How to choose a mold preheating furnace? Balance between energy consumption and rhythm

How to choose a mold preheating furnace? Balance between energy consumption and rhythm
Preheating the mold to above 200 ℃ before production can reduce the thermal shock of the first mold; The selection of preheating furnace depends on three factors: heating rate, furnace temperature uniformity, and unit energy consumption.
Why is preheating necessary
Cold mold direct pouring causes a sudden increase in surface temperature of the first mold cavity, resulting in the highest thermal stress. Cracks often start from this impact.
The mold temperature target for aluminum alloy casting is 200-350 ℃. Below 200 ℃, the probability of cold insulation and insufficient watering increases significantly.
Preheating can also drive away moisture on the surface of the mold cavity. Residual moisture will vaporize when it comes into contact with aluminum liquid, forming pores and even splashing.
The trade-off of heating rate
The temperature rises too quickly, resulting in a large temperature difference between the inside and outside of the mold and high thermal stress. It is recommended to control the heating rate at 50-80 ℃/hour.
It takes about 4 hours to rise from room temperature to 250 ℃, calculated at 60 ℃/hour. This is the time that must be set aside during production scheduling.
Heating up too slowly occupies the furnace and fixtures, affecting the efficiency of changeover. A workshop with a tight production cycle is often equipped with two furnaces to rotate.
Uniformity of furnace temperature
It is recommended to control the temperature difference at different positions inside the furnace within ± 10 ℃. Exceeding the tolerance will cause local overheating or insufficient mold.
The uniformity of the hot air circulation furnace is better than that of the resistance furnace. Large molds require more forced convection.
The temperature measurement points should be arranged at the wheel rim and hub of the mold, rather than just looking at the furnace temperature. The two may differ by 20-30 ℃.
How is energy consumption calculated
The power of the preheating furnace is usually 30-80kW. Calculated based on 4-hour heating and 2-hour insulation, the single power consumption is about 180-480 kWh.
Calculated at 0.7 yuan/degree, the single cost is 126-336 yuan. Change the model once a day, with an annual cost of approximately 30000 to 80000 yuan.
This number should be included in the cost of replacement, rather than ignored as a fixed expense.
Selection of preheating method
Offline preheating furnaces are suitable for workshops with frequent model changes. The mold is preheated in the furnace while the machine keeps running.
The machine is preheated online using a mold warmer or heating rod, which heats up slowly but eliminates the need for lifting. Suitable for continuous production of a single variety.
The flame preheating speed is fast, but the temperature is uneven and the thermal stress is high. It is only recommended for emergency use and not as a routine measure.
The matching method of Xinfeng mold
When delivering the wheel hub mold, Xinfeng Mold will provide a recommended preheating curve, including heating rate, insulation time, and target temperature.
The curve is given based on the weight and structure of the mold. For large molds weighing over 6 tons, it is recommended to reduce the heating rate to 40-50 ℃/hour.
Balance between preheating and energy consumption
During continuous production, it is not necessary to preheat each mold, but after changing molds, shutting down for more than 4 hours, or mold maintenance, it should be preheated again to above 200 ℃ before production.
Practical tips
The sealing strip of the preheating furnace door is a vulnerable part, and it is recommended to replace it every 12 months. Leakage can prolong the heating time by more than 20%.
Preheating records are kept according to the mold number, and when changing the mold, the previous curve can be directly called to reduce repeated debugging.
Frequently Asked Questions
Q: How much temperature should the mold be preheated to?
Answer: Above 200 ℃, the target range is 200-350 ℃.
Q: What is the appropriate heating rate?
Answer: It is recommended to maintain a temperature of 50-80 ℃/hour, with a lower value for large molds.
Q: How long does it take to preheat once?
Answer: It takes about 4 hours from room temperature to 250 ℃.
Q: What is the requirement for furnace temperature uniformity?
Answer: It is recommended to keep the temperature within ± 10 ℃ for better hot air circulation.
Q: How much does it cost to preheat once?
Answer: Approximately 126-336 yuan, calculated based on power and duration.
Q: Can it be preheated online?
Answer: Yes, but it heats up slowly and is suitable for continuous production.
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