CA2045638A1 - Feeder for particulate material - Google Patents
Feeder for particulate materialInfo
- Publication number
- CA2045638A1 CA2045638A1 CA002045638A CA2045638A CA2045638A1 CA 2045638 A1 CA2045638 A1 CA 2045638A1 CA 002045638 A CA002045638 A CA 002045638A CA 2045638 A CA2045638 A CA 2045638A CA 2045638 A1 CA2045638 A1 CA 2045638A1
- Authority
- CA
- Canada
- Prior art keywords
- funnel
- feeder
- gas
- particulate material
- mechanical
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
- B65G53/00—Conveying materials in bulk through troughs, pipes or tubes by floating the materials or by flow of gas, liquid or foam
- B65G53/34—Details
- B65G53/40—Feeding or discharging devices
- B65G53/48—Screws or like rotary conveyors
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B65—CONVEYING; PACKING; STORING; HANDLING THIN OR FILAMENTARY MATERIAL
- B65G—TRANSPORT OR STORAGE DEVICES, e.g. CONVEYORS FOR LOADING OR TIPPING, SHOP CONVEYOR SYSTEMS OR PNEUMATIC TUBE CONVEYORS
- B65G53/00—Conveying materials in bulk through troughs, pipes or tubes by floating the materials or by flow of gas, liquid or foam
- B65G53/04—Conveying materials in bulk pneumatically through pipes or tubes; Air slides
- B65G53/16—Gas pressure systems operating with fluidisation of the materials
- B65G53/18—Gas pressure systems operating with fluidisation of the materials through a porous wall
- B65G53/22—Gas pressure systems operating with fluidisation of the materials through a porous wall the systems comprising a reservoir, e.g. a bunker
Abstract
A feeder for particulate material for connecting a mechanical feeding device (14) to a pneumatic conveying line comprises a funnel (7) formed of a gas pervious material which is mounted in a closed outer housing (1) formed of an impervious material wherein the walls of the funnel and the outer housing together defining a plenum chamber (10) which is provided with an inlet (11) for connection to supply of conveying gas under pressure. The funnel (7) is adapted to form a sealing engagement with the outlet of the mechanical feeding device (14) and the funnel (7) at or towards its narrow end communicates with the pneumatic conveying line. In use, conveying gas, under pressure, enters the plenum chamber (10) and then passes through the walls of the funnel (7). The particulate material delivered to the funnel (7) by the mechanical feeding device is flushed out of the funnel and into the conveying line by the conveying gas. The feeder enables a uniform flow of particulate material using one pressurized gas supply for conveying particulate material from bulk storage to discharge.
Description
WO ~/087~3 2 V -- ` PCT/GBgo/o~lo5 Fee~er for P3rticulate Mate~lal The present inven.ion relates tO a feeder for ~articulats m2 ~rial, fcr instance material in the form of a powder or fibres, filaments or whiskers. More particularly, it relates to a feeder for connecting a mechanical feeding device to a pneumatic conveying line. Feeders of this type, generally known as "par~iculate feeders", are used when it is desired to change the means of transporting a particulate material in a conveying line from a mechanical means (e.g. a screwfeeder) tO a gas driven means (e.g. fluidised bed). Many known particulate feeders are effective only when using large volumes (high velocities) of conveying gas and!or connecting feeder outlet and conveying line diameters of essentially similar size.
; 15 The feeder of the invention is particularly useful as part of a controllable feeder system for conveying particulate material from a hopper to a pneumatic conveying line for controllably supplying said particulate material for incorporation into metals by spray co-deposition in the production of metal matrix composites.
A typical spray co-deposition method of making metal matrix composites comprises the steps of atomising ; a stream of molten metal to form a spray of hot metal particles by subjecting the metal stream to relatively cold gas directed at the stream, feeding a stream of ; particulate ceramic material in a fluidising gas to the atomising zone where said particulate material becomes ;~ incorporated into the metal particles and co-depositing the metal and the particulate material onto a , ~ .
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collecting surface. Co~ventionally, the parti~ulate ceramic material i, c~nveyed pneumatically from 2 hop~er tO the atomising z~ne. However, the am~ien- Dressure conditions at the dis.harge point of the par~:cula;e feed tube are variable because of the highly turbu~ent gas jet flows present in the atomising region. Because of this variable pressure at discharge, any powder feeding device for use in this method which r lies on a gas stream to control particulate feed rate tends to be unreliable, particularly in view of the low conveying line pressures (e.g. 0.3. bar 9) ar,d conveying line flowrates (e.g. 80 dm3/min) used. A
conventional feeding system for transporting a particulate material from bulk storage in a hopper to the atomising zone uses two gas streams: one for introducing the particulate material into the conveying line from bulk storage and one for conveying the particulate material to the atomising zone. Such a system dictates that the two gas streams meet at equal pressure at some point. A change in conditions at this point will obviously cause changes to occur in all gas flows including the feedrate of the particulate material. The use of higher gas flows which might otherwise overcome such a problem is not desirable for a number of reasons. For instance, because of the nature of the spray co-deposition method, it is ~ desirable to keep the flow rate of the gas used to ; convey the particulate material to the atomising zone as low as possible in order that the conveying gas stream does not affect the gas stream used to atomise the molten metal at the atomising zone. Furthermore, high flow rates for the ¢onveying gas are not desirable ~;
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7~ ~ ~ d - -WO90/08723 ~ /G89~0/Q010 since equipment life can be greatly reduced because of the effects of abrasiDn caused by high-speed -~-p2rticulate material which abrasicn could 21s0 result in the degrada~i~n cf the partlcu~2te material i~se'~
5 by size reduct!on and/or contamination. If higner conveying gas flows and larger pipe bore sizes could be used then it might be possible to maintain the conveying velocity at its original levei. However, the geometry and dimensions of the atomising zone are such that the particulate feed entry has to be relatively small (e.g. 7mm diameter) to ensure maximum delivery of the particulate material to the atomising region accurately.
In view of the above, it is clear that there is lS a need for an improved system of feeding particulate material from a hopper to a pneumatic conveyer for use in metal matrix composite production by the spray co-deposition process which system allows for greater control over the feed rate of the particulate material 20 than achieved previou 5 Iy . - .
According to one aspect, the present invention provides a particulate feeder for connecting a ,~
mechanical' feeding device to a pneumatic conveying line ;~ which comprises a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious material, the walls of the funnel dnd the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, wherein the housing at or towards the wide end of the funnel is adapted to form a sealing engagement with' t'he outlet of`the mechanical'feeding device and , wherein the funnel at or towards its narrow end 'l ~ communicates with the pneumatic conveying line.
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3~' - According to another aspect, the pre,ent invention prcvides a ree~er system for conveyins particulate material from a hopper to a pneumatic conveying line for use in a spray co-de~osition proc s, of ~roa~ing me;al matrix composites which feeder system comprises (1 ) d mechdnical feeder device for moving particulate mdterial from a bu]k stor2ge hopper to an - outlet and (2) a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious mdterial, the walls of the funnel and the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, said housing at or towards the wide end of the ; funnel being engaged with the outlet of the mechanical feeder device to form a gas-tight seal therewith and said funnel at or towards its narrow end being in communication with the pneumatic conveying line.
Thus, the feeder system of the invention makes use of a mechanical feeder device to m,ove the particulate material from a bulk storage hopper to a particulate feeder wherein the particulate material is fluidised for introduction to the pneumatic conveying line. The use of the mechanical feeder device overcomes the above-mentioned problems arising from the use of a gas stream to move the particulate material from a storage hopper. This is because, in the case of a mechanical feeder device, the particulate solids , feed rate from the hopper is independent of other process , conditions and is essentially dependent only on the speed of the motor driving the mechanical feeder device.
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Mechanical feeder devices are, of course, well known and include screwfeeders, vlbrating conveyor feeders and rotary valve feeders. We haYe obtaine~
cood results using a screwfeeder in the present invention. In ideal circumstances with a free flowing powder, the solids feedrat~- delivered by a mechani~ ;
feeder device is proportional to the speed of the drive motor. However, in normal circumstances, particulate materials are far from ideal in their flow behaviour and handeability, especially if the particulate material is fine in size, irregular in shape, damp and cohesive. Usually such factors are responsible for variations in powder "bulk density". When a mechanical feeder device operating at a fixed speed is used, fluctuations in the mass flow rate of particulate delivered by the mechanical feeder device may be experienced. It is, therefore, preferable in the present invention for the rate of delivery of particulate by the mechanical feeder device be controlled by a feedback system. To do this, the mechanical feeder device is suspended or loaded on a weighing device (for example, a load cell). The change in weight of the feeder device under operation as a f,unction of time is monitored and aut~matically compared with the change in weight that would be expected for a desired feedrate of particulate. If the actual rate of weight decrease in the system being monitored is greater than that expected, the system compensates by reducing the speed of the feeder device '~ 30 accordingly. Alternatively, if the actual rate of weight decrease is less than expected for the particulate feedrate desired, the system automatically increases the speed of the mechanical feeder devic accordingly. Such controlled feeder devices are known generally as "Loss in Weight" feeders. The process o,~
j ~ sampling the feeders weight, calcuIating the result:ng feedrate and effecting the appropriate motor speed . ~ :
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WO9U/08723 ~ 3 ~ 6;~- -control action is almost continuous during feeder bperation and allowance is made f cr the fini~- ~i me required for data samDling and microproressor progra~
calculation time (Iypically milliseconds per cycle3 5 whi.h is neglisible in terms of syste~ (m~ or) re,ponse time. By using a "Loss in Weight" feeder of thls kind, particulate materials of different kinds can easily and accurately be fed using the same feeding device and change from one particulate material to a different particulate material to be fed to the feeding device can be effected easily and rapidly.
The particulate feeder of the invention for connecting the mechanical feeder device to the pneumatic conveying line typically comprises a fùnnel made of a porous material which is pervious to the conveying gas which, when the feeder is in operation, is supplied to the plenum chamber which lies between the funnel and the external gas impervious housing in which the funnel is mounted. In order that the speeds of the mechanical feeder device involved are acceptable to the particulate materials involved, the discharge part of the mechanical feeder is typically an order of magnitude larger than the diameter of the pneumatic conveying tube. Thus, the funnel in the particulate feeder has to achieve a transition from'an inlet diameter of, for instance, 100 mm to an outlet diameter of, for instance, 10 mm ; with a minimum hold-up volume being created whilst, at the same time, without the transition being made so rapidly that blockages of particulate material are caused in the pneumatic conveying line. The funnel in the particulate feeder of the invention is preferably a conical funnel. However, a non-conical funnel, such as one having a bowl shape wherein the sides curve inward ... ~ ~ .
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'~ ~ ' ' ' ' ' " ' " ' " ' ' ~ ' ' ' '' , . : ' towards the narrow end wnich communicates with the pneum3tic conveying line, can also be used in the present inventicn. In such d case, the inwardly curving sides of the bowl-shape funnel will preferably n^~ ~e so great as to present a sur'a e where any build-up of particulate material could occur during operation Ot the particulate feeder. We have found that the transition is preferably effected by using a conical funnel having a vertical axis and walls at an angle of from 30to 60 to the vertical axis, and more preferably between 30 and 45. The shape of the external housing is not critical although, preferably, it will be large enough to provide uniform filling of the plenum chamber that surrounds the funnel. The funnel used in the present invention is formed of a material which is pervious to the conveying gas that will be supplied under pressure to the plenum chamber during operation of the particulate feeder. Gas-pervious materials such as sintered plastics, filter cloths and woven wire meshes have been used successfully in the present invention for forming the funnel. However, because the conveying gas will be supplied unde'r pressure, during operation, to the plenum chamber, the walls of the funnel should have sufficient mechanical rigidity so that the pervious funnel has sufficient dimensional stability to withstand this pressure. Preferably then, we use material such as sintered metal or perforated metal for forming the funnel for use in the present invention.
In the case of a funnel formed from a perforated metal sheet, the metal sheet imme~iately at the periphery of the perforations may advantageously be deformed away . ~
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. , , - - . . . , , - . . -from the plane of the metal sheet so as to shield the particu]ate material (when the feeder is in operation) frcm the ~er-sr2t;0ns. Preferably, the internal surface o- t~,e funnel should be sufficiently smootn so 5 2; not to ~IIG~ the bulld-u~ o' any ~ar.iculcte materi21 the!eon. In operation, as the particulate material free-falls into the funnel from the mechanical feeder device, the conveying gas which passes throu3h the bowl fro~ the plenum chamber flushes ~.
it towards and into the pneumatic conveying line.
In the accompanying drawings -Figure 1 is a section through a preferred particulate feeder embodying the present;invention;
Figure 2 schematically illustratès the operation of the particulate feeder shown in Figure l;
and Figure 3 is a diagrammatic representation of a feeder system in accordance with the invention.
In Figure 1, a housing 1 formed of a gas impervious material such as stainless steel or aluminium has cylindrical sides 2 and an . upper radial flange 3. The housing has a base 4 which opens into an exit pipe 5 leading to a pneumatic conveying line (not shown). The flange 3 is adapted to abut the base of a mechanical feeder device outlet (not shown) and be fixed thereto by means of bolts placed through.holes 6 provided in said flange. Contained . inside the housing 1 is a truncated conical funnel 7 :
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WO ~/08723 PCT/GB90/0010~_ having sides at an angle of 45 to the vertical and formed of a gas Dervious material. The funnel is lû'2 ed in the hsusing so as to provid~ 2 smooth tr~nsition in si,e from its wide end 8 positioned near 5 ~ o~ ope"ir~ he ~,uu;ing ;o its n~rro~ end whi:h communicates with the exit pipe S. A plenum chamDer 10 is defined by the sides 2 and base 4 of the housing together with the sides of the conical funnel 7. The housing is provided with an inlet 11 ror a supply of a conveying gas introduced under pressure when the particulate feeder is in operation. As can seen from Figure 2, during operation, particulate material 12 free-falls into the particulate feeder from a mechanical feeding device (not shown). Conveying gas supplied und~er pressure to the inlet 11 in the housing 1 enters the plenum chamber 10 from where it passes through the Wdlls of the conical funnel 7. The particulate material 12 falling into the conical funnel meets the conveying gas at or ne~r to the funnel walls from where it is carried by the gas flow down the interior of the funnel and flushed into the exit pipe 5 ; to the pneumatic conveying line (not shown).
In Figure 3 a particulate feeder of the type shown in Figures 1 and 2 is engaged by f]ange 3 at the outlet 13 of a motor driven screwfeeder 14. The screwfeeder 14 in operation feeds particulate material 1~ from a sealed bulk storage hopper 15 to the outlet 13 from where the particulate material free-falls into the conical funnel 7 of the particulate feeder. In order that the conveying gas introduced into the plenum chamber 10, Iying between the housing 1 and the funnel 7, via gas inlet 11 flows in the desired direction and :
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- - . , . . -W090~08723 - 10 - PCT/GB90/0010 at the desired flowrate, a pipe 16 is preferably provided to connect the screwfeeder outlet region 17 to the airspace 18 above the level of particulate material in the hopper. Thus, when the conveying gas is flowins, the gas pr~ssures at 17 and 18 will be equalized so ~ that particulat~ fecd is nc' adversely affected by any pressure build-up in the system. Typically, the pipe 16 will contain or be provided with a device to restrict the flow of particulate material and conveyins gas through the pipe but which still allows the equalisation of pressure between the bulk storagè
hopper and the particulate feeder. For example, the pipe 16 may contain or be fitted with a pressure equalisation valve which only need be opened periodically to relieve any pressure buildup in the system. Such a feature would be advantageous at low flow rates. Alternatively, instead of providing a return line 16, with or without a control valve, to connect the funnel inlet (17) to the top space (18) of the hopper, the top space of the hopper may be connected to a separate gas feed (not shown) which would be controlled automatically to maintain the gas pressure at the top of the hopper at a value equal to the gas pressure at 17. In the case where the volume of gas in the hopper is large, such a system having a separate gas feed to the top space of the hopper would be preferable to a system having a return line 16 since in the latter system pressure equalisation would cause i the flow of gas to be diverted in the funnel with the result that the uniform transport of solids in the 3 conYeying line would be disrupted.
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2 ~ J ~i C3 Woso/08723 1 PCTJGB90/0010 A, mentioned earlier, spray co-deposition processes require a maximum amount of particulate material with a minimum amount Qr carrier gas. This ratio is termed "phase density" and is given the symbcl "~", where -~ = mass flowrate of solids .
mass flowrate of gas Some powders will convey in "dense phase", i.e. ~= 50-200 (approx) at velocities of about 1 m/s.
Experience of handlin3 such powders in this mode is essential as operating conditions are approaching conditions in blocked pipes. However, to ensure accurate operation of a "Loss in Weight" feeder, it is desirable to operate the conveying line at the opposite end of the phase density range (i.e. ~= 1-10 and v = 20-40 m/s) which conditions are analogous to conditions in an open pipe. The other advantage of this regime is that even small discontinuities in powder flow within the conveying line (causing line pressure fluctuations) can be measured easily relative to the normally low line pressure. In "dense" phase conveying, large fluctuations in solids flowrates can go unnoticed since they are masked by the normally high line pressures required.
The feeder system of the present invention canbe made to work quite satisfactorily using phase densities of 20 to 50 at velocities of 10 m/s. This mode of transport (i.e. moving/sliding beds and dunes), however, may not give desirable results in terms of metal matrix composite product structure. The present invention has been used successfully to convey SiC
I powder (F230 grit, F600 grit and F1000 grit) over a ; 35 .
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wO9Ot08723 PCT/GB9O/OO10~
jt~, ~`J .~ 3 - 1 2 range of feedrates from 0.5 to 3.5 kg/min using transport gas flows of from 45 x 10~3 to 85 x 10~3 Nm3/min through nominal 8 mm diameter tubing. Th^
terms "F23C, 600 and 1000 grits" are described in FE?A
Standard 42-G3-1984 and US S~andard ANSI B.7~.12-1975.
As soon as the feeder motor is turned off, the conveying line clears rapidly rather ~han undergoing any gradual reduction in powder level concentration in the conveyin3 line.
EXAMPLE
The feeder system as described above was used to convey various particulate ma~rials at various flow rates. The system was found to work at high solids densities and yet still maintain uniform flow. The 1~ results are shown in the following Taùle-~ i :
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Notes to Table (1) The solids density values are obtained by dividins "Flowrate" by "Gas Flow" x103.
(2) 50:50 wt' mixtur (3) Screwfeeder pressure 1.0 bar 9 ~ 2 kg/min (4) Screwfeeder pressure 3.0 bar 9 ~ 3.5 kg/min (5) Screwfeeder pressure 2.5 bar 9 The first six runs shown in the Table, i.e. those for SiC (F600) at 0.5, 2.0, 3.0 and 3.5 kg/min demonstrate that high solids densitites can be achieved. The other runs in the Table demonstrate the ability of the feeder of the invention to handle a range fo materials and particle sizes. In all cases, a satisfactory uniform flow was achieved.
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; 15 The feeder of the invention is particularly useful as part of a controllable feeder system for conveying particulate material from a hopper to a pneumatic conveying line for controllably supplying said particulate material for incorporation into metals by spray co-deposition in the production of metal matrix composites.
A typical spray co-deposition method of making metal matrix composites comprises the steps of atomising ; a stream of molten metal to form a spray of hot metal particles by subjecting the metal stream to relatively cold gas directed at the stream, feeding a stream of ; particulate ceramic material in a fluidising gas to the atomising zone where said particulate material becomes ;~ incorporated into the metal particles and co-depositing the metal and the particulate material onto a , ~ .
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W090/0~723 PCT/GB90/0010~
collecting surface. Co~ventionally, the parti~ulate ceramic material i, c~nveyed pneumatically from 2 hop~er tO the atomising z~ne. However, the am~ien- Dressure conditions at the dis.harge point of the par~:cula;e feed tube are variable because of the highly turbu~ent gas jet flows present in the atomising region. Because of this variable pressure at discharge, any powder feeding device for use in this method which r lies on a gas stream to control particulate feed rate tends to be unreliable, particularly in view of the low conveying line pressures (e.g. 0.3. bar 9) ar,d conveying line flowrates (e.g. 80 dm3/min) used. A
conventional feeding system for transporting a particulate material from bulk storage in a hopper to the atomising zone uses two gas streams: one for introducing the particulate material into the conveying line from bulk storage and one for conveying the particulate material to the atomising zone. Such a system dictates that the two gas streams meet at equal pressure at some point. A change in conditions at this point will obviously cause changes to occur in all gas flows including the feedrate of the particulate material. The use of higher gas flows which might otherwise overcome such a problem is not desirable for a number of reasons. For instance, because of the nature of the spray co-deposition method, it is ~ desirable to keep the flow rate of the gas used to ; convey the particulate material to the atomising zone as low as possible in order that the conveying gas stream does not affect the gas stream used to atomise the molten metal at the atomising zone. Furthermore, high flow rates for the ¢onveying gas are not desirable ~;
-: ' " . ~ .
, - .
~ -- . - . .
7~ ~ ~ d - -WO90/08723 ~ /G89~0/Q010 since equipment life can be greatly reduced because of the effects of abrasiDn caused by high-speed -~-p2rticulate material which abrasicn could 21s0 result in the degrada~i~n cf the partlcu~2te material i~se'~
5 by size reduct!on and/or contamination. If higner conveying gas flows and larger pipe bore sizes could be used then it might be possible to maintain the conveying velocity at its original levei. However, the geometry and dimensions of the atomising zone are such that the particulate feed entry has to be relatively small (e.g. 7mm diameter) to ensure maximum delivery of the particulate material to the atomising region accurately.
In view of the above, it is clear that there is lS a need for an improved system of feeding particulate material from a hopper to a pneumatic conveyer for use in metal matrix composite production by the spray co-deposition process which system allows for greater control over the feed rate of the particulate material 20 than achieved previou 5 Iy . - .
According to one aspect, the present invention provides a particulate feeder for connecting a ,~
mechanical' feeding device to a pneumatic conveying line ;~ which comprises a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious material, the walls of the funnel dnd the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, wherein the housing at or towards the wide end of the funnel is adapted to form a sealing engagement with' t'he outlet of`the mechanical'feeding device and , wherein the funnel at or towards its narrow end 'l ~ communicates with the pneumatic conveying line.
~ '~ ' ' ,`
, . .- - : . , , : -.
: . :, ,. . ~
3~' - According to another aspect, the pre,ent invention prcvides a ree~er system for conveyins particulate material from a hopper to a pneumatic conveying line for use in a spray co-de~osition proc s, of ~roa~ing me;al matrix composites which feeder system comprises (1 ) d mechdnical feeder device for moving particulate mdterial from a bu]k stor2ge hopper to an - outlet and (2) a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious mdterial, the walls of the funnel and the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, said housing at or towards the wide end of the ; funnel being engaged with the outlet of the mechanical feeder device to form a gas-tight seal therewith and said funnel at or towards its narrow end being in communication with the pneumatic conveying line.
Thus, the feeder system of the invention makes use of a mechanical feeder device to m,ove the particulate material from a bulk storage hopper to a particulate feeder wherein the particulate material is fluidised for introduction to the pneumatic conveying line. The use of the mechanical feeder device overcomes the above-mentioned problems arising from the use of a gas stream to move the particulate material from a storage hopper. This is because, in the case of a mechanical feeder device, the particulate solids , feed rate from the hopper is independent of other process , conditions and is essentially dependent only on the speed of the motor driving the mechanical feeder device.
j ~ .
,. . . . . . . .
~ . . . .
: . . . .
~ ~ , ~ -, : . .
~ ?'~ 3 3 5 PCT/GB90~0010~ ^
Mechanical feeder devices are, of course, well known and include screwfeeders, vlbrating conveyor feeders and rotary valve feeders. We haYe obtaine~
cood results using a screwfeeder in the present invention. In ideal circumstances with a free flowing powder, the solids feedrat~- delivered by a mechani~ ;
feeder device is proportional to the speed of the drive motor. However, in normal circumstances, particulate materials are far from ideal in their flow behaviour and handeability, especially if the particulate material is fine in size, irregular in shape, damp and cohesive. Usually such factors are responsible for variations in powder "bulk density". When a mechanical feeder device operating at a fixed speed is used, fluctuations in the mass flow rate of particulate delivered by the mechanical feeder device may be experienced. It is, therefore, preferable in the present invention for the rate of delivery of particulate by the mechanical feeder device be controlled by a feedback system. To do this, the mechanical feeder device is suspended or loaded on a weighing device (for example, a load cell). The change in weight of the feeder device under operation as a f,unction of time is monitored and aut~matically compared with the change in weight that would be expected for a desired feedrate of particulate. If the actual rate of weight decrease in the system being monitored is greater than that expected, the system compensates by reducing the speed of the feeder device '~ 30 accordingly. Alternatively, if the actual rate of weight decrease is less than expected for the particulate feedrate desired, the system automatically increases the speed of the mechanical feeder devic accordingly. Such controlled feeder devices are known generally as "Loss in Weight" feeders. The process o,~
j ~ sampling the feeders weight, calcuIating the result:ng feedrate and effecting the appropriate motor speed . ~ :
. - ~ :
. . - . ~. . .: , ,. ,.. , ,. . ,,- , , . - .-. . .
WO9U/08723 ~ 3 ~ 6;~- -control action is almost continuous during feeder bperation and allowance is made f cr the fini~- ~i me required for data samDling and microproressor progra~
calculation time (Iypically milliseconds per cycle3 5 whi.h is neglisible in terms of syste~ (m~ or) re,ponse time. By using a "Loss in Weight" feeder of thls kind, particulate materials of different kinds can easily and accurately be fed using the same feeding device and change from one particulate material to a different particulate material to be fed to the feeding device can be effected easily and rapidly.
The particulate feeder of the invention for connecting the mechanical feeder device to the pneumatic conveying line typically comprises a fùnnel made of a porous material which is pervious to the conveying gas which, when the feeder is in operation, is supplied to the plenum chamber which lies between the funnel and the external gas impervious housing in which the funnel is mounted. In order that the speeds of the mechanical feeder device involved are acceptable to the particulate materials involved, the discharge part of the mechanical feeder is typically an order of magnitude larger than the diameter of the pneumatic conveying tube. Thus, the funnel in the particulate feeder has to achieve a transition from'an inlet diameter of, for instance, 100 mm to an outlet diameter of, for instance, 10 mm ; with a minimum hold-up volume being created whilst, at the same time, without the transition being made so rapidly that blockages of particulate material are caused in the pneumatic conveying line. The funnel in the particulate feeder of the invention is preferably a conical funnel. However, a non-conical funnel, such as one having a bowl shape wherein the sides curve inward ... ~ ~ .
., .,, :: - :
: .
,; , .
' ' . ' ': .
'~ ~ ' ' ' ' ' " ' " ' " ' ' ~ ' ' ' '' , . : ' towards the narrow end wnich communicates with the pneum3tic conveying line, can also be used in the present inventicn. In such d case, the inwardly curving sides of the bowl-shape funnel will preferably n^~ ~e so great as to present a sur'a e where any build-up of particulate material could occur during operation Ot the particulate feeder. We have found that the transition is preferably effected by using a conical funnel having a vertical axis and walls at an angle of from 30to 60 to the vertical axis, and more preferably between 30 and 45. The shape of the external housing is not critical although, preferably, it will be large enough to provide uniform filling of the plenum chamber that surrounds the funnel. The funnel used in the present invention is formed of a material which is pervious to the conveying gas that will be supplied under pressure to the plenum chamber during operation of the particulate feeder. Gas-pervious materials such as sintered plastics, filter cloths and woven wire meshes have been used successfully in the present invention for forming the funnel. However, because the conveying gas will be supplied unde'r pressure, during operation, to the plenum chamber, the walls of the funnel should have sufficient mechanical rigidity so that the pervious funnel has sufficient dimensional stability to withstand this pressure. Preferably then, we use material such as sintered metal or perforated metal for forming the funnel for use in the present invention.
In the case of a funnel formed from a perforated metal sheet, the metal sheet imme~iately at the periphery of the perforations may advantageously be deformed away . ~
.
. , , - - . . . , , - . . -from the plane of the metal sheet so as to shield the particu]ate material (when the feeder is in operation) frcm the ~er-sr2t;0ns. Preferably, the internal surface o- t~,e funnel should be sufficiently smootn so 5 2; not to ~IIG~ the bulld-u~ o' any ~ar.iculcte materi21 the!eon. In operation, as the particulate material free-falls into the funnel from the mechanical feeder device, the conveying gas which passes throu3h the bowl fro~ the plenum chamber flushes ~.
it towards and into the pneumatic conveying line.
In the accompanying drawings -Figure 1 is a section through a preferred particulate feeder embodying the present;invention;
Figure 2 schematically illustratès the operation of the particulate feeder shown in Figure l;
and Figure 3 is a diagrammatic representation of a feeder system in accordance with the invention.
In Figure 1, a housing 1 formed of a gas impervious material such as stainless steel or aluminium has cylindrical sides 2 and an . upper radial flange 3. The housing has a base 4 which opens into an exit pipe 5 leading to a pneumatic conveying line (not shown). The flange 3 is adapted to abut the base of a mechanical feeder device outlet (not shown) and be fixed thereto by means of bolts placed through.holes 6 provided in said flange. Contained . inside the housing 1 is a truncated conical funnel 7 :
:
`:
, ' " ' ' ' :
:: . ~ , -. . , ... .. ..
~: .
WO ~/08723 PCT/GB90/0010~_ having sides at an angle of 45 to the vertical and formed of a gas Dervious material. The funnel is lû'2 ed in the hsusing so as to provid~ 2 smooth tr~nsition in si,e from its wide end 8 positioned near 5 ~ o~ ope"ir~ he ~,uu;ing ;o its n~rro~ end whi:h communicates with the exit pipe S. A plenum chamDer 10 is defined by the sides 2 and base 4 of the housing together with the sides of the conical funnel 7. The housing is provided with an inlet 11 ror a supply of a conveying gas introduced under pressure when the particulate feeder is in operation. As can seen from Figure 2, during operation, particulate material 12 free-falls into the particulate feeder from a mechanical feeding device (not shown). Conveying gas supplied und~er pressure to the inlet 11 in the housing 1 enters the plenum chamber 10 from where it passes through the Wdlls of the conical funnel 7. The particulate material 12 falling into the conical funnel meets the conveying gas at or ne~r to the funnel walls from where it is carried by the gas flow down the interior of the funnel and flushed into the exit pipe 5 ; to the pneumatic conveying line (not shown).
In Figure 3 a particulate feeder of the type shown in Figures 1 and 2 is engaged by f]ange 3 at the outlet 13 of a motor driven screwfeeder 14. The screwfeeder 14 in operation feeds particulate material 1~ from a sealed bulk storage hopper 15 to the outlet 13 from where the particulate material free-falls into the conical funnel 7 of the particulate feeder. In order that the conveying gas introduced into the plenum chamber 10, Iying between the housing 1 and the funnel 7, via gas inlet 11 flows in the desired direction and :
. , ~ 35 . .
;. .
:. ' . , - '. , ''. - ' ':
- - . , . . -W090~08723 - 10 - PCT/GB90/0010 at the desired flowrate, a pipe 16 is preferably provided to connect the screwfeeder outlet region 17 to the airspace 18 above the level of particulate material in the hopper. Thus, when the conveying gas is flowins, the gas pr~ssures at 17 and 18 will be equalized so ~ that particulat~ fecd is nc' adversely affected by any pressure build-up in the system. Typically, the pipe 16 will contain or be provided with a device to restrict the flow of particulate material and conveyins gas through the pipe but which still allows the equalisation of pressure between the bulk storagè
hopper and the particulate feeder. For example, the pipe 16 may contain or be fitted with a pressure equalisation valve which only need be opened periodically to relieve any pressure buildup in the system. Such a feature would be advantageous at low flow rates. Alternatively, instead of providing a return line 16, with or without a control valve, to connect the funnel inlet (17) to the top space (18) of the hopper, the top space of the hopper may be connected to a separate gas feed (not shown) which would be controlled automatically to maintain the gas pressure at the top of the hopper at a value equal to the gas pressure at 17. In the case where the volume of gas in the hopper is large, such a system having a separate gas feed to the top space of the hopper would be preferable to a system having a return line 16 since in the latter system pressure equalisation would cause i the flow of gas to be diverted in the funnel with the result that the uniform transport of solids in the 3 conYeying line would be disrupted.
~ '' ~ .. .. . ..
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, - - . .
2 ~ J ~i C3 Woso/08723 1 PCTJGB90/0010 A, mentioned earlier, spray co-deposition processes require a maximum amount of particulate material with a minimum amount Qr carrier gas. This ratio is termed "phase density" and is given the symbcl "~", where -~ = mass flowrate of solids .
mass flowrate of gas Some powders will convey in "dense phase", i.e. ~= 50-200 (approx) at velocities of about 1 m/s.
Experience of handlin3 such powders in this mode is essential as operating conditions are approaching conditions in blocked pipes. However, to ensure accurate operation of a "Loss in Weight" feeder, it is desirable to operate the conveying line at the opposite end of the phase density range (i.e. ~= 1-10 and v = 20-40 m/s) which conditions are analogous to conditions in an open pipe. The other advantage of this regime is that even small discontinuities in powder flow within the conveying line (causing line pressure fluctuations) can be measured easily relative to the normally low line pressure. In "dense" phase conveying, large fluctuations in solids flowrates can go unnoticed since they are masked by the normally high line pressures required.
The feeder system of the present invention canbe made to work quite satisfactorily using phase densities of 20 to 50 at velocities of 10 m/s. This mode of transport (i.e. moving/sliding beds and dunes), however, may not give desirable results in terms of metal matrix composite product structure. The present invention has been used successfully to convey SiC
I powder (F230 grit, F600 grit and F1000 grit) over a ; 35 .
r .
. . . . . . . .
- .
.., :~ :
wO9Ot08723 PCT/GB9O/OO10~
jt~, ~`J .~ 3 - 1 2 range of feedrates from 0.5 to 3.5 kg/min using transport gas flows of from 45 x 10~3 to 85 x 10~3 Nm3/min through nominal 8 mm diameter tubing. Th^
terms "F23C, 600 and 1000 grits" are described in FE?A
Standard 42-G3-1984 and US S~andard ANSI B.7~.12-1975.
As soon as the feeder motor is turned off, the conveying line clears rapidly rather ~han undergoing any gradual reduction in powder level concentration in the conveyin3 line.
EXAMPLE
The feeder system as described above was used to convey various particulate ma~rials at various flow rates. The system was found to work at high solids densities and yet still maintain uniform flow. The 1~ results are shown in the following Taùle-~ i :
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.
WO 90/08723 ~ 3 ~ '' ~ PCr/GB90~00l0 ~3 -E E E E
E E E E
c) E E E E
C ) o C~ o C) X X X X
c c E E E E
O . _ t_) J = = = = = = _ = =
-t~
E
-- Z
~ -- o o c o a,.t V _ ~r, --o _ ' ~ ~L ~E -- ~ ll-~ ~
u~ ~ O a~ o ~ ~ ~ '' E -- --a) _ 0 ._ : ' E
ocn Ln o o o L~ o o . . . . . . .
.
: ' E E E -- 3 ~ -- ~` 3 E G
, C) :., ~ ~ _ -~ , ; ' , E;UBi5TlTUT~ SHEET
. . . ' , ,.~., .. , ~ . . ~ , . . . . . . ..
WO 90/08723 ~ Q3~3 PCI/GB90/0010~
e ._ CJ
CJ
._ ~ ~ = = = = = = .
~ .
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v~ ~ E
o U~ Ln -- _ _ _ O C~
-- ~J
: 3 j O
_ .,, v) ~ c O O O 1~ 1~ 'n In , i ~ z _ o a~
-- E = C~l ao E
`~3 ~
., j j O ~7 0 0 0 ~ O
.
_ ~, C~
o o O
., 1 l) O O E E E E E
C ~ ~ C
a~
~ ~ .C ~ .
:' ~ ~
.~ C ~ .
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qJ ._ _ G ~
C O............... ,C`) : ~
SUBSTITUTE ~SHEET
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woso/o8723 ~38 PCT/GB90~00l0~
Notes to Table (1) The solids density values are obtained by dividins "Flowrate" by "Gas Flow" x103.
(2) 50:50 wt' mixtur (3) Screwfeeder pressure 1.0 bar 9 ~ 2 kg/min (4) Screwfeeder pressure 3.0 bar 9 ~ 3.5 kg/min (5) Screwfeeder pressure 2.5 bar 9 The first six runs shown in the Table, i.e. those for SiC (F600) at 0.5, 2.0, 3.0 and 3.5 kg/min demonstrate that high solids densitites can be achieved. The other runs in the Table demonstrate the ability of the feeder of the invention to handle a range fo materials and particle sizes. In all cases, a satisfactory uniform flow was achieved.
', ' , . .
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., . ~ - ~
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: . : : . ~ -
Claims (11)
1. A particulate feeder for connecting a mechanical feeding device to a pneumatic conveying line which comprises a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious material, the walls of the funnel and the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, wherein the housing at or towards the wide end of the funnel is adapted to form a sealing engagement with the outlet of the mechanical feeding device and wherein the funnel at or towards its narrow end communicates with the pneumatic conveying line.
2. A feeder according to claim 1, wherein the funnel is a conical funnel.
3. A feeder according to claim 2 wherein the sides of the conical funnel are at an angle of from 30° to 60° to the vertical axis.
4. A feeder system for conveying particulate material from a hopper to a pneumatic conveying line for use in a spray co-deposition process of producing metal matrix composites which feeder system comprises (1) a mechanical feeder device for moving particulate material from a bulk storage hopper to an outlet and (2) a funnel formed of a gas pervious material mounted in a closed outer housing formed of an impervious material, the walls of the funnel and the outer housing together defining a plenum chamber which is provided with an inlet for connection to a supply of conveying gas under pressure, said housing at or towards the wide end of the funnel being engaged with the outlet of the mechanical feeder device to form a gas-tight seal therewith and said funnel at or towards it, narrow end being in communication with the pneumatic conveying line.
5. A feeder system according to claim 4, wherein the mechanical feeder device is a motor-driven screwfeeder.
6. A feeder system according to claim 4 or claim 5, wherein the operation of the mechanical feeder device is regulated by an automatic control means to ensure a constant average mass flow rate of particulate material.
7. A feeder system according to any one of claims 4 to 6, wherein the funnel is a conical funnel.
8. A feeder system according to claim 7, wherein the sides of the conical funnel are at an angle of from 30° to 60°C to the vertical axis.
9. A feeder system according to any one of claims 4 to 8, wherein the outlet of the mechanical feeder device has a diameter of about 100 mm and wherein the outlet of the feeder system to a pneumatic conveying line has a diameter of about 10 mm.
10. A feeder system according to any one of claims 4 to 9, wherein the outlet region of the mechanical feeder device is adapted to communicate with the air space above the level of particulate material in the hopper by means of a connectable pipeline.
11. A feeder system according to any one of claims 4 to 9, wherein the air space above the level of particulate material in the hopper is connected to a supply of gas under pressure which supply is controlled to maintain a pressure in the air space equal in value to the pressure existing at the outlet region of the mechanical feeder device.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GB898901580A GB8901580D0 (en) | 1989-01-25 | 1989-01-25 | Feeder for particulate material |
| GB8901580.4 | 1989-01-25 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2045638A1 true CA2045638A1 (en) | 1990-07-26 |
Family
ID=10650559
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002045638A Abandoned CA2045638A1 (en) | 1989-01-25 | 1990-01-25 | Feeder for particulate material |
Country Status (9)
| Country | Link |
|---|---|
| EP (1) | EP0455686A1 (en) |
| JP (1) | JPH04503348A (en) |
| KR (1) | KR910700186A (en) |
| CN (1) | CN1053592A (en) |
| AU (1) | AU624220B2 (en) |
| CA (1) | CA2045638A1 (en) |
| GB (1) | GB8901580D0 (en) |
| WO (1) | WO1990008723A1 (en) |
| ZA (1) | ZA90513B (en) |
Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE4105663A1 (en) * | 1991-02-22 | 1992-09-03 | Metri Airfluid Ag | DEVICE FOR SUPPLYING AN ELECTROSTATIC POWDER COATING DEVICE WITH A POWDER AIR FLOW |
| US7150585B2 (en) * | 2002-10-14 | 2006-12-19 | Nordson Corporation | Process and equipment for the conveyance of powdered material |
| US7849889B2 (en) * | 2006-05-31 | 2010-12-14 | Philip Morris Usa Inc. | Applicator wheel for filling cavities with metered amounts of particulate material |
| DE102009057380A1 (en) * | 2009-12-09 | 2011-06-16 | Uhde Gmbh | Device for feeding a fluid into a solids conveying line |
| RU2671464C1 (en) * | 2017-12-05 | 2018-10-31 | Федеральное государственное бюджетное образовательное учреждение высшего образования Костромская государственная сельскохозяйственная академия | Device for ventilation and transportation of grain heaps |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US1616547A (en) * | 1926-04-03 | 1927-02-08 | Smidth & Co As F L | Handling dry pulverulent materials |
| US2793914A (en) * | 1953-01-02 | 1957-05-28 | Stamicarbon | Apparatus for transporting finely divided solid materials in carrier gas streams |
| DE1197384B (en) * | 1956-06-25 | 1965-07-22 | Frantisek Tikal | Device for conveying powdery or fine-grained goods |
| DE1262900B (en) * | 1962-08-17 | 1968-03-07 | Siderurgie Fse Inst Rech | Pneumatic emptying device for powdery or granular substances in a distribution container |
| US3432208A (en) * | 1967-11-07 | 1969-03-11 | Us Air Force | Fluidized particle dispenser |
| FR2373469A1 (en) * | 1976-12-10 | 1978-07-07 | Colmant Cuvelier | STORAGE AND EXTRACTION DEVICE FOR PULVERULENT PRODUCTS |
| AU550269B2 (en) * | 1981-04-06 | 1986-03-13 | Kockums Industries (Aust.) Pty. Ltd. | Handling particulate material |
| DE3721258A1 (en) * | 1987-06-27 | 1988-04-28 | Krupp Gmbh | Method for the production of dispersion materials |
-
1989
- 1989-01-25 GB GB898901580A patent/GB8901580D0/en active Pending
-
1990
- 1990-01-24 ZA ZA90513A patent/ZA90513B/en unknown
- 1990-01-25 WO PCT/GB1990/000105 patent/WO1990008723A1/en not_active Application Discontinuation
- 1990-01-25 AU AU49637/90A patent/AU624220B2/en not_active Ceased
- 1990-01-25 CN CN90100474A patent/CN1053592A/en active Pending
- 1990-01-25 CA CA002045638A patent/CA2045638A1/en not_active Abandoned
- 1990-01-25 JP JP2502670A patent/JPH04503348A/en active Pending
- 1990-01-25 KR KR1019900702151A patent/KR910700186A/en not_active Application Discontinuation
- 1990-01-25 EP EP90902334A patent/EP0455686A1/en not_active Withdrawn
Also Published As
| Publication number | Publication date |
|---|---|
| JPH04503348A (en) | 1992-06-18 |
| CN1053592A (en) | 1991-08-07 |
| GB8901580D0 (en) | 1989-03-15 |
| KR910700186A (en) | 1991-03-14 |
| AU4963790A (en) | 1990-08-24 |
| WO1990008723A1 (en) | 1990-08-09 |
| EP0455686A1 (en) | 1991-11-13 |
| AU624220B2 (en) | 1992-06-04 |
| ZA90513B (en) | 1990-10-31 |
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