RU2465978C1 - Method of making steel grinding balls and die for flash-free forming of steel grinding balls - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to metal forming and may be used in making steel grinding balls by flash-free forming. Rod stock heated to 1000-1200°C is cut to cut-to-length sections. Produced cut-to-length sections are heated further to 800-1220°C and placed in die assembly. Grinding balls are formed in open press tool for flash-free forming. Said press tool comprise top and bottom plates and top and bottom inserts interacting therewith along supporting planes. Said inserts have working cavities to make spherical forming surface. Spherical surface radius center is shifted from press tool clearance center line along vertical toward moving plate by distance defined from enclosed relations.

EFFECT: flash-free balls of higher durability and impact strength.

5 cl, 3 dwg, 1 ex

Description

The group of inventions relates to the field of metallurgy, namely to the processing of metals by pressure, and relates to the production of steel grinding balls by the method of cloudless stamping, which are intended for use in coal, mining, cement and other industries.

The following methods for the production of steel grinding balls are known:

- screw rolling;

- obtaining balls by casting;

- hot stamping with the formation of a flash.

Upon receipt of steel grinding balls by the method of screw rolling (S.P. Granovsky. New processes and mills for rolling products in screw calibers, Metallurgy, 1980), an unevenly stressed ball structure appears, as a result of which balls in ball mills wear out unevenly.

The method of producing balls by casting a) is more energy-consuming, since the workpiece must be heated to a temperature of 1500 ° C; b) with this method of producing balls, steel does not harden due to compression, which affects the quality characteristics of the balls.

There is a known (forging and volumetric stamping of steel, volume 2, edited by M.V. Storozhev, Moscow, 1968, p. 56) a method of hot stamping with the formation of a burr. The disadvantages of the known method of hot volumetric stamping of balls with the formation of a burr are that a) the technology includes an additional operation to remove the burr, b) increases the consumption of metal due to the fact that the burr is removed in waste; c) the ball at the place of removal of the flake has an unevenly stressed structure, since there is a violation of the integrity of the direction of the steel fibers when the flap is removed, since during the hardening process multiple microscopic cracks occur in the places where the fiber breaks, which result in destruction of the ball during its operation.

A well-known (RU, 2167020, C1) method for producing balls is adopted as the closest analogue for the object “method for the production of steel grinding balls”, which includes cutting a round bar lengthy workpiece into measured lengths, feeding the cut workpieces to a stamping block, and ball-free stamping of balls. In order to increase the accuracy of the product obtained in the known method, a round rod-shaped long workpiece is crimped before the previous stamping in the direction perpendicular to the longitudinal axis to obtain two planes, then the obtained flat workpiece is subjected to periodic clamps in the direction parallel to the obtained planes and perpendicular to the longitudinal axis, with the formation in this direction of convex surface areas. To perform rolling and crimping operations, additional equipment and technological time are required, which increases the cost of the product.

As a prototype for the object “stamp for trouble-free stamping of steel grinding balls”, the well-known (OKHRIMENKO Y.M. Technology of forging and stamping production. - M .: Mashinostroenie, 1966, p. 345-346, Fig. 166 (b)) / 3 / open die for seamless stamping of steel grinding balls, containing movable and fixed plates and mounted on these plates to ensure interaction with them on the reference planes of the upper and lower inserts with working cavities forming a spherical forming surface. The disadvantages of the known stamp that impede the achievement of the following technical result include the execution of working cavities (hemispheres) of the stamp inserts symmetrical with respect to the midline of the interstamp gap (the middle of the minimum gap between the inserts in their working position), while the radius center of the spherical forming surface (R1) of the upper and bottom inserts located on the midline of the interstamp clearance.

When pressing a workpiece into a ball, the flow rates of the metal in the vertical and horizontal directions are different. The metal flow velocity in the horizontal direction is higher, therefore, when the radius of the ball in the equatorial zone is equal to (R1), at the poles there will be a non-filling of the die cavity (insert die), i.e. the radius of the ball at the pole will be less (R1). To fill the entire volume of the working cavities of the inserts, the volume of the workpiece to be laid is increased, which inevitably forms a burr (burr) along the line of the equator of the ball as a result of partial displacement of the metal during deformation into the interstamp gap. That is, a ball made in a known stamp design has a flash (burr) along the equator line.

During hot stamping with the formation of a burr, the ball at the place of the burst has an unevenly stressed structure, since there is a violation of the integrity of the direction of the steel fibers during subsequent removal of the burr, which reduces the strength and impact resistance of the ball to splitting. In the process of hardening, multiple microscopic cracks occur at the points of fiber breakage, which as a result lead to the destruction of the ball during its operation. Such balls in ball mills wear out unevenly.

The problem to be solved when creating a group of inventions is to develop a cost-effective method for the production of steel grinding balls of increased strength and impact resistance to splitting, corresponding in accuracy to the requirements of GOST 7524.

The technical result that can be obtained by implementing the claimed group of inventions is to implement this task.

The specified technical result for the object "method" is achieved due to the fact that the method of production of steel grinding balls includes the dosed supply of preheated to 1000-1200 ° C hot rolled round bar lengthy workpiece to the gas cutting station, oxygen cutting of the workpiece to measured lengths, heating dimensional blanks to a temperature of 800-1220 ° C and moving them to the stamping block, stamping the balls in an open stamp for seamless stamping containing movable and fixed plates and mounted on these plates x with ensuring interaction with them on the reference planes of the upper and lower inserts with working cavities forming a spherical forming surface, in which the displacement S of the radius center of the spherical forming surface of the upper, made with a stamping slope, and the lower inserts vertically relative to the midline of the interstamp gap in the side of the movable plate is uniquely determined by the dependence: S = (1 / 2A2 + S1), where A2 is the interstamp clearance; S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper die insert vertically, which is determined from the following relationship:

,

,

Where:

R _max - the maximum radius of the ball with a regulated manufacturing tolerance;

S2 is the height of the stamping slope;

a is the angle of the stamping slope;

R1 is the radius of the spherical forming surface.

The claimed method for the production of steel grinding balls includes the following steps:

1) Preheating a lengthy hot rolled billet to the optimum temperature.

The optimal heating temperature of the workpiece for its subsequent cutting into measured parts is the combustion temperature of steel in oxygen of 1000-1200 ° C - this means that the cutting costs associated with heating the workpiece with propane will be minimal, that is, we will gain time and cost reduction on propane.

2) Oxygen gas cutting of a hot-rolled circle into measuring cylinders, the mass of each of which should be equal to the mass of the ball.

A dimensional blank for a ball is a cylinder whose mass is equal to the mass of the finished ball. The diameter of the workpiece is selected from the condition d = (2M / ρ · π) ^1/2 , where M is the mass of the ball, ρ is the density, π is 3.14. Thus, the condition of the minimum allowable diameter for the cylinder length 2d is satisfied. With a minimum cylinder diameter, better filling of the press dies occurs, and with a cylinder length </ = 2d there is no critical displacement of the workpiece relative to the axis of the dies (taking the ball size out of the tolerance range).

A feature of gas cutting in the claimed method is the exact dosage of the volume of metal to be inserted into the dies, which means that ultimately the stamped ball will not go beyond tolerance, and is achieved through an automatic highly repeatable process of feeding a long workpiece to the cutting post. Moreover, as a rule, cutting is carried out only by supplying oxygen (reducing the cost of the operation by reducing the use of propane during cutting) in the zone of the intended cut, although the minimum supply of propane is left for process stability.

It is acceptable to integrate cutting in exchange for oxygen cutting, but the implementation of this method requires large capital investments, although this method is more productive and economical in terms of saving metal (steel does not burn out during cutting). This type of cutting can be considered as a further improvement of the technology.

3) Heating the measured workpiece to 800-1220 ° C to equalize the temperature of the workpiece throughout the volume, which contributes to better filling of the streams (working cavities) of the open die for seamless stamping;

4) Ball-free stamping of balls (ball pressing).

5) Quenching of the balls, which, as a rule, is performed under the influence of a cooling medium in the quenching drum, the duration of quenching in which is determined by the temperature of the ball at the outlet and is regulated by the frequency of rotation of the drum.

Improving the mechanical properties of grinding balls (an additional technical result) is also achieved due to the fact that before hardening, the balls are evened out and tempered at 150-200 ° C at a cooling rate of not more than 12 deg / s.

6) Vacation of balls in containers with heat-insulating casing.

As a result of trouble-free stamping of the ball, its uniformly stressed structure is achieved, which in combination with its special heat treatment (temperature equalization, smooth quenching before hardening; calibrated hardening time, self-tempering in special production containers) gives a hardened ball uniformly over the entire area without internal cracks with a hardening depth 2/3 of the radius.

To implement the operation of seamless stamping in the claimed method for the production of steel grinding balls, a new design of open stamp for seamless stamping is used, containing movable and fixed plates and mounted on these plates to ensure interaction with them on the reference planes of the upper and lower inserts with working cavities forming a spherical forming a surface in which the displacement S of the center of the radius of the spherical forming surface of the upper, made with stamping bosom, and the bottom inserts vertically relative to the midline of the interstamp clearance towards the movable plate is uniquely determined by the relationship: S = (1 / 2A2 + S1), where A2 is the interstamp clearance; S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper die insert vertically, which is determined from the following relationship:

,

,

Where:

R _max - the maximum radius of the ball with a regulated manufacturing tolerance;

S2 is the height of the stamping slope;

a is the angle of the stamping slope;

R1 is the radius of the spherical forming surface.

In the claimed design of an open die for trouble-free stamping, stamping without breaking is achieved by shifting the center of the radius of the spherical forming surface (R1), composed of hemispheres of the working cavities of the inserts relative to the center line of the vertical die gap (along the center line of the open die for trouble-free stamping) towards the movable plate (upper pole of the sphere) by the amount

S = (1 / 2A2 + S1), where

S is the offset of the position of the center of the radius of the spherical forming surface of the upper, made with a stamping slope, and the lower inserts vertically relative to the midline of the interstamp clearance towards the movable plate,

A2 - interstamp clearance,

S1 is the vertical distance from the center of the sphere (spherical forming surface) to the lower end of the upper insert of the open die for seamless stamping.

In this case, the value (S1) determined by calculation depends on the height of the stamping slope (S2), the angle of the stamping slope (const = 7 ° according to GOST 7505-89), the radius of the spherical forming surface (open stamp engravings for seamless stamping) R1.

The limitation of (S1) is that the greater the distance (S1), the greater the maximum diameter of the chamfer of the stamping slope. In the end, when the distance S1 increases, such a moment will come when the distance from the center of the radius of the spherical forming surface to the circumference of the maximum diameter of the bevel is greater than the maximum radius of the ball regulated by the manufacturing tolerance. In this case, we can say that S1 takes on the greatest value. The greater the distance S1, the better the occupancy of the stamp poles.

The greatest distance S1 is calculated geometrically (see figure 1) from the following relationship:

,

,

Where:

S2 - the height of the stamping slope,

R1 is the radius of the spherical forming surface (engravings stamp),

R _max - the maximum radius of the ball with a regulated manufacturing tolerance.

a is the angle of the stamping slope,

S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper insert of the open die for seamless stamping.

The position of the radius center of the spherical forming surface is shifted towards the movable plate of the open die for trouble-free stamping, since otherwise the ball will need to be removed from the lower "deep" die by a pusher built into the die, which will complicate the implementation of the circuit. When the center of the radius of the spherical forming surface (R1) is shifted from the midline of the interstamp clearance to the side of the movable plate, the working cavities of the open die inserts for seamless stamping are asymmetric with respect to the midline of the interstamp clearance, and the ball equator is shifted to the upper insert of the open stamp for seamless stamping. The workpiece is stamped into the ball gradually, changing shape during the stamping process, while the radius of the ball at the equator of the spherical forming surface increases from the radius of the workpiece to a radius close to R1. At the moment when the radius of the workpiece is equal to the value of R1, a “backwater” is formed in the equator area of the spherical forming surface, because the metal of the workpiece is in contact with the stamp in the equator zone, as a result of which the metal flow velocity in the horizontal direction will significantly decrease, and the metal will move to the poles of the ball. That is, no flaking will occur in the interstamp gap zone.

Thus, using an open die for seamless stamping of the claimed design, it is possible to obtain balls without a burr with a uniform structure that meet the requirements of GOST 7524. Such balls have increased strength and impact resistance, which guarantees their subsequent use without the risk of a split and increases, accordingly, productivity and time mill services.

The production of such balls can significantly reduce metal costs due to the longer service life of the balls. The mechanical properties of the balls obtained by the method of trouble-free stamping allow them to be used in mills without the risk of splitting, which significantly increases the productivity of the mills and their service life. Another distinctive feature of balls made by the method of trouble-free stamping is their uniform wear over the entire area (increased durability), as a result of which further use of these balls in mills using balls of a smaller diameter is possible.

In addition, it should be noted that with trouble-free stamping, material consumption is reduced, as well as the cost of the process itself is reduced due to the exclusion of the burr removal operation from the production cycle.

The economic efficiency of the claimed method for the production of steel grinding balls is achieved thanks to a) an economical gas cutting system, in which the volume of metal put into the dies is accurately metered and propane consumption is reduced, and b) ball-free stamping of balls using the special design of an open stamp for seamless stamping.

The essence of the group of inventions is illustrated by drawings, where:

- figure 1 shows a portion of the brook of an open die for seamless stamping;

- figure 2 shows a diagram of a forge and press section (layout of equipment);

- figure 3 shows a longitudinal section of an open die for seamless stamping of the claimed design.

An example of the implementation of the claimed method of seamless stamping of grinding balls is a forging section (figure 2), containing:

1 - Laboratory; 11 - crank press; 2 - drive; 12 - elevator; 3 - shifter with tilter; 13 - sprayer system; 4 - pneumatic pusher; 14 - quenching rotor; 5 - feed mechanism; 15 - pumping station; 6 - Rollergang; 16 - sump; 7 - UIN-1 (Induction Heating Unit) 17 - cooling tower; 8 - gas cutting post; 18 - coper; 9 - UIN-2 (Induction Heating Unit); 19 - transmission cart; 10 - Kawasaki robot; 20 - production packaging; 21 - beam crane.

The following is a description of the phased implementation of the method carried out in this area.

A billet in the form of a hot-rolled (hot-rolled) circle enters the workshop on a transfer cart 19 in an amount sufficient for a single shift. The slinger with a beam crane 21 reloads the hot-rolled circle from the cart 19 to drive 2, then, as necessary, the slinger with a crane beam loads the transfer bar 3. From the drive, the transferr receives the command from the main process control controller (GKUP), sets live roll 6 one rod hot-smoked a circle. This process resumes after the rod is removed from the unloading zone onto the roller conveyor by the pusher 4. The pneumatic pusher (P) 4 receives a command to perform its task with (GKUP) after processing the signal from the feed mechanism 5 and feeds the workpiece to the feed mechanism 5. Feed mechanism (MP) feeds the workpiece by measured feeds to the UIN 7.

Each cycle of the feed mechanism consists of the following steps:

- determination of the availability of blanks in the MP;

- if the workpiece is missing, then the MP gives the command (P) to feed the workpiece;

- compression of the workpiece with hydrights;

- the movement of hydrights along with the workpiece using a pull mechanism to the required length;

- pause (MP waits until the workpiece is cut off at the gas cutting station on the other side of the first UIN 7). A pause is set by a temporary relay;

- decompression of the workpiece in hydrights;

- the departure of hydrotees to the starting point using a leash mechanism;

- the process repeats.

With UIN 7, the workpiece, preheated to an optimum temperature of 1000-1200 ° C, enters the gas-oxygen cutting station 8, after which the already measured (cut) workpiece, driven by the next workpiece (hot-rolled bar), is fed up to a temperature of 800-1220 ° C in UIN 9. Robot 10 performs the function of an “intelligent” translator: evaluating the operation of the press 11 of UIN 9 and collecting information from numerous sensors, the robot 10 selects the optimal mode of operation for moving it at a temperature of up to 1100 ° Cpreparations with UIN 9 and installing it in a vertical position in the stream of the lower stamp (lower insert of the fixed plate) of the press 11. Having opened the workpiece, the robot is removed from the stamping zone, and the upper stamp (upper insert of the moving plate), moving to the lower stamp, compresses the workpiece into ball. After lifting the upper stamp, the robot moves the ball into the tray transporting the ball to the elevator 12. The elevator operates in a constant mode and performs the function of lifting the ball blank to the first module of the sprayer system 13, from where the ball rolls into the quenching rotor by gravity 14. From the rotor, the balls after quenching according to the system of trays and skliz fall into a special container 20 for self-tempering. After sufficient time for self-dispensing, tests are carried out on the quality of the selection of balls in laboratory 1 and copra 18. The final stage of the technological cycle is the transportation by the slinger of the balls in the container 20 from the workshop using a beam 21 and a transfer cart 19 with an accompanying label.

The stamping of the ball can take place over several strokes of the press, and after each stroke of the press, the workpiece rotates in the stamp - this allows you to achieve a more regular ball shape, but reduces productivity.

Used in the claimed method, an open die for seamless stamping (Fig. 3) with a plane of connector perpendicular to the direction of stamping, contains lower 22 and upper 23 inserts, which are the working elements of an open stamp for seamless stamping. The lower insert 22, due to centering along the diameter D and clamping by a wedge, is based in the open die plate 24 for seamless stamping, mounted on the stationary part of the press. The upper insert 23, due to pin centering and clamping with two wedges, is based in the open die plate 25 for seamless stamping, which is mounted on the movable part of the press. To install the open die inserts for seamless stamping using the device, holes with a diameter of D1 are made in their design. To freely remove the ball from the upper insert of the open die for trouble-free stamping, its design provides a stamping slope of 7 ° (a section of the conical surface) and openings for exhaust gases to prevent counteraction by gases collected in the stamp between the ball’s pole and the stamp brook.

When an open die is used for seamless stamping, the distance between inserts 22 and 23 changes from a value (A1) sufficient to move the workpiece into the working cavities (streams, engravings) of open die inserts for seamless stamping, to a value (A2) of 2-3 mm , the so-called inter-stamp gap, which is necessary to guarantee the exclusion of collisions between the upper and lower open die inserts for trouble-free stamping and for the possibility of metal exit into the burr in case a larger workpiece is laid than installed but that will protect the press from overload. In the inserts of the open die for trouble-free stamping, working cavities are made forming a spherical forming surface (cavity) with a radius of (R1) at a minimum interstamp clearance. Moreover, in this design of an open die for trouble-free stamping, the position of the center of the radius of the spherical forming surface (R1) is shifted from the midline of the interstamp clearance towards the movable plate 25 vertically by a distance: S = S1 + 1/2 A2, where

S is the displacement of the center of the radius of the spherical forming surface of the upper and lower inserts vertically relative to the midline of the interstamp clearance towards the movable plate,

A2 - interstamp clearance,

S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper insert of the open die for seamless stamping.

When a workpiece is pressed into a ball, the working cavities of the inserts are filled with metal during the deformation of the workpiece, while the workpiece in places of contact with the forming surfaces of the working cavities of the inserts copies the surface of a sphere of radius (R1) composed of the working cavities of the inserts. The radius of the spherical forming surface (R1) is equal to the radius of the forging sphere.

The blank for stamping grinding balls are round bar blanks cut into measured lengths equal in volume to the stamped ball.

The process of stamping a ball occurs in the following sequence:

Heated to 800-1200 ° C measuring workpiece is placed in a vertical position in the stream of the lower stamp (lower, stationary insert of the open stamp for seamless stamping). The upper die (upper, movable insert of an open die for trouble-free stamping), moving to the lower die, compresses the measured workpiece into a ball. After lifting the upper stamp, the ball is moved to the transport tray.

The stamping of the ball can take place over several strokes of the press, and after each stroke of the press, the workpiece rotates in the stamp - this allows you to achieve a more regular ball shape, but reduces productivity.

The following is an example of calculating the main parameter of the open die used for seamless stamping - the amount of displacement of the center of the radius of the spherical forming surface from the midline of the interstamp gap.

Example D (2R1) forging diameter 127 mm R1 radius of the forming spherical surface 63.5 mm A2 (const) interstamp clearance
distance from the center of the spherical forming surface to the end 2 mm S1 top open die insert for seamless stamping 6.5 mm

According to GOST 7524-89, for a ball with a diameter of 120 mm, the upper tolerance field of diameter is 130 (125 + 5) mm, respectively, the upper tolerance field of radius is 65 mm. The offset of the position of the center of the radius of the spherical forming surface R1 is equal to:

S = S1 + 0.5 · A2 - the displacement of the center of the radius of the spherical forming surface from the midline of the interstamp clearance of the upper and lower inserts vertically towards the movable plate - a value that displays the radius of the ball beyond the upper tolerance field.

The greatest distance S1 is calculated from the above mathematical formula, where:

S2 - 2 mm

R1 -127.2 = 63.5 mm

a = 7 °

Rmax = 65 mm

According to the results of the calculations, we obtain:

S1 = 7.21 mm

S = 7.21 + 1 = 8.21 mm

S = 8.21 - maximum offset value.

Thus, the shift in the position of the center of the radius of the spherical forming surface of the upper and lower inserts from the midline of the interstamp clearance vertically towards the movable plate: 1 mm <S <8.21 mm.

The press stroke (A1) depends on the press model. For example, the PKZe-800 press has a stroke of 400 mm. Therefore, the slider lowers (rises) from 0 to 400 mm, the final lowering point of the upper die is the distance of 2-3 mm to the lower insert, therefore, the final lifting point of the upper die is the distance 2 ... 3 mm + stroke (400) mm to the lower insert . The angle of the stamping slope is a constant value equal to 7 degrees.

Claims (5)

1. The method of production of steel grinding balls, characterized in that the dosed supply of pre-heated to a temperature of 1000-1200 ° C hot rolled round bar lengthy workpieces for gas cutting, oxygen cutting of the workpiece to measured lengths, heating the workpieces of measured length to a temperature of 800-1220 ° C and moving them to the stamping block, stamping the balls in an open stamp for trouble-free stamping, containing movable and fixed plates and mounted on these plates to ensure interaction with them on op the upper planes, made with a stamping slope, and the lower inserts with working cavities forming a spherical forming surface, while the center of the radius of the said spherical forming surface is shifted vertically relative to the midline of the interstamp clearance towards the movable plate by the amount of displacement S, which is determined by the following the formula:
S = (1/2 A2 + S1),
where A2 is the interstamp clearance;
S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper die insert vertically, which is determined from the following relationship:

,
where R _max - the maximum radius of the ball with a regulated manufacturing tolerance;
S2 is the height of the stamping slope;
α is the angle of the stamping slope;
R1 is the radius of the spherical forming surface. 2. The method according to claim 1, characterized in that the hardening of steel grinding balls is carried out under the influence of a cooling medium in the hardening drum, while the duration of hardening is determined depending on the temperature of the grinding ball at the outlet of the drum and is controlled by the speed of the drum. 3. The method according to claim 1 or 2, characterized in that before quenching, the temperature of the grinding balls is equalized and subsequently tempered by 150-200 ° C at a cooling rate of not more than 12 deg./s. 4. The method according to claim 1 or 2, characterized in that after quenching additionally produce the release of grinding balls in a container with a heat-insulating casing. 5. An open die for seamless stamping of steel grinding balls, containing movable and fixed plates and mounted on these plates to ensure interaction with them on the reference planes of the upper and lower inserts with working cavities forming a spherical forming surface, characterized in that the center of the radius of the spherical forming the surface is shifted vertically relative to the midline of the interstamp clearance towards the movable plate by the amount of displacement S, which is determined by the following formulas e:
S = (1/2 A2 + S1),
where A2 is the interstamp clearance;
S1 is the vertical distance from the center of the spherical forming surface to the lower end of the upper die insert vertically, which is determined from the following relationship:

,
where R _max - the maximum radius of the ball with a regulated manufacturing tolerance;
S2 is the height of the stamping slope;
α is the angle of the stamping slope;
R1 is the radius of the spherical forming surface.

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