Question 1
______ carbide alloys possess better resistance to diffusion wear under seizure conditions.
A. Medium-grained
B. Ultra-fine grained
C. Coarse-grained
D. Fine-grained
View Answer
Answer: Option C
Explanation:
Coarse-grained carbide alloys possess better resistance to diffusion wear under seizure conditions while fine-grained carbide alloys having the greater abrasion resistance and high hardness are suited for the resistance to the attrition type of wear in the region of partial contact and to shear stresses in the seizure area.
Question 2
______ enables us to shape a larger metallic object by removing a part or thin layer of the metal from its surface to the required shape.
A. Electrical contact materials
B. Bearing materials
C. Tool materials
D. Sintered Friction materials
View Answer
Answer: Option C
Explanation:
Tool material is defined as the one which enables us to shape a larger metallic object by removing a part or thin layer of the metal from its surface to the required shape. Though the various tool materials differ in size and shape, all have a common feature of a wedge shape that is driven asymmetrically into the workpiece material.
Question 3
_________ is used to produce large carbide balls, bushes and hollow sections with more uniform density.
A. Isostatic pressing
B. Extrusion compaction
C. Rolling
D. Forging
View Answer
Answer: Option A
Explanation:
Isostatic pressing is used to produce large carbide balls, bushes and hollow sections with more uniform density. The extrusion compaction of powders in the presence of binders and plasticizers is used for the production of fairly simple shapes such as cemented carbide rods, tubes or rectangular, circular or non-symmetrical cross section of greater length.
Question 4
Cemented carbides are commonly known as ‘Hard Metals’.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Cemented carbides are commonly known as ‘Hard Metals’, because of their high hardness, abrasion resistance, compressive strength and a considerable amount of toughness.
Question 5
During _______, no liquid phase forms and ________ of only the binder metal occurs.
A. Pre-sintering, liquid phase sintering
B. Liquid phase sintering, pre-sintering
C. Pre-sintering, solid phase sintering
D. Solid phase sintering, pre-sintering
View Answer
Answer: Option C
Explanation:
During pre-sintering, no liquid phase forms and solid phase sintering of only the binder metal occurs i.e. little or no shrinkage take place. The pre-sintered compacts have a chalky structure and enough strength for further handling and to withstand machining or slicing operations to be carried out.
Question 6
In hard metal industry, the carbide of _____ is produced by the direct metal-carbon reaction.
A. Tantalum
B. Titanium
C. Molybdenum
D. Niobium
View Answer
Answer: Option C
Explanation:
In hard metal industry, the carbide of molybdenum and tungsten are produced by direct metal-carbon reaction while that of titanium, tantalum, and niobium are produced by metal oxide-carbon reaction since the former technique of production of these metal powders are comparatively expensive.
Question 7
In which organic liquid is the lubricant, paraffin wax dissolved?
A. Gasoline
B. Ether
C. Light hydrocarbons
D. Alcohol
View Answer
Answer: Option A
Explanation:
The addition of lubricant, is done as a solution in an organic liquid such as paraffin wax dissolved in gasoline, camphor in ether or light hydrocarbons and glycol in alcohol and solutions are made in the mixers prior to compacting in order to facilitate pressing and to avoid the formation of defects and cracks in the compacts.
Question 8
Milled powder mixtures are unsuitable for automatic pressing in comparison to agglomerated carbide-cobalt powder mixtures.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
Milled powder mixtures are unsuitable for automatic pressing due to their very poor flow properties, while the agglomerated carbide-cobalt mixture is required for compaction due to their high apparent density and good flow properties in automatic press. Hence, the powders containing about 2% lubricant are frequently agglomerated by compacting them (e.g. pressure= 3.5 tsi).
Question 9
Recarburization is often necessary for carbide produced by the reaction of metal oxide with carbon.
A. TRUE
B. FALSE
View Answer
Answer: Option A
Explanation:
In carbide powder production by direct reaction of metal oxide with carbon, accurate control of final carbon content is difficult due to a combination of reduction and carburization reactions in a single operation, thus often necessitating crushing and recarburization.
Question 10
The classical method of production of cemented carbide tips is ________
A. Hot pressing
B. Infiltration
C. Double-sintering
D. Liquid phase sintering
View Answer
Answer: Option C
Explanation:
The classical method of production of cemented carbide tips is double-sintering process, i.e., cold pressing to produce compacts in similar shapes such as round and rectangular blanks and pre-sintering to produce a material which is machined to final shape and sintered.
Question 11
The modern production of hard metal is attributed to ________
A. Kieffer
B. Schroter
C. Schwarzkopf
D. Osram Studiegesellschaft
View Answer
Answer: Option B
Explanation:
The modern production of hard metal is attributed to Schroter. The technique involves the blending of WC powder with up-to 20% by weight of a metal of the iron group, particularly Co as a binder metal, compaction of the powder mixture and sintering at a temperature close to the melting point of the binder metal.
Question 12
The principle constituents of sintered hard metals are the ______ and _______
A. Metal, reinforcement
B. Metal, carbide powder
C. Non-metal, carbide powder
D. Non-metal, boride powder
View Answer
Answer: Option B
Explanation:
The principle constituents of sintered hard metals or cemented carbides are the metal and carbide powders. The carbides are produced by either carburization of powdered metals with carbon, or by the reaction of metal oxide with carbon.
Question 13
WC is produced by carburization of metallic W powders prepared by the reduction of _______
A. Scheelite
B. Wolframite
C. Tungstic acid
D. Limonite
View Answer
Answer: Option C
Explanation:
WC is produced by carburization of metallic W powders prepared by the reduction of tungstic acid (H2WO4), tungsten trioxide (WO3), ammonium paratungstate. These compounds are produced from either the wolframite or scheelite ores.
Question 14
Which of the following is not a characteristic of hot-pressed material?
A. Hard
B. Ductile
C. Wear- resistant
D. Zero residual porosity
View Answer
Answer: Option B
Explanation:
Hot pressed material is very hard, wear resistant and practically free from residual porosity. In this process, the powder mixture, without the presence of lubricant, is introduced into graphite dies and pressing and sintering operations are carried on simultaneously; the pressure varying from 0.5-2 tsi and the temperature from about 1300-1550°C with direct resistance or induction heating.
Question 15
Which of the following is not a characteristic of vibratory mill used for milling of cemented carbide?
A. Shorter milling time (1-2 days)
B. Wear of balls and mills is reduced
C. Ratio of powders to balls in mills = 1:3.5 – 1:5.5
D. Ratio of powders to balls in mills = 1:1 – 1:3
View Answer
Answer: Option D
Explanation:
Vibratory mills are advantageous over rotary mills because of shorter milling time (1-2 days) in comparison to longer milling time (2-8 days) in rotary mills. Apart from this, wear of balls and mills and hence, the contamination of charge is reduced in the vibratory mill over the rotary mill. However, for rotary mill ratio of powders to balls in mills = 1:1 – 1:3 and for vibratory mill it is 1:3.5 – 1:5.5.
Question 16
Which of the following is the correct sequence of grinding cemented carbides?
A. Rough grinding
B. Coarse grinding, polishing, and fine grinding
C. Rough grinding, and final grinding
D. Fine grinding
View Answer
Answer: Option C
Explanation:
All cemented carbides are ground in two steps. The rough grinding being the first step is usually performed with SiC grinding wheel. The final step is usually done with a metal bonded diamond wheel.
Question 17
Which of the following phases occur during sintering in WC powder due to carbon deficiency?
A. α, β, γ phase
B. θ, η, K – phase
C. δ, θ, η phase
D. β, γ, M – phase
View Answer
Answer: Option B
Explanation:
Carbon deficiency in the tungsten carbide powder results in the formation of brittle carbide phases such as η-phase (Co3W3C), θ-phase (Co3W6C2) and K-phase (Co3W10C4) during sintering. If the material is under-carburized, i.e., the combined carbon content is below about 6.1%, carburization operation is repeated.
Question 18
Why carbide balls are preferred over steel balls in wet milling?
A. Economy purpose
B. Higher iron pick-up
C. Faster production rate
D. Higher carbon pick-up
View Answer
Answer: Option B
Explanation:
In wet milling, if steel balls (0.5 – 1.25 inch in diameter) are used, results in higher iron pick-up (>0.5%) in the charge. Hence, high wear resistant carbide balls (usually cylinders or rectangles with rounded ends) made by hot pressing are widely used.
Question 19
Widia is a trade name of which cemented carbide?
A. WC-Co
B. WC
C. Co-Cr
D. Co-Ni-Cr
View Answer
Answer: Option A
Explanation:
Cemented WC-Co materials with 4 – 13% cobalt was prepared in the same manner as the WC prepared by Schroter, by Fried Krupp in Essen were marketed under the trade name ‘Widia’.