1、 The material selection for the barrel screw is 38CrMoAlA, and the structural characteristics of several types of barrel screws are introduced as follows:
- Differences in conventional, low filler, and high filler structures
(1) Geometric shapes and pairing relationships of screw edges and grooves
Low CaCO3 content: larger between screw flights
High CaCO3 content: The gap between the screw flights should be small, with the aim of improving shear force and increasing plasticization
(2) The role of each regional segment. The screw is generally divided into: feeding section, compression section, blocking section, mixing section, exhaust section, and metering section.
Feed section: Generally, the screw flights gap in the conveying section is large, resulting in fast conveying. Conversely, it is small. It is also related to the formula and CaCO3 components.
Compression, blocking, and mixing: The main impact is on the plasticization ability. If there is no blocking before compression, plasticization can be increased. If there is a blocking, it is not suitable for high calcium. Mixing and compression are set together, usually only suitable for low calcium.
Exhaust section: The plasticizing ability of the material can be observed from the vacuum port, which includes granular, powder, and strip shapes.
Measurement section: If the screw flights clearance is large, the extrusion is fast, otherwise it is small.
- Introduction to the structural characteristics of low and high packing: The feeding section, compression, and mixing of the low packing screw are connected together. During machining, the last section of the feeding section has a smaller lead and becomes a compression section. Then, a groove is made on the compression section and two rounds of material blocking are added to increase plasticization. The exhaust section and metering section at the back have a slightly larger gap compared to the screw edge; The high packing screw structure consists of a feeding section, a blocking section, a compression section, a blocking section, a mixing section, an exhaust section, and a metering section. The screw edge gap between the feeding section and the metering section is relatively small.
- Introduction to screw and barrel constant temperature control structure
Internal circulation: Automatic circulation of distilled water
External circulation: The screw temperature control can be set to control the material temperature. It can protect the screw during the startup and production process, ensuring stable production. If not used, the product needs to change color for the processing technology of the profile.
Barrel temperature control: There are two types: air cooling and oil cooling. Relatively speaking, the accuracy of oil cooling temperature control is greater than that of air cooling temperature control. However, the oil circuit is prone to blockage during use, and the failure rate is higher than that of air cooling.
2、 The influence of screw structure on pipe products
- Requirements for screw structure of PVC pipe products with fillers of less than 30 parts, less than 80 parts, and less than 120 parts:
120 or more CaCO3: The gap between the measuring sections should be small. If the gap between the measuring sections is large, the compression will not be enough. Mixing will increase the number of grooves, which determines the plasticizing effect. High calcium screws will be used; Below 80 portions, high calcium screws are used, but the gap between the feeding and metering section screws is reduced; Less than 30 parts: the feeding mixing section and compression section are connected together, and the measuring section has a relatively large clearance between the screw edges.
- The structural changes of low and high filling screw have an impact on processing technology and mechanical properties of products
Different formulas require different screws, such as the amount of CaCO3 and lubricant. If there is more lubricant, the plasticization effect is not good and the flow performance is significantly improved.
- The impact of high filler production formula on the lifespan of machine barrel, screw, material, heat treatment, etc
The high filler production formula has a significant impact on the wear of the barrel and screw, and its service life is not long. Generally, wear begins in 5-6 months when the content of 100 CaCO3 is above, and after about a year of use when the content of 80 CaCO3 is below, it begins to wear, resulting in quality problems such as blue lines and black lines. Most of the barrel wear occurs above the vacuum port and metering section, and the screw, except for the feeding section, has varying degrees of wear. The barrel and screw measuring section are made of alloy, and their wear and tear are relatively better than ordinary structures, but their service life will not exceed two years.