Screw Pump Keyless Locking Mechanism
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Solution Overview
Problem
Screw pumps face challenges in field refurbishment due to the need for extensive disassembly and complex re-assembly processes, particularly when dealing with compressible media and materials that leave coatings on the screws, which complicates the timing of screw intermeshing and replacement of seals and bearings.
Innovation Solution
A screw pump design featuring a keyless locking mechanism between the screws and shafts, allowing for rotational locking and adjustment without keys or keyways, enabling screws to be slid out without disassembly and allowing for seal replacement without complete disassembly, using materials with dissimilar thermal expansion coefficients for a slip fit at ambient temperatures and interference fit at operating temperatures for secure locking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of repair
If conventional key and keyway locking mechanism is used to fix screws to shafts, then rotational locking is achieved, but disassembly and re-assembly require extensive tearing into the bearing-and-seal carrier and complex timing adjustments
Solution Approach 1:
The locking mechanism is segmented into modular components: a keyless locking ring with axial slots, set screws accessible from the end, and a shaft with corresponding features. This segmentation allows the locking mechanism to be independently accessed and adjusted without disassembling the entire bearing-and-seal carrier, significantly simplifying maintenance procedures.
Solution Approach 2:
The locking function is extracted from the internal key-and-keyway mechanism embedded in the bearing-and-seal carrier and relocated to an external keyless locking ring at the end of the shaft. This extraction makes the locking mechanism accessible from the outside, eliminating the need to tear into the carrier for screw replacement or timing adjustments.
2Manufacturing precision
If screws are locked to shafts using internal keyways requiring carrier disassembly, then secure rotational locking is achieved, but timing adjustment requires loosening and re-tightening helical gears inside the carrier
Solution Approach 1:
The keyless locking ring acts as an intermediary mechanism between the screw and shaft, providing both locking and timing adjustment functions. The axial slots in the locking ring allow for precise angular positioning of the screw on the shaft, while the external set screws enable easy adjustment without internal gear manipulation.
3Ease of repair
If extensive disassembly of bearing-and-seal carrier is performed for screw removal, then screw access is achieved, but seal and bearing access also requires the same disassembly
Solution Approach 1:
The screw locking function is extracted to an external location on the shaft end, allowing screws to be locked and unlocked independently of the bearing-and-seal carrier assembly. This extraction enables seal and bearing maintenance to proceed without disturbing the screw locking mechanism, significantly reducing overall maintenance time.
4Stability of the object's composition
If keys and keyways are used to rotat ionally fix screws to shafts, then rotational locking is achieved, but the locking mechanism requires internal access through the carrier
Solution Approach 1:
The locking mechanism transitions from an internal two-dimensional key-and-keyway interface to an external three-dimensional keyless locking ring with axial slots and end-accessible set screws. This dimensional change moves the locking interface to the end of the shaft, providing both rotational stability and external accessibility.
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 design simplifies the refurbishment process by allowing for in-situ timing adjustments and easy replacement of screws and seals, reducing downtime and maintenance complexity while maintaining precise intermeshing and positive locking of screws to their shafts.
Implementation Method 1
using materials with dissimilar thermal expansion coefficients for a slip fit at ambient temperatures and interference fit at operating temperatures for secure locking
Data Source
AI summary
A screw pump (20) with field refurbishment provisions has screws (40), a base (26), and shafts (50) for the screws (40). The screws (40) have helical flights that intermesh during rotation, and extend between inner and outer ends (44 and 42). The shafts (50) extend between inner and outer ends (68 and 74), and are cantilevered from the base (26) from about the inner end (68) thereof. Each screw (40) is formed with a hollow core (80) for receiving its shaft (50) such that the screw (40) slips onto the respective shaft (50) therefor over the outer end (74) of its shaft (50). The screw pump further includes a keyless locking mechanism (56, 58, 96, or 98) intermediate each shaft (50) and screw (40), which is operative to rotationally lock the shaft (50) and screw (40) together without a key or keyway.