1 The structure and principle of the original brake
As shown in FIG. 1, the brake mechanism of the 20-type lathe adopts a brake-type brake, which is composed of a brake wheel 7, a brake belt 8 and a lever 6. The brake drum 7 is a steel disc mounted on the transmission shaft IV. A brake band 8 is wound around the brake wheel, one end of which is connected to the box body 10 through an adjusting screw 9 and the other end is fixed to the upper end of the lever 6 . Pull the handle 1 through the connecting rod 2 to push the vertical shaft 3 to rotate. The sector gear 4 mounted on the vertical shaft rotates with it, which drives the rack 5 to move horizontally to control the start, stop, and reverse positions of the clutch, and also controls the release and locking of the brake. When the handle 1 is in the upper and lower two positions, the lower end of the lever 6 is located at two convex positions a and c of the rack bar 5, and the braking band is relaxed. When the handle 1 is pulled to the middle to block, the rack is also pushed to the middle, the clutch is released, and the lower end of the lever 6 is at the protrusion b on the rack bar 5, and the brake band 8 is locked in the system. On the moving wheel 7, the machine tool stops quickly.
figure 1
2 Original design defects
When the lathe is parked and shifting, it is generally necessary to turn the main shaft by hand so that the slip gear can be smoothly meshed. When clamping a workpiece, it is often necessary to turn the chuck to a suitable position. The machine is in a braking state when it is parked. The spindle cannot be toggled at all, so that it is not possible to shift gears and it is also inconvenient to set up the workpiece. In order to shift gears, the brake band 8 can only be completely relaxed, but in this way, the brake loses its braking effect. Therefore, the worker's master loosened the brakes and used a reverse brake. However, this kind of braking method will cause a strong impact, produce harsh noise, and seriously affect the life of the gear, and sometimes even cause the gear teeth to break.
3 Improve design
How to make the lathe can be braked quickly when it is parked, and the shift can be smoothly shifted after stopping. The best way is to make the brake work for a short time while parking, and when the machine stops, the brake can be automatically disengaged so that the worker can Can smoothly pull the spindle to achieve shift. The improvement measures are as shown in FIG. 2. An electromagnetic brake is added outside the machine headstock and consists of an electromagnet 11, an armature 12 and a housing 13. The electromagnet 11 is mounted on the housing 13, the housing 13 is mounted on the headstock 10, and the armature 12 is assembled with the adjusting screw 9. When the electromagnet 11 is energized, the armature 12 moves the adjusting screw 9 to the left so that the brake band 8 is locked on the braking wheel 7 . When the electromagnet 11 is de-energized, the adjusting screw 9 and the armature 12 are moved rightward by the spring to release the brake band 8 .
The main motor control circuit of the machine tool is improved at the same time. The original control circuit is shown in Fig. 3, and the improved circuit is shown in Fig. 4. The improved circuit only adds a time relay KT and a stroke control switch SQ than the original circuit, and the electromagnet YB is the electromagnet 11 .
figure 2
image 3
Figure 4
A stopper 14 (see FIG. 1) is mounted on the vertical shaft 3 to control the stroke switch so that when the machine tool is at the parking position, that is, the handle 1 is in the middle, the stopper 14 presses down the stroke switch contact to make it conductive. When the machine is switched on, the limit switch releases the travel switch and the contact opens. Because the vertical axis 3 just passes through the electrical box on the back of the bed, the installed stop, travel switch and time relay can all be installed in the electrical box, and the conversion is very convenient.
The control principle of the improved circuit is as follows: When the handle 1 is lifted or pressed, the machine tool rotates forward or backwards, and at this time, the travel switch is in the release state, the electromagnet YB is not energized, and the brake does not work. When the handle is pulled to the middle, the clutch is released, and the stopper 14 mounted on the vertical shaft presses down the contact, the normally open contact is conducted, and the brake electromagnet YB and the time relay KT are energized at the same time. The armature 12 moves to the left and brakes. When the delay time of KT is reached, the normally closed contact of the delay is turned off, YB is powered off, and the brake is released. At this point you can flip the spindle to shift or clamp the workpiece smoothly. The setting time of the time relay should be greater than the time from the start of the stop to the complete stop of the machine.
4 Conclusion
The improvement of the brake system of the type 20 lathe can not only achieve the intended purpose, but also the mechanical structure and circuit changes are very small. The improved start, stop and brake are still operated by the handle 1 and are very convenient.
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