PG.349-456 Lubrication & Bearings

What is drop lubrication primarily suitable for and what is the saftey precaution?

Mechanisms with short, periodical cycles of work. It should be performed at standstill with the drive motor locked out for safety.

What is the key difference between the oil-can drop method and the oil-dispenser drop system in terms of their appropriate applications?.

The oil-can method is for mechanisms with short, periodical cycles. The oil-dispenser drop system is for continuous or long-cycle systems with minimum to average power outputs (e.g., conveyor chain lube systems).

For systems with continuous or long cycles and minimum to average power outputs (e.g., conveyor chain lube), which oil application method is recommended?

Drop system through an oil dispenser (oiler reservoir with oil flow valve).

In a multi-point distribution system using a sight-feed lubricator, how is the oil delivered to multiple locations?

Gravity-fed through holes punched in a wick-packed distributing pipe. The amount at each location can be controlled by a valve at the container outflow.

What type of lubrication is typically used for low-speed equipment requiring heavy oil that sticks to gear teeth or chain links?

Brush lubrication.

What is the primary advantage of spray lubrication, and under what machine condition is it usually performed?

Spray lubrication provides better oil penetration and can also be used for systems requiring continuous lubrication. It is usually performed when the equipment is at rest.

The oil bath method is also called splash lubrication. What is a critical maintenance requirement of this system, and why?

It requires more frequent oil changes. Impurities that settle at the bottom of the housing must also be removed to prevent contamination of fresh oil.

For heavier equipment using a forced-oil system (e.g., a large speed reducer), describe how the oil reaches the gears and bearings.

An automatic spraying device installed in the base (which also serves as the oil reservoir) pumps oil to the gears and bearings, where it is vaporized to ensure lubrication of all contact points.

Name three maintenance components found in oil systems as well as the function of each.

(1) Filters – remove contaminants from oil;

(2) Desiccant breathers – remove atmospheric moisture as oil level changes at the reservoir;

(3) Sight glasses – used to check the oil level.

What devices are installed on reservoirs/tanks to handle temperature-induced volume changes and remove moisture?

Breathers (desiccant breathers preferred to remove atmospheric moisture).

What portable filtration devices are commonly used to clean gearbox oil in forced oil systems?

External, portable filters (commonly called Kidney Karts).

Explain how grease lubricates a bearing at the contact surface level.

When moving bearing components contact the grease, a small quantity of oil is expressed (released) from the grease to lubricate the surfaces. This oil gradually breaks down through oxidation, evaporation, or centrifugal force, and the grease must continuously re-supply oil to the contact surfaces.

True or False: Sight glasses are used to check oil level in lubrication systems.

True

What are the two key limitations of grease compared to oil?

Grease does not cool the bearing (because it is solid and lacks fluid flow) and it cannot cleanse or flush contaminants the way oil can (with filters).

In an oil bath for a ball bearing, what critical level should the oil reach relative to the bearing?

The oil level should reach the center of the lowest ball (or as indicated by the critical oil level mark).

Greases are classified by the NLGI consistency scale. What NLGI grade corresponds to a practically fluid grease, and what grade corresponds to a very hard grease resembling cheddar cheese?

NLGI Grade 0 (practically fluid) to Grade 6 (very hard, resembling cheddar cheese). The ASTM penetration test is used to assign the grade based on how deep a cone sinks into the grease sample.

What component in a forced oil system helps prevent contamination from airborne moisture?

Desiccant dryer on the expansion chamber/breather.

Name two visual indicators used to monitor oil condition or level.

Sight glasses / bull’s-eye sight glasses and oil level gauges.

Explain how grease actually lubricates a bearing.

Mobile components contact the grease and release a small quantity of base oil onto the surfaces. The grease must continue supplying oil as the initial oil oxidizes, evaporates, or is flung off

Why is soap often added to grease?

It improves adhesion (keeps grease in place, reduces leaks), enhances water tightness, prevents contamination, and increases load-bearing capacity.

What is the difference between simple soap, complex soap, and non-soap greases?

Simple soap greases contain only one type of soap. Complex soap greases resist oxidation and softening at high temperatures. Non-soap greases can function in the presence of acids and alkalines. Lithium soap greases offer extreme pressure resistance, anti-wear properties, and work across a wide temperature range under both humid and dry conditions.

List four major properties used to evaluate greases and briefly define each.

(1) Dropping Point – temperature at which grease transitions from semi-solid to liquid;

(2) Consistency – resistance to deformation under applied force;

(3) Bleeding – percentage of oil that separates from the soap base at rest; (4) Wear Resistance – capacity to protect against abrasion from metal-to-metal contact under overload.

True or False: Greases cool and cleanse mechanisms as effectively as oils.

False. Greases do not cool or cleanse like oils.

What organization’s consistency classification is most commonly used for greases?

Answer: NLGI (National Lubricating Grease Institute).

NLGI (National Lubricating Grease Institute).

Describe the correct procedure for greasing a bearing housing that IS equipped with a vent.

(1) Remove the vent cap while the bearing is NOT operating.

(2) Inject new grease until it spills from the vent.

(3) Leave the vent cap off and slowly rotate the bearing for 1–2 minutes to allow excess grease to escape.

(4) Replace the vent cap and clean the outside.

(5) After a few hours of operation, verify the bearing temperature is normal.

What are the dangers of excessive greasing in a bearing housing?

Over-greasing increases internal friction, raising grease temperature beyond the drop point. This causes the oil to separate from the grease, destroying its lubricating properties. If there is no relief port, grease can blow through the seals. In electric motors, over-filled bearings can contaminate the motor windings.

Why must air be purged ('burped') from a grease gun before use, and what are the safety precautions for using a grease gun?

Air compressed inside a grease gun can expel grease under very high pressure (up to 10,000 lbs/sq. in. or 68,970 kPa), creating a hazard. Safety glasses and gloves must be worn. The gun connector and the fitting should be cleaned before greasing.

What are the key functions a grease must perform in its application.

1.Reduce friction/wear;

2. protect against corrosion;

3. prevent water/foreign substance penetration;

4. last a long time; be compatible with seals;

5. suitable for application method; tolerate some contamination.

In the ASTM grease penetration test, what does a lower penetration number indicate?

A harder/stiffer grease (higher NLGI grade).

What is PTFE (Teflon) lubrication and what conditions is it designed for?

PTFE (polytetrafluoroethylene) is a dry film lubricant that reduces friction between surfaces without grease or oil. It is designed for areas reqring low-friction, corrosion resistance, or dry lubrication, and is applied in a primer coat and topcoat process

If a grease sample shows a penetration depth of 265–295 mm/10 (0.1 mm units) in the ASTM test, what NLGI grade range does this typically correspond to?

NLGI Grade 2 (common multi-purpose grease range).

(Note: Exact ranges are standard NLGI tables; the manual references the penetration test as the basis.)

A bearing requires grease that can handle high loads. Explain qualitatively how soap thickeners affect load-bearing capacity (no numerical formula, but related to grease properties).

Soap increases the load-bearing capacity by improving film strength and adhesion.

In oil bath lubrication, if the ball diameter is D and the critical oil level is set at the center of the lowest ball, express the minimum oil depth required in terms of D.

Oil depth ≈ D/2 (from bottom of housing to center of lowest ball).

(This is a direct geometric relationship shown in the manual’s diagrams.)

For forced oil systems, explain the role of the pump and timer in a multi-bearing setup. If a system has a timer set to cycle every 30 minutes and delivers 0.5 liters per cycle across 4 bearings, calculate the approximate oil delivery per bearing per cycle.

0.5 L / 4 = 0.125 liters per bearing per cycle.

(Basic division based on distribution systems described.)

The manual emphasizes minimizing oil separation from grease. If a grease loses 10% of its base oil due to centrifugal force over a period, and the initial oil content is 85% by weight, calculate the remaining oil percentage after this loss.

Remaining oil = 85% × (1 - 0.10) = 76.5%.

(Simple percentage loss calculation tied to the “oil separation must be minimized” principle in the grease lubrication section.)

How does solid (polymer) lubrication work, and for what applications is it best suited?

Solid lubrication is a polymer molded into the bearing cavity containing countless micro-pores filled with oil. As the bearing operates, oil is released from the pores; at rest, the pores reabsorb it. It is ideal for heavily contaminated environments, hard-to-reach locations, or applications with frequent washdowns.

What is the difference between axial (thrust) and radial loads on a bearing? Give an example of a bearing designed primarily for each.

Axial (thrust) loads are parallel to the centerline of the shaft (pushing/pulling inline). Radial loads are perpendicular to the shaft centerline. Example – Axial: single-row thrust ball bearing. Radial: cylindrical roller bearing (highest radial loads).

What are the three main categories of industrial bearings?

(1) Radial bearings – handle forces perpendicular to the shaft axis (e.g., single-row ball bearing).

(2) Axial/Thrust bearings – handle forces along the shaft axis (e.g., thrust cylindrical roller bearing).

(3) Dual-purpose bearings – handle a combination of radial, axial, and angular forces (e.g., tapered roller bearing).

The four main components of a ball bearing and the function of each.

(1) Inner Race – connects to and rotates with the shaft.

(2) Outer Race – fits into the bore of a housing (stationary).

(3) Balls/Rolling Elements – roll between the races to reduce friction.

(4) Cage – separates the rolling elements and keeps them evenly spaced.

What is a tapered roller bearing best used for, and why is it typically used in pairs?

A tapered roller bearing is the strongest bearing for combined (radial + axial) loads and carries the highest axial loads. It is typically used in pairs because a single tapered roller bearing can only support axial load in one direction; a second bearing facing the opposite direction is needed to handle thrust from both sides.

What is the recommended temperature range for heating a bearing before installation, and why must the temperature not exceed the upper limit?

Bearings should be heated to 80–120°C (170–250°F). The temperature must not exceed 120°C because higher temperatures can damage the bearing's metallurgy, alter its hardness, or degrade its lubricant/seals.

The six primary causes of premature bearing failure.

(1) Contamination (abrasive or water),

(2) Incorrect lubrication,

(3) Incorrect installation method, (4) Misalignment,

(5) Incorrect tolerance (shaft oversized or undersized),

(6) Vibration without movement (False Brinelling), and (7) Flow of electric current through the bearing.

What is False Brinelling and how can it be prevented in electric motors during storage?

False Brinelling is damage caused by small oscillatory movements or vibration while the bearing is stationary, creating indentations in the rarace surface. In electric motors, it can be prevented by periodically rotating the motor shaft during storage.

For a rotating shaft assembly with ball bearings, describe the correct interference fit and axial locking rules.

Both inner races must have an interference (tight) fit on the shaft (shaft toleranced at k6). Both outer races have a clearance fit in the housing (housing toleranced at H7). Both inner races are locked axially (e.g., with KM nuts or circlips). One outer race is locked axially (end cap or circlip). The second outer race is left free to float to allow for thermal expansion.

What does the bearing designation '6205 RSR C3' tell you? Break down each part.

'62' = bearing series designation (deep groove ball bearing, medium series). '05' = bore size code (05 × 5 = 25 mm bore). 'RSR' = one seal (rubber seal on one side). 'C3' = radial play greater than normal (C3 play grouping), meaning more internal clearance than the standard C0/normal grouping.

Vibration Frequency Analysis (Ball Pass Frequencies) A bearing has 12 rolling elements and is mounted on a shaft rotating at 1,800 RPM. Using the formulas from the document, calculate: (a) Ball Pass Frequency Outer Race (BPFO) (b) Ball Pass Frequency Inner Race (BPFI) (c) Fundamental Train Frequency (FTF)

Formulas:

• BPFO = # of rollers × shaft speed × 0.4

• BPFI = # of rollers × shaft speed × 0.6

• FTF = shaft speed × 0.4

Calculations:

(a) BPFO = 12 × 1,800 × 0.4 = 8,640 CPM (cycles per minute)

(b) BPFI = 12 × 1,800 × 0.6 = 12,960 CPM

(c) FTF = 1,800 × 0.4 = 720 CPM

Note: A defective bearing will show vibration components at these non-synchronous frequencies in its vibration spectrum.

Bearing Bore Identification & Unit Conversion Part A: A bearing is labeled with bore size code '07'. What is its bore diameter in millimeters? Part B: A bearing clearance table shows a C3 play grouping minimum of 22 microns for your shaft size. Convert this to inches (thousandths of an inch). Part C: A grease gun can generate pressures up to 68,970 kPa. Verify this converts correctly to lbs/sq. in. (psi). Use: 1 psi = 6.895 kPa.

Part A – Bore Diameter:

For bore codes 04–96: bore diameter (mm) = size code × 5

07 × 5 = 35 mm bore diameter

Part B – Microns to Thousandths of an inch:

Formula: inches = microns ÷ 25,400 (since 1 inch = 25,400 microns) or using the document's shortcut: microns ÷ 25.4 = thousandths of an inch

22 ÷ 25.4 = 0.866 thousandths of an inch ≈ 0.00087 inches

Part C – kPa to psi:

psi = kPa ÷ 6.895

68,970 ÷ 6.895 = 10,002 psi ≈ 10,000 lbs/sq. in. ✓ (confirms the document's stated value)