EP0627022B1 - Device for the electrolytic coating of small parts - Google Patents

Abstract

PCT No. PCT/DE93/00122 Sec. 371 Date Mar. 3, 1994 Sec. 102(e) Date Mar. 3, 1994 PCT Filed Feb. 10, 1993 PCT Pub. No. WO93/17155 PCT Pub. Date Sep. 2, 1993.An apparatus for electrolytically coating small parts, e.g. by electrophoretic deposition from a liquid coating agent, has a screw-type conveyor which can have a tube open at opposite ends to form an inlet and outlet for the parts which are advanced through the tube by screw conveyor means like a helical ribbon. The inlet side of the tube is immersed in a basin of the liquid coating agent whose side walls and front wall form weirs determining the level of the liquid coating agent in the tube while the liquid passes from the tube into a catch basin beyond the rear wall through perforations in the tube. The contacts traversing the tube wall are electrically-conductively coupled to the parts and are tied to one terminal of the DC power source whose other terminal is connected to a plate immersed in the dipping basin.

Description

The invention relates to a device for the electrolytic coating of small parts with electrical conductivity, in particular metal parts, the device comprising a bath of electrically conductive liquid coating agent, the bath with one pole of a direct current source (cathode or anode) is in electrically conductive connection, while the Good to be coated is in electrically conductive connection with the other pole (anode or cathode) of the direct current source and the device consists of a screw conveyor with loading and unloading openings at its ends and with screw conveyors in the inside of the conveyor tube, which has electrically conductive contacts on the inside of its conveyor tube are connected to one pole of the direct current source, and the screw conveyor is inserted with a part of its cross section into a plunge pool which is connected to the other pole.

The so-called electrocoating is carried out with known devices, the coating agent being deposited cathodically or anodically on small metallic parts.

For this purpose, a device is known which consists of a closed drum into which the small metallic parts are filled.

In addition, the coating agent is introduced into the drum, the drum being electrically conductive in the interior and being connected to one pole of a power source, while the coating agent is connected to the other pole of a power source.

When the drum is in operation, the small metal parts assume the potential of the drum, so that the coating agent is deposited on the small parts with the opposite electrical potential. The operation for coating such small parts is very complex, since the drum must first be filled with small parts and then the coated or electrocoated small parts must be removed from the drum again. In the prior art, only a discontinuous mode of operation is possible, so that the number of lacquered small parts applied per unit of time is narrowly limited.

A device for electrolytic coating according to the preamble of claim 1 is known from EP-A-0141 406 and in particular from US-A-19 12 400.

Starting from this prior art, the invention has for its object to provide a device of the generic type, which enables a high throughput of small metallic parts for the purpose of dip painting with little effort.

To solve this problem, it is proposed that the plunge pool be arranged below the front end of the tube in the conveying direction and extend from an area located at a distance in front of the small-parts feed opening to a portion, in particular approximately half, of the length of the tube, wherein the front edge and the side edges of the plunge pool form the coating agent weir edge, which is formed in the conveying direction of the weir rear edge by a region of the conveyor screw, the smallest distance from the deepest point of the tube is at least equal to the weir line in line, preferably protrudes beyond this line of alignment, which protrudes in the conveying direction the edge of the immersion basin lying at the back lies sealingly against the outer wall of the pipe in the area of the screw conveyor forming the rear weir edge, the pipe having a coating agent outlet in the area following in the conveying direction.

This design makes it possible to paint small metallic parts in a continuous, continuous process by means of electro-dipping, a high material throughput being possible with low personnel expenditure.

The small parts can be fed to the screw conveyor with a conventional conveyor. The finished coated small parts can also be removed by means of a conveyor device arranged downstream of the screw conveyor.

It is particularly advantageous that in this way a sufficient fill level of coating agent is maintained within the tube, wherein the coating agent can also be removed from the tube in the area following the actual coating zone and can be supplied to the coating process again by suitable means.

A possible development is seen in the fact that the screw conveyor is designed as a belt screw.

Such screw conveyors are known per se in the prior art, a belt screw in the form of a helically wound belt being rotatably mounted in a stationary tube, by means of which the throughput of small parts is made possible.

Although this device is useful, it is disadvantageous that such a screw conveyor has internal components Bearings are provided and in addition a clamping and clogging of the material to be conveyed is possible due to the relative movement of the belt screw to the pipe surrounding it.

It is therefore preferably provided that the screw conveyor is designed as a conveying tube, the circumferential tube of which is the small-part support member and has a band screw attached to the inner circumference as a pushing member, the open ends of the conveying tube forming the small-part feed and the small-part discharge opening.

Such screw conveyors are also known per se in the prior art.
The advantage of this screw conveyor is that no internal bearings are provided and also due to the fixed arrangement of the belt screw on the rotating tube, there is no jamming or clogging of the material to be conveyed.
It is also advantageous that the delivery and delivery of the material to be conveyed can take place at the pipe ends. Here, too, suitable conveying means for feeding and discharging can be arranged upstream or downstream of the conveying pipe.

It is preferably provided that the height of the belt screw in the area from the small part feed opening to the area forming the rear weir edge is lower than the level height in the tube determined by the weir.

This also enables a sufficient level of the coating agent to be achieved within the tube so that the small parts can be coated evenly and completely.

It is also preferably provided that the tube is perforated at least in the circumferential area immediately following in the conveying direction of the rear edge of the immersion basin, preferably also in the coating zone located in front of it in the conveying direction.

The perforation of the tube in the circumferential area immediately following in the conveying direction of the rear edge of the plunge pool ensures that the coating agent can flow off and drip off there, so that the coated small parts can be discharged at the discharge end of the tube without excess coating agent. In order to promote the access to coating agents in the area of the coating zone of the tube, the perforation of the tube in this area is also beneficial and advantageous.

It is also preferably provided that a collecting basin is arranged below the immersion basin and below the perforated area of the tube.

Excess coating agent which emerges at the perforation zone of the tube following the coating zone can be collected by this collecting basin, as can coating agent, which runs over the front and side weir edge of the plunge pool.

In a further development it is preferably provided that the device comprises a coating agent feed pump, the inlet of which is connected to the collecting basin and the outlet of which leads into the immersion basin or, preferably, to a spray device which is inserted into the front pipe mouth and is aimed at the coating zone of the pipe.

The collecting basin preferably has a shape which leads to a collection of the coating agent at a low point, at which point the coating agent can also be drawn off by means of the coating agent feed pump. The coating agent can then be reintroduced into the coating zone or into the immersion tank by the pump in order to use it for further coating.

A preferred further development is seen in the fact that the tube is made of plastic or other electrical, non-conductive material, in which area from the mouth to the end of the coating zone is interspersed with button-like contact pins which protrude from the tube wall on the inside of the tube and in the circumferential direction on the outside of the tube and / or are connected to one another in the axial direction by externally electrically insulated contact rails, the Contact rails are guided to a circumferential busbar attached to the outside of the pipe near the pipe end, which is connected to a pole of the power source via sliding or rolling contacts.

This arrangement creates an extremely functional device, the contact pins protruding from the tube wall like a mushroom head being continuously cleaned by means of the continuously supplied small parts to be coated, so that a good contact transition between these contact pins and the small parts is made possible.

A further preferred embodiment is seen in the fact that the device is held in a frame which also holds bearing rollers for the tube and a drive motor for the tube, the drive motor being coupled to a drive pinion which engages with a ring gear attached to the outside of the tube stands.

Finally, it is preferably provided that the other pole of the current source is connected to a contact plate which forms the second electrode and which is arranged below the tube in the plunge pool.

An embodiment of the invention is shown in the drawing and described in more detail below.

Fig. 1

eine Ausführungsform der Erfindung im Mittellängsschnitt gesehen;

Fig. 2

im Schnitt II-II der Fig. 1 gesehen.

It shows:

Fig. 1

seen an embodiment of the invention in the central longitudinal section;

Fig. 2

seen in section II-II of Fig. 1.

The device for electrolytic coating (electrodeposition) of small parts with electrical conductivity, in particular metal parts, consists of a screw conveyor, generally designated 1, which has on the inside of its conveyor tube 2 electrically conductive contacts 3, which are connected to one pole of the DC power source, not shown in the drawing are.

The screw conveyor 1 dips with a part of its cross-section into a plunge pool 4, which is connected to the other pole. The level 5 of the immersion basin cuts the cross section of the tube 2 in a secant manner in its lower region. In the exemplary embodiment, the screw conveyor is designed as a conveying tube 2, the circumferential tube 2 of which is the small-part support member, and has a belt screw 6 attached to the inner circumference as a pushing member for the small parts. The open ends of the conveyor tube 2 form the small-part feed opening (on the left in the figure 1) and the small-part discharge opening (on the right in the figure 1).

The plunge pool 4 is arranged below the front end of the tube 2 in the conveying direction and extends from an area located at a distance in front of the small parts feed opening to approximately over half the length of the tube 2. The front edge 7 and the side edge 8 of the dip pool form 4 a weir edge for the coating agent. The weir edge at the rear in the conveying direction is formed by an area of the belt screw, the smallest distance from the deepest point of the tube (in the drawing figures 1 and 2 below) can be equal to the line of alignment of the weir edge, but preferably, as shown in the exemplary embodiment, via this line of alignment, which is indicated by the fill level 5, protrudes. The edge 10 of the immersion basin 4 lying at the rear in the conveying direction lies in a sealed manner (area 11) on the outer wall of the tube 2, specifically in the area of the screw belt (9) forming the rear weir edge. The pipe 2 has a coating agent drain 12 in the area following this area in the conveying direction. The height of the belt screw 6 is in the range from the small part feed opening (left in the drawing FIG. 1) to the area (9) forming the rear weir edge is lower than the level height 5 in the tube 2 determined by the weir. The tube 2 is perforated at least in the peripheral region immediately following in the conveying direction of the rear edge 10 of the immersion basin 4, but preferably also in the coating zone located in front of it in the conveying direction. The perforation is indicated at 13.

A collecting basin 14 is arranged below the immersion basin 4 and below the perforated area 13 of the tube 2.

The coating agent passing over the weir edge 7, 8 and the coating agent running behind the edge 10 can be collected from this collecting basin and fed to the coating process again. For this purpose, the device has a coating agent feed pump 15, the input of which is connected via a line 16 to an outlet opening located at the deepest point of the drain basin 14, while the outlet of which is connected via a connecting line 17 to a spray device 18 which leads into the front opening of the tube 2 is used and aims in the coating zone of the tube 2.

The tube 2 is preferably made of plastic. In the area located from the mouth to the end of the coating zone, the tube 2 is penetrated by button-like contact pins 3, which protrude from the tube wall on the inside of the tube like a mushroom head and are connected to one another in the circumferential direction and / or in the axial direction on the outside of the tube by contact rails 19 which are electrically insulated from the outside.

The contact rails 19 are guided to a circumferential busbar 20 which is fastened to the outside of the casing near the pipe end and which is guided by grinding or Roller contacts 21 are connected to a pole of the power source. This pole can form the cathode, for example, so that the contact pins 3 have corresponding potential. The other pole of the power source is connected to a contact plate 22 which forms the second electrode (in the example, the anode) and which is arranged below the tube 2 in the immersion pool 4 and thus brings the coating agent to the appropriate potential.

The fact that the perforation 13 is formed in the region of the entire coating zone ensures that the coating agent is well flooded. By arranging the contact plate 22 below the perforation 13 in the coating zone, a uniform current flow to the parts to be coated is achieved, and in addition a short path is formed for the current flow from the contact plate 22 through the perforation 13 to the workpieces to be coated, as regards the electrical power to be applied is advantageous. This arrangement results in a uniform workpiece coating with a relatively low output. The entire device is held in a frame 23 and placed on the floor 24. The frame comprises bearing rollers 25 for the tube 2 and a drive motor 26 for the rotary drive of the tube 2, the drive motor 26 being coupled to a drive pinion 27 which is in engagement with a ring gear 28 fastened to the outside of the tube 2. For electrolytic coating, that is first Plunge pool 4 filled so that the fill level 5 is set. Subsequently, small parts can then be filled into the tube 2 through the filling opening, which small parts are then conveyed through the tube 2 due to the belt screw 6. In doing so, they inevitably pass through the zone provided with the coating agent, whereby they are brought to the corresponding electrical potential by contacting the contacts 3, while the coating agent has the opposite potential. The coating takes place at a relatively high voltage and low current, for example at 50 amperes and 220 to 250 volts.

The coating time is about 4 seconds. The coated small parts then pass through the zone of the tube which follows the higher belt area 9 and in which excess coating agent can run through the perforation 13 of the tube 2 and can collect in the collecting container 14. The small parts are then delivered to the delivery opening of the tube, for example placed on a downstream conveyor.

The device according to the invention is extremely compact and very functional, a high throughput of parts to be coated being possible with a short dwell time and with the help of a small number of operating personnel.

The invention is not limited to the exemplary embodiment, but is often variable within the scope of the claims.

In order to give an impression of the size of the device, it is pointed out that in the exemplary embodiment the diameter of the tube is 1 meter.

Claims (10)

1. A device for the electrolytic coating of small parts with electrical conductivity, in particular metal parts, wherein the device comprises a bath of electrically conductive fluid coating medium, the bath is in electrically conductive communication with the one pole of a direct current source (cathode or anode), while the article to be coated is in electrically conductive communication with the other pole (anode or cathode) of the direct current source and the device consists of a worm conveyor (1) with loading and unloading openings at its conveyor pipe ends and with conveyor worms inside the conveyor pipe, the inner side of its conveyor pipe (2) has electrically conductive contacts (3), which are connected to the one pole of the direct current source, and that the worm conveyor (1) is inserted with a part of its cross section into an immersion basin which is connected to the other pole, characterised in that the immersion basin (4) is disposed beneath the end of the pipe (2) at the front in the conveying direction and extends from a region located at a distance in front of the small part supply opening to beyond a part, in particular roughly the half, of the length of the pipe (2), the front edge (7) and the side edges (8) of the immersion basin (4) forming the coating medium weir edge, the weir edge at the rear in the conveying direction is formed by a region (9) of the worm plate (6), the shortest distance of which to the lowest point of the pipe (2) is at least equal to the overflow line (5) of the weir edges, preferably protruding above this overflow line (5), with the edge (10) of the immersion basin (4) lying at the rear in the conveying direction abutting in sealed manner the outer wall of the pipe in the region of the worm plate forming the rear weir edge, with the pipe (2) comprising a coating medium drain (12) in the region following this region in the conveying direction.
2. A device according to Claim 1, characterised in that the worm conveyor (1) is constructed as a worm plate.
3. A device according to Claim 1, characterised in that the worm conveyor (1) is constructed as a conveyor pipe (2), whose circumferential pipe (2) is the small part bearing component and has a worm plate (6) fixed to the inner circumference as a thrust component, with the open ends of the conveyor pipe (2) forming the small part supply and the small part discharge openings.
4. A device according to Claim 1 or 3, characterised in that the height of the worm plate (6) in the region of the small part supply opening to the region (9) forming the rear weir edge is lower than the level (5) in the pipe determined by the weir.
5. A device according to Claim 1, 3 or 4, characterised in that the pipe (2) is perforated (at 13) at least in the circumferential region directly following in the conveying direction of the rear edge of the immersion basin (4), and preferably also in the coating zone located in the conveying direction in front of said region.
6. A device according to one of Claims 1 to 5, characterised in that a collection basin (14) is disposed beneath the immersion basin (4) and beneath the perforated region (13) of the pipe (2).
7. A device according to Claim 6, characterised in that the device includes a coating medium feed pump (15), the inlet of which is connected to the collection basin (14) and the outlet of which leads into the immersion basin (4) or preferably to a spray device (18), which is inserted into the front pipe opening and enters the coating zone of the pipe (2).
8. A device according to one of Claims 1 to 7, characterised in that the pipe (2) is made from plastic or other electrically non-conductive material, in the region located from the opening to the end of the coating zone is covered by knob-like contact pins (3), which on the inner side of the pipe protrude from the pipe wall in the manner of mushrooms and on the outer side of the pipe in the circumferential direction and/or in the axial direction are connected to one another by outwardly electrically isolated contact rails (19), wherein the contact rails (19) are run to a circumferential conductor rail (20) which is attached close to the pipe end on the outside of its casing and which is connected via sliding or rolling contacts (21) to one pole of the current source.
9. A device according to one of Claims 1 to 8, characterised in that the device is mounted in a stand (23), which in addition supports bearing rollers (25) for the pipe (2), with the driving motor (26) being coupled with a driving pinion (27), which is in engagement with a toothed ring (28) attached to the outside of the pipe (2).
10. A device according to one of Claims 1 to 9, characterised in that the other pole of the current source is connected to a contact sheet (22) forming the second electrode, which is disposed beneath the pipe (2) in the immersion basin (4).

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