The basic requirements and special requirements of the weighing system of engineering machinery mixing equipment are put forward. Several problems need to be considered when selecting the sensor of the weighing system of engineering machinery mixing equipment. The influence of the protective structure of the sensor on the operation reliability of the mixing equipment of engineering machinery is analyzed. It is pointed out that the degree of protection represented by the IP code cannot cover all the protection requirements of the engineering machinery mixing equipment for the sensor. Different types of mixing equipment are recommended for sensors with different protection capabilities.
The sensors used in the weighing system usually need to consider the weight limit of the weighing system, the accuracy, the installation space of the sensor, the possible influence of the surrounding environment on the sensor, the type of loading and the life of the sensor. The weighing system of construction machinery mixing equipment is no exception. It's just that different weighing systems have different requirements and different working conditions, so the issues to be considered are different.
Construction machinery mixing equipment usually includes concrete mixing plant (station), asphalt mixing station, stabilized soil mixing and plant, and offshore concrete mixing ship, among which concrete mixing building (station) is the most typical. The following is an example of concrete mixing building (station).
First, the basic requirements of the concrete mixing plant (station) for the weighing system
1.1. Accurate weighing error has a great influence on the strength of concrete, especially the accuracy of water-cement ratio measurement, because the strength and water-cement ratio are linear. Relevant national standards stipulate that the dynamic measurement accuracy of cement, water, admixtures and admixtures is ±1%, and the dynamic measurement accuracy of sand and stone materials is ±2%.
1.2, quickly meet the requirements of the work cycle of the mixing plant.
1.3, the type of multi-weighing pre-selection of more types, the transformation should be convenient to adapt to a variety of ratios and different capacity requirements.
1.4. Simple structure The weighing device should have a simple structure, firm and reliable performance, stable performance and easy operation.
Obviously, the use of the sensor electronic weighing system is more satisfactory than the mechanical scale. Therefore, load cells have become more and more widely used in concrete mixing plant stations. However, objectively speaking, compared with mechanical lever scales, the sensor electronic weighing system still has a lot of work to do in terms of “firm and reliable performance”.
Second, the operating conditions of the load cell in the concrete mixing plant
A big difference from the electronic scales commonly used for business measurement is that the load cells in the concrete mixing plant are in quite harsh operating conditions, and the stress environment is very complicated, and the operating environment of general electronic products More than random.
2.1, ambient temperature and humidity
Concrete mixing stations are usually installed in the open air, and the sensors may be exposed to the sun and rain, and the temperature changes drastically. However, many engineering construction projects are in mountainous or remote areas where natural conditions are rather harsh. Therefore, a larger temperature range and higher humidity conditions must be considered. Concrete requires water during the production process. In the process of water transportation and weighing, a lot of water vapor is also generated, and a relatively humid environment is formed in a certain small range. In the temperature-controlled mixing building, there are different requirements for high temperature conditions and low temperature conditions. In the summer, when running in low temperature conditions, it is necessary to pass cold air below zero and stir with ice. At this time, condensation will appear in the building, which shows the high humidity in the building.
Concrete requires a large amount of cement, coal ash and an appropriate amount of admixture in the production process. These powders produce dust during transport and weighing. Even if it is aggregate, dust is generated during transportation. Some of these dusts will adhere to the sensor surface. Under the combined action of dust and moisture, the sensor will be subject to more severe corrosion.
Therefore, the damage of the powder scale sensor is usually more frequent than the sensors of other scales.
2.3, shock and vibration
During the feeding process, the sand and gravel will have an impact. The sensor should be able to withstand an acceleration of 5g. During the agitation process, continuous vibration is generated, and the vibration generates fatigue damage.
2.4, artificial environment
The human environment is one of the factors that must be considered when designing product reliability. Concrete mixing buildings are generally installed at the construction site. Temporary workers are heavily used on the construction site. A considerable number of temporary workers have a low level of literacy and lack the necessary skills. In the maintenance and cleaning of equipment, it is very likely that the sensor is subjected to sputtering of high-pressure water and overload due to misoperation. Obviously, the sensor must be designed in such a long-term and reliable environment under such environmental conditions.
The above basic requirements and operating conditions can be used as the basis for the selection of load cells for concrete mixing plants (stations).
Third, the subdivision of the selection of symmetric heavy sensors for different types of mixing buildings
The concrete mixing plant of the large and medium-sized water conservancy project, the urban commercial concrete mixing plant, the small-scale water conservancy project, and the concrete mixing building used in the construction of county-level roads are all very different in terms of size, duration of use, and environmental conditions at the installation site. The performance requirements of the concrete produced are also very different. Therefore, there are actually different requirements for the reliability and protection level of the sensor, and should be treated differently. Sensors with high reliability and high degree of protection should be selected for agitating buildings with long continuous operation time, harsh environmental conditions and high performance concrete. The rest can be appropriately reduced. For concrete mixers operating at sea, the need to prevent salt spray is also required.