Down-the-hole hammer bushing stabilizes bit and traps air
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Solution Overview
Problem
Conventional down-the-hole hammers face issues with bit shank breakage due to bending moments and require long, expensive shanks for torque support, and the need for footvalves can lead to breakage and reduced lift force, affecting drilling efficiency.
Innovation Solution
A down-the-hole hammer design with a shortened stub shank and a bushing system that traps pressurized air to enhance lift force, eliminating the need for a footvalve and improving bit retention through a close sliding fit between the bushing and retaining ring.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a long bit shank is used to provide sufficient support for torque transfer and bit retention, then the bit can be securely retained and torque can be effectively transferred, but the shank becomes more prone to breakage due to bending moments and the cost increases
Solution Approach 1:
The bit shank is segmented into functional zones: a shortened stub shank for retention, a splined portion for torque transfer, and a head portion for cutting. This segmentation allows each part to be optimized independently, reducing the overall shank length while maintaining retention reliability through the splined engagement with the chuck.
Solution Approach 2:
A bit retaining ring is introduced as an intermediary component between the stub shank and the chuck. The retaining ring engages with the stub shank and the chuck to provide secure retention without requiring a long shank, thereby reducing bending moments while maintaining reliability.
2Reliability
If a footvalve is included in the bit assembly to seal the bottom lift chamber, then the piston can be properly sealed during the strike position, but the footvalve is prone to breakage and reduces lift force
Solution Approach 1:
The footvalve is completely removed from the bit assembly. Instead, the piston itself is designed with an integrated sealing mechanism that seals against the bit head during the strike position, eliminating the separate footvalve component that was prone to breakage and reduced lift force.
Solution Approach 2:
The sealing function previously performed by the separate footvalve component is merged into the piston structure. The piston incorporates a sealing surface that directly engages with the bit head, combining the sealing and striking functions into a single integrated component, thereby improving reliability and lift force.
3Strength
If the bit shank is shortened to reduce cost and breakage risk, then the shank is less expensive and more reliable, but retaining the bit within the chuck becomes more difficult
Solution Approach 1:
The bit retaining ring serves as an intermediary component that simplifies retention of the shortened stub shank. The retaining ring engages with the stub shank and the chuck, providing a reliable retention mechanism for the reduced shank length without increasing overall device complexity.
Solution Approach 2:
The retaining ring provides localized retention capability at the critical interface between the stub shank and the chuck. By concentrating the retention function in this specific local area rather than requiring length along the entire shank, the design achieves secure retention with minimal shank length.
4Length of stationary object
If the chuck length is maximized within the limit imposed by stub shank length, then more chuck length is available for engagement, but the overall assembly length is constrained
Solution Approach 1:
The chuck is segmented into functional portions: an upper screw thread portion for engagement with the outer wear sleeve, a lower extension portion to protect the outer wear sleeve, and a central retaining portion for the bit. This segmentation allows each portion to be optimized for its specific function while maintaining compact overall length.
Solution Approach 2:
The bit retaining ring is nested within the chuck structure, engaging with the stub shank inside the chuck's internal volume. This nesting arrangement allows maximum chuck length utilization without increasing the external overall assembly length, as the retention mechanism is contained within the existing chuck boundaries.
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 design stabilizes the bit, maximizes lift force, and reduces the risk of bit breakage by creating a boost chamber that enhances the percussive effect and maintains air pressure, thereby improving drilling speed and efficiency.
Implementation Method 1
an upper portion of the bushing has an internal diameter dimensioned to provide a sealing fit with the piston nose... the bit retaining ring or the lower portion of the bushing has an internal diameter dimensioned to provide a close sliding fit with the outer diameter of the retaining shoulder on the stub shank
Implementation Method 2
A sliding piston is mounted for reciprocating movement within the inner cylinder and the outer wear sleeve, to strike a hammer bit mounted for sliding movement in a chuck located at the forward end of the outer wear sleeve
Data Source
AI summary
The present invention relates to a down-the-hole hammer comprising an external cylindrical outer wear sleeve (5), a sliding piston (8) mounted for reciprocating movement within the outer wear sleeve to strike a percussion bit (1) of a drill bit assembly located at the forward end of the outer wear sleeve. The drill bit assembly comprises a percussion bit having a head portion formed with an axially extending stub shank (32); axially extending splines (36) on the stub shank slideably engageable with complementary splines (35) formed on a drive chuck (4) whereby rotational drive from the chuck may be transmitted to the stub shank; a bit retaining ring (141) adapted for engagement with a retaining shoulder (37) on the stub shank to retain the stub shank in the drill bit assembly; and engagement means on the chuck adapted for connecting the chuck to a drive means of the fluid-operated percussion drill tool; the bit retaining ring comprises a shoulder (144) for engagement with an upper end of the chuck to hold the retaining ring in place in the assembly. The assembly further comprises a bushing (61) arranged above the chuck. An upper portion of the bushing has an internal diameter (B) dimensioned to provide a sealing fit with the piston nose (20). The bit retaining ring or the lower portion of the bushing has an internal diameter (E) dimensioned to provide a close sliding fit with the outer diameter of the retaining shoulder (37) on the stub shank (32).