CLS Tribology & Wear Prevention Techniques 3

Question 1

Which type of surface fatigue wear produces shallow, saucer-shaped pits on gear tooth flanks or rolling element bearing raceways?

Accepted Answer

Pitting

Answer

Pitting is a subsurface-initiated fatigue process producing relatively large, shallow pits that are typically visible to the naked eye on gear and bearing surfaces.

Question 2

What does the term 'tribochemical wear' refer to?

Accepted Answer

Wear resulting from chemical reactions between the lubricant, environment, and surface at tribological contacts

Answer

Tribochemical wear involves chemical reactions accelerated by frictional heating and nascent surface activity, producing reaction films or corrosive wear products at the contact.

Question 3

A gear set experiences scuffing. Which lubrication property is most critical to prevent this failure mode?

Accepted Answer

High load-carrying capacity and anti-scuff film formation

Answer

Scuffing is a form of adhesive wear triggered by breakdown of the lubricant film; EP additives that rapidly form shear films under high flash temperature prevent metal welding and tearing.

Question 4

Which property of a solid lubricant makes molybdenum disulfide (MoS₂) effective in reducing friction?

Accepted Answer

Lamellar crystal structure with weak van der Waals bonds between layers

Answer

MoS₂ has a hexagonal lamellar structure; the sulfide layers slide easily over each other due to weak interlayer forces, providing low shear resistance and excellent dry lubrication.

Question 5

When a bearing operates in the 'elasto-hydrodynamic lubrication' (EHL) regime, what unique phenomenon occurs?

Accepted Answer

Elastic deformation of the contact surfaces and pressure-viscosity increase of the lubricant together sustain a fluid film

Answer

In EHL, the high contact pressure causes significant elastic flattening of surfaces and a dramatic increase in lubricant viscosity (piezoviscous effect), enabling a thin but effective separating film.

(CLS) Certified Lubrication Specialist Practice Test

(CLS) Certified Lubrication Specialist Practice Test

CLS Tribology & Wear Prevention Techniques 3