A jaw crusher may sometimes push material back toward the feed opening during operation. In more severe cases, crushed material may be ejected from the feed opening. This phenomenon is known as material return. It can interfere with normal crushing operations and pose a safety risk to operators working near the machine.
Material return is generally associated with component dimensions, force distribution inside the crushing chamber, discharge opening settings, and variations in feed particle size. Identifying the cause is necessary before selecting the appropriate corrective measure.
Main causes of material return in jaw crushers
Component dimensions do not match the design drawings
The jaw plates, toggle plate, and frame of a jaw crusher must be manufactured according to the dimensions and geometric requirements specified in the design drawings. Deviations in jaw plate length or thickness, toggle plate length or angle, and frame cavity dimensions can cause the actual machine geometry to differ from the intended design, affecting the crushing process.
After prolonged operation, the angle between the two jaw plates may exceed twice the friction angle. When this happens, the frictional force between the material and the jaw plates may become insufficient to overcome the upward component of the crushing force. The material is then pushed upward and may slide back toward the feed opening, causing material return.
When investigating problems related to dimensional deviations in non-standard components, the dimensions of the original parts and the fit of replacement components should both be checked. Hansheng Automation provides custom machining of non-standard mechanical components according to customer drawings and machining requirements.
Uneven force distribution inside the crushing chamber
During operation, the moving jaw applies compression to the material. Depending on the movement of the jaw and the contact conditions between the material and the jaw plates, the forces acting on the material in the vertical direction may become unbalanced.
When the upward force component is too large, the material may not continue moving downward through the crushing chamber. Instead, it can slide along the jaw plates toward the feed opening, resulting in material return.
Excessive discharge opening width or severe jaw plate wear
For jaw crushers of the same specification, a wider discharge opening can increase the likelihood of material return. During crushing, the material must maintain effective contact with the jaw plates so that compression and friction can break it down.
When the jaw plates become severely worn after prolonged use, their working surfaces change, which may reduce the friction between the material and the plates. This increases the risk of material return. The jaw plates should therefore be inspected regularly and repaired or replaced according to their actual condition.
Excessive variation in feed particle size
The feed particle size must be suitable for the specifications of the jaw crusher. When material entering the crushing chamber varies considerably in size, large and small particles may become unevenly distributed. This can affect how the material is loaded and crushed.
Significant differences in feed particle size can lead to uneven force distribution and increase the likelihood of material return. Feed size should therefore be controlled during production. Material with widely varying particle sizes should be screened before being fed into the crusher.
How to prevent material return in jaw crushers
Select a crusher that matches the material conditions
Different materials have different size characteristics and crushing requirements. The crusher specification should be selected according to the actual feed material and operating conditions. Matching the equipment to the feed requirements helps reduce operating problems caused by unsuitable material sizes.
Repair or replace worn jaw plates
When material return is related to jaw plate wear, inspect the plates and assess their actual condition. If the wear is limited, the plates can be repaired according to the equipment requirements. If they can no longer meet operating requirements, replace them promptly to prevent further problems during crushing.
Screen the feed and use staged crushing
When the feed contains particles with widely different sizes, screen the material first and separate it by size before crushing. The crushing stages can then be arranged according to the required particle size. For example, use a coarse jaw crusher for pre-crushing, followed by a fine jaw crusher for further size reduction. This helps meet the particle size requirements of subsequent processing operations.
Adjust the jaw plate angle with a wedge-shaped backing plate
If the angle between the two jaw plates is too large, a wedge-shaped backing plate can be installed at the interface between the moving jaw and its jaw plate. This adjustment reduces the angle between the two plates to less than twice the friction angle. It can improve the friction conditions between the material and the jaw plates, reducing the tendency of material to slide back toward the feed opening.
Install a guard plate above the feed opening
If material is ejected from the feed opening during operation, a protective plate can be welded above the opening to prevent material from flying out and striking nearby operators. The guard plate should be fitted with consideration for the machine structure and actual working conditions.
When investigating material return in a jaw crusher, first determine whether the problem is related to component dimensions, jaw plate wear, equipment adjustment, or feed material conditions. Repairs and adjustments should address the identified cause rather than treating every case in the same way. When non-standard mechanical components need to be remade, their dimensions and construction should follow the customer's design drawings and machining requirements.
Hansheng Automation also provides precision machining for non-standard components used in other industries. Our drawing-based services cover mechanical parts for tobacco packaging and filling machinery, as well as precision components for yachts and RC racing cars. We handle custom parts according to the specific drawings and manufacturing requirements of each application.
