5 DIMENSIONS, SURFACES, AND THEIR MEASUREMENT
5.11 Surface roughness is a measurable aspect of surface texture; what does surface roughness mean?
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Answer. Surface roughness is defined as the average value of the vertical deviations from the nominal surface over a specified surface length.
5.12 Indicate some of the limitations of using surface roughness as a measure of surface texture.
Answer. Surface roughness provides only a single measure of surface texture. Among its limitations are: (1) it varies depending on direction; (2) it does not indicate lay; (3) its value depends on the roughness width cutoff used to measure the average.
5.13 Identify some of the changes and injuries that can occur at or immediately below the surface of a metal.
Answer. The changes and injuries include: cracks, craters, variations in hardness near the surface, metallurgical changes resulting from heat, residual stresses, intergranular attack, etc. (see Table 5.1).
5.14 What causes the various types of changes that occur in the altered layer just beneath the surface?
Answer. Energy input to the surface resulting from the manufacturing process used to generate the surface. The energy forms can be any of several types, including mechanical, thermal, chemical, and electrical.
5.15 What are the common methods for assessing surface roughness?
Answer. Common methods for assessing surface roughness are (1) comparison of the specimen surface with standard test blocks having known surface roughness values and (2) stylus-type electronic instruments which measure average roughness.
5.16 Name some manufacturing processes that produce very poor surface finishes.
Answer. Processes that produce poor surfaces include sand casting, hot rolling, sawing, and thermal cutting (e.g., flame cutting).
5.17 Name some manufacturing processes that produce very good or excellent surface finishes.
Answer. Processes that produced very good and excellent surfaces include honing, lapping, polishing, and superfinishing.
5.18 (Video) Based on the video about vernier calipers, are the markings on the vernier plate (moveable scale) the same spacing, slightly closer, or slightly further apart compared to the stationary bar?
Answer: The markings are slightly closer. The 50 markings on the vernier plate fit in place of 49 markings on the stationary bar.
5.19 (Video) Based on the video about vernier calipers, explain how to read the scale on a vernier caliper.
Answer: The object is inserted between the jaws. The distance between the zero on the stationary bar and the zero on the vernier plate (moveable scale) is added to the number that corresponds to the line that exactly lines up on the vernier plate. Only one mark on the veriner plate will line up with a mark on the stationary bar.
5.20 (Video) Based on the video about micrometers, explain the primary factor that makes an English micrometer different from a metric micrometer.
Answer: The thread pitch determines the linear motion of the micrometer for each rotation of the barrel. A metric micrometer will use a different pitch than an English micrometer.
Multiple Choice Quiz
There are 19 correct answers in the following multiple choice questions (some questions have multiple answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each
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correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the correct number of answers reduces the score by 1 point. Percentage score on the quiz is based on the total number of correct answers.
5.1 A tolerance is which one of the following: (a) clearance between a shaft and a mating hole, (b) measurement error, (c) total permissible variation from a specified dimension, or (d) variation in manufacturing?
Answer. (c).
5.2 Which of the following two geometric terms have the same meaning: (a) circularity, (b) concentricity, (c) cylindricity, and (d) roundness?
Answer. (a) and (d).
5.3 A surface plate is most typically made of which one of the following materials: (a) aluminum oxide ceramic, (b) cast iron, (c) granite, (d) hard polymers, or (e) stainless steel?
Answer. (c).
5.4 An outside micrometer would be appropriate for measuring which of the following (two correct answers): (a) hole depth, (b) hole diameter, (c) part length, (d) shaft diameter, and (e) surface roughness?
Answer. (c) and (d).
5.5 In a GO/NO-GO gage, which one of the following best describes the function of the GO gage: (a) checks limit of maximum tolerance, (b) checks maximum material condition, (c) checks maximum size, (d) checks minimum material condition, or (e) checks minimum size?
Answer. (b).
5.6 Which of the following are likely to be GO/NO-GO gages (three correct answers): (a) gage blocks, (b) limit gage, (c) master gage, (d) plug gage, and (e) snap gage?
Answer. (b), (d), and (e).
5.7 Surface texture includes which of the following characteristics of a surface (three correct answers):
(a) deviations from the nominal surface, (b) feed marks of the tool that produced the surface, (c) hardness variations, (d) oil films, and (e) surface cracks?
Answer. (a), (b), and (e).
5.8 Surface texture is included within the scope of surface integrity: (a) true or (b) false?
Answer. (a).
5.9 Thermal energy is normally associated with which of the following changes in the altered layer (three best answers): (a) cracks, (b) hardness variations, (c) heat affected zone, (d) plastic deformation, (e) recrystallization, or (f) voids?
Answer. (b), (c), and (e).
5.10 Which one of the following manufacturing processes will likely result in the best surface finish: (a) arc welding, (b) grinding, (c) machining, (d) sand casting, or (e) sawing?
Answer. (b).
5.11 Which one of the following manufacturing processes will likely result in the worst surface finish: (a) cold rolling, (b) grinding, (c) machining, (d) sand casting, or (e) sawing?
Answer. (d). Also, sawing (e) will yield a poor finish. Either answer is acceptable.
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Problems
5.1 Design the nominal sizes of a GO/NO-GO plug gage to inspect a 1.500 ± 0.030 in diameter hole.
There is a wear allowance applied only to the GO side of the gage. The wear allowance is 2% of the entire tolerance band for the inspected feature. Determine (a) the nominal size of the GO gage including the wear allowance and (b) the nominal size of the NO-GO gage.
Solution: (a) The tolerance band is 0.060 in. Wear allowance = 0.02(0.060) = 0.0012 in.
GO gage will inspect the minimum hole diameter = 1.500 – 0.030 = 1.470 in.
As the gage wears, the dimension will decrease and allow unacceptable parts, so the wear allowance is added to it.
Nominal GO Size = 1.470 + 0.0012 = 1.4712 in
(b) NO-GO gage will inspect the maximum hole diameter = 1.500 + 0.030 = 1.530 in.
No wear allowance is added because this gage should not fit in the hole and wear away.
5.2 Design the nominal sizes of a GO/NO-GO snap gage to inspect the diameter of a shaft that is 1.500 ± 0.030. A wear allowance of 2% of the entire tolerance band is applied to the GO side.
Determine (a) the nominal size of the GO gage including the wear allowance and (b) the nominal size of the NO-GO gage.
Solution: (a) The tolerance band is 0.060 in. Wear allowance = 0.02(0.060) = 0.0012 in.
GO gage will inspect the maximum shaft diameter = 1.500 + 0.030 = 1.530 in.
As the gage wears, the dimension will increase allowing unacceptable parts, so the wear allowance is subtracted from it.
Nominal GO Size = 1.530 – 0.0012 = 1.5288 in
(b) NO-GO gage will inspect the minimum shaft diameter = 1.500 – 0.030 = 1.470 in.
No wear allowance is added because this gage should not fit in the hole and wear away.
5.3 Design the nominal sizes of a GO/NO-GO plug gage to inspect a 30.00 ± 0.18 mm diameter hole.
There is a wear allowance applied only to the GO side of the gage. The wear allowance is 3% of the entire tolerance band for the inspected feature. Determine (a) the nominal size of the GO gage including the wear allowance and (b) the nominal size of the NO-GO gage.
Solution: (a) The tolerance band is 0.36 mm. Wear allowance = 0.03(0.36) = 0.0108 mm GO gage will inspect the minimum hole diameter = 30.00 – 0.18 = 29.82 mm
As the gage wears, the dimension will decrease and allow unacceptable parts, so the wear allowance is added to it
Nominal GO Size = 29.82 + 0.0108 = 29.8308 mm
(b) NO-GO gage will inspect the maximum hole diameter = 30.00 + 0.18 = 30.18 mm.
No wear allowance is added because this gage should not fit in the hole and wear away.
5.4 Design the nominal sizes of a GO/NO-GO snap gage to inspect the diameter of a shaft that is 30.00 ± 0.18 mm. A wear allowance of 3% of the entire tolerance band is applied to the GO side.
Determine (a) the nominal size of the GO gage including the wear allowance and (b) the nominal size of the NO-GO gage.
Solution: (a) The tolerance band is 0.36 mm. Wear allowance = 0.03(0.36) = 0.0108 mm GO gage will inspect the maximum shaft diameter = 30.00 + 0.18 = 30.18 mm
As the gage wears, the dimension will increase allowing unacceptable parts, so the wear allowance is subtracted from it.
Nominal GO Size = 30.18 – 0.0108 = 30.1692 mm
(b) NO-GO gage will inspect the minimum shaft diameter = 30.00 – 0.18 = 29.82 mm.
No wear allowance is added because this gage should not fit in the hole and wear away.
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5.5 A sine bar is used to determine the angle of a part feature. The length of the sine bar is 6.000 in.
The rolls have a diameter of 1.000 in. All inspection is performed on a surface plate. In order for the sine bar to match the angle of the part, the following gage blocks must be stacked: 2.0000, 0.5000, 0.3550. Determine the angle of the part feature.
Solution: H = 2.0000+0.5000 + 0.3550 = 2.8550 in
A = sin-1 (H/L) = sin-1 (2.8550/6.000 ) = sin-1 ( 0.4758 ) = 28.41°
5.6 A 200.00 mm sine bar is used to inspect an angle on a part. The angle has a dimension of 35.0 ± 1.8°. The sine bar rolls have a diameter of 30.0 mm. A set of gage blocks is available that can form any height from 10.0000 to 199.9975 mm in increments of 0.0025 mm. Determine (a) the height of the gage block stack to inspect the minimum angle, (b) height of the gage block stack to inspect the maximum angle, and (c) smallest increment of angle that can be setup at the nominal angle size. All inspection is performed on a surface plate.
Solution: (a) sin A = (H/L); H = L sin A = 200.00 Sin (35.0-1.8)
= 200.00 sin 33.2 = 109.51264 = 109.5150 mm (must round up to insure angle is in tolerance.
(b) H = L sin A = 200.00 sin (35.0 + 1.8) = 200.00 sin (36.8) = 119.80472 = 119.8025 mm (must round down to insure angle within dimensions)
(c) H at nominal angle = L sin A = 200.00 Sin (35.0) = 114.7152 mm
Closest angle to nominal is at H=114.7150; A = sin-1 (H/L) = sin-1 (114.7150/200.000) A = sin-1 (0.573575) = 34.99989953°
At one increment above, H=114.7175; A = sin-1 (H/L) = sin-1 (114.7175/200.000 ) = A = sin-1 (0.5735875) = 35.00077385°
Change in A = 35.00077385 – 34.9989953 = 0.0008743°
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6 METALS
Review Questions
6.1 What are some of the general properties that distinguish metals from ceramics and polymers?
Answer. Typical metallic properties include: high strength and stiffness, good electrical and thermal conductivity, and higher density than ceramics or polymers.
6.2 What are the two major groups of metals? Define them.
Answer. Ferrous metals, which are based on iron; and nonferrous, which includes all others.
6.3 What is an alloy?
Answer. An alloy is a metal comprised of two or more elements, at least one of which is metallic.
6.4 What is a solid solution in the context of alloys?
Answer. A solid solution is an alloy in which one of the metallic elements is dissolved in another to form a single phase.
6.5 Distinguish between a substitutional solid solution and an interstitial solid solution.
Answer. A substitutional solid solution is where the atoms of the dissolved element replace atoms of the solution element in the lattice structure of the metal. An interstitial solid solution is where the dissolved atoms are small and fit into the vacant spaces (the interstices) in the lattice structure of the solvent metal.
6.6 What is an intermediate phase in the context of alloys?
Answer. An intermediate phase is an alloy formed when the solubility limit of the base metal in the mixture is exceeded and a new phase, such as a metallic compound (e.g., Fe3C) or intermetallic compound (e.g., Mg2Pb) is formed.
6.7 The copper-nickel system is a simple alloy system, as indicated by its phase diagram. Why is it so simple?
Answer. The Cu-Ni alloy system is simple because it is a solid solution alloy throughout its entire composition range.
6.8 What is the range of carbon percentages which defines an iron-carbon alloy as a steel?
Answer. The carbon content ranges from 0.02% to 2.11%.
6.9 What is the range of carbon percentages which defines an iron-carbon alloy as cast iron?
Answer. The carbon content ranges from 2.11% to about 5%.
6.10 Identify some of the common alloying elements other than carbon in low alloy steels.
Answer. The common alloying elements in low alloy steel are Cr, Mn, Mo, Ni, and V.
6.11 What are some of the mechanisms by which the alloying elements other than carbon strengthen steel?
Answer. All of the alloying elements other than C strengthen the steel by solid solution alloying. Cr, Mn, Mo, and Ni increase hardenability during heat treatment. Cr and Mo improve hot hardness.
Several of the alloying elements (Cr, Mo, V) form hard carbides with C, which increases wear resistance. Vanadium inhibits grain growth during heat treatment which improves strength and toughness.
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6.12 What is the predominant alloying element in all of the stainless steels?
Answer. Chromium.
6.13 Why is austenitic stainless steel called by that name?
Answer. It is called austenitic because this alloy exists in its austenitic phase at room temperature.
The reason is that nickel has the effect of enlarging the austenitic temperature range to include room temperature.
6.14 Besides high carbon content, what other alloying element is characteristic of the cast irons?
Answer. Silicon.
6.15 Identify some of the properties for which aluminum is noted?
Answer. Aluminum is noted for its low density, high electrical and thermal conductivity, formability, good corrosion resistance due to the formation of a tough oxide film on its surface, and ability to be alloyed and strengthened to achieve good strength-to-weight ratios.
6.16 What are some of the noteworthy properties of magnesium?
Answer. Magnesium is noted for its very low density (lightest of the structural metals), propensity to oxidize (which can cause problems in processing), and low strength; however, it can be alloyed and strengthened by methods similar to those used for aluminum alloys to achieve respectable
strength-to-weight ratios.
6.17 What is the most important engineering property of copper that determines most of its applications?
Answer. Its high electrical conductivity (low resistivity).
6.18 What elements are traditionally alloyed with copper to form (a) bronze and (b) brass?
Answer. The elements are (a) tin and (b) zinc, respectivley.
6.19 What are some of the important applications of nickel?
Answer. The important applications of Ni are (1) as an alloying ingredient in steel, e.g., stainless steel; (2) for plating of steel to resist corrosion; and (3) to form nickel-based alloys noted for high-temperature performance and corrosion resistance.
6.20 What are the noteworthy properties of titanium?
Answer. Titanium is noted for its high strength-to-weight ratio, corrosion resistance (due to the formation of a thin but tough oxide film), and high temperature strength.
6.21 Identify some of the important applications of zinc.
Answer. The important applications of Zn are (1) die castings - zinc is an easy metal to cast; (2) as a coating in galvanized steel; (3) as an alloying element with copper to form brass.
6.22 What important alloy is formed from lead and tin?
Answer. Solder.
6.23 (a) Name the important refractory metals. (b) What does the term refractory mean?
Answer. (a) The refractory metals include columbium (Cb), molybdenum (Mo), tantalum (Ta), and tungsten (W). Mo and W are the most important. (b) Refractory means the capability to withstand high temperature service.
6.24 (a) Name the four principal noble metals. (b) Why are they called noble metals?
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Answer. (a) The principal noble metals are copper, gold, platinum, and silver. (b) Nobel metals are so-named because they are chemically inactive.
6.25 The superalloys divide into three basic groups, according to the base metal used in the alloy. Name the three groups.
Answer. The three groups are (1) iron-based alloys, (2) nickel-based alloys, and (3) cobalt-based alloys.
6.26 What is so special about the superalloys? What distinguishes them from other alloys?
Answer. The superalloys are generally distinguished by their strength and resistance to corrosion and oxidation at elevated temperatures.
6.27 What are the three basic methods by which metals can be strengthened?
Answer. The three basic methods are (1) alloying to form solid solutions and two-phase structures which are stronger than the elemental metals; (2) cold working, in which the strain-hardened metal is stronger and harder than the unstrained metal; and (3) heat treatment - most of the commercial heat treatments are designed to increase the strength of the metal.
Multiple Choice Quiz
There are 20 correct answers in the following multiple choice questions (some questions have multiple answers that are correct). To attain a perfect score on the quiz, all correct answers must be given. Each correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the correct number of answers reduces the score by 1 point. Percentage score on the quiz is based on the total number of correct answers.
6.1 Which of the following properties or characteristics are inconsistent with the metals (two correct answers): (a) good thermal conductivity, (b) high strength, (c) high electrical resistivity, (d) high stiffness, and (e) ionic bonding?
Answer. (c) and (e).
6.2 Which one of the metallic elements is the most abundant on the earth: (a) aluminum, (b) copper, (c) iron, (d) magnesium, or (e) silicon?
Answer. (a).
6.3 The predominant phase in the iron-carbon alloy system for a composition with 99% Fe at room temperature is which one of the following: (a) austenite, (b) cementite, (c) delta, (d) ferrite, or (e) gamma?
Answer. (d).
6.4 A steel with 1.0% carbon is known as which one of the following: (a) eutectoid, (b) hypoeutectoid, (c) hypereutectoid, or (d) wrought iron?
Answer. (c).
6.5 The strength and hardness of steel increases as carbon content (a) increases or (b) decreases?
Answer. (a).
6.6 Plain carbon steels are designated in the AISI code system by which of the following: (a) 01XX, (b) 10XX, (c) 11XX, (d) 12XX, or (e) 30XX?
Answer. (b).
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6.7 Which one of the following elements is the most important alloying ingredient in steel: (a) carbon, (b) chromium, (c) nickel, (d) molybdenum, or (e) vanadium?
Answer. (a).
6.8 Which one of the following is not a common alloying ingredient in steel: (a) chromium, (b) manganese, (c) nickel, (d) vanadium, (e) zinc?
Answer. (e).
6.9 Solid solution alloying is the principal strengthening mechanism in high-strength low-alloy (HSLA) steels: (a) true or (b) false?
Answer. (a).
6.10 Which of the following alloying elements are most commonly associated with stainless steel (two best answers): (a) chromium, (b) manganese, (c) molybdenum, (d) nickel, and (e) tungsten?
Answer. (a) and (d).
6.11 Which of the following is the most important cast iron commercially: (a) ductile cast iron, (b) gray cast iron, (c) malleable iron, or (d) white cast iron?
Answer. (b).
6.12 Which one of the following metals has the lowest density: (a) aluminum, (b) magnesium, (c) tin, or (d) titanium.?
Answer. (b).
6.13 Which of the following metals has the highest density: (a) gold, (b) lead, (c) platinum, (d) silver, or (e) tungsten?
Answer. (c).
6.14 From which of the following ores is aluminum derived: (a) alumina, (b) bauxite, (c) cementite, (d) hematite, or (e) scheelite?
Answer. (b).
6.15 Which of the following metals is noted for its good electrical conductivity (one best answer): (a) copper, (b) gold, (c) iron, (d) nickel, or (e) tungsten?
Answer. (a).
6.16 Traditional brass is an alloy of which of the following metallic elements (two correct answers): (a) aluminum, (b) copper, (c) gold, (d) tin, and (e) zinc?
Answer. (b) and (e).
6.17 Which one of the following metals has the lowest melting point: (a) aluminum, (b) lead, (c) magnesium, (d) tin, or (e) zinc?
Answer. (d).
Problems
6.1 For the copper-nickel phase diagram in Figure 6.2, find the compositions of the liquid and solid phases for a nominal composition of 70% Ni and 30% Cu at 1371°C (2500°F).
Solution: From Fig 6.2, the compositions are observed as follows:
Liquid phase composition = 65% Ni - 35% Cu.
Solid phase composition = 83% Ni - 17% Cu.
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6.2 For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
Solution: From Fig 6.2, measured values of CL and CS are: CL = 5 mm, CS = 12 mm.
Liquid phase proportion = 12/(12 + 5) = 12/17 = 0.71 Solid phase proportion = 5/17 = 0.29
6.3 Using the lead-tin phase diagram in Figure 6.3, determine the liquid and solid phase compositions for a nominal composition of 40% Sn and 60% Pb at 204°C (400°F).
Solution: From Fig 6.3, the compositions are observed as follows:
Liquid phase composition = 56% Sn - 44% Pb.
α phase composition = 18% Sn - 82% Pb.
6.4 For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
Solution: From Fig 6.3, measured values of CL and CS are: CL = 10.5 mm, CS = 15 mm.
Liquid phase proportion = 15/(15 + 10.5) = 15/25.5 = 0.59 α phase proportion = 10.5/25.5 = 0.41
6.5 Using the lead-tin phase diagram in Figure 6.3, determine the liquid and solid phase compositions for a nominal composition of 90% Sn and 10% Pb at 204°C (400°F).
Solution: From Fig 6.3, the compositions are observed as follows:
Liquid phase composition = 78% Sn - 22% Pb.
β phase composition = 98% Sn - 2% Pb.
6.6 For the preceding problem, use the inverse lever rule to determine the proportions of liquid and solid phases present in the alloy.
Solution: From Fig 6.3, measured values of CL and CS are: CL = 7.8 mm, CS = 4.2 mm.
Liquid phase proportion = 4.2/(13) = 0.32 α phase proportion = 7.8/13 = 0.68
6.7 In the iron-iron carbide phase diagram of Figure 6.4, identify the phase or phases present at the following temperatures and nominal compositions: (a) 650°C (1200°F) and 2% Fe3C, (b) 760°C (1400°F) and 2% Fe3C, and (c) 1095°C (2000°F) and 1% Fe3C.
Solution: (a) Alpha + iron carbide, (b) gamma + iron carbide, and (c) gamma.
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7 CERAMICS
Review Questions 7.1 What is a ceramic?
Answer. A ceramic is an inorganic compound, consisting of a metal (or semi-metal) and one or more non-metals.
7.2 What are the four most common elements in the earth's crust?
Answer. Oxygen, silicon, aluminum, and iron.
7.3 What is the difference between the traditional ceramics and the new ceramics?
Answer. Traditional ceramics are based primarily on clay products (e.g., pottery, bricks) while new ceramics are more recently developed ceramics which are generally simpler in chemical composition (e.g., oxides, carbides).
7.4 What is the feature that distinguishes glass from the traditional and new ceramics?
Answer. Glass is noncrystalline (amorphous), while most other ceramics assume a crystalline structure.
7.5 What are the general mechanical properties of ceramic materials?
Answer. Typical mechanical properties include high hardness, brittleness, and no ductility.
7.6 What are the general physical properties of ceramic materials?
Answer. Typical physical properties include electrical and thermal insulating, medium density (mostly below the density of metals), high melting temperatures, and thermal expansion usually less than metals.
7.7 What type of atomic bonding characterizes the ceramics?
7.7 What type of atomic bonding characterizes the ceramics?