Basic forms of injection molding locating rings
Injection molding locating rings are essential components for connecting the injection molding machine to the mold. They come in two basic forms: standard circular locating rings and locating rings with a stop, each suitable for different mold configurations and injection molding machine models. Standard circular locating rings are simple cylindrical structures, with an outer diameter that mates with the locating holes on the injection molding machine’s fixed platen, with a clearance of 0.05-0.1mm to ensure centering accuracy during mold installation. They are typically 10-20mm tall and made of 45# steel or Q235 steel, with a blackened surface treatment for rust prevention. They are suitable for small and medium-sized molds (weighing under 5 tons). For example, molds for injection molding machines with shot sizes of 100-500g typically use standard circular locating rings with diameters of 100mm or 125mm. The positioning ring with stopper has a radial stopper added to the circular positioning ring. The stopper diameter is 5-10mm larger than the outer diameter of the positioning ring and the height is 5-10mm. It cooperates with the stopper groove of the mold fixed die plate to enhance the positioning stability. It is suitable for large molds or high-speed injection molding, and can effectively prevent the displacement of the mold due to vibration during the injection process.
Another basic type of injection molding retaining ring is the flange-type retaining ring. Its structural feature is a flange at the bottom, secured to the mold base plate by bolts. This makes it suitable for applications requiring frequent mold changes. The flange diameter of a flange-type retaining ring is 30-50mm larger than the outer diameter of the retaining ring, and the thickness is 8-12mm. Four to six bolt holes are evenly distributed on the flange, each 0.5-1mm larger than the retaining bolt diameter, making installation and adjustment easy. For example, a 150mm diameter flange-type retaining ring has a 190mm diameter, a 10mm thickness, and four φ10mm bolt holes. Secured with M8 bolts, the radial runout of the retaining ring after installation does not exceed 0.03mm. This type of retaining ring offers easy removal and high positioning accuracy. It is often used in molds for small batches of multiple products, such as when switching between molds for multiple models of home appliance plastic parts, reducing mold changeover time by over 30%.
Locating rings with venting grooves are a specialized design for molds with high venting requirements. Circular venting grooves, 2-3mm wide and 0.5-1mm deep, are machined into the cylindrical or flange surface of the locating ring. These grooves connect to the mold’s exhaust system and help evacuate air between the mold and the fixed platen of the injection molding machine. When the mold cavity is deep or the injection speed is fast, air between the mold and the fixed platen cannot escape, leading to bubbles and underfilling in the molded part. Locating rings with venting grooves effectively address this problem. For example, when molding deep-cavity parts (over 100mm deep), using a locating ring with three venting grooves (0.8mm deep, 2mm wide, and 10mm apart) can increase venting by over 50%, significantly improving part filling. The venting grooves in this type of locating ring must avoid interference with the injection molding machine’s locating holes, and the bottom of the groove must be at least 5mm from the base of the locating ring to prevent weakening of the locating ring.
Adjustable locating rings offer a flexible design to accommodate different locating hole sizes in injection molding machines. They consist of an inner ring and an outer ring. The inner ring is fixed to the mold, while the outer ring can be moved radially via adjusting screws to fine-tune the locating diameter. The adjustment range is typically ±5mm, making them suitable for universal molds that need to be used on different injection molding machines. For example, a universal mold needs to accommodate two injection molding machines with locating hole diameters of 125mm and 130mm. An adjustable locating ring with an inner ring diameter of 120mm and an outer ring adjustable via three circumferentially spaced adjusting screws can be expanded to a maximum of 130mm with an adjustment accuracy of 0.05mm. To use the ring, the outer ring diameter must first be adjusted to the injection molding machine’s locating hole size, then secured with locking screws to ensure the required clearance. The adjustable locating ring is made of a wear-resistant alloy, with the inner ring constructed from hardened 45# steel and the outer ring from tin bronze, to reduce wear during adjustment and extend its service life.
The basic type of locating ring for injection molding should be determined based on factors such as mold size, injection molding machine model, and production process to ensure positioning accuracy and reliability. For high-precision plastic part molds (such as optical lens molds), high-precision locating rings are required, with a clearance of 0.02-0.03mm. Grinding is performed to ensure cylindricity error of no more than 0.01mm. This ensures concentricity between the mold and the injection molding machine and prevents uneven wall thickness in the plastic part due to positioning deviation. For large and heavy molds (weighing over 10 tons), thickened flange-type locating rings with a flange thickness of 15-20mm and a locating ring height of 25-30mm are required to enhance overall rigidity and prevent deformation. Furthermore, the locating ring and the mold base plate must be secured using a compatible method. Welding can be used for small and medium-sized molds (with welding stress relief required). Large molds must be secured with bolts, and bolt strength must be at least 8.8 to ensure they will not loosen during long-term use. By choosing the right locating ring type, mold installation positioning accuracy can be controlled within 0.05mm, providing a fundamental guarantee for part quality.
