WO2003056943A1

WO2003056943A1 - Method and apparatus for automatically coating granular products

Info

Publication number: WO2003056943A1
Application number: PCT/GB2003/000016
Authority: WO
Inventors: Daniel Thomas Exely Ritchie
Original assignee: Forum Products Ltd
Current assignee: Forum Products Ltd
Priority date: 2002-01-08
Filing date: 2003-01-06
Publication date: 2003-07-17
Anticipated expiration: 2004-07-08
Also published as: AU2003201031A1; AU2003201029A1; WO2003056944A1

Abstract

A method and apparatus for automatically coating granular material fed from a supply (6) thereof to a weighing station (20) comprising a supply duct (8a) with an auger therein driven by a motor (9). Liquid additive is fed by a pump (13) from a supply (11) thereof via duct (12) to spray nozzles (19a) positioned around outlet (10) which coat the feed as it falls under gravity into bucket (21). Control means (30) ensure that the coating additive is only sprayed onto granular material leaving outlet (10). Compressed air may be added to the coating applied by the spray nozzles (19a).

Description

Method and Appar tus for Automatically Coating Granular Products

This invention relates to a method and apparatus for automatically coating granular products, particularly but not exclusively, animal feed material.

In the commercial rearing of broiler chickens, it is common practice to add wholewheat grain to manufactured feed compound on site to make savings on broiler ration costs. However, the lower nutritional value of the whole-wheat when compared to the feed compound limits the amount that can be added to the feed compound so the potential to take full advantage of feed-cost savings is limited.

In a broiler house, each bird has its own preference for wheat or compound feed. This can lead to different growth rates and therefore variations in bird weights due to the nutrient gap between the whole-wheat and compound feed. The higher the proportion of wheat supplied to the birds, the greater the problem. This problem can be overcome by mixing an additive with the whole -wheat grain before feeding to close the nutrient gap. One form of additive is a liquid blend of amino acids — lysine and methionine, enzymes such as Avizyme (Trade Mark), soya oil and molasses products. Mixing this additive adds amino acids to the whole-wheat grain thereby bringing its nutrient value closer to that of a manufactured compound feed as the additive boosts lysine intakes and thus narrows the nutrient gap between the whole-wheat and manufactured feed. The inclusion of the feed enzyme Avizyme increases the availabihty of energy and protein in the added wheat thereby helping to improve the food conversion ratio (i.e. the number of kilos of feed to be eaten by a bird to put on 1 kilo of weight) and live weight gain. By narrowing the nutrient gap between the whole-wheat and manufactured feeds, the level of the added wheat can be increased thereby making bigger savings in feed costs.

A major problem with a known apparatus which mixes an additive to the wholewheat is that it is pumped from a supply thereof and mixed with the whole-wheat while it is being conveyed to a weight station by a powered auger located in a supply duct. The additive is poured into the supply duct before it reaches the weighing station and is mixed with the whole-wheat by the action of the auger as it is conveyed along the supply duct. However, because the additive has a high content of molasses and due to the location where it is introduced into the whole-wheat, there is a tendency for the additive to bind with the chaff and wheat dust in the supply duct and coagulate. This can cause the auger to progressively slow down until it finally stops. In some cases, the motor which drives the auger can burn out or, in extreme cases, the supply pipe can even explode due to the build up of pressure therein. Once the auger has stopped, repairs can take some time to carry out and it is not uncommon for the feed apparatus to be "down" for between 4 and 6 hours while it is repaired. This down time will have a dramatic effect on the eventual weight of the birds in the broiler house when they come to be killed particularly if there have been several down times during the period up to slaughter which is not uncommon.

It is an object of the invention therefore to provide a method and apparatus for automatically coating granular products which overcomes or substantially reduces these problems.

According to one aspect of the invention there is provided a method of automatically coating with an additive granular material fed from a supply thereof to a feeding station comprising the steps of transporting granular material from said supply to a weighing station, discharging said granular material so that said material falls under gravity into the weighing station, coating said granular material with the additive as it falls under gravity into the weighing station, weighing the required predetermined quantity of coated granular material at the weighing station, releasing said weighed quantity of coated granular material from the weighing station and transporting said coated granular material to the feeding station.

Preferably the additive is a liquid which is sprayed onto the granular material only while said granular additive is being discharged into the weighing station.

Compressed air may be introduced into the additive before said additive is sprayed onto the granular material thereby ensuring a more even spray delivery so that the granular material can be coated more efficiently and evenly. In a preferred method, a predetermined quantity of manufactured feed is also fed to the weighing station.

According to another aspect of the invention there is provided an apparatus for automatically coating with an additive a predetermined quantity of granular material fed from a supply thereof to a feeding station comprising a hopper for the granular material, feed means for feeding the granular material from the hopper to weighing means, coating means located to apply the coating additive onto the granular material as said material falls under gravity into the weighing means and dehvery means for delivering the weighed quantity of coated material to the feeding station.

Conveniently, the coating means are spray means which apply liquid additive to the granular feed material.

Preferably a duct connects the hopper with the weighing means, said duct having an outiet located above said weighing means. The spray means are preferably mounted on said duct adjacent the outlet thereto and comprise a plurality of spray nozzles mounted on the duct around the periphery of the outlet thereto.

If several outlet ducts or pipes (in some cases four or more pipes) discharge coated granular material directly into the weighing means, the spray-heads and associated valves mounted on each pipe outlet can make the process of adjusting all of the valves to be very time consuming. Furthermore, having to provide spray-heads and supply lines on each outlet substantially increased the capital cost of the equipment.

In order to overcome this problem, a mixing hopper can be provided to receive the granular material as it is discharged from the outlet pipes but before it reaches the weighing means, the coating means being mounted on an outlet for said mixing hopper so that the granular material is coated with additive as it passes through said mixing hopper outlet. This arrangement allows all of the pipes which deliver granular material to the weighing means to discharge directly into the mixing hopper so that the feed can be coated with the hquid additive as it drops through the mixing hopper outlet. The advantage provided by this improvement is that only one set of spray heads and additive dehvery pipes is needed on the mixing hopper outlet to coat the granular material regardless of the number of granular feed dehvery pipes supplying feed thereto. Furthermore, the spray heads are nearer ground level so they are more accessible for maintenance and adjustment, making it easier to deal with any potential blockages at the hquid additive spraying stage.

Conveniently, the mixing hopper is a funnel disposed between the end of the or each feed duct outlet and the weighing means located below them, so the granular material must pass through the funnel from the or each duct to reach the weighing means.

In a preferred embodiment, the funnel outlet is a section of steel tube which may be galvanised.

Preferably, there is a stiff neck-section around the top of the outlet-section of the funnel which may be made of polypropylene or some other suitable plastics material. In the preferred embodiment, the main body of the funnel is a fabric sleeve which forms a chute, and its bottom is connected to the top of the neck- section of the outlet of the funnel.

The apparatus preferably also includes control means operable to regulate the dehvery of the additive to the coating means. The control means can incorporate a modem to allow remote control over the delivery of the additive to the granular feed material via the coating means if required.

A storage container for the hquid coating additive is preferably connected to the spray means by a duct and a pump is provided for pumping said coating liquid through said duct to the spray means. The apparatus also preferably includes control means operable to activate the pump only when granular material is being discharged from the duct into the weighing means.

A second hopper for manufactured feed compound can be connected by a second duct to the weighing means.

The invention is particularly concerned with the automatic coating of granular feed material supplied to broiler houses but it could be used in other applications such as the disinfecting of products or dosing of medicinal products.

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is an dlustration of a prior art method and apparatus;

Figure 2 is an dlustration of a method and apparatus of the invention;

Figure 3 shows in more detail a preferred dehvery system for spraying additive onto the product processed by the apparatus shown in Figure 2;

Figure 4 is the control system for the dehvery system shown in Figures 2 and 3; Figure 5 shows a modified apparatus for spraying additive onto the product processed by the apparatus shown in Figure 2; and

Figure 6 is a schematic view of the spraying head shown in Figure 5.

The apparatus shown in Figure 1 consists of a first hopper 1 for manufactured feed compound which is supported above the ground on legs 2 and having an outlet 3 in its base. A supply pipe 3a is connected to the base of the hopper and extends into the upper region of a weighing station 20 where it terminates in a vertical down- pipe section 5. There is also provided a second hopper 6 for whole-wheat, which is supported above the ground on legs 7 and has an outlet 8 in its base. A supply pipe 8a is connected to the outlet 8 in the base of the hopper and extends into the upper region of the weighing station 20 where it terminates in a vertical down-pipe section 10. Both ends 5 and 10 of the supply pipes 3a,8a are positioned above the open top of a weighing bucket 21 which forms part of a weighing device (not shown). The weighing bucket 21 is positioned above a third hopper 23 which has an outlet 24 in its base connected to a pipe 24a which runs to a feed building 25 wherein it is connected to a feeder pipe 26. Down-pipes 27a,b,c connect the feed pipe 26 to feed trays 28a,b,c respectively. A flexible centreless auger 3B,8B is mounted in the supply pipes 3a,8a powered by motors 4 and 9 respectively. A container 11 for hquid additive is connected to a pump 13 by a pipe 12, a pipe 14 joining the supply pipe 8a for the second hopper 6 at 15.

The motors 4,9 drive the augers 3B,8B within supply pipes 3a,8a to convey material from the hoppers 1,6 into the weighing station 20, where it drops from the down- pipe sections 5, 10 under gravity into the weighing bucket 21. The pump 13 pumps hquid from the container 11 along pipe 14 and into the supply pipe 8a at 15 wherein it mixes with the material from the hopper 6 being conveyed by the auger 8B. The material from the hoppers 1, 6, together with the additive from the container 11 continue to fill bucket 21 until the weighing device (not shown) detects that the required pre-determined weight of material has been reached at which time motors 4, 9 are switched off so that the augers 3B,8B in the feed pipes 3a, 8a stop and no further material exits from the ends 5 and 10 of the supply pipes 3a, 8a.Base 22 of the weighing bucket 21 then opens to release the pre-determined weight of mixed material into the third hopper 23. A motor 29 drives a centreless auger 24B contained within pipe 24a to convey the mixture leaving the hopper 23 via outlet 24 into the feeder pipe 26 within the feed building 25. The mixture is then distributed into down-pipes 27a,b,c and falls under gravity into feed trays 28a,b,c. Problems with this prior art system arise due to the location where the hquid additive from container 11 is mixed with the wheat being conveyed along supply pipe 8a.

Furthermore, the motion of the material in the supply pipe 8a is such that the chaff and dust from the wheat settles on top of the wheat grains as it passes along the pipe. As a significant proportion of the hquid additive is molasses and it enters the supply pipe 8a as a heavy stream from pipe 14, it has a tendency to bind with the chaff and wheat dust and then coagulate. This can cause the auger to bind up and jam, and the continuing driving power from the motor 9 can then destroy the auger. Expensive mechanical repairs are then needed which can hold up the dehvery of feed for 4-6 hours. These problems are overcome in the apparatus of the present invention shown in Figure 2 which is substantially the same as Figure 1 in that it consists of a first hopper 1 for the manufactured feed compound which is supported above the ground on legs 2 and having an outlet 3 in its base. A supply pipe 3a is connected to the base of the hopper and extends into the upper region of a weighing station 20 where it terminates in a vertical down-pipe section 5. There is also provided a second hopper 6 for whole-wheat, which is supported above the ground on legs 7 and having an outlet 8 in its base. A supply pipe 8a is connected to the outlet 8 in the base of the hopper and extends into the upper region of the weighing station 20 where it terminates in a vertical down-pipe section 10. Both ends 5 and 10 of the supply pipes 3a, 8a are positioned above the open top of a weighing bucket 21 which forms part of a weighing device (not shown). The weighing bucket 21 is positioned above a third hopper 23 which has an outlet 24 in its base connected to a pipe 24a which runs to a feed building 25 wherein it is connected to a feeder pipe 26. Down-pipes 27a,b,c connect the feeder pipe 26 to feed trays 28a,b,c respectively. A flexible centreless auger 3B.8B is mounted in the supply pipes 3a, 8a, powered by motors 4 and 9 respectively. A container 11 for hquid additive is connected to a pump 13 by a pipe 12.

It will be noted however that the pump 13 is mounted on top of the container 11, the outlet of the pump being connected by pipe 12 to the weighing station 20. A non-return valve 16 and a filter 17 are mounted in the pipe 12 between the pump 13 and the weighing station 20. Inside the weighing station 20 the pipe 12 is connected to a manifold 18 (shown in more detail in figure 3) which is connected by a pipe 1 to spray-heads 19a mounted around the circumference of the down-pipe section 10 of the supply pipe 8a from the second hopper 6.

The operation of the hquid supply pump 13 and hence the dehvery of hquid from the container 11 to the manifold 18 and spray heads 19a, is controlled by a control unit 30 which monitors the operation of the auger motors 4, 9. Figure 3 is a view on an enlarged scale of the dehvery system for the hquid additive supplied from the hquid container 11 to the spray heads 19a. The system comprises pump 13, hquid dehvery pipe 12 connecting the container 11, non-return valve 16 and filter 17 to the manifold 18. Manifold outlet pipes 19 connect the manifold 18 via adjustable flow nozzles 19b to the spray heads 19a. The pump 13 is electrically connected to a control means 30 which monitors the operation of the auger motors 4, 9. The operation of the control means 30 will be described in more detad later with reference to Figure 4. The container 11 has a capacity of 1000 litres, but this is preferred rather than essential.

Figure 4 is a schematic diagram of the control means 30 for the dehvery system shown in Figures 2 and 3, and comprises a first sensor 33, which is connected to the auger motor 4 for the first hopper 1, and a second sensor 34 which is connected to the auger motor 9 for the second hopper 6. Both sensors 33, 34 are connected to a relay 35 which has a 3-way selector switch 36, positionable in an 'off, an 'A' or a 'B' position. The relay 35 is connected to a motor drive unit 37 which receives electrical 240V single-phase mains supply power through a cable 40 via an electrical filter 38 to prevent power surges. The output from the motor drive unit 37 is a screened power cable 39 which is connected to the pump 13 on the hquid container 11. The relay 35 incorporates a known programmable timer which sets a maximum time that a 'run' signal will be sent to the motor drive unit 37. The motor drive unit 37 is provided with a function whereby a delay can be programmed into the unit between when it receives a signal from the relay 35 to when it supplies power via the output power cable 39 to the hquid feed pump 13.

Material from the hoppers 1,6 falls through the respective outlets 3 and 8 into the supply pipes 3a, 8a and is conveyed by the augers 3B,8B powered by their respective motors 4, 9 to the down-pipe sections 5, 10 where it falls under gravity into the weighing bucket 22.

When the auger motor sensors 33, 34 detect that their respective motors 4 and 9 are running, a signal is sent to the relay 35. If the relay selector switch 36 is set to the corresponding motor, (position 'A' for the motor 4 or position 'B' for the motor 9), an electrical run-signal is sent to the motor drive unit 37, for the duration of time programmed into the maximum run -period timer within the relay 35. Once the motor drive unit 37 receives the signal when the programmed delay time has elapsed, electrical power is converted from the single phase 240 volt mains supply, (via the electrical filter 38) into a 3-phase supply and conducted along the output power cable 39 to the pump 13 on the container 11.

The pump 13 then draws hquid from the container 11 out through the supply pipe 12, and supplies it via non-return valve 16 and filter 17, to the manifold 18 located inside the weighing station 20. The hquid additive then leaves the manifold 18 through th_e manifold outlet pipes 19 and passes via the adjustable flow nozzles 19b to the spray heads 19a which are arranged circumferentially around the end region of the vertical down-pipe section 10 of the supply pipe from the second hopper 6. The ends of the spray heads 19a face inwards towards the centre of the pipe. As the whole-wheat from the second hopper 6 falls under gravity through the down-pipe section 10, hquid from container 11 is sprayed from the spray-heads 19a onto the falling feed, thereby coating it before it reaches the weighing bucket 22.

The auger 3B from the first hopper 1 simultaneously conveys the manufactured feed along its corresponding supply pipe 3a to the down-pipe section 5 where it also falls under gravity into the weighing bucket 21. When the weighing device (not shown) detects that the required pre-determined weight of feed has been reached, the motors 4 and 9 driving the augers 3B,8B stop, thus halting dehvery of feed compound and whole-wheat from the hoppers 1, 6. The motor sensors 33, 34 simultaneously detect that the motors 4 and 9 are not running so the relay 35 to which they are connected stops the 'run' signal being sent to the motor drive unit 37. This cuts off the supply of electrical power to the hquid pump 13 thus stopping further hquid being sprayed from the spray heads 19a around the down-pipe 10.

The base 22 of the weighing bucket 21 is then opened to allow the feed mixture in the bucket 22 to fall into the third hopper 23 located below it. The motor 29 drives the auger 24B within the supply pipe 24a to convey the feed mixture from the hopper 23 via outlet 24 along the pipe up into the feed pipe 26 whereby it falls under gravity via down-pipes 27a,b,c into the feed trays 28a,b,c respectively.

From the foregoing description, it can be seen that the invention provides a substantial improvement over the prior art system shown in Figure 1, because the hquid additive is sprayed onto the wheat, rather than being poured onto it so it is in a finer state, and therefore significantly more effective at being evenly absorbed by the wheat grains. Furthermore, the hquid is added as the wheat falls under gravity past the spray heads 19a, so there is no chance of it coagulating in the supply pipe 8a and the auger cannot jam. The function of the control means 30 is to stop the spray of hquid additive as soon as the conveyance of wheat stops when the required weight of feed material has been reached, thus preventing wastage of hquid additive.

Figure 5 shows an improvement to the apparatus of Figure 1. For the purpose of illustration, only two supply ducts 3a,8a are shown, although there could be more. Granular feed material supply ducts 3a,8a enter the weighing station 20 and terminate in vertical down-pipe sections 5,10 below which a mixing hopper or funnel 100 is located. The funnel 100 preferably comprises a galvanised steel tube section 101 with a rigid plastic frusto-conical section 102 extending upwardly from top edge 101a. The steel tube section 101 acts as the outlet for the funnel 100. A conical fabric section 103 with an upper edge 104 is attached to top edge 102a of the plastic rigid frusto-conical section 102. The outlets for the supply pipes 5,10 are located directly above the funnel 100 within the area defined by the perimeter of its top edge 104.

The weighing bucket 21 of a weighing means (not shown) is located below the steel outlet tube 101.

Mounted around the perimeter of the steel outlet tube 101 is the coating means, which comprises the inwardly facing spray heads 19a connected by pipes 19 to the manifold 18. Valves 19b can be used to adjust the flow rate of the hquid additive supplied from the storage tank 11 to the manifold 18 via the dehvery pipe 12. Compressed air 12b is supplied from a source (not shown) via air-feed pipe 12a into the dehvery pipe 12 just upstream of the manifold 18.

The operation of the apparatus wdl now be described. Granular material such as wheat or feed compound in the hoppers 1,6 falls through their respective outlets 3,8 into the supply ducts 3a,8a and is conveyed along said ducts by augers, powered by auger motors 4,9 to the down-pipe sections 5,10, where it falls under gravity into the open topped fabric sleeve section 103 of the funnel 100. It is guided downwardly towards the steel outlet tube 101 by the rigid plastic flange 102 which prevents the fabric sagging under the weight of the feed material, should it collect in a recess, crease or fold therein.

Referring to Figure 1 , pump 13 draws hquid additive from the container 11 and pumps it through dehvery pipe 12, via non-return valve 16 and filter 17 to the manifold 18. Compressed air 12b is supplied through air-feed pipe 12a into the hquid flow of additive in pipe 12 so that a mixture of hquid additive and compressed air is fed to the manifold 18. The addition of the compressed air promotes droplet formation of the additive in the hquid flow as it continues from the manifold 18 through the outiet pipes 19 via the adjustable flow valves 19b to the spray heads 19a. Thus, when the mixture is emitted from the spray heads 19a, it is as a fine mist of significantly smaller droplets than is achieved with our earlier apparatus. This provides a much more even coating of the granular material falling past the spray heads, and also results in much more efficient use being made of the coating additive hquid.

As the material falls through the outlet steel tube 101 of the funnel 100, it is coated with the hquid additive dehvered from the spray heads 19a which face inwardly and are circumferentially spaced around the steel outlet-section 101. The coated material then falls into the weighing bucket 21 of the weighing device (not shown).

Figure 6 is a schematic version of the modified additive dehvery system shown in Figure 5 with its additional compressed air- eed pipe 12a, which joins the hquid additive dehvery pipe 12 just before the manifold 18. A major advantage of placing the spray heads 19a around the outlet 101 of the funnel 100 is that even though several feed tubes 5,10 may empty into the funnel 100, only one set of spray heads 19a is needed around the outiet to coat the feed material. As the spray heads are located at the base of the funnel 100, they are much more accessible for servicing, adjusting or repairing. Also, any blockages in the outlet 101 can be dealt with more easdy, as only one outlet may need attention instead of several located much higher as in our earlier apparatus.

Claims

1. Apparatus for automatically coating with an additive a predetermined quantity of granular material fed from a supply thereof to a feeding station, comprising a hopper for the granular material, feed means for feeding the granular material from the hopper to weighing means, coating means located to apply the coating additive onto the granular material as said material falls under gravity into the weighing means and dehvery means for delivering the weighed quantity of coated material to the feeding station.

2. Apparatus as claimed in claim 1 wherein the coating means comprise spray means operable to apply hquid additive to the granular feed material.

3. Apparatus as claimed in claim 1 or claim 2 wherein a duct connects the hopper with the weighing means, said duct having an outlet located above said weighing means.

4. Apparatus as claimed in claim 2 or claim 3 wherein the spray means are mounted on the duct adjacent the outlet thereto.

5. Apparatus as claimed in claim 4 wherein the spray means comprises a plurality of spray nozzles mounted on the duct around the periphery of the outlet thereto.

6. Apparatus as claimed in any of claims 2-5 comprising a storage container for the hquid coating additive connected to the spray means by a duct and a pump for pumping said coating hquid through said duct to the spray means.

7. Apparatus as claimed in claim 6 further including control means operable to activate the pump only when granular material is being discharged from the duct into the weighing means.

8. Apparatus as claimed in any of claims 1 to 7 further comprising a second hopper for manufactured feed compound connected by a second duct to the weighing means.

9. Apparatus as claimed in claim 8 wherein an auger is mounted in each duct connecting the first and second hoppers with the weighing means.

10. Apparatus as claimed in claim 9 wherein each auger is a centreless auger driven by a motor.

11. . Apparatus as claimed in any of claims 3 to 10 wherein a non-return valve is mounted in the duct.

12. Apparatus as claimed in claim 11 wherein a filter is mounted in the duct downstream of the non-return valve.

13. Apparatus as claimed in any preceding claim wherein the weighing means comprises a container to receive the coated granular material, said container having an outlet operable to be opened to discharge the coated material into a feed hopper when the amount of coated granular material in the container has reached the required weighed amount.

14. Apparatus as claimed in claim 13 wherein the feed hopper is connected to the feeding station by a duct through which the discharged weighed granular material is transported to the feed station.

15. Apparatus as claimed in any preceding claim wherein a mixing hopper is provided to receive the granular material before it reaches the weighing means, the coating means being mounted on an outlet for said mixing hopper so that the granular material is coated with additive as it passes through said mixing hopper outlet.

16. Apparatus as claimed in claim 15 wherein the mixing hopper is a funnel disposed between the outlet of the or each feed duct and the weighing means so that the granular material must pass through the funnel from the or each duct to reach the weighing means.

17. Apparatus as claimed in claim 16 wherein the funnel outlet is a section of steel tube.

18. Apparatus as claimed in claim 17 wherein a stiff neck-section is provided around the top of the outlet section of the funnel.

19. Apparatus as claimed in claim 18 wherein the main body of the funnel is a fabric sleeve which forms a chute, the bottom of said chute being connected to the top of the neck-section of the outlet of the funnel.

20. Apparatus as claimed in any of claims 12-19 wherein the steel tube is galvanised.

21. Apparatus as claimed in any of claims 13-20 wherein the neck section is made of polypropylene.

22. Apparatus as claimed in any preceding claim further comprising control means operable to regulate the dehvery of the hquid additive to the coating means.

23. Apparatus as claimed in claim 22 wherein the control means incorporates a modem to allow remote control over the dehvery of the hquid additive to the granular feed material via the coating means.

24. A method of automatically coating with an additive a predetermined quantity of granular material fed from a supply thereof to a feeding station comprising the steps of transporting granular material from said supply to a weighing station, discharging said granular material so that said material falls under gravity into the weighing station, coating said granular material with additive as it falls under gravity into the weighing station, weighing the required predetermined quantity of coated granular material at the weighing station, releasing said weighed quantity of coated granular material from the weighing station and transporting said coated granular material to the feeding station.

25. A method as claimed in claim 24 wherein compressed air is introduced into the additive before said additive is applied to the granular material.

26. A method as claimed in claim 24 or claim 25 wherein the additive is a hquid which is sprayed onto the granular material only whde said material is being discharged into the weighing station.

27. A method as claimed in any of claims 24-26 wherein a predetermined quantity of manufactured feed is also fed to the weighing station.