Water Level Sensor Surface Conductivity via Mold Roughness
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Solution Overview
Problem
Water level sensors in fuel filters manufactured using classic plastic injection molding often suffer from reduced electrical conductivity and measurement accuracy due to the formation of a 'spray skin' that lacks fibers on the surface, leading to inadequate fiber alignment and conductivity.
Innovation Solution
The method involves using a fiber-reinforced, electrically conductive plastic with a high proportion of carbon or metal fibers, and either injecting it into a roughened mold or subsequently roughening the surface of the molded sensor to ensure fibers reach the surface, thereby enhancing electrical conductivity and measurement accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a smooth surface plastic injection mold is used, then the surface quality of the injection molded part is improved, but the fiber proportion on the surface is reduced leading to decreased electrical conductivity
Solution Approach 1:
The invention applies different surface qualities to different regions: the mold surface is roughened specifically in the area that will form the sensor surface, while other areas maintain smooth surfaces. This localized roughness ensures fibers reach the sensor surface for electrical conductivity without compromising overall part quality
Solution Approach 2:
Instead of using a smooth mold surface to achieve good surface quality, the invention inverts the approach by using a roughened mold surface. This roughness prevents spray skin formation and ensures fibers reach the surface, thereby improving electrical conductivity while still achieving acceptable surface quality for the sensor function
2Reliability
If a roughened mold surface is used, then the fiber proportion on the surface is increased improving electrical conductivity, but the surface quality of the injection molded part deteriorates
Solution Approach 1:
The roughening is applied only to specific areas of the mold that correspond to the sensor surface, not the entire mold surface. This ensures fibers reach the sensor area for electrical conductivity while other areas of the part maintain smooth surfaces for cosmetic or functional quality
Solution Approach 2:
The invention changes the surface parameter of the mold from smooth to roughened, but controls the degree of roughness to achieve the optimal balance between fiber distribution for conductivity and acceptable surface quality. The roughness parameter is optimized to prevent spray skin while maintaining part quality
3Ease of manufacture
If fibers are aligned parallel to the wall surface, then the injection process is simplified, but the electrical conductivity on the surface is reduced due to isolating spray skin
Solution Approach 1:
Instead of allowing fibers to align parallel to the surface (which creates spray skin), the invention inverts the fiber orientation by using mold roughness to disrupt the flow and force fibers to protrude through the surface, achieving perpendicular or random orientation that ensures conductivity
Solution Approach 2:
The invention converts the harmful effect of spray skin (which isolates fibers) into a benefit by using controlled roughness to prevent spray skin formation entirely. The roughness creates turbulence that distributes fibers uniformly and ensures they reach the surface, turning a potential manufacturing defect into a conductivity enhancement mechanism
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 significantly improves the electrical conductivity and measurement accuracy of the water level sensor by ensuring fibers are present on the surface, allowing for precise water level detection in fuel filters.
Implementation Method 1
The graining of the plastic injection mold or the plastic injection mold allows a different flow pattern to be achieved in the plastic injection mold, whereby the previously laminar flow along the smooth surfaces of the plastic injection molds, which lead to a parallel fiber orientation to the surface, can be avoided. The rough surface of the plastic injection mold causes turbulence on the surface, which distributes the fibers in an unstructured manner
Implementation Method 2
the surface of the water level sensor is roughened by means of sandblasting or by means of CO 2 jets. In this case, the water level sensor is first injected with a conventional plastic injection molding tool or a conventional plastic injection molding mold with a smooth surface and its surface is only roughened in the finished state by the blasting method mentioned.
Data Source
Figure 1~3
AI summary
The invention relates to a method for producing a water level sensor (4) of a fuel filter (1) from electrically conductive plastic, wherein a fiber-reinforced plastic is injected into a plastic injection mold (5, 5'), wherein a plastic injection mold (5) having a rough, in particular grained surface (6) is used, or a plastic injection mold (5') having a smooth surface (6') is used and a surface (8) of the water level sensor (4) is roughened such that at least individual fibers lie on the surface (8) in the finished water level sensor (4). The electrical surface conductivity and measurement accuracy can thus be increased.