BACKGROUND OF THE INVENTION When a drum contains a liquid with two liquid phases, mere circulation of the liquid

often suffices to mix the phases adequately. When the liquid contains a solid phase which may settle and form a denser layer at the bottom of the drum, then lifting the solids is preferable during stirring. A propeller type of impeller rotates the drum contents but does not necessarily produce uniformity. In order to produce more vigorous agitation, the propeller blades are of a larger diameter than the drum aperture. The blades are commonly made of sheet metal and pivotally attached to a sheet metal hub so that the propeller mimics the action of an umbrella and is able to pass through the drum aperture.

Such collapsible impellers have pendant blades which rise to lie perpendicular to the shaft under centrifugal force. Consequently efficient mixing occurs at speeds which cause the blades to spread out. Some liquids are more suited to low speed stirring. If the impeller blades break off or bend, the out of balance forces make the impeller dangerous to use.

US Patent 4,213, 713 describes a one piece agitator consisting of a shaft with an integral arcuate impeller with a diameter larger than the drum aperture. The impeller is threadable through the aperture. The hook shaped impeller has two disc paddles to increase the agitation but the disc diameter is confined by the diameter of the drum aperture. The impeller must be dynamically balanced to permit its use in a handheld portable stirrer. Even small imbalances in such impellers are dangerous because the operator quickly loses control.

SUMMARY OF THE INVENTION A drum stirrer of the type which produces a vortex upon rotation comprising a shaft and a ribbon blade of greater span than the drum port which is separate from the shaft but joined centrally thereto by a link which allows the blade to move in relation to the shaft from a stirring position to an entry/exit position in which the blade and shaft are able to be threaded through the port.

BRIEF DESCRIPTION OF THE DRAWINGS One embodiment of the invention is now described with reference to the accompanying drawings in which:

Figure 1 is a sectional view of a drum with the stirrer in position.

Figure 2 is a perspective view of the impeller in the drive position.

Figure 3 is a side view of the impeller passing through a drum aperture.

Figure 4 is a perspective view of a variant of Figure 2.

DETAILED DESCRIPTION WITH RESPECT TO THE DRAWINGS Referring now to the drawings, a strip of stainless steel 400 x 25 x 3mm 2 is bored at its mid point with a 7mm aperture 4. This is then bent into an S-shaped to function as a stirring blade. Tip to tip measures 200mm. A stainless steel shaft 6, l Omm in diameter is bored near one end on a diameter to receive the upper end 8 of a 6mm wire loop 10.

The lower opposite end 12 of the loop underlies the end 14 of the shaft. The ends of the loop are secured to the shaft by welds 16,18. The loop is substantially semi circular when viewed side on as in Figure 2.

The captive ends of the loop are disposed at an angle of 20°. The angle"A"in Figure 2 is 40°. The upper end 8 of the loop passes perpendicularly through the blade. The face 19 of the blade lies tangential to the rod 6. The loop transmits the rotational force in the rod to the blade which takes up a position with the face parallel to the axis of the rod.

When the rod is at rest the blade is free to slide along the loop to the intermediate part 20 where the blade tilts through about 80° until the blade edge 22 sits in the valley 24 between the loop and the rod. The loop arc is such as to prevent the blade flipping over, ie. turning through 180°. This may be managed by drilling the bore off centre, that is closer to one edge than to the opposite edge. Additionally, the clearance between the rod and the bore may be increased by about lmm. The inclined intermediate part 20 of the loop allows the blade to extend away from the shaft such that the distance x in Figure 3 does not exceed 45mm. This configuration permits passage through the 50mm diameter aperture.

In use the drum cap is unscrewed. The blade is tilted to the position shown in Figure 3 and fed by threading the shaft through the drum aperture 26. During threading the inclination of the blade is checked by contact between the twisted end and the shaft near to the x on the Figure. Once past the aperture the blade tilts as soon as mixing commences to lie in the position shown in Figure 1. The shaft is inserted in the chuck of the stirrer and the mixing speed is selected.

When the rod rotates, the loop transmits rotation to the blade and a vortex forms in the drum liquid. When the stirrer is switched off, the rod is raised until the blade becomes accessible through the drum aperture. The blade tilts by gravity so the leading tip of the blade projects through the aperture, whereupon the trailing end of the blade rises through the aperture because the blade has assumed the position shown in Figure 3. The shaft and blade are rinsed in appropriate solvent and the drum is ready to discharge.

In Figure 4, shaft 6 has a pair of bores which receive the ends 8, 12 of wire loop 10. The bore in the centre of the blade is slightly off centre width wise.

We have found the advantages of the embodiment to be: 1. Robust, cheap construction.

2. Stirring at slow speeds is possible. For some liquids this is desirable.

3. If the blade accidentally strikes the drum wall, the shape of the blade is not usually disturbed sufficiently to generate out of balance forces.

It is to be understood that the word"comprising"as used throughout the specification is to be interpreted in its inclusive form, ie. use of the word"comprising"does not exclude the addition of other elements.

It is to be understood that various modifications of and/or additions to the invention can be made without departing from the basic nature of the invention. These modifications and/or additions are therefore considered to fall within the scope of the invention.