Pick Tool Tip With Depression For Crack Resistance
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Solution Overview
Problem
Existing pick tools face challenges in maintaining structural integrity and preventing crack propagation due to residual stress and material mismatch between polycrystalline diamond (PCD) impact structures and cemented carbide substrates, leading to reduced durability and effectiveness in applications like road milling and coal mining.
Innovation Solution
The design incorporates a PCD impact structure with a rounded conical shape and a depression on the substrate, featuring a ridge and intermediate region with specific curvature and depth, which creates a region of residual axial compression to counteract tensile stress and enhance fracture resistance, bonded to the substrate through ultra-high pressure sintering.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a PCD impact structure is bonded to a cemented carbide substrate, then the hardness and wear resistance are improved, but residual stress and material mismatch cause crack propagation and reduce structural integrity
Solution Approach 1:
The substrate is designed with a non-planar boundary surface featuring a depression and ridge structure, creating local variations in geometry and material properties. This local quality change allows the intermediate region to experience different stress states compared to the bulk substrate, specifically generating compressive residual stress at the PCD-substrate interface where it is most needed to prevent crack propagation.
Solution Approach 2:
The invention employs a composite structure consisting of PCD impact structure bonded to a cemented carbide substrate with a specially designed non-planar interface. The composite design leverages the high hardness of PCD while the tailored substrate geometry compensates for material mismatch stresses, achieving both wear resistance and structural integrity.
2Ease of manufacture
If the PCD impact structure is bonded directly to a planar substrate surface, then the manufacturing is simpler, but crack propagation occurs due to tensile stress at the interface
Solution Approach 1:
The non-planar boundary surface with depression and ridge is designed in advance to pre-establish compressive residual stress at the PCD-substrate interface before the tool is put into service. This preliminary anti-action counteracts the tensile stresses that would otherwise develop during operation and lead to crack propagation, thereby improving crack resistance without significantly complicating the bonding process.
3Strength
If the depression depth and curvature are increased, then the residual compressive stress is enhanced, but the manufacturing precision requirements increase
Solution Approach 1:
The invention specifies optimized parameter ranges for the depression geometry, including depth of 0.1 to 2 millimetres and radius of curvature of at least 0.5 millimetres. These parameter changes balance the need for sufficient compressive residual stress with the practical constraints of manufacturing precision, ensuring that the depression can be effectively formed while achieving the desired stress state for crack prevention.
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 configuration significantly enhances the resistance to crack propagation and extends the working life of the pick tools by optimizing the distribution of residual compressive and tensile stresses, improving their performance in demanding applications.
Implementation Method 1
bonded to the substrate through ultra-high pressure sintering
Implementation Method 2
The impact structure includes a volume in a residual state of axial compression, the compressed volume extending from the depression in the boundary surface to a region of the impact structure remote from boundary surface
Data Source
AI summary
The tip comprises an impact structure (20) formed joined at a non-planar boundary surface of a substrate. The boundary surface includes a depression (34). The impact structure comprises superhard material and has a working end including an apex (22) opposite the depression. The boundary surface of the substrate comprises a ridge at the periphery of the depression and a generally tapered circumferential region (32) depending away from the ridge towards a side of the tip, a lowest point of the depression being directly opposite the apex.