JPH0314919B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for drying automobile body parts after chemical conversion treatment as a pre-painting treatment.

(Prior Art) As a pre-painting treatment for automobile body parts, a chemical conversion treatment is generally performed in which a chemical conversion film such as zinc phosphate is formed on the surface after hot water washing and degreasing treatment. This film is effective in preventing corrosion of the base material and improving the adhesion of paint, but if the subsequent washing and drying processes are insufficient, water may leak into joints, grooves, etc. of car body parts. This may result in poor formation of the electrodeposition coating, or uneven coating, ie, hatch marks, may occur when the electrodeposition film is placed in the electrodeposition bath.

However, even if the above-mentioned drying is sufficiently performed, in the electrodeposition coating for the undercoat, coating unevenness with a locally thick coating occurs, and the coating unevenness sometimes appears as unevenness in the topcoat. Conventionally,
There is no means to prevent this coating unevenness, and the thick coating film has been removed by polishing after the fact.
The present inventors have discovered that the above-mentioned coating unevenness is caused by the drying method after chemical conversion treatment, and have completed the present invention.

(Objective of the Present Invention) Therefore, an object of the present invention is to provide a drying method after chemical conversion treatment that can prevent the above-mentioned coating unevenness from occurring in an electrodeposition apparatus.

(Configuration and Effects of the Present Invention) The above objects of the present invention can be achieved by the following configuration. That is, the drying method after chemical conversion treatment of automobile body parts includes, after applying the chemical conversion treatment to the surface, providing a heating means in at least the final dip tank among the dip tanks, and washing the car body parts with water while raising the temperature. When the car body parts are introduced into a direct hot air drying furnace having a large number of high temperature gas blowing means in the furnace, and the temperature of the car body parts has not risen to the set temperature, at least a part of the inlet side of the direct hot air drying furnace The blowing of high-temperature gas from the high-temperature gas blowing means is stopped, at least a part of the area on the inlet side of the direct hot air drying oven is brought to a high temperature without wind, and after the vehicle body parts are passed through the high temperature without wind, the high temperature is It is characterized by direct hot air drying using gas blowing means.

A common phenomenon that occurs during the drying process after washing with water is that the water film breaks locally at a relatively early stage of the drying process, resulting in a partially dried state. This partially dry state is maintained for a certain period of time, and then when the remaining parts begin to dry, it takes a relatively short time to reach complete dryness.

This phenomenon is thought to be based on the fact that when the surface temperature of vehicle body parts exceeds a certain temperature, drying progresses rapidly. The present inventors have discovered that the thickness of the electrodeposited coating near the boundary between the dry area and the undried area, that is, the wet area in the above-mentioned partially dry state is thicker than other areas, and this is the cause of coating unevenness. I figured it out.

Therefore, in order to prevent the occurrence of uneven coating, it is best to prevent the occurrence of this partially dry state or to shorten the time during which this state is maintained as much as possible.

According to the present invention, at least the final dip tank among the dip tanks is provided with a heating means to raise the water temperature in the tank to preheat and raise the temperature of the car body parts, and after that, high-temperature gas is directly blown in a heating furnace to rapidly increase the temperature of the car body parts. I try to dry it with hot air. In this case, if the water temperature in the dip tank cannot be sufficiently raised due to seasonal factors, etc., and therefore the vehicle body parts cannot be sufficiently preheated and heated in the dip tank, the hot gas can be directly blown from the inlet side of the heating furnace. Stop and heat the vehicle body parts to the desired temperature. The part on the inlet side of the direct heating furnace where gas blowing is stopped receives heat from the hot gas blowing out from the outlet side, creating a high-temperature chamber with almost no wind, and this part suppresses evaporation from the surface of car body parts. It is possible to raise the temperature while That is,
It is possible to compensate for insufficient preheating in the dip tank and raise the temperature to a desired temperature while maintaining the surface of the vehicle body part in a wet state.

Therefore, the continuation of the partially dry state, which is the cause of the above-mentioned uneven coating, can be minimized.

As a means for heating the water temperature in the dip tank, a heating coil for circulating steam may be disposed in the dip tank, and the water temperature can be controlled by adjusting the steam temperature and flow rate. In this case, it is desirable that the surface temperature of the vehicle body parts be raised to about 30°C or higher, and for this purpose the water temperature in the dip tank is preferably 40°C or higher.

A direct heating furnace for direct hot air drying is desirably operated at an internal furnace atmosphere temperature of 110 to 150° C., a residence time of vehicle body parts of 5 to 10 minutes, and a convection flow rate of 6 to 10 m/sec.

The need to stop gas blowing at the inlet side of a direct heating furnace and use a high-temperature chamber to compensate for the lack of preheating occurs mainly during seasons other than summer, and in this case, favorable results can be obtained if the following conditions are met. . Ambient temperature: 50 to 100℃, vehicle body parts retention time: 1 minute (spring/autumn), 1.5 minutes (winter).

(Description of Examples) (Comparative Example) Pre-painting treatment of automobile body parts was carried out as shown in FIG. First, the car body parts were washed with hot water and degreased, then washed with water, and then subjected to a chemical conversion treatment to form a chemical film such as zinc phosphate on the surface.

After the chemical conversion treatment, a dip tank operation in which the car body parts were immersed in a dip tank, that is, a water tank and washed with water, was performed under the following conditions. (Final dip operation) Water temperature: 5°C to 20°C Total immersion time: 2 minutes Tank capacity: 70m ³ Next, the car body parts were spray washed under the following conditions.

Water temperature: 5° C. to 20° C. Spray time: 10 to 20 seconds Spray amount: 200/min Next, the car body parts were dried in a direct hot air drying oven shown in FIGS. 2 and 3. Referring to FIGS. 2 and 3, headers 16 and 18 each having a plurality of spout ports 14 are installed along both side wall surfaces of the direct hot air drying oven 10 in the conveyance direction of the vehicle body parts 12. High temperature gas from these headers 16, 18 and burners 22 is sent by a blower fan 24 to the duct 2.
6 and 28.
The ducts 26 and 28 are provided with regulating valves 32 and 34, respectively, for adjusting the gas amount and controlling the furnace temperature. The vehicle body part 12 enters the furnace from the left in FIG. 3 and is dried by being blown with hot gas while moving to the right.

When a part of the regulating valves 32, 34 is fully closed, the atmosphere in that part changes to a high temperature with almost no wind. Therefore, the surface temperature can be increased while suppressing evaporation from the vehicle body parts as much as possible. The operating conditions of the direct drying oven are as follows.

Atmosphere temperature 110-150℃ Time 5-10 minutes Wind speed 6-10 m/sec Specific components in the atmosphere CO...5-10 ppm Nox...3-4 ppm (Max 15 ppm) Cl... Obtained by processing several ppm or more After electro-deposition coating was applied to car body parts, a problem occurred in which streak-like steps appeared on the surface of the electro-deposition coating. This stripe-like step had a height of 1 μ to 2 μ and a length of 2 mm or more. This example condition is commonly encountered, especially during the winter months, and is likely to occur primarily in bonnet, roof, and trunk parts. Taking bonnets as an example, the above phenomenon was observed in approximately 60% of bonnets.

(Example) As shown in FIG. 4, operations up to chemical conversion treatment were performed under the same conditions as in the above-mentioned comparative example. In this example, the fifth
As shown in the figure, a heating coil 21 through which steam circulates was disposed in the final dip tank 20 to maintain the water temperature relatively high. The operating conditions of the final dip tank are as follows.

Water temperature: 40°C Total immersion time: 2 minutes Tank capacity: 70 m ^3. Next, the car body parts were spray-cleaned using the spray device 30 under the following conditions.

Water temperature: 45℃ Spray time: 10 to 20 seconds Spray amount: 200/min Next, in the drying oven 10 shown in FIGS. 2 and 3, part of the inlet side of the regulating valves 32 and 34 is fully closed, and the The temperature was preheated. The heating conditions are as follows.

Atmospheric temperature: 80° C. Residence time of vehicle body parts: 1.5 minutes Convection flow velocity: 1 m/sec or less Next, hot air drying was performed by blowing high-temperature gas from the outlet 14 at the outlet side of the drying oven 10. The processing conditions in this case are as follows.

Atmospheric temperature: 130°C Retention time of car body parts: 8 minutes Convection flow velocity: No defects were observed on the surfaces of car body parts after electrodeposition coating obtained through treatment at 8 m/sec or higher, even in winter. This is the heating coil 2 in the dip tank.
1 to raise the water temperature, it is possible to raise the surface temperature of the car body parts, and if the temperature in the dip tank is not sufficiently raised due to seasonal factors, etc. This is because the area is kept in a non-evaporative atmosphere and the temperature is raised to the desired temperature in a wet state. That is,
To prevent uneven coating from occurring regardless of fluctuations in the water temperature state of the dip tank.

[Brief explanation of the drawing]

Figure 1 is a schematic flowchart of conventional pre-painting treatment, Figure 2 is a schematic diagram showing a cross section of a drying oven, Figure 3 is a schematic diagram showing a cross section of a drying oven, and Figure 4 is a schematic diagram showing a cross section of a drying oven. ,
A schematic flowchart of a process according to the present invention, FIG. 5 is a schematic diagram of a processing apparatus according to the present invention. Explanation of symbols, 10...Drying oven, 12...Car body parts, 20...Heating coil, 22...Burner, 2
4...Blower fan.

Claims (1)

[Scope of Claims] 1. A method for drying automobile body parts after chemical conversion treatment, which comprises: after applying chemical conversion treatment to the surface, heating means is provided in at least the final dip tank among the dip tanks to raise the temperature of the car body parts; The car body parts are then introduced into a direct hot air drying oven having a large number of high temperature gas blowing means in the oven, and if the temperature of the car body parts has not risen to the set temperature, at least one of the direct hot air drying ovens is heated. Stop blowing out high-temperature gas from a portion of the high-temperature gas blowing means on the inlet side to heat at least a portion of the inlet side of the direct hot air drying oven without wind, and pass the vehicle body parts through the high-temperature without wind region. A drying method characterized in that after drying, direct hot air drying is performed using the high temperature gas blowing means.