GB2023454A - Sieve for particle size analysis of powders - Google Patents

Abstract

A sieve has a hollow body (1) bounded by six rectangular faces, one of which comprises a sieving surface (2). The body is rotated by means of axles (3) on an axis parallel to the sieving surface and central of the faces which the axis intersects. The sieve may be used for the analysis of particle size of a powder in conjunction with a mini-computer to monitor the rate of passage of particles through the sieving surface and to deduce the kinetic residue. Random mixing of the powder particles during rotation of the sieve may be imparted by means of rods (4), as shown, or by crumpled wire mesh or randomly packed spheres. <IMAGE>

Description

SPECIFICATION Improved sieve This invention concerns an improved sieve.

The experimental study of fine particles using woven wire sieves is hampered by the fact that all the apertures are not identical. The probability of a fine particle of a given size encountering a hole- through which it can pass is related not only to the aperture distribution but also to the method of agitation used in the sieving study. When carrying out a sieve fractionation of a powder, the analyst often has to decide in an arbitrary manner that fractionation is complete when some very low rate of passage through the sieve has been achieved.

There have been many extensive studies of the rate at which powder passes through a sieve but these are not usually of general value because of the varied sieving action of the several machines used in the studies.

The present invention provides a novel sieve comprising a hollow body in a rectangular solid shape, one face of which comprises a sieving surface, and means for rotating the body on an axis paraliel to the sieving surface and central of the faces which the axis intersects. Preferabiy, the sieve comprises randomising means mounted in the body. The randomising means may be any means capable of interfering with the flow of powder in the body such as to impart random mixing, and may be randomising rods, crumpled wire mesh or a random packing such as randomly packed spheres, through which the powder could percolate.

The sieving surface may be replaceable with a surface of another nominal aperture size, and/or may be removable or hinged to provide access to the interior so as to charge powders to be characterised into the sieve or to discharge residues. Alternatively, part or the whole of one of the other faces of the body may form a removable cover. The sieving surface may be a woven wire sieve or an electroformed sieve, the latter being very precise but also expensive, and may form part of or the whole of the relevant face.

The invention will now be exempiified and described with reference to the accompanying drawing, which is a perspective view, of a sieve according to the invention.

The sieve has a body 1, conveniently formed of sheet metal which may be fastened by welding, soldering or other means or may be mounted on a framework (not shown), and the whole of one face, 2, is formed by a woven wire mesh sieve which is clipped to the remainder of the body. The body has a central axis of rotation and may be rotated by means of axles, 3, which can be driven directly or indirectly by a motor, e.g. a synchronous electric motor (not shown). Fastened in the body are a plurality, e.g. 1 5 to 20, of randomising rods, 4, which act to encourage randomisation of the fine particles as they move upon rotation of the sieve. The particles bounce off the randomising rods and arrive on the sieving surface with very little lateral movement. Particles passing through the sieve can be caught in a collection hopper which may be continuously weighed.As the seive continues with its rotation, the remaining particles are again randomised as they fall away from the sieving surface In contrast to conventional sieves, the sieve of the invention permits a more straightforward analysis of particle size by means of the concept of kinetic residue as a descriptive parameter of the powder being analysed. In the use of the sieve of the invention, the sieving variable can be taken to be the number of rotations of the sieve, rather than time. The sieve of the invention can be used with a mini-computer to monitor the rate of passage Qf particles through the sieving surface, and to deduce the kinetic residue. The computer can be instructed to then terminate the sieving action, and also can be used to control charging and discharging of the sieve.It is then possible to contemplate an automatic sieving procedure capable of characterising a series of powders, suitable for on-line control of manufactures.

1. A sieve comprising a hollow body in a rectangular solid shape, one face of which comprises a sieving surface, and means for rotating the body on an axis parallel to the sieving surface and central of the faces which the axis intersects.

2. A sieve according to claim 1, comprising randomising means mounted in the body.

3. A sieve according to claim 2, whereing the randomising means is selected from randomising rods, wire mesh and randomly packed spheres.

4. A sieve according to any one of the preceding claims, wherein the sieving surface is a woven wire screen or an electroformed screen.

5. A sieve according to claim 1, substantially as hereinbefore described with reference to the drawing.

6. A sieve according to any one of the preceding claims, associated with a collection hopper capable of catching particles passing through the sieve.

7. A method of sieving comprising charging a sieve according to any one of the preceding claims with a sample of particles, rotating the sieve and monitoring the rate of passage of particles through the sieve.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (7)

**WARNING** start of CLMS field may overlap end of DESC **. SPECIFICATION Improved sieve This invention concerns an improved sieve. The experimental study of fine particles using woven wire sieves is hampered by the fact that all the apertures are not identical. The probability of a fine particle of a given size encountering a hole- through which it can pass is related not only to the aperture distribution but also to the method of agitation used in the sieving study. When carrying out a sieve fractionation of a powder, the analyst often has to decide in an arbitrary manner that fractionation is complete when some very low rate of passage through the sieve has been achieved. There have been many extensive studies of the rate at which powder passes through a sieve but these are not usually of general value because of the varied sieving action of the several machines used in the studies. The present invention provides a novel sieve comprising a hollow body in a rectangular solid shape, one face of which comprises a sieving surface, and means for rotating the body on an axis paraliel to the sieving surface and central of the faces which the axis intersects. Preferabiy, the sieve comprises randomising means mounted in the body. The randomising means may be any means capable of interfering with the flow of powder in the body such as to impart random mixing, and may be randomising rods, crumpled wire mesh or a random packing such as randomly packed spheres, through which the powder could percolate. The sieving surface may be replaceable with a surface of another nominal aperture size, and/or may be removable or hinged to provide access to the interior so as to charge powders to be characterised into the sieve or to discharge residues. Alternatively, part or the whole of one of the other faces of the body may form a removable cover. The sieving surface may be a woven wire sieve or an electroformed sieve, the latter being very precise but also expensive, and may form part of or the whole of the relevant face. The invention will now be exempiified and described with reference to the accompanying drawing, which is a perspective view, of a sieve according to the invention. The sieve has a body 1, conveniently formed of sheet metal which may be fastened by welding, soldering or other means or may be mounted on a framework (not shown), and the whole of one face, 2, is formed by a woven wire mesh sieve which is clipped to the remainder of the body. The body has a central axis of rotation and may be rotated by means of axles, 3, which can be driven directly or indirectly by a motor, e.g. a synchronous electric motor (not shown). Fastened in the body are a plurality, e.g. 1 5 to 20, of randomising rods, 4, which act to encourage randomisation of the fine particles as they move upon rotation of the sieve. The particles bounce off the randomising rods and arrive on the sieving surface with very little lateral movement. Particles passing through the sieve can be caught in a collection hopper which may be continuously weighed.As the seive continues with its rotation, the remaining particles are again randomised as they fall away from the sieving surface In contrast to conventional sieves, the sieve of the invention permits a more straightforward analysis of particle size by means of the concept of kinetic residue as a descriptive parameter of the powder being analysed. In the use of the sieve of the invention, the sieving variable can be taken to be the number of rotations of the sieve, rather than time. The sieve of the invention can be used with a mini-computer to monitor the rate of passage Qf particles through the sieving surface, and to deduce the kinetic residue. The computer can be instructed to then terminate the sieving action, and also can be used to control charging and discharging of the sieve.It is then possible to contemplate an automatic sieving procedure capable of characterising a series of powders, suitable for on-line control of manufactures. CLAIMS

1. A sieve comprising a hollow body in a rectangular solid shape, one face of which comprises a sieving surface, and means for rotating the body on an axis parallel to the sieving surface and central of the faces which the axis intersects.

2. A sieve according to claim 1, comprising randomising means mounted in the body.

3. A sieve according to claim 2, whereing the randomising means is selected from randomising rods, wire mesh and randomly packed spheres.

4. A sieve according to any one of the preceding claims, wherein the sieving surface is a woven wire screen or an electroformed screen.

5. A sieve according to claim 1, substantially as hereinbefore described with reference to the drawing.

6. A sieve according to any one of the preceding claims, associated with a collection hopper capable of catching particles passing through the sieve.

7. A method of sieving comprising charging a sieve according to any one of the preceding claims with a sample of particles, rotating the sieve and monitoring the rate of passage of particles through the sieve.