Analysis on hub structure of wedge wire drum screen assembly system

The hub is suitable for wedge wire rotary drum screen structure with large water chamber width.

The purpose of hub structure shape design: to make the force on the main shaft more reasonable; Minimize the deformation of the spindle.

Structure introduction the spindle assembly system of rotary drum screen is mainly composed of spindle, hub and shaft end support seat.

Both ends of the main shaft are provided with bearing seats, which are connected with anchor bolts through embedded machine seats.

Two structural forms of rotary drum screen spindle

• Its main shaft is the main bearing part of rotary drum screen, which bears both bending moment and torque.
• However, due to the low rotating speed of rotary drum screen (no more than 0.5r/min), the main shaft mainly bears bending moment.
• It mainly bears the full weight of the hub, drum frame and all parts on the drum frame, as well as the water pressure generated by the water level difference inside and outside the rotary drum screen.
• The hub is the main part of the spindle assembly system. The external force on the spindle is mainly transmitted through the hub. The structural form of the hub directly affects whether the force on the spindle is reasonable or not, which is the focus of the whole system.
• Therefore, hub design is the key to the design of spindle assembly system. According to the different structural forms of rotary drum screen, the design forms of wheel hub are also different.

Rotary drum screen structure  

The conventional design of rotary drum screen water inlet mode is generally axial water inlet and radial water outlet.

The spindle system mainly bears the pressure of water and the dead weight of rotary drum screen.

When the diameter of the rotary drum screen is certain, the supporting spoke structure in the drum skeleton is also different according to the width of the water chamber.

In the spindle assembly system, the hub has two structural forms of “disc” and “pyramid”:

• Using a single channel steel as the spoke support framework can meet the stability requirements of the whole system.
• The “I” shaped spokes are used to connect with the hub, which not only ensures the size of each part of the spokes, but also has a large contact area between the spokes and the hub, so that the bolts are only subjected to shear, the stress form is simple, convenient for construction and installation, and the manufacturing process is relatively simple.
• The advantages of the hub design are: simple processing and easy to ensure the matching size of each part.

When the spokes are in “a” shape and the drum net structure is shown in figure (2), using a single channel steel as the spokes support skeleton can not meet the stability requirements of the whole system. If the “circular disc” hub is continued to be connected with the spokes, the following problems exist:

• At the connection end between the spoke and the hub, the spoke must be chamfered and then the steel plate can be welded for bolt connection. Because the channel steel is chamfered and the strength and stiffness are reduced, the reliability of its connection is worse than that directly connected by the spoke and the hub with bolts.
• Moreover, the connecting bolts between the spoke and the hub are high-strength bolts, which are easy to fall off due to inconvenient manual operation.
• The connection strength of drum frame will be greatly reduced, and the equipment has great hidden dangers, which will directly affect the service life of wedge wire screen drum.

On the premise of the same span of the main shaft (the same a), the stress point of the main shaft with “disc” hub is far from the support point at the shaft end (B1 is small), and the included angle of “a” spokes is small, resulting in a large radial component of the main shaft. Through calculation, the main shaft diameter (D1) of this structure is too large, so this scheme design is unreasonable and uneconomical. 。

The stress on the root of the hub is large. Through calculation, this structural form is 2-3 times larger than the “pyramid” structural form, and the service life of the hub is greatly reduced.  

Therefore, we changed the structural shape of the hub from “disc” to “pyramid”. Obviously, the fabrication of “pyramid” hub is more complex than “disc” hub, but its advantages are obvious.

It is characterized by:

• The spoke channel steel is directly connected with the hub by bolts without corner cutting, and the strength and stiffness of the channel steel are not damaged, which enhances the reliability of the connection.
• On the premise of the same span of the main shaft (a is the same), the stress point of the main shaft with “pyramid” hub is close to the support point at the shaft end (B2 > B1). At the same time, the included angle of “a” shaped spokes increases, reducing the component force in the radial direction of the main shaft.
• Through calculation, the main shaft diameter (D2) of this structure. In conclusion, the structural form of the main shaft assembly system is not invariable, but limited by the width of the water chamber in the drum net installation site, and the main difference is the structural shape of the hub.
• The spindle assembly system with “disc-shaped” hub is suitable for drum filter screen structure with small water chamber width.
• On the contrary, the spindle assembly system with “pyramid” hub is suitable for the drum filter structure with large water chamber width.
• The design principle of hub structure shape is to make the force on the main shaft more reasonable.
• Minimize the deformation of the spindle.
• The purpose is to make the whole drum net system run more safe and reliable, and reduce the production cost of the equipment as much as possible.