Molding is the process of converting various shapes of plastics (powders, granules, solutions, and suspensions) into desired shapes or blanks. There are numerous molding methods, primarily including extrusion, injection, calendering, pressing, die casting, hollow forming, and thermal forming in Chongqing plastic bags.
(One) Extrusion Molding
Extrusion molding, also known as extrusion or extrusion molding, is a process that utilizes extruders and extrusion molding dies. During plastic processing, the raw materials for Chongqing plastic bags typically undergo heating and pressure in the extruder barrel. The molten material is then extruded through a mold at the extruder head and cooled to form a continuous product with a specific cross-sectional shape. Extrusion molding holds a significant position in the plastic processing industry, being one of the earliest molding methods and accounting for over one-third of the total plastic production. It can process the majority of thermoplastic plastics and a few thermosetting plastics, with the main products including films, sheets, pipes, rods, filaments, meshes, wire and cable coatings, and special shapes. With additional equipment, it can also produce hollow containers and composites. Moreover, extrusion molding can be used in the blending processing of plastics, completing tasks like coloring, filling, and blending through the extrusion granulation process. Its main characteristics are continuous production, high efficiency, uniform product quality, simple operation, easy process control, and versatility.
(II) Injection Molding
Injection molding, also known as injection molding, is a process that utilizes injection molding machines and molds. During plastic processing, the injection molding machine continuously feeds granular or powdered plastic material into the barrel of the machine, where it is heated and melted into a fluid state.
Afterward, the molten material is injected into the cooler closed mold through the nozzle at the end of the barrel, propelled by the plunger or screw. Under pressure, the material fills the mold, cools, and solidifies to maintain the shape given by the mold cavity, resulting in the finished product. The injection molding of thermosetting plastics is achieved through heating and curing within the mold. The production process of injection molding is cyclic and suitable for all thermoplastic and some thermosetting plastics. Injection molding is one of the most commonly used methods in plastic processing today, with more than half of the plastic molding molds being injection molds, accounting for approximately 20% to 30% of the total volume of plastic products. The applications of these products have expanded from consumer use to various fields of the national economy and are gradually replacing traditional metal and non-metal products. These products mainly include various industrial components, parts for instruments and meters, and casings, etc. The main characteristics of injection molding are short production cycles, high production efficiency; the shapes of the molded products range from simple to complex, and sizes vary from small to large, with precise dimensions: they can be produced automatically and at high speed.
(3) Rolling and Shaping
Calendering is a primary molding method for thermoplastic plastics, involving the extrusion of molten and plasticized material close to its viscosity flow temperature between two or more parallel rolls. As the material passes through the rotating rolls, it undergoes compression and extension, forming continuous sheet products of specified dimensions (with the rolls serving as the molding mold). Alongside extrusion and injection molding, calendering is one of the three main molding methods for thermoplastic plastics. Calendered plastic products account for about one-fifth of the total plastic molding output, including films, sheets, artificial leather, and calendered composite flooring, among others. Suitable thermoplastic materials for calendering include polyvinyl chloride (PVC), polyethylene, polypropylene, ABS, and polyvinyl alcohol, although PVC is currently the most used. Calendering is characterized by its high processing capacity, fast production speed, good product quality, continuous production, and high level of automation. However, it has the drawbacks of large equipment, long production processes, high investment, complex maintenance, and limited product width due to the roll length, which lags behind extrusion in the development of continuous sheet production.
