Capacitor Metal Case Slit Parts Thermal Stress
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Solution Overview
Problem
Conventional case-mold-type capacitors experience compressive and tensile stress due to thermal expansion mismatch between metal cases and epoxy resin, leading to potential detachment or cracking at the interface.
Innovation Solution
A capacitor design featuring a metal case with slit parts on its side face, which allows for expansion and contraction of the thermosetting resin, reducing stress through the formation of these slit parts and using high-viscosity resin covered by a deformable tape to prevent leakage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a metal case filled with epoxy resin is used, then heat dissipation is improved, but thermal expansion mismatch causes compressive and tensile stress leading to detachment or cracking
Solution Approach 1:
The side face of the metal case is segmented into multiple regions by forming slit parts that extend from the open end toward the bottom face. These slits divide the side face into multiple segments that can independently expand and contract, accommodating thermal expansion differences between the metal case and epoxy resin while maintaining overall structural integrity.
Solution Approach 2:
The physical state of the epoxy resin is changed from liquid to solid through controlled heating and hardening. The resin is injected in liquid state to ensure complete filling, then heated to harden it, transforming it into a solid that provides structural support while the slit parts accommodate thermal stress during subsequent heating cycles.
2Strength
If the case is filled with liquid resin and then heated to harden, then the resin provides structural support, but thermal expansion causes stress concentration at the interface
Solution Approach 1:
The side face is divided into multiple segments by slit parts, allowing each segment to independently accommodate thermal expansion. This segmentation prevents stress concentration at the interface between the hardened resin and metal case by distributing thermal stresses across multiple expansion joints.
Solution Approach 2:
The slit parts act as intermediary elements between the metal case and hardened resin, providing a buffer zone that absorbs thermal expansion stresses. These slits allow the case to expand and contract without transmitting excessive stress to the resin interface.
3Reliability
If slit parts are formed in the side face, then thermal stress is reduced, but resin leakage may occur through the slits
Solution Approach 1:
The slit parts are pre-formed in the metal case before resin injection. This preliminary action ensures that the slits are properly positioned and sized to accommodate thermal expansion while preventing resin leakage. The slits are formed at controlled locations and dimensions to balance stress relief with leakage prevention.
Solution Approach 2:
Different regions of the case have different properties: the slit parts provide expansion capability while the covering parts at the open end provide sealing. The local quality of each region is optimized for its specific function - slits for stress relief and covering parts for preventing leakage.
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 design effectively minimizes stress on the resin, reducing the likelihood of detachment and cracking during thermal expansion and contraction, while ensuring reliable filling and attachment to the case.
Implementation Method 1
The epoxy resin and the case undergo thermal expansion by being heated, and then, undergo thermal contraction by being cooled
Implementation Method 2
The epoxy resin and the case undergo thermal expansion by being heated, and then, undergo thermal contraction by being cooled
Implementation Method 3
As a result of heating the case filled with an epoxy resin in a liquid state, the epoxy resin in the case is hardened
Data Source
AI summary
This capacitor includes: a capacitor element; a case made of metal and configured to house the capacitor element; and a thermosetting resin that is filled in the case. The case includes a bottom face and a side face, the side face surrounding four sides of the bottom face. The side face has formed therein a plurality of slit parts, the plurality of slit parts extending from an end, of the side face, at an opposite side to the bottom face toward the bottom face side.