Screw Conveyor: Common Failures & Solutions
What Is a Screw Conveyors?
A screw conveyor (also called an auger conveyor) is an efficient material handling system that moves bulk materials using a rotating helical screw blade. It is highly versatile, capable of horizontal, inclined, and vertical conveying, and is widely used in industries such as:
✔ Metallurgy
✔ Mining & Minerals
✔ Construction
✔ Food & Grain Processing
Key advantages include simple structure, low maintenance, and cost-effective operation.
Working Principle & Key Components
The screw conveyor is mainly composed of motor, reducer, coupling, bearing, sealing seat, shell and screw shaft, and the shell is provided with a feed inlet, a discharge outlet and a cleaning door. The auger shaft rotates under the drive of the motor. The materials enter from the feed inlet at the head, and are pushed by the prefabricated spiral blades on the auger shaft. The materials move along the shell to the tail and are discharged through the discharge port.
Common Fault Analysis
Screw conveyors are mainly used in flour mills and food factories for material discharging, flour blending and other process positions. Although the advantages of screw conveyors are very obvious, there are still some failures in the application process, which makes it unable to give full play to its due technological performance in the production process. According to the use of screw conveyor in the past, the common faults are difficult to start, shaft end, flange connection and cleaning door powder leakage, material blockage at hanging bearing, pipe shaft fracture and collision with shell, etc.
(1) Shaft end, flange butt joint and clean the door for powder leakage
The shaft end is provided with a sealing seat, and there are two cases of powder leakage at the shaft end: one is that due to the unreasonable design of the sealing structure, the corresponding sealing structure is not equipped according to the transported materials and process position during the production and manufacturing of the equipment; The other is caused by the damage of the shaft end seal.
The joint of flange and the cleaning of powder leakage from the door are often caused by incomplete lapping or damage of the sealing strip when installing the sealing strip on the screw conveyor.
(2) Material blockage at suspension bearing
The blockage at the hanging bearing often occurs in the smaller type of screw conveyor. The shell section of the screw conveyor itself is small. Because the hanging bearing is installed at the hanging bearing, the outer diameter of the installed hanging bearing is often larger than the diameter of the pipe shaft. At the same time, the support should be set at the hanging bearing, which greatly affects the cross-sectional area of the material passing through the screw conveyor.
Moreover, the blade at the suspension bearing is disconnected, and the material can only be pushed by the front material when passing through the suspension bearing.
(3) Pipe shaft fracture
The fracture of pipe shaft rarely occurs, but once it occurs, it is bound to cause shutdown. Compared with other faults, the shutdown time is longer and the loss is larger. The main reason is that there are large foreign matters inside the screw conveyor, such as steel pipes, round steel, bolts, etc.
Another reason for the fracture of the pipe shaft is that the clearance between the shaft head and the pipe shaft is too large during the machining process. The torque is mainly transmitted by two bolts during the use. With the increase of the use time, the fatigue limit of the bolt is reached and cracking occurs.
(4) Rubbing against the housing
Rubbing against the shell is a common fault of screw conveyor. The main reasons are as follows:
The clearance between the blade and the shell of the screw conveyor is too small; The straightness deviation of the winch shaft or shell is large; The bolt conveyor is deformed during hoisting and transportation, and the installation quality is poor; The winch shaft is too long, the hanging bearing is not set in the middle, or the spacing of the hanging bearing is unreasonable; The rotation speed of the screw conveyor is too high, and the deflection of the auger shaft is too large during the operation of the screw conveyor.
Troubleshooting
(1) Screw conveyor is difficult to start
When it is difficult to start the screw conveyor, first check whether the reducer motor can work normally. If the reducer motor cannot work normally, it needs to be repaired or replaced; Secondly, check whether the power selection required by the screw conveyor is appropriate. The chain driven screw conveyor can also be solved by adjusting the sprocket on the premise of meeting the output.
(2) Shaft end, flange butt joint and clean the door for powder leakage
In view of the shaft end powder leakage, a reasonable sealing structure should be designed. The common shaft end sealing structures of screw conveyor include felt seal, rotary lip seal, packing seal, air tight seal and multiple seals combined with several sealing forms. When making the screw conveyor, the appropriate sealing structure should be selected according to the conveying materials. Instead of blindly reducing the cost, the simple sealing structure should be adopted to reduce the sealing quality.
The joints of the sealing strip at the flange butt joint and the cleaning door shall be intact during equipment installation. If the sealing strip is damaged, it shall be replaced in time.
(3) Material blockage at suspension bearing
When the smaller conveying materials of the screw conveyor are impurities or lower feet, the pipe shaft shall be thickened as much as possible to avoid the use of hanging bearings. If the conveying distance is too long and the hanging bearings have to be used, the reasonable hanging structure shall be designed to increase the cross-sectional area of the materials passing through the hanging bearings on the premise of meeting the strength. At the same time, the width of the hanging bearings shall be as small as possible to make the discontinuous parts of the blades as short as possible.
(4) Pipe shaft fracture
First of all, during the processing and manufacturing process of the screw conveyor, the quality is strictly controlled, and the coordination between the shaft head and the pipe shaft meets the tolerance requirements.
Secondly, check whether there is any foreign matter inside the silo screw conveyor before startup and commissioning, and start it after there is no foreign matter, because the foreign matter often occurs in the commissioning stage.
(5) Rubbing against the housing
① Select the appropriate gap between the spiral blade and the shell. If the gap is too small, the shell will be wiped, and if the gap is too large, the materials inside the shell of the spiral conveyor will remain.
② The straightness of the capstan shaft and capstan shell during processing shall meet the requirements, especially after the capstan shaft is installed with the head and tail shafts, the shaft runout shall be detected with a dial indicator, and the capstan shaft can be assembled only after passing the inspection.
③ When hoisting, select the appropriate stress point for hoisting. During transportation, it is necessary to fix it firmly and pad the easily deformed parts; During installation, the installation accuracy shall be ensured to prevent flange deflection, and the foundation elevation shall be consistent and fixed firmly.
④ Select the appropriate pipe shaft diameter, wall thickness and segment length according to the winch model.
⑤ The appropriate model and speed shall be selected according to the conveying output of the screw conveyor. The speed shall not be too high, generally not more than 160r/min.
In addition to potential issues during manufacturing, lifting, transportation, and installation, screw conveyors require regular maintenance. Follow the instruction manual to properly lubricate bearings and seals to ensure optimal performance.
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