Comparison of Three Overload Protection Measures for Jaw Crusher

Jaw crusher is mainly used for the primary crushing of large pieces of materials, with harsh working environment and heavy load. It is easy to lead to large overload danger when uneven feeding or non-broken materials enter the crushing chamber. Therefore, the overload protection device of jaw crusher is very important.

This article introduces three kinds of overload protection devices, and the principle and working process of hydraulic overload protection devices.

1. Elbow plate breaking method for jaw crusher

Set the easy break point of elbow plate with low strength. That is to say, when the jaw crusher is overloaded, the stress sensitive area of the elbow plate will break automatically due to the sharp rise of the stress to the limit value, so as to cut off the power transmission and prevent the machine from damage.

Due to the fluctuation of mechanical properties of elbow plate (generally cast iron) and the limitation of calculation accuracy, it is impossible to accurately and quantitatively control the breaking point, and sometimes overload cannot be protected.

Even if the jaw crusher is protected when overload is happen, because the jaw crusher is in an accident state, the equipment cannot run before cleaning, disassembly and replacement, and the process interruption will delay the production.

2. Flywheel torque limiting protection for jaw crusher

Spring friction clutch, hydraulic friction clutch or safety pins are used. This method is widely used in simple pendulum jaw crusher.

Friction clutch should not only ensure the transmission of normal working torque, but also make the transmitted torque not exceed the allowable value. When the unbroken materials entering into crushing chamber, the machine is overloaded and reaches the critical torque. The flywheel slides freely on the shaft, which plays the role of protecting the main parts.

However, because the friction coefficient of clutch is greatly affected by external conditions (such as temperature), the reliability of the clutch is limited. When the clutch is overloaded, it is still necessary to remove the obstacles and stop the machine for repair.

3. Hydraulic protection for jaw crusher

Due to the above two overload protection methods both may have some problems, such as unreliable protection and shutdown treatment in case of accident. Therefore, the safe and reliable hydraulic protection device is widely used.

Working process of hydraulic overload protection device for jaw crusher

The hydraulic overload protection device of jaw crusher is mainly composed of hydraulic cylinder, accumulator, plunger type fuel injection pump, cam device, oil pressure regulating device, action valve, oil filter and oil tank. As shown in Figure 1.

Figure 1 hydraulic overload protection working principle

(1-working hydraulic cylinder, 2-accumulator, 3-plunger type fuel injection pump, 4-cam device, 5-oil pressure regulating device, 6-action valve)

The hydraulic overload protection device adopts oil pressure regulating device to adjust the effective pump oil stroke of plunger type fuel injection pump, and automatically adjusts the oil injection amount according to the small amount of oil leakage in the hydraulic system. The working cylinder uses bolts to limit the limit elongation position, which overcomes the pulse of moving jaw on the hydraulic system oil pressure, and is convenient for the adjustment of ore discharge port.

1) Normal operation

The pressure of the jaw crusher thrust plate acting on the working hydraulic cylinder is less than that of the hydraulic cylinder, the action valve is at the upper limit position, the thrust plate does not move, and the crusher normally breaks materials.

2) Overload protection

When the unbreakable materials enter into the crushing chamber of jaw crusher, the crushing force the jaw crusher increases. At this time, the pressure of the thrust plate acting on the working hydraulic cylinder is greater than the thrust provided by the hydraulic cylinder. The oil pressure in the high-pressure oil chamber of the working hydraulic cylinder increases instantaneously. The throttle valve makes the action valve act, and the system (hydraulic cylinder) discharges oil to limit the maximum thrust (i.e. the maximum crushing force) of the thrust plate for protection the jaw crusher.

3) Troubleshooting

After the unbreakable materials enter the crushing chamber, due to the maximum thrust provided by the working hydraulic cylinder, the piston moves to the right and retracts, correspondingly, the ore discharging port of the jaw crusher increases. Due to the engagement of the crusher jaw, the unbreakable materials gradually move downward and finally discharge from the discharging port, automatically excluding the unbreakable materials in the crushing chamber. If the "products" in the crushing chamber are not qualified, they can be removed by the auxiliary device.

4) Automatic recovery

When the unbreakable materials are automatically removed, the piston is in the retracted position. Due to the decrease of crushing force, the action valve restores its valve core to the upper limit position without instantaneous high pressure in the upper chamber, and no longer discharges oil to the system; meanwhile, the plunger type fuel injection pump pumps oil to the system with the maximum pump oil quantity under the action of the oil pressure regulating device, until the piston of the working hydraulic cylinder moves to the limit position to the left. So far, the jaw crusher returned to normal working state.