GB2051752A - Powder dispenser - Google Patents

Abstract

A powder dispenser is provided in the form of a hopper having a restricted outlet wherein is located a drivable finned shaft. The fins 20 have flanges 22 which prevent the feed of powder from the hopper but, on rotation of the shaft, serve as a screw feeder to dispense powder at a rate dependent upon the speed of rotation of the shaft, or, in a second embodiment, the depth of entry of the fins into the outlet. <IMAGE>

Description

SPECIFICATION Powder dispenser This invention relates to powder dispensers and is particularly concerned with a powder dispenser for use in the make up of photographic solutions.

At the present time, in the make up of certain photographic solutions, powder is added manually to a solvent, being poured from a plastic bag containing a predetermined amount of the powder.

Thus, whilst the quantity added is correct, unless the rate at which it is added is controlled very carefully, wetting of the added powder is uneven, lumpstend to form, increasing the time for dissolving, or the mixture becomes too thick.

It is an object of the present invention to provide a powder dispenser of simple construction which readily permits the controlled dispensation of pow der contained therein.

According to the present invention, there is provided a powder dispenser comprising a downwardly tapering hopper having an outlet at its base, a drivable shaft located within the hopper and coaxially of the outlet, the shaft having radially extending fins with flanges permitting and assisting the dispensation of powder from the outlet at a rate dependent on the speed of rotation of the shaft.

The shaft preferably extends vertically and coaxially of the hopper and is driven by an air motor at its upper end.

The air motor advantageously is a variable speed motor so that the rate of powder dispensation can be controlled. There may be three fins extending equiangularly axially of the shaft, the flange of each fin defining a segment greater than one third of a shallow helix surrounding the shaft and of radial extension substantially equal to that of the adjacent part of the outlet and the hopper.

The fin flanges act as a triple-start feed screw in feeding powder through the outlet whence it falls under gravity.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a vertical section of a powder dispenser in accordance with the present invention; Figure 2 is an elevation, to a larger scale, of part of the dispenser shown in Figure 1; and Figure 3 is a plan view of the part shown in Figure 2.

A powder dispenser constructed according to the present invention comprises a hopper 10 of inverted truncated conical form, a coaxial inverted conical lower part 11 and a support 12. The support 12 may take the form of brackets for clamping the dispenser to the side wall 13 of a container (not shown) into which the powder is to be dispensed. The lower part 11 has an outlet 14 at the bottom thereof. The outlet takes the form of a pipe, coaxial with the hopper, to the end of which an extension feed pipe 15 may be secured.

Avariable speeed air motor 16 supplied with air through a line 17 is supported coaxially over the hopper 10 by struts 18. A shaft 19 extends from the motor 16 down through the hopper 10, the lower part 11 and into the outlet 14. Ajournal (not shown) may be provided in the outlet to receive the end of the shaft.

Three fins 20 are secured to the shaft 19 in the region of the junction of the lower part 11 with the outlet 14. The fins 20 each comprise (see Figures 2 and 3) an axially extending web 21 secured to the shaft 19. The webs 21 are spaced at 1200 intervals around the shaft. The webs 21 each support a flange 22 extending from the upper end thereof. Each flange approximates to a one third segment of a circle and is canted, relative to the shaft 19, to lie in the plane of a shallow helix, a leading edge 23 of each flange serves as a cutting edge of a screw feeder and overlaps slightly the trailing edge 24 of the next adjacent flange. The radial length of the leading edge 23 is substantially equal to the radial distance from the shaft to the adjacent wall of the lower part 11 of the hopper 10.Similarly, the trailing edge 24 of each flange is of radial length substantially equal to the radial distance from the shaft 19 to the adjacent wall of the outlet 14. In this way, a relatively narrow spriral path is presented to the powder when the shaft is stationary and the flow occasioned by gravity alone is small or non-existent.

When the shaft 19 is rotated, the leading edges 23 of the flanges 22 act as a triple start screw feed to permit and assist the flow of powder through the outlet.

In use, the hopper 10 is mounted on the side wall 13 of a mixing container by means of the supports 11 and the air motor 16 and shaft 19 are located coaxially within the hopper by the struts 18 (and the journal in the outlet 14 if a journal is provided).

Powder to be mixed with a solvent in the container is then poured into the hopper 10 and air is supplied via the line 17 at a rate appropriate to the rate at which the powder is to be dispensed. The powder is fed through the outlet 14 (and the extension pipe 15 if provided) into the container where it mixes with and is dissolved in the solvent. Mechanical stirring of the solvent may, of course, be provided.

It has been found that a modification may be necessary in the dispensing of some powders, e.g.

low density powders, which do not flow well. Such powders have a tendency to create a cavity in the hopper above the outlet and thereafter not be dispensed. To overcome this disadvantage, radial spokes (shown in phantom in Figure 1) may be secured to the shaft, above the fins for rotation with the shaft so as to agitate the powder in the hopper and ensure the feed thereof by the fins.

The invention has been described in detail with reference to a particular embodiment thereof but it will be understood that variations are possible. For example there may be one, two or more fins on the shaft 19 each of appropriate shape to dispense powder at a rate dependant on the rate of rotation of the shaft 19.

The hopper 10 and lower part 11 can be of any downwardly tapering shape. The outlet 14 and the shaft 19 need not be coaxial with the hopper or with each other although the fins should be so shaped as effectively to cover the outlet when the shaft is stationary.

Avariable dispensing rate may be achieved by raising or lowering the shaft relative to the outlet 14.

In such instance, a variable speed motor is not essential. To facilitate such an arrangement, the motor may be adjustably mounted on the struts 18 by a ratchet or screw mount enabling fine location of the fins relative to the outlet.

The hopper may be arranged for support centrally of the mouth of a mixing container. This may be achieved by providing a plurality, preferably four, radially extending equi-angularly spaced arms each secured at its inner end to the hopper and braced by a strut, similar to the support 12, so as to form a rigid support forthe hopper which will sit over the mouth of a mixing container.

Powders otherthan photographic powder may be dispensed by the apparatus according to the present invention.

Claims (7)

1. A powder dispenser comprising a downwardly tapering hopper having an outlet at its base, a drivable shaft located within the hopper and coaxially of the outlet, the shaft having radially extending fins with flanges permitting and assisting the dispensation of powder from the outlet at a rate dependent on the speed of rotation of the shaft.

2. A dispenser as claimed in Claim 1 wherein the shaft extends vertically and coaxially of the hopper and is driven by an air motor at its upper end.

3. A dispenser as claimed in Claim 1 or 2 wherein the air motor is a variable speed motor so that the rate of powder dispensation can be controlled.

4. A dispenser as claimed in Claim 1,2 or 3 wherein there are three fins extending equiangularly axially of the shaft, the flanges of each fin defining a segmentgreaterthan one third of a shallow helix surrounding the shaft and of radial extension substantially equal to that of the adjacent part of the outlet and the hopper.

5. A dispenser as claimed in any of Claims 1 to 4 wherein the fin flanges are arranged to act as a triple-start feed screw in feeding powder through the outlet whereafter it falls under gravity.

6. A dispenser as claimed in any preceding Claim further including ratchet means for moving the shaft axially whereby to vary the entry of the fins into the outlet so as to control the flow of powder therethrough.

7. A powder dispenser substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.