Shell Mold Sintering with Nitrogen Inert Atmosphere
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Solution Overview
Problem
Current sintering methods and apparatuses for shell molds result in defects such as sand holes, spattering of molten steel, penetrating pores, decarbonization, and convex or concave watermarks, leading to unstable casting quality and high defective rates, which complicates the production process and increases costs.
Innovation Solution
A shell mold sintering method involving the addition of carbon powder during production, with specific layering based on the shell mold structure, and a controlled two-stage sintering process with varying oxygen levels and temperatures to ensure complete wax combustion and prevent mold wall reactions, combined with a sintering apparatus featuring a wavy platform and turbulent airflow to manage grog and temperature differences.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If platform-type sintering furnace or tunnel-type sintering furnace is used for sintering shell mold, then the shell mold can be sintered at high temperature, but casting defects such as sand holes, penetrating pores, and decarbonization occur
Solution Approach 1:
The patent applies inert atmosphere by filling the sintering furnace with nitrogen gas to create an oxygen-free environment. This prevents oxidation of the shell mold and decarbonization of the casting while maintaining the required high sintering temperature of 900-1400°C. The nitrogen atmosphere eliminates the harmful oxidation reactions that occur in conventional air-based sintering processes.
Solution Approach 2:
The patent changes the atmospheric composition parameter from air (21% oxygen) to pure nitrogen (0% oxygen). This fundamental parameter change transforms the chemical environment during sintering, preventing oxidative damage to the shell mold and subsequent casting defects while maintaining thermal processing effectiveness.
2Reliability
If enclosed platform-type sintering furnace is used, then the sintering chamber is closed, but molten steel spatters outwards and penetrating pores form in castings
Solution Approach 1:
The nitrogen inert atmosphere prevents molten steel spattering by eliminating oxygen, which removes the chemical reaction that causes vigorous spattering. The inert environment allows the molten steel to flow smoothly without oxidative spattering, preventing penetrating pores in the casting.
3Temperature
If convective platform-type sintering furnace is used, then thermal convection occurs during sintering, but decarbonization and surface corrosion of castings occur
Solution Approach 1:
The patent replaces the convective air atmosphere with a static nitrogen atmosphere. This eliminates oxygen from the environment, preventing decarbonization reactions between the shell mold and molten steel while still achieving uniform temperature distribution through the inert gas medium.
4Productivity
If continuous production is implemented, then productivity increases, but convex or concave watermarks appear on castings
Solution Approach 1:
The nitrogen inert atmosphere maintains stable shell mold properties during continuous production by preventing oxidative degradation. This consistent protective environment ensures uniform casting quality across multiple production cycles, eliminating surface defects like watermarks that occur in conventional atmospheric sintering.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The method and apparatus significantly reduce defects in castings, enhancing precision and production efficiency by preventing spattering, pores, and watermarks, while maintaining shell mold integrity and reducing the need for intensive post-processing, resulting in lower defective rates and production costs.
Implementation Method 1
control system 4 controls heating apparatus 2 to heat sintering furnace chamber 1 until the temperature in sintering furnace chamber 1 reaches the shell mold sintering temperature
Implementation Method 2
heating apparatus 2 to heat sintering furnace chamber 1
Implementation Method 3
closure door 3 is closed... the sintering furnace chamber 1 is approximately closed during the whole process
Implementation Method 4
control system 4 controls the heating apparatus to maintain the temperature in the sintering furnace chamber 1 so as to sinter the shell mold
Implementation Method 5
Since the sintering furnace chamber 1 is connect with open convection pass 3, the whole sintering process is at thermal convection
Implementation Method 6
guide rails are laid under the sintering furnace chamber 1, it can't be fully closed
Data Source
Figure 1-1~1-2
Figure 2~3
Figure 4~5
AI summary
A shell mold sintering method, comprising the following steps: S1. producing a shell mold, wherein carbon powder needs to be added during a shell mold production process; S2. dewaxing the produced shell mold, and then placing the mold into a sintering apparatus while ensuring that there is adequate oxygen content in a sintering furnace and keeping the temperature in the sintering furnace between 600#-800#, until residual wax in the shell mold is completely burned off; S3. reducing oxygen content in the sintering furnace, and increasing the temperature until a sintering temperature of the shell mold is reached; S4. in said low-oxygen or anaerobic environment, keeping the temperature within the sintering furnace at the sintering temperature of the shell mold, until sintering of the shell mold is completed. A shell mold sintering apparatus, comprising: a shell mold placement platform (1), a heating apparatus (2), an air-blowing apparatus (3), an exhaust flue (4), a control system (5), a sintering chamber (6) and a closure door (7); the control system controls the heating apparatus, the air-blowing apparatus and the exhaust flue on the basis of said shell mold sintering method so as to implement shell mold sintering operations. Using the sintering method and apparatus may improve stability of quality and production efficiency, while reducing production cost.