Glow Plug Sheath Tube Alloy Composition and Melted Portion Geometry
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Solution Overview
Problem
Glow plugs with sheath tubes made of specific materials face issues with crack formation in the melted portion during the joining process, leading to reduced oxidation resistance due to tensile stress and air infiltration, which compromises their performance in high-temperature environments.
Innovation Solution
A glow plug design featuring a sheath tube made of a Ni-based alloy with a heating coil composed of tungsten or molybdenum, where the heating coil's front end is embedded in a melted portion within the sheath tube, ensuring the coil is not exposed and maintaining oxidation resistance by distributing tensile stress evenly across the melted portion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the sheath tube is made of an alloy containing Ni as the main component with predetermined amounts of Cr, Al, and Y to resist oxidation at high temperatures, then oxidation resistance is improved, but tensile stress concentrates in the central section of the melted portion during joining, causing cracks to form
Solution Approach 1:
The patent changes the compositional parameters of the sheath tube alloy, specifically limiting Al to 0.03 mass% or less and adding Yttrium (Y) at 0.01 to 0.5 mass%. This compositional modification alters the material properties to reduce tensile stress concentration in the melted portion during the joining process, preventing crack formation while maintaining oxidation resistance at high temperatures.
Solution Approach 2:
The patent creates a composite alloy system combining Ni, Cr, Al (in controlled amounts), Y, and optional additional elements (Fe, Co, Cu, Mn, Mo, Ti, Si, B). This multi-element composite material provides both oxidation resistance through Cr and Y, and reduced stress concentration through the optimized alloy composition, resolving the contradiction between durability and joining integrity.
2Temperature
If the sheath tube is made of a conductive material highly resistant to heat and oxidation to operate at higher temperatures, then temperature resistance is improved, but the same material causes tensile stress in the melted portion during joining, leading to crack formation
Solution Approach 1:
The patent modifies the material parameters by precisely controlling the composition of the sheath tube alloy, particularly limiting Al to 0.03 mass% or less and adding Yttrium (Y) at 0.01 to 0.5 mass%. This compositional adjustment allows the material to maintain high-temperature operation resistance while reducing tensile stress concentration during joining, preventing crack formation in the melted portion.
Solution Approach 2:
The patent develops a composite Ni-based alloy incorporating Cr (10-20 mass%), controlled Al (0.003 to 0.03 mass%), Y (0.01 to 0.5 mass%), and optional elements. This composite material structure provides both high-temperature stability and reduced stress concentration during joining, resolving the contradiction between temperature resistance and joining strength.
3Ease of manufacture
If cracks form in the melted portion of the sheath tube during joining, then manufacturing is completed, but oxidation resistance is reduced due to air entrance through the cracks
Solution Approach 1:
The patent applies preliminary anti-action by pre-modifying the alloy composition before the joining process occurs. By limiting Al to 0.03 mass% or less and adding Yttrium (Y) at 0.01 to 0.5 mass%, the material properties are adjusted in advance to prevent tensile stress concentration and crack formation during joining, thereby preserving oxidation resistance without requiring post-processing corrections.
Solution Approach 2:
The patent changes the compositional parameters of the sheath tube alloy to prevent crack formation that would compromise oxidation resistance. The specific composition (Ni with controlled Al and added Y) ensures that the joining process completes successfully without creating oxidation pathways, maintaining both manufacturability and long-term reliability.
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
This design reduces crack formation in the melted portion, enhances oxidation resistance, and allows for intense heat generation at the front end of the sheath tube, maintaining performance in high-temperature conditions.
Implementation Method 1
A heating coil 820 is disposed in the sheath tube 810. The heating coil 820 generates heat when electricity is applied thereto through a center rod 200
Implementation Method 2
the melted portion satisfies 0.46 ≤ a/b, where a is a maximum value of a length of the melted portion in an axial line direction and b is a maximum value of a length of the melted portion in a direction perpendicular to the axial line direction
Data Source
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AI summary
[Object] To provide a glow plug including a sheath tube whose resistance to oxidation can be maintained by reducing the occurrence of cracks in a melted portion of the sheath tube when the sheath tube is formed of a specific material. [Solution] A glow plug 10 includes a sheath tube 810 and a heating coil 820. The sheath tube 810 is made of an alloy containing 50% or more by weight of Ni, 18 to 30% by weight of Cr, 1% or less by weight of Al, and 0.01 to 0.3% by weight of at least one component selected from Y and Zr. A main component of the heating coil 820 is tungsten (W) or molybdenum (Mo). A front end portion 822 of the heating coil 820 is embedded in a melted portion 816 of the sheath tube 810 and is not exposed at an outer surface of the sheath tube 810. When a is a maximum value of a length of the melted portion 816 in an axial line direction OD and b is a maximum value of a length of the melted portion 816 in a direction perpendicular to the axial line direction OD, 0.46 ≤ a/b is satisfied.