Down-the-hole Hammers: Maintenance and Operation
January 2, 2008
All hammers must be frequently disassembled and inspected for damage or wear. How often the hammer will be inspected depends on the drilling conditions. When used for standard dry drilling (little or no water), an inspection every 175 hours to 200 hours will be enough. When using the hammer in wet conditions, in holes where mud is found, in water wells, when using water or foam injection, or when drilling in very hard rock, an inspection should take place every 100 hours. Damaged or worn parts must be replaced immediately. Also, a standard check of the tool after its first day of operation is beneficial to detect any early problems.
When using water or foam injection, remember to clean hammer thoroughly at the end of the day by flushing with clean water and compressed air, and then re-lubricate.
The drilling contractor has the final judgment on the necessity to change or replace parts. Air slips past worn sealing areas, providing less pressure to the piston. When pressure drops, so does penetration. And when penetration becomes inadequate, parts must be repaired or replaced. One factor that determines how much wear there is on parts is large air volume, which compensates for wear between the piston and piston case. Another is the cleanliness of the operating environment, and precise use of lubrication.
Any kind of dirt, dust or dampness can shorten the life of the parts or interfere with the quality of the oil twice as quickly. Close attention to the use of the hammer, its operating pressure, operating hours and penetration rate will inform its owner of safe service intervals.
Hammer OperationsThe hammer’s penetration comes from air flow and air pressure in the piston case. The cleaner the air and the sharper the bit, the better performance and longevity you will get from the hammer.
Close attention should be kept to the hammer’s operation. It is a heavy tool, and can hurt someone or become damaged if dropped. Be sure to have a clear area when moving the hammer. Do not exceed suggested operating limitations for its use. Always use the proper tools for assembly and disassembly. Don’t improvise. This will ensure that your hammer works effectively for a long time to come.
Safety starts with what you’re wearing. Make sure work clothes fit snugly, and there is no excess cloth that can be caught in the equipment. Protect your head with a hard hat, ear guards and eyewear that deflects matter thrown into the air during hammer use. Protect your hands with durable work gloves, and your feet with sturdy steel-toed shoes or boots.
Always be aware of your drilling conditions. Take precautions for every possible occurrence – from weather to chemical mixes in materials that can cause explosions. You should evaluate every site carefully before drilling to be prepared for potential complications.
Compressed air can be dangerous if not used correctly. Never direct air toward any person for any reason. Do not use it to clean anything but the hammer, and make sure it doesn’t blow anything into the hammer.
All safety precautions must be followed. Improper or negligent use of hammers and other drilling products can result in bodily injury or death to persons, and/or severe damage to the hammer and parts.
Some general recommendations concerning hammer use:
1. All persons using the hammer must become extremely familiar with methods of use and mechanical specifications of the hammer prior to use.
2. To maintain the life of your hammer, it should be inspected thoroughly on a regular basis to ensure parts are in good condition. Replace those that are not. Mark new bits with their sizes to help decide which will be the best one to use.
3. Avoid excessive contact with the elements by keeping the hammer indoors overnight and shielding its interior from dirt and other objects with a sufficient cover.
4. During maintenance, use tools specifically designed for the hammer’s measurements. Don’t adapt other tools because they are close in measurement and temporarily convenient; the hammer can be damaged this way, and its lifespan shortened.
Thread PreparationThreads must be properly cleaned before they can be used. If any former thread compound is present, clean thoroughly prior to preparation with a wire brush and solvent. If any irregularities are found on the threads, such as burrs or nicks, remove them with an emery cloth for box threads and a file for pin threads. Dry with compressed air when finished.
Lightly coat threads and mating shoulders with compound of which at least 40 percent must be a powdered lead, zinc or copper. Avoid anything heavier to coat threads that might cause a large reduction in the friction coefficient. Do not let any of the compound find its way into other tool parts while in use.
When using new drill steel, be sure all cuttings have been cleared out. When attaching drill pipe, make sure all parts involved are thoroughly cleaned of mud, dirt and other matter prior to connection. Make sure the pipe is not bent, as this will cause undue stress on parts.
As the hammer is rotated onto drill pipe, make sure thread connections are firm and tight. If not, they may need to be rechecked for excess compound or the shoulder refaced. If the connections seem good, tighten them with a wrench to proper torque. Do not depend on drilling action to tighten the threads later; make sure all are checked and tightened prior to any use.
Lubrication always is the obvious key to maintaining the life and productivity of the hammer. Rock drill oil is an effective lubricant, and has three grades for varying environmental conditions – grades 10 (light), 30 (medium) and 50 (heavy).
To the naked eye, one can evaluate oil consumption by observing the thin layer of oil lubricating the inside of the drill pipe. Consumption of this oil is directly correlated to air consumption. Inlet air pressure and the restriction plug determine air consumption. Temperature will dictate which grade of oil to use. It is important not to under-lubricate or over-lubricate. When a fine film of oil is evident on the bit face and exhaust ports while running the hammer at minimum rate, the lubricator is adjusted properly. Proper adjustment ensures prevention of part damage and correct hammer operation.
On occasion, excess oil will drain down the drill rods into the hammer when it is not in use, and may demand a cleaning of the parts. Also, when using the hammer in cold and wet conditions, place it as far into the hole as possible to take advantage of ground heat. If parts are new, use an extra quart of oil per new joint of drill pipe. Also, use higher grades when in atmospheric conditions that can affect viscosity, such as water.
This article is provided through the courtesy of Eastern Driller’s Manufacturing Co. It is excerpted from the company’s EDM Technical Maintenance and Operation Manual. For more information, visit www.edmmfg.com.