Patent Application
20240328421
In conventional concrete construction, the viscosity of the cementitious material that is used is relatively low. In addition, the material's slump (i.e., a measurement of the workability of a material in which the higher the slump, the more workable the material is) is high. Such low-viscosity, high-slump cementitious materials easily fill the cavities of formwork, such as molds, and self-level for conventional applications, such as slab and road making. As low-viscosity, high-slump cementitious materials are relatively easy to pump, there is a wide variety of pumps that can meet the requirements of such applications.
One relatively new application of cementitious materials is in construction-scale three-dimensional (3D) printing, also known as construction 3D printing, which was pioneered by the inventor of the present disclosure over two decades ago. Construction 3D printing is becoming a new industry in construction and numerous universities, research organizations, and companies are developing the technologies necessary to 3D print cementitious materials. Unlike as in conventional concrete construction, construction 3D printing requires the use of high-viscosity cementitious material mixes that have low slump as the material extruded in the 3D printing process is used to form successive layers of material that must maintain their shape without the assistance of formwork.
Currently, progressive cavity pumps, which have helical shafts that rotate within hard rubber stators, are used in construction 3D printing because such pumps, unlike conventional pumps, are capable of pumping viscous material. Unfortunately, progressive cavity pumps consume large amounts of energy, a substantial portion of which being required simply to overcome the friction generated between the shaft and the stator. For example, large, powerful 3-phase motors are often required to pump cementitious material for extrusion through a nozzle of 3D printing apparatus.
In addition, progressive cavity pumps often can only process mortar instead of conventional concrete, which contains relatively large amounts of both fine aggregate (e.g., sand) and coarse aggregate (e.g., gravel), which cannot be accommodated by progressive cavity pumps unless they are very large, in which case they must be driven by diesel engines and are unsuitable for construction 3D printing. As concrete has numerous technical, economical, and environmental advantages over mortar for building construction, the inability to 3D print concrete is one reason the construction 3D printing industry has struggled to compete with the conventional concrete construction industry.
Furthermore, because of the high friction generated by the abrasive materials contained within cementitious materials, including mortar and concrete, the hard rubber stators used in progressive cavity pumps tend to wear out quickly and must be replaced frequently, which slows the construction process and increases its cost.
In view of the above discussion, it can be appreciated that it would be desirable to have pumps suitable for pumping viscous cementitious material that do not suffer from the limitations and disadvantages associated with progressive cavity pumps.
The present disclosure may be better understood with reference to the following figures. Matching reference numerals designate corresponding parts throughout the figures, which are not necessarily drawn to scale.
As described above, it would be desirable to have pumps suitable for pumping viscous cementitious material that do not suffer from the limitations and disadvantages associated with progressive cavity pumps. Disclosed herein are example embodiments of such pumps, which are suitable for construction 3D printing. In each embodiment, the pumps include a material driving apparatus that is mounted to a rotatable shaft that is rotated to rotate the driving component. In some embodiments, the shaft and its driving component are further reciprocated along a longitudinal axis of the shaft so that the driving component is further alternately displaced in opposite directions within the conduit. Unlike progressive cavity pumps, the disclosed pumps are capable of reliably pumping cementitious materials that contain fine and/or coarse aggregates and, therefore, can be used to pump not only mortar but also concrete. Furthermore, the disclosed pumps do not require as much energy to operate and do not wear out as quickly as progressive cavity pumps.
In the following disclosure, various specific embodiments are described. It is to be understood that those embodiments are example implementations of the disclosed inventions and that alternative embodiments are possible. Such alternative embodiments include hybrid embodiments that include features from different disclosed embodiments. All such embodiments are intended to fall within the scope of this disclosure.
As noted above, one type of pump that can be used to pump viscous cementitious material, including concrete, is non-positive displacement pumps. Unlike positive displacement pumps, non-positive displacement pumps do not trap and drive fixed amounts of fluid material. Instead, non-positive displacement pumps enable slippage of material within the pump whenever the opposing pressure increases, for example, due to the material becoming more viscous due to partial curing. Accordingly, the output of non-positive displacement pumps varies depending upon the extent of restrictions that oppose the flow of the material. A first non-positive displacement pump of this disclosure is the double-propeller pump.
With reference to
In the example of
As can be appreciated from both
The opposing rotation of the propellers 10, 12 facilitates pumping of cementitious materials, such as mortar and concrete. When a viscous material, especially one that contains abrasive particles like cementitious material, is to be driven through a conduit, the friction between the material and the walls of the conduit must be higher than the friction between the material and the surfaces of the propeller blades. If this condition is not satisfied, the material surrounding the blades tends to rotate with the propeller instead of being driven forward through the conduit. Unfortunately, that is typically the case when a single propeller is used to drive the material. One remedial approach is to create opposition to the rotation of the material. Such opposition is created when two closely spaced propellers having opposing blade angles are rotated in opposite directions as depicted in
The efficiency and/or power consumption of the double-propeller pump can be increased by applying high-frequency vibration to the propellers, which could significantly reduce the friction between the propellers and the abrasive material. In some embodiments, this can be achieved using a vibration generator, such as a ultrasonically vibrating horn that transmits high-frequency, low-amplitude vibration to the propeller blades through the pump shafts. It is noted that such vibration could be implemented in each of the disclosed pump embodiments to improve their efficiency and/or power consumption.
In addition to facilitating forward movement of viscous material, the double-propeller configuration also facilitates the pumping of relatively large aggregate that may be contained in the material given that, as is most easily apparent in
It is noted that a rotating propeller would have the added pumping action of a piston that can drive material forward by its linear displacement if the shaft of the propeller were pushed in the direction of material flow. In other words, a rotating propeller that also moves forward in the direction of material flow can provide a higher flow rate and higher pumping pressure as compared to one that only rotates. This phenomenon can be exploited in a double-propeller pump by reciprocating one or both of the propellers of the pump.
As shown in
It has been determined through experimentation that, in the case of viscous material containing abrasive particles, if the ratio of the speed of the linear backward movement of a propeller to its rotation speed is smaller than a threshold, the backward movement of the propeller does not appreciably reduce the forward flow of material. However, the forward motion of the propeller effectively significantly increases the flow. The efficiency is even higher if the reciprocation has a lower linear backward speed than the speed of forward movement. This is due to the fact that the friction between the particulate material and a hard rubber lining within the pump housing is less at higher speeds, much like the braking friction between a road and a car tire, which is less at higher car speeds. In other words, when the propeller reciprocates backward, the material has a lesser tendency to move back with the propeller.
Although such reciprocation increases the flow of viscous material, including cementitious material containing fine and coarse aggregates, naturally flow pulsation may occur as a consequence of the reciprocation. It is noted that this pulsation effect can be reduced or eliminated using a dampener installed between the propeller set and the material outlet. In some embodiments, such a dampener can comprise a diaphragm acted upon by a tension-adjustable spring for adjusting the dampening pressure proportional to the material pressure variations. Such a diaphragm can be installed at an opening on the outlet side of the pump housing.
An alternative configuration of the double-propeller pump is one in which one of the propellers is stationary and, therefore, does not rotate. Although a stationary propeller is not as efficient as a rotating one, it still can provide resistance against rotation of the material volume positioned between the two propellers and, therefore, increase the flow rate. In such a case, the blades of the stationary propeller can be fixedly mounted to the inner walls of the pump barrel. Multiple pairs of rotary/stationary propellers could be provided inside a longer pump barrel. In such a case, all of the rotary propellers could share the same shaft, which could extend through center holes of the stationary propellers.
A further non-positive displacement pump of this disclosure is the hollow-core auger pump. Augers have been used for centuries to move material. As with propellers, the friction between a material and the walls of a conduit through which it is to be driven must be higher than the friction between the material and the surfaces of the auger or the material surrounding the auger will tend to rotate with the auger instead of moving forward. This is especially the case for longer augers that normally exert more forward driving force than shorter augers. It has been determined, however, that this friction problem can be overcome by using a hollow-core auger, i.e., an auger in which the central axial core of the auger is omitted such that only the outer portion of the auger is present. In such a case, the auger has much less surface area and, therefore, generates much less friction with the material to be moved that a conventional, solid-core auger would. When implemented, a hollow-core auger scrapes the material off the walls of the conduit in which the auger is provided and pushes that material forward. Although there is no core to drive the portion of the material within the hollow core of the auger, it has been empirically determined that this material moves along with the portion of material that has been scraped from the conduit walls due to the high friction between the two material portions.
Referring back to
In the embodiment of
As in the case of double-propeller pump, the efficiency of the hollow-core auger pump can increase appreciably if the auger is reciprocated, even by a small amount, along its central vertical axis. Such reciprocation can be effected using a cam-follower apparatus, such as the apparatus 88 shown in
As noted above, another type of pump that can be used to pump viscous cementitious material, including concrete, is positive displacement pumps. One positive displacement pump of this disclosure is the hybrid auger-piston pump, an example of which is illustrated
Positive displacement pumping can provide predictable and consistent flow rates that are required for construction 3D printing. A piston pump is an example of such positive displacement pump. Conventional piston pumps typically include two check valves: an inlet valve that opens when material is sucked in by the piston and that closes when the gathered material is to be driven forward, and an outlet valve that closes when the material is sucked in and that opens when the material is driven forward. While such piston pumps are commonly used for pumping large volumes of high-slump, runny concrete into formwork at construction sites, these pumps are not suitable for viscous materials that contain abrasive particles because excessive force would be required to pass the viscous and abrasive material through the restrictive openings of the check valves. Furthermore, the restrictive opening of the outlet valve may restrict the passage of aggregate and clog the pump. If such a clog occurs and the concrete cures inside the pump, the pump may be unrepairable.
It has been determined, however, that a cementitious material can be extruded at accurate and predictable flow rates using a positive displacement pump comprising a hybrid auger-piston that incorporates a check valve.
The hybrid auger-piston 100 comprises an integrated check valve that includes a planar flap 110 that is pivotably mounted to the trailing edge 108 of the blade 104. In
Because the hybrid auger-piston 100 reciprocates, the flow created by the auger is pulsatile. Specifically, the auger 100 drives the material downward during its downward stroke but the material remains stagnant during the auger's upward stroke. To enable continuous flow, a double hybrid auger-piston system can be used in which the two augers rotate in the same direction but vertically reciprocate in opposite directions.
In
The above-described operation can be achieved by providing a cam-follower apparatus or other mechanism that can provide uniform reversing linear motion. For example, a first cam-follower apparatus can be rotated by a motor and a second cam-follower apparatus can be rotated by the first cam-follower apparatus by means of a sliding mechanical linkage.
A further positive displacement pump of this disclosure is a multi-valve piston pump. Such a pump uses a multi-valve piston that functions as a material driving apparatus that is formed by one or more check valves.
In a first or open orientation of the multi-valve piston 140 shown in
Operation of the multi-valve piston 140 is similar to that of the hybrid auger-piston described above in relation to
Although conventional piston pumps have been used in numerous pump designs, the restrictive size of their check valves make them unsuitable for use with viscous materials that contain coarse aggregates. The multi-valve piston 140 overcomes those problems, however, as each check valve opens wide to enable even large aggregate to pass through the piston. In addition to enabling pumping of concrete, the check valves dramatically reduce the energy consumption of the pumping process, which makes construction 3D printing an attractive alternative to conventional concrete construction. Notably, in cases in which the multi-valve piston pump is to be used to pump lower viscosity materials and/or materials that do not include abrasive materials, there may be no need to rotate the multi-valve piston. Instead, the piston can simply be reciprocated along the direction of the axis of a non-rotating shaft to which the piston is mounted.
In some cases, a suction force may be required to open the valves. Such a suction force can be created using a double-piston arrangement. A double-piston arrangement also has the added advantage of enabling continuous flow for the pump output.
In
It is noted that, depending on the speed of rotation, the valve closure can be nearly instantaneous and the closure of the valves would not need any linear displacement of the valve set. The rapid valve response results in better flow rate accuracy. It is also noted that the rotary motion enables the valves to completely close even when pumping a material mix that has a high concentration of large aggregates. This is true because rotation of each valve's leading edge cuts through the material and, if it hits a large aggregate, it will push the aggregate on one side of the valve or the other while constantly trying to reach the closed state. In this arrangement, the chance of an aggregate jamming a valve and preventing its closure is highly improbable.
According to the above facts, a combination of linear displacement with simultaneous rotation of the valve set can result in very responsive check valves that nearly instantaneously switch from the open to the closed orientation when the piston transitions to the driving mode. In the pulling (suction) mode, the force of the incoming material caused by suction overpowers the force caused by rotation that would normally close the valves, hence the valves open and material passes downstream. The combination of linear and rotary motion of the valves also provides for seamless pumping of fluid mixes that contain large aggregates.
It is noted that the rotation action of the valve sets can be achieved directly by rotating cam-follower apparatuses or separate motors can provide the rotation action. The advantage of the latter arrangement is that the speed of rotation can be set independently of the speed of reciprocation.
It is further noted that a pump can be designed using the same configuration but without rotation action of the check valve sets. The design in this case would benefit from the large openings that the check valve sets offer. However, the advantages of rapid valve response and large aggregate handing, both of which are offered by the rotation action, would not be obtained.
The above disclosure and examples provide a description of the structure and use of illustrative embodiments. Although certain embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments, those skilled in the art could make numerous alterations to the disclosed embodiments without departing from the scope of this invention. As such, the various illustrative embodiments of the devices are not intended to be limited to the particular forms disclosed. Rather, they include all modifications and alternatives falling within the scope of the claims, and embodiments other than the one shown may include some or all of the features of the depicted embodiment. For example, components may be omitted or combined as a unitary structure, and/or connections may be substituted. Further, where appropriate, aspects of any of the examples described above may be combined with aspects of any of the other examples described to form further examples having comparable or different properties and addressing the same or different problems. Similarly, it will be understood that the benefits and advantages described above may relate to one embodiment or may relate to several embodiments. The claims are not intended to include, and should not be interpreted to include, means-plus- or step-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase(s)“means for” or “step for,” respectively.
As it relates to the 3D printing application, the disclosed pumps may be made at two scales of large and small. The large version can serve as a regular ground pump (either in vertical or in horizontal orientation) that receives the material from a mixer and pumps it through a hose to the 3D printing nozzle site. In this configuration, the material that exits a long hose is not necessarily regulated with respect to flow consistency because concrete contains a significant amount of air, which is primarily generated at the mixing stage and that makes concrete a compressible fluid. Accordingly, when the ground pump stops, the material would keep oozing out the hose outlet and the flow stops after a few seconds or even minutes. Also, when the ground pump starts pumping, it may take a while before the pressure builds up in the hose to overcome the static friction of the abrasive fluid with the hose inner wall, thereby resulting in sudden squirting of the material moments after the pump starts running. Furthermore, even during continuous material flow, the rate of flow may keep varying depending on the condition of hose curves, which may constantly change during nozzle movement in the 3D work envelope of the printer robot, hence impacting the material friction in the hose.
To remedy the above issues, a buffer, such as a small reservoir, could be used to store a predetermined amount of material that is received from the ground pump. A smaller version of the disclosed pumps may then be used to take in the material form the small reservoir and pump it through the nozzle with accurate flow regulation and instantaneous on-demand flow start/stop. The ground pump can be automatically turned on and off using feedback received from a sensor that monitors the level of concrete within the small reservoir. When the reservoir nears overflowing, the pump can be stopped and only restarted once the material level reaches a predetermined lower threshold. A sensor could be used to detect the level of concrete in the small reservoir.
This application claims priority to co-pending U.S. Provisional Application Ser. No. 63/087,159, filed Oct. 2, 2020, which is hereby incorporated by reference herein in its entirety.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2021/071713 | 10/4/2021 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 63087159 | Oct 2020 | US |
