PFA Liner Pump Casing Segmentation for Stress Reduction
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Solution Overview
Problem
Conventional methods for manufacturing PFA liners for metal pump casings, such as transfer molding, rotolining, and injection molding, face challenges including high manufacturing costs, long processing times, inability to control liner thickness and density, and residual stress leading to cracks, especially in large pumps operating at high temperatures.
Innovation Solution
The pump casing is divided into a suction casing and a volute casing, with each part molded separately to reduce shrinkage effects and assembled with metal shaft supports for precise fitting and stress distribution, eliminating tensile stress and enhancing structural stiffness and corrosion resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If injection molding is used to manufacture PFA liner for large pump casing, then manufacturing speed is improved, but residual stress causes liner to crack and pump failure
Solution Approach 1:
The pump casing is divided into two separate parts: suction casing and volute casing. Each part is molded separately with its own PFA liner, reducing the total molding area and shrinkage stress. The suction casing includes the suction channel and shaft support, while the volute casing includes the volute channel and discharge channel. This segmentation allows each liner to be manufactured with lower residual stress while maintaining high productivity through injection molding.
2Strength
If pump casing is manufactured as single piece with PFA liner, then structural integrity is improved, but residual stress concentrates and causes liner failure
Solution Approach 1:
The pump casing is segmented into suction casing and volute casing that are assembled together. Each casing has its own PFA liner molded separately. The suction casing liner and volute casing liner are joined at the joint surface, distributing the stress across two separate liner systems rather than one large continuous liner, thereby reducing stress concentration and improving reliability.
Solution Approach 2:
The joint surface between suction casing and volute casing acts as an intermediary connection. The suction casing sealing surface and volute casing sealing surface are pressed against each other to create a hermetic seal, allowing the two separately molded liners to work together as a unified corrosion-resistant system while maintaining structural integrity.
3Manufacturing precision
If transfer molding is used to manufacture PFA liner, then liner quality is improved, but manufacturing time increases to 8-12 hours per cycle
Solution Approach 1:
The manufacturing process parameters are changed from transfer molding to injection molding. Injection molding achieves comparable liner quality with much faster cycle times (normally 10 minutes per cycle). The segmentation into smaller suction casing and volute casing allows injection molding to produce liners with controlled thickness and density while maintaining quality standards.
4Ease of manufacture
If rotolining is used to form PFA liner, then manufacturing cost is reduced, but liner thickness and density cannot be precisely controlled
Solution Approach 1:
The manufacturing process is changed from rotolining to injection molding. Injection molding provides precise control over liner thickness and density through controlled injection parameters, mold temperature, and pressure. This ensures consistent liner quality while maintaining cost-effectiveness for large pump casings.
Data Source
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Figure 1B
Figure 2
AI summary
A structure improvement of a pump casing (4) with a Polyfluoroalkoxy (PFA) liner which improves manufacturing efficiency, reduces manufacturing cost and improves yield strength, more particular to keep the stiffness of the shaft support and improve yield of the pump casing. The metal pump casing (4) with the PFA liner used for handling corrosive liquids includes a suction casing (41) with PFA liner, and a volute casing (42) with PFA liner for accommodating an impeller. The volute casing also collects and then ejects the liquid through a discharge (422). The suction casing (41) with the PFA liner and the volute casing (42) with the PFA liner are separately formed as two workpieces by injection molding process and then assembled to form the pump casing (4) so as to reduce the residual stress applied in the PFA liner.