Should I go for 2 stage or 3 stage crushing? That’s a question we always get asked.
By the way, what’s 2 stage or 3 stage crushing anyway? That’s another common question that may be asked. That question is easier to answer. 2 stage crushing involves just 2 crushers in a crushing plant, i,e, a primary crusher and a secondary crusher. This is usually, although not always, a jaw crusher and a cone crusher.
3 stage crushing just means that there are 3 crushers within the crushing plant. Usually, this consists of a primary jaw crusher, a secondary cone crusher, and a tertiary cone crusher.
Now back to the 1st question. Should you go for 2 stage or 3 stage crushing? Apart from the required size reduction criteria, the answer to this question also involves several considerations such as possible space constraints, capital and operational costs considerations.
Understanding Reduction Ratios and why it is Important?
Reduction ratio is simply the ratio of the size of input material fed into a crusher compared to the size of output materials from the same crusher. As a general guideline, for jaw crushers and cone crushers, a reduction ratio of 4 is considered a good number to work with.
For example, when feed material size into a crushing plant is minus 500mm and the desired size of the end products is minus 32mm. Then, 2 crushers may be enough to produce the end products cost effectively and in accordance to the required product quality, i.e. product shape. This is because the primary jaw crusher with an ideal reduction ratio of 4 will crush and reduce the minus 500mm feed material to output material of minus 125mm. In turn, the secondary cone crusher, similarly with an ideal reduction of 4, will be fed with this minus 125mm material and produce an output of minus 32mm end products.
However, if the feed material size into a crushing plant is minus 500mm and the desired size of the end products is minus 25mm or 20mm, then it might be time to consider 3 stage crushing. If you attempt to produce minus 25mm or 20mm end products with just 2 crushers, then you would be over-extending the capabilities of the crushers and they might not be optimally utilised.
The same goes for particularly harder material to be crushed. Attempting to use only 2 crushers, might result in crushers that are not operating optimally within their ideal crushing range. This will lead to higher operating costs due to higher rate of wear of parts.
When to go for 2 Stage Crushing?
2 stage crushing is best chosen when production capacity requirements are relatively low, material to be crushed is relatively soft, capital budget is limited, or when there is space constraints for a crushing plant. However, we have to be aware of the disadvantages that come with this option. This option often generates more fines and increases the wear on the crusher wear parts. Perhaps the biggest concern to any crushing plant owner is that end products may not be cubically shaped. There is a higher tendency for the end products from a 2 stage crushing plant to be flakier when compared to those from a 3 stage crushing plant.
When is 3 Stage Crushing suitable and why do we usually recommend it?
The 3 stage crushing plant will be more expensive during the initial purchase, when compared to a 3 stage crushing plant. However, the biggest advantage is that it results in better quality end products. As long as the tertiary cone crusher is constantly feed-choked, end products will likelier be cubically shaped. Tonnages can be maintained. Fines production and crushing wear rates can be kept to a minimum.
Although, the best argument for 2 stage crushing is usually that it saves initial capital expenditure. However, over the mid to long term, these savings are usually negated with relatively lower end product quality and production capacity. Inevitably, lower quality end products usually means lower returns in terms of lower selling prices to the market.
All crusher are built to ideally perform within a narrow closed side setting range. With 3 stage crushing, we are often able to operate crushers at a larger closed side setting (CSS) that are within their respective optimal ranges.. If they are made to operate constantly in non-optimal closed side setting ranges, output tonnages will be limited and there will be an inevitable increase in cost per ton of production. Not to mention more frequent changing of wear parts. This is because when a crusher operates at a smaller CSS, over any given period time, the wear parts will need to be changed more frequently in order to maintain that CSS setting. This means that the crushing plant owner will not be maximising the returns on his initial investment, even if it was a smaller.
In short, it is best to seriously consider a 3 stage crushing plant for your next investment. The benefits to product quality and production capacity often outweigh the cost of the initial investment.