Heating Uniformity Control Technology of Single-End Heating Rods for Precision Mold Processing

Uniformity of heating is the basic criterion for evaluating the working performance of single-end heating rods and determining the qualification rate of precision molded goods. uneven temperature of mold will cause product warping, different shrinkage, uneven surface gloss, and divergence of dimensional tolerance. Many quality problems in precision production line are caused by local temperature variation of molds, not faults in parameter settings. Mastering the heating uniformity control technology of single-end heating rods can achieve the full coverage of the mold and the balanced temperature field, and solve the temperature control cause of batch quality faults.

The uneven heating of heating rods is largely manifested in three aspects: internal winding process, exterior fitting state and zoning layout logic. The consistency of the power density of the rod body is determined by the internal resistance wire winding process. The common low-quality heating rods have sparse and uneven winding, so that the power and temperature are high in partial areas and low in sparse sections, and there are noticeable hot spots and cold spots on the surface of the rod. The industrial heating rods are of high quality and employ the equidistant equal-power winding technology, so that the power density is uniform and the temperature output is uniform in the complete heating section.

The main reason for the imbalance of on-site temperature is the unreasonable installation gap. If the heating rod itself is a uniform temperature, uneven fitting gap produced by the roughness of the mold hole and the installation deviation would lead to inconsistent heat conduction speed. The close fitting part has fast heat conduction and high mold temperature, and the gap part has slow heat conduction and low temperature, which leads to disorder in the whole temperature field. The main guaranty to achieve uniform heating is to strictly regulate the installation tolerance and ensure the full and close contact of the rod body and the hole wall.

Overall unreasonable structure of zoning causes mold temperature imbalance. In the case of composite molds with several heating rods, incorrect spacing and power matching will result in temperature superposition or temperature blank zones. An extremely dense arrangement will cause local overheating and heat accumulation, whereas an excessively sparse arrangement will cause insufficient local temperature and unbalanced overall temperature. The professional zoning plan should calculate the heat dissipation radius of each heating rod according to the structure of the mold, realize the smooth coverage of temperature and eliminate the hot and cold alternate places.

Local temperature uniformity is influenced by the effective heating length matching. The effective heating part of the heating rod should be equal to the mold working area. If the heating portion is too long, the exposed part will create dry scorching hot spots; if the heating section is too short, the nearby mold will have insufficient heating and low temperature. Accurate matching of effective heating length makes the heat output fully concentrated in the mold processing area, and achieves consistent temperature rise of the cavity.

Auxiliary temperature detection and closed loop adjustment optimize precision of uniformity. High-precision thermocouples are arranged in multiple positions of the mold to obtain multi-point temperature data in real time. The intelligent temperature control system can dynamically compensate the local temperature deviation by adjusting the output power of each single-end heating rod according to the temperature difference, to achieve high-precision balanced temperature control of the whole mold.

The control of heating uniformity is a systematic work, which includes product process, installation standard and intelligent debugging. The temperature difference of the mold can be controlled within ±0.5℃ by selecting high-quality heating rods, standardized installation, scientific layout and intelligent closed-loop adjustment, which fully meets the processing requirements of high-precision products and greatly improves the batch stability of automated production.