Application of Loss-in-Weight Scale in Plastic Modification Operation

In the plastic modification process, it is often necessary to mix the base materials such as synthetic resins with the required auxiliary materials (such as mineral powder, glass fiber) and additives (such as plasticizers, flame retardants, antioxidants, nucleating agents, etc.) in a certain ratio and enter the compounding extruder. This process of mixing according to the formula is called plastic compounding. Plastic compounding can be traced back to the birth of celluloid in 1870. Since then, with the development of plastic coloring, blending, filling, reinforcement and other modification technologies, the compounding technology of various general plastics and engineering plastics has also been improved. By the late 1970s, 60% of the world's thermoplastics needed to be compounded before processing into special materials or even one-time molded products. At the same time, the research and development of various compounding equipment (co-rotating twin screws, reciprocating single screws, continuous mixers, etc.) has also made great progress.

Early mixing equipment was batch type, requiring multiple materials to be mixed in sequence. Due to the various disadvantages of batch mixing equipment, a US company launched the world's first generation of continuous feeding equipment in 1972, which later evolved into a loss-in-weight (weighting) scale. In the continuous mixing and extrusion process, various raw materials can be added continuously and synchronously through it, and the addition speed of various raw materials is based on the corresponding ratio (formula) to obtain sufficient accuracy.

At present, with the increasing demand for product quality, working environment and automation, the application of loss-in-weight scales is becoming more and more widespread. It is estimated that the proportion of twin-screw extruder production lines equipped with loss-in-weight scales in the domestic market is gradually increasing, about 10-20%, but the overall proportion is still very low, while the proportion in developed countries is 60-70% or higher. It is expected that the market demand for loss-in-weight scales will be explosive in the next few years.

Loss-in-weight scale principle

The loss-in-weight scale uses the weighing hopper and the entire feeding mechanism as a scale body for weighing. As the material flows out of the loss-in-weight scale, the control system collects the weight signal of the scale body at a high speed and high frequency to obtain the weight reduction of the material in the weighing hopper per unit time. Then, through TRUSTAR's unique filtering and optimization processing, the actual flow rate of the loss-in-weight scale is obtained. At the same time, the control system compares this feeding speed with the preset given speed, and calculates the comparison result and feeds it back to the feeding mechanism of the loss-in-weight scale to automatically correct the feeding speed of the feeding mechanism, forming a closed-loop control, so that the actual flow rate is infinitely close to the given flow rate, thereby meeting the control requirements.

Workflow

1. First, the customer's raw material supply warehouse feeds the hopper of the loss-in-weight scale. When the system detects that the material has been added to the set position, the feeding process is automatically stopped;

2. After the feeding is completed, the loss-in-weight scale starts to run. During the operation of the loss-in-weight scale, the weighing sensor collects the flow data in real time and sends it to the weighing controller for processing. After calculation, the real-time processed data is transmitted to the touch screen for screen display and data communication, and the motor speed is controlled on the other hand to achieve the purpose of real-time flow adjustment;

3. During the operation of the loss-in-weight scale, the material in the hopper of the loss-in-weight scale is gradually reduced. When the material in the hopper of the loss-in-weight scale drops to the set feeding range, the Siemens output module controls the feeding device to start feeding. At the same time, the loss-in-weight scale runs in precise volume mode to ensure stable and accurate flow.

Through the reciprocating operation of the above links, the loss-in-weight scale product can continuously and accurately feed and output materials.

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