Ask a plant operator why a cone keeps choking or why a jaw keeps throwing out oversize lumps. The answer often goes back, to one number that no one wrote on the wall. That number is the crusher reduction ratio. The crusher reduction ratio is the key that explains the problem. The crusher reduction ratio gives an idea of how small a piece of equipment is required to crush the stone in a single stage. If you use a wrong crusher reduction ratio, you will have to face consequences in terms of productivity, higher wear and lower product quality.
What Is Reduction Ratio in Crushing?
Crushing ratio is defined as the relationship between the size of rock entering a crushing chamber and the size of output material. For instance, when crushing ratio is said to be 5:1, then the biggest pieces that leave the chamber will be about five times smaller in comparison to their size when entering the chamber. It can be simply described as the ratio between feed and output sizes. So any published ratio is best read as a typical range, not a fixed property of the machine.
Crushing Ratio Formula
The crushing ratio formula is simple: reduction ratio equals feed size divided by product size. Plants usually measure feed and product using the lump or the size that 80 percent of the material passes through. The key is to use the method for both measurements. For example if a jaw crusher gets 600 mm rock. Produces material thats 120 mm the ratio is 600 divided by 120 which is 5 to 1. Then if a cone crusher takes that 120 mm material. Reduces it to 20 mm its ratio is 120 divided by 20 which is 6 to 1. When you look at the process the overall reduction is 600 mm divided by 20 mm which equals 30 to 1. That is also the same, as multiplying the two ratios 5 times 6 equals 30. Stage ratios multiply, so the total is always worked out one stage at a time.
Jaw Crusher Reduction Ratio
The jaw crusher reduction ratio tends to be low as a jaw only crushes large pieces between two plates one time. Jaw crushers operate between 4:1 and 6:1 in the primary crushing process, depending on the type of the feed, the gap and the shape of the plates; therefore, ensure you get the ratio for your machine from the manufacturer. All that a jaw crusher does is provide an opening for large feed. Both Single Toggle and Double Toggle models are covered on the Jaw Crusher page.
Cone Crusher Reduction Ratio
The cone crusher reduction ratio is where the PICS website gives a clear rule of thumb. A cone with coarse-style liners typically gives about 6:1, and 8:1 may be possible in some coarse crushing applications. In the site’s own example, a ¾ inch closed side setting means the maximum feed is 6 × ¾, or 4.5 inches. Feed larger than that pushes the crusher outside its range. The chamber profile has a big say in the final number too, so a cone set up for fine work behaves differently from one built for coarse feed. The range is listed on the Cone Crusher page.
Why Reduction Ratio Matters in Aggregate Crushing?
In aggregate crushing the ratio decides how many stages you need and how hard each one works. Push one machine past its comfortable ratio and you get lower throughput, faster wear and more fines than you wanted. Set it too low and you end up running extra stages for no gain. PICS says its HP Series cones can produce finer product while limiting crushing stages, which lowers investment cost and saves energy. The ratio also drifts as liners wear. When the setting opens up, the product turns coarser and more material goes back around the circuit as circulating load, so watching the ratio over time is a cheap way to catch wear before it shows in the production report. For a complete staged plant, see the 200 TPH 3 Stage Aggregate Crushing page, which describes a jaw crusher, cone crusher and vertical shaft impactor.
What to Check Before Fixing the Ratio
| Factor | What to Check |
|---|---|
| Feed size | Largest lump and typical size range |
| Product size | Target size for the next stage or the final product |
| Closed side setting | Current CSS and how often it is measured |
| Liner condition | Wear on jaw plates or cone liners |
| Rock type | Hardness, abrasiveness and moisture |
| Number of stages | How the total reduction is split across stages |
Conclusion
Crusher reduction ratio is worth checking regularly. Work it out stage by stage, compare it with what each machine is designed for, and measure again as liners wear. Do that and the plant runs with fewer surprises, whichever crushers sit in the circuit. If you are planning the stages of a new line or reviewing an existing one, you can reach the PICS International team through the Contact Us page.