The coupling sleeve is a sleeve-like part with an internal thread that connects the shank adaptor and the drill rod or two drill rods. It is an indispensable accessory in supporting rock drilling tools for rock drilling. In the drilling process, it is in the joint part of the supporting rock drilling tools, bearing the corrosive effects of axial tensile pressure, bending and torsion, contact, friction, and other stresses. Therefore, it is also important to choose the coupling sleeve reasonably.
Classification and characteristics of coupling sleeves
Half-bridge coupling sleeve: There is a small bridge area without thread in the middle; the drill rod thread cannot pass through the middle of the coupling sleeve; the bridge area where the end of the drill rod is against the coupling sleeve; the half-bridge coupling sleeve is most suitable for high-torque equipment; most the wave thread and the stepped thread coupling sleeve are half-bridge type.
Full bridge coupling sleeve: avoid the possibility that the coupling sleeve slowly penetrates the joint along the thread; usually used for outdoor construction; it has the characteristics of better disassembly, and the connection is relatively tight; the probability of being stuck is small.
Conversion coupling sleeve: The two ends of the coupling sleeve have different thread specifications, commonly known as the reducing coupling sleeve, which is used for the connection between products with different thread specifications, and is only used under special circumstances.
Since the coupling sleeve is relatively simple compared to other rock drilling tools, most manufacturers or users do not care about it, and there is not much information about it on the Internet. If it has problems, the operator may scrap it, but it is a great waste for the enterprise. Therefore, some simple methods to solve the failure of the coupling sleeve can help the enterprise to control the cost-effectively.
15 Solutions to Solve the Failure of the Coupling Sleeve
1. The solution to the coupling sleeve end is chipped, cracked, or flared caused by the drill rod not being firmly seated into the coupling sleeve from the mismatch of threads: It is important to standardize on a single source supplier for components to ensure proper thread tolerance. Don’t mix to match.
2. The solution to the coupling sleeve end is chipped, cracked, or flared caused by mixing old thread components with new ones: Install new coupling sleeves with new drill rods.
3. The solution to the coupling sleeve end is chipped, cracked, or flared caused by misalignment of feed: Check affected equipment.
4. The solution to the coupling sleeve end is chipped, cracked, or flared caused by overheating of the coupling sleeve: The maximum running temperature for coupling sleeves is 182℃.
5. The solution to the coupling sleeve end is chipped, cracked, or flared caused by improper heat treatment: Forward for analysis.
6. The solution to the coupling sleeve end is chipped, cracked, or flared caused by the drop of the drill rod when retracting on up holes: Use a rock drill with a shank adapter thread engaged to lower steel.
7. The solution to the coupling sleeve end is chipped, cracked, or flared caused by starting percussion or rotation with the end of the shank adapter resting against the end of the coupling sleeve： Do not engage percussion or rotation if the shank adapter thread end is not aligned inside coupling sleeve.
8. The solution to the failure across the thread section caused by hole deviation or misalignment of the feed-in about the hole direction: Employ straight hole drilling devices.
9. The solution to the failure across the thread section caused by low feed pressure: Monitor feed force and tune to conditions.
10. The solution to the failure across the thread section caused by the heavy rotational loads from drilling with dull bits: Resharpen the bits when the wear flats appear 1/3 dull or discard them when tungsten carbide button height is compromised.
11. The solution to the failure across the thread section caused by the surface layer of the drill rod compromised by nicks or dents: Avoid hammering on the connection. Use a breakout plate to loosen joints. Employ proper care and handling.
12. The solution to pitting or galling in the threads caused by unused blow energy being reflected and absorbed: Adjust percussion and feed pressures to rock conditions.
13. The solution to pitting or galling in the threads caused by drilling with dull drill bits: Resharpen bits when the wear flats appear 1/3 dull or discard them when carbide profile height is compromised.
14. The solution to split coupling sleeves caused by drilling with worn threads: Replace coupling sleeves more frequently.
15. The solution to split coupling sleeves caused by excessive feed pressure: Monitor feed force and tune to conditions.
In Conclusion
To sum up, the failure of the coupling sleeve is mainly due to the wear failure of the internal thread and the bursting failure of the coupling sleeve.
The reason for the wear failure of the internal thread is the inevitable contact friction and stress corrosion in the internal and external thread connection fit. When they reach service life value, the thread fit cannot continue, and the connection fails. Another point is that there is a problem of fit gap between the internal and external threads. If the fit gap is too large, the connection will be unstable, wear will be accelerated; if the gap is too small, it will be difficult to load and unload the thread. Therefore, it is important to know the accurate thread clearance value and ensure the accuracy of thread processing in the manufacture of internal and external threads.
Many factors lead to the cracking failure of the coupling sleeve. The main reason is that the coupling sleeve has internal cracks or brittle failure due to excessive hardness during the raw material, machining, or heat treatment process.
In addition, the failure caused by the selection and use of the equipment by the user during the operation or the thrust of the current equipment not adapting to the formation conditions will also lead to the failure of the coupling sleeve.
Therefore, for product quality problems, enterprises can solve them by choosing a reliable supplier; for improper operation problems, enterprises can make perfect rules and regulations and strengthen the regular inspection of each component and equipment.
