Design of the most popular electronic spiral batch

Design of an electronic spiral batching process scale

Abstract: This paper mainly introduces a spiral batching process scale that improves the design of the spiral feeder, which can be applied to the batching process control assembly line or batching system of powder or materials with certain viscosity

key words: screw feeding process scale flowmeter closed-loop control

1 Overview

with the development of society and the expansion of production scale, the degree of automation of industrial production process is higher and higher, and the means are more and more advanced. Especially recently, the state has paid enough attention to environmental protection issues, and people's awareness of environmental protection is also constantly improving. Therefore, how to reduce environmental pollution, improve the degree of automation, reduce labor intensity, ensure the reliability and safety of production, reduce production costs, and improve product quality and economic benefits is a common concern. In recent years, many large and medium-sized enterprises have carried out process improvement design on the original production equipment, especially in the chemical, metallurgical, building materials and other industries

at the end of 2000, according to the process requirements of a catalyst factory, our company and other manufacturers jointly improved its production process after a period of about one year. It was officially put into operation in May 2002, and the use effect was good, which was specifically reflected in the following aspects: the production efficiency was increased by nearly four times; DCS control system is adopted, and the process control is stable and stable; The reliability of the system is greatly improved; Green design and humanized design are fully reflected; The product quality and qualification rate have been significantly improved; Remarkable energy saving effect. At the beginning of the scheme design, the belt conveyor was selected for material transportation. Due to the particularity of materials (bauxite and kaolin), they are powdery and have good fluidity. Using the belt for transportation, the problem of material leakage has become a major problem to be solved. At that time, there was a screw feeder on the production line. We took this opportunity to consider directly improving the screw feeder according to the needs of the production process. If it is feasible, it can not only easily solve the problem of material leakage, reduce environmental pollution and personal injury, but also save belt conveyors (including electronic belt scales), save a sum of money and bring a series of problems, We began to carry out tentative transformation design. Now the product has a good effect and meets the requirements of production process

2. Working principle of the system

when the system is running, the conveyed materials are measured by the electronic screw batching scale, and the received weight and speed signals are processed by the computer integrator and converted into cumulative value and instantaneous flow, and the cumulative value and instantaneous flow signals are transmitted to the industrial control computer (upper computer) through the RS-485 port, and the 4 ~ 20mA analog current signal is transmitted to the frequency conversion regulator, and then the frequency conversion regulator adjusts the speed of the upper feeder, When the flow increases, reduce the speed of the upper feeder, on the contrary, increase the speed of the upper feeder, so that the flow of materials and the cumulative amount of stages are kept within the set range, so as to complete the measurement and batching of materials. The working principle block diagram of the system is shown in Figure 1

3. System design

from the above working principle, we can easily see that the batching results require various materials to be mixed and proportioned according to a certain proportion. In this way, as long as various materials are mixed according to the preset proportion, the process requirements can be met. Based on our working experience in weighing apparatus for many years and with the help of basic mechanical knowledge, we use CAD for auxiliary design, and use lever structure to design an electronic spiral batching process scale with low noise, no friction, anti vibration, elimination of air flow influence, accurate measurement, convenient installation, commissioning and maintenance, which is suitable for material transportation and measurement under variable flow. Because the screw feeder is a kind of sealing equipment, and it has a power part, if you want to transform it into a metering equipment, there are the following problems: 1 How to adjust the levelness of screw feeder? 2. How to overcome the vibration caused by motor operation? 3. How to eliminate the influence of airflow on measurement accuracy during material transportation? 4. How to solve the problem that a screw feeder can only be used for material conveying and metering with a certain flow. The structure after transformation is shown in Figure 2:

Figure 2 structural diagram of electronic screw scale

1, air duct 2, weighing sensor and connecting and fixing mechanism 3, screw feeder

4, soft connection mechanism 5, support mechanism 6, frame

the electronic screw batching process scale is mainly composed of totalizer, screw feeder, air duct, weighing sensor and connecting and fixing mechanism, soft connection mechanism, support mechanism, frame, etc

3.1 integrator

guided menu operation, with alarm prompt, pulse output function, and can realize automatic simulation or physical calibration, manual/automatic empty scale zero adjustment, zero automatic tracking and other functions

it has the functions of automatic angle compensation, self diagnosis of faults and power failure data retention

liquid crystal display, which displays data such as flow, cumulative measurement, speed (load or time) on the same screen. The wall mounted metal plate plastic sprayed shell is waterproof, dustproof and resistant to strong magnetic field interference

it has the functions of communication, printing, 4 ~ 20mA analog current output, etc

3.2 load cell and connecting and fixing mechanism

the connecting part of screw feeder and load cell and connecting and fixing mechanism is welded with reinforcing plate. The upper end of load cell and connecting and fixing mechanism is connected with reinforcing plate through fixing bolt, and the lower end is adjusted by adjusting positioning block to adjust levelness and connected with frame. The reinforcing plate used is a steel plate with arc shape or similar, which is convenient for welding and ensures that the conveyor has sufficient strength and stiffness; The adjustment and positioning block used is composed of two object blocks with a similar triangular cross-section, which can easily adjust the horizontal position of the screw feeder. The limit of the screw feeder can be adjusted by fixing bolts. After the equipment is adjusted, it is welded and fixed. Vibration reducing rubber plates are placed between the weighing sensor and the reinforcing block to eliminate the impact of vibration

3.3 support mechanism

the connecting part between the screw feeder and the support mechanism is welded with a reinforcing plate, the upper end of the support mechanism is connected with the reinforcing plate, the lower end is connected with the frame, and the support mechanism is connected with the rubber bearing through the connecting shaft. The air duct is installed at the end of the discharge port, one end is connected with the screw feeder, and the other end is connected to the upper feeding mechanism. The rubber bearing shall be used as the support point to ensure that its clearance is 0.05 0.08 mm, and the fastening nut and fastening bolt shall be used for fixation to eliminate the influence of the power part

3.4 soft connection mechanism

handle the inlet and outlet of the feeder, change the hard connection to soft connection, make the modified screw feeder an independent unit, and eliminate the influence of external factors on the measurement accuracy

3.5 exhaust mechanism

add interlayer near the discharge outlet, install air duct, and eliminate the generated gas in time to eliminate the pressure impact caused by gas

3.6 find the center of gravity of the screw feeder

make full use of the advanced CAD technology, carry out force analysis on the computer, and find out the center of gravity of the screw feeder under loading (full load), so as to simulate and calibrate it

4. Reliability verification

4.1 preparation before calibration

y4220.100 screw feeder is selected, with productivity Q of 11.6t/h, inclination of 0 °, rotating speed of 48 r/min, pitch of 160mm, power of 1.5KW, current of 3.7a

according to the formula: q=47d2nt ρψ C (1)

q - material flow (t/h)

d - screw diameter (m)

n - screw shaft speed (r/min)

t - screw pitch (m)

ρ—— Material looseness (t/m3)

Ψ—— Material filling coefficient

c - conveyor inclination coefficient

also set: k=d2t ρ (2)

w=mk (3)

m - the number of pitches

is taken as: Ψ= 0.35, c=1

from formula (1), (2) and (3), it is estimated that about 622 materials remain in the feeder when the feeder is fully loaded. The main types are stable and the annual total amount is fine tuned 5kg (65kg after chemical treatment). The self weight of screw feeder is 88 kg, so we choose lb-p-200 weighing sensor

4.2 equipment calibration

4.2.1 analog calibration

as shown in Figure 3, fix the feeder and sensor, start the motor for no-load operation, calibrate the zero point, and then apply 80 kg weight for analog calibration (linearity and range). It is found that the effect is very good, and the test results are shown in table 1

Table zero cumulative error

Table zero cumulative error

times 12345 error value 0.128%-0.091%-1.117%0.027%0.113%

table range cumulative error

times 12345 error value 0.232%-0.131%-0.241%0.274%0.136%

4.2.2 physical calibration

fix the silo, star feeder, screw feeder, etc. according to the test system structure diagram in Figure 3, and connect the sensors correctly.And integrator, integrator and PID, PID and frequency converter The connection between the frequency converter and the star feeder ensures that the screw feeder is in a relatively independent state

let the PID be in the open circuit state, start the star feeder to run at the maximum speed, ensure that the screw feeder is at full load, and conduct physical calibration. The test results are shown in Table 2. Table 2 cumulative error of measuring range (physical)

times 12345 error value 0.434%-0.391%-0.314%0.273%0.0271%

4.2 closed loop debugging

connect frequency converter and regulator to carry out closed loop debugging of the system. It is difficult to control when there are less materials applied at the beginning and materials in the silo. At the beginning, the system overshoot is serious, but it can be recovered soon. With the reduction of materials in the silo, the control curve fluctuates greatly, However, when the materials in the silo are kept within a certain range, the fluctuation of the control curve is relatively stable, but there is a serious lag phenomenon. However, for the same material, when the material level is stable, the lag time is relatively stable. This problem can be solved by adjusting the internal relevant parameters of PID

5. Existing problems and measures

5.1 existing problems

5.1.1 due to the transportation of powder and granular materials, static electricity is generated due to the friction between the materials and the blades and the cylinder wall during the transportation

5.1.2 there is a lag between the rotation speed of the material and the blade due to friction and blade clearance during the transportation of the material

5.1.3 during the transportation of materials, gas is generated due to the gap, forming air pressure, and the symmetrical quantity causes extremely unstable influence

5.2 measures taken

5.2.1 system grounding and anti-static treatment

the equipment shall be well grounded on site to ensure the elimination of static electricity

5.2.2 make full use of experience and control theory

repeat the test, record the test data, technically process the test data, establish a mathematical model, and use actual experience to modify, adjust PID internal parameters, and completely overcome the lag phenomenon of the system

5.2.3 add an exhaust device

add an exhaust device at the outlet of the feeder to remove the gas in the cylinder in time, on the one hand, eliminate the impact of air flow on the accuracy of measurement, on the other hand, ensure the smooth delivery of materials

6. Conclusion

through the field use verification, this kind of equipment is not only suitable for powder and small granular materials with good fluidity, but also suitable for materials with certain viscosity and poor fluidity. In chemical, metallurgical, building materials and other industries, this kind of equipment and control method are worth promoting in the corresponding systems

reference

1, manual for design and selection of transportation machinery, chemical industry press

2, application of zhanggonghua frequency conversion technology in improving the transformation of new catalyst production process, "otherwise, it is necessary to adjust the control parameters of the experimental machine at any time (also