Plastic Pressure Cover Weld Line Control
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Solution Overview
Problem
Existing methods for producing plastic molded bodies for pressurized applications, such as water meters, face challenges due to the inherent weaknesses of plastics under pressure and tensile forces, diffusion of water into plastics reducing their strength, and the formation of weld lines that compromise mechanical properties.
Innovation Solution
The method involves using injection molds with extra cavities to allow flow through critical weld lines, controlling fiber orientation for enhanced compressive strength, and strategically positioning injection points to form weld lines away from high-stress areas, ensuring optimal fiber reinforcement and reduced cycle times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If plastic is used to replace metal for pressure resistance, then non-magnetic properties and fluid compatibility are improved, but mechanical strength and stability deteriorate
Solution Approach 1:
The patent uses glass fiber-reinforced plastic (GRP) as a composite material to replace solid metal. The glass fibers provide the necessary mechanical strength and pressure resistance, while the plastic matrix maintains non-magnetic properties and fluid compatibility. This composite approach allows the pressure cover to withstand high pressures without magnetic interference with the turbine measurement mechanism.
2Shape
If plastic melt flows around cores during injection molding, then complex shapes with fastening openings are achieved, but weld lines form and mechanical strength deteriorates
Solution Approach 1:
The patent strategically positions injection points and cores before molding to pre-determine weld line locations. By carefully planning the injection path and core positioning, weld lines are directed to occur in non-critical areas of the pressure cover that do not compromise structural integrity, such as away from fastening openings and high-stress regions.
Solution Approach 2:
The patent applies different design considerations to different regions of the pressure cover. Critical areas like fastening openings and high-stress zones are designed to avoid weld lines, while non-critical areas can accommodate weld lines. The reinforcement structure is locally optimized to compensate for potential weld line weaknesses in specific regions.
3Strength
If reinforcement fibers are added to improve strength, then pressure resistance is improved, but injection molding process difficulty increases
Solution Approach 1:
The patent optimizes injection molding parameters specifically for glass fiber-reinforced plastic. This includes adjusting injection pressure, injection speed, mold temperature, and holding pressure to ensure proper fiber distribution and consolidation. The process parameters are tuned to prevent fiber matting, air entrapment, and incomplete filling while maintaining the strength benefits of fiber reinforcement.
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 results in plastic molded bodies with improved mechanical stability and strength, suitable for pressurized applications like water meters, where the plastic components do not interfere with the measured fluid and allow for non-magnetic rotation transfer using permanent magnets.
Implementation Method 1
Weld lines form when cooled flow fronts of the plastic injected into the injection mold meet
Implementation Method 2
water diffuses into the plastics and additionally reduces their strength
Implementation Method 3
the rotation of the turbine can be transmitted to the measuring mechanism with the help of permanent magnets
Data Source
Figure 1~2
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AI summary
The invention relates to methods for producing annular moldings (12) subjected to tensile or pressure loading from plastic by using an injection mold (2) having a main cavity (42), wherein, in addition to the main cavity (42), at least one extra cavity (46) is incorporated in the injection mold (2), wherein the at least one extra cavity (46) is joined to the main cavity (42) by a connecting duct (47). The main cavity (42) is filled with plastic melt in such a way that a flow line (40) is formed in the main cavity (42) in the vicinity of the connecting duct (47) between the at least one extra cavity (46) and the main cavity (42), wherein the cross section of the connecting duct (47) is dimensioned such that, during the filling of the main cavity (42), no plastic melt flows into the extra cavity (46). The filling pressure is increased until plastic melt flows into the extra cavity (46); flow taking place through the flow line (40) produced during the filling of the main cavity (42). Subsequently, the injection mold (2) is opened and the molding (12) removed.