GB2393434A

GB2393434A - Granule metering device

Info

Publication number: GB2393434A
Application number: GB0219582A
Authority: GB
Inventors: Graham Basil
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-08-22
Filing date: 2002-08-22
Publication date: 2004-03-31
Also published as: GB0219582D0

Abstract

A metering device for use in a granular applicator comprises a tubular casing (12, fig.1) having at least one inlet aperture 7A in the side thereof and at least one outlet aperture 7B in the opposite side thereof. A rotor assembly is mounted for rotation within the tubular casing 7 about the central axis thereof such that material entering the or each inlet aperture 7A is carried to the or each outlet aperture 7B. The rotor assembly comprises a support shaft 6 a fluted rotor 4 for each inlet aperture 7A mounted on the support shaft 6 and positioned adjacent the inlet aperture 7A to pick up material entering therethrough, a granule retaining washer 3 on each side of the rotor 4 and mounted for rotation therewith on the support shaft 6 and means 2 for supporting each end of the support tube 6 within the tubular casing.

Description

DESCRIPTION

GRANULE METERING DEVICE

The present invention relates to a metering device for regulating the rate of flow of a granular material from the outlet or outlets of a dispensing apparatus or 5 applicator. One known type of applicator for granular materials comprises a hopper for retaining the granular material and having an opening in the bottom through which material is fed by gravity to a metering device. The metering device is located in a cylindrical chamber which is formed at the bottom of the hopper below the 10 opening therein. One or more outlets are provided in the bottom of the cylindrical housing chamber through which the metered material can exit the applicator.

The metering device itself consists of one or more fluted rotors which are located between fixed shoulders. The rotors are mounted on a shaft which allows them to be rotated within the chamber. As they rotate, material dropping through 15 the opening in the bottom of the hopper is picked up in the space defined between each rotor and transported to the outlet in the bottom wall of the housing chamber.

The rate of flow of material through the metering device is determined by the volume of the space defined between each rotor and the rate of rotation.

In order to allow rotation of the rotors, a clearance is required between each 20 rotor and the fixed shoulder adjacent to it. This gap must be small enough to ensure that material cannot leak through it when the metering device is not in use, e.g. when the applicator is stationary or being transported between work sites.

Setting the gap, either for use or when replacing worn parts of the metering device, is a skilled job requiring careful parts orientation and assembly and requires the metering device to be re-calibrated each time to determine the rate of flow therethrough. With abrasive materials these problems are exacerbated as wear on 5 the rotors will cause the rate of flow to change and will require the rotors to be more frequently replaced. The accepted deviation from the manufacturer's nominal output for a new device is plus 10% at which point the rotors should be replaced. However, setting older units with replacement parts to within plus or minus 10% can be difficult bearing in mind they may comprise between one to 10 twenty-four rotors.

In use, the rotors wear in two separate ways. Initially, the tip of each rotor wears off rapidly. This has the effect of increasing the throughput of material through the metering device until a clearance gap is created and stabilised. Once the clearance gap has stabilised, the rate of change of throughput slows. This 15 clearance gap round the rim of each rotor, though wider than a granule diameter, does not allow granules to leak through. Then, over time, the sides of the rotors and of the fixed shoulders wear with the action of the granules. As this occurs there is an increase in throughput through the metering device, until in extreme cases the metering device actually leaks when not in use. This outcome is rare as 20 by this stage the operator should have taken action to correct the problem. This may entail resetting the rotor gap, but it has to be recognised that the output will be below that of a new rotor and tends to vary more than with new rotors.

Alternatively, the worn rotors can be replaced.

It will be understood that wear also occurs between the rotors and the wall of the housing chamber. To prevent this a wear strip may be provided between the rotors and the wall of the housing chamber, but the strip is narrow and does not prevent wear beyond it.

5 Where replacement of the rotors is required a number of problems can arise.

The metering device is designed to rotate in one direction and some of the rotors only work if rotated in that direction. However, it is possible for the rotors to be fitted the wrong way round. Where this occurs the output rate will not match the setting on the metering device.

10 Minor alignment errors arising during replacement ofthe rotors can cause tight spots or jamming of the rotating parts resulting in inaccurate or patchy application. The shaft carrying the rotors is supported in end bearings. These are vulnerable to dust build up leaking in via the gap between the rotors and the 15 shoulders. This dust can form a paste that jams up the bearings.

It is an object of the present invention to provide a metering device which is less prone to wear than conventional metering devices.

It is another object of the invention to provide a metering device which is simple to fit.

20 It is another object of the invention to provide a metering device which provides a reliable output throughout the working life thereof.

It is still another object of the invention to provide a metering device which eliminates wear on the walls of the housing chamber therefor.

It is still another object of the invention to provide a metering device which is less sensitive to alignment errors and is, therefore, not as vulnerable to binding.

According to the present invention there is provided a metering device for use in a granular applicator comprising a tubular casing having at least one inlet 5 aperture in the side thereof and at least one outlet aperture in the opposite side thereof, and a rotor assembly mounted for rotation within the tubular casing about the central axis thereof such that the material entering the or each inlet aperture is carried to the or each outlet aperture, the rotor assembly comprising a support shaft, a fluted rotor for each inlet aperture mounted on the support shaft and positioned 10 adjacent the inlet aperture to pick up material entering therethrough, a granule retaining washer on each side of the rotor and mounted for rotation therewith on the support shaft and means for supporting each end of the support tube within the tubular casing.

Preferably, the support shaft is supported at each end in an end bush.

15 Conveniently, the support shaft is tubular and is belled out at each end to retain the end bushes, the rotors and the granule retaining washers thereon.

Preferably, the rotor assembly is retained within the tubular casing by a clamping ring. Each clamping ring may form an interference fit in the end of the tubular casing or it may be welded or otherwise fixedly secured.

20 Preferably, each of the end bushes defines a cylindrical projection which is adapted to be received in a respective one of the clamping rings, the facing surfaces of the projection and of the clamping ring forming bearing surfaces to allow the rotor assembly to rotate freely relative to the tubular casing.

Conveniently, the support shaft is comprised of an hexagonal tube and is adapted to be connected to a drive shaft.

The granule retaining washers are preferably of the same diameter or greater than the diameter of the fluted rotor, thus ensuring that granules are retained 5 within the flutes thereof.

Preferably, each of the inlet apertures in the wall of the tubular casing is of a width which is equal to or less than the width of the fluted rotor associated therewith. In this way granular material is directed into the fluted rotor and is unable to leak past the sides of the fluted rotor into the interior of the metering 10 device itself.

An embodiment of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which: Fig. 1 shows a schematic view of a granular applicator with the metering device thereof removed from the housing chamber located at the bottom of the 15 hopper; and Fig. 2 shows an exploded view of a metering device in accordance with the present invention.

Referring to Fig. 1, there is shown a granular applicator comprising a hopper 10 for retaining the granular material and having an opening 11 in the 20 bottom thereof. The opening 11 leads into a cylindrical chamber 12, which is intended to house a metering device (not shown). Two outlets 13, 14 are provided in the bottom of the cylindrical chamber 12 through which the retained material can exit the applicator.

Referring now to Fig. 2, there is shown an exploded view of a metering device in accordance with the present invention for use in the applicator of Fig. 1.

The metering device consists of a tubular casing 7, adapted to be received within the cylindrical chamber 12 of the applicator shown in Fig. 1, and a rotor assembly, 5 which is retained within the tubular casing 7 by means of a clamping ring 1 inserted in each end thereof.

The tubular casing 7 comprises a pair of inlets 7A in the wall thereof which are so positioned as to be in alignment with the opening 11 in the bottom of the hopper 10 of the applicator, and an outlet 7B which is so positioned as to be in 10 alignment with the outlets 13 and 14 in the bottom of the cylindrical chamber 12.

The tubular casing 7 is fixedly retained against movement and rotation within the cylindrical chamber 12.

The rotor assembly located within the tubular casing 7 comprises an elongate, tubular, support shaft 6 of hexagonal cross section. The hexagonal cross 15 section allows the components mounted thereon to be secured against rotation on the shaft. The shaft 6 is tubular to allow a drive shaft (not shown) to be inserted therethrough for the purpose of rotating the rotor assembly about its longitudinal axis within the tubular casing 7.

The support shaft 6 supports a pair of fluted rotors 4, each of which is 20 bounded on each side by a granule retaining washer 3, and separated by three spacers 5. Each of the fluted rotors is positioned on the shaft 6 so as to align with a respective one of the two inlets 7A. The flutes in the side of the fluted rotors 4 are dimensioned so as to receive granules of the material to be metered as the

material drops through each of the inlets 7A. The granules are then transported to the outlet 7B by rotation of the rotor assembly within the tubular casing 7. The rotors 4 are typically formed from polypropylene or some other wear resistant material. The depth, width and number of flutes, together with the circumference 5 of the fluted rotors determines the rate at which material is metered by the metering device. The ends of the inlets 7A in the tubular casing 7 provide a shearing edge which limits the amount of material contained within the flutes of the fluted rotors 4, regardless of the direction of rotation thereof.

The granule retaining washers 3, which may be formed from stainless steel, 10 are of the same diameter as the fluted rotors 4, or greater, and form a close fit with the internal wall of the tubular casing 7 without interfering with rotation of the rotor assembly therein. The washers 3 ensure that granules entering the flutes of the fluted rotors 4 cannot escape therefrom, thus ensuring accurate metering of material. 1 S The spacers 5, which may be formed from polypropylene or some other wear resistant material, have a diameter smaller than the internal diameter of the tubular casing, thus forming a clearance therebetween. Any dust and debris which escapes past the retaining washers 3 is able to pass through the clearance to the outlet 7B, thus preventing a build up of material within the metering device which 20 would adversely affect operation thereof An end bush 2 is mounted on each end of the support shaft 6 and serves the dual purpose firstly of retaining the fluted rotors, retaining washers and spacers on the support shaft and secondly, of supporting the shaft or bearing surfaces provided

by the clamping rings 1 so that the rotor assembly can rotate freely within the tubular casing 7. The bearing surfaces of the clamping rings I are oil impregnated to facilitate rotation, and the clamping rings I are secured in the tubular casing either by an interference fit or by suitable fixing means such as spot welding.

5 The metering device ofthe present invention serves as a simple replacement for conventional metering devices, being shaped and dimensioned such that it can be inserted directly into the housing chamber of existing applicators. Being a sealed unit there is no replacement of worn parts, nor any adjustment during the working life of the metering device. This is markedly different from conventional 10 metering devices which have to be set up in the applicator by an operator over whom the supplier ofthe metering device has no control. With the metering device of the present invention it is possible for the manufacturer to set the output to within a given tolerance range for the particular product to be dispensed and, having set the output, it is possible to specify the point at which the output has 15 risen to an unacceptable level, at which point the metering device is simply replaced.

Claims

1. A metering device for use in a granular applicator comprising a tubular casing having at least one inlet aperture in the side thereof and at least one outlet aperture in the opposite side thereof, and a rotor assembly mounted for 5 rotation within the tubular casing about the central axis thereof such that material entering the or each inlet aperture is carried to the or each outlet aperture, the rotor assembly comprising a support shaft, a fluted rotor for each inlet aperture mounted on the support shaft and positioned adjacent the inlet aperture to pick up material entering therethrough, a granule retaining washer on each side of the rotor and 10 mounted for rotation therewith on the support shaft and means for supporting each end of the support tube within the tubular casing.

2. A metering device according to claim 1, wherein the support shaft is supported at each end in an end bush.

3. A metering device according to claim I or 2, wherein the support 15 shaft is tubular and is flared at each end to retain the end bushes, the rotors and the granule retaining washers thereon.

4. A metering device according to claim 1, 2 or 3, wherein the rotor assembly is retained within the tubular casing by a clamping ring.

5. A metering device according to claim 4, wherein each clamping ring 20 forms an interference fit in the end of the tubular casing or it may be welded or otherwise fixedly secured.

6. A metering device according to claim 4 or 5, wherein each of the end bushes defines a cylindrical projection which is adapted to be received in a respective one of the clamping rings, the facing surfaces of the projection and of the clamping ring forming bearing surfaces to allow the rotor assembly to rotate 5 freely relative to the tubular casing.

7. A metering device according to any preceding claim, wherein the support shaft is comprised of an hexagonal tube and is adapted to be connected to a drive shaft of the granular applicator.

8. A metering device according to any preceding claim, wherein the 10 granule retaining washers are preferably of the same diameter or greater than the diameter of the fluted rotor, thus ensuring that granules are retained within the flutes thereof.

9. A metering device according to any preceding claim, wherein each of the inlet apertures in the wall of the tubular casing is of a width which is equal 15 to or less than the width of the fluted rotor associated therewith.

10. A granular applicator comprising a hopper for retaining granular material having an opening in the bottom through which material is fed by gravity to a cylindrical chamber housing a metering device in accordance with any of claims 1 to 9, and one or more outlets in the bottom of the cylindrical housing, each 20 of which outlets is associated with a respective outlet aperture of the metering device. A metering device substantially as hereinbefore described with

reference to Fig. 2 of the drawings.

12. A granular applicator in combination with a metering device substantially as hereinbefore described with reference to Figs. I and 2 of the drawings. s