Methods for balancing grinding wheels. How to balance a grinding wheel. Causes of the imbalance of the circle

If the center of gravity of the wheel coincides with the axis of its rotation, then the wheel is balanced and can work reliably at high circumferential speeds. The imbalance of circles arises from their irregular shape; location mounting hole with eccentricity relative to the periphery
circle rii; uneven density of the material, etc. The circles are balanced on special stands (Fig. 13.53, a). Prisms, disks and cylindrical rollers are used as supports. The circle is mounted on a mandrel and placed on rollers. Balancing is performed by two segments (Fig. 13.53, b) by moving them along the groove of the flange from the front side. In the absence of balance, the heavy part of the circle falls down. By moving the segments, the degree of balance of the circle is again checked until the circle in any of its positions on the supports is at rest. It is necessary to balance all circles with a diameter greater than 100 mm. Before balancing, the wheel must be inspected to make sure there are no cracks. Wheels can be balanced directly on the grinding machine using special mechanisms.
13.34. ACTIVE CONTROL WHEN GRINDING
Grinding usually completes technological process and sizes are final. A significant part of the working cycle time on automated grinding machines (up to 30% of auxiliary time) is spent on measuring the workpieces being ground. Therefore, dimensional control automation is used, which greatly improves the grinding performance.
Machine tools are equipped with active control systems (Fig. 13.54). With active control, the actual size of the workpiece before processing (or the dimensions of the workpiece to be machined) is compared with the specified size. Devices that carry out and generate such a comparison and the corresponding signal of measuring information are called active control devices. These devices work by the method of direct or indirect measurement. With direct measurement, the sensitive element of the device is in contact with the surface to be treated.

Workpiece wear, with indirect - does not contact. Devices are mechanical, electrocontact, pneumatic, inductive, etc.
The means of active control contain: a measuring device; measuring equipment; command device; command signal amplifier; alarm devices; power sources. The measuring device provides information in the form of indicators. The command device converts the measurement information into discrete signals - commands
for automatic control processing. Measuring equipment is lever mechanisms, prisms, etc. The command signal amplifier amplifies the electrical signals of measuring instruments. Signaling devices provide information about the execution of commands. Depending on the production conditions, simplified active control schemes are used, in which only some of the indicated elements are used.
For active control, various measuring instruments are used (indicators; pneumatic; inductive, etc.). On fig. 13.55 shows diagrams of measuring instruments with mechanical (Fig. 13.55, a) and pneumatic (Fig. 13.55.6) devices. The measuring device is fixedly connected with the measuring equipment 1. Information about the size of the workpiece is given on the scale of the device 2. Processing is controlled manually. Measuring equipment1 (Fig. 13.55.6) performs non-contact measurements by means of a pneumatic sensor. Measurement information is given out on a scale by device 2 and is transmitted to executive bodies machine, which make the necessary movements. The execution of command signals is controlled by block 5.
On fig. 13.56, and shows a single-contact measuring

Device for measuring the radius R of the workpiece 1, installed in the centers round grinding machine, via reading device 2. Three-contact measuring device with a clamp 8 for measuring the diametrical dimension D of the workpiece 2 on the same machine is shown in fig. 13.56, b. Bracket 8 self-adjusts on the surface of the workpiece 2 by means of tips 1, 9, which are constantly pressed by a lever system with hinges 4, 6 under the action of load 3 (or spring). Tips 1, 5 are measuring elements, and on-

Tip 9 - the base element. The rod 5 can move relative to the bracket 8. The amount of movement is perceived by the reading device 7.
On fig. 13.57 shows a device for measuring the diameter - holes in the workpiece when grinding on an internal grinding machine. The measuring tips 7, 8, fixed on the levers 1, 2 by means of a spring 3, are in contact with the surface to be treated 6. The levers are located on the hinges 9, 10. The lever 4 is installed on the hinged support 11 of the lever 1, which summarizes the movements of both tips 12 and transmits the total displacement measuring instrument 5.

A diagram of the setup system of a centerless grinder is shown in Figure 13.58. Part /, processed on the machine, is transferred by the transport device to position 2, where it is measured by transducer 3. When the controlled size goes beyond the established tolerance field, transducer 3 issues a signal - a command to executive device 4 (ratchet solenoid).
When the electromagnet is turned on, the ratchet wheel turns and moves the grinding headstock through the screw mechanism by an amount corresponding to the setting pulse (1-2 microns).
The layout of the setup system for a two-spindle surface grinder is shown in fig. 13.59. When rotating round table 10 workpieces 2 are fed under the measuring device 3, the tip of which is in contact with the machined surface. When the wheel wears / the height of the workpieces to be ground increases.
When the size of the blanks becomes equal to the adjustment size, the device 3 is triggered and issues a signal (command for adjustment), which goes to the amplifier 4 and then to the starter, which includes the electric motor 5, from which, through the gearbox 6, bevel gear 7 and screw 8, the movement is transferred to the grinding headstock 9. The latter makes small adjustment movements.
To control and measure machined surfaces, various universal measuring instruments are used: calipers, micrometers, brackets, gauges, etc.

Assembly and preparation grinding wheels. Before mounting on the machine, the wheels should be checked for compliance with their hardness and grit values specified in technological map. Each circle must be carefully examined and checked by light tapping with a wooden mallet for cracks in it (the sound should be clear, without rattling).

Circles 1 (Fig. 9.16) should be assembled on the mandrel 2 according to the grinding machine setup drawing. Landing a circle on the mandrel should be easy, without the use of force to avoid breaking it. The gap between the seat, the mandrel and the hole diameter of the circle should be 0.3 ... 0.5 mm; the deviation from the perpendicularity of the ends of the circle to its axis should not exceed 0.15 mm (at the periphery of the circle with a diameter of 500 ... 600 mm), which is achieved by turning the ends of the circle, maintaining dimensions A, B, C and D. cardboard oiled pads 4 up to 1 mm thick; when fixing circles on the faceplate using flanges, it is necessary that the latter are precisely centered. To avoid distortion of the flanges and the destruction of the circle when assembling it on the faceplate, nuts 3 should be tightened alternately (through 180° from opposite sides).

Test of endurance. Before working on the machine, the wheels are tested for strength by trial rotation at high speed. For this issue special machines, providing wheel speeds 1.5 times higher than the operational speed. Tests should be carried out with a delay in time at a given test speed. The test mode is automated. Management is carried out from the remote control. The circle is tested according to a given program - acceleration, holding at a test speed and braking to a complete stop. The speed is infinitely adjustable. Test benches are equipped with lifting and installation devices. The circle is put on the flanges, while it is necessary to pay attention to the fact that the gap between the inner hole of the circle and the mounting diameters of the flanges is uniform around the entire circumference.

Balancing circles. In order to achieve high precision and vibration-free grinding of workpieces, the wheels and faceplate assembly must be balanced. When working with an unbalanced circle, the machined surface turns out to be faceted, wavy, and the spindle bearings wear out quickly. The reasons for the imbalance of the circle may be the uneven distribution of mass in the body of the circle, the eccentric location of the mounting hole in relation to outer surface circle, non-parallelism and non-perpendicularity of the ends, uneven impregnation of the circle with coolant, incorrect installation - non-concentric installation of the circle, etc.

With an unbalanced circle, centrifugal force arises, which causes vibrations. With high-speed grinding, the risk of wheel breakage from cutting forces decreases, but the risk of breakage from centrifugal force increases.

The circle is balanced outside the grinding machine on balancing stands. A circle mounted on a mandrel is mounted on supports - cylindrical rollers or disks (Fig. 9.17). Both devices (Fig. 9.17, a, b) have general disadvantage- a large friction torque, which reduces the balancing accuracy. The use of the "air cushion" principle made it possible to create a rational design of the device for static balancing (Fig. 9.18). The advantage of the "air cushion" device is that the mandrel with the circle easily rotates under the influence of a small moment of forces. To bring a mandrel with a circle mounted on cylindrical rollers out of rest, a moment is required that is 7 times greater, and with disks, 40 times greater.

On the spindle of the machine, the circles are fixed with the help of a faceplate, in the end grooves of which weights are placed - segments for balancing the circles. Balancing is done by changing the position of three weights in the annular undercut of the grinding wheel flange. An unbalanced circle with a heavier part will turn down. By moving the weights in the faceplate, they ensure that the circle in any position on the supports remains motionless. As the wheel wears out, its balancing may be disturbed due to the uneven distribution of mass in the body of the circle, so it is advisable to re-balance the wheel. To do this, it is recommended to rotate the wheel at operating speed for 1-2 minutes, turning off the cooling, so that the liquid does not accumulate in the pores of the lower part of the wheel and does not disturb the balance.

In more critical cases, balancing scales are used. With careful manufacturing of balance parts, the balancing accuracy can be brought to a residual center of gravity displacement of 5 µm. The average balancing time is 15...20 min. Balancing scales are designed for balancing grinding wheels with a diameter of 200 to 600 mm. Devices for balancing wheels directly on the grinding machine are also used.

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Assembly and preparation of circles. Before installation on the machine, the wheels should be checked for compliance with their hardness and grit values specified in the technological map. Each circle must be carefully examined and checked by light tapping with a wooden mallet for cracks in it (the sound should be clear, without rattling).

Test of endurance. Before working on the machine, the wheels are tested for strength by trial rotation at high speed. For this, special machines are produced that provide a circle speed 1.5 times higher than the operational one. Tests should be carried out with a delay in time at a given test speed. The test mode is automated. Management is carried out from the remote control. The circle is tested according to a given program - acceleration, holding at a test speed and braking to a complete stop. The speed is infinitely adjustable. Test benches are equipped with lifting and installation devices. The circle is put on the flanges, while it is necessary to pay attention to the fact that the gap between the inner hole of the circle and the mounting diameters of the flanges is uniform around the entire circumference.

Balancing circles. In order to achieve high precision and vibration-free grinding of workpieces, the wheels and faceplate assembly must be balanced. When working with an unbalanced circle, the machined surface turns out to be faceted, wavy, and the spindle bearings wear out quickly. The reasons for the imbalance of the circle can be the uneven distribution of mass in the body of the circle, the eccentric location of the mounting hole in relation to the outer surface of the circle, the non-parallelism and non-perpendicularity of the ends, uneven impregnation of the circle with coolant, improper installation - non-concentric installation of the circle, etc.

The circle is balanced outside the grinding machine on balancing stands. A circle mounted on a mandrel is mounted on supports - cylindrical rollers or disks (Fig. 9.17). Both devices (Fig. 9.17, a, b) have a common drawback - a large friction moment, which reduces the balancing accuracy. The use of the "air cushion" principle made it possible to create a rational design of the device for static balancing (Fig. 9.18). The advantage of the "air cushion" device is that the mandrel with the circle easily rotates under the influence of a small moment of forces. To bring a mandrel with a circle mounted on cylindrical rollers out of rest, a moment is required that is 7 times greater, and with disks, 40 times greater.

Adjustment of center circular grinding machines. It is recommended to carry out the adjustment in the following sequence:

check the operation of all machine components in the adjustment mode and eliminate the malfunctions that have arisen;
set the speed of the longitudinal movement of the dressing mechanism and perform (if it is necessary to install a new grinding wheel) preliminary dressing with the copier turned off (usually such dressing is done with a diamond substitute);
balance the grinding wheel and then check the balance quality;
edit the grinding wheel using a copier (if necessary);
install centers in the front and tailstocks and align their alignment;
set the headstock and tailstock at a given axial distance;
install the workpiece in the centers (chuck) and check the reliability of its fastening;
reconcile mutual arrangement grinding headstock with workpiece in axial and radial directions;
place stops to change the direction of movement of the table during longitudinal grinding;
set the specified processing modes;
when grinding long workpieces, install the steady rest (lunettes);
install and adjust according to the standard measuring device to control the diameter of the outer surface and control the cycle of the machine;
perform trial grinding of two or three workpieces, measuring their errors and correcting the position of the grinding headstock and setting measuring device;
at positive results for workpiece processing, install an automatic cycle on the machine and check the operation of the machine by processing a batch of workpieces with the required productivity and accuracy.

Installation and alignment of centers. Before installing the centers, it is necessary to check whether there are any nicks in conical holes in the headstock spindles, they should be cleaned of dirt and lubricated with oil. Check the corners of the centers with a template, and the fit of the shanks - by paint. The alignment of the centers should be determined by special mandrels 3 (Fig. 9.19) installed in the front 1 and rear 4 headstocks. Check the position of the cylindrical surfaces of the mandrels with indicator 2 along the entire length of the generatrix of the mandrels. If the deviation exceeds 0.01 mm, correct the misalignment by turning the headstock or shifting the tailstock.

Installing the tailstock. Install tailstock to the desired position and fix it securely to the table with the two clamping screws. The clamping force of the part by the rear center should be moderate. The lighter and thinner the part, the less this effort should be. It should be remembered that excessive clamping force leads to rapid wear of the centers and, consequently, to a deterioration in the quality of processing. Weak clamping of the part is also unacceptable, since under the pressure of the circle on the part, the rear center may shift and the machining accuracy will be impaired. When grinding long parts, the required number of steady rests is set to prevent part deflection under the action of forces arising during processing.

Then you should adjust and check the cooling system and filtering of the working fluid.

Arrangement of stops. After the workpiece to be ground is installed in the centers, it is necessary to start placing stops to change the direction of movement of the table during longitudinal grinding. To set the relative position of the circle and the part in the direction of the axis of the part, a reference part is placed in the centers of the machine. The grinding headstock is informed of the installation movement in the direction of the axis of the part. As a base, the left end of the part is usually used, the position of which remains constant for any length of the part. For test moves during adjustment, the electric motor of the headstock of the circle and the parts are turned on, after which the circle is brought to the part until a spark appears and the table is manually moved. If in this case the spark is uniform along the entire length of the part, then you can turn on automatic feed. After making several moves, check the diameter of the part at both ends and, if it turns out to be conical, align the position of the table.

Machine setup. When setting up the machine, you need to use the existing cross feed dial, which facilitates the setting. After making sure that the part rotates at the required speed and the position of the stops for switching the table stroke corresponds to the required grinding length, it is necessary to carefully bring the wheel to the part until a spark appears. In this position, the dial should be released and, without moving the cross feed handwheel, move it so that the number of divisions between the zero division on the cross feed mechanism housing and the zero division of the dial corresponds to half the allowance for the diameter of the part. After that, having fixed the dial, it is possible to process the part by turning on the automatic feed, which is turned off by the cross feed stop when the zero divisions of the dial and the body of the cross feed mechanism are aligned. Two or three divisions before the zero position, it is necessary to check the size of the part in order to prevent the removal of excess metal, and, if necessary, make appropriate adjustments to the setup. When grinding to the stop, it is necessary to periodically correct the position of the wheel to compensate for wear.

Adjustment of measuring and control devices. Measuring devices are installed according to the reference part at the measurement positions. First, a preliminary adjustment is performed along the axis of the part, and then finally set to the zero position. When adjusting devices with lever systems, it is necessary to perform independent adjustment of the horizontal and vertical levers. After the final adjustment of the measuring instruments, it is necessary to fix the position of the nodes so that the fixation is reliable and the adjusted exact relative position of the parts and assemblies of the device is maintained even after they are fixed.

During test grinding, check the manual feed the state of the spark along the length of the surface to be ground. If the spark is uniform along the entire length, then you can turn on the automatic feed. After grinding the part, it is necessary to check the diameter of the necks in the two most distant sections. If there is a taper, it is necessary to adjust the position of the table in the horizontal plane by turning its upper part relative to the lower one. To monitor the angle of rotation during adjustment, use a special dial or adjustment device with an indicator (Fig. 9.20). The device is attached to the lower table of the machine on cracker 3 and has two rotary elements 1 and 4, with which the indicator 2 is installed in various positions along the height and width of the machine table. The table setting is finally checked by repeated trial grinding.

For pneumatic gauge great importance has the correct adjustment of the device and the corresponding tare of the scale of the reading device, which is carried out according to the standards. To measure the scale holes, pneumatic instruments are calibrated using adjusting rings. The kit must include at least two adjusting rings corresponding in size to the maximum diameters of the measured part for which the instrument is calibrated. On the setting rings, control points are applied to the scale of the device, intermediate values are obtained by dividing the segments between the points; applied on the rings, in equal shares, in order to obtain the required division price. Proper operation pneumatic instrument is essential for the accuracy and reliability of its operation.

Features of setting up surface grinding machines. Adjustment of machines with rectangular table and a magnetic plate, you should start by checking the operation of the machine components, as well as checking the serviceability of the magnetic plate or fixture for mounting and clamping the workpiece. In case of deviation from the flatness of the table and the magnetic plate, they must be ground to the required deviation from the flatness according to the data of the machine passport. Further adjustment is recommended to be carried out taking into account the following features.

When using a magnetic plate, place a workpiece(s) on the plate, ensuring that each workpiece overlaps two poles. Check clamping force. After setting the workpiece, turning on the electromagnetic plate and feeding the table, the grinding wheel should be gradually brought into contact with the workpiece to be machined (to avoid its impact).

When setting up machines with a rectangular table, place stops that switch the direction of the table, while ensuring an overrun, which is determined by the size of the circle and the method of grinding (periphery or end face). Arrange stops that limit the transverse movement of the grinding headstock, while ensuring that the circle does not exceed 0.3 of its height relative to the edge of the plate. Depending on the length and speed of the longitudinal stroke of the table, set the frequency of double strokes. Set the required values for the transverse and vertical feeds. Set up a measuring and control device that cycles the machine and automatically stops the machine at the end of processing.

Our company offers devices for static balancing of grinding wheels and their mandrel for various faceplate sizes.

Devices with parallel knives PB-01.000 and PB-02.000

These balancing devices are used for balancing grinding wheels and cutters.

Disk balancing device PBD-01.000

Why is it necessary to balance grinding wheels and cutters?

During operation, the grinding wheel reaches high speeds. Even the slightest imbalance in it leads to the appearance of significant centrifugal forces. And this, in turn, negatively affects the operation of the entire machine and the quality of products.

There are several reasons for the appearance of imbalance in the circle. Firstly, this is the uneven distribution of mass in the body of the circle; secondly, the eccentricity of the circle in relation to the axis of the machine spindle (improper fit in the flanges), imbalance of the flanges; thirdly, the irregular geometric shape.

Grinding wheel balancing devices with parallel blades help to find the place of imbalance. Parallel knives or prisms are the simplest device, the principle of which is static balancing. The main requirement is that they must be fixed on a rigid base strictly parallel and horizontally. The essence of static balancing is as follows: when the mass distribution changes, the center of mass is brought to the axis of rotation. Unbalance correction must be carried out at the largest radius due to the fact that the influence of the mass of the corrected metal on the balance of the circle increases the more, the greater the distance from the axis.

Balancing is performed in 5 stages:

rough balancing;
fine balancing;
choice of location and size of working balancing weights;
installation and fastening of working balancing weights;
balancing quality control.

Balancing high-speed cutters for woodworking machines

In addition to balancing grinding wheels and milling cutters, these devices are used for balancing typesetting high-speed cutters of woodworking machines.

For accurate and quiet work, the wheel must be balanced so that its center of gravity coincides with the center of rotation. When working with an unbalanced circle, the machined surface turns out to be faceted, wavy, and the spindle bearings wear out quickly. The reasons for the imbalance of the circle can be the uneven distribution of mass in the body of the circle, the eccentric location of the mounting hole in relation to the outer surface of the circle, the non-parallelism and non-perpendicularity of the ends, uneven impregnation of the circle with coolant, improper installation - non-concentric installation of the circle, etc.

Rice. 54. Stand for balancing grinding wheels: a - with two smooth cylindrical forks, b - with rotating disks, c scheme for attaching weights for balancing the wheel

A circle mounted on a mandrel is mounted on supports - cylindrical rollers or disks (Fig. 54). Both devices (Fig. 54, a, b) have a common drawback is big friction torque, which reduces the balancing accuracy. The use of the "air cushion" principle made it possible to create a rational design of the device for static balancing (Fig. 55). The advantage of the device on the "air cushion" is that the mandrel with the circle easily rotates under the influence of a moment of 1×10-5 N×m. To bring a mandrel with a circle mounted on cylindrical rollers out of rest, a moment of 7 times more is required, and with disks - 40 times more.

Rice. 55. Designs of devices for static balancing of grinding wheels: a - on an air cushion, b - on plane-parallel rulers, c - with two pairs of rotating disks

On the spindle of the machine, the circles are fixed with the help of a faceplate, in the end grooves of which weights are placed - segments for balancing the circles. Balancing is done by changing the position of three weights in the annular undercut of the grinding wheel flange. An unbalanced circle with a heavier part will turn down. By moving the weights in the faceplate, they ensure that the circle in any position on the supports remains motionless. As the circle wears out, its balancing may be disturbed due to uneven distribution of mass in the body of the circle. Therefore, it is advisable to re-balance the circle. At the end of the shift, it is recommended to run the wheel at operating speed for 1-2 minutes, turning off the cooling, so that the liquid does not accumulate in the pores of the lower part of the wheel and does not disturb the balance.

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