The starting point to understanding how cone crushers work – and how they can make your mine or quarry more productive. The following article covers the basics of cone crushing, including chamber structure, open-side, and closed-side settings, eccentric throw, and more.
INSIDE YOUR CONE CRUSHER
The basic principle is straightforward: the material to be crushed (the feed), drops into the crushing chamber. The mantle is a moving part that gyrates in an eccentric motion. That is, it does not remain completely centred – it swings slightly as it rotates, continually altering the gap between the mantle and the concave (the ring outside the mantle that stays fixed in place.) As the mantle moves, it crushes the material against the concave at the points where the gap is smallest (the stones in the feed are also compressed against each other – that’s known as interparticle crushing).
THE OPEN SIDE & THE CLOSED
As the feed is crushed, it falls and exits the crusher through the space at the bottom. The eccentric gyration of the mantle means that at any moment this space is narrowest at one point, and widest at the opposite point. The widest distance is known as the open side setting (OSS) and the narrowest, the closed side setting (CSS). These settings are important. The OSS is the largest distance between the concave and the mantle at the bottom of the crusher, so it determines the largest particle size of the outgoing product. As the smallest distance between the concave and the mantle, the CSS is the final crushing zone, and is vital for determining the product size, as well as energy consumption and crusher capacity.
KNOW YOUR FEED
It is hard to overstate the importance of feed size in a cone crusher. It is vital that you know, as accurately as you can, the size distribution of the raw material. The Sandvik CH cone crusher can be calibrated to achieve specific results, maximize productivity, and minimize wear, but any calculation will be undermined without a solid understanding of what is going into the crusher. Sampling is a vital part of the crushing process, to ensure that you know the size distribution of the feed. It is crucial that sampling is done regularly, especially when there are changes in blasting, mining, or any other upstream processes.
WHAT IS THE ECCENTRIC THROW?
The eccentric throw is one of the most important parameters in defining the job that your cone crusher does. The mantle in a cone crusher spins in conical pendulum motion. That means it doesn’t stay in the centre of the chamber – it sweeps around moving closer and further away from the concave. This is what creates the crushing action. At a given point on the concave, material is crushed when the mantle is closest, and it falls down the chamber when the mantle is furthest away.
HOW IT WORKS
The eccentric throw is the extent to which the mantle veers from its axis, so it defines the rate at which the material falls through the chamber. If your set-up has a high eccentric throw, then material will fall further with every rotation of the mantle – the mantle moves further away from the concave so there is more room for particles to drop.
You can think about this in terms of crushing zones. The height of a crushing zone is the distance a particle will fall during one revolution, so a chamber with a high eccentric throw will have fewer crushing zones – particles will fall further in one revolution. Thus, having a higher eccentric throw will deliver a coarser product, since it will have been crushed fewer times in its descent through the chamber.
The eccentric throw also defines a second parameter – the capacity of your crusher. A higher eccentric throw means fewer crushing zones, so the journey through the crusher is quicker. The quicker the journey through the crusher, the greater its capacity. Therefore, altering the eccentric throw settings significantly changes the way your crusher works – without making any adjustments to the concave. If you increase the eccentric throw, you can increase capacity. If you decrease the eccentric throw, your output will be less coarse.
Coarse output often has to be re-circulated, costing you time and money. Getting the right eccentric throw is about balancing these two factors – capacity and output gradation – to reach the most efficient overall outcome.
FIND THE BALANCE
Sandvik CH cone crushers help you find the balance between tonnage and exactness, by allowing you to change the eccentric throw quickly and easily. They are constructed with an adjustable eccentric bushing. By turning the keys on the bushing, you can easily change the eccentric throw to the one that best suits your goals, allowing you flexibility and versatility.
Article originally posted by Sandvik Rock Processing