Rock Bolt Shear Nut and Lock Nut for Consistent Pretension
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Solution Overview
Problem
Existing rock bolts face issues with inconsistent torque requirements for shear pin breakage, limited pretension due to resin strength variability, and spatial constraints in underground mining, leading to inefficient and time-consuming tightening processes.
Innovation Solution
A shear nut design with separable portions that allow controlled torque application, a lock nut arrangement for counter-moment creation, and a driver apparatus with planetary gear mechanisms for torque multiplication, enabling consistent tensioning and efficient installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a shear pin is used to prevent nut rotation during resin mixing, then the resin can be properly mixed, but the torque required to break the shear pin is inconsistent
Solution Approach 1:
The nut is divided into a first portion and a second portion connected by a frangible connecting portion. This segmentation allows the nut to function as a shear pin mechanism while providing more controlled and consistent torque application during the shearing process, improving both reliability and torque consistency.
Solution Approach 2:
The design changes the physical parameters of the connecting portion (frangible connection with controlled strength) to achieve predictable shearing at a specific torque threshold. This parameter control ensures consistent torque application while maintaining the resin mixing function.
2Strength
If resin strength is increased to support higher tightening torque, then higher pretension can be achieved, but resin variability limits the permissible axial tension
Solution Approach 1:
The frangible connecting portion is designed to shear at a predetermined torque threshold before the resin reaches its full strength. This preliminary action allows the bolt to be installed and the nut to be initially tightened without relying on the resin's full strength, thereby achieving consistent pretension despite resin variability.
Solution Approach 2:
The frangible connection acts as a cushioning mechanism that limits the torque transfer to the resin during installation. By controlling the shearing torque, the design protects the resin from excessive stress that would otherwise be limited by its variable strength, ensuring reliable pretension achievement.
3Power
If a stabilizer arm is used to create counter-moment, then torque multiplication is achieved, but spatial constraints in underground mining prevent its use
Solution Approach 1:
The counter-moment creation function is merged into the nut assembly itself through the lock nut arrangement. The lock nut engages with the bolt thread to provide the counter-moment internally, eliminating the need for an external stabilizer arm and making the system suitable for confined mining spaces.
Solution Approach 2:
The lock nut is nested within or adjacent to the first portion of the nut assembly, creating a compact integrated system. This nested arrangement allows the counter-moment mechanism to be contained within the same space as the torque application mechanism, solving the spatial constraint problem.
4Force
If external torqueing devices are used to tighten nuts, then sufficient torque can be applied, but setup time increases and spatial constraints are violated
Solution Approach 1:
The nut assembly is designed to be self-contained with all necessary components (first portion, second portion, connecting portion, lock nut) integrated into a single unit that can be installed and tightened using standard hand tools. This self-service design eliminates the need for complex external torqueing devices and reduces installation time.
Solution Approach 2:
The nut assembly performs multiple functions (resin mixing prevention, torque multiplication, counter-moment creation, and pretension application) through its integrated components, replacing the need for multiple separate devices and procedures, thereby reducing installation time and spatial requirements.
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 provides consistent torque application, enhances pretensioning capabilities, and facilitates efficient rock bolt installation despite spatial constraints, improving the stability and speed of underground operations.
Implementation Method 1
a driver apparatus with planetary gear mechanisms for torque multiplication
Implementation Method 2
driver apparatus with internal means for creating a counter moment when tightening or loosening a part such as a bolt or a nut
Implementation Method 3
the shear pin is supposed to shear, allowing the nut to rotate relative to the bolt
Implementation Method 4
a moment is exerted on the nut, and the counter-moment is created by adhesion or friction between the rock bolt and the rock body
Data Source
AI summary
A shear nut 10, a lock nut 62 (together forming a nut arrangement 60 for a bolt 12), and a driver (110, 500, 600, 700) used while installing the nut arrangement 60. Particularly, the bolt 12 is a rock bolt. The shear nut 10 comprises first and second portions (14, 18) connected by a connecting portion 22. The second portion 18 comprises an engaging formation 20 configured to interact with the bolt 12 to limit the extent to which the second portion 18 operatively advances axially along the bolt 12. The first portion 14 has an internal thread. In use, the first and second portions (14, 18) are configured to become separated at the connecting portion 22, when the engaging formation 20 interacts with the bolt 12 and a predetermined moment is applied to the first portion 14.