Selection, erosion mechanism, and replacement criteria for lifting pipes in differential pressure casting molds for wheel hubs | CPC mold lifting system operation and maintenance
The differential pressure of the wheel hub and the erosion perforation of the CPC reverse pressure casting riser caused 43% of batch castings to have slag, gas leakage, and interrupted filling accidents.
The silicon nitride riser is exposed to aluminum liquid environment above 745 ℃ for a long time, which accelerates the corrosion of grain boundaries and increases the wall thickness loss rate by 62%.
The temperature difference between the inner and outer walls of the riser is greater than 95 ℃, and thermal stress is repeatedly applied, leading to the preferential generation of radial microcracks. The aluminum liquid infiltrates and cracks quickly collapse.
The gap between the riser and the sprue sleeve is greater than 0.25mm, and aluminum liquid enters through the gap, continuously flushing the interface position and rapidly eroding the enlarged hole.
The roughness of the inner wall of the riser is higher than Ra1.2, and the aluminum liquid adheres to the nodules, which continue to grow and change the filling cross-sectional area and filling curve.
The depth of the aluminum liquid level inserted into the bottom of the riser is less than 45mm, and under the pressure difference, the slag layer and oxide scale are sucked in, causing a surge in poor slag inclusion.
The riser is a core consumable part of CPC reverse pressure casting molds and wheel hub differential pressure casting molds, and the low-pressure die-casting mold (LPDC) is also equipped with a silicon nitride riser; Gravity casting molds are generally not equipped with liquid lifting tubes. Motorcycle wheel hub casting molds, low-pressure wheel hub casting molds, structural component casting molds, aluminum alloy wheel hub molds, aluminum casting forming molds, low-pressure casting tooling molds, and failure of the lifting pipe are high-risk shutdown faults. Once perforated, aluminum liquid is easily poured into the pressure pipeline. According to the overseas on-site statistics of Zhejiang Xinfeng Machinery, the conventional stable life range of silicon nitride riser is 8000-15000 mold cycles, while aluminum liquid with excessive iron content and long-term high temperature will be compressed to within 3000 mold cycles. Silicon carbide composite riser has stronger resistance to aluminum corrosion, but its procurement cost is 45% higher than that of silicon nitride, and it is mostly used for high-end orders of new energy structural components. When installing the riser, it is necessary to reserve a radial thermal expansion gap, and if the pressure is too tight and the temperature rises, it will directly break. Visual inspection of inner wall nodules and bottom thinning during each shutdown maintenance; If the original loss of wall thickness exceeds 1/4, it must be replaced in advance and cannot wait for perforation. Many Southeast Asian customers are accustomed to waiting for aluminum leakage before replacing, which can easily damage crucibles and pressure pipelines, resulting in repair losses far exceeding spare parts costs. For overseas orders, it is recommended to include 2 spare liquid lifting tubes with the mold to shorten the downtime of the production line.
FAQ
1. Question: What is the upper limit of safe aluminum liquid temperature for silicon nitride riser?
Answer: Try to control the temperature of the aluminum liquid to not exceed 745 ℃ for a long time.
2. Question: What is the upper limit of the gap between the riser and the sprue sleeve?
Answer: The docking gap should be controlled to be ≤ 0.25mm to prevent aluminum erosion.
3. Question: What is the minimum depth at which the bottom of the liquid lifting tube is immersed in the aluminum liquid?
Answer: The insertion depth below the liquid level should not be less than 45mm to avoid slag.
4. Question: What is the standard lifespan range for silicon nitride riser tubes?
Answer: Normal operating conditions range from 8000 to 15000 cycles.
5. Question: What are the advantages and disadvantages of silicon carbide liquid lifting tubes?
Answer: Corrosion resistance is better, but the procurement cost is about 45% higher.
6. Question: How much wall thickness loss does the riser need to be replaced?
Answer: If the original wall thickness loss exceeds 1/4, it is recommended to replace it in advance.
