Injection Molded PTC-Ceramics With Low Metallic Impurities
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Solution Overview
Problem
Existing methods for producing ceramic molded bodies with a positive temperature coefficient (PTC) often result in shifted resistivity values due to metallic impurities, which can be introduced during the manufacturing process, affecting the desired electrical properties of the PTC-effect.
Innovation Solution
The method involves using a feedstock with less than 10 ppm of metallic impurities, achieved by employing tools coated with hard materials like tungsten carbide to minimize abrasion, and a specific composition of Barium titanate-based ceramic filler with a matrix binder, allowing for injection molding of complex shapes while maintaining the PTC-effect characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional injection molding tools are used without special coatings, then the manufacturing process is simple and cost-effective, but metallic impurities are introduced through tool abrasion, shifting the resistivity values and affecting the PTC-effect characteristics
Solution Approach 1:
A coating layer is introduced as an intermediary between the tool and the ceramic feedstock. This coating acts as a sacrificial barrier that prevents direct contact and abrasion between the tool and the PTC-ceramic material, thereby preventing metallic impurity contamination while maintaining the simplicity of the injection molding process itself
Solution Approach 2:
The coating on the injection molding tools is designed to be consumable rather than permanent. As the coating wears down during use, it is replaced rather than attempting to preserve the original tool surface. This approach is more cost-effective than using expensive abrasion-resistant tool materials while maintaining product quality
2Manufacturing precision
If the feedstock contains higher levels of metallic impurities, then the manufacturing process is less sensitive to contamination, but the resistivity values shift and the PTC-effect characteristics are degraded
Solution Approach 1:
Measures are taken in advance during the feedstock preparation and injection molding process to prevent metallic impurity contamination before it can affect the PTC-ceramic material. This includes using coated tools and controlling the manufacturing environment to maintain impurity levels below 10 ppm, thereby preserving the electrical properties without requiring post-processing remediation
3Adaptability or versatility
If complex shapes are produced through injection molding, then the versatility and functionality of the PTC-ceramic bodies are enhanced, but the risk of introducing metallic impurities through tool contact increases
Solution Approach 1:
The coating on injection molding tools serves as a mediator that enables the production of complex-shaped PTC-ceramic components without direct metal-to-ceramic contact. The coating allows the tool geometry to be transferred to the feedstock while preventing metallic impurity contamination, thereby enabling shape complexity without sacrificing purity
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 approach ensures the production of PTC-ceramic molded bodies with controlled resistivity and temperature coefficient, maintaining the desired electrical features without significant shifts, enabling the creation of complex shapes and dimensions with precise thermal management capabilities.
Implementation Method 1
the PTC-effect of ceramic materials comprises a change of the electric resistivity ρ as a function of the temperature T. While in a certain temperature range the change of the resistivity ρ is small with a rise of the temperature T, starting at the so-called Curie-temperature T C the resistivity ρ rapidly increases with a rise of temperature
Implementation Method 2
In the injection molding process, a so-called feedstock comprising a ceramic material is injected into a mold exhibiting the desired shape of the body
Implementation Method 3
sintering the molded body
Data Source
Figure 1
Figure 2~3
AI summary
An injection molded body includes a ceramic material with a positive temperature coefficient containing less than 10 ppm of metallic impurities. A method for producing the injection molded body includes providing a feedstock for injection molding containing less than 10 ppm of metallic impurities, injecting the feedstock into a mold, removing a binder, sintering the molded body, and cooling the molded body.