Method for manufacturing a tub section for a washing machine
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Solution Overview
Problem
The existing manufacturing methods for washing machine tub sections face challenges such as unsatisfactory dimensional stability, poor adhesion between metal and plastic, and extended cooling times due to differences in material coefficients of contraction and densities, leading to increased costs and potential defects.
Innovation Solution
A method is introduced where a high-strength plastic sleeve is molded around the bearing hub, allowing for a separate high-strength region around the bearing hub and a low-strength region elsewhere in the tub, using a smaller amount of expensive material for the sleeve and more affordable material for the rest of the tub, with the sleeve being installed over the bearing hub cold and injected separately to reduce thermal shock and improve cooling times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a metal bearing hub is heated to 40-60°C before plastic injection to avoid thermal shock, then thermal shock is reduced, but the cooling time extends to more than 8 hours due to the metal acting as a heat-retaining core
Solution Approach 1:
The patent divides the tub structure into two distinct parts: a metal bearing hub and a separate plastic bearing housing that is injection-molded around it. This segmentation allows the plastic housing to be removed after injection, enabling the metal hub to be preheated without extending the overall cooling time of the entire tub assembly, as the plastic can be detached once cooled.
Solution Approach 2:
The patent extracts the plastic bearing housing from the permanent structure, making it a temporary mold that is removed after injection. This allows the metal bearing hub to be heated beforehand without creating a permanent heat-retaining core in the final product, thus reducing the effective cooling time while maintaining adhesion quality during the injection process.
2Strength
If the bearing hub is made larger to support high-speed rotation, then the mechanical strength increases, but the weight increases from 1 kg to 2 kg
Solution Approach 1:
The patent uses a composite structure combining metal bearing hub with plastic bearing housing and plastic tub sections. The metal hub provides the necessary mechanical strength for high-speed rotation, while the plastic components provide structural support and reduce overall weight compared to a fully metal construction, achieving an optimal strength-to-weight ratio.
3Strength
If plastic formulation with filler material is used to manufacture the tub section, then the mechanical strength increases, but the dimensional stability decreases due to differences in coefficients of contraction
Solution Approach 1:
The patent segments the tub into metal bearing hub and plastic bearing housing components that are injection-molded separately. This allows each component to be optimized independently: the metal hub maintains dimensional stability, while the plastic housing with filler materials provides the necessary mechanical strength without compromising overall dimensional stability.
Solution Approach 2:
The patent applies different material properties to different regions: the bearing hub area uses metal for dimensional stability, while other tub sections use plastic formulations with filler materials for mechanical strength. This local differentiation resolves the contradiction by assigning material properties based on functional requirements of each specific region.
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 reduces manufacturing costs, enhances dimensional stability, and allows for faster cooling, while ensuring the mechanical strength requirements are met, particularly around the bearing hub, thereby improving the reliability and efficiency of the tub section production.
Implementation Method 1
a metal-plastic bond is achieved at the interface of the two materials
Implementation Method 2
In order to avoid thermal shock when the plastic injection is performed next to the metal bearing hub, the latter needs to be heated ahead of time
Implementation Method 3
differences in coefficients of contraction of the materials and in their cooling curves
Data Source
Figure 1
Figure 2A~2C
Figure 3~4
AI summary
Method for manufacturing a tub section 14 for a washing machine that has a plastic tub inside which a rotating drum can be housed whose rotational shaft is supported on bearings provided for in the inner face of a bearing hub 6 made of metal, wherein the tub is installed radially over the outer surface 6A of the bearing hub by a plastic injection process, and between the outer surface of the bearing hub and the tub there is a sleeve made of plastic material 17, 46a, 46b. The method includes the steps of: moulding the sleeve of plastic material, installing the sleeve tightly fit over the outer surface of the bearing hub forming a hub assembly, and injecting the plastic tub over the hub assembly.