How do raw material characteristics affect product particle size during crushing?

In the crushing process, the raw material characteristics are one of the core factors affecting the product particle size. Its physical and chemical properties will directly change the crushing difficulty, crushing method and particle distribution. Today, Shengbang Machinery will analyze the impact mechanism and response strategies of raw material characteristics on product particle size from six key dimensions.

1. Hardness and compressive strength
Influence mechanism
The higher the hardness (such as Mohs hardness ≥ 6), the greater the crushing force required for crushing. Under the same equipment parameters, the product particle size is coarser and it is easy to cause equipment wear (such as the wear rate of jaw plate and hammer increases by more than 30%).
Low hardness ore (such as fluorite Mohs hardness 4) has low crushing energy consumption and is easy to produce fine particles, but the particle size distribution may be uneven due to insufficient crushing force.
Coping strategy
1. Equipment selection to match hardness
High hardness ore (such as iron ore): Cone crusher (laminated crushing, large crushing force) is preferred, the discharge port can be set to 15-30mm, and the fine crushing cone crusher can be used to achieve a particle size of ≤10mm.
Low hardness ore (such as fluorite): Impact crusher (impact crushing, high proportion of fine particles) can be used, the rotor speed is increased to 1500r/min, and the screen plate aperture is set to 5mm to control the fine particle size.
2. Adjustment of the crushing ratio of segments
For high-hardness ores, the crushing ratio of coarse and medium crushing needs to be increased (e.g., the coarse crushing ratio is increased from 5 to 7) to avoid excessive load in the fine crushing stage.
2. Mineral structure and dissociation characteristics
Influence mechanism
Ores with developed bedding (such as schist-type fluorite ore) are easy to crack along the bedding plane during crushing, and the product particle size is uniform and the fine particle content is high (-5mm can account for more than 60%).
Dense block structure ores need to overcome more internal chemical bonds during crushing, which is easy to produce coarse particles and needle-like particles (needle-like content can reach 25%), and the over-crushing rate is low.
For ores containing fissures, the fissures reduce the difficulty of crushing, but the uneven distribution of fissures may cause fluctuations in product particle size (such as the fluctuation of -3mm particles in the same batch of ore by ±15%).
Countermeasures
1. Optimize the crushing chamber type
Ores with developed bedding: Use impact crushers (use impact energy to crush along the bedding) and configure circular vibrating screens (screen surface inclination 20°) to improve the efficiency of fine particle screening.
Dense ores: Use cone crushers (laminated crushing + slow extrusion), and use vertical shaft impact crushers (VSI) to reduce needle-like particles (controllable to ≤10%).
2. Pre-screening to remove fissure ores
Pre-screening (aperture 10mm) is used to separate fragile fine particles to avoid excessive crushing.
3. Moisture content and mud content
Influence mechanism
When the moisture content is ≥8%, fine particles tend to agglomerate into “mud balls”, blocking the crushing chamber and screen (such as the vibrating screen penetration rate drops from 85% to 50%), resulting in coarse particles in the product carrying fine mud, and the actual effective particle size becomes coarser.
After the sticky minerals (such as clay-containing fluorite) agglomerate to form a “buffer layer”, the efficiency of crushing force transmission is reduced, and the proportion of coarse particles increases by 20%-30%.
When the mud content is ≥15%, the mud fills the gap in the crushing chamber, hindering the effective crushing of coarse particles, and the mud and qualified particles cannot be distinguished during screening, resulting in a decrease in the qualified rate of product particle size.
Countermeasures
1. Drying and ore washing pretreatment
High-water content ore (such as open-pit fluorite): first dried by a drum dryer (inlet temperature 600℃, outlet moisture content ≤5%).
High-mud ore: A combination of a trough ore washer + a spiral classifier is used to remove -2mm mud (mud content ≤5% after washing) to avoid affecting crushing and screening.
2. Anti-sticking design
An anti-sticking coating (such as polytetrafluoroethylene) is used on the inner wall of the crushing chamber, and the screening machine is replaced with a large-aperture polyurethane screen (such as 8mm aperture, the opening rate is increased to 75%) and an ultrasonic screen cleaning device is installed.

4. Feeding particle size composition
Influence mechanism
The proportion of coarse particles in the feed is too high (such as + 300mm particles> 30%), and the jaw crusher needs to be overloaded frequently, resulting in the instantaneous expansion of the discharge port and the fluctuation of the particle size of the coarse crushing product (such as from ≤200mm to ≤250mm).
The feeding of the medium crushing equipment (such as cone crusher) is uneven, the lamination crushing effect is deteriorated, and the proportion of + 50mm particles in the product increases by 15%.
The feeding particle size is too uniform (such as 80% is 100-150mm), which is easy to form “single particle crushing” during crushing, the fine particle content is low (-10mm accounts for <20%), and the energy consumption utilization rate is low.
Coping strategy
1. Pre-screening to control the feed gradation
Set a fixed grid screen (aperture 300mm) before coarse crushing to remove oversized materials (>500mm) to avoid blockage.
Use a vibrating screen to grade the material before feeding (e.g., the screen hole is 80mm), and divide the material into two levels: <80mm and 80-300mm, and enter different crushing paths respectively to balance the equipment load.
2. Reasonable setting of crushing ratio
When the proportion of coarse particles in the feed is high, the coarse crushing ratio is increased from 5 to 6, and the medium crushing ratio is reduced from 4 to 3.5 to avoid single-stage load overload.
V. Mineral density and shape
Influence mechanism
High-density ore (such as fluorite ore containing barite, density > 3.0t/m³), under the same crushing force, the particle inertia is large, the crushing difficulty increases, and the product particle size is coarsened (e.g., under the same conditions, the proportion of -5mm particles is 10%-15% lower than that of low-density ore). “Bounce over-crushing” is easy to occur during impact crushing, resulting in an increase in over-crushing rate (e.g., 15% of -0.1mm fine mud is mixed in +0.5mm particles).
Flake or plate-like particles (such as shale-type fluorite) are easy to break along the short axis during crushing, and the proportion of flake particles in the product is high (up to 40%), which affects subsequent processes (such as reduced reagent adsorption efficiency during flotation).
Countermeasures
1. Adjust the direction of crushing force
High-density ore: Use cone crusher (vertical extrusion crushing) instead of impact crusher to increase the crushing force action time (from 0.1s to 0.3s) and improve crushing efficiency.
Flake ore: Use roller crusher (shear + extrusion) or vertical shaft impact crusher (high-speed impact + self-grinding) to shape and reduce flake particles (can be reduced to ≤20%).
2. Combination of grading and sorting
After crushing, use a shape screen (such as an elliptical hole screen, long axis / short axis = 2:1) to separate the flake particles and return them to the crusher for re-crushing.
VI. Raw material humidity and temperature
Special scenario impact (such as low temperature or high temperature ore in winter)
In low temperature environment (<0℃), ore with moisture content >5% is easy to freeze into blocks, forming “ice inclusions” during crushing, resulting in finer measured particle size after crushing (particles disperse after ice melts), but the actual effective mineral particle size is coarsened.
For high temperature ore (such as smelting slag waste heat ore, temperature >200℃), the bearings of crushing equipment are prone to overheating (temperature >80℃), and are forced to reduce the speed (such as cone crusher speed from 300r/min to 200r/min), resulting in coarser product particle size (+10mm particle proportion increases by 25%).
Coping strategy
Temperature pretreatment
Low temperature ore: Thaw in the preheating bin (temperature 15-20℃) for 2 hours before crushing, and the moisture content drops to below 3%.
High-temperature ore: first cool it down by air cooling (cooling to <50℃) to avoid overheating of the equipment and prevent over-crushing caused by thermal embrittlement of the ore (for example, when the temperature is >300℃, the -0.1mm fine powder increases by 30%).

Raw material characteristics change the crushing energy consumption, particle force mode and equipment working state, which ultimately affects the coarseness, uniformity and shape of the product particle size. In actual production, it is necessary to establish a “raw material characteristics database” to monitor the hardness, moisture content and other indicators of the ore in real time, dynamically adjust the crushing parameters (such as discharge port, rotation speed, crushing ratio), and eliminate adverse effects through pretreatment (ore washing, drying, grading) to achieve precise control of particle size. If you have more questions about production line configuration and equipment selection quotation, you can contact Shengbang Machinery WhatsApp +8613949025317 for more details