Proper lubrication is essential for the efficient operation of reduction gears. This includes supplying the proper amount of oil to the gears and bearings, and keeping the oil clean and at the proper temperature. All abnormal noises and vibrations must be investigated and corrective action must be taken immediately. Gears and bearings must be inspected in accordance with cur-rent instructions issued by NAVSEA, the type commander, or other proper authority.

Lubrication of Gears and Bearings

The correct quantity and quality of lubricating oil must be available at all times in the main sump. This oil must be clean and it must be supplied to the gears and bearings at the pressure specified by the manufacturer. In order to supply the proper quantity of oil, several conditions must be met. The lubricating oil pump must deliver the proper discharge pressure, and all relief valves in the lubricating system must be set to function at their designed pressure. Too small a quantity of oil will cause the bearing to run hot. On the other hand if too much oil is delivered to the bearing, the excessive pressure will cause the oil to leak at the seal rings, and may also cause the bearing to overheat.

Lubricating oil must reach the bearing at the proper temperature. If the oil is too cold, there will be insufficient oil flow. If the oil supply is too hot, some lubricating capacity is lost. For most main reduction gears, the normal temperature of oil leaving the lube oil cooler should be between 120F and 130F. For full power operation, the temperature of the oil leav-ing the bearings should be between 140F and 160F. The maximum temperature rise of oil passing through any gear or bearing, under any operating condition, should not exceed 50F, and the final temperature of the oil leaving the gear or bearing should not exceed 180F. Temperature rise and limit may be monitored by a thermometer or by a resistance temperature element installed where the oil is discharged from the bearings.

Cleanliness of lubricating oil cannot be overstressed. The oil must be free from such impurities as water, grit, metal, and dirt. Par-ticular care must be taken to remove metal flakes and dirt when new gears or bearings are wearing in or after they have been opened for inspection. Lint or dirt, if left in the system, may clog the oil spray nozzles. The spray nozzle passages must be open at all times. Spray nozzles should not be altered without proper authorization.

Although the lubricating oil strainers perform satisfactorily under normal operating conditions, they cannot trap particles of metal and dirt which are fine enough to pass through the mesh. These fine particles can become embedded in the bearing metal and cause wear on the bearings and journals. These fine abrasive particles passing through the gear teeth act like a lapping com-pound and remove metal from the teeth.

EFFECTS OF WATER AND ACID IN OIL.Water in the oil is extremely harmful. Even small amounts soon cause pitting and corrosion of the teeth. Acid can cause even more serious problems. The oil must be tested frequently for water, and periodic tests should be made for acid content. Immediate corrective measures must be taken when saltwater is found in the reduction gear lubricating oil system.

Occasionally gross contamination of the oil by saltwater occurs when a cooler leaks or when leaks develop in a sump. The immediate location and sealing of the leak is not enough. Additional steps must be taken to remove the contaminated oil from all steel parts. Several instances are known when, because such treatment was postponedsometimes for a week or lessgears, journals, and couplings became so badly corroded and pitted that it was necessary to remove the gears and recondition the teeth and journals. Saltwater contamination of the lubricating oil may also cause bearing burnout.

Water, in small amounts, is always present within the lubrication system as a result of condensation. Air which enters the units contains moisture. This moisture condenses into water when it strikes a cooler surface and subsequently mixes with the oil. The water displaces the oil from the metal surfaces and causes rusting. Water mixed with oil also reduces the lubricating value of the oil itself.

When the main engines are secured, the oil should be circulated until the temperature of the oil and that of the reduction gear casing approximate the engineroom temperature. While the oil is being circulated, the cooler should be operated and the gear should be jacked continuously. The purifier should also be operated to renovate the oil while the oil is being circulated and after the oil circulation is stopped until water is no longer discharged from the purifier. This procedure eliminates condensation from the interior of the main reduction gear casing and reduces rusting in the upper gear case and gears.

Generally, lubricating oil will be maintained in good condition if proper use is made of the purifier and settling tanks. However, if the purifier does not operate satisfactorily and does not have the correct water seal, it will not separate the water from the oil. You can check for the presence of water by taking small samples of oil in bottles, and allowing the samples to settle. These samples should be taken from a low point in the lube oil system.

Samples of lubricating oil should be tested at every opportunity for acid, water, and sediment content at a naval shipyard (or other similar activity). With continuous use, lube oil increases in acidity, and free fatty acids form a mineral soap which reacts with the oil to form an emulsion. As the oil emulsifies, it loses its lubricating quality. Once the oil has emulsified, the removal of water and other impurities becomes increasingly difficult.

When the formation of a proper oil film is rendered impossible, the oil must be renovated. Sometimes, when a ship from the reserve fleet is placed back in commission, the rust preventive compound is not removed completely. The residue of this compound may cause serious emulsification of the lubricating oil. Operating with emulsified oil may result in damage to the bear-ings or the reduction gears. Since it is extremely difficult aboard ship to destroy emulsions by heating, settling, and centrifuging, you must make sure that emulsions do not occur. At the first indication of an emulsion, the plant should be stopped and the oil renovated.

MAINTAINING FOR PROPER OIL LEVEL.It is of extreme importance that the quantity of oil in the sump be maintained within the prescribed maximum and minimum levels. Too much oil as well as too little oil in the sump can lead to trouble. If the oil level is above the prescribed maximum and the bull gear runs in the oil, the oil foams and heats as a result of the churning action. If the oil level is below the prescribed minimum, it may lead to a low lube oil casualty such as a damaged bearing or gears. In gear installations where the sump tank extendsup around the bull gear, and the normal oil level is above the bottom of the gear, an oil-excluding pan (sheet metal shield) is fitted under the lower part of the gear to prevent its running in the sump oil. Under normal conditions, the bull gear comes in contact with only a small quantity of oil. The oil which tends to fill the pan is swept out by the gear and is drained back to the sump. When there is too much oil in the sump, the engines must be slowed or stopped until the excess oil can be removed and normal conditions restored. Routine checks should be made to see that the lubricating oil is maintained at the proper level. Any sudden loss or gain in the amount of oil should immediately be investigated.