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FRB BEARINGS Cross roller bearing in the application of the NC machine tool spindle
 

With the development of science and technology and the rise and maturity of advanced manufacturing technology in the world, higher requirements have been put forward for numerical control processing technology.As the core part of machine tool, rotary table has been widely used in all kinds of nc milling machines, boring machines, various vertical milling machines and milling machines.

In machine tool design, in addition to the required rotary table can carry the workpiece weight well, also need to ensure that they are within the scope of the carrying capacity with high rotation accuracy, ability to resist capsizing and high speed capability, the ability as the main index of machine tool, is the most basic reflect the working performance of the spindle components.

In this paper, two kinds of bearing structures applied on the spindle of a CNC vertical lathe are used as examples, and the bearing structure of the rotary table on the CNC vertical lathe is analyzed.

1.The structure of traditional combination bearing on CNC vertical lathe.
The spindle structure of VTC250140 CNC vertical lathe for our customers is shown in figure 1.This kind of traditional combination bearing structure of the worktable and workpiece load mainly depends on the bearing bearing of the thrust ball bearing, and the Angle contact ball bearing is used to realize the centering.Main motor from a series of transmission gear box, power transmission to turn the big gear ring, a large ring gear by thrust ball bearing and angular contact ball bearing outer ring, drive the workbench support and put together with the rotary table rotation, so as to realize the rotation movement of the lathe workbench.
 

FIG 1.    the structure of the combined bearing on the rotary table.

1. Base   2. Gear ring   3. Table support   4. Thrust ball bearing   5. Spindle.
6. Angular contact ball bearing    7. Rotary table.

2.FRB BEARINGS Cross roller bearing on the NC vertical lathe structure
1) introduction of cross roller bearings developed by FRB BEARINGS.The so-called cross roller bearing (as shown in figure 2) is a series of angular contact rolling bearing adjacent roller in a v-shaped grooved rolling surface of 90 degrees, which is kept perpendicular to each other through a spacer.Make half roller carry axial load in one direction, while in the opposite direction of axial load by the other roller bear, make a cross roller bearings can bear radial load, axial load and torque load, etc. All the direction of the load.
 


2) The application of cross roller bearing in the trolley.The main shaft structure of the above products is designed by quadratic design, and the structure is changed into a bearing group with cross roller bearing instead of thrust ball bearing and angular contact ball bearing, as shown in FIG. 3.Main motor through a series of transmission chain makes the big gear ring with cross roller bearing outer ring spinning, rotary worktable directly with the big gear ring directly and thereby giving impetus to the rotation of the workbench, the structure of the spindle rotary worktable structure more simple.The rotary precision of the worktable realizes the pre-tightening control of the bearing by adjusting the thickness of the adjusting pad under the bearing gland, effectively reducing the assembly time.Due to the change of structure, the height of the center of gravity is reduced, so that the spindle structure has a high performance of reverse torque.Because the rolling body of the cross rolling bearing is only rolling without relative sliding, the whole structure is low vibration, low noise, low heating, and the corresponding lubrication and cooling oil consumption is also less.

FIG.3

The cross roller bearing structure has the following characteristics by comparing with the traditional thrust ball bearing and angular contact ball bearings.
1) cross roller bearing effectively simplifies the structure of lathe spindle.Plain bearing group of the structure of the complex, need to consider the installation of two bearings, and thrust ball bearing on the lateral force or flip torque by only small diameter of the tapered roller bearing, the spindle size small, poor rigidity.Cross roller bearing is a cross roller bearing which replaces the traditional two bearing arrangement design, which can reduce the spindle length and save the spindle processing cost.

2) The structure of cross roller bearing greatly simplifies the design of lubrication and cooling oil circuit.Plain bearing thrust bearing in the groups of roller bearings, their linear velocity is different, can produce sliding friction lead to high heat, easy to wear and tear of the original structure, need to consider giving up and down two bearing sufficient lubrication, and need to use high flow away the heat generated by the friction lubricating oil, and the bearing oil cavity lubricant oil shortage, oil pressure is not enough or lubricating oil road filter is easy to produce bearing heating becomes angry, not in time to a spindle to grind the phenomenon of death.The amount of lubrication and cooling oil can be reduced by the non - relative sliding between the rollers in the cross roller bearings.

3) The precision of bearing is easy to adjust.Because the combination bearing adopts clearance fit, the vibration and impact of machine tool will cause the spindle eccentric, which will affect the rotation precision of the machine tool.The cross roller bearing is simple to install. When the bearing is installed, only the cross roller bearing should be preloaded to the recommended value, which is easy to adjust and repair according to the original installation.



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