1. Field of the Invention
The present invention relates to an electrodeposition method for an automobile and the like, and more particularly, to an electrodeposition method which prevents an electro sag which ejects from a joint of steel plates.
2. Description of the Related Art
An automobile body (so-called white body) which has been subjected to a welding step is subjected to an electrodeposition as a primer coating for securing an anticorrosive property. In recent electrodeposition, the body is dipped into cation electrodeposition paint for bringing the body into cathode and bringing electrode in a dipping tank (electrodeposition paint) into anode, so that an electrocoating is deposited on a surface of steel plate of the body by electro phoresis.
If the automobile body is subjected to the electrodeposition by a so-called dipping process in which the body is entirely dipped into the electrodeposition paint, it is possible to form a coating on an inner plate, a bag-like structured portion and a joint of steel plates on which a spray coating can not apply. Therefore, the dipping process is widely carried out as effective means for securing the anticorrosive property.
In the dipping electrodeposition method of this type, since the electrodeposition paint is remained on inner and outer surfaces of the automobile body immediately after the automobile body is pulled out from the dipping tank, there are provided setting zone and washing zone after the dipping tank, so that the remained electrodeposition paint is washed out by taking a long setting time or spraying clean water.
As a method for removing the remained electrodeposition paint, there are a conventionally know method in which a plurality of air nozzles are provided in a preheating zone before baking and drying steps so that high pressure air is sprayed to the automobile body to blow away the clean water attached to the body (see Japanese Patent Application Laid-open No. 6-228,794 for example), and a conventionally known method in which washed automobile body is inclined together with a hanger in such a manner that a rear portion of the body is higher so that washing water is discharged, and in the preheating zone before baking furnace, the body is inclined such a manner that a front portion thereof is higher so that the amount of residual washing water is reduced at the entrance of the baking furnace (see Japanese Patent Application Laid-open No. 6-235,094 for example).
However, in the above-described conventional methods, although it is effective to remove the electrodeposition paint attached on the surface of inner and outer plates or the electrodeposition paint remained in the bag-like structure or on a flower, the electrodeposition paint entered into between the joint surfaces of the steel plates can not be removed.
For example, as shown in FIG. 1A, a joint portion B between a side sill 50 and a center pillar 60 has a structure in which a center pillar outer panel 61 is fitted over a side sill outer panel 51 as shown in FIGS. 1B and 2, and the electrodeposition paint entered a clearance of the fitted surface D by capillary action ejects in the baking furnace, and such electrodeposition paint flows into the sill outer and hardened. (Refer to FIGS. 3 and 4) If such an "electro sag" which is a kind of rough surface is generated, there is a problem that a quality of finished product is deteriorated, and a lot of time is required for correcting operation.