Jaw Crushers are a popular choice for the primary crushing of a variety of materials, including hard, abrasive and non-friable materials that may be wet but are not sticky.
Crushing of the material takes place between a stationary and moving or swing jaw plate. The swing jaw plate is mounted on a pitman, which is given a reciprocating motion. When the pitman moves toward the stationary jaw, the material is squeezed and broken until it is to a size where it can be discharged out of the bottom of the crushing chamber.
Product size adjustments can be made by increasing or decreasing the closed-side setting, which is the distance between the stationary jaw plate and the swing jaw plate at the bottom of the crushing chamber.
There are two main styles of Jaw Crushers: shim-adjust and hydraulic.
What is a shim-adjust Jaw Crusher?
Shim-adjust Jaw Crushers feature shim plates to maintain the closed-side setting. The shims are located behind the swing jaw as part of the adjustment system, which also includes a hydraulic ram, slide beam with locking wedge, wedge-locking tool, and an on-board hydraulic and electrical system.
What is a hydraulic Jaw Crusher?
Hydraulic Jaw Crushers feature hydraulics instead of shims to maintain the closed-side setting. The adjusting components I’m on a hydraulic Jaw Crusher include flange-mounted double-acting cylinders, manifold, slide beam with slide bars and a remote hydraulic and electrical control system.
Making a product size adjustment
If you need to change your product size or accommodate for general wear on the jaw dies, you can increase or decrease the discharge opening by adjusting the closed-side setting. Moving the swing jaw closer to the stationary jaw decreases the closed-side setting, while moving the swing jaw further from the stationary jaw increases the closed-side setting.
For a traditional shim-adjust Jaw Crusher, adjusting the closed-side setting is a bit labor-intensive and requires a complete plant shutdown while the adjustment is being made. Lockout/tagout and all safety procedures must be followed while performing the adjustment to reduce the risk of injury. You also need to make sure you have the appropriate tools, typically wrenches of varying size, to perform the task
The actual adjustment requires the addition or removal of shims to increase or decrease the discharge opening. The procedure involves relieving tension on the toggle plate, adding or removing shims as required and tensioning the toggle plate. Adding shims decreases the closed-side setting for a smaller product size. Removing shims increases the closed-side setting to make a larger product size. The number of shims you add or remove depends on how big of an adjustment change you want to make, and the shims are typically marked to indicate size and supplied in various size increments.
For hydraulic Jaw Crushers, adjustments to the closed-side setting can be made while the machine is in operation, though it is recommended that you stop the feed coming into the crusher while the adjustment is being made to avoid causing potential damage. Simply press a button on the control panel to indicate you want to increase the closed-side setting, or the button for decreasing the closed-side setting, and the swing jaw will automatically move backward or forward. No shutdown or tools are required for making adjustments with a hydraulic Jaw Crusher.
Handling tramp material
Another area where hydraulic and shim-adjust Jaw Crushers differ is in their ability to handle tramp metal in the feed. If an uncrushable material, such as a loader bucket tooth, enters the crushing chamber on a shim-adjust machine, the toggle plate will break to ensure the crusher is not catastrophically damaged.
The toggle plate is quite heavy, and when it breaks, it may fall on whatever is below the crusher and cause damage to that item. Not only that, but when the toggle plate breaks, the Jaw Crusher is out of operation until a new toggle plate can be installed.
Hydraulic Jaw Crushers offer automatic tramp metal relief in the event an uncrushable material enters the chamber. In this case, the crusher will sense the uncrushable and automatically increase the closed-side setting to pass the metal through. Once the metal has discharged, the crusher will then automatically reset itself to the designated closed-side setting, moving back into the position it was in before the uncrushable event.
The hydraulic Jaw Crusher will perform a similar chamber-clearing relief action in the event of a power failure or overload. However, a power overload can be triggered by crushing extremely hard material, in which case, the hydraulics may unwantedly relieve and clear the chamber.
Operation and maintenance
In terms of operation, hydraulic Jaw Crushers and shim-adjust Jaw Crushers follow the same principles of compression crushing for material size reduction. Besides the adjustment assemblies, they feature the same components. They offer the same ratio of reduction, can handle the same types of material and are sized the same way.
Maintenance differs slightly with the two different Jaw Crushers, as the hydraulic Jaw Crusher features a hydraulic system that must be maintained.
Shim vs. hydraulic
The main difference between hydraulic and shim-adjust Jaw Crushers is the method of product size adjustment. Shim-adjust Jaw Crushers employ the use of shims to change the closed-side setting, while hydraulic Jaw Crushers rely on hydraulics to make changes with the push of a button.
Additionally, hydraulic Jaw Crushers offer automatic tramp metal relief and automatic chamber clearing in the event of a power surge or failure. Keep this in mind when deciding which style of Jaw Crusher may be right for you.
Most of the time, though, it comes down to a matter of preference. If you are looking for a lower capital investment, don’t mind some downtime to make product size adjustments, are crushing an extremely hard material and/or have little to no instances of tramp metal infiltrating the feed, a shim-adjust Jaw Crusher is a great option. If you make frequent adjustments to the closed-side setting, experience power losses and/or are concerned with tramp metal in the feed, a hydraulic-adjust Jaw Crusher is the better option.
