Sucker Rod End Fitting Wedge Geometry for Breakage Resistance
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Solution Overview
Problem
Fiberglass sucker rod strings in secondary recovery systems face issues with compressive forces causing breakage at the connection points between rod segments and end fittings, leading to costly remedial operations due to uneven distribution of forces during reciprocation.
Innovation Solution
The design of end fittings with a wedge system that includes outer, intermediate, and inner wedge portions, each with specific leading and trailing edge lengths and angles, to distribute compressive forces along the length of the rod segment, reducing the risk of breakage by managing forces more evenly.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If fiberglass rod segments are used in sucker rod strings, then weight is reduced and energy consumption is decreased, but compressive forces cause breakage at connection points between rod segments and end fittings
Solution Approach 1:
The end fitting is segmented into multiple wedge portions (outer wedge portion, intermediate wedge portion, inner wedge portion) that are arranged axially in sequence. Each wedge portion has progressively smaller dimensions, creating multiple contact points along the rod segment that distribute compressive forces, preventing concentration at a single location and reducing breakage risk
Solution Approach 2:
Different wedge portions are designed with different local geometries and dimensions. The outer wedge portion has larger dimensions than the intermediate wedge portion, which in turn is larger than the inner wedge portion. This gradient in local qualities allows each section to handle specific force distributions, with the broader outer portion absorbing initial compressive loads and transferring them progressively inward
2Ease of manufacture
If conventional end fittings are used with fiberglass rods, then manufacturing is simpler, but compressive forces are concentrated at single points causing rod breakage
Solution Approach 1:
The end fitting is divided into multiple wedge portions (outer, intermediate, inner) that can be manufactured as integrated features within a single molding operation. The segmented geometry is achieved through standard composite manufacturing techniques, maintaining ease of manufacture while creating multiple force distribution points along the rod segment
Solution Approach 2:
The wedge portions are arranged axially along the length of the end fitting, adding a dimensional aspect to force distribution. Instead of a single contact point, the axial arrangement of multiple wedge portions with progressively smaller dimensions creates a distributed force profile along the rod segment, transforming point-load stress into distributed stress
3Reliability
If resin material is introduced into the end fitting for bonding, then the rod is secured against removal, but protruding resin sections migrate toward narrower portions under compressive force
Solution Approach 1:
The resin material is distributed across multiple wedge portions rather than concentrated in a single cavity. Each wedge portion contains resin that is laterally constrained by adjacent wedge structures, preventing migration under compressive loads. The segmented resin distribution ensures bonding strength while eliminating the harmful migration effect
Solution Approach 2:
The wedge portions act as intermediary structures between the rod segment and the resin material. These wedges laterally constrain the resin, preventing it from migrating axially under compressive forces while still allowing the resin to bond effectively to the rod surface. The wedge geometry mediates the interaction between bonding requirements and force distribution
Data Source
AI summary
Sucker rods include end fittings having an outer wedge portion proximate to an open end, an inner wedge portion proximate to a closed end, and an intermediate wedge portion between the outer and inner wedges. Each wedge includes a leading edge, a trailing edge, and an angle between the leading and trailing edges. The triangular configuration, length of the leading edge, the length of the trailing edge, and size of the angle in each wedge portion cause distribution of force, such that compressive forces distributed to the rod proximate the closed end exceed compressive forces distributed to the rod proximate the open end. An automated installation procedure installs the end fitting through the use of multiple chucks, positioned by servo motors along a fitting table.