Granular material scoop and near-vertical lifting feeder/conveyor

An integrated granular-material scoop and near-vertical lifting feeder/conveyor includes special connections and skirts between a bullnose rotating scoop and an open-helical screw that provides the rotations and material lift and evacuation. A conical working-face of the bullnose rotating scoop has symmetrically distributed graters and vents to break loose and force-in granular material from natural deposits and cargo holds. The bullnose rotating scoop and the open-helical screw its attached to move the material into a continuous layer on the inside surface of an outer stationary sheathing. A motor drive attached to the open-helical screw above at the delivery end provides the lifting force necessary.

BACKGROUND

1. Field of the Invention

The present invention relates to vertical screw conveyors for vertical lifting of loose granular materials, and more particularly to open helix type flexible tube conveyors without a central shaft that are fitted at their distal ends with a rotating conical scoop with symmetrically distributed radial scoops around its working face.

Conventional helix conveyors, screw conveyors, spiral conveyors, auger conveyors, and other flexible screw conveyors typically use a rotating spring steel or stainless-steel flexible screw inside a stationary pipe. The flexible screw inside is driven by an electric motor normally located at a discharge end of such conveyors. This simple design offers advantages over rigid screw conveyors, bucket elevators, drag chain conveyors, aero mechanical conveyors and other equipment intended to transport powder and bulk solid materials under certain conditions and for many materials. But they do have trouble moving, and especially initially feeding, materials vertically straight up.

The trouble starts at the distal end. The material has to be quickly accelerated up to speed high enough for the centrifugal force against the outer wall to create enough friction to keep it from falling, back down. Most commercial open-coil helical screw conveyor systems sold today tilt the whole conveyor, or at least the distal end, to the side to help the distal-end intake and to pack the material into the layer on the wall better.

The intake end of a flexible screw conveyor tube is typically equipped with a charging adapter, a U-shaped trough that connects to the outlet of a hopper or directly to the outlet of process equipment such as a bulk bag discharger, bag dump station, grinder, crusher, screener, blender, reactor or storage vessel of any kind.

Conventional “flexible” conveyors usually have diameters in the two- to four-inch range, and rotate at several hundred RPM. Fast enough that the G-levels developed inside from centrifugal force rises to three to four G's, that is if they are to function well. Even at 2-G's such would barely function. Too much developed centrifugal force causes other problems with stiction. Some suppliers of such conveyors mention having flexible pipes with a maximum diameter of 8-inches. Of course, with lower rotational speeds to keep the centrifugal forces developed inside at optimal and functional levels.

The typical outer casings are usually a very thick plastic tube that can be bent slightly, but are typically quite stationary in use. They are not usually moved around and flexed in different directions. Such bends enables the lifting feeder/conveyor to be positioned in a near vertical orientation, after the tilted entrance region, e.g., to save floor space. If these could be fed effectively at the steeper inclinations that approach vertical, they would probably not need to be bent at all. Anyway, bends have a cost in higher wall loads and wear, and provide very little benefit in return.

Large holds in modern cargo ships are used worldwide to store and transport dry granular materials like grains, cement, ores, and plastics. Pouring these materials into the cargo holds is easy enough, but special dry granular material vertical conveyors are needed to extract them. Specialized ship-unloading screw conveyors with central shafts and vertically oriented are fed by counter rotating scoops that force-feed the lifting feeder/conveyor. These can be get as large as 24-inches in diameter, and can move 2400-tons of bulk material every hour out of the hold of a ship. Siwertell (Cargotel Company, Sweden) is one maker of those big conveyors, and they are in a class by themselves.

In the Siwertell-type vertical screw conveyor a separately powered outer pipe surrounds a stationary conveying tube. The outer pipe has scoops at the bottom that feed material into the conveying screw. The stationary conveying tube between the open-helical screw108and the outer scoops stops one flight short of the bottom end, and counter rotating scoops bring material into the reach of the open-helical screw.

Not so different in construction from the conveyors described here are devices proposed for use in extraterrestrial missions that plow into regolith and pull up grains and powders of the regolith. These require a special plow-head with grater-like scoops and ways to move the materials in reduced gravity environments.

Conventional vertical conveyors to plow and lift dry granular materials generally need some horizontal tilt at their plow-tip ends, or need to be deeply submerged in a granular material, to get the material to fill inside the screw and move up to the surface. We describe an improvement of such a mechanism in our U.S. Pat. No. 9,334,693, issued May 10, 2016. Its flexible auger screw uses a central driveshaft in the main pipe and both external scoops and internal lifts radially arranged around a plow-head nose shell.

Another practical problem in reduced-gravity environments is that cohesive materials can sometimes be a problem to transport from a collection site to a collecting and processing site. Granular solids cannot simply be pushed along inside a cylinder with a piston, because frictional loads in a granular slug pushed along a pipe increase exponentially with the length of the slug. So screw conveyors have been conventionally used for transporting free-flowing granular solids over modest distances.

The present inventor, Otis Walton, describes a few centrifuging conveyors for moving granular solid materials over a wide range of cohesion strengths, in U.S. Pat. No. 8,607,966, which issued Dec. 17, 2013. A screw auger is fixed to the outside surface of a fixed inner shaft. A matching, but rotating outer pipe is slipped over the outer diameter of the auger screw. The outer pipe is rotated at a high enough rate to induce granular materials introduced at an input end to cling to the outer pipe's interior walls. The auger screw will act on these clinging layers to move the granular material along to an outlet end, without clumping or clogging.

These centrifuging conveyors need feeders that can introduce granular solid materials at an input end that are boosted in speed enough to have the necessary centrifugal forces come into action. Vertical and steeply inclined orientations need specially adapted scoop-type feeders, as illustrated byFIG. 4Bin U.S. Pat. No. 8,607,966. Granular solid material is scooped into bullnose rotating scoop102409externally louvered scoops410. Axially tapered and tilted inner blades411ramp up and boost the introduced materials to near the speed of rotation of bullnose rotating scoop102409to start the materials moving along toward the outlet end in the layers clinging to the interior walls.

The outer pipe rotates on its axis at a rate high enough for even cohesive materials to form in layers on the interior walls. Curved auger screw blades that are either stationary or rotated at a different rate move the materials along inside. As the incoming materials are fed in, a difference in the rotational rates of the interior walls and the set angles of the several blades will dictate how fast the cohesive material is moved along the walls of the interior.

The present invention improves over conventional screw-auger conveyors with stationary outer pipes. Conventional screw-auger conveyors rotate only an inner helical screw inside of the stationary pipe. Conventional screw augers typically operate in one of two modes, in orientations where the axis is near horizontal they typically operate with slow rotation of the inner screw, and they function by material moving up the rising face of the rotating helical screw and then sliding back down its advancing face-inducing axial displacement. These slow-rotating augers, whether they are open-coil augers, or central-shaft screw-augers, will stop working if the screw axis is tilted up to steep angles, or in a near-vertical orientation. Near-horizontal auger conveying, at these low rotation rates, depends on gravity to help convey dry granular solids.

Conventional screw-augers can, however, be operated in such a manner that they convey material vertically, but in this case higher rotation rates are involved and the flow modes and mechanisms that move the materials along inside up the length are significantly different from those operating in slowly rotated screw conveyors. Gravity is no longer helping and must be overcome instead.

In this vertical conveying mode the fast-rotating screws fling the material out to the outer interior walls where friction keeps it from sliding back down, and it can be pushed up along the wall by the helical screw auger as it rotates. The friction of the material moving in a spiral upward path along the outer wall also minimizes the amount of material that falls back down any gap that exists between the open-helical screw108and wall. High rotation rates are needed to create the high centrifugal force required for this mode of near-vertical screw-conveying to function. However high rotational rates create problems at the bottom inlet feeds.

A majority of heavy industrial vertical screw conveyor are sold with attached, but separately powered, horizontal feed augers to force-feed the inlet. Other vertical conveying systems have scoops on separately rotating outer pipes to force materials into the conveying systems. Feeding vertically oriented conventional screw-auger conveyors is difficult, and few satisfactory solutions have been developed other than the separate horizontal feed augers.

Some attempts to get good enough inlet feeds for vertical screw conveyors have a retracted outer casing at the distal end that exposes several of the open-helical screw108flights. This arrangement can act as a feeder. But screw extensions out beyond the end of the casing can actually fling material out and away from the open-helical screw108entry. The centrifugal effects in the swirling material are responsible for feed-starving that gets worse if the rotation rates increase, or gravity is reduced.

Vertical conveying tests under lunar gravity conditions aboard NASA's reduced gravity aircraft with lunar stimulants proved fast rotating screws would feed-starve and not be very effective.

There is a general need therefore for a device that can quickly feed enough material into vertical screw-auger conveying systems. And in the field of space exploration and in-situ resource utilization, there is a need for devices to extract subsurface materials through small entry holes into the surface of the moon or Mars, e.g., to preserve volatiles from Space. A plow-head feeder is needed for connection to flexible conveying systems when excavating materials. And one that can convey the materials to the surface through a small sealed inlet hole, and thus meet the needs of future space exploration missions.

SUMMARY OF THE INVENTION

Briefly, integrated granular-material scoop and near-vertical lifting feeder/conveyor embodiments of the present invention include special connections and skirts between a bullnose rotating scoop and an open-helical screw that provides the rotations and material extraction. A conical working-face of the bullnose rotating scoop has symmetrically distributed graters and vents to break loose and force-in granular material from natural deposits and cargo holds. The bullnose rotating scoop and the open-helical screw it's attached to accelerate the material into a continuous layer moving along an upwardly-directed helical flow-path and covering the entire inner surface of an outer stationary sheathing. A motor drive attached to the open-helical screw above at the delivery end provides the lifting force necessary.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Feeder/conveyor embodiments of the present invention are configured to collect, accelerate and convey regolith and other dry granular materials near vertically out of their natural deposits and cargo holds. A distal end is fitted with a rotating bullnose scoop102and forward facing grater scoops to collect and accelerate the regolith and other dry granular materials up to the inner wall of the helical screw auger. If the materials are not loose enough to flow into the center, the feeder/conveyor can be swept around inside a cavern from a single central position above, or can traverse over the lateral range of a cargo hold.

Embodiments of the present invention would not ordinarily be described as a drill. Rather, they aggressively collect material from a central coring that is slightly smaller in diameter than an outer sheath pipe diameter. It would there be difficult to “drill” into stiff deposits that didn't yield easily to the forward shoulders of the outer sheath pipe. Here, we prefer to refer these embodiments as granular material feeder/conveyors. And their particular talents are in steeply-inclined uses with open-coil helical screw conveyors.

The illustrating of the preferred embodiment proved to be challenging. So we present a series of Drawings inFIGS. 1A-1Cthat represent how the pieces inFIGS. 1A and 1Bare combined to form the more complete assembly ofFIG. 1C. A granular material scoop and near-vertical lifting feeder/conveyor100comprises a bullnose rotating scoop102with a symmetrically disposed conical working face104. A number of symmetrically distributed graters and vents106are sized and arranged to break loose and force-in granular material laying beneath it that exist in natural deposits and the cargo holds of ships, other transport containers, and warehouses. The symmetrical distribution and sizing of the graters and vents106is important to the elimination of vibrations, wobbling, and undulations, especially at the conical working face104. The apex and circular base of the conical working face104must therefore be concentric to the axis of rotation of an open-helical screw108that provides a rotating force110.

Such rotating force110translates down to the bullnose rotating scoop102. A second equally important aspect of the rotating force110is it provides a material lift-and-evacuation function to any of the granular materials forced-in at the bottom tip. The rotating force110is typically generated by a motor coupled to the open-helical screw108at a delivery end at the top. In regolith collecting applications on extraterrestrial bodies, such motor would be above the ground surface.

A partial cylindrical “inner” skirt112is fastened between a bottom coil114above a distal end116of the open-helical screw108and an upper circular rim118of the bullnose rotating scoop102. Such provides mechanical support between them. The partial cylindrical inner skirt112further provides an initial material containment of forced-in granular materials. An outer stationary cylindrical sheathing120fully encloses a length of open-helical screw108and allows a protrusion of the bullnose rotating scoop102. The whole granular material scoop and near-vertical lifting feeder/conveyor100is typically 100-diameters or more in length.

A partial cylindrical “outer” skirt122is welded or otherwise fastened between the bottom coil114at a distal end116of the open-helical screw108and the upper circular rim118of the bullnose rotating scoop102. Such provides a boosted material containment of forced-in granular materials. The partial cylindrical outer skirt122provides additional feeding capability as described in more detail later.

The outer stationary cylindrical sheathing120can advantageously be made to be flexible and steerable. The open-helical screw108is typically made of stainless steel, and is able to flex along with the outer stationary cylindrical sheathing120. The fit between the two allows the open-helical screw108to be turned inside, and generally includes enough radial-direction gap that a typical conveyed particle would not become wedged between the screw and the outer casing. The inclusion of such a gap improves robustness of operation.

FIG. 2shows an application200in which a motor drive202is connected to a lifting feeder/conveyor100at a top end of its open-helical screw108. Such provides the rotational force110and must be sufficient for the breaking loose and the forcing-in the granular materials laying just below and contacting the bullnose rotating scoop102.

The application200is used to collect and lift dry granular materials laying below at nadir in a natural deposit or store210. For example, the grain storage cargo holds of ships, or the natural deposits of regolith on extraterrestrial bodies in Space. The lifting feeder/conveyor100is capable of being operated at near vertical or even vertical, unlike conventional open-coil helical-screw conveyors.

A method embodiment of the present inventions enables the collection and lifting of granular materials from natural deposits, warehouse stores, transport containers, and ship cargo holds. The method includes scraping loose any granular-material laying in natural deposits and cargo holds vertically from above with bullnose rotating scoop102. Then, accelerating the granular-material that was scraped loose with a number of symmetrically distributed graters and vents disposed in a conical face of the bullnose rotating scoop102and moving up to the conveyor section. Then containing, forming, and controlling movement of loose granular-material onto the inside surface of a partial cylindrical skirt112and/or122fastened between a bottom coil114at a distal end116of an open-helical screw108providing a rotation force110and material lift. Then conveying the loose granular-material inside into a continuous layer moving helically up the sheathing wall, lifted by a turning of the open-helical screw inside a stationary outer sheathing.

Such requires a sizing and arranging of the outer stationary cylindrical sheathing120to fully dispose within its full length the open-helical screw108, and positions the bullnose rotating scoop102to protrude from a bottom end. And in operation, positioning the bottom end to be essentially nadir to a top delivery end of the stationary outer sheathing, and collecting the granular material from above where it lays in natural deposits, transport containers and cargo holds.

FIGS. 3A and 3Brepresent an application300in which a lifting feeder/conveyor301is used to empty material from a transport container of significant lateral area. It is assumed that the top motor drive has separate controls that can both translate and tilt the conveyor. Utilizing those controls the conveyor can collect material from the entire container volume either by lateral translation or by utilization of tilting and vertical displacement to cover the entire bottom surface of the container. The conveyor is capable of collecting material and conveying it to the exit in vertical orientation, or when it is tilted at almost any angle. The lifting feeder/conveyor301is swept, twisted and turned to collect material from a wide fan area below the collection point at the exit. The lifted material outflow304delivers the material to other processes or conveyors as desired.

In general, the bullnose rotating scoop102attaches to the open-helical screw108at its end. The open-helical screw108is the means by which torque is delivered to move material and rotate the bullnose rotating scoop102. Various means of securely fastening the bullnose rotating scoop102to the open-helical screw108can be employed, such as welding, soldering, brazing, gluing or machine-screw fasteners. The inner skirt112is a convenient means of accomplishing the attachment, and such distributes the loads around a larger portion of the open-helical screw108.

Unfortunately there is nothing much at play to move material up the walls of the inner skirt112, except any momentum the material gains as it enters the skirt after leaving the bullnose rotating scoop102. Such momentum can carry the material a short distance slightly greater than one skirt-radius upward along the axis. The inner skirt112delivers material to the top surface of the open-helical screw108, but if the skirt material is a perforated sheet, the material that passes through will also get picked up by the rotating helical screw.

The inner skirt112may appear to be a fundamental part of moving material axially up to the open-helical screw108, but as soon as any material gets inside the outer stationary sheath120above rim118, the material will be picked up and conveyed by the rotating helical screw108. The primary function of the inner skirt112is a means of structural attachment to the helical screw108that is not biased or skewed to one side of the open-helical screw108. The torque transmitted to the bullnose rotating scoop102is better distributed around the circumference of rim118. The inner skirt could be comprised of multiple sections of a cylindrical sheet, with vertical open gaps or slots between the individual sections of the cylinder.FIGS. 1B and 1Cshow an inner skirt made of two sections, each covering approximately one-quarter to one-third of the circumference of the cylinder, with a gap between them that allows material to flow out to the outer stationary sheath120.

Any extension of the helical screw108beyond the point where the bullnose rotating scoop102contacts the open-helical screw108might move a small amount of material into the conveying line, but such will mostly just throw material away from the open-helical screw108area due to momentum. There is therefore little reason to extend the open-helical screw108beyond the point where it contacts rim118of bullnose rotating scoop102.

However, if the open-helical screw108were to be extended a short distance beyond the end of outer stationary sheath120, and had a short outer skirt122attached to it as shown inFIG. 1B, then such can function like an auxiliary scoop that brings material into the lifting feeder/conveyor. If such outer skirt122is too lengthy, e.g., the axial extent is greater than a length equivalent to one outer-radius of the open-helical screw108, then the frictional forces on the walls of bullnose rotating scoop102and the open-helical screw108will tend to plug up, and block the flow through bullnose rotating scoop102. A scoop that was closer to one diameter tall was tested and it was ineffective in picking up material.

Rigid attachments of the inner bullnose rotating scoop102to the open-helical screw108provide a convenient location to support the top of such an outer scoop wall. E.g. along the rim118of bullnose rotating scoop102. But such attachment cannot close off the top opening into the helical screw conveying region. The outer skirt122can be made as shown inFIG. 1B, without any support at the top, but preferred embodiments include a stiffening means to increase resistance to deformation of the outer skirt122. Such as by attaching it, at its top, to a section of a supporting ring attached to the outside of the top lip of the bullnose rotating scoop102.

The outer skirt122, advances significantly over the prior art.

With reference toFIG. 1C, there appears to be a small gap124as shown between the open-helical screw108and the outer stationary sheath120. Most would assume that any gap124would degrade the conveying performance. But, including such gap124reduces the torque needed in rotating force110, and the consequential reductions in power consumption by the motor from usually more than makes up for the conveying efficiency losses due to material raining down through the gap124. Of course there are limits to the gap size for proper functioning, but in general, larger gaps improve robustness by reducing jamming and lowering friction loads, but also adversely impact efficiency due to the resulting material leakage. For many applications, robust operation is at least as important as energy efficiency.

Both skirts112and122prevent newly entering materials from escaping upward lifting by open-helical screw108. The dry granular materials have nowhere to go but up because of these skirts.

The inner skirt112should be solid sheet metal, but can have large perforations. It serves two functions; it is primarily a means to connect the bullnose rotating scoop102to the open-helical screw108. As long as its axial extent is less than a radius in magnitude, it can be solid and may provide extra oomph in transporting material further up before dumping it on the open-helical screw108. If the height is increased to more than one skirt radius, there must be a means to let the granular material to go through the skirt while maintaining its structural role of supporting the circumference of the top of the funnel. The illustrations here show them as partial sections of a cylinder. But they could alternatively just be a cylinder that has large holes above one radius axial distance above rim118.

A perforated cylindrical shell with holes is preferred, with perforations each large enough to exceed the largest particles expected to be conveyed by 2-3 times. But anything larger than even one-particle diameter will probably keep jamming of the material shearing over it from being a problem. A cylindrical shell would be an easy method of attaching bullnose rotating scoop102to an open coil. As opposed to requiring the open coil to be formed into a flat circle at the end like an automobile overhead-valve spring. And the method described here allows its use as an extra material scoop.

Having only one outer scoop on a feeder makes it non-symmetric and may put bending loads on it or other asymmetric loading that might be undesirable. Using the bullnose rotating scoop102available as a support, a second short scoop with a section of a second helical coil could be attached 180-degrees opposite to the one that is an extension of the main open helical auger. This would just wrap around about one-half of a circumference and stop. Thus delivering material into the outer stationary sheath120on the other side. As the open-helical screw108comes around, it would pick up this material and lift it up along the conveyor with whatever else was inside the outer stationary sheath120. It would probably not be possible to have a second short scoop-like section that stopped right at rim118. The scoop should stop there but the screw it is attached to would probably need to be extended some distance up the outside of the inner skirt in order to achieve sufficient structural strength, with the screw attached to the inner skirt over this extended distance.

The embodiments described here primarily focus on uses as a feeder for conveying granular materials, especially in feeding open coil helical screws used in steeply inclined or even vertical orientations.

Open coil screws may lose some efficiency when vertically oriented because the materials inside being transported can fall back down through the central opening. Centrifugal force tends to keep the material being conveyed on the outer sheath wall, and the conveyors operate with a hollow core region along their entire length. Some commercial open-coil screw manufactures suggest placing a stationary pipe in the center to control any potential fallback in the hollow core. Several manufacturers of “flexible conveyors” describe their applications as needing to start out at a 45-degree incline before gently bending up to vertical runs. In practice, most actual applications avoid any bending, because bends will cause the relatively stiff helical coil to rub against the flexible outer pipe wall. The resulting friction takes energy and causes component wear. As a result, no conventional products seem really to be able to feed in any orientation approaching near-vertical.

Bullnose rotating scoop102swith grater-blade like scoops are connected to cylindrical tubes that just fit inside an open helical coil. That helical coil then feeds material up the inner pipe when rotated. Such inner pipe is rigidly attached by welding it to the helical coil.

The inner rotating structure is abbreviated at the point it encounters the helical coil, inside an outer stationary outer sheath120. The total vertical extent of this inner pipe-like shell is only about one inner-pipe-radius, which is about as far as inertia can move the materials in before they really slowdown. If a bullnose rotating scoop102is attached to a rotating pipe with no other means of conveying, materials will move a little less than a diameter into the pipe before stopping. By abbreviating the inner skirt at less than one radius in total axial length, the materials flowing inside of it should fall off the end of the inner cylinder and onto the rotating helical coil screw so they can then be conveyed vertically up inside the stationary outer stationary sheath120.

Bullnose rotating scoop102and its short cylindrical pipe-like extension does not impart significant velocity to material outside the feeder. But once the material that gets into bullnose rotating scoop102it moves both radially and axially and spreads out to the circumference of the inner skirt due to a combination of inertial, centrifugal, and Coriolis forces; axial momentum then carries it to the start of the helical screw rotating inside its housing. If the open helix extends beyond the housing in a steeply inclined orientation, it will throw any material it contacts out by centrifugal force. If that occurs, not very much will convey into the housing above.

If a helical screw conveyor is buried deep enough in granular material, it can self-feed. But at shallow insertions or burial depths into material beds, the unit will not self-feed. That is why all of the commercial versions of open-coil helical screw conveyors start at about a 45-degree incline, with a half-pipe on the bottom and material piled on top to resist the centrifugal action trying to throw material radially away from the open-helical screw108. Screws with a central shaft have similar problems, but the issues seem to be quite a bit more severe for the open coil screws—since none are sold to pick up material vertically, or at steep inclinations. Our target application would be more than just exactly vertical, and should include orientations that have steep inclination of the feeder.

Commercial flexible conveyors are usually in the 2-inch to 4-inch size range and are rotated at several hundred RPM. The g-level from the centrifugal force inside against the outer walls needs to be on the order of 3-4 Gs for them to function right. At 2× gravity they would barely function. Some suppliers mention a maximum diameter of 8-inches. The outer casing is usually a very thick plastic tube that can be bent slightly (the pictures of installed units look like they are typically stationary (so that they would not be moving around and flexing in different directions). The flexing appears to be primarily so they can get to a near vertical orientation (to save floor space). If they could be fed effectively at a steep inclination, they would probably not use a bend in the conveying (bends add high wall loads and wear and little benefit).