What is PVC cartoon pendant? Many people have some understanding of it, but the process of how PVC doll manufacturers shape dolls is still relatively unclear. So, let's uncover how PVC cartoon ornaments are manufactured and shaped.
1. Extrusion molding: The continuous molding of a polymer melt through a certain shaped die under the extrusion action of the screw or plunger of an extruder, resulting in a continuous product with a constant cross-sectional shape.
2. Injection molding: granular or powdered plastic is added to the barrel of an injection machine, heated and melted into a flowing state, and then injected into a closed mold at high pressure and speed from the nozzle at the front end of the barrel under the rapid and continuous pressure of the plunger or screw of the injection machine. After the molten material filled with the mold cavity is cooled or heated and solidified under pressure, the mold is opened to obtain products corresponding to the mold cavity. (Heating the plastic to reach a molten state and applying high pressure to the molten plastic to fill the mold cavity)
3. Rolling forming: passing materials close to the viscous flow temperature through a series of parallel rollers rotating in opposite directions, subjecting them to compression and stretching, and forming thin sheet-like products with a certain thickness and width.
4. Secondary molding: The technology of obtaining the final shape of a product by re molding the profile obtained by one-time molding of polymer materials under certain conditions.
5. Hollow blow molding: a secondary molding technology that uses gas pressure to blow expand a rubber like billet closed in a mold cavity into a hollow product.
6. Reaction injection molding
The process of mixing two or more low molecular weight liquid raw materials with high chemical activity under high pressure (14-20MPa) at a certain temperature, causing them to collide and mix with each other, and immediately injecting them into a closed mold cavity to complete polymerization, cross-linking and curing reactions, and form products.
7. Thermoforming: The sheet is clamped on a frame and heated to a softened state. Under external force, it is tightly attached to the mold surface, and after cooling and shaping, the product is obtained.
8. Rolling effect:
During the rolling and forming process of polymer materials, thermoplastic materials are subjected to significant shear forces when passing through the gaps between the rolling rollers. Therefore, polymer macromolecules are oriented and arranged along the rolling direction, resulting in anisotropic physical and mechanical properties of the resulting film. This phenomenon is called the rolling effect.
The rolling effect is influenced by factors such as temperature, roller speed and speed ratio, gap stock, and product thickness.
9. The compression ratio of the screw, the ratio of the volume of the first screw slot in the feeding section to the volume of the last screw slot in the homogenization section. In an extruder, the screw can be divided into three sections: feeding section (40% screw length), compression section (35%), and homogenization section (metering section) (25%). Feeding section - with a smaller bottom diameter, its main function is to transport raw materials to the later section. Compression section - changes in bottom diameter, mainly used for compacting, melting materials, and establishing pressure. Homogenization section (metering section) - Squeeze the melted material in the compression section to the front end of the screw at a constant temperature and quantity. The geometric compression ratio of a screw refers to the ratio of the volume of one screw groove in the feeding section to the volume of the last screw groove in the homogenization section (metering section) of the screw. Its value is generally 2-4. Relatively speaking, the larger the compression ratio, the more uniform the plasticization of the plastic.
10. Inflation ratio:
The inflation ratio is one of the key control points in the production process of blown film.
(1) The ratio of the maximum transverse diameter of the blow molding cavity to the outer diameter of the tubular billet during hollow blow molding
(2) The ratio of the diameter of the blown film to the diameter of the die during film blowing.
The inflation ratio is the transverse expansion multiple of the film, which is actually the transverse stretching of the film. The stretching will have a certain degree of orientation effect on the plastic molecules. As the inflation ratio increases, the film becomes thinner. Although it can save materials, the film is prone to wrinkles and the strength of the film decreases; If the inflation ratio is too small, it will increase consumption, reduce the effective volume of the product, make the product thicker, and prolong the cooling time, resulting in increased costs. Therefore, according to the type and properties of the material, the shape and size of the product, and the size of the pipe blank, the blowing ratio and traction ratio should be appropriately matched to produce good products. For example, in general, the blowing ratio of low-density polyethylene (LDPE) film should be controlled between 2.5-3.0.
11. Stretching ratio: Stretching ratio refers to the multiple of the length stretched per unit length of the divided filament (blank filament) during flat filament stretching, or described as the ratio of the stretching (two pulls) speed to the stretching (one pull) speed.
The stretch ratio is the most important process indicator in the production of flat wire. The stretch ratio, also known as the stretch multiple, is a unidirectional stretching process performed below the melting point temperature. The stretching process is an orientation process to obtain high strength and other physical and mechanical properties of the flat wire. Generally, the stretch ratio is controlled at 4-7 times, and for special needs of flat wire, the involvement ratio can reach 11 times.
12. Molding shrinkage rate: refers to the percentage of the reduction in the size of a plastic part at room temperature after it is removed from the mold and cooled to room temperature, relative to its original uncooled size. Due to the fact that shrinkage is not only the thermal expansion and contraction of the resin itself, but also related to various forming factors, the shrinkage rate of the molded plastic part should be referred to as the molding shrinkage rate. This concept is commonly used in polymers.
13. Deflection: It refers to the linear displacement of the axis of a member in the direction perpendicular to the axis or the linear displacement of the middle surface of a plate or shell in the direction perpendicular to the middle surface when subjected to force or non-uniform temperature changes.
14. Weld mark: refers to the surface defect caused by the fusion of two streams of material.
A linear mark on the surface of a plastic part, caused by several streams of injected or extruded material flowing and converging in the mold. The molten material is not completely fused at the interface and cannot be fused together, resulting in fusion marks that affect the appearance quality and mechanical properties of the plastic part.
In terms of the reasons for the formation of weld lines, in order to reduce weld lines, it is necessary to reduce the possibility of material "merging after diversion" during injection or extrusion processes. To reduce and eliminate this phenomenon, there are the following methods:
1) Raise the mold temperature
2) Adjust injection speed
3) Comprehensive exhaust
4) Keep the surface of the mold clean
5) Adjust injection pressure and plasticizing pressure
6) Reasonably set the gate position