The composition and function description of the multi-component batching system in the spunmelt nonwoven production line

In the spunmelt nonwoven production line, including the main raw materials, a raw (auxiliary) material is called a component, depending on the type of raw (auxiliary) materials added, how many components are configured in the batching system. A general production line has at least two components. Three components are a common configuration. The four components can meet more complex products (such as adding brighteners, color masterbatches, functional masterbatches or cooling masterbatches at the same time ), and a small number of production lines are equipped with a five-component batching system.　　The multi-component batching system of the spunmelt production line is generally composed of a feeding device, a storage device, a metering device, and a mixing device.　　1. Feeding device The function of the feeding device is to provide the system with the main materials (polymer chips) and auxiliary materials (color masterbatch, functional masterbatch or cooling masterbatch, etc.) required by the production process. Commonly used feeding methods include compressed air (or high-pressure air flow) positive pressure feeding and vacuum negative pressure suction.　　Second, storage device 　　The function of the storage device is to temporarily store the materials conveyed by the feeding device, and to continuously feed the metering device installed below it. The number of the storage device is the same as the number of components. Generally, the largest storage hopper is used to store polymer chips, called the main hopper, and the others are called auxiliary hoppers.　　3. Metering device 　　The metering device can send the material of this component into the mixing device below according to a predetermined ratio. The proportion of materials is calculated by weight, while the metering device is operated and calculated by volume flow. For a specific material, there is a proportional relationship between weight and volume, and this ratio is the material's bulk density.　　 The bulk density of a bulk material is not its density, but the weight of the material in a unit volume including a large number of voids. In addition to the density of the material, it is also related to the particle size and uniformity of the material, so it should not be confused. For example, the density of polypropylene (PP) is 0.91, while the bulk density of some PP slices is less than 0.6.　　The number of metering devices corresponds to the number of components. Commonly used metering methods include measuring cup type, screw type and weighing type.　　01. Measuring cup type measuring 　　 Measuring cup measuring method is graded measurement, which is characterized by intermittent feeding, small setting range and low precision. Because it relies on gravity feeding, it is more sensitive to high and low fluctuations of the material level in the mixing tank. When the material level is too high, it will block the feed and affect the accuracy of measurement. Due to the low measurement accuracy, the calculation process is troublesome and there are many faults. Therefore, the measuring cup type measurement method has been basically eliminated in the new production line.　　02. Screw type measurement 　　 Screw type measurement is continuous measurement, can feed continuously, has a large setting range and high precision. The form of the metering screw is similar to the screw of the screw conveyor, although the displacement of each revolution of the screw will decrease with the increase of the speed, which is not a constant. However, in production practice, if there are not particularly strict requirements, it can generally be treated as a constant, thereby simplifying the production preparation and process calculation process, and the errors that appear can be corrected during trial production to meet product quality requirements . 03. Weighing type metering In the process formula, the ratio of various materials is calculated in proportion to weight. Measuring cup type metering and screw type metering are actually indirectly adjusting the adding ratio by measuring the total volume of each material , It is easy to occur due to the irregular change of the material bulk density resulting in a large deviation in the ratio. However, the measurement method of directly weighing the material weight can avoid this error. Weighing type measurement has high accuracy and is not affected by changes in material shape, but it has complex structure, long action process and high cost, so it is not widely used in non-woven fabric production lines.　　Four. Mixing device 　　The function of the mixing device is to mix the materials sent by each component metering device to make the distribution of various materials uniform. There are two mixing methods: gravity dispersion and mechanical stirring. Most of the non-woven fabric production lines use mechanical agitating mixing devices, which use a mixing paddle installed in the mixing tank to mix the materials evenly.　　The mixing state of materials includes the height of the material level, the fluctuation range of the material level, and the operating state of the stirring blade. Although various materials will be further mixed in the subsequent processing and flow process to make the distribution of various materials in the melt tend to be uniform, the operating state of the mixing hopper still has a significant impact on the quality of the product. When the materials are not uniformly mixed, the most common phenomenon is the chromatic aberration in the production of colored products. In severe cases, the spinning will be unstable, and the phenomenon of broken filaments and dripping will occur.