How Much Do You Know About Spiral Classifier For Classifying Equipment?

In the beneficiation process, the ore needs to be ground to a certain fineness to fine-grained embedded useful minerals and veins fully dissociated and realize the separation, while avoiding excessive grinding to prevent sludge on the selection process has a negative impact, which requires classifying equipment will be grinding products in the particle size of the unqualified portion of the mill to return to the mill for cyclic milling, the particle size of the qualified portion of the timely separation out of the separation to the selection operation, to avoid unnecessary milling. From the technical and economic significance perspective, the classification operation in the grinding operation can be said to play a vital role.

Classifying Equipment

The classifying equipment with more applications in mineral processing plants mainly includes mechanical classifiers and hydrocyclone. Among them, the mechanical classifier contains a spiral classifier, a rake classifier, a floating tank classifier, and other types. With the continuous improvement of grading requirements, the rake classifier due to its complex structure and poor grading effect, is gradually replaced by the spiral classifier. The floating tank classifier due to its large footprint and low grading efficiency, is gradually replaced by the hydrocyclone. Therefore, the spiral classifier and hydrocyclone are the main choice for classification operations in today’s mineral processing plants. Although the rapid development of the cyclone once made the spiral classifier lose its importance, with the changing needs of the beneficiation plant, it has been found that the spiral classifier also has its superiority.

Spiral Classifier

The spiral classifier is primarily used in mineral processing to separate materials based on particle size by utilizing a rotating spiral screw within an inclined trough, where larger particles settle to the bottom and are carried upwards by the spiral, while finer particles overflow with the water at the lower end; essentially, it classifies materials based on their settling velocity in a water slurry, with coarser particles being separated from finer ones.

Spiral Classifier Advantages

• The returned sand is automatically lifted to a certain height and then directly returned to the feeding end of the ball mill, eliminating the need for a combined feeder and greatly saving the investment in equipment and civil construction;
• The continuity and stability of sand return and the high concentration of sand return are conducive to increasing the concentration of grinding ore, and thus improving the grinding efficiency;
• The grading size can be controlled according to the different feeding quantities and overflow concentrations;
• Simple structure, convenient operation and management, reliable operation, and low maintenance cost.

Spiral Classifier Types

According to the overflow weir height

According to the overflow weir height, that is, the position of the spiral in the flume is different from the height of the slurry surface, the spiral classifier can be divided into three types: high weir type, low weir type, and sinking type. 

• High weir spiral classifier
  The overflow weir position of high weir spiral classifier is usually higher than the bearing center at the lower end of the spiral shaft, and lower than the upper edge of the spiral at the overflow end, so its settling area is larger than that of the low weir spiral classifier, and the weir height can be adjusted within a certain range, i.e., the area of the settling area can be changed a little according to the grading demand, to regulate the grading granularity.
• Low weir spiral classifier
  The low weir spiral classifier overflow weir is often lower than the center of the overflow end bearing, so the area of settlement area is too small, the overflow production capacity is too low, and the stirring of the spiral on the slurry surface is large, so it is only used for flushing the sand ore and coarse grains dewatering that contain little mud in actual production, and is seldom used in milling and classification operations.
• Submerged spiral classifier
  The submerged spiral classifier overflow ends generally with 4-5 turns of spiral blades, all spiral blades are submerged under the liquid surface in the settling area, so the area of the settling area is a large, deep grading pool.

Due to the difference in structure between the high weir type and submerged spiral classifier, the two play different roles in grading operations. High weir spiral classifier is more suitable for separating coarse grains with a particle size larger than 0.15mm, often used in the first stage of milling; while the submerged spiral classifier is more suitable for separating overflow products with a particle size smaller than 0.15mm due to its smooth grading surface, high overflow yield and fine particle size, often used in the second stage of milling to form a joint unit with the mill.

According to the number of spiral shaft

According to the number of spiral shafts, the spiral classifier can be divided into single spiral and double spiral. The grading performance of the two is the same, but the double spiral classifier in the sand processing capacity, overflow processing capacity, and the same specification spiral diameter are significantly larger than the single spiral classifier. And the price of the double spiral classifier is much higher than the single spiral classifier. So it is more suitable for large-scale milling machines with the use.

Mineral processing experts suggest that the single spiral classifier should be used as much as possible under the determined processing capacity. According to statistics, the spiral working load of the double spiral classifier is 0.6-0.75 times of the single spiral classifier, and the efficiency is relatively low. Therefore, when choosing the spiral classifier, it is necessary to determine its appropriate spiral speed and number according to the processing capacity.

The various types of classifying equipment mentioned above have their advantages and have different degrees of influence on the classification efficiency of the equipment. For the current different classification needs, different types of classifying equipment have been optimized and improved accordingly, to obtain good classification results. Each plant selection in the classifying equipment must grasp the characteristics of its type and working principle, combined with their plant production needs to consider the ideal process and equipment.