This invention relates to a coating device for applying a liquid such as an oil onto a workpiece, namely, an object to be coated.

For the purpose of improvement in lubricity and corrosion resistance as well as protection, an electrical contact contained in a connector may be coated with a high-viscosity liquid generally called a contact oil. The contact oil is applied by liquid dipping or direct spraying.

A coating method using liquid-dipping technique comprises the steps of preparing a diluted oil obtained by diluting the oil with an organic solvent and dipping a workpiece in the diluted oil to apply the oil to the workpiece. As shown in Figs. 1 and 2, the workpiece 21 such as a plated long and narrow ribbon member is transferred from a supply roll 22 through a continuous plating unit 31 to a take-up roll 23. The continuous plating unit 31 comprises a preprocessing portion 32 for executing a preprocessing step, a plating portion 33 for executing a plating step, a dip coating potion 34 for executing a dip coating step, and a dehydrating portion 35 for executing a dehydration step.

The dip coating portion 34 has a dip coater 34A for dip coating the workpiece 21 with the diluted oil. In the dip coater 34A, a tank 34B is disposed at its center for containing a liquid. Two pairs of transfer rollers 34C are arranged on both sides of the tank 34B, one pair on the left side and the other pair on the right side. Above each pair of the transfer rollers 34C, cooling pipes 34D are disposed. At the top of the dip coater 34A, an air duct 34E is <BR> <BR> connected. The tank 34B contains the diluted oil, i. e. , a solution obtained by diluting the oil to about 0.1-20% in volumetric ratio by the use of an organic solvent such as a chlorine-based solvent. The dehydrating portion 35 has a dryer 35A for dehydrating the workpiece 21.

The workpiece 21 is transferred by the two pairs of transfer rollers 34C from the right side to the left side in Figs. 1 and 2. While passing through the liquid tank 34B, the workpiece 21 is dipped in the diluted oil and coated with the diluted oil. Immediately thereafter, the solvent alone is volatilized by the dryer 35A from the diluted oil adhered to the workpiece 21. As a consequence, a film of an oil component is fixed as a coating to the workpiece 21.

In the coating method using liquid dipping, it is possible to uniformly apply the oil to the workpiece to a very small thickness. Therefore, it is possible to strictly control the coating operation so that the oil is very uniformly and thinly applied.

However, since the chlorine-based solvent or the similar organic solvent is used, there arises a problem of ozone layer destruction.

Another coating method using direct-spraying technique is carried out by directly spraying a liquid concentrate by a two-fluid spray to coat the workpiece. As shown in Fig. 3, the two-fluid spray 41 is supplied with an oil fed from a pressure tank 42 under pressure and with compressed air. The oil and the compressed air are mixed in the two-fluid spray 41 into a mixture which is directly sprayed towards an object or a workpiece 43 to thereby coat the workpiece 43 with the oil.

However, in the coating method using the direct spraying, the mist particle size and the flow rate distribution are nonuniform but exhibit wide variation. Therefore, it is difficult to control the coating operation in a very small amount. In addition, splash loss of the oil due to spraying is great.

Summary of the Invention.

It is therefore an object of this invention to provide a coating device capable of uniformly coating a workpiece with a very small amount of a coating material without using an organic solvent.

Other objects of the present invention will become clear as the description proceeds.

According to this invention, there is provided a coating device comprising a primary spray for injecting a liquid to produce original mist, a mist box connected to the primary spray and supplied with the original mist for producing a fine mist having a very small particle size, and a secondary spray connected to the mist box for spraying the fine mist towards a workpiece.

Brief Description of the Drawing : Fig. 1 is a schematic view of an existing coating device using liquid- dipping technique; Fig. 2 is an enlarged view of a characteristic part of the coating device illustrated in Fig. 1; Fig. 3 is a schematic view of another existing coating device using direct-spraying technique; Fig. 4 is a schematic view of a coating device according to one embodiment of this invention, which using mist-blowing technique; Fig. 5 is a view for describing experimental conditions and experimental results for the direct-spraying technique and the mist-blowing technique; and Fig. 6 is a graph showing amounts of an applied oil for the direct- spraying technique and the mist-blowing technique.

Description of the Preferred Embodiment : Referring to Fig. 4, description will be made of a coating device according to one embodiment of this invention. As will become clear from the description, the coating device uses mist-blowing technique and therefore may be called a mist blow coating device.

The coating device illustrated in the figure is a device for applying a small amount of a contact oil as one of high-viscosity liquids by the use of a spray. The coating device comprises a rectangular housing 1. In the housing 1, a rectangular mist box 2 is disposed on the lower left side while a primary spray 3 is disposed on the lower right side.

The primary spray 3 is adapted to mix the oil in a liquid phase supplied from a liquid tank (not shown) and compressed air into a mixture and to spray the mixture through an injection port 3A into the mist box 2 in an atomized fashion to produce original mist. The mist box 2 has a wall portion 2A faced to the injection port 3A. As will later be described, the wall portion 2A serves to separate a liquefied part from the original mist to leave fine mist having a very small particle size alone.

The mist box 2 has a right side wall provided with an air inlet 2B formed at an upper part thereof and a bottom wall connected to an oil collecting drain 4 located at its right side. The mist box 2 has a top wall provided with a secondary spray 5. The secondary spray 5 has a sucking portion 5A protruding into the mist box 2 and a blowing portion 5B facing a workpiece (for example, a conductive contact included in a connector) 11 arranged above the secondary spray 5. Use may be made as the workpiece 11 of a conductive contact included in a connector known in the art.

The secondary spray 5 has an accelerating portion 5C between the sucking portion 5A and the blowing portion 5B. The accelerating portion 5C is provided with a compressed air inlet 5D formed on its lateral side. When the secondary spray 5 is operated, compressed air flows through the compressed air inlet 5D into the accelerating portion 5.

The housing 1 has an inlet 1A and an outlet 1 B formed at an upper part of its right side wall and at upper part of its left side wall, respectively, to allow the workpiece 11 to be transferred through the housing 1. The housing 1 is connected to a mist collector 6 at a lower part of the right side wall thereof.

The oil collecting drain 4 penetrates through the bottom wall of the housing 1 around its center.

Description will be made of an operation of applying the oil to the workpiece 11. By the primary spray 3, the original mist is sprayed into the mist box 2 as a primary spraying operation. At this time, large mist particles in the original mist are liquefied upon collision against the wall portion 2A of the mist box 2 to be reserved in a lower part of the mist box 2 as a liquefied oil. The liquefied oil is collected by the oil collecting drain 4 to be discharged outside of the mist box 2 and the housing 1. As a consequence, small mist particles alone are left in the mist box 2 as the fine mist mentioned above. The liquefied oil collected can be reused so that splash loss of the oil can be reduced. The oil collecting drain 4 forms liquid discharging means.

Next, the secondary spray 5 sucks the fine mist from the mist box 2 to the sucking portion 5A and blows the fine mist from the blowing portion 5B as a secondary spraying operation. In this event, the fine mist is sprayed towards the workpiece 11. As a consequence, the inside of the mist box 2 has a negative pressure so that air is introduced through the air inlet 2B. At this time, since the compressed air is introduced through the compressed air inlet 5D into the secondary spray 5, the amount of air in the acceleration portion 5C is increased so that the secondary spraying operation is accelerated and the fine mist is blown at an increased speed. By increasing the speed in the secondary spraying operation, strong impact force is produced when the fine mist collides with the workpiece 11. This results in an increase in wettability of the workpiece 11 to the oil. Therefore, even with the fine mist, uniform and thin coating with a small amount of the oil is possible.

The fine mist staying in the housing 1 is discharged from the housing 1 by the mist collector 6. Thus, the mist collector 6 serves as mist discharging means.

Referring to Figs. 5 and 6, description will be made of conditions and results of experiments for the direct-spraying technique and the mist-blowing technique.

In the figures, "Direct Spraying" (1) to (3) represent the conditions and the results of the experiments using the coating device illustrated in Fig. 3.

"Mist Blow" (1) and (2) represent the conditions and the results of the experiments using the coating device illustrated in Fig. 4."AIR Pressure" represents the pressure of the compressed air blown from the spray 41 or the primary spray 3. "Liquid Tank Pressure"represents the pressure of the oil flowing into the spray 41 or the primary spray 3."Mist Blow Pressure" represents the pressure of the compressed air flowing into the secondary spray 5.

By the use of an electron micrograph, the appearance of the processed surface of the workpiece was observed. In case of Mist Blow (1) and (2), it has been confirmed that fine particles having a diameter of about 10 to 20 u m were densely applied. In case of Mist Blow (1) and (2), it has also been confirmed that the oil is applied to the workpiece uniformly and in a small amount, as compared with each of Direct Spraying (1) to (3).

While the present invention has thus far been described in connection with a few embodiments thereof, it will readily be possible for those skilled in the art to put this invention into practice in various other manners. For example, a plurality of primary sprays, a plurality of secondary sprays, and a plurality of mist boxes may be arranged in the housing. Furthermore, a plurality of sucking portions 5A and a plurality of blowing portions may be provided for a single secondary spray. As the high-viscosity liquid, not only the contact oil but also a press oil, a cutting oil, a lubricating oil, and so on may be used. Not only the contact of the connector but also various articles such as strip-shaped or comb-shaped continuous plate products can be used as an object to be coated.