CA1075186A

CA1075186A - Conveyor

Info

Publication number: CA1075186A
Application number: CA292,722A
Authority: CA
Inventors: Eric S. Larter
Original assignee: W D AND H O WILLS (AUSTRALIA) Ltd
Current assignee: W D AND H O WILLS (AUSTRALIA) Ltd
Priority date: 1976-12-20
Filing date: 1977-12-08
Publication date: 1980-04-08
Also published as: BR7708393A; AU3147677A; FR2374232A1; JPS5391279A; DE2755817A1; AU512922B2

Abstract

CONVEYOR
ABSTRACT

Apparatus for the conveying of articles in the form of a substantially horizontal conveyor pan and means to move the pan such that the projection on a vertical plane extending in the conveying direction of the locus of each point on the pan is a smooth closed curve, preferably circular; and the conveying direction of the articles is in a sense opposite to that of the horizontal component of the velocity of the pan at its point of maximum elevation. A method of conveying articles in this manner is also described.

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Description

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r~his inven-tion rela-tes -to a ~ethod and apparatu~ f`or the conveying of articles.
Al-though the invention was originally ~evelope~ to facilitate the transpor-tation of tobacco during the ~narlufacture of cigarettes and smoking -tobacco, its utility has been demonstrated for the transportation of a wide range of solid materials ranging from powdered and granular articles such as sugar to heavy integral objects such as steel bars.
~wo types of conveying apparatus in general uC;e :Lor the transportation of solid materials are continuous bel-t conveyorC;
and vibrating pan conveyors. Each of these -types of conveyor has disadvantages which can be overcome substantially or in par-t by the use of conveying appara-tus according to the present invention in si-tuations where the conventional -types of con-veyor are presently used.
A major disadvantage in belt conveyors is inherent in the use of a flexible or articulated belt. ~hese belts have a tendency to become slack and are readily damaged, requiring replacement and maintenance. Some amount of spillage or 105s ; 20 from the side of the belt is generally unavoi~able. Depending on the material being conveyed, there is a greater or lesser tendency for material to adhere to the belt and so be carried back by the returning part of the belt. A-t the very least, ; this results in further spillage, and it may cause further damage to the conveyor. ~he l~st mentioned problem is particularly serious with materials such as tobacco which ~ have a low bulk density and a tendency to adhere to the belt.
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When such materials are conveyed by a be:Lt conveyor, it is essential to provide a scraper or doctor blade physically to remove material from the belt ancl the downstream end of the conveyor. ~owever, these devices are never entirely satisfac-tory, and some "carry-over" is inevitable.
As it will be necessary now to refer to the drawings, these drawings first will be briefly described.
Figure 1 is a diagrammatic side elevation of a well known vihrating pan conveyor;
Figure 2 illustrates the path of motion of any given point on the conveyor pan of Figure l;
Figure 3 is a diagrammatic side elevation of a previous-ly proposed modification to the vibrating pan conveyor of Figure l;
Figure 4 illustrates on an enlarged scale the path o~
motion of any giv~n point of the conveyor pan of Figure 3;
Figure 5 illustrates the path of motion of an article during one cycle of the conveyor pan of the present invention;
Figures 6 to 10 illustrate the observed paths of two points spaced one inch apart on a single wooden block being conveyed by apparatus of the present invention over a range of angular velocities imposed upon the conveyor pan. In each case t the locus of each point on the conveyor pan was a circle o one inch diameter, as shown, produced by a crank arrangement having a throw of 0.5 inches. The resultant conveying direction is indlcated by an arrow and the conveying velocity is stated in feet per minute.
Figure 11 is a graph showing the variation in conveying speed with increasing angular velocity in respect of four ~:~ B

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~'7~i!36 differen-t materials. Again, -the locus of each point on the conveyor pan was a circle of one inch diclmeter. The materials corresponding to the various curve numbers are as follows:
1: The wooden block of Figures 6 to 10 2: Ready rubbed tobacco

3: Sugar

4: Flour Figure 12 is a graph similar to Figure 11 but showing the effect of varying the crank throw in four stages Erom 1.5 inches to 0.25 inches, while maintaininy the same material, in this case ready rubbed tobacco;
Figure 13 is a partly sectioned side elevation of a con-veying apparatus according to the invention;
Figure 14 is a plan view of the apparatus shown in Figure 13;
Figure 15 is an enlarged sectional view taken on line I-I
of Figure 13;
Figure 16 is a sectional view similar to Figure 15 but illustrating a further embodiment of the invention;
Figure 17 illustrates the observed path and conveying speed of a point on the wooden block of Figures 6 to 10 when conveyed by apparatus of the present invention whexe the locus of each poînt on the conveyor pan was a circle of two inches diameter and the angular velocity was ~00 r.p.m.;
Figure 18 is similar to Figure 17 but illustrates the effect of providing a coating layer of low friction material between the article and the conveyor; and Figure 19 is similar to Figure 18 but illustrates the further effect-of a light oil film applied to the low B 30 friction coating. ~ -3a-~L~'75~

The problems of spillage and "carry~over" are largely avoided by use of a vibrating pan conveyor and one well known conveyor of this type is illust:rated diagrammatically in E'igure 1 of the accompanying drawings. Such a conveyor comprises an elongated channel-shaped pan 20 which is support-ed in cantilever fashion on a series of parallel, leaf springs 21. In the illustrated example, the pan is urged to vibrate by a motor driven eccentric arm 22 such that every point on the conveyor pan moves in a substan-tially linear path as shown in Figure 2. In normal operation, the pan vibrates at the natural resonance ~requency of the system and unbalanced forces are reduced by appropriately arranged counterweight~.
The principle of operation of a vibrating conveyor of th.is type requires the articles to be projected upwardly from the surface of the pan in the direction shown by Figure 2 such that each behaves as a projectile and travels a pre-determined distance along the conveying direction before compacting the conveyor pan to be urged once again from its surface as indicated by the broken lines 23 in Figure 1.
Because of the asymmetry of the springs, such a conveyor ` ~ can be used to convey material in one direction only. Further-more, since it is designed to operate at its resonance .. ~ .

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frequency, -the conveyor i5 not adapted to provide any variation of the speed of conveying.
More importan-tly, because -the articles leave the pan at each oscillation, vibrating pan conveyors tend to be noisy in operation. Further problems involve rnechanical stress arising from the reciprocal motion and a tendency for finer grade material to be segregated from the coarser material when bulk materials of varying size are conveyed. Also, degradation can occur each time -the material returns to 10~ the pan.
In order -to provide a reversible conveyor it has previously been proposed to moun-t the conveyor pan 20 upon eccentric cranks 24 as shown in ~igure 3 such that each point on -the pan is caused to execute a circular motion as shown in the enlarged Figure 4. ~s in the case of the spring rnounted vibrating conveyor, each article is moved along the pan by being repeatedly hurled from the surface of the pan as it travels past its point of maximum elevation with a forward velocity component which is transferred to the article upon its launching.
It will be noted from Figures 3 and 4 that the path of each article, as illustrated in broken lines 25, is substantially ., identical with that of the leaf spring conveyor of Figure 1.
F~rthermore, i-t should be noted that the conveying direction of the articles is in the same sense as -that of the i horizontal co~ponent of the velocity of the pan at its point o~ maximum elevation.
It is an object of an aspect of th2 presen~ in~ention to p~de -4~
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In accordance with one aspect of this invention there is provided an apparatus for the conveying of articles comprising a substantially horizontal conveyor pan and means for moving said pan, comprising: a pluralit:y of spaced parallel crank-shafts provided with cranks, a bearing means on each of said cranks for supporting said conveyor pan; counterweight means supported on each of said crankshafts for balancing centri-fugal forces applied to the crankshafts by said conveyox pan, the projection on a vertical plane extending in the conveying direction of the locus of each point on said pan is a smooth closed circle; and means for rotating the crankshafts at a speed which conveys sa.id articles in a direction opposite to the horizontal component of the velocity of said pan at its point of maximum elevation.
In accordance with another aspect this invention there is provided a method for conveying articles along a substantially ~; 20 horizontal pan by moving said pan such that: the locus of each point on said pan moves in a path the projection of which ~ on a vextical plane extending in the conveying direction is a .~ smooth closed circle, said points being moved in said path at a velocity which causes said articles to move in a conveying direction which is in a sense opposite to that of the horizon-tal component of the velocity of said pan at its point of maxi--~. mum elevation.
Preferably also, the angular velocity of the conveyor pan : -5 ;~ B
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~5~1~36 is chosen so -that -the articles remain in contact with the pan throughout each cycle or, if they lift from it, do not do so to a significant extent.
Preferred embodiments of the invention will now be des-cribed, by way of example only, with reference to -the accom-panying drawings.
The principle of operation of a conveyor according to the present invention may be understood by considering Figure

5 of the accompanying drawings which illustrates diagrammatical-; 10 ly in heavy lines the actual path traversed by an article during one cycle of the conveyor pan~ The actual path o:f that point on the conveyor pan initially in contact with the particle is given by the accompanying circle shown in broken ,...

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Initially, the article rests on -the conveyor pan at position 0 and moves toge-ther with the conve~or until a point 1 is reached where the horizontal componen-t of the forces imposed upon the article exceed -the opposing fric-tional force and the ar-ticle begins to slide along the pan a~ it rises with it to posi-tion 2 A-t -this point, the pan has reached position 2 where its downward accelera-tion is a-t a maximum value such tha-t the pan tends to accelerate downwardly away from the article which falls after it.
Preferably) however, the velocity is such that -the article does not lose contac-t with the pan which slides under i-t in a backwards direction. As the pan continues its downward motion, the vertical force exerted between the article and the pan increases from essentially zero and the resulting increase in frictional force tends to move the article from its position of subs-tantially ver-tical decent. Even-tually, the frictional force is sufficient to adhere the article once again to the pan at point 3 from which it travels with the pan in the same circular arc to point 0 prior to commencing the cycle once again from point 0 .
It will ~e observed that in one cycle, the article has traversed a horizontal distance from 0 to 0 in a direction opposite to that of the horizontal component of the velocity of the pan at point 2. ~his direction of motion is directly opposite to that achieved by vibrating conveyors of the type illustrated in Figure 3 where ar-ticle translation is C

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achieved by an impulsive or balistics approach which deliberately and vigorously projects the particle frorn tlle surface of the pan to achieve -the required translation.
It will be appreciated -that the path of movement illustrated in ~igure 5 is a diagrammatic representation Or the behaviour of a particular article moving on a particular pan which is provided with a particular angular velocity.
Figures 6 to 10 were obtained experimen-tally by observing~
the motion of two point sources of' light vertically spaced apart by one inch on a wooden block moving along a conveyor according to the present invention which was driven at a number o~ increasing angular vel~cities. The resultant figures were each obtained photographically by time exposure o~
the light traces. The conveying velocity stated was -then determined and the results plottèd on the graph of Figule 11.
In each case, the crank throw was 0.5 inches, giving a total vertical displacement of one inch.
Referring to Figure 6 it can be seen -that at 280 r.p.m.
the article progresses in a forward direction at a velocity of 11 feet per minute. It will be noticed~ however, that the . .
article travels in a backward direction over part of the cycle from poin-t 6 to point 7, this backward movement being ` characterised by a closed loop in -the path. ~s the angular velocity is increased~ the amount of backward movement, as evidenced by the size of the closed loops, becomes progressively less to the point where the loops disappear in Figure 9.
~his figure corresponds approximately to the situation _g_ , .
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illustrated diagrammatically in ~igure 5.
~ he results of the experiment are displayed in graphical form by curve 1 of Figure 11 with points 6 to 10 corresponding with Figures 6 to 10 respectively. From curve 1 it ~ e observed that the conveying speed increases approxirnately linearly until the position generally corresponding with ~igure 9 is reached. When the conveyor speed was increased beyond this value -the conveying speed u~s observed -to decrease as evidenced by the point 10 corresponding to -the situation illustrated in ~igure 10. ln this region, the article begins to lift from -the surface of the tray as indicated by the intrusion of the peaks of the lower trace past the troughs of the upper trace in Figure 10. If the angular velocity of -the eonveyor is increased still further, the conveying speed will reduce to zero, at which point the artic:Le is simply projected vertically from the same point on the conveyor during each successive cycle.
Upon a further increase in angular velocity, the eonveying speed will begin to increase in a negative sense as the ecnveyor behaves in the same manner as previously . .
known vibratory conveyors.
~ he effect on the eonveying characteristics of varying the crank throw can be seen in ~'igure 12 which displays eonveying speed against eonveyor pan angular velocity in R.P.M. in respeet o~ ready rubbed tobacco over a range of erank throws from 1.5 to 0.5 inches It ~ill be observed that the curve for a crank thro~ of 0.5 inches correspond ' ; --10--,, : - .
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to a portion of curve 2 for tobacco in Figure 11, A particular working èmboclimen-t of the invention can be seen in ~igures 13, 14 and 15. Referring to these drawings, the conveyor comprises a channel-shaped pan 31 formed of suitable light gauge ma-terial and secured to a wooden base 32 for added rigidity. ~he base in turn is rnounted to a support frame 33 which carries 4 bearings 34 wllich engage the cranks 35 of two spaced crank shafts 36 and 37. 'l'he conveyor pan 31 is generally horizontal and may accomrnoda-te an upward slope of up to about 5 depending upon the pan material and -the articles being conveyed.
Each crank shaft is moun-ted -to a base frame 38 by a pair of bearings 39 and maintained in phase by pulle~-s 40 and belt 41 such that ro-tation of -the crank shaft causes each point on the conveyor to travel in a circular path when projected on a plane normal to the axis of rotation of the crank sha~ts. Drive to the conveyor is provided by a motor and gearbox assembly 43 which drives crank shaft 36 through belt 44 and pulley 45. r~he belt 41 may be provided w~th an adjustable belt -tensioning device 48. Out of balance ~ ces are preferably balanced by counterweight 49 wllich is ~/~D
supported by~*r bearings 50 from a orank 51 on each crank shaft, the crank 51 being disposed 180 from cranks ~5.
The illustrated conveyor may be extended -to any convenient length and, as shoum in ~igures 13 and 14 may be arranged to transport material around corners. In the ~ corner arrangement, best illustrated in ~igure 14~ the upstream ; ' .

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conveyor pan 53 overlays the downs-tream pan 31 and may be provided at i-ts leading edge wi-th a sealing flap 5~. 'rhe ups-tream conveyor is otherwise identical -to the downs-tream conveyor and takes its drive from crank shaft 37 through a bevel gear unit 55 which maintains both conveyors in phase so that both conveyor pans move in sychronism in a vertical sense such that the ver-tical spacing between the overlaying portions remains substantially cons-tant.
If the respective crank throws are substantially identical and ths two conveyors are correc-tly spaced and phased, there would be no need for overlap. In -this case, both adjoining end faces of the conveyor pans could be closely spaced in horizontal register and aligned in the direc-tion of relative movement such -that their spacing remains cons-tant as they slide along the axis of` symmetry of the corner when viewed as shown in ~igure l~. Clearly, this arrangement is not suited to the conveying of fine particulate material.
If the conveyor is to be used in transpor-ting particulate ma-terial such as tobacco9 the pan may be provided along its length with one or more transversely extending ridges ~6.
Each ridge 56 includes an upwardly inclined planar face 57 which -temporarily arrests the flow of material along the conveyor and causes a predetermined quantity to accumulate behind it and thereafter flow over it in a continuous stream. ~his arrangement tends to even out the flow of material and distribute it across the width of the conveyor.
In a further modification of the invention, the co~mter-~ _.. _ .. . .

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weight 49 may be replaced by a lower conveyor 58 as shown in ~igure 16. The arrangemen-t is otherwise identical in operation to that previously described and like components are provided with corresponding reference numerals. I-t will be noted that the conveying direction for the lower conve~or is identical to that of the upper conveyor.
The embodiment of Figure 16 is particularly well adapted for use as a storage device where it is necessary to accumulate a quantity of con-tinuously fed material for subsequen-t processing at a later stage. In this instance, both upper and lower conveyors 31 and 58 are in condui-t form with each being provided wi-th a roof 60 and 61 respectively and a door at their downstream ends (not shown) so that with the door closed, material can be allowed to build up against the door and roof. When the material is subsequently required for further processing, the end door is opened and the material will be gradually dischargecl therethrough. In the case of tobacco, for example, the feeding characteristics of the present invention are such that the product is not degraded by successive and prolonged impact or deleteriously compressed during the storage process.
It has been found that the performance of the conveyor can be improved if the surface of the pan is coated with a ~ low friction material such as polytetrafluroethylene (PT~E) or a high density polyethylene such as that known by the trade name PAC~INE, This latter material has similar low-~ friction proper-ties to that of P~ but does no-t suffer from : , ` 13 ~. ' .

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toxicity problems associa-ted with the fluorine con,tent of Pr~E which makes it undesirable for use in the -tobacco industry, ~he effect of using a low friction coating is demonstratea in Figures 17 to 19. ~he figures illustrate the path of' the wooden block of Figures 6 to 10 on a conveyor having a erank throw of 1" and a-constan-t angular velocity of 200 r.p.m.
in eac,h case.,, In Figure 17, no low frietion coating was used a~d the observed conveying veloeity was 38.7 fee-t per minute.
However, the use of a Pae-tine layer in ~igure 18 produeed a eonveying veloei-ty of 50 fee-t, per minu-te. In a further experi~ent, a film of oil on -the Pactine layer produced a eonveying veloeity of 56.7 feet per minute as sho~/n in Figure 19.
It should also be noted that in conditions of redueed frietion the observed artiele path is much smoother -than ~ would otherwise be the ease, as ean be seen by coulparing the relatively sharp peaks of ~igures 6 to 10 and 17 with the sof-ter eurves of Figures 18 and 19.
A major advantage of eonveying apparatus according to the present invention arises from -the fact that the material being eonveyed is no-t subjeeted to violent forces at high frequeneies as in the ease of previously known eonveyors.
~ As a result, noise levels are low and very little degradation and segragation of the eonveyed ma-terial takes place.
~urthermore, beeause -the rotational speeds are low in eomparison wi-th the frequency of vibrating pan conveyors, ' .

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5~1~6 wear and main-tenance is mi.nimal. Moreover, out of balance forces can be effectively opposecl by counterweights such that the transmission of vibration is minimised.
~ he present invention also permits the ready variation of conveying velocity and direction simply by altering the cyclic speed of the convegor without the need for changing system parameters such as springs and counterweights for each di.fferent speed. Furthermore, the conveyor~ can be designed with a reduced overall heigh-t since they do not require bulky leaf springs as in ~he case of most of the : previously known vibrating pan conveyors.
Although the invention has been described with reference to specific examples, it will be appreciated that the invention . . .
may be embodied in many other forms without departing from ~ the scope of the inventive concept.
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Claims

CLAIMS:

1. Apparatus for the conveying of articles comprising a substantially horizontal conveyor pan and means for moving said pan, comprising: a plurality of spaced parallel crankshafts provided with cranks, a bearing means on each of said cranks for supporting said conveyor pan; counterweight means supported on each of said crankshafts for balancing centrifugal forces applied to the crankshafts by said conveyor pan, the projection on a vertical plane extending in the conveying direction of the locus of each point on said pan is a smooth closed circle; and means for rotating the crankshafts at a speed which conveys said articles in a direction opposite to the horizontal component of the velocity of said pan at its point of maximum elevation.

2. Apparatus as claimed in Claim 1 wherein each said crankshaft supports said conveyor pan on two spaced cranks and said counterweight is mounted between said two spaced cranks on one or more intermediate cranks said one or more intermediate cranks being disposed at 180° from said two spaced cranks.

3. Apparatus as claimed in Claim 1 wherein a further substantially horizontal conveyor pan is supported on one or more further cranks on each of said crankshafts, said one or more further cranks being disposed at 180° from said one or more cranks supporting said first mentioned conveyor pan.

4. Apparatus as claimed in Claim 3 wherein the crank throw of said one or more further cranks supporting said first mentioned conveyor pan is equal to that of said one or more cranks.

5. Apparatus as claimed in Claim 3 wherein each said crankshaft supports said first mentioned conveyor pan on two spaced cranks and said one or more further cranks are arranged between said two spaced cranks.

6. Apparatus as claimed in Claim 3 wherein said further conveyor pan is disposed beneath said first mentioned conveyor pan and arranged to act as a counterweight to balance centri-fugal forces applied to said crankshafts by said first mention-ed conveyor pan.

7. Apparatus as claimed in Claim 1 including a second substantially horizontal conveyor pan arranged upstream of said first mentioned conveyor pan and in coveying relationship there-with, said first mentioned and second conveyor pans being inter-locked to move in synchronism in a vertical direction such that they remain in substantially constant vertical relationship while the projection on a vertical plane extending in the con-veying direction of said second pan of the locus of each point on said second pan is a smooth closed curve and the conveying direction of said second pan towards said first mentioned pan is in a sense opposite to that of the horizontal component of the velocity of said second pan at its point of maximum eleva-tion.

8. Apparatus as claimed in Claim 7 wherein the floor of said second conveyor pan at its downstream end partially over-laps the floor of said first mentioned conveyor pan.

9. Apparatus as claimed in Claim 7 wherein said curve is identical in the case of both conveyor pans.

10. Apparatus as claimed in Claim 1 wherein said articles remain in contact with said pan throughout each cycle of said pan or, if they lift from it, do not do so to a significant extent.

11. Apparatus as claimed in Claim 1 wherein the floor of said conveyor pan is coated with a low friction material.

12. Apparatus as claimed in Claim 1 wherein said conveyor pan is of thin sheet material secured to a wooden base.

13. Apparatus as claimed in Claim 1 wherein said conveyor pan is in the form of a conduit.

14. Apparatus as claimed in Claim 13 wherein said conduit has a door at its downstream end.

15. Apparatus as claimed in Claim 3 wherein said second and said first mentioned conveyor pan are each in the form of a conduit.

16. Apparatus as claimed in Claim 15 wherein each said conduit has a door at its downstream end.

17. A method of conveying articles along a substantially horizontal pan by moving said pan such that: the locus of each point on said pan moves in a path the projection of which on a vertical plane extending in the conveying direction is a smooth closed circle, said points being moved in said path at a velocity which causes said articles to move in a conveying direction which is in a sense opposite to that of the horizon-tal component of the velocity of said pan at its point of maxi-mum elevation.

18. A method as claimed in Claim 17 wherein said conveyor pan is supported by bearings on one or more cranks on each of a plurality of spaced parallel crankshafts.

19. A method as claimed in Claim 18 wherein said crank-shafts support a counterweight arranged to balance centrifugal forces applied to said crankshafts by said conveyor pan.

20. A method as claimed in Claim 19 wherein each said crankshafts supports said conveyor pan on two spaced cranks and said counterweight is mounted between said two spaced cranks on one or more intermediate cranks said one or more intermediate cranks being disposed at 180° from said two spaced cranks.

21. A method as claimed in Claim 23 wherein a further sub-stantially horizontal conveyor pan is supported on one or more further cranks on each of said crankshafts, said one or more further cranks being disposed at 180° from said one or more cranks supporting said first mentioned conveyor pan.

22. A method as claimed in Claim 21 wherein the crank throw of said one or more further cranks is equal to that of said one or more cranks supporting said first mentioned convey or pan.

23. A method as claimed in Claim 21 wherein each said crankshaft supports said first mentioned conveyor pan on two spaced cranks and said one or more further cranks are arranged between said two spaced cranks.

24. A method as claimed in Claim 21 wherein said further conveyor pan is disposed beneath said first mentioned conveyor pan and arranged to act as a counterweight to balance centrifu-gal forces applied to said crankshafts by said first mentioned conveyor pan.

25. A method as claimed in Claim 17 including the step of moving articles from a second substantially horizontal con-veyor pan onto said first mentioned conveyor pan, said second pan being arranged upstream of said first mentioned conveyor pan and in conveying relationship therewith, said first mentioned and second conveyor pans being interlocked to move in synchronism in a vertical direction such that they remain in substantially constant vertical relationship while the projec-tion on a vertical plane extending in the conveying direction of said second pan of the locus of each point on said second pan is a smooth closed curve and the conveying direction of said second pan towards said first mentioned pan is in a sense opposite to that the horizontal component of the velocity of said second pan at its point of maximum elevation.

26. A method as claimed in Claim 25 wherein the floor of said second conveyor pan at its downstream end partially over-laps the floor of said first mentioned conveyor pan.

27. A method as claimed in Claim 25 wherein said curve is identical in the case of both conveyor pans.

28. A method as claimed in Claim 17 wherein said articles remain in contact with said pan throughout each cycle of said pan or, if they lift from it, do not do so to a significant extent.

29. A method as claimed in Claim 17 wherein the floor of said conveyor pan is coated with a low friction material.

30. A method as claimed in Claim 17 wherein said conveyor pan is of thin sheet material secured to a wooden base.

31. A method as claimed in Claim 17 wherein said conveyor pan is in the form of a conduit.

32. A method as claimed in Claim 31 wherein said conduit has a door at its downstream end.

33. A method as claimed in Claim 21 wherein said further and said first mentioned conveyor pan are each in the form of a conduit.

34. A method as claimed in Claim 33 wherein each said conduit has a door at its downstream end.

35. Apparatus as claimed in Claim 1 wherein said conveyor pan includes a ridge extending across the conveying direction said ridge being adapted to accumulate a predetermined quantity of particulate material behind it and thereafter permit material to flow over it in said conveying direction.

36. Apparatus as claimed in Claim 35 wherein said ridge includes a plane inclined upwardly from the floor of said convey-or pan in said conveying direction.