Design and correctness of the safety brake of the

Design and correct use of CD10 t electric hoist safety brake

I. structural characteristics and working principle of safety brake

safety brake of CD10 t electric hoist hoisting mechanism brake drum designed according to the requirements of TSG. It is characterized by simple structure and few parts. The braking torque increases with the increase of load, and the braking torque reaches the maximum at full load. When the rotor shaft of the conical rotor motor, the working brake of the motor, the coupling, the intermediate shaft, the transmission gear and gear shaft of the reducer and any part of the hollow shaft break, the safety brake can reliably support the rated load. When the working brake fails and cannot support the load and the load drops, the safety brake can also work normally to support the load. Because the parts are not damaged, press the lifting button of the electric hoist at this time to raise the load for a certain distance, the safety brake can return to the non working state, and then press the lowering button of the electric hoist to make the load land smoothly. The working brake of conical motor can be repaired or adjusted

Figure 1 is the structural diagram of safety brake. Its working principle: is there any zigzag deformation of the swing rod? When the working brake fails or the transmission parts are broken, the load drops rapidly so that the centrifugal block 3 opens under the action of centrifugal force, the stop block 5 quickly catches the centrifugal block 3 and presses the brake arm 1 tightly, and the friction plate 2 presses the drum to stop the load

10 t electric hoist safety brake design difficulties that should be paid attention to:

(1) design of brake low-speed shaft. The brake is placed in the drum, and the inner cavity space of the drum with an outer diameter of 0.35 in is very small, while the braking torque is relatively large. When the braking safety factor is taken as 1.25, the braking torque is 11.1 n M

Figure 1 Schematic diagram of safety brake

left side: braking state right side: closed state

1. Brake arm 2. Friction plate 3. Centrifugal block 4. Centrifugal block seat 5. Stop block 6. rolling bearing 7. Shaft bolt 8. Arm seat

(2) friction plate has higher pressure than that. The friction plate with allowable specific pressure P 1 N/mm, friction coefficient f -0.45 and maximum allowable temperature T 200 ℃ should be selected. The oil immersed steel wire rope wound on one side of the drum is easy to break because the safety brake works and the drum temperature rises and the lubricating steel wire rope loses oil

(3) the electric hoist breaks at low speed, such as the hollow shaft or the last stage big gear, the load drops quickly, and the safety brake can brake quickly; If the high-speed shaft is broken, the moment of inertia of the high-speed shaft is large, while the moment of inertia of the slow shaft is converted to the high-speed shaft, which is only 15% of the moment of inertia of the high-speed shaft. The speed of load reduction has an acceleration process. When the drum reaches a certain speed, the centrifugal force can open the centrifugal block, and the safety brake can brake the load. Therefore, it may cause that the safety brake (i.e. the sample is not in the jaw, in the jaw, in the parallel section or outside the gauge distance) cannot brake quickly

II. Adaptability between working level and working conditions of 10 t electric hoist

at present, there are only CD type 10 t electric hoist with rated lifting capacity greater than 5 t, and its working level is m3. The M3 working level is T2 ~ T4 according to the utilization level of the mechanism, and the load states are L1 and L2. The design service life of T2 ~ T4 is 8 years, the working time is 800 ~ 3200 h, the annual working time is 100 ~ 400 h, the daily working time is 0.4 ~ 1.6 H (half of which is the lifting time, the other half is the no-load time), and the lifting time of a day is only 12 ~ 48 min. The utilization level belongs to infrequent use or frequent leisurely use. The load state of the mechanism is u ~ L2, and the load spectrum coefficient km= (0.125 ~ 0.25). In the half time of no-load and half time of lifting load, the time of lifting rated load only accounts for 10% - 16.7%; The weight of the lifting load is 10% - 20% of the rated load, and the occupied time is 40% - 50%; The weight of the lifting load at other times is 40% - 73.3% of the rated load. However, the lifting equipment for lifting molten metal mostly refers to metallurgical cranes, including casting cranes. The working level of the main lifting mechanism is M6 and M7; Utilization grade T6, T7; Load state L3, L4. From this analysis, it can be seen that the 10 t electric hoist with the working level of M3 cannot meet the use requirements of the foundry workshop. Although the production scale of small foundries cannot be compared with that of large metallurgical foundries, they are all production equipment for lifting molten metal. At this time, the working level of the electric hoist should be M5 and M6; The utilization grade is T5 and T6, and the working time of one year should be 3.25 ~ 6.46 h; The load states are L2 and L3, and the load spectrum coefficient k = (0.25 ~ 0.5). At present, there is no electric hoist with the working level of M5 and M6 in China. The literature [3 ~ 4] puts forward the design method to improve the working level. The current m3 electric hoist is increased to M5 and M6, and the lifting capacity is degraded according to the priority number of R10, from 5 t and 10 t to 4 T, 3.2 T, 8 T and 6.3 t. The original designed electric hoist is checked and calculated according to the changed lifting capacity and working level of the hook, steel wire rope, drum, reducer gear teeth, gear shaft, rolling bearing, single key and spline, coupling and other main parts. The corresponding supporting conical rotor motor can be operated at M5 and M6 levels; The lifting capacity is 4 T, 8t, 3.2 T and 6.3 t respectively (the lifting speed remains the same); Conical motors with power of 5.6 kW, 9.8 kW (jc25%) and 4.5 kW, 7.7 kW (jc40%) are selected; Or use the existing conical motor to conduct type test according to the above power and power continuity rate. The performance parameters of the ex factory 10 t electric hoist should be re marked as lifting capacity P =80 kn, lifting speed v=7 M/min, working level M5 (jc25%); Lifting capacity P =63 kn, lifting speed v=7 M/min, working level M6 (jc40%)

III. measures to prevent the load falling of electric hoist brake

since the production and application of CD/MD electric hoist, there have been few reducer accidents causing load falling. However, the 10 t electric hoist has repeatedly suffered from the bending of the intermediate shaft and slipping off the coupling at home and abroad, causing the load to fall. Literature [5] analyzes the design defects of the domestic lithium iron phosphate material output continuous growth device of the 10 t electric hoist tire coupling. The enterprise has made improvements. The bearing seat is welded in the drum with a lifting height of H 18 inches, and the intermediate shaft is supported by rolling bearings; And use claw type elastic coupling. In order to enable CD/MD electric hoist to safely lift liquid metals and dangerous goods, references [6 ~ 7] introduced self-made brakes and caliper brakes for supporting braking loads used in electric hoists in order to change this kind of market chaos. When two supporting brakes are installed, the safety factor of each brake shall not be less than 1.25. This is less than the allowable value of 1.5 when installing a support brake. The braking torque of the motor can be adjusted in the range of more than and close to 1.25. The two supporting brakes are at the two ends of the high-speed shaft. The braking effect is good, the relative dynamic load is small, and the impact on the braking motor is small