What Is The Rotational Speed Of The Crushing Teeth Of The Mineral Sizer

The rotational speed of the rollers in the Mineral sizer is a key parameter of the equipment, but it does not have a fixed value. Instead, it is set based on various factors. The setting of the rotational speed of the crushing teeth rods directly affects the crushing efficiency, product particle size, and the wear degree of the Mineral sizer.

Speed range

Generally speaking, the rotational speed of the mineral sizer used for mineral crushing is relatively low, typically ranging from 15 to 60 RPM (revolutions per minute). This range is lower than that of similar equipment used for crushing coal or other soft materials.

Low-speed range (15-30 RPM): Often used for processing hard and abrasive ores (such as iron ore, copper ore).

Medium-speed range (30-50 RPM): Used for medium-hard or viscous materials.

Higher speed (>50 RPM): May be used for softer or non-abrasive materials, but is less common in mineral processing.

Factors determining the rotational speed

Material characteristics

Hardness and abrasiveness

This is the primary consideration. The harder the material and the stronger its abrasiveness, the lower the rotational speed should be. High rotational speed will intensify the impact and wear between the toothed rollers and the hard material, leading to a sharp decline in the lifespan of the crushing teeth, generating excessive powder, and potentially damaging the mineral sizer.

Feed particle size

The larger the feed size, the greater the crushing force required. Usually, a lower rotational speed is needed to provide higher torque (shear force) for “slow work produces fine results” extrusion and shearing crushing.

Output particle size requirements

If there is a strict upper limit on the product particle size (i.e., no large particles are allowed), the rotational speed can be appropriately increased because a higher rotational speed means more material passes through the crushing chamber per unit time and more “checks” on the material, which helps control the maximum particle size.

Humidity and viscosity

For moist and viscous materials, high rotational speed may cause the material to adhere to the toothed rollers, resulting in blockage. At this time, a lower rotational speed may be required, and special tooth shapes (such as self-cleaning teeth) may be combined to solve the problem.

Crushing Principle and Mechanism

The core crushing principle of Mineral Sizer is “quasi-static pressure shearing”, which mainly relies on huge shear force and compression to crack and shred the materials, rather than relying on high-speed impact like hammer crushers.

Low speed = high torque, high shear force: By reducing the rotational speed, the power provided by the motor can be more fully converted into huge torque, which is crucial for shearing large and hard materials.

High speed = high impact, more powder: Increasing the rotational speed will increase the component of impact crushing, which not only accelerates wear but also generates excessive powder (-0.5mm), which may not be the desired product.

Design and Specifications

Roller Diameter

This is an important design parameter. At the same line speed, the larger the roller diameter, the lower its rotational speed (RPM). The equipment manufacturer has already determined the relationship between the roller diameter and the applicable speed range during the design process.

Drive Power

Speed and torque jointly determine power (power ≈ torque × speed). When the motor power is fixed, choosing a lower speed can result in higher available torque.

Gear Design and Arrangement

Different gear shapes (such as bullet-shaped, eagle-beak-shaped, etc.) and arrangements (spiral arrangement, checkerboard arrangement) have an impact on the “engagement” ability of the material and the crushing efficiency, and also affect the selection of the optimal speed.

Processing Capacity Requirements

Theoretically, under the condition that all other factors remain unchanged, increasing the rotational speed will accelerate the movement of materials through the crushing chamber, thereby enhancing the processing capacity. However, such an increase comes at a cost (as mentioned earlier, wear and increased powder content). Therefore, a balance needs to be struck between meeting the production output and ensuring economic efficiency (such as spare parts costs and energy consumption).

The Impact of Roller Speed Adjustment on the Production Capacity of Mineral Sizer

The adjustment of roller speed does not follow a simple linear relationship of “the higher the speed, the greater the production capacity”. Instead, it is a complex balance with an optimal range, and its impact on production capacity has both positive and negative aspects.

Positive impacts

Increased material flow rate

The higher the speed, the more materials pass through the crushing chamber per unit time, which is equivalent to accelerating the conveying speed and increasing the instantaneous feeding volume. This theoretically increases the production capacity.

Improved throughput

For some materials with good fluidity and not prone to adhesion, a higher speed helps to discharge the already crushed materials from the discharge outlet more quickly, reducing the retention in the crushing chamber, creating space for subsequent materials to enter, and thereby improving the overall throughput efficiency.

Negative impacts

“Regrinding” or “Over-milling”

Shortened residence time

The time that materials are held, squeezed and sheared by the toothed rollers in the crushing chamber is reduced. This may cause large chunks of materials to be discharged without being fully crushed, resulting in substandard large-sized products. These large products need to be returned to the mineral sizer for further processing (i.e., “regrinding”) during the closed-loop cycle. This actually increases the actual load of the mineral sizer, but does not increase the output of final qualified products.

Increased proportion of impact crushing

Excessive rotational speed will cause the crushing mechanism to shift from the efficient “quasi-static shear” to the less efficient “impact crushing”. This not only intensifies wear but also generates excessive fine powder (over-milling), which may not be the products demanded by the market, thus wasting energy and capacity.

Accelerate wear and reduce operational continuity

The higher the rotational speed, the more times the gear rollers collide and rub against the hard materials. This directly leads to an exponential increase in the wear rate of easily damaged parts such as the crushing teeth and the shaft sleeves.

Faster wear means:

More frequent shutdowns for replacement

The mineral sizer cannot operate continuously, the effective operation rate decreases, and the total actual production capacity (measured in days and weeks) does not increase but decreases instead.

Maintenance costs soar

The costs of spare parts and labor increase significantly.

Increased energy consumption, reduced efficiency

To drive at a higher speed, more energy is required to overcome the inertia force of the material and the increased friction losses.

At the same time, due to the reduced crushing efficiency (more energy is wasted on impact and friction heat generation rather than being used for effective crushing), the energy consumption per unit output (kWh/ton) will significantly increase, making production uneconomical.

Equipment vibration and overload risk

At high speeds, if extremely hard or non-crushable objects (such as iron) are encountered, the impact force will be greater, which is likely to cause violent vibration of the mineral sizer, even leading to the breakage of safety pins or overload shutdown of the motor, resulting in unplanned downtime.