Locking Device Hardness Gradient for Bolt Extraction
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Solution Overview
Problem
Existing mechanical connection methods for ground engaging tools (GET) to buckets in earth-moving equipment face issues such as complex and costly replacement processes, stress concentrations leading to cracking, and deformation of connecting bolts, which can result in seizure and difficulty in removing the GET.
Innovation Solution
A lock system with a force applying member and a force receiving member, where the relative hardnesses are designed to prioritize deformation of the force receiving member over the body or force applying member, allowing for deformation that maintains the locking function and facilitates easy removal, with a preferred hardness ratio of 0.7 to 0.9 between the members.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If bolts and fastening devices are used to mechanically attach GET to bucket lips, then the replacement process becomes simpler and faster, but the connecting bolts deform under large forces making them difficult to extract
Solution Approach 1:
The locking device is designed as a disposable component that deforms preferentially under excessive load rather than the bolt. When the locking device deforms, it shears off and allows the bolt to be easily removed, sacrificing the cheaper locking device to preserve the more valuable bolt and extraction process
Solution Approach 2:
The locking device acts as an intermediary between the bolt and the GET/bucket lip assembly. It absorbs the deformation and failure modes that would otherwise affect the bolt, serving as a protective intermediary that fails in a controlled manner to maintain bolt extractability
2Strength
If the hardness of the force applying member is increased to prevent deformation, then the locking device becomes more resistant to wear, but it may seize within the locking device when deformation occurs
Solution Approach 1:
Different components have different hardness values optimized for their specific functions. The force receiving member has lower hardness (30-50 HRC) to deform preferentially, while the force applying member has higher hardness (50-65 HRC) to resist wear and deformation. This local differentiation of material properties ensures controlled failure modes
Solution Approach 2:
The potential harm of deformation is converted into a beneficial controlled failure mode. By designing the force receiving member to deform preferentially due to its lower hardness, the system transforms what would be a catastrophic failure into a controlled shear-off that actually enables easier removal of the assembly
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
The solution prevents seizure of the locking device and allows for easy removal and replacement of GET, reducing maintenance complexity and costs by ensuring deformation occurs in the force receiving member, maintaining the locking function and enabling straightforward re-use of the lock system.
Implementation Method 1
the relative hardnesses of the body, the force applying member and the force receiving member are such that the application of a sufficiently large force to the protruding portion of the force receiving member will preferentially cause deformation of the protruding portion of the force receiving member
Data Source
AI summary
A lock for an attachment system that connects a ground engaging tool to a bucket lip. The lock is disposed, in use, between lug of a lip of the bucket and the ground engaging tool. The lock has a body, a force applying member and a force receiving member. Application of force by the force applying member causes the force receiving member to protrude from a first side of the body and to engage the lug. Relative hardnesses of the lug, the body, the force applying member and the force receiving member are such that application of a sufficiently large force via the lug to the protruding portion of the force receiving member preferentially deforms the protruding portion of the force receiving member ahead of deformation of the body or the force applying member as a preferred lock failure mode.