Lubricants Questions and Answers

Answer: C

The coiled molecule occupies little volume in cold oil and expands as the temperature rises, offsetting part of the thinning. Its drawback is that shearing in service breaks the chains and the improvement is progressively lost.

Answer: D

Correct answer: like a 20 grade when cold and a 40 grade when hot

The W number is the cold rating and the second number the rating at operating temperature, so the oil is thin enough to circulate on a cold start yet still gives the film of a 40 grade when hot. A single grade oil cannot do both, which is what viscosity index improvers were developed to achieve.

Answer: A

The kinematic quantity has units of area per unit time, the centistokes in which oils are normally graded, and it is what a capillary viscometer measures directly. The dynamic value in pascal seconds follows by multiplying back by the density.

Answer: B

Correct answer: ignites momentarily on application of a flame

The flash point is the temperature at which enough vapour has accumulated to flash on the application of a flame, and it flashes rather than continues to burn. It is a safety and volatility measure rather than a lubrication property, and it must comfortably exceed the working temperature.

Answer: C

Correct answer: 5 to 40 degrees

The fire point is the temperature at which the vapour, once lit, continues to burn for at least five seconds, and it lies a little above the flash point - typically five to forty degrees, depending on the oil. The two are determined in the same apparatus and reported together.

Answer: D

The haze itself is harmless, but the crystals are large enough to choke a filter element or a narrow passage and starve the bearings. Flow stops altogether only at the lower pour point, so the cloud point gives the earlier warning.

Answer: A

The oil must still flow at the lowest ambient the machine will meet, or it cannot be pumped at start-up and the bearings run dry until it warms. The flash point governs the opposite end of the range and the other two say nothing about low-temperature behaviour.

Answer: B

Co-crystallising with the paraffin prevents the plate-like crystals from interlocking into a gel, so the oil still flows though wax is present. It does not lower the cloud point, which is why the two figures diverge in a treated oil.

Answer: C

Correct answer: completely miscible with an equal volume of aniline

The aniline point measures the aromatic content indirectly: aromatics dissolve aniline readily, so an oil rich in them becomes miscible at a low temperature. A high aniline point therefore indicates a paraffinic oil, which is what is wanted for a lubricant, since aromatics oxidise more readily and attack rubber seals.

Answer: D

Oxidation produces organic acids that corrode bearing metals, so the value is monitored to decide when to change the charge. In an engine oil the reserve alkalinity is tracked instead, since the detergent is there to neutralise them.