Journal Bearing Sliding Layer with Anisotropic Thermal Expansion
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Solution Overview
Problem
Conventional sliding members for journal bearings are prone to surface cracks and shear failure due to thermal expansion and frictional heat during startup, leading to damage and reduced operational reliability.
Innovation Solution
A sliding member with a partially cylindrical shape, featuring a synthetic resin sliding layer with controlled linear expansion coefficients in different directions and incorporating solid lubricants, fillers, and fibrous particles, along with a porous metal back-layer to enhance bonding and reduce thermal expansion anisotropy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the resin composition of the sliding layer is thermally expanded in an almost isotropic manner, then the sliding layer maintains uniform dimensional stability, but damage such as cracks extending in the circumferential direction occurs on the surface of the sliding layer due to dragging by the shaft member
Solution Approach 1:
The patent applies asymmetry by designing the thermal expansion characteristics to be anisotropic rather than isotropic. Specifically, the linear expansion coefficient in the circumferential direction (KS) is made smaller than that in the axial direction (KJ), creating an asymmetric expansion pattern that prevents crack formation during startup sliding. This asymmetric thermal expansion behavior allows the resin composition to expand differently in different directions, avoiding the stress concentration that leads to circumferential cracking.
Solution Approach 2:
The patent changes the thermal expansion parameters by controlling the linear expansion coefficients KS and KJ to satisfy specific relationships (KS < KJ and KS/KJ ≥ 0.5). This parameter control is achieved through the selection and formulation of resin composition, including the use of specific polymers and additives that exhibit the desired anisotropic thermal expansion characteristics. By adjusting these parameters, the patent prevents crack formation while maintaining dimensional stability.
2Stability of the object's composition
If the amount of thermal expansion of the resin composition is approximately same between the in-plane direction and the thickness direction, then the sliding layer maintains uniform expansion, but shear failure occurs at the interface between the back-metal layer and the sliding layer
Solution Approach 1:
The patent applies asymmetry by making the thermal expansion anisotropic, specifically ensuring that the linear expansion coefficient in the thickness direction (KT) is larger than the average of the in-plane coefficients ((KS+KJ)/2). This asymmetric expansion pattern creates differential expansion between the sliding layer and the back-metal layer, reducing shear stress at the interface and preventing shear failure while maintaining overall dimensional stability.
Solution Approach 2:
The patent controls the thermal expansion parameters by establishing specific relationships between KT, KS, and KJ (KT > (KS+KJ)/2 and KT/((KS+KJ)/2) ≥ 0.8). These parameter relationships are achieved through careful selection of resin composition and formulation, creating a sliding layer with tailored anisotropic thermal expansion characteristics that prevent interfacial shear failure while maintaining bonding strength.
3Ease of operation
If a sliding layer including resin composition is coated on a back-metal layer, then the sliding member provides low friction and wear resistance, but the sliding layer is prone to cracks and shear failure during startup due to thermal expansion and frictional heat
Solution Approach 1:
The patent changes the thermal expansion parameters of the sliding layer by controlling the linear expansion coefficients KS, KJ, and KT to satisfy specific relationships. This parameter control is achieved through the selection and formulation of resin composition, including the use of specific polymers (such as polyether ether ketone, polyimide, polyacetal) and additives. By adjusting these parameters, the patent prevents crack and shear failure formation during startup while maintaining the low friction and wear resistance properties of the sliding layer.
Solution Approach 2:
The patent uses composite materials by formulating the sliding layer with specific resin compositions that exhibit the desired anisotropic thermal expansion characteristics. The sliding layer is composed of polymer matrices combined with functional additives and fillers that provide both the low friction/wear resistance properties and the controlled thermal expansion behavior. This composite structure allows simultaneous achievement of sliding performance and damage resistance during startup.
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 controlled thermal expansion and reinforced composition of the sliding member minimize the likelihood of cracks and shear failure, ensuring improved durability and reliability during startup and operation.
Implementation Method 1
a portion of the resin composition near the sliding surface in contact with the shaft member is dragged by the shaft member and elastically deformed in a rotation direction of the shaft member. It was found that, in this case, if the resin composition of the sliding layer is thermally expanded, due to frictional heat generated by sliding
Data Source
AI summary
Provided is a sliding member for a journal bearing. The sliding member includes a back-metal layer and a sliding layer, and has a partially cylindrical shape. The sliding layer includes a synthetic resin and has a sliding surface. The sliding layer has a linear expansion coefficient KS in a direction parallel to a circumferential direction of the sliding member, a linear expansion coefficient KJ in a direction parallel to a center axis direction of the sliding member, and a linear expansion coefficient KT in a direction perpendicular to the sliding surface, and the linear expansion coefficients KS, KJ, and KT satisfy the following relations (1) and (2): Relation (1): 1.1≤KS/KJ≤2; and Relation (2): 1.3≤KT/{(KS+KJ)/2}≤2.5.