What causes material return from the jaw crusher during operation of a sand and gravel production line?

The main reasons for material backflow in jaw crushers during operation of a sand and gravel production line are as follows:

1. Equipment inherent problems

Substandard dimensions of jaw crusher parts, such as jaw plate length, thickness, toggle plate length and angle, and frame cavity dimensions, do not meet drawing requirements, leading to decreased mechanical performance. After prolonged use, the included angle between the two jaw plates exceeds the standard friction angle, resulting in insufficient friction between the material and the jaw plates, unable to overcome the upward component of the crushing force.

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2. Uneven force on crushed material

During the application of force by the movable jaw plate, the force on the material to be crushed in the vertical direction within the crushing chamber may become uneven. Especially when there is an upward component force, the material may experience an upward pushing force, causing it to be pushed out of the crushing chamber instead of being effectively crushed; this phenomenon is called backflow. To reduce backflow, the movement trajectory of the movable jaw plate and the design of the crushing chamber need to be optimized to ensure balanced force on the material during crushing, thereby improving crushing efficiency.

3. Excessively Wide Discharge Opening

Many laypeople believe that the wider the discharge opening of a jaw crusher, the better. However, for jaw crushers of the same specifications, a wider discharge opening increases the likelihood of material backflow. During crushing, the material directly contacts the jaw plates, generating friction. The more severe the wear on the jaw plates, the greater the possibility of material backflow.

4. Large Size Differences in the Material to be Crushed

Generally, jaw crushers feed materials of similar sizes to ensure uniform feeding. When the size of the material to be crushed varies greatly, material backflow is very likely to occur.