WO2017035613A1 - Grinding- rolls for ore and method for obtaining maximum efficiency - Google Patents

Abstract

Description of grinding rolls for ore (1) composed of: two motors (6,6'}, one mobile roller (3), one fixed roller (2), hydraulic cylinders (4) and feeding column (5|. The grinding rolls (1) being provided with a means for controlling efficiency configured for making ongoing measurements and adjustments of their components aiming at reaching the maximum efficiency of the machine. A method for obtaining maximum efficiency of grinding rolls (1) is also described, which has the following steps: (i) determining the zero GAP; (ii) determining a set point that is equal to the optimum working point of the grinding rolls; (iii) automatic handling of pressure until the set point is reached.

Description

"GRINDING ROLLS FOR ORE AND METHOD FOR OBTAINING MAXIMUM EFFICIENCY

OF GRINDING ROLLS*

Field of the invention

[001] The present invention consists of grinding roils for iron ore and a method for maximizing the efficiency of grinding roils.

Background of the Invention

[002] The invention refers to grinding roils for iron ore, provided with a means for controlling efficiency and a method set up for maximizing the efficiency of grinding.

[003] Grinding roils are extremely important equipment in the ore pelleting process. The pelleting process includes the steps of comminution, agglomeration, and pellet burning. The comminution step is responsible for the fragmentation of the ore, white the agglomeration step is responsible for the pellet formation. The grinding roils in question are used in the first step, i.e., the ore comminution step.

[004] The grinding rolls is a relatively simple equipment, which consists of: two roils supported by roller bearings, being one of the rolls fixed and the other mobile; two electrical motors are responsible for transmitting the torque to the rolls; hydraulic cylinders are responsible for forcing the mobile roll against the fixed roll; and a feeding column, set up to distribute the ore evenly between the rolls.

[005] The grinding rolls operate as follows: the ore is directed in the feeding column whose function is to distribute the material evenly between the rolls. The rolls spin in opposite ways, in order to force the material through the opening defined between both structures (GAP) until the moment the ore reaches the compression zone. The compression zone is the region where the ore is repressed or depressed, it starts in the superior part between both rolls and towards the center the pressure increases up to the maximum point in the centeriine of both rolls. The hydraulic cylinders are responsible for forcing the mobile roil against the fixed roll, in order to comminute the material in the compression zone (see figures 1 and 2 of the drawings). [006] In the state of art, aiming at a better utilization of grinding rolls, adjusts are made In their components for achieving a better performance of the machine for a given work condition.

[007] A physical stopper is installed in the machine to delimitate the level of free mobility of the mobile roll. The stopper prevents the roils from hitting each other, avoiding the abrasion or fracture of those components, the "Zero GAP," which is the shortest distance regulated between both roils, is set through manual regulation thereof.

[008] In a first form of adjustment tests are done and, in possession of different variables and results, a Zero Gap and initial working pressure are defined.

[009] In normal conditions, the press operator will not change the working pressure or GAP, only upon special causes including low feeding, low performance, or some operating restriction of the equipment there is an interference of the operator,

[010] The level of the ore column, i.e., the control the ore height presents on grinding rolls, is set by the engineer responsible for the area and should be the highest possible value with lower standard deviation. Once the value is set, it is kept definitively throughout its operation.

[011] The pressure during the process is kept constant and as high as possible, so that the torque of the rolls is the highest achievable. However, if the pressure is too high, the mobile roll will be driven to the stopper and will not contribute to the transfer of energy from the rolls to the ore comminution work. In other words, there an optimum hydraulic working pressure exists, an overage will cause the roll to remain still on the stopper and, depending on conditions, the material starts to be extruded instead of pressed. Too tittle pressure makes the material to pass between the rolls without being pressed.

[012] The rotation of the rolls is variable depending on the ore column level. The entire PLC logic commanding the frequency inverter is programmed for keeping column level constant. Notwithstanding, since the rotation of the rolls is affected by other factors present in the process, it becomes unstable, requiring constant adjusts in the equipment.

[013] The operator has the pressure control at operator's hands, in addition to knowledge on press operation, the operator is required to know the morphological conditions of the ore, humidity level, particle size, wearing of rolls, pneumatic spring pressure, column level, rotation of rolls, and zero GAP. In possession of all this information, the operator can correctly set up the hydraulic pressure for that specific condition. Minutes later, if any variable changes, the setup will no longer be optimum and another setup will be necessary. That means, the control also shows itself as susceptible to human failures, once the machine setups are made by an operator.

[014] The state of the art includes grinding roils provided with means for controlling the opening between rolls automatically, however, none of the grinding rolls included in the state of the art is capable to analyze all variables, equating them, and take adequate actions for bringing it again to the optimum point.

[015] Document USS154364, filed on September 28, 1990 mentions a technique configured for the comminution of food grains like: soybean, wheat, corn, etc That technique allows an adjust relating to the distance between the rolls for protection and better efficiency depending on the work one intends to perform. That adjustment is made through an electrical motor linked to the grinding rolls and a sensor responsible for measuring the distance between the rolls, The motor linked to the grinding rolls is configured to increase and reduce the distance between rolls, in order to reach the necessary working mode for the type of grain to be comminuted. Grains that need more particle breaking require a shorter distance between rolls, while grains that need less particle breaking required a larger distance between rolls.

[016] The technique disclosed in USS154364 also allows making manual adjusts in the distance between rolls. Such adjustments are made through a lever that performs a male and female threading movement, pushing the mobile roll against the fixed roll. [017] The technique disclosed in US5154364 allows avoiding accidents that damage the grinding roils, once the distance between rolls is adjusted With an electrical motor whenever necessary. The distance between roHs is also adjusted to become the most adequate possible to the process, thus achieving a safety and efficiency improvement of grinding rolls.

[018] However, the mentioned technique does not apply to grinding rolls for ore, because it does not consider the variables involved in ore comminution, including; feeding column level, morphological characteristics, rotation of rolls, and other factors inherent to the ore comminution process with grinding rolls.

[019] Therefore, it is possible to conclude that the state of the art does not include any technology of automated control, configured for maximizing the efficiency of grinding roils with the control of all variables present in the ore comminution operation. Nor is there any method configured for obtaining maximum efficiency in ore grinding rolls.

Object of the invention

[020] The object of the present invention is the iron ore grinding rolls provided with a control means for keeping its maximum efficiency throughout the operation time.

[021] The object of this invention is also an iron ore grinding rolls that is more economical, more efficient, and less susceptible to human failures than conventional grinding rolls,

[022] The object of the invention is also maximizing the delivery of the finished product, provided with superior quality compared to that delivered by grinding rolls with conventional controls.

[023] Finally, the object of the invention Is also a method for obtaining maximum energy efficiency in grinding rolls.

Brief description of the invention

[024] The objects of this invention are achieved by ore grinding rolls, which are composed of: two motors; a fixed roll linked a reduction gear and to the motor through a cardan shaft; a mobile roll arranged in the same way, but with a degree of freedom for radial movement; hydraulic cylinders mounted on roller bearing housing, arranged perpendicularly to the radial face of the mobile roller in order to force it against the fixed roller; and a feeding column arranged perpendicularly to both rollers, just above the gap defined between both structures; the ore grinding roils being provided with a means for controlling efficiency.

[025] The objects of this invention are also achieved by a method for obtaining maximum efficiency for grinding roils. This method is composed of the following steps: (i) determining a zero GAP; (ii) determining a set point that is equal to the optimum working point of the grinding rolls; (Hi) handling the pressure until the set point is reached.

Brief description of the drawings

The present invention is described with more details with reference to the respective drawings:

Figure 1 is a perspective view of grinding rolls for ore;

Figure 2 is a front view of operating rollers;

Figure 3 is a chart relating the pressure on roils to the gap between the rolls;

Figure 4 is a chart relating the motor torque and the pressure on rolls;

Figure 5 is a chart relating the rotation of roils and the motor torque;

Figure 6 is a chart relating; the motor torque and the gap between rolls;

Detailed description of the invention

[026] The present invention refers to grinding rolls for iron ore 1, provided with a means for controlling efficiency. The present invention also refers to a method for controlling the efficiency of grinding rolls for ore 1.

[027] Grinding rolls for ore X consist in a machine used in the comminution process of different types of ore (figure 1). Grinding rolls 1 are composed of: two rolls 2,3 mounted on roller bearings, being a fixed one 2 and a mobile one 3; two electrical motors 6,6' responsible for transmitting torque to rolls 2,3; hydraulic cylinders 4 responsible for pushing the mobile roller 3 against the fixed roller 2 grinding the ore that passes between both of them; and a feeding column 5 that distributes the ore evenly between rollers 2,3 (figures 1 and 2).

[028] The elements mentioned are responsible for the efficiency of the machine and the final product result. Therefore, an automated monitoring and adjustment of those components is necessary.

[029] The state of the art includes two types of control. A first form of control is made regarding pressure definition, and a second form of control is made regarding the gap between rotters 2,3. However, both forms of control do not involve all components that affect the efficiency of the machine, and, additionally, the first form of control mentioned is performed through an operator, being, therefore, susceptible to human failure.

[030] The grinding rolls 1 of the invention consist in a means for controlling efficiency, which is responsible for adjusting and controlling automatically ail components affecting the efficiency of grinding rolls X that are involved in the comminution process. The means for controlling efficiency is set up for controlling - directly or indirectly - virtually all variables involved in the comminution process,

[031] The first variable controlled is the shortest distance allowed between roHers 2,3. That distance is called zero GAP and consists in a safety clearance established by a physical stopper provided inside the machine. Said stopper sole function is preventing that mobile roller 3 hits fixed roller 2, damaging the surface of rollers 2,3, or even more serious averages to grinding rolls 1.

[032] The second variable controlled is the operating distance between rollers 2,3, i.e., the gap between rollers 2,3 during the operation of the machine. That distance is called operating GAP and is regulated through the pressure performed by hydraulic cylinders 4, so that, high pressures tend to close the operating GAP and reduced pressures tend to open it, figure 3. Because It is controlled through the handling of a third variable (hydraulic pressure), the operating GAP is a variable indirectly controlled by the press 1.

[033] The third controlled variable is the torque provided by motors 6,6'. Torque, by definition, is the component of a force that is arranged perpendicularly to the rotation axis of a given object, is the portion of a force that effectively causes an object to spin around its own axis. The torque of rollers 2,3 can be measured by the energy motors 6,6' require to perform the work while attempting to fragment the ore.

[034] The torque can be measured by the electrical current consumed by motors 6,6', i.e., the more electrical power motors 6,6' consume, the higher is the power transferred to ore comminution (the electrical energy is transformed into mechanical work, and more electrical energy used results in more work performed). In other words, a greater consumption of energy implies a greater comminution rate. The torque control is given by other two variables, namely: the pressure made by hydraulic cylinders 4 and die rotation of rollers 2,3. Because it depends on controlling other two variables to be changed, the torque is a variable indirectly controlled by the press.

[035] The fourth controlled variable is the pressure performed by the hydraulic cylinders 4. The hydraulic pressure made on an area reverts into the force mobile roller 3 makes on the fixed roller 2. Pressure is regulated as a function of the operating GAP intended to the work, i.e., a lower operating GAP requires high pressures, while a larger operating GAP requires lower pressures.

[036] The fifth controlled variable is the rotation of rollers 2,3, whose function is regulating the flow of material passing between rollers 2,3. The rotation of rollers 2,3 is controlled by motors 6,6', and regulated according to the amount of material present in the feed column 5 in a given moment.

[037] The sixth controlled variable is the level 8 of the feeding column 5, i.e., the volume of ore found in the feeding column 5 in a given instant. The level 8 rises or drops based on the difference between the flow of ore mass in the intake, at the upper part of the feeding column 5 and the ore flow passing through the press 1. A stable level thereof is pursued, because the balance point of the system stays the same and there is no variation in the optimum point of work. Additionally, it is avoided the risk of column 5 overtopping, press 1 overcharging, or becoming temporarily unserviceable, in the event of lack of material inside the feeding column 5.

[038] The sole variable that cannot be controlled by press 1 is ore humidity, which is a characteristic of the raw material and from previous processes, and is defined as percentage to the weight of that material. When the humidity percentage is too high, the friction between the surface of rollers 2,3 and the processed material decreases, making rollers 2,3 case to press the material and start to extrude it, i.e., the material "slides⁰ through the GAP instead of being pressed. In other words, when the ore is wet, rollers 2,3 cannot drag the material to compression zone 9. That causes the rotation of rollers 2,3 to increase in order to keep the column level and, additionally, also causes the operating GAP to decrease under the extrusive effect of the material in the compression zone and reduces comminution, making motor power to drop substantially. In addition to ail inconveniences mentioned, the extrusion of material results in the early wearing of rollers, because a relative movement between the surface of stud pins and the material is caused, what is undesirable. Serrated marks on the surface of pins similar to "shark tooth¹' attest to this movement of the ore.

[039] Those are the controlled and non-controlled variables found in the comminution process using grinding rolls 1. It is known that those variables interact with each other, i.e., the modification of one variable causes changes to the other variables, in order to such interaction between variables be better understood, a table is shown below disclosing the effect each change Hi a given variable on the remaining variables of the process.

[040] *the increase of pressure causes the Increase of torque up to a certain limit After the "optimum" point the pressure increase mates torque to drop and then, when the roller is fixed on the stopper, the torque stays constant even increasing the pressure, and the exceeding force (which is not used for processing the material) is transferred to the press chassis; *once on the stopper, the pressure increase has not influence on rotation or GAP; ** there is also on rotation an ideal point. The lower rotation will not necessarily result in a higher torque; ***the same applies to the operating GAP. It is desirable that a balance point is reached and, above or below that point, the torque will decrease; note: the column increase will cause the torque and the operating GAP to rise.

[041] The rotation of rollers 2,3 controls the amount of ore pressed, i.e., the mass of material passing between rollers 2,3.

[042] The rotation of rollers 23 increases according to the level 8 of feeding column 5 increase, i.e., a level above the set point of feeding column 5 requires a raster rotation of rollers 2,3 , in order to increase the flow of material processed by press 1 in a given moment. On the other hand, a level 8 below the set point in feeding column 5 requires a slower rotation of rollers 2,3, in order to reduce the flow of material mass processed by press 1 in a given moment.

[043] The efficiency control reduces the tosses of the conventional system to the minimum, continuously regulating the process parameters in order to transform the maximum amount of electrical power into comminution work.

[044] As previously discussed, the operating GAP is established through the pressure made by the hydraulic cylinders 4. in a normal work, a high pressure tends to reduce the operating GAP, while a reduction In the pressure tends to increase the operating GAP. The pressure made by the hydraulic cylinders 4 also affects the torque, the value of the latter being, to a certain limit, directly proportional to the amount of pressure made by hydraulic cylinders 4, figure 4.

[045] However, when the operating GAP is reduced, it is also reduced the flow of material passing between rollers 2,3, and when that happens, the rotation of rollers 2,3 is automatically increased, so that the level 8 in the feeding column 5 is kept stable. However, the increased rotation of rollers 2,3, commencing at a certain point, has a negative impact to torque (table 1 and figure 5).

[046] In brief, within certain values, the higher the pressure made by the hydraulic cylinders 4, the lower the operating GAP, and the higher the press torque. Paradoxically when the operating GAP is reduced, the flow of material processed by press 1 is limited, causing the level 8 in feeding column 5 to increase, and when that occurs, press 1 reacts automatically, determining an increase in the rotation of rollers 2,3, which, in turn, from a certain point, reduces the torque of press 1.

[047] That complex relation between variables is pictured in figure 6, showing a second degree equation relating torque and operating GAP (for the same feeding rate). The vertex of the parabola shown in figure 6 is the point where press 1 works with the highest possible torque. That point is called "optimum work point 15" and is found between regions A and B of the chart.

[048] In region A, the torque is affected by the high rotation of rollers 2,3, while in region B the torque is affected by the tow pressure made by the hydraulic cylinders 4. In the optimum work point 15, the torque is maximum, what implies in a high comminution rate. The optimum work point 15 varies depending on the properties of the processed material, being affected, for example, by humidity and the natural qualities of the ore processed at a given moment.

[049] Based on the ratio between the variables described above, a set point is pursued for the operating GAP equal to the optimum work point 15 shown in figure 6. In other words, the operating GAP is regulated for the maximum torque. Each rate of feeding, humidity, roller surface setting, column level, hydro-pneumatic spring pressure, requires an efficiency curve, therefore the difficulty and complexity in finding a set point for the system.

[050] The optimum work point 15 is determined as follows: firstly, it should be implemented an operating GAP control as a function of the pressure, i.e., an operating GAP set point is defined {a 1mm difference between minimum and maximum is recommended the (ex: 5mm min. and 6mm max.)), thence, the pressure is modulated for reaching the goal. Subsequently, the operating GAP should be changed, commencing with a wider opening down to the minimum gap, reminding that the feeding should be constant plotting, therefore, the curve 6.

[051] When the working GAP is lower than the defined one (set point), it possibly means that the material humidity increased, resulting in closing the operating GAP by reducing the friction ratio between the material and rollers 23, and also the extrusion of material in compression zone, occurring therefore the behavior mentioned above. Likewise, the increased rotation reduces the torque.

[052] On the other hand, when the reverse ocmrs, the working GAP tends to be larger than the defined one (set point), thus the rotation slows down and rollers open, thence a pressure stroke is necessary for increasing the torque.

[053] After the optimum work point 15 is determined, the efficiency control means changes the system pressure in order to keep the set point of the operating GAP according to the determined setting.

[054] Within the same feeding range, to achieve the determined set point, press 1 automatically adjusts the pressure provided by the hydraulic cylinders 4.

[055] When the set point is found, the pressure is kept constant.

[056] Thus, the grinding rolls 1 achieve an efficient control system, which aims at maximizing the transfer of energy for the comminution process and larger volumes of processed material for period of time.

[057] ft should be noted that, in order to the operating GAP to operate at different set points, within the limit of freedom defined, it is necessary that the zero GAP has the lowest value possMe, otherwise, the press stoppers could prevent rafters 2,3, from operating at an optimum work point 15 defined as an operating GAP that is too small.

[058] In its preferred arrangement, the grinding rolls for ore 1 operate with the following values: a zero GAP quite close to zero, an operating GAP between 3 and 12 mm, and a torque between 75 and 9896 of its maximum power.

[059] Considering the considerations described herein, in addition to grinding roils 1, the invention also consists of a method for obtaining maximum efficiency of grinding rolls 1. That method is composed of the following steps:

i) establishing a minimum distance between mobile roller 3 and fixed rotter 2 with a physical stopper;

it) determining a set point for the operating GAP, which set point coincides with the optimum working point 15;

iH) control the pressure provided by the hydraulic cylinders 4 until the operating GAP set point is achieved;

[060] Alternatively, that method can include a fourth step, consisting in increasing the pressure made by hydraulic cylinders 4, until the operating GAP is in on the verge of becoming lower than the set point determined in step ij.

[061] In this case, the method can be defined as follows:

i) determine a minimum distance between mobile roller 3 and fixed roller 2 with a physical stopper;

iij determining a set point for the operating GAP, which set point coincides with the optimum working point 15;

iii) control the pressure provided by the hydraulic cylinders 4 until the operating GAP set point is achieved;

iv) As soon as the operating GAP reaches the set point, the pressure is no longer changed.

[062] Thus, it is concluded that the invention achieves the goals it is intended to, being more economical, efficient, and less susceptible to human failures than conventional grinding roils and allowing a finished product provided with higher quality.

[063] A higher economy is achieved through lower specific power consumption by the machine, and also by system automation, which does not require a full-time operator to adjust the rotation and torque of the press 1. The higher efficiency is achieved through an automated control, which secures the higher possible comminution for a determined moment.

[064] The higher quality of the finished product of the press in the invention, in turn, comes from the fact the grinding rolls 1 in the present invention are capable to deliver a finished product with finer particle size than the particle size required for ore pelleting.

[065] After describing some examples of preferred invention embodiments, it should be noted that the scope of protection granted by the present document includes all other alternates applicable to the embodiment of the invention, which is only defined and limited by the content of the enclosed table of claims.

Claims

1. Grinding rolls for ore (1), composed of; two motors (6,6*); one fixed roller (2) linked to a reduction gear and to the motor (6) through a first cardan shaft; one mobile roller (3) linked to a reduction gear and to the motor (6') through a second cardan shaft, which is provided by a degree of freedom for radial movement; hydraulic cylinders (4) mounted on roller bearing housing, arranged perpendicularly to the radial face of the mobile roller (3), arranged for forcing it against the fixed roller (2); and a feeding column (5) arranged perpendicularly to both rollers (2,3), just above the gap defined between both structures; characterized by the fact the grinding rolls (1) are provided with a means for controlling efficiency.

2. Grinding rolls for ore (1), according to claim 1, characterized by the fact the means for controlling efficiency is configured for performing ongoing measurements of the distance between rollers (2,3) and make automatic adjustments capable to correct the distance between rollers (2,3), keeping that equal to a metric value previously adjusted.

3. Grinding rolls for ore (1), according to claim 1, characterized by the fact the means for controlling efficiency is configured for maximizing the torque provided by the motors (6,6').

4. Grinding rolls for ore (1), according to claim 1, characterized by the fact the means for controlling efficiency is configured for keeping the ore level (8) in the feeding column (5) constant; that control being made by handling the rotation of the rollers (2,3)-

5. Grinding rolls for ore (1), according to claim 2, characterized by the fact the automatic adjustments in the distance between the rollers (2,3) are performed by adjusting the pressure provided by the hydraulic cylinders (4).

6. Grinding rolls for ore (1), according to claim 2, characterized by the fact the metric value of the distance between the rollers (¾3) varies from 3 to 12 mm.

7. Grinding rolls for ore (1), according to claim 3, characterized by the fact that the power provided by the motors (6,6') varies from 75% to 98% of their maximum power.

8. Grinding rolJs for ore (1), according to claim 3, characterized by the fact that the automatic adjustments affect the torque provided by motors {6,6*) and are performed by adjusting the pressure provided by the hydraulic cylinders (4).

9. Grinding rolls for ore (1), according to claim 3, characterized by the fact that the automatic adjusts affect the torque provided by the motors (6,6') and are performed by adjustments to the rotation of the rollers (2,3).

10. Grinding rolls for ore (1), according to claim 3, characterized by the fact that the automatic adjustments affect the torque provided by motors {6,6') and are performed by simultaneous adjustments to the rotation of rollers (2,3) and the pressure provided by the hydraulic cylinders (4).

11. Method for obtaining the maximum efficiency for grinding rolls (1) characterized by the performance of the following steps:

i) Establishing a minimum distance between the mobile rotter (3} and the fixed roller (2) with a physical stopper;

ii) Determining a set point for the operating GAP, which set point should be the same optimum work point (15) of the press (1); and

Hi) Controlling automatically the pressure made by the hydraulic cylinders (4) until the set point of the operating GAP is achieved;

iv) As soon as the operating GAP reaches the set point, the pressure is no longer changed.