Injection mold slider T-block
The T-block on the movable mold slider is the core, load-bearing component of the lateral core-pulling mechanism. It primarily connects the slider to the movable mold plate. The T-slot ensures smooth sliding of the slider and withstands the lateral forces generated during core pulling, ensuring precise and reliable core pulling. In the molding of parts with side holes, undercuts, or complex lateral contours, the performance of the movable mold slider’s T-block directly impacts the mold’s service life and part dimensional accuracy. For example, a mold for an automotive door handle suffered slider jamming due to wear on the T-block, resulting in flash and damage to the mold cavity. Replacing the T-block with a high-strength T-block completely resolved the issue, extending the mold’s service life to over 500,000 cycles. The T-block’s design must balance strength, wear resistance, and guiding accuracy. Its structural parameters and material selection are determined based on the core-pulling force and production batch size.
The structural design of the T-block in the injection mold’s movable slider must meet the dual requirements of force transmission and guidance. The T-block is typically composed of a head and a stem. The head is T-shaped and fits into the T-slot at the bottom of the slider, while the stem is fixed to the movable mold plate, forming a sliding guide mechanism. The width and height of the T-block head must match the slider’s T-slot, with a clearance of 0.02-0.05mm to ensure smooth, flexible movement of the slider without loosening. The connection between the head and stem requires a rounded transition (radius ≥ 3mm) to avoid stress concentration that can lead to fracture. The length of the T-block is determined by the slider’s stroke and is typically 20-30mm longer than the slider’s maximum stroke to ensure that the slider maintains effective contact with the T-block throughout its entire motion. For example, for a mold with a 50mm slider stroke, the T-block length must be ≥70mm to prevent the slider from detaching from the T-block, causing core pulling to deviate. In addition, T-blocks can be installed in two ways: fixed and adjustable. The fixed type is directly fastened by screws and is suitable for occasions where the core pulling force is stable; the adjustable type uses gaskets or wedges to adjust the fitting clearance and is suitable for high-precision core pulling mechanisms.
The material selection and heat treatment process for T-blocks are crucial to their performance. Because T-blocks are subject to significant lateral forces and friction during operation, high-strength and wear-resistant materials are required. Commonly used materials include 45# steel, Cr12MoV, and SCM440 alloy structural steel. 45# steel, after quenching and tempering (hardness 28-32 HRC), is suitable for molds with small to medium core pulling forces (<50 kN). Cr12MoV, after quenching and tempering (hardness 58-62 HRC), significantly improves its surface hardness and wear resistance, making it suitable for molds with high core pulling forces (>100 kN) or high-volume production. SCM440, after carburizing and quenching (carburized layer thickness 0.8-1.2 mm, surface hardness 58-62 HRC), combines high strength and toughness, making it suitable for core pulling mechanisms under complex operating conditions. For example, the T-block in a large appliance mold is made of SCM440 material. After carburizing and quenching, its service life is three times longer than that of 45# steel. Furthermore, the sliding surface of the T-block is ground to a roughness of less than Ra0.8μm. Nitriding (nitriding layer thickness 0.1-0.2mm) can further enhance surface hardness and wear resistance.
The precision of the fit between the T-block, the slider, and the movable platen directly impacts the stability of the core-pulling mechanism. The T-block head and the slider’s T-slot utilize a clearance fit (H7/f6) to ensure the slider can slide flexibly under load while avoiding impact and vibration caused by excessive clearance. The T-block stem and the mounting hole of the movable platen utilize a transition fit (H7/m6) to ensure the T-block is securely fixed and free of looseness. During assembly, the parallelism and perpendicularity of the T-block must be checked. The parallelism error must be ≤0.02mm/m, and the perpendicularity error must be ≤0.01mm/m. Failure to do so can cause the slider to jam or wear unevenly. For example, during assembly of a mobile phone casing mold, the T-block’s perpendicularity exceeded the tolerance by 0.03mm/m, resulting in abnormal noise during slider movement. After adjustments, the noise was eliminated, and core-pulling accuracy was improved to ±0.01mm. In addition, grease (such as molybdenum disulfide grease) needs to be applied to the contact surface between the T-block and the slider to reduce the friction coefficient. It needs to be refilled every 1,000 molds to ensure smooth sliding.
Maintenance and troubleshooting of T-blocks are crucial to ensuring the long-term, stable operation of the core-pulling mechanism. During daily production, T-block wear should be regularly inspected, and the clearance should be measured with a feeler gauge. If the clearance exceeds 0.1mm, the T-block should be replaced or the T-slot of the slider repaired. If scratches or lacerations are found on the T-block surface, they should be polished with an oilstone to remove burrs and prevent further wear. If a T-block deforms or breaks due to excessive core-pulling force, the force should be recalculated, and a larger or stronger T-block should be replaced. The synchronization of the core-pulling mechanism should also be checked to avoid unilateral force. For example, a T-block in a mold broke due to asynchronous core-pulling on both sides. After adjusting the situation by adding a synchronizing gear, force uniformity was significantly improved, and the breakage has ceased. Furthermore, during mold storage, the slider should be secured in the closed position to prevent the T-block from long-term deformation. Anti-rust oil should also be applied to the sliding surface to prevent rust. Through scientific design, reasonable material selection and standardized maintenance, the T-block of the injection mold slider can effectively ensure the stable operation of the lateral core pulling mechanism and provide reliable support for the molding of complex plastic parts.
