JPH03146173A - Coating method - Google Patents

Abstract

PURPOSE:To improve durability of a rotating device by setting the speeds for rotating a material to be coated around a horizontal axial line in the setting process and in the stoving process different from each other corresponding to the different sagging speeds of the coating material. CONSTITUTION:In the stage of transferring from the coating process to the setting process, a sprocket 28 for applying the rotation force of a body W is engaged with a fixed chain 93. When the sprocket 28 is started to be engaged with a chain 21, the rotation speed of the body W is increased because the driving direction of the chain 21 is opposed to the driving direction of a wire 5. When a transfer truck D is further moved forward and reaches the stoving process, operation levers 60 and 61 are put in the increased speed state by a striker 95 for increasing the speed to further increase the rotation speed of the body W. Thus, the rotation speed of a material to be coated can be minimized as small as possible to minimize the load to a rotation device and improve its durability.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a coating method.

(Prior Art) A painting line generally includes a painting process, a setting process, and a baking process in sequence. In the painting process, the paint is applied to the object to be coated to a predetermined thickness, in the setting process the paint is dried (I11), and finally in the baking process the paint is baked and dried.

By the way, JP-A-63-178871 discloses that in the painting process, paint is sprayed to a thickness exceeding the sag limit, that is, to a thickness that causes the paint to sag in the setting process and the baking process. It has been proposed that by rotating the object to be coated around a substantially horizontal axis during the baking process, the coating thickness can be made extremely thick while preventing sagging, thereby increasing the smoothness of the painted surface. , this publication also discloses that the object to be coated can be rotated using a rotating platform equipped with a rotating device for rotating the object to be coated.

The rotational speed of the object to be coated needs to change from a vertical state to at least a horizontal state before the paint starts to sag. It is necessary to take this into consideration when setting.

(Problems to be Solved by the Invention) However, rotating the object to be coated places a considerable burden on the rotating device. Particularly when the object to be coated is large and heavy, such as an automobile body, the burden is heavy.

On the other hand, the operating time of a coating line is quite long, and therefore the durability of the rotating device becomes an issue.

The present invention was made in consideration of the above circumstances, and
A coating method that improves the durability of the rotating device that rotates the object, assuming that the object to be painted is rotated during the setting process and the baking process to prevent paint from sagging. The purpose is to provide

(Structure and operation of the invention) In order to achieve the above object, the present invention has the following structure. That is, in a painting method in a painting line that sequentially includes a painting process, a setting process, and a baking process, in the painting process, the paint is applied to a thickness greater than that which causes paint sag in each of the setting process and baking process. In the setting step and the baking step, the object to be coated is rotated about a substantially horizontal axis to prevent the paint from dripping, and the object to be coated in the setting step and the baking step is The rotational speeds are set to be different depending on the difference in paint dripping speed.

With this configuration, the rotational speed of the object to be coated can be set to the minimum required level in accordance with the difference between the paint sag rate in the setting process and the paint sag rate in the baking process. More specifically, for example, when using a solvent-diluted thermosetting paint, which is the most common paint for automobile bodies, the paint sag rate is greater in the baking process than in the setting process. Therefore, in this case, the rotational speed of the object to be coated in the setting step may be lower than the rotational speed of the object to be coated in the baking step.

As mentioned above, if the paint sag rate in the setting process is lower than the paint sag rate in the baking process, the rotational speed at the initial stage of rotation of the object to be coated can be made smaller. This is also preferable in terms of preventing so-called edge accumulation, in which paint tends to accumulate thickly on the edges of the object to be coated.

(Effects of the Invention) As described above, according to the present invention, the rotation speed of the object to be coated, which is performed to prevent paint from dripping, is made as low as possible, and the rotation speed of the object to be coated is reduced as much as possible. It is possible to reduce the burden and improve its durability.

(Example) Examples of the present invention will be described below based on the attached drawings. In addition, in the examples, the object to be coated is an automobile body,
This is based on the assumption that the painting line is for topcoating and that the topcoat is a solvent-diluted thermosetting paint.

In FIG. 8, the painting line includes a painting process A, a setting process B, and a baking process C.

In the painting process A, a top coat paint is sprayed to a predetermined thickness onto an automobile body W as an object to be coated, which has been coated with an intermediate coat (generally electrostatic atomization coating). Setting process B
Now, at room temperature or slightly higher temperature,
The sprayed top coat is pre-dried. More specifically, the solvent in the paint is appropriately volatilized, thereby preventing pinholes from occurring during the subsequent baking process. In the baking process C, the temperature is higher than that in the setting process B, for example 140°C.
The paint is baked and dried at a certain temperature. and,
After the baking step C, the body W as the object to be coated is supplied to an assembly line.

The thickness of the paint sprayed in the painting process A is set to be at least thick enough to cause sagging in both the setting process B and the baking process C. FIG. 7 shows the relationship between coating film thickness and sag rate for setting process B and baking process 0, respectively.

As is clear from this Figure 7, the sagging speed is
The thicker the thickness, the larger it becomes. Furthermore, if the thickness of the coating 11A is the same, the sagging speed in the setting culm B will be smaller than the sagging speed in the baking step C.

In the setting process B and baking process C,
The body W is rotated around a substantially horizontal axis from before the paint starts to sag until it stops.

The rotational speed of the body W at this time is made smaller in the setting step B than in the baking step C, taking into account the difference in sagging speed.

Here, paint sag refers to the movement of the paint that can be visually confirmed when the paint is left in the sprayed state (it appears as streaks when the paint hardens).
Generally, sagging is considered to have occurred when paint transfer or force of about 2 mm is confirmed. Therefore, spraying paint to a thickness that exceeds the sag limit means spraying the paint at a thickness that will cause at least 2 mm of movement if left as is, and the more fluid the paint used, the more the sag will occur. The critical thickness becomes smaller. This amount of sagging is the limit.”
- To achieve a thickness of <
(l-stage blowing), or the final thickness may exceed the sag limit by spraying two or three times (multi-stage blowing). Furthermore, when rotating the object to be coated around a substantially horizontal axis, it is sufficient to ensure that the paint does not move significantly due to the action of gravity, so the paint does not have a large flow state that would cause sag. The rotation may be performed continuously or intermittently in one predetermined direction (or, forward and reverse rotations may be performed continuously or intermittently during the period of time until the paint hardens). As for the rotation angle range, it is sufficient that the direction in which gravity acts is reversed for any part where the paint is sprayed to a thickness exceeding the sag limit, and 270 degrees is sufficient. The axis of rotation of the object to be coated may be inclined within a range of about 30 degrees with respect to the true horizontal axis, and this axis of rotation may also be swung.

The rotational speed of the body W varies depending on the film thickness and viscosity of the sprayed paint, but is basically set to a rotational speed within a range between the following lower limit and upper limit. That is, the lower limit of the rotational speed is the minimum value of the rotational speeds at which the painted surface can be brought from at least a vertical state to a horizontal state before the paint on the painted surface moves by gravity and sag. The upper limit is the maximum rotational speed at which no sagging occurs due to the centrifugal force generated by rotation, and is 380 cm at the rotating tip of the object to be coated.
It is better to set it to 7 seconds or less. In the present invention, such conditions are set such that the rotational speed is such that .gamma.14 is obtained, and the rotational speed in the setting step B is made smaller than the rotational speed in the baking step C.

A specific example of theoretically determining the rotational speed will be described using a case where the paint dripping speed is 12 mm/min.

In this case, in order to keep the paint dripping length to 2 mm or less, 2
The body W is reversed in /12 minutes, which means that the body W is rotated once in 1/3 minute, and the rotational speed at this time is 3 rpm. However, the actual rotational speed is preferably set to be thicker (earlier) than the above-mentioned theoretical rotational speed to allow for some margin.

(Blank below c) Next, with reference to FIGS. 1 to 6, a description will be given of a transport vehicle that transports the body W and a portion that changes the rotational speed of the body W using this transport vehicle.

In FIG. 1, a conveyance cart has a base plate 1 and can travel on rails 3 using running wheels 2 provided on the base plate 1. As shown in FIG. A stay 4 is integrated below the substrate 1, and a pulling wire 5 is fixed to the stay 4 as a main conveyor. As a result, the carriage is conveyed (driven) from the left side to the right side in the figure under the pulling force of the wire 5.

A pair of front and rear supports 6.7 are erected on the substrate 1, and the body W is rotatably supported by the pair of supports 6.7. That is, a front rotation jig 8 or a rear rotation jig 9 is fixed to the front and rear of the body W, and the rotation shaft portion 8a of the front rotation jig 8 is rotatably supported by the front support 6 via a bearing 10. A rotating shaft portion 9a of the rear rotating jig 9 is rotatably supported on the rear support 7 via a bearing 11. Of course, both the rotating shaft portions 8a and 9a are on the same straight line β, and the axis 2 is set to be a substantially horizontal axis extending in the front-rear direction of the body W.

A chain 21 as a sub-conveyor is disposed along the wire 5 as the main conveyor. This wire 5
The body W is rotated by using the relative speed difference between the chain 21 and the chain 21, and the mechanism for this rotation will be described below.

First, the main part of the rotation mechanism is installed in the rear support 7, and its appearance is shown in FIGS. 2 and 3. In FIGS. 2 and 3, reference numeral 22 denotes a continuously variable transmission as rotational speed adjusting means, and a sprocket 23 provided on its output shaft 22a is connected to the rotational axis of the rear rotation jig 9 via a chain 24. It is interlocked with a sprocket 25 provided on the portion 9a.

A sprocket 26 provided on the input shaft 22b of the continuously variable transmission 22 is interlocked with the chain 21 as a sub-conveyor as follows. That is, a gearbox 27 is provided on the substrate 1 near the chain 21, and a sprocket 28 provided on an input shaft 27a of the gearbox 27 is engaged with the chain 21. The rotation of the sprocket 28 is extracted as the rotation of the output shaft 27b of the gear box 27, and the rotation of the output shaft 27b is transmitted to the gears 29, 30, shaft 31, and universal joint 3.
2. Shaft 33, shaft 35 via universal joint 34
transmitted to. The rotation of the shaft 35 is transmitted to the sprocket 26 provided on the input shaft 22b of the continuously variable transmission 22 via the sprocket 36, chain 37, sprockets 38, 39, and chain 40. Thereby, when the sprocket 28 that engages with the chain 21 as a sub-conveyor is rotated, the body W is rotated. The rotational speed of the body W is determined by the rotational speed of the sprocket 28 and the gear ratio of the continuously variable transmission 22. In addition, 41 is the idle sprocket, 4
Reference numeral 2 denotes a torque limiter, and the torque limiter 42 performs a sliding action when a large rotational load is applied to the workpiece W to protect the interlocking mechanism between the sprocket 28 and the workpiece W.

The gear ratio of the continuously variable transmission 22 is changed by a transmission mechanism including a transmission 51. That is, the gear ratio adjustment shaft 22c of the continuously variable transmission 22 is connected to the output shaft 51a of the transmission 51 via the joint 52. The input shaft 51b of the transmission 51 is interlocked with a sprocket 59 provided on an output shaft 58a of a gearbox 58 via a sprocket 53, a chain 54, sprockets 55, 56, and a chain 57. This gearbox 58 has two operating levers 60.61. One operating lever 60 has a linear shape, and the other operating lever 61 has an oval shape, and both levers 60 and 61 are interlocked with each other by gears 62.63 (the rotation center of the operating lever 60.61). (denoted by reference numeral 60a or 61a). This same operation lever 6
0.61 is the input shaft 58b (60
When the continuously variable transmission 22 is in the state shown in FIG. 2, the continuously variable transmission 22 is brought into a deceleration state, and from this state shown in FIG. (The control lever 61 rotates approximately 9 degrees counterclockwise.)
When the rotation is 0°, the continuously variable transmission 22 is brought into a speed increasing state. Note that the transmission 51 is provided on the operating lever 6.
Continuously variable transmission 22 with a small rotation amount of 0 or 61
This is to significantly change the gear ratio.

The sprockets 55 and 56 interposed between the gearbox 58 and the continuously variable transmission 22 are connected to each other by the shaft 7.
It is integrated into 1. At one end of this shaft 71,
Cam 72 is fixed. This cam 72 has a body W
This is for operating a stopper mechanism S for fixing the body in a predetermined posture (the posture shown in FIG. 1). This stopper mechanism S is shown in FIGS. 4 and 5, and will be described below. First, the post-rotation jig 9 is equipped with a fixed claw 73 and a movable claw 74, as shown in FIG. On the other hand, a stopper rod 76 is slidably held in a casing 75 fixed to the rear support 7. This stopper rod 76 can selectively take the retracted position shown in FIG. 4 and the extended position displaced to the left from that shown in FIG. (See Figure 5). At this advance position,
The stopper rod 76 approaches the rotating jig 9 from below in FIG. 5, flips up the movable claw 74, and comes into contact with the fixed claw 73. Then, the movable claw 74 that has been sprung up returns to the position shown in FIG. W rotation lock). Then, when the stock rod 76 is moved from the state shown in FIG. 5 to the exit position shown in FIG. 4, which is the position shown in FIG. 4, the body W can be rotated again.

As shown in FIG. 4, a locking recess 76a is formed in the side surface of the stopper rod 76, and a ball 77 that can be fitted into the locking recess 76a is provided. this ball 7
7 is in contact with one end of a locking rod 78 that is slidably fitted into the casing 75, and the other end of the locking rod 78 is in contact with
A roller 79 that comes into contact with the cam 72 is rotatably held. The locking rod 78 is biased by a spring 80 in a direction in which the roller 79 comes into contact with the cam 72 . On the other hand, the cam 72 has a substantially circular shape as a whole, and a recess 72a is formed in a part of the cam 72. As a result, when the roller 79 is in a position other than the recess 72a, the ball 77 fits into the locking recess 76a, and when the roller 79 falls into the recess 72a, the ball 77 comes out of the locking recess 76a. It is said that this is a possible location. The stopper rod 76 is always urged in the advanced position by the spring 81, that is, in the direction in which the locking recess 76a and the ball 77 are disengaged, and when the roller 79 falls into the recess 72a, the stopper rod 76 advances. It is said that it can be moved to any position.

A manual operating lever 82 is integrated into the stopper rod 76, and by retracting the operating lever 82 against the spring 81, the stopper rod 76 is returned to the retracted position shown in FIG. Then, by slightly rotating the operating lever 82 from the exit position in the circumferential direction of the stopper rod 76, the operating lever 82 moves toward the casing 7.
5, and is held at the above-mentioned exit position. In other words, when regulating the rotation of the body W, the operating lever 82 is removed from the stepped portion 75a in advance so that the stopper rod 76 is locked only by the ball 77.

FIG. 6 shows the arrangement relationship between the wire 5 as the main conveyor and the chain 21 as the sub-conveyor. The wire 5 is endless and driven by a motor 91. Similarly, the chain 21 is also endless and driven by a motor 92. In order to paint the body W, the wire 5 undergoes the aforementioned painting process A, setting process, and baking process C. The chain 21 is provided along the wire 5 only in the setting process B and the firing process C in order to rotate the body W at a predetermined rotational speed in the setting process B and the firing process C. In addition, a fixed chain 93 is installed at the boundary between the painting process A and the setting process B in order to smoothly start the rotation of the body W.
is provided.

Next, focusing on the rotational speed of the body W, processes A, B, and C
They will be explained one by one. First, before the conveyance carriage comes to the painting process A, the operating lever 60.6I is set to the deceleration position as will be described later. However, since there is no rotating chain 93.21 in this painting process A part, the body W
This rotation is not performed in the painting process A.

At the stage of transitioning from painting process A to setting process B,
Sprocket 28 for extracting rotational force from body W
is engaged with the fixed chain 93. At this time, the lever 60 is already in the deceleration state shown by the solid line in FIG. 1, and therefore the rotational speed of the body W at this time is low. This is done in consideration of the fact that the body W is starting to rotate. However, in the embodiment, a striker 96 for deceleration is provided just before the body W begins to be rotated by the chain 93 to ensure a deceleration state.

When the sprocket 28 starts to be engaged with the chain 21, the rotational speed of the body W increases because the driving direction of the chain 21 is opposite to the driving direction of the wire 5.

When the conveyance carriage further advances and reaches the baking step C, the speed increasing striker 95 causes the operation lever 60.
61 is brought into a speed increasing state, and the rotational speed of the body W is further increased.

Immediately after the baking process is completed, the sprocket 28 is still engaged with the chain 21, and the body W continues to be rotated. However, at this time, the operating levers 60, 61 are brought into a decelerating state by the deceleration striker 96, and the rotational speed of the body W is reduced in preparation for stopping rotation. Then, the transport vehicle is operated by operating levers 6o, 6.
1 will return to the painting process A while maintaining the deceleration state.

Immediately before the sprocket 28 is disengaged from the chain 21, the operating lever 82 of the stopper mechanism S is brought to the unlocked position, that is, the stopper rod 76 is locked only by the ball 77. As a result, the rotation of the body W is eventually stopped by the stopper rod 76 in the predetermined posture shown in FIG.

The wire 5 is driven and stopped by a manual switch 100. When the wire 5 is stopped, if the paint on the body W in the setting process B or the baking process C is not sufficiently cured, blurring will occur. At this time, a signal indicating that the wire 5 is to be stopped is output from the control unit Ul for controlling the motor 91, which receives input from the switch lOO, to the control unit U2 for controlling the drive of the chain 21. Then, the control unit U2 increases the driving speed of the chain 21 so as to maintain the relative speed difference before the wire 5 stopped, and maintains the rotational speed of the body W in the same state as before the wire 5 stopped. .

The switch 101 instructs to change the conveying speed of the wire 5. Also at this time, the control unit U2 changes the speed of the chain 21 in response to the change in the speed of the wires and ears 5 to maintain the rotational speed of the body W constant. Note that the switch 102 is used to issue commands to drive and stop the chain 21.

[Brief explanation of the drawing]

FIG. 1 is a side view showing an example of a transport vehicle for transporting an automobile body. FIG. 2 is a plan view showing a mechanism for rotating an automobile body using the relative speed difference between the main and sub conveyors. FIG. 3 is a view taken in the direction of the arrow in FIG. 2. FIG. 4 is a side sectional view showing an example of a stopper mechanism for stopping an automobile body at a predetermined rotational position. FIG. 5 is an explanatory diagram showing the relationship between the rotating jig and the stopper rod when stopping the automobile body in a predetermined rotational posture. FIG. 6 is a simplified plan view showing an example of the overall layout of the main conveyor and the sub-conveyor. FIG. 7 is a diagram showing the relationship between paint dripping speed and coating film thickness for the setting process and the baking process. FIG. 8 is a block diagram showing the painting line. 92: Motor (for sub-conveyor) 95 Nist striker (for changing gear ratio) 96: Striker (for changing gear ratio) 1 2 8 0 1 1: Painting process: Setting process: Baking process: Automobile body (subject to be coated): Conveyance Dolly: Wire (main conveyor): Chain (secondary conveyor): Continuously variable transmission (for adjusting rotation speed): Sprocket (for taking out rotation): Control lever (for changing gear ratio): Operating lever (for changing gear ratio): Motor (for main conveyor) Figure 7 Painting time (minutes)

Claims (1)

[Claims] (1) In a painting method in a painting line that sequentially includes a painting process, a setting process, and a baking process, in the painting process, the paint is sprayed to a thickness greater than that which causes paint sag in each of the setting process and baking process. In the setting step and the baking step, the object to be coated is rotated about a substantially horizontal axis to prevent paint from dripping, and the rotational speed of the object in the setting step and the baking step is The painting method is characterized in that the settings are set to be different from each other depending on the difference in paint sagging speed.