Analysis of Belt Weigher in Application

1、 Overview

Belt scale is widely used in electric power, port, metallurgy, cement building materials, mining and other industries because of its continuous and automatic dynamic weighing characteristics. It is used for internal accounting, production control, import raw materials, port and wharf trade measurement, and supervision and management of public institutions. The author has made a comprehensive analysis of the application management of various industries in recent years, and made corresponding evaluation on the status of the research and application.

2、 Application analysis of belt scale in port and thermal power plant

The belt scale installed in port and wharf is used for commercial settlement, which requires good stability, good repeatability and high weighing accuracy. Based on the above requirements, the belt scale using multi roller suspension scale is used. For example, Shanghai port is jointly developed by many domestic manufacturers of belt weighers, and six sets of weighing roller suspension scales are used as the commercial settlement evidence for weighing by ships; Shanghai Baoshan Iron and steel company uses two groups of suspension weighing roller scales of Kubota, Japan, to weigh ore trade settlement from Australia; Beilun port, Ningbo, Zhejiang Province, is a complete set of equipment imported from Japan, Yama  To) commercial Weighing and measurement of two sets of roller suspension scale frame of company; Yingkou Xiangcheng port in Liaoning Province is a suspended scale frame which introduces Japanese big and technical technology. Therefore, all scales used in commercial measurement are made of high precision scale frame. In order to improve the weighing accuracy and long-term stability, Shanxi Xinyuan automation instrument company has developed the conventional two sets of idler, three sets of idler and four sets of idler suspension type to two four sets of supporting rollers in series into eight sets of double scale stands. The instrument adopts double channel input, the scale frame increases sampling time, and the stability and accuracy are improved, but the installation conditions are improved, The difficulty of debugging has increased obviously. In order to improve the accuracy and long-term stability of commercial measurement, Nanjing Sanye Industrial Control Co., Ltd. has developed an array belt scale. The so-called array type is composed of two roller straight bearing scales with multiple units, which can collect a large amount of weighing data. The weighing accuracy should be relatively high, the technical content of field installation and commissioning is higher, and the installation conditions and technical requirements are higher. It is found that most of the products are used in the mining industry to weigh on horizontal belt, and the accuracy of measurement is also improved. The application environment of commercial scale is basically long belt conveyor, with good belt quality and good circumference from tens of meters to hundreds of meters. The belt width is 1200mm-2000mm, and the belt thickness is 10-15mm; The high flow transportation is 800t / H ~ 2250t / h, and the maximum flow is up to 6000t / h; The material is evenly transported and the phenomenon of material breaking is less, which is very beneficial to weighing. It is not conducive to weighing that the belt runs faster, and it is usually 1.6m/s ~ 3.15m/s. But the flow is large, the performance is stable, and the high accuracy can be obtained with more collection amount. The fuel metering management of thermal power plants generally adopts four roller suspension scale frame for the commercial measurement of coal in the plant, and the coal business measurement of the mine mouth power plant is used as the commercial accounting measurement. As an internal assessment, four sets of weighing roller double bar trunnion trunnion support scale frame are generally used as the internal assessment. The accuracy of weighing is lower than that of the incoming coal, and the cost is lower than that of the coal in the plant. Therefore, it has low sensitivity, but good stability, and is suitable for weighing with large flow. Therefore, it is widely used in coal metering in thermal power plant. This scale frame is also used in coal preparation plant to calculate coal preparation quantity. In Shouyang fenlei coal preparation plant, Shanxi Xinyuan automation instrument company adopts Ramsey technology to produce belt scale frame supported by four supporting roller trunnions with double bar bar. The different is that channel steel is used as main lever and auxiliary lever instead of rectangular steel pipe. Whether the deflection of the equal distance between them is completely equal has not been obtained. Because the belt length has the choice of the best position for the selection of the scale frame, the belt tension device has a certain compensation effect on the belt tension change.

The bar of the straight line before and after the scale frame.Japan Yamato Co., Ltd. requires that the straight-line section be the distance of five groups of idlers in front and back of the scale frame, and Ramsey requires that the straight-line section be the distance of four groups of idlers in front and back of the scale frame. The port belt weigher can carry out regular inspection and dynamic zero point calibration when there is no ship's incoming materials. The thermal power plant has two transportation lines and standby lines, and it can also easily complete regular inspection and dynamic zero point calibration, which plays a great guarantee for maintaining the weighing accuracy of the belt weigher. The author has been in Guangdong Taishan Power Plant for more than 30 days of field test, proved that the conveying capacity is large, the conveying speed is fast, the belt width, the belt length, the belt thickness, the belt quality is quite good, the high-quality belt its tension change is small, so the short-term zero stability, the long-term zero stability can reach the belt scale examination standard. In a power plant in Fujian Province, when the author used it for half a year after re debugging and passing the inspection, one section of the three-stage adhesive ring belt was torn, and different types of belt were replaced. The belt hardware was different, the belt winding degree was different, and the symmetry weight was changed. The lesson is that the same type of Belt should be used for the same belt conveyor. In a power plant in Jilin Province, it is located at the inclined 16 ° The suspension scale frame is installed on the belt conveyor. The manufacturer and the user do not know that the suspension scale frame can not be installed on the inclined belt for more than 6 hours °， This index is the conclusion drawn by scientific researchers through experiments, that is to say, it exceeds 6 ° Symmetry weight has an effect. The longitudinal limit rod tightly pulls the inclined gravity under the scale frame, which can not affect the weighing!

In a power plant of Shanxi Province, the inclination of belt conveyor is 21 °， Parallel bar four idler scale frame indicates that the inclined belt does not exceed 17 °， Some manufacturers mark no more than 18 °、 twenty °， This will not only cause repeated weighing of materials, but also affect the weighing of belt scale. Pattern belt can be used to solve the problem of material slipping and repeated weighing. The parallel bar multi idler scale frame exceeds the weighing level limit. In other words, this belt does not have the conditions to install the belt scale. In ports and power plants, belt scales are mostly used in high speed, large flow, wide belt and long leather. During the verification, it is stipulated that the short-term zero point stability shall be evaluated in 3 minutes or a whole belt circle, and the long-term zero point stability shall be evaluated in 3 hours. In use should be: 24 hours to assess short-term zero stability, 168 hours to assess long-term zero stability. The assessment of belt scale stability is essentially in the assessment of belt changes, belt moisture and belt surface moisture changes are completely opposite, so the author thinks that the key to assess the belt scale is to assess the quality of the belt and belt tension device. Some conveyor design departments just carry materials up. Excellent designer, considering the conveying capacity, maximum flow, common flow, belt wear degree, power consumption, belt tension change, select the belt tension device, make the belt work in the best state, also provide good installation conditions for the belt scale. The length of conveyor belt in thermal power plant is generally between 300m and 400m, and the inclination is 10 °～ eighteen ° In the lifting state, four groups of parallel bar idler scale frame are generally used. According to the national standard GB 10595-89 technical conditions of belt conveyor, it is installed in the conveying system of thermal power plant. In order to prevent belt slipping and over tension, namely "Ribbon" phenomenon, the tension is basically constant. Car type tension device, heavy hammer type tension device and zyj50024d belt hydraulic tension device are adopted. The dynamic zero point stability of belt scale is effectively stabilized. Considering the conveying capacity, maximum flow, common flow, belt wear degree, power consumption and belt tension change, the belt tension device is selected to make the belt work in the best state and provide good installation conditions for the belt scale. The so-called durability of belt scale in recent years, there are still many people to study, the author thinks that the durability test of belt scale is of little significance, is it 3-5 years, or 7-8 years. It is not so much the durability of the belt scale as the durability of the belt. The key is to see the durability time of the belt. When the belt weigher is used in different environment pollution, damp, dusty, sulfur trioxide, toxic and harmful gas corrosion to the metal body, some weigher frames rust in less than half a year on site, and they rust when they are washed with water every day in coal transportation. The processing technology of weigher frame is generally painting antirust paint, topcoat, bluing, blackening and galvanizing, in order to save production cost, Many scales are painted with only one layer of finish paint, and the collision area begins to rust during installation. After sales service found that coastal power plant belt scale frame less than a year screw rust. Power plant is divided into state maintenance and planned maintenance. Now it is called spot inspection (partial maintenance) and surface inspection (comprehensive maintenance). Belt conveyor system roller rotation part wear faster, local spot check more, replace a section of belt, a weighing roller are related to the durability of the belt scale. The reason why the verification period of belt scale is set as year comes from the fact that the planned maintenance of belt conveyor is also set as year. Many large belt conveyor maintenance plan 3 ~ 5 years, good quality, good maintenance of the conveyor is even 10 ~ 30 years. If the conveying state is good, the weighing accuracy will not exceed the error range. 3、 Analysis of the application of belt weigher in cement industry ordinary portland cement production is to input limestone + clay + iron concentrate into ball mill according to proportion, grind into mixed raw meal, and then calcine at 1450 ℃ to form clinker. The clinker and gypsum are mixed in proportion and finely ground into cement, which is the so-called "two grinding and one burning" cement production process. In the raw meal system, limestone, clay and iron concentrate need three belt weighers to measure and control the feeding amount. Some raw materials are processed as (limestone, silicate ore) + iron concentrate + clay + coal + three wastes; The clinker is gypsum, fluorite + coal gangue + three wastes + compound stabilizer. It is more complicated to measure and control the feeding amount of belt scale.

3. Installation requirements of belt scale

Belt scales are installed on multiple belts, forming a belt scale group. There are many belt weighers using Schenker technology in the production control of cement and chemical industry in China. The weighing interval on the scale frame is 1m, and the interval on the auxiliary weighing section should be unified as 1m, and the belt winding degree is the same. The belt scale with high weighing accuracy is required to strictly control the interval distance.

(1) There is no other choice for belt weigher installation. There is only one conveyor belt from the single material storage bin to the main conveyor belt, which can only be installed on this belt.

(2) The selection range of the installation position of the belt scale is very small, and the distance from the single bin to the main belt will not be too long.

(3) There is no other choice for the length of the belt conveyor. The length of the belt conveyor depends on the site design. Generally, it is not too long, most of it is more than ten meters long, and there is no belt tension device designed. The designers only design from the perspective of conveying materials, and they do not pay attention to the weighing of the materials.

(4) There is no choice for the inclination angle of the belt conveyor, that is to say, the inclination angle of the belt conveyor is as big as it is designed.

(5) There is no other choice for belt conveying speed. In the design of batching system, the single material belt conveying capacity and conveying speed are fixed and cannot be changed at will.

(6) Now when installing the belt scale, we pay attention to the batching function, but ignore the control effect.

(7) There are not many cases of loading in the whole circle. It is common that the loading stops after a period.

(8) It is difficult to calibrate the dynamic zero point of belt scale, and the daily inspection method and implementation are difficult to implement.

4、 Application analysis of belt weigher in metallurgical industry

A standard parallel bars four groups of scale frame installation tilt 17 ° Or on the horizontal belt, the four groups of idlers of the scale frame are the weighing idlers, the four groups of idlers in front and back are called the auxiliary idlers, and the 4.8m in front and back of the effective weighing section are called the auxiliary weighing section, that is to say, the scale frame can only be installed when the linear section reaches 14.4m. In the production process of an aluminum plant, four belt scales are required to be installed. The user puts forward that the accuracy is 0.5%. The sales staff thinks that the accuracy of two groups of roller scales of horizontal bar is 1.0%, and that of four groups of roller scales of parallel bar is 0.5%. Contract signing, equipment installation and debugging, installation personnel is a novice, hanging code inspection can not meet the requirements. The original length of the belt conveyor is less than 10m, the straight section is less than 6m, and the scale frame with an interval of 1.2m is installed. There is no auxiliary weighing section, so the accuracy can not be achieved. Someone proposed to dismantle the auxiliary lever, so that there is an auxiliary weighing section, and the accuracy of the two groups of scale frames is still 1.0%. This is to tell users that the belt conveyor in your factory does not have a belt scale with installation accuracy of 0.5%. On the prototype test, four groups of parallel bars supporting scale frame can be tilted 17 ° If the weighing accuracy on the belt conveyor reaches 0.5%, then it can also reach 0.5% on the horizontal belt conveyor. The inclined belt conveyor is used for lifting, while the horizontal belt conveyor is used for transferring. The weighing condition is obviously better than that of the inclined belt conveyor. Therefore, the weighing accuracy may be higher than 0.5% whether the parallel bar scale or the suspension scale is used. That is to say, it can be tilted at 17 ° The accuracy of weighing on the belt conveyor can reach 0.5%, and the on-site conveyor must have the same operation conditions as the prototype conveyor.

5、 Understanding of durability of belt scale

In modern Chinese dictionaries, only "durable" is interpreted as "durable, firm and durable". Baidu durability definition: "structure in normal use and maintenance conditions, with the continuation of time can still meet the predetermined functional requirements." In the verification regulation, the durability test of belt scale is: "a test to test whether the belt scale (EUT) can maintain its performance characteristics after a specified service period." The service cycle of belt scale is 8 years or 10 years national verification regulation has not been specified clearly, only the "belt scale verification period generally does not exceed 1 year". The author thinks that the durability of belt scale should be divided into two parts: the quality durability of belt scale and the durability of system weighing quality.

（1） The quality durability of belt scale body

It involves the quality of the material in the production of the scale frame, and the processing of the scale frame has multi-layer paint protection and single layer paint protection; The weighing sensor has inert gas protection and no inert gas protection, and lever type conversion protection for the sensor; The stainless steel shell of speed sensor is protected, and the anti shock and anti slip protection of speed measuring roller is provided; The selection of the instrument components, the replacement of manual welding by high temperature solidification, the flange of parts and galvanizing are all the conditions to guarantee the durability.

（2） System weighing quality durability

The scale frame is designed with weighing force measurement type, instrument data processing ability, resolution, sampling rate and anti-interference capability; The working environment, angle, length and quality of belt, quality and vibration of belt conveyor, quality of idler, belt deviation correction device, belt tension device, etc. are all related to the durability of weighing quality, which is related to the lip and teeth, and the bone and meat are related. Therefore, the belt scale is better than the installation and commissioning, the belt scale is not as good as the belt quality and the belt quality, as well as the belt tension device. It is suggested that the Department with economic conditions and scientific research capacity should develop belt tension indicator and belt tension monitoring controller while developing high accuracy belt scale.

6、 Application analysis of belt scale in mining industry

Although the belt conveyor does not meet the requirements for installing the belt scale and does not need to be reformed, it can only be installed on the belt without any choice. The inclination angle of DT75 and dt62 idler of normal specification belt conveyor is 30 °、 thirty-five °， For the purpose of transporting more materials, the supporting roller of mine conveyor reaches 45 °、 sixty °。 forty-five ° You can't install a belt scale, 60 ° It brings more difficulty to the installation of belt scale. If the belt scale is not equipped with installation conditions strictly, it is required to drive the installation at 60 for economic benefit ° Belt scale on belt conveyor, belt groove angle is 35 when no-load °， 60 at loading °， I don't know how accurate this weighing method can bring to belt scale. In order to save production cost, a mining enterprise has decided to install a belt scale to measure the incoming materials in a long belt, and at the same time, the return belt is used to transport the incoming materials. It is decided to install a belt scale for measurement on the upper and lower belts respectively, which has aroused great interest of the author and decided to design the spot mining point, but it was lost in the bidding process.

7、 Closing remarks

At present, belt scale is divided into four parts: weighing sensor, speed sensor, weighing scale frame and cumulative display, and others are divided into three parts: load carrier, displacement sensor and cumulative controller. The load carrier includes: belt (effective weighing section, auxiliary weighing section), weighing roller, auxiliary idler, weighing scale frame and weighing sensor. The latter is a more scientific division. Belt scale is widely used in port, wharf, thermal power plant, furnace, metallurgy, mining, cement industry, etc.

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