CA1185546A - Transport of particulate solids - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

Accumulations of adherent solid particles, e.g., damp ore concen-trates, are loosened for flow through solids transport conduits by displacement of prestressed pneumatically operable flexible member joined air-tight to rigid restraining member. Advantageous embodiment has polyurethane polymer cast and cured in-place on steel retainer.

Description

TRANSPORT OF PARTICIJLAT~ SOLIDS

FIELD OF THE lNVENTlON
The present invention relates to transport movement of solid particles (also referred to ~s particulate solids9 or solids) and more particularly ~o control of flows of solids having adherent characteristics tending to result in the solids sticking to each other and to other surfaces.

BACKGROUND ART
There are many needs for transport o large quantities o~ solid p~rticles from one place to another, such as for movement between locations of successive steps in ~n industrial process. Control of rate of movement is often important for ~eeding into processing apparatus or in$o a further transport means, for instance, when solids are dropped to nOw down through Q chute and thence onto ~ moving eonveyor. Particle movement by gravity flow, or possibly gas-driven flow, through tr~nsfer ~essels such as open chutes or tubular conduits has been known as ~ useful tr&nsfer method. Yet, difficul~ies in attempts at achieving consistently uniform rates occur in ~ow o solids having adherent (or s$icky) char~cteristics that resul~ in particles sticking to vessel walls and clumping together and restricting or interrupting the flow nnd then, intermittently9 ~t variously uncertain times, being released in variously sized 20 masses or ~ls~ plugging the vessel solid and causing delay and expense for clearing. Among other things, stickiness and other adherency are oPten associated with dampness OI solid particles, e.g.9 ore particles that have been concentrated in a ~ilter cake and then partially loosened mechanically for transmission to further processing.
Hereto~ore, in view of sti~king, plugging snd other solids transport difficulties $here h~ve been ~ttempts to activate or maintain and control p~rticle flow with ~pparatus whereby trsnsport chutes are sprin~mounted on trunn~ i ~ c~

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and the entire chute is oscillated; vibrators (electric, mechani-cal or pneumatic) are placed on the walls of chutes, conduits or other transfer vessels; chain-driven blades are used to scrape the vessel walls and move particles and lumps along the vesseli and, also, air lances are operated manually to direct air streams at sticking, build-up and clogging places where transport dif-ficulties are noticed. However, even though some aid may be obtained with such attempts, full satisfaction is negated by dis-advantages such as those of being mechanically overelaborate and costly, conducive to excess abrasion, vibration and maintenance difficulties and to intensity of energy, labor and supervisory expenditures.
SUMMARY OF THE INVENTION
There has been discovered new means for facilitat-ing desired flow of particulate solids having adherent character-istics. It is an object of the invention to provide apparatus that assists transmission of solid particles.
The present invention may generally be defined as an apparatus for expediting solids flow within a vessel, the apparatus being registered with the vessel to at least partially envelop the solids as they flow within the vessel, the apparatus comprising a retainer having an open face, means for affixing the retainer to the vessel, and a flexible polymeric member bonded to the outside periphery of retainer and spanning the open face of the retainer. The flexible member is in fluid flow contact with the particles, the flexible member and retainer forming an inter-nal void therebetween. A spacer is disposed within the void ; ~ -2-and an orifice extends through the spacer and communicates with the internal void and the retainer.
Other objects and advantages will be apparent from the following description and accompanying drawing wherein:
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a plan view of an embodiment of the article of the invention.
Figure 2 is an end view of the article viewed in Figure 1.
Figure 3 is a side view of a vertical section on line 3-3 of Figure 1.
Figure 4 is a partially cutaway perspective and par-tially schematic depiction of a solids flow vessel comprising a plurality of the article of Figure 1.
Figure 4A is a detail view, on an enlarged scale, -toward a cross section taken through line 4A-4A on Figure 4.
~igures 5A, 5B, 5C and 5D are vertical sectional illustrations of side views of successive s-tages of operation of the invention.
Figures 6 and 7 are sectional side views of vari-ations of embodiments of the invention.
The present invention contemplates displacing and loosening accumulations of solid particles in a Elow vessel with a pneumatically operable compound article havin~ a rigid member and an elastically flexible member that are bonded together peripherally -to enclose a pressurizable internal space between the two - a-members and hold the flexible member prestresse~ in tension and biased taut ~cross a portion of the rigid member. An orifice through one of the members, generally the rigid member, provides for ~luid pressure communication with a fluid pressure source, e.g., an air compressor The tension bias pulls unobstructed portions of the flexible member straight when the space between the 1exible member (the flexor) And the rigid member (the retainer) is unpressurized. Herein, pressure refers to gauge pressure relative to the ambient atmospheric pressure; unpressurized and depressurized (deprived of pressure) refer to the ~ondition that has the internsl spaee at the~ame pressure as the ~ pressure outside the flexor, thus referring to zero gauge pressure. Pressurization of the intern~l space extends the flexor and displaces accumulations of solid particles on the outer surface of the flexor.
Then, depressurization enables automatic retraction by action of the tension bi~s, with sudden return or "snapback1' when rapidly depressurized. Accordingly, rapid- depressurization tends to create voids between the particles and the flexor, and results in the solids becoming loose and free to flow through the vessel by gravity or other propelling force acltive therein. As the frequency and duration of the pressurization and depressuriæation pulse can be controlled, advantageously withtiming apparatus, e.g., mechanical or electronic clocl<s ~nd programmers, incor-poration of the flexor-retainer article as a pulsator in a flow vessel serves for governing the rate of solids flow through the vessel, thus aiding uniformity of feed to subsequent processing.
Low hysteresis in flexing actions such as elastic extension, retraction ~nd bending characterize the elastomer material of the flexor and benefit long life ~bility to return to shape. These and other advantageous characteristics? e.g., tear resistance, rebound, abr~sion resistance and tensile strength, are specially achieved with flexors utilizing polyurethane polymlers in accordarlce with the invention.

PREFERRED MODE FOR CARRYING UT THE INVENTION
Turning now to viewing the accompanying drawing in conjunction with this specific~tion, Figures 1 to 4A refer to An example of the article formed in a rectangular configuration. Article ~pulsator) 10 has flexible elastomer member (flexor3 11 joined to rigid member (retainer) 12 by ~ir-tight bond 13 at peripheral portion 14 surrounding centr~l portion 15. Wood spacer 16 is bonded to the retainer but not to the flexor. Thus the central portion of the flexor, which has the form of a sheet, is moveable away from the spacer. Also, it is to be noted, flexor 11 is stretched straight snd flAt above the spacer. Generally, there is At least a small amount of air space ~etween flexor and spacer. Threaded orifice 17, which is bonded to the retainer, is for fluid pressure communication ~hrough retainer port 18. Studs 19 and 20 are threaded in the retainer to provide means for mounting the article in A flow vessel. Broken line 11 Disp. depicts a displaced position of the central portion of the flexor extending between bond 13 at retainer arm portions 12A and 1213 when ~ir pressure is applied through inlet/outlet port18, thus expan~ing the internal air space 21. Thereaf~er, when the article is depressurized, the tension bias aut~retracts the flexor to the flexor 11 position extending straight between retainer arms 12A and 12B. And, in view of the rectangular comiguration of retainer 12~ it is unders$ood that retainer 12 holdsflexor 11 flat when depressurized. Tension bias is advantageously obtained by cas~ing ~nd heat-curing the elastomer in place on the retainer.
~ igure 4 illustrates, with a cutaway view~ article 10 and A plurality of like articles, lOSl and lOS2, mounted on the bottom and sides of flow vessel 22,which is a rec~angularly cross-sectioned chute for gravity powered transport of ore particles 23 from concentrator 24 to conveyor 25. Fluid pressure communication with the pulsator articles is provided by manifolding~ valves and 20 an air compressor (not shown).
~ igures 5A, SB, 5C and 5D refer to successive operational conditions wherein solids, e.g., damp ore ~oncentrate particles, are accumulated and then discharged when the flexor is at different positions while disposed at the floor OI
a sloping chute. At 5A, an accumulation 26 of adherent solids 23 has built-up onnexor 11 while the flexor is held straight in tension above spacer 16 by retainer 12 at a time when the flexor is in the depressurized condition, and thus is in the retracted position with interior space 21 being very small; at SB, space 21 is pressurized through inlet/outlet por~ 18, nexor 11 is extended and solids 23 aredisplaced; ~t 5C, void 21 had been left below the solids by rapid depressurization 30 and aut~retraction of the flexor; and, at 5D, the mass of solids has collapsed and is flowing down the chute.
It is to be understood that without the pulsing action of the flexor, the accumulated mass of solids would continue to build up until the weight of the accumulation, along with impact of additional solids and possible chance vibra-tion3 would overcome friction and adhesion and suddenly discharge the mass down the chute at an undesirably irregular time, occassionally jamming the conveyor~
or, also undesirably, until eontinual accumulation would clog ~he chute.

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The flexor in the article of the invention comprises an abrasion-resistant elastomer, advantageously a heat-s~ured polyurethane in the cast and cured condition characterized by a hardness of Shore A 30 to Shore A 95, e.g~, about 80 Shore A. Also advantageously, the~ elastomer is characterized by a shrinkage of at least 1% linearly, e.g., about 1-1/2%, and up to 2%. Good resistance to abrasion, including resistance to impact, is required for overcoming of scratching and piercing and other wear tendencies of solids flowing onto and along the flexor. Retention and stability of elastic characteristics, and endurance of repetitious flexing, stretching and retracting, is also needed for satisfactorily long life. Moreover, the elastomer should be sufficiently inert chemic~lly to avoid deterior~tion by chemical reaction with the solids to be transported.
Rubber is not safisfactory foI the flexor.
Mild steel is generally satisf~ctory for the retainer~ Other satisfac-torily rigid materials, including specially corrosion resistant or high strengthsteels or other alloys ean be used ~ccording to service requirements. Rigidity is needed to be sufficient for resisting distortion by the flexor inasmuch as the flexor, bonded to the retainer, is biased taut with prestress in tension pulling on the retainer. Furthermore~ when pressuriæation of the internal space between thetwo members exends the flexor elastically, additional stresses are exerted against the rigidity of the retainer holding the extended flexor~
The spacer can be OI woodg composition board or metal. ~ome embodiments are contemplated without spacers. Where desired, a spacer can aid rigidity OI the retainer.
And, when applicable, a spacer c~n provide special support for the flexor in the event of an accidental overload OI solids dropping on the flexor.
Since the flexor has tensile stresses bound in, or l'locked-in~', initislly, ~rom the time it is attached to the retainer and prepared for use, the flexor in the ~rticle of the invention is prestressed in tension when ready ~or use. And inasmuch as the prestress of the flexor pulls the flexor back to the initial position when depressurized after extension by pressurization, the flexor in the article of the invention is self-retracting, or aut~retracting.
For the present invention, flexors having good prestress character-istics and good bonding vf flexor and retainer together at peripheral portions have been made by casting and heat-curing polyurethane polymers in place against steel ~etfliners. For ins~ance, a polymer for a ~lexor is cast in an open pan-like mold wherein a retainer shaped like that referred to in Figure 1, and having the spacer prebonded inside, is suspended upside down with clearances at mold walls and bottom controlled to re~ult uniformly in the required thickness of the polymer casting. Prepar~tions for casting include applying a urethane bonding primer to those peripheral areQs of the retainer that are to be bonded to the flexor, coating the exposed areas of the spacer with ~ mold release agent, and temporarily closing the inlet/outlet port. The polymer mixture, which can comprise a urethane polymer and a curative agent(s~ with or without a catalyst, is poured into the mold and while there solidifies as ~he flexor and bonds to peripheral areas of the retainer. The polymer is then post cured9 usually after removal from the mold. The flexor shrinks (to the extent permitted by the retainer) during the curing and the cooling down after post curing. Inasmuch as the polymer of the flexor is characterized by shrinkage when solidified and cured without retraint,internal stresses arise and are held in the flexor when solidified ~nd cured while restrained by the retainer~ Thus the flexor is prestressed in tension and biasedt~ut and straight9 and, in the present instance, also flat.
Benefit of tensile prestress in two transverse (bilateral~ directions, e.g., across the length and width of the rectangle viewed in Figure 1, is obtained especially well in the central area of a flexor that is cast and cured in-place on the retainer and thus bonded to the retainer along all the periphery.
'rhe invention is also applicable in configurations that vary from the rectangular form of pulsator 10, Figures 1-3. For some embodiments the flexor can be bound prestressed on a section of tubular conduit with the conduit section serving as the retainer and an inlet/outlet port provided in the conduit wall.
Figures 6 and 7 depict ~aried configurations of pulsators in conduits for conducting flow of adherent solids (not shown). In pulsator 30 (Figure 6), retainer 31 is a cylindrical conduit section having inlet/outlet port 32 opening toward prestressed flexor 33, which is an elastomer that is bonded air-tight and prestressed in tension to each end OI the conduit section and encloses air space34. When not pressurized, the nexor is ~t retracted position 33R. Internal pressurization~ e.g., with air admitted through port 32, extends the flexor to the displ~ced positions such as 33D. And, upon release of internal pressure the prestress of the flexor rapidly retracts, e.g., snaps-back, the flexor to retracted position 33R, thereby serving to dislodge and move caked or trapped solids by displacement and sudden release. For pulsator 35 of Figure 7 another cylindrical~onduit section serves as retainer 36 holding prestressed flexor 3~ bonded air tigh to enclose internal air space ~9 and en~ble pressurization and depressurization sj through inlet/outlet port 37 and prestress action to move the flexor to displaced position 38D and back to retracted postion 38R by autoretraction. The conduit sections in Pigures 6 ~nd 7 can be mounted with the longitudinal axis oriented vertically or inclined to the vertical. It is to be noted that even with the axis vertical, $hen, when the nexor is moved to the displaced position, adherent solids that may have accumulated on the upper portion of the flexor surface are moved to a situa~ion of being supported from below, and then when the flexor is rapidly retracted, the support is suddenly removed, ~nd the solids are released to drop by gravity.
For benefit of durability the flexor thiclcness is essentially uniform to ~void excessive stress concentr~tion in localized bulging during inflation. Also, undue stress concentration is avoided at places where ~he retainer holds the nexor, e.g., by liberal radiusing of corners~
~ or advantageously efficient operation of the pulsator, the pressure communication facilities, e.g., tubes, valves manifolds or tanks, are of relatively short lengths and large diameters and valves are quic16 acting at low pressures such as about 3 to 7 psi (0.021 to 0.048 mpa), e.g.j air piloted 3-w~y valves. Yery good operational results hhve been obt~ined when air piloted 3-way valves were mounted directly on the retainers. Generally, pressures and communication 20 arrangements are coordinated with flexor strength9 prestress and expansion volume to enable desirable extension and retr~ction tirnes, such as extension pressure impulses of 5 to 10 seconds and much shorter retraction times9 e.g., a second or less. It is advAntageous for retraction to be very rapid and to be complete in the shortest time that is practical to ~ccomplish. In view of the shortness of the retr~ction time, the total time of the pulse9 which is extension plus retraction, is for practical purposes viewed as being equal to the extension impulse time.
In ~n example, solids flow through a rectangularly cross-sectioned, downwardly sloping, chute w~s successfully governed with time-con~rolled 30 pneumatic operation of four flexor-retainer articles (pulsators) of the type referred to by ~igures 1 to 3. The pulsators were aligned end-to-end in sequential flow positions 1, 2, 3 and 4 on the floor of the chute. Air valves on the pulsators ~one valve each) were actuated by Q mech~nical timer that acted to control the pr;eumatic operQtion cycle to be~ six minutes delay of pressurization (while solids flow down the chute and a portion builds up on the flexor surfaces at the chute floor~: then, ten-second impulses actuate pressurization of each flexor individually, one at a time, in sequence, llvith depressurization and auto-retraction at the end OI each 10 second impulse; and then a reeycling return to commence another cycle again with a six-minute delay. Thus, ~he cycle was: 6 min. delay plus lO~sec. #1 plus 10-sec. #2 plus 10-sec. #3 plus lû sec. #4.
The present invention is particularly applicable to the construction and operation of mill and refinery plant structures, such as for concentrating ores or other minerals in parti~ulate form ~nd may also be applied in materials handlingapparatus for moving other partieulate solids. The invention is especially beneficial for maintaining and controlling flow of solid particles through conduits, including tubes and closed-top s~r partially open chutes, and provides ~dvantages toward overcoming difficulties tending to arise from adhesive, abrasive or corrosive characteristics of particles that are transported in conduits. Transport movement may be by gravity flow, power driven fluid flow or other motive means.
Particle sizes present may be a variety of small sizes, e.g., 0.û02 in. ~0.05 mm~ to 0.25 in. (6.35 mm), or range from dust to pebble size.
For purposes of this specification and claims, both English and Metric units have been used. C)riginal disclosures were made in English units9 Metric units being obtained by conversion. If any discrepancy exists between these units, the English units shall control.
Although the present invention has been described in conjunction with preferred embodiments it is to be understood that modifications and variations may be resorted to without departing from the basic concept and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be within the purview and scope of the invention and following~ claims.

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows.

1) In combination with a solids flow vessel, an apparatus for expediting solids flow within the vessel, the apparatus registered with the vessel to at least partially envelope the solids as they flow within the vessel, the apparatus comprising a retainer having an open face, means for affixing the retainer to the vessel, a flexible polymeric member bonded to the outside periphery of retainer and spanning the open face of the retainer, the flexible member in fluid flow contact with the particles the flexible member and retainer forming an internal void therebetween, a spacer disposed within the void, an orifice extending through the spacer and communicating with the internal void and the retainer.

2) The combination according to claim 1 wherein the flexible member includes a polyuerthane polymer cast and cured in place on the retainer.

3) The combination according to claim 1 wherein the orifice communicates with a pressurized air source and valve means for pressurizing and depressurizing the apparatus to cause the flexible means to charge position against the particle flow within the vessel.

4) The combination according to claim 1 wherein a plurality of apparatus are mounts adjacent to one another in the vessel.

5) The combination according to claim 1 wherein the vessel is a chute.