Crushing is the reduction of large material into smaller sizes. It is often one

Crushing is the reduction of large material into smaller sizes. It is often one of the first steps in any aggregate or mineral processing plant and is accomplished with various types of crushing equipment. These machines employ various forces to reduce the material to the required size. The crushing process can be accomplished in one or more stages – primary, secondary, tertiary and quaternary – and include a variety of crusher types. The Complete Guide to Crushing Crusher Guide.indd 1 Crusher Guide.indd 1 4/5/2022 1:31:17 PM 4/5/2022 1:31:17 PM Crushing Stages 2 | The Complete Guide to Crushing Primary Crushing The primary crushing stage is the first stage in a crushing circuit. The main goal with primary crushing is to reduce the raw material into a smaller size that can be easily transported on a conveyor belt for further handling downstream. Primary crushers are sized to be able to accept large feed sizes without blocking or plugging. Typical primary crushers in aggregate applications include Jaw Crushers and Gyratory Crushers due to their ability to reduce large lumps of material to smaller sizes, but Impact Crushers and Hammermills can also be used in certain applications if the material is not overly abrasive. In minerals processing applications, Feeder-Breakers, Roll Crushers and Sizers are typically found in the primary crushing stage. Types of Primary Crushers: Feeder-Breakers // Gyratory Crushers // Hammermills Impact Crushers // Jaw Crushers // Roll Crushers // Sizers Secondary Crushing Secondary crushing, also referred to as intermediate crushing, further reduces the material for final crushing or for final product sizing. Impact Crushers, Cone Crushers and Hammermills are commonly used as secondary crushers in aggregate applications, while Secondary Sizers and Double Roll Crushers are commonly used for the secondary size reduction of many minerals. Types of Secondary Crushers: Cone Crushers // Double Roll Crushers // Hammermills Impact Crushers // Secondary Sizers Tertiary/Quaternary Crushing Tertiary and quaternary are considered fine crushing stages, but not every application will require them. These stages focus on the quantity (or capacity) and quality (particle size, shape, etc.) of the final product. Types of Tertiary/Quaternary Crushers: Cone Crushers // Fine-Grinding Sizers // Tertiary Sizers Roll Crushers // Vertical Shaft Impact Crushers Crusher Guide.indd 2 Crusher Guide.indd 2 4/5/2022 1:31:18 PM 4/5/2022 1:31:18 PM 3 | The Complete Guide to Crushing Closed Circuit vs. Open Circuit Crushing operations can be open circuit or closed circuit. An open-circuit operation is where the feed material is only run through the crusher once. This usually occurs in a primary (and sometimes a secondary) operation where uniformity of the product size is not as critical. In an open circuit, material never goes back to the same machine twice. A closed circuit is an operation where the material is returned to the crusher until it is of a size that will pass through the product screen. • The type of material to be processed • The feed size of the material • The desired product size • The expected capacity • The reduction ratio Factors That Affect The Crushing Process Feed Size When determining the feed size, consider the realistic expectation of the feed, not the biggest piece that could go through the plant. A feed size that is too large can cause the top of the crushing chamber to wear faster than the bottom, as well as decrease production if the feed opening becomes blocked by the oversize. A feed size that is too small can have the opposite effect. Undersized feed material will cause the majority of the crushing to take place in the lower portion of the chamber, causing increased wear to the bottom of the chamber. In this scenario, production will also be decreased due to a poor reduction ratio. Product Size and Capacity The product size is what you want to make, while capacity is how much product you want to make. Most products being produced must meet a specification of the various sizes within the product gradation. Ratio of Reduction The reduction ratio is dictated by the product size versus the feed size. It affects the overall throughput of the machine, the shape of the output product, the wear cost associated with this stage of the process and the horsepower needed to complete the expectation. In other words, it is a measure of the amount of work being done at this stage of reduction. A simple method, but not the most accurate, for calculating the reduction ratio in the field is to divide the top size of the feed material by the top size of the output. If 100% of the feed is passing 6” and 100% of the output is passing 2”, the reduction ratio is 3:1 However, to get a true measure of the amount of work being performed by the crusher, the P80 method should be used. The P80 method divides the 80% passing in the feed by the 80% passing the output. If 80% of the feed is passing 4” and 80% of the output is passing 3/4”, the reduction ratio would be 5.3:1 (4”/.75”) Crusher Guide.indd 3 Crusher Guide.indd 3 4/5/2022 1:31:18 PM 4/5/2022 1:31:18 PM 4 | The Complete Guide to Crushing Compression Crushers Compression crushers reduce material as it advances downward through a chamber by squeezing it between a moving surface and a stationary surface. When the feed material is squeezed in a compression chamber, it shatters or breaks to fill the air pockets or voids in the chamber. Gravity is the main factor in the flow of the material through the compression machine. For every closing or squeezing of the crushing chamber, which forces the reduction of the feed material, there is a subsequent opening of the chamber to allow material to flow further into the chamber or to discharge from the crusher. The output is changed by adjusting the setting or gap at the discharge point of the machine. The discharge point is the distance between the moving surface and the stationary surface at its smallest point. Types of Compression Crushers: Cone Crushers // Gyratory Crushers // Jaw Crushers Roll Crushers // Sizers In a compression crusher, the top size discharging from the crusher is twice the size of the setting. For example, if the gap between the moving surface and the stationary surface is 1”, the top size of the material discharging from the machine will be 2”. A 1” setting does not reduce every piece of material to minus 1”; some oversize will still be present. The tighter or closer the setting, the lower the throughput. Compression crushers are volumetric machines. Tightening the discharge setting will yield a smaller product, but volume will be lost so throughput will be reduced. A tighter setting, with the same feed, will increase the reduction ratio. A higher reduction ratio will require a higher horsepower, as more work requires more horsepower. Compression-type crushers are used extensively in construction aggregate applications. They handle large feed lumps, have a high ratio of reduction and handle extremely abrasive material with minimum wear. However, compression crushers often require high headroom and high horsepower. They can create a slabby product, which can cause problems with further handling. They are not ideal for handling wet, sticky feeds. Crusher Guide.indd 4 Crusher Guide.indd 4 4/5/2022 1:31:19 PM 4/5/2022 1:31:19 PM 5 | The Complete Guide to Crushing Jaw Crushers Jaw Crushers are the most common compression-type crusher. They consist of a stationary piece of steel (called a jaw die) and a moving piece of steel (called the swing jaw die) that come together to form a V-shaped chamber. The swing jaw die moves back and forth toward the stationary jaw die, compressing the feed material between the two surfaces. Jaw Crushers use the entire chamber to crush the material, so that the initial breakage happens on the first squeeze and subsequent squeezes continue to break the material as it advances farther down the chamber toward the discharge. These type of crushers produce flat, elongated pieces compared to Gyratory Crushers and Impact Crushers. The gradation is controlled by adjusting the spacing between the jaw dies at their closest point. For hydraulic-adjust Jaw Crushers, the discharge setting can be opened or closed by relieving or expanding the hydraulics. For shim-adjust Jaw Crushers, the discharge setting can be opened or closed by adding or removing shims to decrease or increase the opening. The top size of the feed material should be no larger than 80% of the opening of the chamber so that it gets pulled down into the machine and doesn’t sit on top. Keeping the chamber full helps to push the material through to the discharge. Pre-screening before the Jaw Crusher is recommended to remove the fine particles. In the event an uncrushable material enters the chamber, either the toggle on a shim-adjust Jaw Crusher will break or the hydraulics on the hydraulic-adjust Jaw Crusher will relieve, allowing the material to pass. Proper Speed For Your Jaw Crusher Selecting the proper speed for the given feed and desired uploads/Industriel/ crusher-guide.pdf

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