Design of various parameters of screw conveyor

The conveying capacity of the conveyor must be greater than the total amount of incoming material; the material cannot produce a jump tumbling perpendicular to the conveying direction; the material advances along the axial direction; the material has as large an axial conveying speed as possible, and the axial velocity of each point is greater than Circumferential speed.

The design method of each parameter is as follows:

(1) Spiral speed

When the spiral speed is low, the effect of retarding material flow on material movement is not significant. Once the screw speed exceeds the critical speed, the material will produce a jump tumbling perpendicular to the conveying direction, which acts to stir the material rather than axially. At this time, the conveying efficiency is lowered, the energy consumption is large, and the equipment wear is accelerated. In order to avoid this phenomenon, the spiral speed cannot exceed its critical speed. The empirical formula for critical spiral speed is:

(2) Spiral outer diameter

In the case where other parameters are determined, the curve of the axial movement speed Vz and the peripheral speed Vt of the material in the trough as a function of the spiral radius r of the material is as follows:

Speed versus radius curve

Analysis of this curve shows that in selecting the outer diameter of the spiral, in addition to meeting several requirements mentioned at the beginning of the article, it should be ensured that the selected outer diameter is on the right side of the BB line in the figure. For an open screw conveyor, the outer diameter of the spiral increases the manufacturing cost and is not conducive to cooling. Moreover, the outer diameter value does not necessarily have to be an integral multiple of 500.

(3) pitch

According to the curve of the speed change with radius under different pitches, there is a corresponding relationship between the choice of the helical pitch and the outer diameter of the spiral. The larger the pitch, the larger the corresponding outer diameter of the spiral. After the outer diameter of the spiral is determined, there is a minimum pitch corresponding to it, that is, a suitable pitch.