GB2187975A - Grinding mill - Google Patents

Abstract

A manual grinding mill for maize and other hard, brittle grains comprises a hopper 13 for receiving granular material, means 6, 7 for providing relative rotation between grinding plates 16, 17 and a feed roller or axially tapered cracking cone 24 for cracking the grains of material during passage between the hopper 13 and the plates 16, 17. The cracking is achieved in a tapered cracking zone defined between the feed roller 24 and a curved cracking plate 27. The feed roller is provided with flutes 25 to entrain the grains and drive them into the cracking zone. One axial end of the clearance is effectively closed by a deflector plate 26 to prevent the grains by-passing the cracking zone. The feed roller 24 is mounted on a common manual drive shaft 5 with the rotary grinding plate 16. <IMAGE>

Description

SPECIFICATION Grinding mill This invention relates to grinding mills; and more particularly but not solely, to manually operable mills for cereal products.

In many under-developed and emergent countries, there is a need for hand-operated grinding mills for cereal products. In such mills, the grains are fed between grinding plates having raised ribs and spring-loaded together, with the spring loading being variable to allow the fineness of the grinding to be controlled.

With brittle, hard grains, such as maize, rice and wheat, there is a need for a preliminary cracking or crushing step so that the whole grain is not fed directly between the grinding plates.

It is an object of the invention to provide a comparatively inexpensive arrangement for achieving this, which is also effective and durable.

In accordance with the invention, there is provided a grinding mill comprising a hopper for receiving granular material to be ground, grinding plates, means for providing relative rotation between the grinding plates, and means for cracking the grains of material during passage between the hopper and the plates, in which the cracking means comprises a feed roller at the bottom of the hopper and a curved plate defining with the feed roller a clearance tapering circumferentially in the direction of rotation of the feed roller so as to crack the grains.

The feed roller is preferably fluted to provide grooves to entrain the grains and drive them into the said clearance, and it may be also axially tapered.

One axial end of the clearance may be effectively closed by a deflector plate to prevent the grains by-passing the clearance.

The feed roller may be mounted on a common shaft with a rotary grinding plate, and the said common shaft is normally provided with a turning handle for manual operation.

The invention will be further described with reference to the accompanying drawings, in which; Figure 1 is a perspective external view of a preferred form of mill in accordance with the invention; and Figure 2 is an exploded perspective view showing the component parts of the mill of Fig. 1.

Turning first to Fig. 1, this shows the externally visible parts of a hand grinder for maize or other hard and brittle grains. It comprises a body 1 which is clamped between a support plate 2 and a clamping plate 3 by means of screws 4. A shaft 5 has a crank 6 and a handle 7 mounted thereon for rotation of the shaft in the direction indicated by an arrow 8, which is cast onto a hub 9 secured, by means of a boss 11, to the shaft 5.

Fig. 1 also shows an adjusting hand wheel 12 which is mounted on the opposite end of the shaft 5 and a feed hopper 13 for the grains to be ground.

It will be appreciated that the hand-operated grinder is adapted to be used where no electric power is available, and the support plate 2 is provided with fixing holes 14 by which it can be nailed to a tree stump or other suitable and available base.

Fig. 2 is an exploded view of the grinder of Fig. 1 and shows all of the parts hitherto described, using the same reference numerals, together with further details. Attached to the hub 9 by screws such as the screw 15 is a rotary grinding plate 16 which co-operates with a static grinding plate 17 which is itself secured within an enlargement 18 of the housing 1 by further screws such as the screw 20 and self-locking nuts 19. As will be seen, one of these nuts also serves to secure the hopper 13 to the enlargement 18.

The shaft 5 runs in a sleeve bearing 21 and a roller bearing 22 mounted in the housing 1, and a Belleville washer stack 23 is mounted between the hand wheel 12 and the bearing 22 to provide an adjustable spring loading together of the grinding plates 16 and 17.

A cracking cone 24 is solidly mounted on the shaft 5 so as to underlie the hopper 13. It will be seen that the cracking cone 24 is tapered away from the grinding plates 16 and 17, and is provided with surface grooves or flutes 25. The larger end of the cracking cone 24 is located adjacent a fixed deflector plate 26 which prevents grains falling over the end of the cracking cone 24.

Mounted in the housing adjacent the cracking cone 24 is a curved cracking plate 27 secured by means of a screw 28. The cracking plate 27 is mounted so that it defines with the cracking cone 24 a tapering clearance, forming a cracking zone, which is wider at the top than at the bottom. Accordingly, grains from the hopper are entrained by the flutes or grooves 25 and carried into this cracking zone and are then crushed as the clearance tapers circumferentially in the direction of rotation. The grains are prevented from leaving the cracking zone via the ends of the flutes 25 at one end by the deflector plate 26 and at the opposite end by the wall of the enlargement 18.

The crushed grains thus enter an annular space defied between the shaft 5 and inner peripheries 1 6a and 1 7a of the grinding plates. From this annular space, the crushed grains pass between the grinding plates 16 and 1 7 and the resulting flour reaches a collecting zone in the outer part of the casing enlargement 18, from where it is collected via an aperture 31. Spring pins 32 are mounted in the hub 9 to project into the collecting zone to sweep the flour therearound towards the aperture 31.

The combination of the grooved cracking cone 24 and the tapered cracking plate 27 has been found to provide an efficient crushing of the grain as a preliminary step to grinding, and it will be seen that the cracking plate 27 is fairly easily replaced should it become worn. The presence of the deflector plate 26 is important in preventing by-passing of the cracking zone or clearance formed between the cracking cone 24 and cracking plate 27.

Various modifications may be made within the scope of the invention.

Claims (7)

1. A grinding mill comprising a hopper for receiving granular material to be ground, grinding plates, means for providing relative rotation between the grinding plates, and means for cracking the grains of material during passage between the hopper and the plates, in which the cracking means comprises a feed roller at the bottom of the hopper and a curved plate defining with the feed roller a clearance tapering circumferentially in the direction of rotation of the feed roller so as to crack the grains.

2. A grinding mill as claimed in claim 1, in which the feed roller is fluted to provide grooves to entrain the grains and drive them into the said clearance.

3. A grinding mill as claimed in claim 1 or 2, in which one axial end of the clearance is effectively closed by a deflector plate to prevent the grains by-passing the clearance.

4. A grinding mill as claimed in any of the preceding claims, in which the feed roller is mounted on a common shaft with a rotary grinding plate.

5. A grinding mill as claimed in claim 4, in which the said common shaft is provided with a turning handle.

6. A grinding mill as claimed in any of the preceding claims, in which the feed roller is axially tapered.

7. A manually operable grinding mill substantially as hereinbefore described with reference to the accompanying drawings.