WO1995000241A1

WO1995000241A1 - Method of blending material and plant therefor

Info

Publication number: WO1995000241A1
Application number: PCT/NZ1994/000062
Authority: WO
Inventors: Kevin John Hobson; Lyall James Manson; Herbert Graham Paintin
Original assignee: Merivale Anita Bernadette; Kevin John Hobson; Lyall James Manson; Herbert Graham Paintin
Priority date: 1993-06-21
Filing date: 1994-06-16
Publication date: 1995-01-05
Also published as: AU7009894A

Abstract

Equipment (2) and a method is provided for the controlled blending of particulate matter (animal, vegetable or mineral) producing an aggregate with a pre-determined particle size distribution. The equipment (2) includes a plurality of containers (3) each with control means (4, 5) for varying the rate of outflow of material onto a mixing means (6). With the particle size or size range for material for each container (3) pre-determined, and the rate of outflow preset, an aggregate as described is produced in a continuous or batch operation. Particle size range of the aggregate can be 0 to 5 millimetres (or less) or up to 65 millimetres or more.

Description

TITLE: METHOD OF BLENDING MATERIAL AND PLANT THEREFOR

TECHNICAL FIELD

The present invention provides a blending plant for blending aggregate (as hereinafter defined) in either a continuous or a batch process, such that the end product has a pre-determined particle size distribution or a distribution that falls within a pre- determined range of such distributions. BACKGROUND

High quality, crushed mineral aggregates are required for use in road construction, and particularly to meet the appropriate roading authority's standards. Such a standard is usually set as an "envelope" of ranges of the maximum and minimum amounts of any one particle size for a range of particle sizes, within an aggregate. Such an "envelope" is shown by the lines C, D in Fig. 4. At present such a standard is difficult to achieve reliably with available machinery, in an economic manner.

A further problem is that at present the source of the stone or raw material for production of the mineral aggregate (i.e. the quarry) frequently is a determining factor in the particle size distribution of the aggregate which may not conform to the required envelope of sizes.

Also it is often the case that with organic or animal particulate products it is advantageous to have a mix where the particle size range is a known, pre-determined range.

For example, with such products as seeds, peas, and hops, a size range is often required. Equipment for producing such a product by either a batch or continuous process is not always economically available.

An object of the present invention is the provision of equipment to produce aggregate to a required pre-determined particle size range (and thus to a pre-determined standard) in a manner which overcomes the problems outlined above. A further object of the invention is the provision of a method for use of the equipment of the present invention.

For the purposes of this specification, the following terms include the assigned meanings, but are not limited thereto:

"aggregate" - an aggregation of particulate matter (or material), whether animal, vegetable or mineral;

"particle size distribution" - the proportion by weight of particles of different diameters or sizes in an aggregate, or a pre-determined range of proportions by weight of particles of different diameters;

-1- "sand" - natural mineral particles, usually between 4.75 mm and 0.6 mm in diameter; "fine aggregate" - material particles with a minimum diameter of less than 5 mm. DISCLOSURE OF THE INVENTION

The present invention provides equipment for the controlled blending of aggregate (as hereinbefore defined), said equipment including: at least two containers each provided with an opening through which each said container can be filled with particulate material, and with an emptying means which is capable of allowing material to leave the container at a pre-determined rate to form an outflow; control means for controlling the emptying means and the rate at which the material leaves each container; mixing means for mixing the outflows of material from each container to form an aggregate; and conveying means to convey the aggregate away from said containers; wherein the control means are preset so that the amount of material from each container being mixed by the mixing means is in accordance with a pre-determined requirement; and wherein the particle size range or particle sizes of said particulate material are pre-determined for each container; whereby the particle size distribution of the aggregate is pre-determined.

Preferably at least three or four or more said containers are used and are shaped, open hoppers each fitted with a feed line thereunder. Preferably each hopper incorporates a low level monitor which provides advance warning if it is uncovered (i.e. if there is not particulate material all around it). Preferably also, said conveying means includes a conveyor belt running under all the hoppers and onto which each feed line from each hopper dumps its material.

Preferably also said equipment includes means to monitor the overall weight (and thus the volume) of aggregate being produced from the equipment connected to the means to control the rate of emptying from each hopper. Preferably the equipment further includes one or more grading screens or grading sieves over each hopper so that the range of sizes of material emptied into each hopper is very accurately pre-determined.

Preferably said equipment is portable (that is, capable of being towed/driven from one site to another). Also preferably said equipment is capable of carrying out the method described below as a continuous process, rather than as a batch process.

The present invention also provides a method for the batch or continuous controlled blending of aggregate, said method including: the provision of the equipment as described above; filling each said container with particulate material of differing but predetermined sizes; controlling the emptying of each said container at a pre-determined rate; mixing the outflow from said containers; and conveying the aggregate away from said containers; wherem by pre-determining and monitoring the sizes or the range of sizes of material placed in each container and by controlling the rate of emptying of each said container, aggregate of a pre-determined, required particle size distribution can be produced.

Preferably at least four containers are provided, each with a differing range of particle sized material.

BRIEF DESCRIPTION OF THE INVENTION By way of example only, a preferred embodiment of the present invention is described in detail with reference to portable blending equipment and for mineral aggregate for use on a basecourse (i.e. the layer of material constituting the uppermost structural element of a road pavement, immediately beneath the wearing surface) road and with reference to the accompanying drawings, in which:- Fig. 1 is a side view of the equipment of the present invention;

Fig. 2 is a section view of the equipment of the present invention along the line AA of Fig. 1;

Fig. 3 is a side view of a hopper of the equipment of the present invention; and Fig. 4 shows a particle size distribution graph.

MODEFORCARRYINGOUTTHEINVENTION

Referring to Figs. 1-3, a blending plant 2 is thereshown with four hoppers 3. Each hopper 3 is in the shape of an inverted truncated pyramid with a vibrating feeder 4 thereunder and is open at the top. Each feeder 4 has associated with it an adjustable feed regulating gate 5 (of known type). Each feeder 4 empties onto a conveyor belt 6 and each feeder 4 is driven by known means, eg a small electric motor 12. If so desired one motor can drive all the feeders 4. The motors 12 can be run by an electric generator (portable or fixed) or an engine or by mains power, as is desired.

The hoppers 3 are positioned in a line (as shown in Fig. 1), with each of the feeders 4 conveying material onto the conveyor belt 6 under the hoppers 3. In practice it has been found that the best mixing occurs when the first hopper 3 (from which a feeder 4 first conveys material to the conveyor belt 6) contains the coarsest material and the last hopper If so desired, the following features may be added: one or more grading screens 7 or sieves (operating in known manner) can be positioned above each of the hoppers 3 or above only a selected number of the hoppers 3. Such a screen 7 (or screens) can be any type of screen, for example, eccentric cam-operated vibrating screens of known type. Thus additional control may be gained as to the precise size or size range of the material entering each hopper 3. The grading screen 7 can be fitted with an oversize chute 8 for the conveyance from the plant 2 of any oversize material.

Each hopper 3 can be fitted with an individual overflow chute 9 and with an overflow conveyor belt 10 (Fig. 2), for removal of any material from that hopper 3 which is excess to requirements for the blending of the desired aggregate. If so desired, an overflow chute 9 and overflow conveyor belt 10 can be fitted to the opposite side of each hopper 3 so that there are two such sets of items for each hopper 3.

Each hopper 3 may also be fitted with one or more low level probes 11 or sensors. Each such probe 11 can be any suitable known probe for sensing when said probe is not entirely surrounded by material. Therefore the level of material in each hopper 3 can be monitored and the amount of material in the hopper 3 can be topped up as required. If so desired, such probes 11 can be attached electrically or electronically to known devices for refilling the hopper 3 automatically (eg a conveyor belt from a source of material for that hopper 3 (not shown)). The above described equipment works as follows: mineral material from known, existing crushing equipment (or material from a stock pile) is screened to reduce the maximum particle size to 20 mm. This provides an appropriate starting material for most standards for basecourse roads. However, any particle size (eg. 40 mm or 65 mm) can be used as the starting material, depending upon the desired particle size distribution of the resultant mineral aggregate.

This material is fed onto the grading screen 7 of the plant 2. The screen 7 is pre¬ selected so that any material which is larger than the desired largest size of particle is conveyed to the oversize chute 8 (Fig. 1). This reject material can be returned to the crushing plant or stockpiled for later crushing or other use. The vibrating scτeen(s) 7 sorts the material into 3 fractions of sizes: for example, fine aggregate and particles less than 10 mm in diameter; particles between 10 and 20 mm in diameter; and particles greater than 20 mm in diameter. This last fraction is returned via the oversize chute 8, as described above. The other two fractions drop each to a different hopper 3 by the arrangement of the screen(s) 7. Another hopper 3 is loader-fed with (for example) washed sand. The rate of outflow of each hopper 3 is pre-determined from the desired particle size distribution of the aggregate wanted. This rate of outflow is then pre¬ set on the adjustable feed regulating gate 5 for each hopper 3. The blending plant 2 is started and the material from each hopper 3 is transferred to the conveyor belt 6 by the respective feeder 4. The rate of transfer is pre-set on the feed regulator gate 5. The mixing (or blending) on the conveyor belt 6 is best effected when the first hopper 3 in the sequence contains material with the largest particle size and the last hopper 3 in the sequence contains material with the smallest particle size. Such an order is not essential however.

If a probe 11 detects that the amount of material in the respective hopper 3 is getting too low (that is, the probe 11 is uncovered), the plant 2 can be pre-set so that the conveyor belt 6 stops along with the feeders 4. Alternatively, known equipment (not shown) can be provided so that as soon as the amount of material in a hopper 3 gets too low the probe 11 can activate further equipment so that more material is screened by the grading screen 7. Any excess material being fed to any one hopper 3 can be conveyed away from the plant 2 by the respective overflow chute 9 and overflow conveyor belt 10. Thus with relatively minor adjustment the plant 2 can operate on a batch basis to produce a batch of mineral aggregate of a pre-determined particle size distribution. As an alternative, the plant 2 can be set up to run on a continuous basis to continuously produce mineral aggregate as required by use of appropriate monitoring and control systems.

The plant 2 has been described above with reference to four hoppers 3. The operation of the plant 2 was described using only three hoppers 3. The fourth hopper 3 can be left out of the operation of the plant 2, or can be included, with a material with a different particle size distribution from that in the other hoppers 3. For example, the particle size range for each of the hoppers 3 could be sand, 5 to 10 mm diameter particles, 10-15 mm diameter particles and 15-20 mm diameter particles, if so desired.

Alternatively, the fourth hopper 3 (which can be any one of the hoppers 3) can be the one hopper 3 that is not used as it is "down" for, for example, routine maintenance, repairs, replacement, etc. Thus the plant 2 can continue to operate whilst routine maintenance or other work or modification is carried out.

A further quality control measure which can be included if so desired is a belt weigher 13 associated with one end of the conveyor belt 6. This can be used to monitor the weight of aggregate produced. It can also be used to calibrate and set the feed rates from the hoppers 3 individually. It can further be used to switch off the plant 2 once a pre¬ determined amount of aggregate has been produced.

To permit the plant 2 to be transported easily from one site to another it can be constructed within the framework of an attachable semi-trailer unit (not shown) for road transportation. The line FF (Fig. 2) is the line of the axles of rear wheels (not shown) for such a unit and support members 14 (Fig 2) form part of such a semi-trailer unit. The plant

2 can be a static unit in a quarry or a skid-mounted portable unit, as is desired.

The invention has been described with reference to a plant 2 with four hoppers 3 in the shape of truncated isosceles pyramids, in a line. It will be appreciated that the configuration of the hoppers 3 may be altered, or the number of hoppers may be increased or decreased. For example the equipment could include six hoppers 3 in two rows of three, all feeding onto a common conveyor belt, or onto a conveyor belt connected with each line of hoppers (which belts later feed onto a common conveyor belt). The hoppers 3 may also be covered either partially or totally, and include inlet means for the material for that hopper 3.

Also, it will be appreciated that the shape of the hoppers 3 may be varied, for example the hoppers 3 may be in the shape of an inverted truncated cone. Also a mixing means other than the belt 6 described above may be used, for example the feeders 4 may empty into a rotating vessel with a separate outlet to allow for continuous throughflow mixing.

Also, if desired, the vibrating feeders 4 could be any other known type of feeder tray or belt (eg belt feeders). With the above-described equipment and ratios of materials used in the description of the operation of the equipment (above) the resultant particle size range is as shown on Fig. 4, line E. The curved lines C, D represent an "envelope" criteria for a specification for aggregate for basecourses for roads (Transit New Zealand M/4 specification). This specification for the aggregate was used to pre-determine the settings for the feed regulatory gates 5 and the particle size range of the material entering the hoppers 3. The resultant aggregate particle distribution range is shown by line E. The above described equipment has been described with reference to vibrating feeders 4 with a feed regulating gate 5. An alternative mechanism, if so desired, is to have a fixed opening at the bottom of a hopper 3 with a belt feeder of variable speed. A load cell or weigher can be used to monitor the weight of material on the belt. With appropriate control equipment the resultant aggregate can be continuously monitored by monitoring the weight on the belt feeders and varying their speed to control the weight of material from the hopper to the conveyor belt 6. Such monitoring equipment can be computer controlled for total automation of the equipment. The above described method and detailed description discloses an aggregate which is unbound (and can be used as such for forming basecourses for roads). However, it will be appreciated that a solid particulate binding agent can also be mixed into the aggregate from one of the hoppers 3. An example of a suitable binding agent is cement. Also, with appropriate modification to a hopper 3 a fluid (eg water or a fluid or non-particulate binding agent) can be added to the aggregate. This leads to the formation of a bound aggregate. If so desired, more than one hopper 3 can be used for such non-particulate material, with appropriate modification to the equipment.

The invention has been described above with reference to a mineral aggregate. As seen by the definition of the term 'aggregate' the equipment of the invention can also be used for obtaining graded particulate aggregate of animal or vegetable origin.

The method and blending equipment of the invention can be used to obtain mixes of particulate matter for or from crops (eg cereals) or seeds (of all types) where the particle size of the resultant aggregate or end product is to be of a pre-determined particle size distribution. Such crops as hops, peas and cereals such as wheat are particular examples of such plants and vegetable matter. However any other forms of particulate matter (whether animal or vegetable (eg marine shells)) can be used in the method and plant of the present invention.

The invention has been described above with a particle size range of up to 20 mm. It will be appreciated that the range of sizes of particles can be far greater than 0 to 20 mm. It can also be far narrower. For example, the equipment can be used for fine aggregate (or smaller) only.

The only limitation on the plant of the present invention has been found to be the size of the mesh on any screens used or openings (and the control thereof) on the containers. Thus fine seeds can also be mixed to a pre-determined particle size range in the plant of the present invention, using the method of the present invention. Further, all the particle ranges used to obtain the pre-determined particle range may fall within the definite of "fine aggregate".

Claims

CLAIMS:

1. Equipment for the controlled blending of aggregate (as hereinbefore defined), said equipment including: at least two containers each provided with an opening through which each said container can be filled with particulate material, and with an emptying means which is capable of allowing material to leave the container at a pre-determined rate to form an outflow; control means for controlling the emptying means and the rate at which the material leaves each container; mixing means for mixing the outflows of material from each contamer to form an aggregate; and conveying means to convey the aggregate away from said containers; wherem the control means are preset so that the amount of material from each container being mixed by the mixing means is in accordance with a pre¬ determined requirement; and wherein the particle size range or particle sizes of said particulate material are pre-determined for each container; whereby the particle size distribution of the aggregate is pre-determined.

2. Equipment as claimed in claim 1 wherein each said container is a shaped hopper fitted with a feed line thereunder and said control means includes a feed regulating gate.

3. Equipment as claimed in claim 1 wherein said emptying means is an opening of fixed size and said control means includes a conveyor belt feed of variable speed.

4. Equipment as claimed in any one of the preceding claims wherein each container includes a low level monitor providing warning if it is uncovered.

5. Equipment as claimed in any one of the preceding claims wherein said conveying means and said mixing means are combined and include a conveyor belt running under all the containers and onto which the outflow from each container falls.

6. Equipment as claimed in any one of the preceding claims wherein said equipment includes monitoring means to monitor the overall weight of aggregate being produced by said equipment; said monitoring means being connected to said control means.

7. Equipment as claimed in any one of the preceding claims wherem said equipment further includes one or more grading screens over each said container.

8. Equipment as claimed in any one of the preceding claims wherein said containers are positioned in line, said particulate material for each container being graded such that the first container in the line has material of the largest size and the last container in the line has the particulate material of the smallest size, with a gradation therebetween.

9. Equipment as claimed in any one of the preceding claims wherein said equipment includes one or more containers for feeding non-particulate matter into the aggregate.

10. Equipment as claimed in any one of the preceding claims wherein said equipment is capable of being towed by a vehicle.

11. Equipment as claimed in any one of the preceding claims wherein said equipment is automatically operated in a continuous process.

12. A method for the batch or continuous controlled blending of aggregate, said method including: the provision of the equipment as claimed in any one of claims 1 to 8; filling each said container with particulate material of differing but predetermined sizes; controlling the emptying of each said container at a pre-determined rate; mixing the outflow from said containers; and conveying the aggregate (as hereinbefore defined) away from said con- tainers; wherein by pre-determining and monitoring the sizes or the range of sizes of material placed in each container and by controlling the rate of emptying of each said container, aggregate of a pre-determined, required particle size distribution can be produced.

13. A method as claimed in claim 12 wherem said method includes filling one or more of said containers with a non-particulate, solid or fluid binding agent, the outflow of said container being mixed with the outflow from the remaining containers.

14. The aggregate as produced by the method as claimed in either claim 12 or claim 13.

15. The aggregate as produced by the equipment as claimed in any one of claims 1 to 12.