Coating material spray gun having adjustable flow rate

Abstract

 In a spray gun of the present invention, a coating material circulation flow passage (7) is formed in a spray gun body (1) so as to introduce a coating material from a pump into an inside of the spray gun body (1) and return the coating material to the pump. A branch flow passage (12) is branched off from the coating material circulation flow passage (7) and connected to a coating material chamber (6) communicated with a coating nozzle (2). Further, a flow rate adjusting valve assembly (15,29) is provided in the branch flow passage (12).

Description

[0001] The present invention relates to a coating material spray gun. Specifically, the present invention relates to a spray gun having a circulation passage for enabling continuous flow of a coating material, wherein a flow rate adjusting valve is provided in a branch passage which permits communication between the circulation passage and a coating material chamber connected to a coating nozzle.

[0002] In spray coating using a spray gun, when use is made of a coating material containing a precipitable pigment or a thixotropic coating material such as an aqueous coating material, it is required to maintain constant circulation of the coating material between the spray gun and a pump, so as to avoid precipitation of the pigment or a change in viscosity of the thixotropic coating material. Therefore, a circulation type spray gun such as that shown in Fig. 6 has been conventionally used. In this spray gun, a Y-shaped joint 67 is connected to a coating material supply portion of a spray gun body 61. The Y-shaped joint 67 provides a circulation passage of a coating material, which flows from an inlet 67a to an outlet 67b of the Y-shaped joint. A communication passage is branched off from the circulation passage and extends to a flow passage formed within the spray gun. The coating material in the Y-shaped joint 67 flows through the communication passage into the spray gun, and is discharged from a coating nozzle.

[0003] To effect circulation of the coating material, it is required to use a return hose for returning the coating material to the pump, which has substantially the same length as a supply hose for supplying the coating material from the pump into the Y-shaped joint. Due to the effect of the pressure required for circulation at a desired flow rate, the pressure of the coating material within the circulation type spray gun is made as high as, for example, 0.3 MPa, as compared to the pressure (for example, 0.1 MPa) of the coating material within a non-circulation type spray gun. Generally, when the coating material has a low viscosity or a thin coating film is desired to be formed, the degree of opening of a needle valve relative to the coating nozzle is adjusted so as to reduce the rate of discharge of the coating material (hereinafter, frequently referred to simply as "the rate of discharge"). In the above-mentioned circulation type spray gun, the degree of opening of the needle valve must be lower than that in the non-circulation type spray gun due to the high pressure of the coating material within the circulation type spray gun.

[0004] Generally, in a spray gun, the diameter of an opening of the coating nozzle is 0.8 mm to 1.3 mm and the rate of discharge is about 150 ml to 200 ml/min. However, the rate of discharge can be lowered by a great extent, depending on the type of workpiece to be coated with the coating material. For example, in applications relating to portable phones and notebook computers the production of which has been increasing in recent years, the coating material applied on a casing made of an alloy of magnesium is costly. Therefore, a distance between the coating nozzle and the casing is set to a value as small as about 70 mm to 130 mm and the rate of discharge is set to a value as small as about 50 ml/min., to thereby increase coating efficiency.

[0005] In this case, as the degree of opening of the needle valve relative to the coating nozzle is made lower so as to decrease the rate of discharge, the effect of non-uniformity in the gap between the needle valve and the coating nozzle becomes serious, which non-uniformity is generated because the coating nozzle and the needle valve are not in a precisely coaxial relationship. That is, due to the non-uniformity in the gap between the needle valve and the coating nozzle, the rate of ejection of the coating material becomes non-uniform, leading to irregularities in configuration and shade of a pattern of the coating material ejected onto the workpiece. As a countermeasure, consideration has been given to reducing the diameter of the opening of the coating nozzle to a value as small as, for example, 0.5 mm, while making the needle valve thinner, thus increasing the gap between the needle valve and the coating nozzle, i.e., the degree of opening of the needle valve. In this arrangement, however, it is impossible to increase the rate of discharge to a desired level which varies depending on the site for coating or the type of workpiece.

[0006] As a countermeasure, Japanese Utility Model Registration No. 2599940 discloses an arrangement such as that shown in Fig. 7. In this arrangement, a U-shaped joint 77 containing a throttle valve 74 is connected to a coating material supply portion of a spray gun body 71. By this arrangement, a pressure drop is effected by the throttle valve 74, while circulation of a coating material through the U-shaped joint 77 is secured, thus making it possible to set the pressure of the coating material within the spray gun to a level equal to the pressure of the coating material within the non-circulation type spray gun.

[0007] However, in the arrangement of Fig. 7, it is necessary to provide a connecting mechanism between the U-shaped joint 77 and the spray gun body 71, so that a non-circulation region has an extremely large length and the connecting mechanism and the U-shaped joint 77 exist as a rigid object protruding outside the spray gun body 71. When this arrangement is applied to a hand spray gun, the hand spray gun has poor operability. When the arrangement is applied to an automatic spray gun, the assembly of the spray gun to an automatic coating apparatus becomes difficult due to interference of the joint. Further, when it is desired to change the color of a coating, the coating material must be rapidly expelled from the spray gun and sufficient cleaning liquid must be passed through the spray gun. However, in the above-mentioned arrangement, a cumbersome operation is necessary for effecting full opening of the throttle valve 74 and re-setting the degree of opening of the throttle valve 74.

[0008] In view of the above, the present invention has been made. It is an object of the present invention to provide a spray gun which can be easily adjusted for conducting discharge of a coating material at a low rate, while securing circulation of the coating material.

[0009] According to the present invention, there is provided a spray gun comprising: a spray gun body; a coating material circulation flow passage formed in the spray gun body so as to introduce a coating material from a pump into an inside of the spray gun body and return the coating material to the pump; a branch flow passage branched off from the coating material circulation flow passage and connected to a coating material chamber communicated with a coating nozzle; and a flow rate adjusting valve assembly provided in the branch flow passage.

[0010] In the above-mentioned spray gun, the flow rate adjusting valve assembly may comprise a valve seat provided in the branch flow passage and a throttle valve provided in a coaxial relationship with the valve seat. A degree of opening of the throttle valve relative to the valve seat may be adjusted by operating an operating portion of the throttle valve outside the spray gun body.

[0011] The throttle valve may be provided so as to intersect the coating material circulation flow passage.

[0012] In the spray gun of the present invention, a driving device may be connected to the operating portion of the throttle valve so as to enable full opening of the throttle valve in response to a signal applied to the driving device.

[0013] The foregoing and other objects, features and advantages of the present invention will be apparent from the following detailed description and appended claims taken in connection with the accompanying drawings.

[0014] Fig. 1A is a front view of a head portion of a spray gun according to a first embodiment of the present invention.

[0015] Fig. 1B is a cross-sectional view of the head portion, taken along the line A-A of Fig. 1A.

[0016] Fig. 2A shows a cross-sectional detail of the head portion of the spray gun, taken along the line B-B of Fig. 1B.

[0017] Fig. 2B is a cross-sectional detail of that portion of a modified example of the spray gun corresponding to the portion shown in Fig. 2A.

[0018] Fig. 2C is a cross-sectional detail of that portion of another modified example of the spray gun corresponding to the portion shown in Fig. 2A.

[0019] Fig. 3A is a front view of a spray gun according to a second embodiment of the present invention, which is an automatic spray gun having a circulation flow passage and a valve provided therein.

[0020] Fig. 3B is a cross-sectional view of the spray gun, taken along the line A-A of Fig. 3A.

[0021] Fig. 4A is a cross-sectional view of the spray gun, taken along the line B-B of Fig. 3B, wherein a throttle valve is in a normal position.

[0022] Fig. 4B is a cross-sectional view of the spray gun, taken along the line B-B of Fig. 3B, wherein the throttle valve is in a full-open position.

[0023] Fig. 5 is a cross-sectional view of the spray gun according to the second embodiment of the present invention, in which a part of a spray gun body is formed by a manifold base.

[0024] Fig. 6 shows a conventional spray gun having a joint portion provided by a Y-shaped circulation joint attached to a body of the gun.

[0025] Fig. 7 shows a conventional spray gun having a joint portion provided by a U-shaped circulation joint attached to the body of the gun, the U-shaped joint having a throttle valve provided therein.

[0026] A spray gun according to a first embodiment of the present invention is described below. The spray gun in this embodiment comprises a spray gun body 1 with a circulation flow passage and a flow rate adjusting valve assembly being provided therein.

[0027] Fig. 1A is a front view of a head portion of the spray gun which may be a hand spray gun or an automatic spray gun. Fig. 1B is a cross-sectional view of the head portion, taken along the line A-A of Fig. 1A. Fig. 2A shows a cross-sectional detail of the head portion of the spray gun, taken along the line B-B of Fig. 1B. Figs. 2B and 2C show modified examples of the spray gun, each showing a cross-sectional detail of that portion of the modified example corresponding to the portion shown in Fig. 2A.

[0028] Referring to Fig. 1B, a coating nozzle 2 is threadably engaged with the inside of a distal end portion of the gun body 1. At an outer periphery of the nozzle 2, an air cap 3 is fixed to the gun body 1 in a coaxial relationship, by means of a cap nut 4. A coating material chamber 6 having substantially the same diameter as a bore 2a of the nozzle 2 is formed so as to communicate with the bore 2a. A circulation flow passage 7 (see Fig. 2A) is formed in proximity to the coating material chamber 6. Opposite end portions of the circulation flow passage 7 provide a coating material inlet 8 and a coating material outlet 9 on an outer surface of the gun body 1. A branch flow passage 12 branched off from the circulation flow passage 7 is connected to the coating material chamber 6.

[0029] Fig. 2A shows an example in which the circulation flow passage 7 is formed so as to horizontally extend in proximity to a lower portion of the coating material chamber 6. Figs. 2B and 2C show modifications of the example of Fig. 2A. That is, Figs. 2B and 2C are cross-sectional views of the modified spray guns, taken along the lines corresponding to the line B-B of Fig. 1B. In Fig. 2B, the circulation flow passage 7 comprises a flow passage 7a and a flow passage 7b arranged in an inverted V-shaped form. The coating material inlet 8 and the coating material outlet 9 are formed by respective outer end portions of the flow passages 7a and 7b. In Fig. 2C, the circulation flow passage 7 comprises the flow passages 7a and 7b extending perpendicularly to a central portion of the circulation flow passage 7, and the coating material inlet 8 and the coating material outlet 9 are formed by respective outer end portions of the flow passages 7a and 7b. Various modifications, including those described above, are possible with respect to positioning of the circulation flow passage 7, the coating material inlet 8 and the coating material outlet 9 in the gun body 1.

[0030] The configuration of the branch flow passage 12 is not limited to that shown in Figs. 1B to 2C, although it is preferred that the circulation flow passage 7 and the coating material chamber 6 be connected by a flow passage as short as possible and as simple as possible. In the first embodiment, there is no sufficiently large space around the coating material chamber 6. However, by providing a throttle valve 14 so as to intersect the circulation flow passage 7, formation of the circulation flow passage 7 and disposition of a flow rate adjusting valve assembly 15 (described later) can be easily conducted within a small space around the coating material chamber 6.

[0031] Coating material hoses 10 and 11 can be connected to the gun body 1 by various methods. For example, a joint for connection with the coating material hoses 10 and 11 may be formed by forming threads at the coating material inlet 8 and the coating material outlet 9. Alternatively, rigid pipes connected to the coating material hoses 10 and 11 may be press-fitted into the coating material inlet 8 and the coating material outlet 9. The coating material hose 10 extending from a pump (not shown) is connected to the coating material inlet 8 for supply of the coating material and the coating material is returned to a coating material container (not shown) through the coating material hose 11 connected to the coating material outlet 9. Thus, the coating material can be circulated through the circulation flow passage 7 in a sufficiently large volume.

[0032] The flow rate adjusting valve assembly 15 comprises a valve seat 13 provided in the branch flow passage 12 which permits communication between the circulation flow passage 7 and the coating material chamber 6 and a throttle valve 14 provided in a coaxial relationship to the valve seat 13. The throttle valve 14 comprises: a throttle valve working portion 14a in a needle-like form which includes a tapered distal end portion of the throttle valve 14; a valve shaft 14b threadably engaged with the gun body 1 on a side opposite to the branch flow passage 12 relative to the circulation flow passage 7; and a knob-like operating portion 14c at an outer end portion of the valve shaft 14b. In order to adjust the degree of opening of the throttle valve 14 relative to the valve seat 13, the throttle valve 14 is reciprocally moved by rotating the operating portion 14c. Alternatively, an open area of the branch flow passage 12 may be changed by reciprocally moving a valve body disposed perpendicularly to the branch flow passage 12 or rotating a valve body having a bore, which is capable of rotating about the axis perpendicular to the branch flow passage 12.

[0033] Consequently, even when the pressure of the coating material within the circulation flow passage 7 is high due to the need to secure a sufficient amount of circulation for a precipitable coating material or an aqueous coating material, the pressure of the coating material within the coating material chamber 6 can be adjusted by adjusting the degree of opening of the throttle valve 14 relative to the valve seat 13, to thereby adjust the rate of spray discharge of the coating material to a small value. Therefore, it is unnecessary to effect a substantial restriction of the coating material between the nozzle 2 and a needle valve 5. Consequently, it is possible to avoid the problem of irregularities in configuration and shade of a pattern of the discharged coating material, which is likely to occur in a conventional spray gun due to a substantial restriction of the coating material between the nozzle 2 and the needle valve 5. Further, it is unnecessary to suspend a joint from the spray gun. Therefore, when the spray gun is a hand spray gun, it is possible to avoid the problem of poor operability of the hand spray gun. When the spray gun is an automatic spray gun, it is possible to avoid difficulty in assembling the automatic spray gun to an automatic coating apparatus due to interference of a Y-shaped or U-shaped joint.

[0034] The first embodiment of the present invention can be applied to both a hand spray gun and an automatic spray gun. In the automatic spray gun, the rate of discharge can be increased depending on the site for coating and the color of a coating can be changed, in accordance with a preliminarily determined program. Upon changing the color of a coating, the coating material must be rapidly expelled from the piping through the nozzle 2 and a cleaning liquid must be passed through the piping to clean both it and the inside of the spray gun. In this case, because the rate of discharge cannot be increased while the flow of coating material is regulated by the throttle valve 14, the throttle valve 14 must be fully opened. Thus, when the first embodiment is applied to an automatic spray gun, it is required to rapidly move the throttle valve 14 to a full-open position. If this cannot be achieved, merits of the automatic spray gun cannot be fully utilized.

[0035] Figs. 3A to 5 show an automatic spray gun 18 according to a second embodiment of the present invention. The automatic spray gun 18 enables full opening of the throttle valve by means of a piston. In Figs. 3A to 5, the parts or members having the same characteristics as those in the first embodiment are designated by the same reference numerals and characters, with explanation thereof being omitted. Fig. 3A is a front view of the automatic spray gun 18, and Fig. 3B is a cross-sectional view of the automatic spray gun 18, taken along the line A-A of Fig. 3A. Fig. 4A is a cross-sectional view of the automatic spray gun 18, taken along the line B-B of Fig. 3B, in which a movable throttle valve 21 described later is located in a normal regulating position. Fig. 4B is a cross-sectional view of the automatic spray gun 18, taken along the line B-B of Fig. 3B, in which the throttle valve 21 is located in a full-open position.

[0036] As shown in Fig. 3B, a piston 5a is fixed to the needle valve 5. The position of the piston 5a is adjusted by application of air pressure. A mechanism for controlling the position of the piston 5a is known and therefore, no further explanation is made with regard to this mechanism.

[0037] In a gun body 19 of the automatic spray gun 18, the circulation flow passage 7 is formed in proximity to the coating material chamber 6. Opposite end portions of the circulation flow passage 7 provide the coating material inlet 8 and the coating material outlet 9. The throttle valve 21 has a tapered distal end portion providing a working portion 21a, so as to adjust the degree of opening of the throttle valve 21 relative to the valve seat 13, which is provided in the branch flow passage 12 connecting the coating material chamber 6 and the circulation flow passage 7. A piston 23 is fixed to an operating portion 21b of the throttle valve 21. A lock nut 27 for adjustment of the degree of opening of the throttle valve 21 is threadably engaged with an end portion of the operating portion 21b.

[0038] Normally, as shown in Fig. 4A, the piston 23 is biased under the force of a spring 25 in a direction for pressing the throttle valve 21 against the valve seat 13. Movement of the piston 23 is restricted due to abutment of the lock nut 27 against a cover 26, so as to maintain the degree of opening of the throttle valve 21 relative to the valve seat 13. The cover 26 is threadably engaged with a cylinder 20. By rotating the cover 26, the rest position of the lock nut 27 relative to the cylinder 20 can be changed, to thereby adjust the degree of opening of the throttle valve 21 relative to the valve seat 13. After adjustment of the degree of opening of the throttle valve 21, the cover 26 is fixed by a fixing nut 26a.

[0039] Fig. 4B shows a state in which the piston 23 is operated. Compressed air is supplied from a control device (not shown) to a piston chamber 28 and the piston 23 biased by the spring 25 is moved upward. Consequently, the throttle valve 21 is brought into a full-open position relative to the valve seat 13, thus making it possible to increase the flow rate of the coating material supplied from the branch flow passage 12. For changing the color of a coating, the coating material can be rapidly expelled from the piping through the nozzle 2 and a cleaning liquid can be passed through the piping to clean both it and the inside of the spray gun. A structure for adjustment of the degree of opening of the throttle valve 21 and a method for controllably effecting full opening of the throttle valve 21 are not limited to this embodiment, and various structures and methods can be employed.

[0040] In the present invention, a part of the gun body may be formed by a separate body as an air supply manifold. In this case, the expression "gun body" in the present invention means the body portion of the spray gun including the manifold. Fig. 5 shows a manifold type automatic spray gun comprising a manifold base 30 and an automatic spray gun 18a. In this manifold type automatic spray gun, a valve structure comprising the throttle valve 21 and the valve seat 13 and a driving device 29 may be incorporated into the manifold base 30. In the manifold base 30, a flow passage 31 for compressed air used for operating the driving device 29 and a flow passage 32 for compressed air used for operating the piston 5a of the spray valve spindle 5 are formed, in addition to the circulation flow passage 7. The flow passage 32 supplies air to a cylinder portion 5b receiving the piston 5a. Further, a flow passage for air used for atomization of the coating material and a flow passage for air used for patterning of the coating material are provided in the manifold base 30, although not shown. The arrangement of Fig. 5 is advantageous in that the piping for the coating material and the compressed air can be collected within the manifold base 30.

[0041] The spray gun of the present invention is arranged in the above-mentioned manner. The present invention is advantageous in the following points.

[0042] In spray coating, when circulation of a coating material is required, a circulation flow passage for the coating material can be formed within the spray gun body, so that a region between the coating material chamber and the circulation flow passage can be reduced. Further, for conducting discharge of the coating material at a low rate, adjustment of the rate of discharge can be easily conducted by means of a throttle valve, while a sufficient amount of circulation is secured. Therefore, it is possible to avoid the problem of irregularities in configuration and shade of a pattern of the discharged coating material, which is likely to occur due to a substantial restriction in the nozzle opening.

[0043] It is possible to avoid the problem of poor operability of the spray gun, which is likely to occur when a Y-shaped or U-shaped joint is externally attached to the spray gun.

[0044] When the circulation flow passage and the throttle valve are provided within the gun body of an automatic spray gun, full opening of the throttle valve can be effected by means of a piston. Therefore, ejection of the coating material from the piping and the inside of the spray gun and cleaning of the piping and the inside of the spray gun can be easily conducted.

Claims

1. A spray gun comprising:

a spray gun body (1) having a coating nozzle (2) and a coating material chamber (6) connected to the coating nozzle; and

a mechanism for supplying a coating material to said coating material chamber from a pump,

   characterized in that said mechanism comprising:

a coating material circulation flow passage (7) formed in the spray gun body so as to introduce the coating material from the pump into an inside of the spray gun body and return the coating material to the pump;

a branch flow passage (12) branched off from the coating material circulation flow passage (7) and connected to the coating material chamber (6); and

a flow rate adjusting valve device (15, 29) provided in the branch flow passage (12).

2. A spray gun according to claim 1, wherein the flow rate adjusting valve device (15, 29) comprises a valve seat (13) provided in the branch flow passage (12) and a throttle valve (14, 21) provided in a coaxial relationship with the valve seat and wherein a degree of opening of the throttle valve relative to the valve seat is adjusted by operating an operating portion (14c, 21b) of the throttle valve outside the spray gun body (1).

3. A spray gun according to claim 2, wherein the throttle valve (14, 21) is provided so as to intersect the coating material circulation flow passage.

4. A spray gun according to claim 2 or 3, wherein a driving device (29) is connected to the operating portion (21b) of the throttle valve (21) so as to enable full opening of the throttle valve in response to a signal applied to the driving device (29).

5. A spray gun according to claim 4, wherein the driving device includes a piston (23) secured to the throttle valve (21), a cylinder portion (20) formed in the spray gun body (1) receiving the piston so that a piston chamber (28) is formed on the side of the piston which is closer to the valve seat (13), a spring (25) biasing the piston towards the valve seat (13) and an air passage (31) for supplying air to the piston chamber (28).

6. A spray gun according to claim 5, further comprising a cover (26) which threadably engages with the cylinder portion (20) to close the end of the cylinder portion remote from the valve seat (13) with a portion of the throttle valve (21) extending therethrough, wherein a stopper (27) is provided on the throttle valve so that the stopper determines the position of the throttle valve when the stopper engages with the cover (26).

7. A spray gun according to claim 5 or 6, further comprising a spray valve spindle (5) having a spindle piston (5a) fixed thereto and a cylinder portion (5b) receiving the spindle piston, wherein a portion of the gun body (1) is formed by a separate manifold member (30) secured to the rest of the gun body, the manifold member defining therein air passages for respectively supplying air to the cylinder portions (5b, 20).

Drawing