WO2002018063A1

WO2002018063A1 - Low temperature spray coatable enamel powder or paste, preparation process thereof and spray coating apparatus therefor

Info

Publication number: WO2002018063A1
Application number: PCT/US2000/020801
Authority: WO
Inventors: Qi-Xin Lin
Original assignee: AMEASIA INTERNATIONAL Inc
Current assignee: AMEASIA INTERNATIONAL Inc
Priority date: 2000-08-16
Filing date: 2000-08-25
Publication date: 2002-03-07
Anticipated expiration: 2003-02-25
Also published as: FR2813213A3; DE20014061U1

Abstract

The invention relates to a low temperature spray coatable powder and a spray coating apparatus therefor. The spray coatable powder comprises (in parts by weight) 45 silicon oxide; 17-23 boron trioxide; 10-12 lithium oxide; 8-26 titanium dioxide; 25-30 calcium fluoride, sodium fluorosilicate or antimony oxide; 5-7 cobalt oxide, nickel oxide or molybdenum oxide; 8-25 zinc oxide: 1-12 zirconium oxide, aluminum oxide, or magnesium oxide, 6-8 barium oxide; 1-3 copper oxide. The flame spray coating apparatus comprises a gun body (1), spray head (2), handle (4), powder hopper (5), powder advancing mechanism (6), flame collector (7), air supplying port (7-1), powder feeder (10), powder carrying gas control valve (32), main gas switching valve (33), air control valve (34), combustion gas control valve (35), hopper body (51), hopper lid (52), gas adjusting valve (53), pushing rod (61), pushing rod shell (62), decelerator (63), micrometer (64), motor switch (65), advancing mechanism shell (66), quick plugs (91, 92), powder flow control valve seat (181), powder-carrying gas control valve seat (182), air control valve seat (183), combustion gas control valve seat (184), main gas switching valve seat (185).

Description

Low Temperature Spray Coatable Enamel Powder or Paste, Preparation Process Thereof and Spray Coating Apparatus Therefor

BACKGROUND OF THE INVENTION

1. Field of the invention

The invention relates to a non-metallic inorganic material for spray-coating on surface of articles made of metal such as steel, to form an enamel or glass liner thereon, which exhibits corrosion proof, heat resistant and insulation properties, and to a flame powder spraying gun, particularly, to a special tool for heat spray-coating, spray-welding or spray-melting.

2. Description of the prior art

An enamel powder is also referred as porcelain powder or porcelain glaze powder, while an enamel paste is also referred as porcelain paste or porcelain glaze paste. Conventionally, protection of surface of steel products is effected by a variety of approaches. In case of painting, coating or spray-coating, disadvantages such as, for example, aging, easy peelable, and the like, are accompanied that results in a short service life of the protective coating. On the other hand, use of an electric spray coating means gives poor chemical stability and results in a short service life also. As for longer service life, it is preferred to adopt enameling or glass lining, comprising placing metallic works immerse coated in an enamel paste or spray coated with an enamel powder in an oven or baking chamber, where the metal reacts physicochemically with the inorganic material under an elevated temperature to combine into an integral body. However, there are deficiencies associated with these methods and products therefrom. One of such deficiencies is, when the product fractures in use, repairing with an enamel paste or powder will result in enamel fracturing, and consequently, repairing is permissible only with other protective materials such as paints. The second deficiency is derived from the fact that the enamel coating or glass lining on the product should be performed in an oven or baking chamber, and thereby the size and shape of the product will be restricted by the heating apparatus such as the oven or baking chamber. The third deficiency come from that an elevated temperature, up to 780°C or higher, is necessary ior calcinations, which will increase the consumption of fuel and tendb to distort the product, since, at a temperature higher than 721 °C , a structural transformation of the labeled iron, i.e., transformation of a iron into γ iron, will take place and, in this temperature region, the degree of transformation becomes larger with the increase of the temperature.

On the other hand, in the use of the conventional flame powder spray gun, spray-coating materials such as various self-melting alloy powder or metallic porcelain powder or partially pure oxides are fed in to the powder hopper of a spray coating gun. After igniting, adjusting the flame and preheating works with the spray gun, the powder delivering switch on the powder hopper is opened, under the action of the powder's own weight and the carrying of the gas flowing in the spraying cavity, the powder passes then into the powder feeding channel. Finally, after properly adjusting the powder flow control valve and the powder/gas control valve to deliver a satisfactory amount of the powder, the spray coating can be carried out. Requirements on the spray coating powder in the use of this spray gun are as follow: (a) the powder should be dry enough, (b) a small particle size is required to be ≥ 200 mesh, and (c) the crystal of the powder is desirably to be spheroid or cylindrical, otherwise the spray powder can not enter uniformly into the powder feeding channel, and the mix can not be sprayed homogeneously, and, as a result, a normal operation can not be performed. Therefore, the application of the spray gun of such structure is greatly restricted.

Accordingly, there are many disadvantage associated with the conventional means described above, and an improvement is needed thereto.

In view of disadvantages derived from the above-mentioned traditional producing and spray coating apparatuses for the enamel powder and enamel paste and on the purpose for improving the same, the inventor has carried out an intensive study, and as the result, provides an improved process for preparing a low temperature spray coatable enamel powder or paste and spray coating apparatus therefor.

SUMMARY OF THE INVENTION

Accordingly, one object of the invention is to provide a low temperature spray coatable enamel powder or paste, characterized in that it can be prepared in situ during its use, enameling or glass lining can be operated outside of an oven or baking chamber, and can be used for repairing the product coated therewith.

Another object of the invention is to provide a spray coating apparatus, comprising a flame powder spray gun, characterized in that the spray coating powder used therewith can have a dryness not so high and a larger particle size, as well as no particular requirement on the grain shape of the powder, and thereby, can be useful for a wider application range.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings disclose an illustrative embodiment of the present invention, which serves to exemplify the various advantages and objects hereof, and are as follows:

Figure 1 is a three-dimensional outlook exploded view of the flame powder spray gun according to the invention;

Figure 2 is a schematic structure view of Figure 1;

Figure 3 is a schematic view showing the transferring of the powder feeding mechanism in Figure 1 ;

Figure 4 is a schematic structural view showing the powder feeding gas control valve, the air control valve and the combustible gas control valve in Figure 1 and 2;

Figure 5 is a schematic structural view showing the main gas switching valve in Figure 1 and 2; and

Figure 6 is a schematic view showing the provision of a powder/gas feeder at the feeding port of the gun body.

Meanings of symbols for main representative elements:

1 Gun body

10 Powder feeder

11 Powder feeding channel

12 Gas feeding channel

13 Upper air feeding channel

14 Lower air feeding channel

15 Combustible gas feeding channel

16 Mixed gas channel

171 Powder flow control valve cavity 172 Mixed gas charging piston cavity

173 Spray head cavity

181 Powder flow control valve seat

182 Powder-carrying gas control valve seat

183 Air control valve seat

184 Combustible gas control valve seat

185 Main gas switching valve seat 19 Air charging channel

2 Spray head

21 Powder/gas channel

29 Connecting cap

31-1 Powder flow control valve

32 Powder-carrying gas control valve 32-1 Valve piston

33 Main gas switching valve 33-2 Upper valve piston

33-1 Lower valve piston

331 Steel ball

332 Spring

333 Steel piston cover

334 Pressing sheet

335 Spanner

34 Air control valve 34-1 Valve piston

35 Combustible gas control valve 35-1 Valve piston

36-3 Combustible gas inlet

36-2 Air inlet

36-1 Mixed gas inlet

37 Feeding line

37-1 Powder/gas channel

4 Handle

5 Powder hopper

51 Hopper body

52 Hopper lid

53 Gas adjusting valve

6 Powder advancing mechanism 61 Pushing rod 61-1 Helical recess

62 Pushing rod shell

62-2 Outlet

62-1 Inlet

63 Decelerator

63-9 Dynamic output shaft

63-2 Dynamic input shaft

63-1 Housing

64 Micromotor

64-1 Housing

65 Motor switch

66 Advancing machine socket

7 Flame collector

7-1 Air supplementing port

91 Quick plug

92 Quick plug

DETAILED DESCRIPTION OF THE PREFRRED EMBODIMENT

As described above, in one aspect, a low temperature spray coatable enamel powder or paste provided according to the invention comprises following components (parts by weight): 6-22 parts of sodium oxide, 8-26 parts of titanium dioxide as a flux; 25-30 parts of calcium fluoride, sodium fluorosilicate or antimony oxide as wetting agent, 5-7 parts of cobalt oxide, nickel oxide or molybdenum oxide as densifier, 8-25 parts of zinc oxide as melting modifier, 1-12 parts of zirconium oxide, aluminum oxide or magnesium oxide as melting modifier, 6-8 parts of barium oxide as melting modifier, and 1- 3 parts of cupper oxide as melting modifier.

In another aspect, the invention provides a process for preparing a low temperature spray coatable enamel powder or paste, comprising using quartz, borax, lithium carbonate, pure alkali, titania, fluorite, and barium or antimony molybdate as the raw material of silicon dioxide, boron trioxide, lithium oxide, sodium oxide, titanium dioxide, calcium fluoride, and molybdenum oxide, respectively; after converting the chemical composition of the enamel into a formulation based on the above-mentioned raw materials, weighing precisely each raw material and mixing thoroughly; charging the mixed raw material into a melting furnace, raising stepwisely the temperature to 1000-1050°C to yield a melt; pouring the melt in a cold water to quench into an enamel clinker; and finally, grinding the enamel clinker in a ball mill or gas flow crusher into a fine powder.

Optionally, the above-mentioned low temperature spray coatable enamel paste can comprise 1-3 parts by weight of coloring agent, such as, cobalt oxide, nickel oxide, iron oxide, cupper oxide, chromium oxide or mixture thereof.

The spray coating apparatus according to another aspect of the invention comprises a gun body and, provided thereon, a spray head, a powder flow control valve, a powder-carrying gas control valve, a main gas switch valve, an air control valve, a combustible gas control valve, a mixed gas piston, a charging line and a handle, and a hopper body provided with a powder hopper, the structure of said apparatus is characterized in that it comprises additionally a powder stuff advancing mechanism, the inlet of said mechanism is communicated with the outlet of said hopper body, and the outlet of said mechanism is communicated with the powder feeding channel provided in the gun body.

The above-mentioned powder stuff advancing mechanism comprises a pushing rod, a pushing rod shell, a decelerator, and a micromotor. Said pushing rod is a rod provided with a helical recess. The pushing rod shell is provided with an inlet and an outlet, wherein said inlet and outlet are also the inlet and the outlet of said powder stuff advancing mechanism, respectively; and said pushing rod shell is fixed on said gun body through the seat of the advancing mechanism. The shell of said decelerator is fixed on the shell of said pushing rod. The shell of said micromotor is fixed on the shell of said decelerator. The output end of the shaft of said micromotor is securely connected with the power input wheel of said decelerator. The power output shaft of said decelerator is securely connected with said pushing rod.

The hopper body of the above-mentioned powder hopper is a straight-through type hopper body, provided on the upper portion of its wall with a gas-adjusting valve.

Further, the flame powder spray gun according to the invention is provided on the gun body with a flame collector that slips on the outside of said spray head and is provided with a plurality of air supplementing port near said spray head.

The above-mentioned flame collector has a ratio of the inner diameter to the equivalent length of 1 :3-1 :4.5, and preferably, said ratio of the inner diameter to the equivalent length of the flame collector is in the range of 1 :3.5 - 1 :4.

In a preferred embodiment, the above-mentioned flame collector has an equivalent length of 120 - 130 mm, and a inner diameter of 30-40 mm.

The invention will be illustrated in more detailed by means of the following non-limiting examples.

Example 1 : low temperature spray coatable enamel powder

The composition of the low temperature spray coatable enamel powder comprises, by weight, 45 parts of silicon dioxide as the base, 17 parts of boron trioxide as the base and flux, 12 parts of lithium oxide as a flux, 18 parts of sodium oxide as a flux, 20 parts of titanium dioxide as a flux; 30 parts of calcium fluoride, sodium fluorosilicate or antimony oxide as wetting agent, 5 parts of cobalt oxide, nickel oxide or molybdenum oxide as densifier, 10 parts of zinc oxide as melting modifier, 1.5 parts of zirconium oxide, aluminum oxide or magnesium oxide as melting modifier, and 1 part of chromium oxide as coloring agent.

By using quartz, borax, lithium carbonate, pure alkali, titania, fluorite, barium or antimony molybdate, zinc white, alumina and barium carbonate as the raw material of silicon dioxide, boron trioxide, lithium oxide, sodium oxide, titanium dioxide, calcium fluoride, molybdenum oxide, zinc oxide, aluminum oxide and barium oxide, respectively; charging the mixed raw material into a melting furnace, raising stepwisely the temperature to 1050°C to yield a melt; pouring the melt in cold water to quench it into an enamel clinker; and finally, grinding the enamel clinker in a ball mill into a fine powder of a particle size passing a sieve of 400 mesh, to yield a low temperature enamel powder.

The calcining temperature of the thus obtained enamel powder is 640°C , and the thermal expansion coefficient of its porcelain layer is essentially as same as that of Q235 steel, so that the low temperature enamel powder produced above can be flame melted by a flame powder spray gun or a surface sintering machine, and then can be spray coated on the surface of Q235 steel product or structure to form a straw green porcelain layer. This porcelain layer has excellent properties such as corrosion proof, heat resistance, insulation and the like, that it can resist to attack by air, sea water, saline, a variety of salt compound, and various bacteria, and that it is very stable in an environment of pH 3-12, so that it can have a long service life of up to several tens years.

Example 2 : low temperature spray coatable enamel paste

The composition of the low temperature spray coatable enamel paste comprises, by weight, 45 parts of silicon dioxide as the base, 17 parts of boron trioxide as the base and flux, 12 parts of lithium oxide as a flux, 18 parts of sodium oxide as a flux, 20 parts of titanium dioxide as a flux; 30 parts of calcium fluoride, sodium fluorosilicate or antimony oxide as wetting agent, 5 parts of cobalt oxide, nickel oxide or molybdenum oxide as densifier, 10 parts of zinc oxide as melting modifier, 1.5 parts of zirconium oxide, aluminum oxide or magnesium oxide as melting modifier, 6 parts of barium oxide as melting modifier, 1 part of chromium oxide as coloring agent, 3 parts of clay, 5 parts of liquid paraffin, and. 250 parts of water.

By using quartz, borax, lithium carbonate, pure alkali, titania, fluorite, barium or antimony molybdate, zinc white, alumina and barium carbonate as the raw material of silicon dioxide, boron trioxide, lithium oxide, sodium oxide, titanium dioxide, calcium fluoride, molybdenum oxide, zinc oxide, aluminum oxide and barium oxide, respectively; after converting the chemical composition of the enamel into a formulation based on the above-mentioned raw materials, weighing precisely each raw material and mixing thoroughly; charging the mixed raw material into a melting furnace, charging the mixed raw material into a melting furnace, raising stepwisely the temperature to 1050°C to yield a melt; pouring the melt in cold water to quench it into an enamel clinker; and finally, wet grinding the enamel clinker together with the clay and liquid in a ball mill to yield a low temperature enamel paste.

The calcining temperature of the thus obtained enamel paste is 640 °C , and the thermal expansion coefficient of its porcelain layer is essentially as same as that of Q235 steel. In use of the low temperature enamel paste produced above, a steel work can be immersed in or can be coated with the paste. After drying the coating, in case of a larger work, a surface-sintering machine can be used to process the coating, or in case of a small work, it can be baked in an oven, to form a straw greenish porcelain layer on the steel work.

The spray coating apparatus used can be referred to example A and B below.

Example A

Referring to Figure 1 and 2, the spray coating apparatus comprises a gun body 1 made of copper or cast iron, a powder feeder 10, being one part of said gun body 1 and provided with a powder feeding channel 11 ; said gun body 1 being provided further a protecting gas feeding channel 12, an upper air feeding channel 13, a lower air feeding channel 14, a combustible gas feeding channel 15, a mixed gas feeding channel 16, a charging line, a powder flow control valve 171, a mixed gas piston cavity 172, a spray head cavity 173, a powder flow control valve seat 181, a powder-carrying gas control valve seat 182, an air control valve seat 183, a combustible gas control valve seat 184 and a main gas switch valve seat 185. the powder flow control valve cavity 171 is communicated with the powder feeding channel 11 , the charging line, and the protecting gas feeding channel 12, respectively. A valve cavity that fits with the valve piston of the powder-carrying gas control valve 32 is provided on the gas outlet of the upper air feeding channel 13 in a manner that the upper air feeding channel 13 is communicated with the powder flow control valve cavity 171 through the valve cavity. A three-way valve piston cavity that fits with the upper valve piston 33-1 is provided on the gas inlet of the upper air feeding channel 13 and the lower air feeding channel 14 in a manner that the gas inlet of the upper air feeding channel 13, the gas inlet of the lower air feeding channel 14 and the gas outlet of the air feeding channel 19 are communicated through the valve piston cavity. The mixed gas piston cavity 172 is communicated with the lower air-feeding channel 14, the combustible gas feeding channel 15 and the mixed gas channel 16, respectively. A valve piston cavity that fits with the lower valve cavity 33-2 of the main gas switching valve 33 is provided on the combustible gas feeding channel 15.

The spray head 2 is fixed in the spray head cavity 173 through a connecting cap 29. The charging line 37 is provided in the charging line cavity of the gun body 1. The powder/gas channel 21 of the spray head 2 is communicated with the powder/gas channel 37-1 of the charging line 37.The powder flow control valve 31 is provided in the powder flow control valve cavity 171 of the gun body 1 in a manner that the gas outlet of it powder-carrying gas channel 31-1 is communicated with the inlet of the powder/gas channel 37-1 of the charging line 37, and the powder outlet of the powder feeding channel 11 is communicated with the gas outlet of the powder-carrying gas channel 31-1 of the powder flow control valve 31 via the powder flow control valve cavity 171. the powder-carrying gas control valve 32 is provided on the powder-carrying gas control valve seat 182 of the gun body 1 in a manner that its valve piston 32-1 fits with the piston cavity provided on the gas outlet of upper air feeding channel 13, and the upper air feeding channel 13 is communicated with the gas inlet of the powder-carrying gas channel 31-1 of the powder flow control valve 31 through said valve piston cavity and the powder flow control valve cavity 171. The gas outlet of the protecting gas feeding channel 12 is communicated with the gas inlet of the powder-carrying gas channel 31-1 of the powder flow control valve 31 through the powder flow control valve cavity 171. The main gas switching valve 33 is provided on the main gas switching valve seat 185 of the gn body 1 in a manner that its upper valve piston 33-1 fits with the three- way valve piston cavity of the upper air feeding channel 13 and its lower valve piston 33-2 fits with the valve piston cavity of combustible gas feeding channel 15. A mixed gas piston 36 is provided in a mixed gas piston cavity 172 of the gun body 1 in a manner that the gas outlet of its mixed gas channel 36-1 is communicated with the mixed gas channel 16 of the gun body 1, its air inlet 36- 2 is communicated with the lower air feeding channel 14 and its combustible gas inlet 36-3 is communicated with the gas outlet of the combustible gas channel 15 through the mixed gas piston cavity 172. The air control valve 34 is provided on the air control valve seat 183 of the gun body 1 in a manner that its piston 34-1 fits with the valve piston cavity provided at the gas outlet of the lower air-feeding channel 14. The combustible gas control valve 35 is provided on the combustible gas control valve seat 184 of the gun body 1 in a manner that its valve piston 35-1 fits with the valve piston cavity at the gas outlet of the combustible gas-feeding channel 15. The handle 4 is fixed on the handle seat of the gun body 1. A plurality of air supplementing port 7-1 is provided on the flame collector 7 near the spray head. The flame collector 7 has an equivalent length (from the forward end of the spray head 2 to the outlet of the flame collector) of 125 mm, and an inner diameter of 35 mm. The powder advancing mechanism 6 is consisted of a pushing rod 61, a pushing rod shell 62, a decelerator 63, a micromotor 64 and a motor switch 65. The pushing rod 61 is a rod with a helical recess 61-1 and is provided in the pushing rod shell 62. The pushing rod shell 62 is provided with an inlet 62-1 and an outlet 62-2 in a manner that the inlet 62-1 is the outlet of the powder advancing mechanism 6 and the outlet 62-2 is the inlet of the powder advancing mechanism 6. The pushing rod shell 62 is fixed on the advancing mechanism seat 66 that is in turn fixed on the gun body 1. The shell 63-1 of the decelerator 63 is fixed on the pushing rod shell 62. The shell 64-1 of the micromotor 64 is fixed on the decelerator shell 63-1. The output end of the motor shaft of the micromotor 64 is securely connected with the power input end 63-2 of the decelerator 63, while the power output shaft 63-9 is securely connected with the pushing rod 61. Figure 3 depicts the power transferring relationship within the decelerator 63.The motor switch 65 is fixed on the advancing mechanism seat 66. The connection ends of the motor switch 65 and the micromotor 64 as well as the power supply socket are connected with one another according to the electric principle.

The hopper body 51 of the powder hopper 5 is a straight type hopper. The hopper body 51 is welded and fixed on the pushing rod shell 62. A gas adjusting valve 53 is provided on the hopper wall of the hopper body 51. The inlet of the powder stuff advancing mechanism 6 is communicated with the outlet of the hopper body 51, while the outlet of the powder stuff advancing mechanism 6 is communicated with the inlet of the powder-feeding channel 11 of the gun body 1.

Referring to Figure 4, all of the powder-carrying gas control valve 32, the air control valve 34 and the combustible gas control valve 35 have a structure of needle valve. As valve pistons 32-1, 34-1 and 35-1 of corresponding needle valves move downwardly under the action of rotation buttons, corresponding vents will become narrow and straight till completely blocked. On the other hand, as valve piston 32-1, 34-1 and 35-1 of corresponding needle valves move upwardly under the action of rotation buttons, corresponding vents will be opened till the greatest extent.

Referring to Figure 5, the upper and the lower pistons of the main gas switch valve 33 have the same structure as a spring-and-ball type valve piston. A steel ball 331 protrudes upwardly out of the steel piston cover 333 under the action of the spring 332. The protrusion of the pressing sheet 334 enters deeply in the recess cavity on the lower surface of the spanner 335 and moves horizontally with the spanner 335. As the pressing sheet 334 is at left position under the action of the spanner 335, the steel ball 331 is in the recess cavity at the lower surface of the protrusion of the pressing sheet 334, that makes upper and lower air feeding channels as well as the combustible gas feeding channel being in a state of communication with one another. On the other hand, as the pressing sheet 334 is at right position under the action of the spanner 335, the steel ball 331 is pressed by the pressing sheet, that blocks upper and lower air feeding channels as well as the combustible gas-feeding channel, and thereby achieves the purpose of controlling.

Referring to Figure 1 again, when the spray gun described above is used, the quick plugs 91, 92 are fixed on gas inlets of the air feeding channel 19 and the combustible gas feeding channel 15, respectively, through their connecting caps. The other end of the quick plug 91 is connected to a compressed air supplying line, while the other end of the quick plug 92 is connected to a liquefied petroleum oil supplying line through a reducing valve. The powder is loaded in the hopper body 51 of the powder hopper 5, the hopper lid 52 is closed, and gas adjusting valve 53 on the hopper body 51 is communicated with the pressurized air so that the gas adjusting valve 53 presents in a slightly opened state and thereby applies a slight pressure on the powder stuff in the hopper body 51. Then, the main gas switch valve 33 and the combustible gas control valve 35 are opened, and the flame collector 7 is ignited with an electric igniter. Next, the air control valve 34 is opened, and the air control valve 34 and the combustible gas control valve 35 are adjusted to optimize the flame. Then, the powder- carrying gas control valve 32 is opened and adjusted such that the emerging flame has a desired flow velocity. The motor switch 65 is turned on to drive the powder stuff advancing mechanism by the pushing rod 61 and thereby feeds the powder stuff into the powder stuff channel 11 in the gun body 1, pushes it into the powder gas channel 37-1 of the feeding line 37, ejects out of the spray head 2 under the pushing of the pressurized air and being softened or melted in the flame collector 7, followed by spraying over the work together with the gas flow. Wherein, the air control valve 37 and the combustible gas control valve 35 are adjusted accordingly such that a desired softening or melting of the powder in the flame can be achieved.

When powder in the hopper 51 is completely sprayed, all valves are closed, the powder stuff is re-load and the procedure described above is repeated.

In the above practice, the powder flow control valve 31 is opened to the most, and the rotation speed of the micromotor can be adjusted by adjusting the voltage of the power supply. When the powder sprayed is a superfine particle of a size of ≥ 180 mesh, the control of the powder flow should be pei formed by combining the adjustment of the rotational speed of the micromotor and the extent of the opening of the flow control valve 31.

Example B

Referring to Figure 6, the spray coating apparatus of this example is essentially identical to that of Example A except that the powder feeder 10 is a component that has a upper cylindrical portion of a less diameter, a lower cylindrical portion of a larger diameter, and a powder feeding channel 11 provided therein, wherein the position of said powder feeding channel 11 is the same as the powder feeding channel 11 in the gun body 1 of Example A.

In other embodiment of the invention, the combustible gas inlet can be communicated with the supplying lines of acetylene gas, propane gas and coal gas through reducing valves, whereas the air inlet can be communicated with the corresponding supplying lines of oxygen or pressurized air.

The low temperature spray coatable enamel powder or paste and the spray coating apparatus therefore provided according to the invention have following advantages:

1. When they are applied on a steel work or its constitutive component, since the calcinations temperature is 600-700°C , and the product is not liable to distort, the quality of the product can be improved. 2. Since the calcining temperature is low, after forming a porcelain coating on the surface of the steel, no temperature reducing in an oven or baking chamber like that necessary for other enamel products should be carried out and instead, can be cooled directly in air. Accordingly, enameling or glass lining can be performed straightly in an oven or baking chamber, or accomplished in the field. For example, the spray coatable enamel powder can be spray applied on the surface of a steel article after being flame melted by a flame powder spray gun, or can be spray coated on the surface of steel by a surface sintering mechanical spray coating technique. 3. Since the expansion of porcelain is higher than that of steel under high temperature, but less than that of steel at low temperature. In a technique of the prior art, when a finished product is removed out of the furnace to be cooled, at the beginning, the shrinkage of the enamel coating is higher than that of the iron, but, at a temperature of 400-500°C, is less than that of the iron. Therefore, in the selection of a formulation of an enamel powder according to the conventional experience, it is desirable for its thermal expansion coefficient to be 60-80% of that of the iron. On the contrary, because the calcining temperature used in the process according to the invention tends to be lower, in the formulation of the low temperature spray coatable enamel powder or paste according to the invention, the thermal expansion coefficient of the finished enamel coating can be set to be as +95-105%. As the result, if the finished product is fractured in use, due to the same or similar thermal expansion coefficient therebetween, it is convenient to repair it with the low temperature spray coatable enamel powder or paste according to the invention. Consequently, the application range of the invention is further extended. 4. Since the spray-coating gun according to the invention is provided with a powder stuff advancing mechanism, the powder stuff can be charged uniformly into the powder-feeding channel of the gun body and spray coated homogeneously. Further, in the spray-coating practice of the spray- coating gun according to the invention, no high dryness is required to the powder being spray-coated, and instead, it can be used as long as it is a powder and can have larger particle size. Moreover, no special requirement to the grain shape of the powder is set so that, for example, an effect of uniformly feeding and spray coating can be achieved also for a powder having a polygonal shape. 5. By providing a gas control valve on the wall of the hopper body, during powder spraying, a downward pressure on the powder stuff can be generated and maintained through just opening the valve slightly, and the uniformity of powder feeding can be assured further.

6. By providing a flame collector on the spray head, a variety of combustible gas, such as, for example, liquefied gas, acetylene gas, propane gas and coal gas, can be selected and used optimally in the spray coating gun according to the invention depending to the melting point of the powder stuff. 7. Owing to the simple structure of the spray coating gun according to the invention, its maintenance is convenient and its operation is easy.

Many changes and modifications in the above described embodiment of the invention can, of course, be carried out without departing from the scope thereof. Accordingly, to promote the progress in science and the useful arts, the invention is disclosed and is intended to be limited only by the scope of the appended claims.

Claims

What is claimed is:

1. A low temperature spray coatable enamel powder, characterized in that it comprises following components (parts by weight): 45 parts of silicon dioxide as the base, 17-23 parts of boron trioxide as the base and flux, 10- 12 parts of lithium oxide as a flux, 8-26 parts of titanium dioxide as a flux; 25-30 parts of calcium fluoride, sodium fluorosilicate or antimony oxide as wetting agent, 5-7 parts of cobalt oxide, nickel oxide or molybdenum oxide as densifier, 8-25 parts of zinc oxide as melting modifier, 1-12 parts of zirconium oxide, aluminum oxide or magnesium oxide as melting modifier, 6-8 parts of barium oxide as melting modifier, and 1-3 parts of cupper oxide as melting modifier.

2. A low temperature spray coatable enamel powder as recited in claim 1 , characterized in that it is obtainable by using quartz, borax, lithium carbonate, pure alkali, titania, fluorite, barium or antimony molybdate, zinc white, alumina and barium carbonate as the raw material of silicon dioxide, boron trioxide, lithium oxide, sodium oxide, titanium dioxide, calcium fluoride, molybdenum oxide, zinc oxide, aluminum oxide and barium oxide, respectively; after converting the chemical composition of the enamel powder into a formulation based on the above-mentioned raw materials, weighing precisely each raw material and mixing thoroughly; charging the mixed raw material into a melting furnace, raising stepwisely the temperature to 1000-1050°C to yield a melt; pouring the melt in cold water to quench it into an enamel clinker; and finally, grinding the enamel clinker in a ball mill or gas flow crusher into a fine powder.

3. A low temperature spray coatable enamel powder as recited in claim 1, comprises further 1-3 parts by weight of a coloring agent.

4. A low temperature spray coatable enamel powder as recited in claim 3, wherein said coloring agent is cobalt oxide, nickel oxide, iron oxide, copper oxide, chromium oxide or mixture thereof.

5. A low temperature spray coatable enamel paste, characterized in that it comprises following components (parts by weight): 45 parts of silicon dioxide as the base, 17-23 parts of boron trioxide as the base and flux, 10- 12 parts of lithium oxide as a flux, 8-26 parts of titanium dioxide as a flux; 25-30 parts of calcium fluoride, sodium fluorosilicate or antimony oxide as wetting agent, 5-7 parts of cobalt oxide, nickel oxide or molybdenum oxide as densifier, 8-25 parts of zinc oxide as melting modifier, 1-12 parts of zirconium oxide, aluminum oxide or magnesium oxide as melting modifier, 6-8 parts of barium oxide as melting modifier, 1-3 parts of cupper oxide as melting modifier, 3-7 parts of clay and suitable amount of water.

6. A low temperature spray coatable enamel paste as recited in claim 5, characterized in that it is obtainable by using quartz, borax, lithium carbonate, pure alkali, titania, fluorite, barium or antimony molybdate, zinc white, alumina and barium carbonate as the raw material of silicon dioxide, boron trioxide, lithium oxide, sodium oxide, titanium dioxide, calcium fluoride, molybdenum oxide, zinc oxide, aluminum oxide and barium oxide, respectively; after converting the chemical composition of the enamel paste into a formulation based on the above-mentioned raw materials, weighing precisely each raw material and mixing thoroughly; charging the mixed raw material into a melting furnace, raising stepwisely the temperature to 1000-

1050°C to yield a melt; pouring the melt in cold water to quench it into an enamel clinker; and finally, wet grinding the enamel clinker together with the clay and water in a ball mill to yield a low temperature spray coatable enamel paste.

7. A low temperature spray coatable enamel paste as recited in claim 5, comprises further 1-3 parts by weight of a coloring agent.

8. A low temperature spray coatable enamel paste as recited in claim 5, wherein said coloring agent is cobalt oxide, nickel oxide, iron oxide, copper oxide, chromium oxide or mixture thereof.

9. A spray coating apparatus, comprises a gun body and, provided thereon, a spray head, a powder flow control valve, a powder-carrying gas control valve, a main gas switch valve, an air control valve, a combustible gas control valve, a mixed gas piston, a charging line and a handle, and a hopper body provided with a powder hopper, the structure of said apparatus is characterized in that it comprises further a powder stuff advancing mechanism, the inlet of said mechanism is communicated with the outlet of said hopper body, and the outlet of said mechanism is communicated with the powder feeding channel provided in the gun body.

10. A spray coating apparatus as recited in claim 9, wherein said powder stuff advancing mechanism comprises a pushing rod, a pushing rod shell, a decelerator, and a micromotor; wherein said pushing rod is a rod provided with a helical recess; wherein said pushing rod shell is provided with an inlet and an outlet, wherein said inlet and outlet are also the inlet and the outlet of said powder stuff advancing mechanism, respectively; and said pushing rod shell is fixed on said gun body through the seat of the advancing mechanism; wherein the shell of said decelerator is fixed on the shell of said pushing rod; wherein said shell of said micromotor is fixed on the shell of said decelerator; and wherein the output end of the shaft of said micromotor is securely connected with the power input wheel of said decelerator, and the power output shaft of said decelerator is securely connected with said pushing rod.

11. A spray coating apparatus as recited in claim 9, wherein said hopper body of said powder hopper is a straight hopper body and a plurality of gas adjusting valve are provided on the upper portion of the wall of said hopper body.

12. A spray coating apparatus as recited in claim 9, 10 or 11, comprises further a flame collector fixed on said gun body, wherein said flame collector is slipped on aid spray head and is provided thereon with a plurality of air supplementing ports near said spray head.

13. A spray coating apparatus as recited in claim 12, wherein said flame collector has a ratio of inner diameter to its equivalent length in a range of

1 : 3 to 1 : 4.5.

14. A spray coating apparatus as recited in claim 13, wherein said flame collector has a ratio of inner diameter to its equivalent length in a range of

1 : 3.5 to 1 : 4.

15. A spray coating apparatus as recited in claim 12, wherein said flame collector has a equivalent length of 120-130 mm and an inner diameter of 30-40 mm.