Friction Fit Drill Bit Adaptor for Self-Drilling Rock Bolts
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Solution Overview
Problem
Existing self-drilling rock anchors face issues with drill bit detachment under high loads and require larger diameters for sufficient material thickness, leading to unnecessary hole size and increased resin requirements, which increase costs and reduce installation stiffness.
Innovation Solution
A friction fit system using an adaptor with a first taper for engagement with the rock bolt and a second taper for engagement with the drill bit, providing a self-locking connection without the need for threads or welding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the drill bit body is made with sufficient diameter to support threads, then the drill bit strength is improved, but the hole size drilled increases beyond necessity
Solution Approach 1:
The drill bit assembly is segmented into a separate adaptor component that provides the threaded connection interface with the rock bolt shank, while the drill bit body itself can be smaller diameter. The adaptor acts as an intermediary that carries the threading function, allowing the drill bit to be optimized for drilling performance without needing excessive diameter for thread support.
Solution Approach 2:
The adaptor serves as an intermediary component between the drill bit and the rock bolt shank. It provides the threaded male interface that engages with the female thread in the shank bore, while the drill bit attaches to the adaptor via friction fit. This mediator allows the drill bit to be smaller while still achieving sufficient connection strength through the adaptor's threading.
2Reliability
If a larger diameter drill bit is used to ensure sufficient material thickness, then the connection reliability is improved, but the resin requirement increases, increasing cost and decreasing stiffness
Solution Approach 1:
The connection system is segmented into the adaptor with external threading and the rock bolt shank with internal threading. This segmentation allows the threading function to be provided by the adaptor rather than requiring the drill bit body to be large, thereby reducing hole diameter and resin volume while maintaining connection reliability through the threaded interface.
Solution Approach 2:
The invention changes the geometric parameters of the connection system by introducing a separate adaptor component with optimized threading dimensions. This allows the effective connection parameters (thread engagement length, thread profile) to be independent of the drill bit body diameter, enabling reliable connection with smaller hole sizes and reduced resin requirements.
3Strength
If thread engagement is used to connect the drill bit to the rock bolt, then the connection strength is improved, but the device complexity increases due to threading requirements
Solution Approach 1:
The adaptor acts as an intermediary that consolidates the threading complexity into a single component. The male threads are formed on the adaptor body rather than requiring complex threading in the drill bit body or shank. This intermediary approach simplifies the overall device by concentrating the threaded connection functionality in one element that can be easily manufactured and assembled.
4Strength
If the rod diameter is increased to provide sufficient material for tapered end attachment, then the attachment strength is improved, but the hole size and resin requirement increase
Solution Approach 1:
The attachment system is segmented into the adaptor with tapered friction-fit surfaces and the rock bolt shank. The adaptor provides the tapered interface that engages with the shank bore, allowing the shank to maintain its original diameter without needing additional material thickness for taper formation. This segmentation enables strong attachment while minimizing hole size and resin 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 friction fit system ensures secure attachment of the drill bit to the rock bolt, preventing detachment under high loads while minimizing the hole size and resin requirements, thus reducing costs and maintaining installation stiffness.
Implementation Method 1
the first taper and the second taper are adapted for friction fit in a bore of the shank and a recess in the drill bit respectively
Data Source
AI summary
The invention provides an adaptor for connecting a drill bit to a hollow shank of a self-drilling rock bolt, the adaptor including a body which extends in an axial direction between a distal end and a proximal end, a tubular conduit which extends between the ends, an abutment surface formed in an outer surface of the body that divides the body into a proximal portion and a distal portion, wherein at least a part of the proximal portion includes a first taper which tapers towards the proximal end, wherein at least a part of the distal portion includes a second taper which tapers towards the distal end, and wherein the first taper and the second taper are adapted for friction fit in a bore of the shank and a recess in the drill bit respectively.