Lubricants Questions and Answers

Answer: A

Correct answer: one gram of the oil

The saponification value is expressed in milligrams of potassium hydroxide per gram of oil, so it is inherently a per-gram figure. It measures the ester content, since only esters are saponified, and it therefore distinguishes a vegetable or synthetic ester oil from a mineral one.

Answer: B

Correct answer: zero, containing no glycerides

Saponification acts on esters, and a mineral oil is a mixture of hydrocarbons with no ester groups at all, so it consumes essentially no alkali. A measurable value in a mineral oil therefore indicates either a fatty oil blended in as an additive or oxidation products formed in service.

Answer: C

Correct answer: unsaturated compounds

The iodine value measures how much iodine the oil will add across its double bonds, so it is a direct count of unsaturation. It matters because unsaturated compounds oxidise readily, thickening the oil and forming gums and acids, so a low iodine value indicates better oxidation stability.

Answer: D

It indicates how much carbonaceous deposit the oil would leave on hot surfaces such as piston rings and valve stems. A heavy residue makes an oil unsuitable for high-temperature service however good its other properties.

Answer: A

Water inevitably finds its way in, and an oil that separates lets it be drained from the reservoir instead of circulating as an emulsion that corrodes and impairs the film. A cutting fluid, by contrast, is required to emulsify readily.

Answer: B

Correct answer: thickened by a dispersed agent

A grease is a semi-solid dispersion, not a compound: the thickener - a metallic soap or a clay - forms a fibrous or platelike network that holds the oil, and the oil is released to the contact under shear. Nothing is chemically combined, which is why the oil can be squeezed out and why bleeding is a failure mode.

Answer: C

Correct answer: begins to flow and the first drop falls

The drop point is measured by warming a sample until the thickener structure collapses and the first drop falls from the cup, and it marks the upper temperature at which the grease will hold together. It is not the maximum service temperature, which is set well below it because the grease softens before it drops.

Answer: D

A standard cone is allowed to sink into the sample and the depth in tenths of a millimetre is reported, which is the basis of the consistency numbering. A worked penetration on the same sample shows how the grease stands up to mechanical shearing.

Answer: A

Calcium soap greases of the traditional type need a small proportion of water to hold the structure together, and losing it breaks the grease down. Its merits are cheapness and excellent resistance to washing out by water.

Answer: B

It emulsifies and is carried away, leaving the bearing dry, though it serves well at higher temperatures than calcium in dry conditions. Lithium soap combines a high drop point with water resistance, which is why it has largely displaced both.