I. Preface
With the development of the grain and feed industry and the improvement of its production, processing and storage and transportation automation, manual weighing packages are adopted
The original way of loading has been replaced by intelligent computer-controlled quantitative packaging scales (hereinafter referred to as packaging scales), and even by fully automated weighing and packaging production lines controlled by computers. This has also greatly enhanced work efficiency, reduced labor intensity, and improved the working environment for workers. Grain and feed enterprises can select packaging scales based on their own process requirements and material properties. During the usage process, they also pay more attention to maintenance, repair and calibration, which enables them to use packaging scales better and ensure their weighing accuracy at the same time. Even if grain and feed enterprises can correctly select packaging scales based on their own process requirements and material properties, but do not pay attention to maintenance, repair and calibration during use, they may not be able to use the packaging scales well, let alone ensure the weighing accuracy of the packaging scales. If enterprises engaged in grain and feed cannot correctly select packaging scales based on their own process requirements and material properties, and do not attach importance to maintenance, repair and calibration during use, or use them poorly or not at all, it is even more impossible to ensure the weighing accuracy of the packaging scales. This phenomenon is still quite common in grain and feed production enterprises, causing inconvenience to the enterprises and even leading to unnecessary economic losses.
At present, domestic enterprises that produce packaging scales require user units to make correct selections, and user units also hope to produce packaging scales
Enterprises provide high-quality products that meet their own process requirements and material properties. However, not many packaging scales are used well. The main problem is that the packaging scales cannot adapt to some materials with different mechanical and physical properties, resulting in the weighing accuracy not meeting the national requirements (0.2%). There are many factors that affect the accuracy of packaging scales. We must identify the main influencing factors in order to find solutions. This is the issue we have seriously discussed in this article.
Ii. Overview of Packaging Scales
There are many domestic manufacturers of packaging scales of the same type. Judging from the principle and structure of packaging scales, they are basically the same
How much difference there is? Packaging scales are all composed of mechanical devices and computer intelligent control parts, and can all complete fast and slow feeding and quantitative weighing
Processes such as weighing, bag clamping and loosening, and seam conveying. The mechanical device includes the feeding mechanism, mechanical scale body (including scale bucket, transition bucket and bag clamping bucket), bag clamping and loosening mechanism, bag sewing and lifting mechanism, belt conveying equipment, pneumatic components, etc. The computer intelligent control section includes load sensors, electric intelligent weighing instruments and PLC program controllers, etc.
Except for manual bagging, packaging scales generally have the following functions: fast and slow feeding and quantification, bag clamping and unloading are all controlled by PLC programs. Some packaging scales are directly controlled by computer intelligent weighing instruments with programs, except for on, off and indicator lights, relay
Electrical components such as appliances have been reduced to the minimum. Self-falling packaging scales can operate without relay components, ensuring absolutely reliable and error-free operation. The Diannao intelligent weighing instrument can set parameters such as fast and slow feeding amounts, display over-tolerance and overload alarms, and can be equipped with a print output. Some computer intelligent controllers have functions such as weight or package count accumulation and communication with the upper computer through the RS232 port. Some packaging scales are equipped with electronic counters on their display panels to record the number of packages, preventing the loss of package data in case of power failure. Some packaging scale manufacturers use imported intelligent weighing control instruments, while others use domestic ones. Whether imported or domestic, the accuracy of its A-D conversion and the reliability of its program control have reached A considerable level. The weighing control instrument and PLC program controller, especially the PLC program controller, are generally imported and have high reliability. Their impact on the weighing accuracy of the packaging scale is not significant. Therefore, no further discussion will be made here. Iii. The Impact of Feeding Method on the Weighing Accuracy of Packaging Scale The process requirements are mainly related to the feeding method of the packaging scale. Correctly selecting the feeding method of the packaging scale can ensure that the quality of the material is not affected during the feeding and conveying process, and also ensure that the fast and slow feeding of the packaging scale is stable and reliable, which is conducive to improving the weighing accuracy.
When grain and feed production enterprises choose packaging scales, they should consider the type of their products and what kind of materials they contain
Physical properties, such as the shape, particle size, bulk density, surface friction coefficient, fluidity and adhesion of packaging materials, etc. What type of packaging scale should be selected based on the physical properties of the packaging materials? No packaging scale can adapt to the weighing and packaging of various materials with different physical properties. That is to say, the adaptability of packaging scales to materials is relatively poor. The prominent advantage of the packaging scale with belt feeding is that the feeding will not cause the material to break or automatically grade, and will not affect the product quality. Therefore, this packaging scale is most suitable for weighing and packaging materials such as pressed granular materials, expanded granular materials, expanded sheet materials and cake meal. This packaging scale also has some shortcomings, namely, its sealing performance is relatively poor. Although complete powder feed can also be weighed and packaged, its effect is inferior to that of pellet feed. Packaging scales with belt feeding should not be used for legume granules with good fluidity, premixes containing stone powder as the carrier, and special feeds such as eel, shrimp and crab with slight adhesion. For granular materials with good fluidity such as rice, wheat and beans, self-falling feeding and packaging scales can be selected. For premixes with stone powder or attapulgite as carriers and good fluidity, packaging scales with screw conveyors for feeding can be used. Moreover, it is required to adopt inclined screw conveyors with an outlet higher than the inlet for feeding to prevent materials from still flowing out of the screw conveyor blades when the screw conveyor stops rotating, which may affect weighing or pollute the environment. For slightly sticky and fine-grained eel, shrimp, crab feed and additives, etc., a packaging scale with screw conveyor feeding can be selected. The notable feature of the packaging scale with screw feed is its excellent sealing performance, which makes it less likely to cause dust leakage.
As mentioned above, choosing the appropriate feeding method can meet the required process requirements. The feeding of the packaging scale is fast, stable and symmetrical
The measurement accuracy will not be greatly affected.
Iv. Main Factors Affecting the Accuracy of Packaging Scales
The influence of the feeding method of the packaging scale on its accuracy has been discussed in detail. Apart from the feeding method, the other parts of the packaging scale vary greatly due to differences in the application scenarios, industries, weighing ranges, and accuracy requirements. Different types of packaging
Other parts of the scale also have their own specificities and unique structures to adapt to certain specific occasions and requirements. The main factors considered in the design of other parts of the packaging scale are the physical properties of the packaging materials to be weighed, including the particle size, bulk density, spillability, fluidity, hygroscopicity and adhesion of the materials. The different properties of the materials to be weighed and packaged determine the diversity of the structure of other parts of the packaging scale. To adapt to the diversity of materials, the other parts of the packaging scale have various structural forms and are divided into multiple types. Different types of packaging scales not only have different feeding methods, but also have different structural forms in other parts. Some packaging scales contain scale hoppers, transition hoppers and bag clamping hoppers. Some packaging scales only have bag clamping hoppers but no scale hoppers or transition hoppers. Some packaging scales are equipped with a material cutting device at the feed outlet. Some packaging scales are equipped with a cut-off door at the end of the screw conveyor's feeding and discharging shaft. Some intermediate weighing scales that do not require packaging bags and only serve the purpose of measurement do not include bag-holding hoppers, etc.