Patent Application
20120148373
The present invention relates in general to blast furnaces, and more particularly, to a hydraulic distributor for top charging a blast furnace.
A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals. In a typical blast furnace, fuel and metal ore are continuously supplied through the top of the furnace and air is blown into the bottom of the chamber. Chemical reactions take place throughout the furnace as the material moves downward. The end products are typically molten metal and slag phases tapped from the bottom of the furnace, and flue gases exiting from the top of the furnace. One conventional use of a blast furnace is for smelting iron ore to produce pig iron, an intermediate material used in the production of commercial iron and steel.
Modern furnaces are equipped with an array of supporting facilities to increase efficiency. The various raw or burden materials are weighed to yield the desired hot metal and slag chemistry. The raw materials are introduced into the furnace through the top of the blast furnace. There are different ways in which the raw materials may be charged into the blast furnace. For example, some blast furnaces use a “double bell” system where two “bells” are used to control the entry of the raw material into the blast furnace. The purpose of the two bells is to minimize the loss of hot gases in the blast furnace. First the raw materials are emptied into the upper or small bell. The bell is then rotated a predetermined amount in order to distribute the charge more accurately. The small bell then opens to empty the charge into the large bell. The small bell then closes, to seal the blast furnace, while the large bell dispenses the charge into the blast furnace.
A more recent design is to use a “bell-less” system. A bell-less system uses multiple hoppers to contain each raw material, which is then discharged into the blast furnace through valves. The hopper system with valves are more accurate at controlling how much of each constituent is added, as compared to a conventional bell type system, thereby increasing the efficiency of the furnace. Further, some of these bell-less systems also implement a chute in order to precisely control where the charge is placed.
The charging procedure is an important means for influencing the gas distribution and performance of the furnace. Proper distribution of the burden materials entering the top of the blast furnace is essential to efficient operation of the furnace. Various designs exist for the burden charging process. For example: gimbal; top-charger; roto-charger; bell top, rotating chute, etc.
Conventional rotating chute designs use a complex and sensitive planetary gearbox for tilt and rotation. One such conventional electro/mechanical design is the Model PW bell-less top charging equipment. This conventional design includes multiple moving parts and is complicated to design and manufacture. Also, these conventional rotating chute designs have complex cooling systems. In addition, conventional rotating chute designs have sensitivity of tilting gearboxes for extreme positions and for lubrication. All this leads to higher cost for manufacturing and maintenance.
What is needed is a hydraulic distributor for a blast furnace that meets one or more of the following short comings in conventional blast furnaces: improves the control of the distribution of burden materials within a blast furnace; exceeds conventional gearbox capacities; improves repeatability and precision of chute positions; reduces complex components; reduces manufacturing and maintenance costs; improves bearing design; simplifies the chute change process; reduces refractory lined rotating mass; provides an efficient cooling system; and/or improves redundancy for rotation and tilt.
Embodiments of the present invention address and overcome one or more of the above shortcomings and drawbacks, by providing devices, systems, and methods for safely and efficiently top charging a blast furnace. This technology is particularly well-suited for, but by no means limited to, a bell-less blast furnace. The hydraulic distributor for a blast furnace according to embodiments of the present invention provides an improvement over prior designs, including improved repeatability and precision control of the distributor chute and hence the placement of materials within the furnace. The hydraulic distributor provides a less complex design and construction, as compared to convention electro/mechanical gear designs, resulting in reduced costs for manufacturing and maintenance.
The hydraulic distributor of the present invention helps ensure proper distribution of the burden materials entering the top of the blast furnace thereby improving the performance and efficiency of the blast furnace operation. The hydraulic distributor provides for controlled, systematic charging resulting in improved productivity and operation of the furnace.
According to one embodiment of the invention, a hydraulic distributor for a bell-less top gearbox of blast furnace is provided. The hydraulic distributor includes a main housing or shell, an inner ring, a trunnion, and an actuator ring. The inner ring, trunnion, and actuator ring are located within the main housing and are operatively coupled to one another to effectuate rotation and tilt of a distributor chute coupled to the hydraulic distributor via a chute cradle. The inner ring acts to lift the distribution chute. The trunnion acts to rotate the distributor chute. The actuator ring acts to lift and rotate the distributor chute.
A control system, electronics and hydraulics are provided to control the operation of the hydraulic distributor. For example, the control system controls the electronics and hydraulics to manipulate the movement of the inner ring 110, trunnion 120, and actuator ring 130, which in turn cause tilt and rotation the distributor chute 102, as desired. For example, the control system may be programmed with a burden distribution model for a particular blast furnace (or smelting process) to precisely control the placement of burden material within the furnace.
Hydraulic tilt cylinders assemblies are provided to control the angle (or tilt) of the distribution chute. The angle (or tilt) of the distributor chute may be controlled by hydraulic cylinder stroke. Linear transducers in the hydraulic cylinders give a precise location of the cylinder stroke. This position dictates the angle of the distribution chute. The hydraulic tilt cylinders provide repeatability of the same angle at the correct position.
The hydraulic tilt cylinders are mounted to the top and outside of the hydraulic distributor housing and connecting rods extend into the main housing to link the hydraulic cylinders to the inner ring. The hydraulic cylinders extend and retract causing the inner ring to move down and up, respectively.
In one embodiment, the inner ring is connected to the actuator ring through a connection using a roller slewing bearing. The bearing connect is designed to allow the actuator ring the ability to rotate in a continuous 360 degree motion and move up and down based on the movements of the inner ring. The actuator ring is then connected to pivoting crank shafts by utilizing appropriate linkage, crank arms, and roller assemblies. The rollers and crank arms force the crank shafts to pivot as the actuator ring moves up or down. This crank arms to crank shaft connection transfers the vertical motion, up and down, into a horizontal rotation motion that in turn tilts the distribution chute up or down. In one embodiment, the crank shafts pivot on a set of bearings located in the trunnion ring with a fixed connection to the cradle. The other end of the crank shafts may be connected to the actuator ring. The distribution chute is connected to the distribution chute cradle. As the crank shafts tilt the distribution chute cradle, the cradle tilts the distribution chute.
Rotational drive assemblies control the rotation of the chute. Chute rotation may be accomplished with a gear motor and pinion that drives a geared slewing bearing at a constant RPM. An encoder internal to the rotation drive motor may be used to determine and control chute rotation angle.
The rotation drives are is mounted to the top and outside of the hydraulic distributor housing. In one embodiment, the rotation drive 140 has a motor 141 that may be operatively coupled to a gear reducer. The gear reducer may be coupled to a shaft with a drive pinion keyed to the shaft that extend into the housing. The drive pinion rotates an externally geared roller slewing bearing. The trunnion may be bolted to the outside externally geared race of the slewing bearing. The bearing connection transfers the rotation motion from the rotation drive to the trunnion. The inside race of the slewing bearing is stationary and may be bolted to the hydraulic distributor housing.
As the trunnion rotates, the crank shafts mounted through the trunnion then rotate about the vertical centerline of the hydraulic distributor. The crank shafts may be connected to the distribution chute cradle. As such, the distribution chute cradle rotates as the crank shafts are rotating about the vertical centerline of the hydraulic distributor. Rotation of the distribution chute cradle rotates the distribution chute.
According to one aspect of the invention, the hydraulic distributor provides for redundancy of operation. For example, the hydraulic distributor may include multiple and redundant rotational drive assemblies for rotating the chute. For example, the hydraulic distributor may include multiple and redundant hydraulic cylinder assemblies for tilting the chute.
According to another aspect of the invention, the ease of maintenance. For example, rotational drive assemblies are mounted to the top cover plate of the hydraulic distributor allowing for ease of access and/or replacement. For example, hydraulic cylinder assemblies are mounted to the top cover plate of the hydraulic distributor allowing for ease of access and/or replacement. Further, the location of the hydraulic cylinder assemblies on the outside of the hydraulic distributor also facilitates easier calibration of the hydraulic cylinders.
According to another embodiment of the invention, the hydraulic distributor simplifies the chute change process. For example, the distribution chute may include an improved chute cradle design and chute access door in a top portion of the blast furnace to allow the chute to be repaired or replaced without having to enter the hydraulic distributor. Also, the distribution chute may be designed to simply insert into the cradle, so that no pins are required. Also, tilt lockout pins may be provided to lock the chute in position and prevent tilt movement.
In some embodiments of the invention, the hydraulic distributor is manufactured using substantially all fabrication techniques. In other embodiments, the hydraulic distributor is designed and manufactured as a standard unit (e.g., standard size and dimensions). A standardized design allows the hydraulic distributor to easy replace a conventional gearbox and allows the hydraulic distributor to be placed in the identical same location as a conventional gearbox in which it is replacing. A standardized hydraulic distributor also provides the advantage of having substantially the same burden distribution characteristics as the gearbox it is replacing.
In some embodiments of the invention, the hydraulic distributor includes an improved and more reliable cooling system. The cooling system may include a simple once through water system. The cooling system may include a shower cooled system.
In some embodiments of the invention, the hydraulic distributor includes an improved and more reliable nitrogen system. The nitrogen system may include nitrogen that is injected at a regulated pressure into the hydraulic distributor housing at a pressure higher than the top pressure of the blast furnace to prevent blast furnace gas from entering the hydraulic distributor. In emergency situations, the nitrogen system may be used as an emergency backup for cooling the hydraulic distributor.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings.
The foregoing and other aspects of the present invention are best understood from the following detailed description when read in connection with the accompanying drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments that are presently preferred, it being understood, however, that the invention is not limited to the specific instrumentalities disclosed. Included in the drawings are the following Figures:
The above problems in the prior art have motivated the creation of a hydraulic distributor for a blast furnace that solves one or more of the above-identified problems or shortcomings of conventional blast furnaces. The hydraulic distributor receives and distributes burden material (also referred to as raw material) inside a blast furnace. In particular, the hydraulic distributor, according to embodiments of the invention, precisely distributes burden material in a specific area within the furnace, which makes the process work better. This is accomplished through the improved control of the rotation and tilt of the distributor chute.
In some embodiments, the hydraulic distributor is for a bell-less top gearbox of a blast furnace. The hydraulic distributor eliminates the complex planetary gear box for lift and rotation of the distributor chute and provides one or more advantages over conventional gear box designs. For example, the hydraulic distributor improves repeatability of chute positions for charging ring locations. For example, the hydraulic distributor improves revolution speed of chute position changes. For example, the hydraulic distributor provides redundancies for rotation and tilt. For example, the hydraulic distributor improves bearing configuration. For example, the hydraulic distributor is easier to maintain than conventional gearboxes. For example, the hydraulic distributor reduces maintenance costs though reduced complexity and ease of access of components. For example, the hydraulic distributor provides externally mounted hydraulic cylinders. For example, the hydraulic distributor provides externally mounted rotational drives. For example, the hydraulic distributor provides for external tilt angle calibration. For example, the hydraulic distributor simplifies the water cooling system. For example, the hydraulic distributor allows for a heavier distribution chute. For example, the hydraulic distributor simplifies the chute change or replacement. For example, the hydraulic distributor has an improved ability to withstand top temperature and pressure requirements under normal blast furnace operations and during excursions.
To achieve the requirements for reliability, repeatability and low maintenance cost the hydraulic distributor design of the present invention uses hydraulic technology in place of conventional electro-mechanical technology. Use of hydraulic technology to control the distribution chute position (e.g., rotation and tilt) provides a number of advantages in comparison to the conventional gearbox design that utilizes complex mechanical gearing and mechanical brakes.
The hydraulic distributor comprises a future generation of blast furnace charging systems. Essentially, the hydraulic operation results in a stronger more compact design with a more reliable operation that produces more accurate and repeatable chute positions with less maintenance. Also, the hydraulic distributor does not have to rely on limit switches at the end positions of travel, since this position is dictated by the cylinder stroke. A limitation of conventional non-hydraulic designs is that if limit switches do not work, the device runs through the end positions resulting in mechanical damage to the equipment.
The angle (or tilt) of the distribution chute may be controlled by hydraulic cylinder stroke. Linear transducers in the hydraulic cylinders give a precise location of the cylinder stroke. This position dictates the angle of the distribution chute. This hydraulic distributor system results in the repeatability of the same angle at the correct position. Also, the design of the hydraulic valve system holds this position and provides a fast response to changes in chute positions. The hydraulic distributor design eliminates relying on brakes to stop the chute and eliminates differences from chute angle due to gear wear. In addition, the hydraulic cylinders are located on the exterior of the hydraulic distributor thereby allowing the chute angles to be calibrated without stopping the furnace by determining the stroke position of the cylinders.
The rotation of the chute may be accomplished with a gear motor and pinion that drives a geared slewing bearing at a constant RPM. In some embodiments, the hydraulic distributor may be supplied with two rotation drive assemblies, one operating and one standby. An encoder internal to the rotation drive motor may be used to determine and control chute rotation angle.
For example, an iron making blast furnace may comprise a tall chimney-like structure lined with refractory brick 32. Coke, limestone flux, and iron ore (iron oxide) may be charged into the top of the furnace in a precise filling order which helps control gas flow and the chemical reactions inside the furnace. Uptakes 26 allow the hot, dirty gas to exit the furnace dome, while bleeder valves (not shown) may protect the top of the furnace from sudden gas pressure surges. The coarse particles in the gas may settle in the dust catcher (not shown) and may be discharged from the furnace for disposal, while the gas itself may flow through a venturi scrubber (not shown) and a gas cooler (not shown) to reduce the temperature of the cleaned gas.
A casthouse 34 at the bottom half of the furnace may include the bustle pipe, tuyeres and the equipment for casting the liquid iron and slag. One or more tapholes may be drilled through the refractory clay plug(s) allowing liquid iron and slag to flow down a trough through a skimmer opening, separating the iron and slag. Modern, larger blast furnaces may have multiple tapholes and casthouses. Once the pig iron and slag has been tapped, the taphole is again plugged with refractory clay, or other suitable material.
Tuyeres may be used to implement a hot blast, which may be used to increase the efficiency of the blast furnace. The hot blast is directed into the furnace through water-cooled copper nozzles called tuyeres near the base. Oil, tar, natural gas, powdered coal and oxygen can also be injected into the furnace at tuyere level to combine with the coke to release additional energy which is necessary to increase productivity.
As shown in
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Access doors 109 are provided for allowing access to the components housed in main housing 104. The access doors 109 may include a hinged pivot, bolted flange connection and a packing seal to provide quick open or closing action of the access doors 109. As shown, the upper access doors may provide access to: the hydraulic tilt cylinder 150/inner ring 110 connections; rotation drive pinions 144 and the top slewing bearing 145a and actuator ring grease reservoirs. As shown, two lower doors may provide access to: crank shafts 180; crank arms 184; rollers assemblies 186 (see
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As shown in the figures, the hydraulic distributor 100 also includes one or more rotational drive assemblies 140 and one or more hydraulic tilt cylinder assemblies 150. The rotational drive assemblies 140 act to rotate the distributor chute 102. The hydraulic tilt cylinder assemblies 150 act to lift the distributor chute 102.
Multiple rotational drive assemblies 140 may be provided. As shown, two rotational drive assemblies 140 may be positioned 180 degrees apart from one another and may be mounted to the top cover plate 106 of the main housing 104. Mounting of the rotational drive assemblies 140 allows for ease of maintenance or replacement of rotational drives without entering the hydraulic distributor shell 104.
As shown in
In one embodiment, the rotational drive 140 may be powered by a 10 HP AC, 480V, 3-phase, 1,800-RPM electrical motor with an encoder internal to the motor. This encoder is used by the control system (e.g., the PLC) to determine chute rotation angle.
Multiple hydraulic tilt cylinder assemblies 150 may be provided. As shown, four hydraulic tilt cylinder assemblies 150 may be positioned 90 degrees apart from one another and may be mounted to the top cover plate 106 of the main housing 104. In one embodiment shown in
As shown in
The hydraulic distributor 100 uses two types of motion to control the distribution chute 102—tilt and rotation. The following is an explanation of how an exemplary hydraulic distributor controls tilt and rotation in one embodiment of the invention.
The distribution chute tilt motion may be achieved as follows:
See
In some embodiments, the minimum distribution chute angle is about 3 degrees (offset from vertical). In some embodiments, the maximum distribution chute angle is about 55 degrees (offset from vertical). In some embodiments, the distribution chute tilt angle change speed is about 3 degrees per second.
The distribution chute rotational motion may be achieved as follows:
See
In the illustrated embodiment, there are two chute rotation drives 140, each with a motor 141 and an integral gearbox 142, but only one rotational drive is in service at any time. The second rotational drive is a spare and is mechanically disengaged. In one embodiment, the functioning chute rotation motor and gearbox drive the chute with an effective overall gear reduction of approximately 217:1. The chute rotation motor may be powered via a variable frequency drive (VFD). In one embodiment, the Accel/Decel ramps in the VFD may be set at about 5 seconds; and during normal operation, the chute may rotate at constant speed of about 8 RPM.
When homing, the chute may rotate at a slow speed, approximately 0.1-0.8 RPM (which may be set via the HMI). The normal operating speed and the homing speed can both be set from the HMI. The direction of rotation may be selected through the HMI. In normal operation, the direction of rotation may be reversed periodically.
The hydraulic distributor includes a rotating chute with chute slope control capabilities. A control system may be provided to control the operation of the hydraulic distributor through primarily hydraulics and electronics. Hydraulics are generally used to move mechanical components while the electronics are generally used to control the components. The control system may control components of the hydraulic valve stand, the hydraulic distributor, and a Human-Machine Interface (HMI). In a typical blast furnace operation, rotational speed (e.g., motor speed) is constant, and the angle (lift and tilt) of the distribution chute and the flow rate of material may be adjusted.
In one embodiment the hydraulic distributor control system may include a controller (e.g., an Allen-Bradley® ControlLogix PLC with I/O) and two variable-frequency drives (VFDs) (e.g., Allen-Bradley® Powerflex 700 VFDs). The PLC may communicate with the Powerflex 700 VFD via a control network (e.g., Controlnet).
The I/O may be controlled by a PLC which in turn may communicate with the existing control system and the HMI via a suitable communications protocol (e.g., Ethernet/IP). The I/O reads all field devices and the logic may be solved in the PLC. The rotational motor may include an encoder, which may be wired to a VFD. The encoder data may be read by the PLC via the Controlnet connection to the PLC.
In certain embodiments, for example retrofit application, the status of all the I/O on the control system may be displayed on the existing HMI and, to the extent possible, the appearance and functionality of all icons and operator interactions may be unchanged from the existing system. Certain functions and instruments on the hydraulic distributor may also be added to the HMI displays. The HMI thereby displays the status of all the I/O devices associated with the hydraulic distributor. Alternatively, in new installations a new HMI may be provided that includes all of the necessary I/O devices associated with the hydraulic distributor.
A proximity switch assembly 148 (See e.g.,
Also, embodiments of the distribution chute may include an improved cradle design to allow the chute to be exchanged without having to open the hydraulic distributor doors or enter the hydraulic distributor case. In such embodiments, the chute change door 56 on the blast furnace 10 is the only portal opening required to exchange the chute 102 (see
Tilt lock-out pins 172 may be provided for locking out tilt function during maintenance (see e.g.,
In some embodiments, the cooling system of the hydraulic distributor is a simple once through water system—instead of closed loop cooling which would increase the capital and operating cost of the system. In some embodiments, such as the embodiment illustrated in
In the illustrated embodiment, the hydraulic distributor includes four 2″ water inlet pipes 108a. These pipes connect to an enclosed trough located inside the top cover 106. The trough discharges into a shower ring-pipe below the trough. The internal shower ring-pipe has holes in it which are positioned to directly spray the cooling water onto the feeder spout bushing. The water cascades down the feeder spout bushing and onto the top of the trunnion 120. The water collects in a shallow pool on top of the trunnion horizontal surface. The water then overflows a weir wall to cascade down the trunnion's vertical surface and is collected in a trough located at the bottom of the hydraulic distributor shell 104. Once in the bottom trough, two paddles connected to the rotating trunnion continually rotate to keep the water stirred up and prevent settlement from falling out of the water and building an insulating layer of debris in the bottom of the hydraulic distributor. Further, in order to provide additional heat protection to the hydraulic distributor, refractory may be applied to all surfaces exposed to the inside of the blast furnace.
In some embodiments, nitrogen may be injected at a regulated pressure into the hydraulic distributor housing at, for example, two nitrogen inlet ports 108c (See e.g.,
In an emergency situation, such as loss of cooling water, the nitrogen regulating valve may open to allow nitrogen (e.g., about 1500-2000 SCFM of nitrogen) into the hydraulic distributor for emergency cooling. In an exemplary embodiment, one of the two inlets may be reversed to become an exhaust to prevent pressure from building too high in the hydraulic distributor shell. This emergency cooling is only intended to provide short term cooling to protect the hydraulic distributor.
Preferably, redundancy is provided for both the tilt and rotation motions. For example, multiple hydraulic cylinders may be provided in some embodiments of the hydraulic distributor such that the distribution chute tilt is able to continue to operate even if one of the multiple hydraulic cylinders fails. Also, embodiments of the hydraulic distributor may be designed such that a cylinder can be easily replaced. For example, the cylinder may be mounted outside the hydraulic distributor housing. In addition, embodiments of the hydraulic distributor may include distribution chute rotation redundancy by featuring a complete spare drive assembly which may be, for example, mounted on the top cover plate 180 degrees away from the other rotation drive on the outside of the hydraulic distributor housing. Further, the rotation drives may be designed with an eccentric mounting flange. This design allows for a quick change over from the primary to the backup drive.
The hydraulic distributor according to embodiments of the present invention is built using substantially all fabrication techniques—as opposed to casting techniques. Further, the hydraulic distributor according to embodiments of the present invention may be standard (e.g., standard size and dimensions) so that it may replace a conventional gearbox (e.g., a PW electro/mechanical gearbox). The standardized hydraulic distributor may be set in the identical same location as a conventional gearbox it is replacing without requiring any modifications to it or the furnace. This provides an improvement over conventional designs that were custom built to a particular furnace or application. A standard hydraulic distributor results in ease of installation, reduced down time, and cost savings when replacing a gearbox.
In addition, a standard hydraulic distributor having substantially the same dimensions as the gearbox it is replacing will also result in the distribution chute distributing burden material exactly the same and in the same locations as the gear box it is replacing. This may have a big impact on costs. The reason for this is that each blast furnace has a specific burden distribution model. A burden distribution model controls the distribution of burden material so as to optimize and improve performance. For example, burden distribution model dictates the rotation and lift of the distribution chute to precisely locate material within the furnace. If a hydraulic distributor is not standard or the same as the gearbox it is replacing, then all the burden distribution models have to be updated or new burden distribution models must be generated. With a standard hydraulic distributor that fits identically in the same location as the gearbox it is replacing, the hydraulic distributor will distribute material in the same location and the existing burden distribution models may be used.
Chute rotation calibration may be accomplished as follows:
In some embodiments, the chute slope is mechanically limited to a range of 3-55 degrees. The chute slope may be controlled by the operator through the HMI. In the illustrated embodiment, there are four hydraulic tilt cylinders that control the chute slope. The hydraulic tilt cylinders extend to raise the chute and retract to lower it. The hydraulic tilt cylinders may be controlled by a hydraulic valve stand (described in more detail below), and the position of each hydraulic tilt cylinder may be sensed by a feedback device, such as a linear transmitter. The four linear transmitters may generate an analog signal which may be an input to the PLC of the control system. The position of each cylinder may be displayed on the HMI. The chute slope may be determined by the PLC based upon a calculation from the four linear transmitters.
Chute slope calibration may be accomplished as follows:
The hydraulic tilt cylinders may be designed to have extra stroke at both the min and max positions of the chute, e.g., 3 degrees and 55 degrees. Stop blocks (not shown) may be provided to prevent the hydraulic tilt cylinders from being able to stroke past the min and max degree positions. When the hydraulic tilt cylinders stroke to the extreme positions, the inner ring, which the hydraulic cylinders lift and lower, comes up against these stop blocks. The purpose of this design is to make it quick and easy to replace a hydraulic tilt cylinder. There is no need to spend time shimming or adjusting the cylinder to get the chute at exactly 55 degrees when the cylinders are completely extended or at exactly 3 degrees when the cylinders are completely retracted since there is extra stroke in the cylinders.
The PLC program may be zeroed as follows:
The following lists basic operating data and parameters of an exemplary hydraulic distributor:
Although the invention has been described with reference to exemplary embodiments, it is not limited thereto. Those skilled in the art will appreciate that numerous changes and modifications may be made to the preferred embodiments of the invention and that such changes and modifications may be made without departing from the true spirit of the invention. It is therefore intended that the appended claims be construed to cover all such equivalent variations as fall within the true spirit and scope of the invention.
