame type or of electric arc type. In the flame type metal spraying device, the place at which heating of such a circular wire is started is the outer boundary of the wire, and the heat thus applied is conducted from the outer boundary towards the core of the metal wire. In the electric arc type metal spraying device, an electric arc is generated at the meeting point oif two metal wires, namely, at a common point at which the circular cross sections of the two wires are held in mutual contact, and the heat generated by the arc is conducted from the common point of contact toward the outer boundaries of the circular wires. It is generally known that the amount of heat reaching any given point in a heat conductor is inversely proportional to the distance of the point from the heat source and directly proportional to the heating area.

In the metal spraying device of the type involving continuous feeding and melting of a metal wire, therefore, advantageous operational results can be obtained by decreasing the diameter of the metal wire or increasing the area of the metal to which the spraying device applies heat, such modifications of course being possibly only within certain limits. A decrease in the diameter of the metal wire entails an inevitable decrease in the volume of molten droplets of metal to be ejected. Since metal spraying devices of this type are invariably constructed so that the conversion of a solid metal wire into molten droplets is accomplished by blowing a continuous stream of compressed air to the portion of the metal wire which has fully been melted by heating, the length of the molten portion of metal wire is limited to the order of from about 2 to 10 mm. An attempt at enlarging the total area of heat application by increasing the feeding speed of the metal wire, therefore, renders it difficult to convert the metal into fine droplets since the wire will fail to be completely melted to the core and the droplets will not be fine and molten but coarse and semi-molten.

Further in the case of the flame type metal spraying device, the idea of increasing the volume of gas flame may be proposed as a possible solution. However, no increase in the heating area can be obtained without increasing the diameter of the metal wire and consequently the distance of heat transmission is increased proportionally, because the heat is inwardly conducted solely via the outer boundary of the metal wire. Increasing the diameter of the metal wire also has a disadvantage in that the metal spraying device must incorporate therein a sufficiently large mechanism for the feeding of the metal wire to the device. For this reason, the metal wires used with the conventional flame type metal spraying devices have their diameters limited to about 5.6 mm and those with the electric arc type metal spraying devices to about 3 mm.

An object of the present invention is to provide metal wires for the metal spraying device, which metal wires provide notably improved efficiency of metal spraying.

According to the present invention, there is provided a method of metal spraying as hereinbefore defined which comprises utilizing as metal to be sprayed, a metal wire of polygonal cross-section. The term "polygonal" includes tri-and quadri-lateral crosssections.

In a further aspect of the invention there is provided a metal spraying device including a polygonal metal wire supply means adapted to supply a wire of polygonal cross-section to a heating station.

In the case of an electric arc type metal spraying device, two metal wires are continuously supplied in directions intersecting each other at a specified angle and are melted by means of an arc generated at and near the common point of contact between the two metal wires.

The two metal wires having an angular cross section form a linear contact and provide a larger area of heat transmission than do metal wires of a circular cross section which form a point contact. Consequently, use of the metal wires of the present invention not only contributes to promoting and stabilizing the melting speed of wires but also enables electric brushes designed for delivery of an electric current to be brought into direct contact with the wires.

In the case of the flame type metal spraying device, the metal wire is heated and melted inwardly from the outer boundary thereof. The metal wire having an angular cross section has a larger surface than that of the circular metal wire having an equal sectional area. Thus, the former wire has a higher melting speed than the latter wire.

Further, the metal wire is continuously fed to the heating and melting zone by means of a pair of pinch rollers. The metal wire of the present invention forms a linear contact with such pinch rollers, and the linear contact permits the feeding of the metal wire to proceed with added smoothness.

The other objects and characteristic features of the present invention will become apparent from the detailed description to be given hereinbelow with reference to the accompanying drawings.

Figure 1 is an explanatory diagram of metal wires of the present invention used in an electric arc type metal spraying device.

Figure 2 is an enlarged view illustrating the state of contact between the two metal wires.

Figure 3 is a sectional view illustrating the use of a metal wire of the present invention in a flame type metal spraying device.

Fig. 1 is a schematic diagram of an electric arc type metal spraying device. A pair of metal wires 1 are paid out by a pair of feed rollers 2 and, with the aid of guides 3, the two metal wires 1 are brought into mutual contact at a prescribed angle. While traveling between the feed rollers 2 and the guide 3, each metal wire is kept in sliding contact with an electric brush 4 and a roller 5 which are opposed to each other across the metal wire. Thus, the two angular metal wires are supplied with plus and minus electric potentials. The electric potentials are also applied to the guides 3 to ensure high efficiency of electric current supply. A blow tube 6 for compressed air is interposed equidistantly between the two guides 3 and serves the purpose of directing a continuous stream of compressed air to the point at which the two metal wires 1 meet.

In the metal spraying device of the construction described above, when the metal wires 1 are paid out through the feed rollers 2 and forwarded by the guides 3, they produce an arc at the point of their mutual contact because they are carrying plus and minus electric potentials. The arc heats and melts the metal wires, and the molten metal is sprayed by the continuous stream of compressed air and deposited fast on a given article (not shown). This arc is generated at the point at which the two metal wires come into mutual contact. When the metal wires in use have an angular cross section as contemplated by the present invention, they produce a linear contact as shown in Fig. 2. Consequently, the arc is generated throughout the entire length of the linear contact formed between the two metal wires.

When the two angular metal wires are given a rectangular cross section and are made to confront each other on their respective long sides so as to generate the arc along the long sides, the spraying speed is increased and the volume of the molten metal to be sprayed is notably increased even if the short sides of their rectangular cross sections are equal in length to the diamters of circular metal wires, because the amount of heat reaching the various points of the wire is in inverse proportion to their distance from the heat source and in direct proportion to the area of heat application. To cite an example, a case in which conventional circular metal wires 3 mm in diameter are used in an electric arc type metal spraying device will be compared with a case in which angular metal wires of the same material having a rectangular cross section of 10 mm (long side) and 2 mm (short side) are used in the same device. It is assumed that the metal wires of both cases aro paid out at one fixed speed. The cross-sectional area of the circular metal wires in the informer case is found to be about 14.13 mm2 as shown in Formula (1) and that of the rectangular metal wires to be about 40 mm2 as shown in Formula (2).

1.52xrrx2 = 14.13 (1) 2x10x2=40 (2) Since the amount of heat conducted is in inverse proportion to the distance of heat conduction, it is learned from Formula (3) that the metal spraying capacity obtained by use of the rectangular metal wires 2 x 10 mm in cross section is about 4.2 times that obtained by use of the circular metal wires 3 mm in diameter.

4000x-3 4.2 14.13 2 (3) Now, the operation of this invention applied to the flame type metal spraying device will be described with reference to Fig. 3.

A contact tip 7 is axially penetrated by a metal wire 1 which is paid off by a pair of feed rollers 2. On the outside of the contact tip 7, there are provided an annular slit 8 for ejecting a mixed gas consisting of an inflammable gas and oxygen and an annular slit 9 for blowing out a continuous stream of compressed air, with the latter slit situated further from the contact tip 7 than the former slit 8.

In the metal spraying device of the construction just described, when the metal wire 1 is paid out to the leading end of the contact tip 7 by means of the feed rollers 2, the protruding tip of the metal wire is melted by the flame of the mixed gas from the slit 8 and the molten metal is ejected by the continuous stream of compressed air from the slit 9 against an article (not shown) being sprayed.

As is evident from the foregoing description, the metal wire is heated and melted gradually inwardly from the outer boundary. When the metal wire has an angular cross section as contemplated by the present invention, the area of the outer boundary exposed to the flame is greater than in a circular metal wire having an equal cross-sectional area. Thus, the angular metal wire provides a higher melting speed of the metal than the circular metal wire.

Now, a case in which a conventional circular metal wire 5.6 mm in diameter is used with the device and a case in which an angular metal wire having a rectangular cross section of 10 mm (long side) and 2 mm (short side) will be compared by way of illustration.

In the case of the flame type metal spraying, the metal wire gradually melts inwardly from its outer boundary toward its core. In this case, however, the factor of heat conduction velocity is negligible, because the wire has high heat conductivity because of its metallic property and the wire has a small cross-sectional area. Since the amount of heat to be conducted is in direct proportion to the surface area available for heat conduction, the surface area of the angular metal wire is found to be about 1.36 times that of the circular metal wire as shown in Formula (4). (2 + 10) x 2 . 1.36 (4) 5.6 x ir Since the metal spraying speed can be heightened by the reciprocal of the ratio of cross sectional areas which is found to be about 0.81 as shown in Formula (5), the metal spraying capacity obtained with the angular metal wire is calculated to be about 1.7 times that obtained with the circular metal wire as shown in Formula (6).

2x10 0.81 (5) 2.82 x ir 1.36. L 1.7 (6) 0.81 When the metal spraying is effected by use of the angular metal wire having a cross section of 2 x 10 mm, the heating capacity of the flame required for heating is about 1.36 times that required when there is used the circular metal wire having a diameter of 5.6 mm.

Since the metal spraying capacity with the angular metal wire is about 1.7 times that with the circular metal wire, the thermal efficiency in the former case is still about 25% higher than that in the latter case.

Although the values mentioned are those found by calculation, actual experiments using these metal wires gave substantially the same relative values as those touched upon above.

The angular metal wires for metal spraying according to the present invention can be made by using metals and alloys of the class heretofore employed for the purpose of metal spraying. Although the cross sections of these metal wires may be in the shape of squares, they will be more advantageous in the shape of rectangles in due consideration of the velocity of heat conduction. At present the largest allowable diameter of circular metal wire is 3 mm for use in the electric arc type metal spraying device and 5.6 mm for use in the flame type metal spraying device. Thus, the largest allowable length of the short side of the rectangular cross section is 3 mm for use in the former device and 5.6 mm for use in the latter device. With due consideration to the shape of the guide or the contact tip in the device and in view of the convenience of practical use, the length of the long side of the rectangular cross section is about ten times that of the short side.

As is evident from the foregoing description, the invention permits the velocity of heat conduction to be increased and consequently the feeding speed of the metal wire to be heightened because of the angular cross sections given to the metal wires for the metal spraying. As a natural consequence, the amount of the molten droplets of metal to be sprayed per unit time can be increased. Moreover, the angular metal wires are more easily fabricated than the circular metal wires and they provide greater areas for contact with the feed rollers and, therefore, add to the smoothness with which they are forwarded to the heating and melting zone of the device. All these advantages add up to greatly lower the cost of metal spraying operation.

WHAT WE CLAIM IS: 1. A method of metal spraying as hereinbefore defined which comprises utilizing as metal to be sprayed, a metal wire of polygonal cross-section.

2. A method according to claim 1 wherein said cross-section is a square.

3. A method according to claim 1 wherein said cross-section is a rectangle.

4. A method according to claim 3 wherein the length of the long sides of the rectangular cross-section is not more than 10 times that of the short sides.

5. A metal spraying device including a polygonal metal wire supply means adapted to supply a wire of polygonal cross-section to a heating station.

6. A device according to claim 5 wherein said supply means incorporates a pair of nip rolls.

7. A device according to claim 5 or claim 6 wherein the wire supply means is adapted to supply a wire of a square cross-section.

8. A device according to claim 5 or claim 6 wherein the wire supply means is adapted to supply a wire of rectangular cross-section.

9. A device according to claim 8 wherein the rectangular cross-section is such that the length of the long sides are not more than 10 times that of the short sides.

10. A device according to claim 5 substantially as hereinbefore set forth with reference to and as illustrated in Figures 1 and 2 or 3 of the accompanying drawings.

11. A method of metal spraying according to claim 1 and substantially as hereinbefore set forth with reference to and as illustrated in Figures 1 and 2 or 3 of the accompanying drawings. . - - -.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **. device and in view of the convenience of practical use, the length of the long side of the rectangular cross section is about ten times that of the short side. As is evident from the foregoing description, the invention permits the velocity of heat conduction to be increased and consequently the feeding speed of the metal wire to be heightened because of the angular cross sections given to the metal wires for the metal spraying. As a natural consequence, the amount of the molten droplets of metal to be sprayed per unit time can be increased. Moreover, the angular metal wires are more easily fabricated than the circular metal wires and they provide greater areas for contact with the feed rollers and, therefore, add to the smoothness with which they are forwarded to the heating and melting zone of the device. All these advantages add up to greatly lower the cost of metal spraying operation. WHAT WE CLAIM IS:

1. A method of metal spraying as hereinbefore defined which comprises utilizing as metal to be sprayed, a metal wire of polygonal cross-section.

2. A method according to claim 1 wherein said cross-section is a square.

3. A method according to claim 1 wherein said cross-section is a rectangle.

4. A method according to claim 3 wherein the length of the long sides of the rectangular cross-section is not more than 10 times that of the short sides.

5. A metal spraying device including a polygonal metal wire supply means adapted to supply a wire of polygonal cross-section to a heating station.

6. A device according to claim 5 wherein said supply means incorporates a pair of nip rolls.

7. A device according to claim 5 or claim 6 wherein the wire supply means is adapted to supply a wire of a square cross-section.

8. A device according to claim 5 or claim 6 wherein the wire supply means is adapted to supply a wire of rectangular cross-section.

9. A device according to claim 8 wherein the rectangular cross-section is such that the length of the long sides are not more than 10 times that of the short sides.

10. A device according to claim 5 substantially as hereinbefore set forth with reference to and as illustrated in Figures 1 and 2 or 3 of the accompanying drawings.

11. A method of metal spraying according to claim 1 and substantially as hereinbefore set forth with reference to and as illustrated in Figures 1 and 2 or 3 of the accompanying drawings. . - - -.