Several Analyses on Improvements to Screw Conveyors

Release time:

2021-06-24

In the operation of screw conveyors, there is still a significant issue of high breakage rates for the materials being conveyed—especially when conveying leguminous materials. The primary reason is that the clearance between the screw blades and the conveyor casing exceeds the thickness (or even the height) of the material being conveyed, leaving gaps in the middle of the material stream during transport. Due to the high rotational speed, high rigidity, and high bending stiffness of the central shaft, the shaft tends to vibrate under the influence of centrifugal force. As the spiral blades fixed to the central shaft cut through the material, the breakage rate of the conveyed materials increases dramatically. At the same time, the sharp edges of the screw blades can also damage the material itself. To address the problem of excessive material breakage in screw conveyors, the following aspects should be carefully considered:

Reduce the spindle speed;

The screw conveyor increases the core shaft diameter to enhance its stiffness.

The screw conveyor reduces the clearance between the screw blades and the casing.

The screw conveyor adds one or more supports to the spindle.

When the rotational speed of the screw conveyor’s main shaft is reduced, although this can help minimize shaft vibration, to maintain the original production rate essentially unchanged, the solution involves increasing the diameter of both the housing and the screw blades—albeit at the cost of higher expenses and a larger overall machine size. Moreover, this approach is applicable only to the production of new products; it cannot be implemented on existing user equipment.

Increasing the diameter of the screw conveyor’s core shaft can enhance its stiffness and reduce shaft vibration. However, excessively increasing the core shaft diameter does not significantly improve stiffness—especially when the core shaft is long, this effect becomes even more pronounced. Not only does this lead to higher costs, but it also fails to deliver noticeable improvements.

Reducing the clearance between the spiral blades and the casing—specifically, making it smaller than the thickness of the material being conveyed—can prevent material from accumulating at the blade tips and reduce the likelihood of material being sheared. However, screw conveyors typically span several meters or even tens of meters in length (with horizontal or slightly inclined long-distance conveying being common). To maintain a small clearance between the spiral blades and the casing, it is necessary to machine the outer circumference of the blades on the central shaft and to precisely finish the inner diameter of the casing. For such long sections, specialized machining equipment is essential. Meanwhile, the blades of screw conveyors tend to wear out rapidly during operation, causing the clearance between the spiral blades and the casing to increase over time. In other words, this small clearance exists only during the initial stages of use; once the blades have worn to a certain extent, they will start cutting the conveyed material again, thereby increasing the rate of material breakage in the screw conveyor. Additionally, due to the rigidity of the central shaft, collisions between the spiral blades and the casing can generate noise.

Jiangsu Yaxing

Address: Qingdun Industrial Park, Hai'an City, Jiangsu Province

Phone: 86-513-88483622 ，86-513-88480666,

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