← MES Jr. Grade
Past Questions
The mechanism of material removal in EDM process is
A)
Melting and Evaporation
B)
Melting and Corrosion
C)
Erosion and Cavitation
D)
Cavitation and Evaporation
Electrical Discharge Machining (EDM) is a non-traditional machining process that removes material through a series of rapidly recurring electrical sparks between an electrode (tool) and a conductive workpiece, submerged in a dielectric fluid.
1. **Mechanism**: When a voltage is applied, a plasma channel is formed between the tool and the workpiece. This channel generates intense localized heat (reaching temperatures of 8,000°C to 12,000°C).
2. **Material Removal**: This extreme heat causes a small volume of the workpiece material to instantly melt and some to evaporate (vaporize).
3. **Flushing**: When the current is switched off, the plasma channel collapses, and the dielectric fluid flushes away the molten metal, leaving behind a small crater.
Why other options are incorrect:
- **Corrosion (Option b)**: This is the primary mechanism for Electrochemical Machining (ECM), not EDM. EDM is a thermal process, not a chemical one.
- **Erosion and Cavitation (Option c & d)**: Cavitation is typically associated with Ultrasonic Machining (USM) or fluid dynamics in pumps. While 'erosion' is a general term for material loss, the specific physical mechanisms in EDM are thermal (melting and evaporation).
Carburising flame is normally used to weld
A)
Copper alloys
B)
Stainless steel
C)
Phosphor bronze
D)
Stellite
In oxy-fuel welding, there are three primary types of flames: Neutral, Oxidizing, and Carburizing.
1. **Carburising Flame**: This flame has an excess of acetylene. It creates a reducing atmosphere (rich in carbon) which prevents the oxidation of the metal and adds a small amount of carbon to the surface. It is specifically used for welding high-carbon steels, hard-facing materials, and alloys that are prone to oxidation or require a reducing environment to prevent the loss of alloying elements. **Stellite** (a cobalt-chromium alloy) is a hard-facing material that requires a carburising flame to prevent the oxidation of its alloying elements during the welding process.
2. **Neutral Flame**: Used for most common steels, cast iron, and copper.
3. **Oxidizing Flame**: Used primarily for copper alloys (like phosphor bronze) and brass, as the oxide layer formed helps prevent the evaporation of zinc or other volatile elements.
Comparing the options:
- **Copper alloys** and **Phosphor bronze** (Options a and c) typically require an oxidizing flame to prevent the loss of volatile components.
- **Stainless steel** (Option b) is generally welded with a neutral flame to avoid carbon pickup (which would reduce corrosion resistance).
- **Stellite** (Option d) requires the reducing atmosphere of a carburising flame to maintain its metallurgical properties.
Which one of the following methods can be used for forecasting when a demand pattern is consistently increasing or decreasing?
A)
Regression analysis
B)
Moving average
C)
Variance analysis
D)
Weighted moving average
Step-by-step reasoning:
1. **Analyze the Demand Pattern**: The question specifies a demand pattern that is 'consistently increasing or decreasing'. In forecasting terminology, this is known as a 'Trend'.
2. **Evaluate Option (a) Regression Analysis**: Regression analysis (specifically linear regression) is a mathematical approach used to model the relationship between a dependent variable (demand) and an independent variable (time). It is specifically designed to identify and project a trend line, making it the ideal tool for consistently increasing or decreasing patterns.
3. **Evaluate Option (b) Moving Average**: A simple moving average smooths out short-term fluctuations to highlight a long-term level. However, it 'lags' behind the actual data when a trend is present, meaning it will consistently under-forecast an increasing trend and over-forecast a decreasing trend.
4. **Evaluate Option (d) Weighted Moving Average**: While it allows more weight to be given to recent data to reduce the lag compared to a simple moving average, it still cannot mathematically project a trend line into the future; it remains a smoothing technique.
5. **Evaluate Option (c) Variance Analysis**: This is a financial or quality control tool used to analyze the difference between planned/standard costs and actual costs. It is not a forecasting method.
Conclusion: Since regression analysis is the only method listed capable of modeling a trend, it is the correct choice.
Which of the following is not a phase of project management?
A)
Project being
B)
Project scheduling
C)
Project controlling
D)
Project planning
Project Management typically consists of several distinct phases or functions to ensure the successful completion of a project. The standard phases include: 1. Project Planning (defining goals, scope, and resources), 2. Project Scheduling (creating a timeline, assigning tasks, and determining sequences using tools like CPM or PERT), and 3. Project Controlling (monitoring progress, managing risks, and making adjustments to stay on track). 'Project being' is not a recognized technical term or phase in project management methodology. It is a linguistically incorrect phrase in this context.
Which of the following functions of an organization consists of all activities directly related to the production of a good or service?
A)
Operations
B)
Marketing
C)
Accounting
D)
finance
In the context of Industrial Engineering and Business Management, an organization is typically divided into several core functions.
1. **Operations (Correct):** This function is responsible for the 'transformation process.' It encompasses all activities directly involved in converting inputs (raw materials, labor, energy) into finished outputs (goods or services). This includes manufacturing, assembly, quality control, and supply chain management.
2. **Marketing (Incorrect):** This function focuses on identifying customer needs, promoting the product, managing sales, and distributing the finished good to the consumer. It deals with the demand side, not the production side.
3. **Accounting (Incorrect):** This is a support function that involves recording, summarizing, and reporting financial transactions to track the organization's performance.
4. **Finance (Incorrect):** This function manages the organization's capital, budgeting, investments, and funding sources to ensure the company has the necessary resources to operate.
Since the question specifically asks for activities 'directly related to the production of a good or service,' the correct answer is Operations.
Which one of the following is not a technique of inventory control?
A)
ABC analysis
B)
FSN analysis
C)
GOLF analysis
D)
LTS analysis
Inventory control techniques are used to categorize items based on specific criteria to optimize management and reduce costs.
1. **ABC Analysis (Always Better Control):** This is the most common technique, categorizing items based on their consumption value (Annual usage rate × Unit cost). 'A' items are high value, 'B' are moderate, and 'C' are low value.
2. **FSN Analysis (Fast, Slow, Non-moving):** This technique categorizes items based on their movement or consumption rate over a period of time to optimize storage and warehouse space.
3. **GOLF Analysis (Grading Of Low-cost Fast-moving):** This is a specialized analysis used to manage items that have low unit costs but are consumed very rapidly, ensuring they don't stock out despite their low value.
4. **LTS Analysis:** There is no standard inventory control technique known as 'LTS analysis' in industrial engineering or supply chain management. While 'LTS' might stand for 'Long Term Storage' in general logistics, it is not a recognized classification/analysis technique like ABC, FSN, or GOLF.
Therefore, LTS analysis is not a recognized technique of inventory control.
Which one of the following techniques is used for determining allowances in time study?
A)
Acceptance sampling
B)
Linear regression
C)
Performance rating
D)
Work sampling
In Time and Motion study, the 'Standard Time' is calculated as: Standard Time = Normal Time + Allowances. Allowances are added to account for personal needs, fatigue, and unavoidable delays.
1. **Work Sampling (Option d):** This is a statistical technique used to determine the proportion of time spent by workers on various activities. It is specifically used to determine the percentage of time spent on non-productive activities (like fatigue, personal needs, or machine downtime), which directly provides the data needed to calculate the 'allowances' in a time study.
2. **Acceptance Sampling (Option a):** This is a quality control technique used to decide whether to accept or reject a batch of products based on a sample. It has nothing to do with time study allowances.
3. **Linear Regression (Option b):** This is a statistical method used to model the relationship between a dependent variable and one or more independent variables. While it can be used for forecasting, it is not a standard technique for determining allowances.
4. **Performance Rating (Option c):** This is used to convert the 'Observed Time' into 'Normal Time' by adjusting for the worker's pace (speed) relative to a standard worker. It determines the efficiency of the operator, not the allowances for delays or fatigue.
One of the assumptions behind orthogonal cutting is,
A)
that the rake angle is positive
B)
that the tool is only cutting with one edge and one point
C)
the shear plane is a function of before and after chip thickness
D)
none of these
Orthogonal cutting is a simplified 2D model of metal cutting where the cutting edge is perpendicular to the direction of tool travel.
1. Analysis of Option (c): In the Merchant's circle analysis and the fundamental geometry of orthogonal cutting, the shear angle (φ) is defined by the relationship between the uncut chip thickness (t) and the actual chip thickness (t_c). The formula is tan(φ) = r cos(φ) / (r - (t/t_c)), or more simply, the ratio of thicknesses determines the orientation of the shear plane. Therefore, the shear plane is indeed a function of the chip thickness before and after cutting.
2. Analysis of Option (a): The rake angle can be positive, zero, or negative in orthogonal cutting. While a positive rake angle is common to reduce cutting forces, it is not a required 'assumption' for the model to be orthogonal.
3. Analysis of Option (b): This describes 'point cutting' or 'single-point turning' in a general sense, but orthogonal cutting specifically assumes a wide tool edge relative to the width of the cut to ensure the flow of chips is two-dimensional (perpendicular to the cutting edge), not that it cuts with a single 'point'.
Therefore, the geometric relationship between the chip thicknesses and the shear plane is a core assumption/characteristic of the orthogonal cutting model.
Green sand is a mixture of
A)
30% sand and 70% clay
B)
50% sand and 50% clay
C)
70% sand and 30% clay
D)
90% sand and 10% clay
Green sand is the most commonly used molding material in foundries. It is called 'green' not because of its color, but because it contains moisture when the mold is poured. The typical composition of green sand consists of: 1. Silica Sand (approx. 85% to 95%): This acts as the refractory material that withstands the high temperature of molten metal. 2. Clay (approx. 5% to 15%): Usually bentonite, which acts as a binder to provide strength and shape to the mold. 3. Water (approx. 2% to 5%): This activates the clay to make it sticky. Among the given options, '90% sand and 10% clay' falls perfectly within the standard industrial range for green sand composition. Options a, b, and c suggest clay contents (30% to 70%) that are far too high; such a mixture would lack the necessary permeability and refractory properties, leading to gas defects and mold failure.
Directional solidification in castings can be improved by using
A)
chills and chaplets
B)
chills and padding
C)
chaplets and padding
D)
chills, chaplets and padding
Directional solidification is the process of controlling the solidification of a casting so that it occurs in a specific direction, typically from the farthest point toward the riser. This prevents shrinkage cavities and porosity.
1. **Chills**: These are metal inserts placed in the mold wall to increase the cooling rate in specific areas. By rapidly removing heat from a particular section, chills initiate solidification there first, effectively 'pushing' the liquid metal flow toward the riser.
2. **Padding**: This involves adding extra material to the casting design to create a tapered section. This ensures a continuous path of liquid metal from the riser to the shrinking areas, preventing the 'pinch-off' effect where a section solidifies prematurely and isolates a shrinkage cavity.
**Why other options are incorrect:**
- **Chaplets**: These are small metal supports used to hold the core in place within the mold. While they are essential for mold stability, they do not influence the thermal gradient or the direction of solidification. Therefore, any option containing 'chaplets' (a, c, and d) is incorrect in the context of improving directional solidification.
Atomic packing factor (APF) in the case of copper crystal is
A)
0.52
B)
0.68
C)
0.74
D)
1.633
Step-by-step reasoning:
1. **Identify the Crystal Structure of Copper**: Copper (Cu) is a transition metal that crystallizes in a Face-Centered Cubic (FCC) lattice structure.
2. **Define Atomic Packing Factor (APF)**: APF is the ratio of the volume of atoms in a unit cell to the total volume of the unit cell. Formula: APF = (Number of atoms per unit cell × Volume of one atom) / Volume of unit cell.
3. **FCC Parameters**:
- Number of atoms per unit cell (n) = 4
- Volume of one atom (assuming spherical) = (4/3)πr³
- Relationship between lattice constant (a) and atomic radius (r) for FCC: a = 2√2r
4. **Calculation**:
- Volume of unit cell (V_cell) = a³ = (2√2r)³ = 16√2r³
- Total volume of atoms = 4 × (4/3)πr³ = (16/3)πr³
- APF = [(16/3)πr³] / [16√2r³] = π / (3√2) ≈ 0.74.
Analysis of options:
- Option (a) 0.52 is the APF for a Simple Cubic (SC) structure.
- Option (b) 0.68 is the APF for a Body-Centered Cubic (BCC) structure.
- Option (c) 0.74 is the APF for FCC and Hexagonal Close-Packed (HCP) structures, which applies to Copper.
- Option (d) 1.633 is physically impossible as APF cannot exceed 1.0.
A major difference between plasma arc welding and TIG welding.
A)
Flux is not used
B)
Construction of torch is different
C)
Gas is not used
D)
Tungsten electrode is not used
To determine the major difference between Plasma Arc Welding (PAW) and Tungsten Inert Gas (TIG) welding, let's analyze the characteristics of both processes:
1. **TIG Welding (GTAW):** Uses a non-consumable tungsten electrode. The arc is struck between the electrode and the workpiece in an open-arc configuration. The shielding gas flows around the electrode to protect the weld pool.
2. **Plasma Arc Welding (PAW):** Also uses a non-consumable tungsten electrode, but the electrode is placed inside a copper nozzle. The arc is constricted by a small orifice in the nozzle, creating a high-velocity 'plasma jet' of ionized gas. This constriction increases the energy density and temperature of the arc significantly compared to TIG.
**Evaluating the Options:**
- **(a) Flux is not used:** Incorrect. Neither TIG nor PAW typically uses flux; therefore, this is a similarity, not a difference.
- **(b) Construction of torch is different:** Correct. The PAW torch is significantly more complex because it requires a nozzle to constrict the arc and a separate gas delivery system for the plasma gas and the shielding gas. TIG torches are simpler, open-arc designs.
- **(c) Gas is not used:** Incorrect. Both processes rely heavily on inert gases (like Argon) for shielding and, in the case of PAW, for creating the plasma.
- **(d) Tungsten electrode is not used:** Incorrect. Both TIG and PAW utilize a non-consumable tungsten electrode.
Therefore, the fundamental physical and operational difference lies in the design and construction of the torch.
Which of the following material in the final structure of steel increases the strength of steel?
A)
Martensite
B)
Pearlite
C)
Ledeburite
D)
Austenite
In material science and metallurgy, the strength and hardness of steel are primarily determined by its microstructure, which depends on the carbon content and the cooling rate (heat treatment).
1. **Martensite (Option a):** This is formed when austenite is quenched (cooled rapidly). It has a Body-Centered Tetragonal (BCT) structure that is highly strained due to trapped carbon atoms. This internal strain prevents dislocation movement, making martensite the hardest and strongest constituent of steel. Therefore, it significantly increases the strength of the final structure.
2. **Pearlite (Option b):** This is a lamellar mixture of ferrite (soft) and cementite (hard). While it provides a good balance of strength and ductility, it is significantly softer and weaker than martensite.
3. **Ledeburite (Option c):** This is a eutectic mixture of austenite and cementite found in cast irons or high-carbon steels. While hard, it is also very brittle and is not the primary phase used to 'increase strength' in structural steel in the way martensite is.
4. **Austenite (Option d):** This is a face-centered cubic (FCC) phase that is stable at high temperatures. It is generally soft, ductile, and non-magnetic. While it can be stable at room temperature in some stainless steels, it does not provide the high strength associated with martensite.
What is the atomic packing factor of BCC structure?
A)
0.54
B)
0.72
C)
0.68
D)
0.94
The Atomic Packing Factor (APF) is the fraction of the volume of a unit cell that is occupied by hard-sphere atoms.
Step-by-step calculation for Body-Centered Cubic (BCC) structure:
1. **Number of atoms per unit cell (n):** In BCC, there is one atom at each of the 8 corners (each shared by 8 cells) and one atom at the center.
n = (8 * 1/8) + 1 = 2 atoms.
2. **Relation between atomic radius (r) and lattice constant (a):** In BCC, the atoms touch along the body diagonal of the cube.
Body diagonal = 4r = √3 * a
Therefore, a = 4r / √3.
3. **Volume of atoms (V_atoms):** Assuming atoms are spheres, V = n * (4/3)πr³
V_atoms = 2 * (4/3)πr³ = (8/3)πr³.
4. **Volume of the unit cell (V_cell):** V_cell = a³ = (4r / √3)³ = 64r³ / (3√3).
5. **APF Calculation:**
APF = V_atoms / V_cell = [(8/3)πr³] / [64r³ / (3√3)]
APF = (8π / 3) * (3√3 / 64) = (π√3) / 8
APF ≈ (3.14159 * 1.732) / 8 ≈ 0.68.
Comparison with other options:
- 0.52 (approx 0.54 in some contexts) is associated with Simple Cubic (SC) structures.
- 0.74 (not listed, but 0.72 is close) is associated with Face-Centered Cubic (FCC) and Hexagonal Close-Packed (HCP) structures.
Which of the following tool material will offer lower friction and higher resistance to cracks and wear?
A)
HSS
B)
TiC
C)
WC
D)
TiCN
To determine the best tool material for lower friction and higher resistance to cracks and wear, we must compare the properties of the given materials:
1. **HSS (High-Speed Steel):** While tough, it has significantly lower hardness and wear resistance compared to carbides and ceramics. It has a higher coefficient of friction than coated tools.
2. **TiC (Titanium Carbide):** Offers high hardness and good wear resistance, but it is more prone to chemical wear and has a higher friction coefficient compared to carbonitrides.
3. **WC (Tungsten Carbide):** The industry standard for hardness and toughness. However, as a base material, it lacks the low-friction surface properties provided by advanced coatings.
4. **TiCN (Titanium Carbonitride):** This is a hybrid of TiC and TiN. It combines the high hardness and wear resistance of TiC with the lower friction and better lubricity of TiN. TiCN coatings are specifically engineered to provide a very hard surface that reduces the coefficient of friction (reducing chip adhesion) and increases resistance to abrasive wear and crack propagation compared to pure carbides or HSS.
Therefore, TiCN is the superior choice for minimizing friction while maximizing resistance to wear and cracking.
Eutectoid reaction occurs at
A)
600°C
B)
723°C
C)
1147°C
D)
1493°C
In the context of Material Science and the Iron-Carbon (Fe-C) equilibrium phase diagram, a eutectoid reaction is an isothermal, reversible reaction in which one solid phase transforms into two different solid phases upon cooling. Specifically, for the Fe-C system, the eutectoid reaction occurs when austenite (γ) transforms into pearlite (a lamellar mixture of ferrite α and cementite Fe3C). This reaction occurs at a constant temperature of 723°C (often rounded to 727°C in some textbooks) at a carbon concentration of approximately 0.76% to 0.8% C.
Analysis of other options:
- 600°C: This is not a characteristic critical temperature for major phase transformations in the Fe-C system.
- 1147°C: This is the Eutectic temperature, where a liquid phase transforms into two solid phases (Austenite and Cementite).
- 1493°C: This is the melting point of pure iron.
Which of the following alloying element can be used to deoxidize steels?
A)
Phosphorous
B)
Carbon
C)
Cerium
D)
Selenium
Deoxidation is the process of removing dissolved oxygen from molten steel to prevent the formation of gas pores and blowholes during solidification. This is achieved by adding elements that have a higher affinity for oxygen than iron does.
1. **Cerium (c):** Rare earth elements like Cerium (Ce) are powerful deoxidizers. They react with oxygen to form stable oxides (e.g., CeO2), which then float to the surface as slag. Cerium is often used to refine grain structure and remove impurities like sulfur (desulfurization) and oxygen.
2. **Phosphorous (a):** Phosphorus is generally considered an impurity in steel. It causes 'cold shortness' (brittleness at low temperatures) and does not act as a deoxidizer.
3. **Carbon (b):** While carbon is the primary alloying element in steel, it is not used as a deoxidizing agent. In fact, the reaction between carbon and oxygen produces carbon monoxide (CO) gas, which can lead to porosity if not managed.
4. **Selenium (d):** Selenium is typically an impurity or used in very specific alloys for machinability; it is not used for deoxidation and can negatively impact the weldability and toughness of the steel.
Break even point is the point, where
A)
fixed and variable cost lines intersect
B)
fixed and total cost lines intersect
C)
variable and total cost line intersect
D)
sales revenue and total cost line intersect
The Break-Even Point (BEP) is defined as the level of production or sales volume at which the total revenue equals the total cost. At this point, the organization earns zero profit and suffers zero loss.
Mathematically: Total Revenue (TR) = Total Cost (TC).
Since Total Cost is the sum of Fixed Costs (FC) and Variable Costs (VC), the equation is: TR = FC + VC.
On a Break-Even Chart:
1. The Total Revenue line starts from the origin (0,0) and slopes upward.
2. The Total Cost line starts from the Fixed Cost value on the y-axis and slopes upward.
3. The point where these two lines intersect is the Break-Even Point.
Why other options are incorrect:
- Option (a): The intersection of fixed and variable cost lines does not represent a financial equilibrium point.
- Option (b): The total cost line is always higher than the fixed cost line (unless variable costs are zero), so their intersection does not define the break-even point.
- Option (c): The total cost line is always higher than the variable cost line (unless fixed costs are zero), so their intersection does not define the break-even point.
The central processing unit in CNC consists of which of the following parts?
A)
Operating system unit
B)
Secondary memory
C)
Arithmetic Logic Unit
D)
Read only memory
In a CNC (Computer Numerical Control) system, the Central Processing Unit (CPU) acts as the 'brain' of the machine. The CPU is responsible for interpreting the G-codes and M-codes (part programs) and calculating the precise coordinates for tool movement. The core component of any CPU that performs these mathematical calculations (addition, subtraction, multiplication) and logical operations (comparisons) is the Arithmetic Logic Unit (ALU).
Why other options are incorrect:
- a. Operating system unit: The OS is software that manages hardware resources; it is not a physical 'part' or hardware component of the CPU itself.
- b. Secondary memory: This refers to external storage (like hard drives or USBs) used for long-term storage of programs, not a part of the CPU.
- d. Read only memory (ROM): While ROM is used in CNC systems to store the firmware or boot-up instructions, it is categorized as memory/storage, not the processing unit (CPU) itself.
The term value in value engineering refers to-
A)
depreciation
B)
selling price
C)
cost
D)
utility
In Value Engineering (VE), 'Value' is defined as the ratio of Function (Utility) to Cost. The formula is expressed as: Value = Function / Cost.
1. **Function/Utility**: This refers to the specific purpose a product or service serves or the utility it provides to the customer. If a product performs its intended function more effectively, its utility increases.
2. **Cost**: This is the amount of money required to produce the product.
To increase the 'Value' of a product, one must either increase the utility (function) while keeping the cost constant, or decrease the cost while maintaining the same level of utility. Therefore, in the context of value engineering, the term 'value' is fundamentally linked to the utility or function provided relative to the cost.
Why other options are incorrect:
- **a. Depreciation**: This is an accounting term for the decrease in value of an asset over time, unrelated to the core definition of Value Engineering.
- **b. Selling Price**: This is the market price at which a product is sold; while it relates to profit, it does not define the inherent 'value' (utility/cost ratio) of the design.
- **c. Cost**: Cost is the denominator in the value equation. While it affects value, it is not what 'value' refers to; rather, value is the optimization of utility against this cost.
IZOD test measures
A)
hardness
B)
ductility
C)
impact-strength
D)
grain size
The Izod test is a standardized test used to determine the impact resistance (or impact strength) of a material. It involves a weighted pendulum that strikes a notched specimen of the material; the energy absorbed by the specimen during fracture is measured, which indicates the material's toughness and its ability to resist sudden loads.
Why other options are incorrect:
- a. Hardness: Measured by tests such as Rockwell, Brinell, or Vickers tests, which measure resistance to indentation.
- b. Ductility: Measured by tensile tests (elongation and reduction in area) or bend tests.
- d. Grain size: Determined through metallographic examination using a microscope and standards like ASTM E112.
Computer will perform the data processing functions in
A)
NC
B)
CNC
C)
DNC
D)
none of these
To understand the correct answer, we must distinguish between the three types of numerical control systems:
1. NC (Numerical Control): In early NC systems, the instructions were stored on punched tapes. The machine used hard-wired logic circuits to interpret these instructions. There was no general-purpose computer integrated into the machine to process data; it simply executed the fixed logic of the hardware.
2. CNC (Computer Numerical Control): CNC is an evolution of NC where a dedicated microprocessor (computer) is integrated into the machine tool's control system. This computer performs the data processing functions, such as interpolating coordinates, calculating tool paths, and allowing the operator to edit the program directly on the machine (on-board memory).
3. DNC (Direct Numerical Control / Distributed Numerical Control): DNC refers to a system where a central mainframe computer distributes programs to multiple CNC machines. While a computer is involved in the overall network, the specific 'data processing' for the machine's movement is handled by the CNC controller of the individual machine.
Therefore, the integration of a computer to perform data processing functions within the machine control is the defining characteristic of CNC.
“Alligatoring” is a defect associated with ;
A)
forging process
B)
casting process
C)
extrusion process
D)
rolling process
Alligatoring is a specific defect that occurs during the rolling process, particularly in the rolling of slabs or blooms. It is characterized by the splitting of the workpiece along the horizontal center plane, causing the ends to open up like the jaws of an alligator. This happens due to non-uniform deformation; specifically, when the center of the material is subjected to longitudinal tensile stresses while the surface is under compression, or when there are internal inhomogeneities (like segregation or impurities) in the ingot.
Why other options are incorrect:
- a. Forging process: Common defects include laps, folds, and internal cracks, but not alligatoring.
- b. Casting process: Common defects include blowholes, shrinkage, and porosity.
- c. Extrusion process: Common defects include surface cracking (fir-tree defect) and piping/tailing.
Which of the following engineering materials is the most suitable candidate for hot chamber die casting?
A)
Lowcarbon steel
B)
Titanium
C)
Copper
D)
Tin
Hot chamber die casting (also known as gooseneck casting) is a process where the melting furnace and the injection mechanism are integrated into one unit. The molten metal is pushed up through a submerged gooseneck into the die. This process is only suitable for metals with low melting points and those that do not react chemically with or dissolve the steel components of the casting machine (such as the pump and cylinder).
1. **Tin (Option d):** Tin, Zinc, and Lead alloys have low melting points and do not attack the steel components of the machine, making them ideal for hot chamber die casting.
2. **Low carbon steel (Option a):** Steel has an extremely high melting point (approx. 1500°C), which would melt the casting machine itself. It is processed via sand casting or investment casting.
3. **Titanium (Option b):** Titanium is highly reactive at high temperatures and has a high melting point. It requires vacuum melting and specialized molds, not hot chamber die casting.
4. **Copper (Option c):** Copper and its alloys (like brass) have higher melting points than zinc/tin and, more importantly, they tend to dissolve the steel of the injection mechanism (chemical attack/erosion), making them unsuitable for hot chamber processes. They are typically cast using cold chamber die casting.
Fuel used in a cupola consists of
A)
hard coke
B)
furnace oil
C)
electricity
D)
Steam coal
A cupola furnace is used primarily for melting cast iron. It is a vertical cylindrical furnace where the fuel and the charge (metal) are layered. The fuel used in a cupola is 'hard coke' (metallurgical coke). Coke is preferred because it provides the necessary heat for melting the iron and, more importantly, it possesses high structural strength to support the heavy burden of the metal charge above it without crushing, ensuring that the air blast can pass through the furnace effectively.
Why other options are incorrect:
- b. Furnace oil: This is a liquid fuel used in some induction or reheating furnaces, but not as the primary fuel/support medium in a cupola.
- c. Electricity: Electricity is used in Electric Arc Furnaces (EAF) or Induction Furnaces, not in a cupola furnace.
- d. Steam coal: While coal is the raw material for coke, raw steam coal cannot be used in a cupola because it would collapse under the weight of the charge and would not provide the necessary permeability for the air blast.