GB2280123A

GB2280123A - Cleaning and phosphating ferrous workpieces in tanks having rotary impellers for liquid agitation

Info

Publication number: GB2280123A
Application number: GB9315180A
Authority: GB
Inventors: Jim Pearce
Original assignee: B SA
Current assignee: B SA
Priority date: 1993-07-22
Filing date: 1993-07-22
Publication date: 1995-01-25
Also published as: GB9315180D0

Abstract

A process for cleaning and phosphating ferrous workpieces involves immersing the workpieces in a liquid in a tank (20) and agitating the liquid in the tank by means of a rotary impeller (24). Two impellers (24) are provided on opposed upstanding walls, which are driven by external electric motors (30). The tank (20) is also provided with a heater (22) immersed in the liquid to heat it. The rotary impellers comprise a disc (24) with radial blades (25) having a low profile and rounded edges. A series of three tanks are used comprising respectively an aqueous cleaning and phosphating solution, cold rinse water and hot rinse water. <IMAGE>

Description

PROCESS AND APPARATUS FOR THE TREATMENT OF WORKPIECES This invention relates to an industrial process and apparatus for the treatment of workpieces.

Various industrial processes for the treatment of workpieces are well known, one such treatment being the cleaning and phosphating of ferrous workpieces frequently carried out prior to painting. Known methods of treatment include multi-stage spraying with liquids, and immersing in tanks containing still or agitated liquids. Suitable liquids may be mild or corrosive and include acids, alkalis, inhibited acids, inhibited alkalis, soaps, and detergents, using water or hydro-carbons as solvents.

Recent regulations now in force are designed to curb the use of hydro-carbon solvents for health and safety reasons, resulting in a widespread change to the use of water-based processes which are relatively less expensive to install and operate. The effectiveness of processes involving liquids in tanks, and particularly water-based liquids, is significantly improved by agitation, and known methods of agitating liquid in a tank include jetting air through a manifold normally disposed at the bottom of th & tank, employing vertically reciprocating platforms which alternately raise and lower the workpieces from and into the tank, drawing liquid from the bottom of the tank by means of a pump and discharging it on or near the surface, using ultrasonics the cavitation effect of which generates bubbles on the surfaces of the workpieces which dislodge dirt as they burst, and employing so-called "camel's back" conveyor systems for the workpieces.

The object of the present invention is to provide an industrial treatment process and apparatus for inexpensively and effectively agitating liquid in a tank.

According to one aspect of the invention, an industrial process for the treatment of workpieces comprises immersing them in a tank of liquid and agitating the liquid by means of at least one rotary impeller.

According to another aspect of the invention, an industrial process for the treatment of workpieces comprises immersing them successively in a plurality of tanks containing different liquids, and agitating the liquid in at least one of the tanks by means of at least one rotary impeller.

According to a further aspect of the invention, an industrial process for the treatment of workpieces comprises immersing them in a first tank containing a chemical solution and agitating the solution by means of at least one rotary impeller; next immersing them in a second tank containing cold water, passing a flow of cold water continuously through the second tank, and agitating the cold water by means of at least one rotary impeller; and then immersing them in a third tank containing hot water.

Preferably, the last-mentioned process further comprises heating the chemical solution in the first tank and the water in the third tank.

The treatment may comprise the cleaning and phosphating of ferrous workpieces.

The treatment is preferably water-based.

According to yet another aspect of the invention, apparatus for carrying out any of the processes defined above comprises a tank provided with at least one internal rotary impeller.

Preferably, the or each impeller is driven by an external electric motor.

The tank may be provided with two impellers on opposite walls thereof.

One practical embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings of which: Figure 1 is a side elevation of an installation for the cleaning and phosphating of ferrous workpieces; Figure 2 is a plan view on a larger scale of the left-hand tank in Figure 1; Figure 3 is an elevation on an even larger scale of a rotary impeller; and Figure 4 is a section on the axis of the impeller.

Referring now to the drawings, an installation for the cleaning and phosphating of ferrous workpieces comprises three comparatively large tanks fabricated from either mild or stainless steel and disposed in line above a common drain pipe 10. The installation is surrounded by a low wall (not shown) to contain spillage. Each of the tanks has a mains water feed 12 which drops say six inches to tank height or uses a separate header tank, and a drain valve 14 with an associated strainer 16. The bottom of each tank is inclined slightly downwards towards its drain valve 14, and each of the drain valves 14 is disposed above a grating 18 communicating with the drain pipe 10.

The left-hand tank 20 constitutes the first tank in the process, and contains an aqueous solution of detergent for cleaning and phosphoric acid for phosphating. The tank 20 is provided with a heater 22 using gas, electricity or oil as convenient, and is insulated to minimise heat loss. The tank 20 is also provided with two internal rotary impellers 24 fixed to respective shafts 26 mounted in bearings and seals (not shown) carried by housings 28 fixed to opposite side walls of said tank. Each of the impellers 24 is formed of a material resistant to the solution and is rotated to agitate the solution by an external electric motor 30 with a pulley 32 secured on its shaft which drives a pulley 34 secured on the associated shaft 26 by way of a vee-belt 36 with a protective cover (not shown). A typical impeller is shown in Figures 3 and 4.It comprises a disc 24 attached at its outwardly directed face to axle 26, about which it may be rotated.

Its inwardly directed face (with respect to the tank wherein it is located) is provided with a plurality (six are shown in Figure 3) of blade members 25 disposed to radiate from a central hub 27. Each of these blade members 25 has a low profile and may have rounded edges.

Nevertheless, rotational movement of the impeller in the liquid in the tank will cause its agitation, but should not interfere with the article being treated.

The second tank 38 which is also insulated contains colit water for rinsing to remove at least 90 per cent of the first stage chemicals, and a flow of cold water is passed continuously through it from its mains water feed 12 to a weir 40 from which an overflow pipe 42 discharges to one- of the gratings 18. The tank 38 is provided with, one internal rotary impeller 44 indentical to each of the impellers 24 of the tank 20 to agitate the cold water.

The third tank 46, which is not insulated, contains hot water for final rinsing and for heating the workpieces to expedite subsequent drying, and to this end is provided with a heater 48 indentical to the heater 22 of the tank 20.

The tank 46 has no rotary impellers and thus contains static hot water to which chemicals can be added if desired to complement the process.

In operation, workpieces are immersed successively, either singly or in batches depending upon their size, for say five minutes in each of the tanks 20, 38 and 46. The strength of the solution in the tank 20 is, say, three to four per cent by volume, and the temperature of the liquid in the tanks 20 and 46 is, say, 45 to 55 degrees centigrade.

It should be understood that different installations, chemical solutions and process variations all falling within the scope of the invention can be employed to achieve different results, including for example the cleaning of plastics and aluminium, the prevention of rusting, and the removal of oxides. In practically every case, however, agitation of the chemical solution and/or the rinse water greatly improves the performance of the process. The use of a rotary impeller as hereinbefore described is an inexpensive and effective way of agitating a liquid without displacing workpieces immersed therein.

Claims

1. An industrial process for the treatment of workpieces comprising immersing said workpieces in a tank of liquid and agitating the liquid by means of at least one rotary impeller.

2. A process as claimed in claim 1 which comprises immersing the workpieces successively in a plurality of tanks containing liquids and agitating the liquid in at least one of the tanks by means of at least one rotary impeller.

3. A process as claimed in claim 2 comprising immersing said workpieces in a first tank containing a chemical solution and agitating the solution by means of at least one rotary impeller; next immersing said workpieces in a second tank containing cold water, passing a continuous flow of cold water through said second tank and agitating said cold water by means of at least one rotary impeller; and next immersing said workpieces in a third tank containing heated water.

4. A process as claimed in claim 3 comprising the steps of heating the chemical solution in the first tank and heating the water in the third tank.

5. A process as claimed in any one of the preceding claims in which said treatment comprises the cleaning and phosphating of ferrous workpieces.

6. A process as claimed in any one of the preceding claims in which said treatment is water based.

7. An apparatus for the treatment of workpieces in accordance with the industrial process of any one of the preceding claims comprising a tank provided with at least one rotary impeller for agitating a liquid in said tank.

8. An apparatus as claimed in claim 7 in which said tank is has a base with at least one upstanding wall extending therefrom and said at least one rotary impeller is mounted on said upstanding wall.

9. An apparatus as claimed in either claim 7 or claim 8 in which said rotary impeller comprises a disk rotatably mounted on an axle and having blade members disposed to radiate from a central hub of said disc.

10. An apparatus as claimed in claim 9 when appended to claim 8 in which said disc extends parallel to said upstanding wall.

11. An apparatus as claimed in any one of claims 7 to 10 in which said rotary impeller is driven by an external motor.

12. An apparatus as claimed in any one of claims 7 to 11 in which said tank comprises a heater to be immersed in a liquid contained in said tank to heat said liquid.

13. An apparatus as claimed in any one of claims 7 to 12 comprising a plurality of tanks with at least one tank having at least one rotary impeller for agitating a liquid contained in said tank, whereby the workpiece is to be successively received in said plurality of tanks during its treatment.

14. An apparatus for the treatment of workpieces substantially as herein described with reference to the accompanying illustrative drawings.

15. An method of treatment of workpieces as claimed in any one of claims 1 to 6 and substantially as herein described.