I. Prevention that is based on design
Accurate calculation of expansion clearance: The allowance should be calculated strictly in accordance with the thermal expansion formula ΔL = L × α × ΔT, with a safety margin of 1.5-2 times. The axial clearance for a 100mm manifold plate that has been heated to 200℃ must be at least 0.5mm.
Floating positioning structure: The hot runner plate's rigid positioning around its entire circumference is replaced with a floating positioning ring design, which enables the hot runner to move freely along the expansion direction and eliminates the rigid constraint of the mounting holes.
Strict tolerance control: The coaxiality is maintained at a minimum of ≤0.02mm to prevent unilateral clogging that may result from localised off-center loading. The positioning ring fit tolerances adhere to the H7/js6 standard.
The design of the cold divide is: The hot runner component's height is less than the depth of the hot runner plate groove, which enables a cold gap to prevent direct pressure damage to components due to thermal expansion. II. Machining Process Prevention
Drawings with Clearly Delineated Gaps: The thermal expansion allowance for each mating surface should be explicitly indicated in the machining drawings, such as the "0.7mm gap between hot runner plate and upper template," to prevent machining personnel from performing standard zero-fit machining.
Polishing of Mating Surfaces in the Mirror: To prevent jamming during thermal expansion and eliminate residual burrs, the interior walls of the mounting holes should be mirror polished to a roughness Ra≤1.6μm following machining.
Verification and Coordinated Measuring: Use a coordinate measuring machine to confirm that all allowances meet design requirements by verifying the coaxiality and mating dimensions of the mounting apertures after machining. It is imperative that defective components are excluded from the assembly procedure.
III. Operational Prevention During Installation
High-Temperature Anti-Gas Agent Pre-Coating: To prevent adhesion and seizing at high temperatures, apply a high-temperature molybdenum-based anti-gasting agent to all metal mating surfaces in an even manner prior to the installation of a hot runner.
Diagonal Bolt Tightening: The preset torque values are rigorously adhered to as the hot runner bolts are tightened diagonally in stages. Uneven stress on the heated runner plate is prevented by prohibiting single-sided, one-time tightening.
Verification of Cold State Clearance: Use a feeler gauge to re-measure all reserved clearances after installation to ensure that the hot runner can move freely in the expansion direction without any jamming points.
IV. Daily Prevention at the Operation and Maintenance End
Heating Strategy Segmented: When the hot runner is initiated and begins to heat up, the temperature should be raised by 50°C every 30 minutes. Do not immediately increase the temperature to the operating temperature; instead, allow all components of the hot runner to expand in a uniform and synchronised manner.
Regular Inspection and Calibration: The system should be disassembled every three months to assess the wear of the mounting hole mating surfaces, replenish anti-seize agent, and re-measure the reserved clearance for thermal expansion.
Addition of Displacement Monitoring Sensors: To monitor the thermal expansion displacement in real time, install displacement sensors on the side of the heated runner plate. An audible and visual alarm will be promptly activated to identify potential jamming if the displacement surpasses the limit.
