Introduction
Rotationl Speed is the rotation speed of the motor spindle in the hard disk, which is the maximum number of revolutions that the hard disk platter can complete in one minute. The speed of rotation is one of the important parameters indicating the grade of the hard disk. It is one of the key factors that determine the internal transmission rate of the hard disk, and it directly affects the speed of the hard disk to a large extent. The faster the rotation speed of the hard disk, the faster the hard disk can find files, and the transmission speed of the relative hard disk has also been improved. The hard disk speed is expressed in revolutions per minute, and the unit is expressed as RPM. RPM is the abbreviation of Revolutions Perminute, which is revolutions per minute. The larger the RPM value, the faster the internal transfer rate, the shorter the access time, and the better the overall performance of the hard drive.
The spindle motor of the hard disk drives the platters to rotate at a high speed, generating buoyancy to make the head float above the platters. To bring the sector of the data to be accessed below the head, the faster the speed, the shorter the waiting time. Therefore, the rotational speed determines the speed of the hard disk to a large extent.
The speed of ordinary hard disks for household use is generally 5400rpm and 7200rpm. High-speed hard disks are now the first choice for desktop users; for notebook users, they are mainly 4200rpm and 5400rpm, although some companies have already released them. 7200rpm notebook hard drives are still relatively rare in the market; server users have the highest hard drive performance requirements. The SCSI hard drives used in servers basically use 10000rpm, even 15000rpm, and their performance is much higher than that of household products.
Higher speed can shorten the average seek time and actual read and write time of the hard disk, but with the continuous increase of the hard disk speed, the temperature rises, the motor spindle wears more, and the working noise increases. Great negative impact. The speed of notebook hard disks is lower than that of desktop hard disks, which is affected to a certain extent by this factor. The internal space of the notebook is narrow, and the size of the notebook hard disk (2.5 inches) is also designed to be smaller than that of the desktop hard disk (3.5 inches). The increase in temperature caused by the increase in speed puts higher requirements on the heat dissipation performance of the notebook itself; the noise becomes larger. , And must take necessary noise reduction measures, these have put forward more requirements on the notebook hard disk manufacturing technology. At the same time, the increase in speed, while the others remain unchanged, means that the power consumption of the motor will increase, the more electricity is consumed per unit time, and the working time of the battery is shortened, so that the portability of the notebook will be affected. Therefore, notebook hard drives generally use a relatively low-speed 4200rpm hard drive.
The speed changes with the increase of hard disk motors. Now fluid dynamic bearing motors have completely replaced traditional ball bearing motors. Liquid bearing motors are usually used in the precision machinery industry. It uses mucosal fluid oil bearings and replaces balls with oil films. In this way, direct friction of the metal surface can be avoided, and noise and temperature can be reduced to a minimum; at the same time, the oil film can effectively absorb vibration, so that the anti-vibration ability is improved; it can also reduce wear and increase life.
Formula of spindle speed
The spindle speed should be selected according to the allowable cutting speed and the diameter of the workpiece (or tool). The calculation formula is: n=1000v/πD
v----cutting speed, the unit is m/min, which is determined by the durability of the tool;
n---spindle Rotation speed, the unit is r/min;
D----workpiece diameter or tool diameter, the unit is mm.
The calculated spindle speed n should be selected according to the machine manual at the end of the machine tool's own or close speed. In short, the specific value of cutting parameters should be determined by analogy based on the performance of the machine tool, related manuals and combined with actual experience. At the same time, the spindle speed, cutting depth and feed speed can be adapted to each other to form the best cutting amount.
Steps to determine the spindle speed
Determining the spindle speed during processing is a very important link, which is directly related to the tool life and the processing effect of the workpiece.
1. To determine the spindle speed, we must first start with the material. The higher the hardness of the material, the lower the spindle speed during processing. The more viscous the material, the higher the spindle speed during processing.
2, the determination of the spindle speed should be based on the diameter of the tool used. The larger the tool diameter, the lower the spindle speed.
3. The determination of the spindle speed also depends on the use of the spindle motor.
4. When the spindle speed decreases, the output power of the motor also decreases. If the output power is low to a certain level, it will affect the processing, which will adversely affect the life of the tool and the workpiece. Therefore, When determining the spindle speed, pay attention to ensuring that the spindle motor has a certain output power.
In general, the spindle speed should be determined according to the material, tool diameter and output power. When determining the spindle speed, you must analyze it according to your own specific situation to finally determine the spindle speed. Don't use the recommended parameters.
The influence of spindle speed on machining
The influence caused by the excessive axial movement of the spindle:
1. Use a dial indicator to align the center hole of the workpiece , After the workpiece coordinate system is established, the disc-shaped workpiece is machined with circular equal-division holes, and the position error of each hole and the hole center is too large.
2. Use a big end milling cutter to mill the plane, and the center of the workpiece is concave; take the worktable as the reference, end mill the upper surface of the workpiece, and the workpiece is inclined.
3. After boring, the axial generatrix of the hole is not perpendicular to the base surface, and the workpiece hole distance error is too large.
4. Use a new end mill to mill the workpiece, and the workpiece surface is inclined.
5. After drilling, it is elliptical after inspection.
6. The end milling plane and the two-pass tool are not flat.
Excessively high spindle speed will cause the following problems:
1. Use a dial indicator to align the center hole of the workpiece. After the workpiece coordinate system is established, process the circular equally divided hole of the disc-shaped workpiece. The position error between each hole and the hole center is too large.
2. Use a big end milling cutter to mill the plane, and the center of the workpiece is concave; take the worktable as the reference, end mill the upper surface of the workpiece, and the workpiece is inclined.
3. After boring, the axial generatrix of the hole is not perpendicular to the base surface, and the workpiece hole distance error is too large.
4. Use a new end mill to mill the workpiece, and the workpiece surface is inclined.
5. After drilling, it is elliptical after inspection.
6. The end milling plane and the two-pass tool are not flat.
Measures to be taken when the speed is too high
1. First, improve the rotation accuracy of the spindle. The spindle bearing is a key part that affects the rotation accuracy of the spindle. For precision machine tools, precision rolling bearings can be used, as well as multi-oil wedge hydrodynamic bearings and hydrostatic bearings. At the same time, the accuracy of the parts matched with the bearing should be improved. Secondly, it is necessary to reduce the influence of spindle rotation error on parts processing. The spindle structure with separation of motion and positioning can be adopted, so that the rotation accuracy of the workpiece during processing is not affected by the spindle rotation error of the machine tool, so that the spindle rotation error is not reflected on the workpiece.
2. Reduce the guide error of the machine tool guide rail (mainly caused by the manufacturing, installation error and wear of the guide rail): 1) Improve the manufacturing accuracy of the guide rail 2) Choose a reasonable guide rail shape and guide rail combination form, and If possible, increase the mating length of the worktable and the bed guide rail. 3) Use hydrostatic guide rails or reasonable oil scraping and lubrication methods. 4) Ensure the installation technical requirements of the machine tool and improve the assembly accuracy of the machine tool.
3. The machining accuracy of CNC machine tools (especially CNC machine tools with open loop systems) depends to a large extent on the accuracy of the feed drive chain. In addition to reducing the machining errors of transmission gears and ball screws, another important measure is the use of backlash-free transmission pairs, and it has become a trend to replace gears with synchronous belt transmission. For the cumulative error of the ball screw pitch, a pulse compensation device is usually used to compensate the pitch accuracy.