MEANS IN CURTAIN-PAINTING MACHINES

Abstract: Painting with curtain-painting machines (9-12) is complicated by the occurrence of air bubbles in the paint, causing an uneven paint surface. This is avoided by allowing the paint to pass a compensator with overflow (6), the paint being supplied to the compensator (5) at a level below that of the overflow (6) in such a manner that air enclosed therein strives upwards towards the space above the overflow.

Description: Means in curtain-painting machines The present invention relates to a curtain-painting machine. In such installations a conveyor is used where objects to be painted are moved at a predetermined speed and pass a liquid curtain of paint, varnish or some other liquid with which they are to be coated. The liquid is sprayed from a nozzle arranged transverse to the conveyor. The nozzle has the shape of a long, narrow slit. The liquid jet from the nozzle is in the form of a thin curtain and is collected in a transverse trough located below the conveyor. It has proved extremely difficult to ensure that the coating liquid from the nozzle is free from air in the form of air bubbles. Those bubbles which have not been eliminated will appear in the coating on the objects passing through the liquid curtain and burst during the subsequent drying process. Craters thus occur and the coated surfaces are therefore not smooth and must there¬ fore be ground and re-coated. It has been found that the rejection rate for objects passing a liquid curtain is about 10$ due to the occurrence of air bubbles. It has also been found that air enters the coating liquid partly during the mixing process and partly when the liquid is pumped to the spray head of the coating machine. Pumping has hitherto been performed by centrifugal pumps and such pumps have a tendency to m iχ air into the coating mixture. The object of the present invention is to eliminate as far as possible the formation of air bubbles in the coating liquid. This is realized according to the present invention by the coating liquid, before being supplied to the spray head, being allowed to pass through a liquid container provided with an overflow, the coating liquid being supplied to the container at a level below that of the overflow, with such a flow direction that air enclosed in the coating liquid strives towards the space in the liquid container located above the overflow, thus liberating the enclosed air. According to a preferred embodiment of the present invention, the outflow direction of the coating liquid supplied can be selected in such a way relation to the overflow that liberated air flows along or close to the inner surface of the liquid container, preferably in such a way that the flow-path for the liberated air covers ca.75? of the inner periphery of the liquid container. The liquid container thus acts as air separator. The coating liquid is preferably supplied to the spray head from the bottom of the liquid container. According to the invention, furthermore, it is advantageous to supply coating liquid to the liquid container by means of a plunger pump instead of a centrifugal pump. Additional characteristics of the present invention are revealed in the following claims. The invention will be described in more detail with reference to the accompanying two drawings in which Fig.1 shows a curtain-painting machine and Fig.2 shows a compensator included in the installation according to Fig.1. Figure 1 shows an installation comprising a curtain-painting machine which might be the Spanish-made Barberan, for instance. In the draw¬ ings 1 is a paint container which is supplied with paint in one way or another from a paint-mixer. The paint container is connected by a pipe 2 to a pump 3 to convey the paint further. The pump may have the same or equivalent characteristics as a pump manufactured by Atlas Copαo under the designation Ecco Flow A 41. The pump is described in leaflet Sw 13010 b. The pump is joined by a pipe 4 to a paint compensator 5 having an outlet pipe 6 acting as overflow. The orifice 7 of the pipe 4 inside the paint compensator 5 is at a level below that of the overflow. The orifice is so directed that the air contained in the paint flowing from the orifice strives upwards towards the top of the paint compensator. Furthermore, the orifice is so directed that liberated air endeavours to flow along the inner surface of the paint compensator 5 to the pipe 6. A suitable placing of the orifice 7 in relation to the pipe 6 should be such that liberated air can flow along ca.75? of the inner periphery of the paint compensator before reaching the pipe 6. A pipe 8 at the bottom of the paint compensator 5 conrjects this to a curtain head or spray head 9 having an opening in the form of a long, narrow slit. An outlet pipe 10 is provided in the curtain head 9 for the paint which does not flow through the narrow slit. Said outlet pipe 10 connects the curtain head to the return channel 11. The pipe 6 is also connected to said return channel 11. Between the curtain head 9 and the return channel 11 is a space 12 or passage for objects to be coated with paint. The arrow 13 indicates the direction of movement of said objects. The return channel is provided with a feedback pipe 14 to return unused paint collected in the return channel 11 to the paint container 1. The paint compensator is closed at the top by a closure 15. The installation described functions as follows. Paint is first mixed in a conventional mixer and then supplied to the container 1. The paint in the container 1 is pumped by pump 3 to paint compensator 5. When so much paint has been supplied to the compensator 5 that the level is up to the overflow or outlet pipe 6, the flow direction of paint subse¬ quently supplied to the container will be up towards the liquid level of the overflow. • Air inclusions in the paint will therefore strive towards the surface, pass this and collect in the space above the liquid level. Air liberated is removed through the pipe 6. The paint is supplied from the compensator 5 to a curtain or spray head 9 and leaves the narrow slit of the curtain head to form a liquid curtain which flows down to the return channel 11. The objects to be painted are passed at a predetermined rate through the gap 12 and thus through a curtain of paint. Painting is not normally started until the compen- sator 5 contains only paint without any air bubbles and the curtain- painting machine must therefore run for a while after the compensator has been filled to the overflow. This is so that the quantity of paint in the compensator before reaching the overflow level can be returned to the paint container 1. OMPI It has proved advantageous to direct the orifice 7 and pipe 6 in such a way that the air released can flow approximately three quarters of the way around the inner surface of the compensator before liberated air reaches the outlet 6. The use of a plunger pump 3 to supply paint to the paint .compensator 5 has the advantage that paint supplied to the compensator contains less air bubbles than if it had been supplied via a centrifugal pump.

Claims: CLAIMS 1. Means for reducing the occurrence of air, air bubbles for in¬ stance, in paint, varnish and the like in liquid form, in plant and equipment for applying paint such as curtain-painting machines, characterised by a compensator (5) having an overflow (6), an outlet (8) to plant or equipment (9-12) located below the level of the overflow (6), preferably at the bottom of the com¬ pensator (5), and an inlet (4) with orifice (7) so arranged that, when the paint level in the compensator (5) is above the orifice (7), preferably up to the overflow (6), the air in the paint supplied strives to leave it via the surface of the liquid in the compensator (5). 2. Means according to claim 1, characterised in that said orifice (7) of the inlet (4) is so arranged that air liberated flows along or close to the inner surface of the compensator (5) to the overflow (6). 3. Means according to claim 2, characterised in that the orifice (7) and the overflow (6) are so positioned in relation to each other that the path for the liberated air covers ca.75? of the inner periphery of the compensator (5). 4. Means according to any of the preceding claims, characterised in that paint is supplied to the compensator (5) via a plunger pump.

Inventors: ELF ROY VERNER LENNART, ELF, ROY, VERNER, LENNART
Applicants: ELF ROY VERNER LENNART, ELF, ROY, VERNER, LENNART
Application year: 1984
Main classification: B05C5
IPC codes: B05C5