Raw Material Loading: The process begins with loading the appropriate raw materials, such as PVC (polyvinyl chloride) pellets or silicone compounds. These materials are usually stored in hoppers. For example, in the case of PVC production, the PVC pellets are fed into a heating chamber. The pellets are carefully measured and dispensed to ensure the correct amount for each molding cycle.
Mixing and Melting: The raw materials are then heated and mixed. In a PVC drip molding line, the heating elements raise the temperature of the PVC pellets to their melting point. This typically occurs in a barrel – like structure with a screw – type agitator. The agitator rotates, ensuring that the material is evenly melted and any additives (such as colorants, stabilizers, or plasticizers) are well – distributed. The temperature and mixing speed are carefully controlled to achieve the desired consistency of the molten material. For silicone, the process is similar, but the temperature and additives are adjusted according to the specific requirements of silicone molding.
Molding Process
Injection or Drip Mechanism: Once the material is in a molten state, it is transferred to the molding area. In an automatic drip molding line, the material is either injected or dripped into the mold cavities. In a drip – based system, the molten material is carefully dispensed in a controlled manner through precision nozzles. The nozzles are designed to ensure a consistent flow rate and droplet size. For example, when making small keychain pendants, the droplets are precisely controlled to fill the intricate details of the mold. In an injection – molding – like setup (which may also be part of an “automatic drip molding” process in a broader sense), the molten material is forced into the mold under pressure through a runner system.
Mold Closing and Shaping: The molds are designed to give the final product its shape. The molds close tightly around the molten material, and the material takes the shape of the mold cavity. The molds are usually made of metal and have a high – precision finish to ensure accurate replication of the desired product shape. The pressure inside the mold is maintained for a specific period to allow the material to cool and solidify properly. For example, when making PVC soles, the mold is shaped to match the exact contours of the sole, and the material is held in the mold until it hardens enough to retain its shape.
Cooling and Solidification
Controlled Cooling: After the material is in the mold, it undergoes a cooling process. Cooling channels are often built into the molds. These channels allow a coolant (usually water or a specialized cooling fluid) to circulate around the mold. The rate of cooling is carefully controlled because if the material cools too quickly, it may develop internal stresses and cracks. If it cools too slowly, the production cycle time will be too long. For example, in the production of silicone insoles, the cooling process is adjusted to ensure that the silicone sets evenly and without defects.
Solidification and Mold Release: As the material cools and solidifies, it takes on its final form. Once the material has reached the appropriate solid state, the molds open, and the finished product is ejected. The ejection mechanism can be mechanical, using ejector pins that push the product out of the mold. In some cases, a small amount of air pressure may also be used to assist in the release of the product from the mold.
Post – Processing and Quality Control
Trimming and Finishing: After the products are removed from the mold, they may require some post – processing. This can include trimming any excess material (known as flash) that may have formed during the molding process. For example, if there is a small amount of overflow material around the edges of a PVC trademark tag, it is carefully trimmed off to give the product a clean and finished look. Some products may also require additional finishing steps such as polishing, painting, or adding a protective coating.
Quality Inspection: The products then go through a quality control process. This can involve visual inspection to check for any surface defects, such as air bubbles, cracks, or incomplete filling of the mold. The dimensions of the products are also measured to ensure they meet the required specifications. Automated inspection systems may be used in some cases, such as cameras that can detect and flag products with visible defects. Samples may also be tested for physical properties like hardness, flexibility, or adhesion (if applicable) to ensure that the products meet the quality standards for their intended use.
