Selection method of electric spindle bearing for engraving machine

I. Introduction

Computer-controlled engraving machines are becoming more and more popular. They are widely used in door and window engraving in the construction industry, heavy mold engraving in the mechanical industry, mold engraving in the plastics industry, and engraving and grinding of mobile glass panels. In the past, this kind of engraving machine was mainly imported, and now the domestic engraving machine has also made great progress and development. Therefore, the production of the electric spindle used in the engraving machine has also been gradually localized. However, since the prototype of China's engraving machine spindle is mostly imported from abroad, the high-speed bearings it used were also provided by some famous foreign bearing manufacturers. For example, FAG, SKF, NSK, SNFA, GMN and other companies. In the process of localization, because the spindle manufacturers are not very proficient in the selection of bearings, they often mistype and misuse, causing unnecessary trouble to the end users. For this reason, it is necessary to use the current spindle bearings for engraving machines most likely to appear. The problem of mis-selection theoretically analyzes the consequences of mis-selected bearings for users.

Second, the wrong choice of bearing selection;; the use of ordinary high-speed type selected ultra-high speed bearings

Most of the bearings in the high-speed shafting system use angular contact ball bearings. These bearings have the same outer dimensions (ie, inner and outer diameters, widths), and there are many internal structures, such as ordinary angular contact ball bearings, high-speed angular contact ball bearings, and ultra-high speed. Angular contact ball bearings, the biggest difference is the size of the rolling element (ball), the ball diameter of the ordinary angular contact ball bearing is the largest, the ball diameter of the high-speed angular contact ball bearing is medium, and the ball diameter of the super high-speed angular contact ball bearing is the smallest, the limit The rotational speed is increased and the dynamic load (Cr) is decreased. In addition, the rolling element material can be divided into two types: bearing steel ball and ceramic ball. The cage material is divided into metal cage and engineering plastic cage. The contact angle is also divided into 15 degrees, 25 degrees, 30 degrees, 40 degrees, 60 degrees, etc. In order to obtain different stiffness, the pre-tightening force of the assembled bearing is divided into light, medium and heavy. In short, the selection of angular contact ball bearings is more complicated than other general-purpose bearings. At present, there are selections of limit speed, dynamic load capacity, contact angle and pre-tightening force in the selection of engraving electromechanical spindle bearings. However, the most important mis-selection is that the relationship between the limit speed and the dynamic load capacity cannot be squared. The problem is that the limit speed is more than the dynamic load capacity is insufficient, resulting in a shortened service life. More precisely, the ordinary high-speed 70 series should be used instead of the H70 series.

Third, the theoretical analysis of the life style disorder caused by the selection error

At present, the rotational speed of the electromechanical spindle is 24,000 rpm and 18,000 rpm. We compare the H7004~H7008 and 7004~7008 with the 24000 rpm spindle.

All models work in DT pairing mode, and the working speed can reach 24,000 rpm. However, the ordinary high-speed ball diameter is much larger than the ultra-high-speed bearing ball diameter, and the corresponding dynamic load capacity is also much larger, then Under the same working conditions, the service life is long.

Fourth, life calculation

The service life is now calculated using the 7008 C/HQ1 and H7008 C/HQ1 as examples.

Set the radial cutting force Fr=1220N, the axial load is the preload force Fa=300N, the equivalent dynamic load P=XFr+YFa, find X=0.44 from the bearing sample, Y=1.36

Then P=0.44x1220+1.36x300=945N

Take the working speed of 20000 rpm, 7008 C/HQ1 bearing service life

H7008 C/HQ1 service life:

The calculation results show that 7008 C/HQ1 has a service life of 2468h and H7008 /HQ1 has a service life of only 987H, which means that the service life of 7008 C/HQ1 is 2.5 times that of H7008 C/HQ1.
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What are the characteristics and uses of roller bearings?

1: The roller and the raceway are in line contact or repaired line contact, and have a large radial load capacity, which is suitable for those subjected to heavy load and impact load.

2: The friction coefficient is small, suitable for those high speeds, and the limit speed is close to the deep groove ball bearing.

3: The N-type and NU-type can move axially, and can adapt to the change of the relative position of the shaft and the shell caused by thermal expansion or installation error, and can be used as a free end support.

4: The machining requirements for the shaft or the seat hole are relatively high, and the relative deflection of the outer ring axis after the bearing is installed must be strictly controlled to avoid contact stress concentration.

5: The inner ring or the outer ring can be separated to facilitate the installation and disassembly of the bearing.

The main applications are: large and medium-sized motors, rolling stock, machine tool spindles, internal combustion engines, generators, gas turbines, gearboxes, rolling mills, vibrating screens, and lifting and transporting machinery.

Ball bearings and roller bearings are both rolling bearings. The simplest one is that the rolling elements are balls, which are steel balls. The other rolling element is a steel column.
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