Multi-component batching system in a spunmelt nonwoven production line

In the spunmelt nonwoven production line, including the main raw materials, one raw (auxiliary) material is called a component, and how many components are disposed in the batching system depending on the type of raw (auxiliary) material added. The general production line has at least two components, three components are the more common configuration, and the four components can satisfy more complicated products (such as: adding whitening agent, masterbatch, functional masterbatch or cooling masterbatch) ) The production requirements, as well as a small number of production lines are equipped with a five-component batching system.

The multi-component batching system of the spunmelt production line generally consists of a feeding device, a stocking device, a metering device and a mixing device.

First, the feeding device

The function of the feeder is to provide the system with the main materials (polymer chips) and excipients (masterbatch, functional masterbatch or cooling masterbatch, etc.) required for the production process. Commonly used feeding methods are compressed air (or high pressure air flow) positive pressure feed and vacuum negative pressure suction.

Second, the storage device

The function of the storage device is to temporarily store the material conveyed by the feeding device and supply the metering device underneath it in a continuous manner, the number of the storage device being the same as the number of components. The largest storage hopper is generally used to store polymer chips, called the main hopper, and the others are called auxiliary hoppers.

Third, the metering device

The metering device can feed the material of the component into the mixing device below according to a predetermined ratio. The ratio of materials is calculated by weight, and the metering device is operated and calculated according to the volume flow. For a specific material, there is a proportional relationship between weight and volume. This ratio is the “weight” of the material.

The bulk density of bulk materials is not its density. It is 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 cannot be confused. For example, polypropylene (PP) has a density of 0.91, while some PP chips have a bulk density of less than 0.6.

The number of metering devices corresponds to the number of components. Commonly used measuring methods are three types: measuring cup type, screw type and weighing type.

01. Measuring cup measurement

The measuring method of the measuring cup is a graded measuring, which is characterized by intermittent feeding, small setting range and low precision. Because it relies on gravity feeding, it is sensitive to the high and low fluctuations of the material level in the mixing tank. When the material level is high, it will block the feeding and affect the accuracy of the measurement. Due to the low measurement accuracy, the calculation process is troublesome and the faults are also high. Therefore, the measuring cup type metering method has been basically eliminated in the new production line.

02. Screw metering

The screw type metering is continuous metering, which can continuously feed, set the range and have high precision. The form of the metering screw is similar to the screw of a screw conveyor, although the amount of each revolution of the spiral decreases with increasing speed, not a constant. However, in production practice, if it is not particularly strict, it can generally be treated as a constant, which simplifies the production preparation and process calculation process, and the error can be corrected during trial production to meet product quality requirements. .

03. Weighing measurement

In the process recipe, the ratio of various materials is calculated by the ratio of weight. The measuring cup type and the screw type metering are actually indirectly adjusting the proportion of addition by measuring the total volume of each material, which is easy to occur due to the bulk density of the material. The irregular changes cause a large deviation in the ratio. However, the measurement of the weight of the material directly can avoid this error. Weighing type measurement has high precision and is not affected by material shape change, but the structure is complicated, the action process is long, and the cost is high, so it is not widely used in the nonwoven fabric production line.

Fourth, mixing device

The function of the mixing device is to mix the materials sent by the components of the metering device to make the distribution of various materials uniform. There are two types of mixing methods: gravity dispersion and mechanical agitation. Most of the non-woven fabrics used in the production line are mechanically agitated mixing devices, and the materials are stirred evenly by a stirring paddle installed in the mixing drum.

The material mixing status includes the level of the material level, the fluctuation range of the material level, and the operating state of the stirring paddle. Although various materials will be further mixed in the subsequent processing and flow process, the distribution of various materials in the melt tends to be uniform, but the operation state of the mixing hopper still has a significant influence on the quality of the product. When the material is mixed unevenly, the most common phenomenon is the color difference when producing the colored product. In severe cases, the spinning is unstable, and the broken wire and the melt are broken.