- 1. The main purpose of pre-forging heating is to improve the plasticity of the metal
l Heating can intensify the atomic vibration inside the metal, weaken the bonding force between atoms, thereby increasing the plasticity of the metal and making it easier to deform.
l Reduce deformation resistance: As the temperature increases, the yield strength and tensile strength of the metal will decrease, which means that the force required to be applied during the forging process will decrease, which is beneficial for the forming of the forging. Beneficial for metal flow forming: After heating, the fluidity of the metal is enhanced, which can more evenly fill the mold cavity and reduce forging defects such as folding and cracking.
l Obtaining good microstructure and mechanical properties after forging: A reasonable heating system can enable forgings to obtain uniform and fine grain structure during the forging process, thereby improving the mechanical properties and service life of forgings.
- 2. The methods of pre-forging heating are mainly divided into two categories: electric heating and fuel heating
l Electric heating resistance heating: using the heat generated by the electric current passing through the electric heating element in the furnace to heat the metal. This method has fast heating speed, accurate furnace temperature control, good heating quality, less workpiece oxidation, good working conditions, and is easy to achieve automated operation. But the equipment investment is large, the electricity cost is expensive, and the heating cost is high.
l Contact electric heating: The heated billet is directly connected to the circuit, and when the current passes through the billet, it is heated due to the resistance heat generated by the billet itself. This method has high heating efficiency, but attention should be paid to the uniformity of current distribution and the conductivity of the billet.
l Salt bath furnace heating: using salt solution to conduct electricity and generate a large amount of resistance heat to heat metals. This method has good heating uniformity, but the equipment is complex and the maintenance cost is high.
l Induction heating: Under the action of the alternating magnetic field generated by the introduction of alternating current into the inductor, an alternating electric potential is generated inside the metal billet placed in the alternating magnetic field, and an alternating eddy current is formed.
l Eddy current heating and hysteresis loss heating cause the billet to be heated. This method has fast heating speed, high efficiency, and good heating uniformity. Fuel heating is the use of the heat energy generated during the combustion of solid (coal, coke, etc.), liquid (heavy oil, diesel, etc.), or gas (coal gas, natural gas, etc.) fuels to heat the billet. This method has strong universality, low investment, relatively easy construction, and low fuel costs. But the working conditions are poor, the atmosphere and temperature inside the furnace are difficult to control, and the heating quality is easily affected. In actual production, the production of small and medium-sized forged chain wheels often uses chamber furnaces, continuous furnaces, or rotary bottom furnaces that use oil, gas, natural gas, or coal as fuel to heat steel materials. Large forged sprocket blanks or steel ingots often use bottom chamber furnaces fueled by oil, gas, and natural gas.
The purpose of pre-forging heating is to improve the plasticity and flowability of the metal, reduce deformation resistance, and thus obtain good post forging microstructure and mechanical properties. The selection of heating method needs to be comprehensively considered based on various factors such as specific forging requirements, investment benefits, energy situation, and environmental protection.
Post time: Dec-13-2024
