Down hole hammers require a continuous supply of the correct type of rock drill oil to operate efficiently. Proper lubrication of a down hole hammer is the most important and least expensive maintenance item on the drill rig. The following chart lists the minimum amount of rock drill oil required for the operation of all Numa hammers.
| CONVENTIONAL | ||
| Hammer | Oil Required | |
|
Imperial qt. per hour |
Metric litre per hour |
|
| Patriot 35A | 1 | 1 |
| Patriot 40/Champion 40 | 1 | 1 |
| DCS5/Patriot 50 | 2 | 2 |
| DCS6/Patriot 60W/WQ/Challenger 6 | 2 | 2 |
| Patriot 80/Challenger 80/80Q | 3 | 3 |
| Challenger 100 | 4 | 4 |
| Patriot 120/Challenger 120 | 5 | 5 |
| Patriot 125/Challenger 125 | 5 | 5 |
| Patriot 180 | 10 | 10 |
| Patriot 240 | 16 | 15 |
| Champion 330 | 20 | 19 |
| REVERSE CIRCULATION | ||
| Hammer | Oil Required | |
|
Imperial qt. per hour |
Metric litre per hour |
|
| Patriot RC46 | 2 | 2 |
| Challenger RC100 | 4 | 4 |
| Champion RC160 | 10 | 10 |
| Champion RC210 | 16 | 15 |
| Champion RC300 | 20 | 19 |
Listed below are several acceptable rock drill oils that are available.
| Company | Medium SAE 30 | Heavy SAE 50 |
| Exxon/Esso | Aroc 150 | Aroc 302 |
| Shell | Torcula 150 | Torcula 320 |
| Texaco/Caltex | Rock Drill Lube 100 | Rock Drill Lube 320 |
| Chevron | Vistac 150 | Vistac 320 |
Rock drill oils and Numa Lube are the only acceptable lubricants for DTH hammers. SAE 50 rock drill oil should be used in ambient temperatures of 80° fahrenheit (27° celcius) or higher. Contact Numa for acceptance of alternative rock drill lubricants.
Testing down hole hammers without lubrication has proven that in less than one minute of drilling, temperatures of the piston surface can exceed 1400° F (752°C). These excessive temperatures generate heat checks (fine cracks) on the surface finish that may propagate through impact and initiate piston failure.
Decarburization also occurs as a result of high temperatures which greatly reduces the tensile strength of the material allowing fractures to initiate.
Corrosion is the deterioration of a material due to a reaction with its environment. Air, water and most of the drilling fluids and polymers are all corrosive.
Rinse all drilling equipment thoroughly upon completion of drilling with foams/polymers in order to help reduce the occurance of corrosion.
The most detrimental type of corrosion encountered in down hole hammers is oxidation cavitation (finite notches in the material surfaces). The easiest areas for this condition to exist are in the non-moving areas of the hammer. For example, thread roots and "O" ring grooves are common places to find oxidation cavitation.
The best preventative action against corrosion is to keep the down hole hammer well lubricated with rock drill oil.
| Note: When finished drilling with foam, it is necessary to rinse all drilling tools with fresh clean water and lubricate them properly. Prolonged exposure to the atmosphere creates a corrosive reaction between the steel and the foam. Corrosion stress risers are a common cause of drilling tool failures. |
Contamination from foreign material entering the hammer is the second most common cause of down hole hammer and bit failure. Foreign material enters the hammer or drill string when connections are being made. Be sure to keep all connections covered and clean at all times.
When connecting a hammer to a drill string, it is usually a good idea to cover the connection to the hammer and blow high pressure air and water through the drill string for several seconds to remove any loose scale, rust or other foreign material.
When installing a bit in the hammer, take care to remove any cuttings or foreign material from the bit shank.