Spiral Classifier Overview

The spiral classifier is one of the equipment for mineral processing. It is a kind of equipment for mechanical classification based on the principle that the specific gravity of solid particles is different and therefore the precipitation speed in the liquid is different. It can filter the powder ground in the ball mill, and then use the spiral blades to rotate the coarse material into the mill feed port, and discharge the filtered fine material from the overflow pipe.

Benefits of Using A Spiral Classifier

Why choose a mechanical screw over a simple screen or a high-tech cyclone? The answer lies in operational steadiness.

• 1. Stability in Closed Circuits:The classifier acts as a buffer. If the ball mill surges or the feed rate fluctuates, the large pool of the spiral classifier absorbs the shock. It delivers a consistent overflow density to the next stage, which is critical for flotation efficiency.
• 2. No Auxiliary Pressure Needed:Unlike Hydrocyclones, which require high-pressure slurry pumps that consume massive electricity, the Spiral Classifier works via gravity. The slurry flows in, and the sand is lifted mechanically.
• 3. Sand Return is Automatic:The machine elevates the clean sand high enough so it can slide back into the Ball Mill feed chute by gravity. This eliminates the need for an extra pump or conveyor belt for the return load.
• 4. Washing and De-sliming:Beyond sizing, the agitation of the screw washes the sand. It effectively scrubs clay and slime off the ore particles, acting as a high-capacity washing machine.

What are Different Classification of Spiral Classifier?

Not all classifiers utilize the same design. The choice depends on the required particle size of the overflow (separation mesh).

1. High Weir Spiral Classifier:

• Design: The top of the spiral blades at the lower end is higher than the overflow liquid level. The spiral is not fully submerged.
• Application: Used for Coarse classification (particle size > 0.15mm / 100 mesh). The settling area is smaller, so coarse particles settle out while only fines overflow.
• Common Use: First stage grinding or silica sand washing.

2. Submerged Spiral Classifier:

• Design: The changing weir is high, and the spiral blades at the lower end are completely underwater.
• Application: Used for Fine classification (particle size < 0.15mm / 200 mesh). The deep pool creates a large quiet zone, allowing even fairly fine particles to settle, so only the very finest mud overflows.
• Common Use: Second stage grinding or maximizing recovery of fine minerals.

What is a Spiral Classifier Used For?

The Screw Classifier is versatile across the mining and aggregate sectors.

• 1. Mineral Processing (Closed Circuit Grinding):This is the primary function. It works in tandem with a Ball Mill. The classifier ensures that no huge rocks enter the flotation cells and no fine dust stays in the mill. It increases the capacity of the grinding circuit by 30-50%.
• 2. Silica Sand Washing:For glass manufacturing or construction sand, the product must be free of clay and silt. A classifier acts as a Sand Washer. It agitates the sand, rubs particles together to remove impurities, and lifts the clean sand out while the dirty clay water overflows.
• 3. De-sliming and De-watering:Before processing certain ores (like phosphate), removing the “slime” (ultra-fine clay) is necessary because it consumes chemical reagents. The classifier effectively separates this slime.
• 4. Phosphate and Coal Washing:Similar to metal mining, these industries use classifiers to separate waste shale from the valuable product based on density and size.

Spiral Classifier Advantages

• The energy consumption of spiral classifier is 50% lower than other classification equipment, and the output is also increased by 50%.
• The water tank has a large slope, which is convenient for forming a closed-circuit ring grinding operation with the ball mill, and forms a self-flow sand return.
• Simple operating process and stable working status, greatly reducing maintenance costs.
• Its spiral structure can ensure a large enough settling area to extend the material suspension time, which is more conducive to the even distribution of materials during the classification process.
• Users can adjust the parameters of the spiral classifier according to their needs, such as spiral speed, inclination and outlet size to achieve different classification requirements.

What are the Key Components of Spiral Classifier?

The machine’s rugged simplicity is its engineering virtue.

• 1. The Tank (Trough):A long, U-shaped steel vessel. It is set at an incline (usually 12-18 degrees). ZONEDING reinforces the tank with channel steel to prevent twisting under load.
• 2. The Main Shaft and Spiral (Screw):A massive hollow shaft runs the length of the machine. Spiral flights (discs) are welded onto it.
  • Wear Liners: The edges of the spiral are covered with cast iron or TPU (High-performance polyurethane) wear plates. These are the parts that touch the rock, and they are replaceable.
• 3. The Drive Unit:A motor and a heavy-duty gearbox reduce the speed to a slow rotation (usually 4-8 RPM).
• 4. The Lifting Mechanism:This is a critical safety feature. It can be electric or manual. If the power fails, the slurry in the tank settles and turns into cement. The lifting mechanism lifts the entire screw shaft out of the “sand trap” instantly. This allows the operator to restart the machine without snapping the shaft.

Main structure of the Spiral Classifier

The spiral classifier mainly consists of the following components:

• Transmission Device: Includes an electric motor, reducer, cylindrical gear pair, and bevel gear, responsible for driving the rotation of the spiral.
• Spiral Body: Composed of a hollow shaft, supports, spiral blades, and lining iron, which is the main working part of the classifier.
• Tank: Holds the entire slurry and bears the weight of the machine and all its loads. Constructed by welding steel plates and various steel sections.
• Lifting Mechanism: Used to raise or lower the spiral for maintenance or to adjust the processing level within the tank.
• Lower Bearing (Bushing): Supports the spiral and bears the load during operation.
• Discharge Valve: Located at the bottom of the tank, allowing the slurry to be drained when necessary.

How Does the Spiral Classifier Work In Mineral Processing Plant?

The operation relies on Stokes’ Law regarding terminal settling velocity.

• 1. Feeding:Slurry from the Ball Mill enters the classifier tank from a side inlet located in the middle of the pool.
• 2. Sedimentation:The heavy, coarse grain sands sink to the bottom of the U-shaped tank. The light, fine grains flow toward the bottom end of the tank in the upper layer of water.
• 3. Conveying (The Screw):The rotating spiral scrapes the settled sand from the bottom. It conveys this sand up the incline. As the sand moves up, water drains out of it back into the pool (dewatering).
• 4. Discharge:
  • Sands (Underflow): The coarse sand reaches the top and falls into a chute, which guides it directly back into the ball mill inlet for re-grinding.
  • Overflow: The fine suspended particles drift over the weir at the bottom and flow by gravity to the Agitator Tank or Flotation Machine for the next stage of extraction.

Principle of Spiral Classifier 

Technical Parameter of Spiral Classifier

Model	Spiral  Diameter (mm)	Trough  Length (mm)	Spiral  rotate  speed (r/min)	Processing  capacity（t/d）		Motor  Power （kw）		Dimensions （mm≤）			Total  weight （t）
				Sand -return	Overflow	For  driving	For  lifting	Length	Width	Height
FG-3	300	3000	12-30	80-150	20	1.1	—-	3850	490	1140	0.7
FG-5	500	4500	8-12.5	135-210	32	1.1	—-	5430	680	1480	1.9
FG-7	750	5500	6-10	340-570	65	3	—-	6720	980	1820	3.1
FG-10	1000	6500	5-8	675-1080	110	5.5	—-	7590	1240	2380	4.9
FC-10		8400		675-1080	85	7.5	—-	9600	1240	2680	6.2
FG-12	1200	6500	4-6	1170-1870	155	7.5	2.2	8180	1570	3110	8.5
FC-12		8400		1170-1870	120	7.5	2.2	10370	1540	3920	11.0
2FG-12		6500		2340-3740	310	15	4.4	8230	2790	3110	15.8
2FC-12		8400		2340-3740	240	15	4.4	10370	2790	3920	17.6
FG-15	1500	8300	4-6	1830-2740	235	7.5	2.2	10410	1880	4080	12.5
FC-15		10500		1830-2740	185	7.5	2.2	12670	1820	4890	16.8
2FG-15		8300		2280-5480	470	15	4.4	10410	3390	4080	22.1
2FC-15		10500		2280-5480	370	15	4.4	12670	3370	4890	30.7
FG-20	2000	8400	3.6-5.5	3290-5940	400	11-15	3	10790	2530	4490	20.5
FC-20		12900		3210-5940	320	11-15	3	15610	2530	5340	28.5
2FG-20		8400		7780-11880	800	22-30	6	11000	4600	4490	35.5
2FC-20		12900		7780-11880	640	22-30	6	15760	4600	5640	48.7
FG-24	2400	9130	3.67	6800	580	15	3	11650	2910	4970	26.8
FC-24		14130		6800	490	18.5	4	16580	2930	7190	41.0
2FG-24		9130		13600	1160	30	6	12710	5430	5690	45.8
2FC-24		14130		13700	910	37	8	17710	5430	8000	67.9
2FG-30	3000	12500	3.2	23300	1785	40	8	16020	6640	6350	73.0
2FC-30		14300		23300	1410	—-	—-	17091	—-	8680	84.8