The heating process of material heat treatment in well type nitriding furnace is a high temperature heat source and a heat exchange process to transfer heat to low temperature workpiece. Understanding the heat transfer process is of great significance for improving the heating quality of workpiece and saving energy.
1. The basic heat transfer modes of well type furnace are divided into conduction, convection and radiation
Conduction heat transfer - refers to the heat transfer mode without macroscopic particle movement, which depends on the vibration, diffusion or free electron movement of molecules (atoms) and can occur in solids, liquids and gases.
Convective heat transfer refers to the heat transfer mode in which the particles in different parts of the temperature have relative displacement, which can occur in liquid and gas.
Radiative heat transfer - a temperature object emits radiant energy in the form of electromagnetic waves and converts it into heat energy after being absorbed by another object that does not contact it. (between an object and another object)
2. Materials and properties of common electric heating elements
(1) Iron Chromium Aluminum (Fe Cr Al) electrothermal alloy elements are widely used
Features: good high temperature performance (Al2O3), high resistivity, small resistance temperature coefficient, small density and low cost. But the plasticity is poor, the processing is difficult, the high temperature strength is low, and the welding performance is poor. Common brand:
For low temperature resistance furnace: 1Cr13A14;
For medium temperature resistance furnace: oCr13Al6Mo2;
For high temperature resistance furnace: oCr27Al7Mo2 (1300 ℃)
(2) Ni Cr electrothermal alloy element
Features: low resistivity, high density, good plasticity, good processability, high temperature strength and welding performance, low melting point. But the cost is high, and it is mainly used for small electric furnace in laboratory.
Common brands: Cr20Ni80 is used in resistance furnace with temperature below 1000 ℃, and Cr15Ni60 is used in low-temperature furnace. It is an electric heating alloy. Tungsten and molybdenum are easy to be oxidized at high temperature. It is used in vacuum furnace with temperature of 1800 ℃ and 2400 ℃ respectively. The resistance is small and the resistance temperature coefficient is large. The voltage regulator is equipped when using.
(3) Silicon carbide electric heating element - high temperature furnace
Features: Long term operation at 1350 ℃ in oxidizing atmosphere (service life drops sharply in alkali, hydrogen and steam). Large resistance temperature coefficient, equipped with voltage regulator. "Aging" after 60~80 hours of use, new and old cannot be mixed.
(4) Molybdenum disulfide electric heating element - high temperature furnace
Features: good high temperature performance. In the atmosphere of air, steam, carbon dioxide, etc., the working temperature can reach 1700 ℃ (but 400 ℃~700 ℃ is easy to oxidize, avoid use). The resistance temperature coefficient is very large, and the voltage regulator is equipped.
(5) Graphite electric heating element - vacuum furnace
Features: In neutral atmosphere or vacuum, the operating temperature is 1400 ℃~2500 ℃. Avoid using in oxidation atmosphere. The thermal expansion coefficient is small, the thermal conductivity is large, and it can be quenched and heated easily.
The above is the relevant content introduced to you by the well type carburizing furnace, and I hope it will be helpful to you.