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Mechanical mixing equipment works with the selection of load cell
This paper engineering machinery mixing equipment weighing system and the basic requirements for special requirements, proposed construction machinery mixing equipment weighing system used to be considered when the sensor several issues, the focus of sensor protective structure on the construction machinery mixing equipment reliability of operation, pointing out that the code generation IP Table protective levels can not cover mechanical mixing equipment works full protection of the sensor requirements. Recommendations different types of mixing equipment selection of different defensive capabilities of the sensor.
???? Weighing System sensors normally used in the weighing system to consider the amount of limited accuracy, sensor installation space, the environment may affect the sensor, load and the type of sensor, such as the life span of various factors. Engineering machinery mixing equipment weighing system is no exception. The weighing system is different because of different demands, different working conditions, to be considered by focusing on different issues only.
???? Engineering machinery mixing concrete mixing equipment usually include floor (stations), the asphalt mixing plant, stabilized soil mixing concrete mixing plants and ships at sea, mixing them with concrete floor (stations) the most typical. Below the concrete mixing plant (stations) as an example for analysis.
1 concrete mixing plant (station) on the basic requirements Weighing System
1.1 accurate weighing error on the strength of concrete is strongly influenced, in particular water-cement ratio measurement precision, because strength and water-cement ratio is linear. The relevant national standards, cement, water, additives, the admixture of dynamic measurement accuracy of ± 1%, sand, stone dynamic measurement accuracy of ± 2%.
1.2 Quick meet mixing station duty cycle requirements.
1.3 variety that money to the type of pre-selection, to facilitate the transformation to adapt to a variety of different ratio and capacity requirements.
1.4 simple structure weighing devices to simple structure, solid and reliable, stable performance, easy operation.
???? Clearly, the use of electronic weighing system sensor machinery weighing more than meet the requirements. Therefore, the load cell floor in the concrete mixing stations to be more widely used. However, objectively speaking, compared with the mechanical lever scales in the "solid and reliable, stable performance," as a sensor electronic weighing system has much work to do.
2 concrete mixing stations floor in the load cell operating conditions
???? For commerce and the general measurement of electronic scales a great difference is, in concrete mixing stations floor load cell in a very adverse operating conditions, stress environment is very complex, and the general electronic products compared to the operating environment, a greater randomness.
2.1 ambient temperature and humidity
???? Concrete mixing station is normally open floor installation, sensor may be subject to the sun and rain, temperature dramatic changes. And many construction projects are in very bad natural conditions in the mountains or remote areas. Therefore, we must consider greater temperature range and higher humidity conditions. Concrete in the production process needs water. In the delivery of water and weighing process and also have a lot of water in the gas, in some form within relatively small humid environment. Stir in the temperature control in the House, there are high-temperature and low-temperature conditions of the different requirements of condition. Running in the summer when low-temperature condition to the zero-below cold wind and加冰stirring, then building a condensed water will be well demonstrated high humidity building.
2.2 dust
???? Concrete in the production process requires a large amount of cement, coal ash and the appropriate amount of admixture. These were in the transportation and powder weighing process will produce dust. Even the aggregate, in the course of transmission have also dust. Some of these dust sensor will be attached to the surface. The dust and water vapor in the common role, the sensor will be more serious corrosion. Therefore, the damage powder weighing sensors usually weigh than the other sensors more frequently.
2.3 Shock and Vibration
???? In the feed process, the impact of aggregate will have. Sensors should be able to bear 5 g acceleration. Stir in the process, will have sustained vibration, and vibration would have fatigue damage.
2.4 man-made environment
???? Man-made environment is the product reliability design one of the factors that must be considered. Concrete Mixing floor installed at the construction site in general. Large-scale use of temporary workers on site, of which a considerable number of temporary low level of education, lack of the necessary skills. In terms of facilities, such as the maintenance and cleaning work, the sensor may be in the high-pressure water sputtering, misoperation caused overload, and so on. Clearly, the sensor should be in such an environment and a long-term reliable under the conditions of the operation is to carry out some special design.
????? These basic requirements and operating conditions can be used as concrete mixing plant (stations) by the load cell selection basis.
Three concrete mixing plant (stations) to use when weighing sensor to be considered by the Selection Problems
3.1 weighing sensor payload capacity determination
???? Weighing sensor payload capacity usually
???? Hopper sensor rated load = + rated themselves that weight
???? (0.6 ~ 0.7) × only a few sensors
????? In fact people in the choice of sensor integrated capacity even when they consider the size and impact load selected safety factor. Safety factor with the choice of sensor sensitivity closely related. Domestic and foreign common strain load sensor sensitivity majority of 2 mV / V, but there are 1 mV / V, such as column sensor; Also 3 mV / V, as some cantilever sensor and sensor plate Central; Twisted ring sensor usually 2.85 mV / V. Stir upstairs in the use of sensors are basically 2 mV / V.
3.2 weighing the choice of sensor accuracy
???? The choice of sensor accuracy of the weighing system to meet the accuracy requirements, is not one-sided pursuit of the high level sensor accuracy. In multi-sensor combination used only when its integrated error
Δ r = δ / √ n
Where, δ only a single sensor accuracy, the use of combinations of n is only a few sensors.
????? Currently stirring upstairs popular S-type sensor, the cantilever sensor, the sensor plate ring, linear, hysteresis, repeatability, and temperature sensitivity effects of creep, and other key indicators vast majority of manufacturers are is better than 0.05%, the majority of manufacturers better than 0.03%, some manufacturers better than 0.02%. Its integrated single sensor error of close to or better than 0.1%. Multi-sensor combination only after its integrated error even smaller. It can be said that the general load cell manufacturers of products to meet the requirements.
????? Previously, many manufacturers stirring floor, its provisions static accuracy of the weighing system, respectively 0.1% and 0.3% respectively. Thus, the use of single-sensor weighing only, individual indicators of 0.05% of the sensor will satisfy 0.3% precision weighing requirements. The use of three over the weigh-sensor, single indicators 0.05% sensors can also meet 0.1% accuracy requirements.
???? It must be pointed out is that the accuracy of the weighing system is static precision, while the concrete is the national standards require dynamic accuracy, which is due to the constant weighing of raw materials for the material in the body of gravity weighing the impact of errors increased significantly. Above 0.1% and 0.3% respectively, the ability of static accuracy reached 1% and 2% of the dynamic accuracy for feeding system with the design.
????? Now, many manufacturers provisions of the accuracy of its weighing system in the 0-rated weighing that money within the cement, water, additives ± 1%, sand, stone ± 2%. Notes, ready-mixed concrete national standards require that physical measurement accuracy, and general measurement instruments 0 ~ 20% of the relative error greater, or concrete mixing plant (station) provides the industry standard in the 20 ~ 100% of the weighting of the meet cement, water, additives ± 1%, sand, stone ± 2% of the more practical measures to allow some deviation. A more reasonable approach is the use of precision weighing instrument tagging industry terminology to express that as a cumulative hopper scales should be used in automatic weighing accuracy of the grading marks 1.0 and 2.0. Such scale test project in line with the purposes, including both materials testing (determining the accumulated error) also includes static test.
?? Automatic Weighing at its maximum allowable error in Table 1.
Criteria used in a static load test and non-automatic weighing, should meet the requirements in Table 2.
????? Usually 1.0 weigh design for the 1000 points, 2.0 Balance of design for 500 points. We can see that the range in the high-1.0 scale error is 0.15%, 2.0 Balance of error is 0.3%, not manufacturers than before provisions of 0.1% and 0.3% static high accuracy. But in the low range of accuracy is indeed increased. Under such circumstances the need to confirm the selection in the low range of the sensor can also meet the requirements.
???? According to weigh the degree of choice of the simplest sensor is 1,000 points method of selection of 1000 at the weigh-in sensors, 500 hours of the weigh-selection 500 points of the sensors. National standards in weighing sensor accuracy is to use the degree to express, but because of various reasons, most production plants that still use single indicator sensor accuracy. According to individual users to calculate indicators integrated precision error. Choose up trouble point.
????? The concrete mixing of foreign developed countries floor general with precision weighing system to the degree that, in the 1000 Indexing. They may be related to the use of high-performance concrete high proportion of the.
????? As the economy and the continuous development of technology, ultra-high-rise building, long bridges, large-scale water conservancy projects, as well as other exposed to the harsh environment in the construction of concrete performance raised higher and higher demands, concrete technology has also entered the high-tech age, the proportion of high-performance concrete continuous improvement. In addition to producing high-performance concrete correct selection of raw materials, determine a reasonable process parameters, the construction technology of control is also very important. Stir ingredients in the concrete floor, the accuracy of the system is important.
3.3 sensor structure forms of choice
????? Commonly used a pull-type S-shaped sensors, the plate center ring and ring cruciate tendons, such as plate. Cross center ring reinforcement plate high accuracy sensors, anti - partial contains excellent performance, but higher prices are normally only used in high-precision measurement occasions. Mixing upstairs is commonly used S-type sensors and sensor plate Central. S-type sensor which its high accuracy, anti - partial-carrying capacity, at the same time can bring overload protection, the wide range of use of the advantages of the largest.
???? Popular pressure sensor of a cantilever beam, Spoke, column, bridge, such as ring-twisting. Considered accuracy, range of installation, price and other factors, the vast majority of production plants to choose stirring floor of the cantilever.
3.4 load type of consideration
???? Concrete production mainly uses sand, gravel, cement and water, additives, admixture. Several materials weigh the impact of a few stone as the greatest. In the large family of electronic scales, such is not the greatest impact, the sensor can generally bear overload situation.
????? From the author of the survey, the sensor overload and damage due to the situation from time to time. For example, a control system fault, causing heavy material disposal and the next, causing overload. Also the use of human factors during the overload, especially the small range sensor for the operator stampede Scale Frame and overload damage things happen from time to time. Therefore sensor, sensors whether Weighing System Overload Protection for the reliable operation of a certain influence.
Sensor performance indicators have two with this, first allowing overload, first limit overload.
Allow overload refers to shed the load, sensor performance indicators unchanged. Limit overload refers to the load sensor does not produce harmful permanent mechanical deformation.
???? General overload sensor allows for 150%, and overload limit in 200% ~ 300%. Some of the sensor with overload protection are likely to exceed the scope of one. Sensors such as Putian factory CFCKN-1 - because of their special sensor design, allowing the load as high as 500%. Such frequent overload sensor in the case can reliably work.
3.5 sensor protection rating
???? Sensor IP protection levels that are usually used. General sensor manufacturers said their products have reached IP67 level, a small number of manufacturers of some products to IP68 level.
????? We know that the IP code is expressed by not more than 72.5 kV voltage electrical products protective shell of grading. National standards "GB4208-93 shell protection levels", IP67 means the product can dust, and against short-term immersion; IP68 means the product can dust, and against continued diving impact. It must be pointed out is that such protection does not include mechanical damage, corrosion, or external influences such as humid environmental conditions. Usually involving such protection provided by the relevant product standards. Weighing sensors and general electrical products and secondary products of different instruments, it is also a force component in the operation of constantly being produced and the role of deformation. There is also likely to be shock, impact or impact such a mechanical damage, dust and water vapor to the more common under severe corrosion and in extremely humid conditions running. This is GB4208-93 under the test conditions are quite different.
???? Have encountered such a situation: a weigh-ore mines on selected imports sensor, a large steel ladle weigh on the selection of an internationally renowned brands sensors, are welded, sealed and very beautiful, to IP68 level. But in actual life very short scene. In the last resort circumstances, the trial of Putian sensor plant products. The accident came as the result of their service life in excess of imports sensor. One in a large steel ladle weigh on the sensor has been in operation for seven years, are still running.
In these two examples, the fact is the protection of distinction. First, there were still no shell casing; Second, weld design. Third, sealing materials.
???? Generally speaking, the design is better than no shell casing design; The design of the weld seam should be avoided as far as possible by force. In the unavoidable circumstances, will have to check weld strength, in particular the fatigue strength. Fatigue cracks are caused minor tidal lead entry, the important reasons for sensor failure. The aforementioned welding of a world-renowned brand sensor at the scene sealed the reasons for the short life of excessive reliance on the welding is sealed, the internal strain tablets only a thin plastic seal level, once weld cracks, moisture sensor on the role in the rapid failure. In sealing materials need to be reminded that, through IP67 half-hour soaking test sensors may not be able to know, sensor-standard damp heat in the 12-cycle test.
???? Subject to the impact of price competition, many canceled sensor plant protection frames, pull-type sensor is even worse. The current domestic production of S-type sensor, the sensor plate Central almost canceled shell.
???? Indeed, on many occasions there is nothing wrong with doing so. However, in such a concrete mixing plant environmental conditions, may not be the best choice. I plant for the design of the Three Gorges Project mixing plant production CFCKN-1 Case closure welding sensor service life up to 10 years. We have seen the United States and Japan upstairs Europe concrete mixing with the pull-type sensor is with the protection of the majority of the shell. They think that should be a semi-permanent sensor devices, life should not be less than 106 times.
??? Years of practice has proved that, CFCKN-1-S-type sensor and sensor ordinary compared to a minimum the following advantages:
① shell thickness, and against mechanical damage, in particular the strong anti-collision outside;
② weld depth, corrosion resistance to wear a long time;
③ overload protection gap is within the shell, do not dust or debris accumulated by blocking;
Weighing sensor design is a reasonable shell weighing device "solid and reliable, stable performance," an important guarantee for selection, must be seriously considered.
360 different types of mixing the selection of load cell breakdown
???? Large and medium-sized water conservancy projects of concrete mixing plant, urban commercial concrete mixing plant, small irrigation works and highway construction in the county used in the concrete mixing plant size specifications, the use of continuous-time, the installation locations environmental conditions are very different from the production of concrete performance requirements are very different . Therefore, the reliability of the sensor, the protective properties in grades also have different requirements, should be treated differently. Long hours of continuous operation, harsh environmental conditions and the production of high-performance concrete mixing plant should choose reliability, a high level of protection sensors. The remaining requirements can be appropriately reduced. For running on the concrete mixing vessel at sea, it is also necessary to consider the request of anti-salt spray, not individually elaborate here on the.