Chp 3, 8, 9

Question 1

What are the general definitions of nonpermanent, semipermanent and permanent fasteners?

Answer 1

Nonpermanent - such as nut and bolt, can be readily disconnected without damaging the fastener.

Semipermanent - such as cotter pins, may be disconnected, but some damage may occur to the fastener.

Permanent - such as rivets, adhesives or welds, are not intended to be disassembled.

Question 2

Describe the primary difference between self-tapping screws, and bolts and machine screws.

Answer 2

Self tapping screw is a threaded fastener with a tapered point and screw threads that bite into a compressible or deformable material as it is driven.

In contrast to self tapping screws, bolts and machines screws are intended to be used with preformed internal threads.

Question 3

Describe the generally accepted differences between bolts and machine screws.

Answer 3

The difference between a bolt and a machine screw is not clearly defined. However, the industry, by general consensus, distinguishes them by size, thread length, drive style and application.

Question 4

How are bolt and machine screw sizes designated?

Answer 4

They include a nominal thread diameter and the number of threads per inch (TPI), separated by a hyphen. Designated with either gauge numbers or fractional inch sizes.

Question 5

What is the purpose of a washer?

Answer 5

Its purpose is to spread the load (tightening force) over a larger area.

Question 6

What features or techniques contribute to a nail’s holding strength?

Answer 6

A nail derives its holding strength by friction with wood along its length. The nail also provides strength to two pieces of wood in shear (sliding force). Certain features or nailing techniques can maximize holding strength.

Question 7

How are solid rivets installed?

Answer 7

Solid rivets are pneumatically, hydraullically or electromagnetically pressed into place, often without the need for preheating.

Question 8

How is a blind rivet installed?

Answer 8

To fasten a blind rivet, first the rivet pin is inserted into a blind rivet gun. The rivet assembly is inserted fully into the predrilled hole, and the rivet gun handle is ratheted several times. The gun grips the pin and pulls it through the rivet body, forcing the pin head to expand the softer rivet body material and form the second rivet head. As the pin head reaches the assembled components, resistance increases, and the force of continued ratcheting then breaks the pin.The fastening is then complete, and the broken pin can be discarded.

Question 9

How are the different types of keys used?

Answer 9

Parallel keys are used for transmitting unidirectional torques in shafts and hubs that do not have heavy starting loads.

Taper keys are used for transmitting heavy unidirectional torques in shafts and hubs that are reversed frequently and subject to vibration.

Woodruff keys are used for transmitting light torques or aligning parts on tapered shafts.

Question 10

What are some common characteristics of polymer adhesives?

Answer 10

They are more flexible, have greater impact resistance, and are stronger than other types of adhesives. They can also support both alternating and static loads.

Question 11

How is cyanoacrylate adhesive cured?

Answer 11

Curing begins by contact with the moisture found on the surface of the workpiece or in the environment. Applying a thin layer of water or even breathing on a material may add enough moisture for a strong bond.

Question 12

What is the general procedure for applying adhesive tape?

Answer 12

The mating surfaces should be cleaned of all oil, grease, water, rust, dust and dirt. The tape is pressed firmly into position, eliminating all entrapped air. Whenever possible, tape should be applied in ambient temperatures above 40 degree F.

Question 13

How is electricity used in arc welding processes?

Answer 13

All arc welding processes require a welding machine that connects to a facility’s electrical supply and converts the power to the voltage, current and waveform required for the welding job. An electrode from the welding machine carries the electrical current to the workpiece, where it jumps the small gap and creates an arc. The current then returns to the machine through the grounding claim, completing an electrical circuit. A shielding gas is needed to stabilize the arc and protect the molten metal from impurities in the air.

Question 14

What is the main difference between shielded metal arc welding (SMAW) and gas metal arc welding (GMAW)?

Answer 14

SMAW makes use of the shielded gas emitted from a consumable electrode while GMAW uses a continuous wire electrode which maintains the arc and is fed continuously by a wire feeder as it is consumed by the weld.

Question 15

What is the difference between brazing and soldering?

Answer 15

Brazing is a joining process that joins parts by heating a filler metal to temperature greater than 840 degrees F but less than the melting point of the base metal.

Soldering is a joining process that joins parts by heating a filler metal to temperatures up to 840 degrees F but less than the melting point of the base metal.

Question 16

Aside from reducing friction, list three additional ways lubricant helps ensure smooth and safe operation of tools and machines.

Answer 16

1. To prevent wear.
2. Act as a collant for moving parts.
3. Act as a barrier under load pressure.
4. Prevent adhesion or galling of materials.
5. Prevent corrosion.

Question 17

When do the effects of boundary lubrication mostly occur?

Answer 17

Mostly during stopping, starting and periods of severe operation.

Question 18

Define chemisorption.

Answer 18

A chemical absorption process in which weak chemical bonds are formed between liquid or gas molecules and solid surfaces.

Question 19

What is a liquid lubricant used for and why is it the preferred lubricant?

Answer 19

Besides reducing friction, liquid lubricants are used for heat removal or as a sealer. Liquid lubricants are the preferred lubricants because of thier reliability, versatility and flexibility.

Question 20

List three examples of lubricant additives and explain how each one protects a machine from harm.

Answer 20

Oxidation inhibitors (to provide long bearing or gear life).

Rust inhibitors (to prevent rust).

Fatty materials (to improve film strength).

Powdered lead or graphite (to prevent galling).

Viscositly index improvers (to ease machine movement in cold weather).

Demulsifiers (to separate out water).

Question 21

What does the viscosity index scale show?

Answer 21

A scale used to show the magnitude of viscosity changes in lubrication oils with changes in temperature.

Question 22

What are SAE viscosity ratings based on?

Answer 22

Its ability to flow at a specific temperature. It is a number assigned based on the volue of a base oil that flows through a specific orifice at a specified temperature, atmospheric pressure and time period.

Question 23

List two advantages of using synthetic fluid as opposed to petroleum-based lubricant.

Answer 23

One major advantage synthetic lubricant has over petroleum lubricant is that synthetic lubricant viscosity changes less with temperature changes. Another advantage is that the oxidation rate of a synthetic lubricant is more stable at higher temperatures.

Question 24

Define semisolid lubricant.

Answer 24

It combines low viscosity oils with thickeners, such as soap or other finely dispersed solids.

Question 25

Explain how an increase in temperature affects grease consistency.

Answer 25

Grease typically softens as temperature increase. As temperatures increase, greases become soft enough to separate the oil rom the thickener.

Question 26

Determine why graphite is useful as a solid lubricant and exxplain why it is not useful when humidity is absent.

Answer 26

It is useful as a solid because it has low shearing forces, especially between each graphite flake layer. In addition, although graphite slides easily over itself, it also adheres well to bearing surfaces. It also has a low coefficient of friction and an ability for service in temperatures up to 500 degrees C.

It is not useful as a solid lubricant because it requires moisture, such as atmospheric humidity, to be effective.

Question 27

Explain why oil must be replenished in order to ensure all parts within a mechanical apparatus receive the proper amount of lubrication.

Answer 27

Because oil, being a liquid, does not cling to and remain on the side of moving parts. In addition, splashing or sloshing vaporizes the oil, thus reducing the amount of oil present for an application.

Question 28

List the four systems associated with oil application.

Answer 28

Submersion system, wick system, drip system and centralized system

Question 29

Define oil analysis.

Answer 29

A predictive maintenance technique that detects and analyzes the presence of acids, dirt, fuel and wear particles in lubricating oil to predict equipment failure.

Question 30

What does the practice of wear particle analysis focus on?

Answer 30

It focuses on the size, quantity, shape and composition of the particles produced from worn parts.

Question 31

Define radial load, axial load and radial and axial loads and give an example of each.

Answer 31

A radial load is a load in which the applied force is perpendicular to the axis of rotation. Ex - A rotating shaft resting horizontally on, or being supported by, a bearing surface at each end.

An axial load is aload in which the applied force is parallel to the axis of rotation. Ex - A rotating vertical shaft has an axial load due to the weight of the shaft itself.

Radial and axial loads occur when a combination of the two loads are present. Ex - The shaft of a fan blade is supported horizontally (radial load) and is pulled or pushed (axial load) by the fan blade.

Question 32

Why are rolling contact bearings referred to as anti-friction bearings?

Answer 32

Because they are designed to roll on a film of lubricant, which separates the metal components.

Question 33

What do dark discolored metals, rusting surfaces, and split or fractured rings indicate about failed or failing bearings?

Answer 33

Dark discolored metals indicate high temperatures, rusting surfaces indicate high moisture and/or improper lubrication, and split or fractured rings indicate an improoper fit or assembly.

Question 34

Why are bearings designed for thrust loads installed in only one direction?

Answer 34

To prevent the load from separating the bearing components.

Question 35

Why is mixing different manufacturer’s bearings typically not recommended?

Answer 35

It is not recommended because each angular-contact ball bearing has a ground finish on the back and face.

Question 36

Define plain bearing.

Answer 36

A bearing in which the shaft turns and is lubricated by a sleeve.

Question 37

What two types of babbitt metals work best for plain bearing loads?

Answer 37

Tin-base and lead-base babbitt metals

Question 38

Explain how a Brinell hardness test works.

Answer 38

It measures the hardness of a metal or alloy by hydraulically pressing a hardened steel ball into the metal to be tested and then measuring the area of indentation.

Question 39

Why is it important to never strike a bearing directly with a hammer during bearing removal?

Answer 39

Because these are both hardened metals that can shatter when struck together.

Question 40

Define spalling.

Answer 40

It is the flaking away of metal pieces due to metal fatigue.

Question 41

Define fretting corrosion and list two examples of when it becomes harmful.

Answer 41

Fretting corrosion is the rusty appearance that results when two metals in contact are vibrated, rubbing loose mnute metal particles that become oxidized. It becomes harmful when the oxidation breaks down supporting wall surfaces to create looseness. It is also harmful as its oxidation particles (oxides) mix with and break down the bearing lubricant.

Question 42

How does thrust damage on ball bearings appear?

Answer 42

It appears as marks on the shoulder or upper portion of the inner and outer race and will be anywhere from a slight discoloration to heavy galling (adhesive wear).

Question 43

Which way should bearings that can be mounted in either direction face and why?

Answer 43

They should be mounted with the part number facing out for ease of future identification.

Question 44

List at least eight different precautions that should be taken when mounting bearings.

Answer 44

1. Know the bearing function in a machine.
2. Keep all bearings wrapped or in their sealed container until ready to use. Reusable bearings should be treated as new.
3. Maintain clean tools, hands, and work surface, and work in a clean environment.
4. Use clean, lint-free cloths when wiping bearings.
5. Never attempt to remove the rust preventive compound used by the manufacturer unless specifically recommended.
6. Use the best bearings available within reason. The life and reliability of a bearing is generally related to its cost.
7. Always follow the instructions of the heating equipment manufacturer when bearings are to be heated for assembly.
8. Use rings, sleeves, or adaptors that provide uniform, square and even movements.

(or any 8 of the 12 precautions listed on pages 252-253).

Question 45

Define tapered bore bearing.

Answer 45

A bearing that uniformly increases or decreases from one face to to the opposite face.