Non-Circular Molding Pin for Circular Plastic Tank Surface
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Solution Overview
Problem
Conventional molding methods for fluid reservoirs with circular cylindrical sliding barrels and variable outer surfaces fail to produce perfectly circular internal surfaces due to material shrinkage, leading to leaks when used with conventional follower pistons, and existing solutions like oval pistons are costly and limited in shape.
Innovation Solution
A non-circular cylindrical molding pin is used to shape the internal surface, with cross-sectional dimensions inversely proportional to the tank's wall thickness, allowing for material shrinkage without stress and resulting in a perfectly circular cylindrical internal surface after cooling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional circular cylindrical molding pin is used to form the internal surface, then the molding process is simple and fast, but the internal surface becomes non-circular after cooling due to material shrinkage, causing leaks
Solution Approach 1:
The patent applies asymmetry by using a non-circular molding pin (with rectangular or square cross-section) to create a circular cylindrical internal surface. The molding pin's dimensions are specifically designed to account for differential shrinkage in different directions, where the pin's width and height are made unequal to compensate for the greater shrinkage occurring in the direction of smaller wall thickness, thereby achieving a perfectly circular internal surface after cooling
Solution Approach 2:
The patent changes the geometric parameters of the molding pin from a conventional circular cross-section to a non-circular cross-section (rectangular or square) with specific width and height dimensions. These parameters are calculated based on the wall thickness distribution, where the pin dimensions are set such that width < height when the wall thickness in the width direction is smaller than in the height direction, compensating for differential shrinkage and ensuring circularity of the internal surface
2Manufacturing precision
If the wall thickness is increased to reduce shrinkage, then material shrinkage is reduced, but the molding pin must be removed before cooling to allow stress-free shrinkage, adding process steps
Solution Approach 1:
The patent applies preliminary action by removing the molding pin from the mold cavity before the plastic material is fully cooled. This timing is critical: the pin is extracted when the material is still warm and pliable but has maintained its molded shape, allowing the material to subsequently shrink freely without the constraint of the pin, thereby preventing distortion of the internal surface while enabling the use of a simple non-circular pin design
Solution Approach 2:
The patent provides beforehand cushioning by designing the molding pin with dimensions that pre-compensate for the expected material shrinkage. The pin's non-circular cross-section is specifically dimensioned to account for differential shrinkage in different directions, so that after the material cools and shrinks, the internal surface naturally becomes perfectly circular without requiring additional correction steps
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 method enables the production of fluid reservoirs with circular cylindrical internal surfaces suitable for conventional follower pistons and variable outer shapes, preventing leaks while reducing manufacturing costs and expanding shape options beyond circular forms.
Implementation Method 1
the tank will thus cool down, thus inevitably undergoing material shrinkage phenomena, well known in the field of plastic molding
Data Source
Figure 1~3b
AI summary
The invention relates to a method for manufacturing a fluid material tank (1) that is to be combined with a dispensing member (4), such as a pump, so as to form a fluid material dispenser. The tank (1) includes a circular cylindrical inner surface (12) that defines a slide drum in which a follower piston (2) sealingly slides. The tank (1) includes an outer surface (13) having any shape and being separated from the inner surface by means of a variable wall layer (Emin). The method includes molding the tank (1) in a mold using a molten plastic material, characterized in that the inner surface (12) is formed by a non-circular cylindrical mold pin so as to take into account the occurrence of contraction of the material after cooling in order to obtain a circular cylindrical inner surface (12).