EP0040369A1

EP0040369A1 - Apparatus for the surface treatment of an object

Info

Publication number: EP0040369A1
Application number: EP81103487A
Authority: EP
Inventors: Yoshinobu Takahashi; Yasuo Tokushima; Kentaro Ogata; Mamoru Suzuki; Jyoji Ito; Kenji Fukuta
Original assignee: Toyota Motor Corp
Current assignee: Toyota Motor Corp
Priority date: 1980-05-12
Filing date: 1981-05-07
Publication date: 1981-11-25
Also published as: DE3162243D1; EP0040369B1

Abstract

An apparatus for applying surface treatment on an object-to-be-treated which is continuously moved in a treating liquid usually by a hanging conveyor. The apparatus is provided at the bottom portion of a treating vessel (3, 20, 60) with one or more hoppers (18, 22, 64), which function to collect the deposited sludge for exhausting the same through the lower portion of the hoppers (18, 22, 64) outside the treating vessel (3, 20, 60). Further, the apparatus is provided with a plurality of slant plates (24,68,70) disposed above the bottom of the treating vessel (20, 60), being inclined in the same direction, with a predetermined inter-distance among them, so as to facilitate a sludge produced in the vessel to be gradually precipitated or deposited down on the bottom thereof.

Description

This invention relates to an apparatus for surface treatment effectively applicable for treating or finishing the surface of metal articles or objects when chemical coating, plating, etching, etc., is carried out.
Various methods have conventionally been known for treating or finishing the surface of metal articles, such as chemical coating, plating, etching, etc. Above all chemical conversion treatment for forming some kinds of corrosion resistant films on the surface of steel plates or steel bars by means of chemical reaction or electro-chemical reaction is known, and more particularly phosphating, wherein zinc phosphate, manganese phosphate, ferrous phosphate, etc., are employed, is widely known. And it is widely practiced as a method of surface preparation when steel members are coated in the field of, for example, car assem- blying, bridge building, or manufacturing of household electrical appliances.
When practicing such a surface treatment objects-to-be-treated must be in general contacted with the treating liquid, and either of two ways, a spraying method in which the liquid is sprayed over the surface of the objects-to-be-treated and a dipping method in which the objects are dipped in the liquid, is selected for contacting the objects with .the liquid. The former spraying method is unsuitable for treating objects of complicated shape, for example car bodies which have portions difficult to be uniformly treated by spraying such as a fender, a door, or a constructed part into a box-like shape. The liquid is liable not to sufficiently reach the inside surface of complicated corner, leaving sometimes untreated portions or sometimes unsatisfactorily treated portions. The latter dipping method is much better than the former in respect of the liquid reaching to many quarters of the objects-to-be-treated, but it still leaves something to be desired because the sludge produced in the period of dipping'of the objects-to-be-treated into the liquid is deposited on the bottom of a treating vessel so as to cause some troubles in a continuous surface treatment.
In a chemical conversion process as one of the surface treatments, more specifically speaking chemical reaction taking place between a steel plate as an object-to-be-treated and a treating liquid containing phosphate produces attempted crystal coating on the surface of the steel plate. In the course of this chemical reaction, however, by-products called sludge are produced there. This chemical conversion sludge created in the course of a side reaction did not give rise to so serious problematical trouble in the conventional spray method as shown in Fig. 1 wherein phosphate conversion coating was made on the surface of the object Wi by means of the spraying S, because the forced pressure of the spraying S naturally prevented sticking of the sludge onto the coated surface of the object W1. The sludge has however recently become a serious factor for deteriorating the quality of the articles since the surface treatment had been gradually changed to the full dipping treatment method, wherein the object W₂ is completely dipped in the treating liquid. In this full dipping method the sludge is liable to be floated in suspension in the treating liquid. This kind of chemical conversion sludge is not only floated in a treating vessel containing the liquid but also flung up from the bottom of the vessel on which it has once been deposited due to the movement of the object-to-be-treated W₃ in the vessel. The sludge possibly stuck to the crystal coating or contained in the formed coating deteriorates the corrosion resistance of the coating or adversely affects the forthcoming electro- depositing process. It is therefore highly desirable to advantageously discharge or exhaust such harmful problem- arising sludge out of the vessel.
Conventionally leading of the liquid out of the system or vessel, by recycling the same outside and inside the vessel, was practiced for removing the sludge. A sludge removing apparatus disposed outside the vessel is apt to occupy an innegligible space and impose an innegligible cost. It is naturally accompanied by some other problems such as complicacy of piping for recycling, increasing of the recycled amount of the liquid, etc., and a still unsolved problem is flinging up of the deposited sludge on the vessel bottom.
It is a primary object of this invention, which was made against such a background, to provide an apparatus for the surface treatment, being substantially relieved of the conventional disadvantages, capable of continuously removing the sludge produced in the full dipping method from the bottom of the treating vessel.
The apparatus for performing the above-mentioned surface treatment in accordance with this invention is provided, as an essential feature, at the bottom portion of the treating vessel with one or more hoppers, which function to collect'the deposited sludge for exhausting the same through the lower portion of the hopper outside the treating vessel. Another essential feature of this invention is provision of a plurality of slant plates disposed above the bottom of the treating vessel containing the treating liquid for performing an aimed surface treatment by dipping an object-to-be-treated in a treating liquid such as chemical conversion solution like phosphate; the slant plates are disposed, being inclined in the same direction, with a predetermined inter-distance among them. The sludge produced in the treating liquid is gradually precipitated, while being floated therein, on the bottom of the vessel through the gap or clearance between the slant plates, which are not contacted with the vessel bottom. This disposition of the slant plates facilitates the sludge produced in the vessel to be gradually precipitated or deposited down on the bottom thereof, by well functioning as protecting walls, almost not being affected by the flowing of the liquid and the movement of the objects-to-be-treated. In'such an apparatus the deposited sludge can not be flung up into the liquid again by virtue of the slant plates, but can be easily taken away out of the vessel.
A few concrete examples will be described hereunder with reference to the appended drawings, in which:

Fig. 1 is a schematic cross-sectional view of a conventional surface treatment apparatus;
Fig. 2 is a schematic transverse sectional view of an embodiment of an apparatus for surface treatment in accordance with this invention; and
Figs. 3 and 4 are respectively a schematic transverse sectional view of a different embodiment of an apparatus for surface treatment in accordance with this invention.

An apparatus shown in Fig. 2 relates to, for example, zinc phosphating process as a preliminary treatment on an object-to-be-treated W₂ such as a car body when it is applied with coating. As a first step for applying the zinc phosphate treatment the object W₂ is degreased with a -trichloroethylene or alkaline solution, followed by water cleaning and contact with titanium phosphate solution as a second step. In this. way nuclei of phosphate coating crystals are formed on the surface of the object W₂. An object W₂ which has been applied with such surface preparation is conveyed, being suspended from a hanging conveyer 2 as shown in Fig. 2, from left to right for being dipped into treating liquid 4 at the left part of a treating vessel 3.
The object W₂ which has been dipped into the treating liquid 4 at the initial stage of the process, i.e., left end of the treating vessel 3 is gradually conveyed toward the final stage on the right side end for being completely covered in the meantime by the continuously grown zinc phosphate crystals all over the surface thereof. The time required for this process is within the range of 60-300 seconds.
The treating vessel 3 is provided on the end of the initial stage side, namely on the left side end, with an overflow outlet 3a for allowing the overflow of the liquid 4 therefrom, and the overflowed liquid 4 is recovered by a recovering tank 5 for being reservoired therein. Over the recovering tank 5 a shelter plate 5a is disposed for sheltering the forthcoming objects W₂ not to be affected by the mist or vapor of the liquid 4. The liquid 4 recovered into the recovering tank 5 is returned by way of a return passage 6, after having been heated to a predetermined temperature while passing through a heat exchanger 8 due to the action of a pump 7, to a gush-spraying pipe 9, having a suitable number of gush-spraying openings or holes, disposed above the bottom of the treating vessel 3. The liquid 4 in the treating vessel 3 is due to this recycle thereof imparted a counterflowing force against the movement direction of the objects W₂, which largely contributes to promoting uniform contact between the liquid 4 and the travelling objects W₂ therein.
In this surface treatment process of the objects W₂ sludge consisting of ferrous phosphate and others is produced as mentioned above, and one or more hoppers 18 of funnel shape are formed as extensions from the bottom portion of the vessel 3 for depositing or precipitating the sludge on the bottom of the hopper 18. The sludge piled to a predetermined amount is discharged from the lower portion of the hopper(s) 18 by the action of a pump (11) or head pressure into a sludge containing liquid passage 10 for being filtered by a filter 12, or a solid-liquid separating means. The filtrate is recycled through a filtrate return passage 14 by the action of a pump 13 to a gush-spraying device 15 disposed on the final stage side of the vessel 3 so as to be gush-sprayed there. In this case the filter 12 may be replaced by a centrifugal separator or the like. At this position, i.e., the final stage of the vessel 3, the object W₂ is lifted out of the liquid 4, so the gush-spraying 17 of the recycled liquid at this position is highly effective in double advantage of washing away the sludge attached to the object W₂ and recovering the residual heat thereof. The object W₂ is washed then by a water gush-spraying pipe 16 for the purpose of washing away the still residual sludge and' cooling by means of recovering the still residual heat and consequently preventing the object W₂ from being dried. The zinc phosphating coating formed in this way is chiefly made of fine particles of phosphophyllite highly excellent in corrosion resistance and uniform regardless of position in, and shape of, the object-to-be-treated W₂.
According to the structure of the above-mentioned embodiment, the sludge produced in the course of a surface treatment is facilitated to drop downwards to be deposited quickly owing to the shape of the hopper, made one or more in number, extending downwards from the bottom of the vessel in an almost inverted triangle shape, gradually diminished its width toward the lower end thereof. Separating efficiency of the liquid and the sludge in the vessel is enhanced satisfactorily, and the liquid is effectively recovered through the separation by the solid-liquid separating means for minimizing the liquid loss. The gush-spraying of the object W₂ just lifted out-of the liquid in the vessel with the recycled liquid from the separating means is quite effective and rational in either of the sludge washing away and of the heat recovering.
In another embodiment of this invention shown in Fig. 3 a treating vessel 20 of different shape from the prior art is disposed for containing zinc phosphating solution which is a kind of known liquid for chemical conversion treatment. This vessel 20 is provided with four hoppers 22 (generally several in number) of funnel shape at the bottom portion thereof, being horizontally arranged in series in parallel to a conveying direction Y of the objects-to-be-treated W₃. Within those hoppers 22 a multiplicity of slant plates 24 inclined by an angle (a) of 45-90° against the conveying direction of the objects W3 are arranged parallelly with each other, keeping away from a wall surface 23 of the hopper 22 with a predetermined distance, viz., being not in contact therewith. Those slant plates 24 function as protector walls for preventing the deposited sludge from being stirred by the flowing movement of the treating liquid. Besides, each hopper 22 is provided at the lower end thereof with a one-way valve 26.
The treating vessel 20 is further provided with undermentioned several devices: a slant gush-spraying pipe 28 and a horizontal gush-spraying pipe 30 disposed on the rightward end portion, in Fig. 3, of the vessel 20 for gush-spraying the treating liquid to the objects W₃ which are moved by a inclined conveyor 27 into the liquid in the vessel 20; a gushing nozzle 34 disposed, above a horizontal bottom portion 32 of the vessel 20 on the rightward side away from the hoppers 22, in communication with the slant gush-spraying pipe 28, for gushing the liquid toward the hoppers-arranged direction; and a recovering tank 36 for reservoiring the liquid overflowed out of the treating vessel 20.
In this embodiment of such a structure the objects W₃ are transported in suspended state from the conveyor 27 in the direction designated with the arrow Y for being dipped into the liquid, while a part of the-liquid reservoired in the recovering tank 36 is led, via conduits 38, 40, to the slant gush-spraying pipe 28 and via conduits 38, 42 to the horizontal gush-spraying pipe 30 by the action of a pump P₄, for being gush-sprayed onto the just incoming objects W₃. The rest of the liquid in the recovering tank 36 is led, by the action of pumps P₅, P₆, via conduits 38, 44 back into the vessel 20 for being recycled, while making a counterflow in the direction designated by an arrow X against the movement of the objects IV3 in the liquid, to the recovering tank 36.
In the'initial stage of the dipping of the objects W₃, from the beginning of dipping to the start of leftward movement in Fig. 3 after the complete dipping, strong or vehement chemical reaction progresses between the object W₃ and the treating liquid while producing large amount of sludge. The sludge is however precipitated by the action of gravity in each of the hoppers 22 extended from the lower portion of the vessel 20 and on the horizontal portion 32 is collected into the hopper 22 by virtue of the gush-spraying of the liquid ,from the gushing nozzle 34 disposed on the conduit 40. The sludge precipitated into the hoppers 22 comes first onto each of the parallelly arranged slant plates 24 and then drops through the gap therebetween as far as the wall surface of the individual hoppers 22, for finally being collected along the wall surface in the lower portion 46 of the respective hopper 22. The sludge collected there in this way is intermittently delivered to a separater 50, by the action of a pump P_7. via the one-way valve 26 and the conduit 48. The liquid containing the thus collected sludge is separated at the separater 50, which is located out of the recycling circuit, for being returned to the recovering tank 36 or to a gush-spraying device (see 15 in Fig. 2) disposed on the final stage side of the vessel 20.
As the slant plates 24 arranged horizontally with each other in the lower portion of the vessel 20, and particularly in this case within the hoppers 22, are inclined against the flowing direction X of the liquid, i.e., the same direction to the object conveyance, stirring of the sludge collected in the lower portion 46 by the liquid flowed into between the slant plate 24 can not occur. And the conveyance operation of the objects as well as the gush-spraying of the liquid from the slant gush-spraying pipe 28 and the horizontal gush-spraying pipe 30 can not cause stirring or flinging up of the sludge, either, because the slant plates 24 well prevent the phenomenon by functioning as protector walls. In other words, the above described structure effectively protects the objects-to-be-treated IV3 from being deteriorated in quality by sticking of the sludge in floatation or flung up from the lower portion 46 of the hopper 22 in the course of the surface treatment. As described earlier the sludge deposited on the horizontal portion 32 is also removed therefrom into the lower portion 46 of the hopper 22 by the gushing of the liquid from the gushing nozzle 34, which means complete relief of the sludge from the bottom portion of the vessel 20. This invention can be said to have succeeded, through remarkable decrease of the floating and depositing sludge, in improving the quality of the surface treatment, particularly the anti-corrosion coating quality, of the objects-to-be-treated W₃.
In the description of the above embodiment all of the hoppers 22 arranged in series are of the same size, but a modified type wherein the nearest hopper 22 to the object- incoming side end is made the largest in capacity and others are made gradually smaller toward the leftward end is preferably recommended, because the sludge producing rate is largest at the initial stage of contact between the object W₃ and the liquid.
Still another embodiment will be described with reference to Fig. 4, wherein an object W₄ suspended by a conveyor 62 is, after it has been completely dipped in zinc phosphating solution contained in a treating vessel 60, moved therein for being given chemical conversion treatment in the meantime just like in the previous embodiment. The only difference lies-in the structure of the bottom portion of the vessel 60. In this embodiment only one hopper 64 of funnel shape is formed at the leftward end of the bottom portion, and the rest of the bottom portion is left as a flat portion 66. Above the flat portion 66 a multiplicity of slant plates 68 inclined at an angle (S) of 45-90° are arranged, parallelly to each other with a predetermined interdistance, in the horizontal direction and along the conveyance direction Y of the objects-to-be-treated W₄. They are not in contact with the flat portion 66, just like slant plates 70 which are similarly arranged in the hopper 64 parallelly with each other and kept'away from a wall surface 72 of the hopper 64 by a predetermined distance.
On the flat portion 66 a suitable number of gushing nozzles 74 are arranged parallelly thereto for gushing the liquid toward the hopper 64 so as to wash away the deposited sludge thereon.
When an object W₄ suspended from a conveyor 62 is transported in the direction designated with an arrow Y to be dipped into the liquid in an apparatus of such a structure, producing of the sludge is begun by the chemical conversion treatment.. And the sludge thus produced is precipitated through the clearance(s) between the slant plates 68 onto the flat portion 66 of the vessel 60 and also to the lower portion of the hopper 64 along the slant plates 70 while passing the clearance(s) therebetween. The liquid in a recovering tank 76 is via conduits 78, 80 by the action of a pump P₈ led to each of the gushing nozzles 74 for being gushed therefrom respectively. The sludge deposited on the flat portion 66 is therefore collected to the hopper 64 passing through the clearance formed between the slant plates 68 and the flat portion 66. The sludge collected in the hopper 64 is led via a one-way valve 82 and a conduit 84 by the action of a pump Pg to a separater 86 which is located outside the recycle circuit of the liquid. The separated liquid in the separater 86 is returned to a recovering tank 76 or to a gush-spraying device 15, disposed on the final stage side of the vessel 60, which is shown in Fig. 2. The remaining liquid in the recovering tank 76 is led via conduits 78, 88 by the action of pumps P_lOand P₁₁ to the vessel 60 for being flowed in the direction designated with an arrow X so as to be re-utilized to the chemical conversion treatment of the objects W₄.
As the slant plates 68, 70 are, just like in the previous embodiment, inclined in the reversed direction X of that of the flowing of the liquid, they not only prevent the liquid from flowing therebetween but also prevent the deposited sludge from being flung up when the objects W₄ are moved in the liquid by functioning as protective walls.
This embodiment is particularly featured in eliminating disposition of many hoppers and consequently simplifying the structure of the bottom portion of the vessle, and besides in uniformalizing the shape of, as well as reducing the size of, the slant plates.
In the foregoing embodiments the slant plates 24, 68, 70 are all inclined with an angle (a, β) of 45-90° in the conveying direction of the objects W, the direction marked the arrow Y, that is reversed against the flowing direction of the liquid marked the arrow X. And it is true that the inclined direction of the slant plates is in the same way as the direction of conveyance of the objects W for the better effect of the slant plates as the protective walls, but this invention is not limited to this way of arrangement. A multiplicity of slant plates inclined in the inverted direction to the above embodiments are also allowable. As to the angle of inclination (a, S) of the slant plates 24, 68, 70, in this instance, the preferable range lies within 45-90°, as an angle larger than 45° is favorable for smoothly sliding down the sludge without staying on the plate, an angle less than 45° being contrary undesirable because of easy piling up of the sludge on the plate. This tendency of arresting the sludge of smoothly falling down from the surface of the plate, which consequently obliges the plate to be curtailed its length according to the extent of turbulence of the treating liquid.
Summarising the above described details of this invention, structure of the bottom portion of the treating vessel used for the surface treatment has been improved, accompanied by disposition of a multiplicity of slant plates functioning as the protective walls, with a remarkable result of preventing the sludge from being flung up in the course of the treatment for being smoothly removed out of the treating vessel. This effect of having enhanced the quality of treatment by preventing the once deposited sludge from being stirred up into the treating liquid and the recycling efficiency of the treating liquid by effectively removing the sludge therefrom is very significant from the standpoint of industrial efficiency.

Claims

1. An apparatus for surface treatment for applying a predetermined surface treatment on an object-to-be-treated by means of dipping said object in a treating liquid contained in a treating vessel, said apparatus characterized in that one or more hoppers (18, 22, 64) of funnel shape are disposed at the bottom portion of said treating vessel (3, 20, 60), in which said object (W) is dipped, for collecting precipitated sludge into said hoppers (18, 22, 64), and that said collected sludge is removed out of said treating vessel .(3, 20, 60) from the lower portion of said hoppers (18, 22, 64).

2. The apparatus in accordance with claim 1 characterized in that said object-to-be-treated (W) is continuously moved for being applied said predetermined surface treatment, by being dipped in said treating liquid contained in said treating vessel (3, 20, 60) while it is moved.

3. The apparatus in accordance with claim 1 characterized in that said surface treatment is a phosphating for forming a phosphate conversion coating on the surface of said object-to-be-treated (W).

4. The apparatus in accordance with claim 1 characterized in that a multiplicity of slant plates (24, 68, 70) inclined in the same direction are disposed, above the bottom portion of said treating vessel (3, 20, 60) containing said surface treating liquid, with a predetermined inter-distance so that floating sludge in said liquid may be precipitated through the clearance between said slant plates (24, 68, 70) onto the bottom portion of said treating vessel (3, 20, 60).

5. The apparatus in accordance with claim 4 characterized in that said slant plates (24, 70) are arranged in said hoppers (22, 64).

6. The apparatus in accordance with claim 4 or claim 5 characterized in that the multiplicity of slant plates (24, 68, 70) inclined in the same direction are disposed in a horizontal arrangement above flat portion (32, 66) of the bottom portions of said treating vessel (20, 60) where said hopper (22, 64) is not disposed, and at least one gushing nozzle (34, 74) is disposed above said flat portion (32, 64) for washing away the sludge precipitated on said flat portion (32, 64) with the gushing liquid into said hoppers (22, 64).

7. The apparatus in accordance with claim 4 characterized in that the angle (a, S) formed between said slant plates (24, 68, 70) and the direction of conveyance of the object-to-be-treated (W) is within the range o-f 45-90°.

8. The apparatus in accordance with claim 1 or claim 2 characterized in including conduit (10, 48, 84) connected to the lower portion of said hopper (18, 20, 64) for exhausting the sludge and a solid-liquid separating means (12, 50, 86) disposed in said conduit (10, 48, 84).

9. The apparatus in accordance with claim 8 characterized in that the treating liquid separated by the solid-liquid separating means (12) to be in a liquid phase is led to a gush-spraying means (15) disposed on.the object (W)-taking out side of said treating vessel (3) so that the object (W) taken out of the liquid may be gush-sprayed with said liquid by said gush-spraying means (15).

10. The apparatus in accordance with claim 2 characterizing in comprising an overflow outlet (_'3a) disposed on the side of said treating vessel (3) where the object (W) is initially dipped in the liquid, a recovering tank (5, 36, 76) for reservoiring the overflowed treating liquid, and a return passage (6, 38, 78) for returning said liquid from said recovering tank (5, 36, 76) to said treating vessel (3, 20, 78) by way of said return,passage (6, 38, 78) so that a counterflow of the liquid is made in said treating vessel (3, 20, 60) for being flowed in a reversed direction against the direction of conveyance of said object-to-be-treated (W).