Two-Part Plunger Rod Sealing Seat Without Parting Line Flash
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Solution Overview
Problem
Existing plunger rods in multichannel pipettes suffer from tilting clearance during reciprocating motion, leading to reduced precision and accuracy in liquid aspiration due to mold-related parting line flash and potential leaks at the sealing seat, which are difficult to detect and costly to rectify.
Innovation Solution
A two-part plunger rod design with a first and second component, where the parting line is positioned away from the sealing seat, ensuring tight manufacturing tolerances and eliminating mold-related flash, enhancing sealing integrity and service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a one-piece injection molding is used for the plunger rod, then the manufacturing process is simple, but mold-related parting line flash occurs over the entire length including the sealing seat region
Solution Approach 1:
The plunger rod is divided into two separate components: a first plunger rod component and a second plunger rod component. The sealing seat is formed on the first component, while the second component is connected to it. This segmentation allows the parting line to be positioned away from the sealing seat, eliminating parting line flash in the critical sealing region and enabling high sealing quality without compromising manufacturing simplicity.
2Ease of manufacture
If a mold parting line is provided along the longitudinal axis for easy demolding, then demolding is simple, but parting line flash is generated over the entire length of the plunger rod
Solution Approach 1:
By segmenting the plunger rod into two components with the parting line positioned away from the sealing seat, the harmful parting line flash is confined to non-critical regions. The first component can still be easily demolded while the second component is separately formed and connected, eliminating flash in the sealing region without complicating the overall manufacturing process.
Solution Approach 2:
The sealing seat region is extracted from the injection molding process of the second component. The sealing seat is formed on the first plunger rod component in a separate molding cycle, and the second component is subsequently connected to it. This extraction removes the sealing seat from the path of the parting line, eliminating parting line flash generation in that critical area.
3Manufacturing precision
If deflashing process is applied to remove parting line flash, then flash is reduced, but residual particles may adhere to the plunger rod causing sealing issues
Solution Approach 1:
The sealing seat is extracted from the region where parting line flash is generated. By forming the sealing seat on the first plunger rod component in a separate injection molding process, the sealing surface is completely removed from the flash generation zone. This eliminates the need for deflashing operations near the sealing seat and prevents residual particles from compromising seal integrity.
Data Source
AI summary
The invention relates to a plunger rod (10) for a liquid transfer device (100), the plunger rod (10) being of two- or multipart construction. The plunger rod (10) has a first plunger rod component (12), in operative connection with an actuating device (110) of the liquid transfer device (100), and a second plunger rod component (14). The plunger rod (10) comprises a sealing seat (16) for receiving a sealing element (18) for the plunger rod (10), wherein a parting line (20) between the first plunger rod component (12) and the second plunger rod component (14) is configured so the sealing seat (16) is free of parting line flash (22). The invention includes a method for producing a plunger rod (10) and a liquid transfer device (100), in particular a pipette (102, 104, 106) and/or a multichannel bottom part (108) for a pipette (102, 104), with such a plunger rod (10).