Lubricants Questions and Answers

Answer: C

Correct answer: 1-Q, 2-P, 3-R

Each thickener has its own weakness. Calcium soap loses its structure above about 80 degrees, since it depends on water of crystallisation. Sodium soap is water soluble and washes out where moisture is present. And a clay thickener has no melting point at all, so the limit is set by oxidation of the base oil instead.

Answer: D

A full oil wedge gives the thickest film, an adsorbed layer a few molecules thick the next, and a reacted inorganic film at the contact spots the thinnest. The governing property changes from viscosity to oiliness to additive chemistry.

Answer: A

Correct answer: 1 and 3 only are correct

Statements 1 and 3 are correct: viscosity falls as temperature rises, and graphite needs adsorbed moisture so it lubricates poorly in a vacuum. Statement 2 is the reverse of the truth - a mineral oil contains no esters and so has a saponification value of essentially zero, which is how it is distinguished from a fatty oil.

Answer: B

Blackening shows the detergent-dispersant is holding the soot in suspension where the filter can reach it, which is the additive working as intended. Acidity, viscosity loss and water each indicate genuine degradation or contamination.

Answer: C

Correct answer: ready emulsification with water

A turbine oil must do the opposite: water inevitably finds its way in, and the oil must release it quickly in the reservoir so that it can be drained. An oil that emulsifies would carry the water round the system. Ready emulsification is wanted in a cutting fluid, where it is the whole point of a soluble oil.

Answer: D

Correct answer: poor oiliness, the film having been squeezed out

At low speed and heavy load the hydrodynamic film cannot be generated, and the bearing runs in the boundary regime where what matters is the oil’s ability to adhere to the metal and shear easily - its oiliness - rather than its bulk viscosity. An oil correct on viscosity may still fail here, and an oiliness or extreme pressure additive is the remedy.

Answer: A

The long polymer chains are broken by repeated passage through the bearings and the improver's thickening effect is progressively lost. Oxidation would raise the viscosity and the acid value together rather than lowering it.

Answer: B

Correct answer: both the assertion and the reason are true and the reason explains the assertion

Both are true and the reason states the requirement precisely. The engine must be started cold, when a thick oil would not reach the bearings, and must be protected hot, when a thin one would not carry load. Only an oil whose viscosity changes little between the two conditions can do both, which is exactly what a high viscosity index means.

Answer: C

Viscosity does govern the hydrodynamic film, which is what the reason states, but once the film has been squeezed out the duty is boundary and oiliness or additive chemistry takes over. The assertion overreaches by saying every regime.

Answer: D

Its layers shear low unaided, so it serves in vacuum and in dry gases where graphite fails. Graphite is cheaper and a better electrical conductor, which is why it is retained for brushes and for ordinary atmospheric duty.