The difference between a good and excellent tool is what it's used for. Knowing which crushing plant to use is similar, all are good, but which works with your material and spec? The goal is to sell rock/gravel, not just buy a crusher; the crusher is the means to the end. In this article, we'll be discussing Mobile Jaw Crushers and questions we can answer in determining a Jaw's suitability to your quarry. (We use quarry broadly here, it could equally apply to a contractor or recycler.)
What is the feed material?
A Jaw excels with a mix of feed material with little fines present, and the largest rocks are no bigger than 70% of the inlet. Too many fines will cause low production or clogging if a large amount of fines is present an active pre-screen will remove them and increase production and product quality, particularly when a bony spec is needed.
Jaws are equally at home with rocks of different hardness and can competently crush materials with high hardness like Basalt or Blue Rock well. Often Jaws are preferred here due to their capability and ease of use, though they may not produce a complete product and requires extra shaping from a secondary crusher like a Cone or Impactor.
What are the specification requirements?
Jaws are generally primary crushers, used to reduce large feed sizes into an acceptable size for the secondary crusher to shape. This is their strength, Jaws have large inlets, and crushes large material easily since they have excellent mechanical advantage here. Their downfall is that their geometry and action means that they have a limited reduction ratio of 3:1. Additionally, the larger the Jaw, the larger the smallest achievable C.S.S is, meaning a secondary crusher might be required to produce smaller products regardless.
Cubical Shape index is another specification related requirement that is not a Jaws strong point; Jaws can suffer from products that come out 'slabby' or sometimes referred to as 'dinner plates'. The elongated shape is due to compression-based crushing and is rectified with a secondary if required, but not always.
There are scenarios where the Jaw is a single crusher; producing large GAP products is ideal. Jaws are also the cheapest in such scenarios.
What are the versatility requirements?
For Quarries versatility will be whether the plant is required to create all of the products necessary to sell or in enough quantity for more specific applications. Contractors, on the other hand, may have more versatility requirements in product scope and mobility.
Mobile Jaw Crushers clearly lend themselves to mobile crushing applications at quarries or temporary sites; they also come in a range of sizes that will determine how cost-effective they are to transport and how frequently.
Unlike Impact Crushers (sometimes called a hammer mill), a Jaw Crushers minimum C.S.S goes up with its inlet/jaw chamber size. The larger the Jaw, the more capable it will be in large and high throughput applications at the expense of making smaller products.
A Jaw's lack of ability to crush down to small GAP sizes and compression action also means it tends to produce more bony products and fewer fines, depending on what envelope or grade is required this is either a big plus or a drawback. Of course, the amount of fines produced is dependent on the material, but in comparison to Impactors and Cones, Jaws produce the least.
Operating costs
The cost per tonne operating a Jaw Crusher is relatively low as the wear items for a Jaw last well, however, the smaller C.S.S on a jaw the higher the wear cost will be with diminishing production. 75mm is the optimal minimum for a Jaw, anything smaller is in-efficient and costly (except soft materials like lime). Also, a small C.S.S is hard on a Jaw as this usually means a high reduction ratio. For a detailed explanation on how Jaw Crushers work see our article How Jaw Crushers Work.
Ease of use
A Jaw is one of the simplest crushers to operate and requires the least amount of operator training to operate and maintain correctly. Jaw Crushers make an excellent tool that you can have more than one person able to run, giving flexibility to a contractor who has his team trained to operate it.
Jaws are even easier to set up than Impactors and Cones have one operator set variable (C.S.S) to start crushing and have the lowest daily maintenance requirements. Its what has made Jaws so popular in the industry.
Is a Jaw Crusher right for my business?
In summary, a Jaw Crusher could be the right solution for your business if a Jaw matches your material source, required output or specification, and is versatile enough to keep busy and producing the differing amount of materials you may need.
Things to consider when purchasing a Jaw is that shape index is hard to achieve and likely very hard to meet any medium spec or envelope in one pass and will need a secondary shaper. The additional investment for a shaper and even screen is worth considering as this will increase operational costs, transport costs, potentially staffing and of course capital investment.
As a primary crusher taking large to medium material, the Jaw excels and leads in wearability and ease of use.
*Post screen is optional
**when processing optimal size of feed and output, results can vary
***Assume 1,000 working machine hours at 90% optimal production per hour
**** based on standard weights and dimensions, please check with transport company as permit requirements vary by region and can change
