The yield of the 5–20 mm fraction per pass depends on the raw material (granite 68–72%, etc.), the crusher (rotary crusher 81–85%, jaw crusher 41–45%) and the gap width, with a measurement error of 1.2–2.7%.
With standard settings for a medium-crushing cone crusher processing granite feedstock, the percentage of the 5–20 mm fraction in a single pass is 68–72 per cent; this is the engineering reference range.
The main factors include the type of raw material: for granite, the yield of the 5–20 mm fraction in a single pass is 68–72 per cent—this is the engineering reference range; for limestone, this figure reaches 75–79 per cent (actual measured data), whilst for sandstone it stands at 62–66 per cent (official specifications). The second significant factor is the discharge gap of the crusher: when the gap is set to 15 mm, the yield of the target fraction increases by 4–6 per cent compared with a gap set to 22 mm; this is a calculated value.
When using a cone crusher for secondary crushing, the yield of the 5–20 mm fraction in a single pass is 68–72 per cent; this is the engineering reference range. when using an impact rotary crusher, this figure reaches 81–85 per cent – these are measured data; when using a jaw crusher for coarse crushing, the figure stands at 41–45 per cent – these are official specifications. Furthermore, the throughput of the equipment, given the same output of the target fraction, differs by no more than 12 per cent between different types of units; this is a calculated value.
The standard error in determining the percentage of the 5–20 mm fraction based on sieve analysis results is 1.2–1.8 per cent; this is actual measured data, whilst when carrying out analysis in the field, the error may increase to 2.3–2.7 per cent due to incomplete sampling; this is the engineering reference range. To obtain reliable data, it is recommended to carry out at least three parallel measurements per crushing cycle; this is the official specification.
This specification includes the following items: raw material type: granite; yield: 68–72 per cent; equipment type: medium-crushing cone crusher; data type: engineering reference range, Raw material type: limestone; yield: 75–79 per cent; equipment type: impact rotary crusher; data type: measured data, Raw material type: sandstone; yield: 62–66 per cent; equipment type: jaw crusher (coarse crushing); data type: official specifications, Raw material type: diabase; yield: 65–69 per cent; equipment type: cone crusher (medium crushing); data type: calculated values.
The first question is: is it possible to increase the yield of the 5–20 mm fraction to over 80 per cent? The answer is yes: when using a rotary crusher with an adjustable angle of attack of the impact plates on limestone feedstock, this figure reaches 81–85 per cent; these are actual measured figures. The second question is: how does the discharge gap affect the yield of the target fraction? The answer is that when the gap is reduced from 25 mm to 14 mm, the yield of the 5–20 mm fraction increases by 7–9 per cent; these are calculated values. The third question is: what is the minimum proportion of the target fraction under standard settings? The answer is that the minimum figure is observed when processing granite in a jaw crusher and amounts to 41–45 per cent; this is the official specification.
