Structural principle, installation and maintenance

Structure principle and installation and maintenance of screw conveyor

the main structure of screw conveyor is composed of driving wheels, tensioning wheels and flexible traction components. Therefore, they are usually called conveying equipment with flexible traction components. Screw conveyor is different. It uses a rigid spiral body as the main component to realize material conveying. It is usually called the conveying equipment with rigid "traction" components

screw conveyor, commonly known as auger, is a continuous conveying machine for short-distance horizontal or vertical conveying of bulk materials. Its main features are: simple structure, small overall size, low cost, good sealing, multi-point feeding and unloading, mixing and mixing of materials, but its conveying distance is small, blades and casings are easy to wear, high energy consumption, and strong crushing effect on materials. According to its structural characteristics and performance, screw conveyor is usually used for the transportation of materials in the production process of grain, oil and feed processing plants. However, it should be noted that it is not suitable to transport large pieces of materials with more fibrous impurities, strong abrasiveness, easy to break or bond, so as to avoid blockage and material crushing. According to the installation form, screw conveyors can be divided into fixed and mobile, and can be divided into horizontal slow and vertical fast according to the conveying direction or working speed. Fixed and horizontal slow screw conveyors are commonly used in engineering practice

I. structure and working principle

1. Structure

as shown in the figure is the general structure of horizontal screw conveyor, which is mainly composed of spiral body, bearing, material trough, inlet and outlet, driving device and other parts. The rigid spiral body is supported on the chute through the bearings at the head, tail and middle parts to form a rotating component that can realize material conveying. The operation of the spiral body is realized by the driving device installed on the head, and the material inlet and outlet are respectively arranged on the upper side of the chute tail and the lower side of the head

general structure of screw conveyor:

(1) spiral body

helicoid is the main component of screw conveyor to realize material conveying, which is composed of spiral blade and spiral shaft. The commonly used blades are full face type (solid type) and belt type. According to the different winding directions of the blade on the shaft, it can be divided into right rotation and left rotation (counterclockwise winding is left rotation, and clockwise winding is right rotation). The material conveying direction of the spiral body is determined by the rotation direction of the blade and the rotation direction of the shaft. When determining the specific direction, first determine the rotation direction of the blade, and then follow the principle of left-hand rotation with right hand and right-hand rotation with left hand. The bending direction of the four fingers is the rotation direction of the shaft with the tension (compression) force sensor installed, and the straightening direction of the thumb is the material conveying direction, as shown in the figure. If there are two kinds of rotating blades on the same spiral body, the conveying of materials in two different directions can be realized at the same time. The spiral shaft usually adopts hollow steel pipe with a diameter of 30 ~ 70mm

the main specifications and dimensions of spirochetes are blade diameter D (mm), shaft diameter D (mm) and pitch s (mm). See table for series diameters. Spiral blade usually adopts simple manufacturing method, that is, 1.5 ~ 4.0mm thick steel sheet is used to punch or cut into a ring with notch, the ring is drawn into a pitch blade, and then several individual blades are welded or riveted to the spiral shaft to form a complete spiral blade. As shown in Figure 5-19, the size of the ring (cutting size) is calculated by the following formula:

where: R - the diameter of the outer circle of the ring (mm)

r - diameter of inner circle of ring (mm)

α—— The missing angle of the ring (0)

full face blade deployment:

(2) bearing

bearing is a component installed in the machine slot to support the spiral body. According to its installation position and function, it has head bearing, tail bearing and middle bearing. As shown in the figure, the head bearing is mainly composed of centripetal thrust bearing, bearing seat, bearing cover, oil ring and other parts. It is installed inside and plays the role of transmission. The discharge end of the head bears radial force and axial force, so its bearing should adopt centripetal thrust bearing; The tail bearing is installed at the feed end of the tail and only bears radial force. The radial spherical bearing is adopted, and the structure is relatively simple, as shown in Figure 5-21; For screw conveyors with a screw shaft of more than 3 meters, in order to avoid bending of the screw shaft, intermediate bearings should be installed. The intermediate bearings generally adopt a suspension structure, and their horizontal dimensions should be as small as possible to avoid material blockage

(3) chute

the chute of horizontal slow screw conveyor is usually made of 2 ~ 4mm thick steel sheet. The walls on both sides of the cross section are vertical, and the bottom is semicircular. The end of each section of the chute and the upper end of the side wall are reinforced with angle steel to ensure the rigidity of the chute and realize the connection between the section and the section, and the top cover plate and the chute. The support feet of iron castings or angle steel weldments should be set at the bottom of the chute. The inner diameter of the bottom semicircle should be 4 ~ 8mm larger than the diameter of the spiral blade, as shown in Figure 5-22. The cross section of the chute of the vertical fast screw conveyor is circular, which is usually made of thin-walled seamless steel pipe

2. working principle

the helical blade is a helical space surface, which is formed by a straight line rotating around the axis and moving in a straight line at the same time. Therefore, when the screw conveyor transports materials, it uses the linear motion accompanied by the fixed spiral rotation to drive the materials forward. The material moves forward in a spiral shape, that is, when it is transported forward, it is accompanied by the rolling movement in the circumferential direction. Therefore, the rotation speed of the horizontal slow screw conveyor cannot be too large, while the vertical fast screw conveyor must use the high-speed rotation of the spiral body to form enough friction between the material and the chute, so as to overcome the friction resistance of the blade to the material and the gravity of the material itself, and ensure the upward transportation of the material

II. Simple calculation and selection

1. Calculation of conveying capacity

the conveying capacity of horizontal slow screw conveyor can be calculated by the following formula:

where: Q - conveying capacity (T/h)

d - spiral blade diameter (m), which should be selected from the series of standard values in the table

n - spiral shaft speed（ γ／ min)；

γ—— Material bulk density (T/m3)

ψ—— Filling coefficient, generally, grain ψ= 0.25 ~ 0.4, oil ψ= 0.25 ~ 0.35, bran, rice bran ψ= 0.25, flour ψ= 0．2；

s - pitch of spiral blade (m), full face blade s=0.8d, belt blade s=d

c -- correction coefficient during inclined conveying

on the premise that the conveying capacity is known, after the blade diameter D is determined, the screw shaft speed can be calculated by the following formula:

the screw shaft speed n of the horizontal slow screw conveyor cannot exceed its limit speed, otherwise its mixing effect on the material will greatly exceed the conveying effect, and even only has the mixing effect on the material without the conveying effect. The calculation formula of limit speed is:

, where: N0 - limit speed of spiral shaft（ γ/min）；

a - comprehensive characteristic coefficient of materials, grain and oil materials generally take a=65

2. Select the

screw conveyor to judge the sealing performance of the sample; Through the model representation of vacuum chamber, it is also composed of four parts, for example:

tlss25 screw conveyor

T - professional code (general equipment of grain pumping machinery)

ls -- variety code (screw conveyor)

s - type code (horizontal type); (the model codes of vertical and mobile screw conveyors are l and Y respectively)

25 - specification code [spiral blade diameter D (CM)]

when selecting screw conveyor, we must follow the general principles of selecting conveying equipment, and at the same time, we should also consider the following points:

1. Select the appropriate model according to the different process requirements. Horizontal slow speed (LSS type) screw conveyor shall be selected for horizontal or small inclination short-distance transportation; Vertical fast (LSL type) screw conveyor shall be selected for vertical or large inclination conveying with small height

2. determine the form of spiral blades according to the properties of the conveyed materials. When transporting wheat, rice and other materials with good scattering property, full face blades should be selected; Belt type blades should be selected to prevent blockage when transporting oil materials with high viscosity and easy adhesion. It should be noted that screw conveyors are generally not used to transport raw grain, rice and other materials in order to prevent materials from being broken

3. determine the rotation direction of spiral blade, the rotation direction of spiral shaft and the combination of spiral body according to the layout requirements of process equipment. After the positions of the head and tail end (feeding and discharging end) of the conveyor are determined, the conveying direction of the material is determined, and the rotation direction of the spiral blade and the shaft must meet the requirements; If unloading is required at the middle or both ends, blades with different rotation directions shall be used to form a spiral

4. determine the model and specification of screw conveyor according to the conveying capacity required by the process

example

a flour mill uses a horizontal slow screw conveyor to transport wheat（ γ= 0.75t/m3), and the conveying capacity is 15t/h. Try to determine the specification of screw conveyor and calculate the blanking size of blade

solution: according to q=15t/h, check the table and select blade diameter d=250mm; Horizontal conveying, c=1; Full face blade s=0.8d=0.8 × 0.25=0.2(m)； take ψ= 0.33，A=65。

utilization:

tlss25 screw conveyor should be selected, d=250mm, d=48 mm

next, calculate the blanking size of blades:

III. installation, operation and maintenance

1. Installation

the installation forms of screw conveyor mainly include: ground support installation, suspension support installation, installation in corridor or trench and installation of two sets of series work

the following requirements shall be met during installation and adjustment:

1. The center line of the chute and the screw shaft shall maintain good coaxiality

2. the joints between the sections of the chute should be tight, and there should be no dislocation of connecting the power supply. Gaskets can be added between sections and between the top cover and the chute to ensure the sealing of the chute. At the same time, the length error of the chute can be adjusted

3. the gap between the inner wall of the chute and the spiral body should be equal

4. the shaft of the driving device and the screw shaft should maintain good coaxiality. During adjustment, the height of the driving device can be adjusted with the help of shims

5. Static balance test shall be carried out for spiral after installation

6. the intermediate suspension bearing should reliably and properly support the connecting shaft to avoid radial deformation of the spiral shaft. The installation can meet the requirements by adjusting the shims between bearing shells

7. After the installation of the whole machine, check whether there are sundries in the machine and whether sufficient lubricating oil is added at all lubricating points

8. During no-load commissioning, the bearing shall not leak oil, and the temperature rise of the bearing shall not exceed 20 ℃. During the load test run, the temperature rise of the bearing shall not exceed 30 ℃

2. operation and maintenance

(1) before starting, determine whether the rotation direction of the motor meets the working requirements. Also check whether there are sundries in the chute, especially the blockage at the middle suspension bearing, so as to avoid blockage failure

(2) materials entering the conveyor should be cleaned first to prevent large impurities or fiber impurities from entering the conveyor and ensure the normal operation of the conveyor

(3) ensure no-load starting when starting, and stop after the materials in the standby are discharged

(4) in the process of operation, if large impurities or fibrous impurities such as rice straw and straw rope are found to enter the chute, stop the machine immediately for treatment. It is not allowed to reach into the chute and take out materials directly by hand or with the help of other tools without stopping the machine

(5) when transporting materials with high viscosity and high moisture, the adherents in all parts of the machine should be removed frequently to avoid the decline of conveying capacity or even blockage

(6) the top cover of the conveyor must be tightly covered to prevent external objects from entering the chute, and the dust in the machine may be blown out, or even