Question 1

Gating System in Casting — What Is the Primary Function of a Gate? Within a standard sprue–runner–gate system, what is the specific purpose of the gate relative to the mould cavity?

Accepted Answer

Introduction / Context: Gating systems regulate the flow of molten metal from the pouring basin through the sprue and runner to the mould cavity. Each element has a distinct role, and correct terminology avoids design mistakes that lead to defects. Given Data / Assumptions: Sprue connects pouring basin to runner. Runner distributes metal horizontally. Gate is the final controlled opening into the cavity. Concept / Approach: The gate controls the final entry conditions (velocity, turbulence, and direction) as metal enters the mould cavity. Its shape and location strongly affect defect rates such as erosion, inclusions, and cold shuts. Reservoir and feeding functions are handled by risers, not gates, while vents discharge gases and air. Step-by-Step Solution: Map each component: sprue → runner → gate → cavity.Recognize that the gate is the last flow restriction before the cavity.Therefore, its primary function is to deliver molten metal into the cavity under controlled conditions. Verification / Alternative check: Foundry handbooks define gates as the inlets to the casting, designed to minimize turbulence and defects. Why Other Options Are Wrong: Reservoir/feeding: functions of risers, not gates.Delivering from basin to gate: performed by the sprue and runner, not the gate itself.Vent function is handled by vents and cores, not gates. Common Pitfalls: Confusing feeders with gates, leading to poor feeding design. Final Answer: deliver molten metal into the mould cavity

Question 2

Foundry Tooling — What Is a Riddle Used For? In sand moulding practice, identify the primary use of a riddle during mould preparation and sand handling.

Accepted Answer

Introduction / Context: Foundry tools have specific functions. The term “riddle” refers to a sieve used to condition moulding sand by removing lumps and foreign matter, thus improving surface finish and reducing defects. Given Data / Assumptions: Green sand moulding method. Need for uniform, fine sand to face the pattern and cavity. Objective is defect prevention and easily collapsible sand. Concept / Approach: Passing facing sand through a riddle reduces large particles and debris that could mar the mould surface, cause erosion, or embed in the casting. Clean, uniformly graded sand improves permeability and reduces inclusions. Step-by-Step Solution: Identify the tool: a riddle is a sieve.Apply its function: removing lumps and contaminants from moulding sand.Conclude its primary use is cleaning/conditioning sand before ramming. Verification / Alternative check: Standard foundry practice specifies riddled facing sand near the pattern for improved surface quality. Why Other Options Are Wrong: Smoothing/depression cleaning uses slicks and trowels.Moistening is done with water spray or swab, not a riddle.Reinforcement relates to gaggers/chaplets, not riddles. Common Pitfalls: Skipping riddling leads to rough surfaces and sand inclusions. Final Answer: cleaning the moulding sand

Question 3

Limits and Fits — Define a Basic Hole According to the hole-basis system of limits and fits, a “basic hole” is defined by which deviation condition?

Accepted Answer

Introduction / Context: Limits and fits standardize permissible size variations to ensure interchangeability. The hole-basis system fixes the hole’s lower limit at the basic size, while the shaft deviations vary to obtain different clearances or interferences. Given Data / Assumptions: Hole-basis system (commonly used in design and manufacturing). Basic size is the nominal dimension used for the tolerance framework. Deviations measured from the basic size: upper (ES) and lower (EI) for holes. Concept / Approach: In the basic hole system, EI (lower deviation) = 0. The tolerance zone for the hole extends upward from the basic size by the prescribed tolerance amount. Shafts are assigned deviations to create required fits (clearance, transition, or interference). Step-by-Step Solution: Define basic hole: EI = 0 → minimum hole size equals basic size.Upper deviation ES is positive for clearance fits, zero for H7 basic hole with zero upper tolerance? No; ES defines the upper limit relative to basic size and varies with tolerance grade.Thus the defining condition is “lower deviation is zero”. Verification / Alternative check: Standards such as ISO system of limits and fits designate hole basis with letter H (EI = 0). Why Other Options Are Wrong: Upper deviation zero corresponds to a specific case (basic shaft g/h), not the hole-basis definition.Both deviations zero would imply zero tolerance, impractical.Other statements do not reflect the standardized definition. Common Pitfalls: Confusing hole-basis (EI = 0) with shaft-basis (es = 0 for shafts). Final Answer: lower deviation is zero

Question 4

Feeding Requirements — Which Alloy Needs the Largest Riser? For the same casting size and similar conditions, which metal typically requires the largest riser to compensate for solidification shrinkage and avoid feeding-related defects?

Accepted Answer

Introduction / Context: Risers (feeders) supply liquid metal to compensate for volumetric shrinkage during solidification. The required riser size depends on the alloy’s freezing characteristics and shrinkage behavior. Given Data / Assumptions: Same casting geometry and mold conditions. Comparison among common foundry metals. Goal is to prevent shrinkage cavities and porosity. Concept / Approach: Steel exhibits relatively high solidification shrinkage and a pasty (mushy) freezing range that demands sustained feeding. Grey cast iron often shows graphitization expansion that partially offsets shrinkage, reducing feeder demand. Aluminum and copper-base alloys have lower feeding difficulty than steel for equal geometry, though still require appropriate risers and chills. Step-by-Step Solution: Compare shrinkage behavior: steel has higher volumetric shrinkage without compensating expansion.Assess freezing range: steel’s feeding distance is limited, necessitating larger or multiple risers.Conclude that, for equal size castings, steel typically requires the largest riser. Verification / Alternative check: Foundry design rules and modulus calculations (Chvorinov-based) often result in larger riser volumes for steel than for grey iron. Why Other Options Are Wrong: Cast iron: graphite expansion reduces feeder demand.Aluminium/copper: still shrink, but generally easier to feed than steel for the same shape. Common Pitfalls: Assuming the lightest metal needs the largest riser; density is not the deciding factor. Final Answer: Steel

Question 5

Oxy-Acetylene Flame — Location of Maximum Temperature In a neutral oxy-acetylene flame used for welding, where does the maximum flame temperature occur relative to the visible flame zones?

Accepted Answer

Introduction / Context: A neutral oxy-acetylene flame exhibits two distinct luminous zones: an inner cone (primary combustion) and an outer envelope (secondary combustion). Knowing where the peak temperature lies helps a welder position the flame for efficient heating and fusion. Given Data / Assumptions: Neutral flame with approximately equal oxygen and acetylene flow for welding steel. Standard welding tip and normal gas pressures. Observation of visible inner cone and outer envelope. Concept / Approach: The primary combustion zone (inner cone) attains very high temperatures due to intense, near-stoichiometric combustion. Practical welding guidance places the work near the tip of the inner cone to capitalize on the maximum heat, achieving rapid melting with minimal oxidation when properly adjusted. Step-by-Step Solution: Identify flame zones: inner cone (primary) and outer envelope (secondary).Associate maximum temperature with the intense primary combustion region.Therefore, select “at the inner cone”. Verification / Alternative check: Standard welding texts instruct holding the inner cone close to the work for maximum heating efficiency. Why Other Options Are Wrong: Outer cone: cooler than the primary zone.Between cones: heat exists, but peak guidance is referenced to the inner cone tip.Torch tip/nozzle interior: not a combustion zone and not at peak temperature. Common Pitfalls: Confusing the exact peak location as slightly beyond the inner cone; in practice welders target the inner cone region for maximum heat. Final Answer: at the inner cone

Question 6

Foundry Hand Tools — Confirm the Function of a Slick In manual mould making and finishing, is a slick used for repairing imperfections and finishing the mould surface prior to closing the box?

Accepted Answer

Introduction / Context: A slick is a flat, smooth-bladed foundry tool used during mould finishing. Clear understanding of common hand tools helps maintain surface quality and reduce rework in green sand moulding. Given Data / Assumptions: Moulds are prepared in cope and drag using green sand. After ramming and pattern withdrawal, minor surface flaws may remain. Objective is surface correction without damaging edges or draft. Concept / Approach: The slick’s flat, polished surface allows gentle scraping and smoothing to repair small tears, scabs, and scratches. It is especially useful for finishing corners, fillets, and shallow depressions so that the casting surface reproduces accurately and requires minimal fettling later. Step-by-Step Solution: Identify defect after draw (e.g., small breaks or roughness).Use slick to smooth and restore intended geometry.Brush off debris and lightly dust with parting if needed before closing. Verification / Alternative check: Foundry manuals list slicks and trowels as finishing tools distinct from gating tools and rammers. Why Other Options Are Wrong: Gate cutting uses gate knives or lifters, not slicks.Ramming uses peen and butt rammers; slicks are not ramming tools.Limiting slicks to cores is incorrect; they are used on moulds as well. Common Pitfalls: Over-smoothing can close intended vents or alter dimensions; finish lightly and check with gauges. Final Answer: Correct

Question 7

Foundry defects — understanding “shift” in sand casting In sand casting practice, a “shift” defect refers to a visible mismatch between the cope and drag impressions after pouring and solidification. Which description best captures this defect in a …

Accepted Answer

Introduction / Context: In foundry engineering, classifying surface and dimensional defects is essential for root-cause analysis and process improvement. A common dimensional defect in sand casting is called a “shift.” Understanding how and why a shift occurs helps technicians correct molding and core-setting practices before large scrap losses occur. Given Data / Assumptions: Process: conventional green-sand or dry-sand casting with cope (top flask) and drag (bottom flask). Observation: final casting shows misalignment between features that should be coaxial or coplanar. No changes to pattern size; defect is positional, not volumetric shrinkage. Concept / Approach: A shift defect is produced by relative displacement of the cope and drag mold halves (or cores) during mold assembly, handling, closing, or metal-pouring operations. Because the mold impressions no longer register, the casting surfaces formed by opposite mold halves are offset. This is distinct from defects like swell (surface bulging from weak ramming), scabs (adhering sand lumps), or blowholes (gas cavities), which have different causes and appearances. Step-by-Step Solution: Identify that the defect is an offset of features, not a change in overall size.Link the offset to cope–drag misregistration due to worn or damaged locating pins, poor closing practice, or movement under metallostatic pressure.Conclude that “shift” means mismatch between top and bottom mold halves causing displaced contours on the casting. Verification / Alternative check: Inspect parting line region; a stepped discontinuity aligned with the parting plane strongly indicates shift. Checking flask alignment pins and closing fixtures further confirms the diagnosis. Why Other Options Are Wrong: General enlargement: typical of pattern allowance errors, not misalignment. Rough lumps near ingates: characteristic of scabs or run-outs, not shift. Sand patches on upper surface: related to erosion/scabbing; different mechanism. Internal cavities from gas: describes blowholes or porosity, not external misalignment. Common Pitfalls: Confusing shift with core print misplacement; a core shift is similar but pertains to internal cavities, whereas mold-half shift affects external geometry along the parting line. Final Answer: results in a mismatching of the top and bottom parts of a casting

Question 8

TIG (GTAW) of aluminium — choice of current for oxide cleaning and arc stability When welding aluminium using TIG (gas tungsten arc welding), is alternating current (AC) commonly employed to obtain cathodic cleaning and a stable arc?

Accepted Answer

Introduction / Context: Gas tungsten arc welding (TIG/GTAW) of aluminium requires special attention to the refractory oxide film (alumina) that forms instantly on the surface. This oxide has a much higher melting temperature than the base aluminium and can prevent wetting and fusion unless properly managed. Given Data / Assumptions: Base metal: aluminium and its common alloys. Process: TIG (GTAW) with inert gas shielding (typically argon or argon–helium blends). Objective: select the appropriate current type to achieve cleaning and stable puddle control. Concept / Approach: Alternating current is widely used in TIG welding of aluminium because the electrode-positive half-cycle provides cathodic cleaning (oxide disruption), while the electrode-negative half-cycle concentrates heat in the work for penetration and keeps the tungsten from overheating excessively. Modern power sources add balance control and high-frequency stabilization, improving arc initiation and bead quality on both thin and thick sections. Step-by-Step Solution: Recognize the need to remove alumina film for proper fusion.Use AC so that the EP portion scrubs oxide and the EN portion deepens penetration.Apply high-frequency (HF) start and AC balance to stabilize and tune the cleaning action. Verification / Alternative check: Production practice confirms AC as the standard for most aluminium TIG work; DCEN is reserved for special conditions with helium shielding on thick sections and meticulous pre-cleaning. Why Other Options Are Wrong: “Incorrect” or “only for foils”: AC is broadly applicable, not limited to thin stock. “Only with helium”: argon is common; helium mixtures are optional for heat input. “DCEN is always preferred”: DCEN lacks inherent oxide cleaning and risks lack of fusion without extensive prep. Common Pitfalls: Misadjusting AC balance leading to excessive tungsten balling (too much EP) or poor cleaning (too little EP). Also neglecting solvent and stainless-brush cleaning prior to welding. Final Answer: Correct

Question 9

Shielding in arc welding — electrode size choice without protective flux or gas The statement “A large electrode is used in un-shielded arc welding” is being evaluated. Considering arc stability, spatter, and metallurgical protection, is this statem…

Accepted Answer

Introduction / Context: Arc welding processes rely on either flux coverings (SMAW), shielding gases (GMAW/GTAW), or self-shielding flux cores (FCAW) to protect the molten pool from atmospheric contamination. The legacy term “un-shielded arc welding” describes an arc without adequate flux or gas protection, which is poor practice for structural-quality welds. Given Data / Assumptions: Scenario: arc welding attempted without flux coating or shielding gas. Question addresses choice of electrode diameter/size. Focus is on arc stability and weld quality. Concept / Approach: Merely increasing electrode size in the absence of shielding does not solve metallurgical problems such as oxidation and nitrogen absorption. Larger electrodes generally require higher current, which aggravates spatter and oxidation in an unprotected arc. Quality welding necessitates adequate shielding; electrode size is selected according to joint thickness, position, and current range within a correctly shielded process. Step-by-Step Solution: Acknowledge that shielding is essential to protect the weld pool.Note that electrode size must suit current density and heat input for the joint, not compensate for missing protection.Conclude that advocating a “large electrode” for an un-shielded arc is incorrect. Verification / Alternative check: Standard welding procedures (WPS) always specify shielding method. None endorse increasing electrode diameter to replace shielding effectiveness. Why Other Options Are Wrong: “Correct”: contradicts welding science; porosity and brittleness result without shielding. “Correct only for stainless” or “only with high current”: alloy or current does not negate the need for protection. “Small electrodes are always mandatory”: size is application-specific, but shielding remains non-negotiable. Common Pitfalls: Attempting arc welds without proper flux or gas; confusing electrode size effects with shielding effects; ignoring preheat/interpass requirements. Final Answer: Incorrect

Question 10

Oxy-acetylene technique — what does “Linde welding” typically use? Traditional “Linde” oxy-acetylene practice emphasizes smooth bead and sheet work. Which combination of flame type and torch travel technique is most associated with it?

Accepted Answer

Introduction / Context: Oxy-acetylene welding offers multiple flame chemistries (carburising, neutral, oxidising) and two principal techniques: forehand (leftward) and backhand (rightward). The choice influences bead shape, penetration, and oxidation control, especially on steels and nonferrous metals. Given Data / Assumptions: “Linde welding” refers historically to the Linde oxy-acetylene method popular in instructional texts. Goal: identify the typical pairing of flame and technique associated with that method. Base metals: thin to moderate sections where smooth travel and surface quality matter. Concept / Approach: The Linde approach classically demonstrates a neutral flame to avoid excess oxygen or carbon pickup and employs forehand (leftward) technique for sheet and light sections. Leftward travel positions the torch ahead of filler, promoting preheat of the joint line and good puddle control. Oxidising or carburising flames are specialized choices for certain materials and are not the default. Step-by-Step Solution: Select neutral flame to maintain balanced chemistry.Choose leftward (forehand) travel for smooth sheet welding and lower distortion.Conclude that “neutral flame and left-ward technique” is the best match. Verification / Alternative check: Training manuals illustrate leftward technique for thin sheet with neutral flame profiles showing sharply defined inner cones and proper feather length control. Why Other Options Are Wrong: Right-ward with neutral flame: used on thicker sections; not the typical Linde pairing. Oxidising or carburising flames: risk surface defects or composition changes when used indiscriminately. Backhand weaving only: weaving is optional and not a defining feature. Common Pitfalls: Misidentifying flame by cone appearance; using oxidising flame on alloys prone to oxidation; confusing leftward/rightward terminology with hand dominance. Final Answer: neutral flame and left-ward technique

Question 11

Hand tools — removing “pinning” from a file clogged by soft metal When filing soft metals, the file teeth can clog with small chips (pinning). What is the proper tool or method to clean the file effectively without damaging the teeth?

Accepted Answer

Introduction / Context: Filing performance depends on sharp, open teeth. When working soft metals such as aluminium, copper, or mild steel, chips can wedge between teeth, a condition called “pinning.” This not only reduces cutting efficiency but also scratches the work surface. Given Data / Assumptions: Hand file used on soft metals. Clogging observed as bright metallic specks between teeth. Objective: restore cutting action safely. Concept / Approach: A file card is a specialized, stiff-bristled brush designed to sweep out impacted chips without dulling the teeth. Some file cards include a short-wire brush and a “pick” for stubborn debris. Water, acids, or heating can corrode or soften the file or pose safety risks without improving the mechanical removal of chips. Step-by-Step Solution: Hold the file teeth up and brush along the tooth direction using a file card.Use a file pick to dislodge persistent pins at the gullets.Apply a light chalking before filing soft metals to reduce future pinning. Verification / Alternative check: Toolroom best practices endorse file cards as the standard cleaning method; frequent cleaning prolongs file life and improves surface finish. Why Other Options Are Wrong: Water washing: ineffective for mechanically embedded chips. Rubbing on wood: may remove loose debris but is inconsistent. Dilute acid: risks corrosion and is unnecessary. Heating and quenching: damages file hardness and temper. Common Pitfalls: Brushing across (not along) the teeth, which can round edges; using wire wheels too aggressively; neglecting chalk, which helps prevent pinning. Final Answer: using file card

Question 12

Industrial gas safety — identification color for oxygen cylinders According to common shop practice and standard coding followed in many regions, what is the usual identification color for an oxygen gas cylinder used in welding and cutting plants?

Accepted Answer

Introduction / Context: Gas cylinder color coding helps prevent dangerous mix-ups in welding shops and industrial facilities. Oxygen, acetylene, LPG, nitrogen, and other gases are assigned distinctive colors for quick recognition. Although standards can vary by jurisdiction, many traditional curricula and exam syllabi reference a widely used coding in which oxygen cylinders are black (often with a white neck/shoulder in some codes). Given Data / Assumptions: Setting: welding and cutting shop. Objective: identify the usual color associated with oxygen cylinders per commonly taught codes. Awareness: regional nuances may add a white shoulder; the body is frequently black. Concept / Approach: Color coding provides a first-line visual cue. Beyond color, cylinders should be verified by labels, valve type, and content tags. For educational questions, “black colour” is the accepted answer aligned with traditional coding schemes used in many training programs. Step-by-Step Solution: Recall standard training convention: oxygen → black body (often white shoulder).Differentiate from acetylene (maroon in many schemes) and nitrogen (grey/black variants), etc.Select black as the expected response. Verification / Alternative check: Shop audits confirm technicians rely on both color and labeling; labels are mandatory to avoid sole reliance on paint. Why Other Options Are Wrong: White, maroon, yellow, silver-red: associated with other gases or nonstandard shop markings. Common Pitfalls: Assuming color alone is sufficient identification; always check content labels and valve connections before use. Final Answer: black colour

Question 13

Torch angles — comparing forehand (leftward) and backhand (rightward) gas welding Relative to backhand welding, the angle between the torch and the work in forehand welding is typically:

Accepted Answer

Introduction / Context: In oxy–fuel welding, torch and filler rod angles govern heat distribution, bead contour, and penetration. Two principal techniques are forehand (leftward) and backhand (rightward). Understanding their geometry helps select the suitable method for thickness and joint type. Given Data / Assumptions: Forehand (leftward) technique is used mainly for thin to moderate sheets. Backhand (rightward) technique suits thicker sections requiring deeper penetration. Angles given are typical classroom values, not absolute rules. Concept / Approach: Forehand welding generally uses a smaller torch angle relative to the work surface (often around 40°–50°), with the torch pointing in the direction of travel to preheat ahead of the puddle. Backhand welding uses a larger torch angle (often around 60°–70°) with the torch trailing the puddle for concentrated penetration. Hence, the forehand torch angle is “less” than that used in backhand. Step-by-Step Solution: Define torch angle conventions for both techniques based on training practice.Compare typical ranges: forehand 40°–50° versus backhand 60°–70°.Conclude that forehand angle is smaller (less) than backhand angle. Verification / Alternative check: Demonstration welds show broader preheat and lower penetration in forehand at the smaller angle; macro-sections confirm profile differences. Why Other Options Are Wrong: Same: contradicts standard teaching. More: backhand uses the greater angle. “Always > 80°”: impractical and not representative. Indeterminate: while angles are adjustable, typical practice clearly differs. Common Pitfalls: Confusing torch and rod angles; using backhand angles on thin sheet and causing burn-through or distortion. Final Answer: less

Question 14

Materials science — approximate recrystallisation temperature of steel For process planning in hot working and annealing, what is a representative recrystallisation temperature for plain carbon steel?

Accepted Answer

Introduction / Context: Recrystallisation temperature defines the threshold above which cold-worked metals form new strain-free grains during annealing, drastically reducing hardness and restoring ductility. For steels, this value guides heat-treatment schedules and distinguishes cold from hot working regimes. Given Data / Assumptions: Material: plain carbon steel with prior cold work. Seeking a representative temperature rather than an exact value for all compositions and degrees of deformation. Ambient to elevated temperature processing environment. Concept / Approach: Recrystallisation temperature is often approximated as 0.3–0.5 times the absolute melting temperature. For steel, practical shop guidance pegs typical recrystallisation around 450–600° C, with 600° C commonly cited in examination settings as a representative value ensuring complete recrystallisation for many conditions. Step-by-Step Solution: Note the empirical range for steels (approximately 450–600° C).Select the exam-standard benchmark of 600° C as the representative answer.Recognize that exact temperature depends on carbon content and prior deformation. Verification / Alternative check: Metallography after annealing shows equiaxed, strain-free grains above the recrystallisation threshold, with hardness dropping significantly from the cold-worked condition. Why Other Options Are Wrong: 400° C: typically below full recrystallisation for many steels. 800° C: closer to austenitizing temperatures, exceeding the need for simple recrystallisation. “None of these”: 600° C is a valid representative value. 200° C: far too low for steel recrystallisation. Common Pitfalls: Confusing stress-relief (lower temperatures) with full recrystallisation; assuming a single exact temperature for all steels regardless of prior work. Final Answer: 600° C

Question 15

Sheet-metal process definitions — is “forming” a metal-removal operation? Consider the statement: “Forming is the operation of removing metal to the desired shape from the edge of a plate.” Decide whether this statement is correct based on manufactu…

Accepted Answer

Introduction / Context: Manufacturing processes are broadly categorized as material removal (machining, shearing) and material forming (plastic deformation without chip removal). Precise terminology is important for process planning, tooling, and cost estimation. Given Data / Assumptions: The statement attributes “removing metal” to forming. Edge manipulation of a plate is mentioned. We rely on standard definitions used in sheet-metal fabrication. Concept / Approach: Forming changes shape by plastic deformation without removing material, examples being bending, drawing, flanging, hemming, beading, and deep drawing. Operations that “remove metal,” such as trimming or shearing, belong to cutting processes. Therefore, describing forming as metal removal is terminologically incorrect. Step-by-Step Solution: List forming operations: bending, drawing, stretching, flanging.Contrast with cutting operations: shearing, blanking, trimming, punching.Conclude that the statement equates forming with cutting and is therefore incorrect. Verification / Alternative check: Process handbooks separate forming (no material loss) from cutting (material removal). Edge finishing by “trimming” is cutting and not called forming. Why Other Options Are Wrong: “Correct” or conditional variants: contradict the standard taxonomy. “Neither correct nor incorrect”: definitions are formal and widely accepted. Common Pitfalls: Using “forming” loosely to describe any shape change; failing to distinguish trimming (removal) from flanging (forming) at plate edges. Final Answer: Incorrect

Question 16

Resistance welding — suitable thickness range for seam welding Continuous resistance seam welding is most suitable for producing leak-tight joints within which thickness range of sheet metals?

Accepted Answer

Introduction / Context: Resistance seam welding uses rotating wheel electrodes to create overlapping nuggets forming a continuous weld. It is widely used for thin sheet fabrications such as fuel tanks, drums, and sealed containers where leak-tightness is essential. Given Data / Assumptions: Joint type: lap joints in sheet metals. Process: resistance seam welding with controlled current pulses and wheel pressure. Objective: typical thickness capability rather than absolute limits for special machines. Concept / Approach: Seam welding is optimized for thin gauges because current density, heat generation, and nugget overlap must be controlled precisely without excessive expulsion. Standard installations handle from foil-like thicknesses (tens of microns) up to about 3 mm total stack for reliable, consistent seams. Thicker sections demand very high current and force, making process control and electrode life problematic. Step-by-Step Solution: Recognize that resistance welding current scales poorly for thick sections.Recall that seam welding is common for thin sheet assemblies requiring leak-tight joints.Select the range up to approximately 3 mm as the practical limit for standard equipment. Verification / Alternative check: Application catalogs from seam welder manufacturers list optimal single-sheet thicknesses in the sub-millimeter to low-millimeter range, with total lap thickness typically not exceeding about 3 mm for routine production. Why Other Options Are Wrong: 3–5 mm, 5–8 mm, 8–10 mm, 10–15 mm: beyond common economic and technical limits for seam welding and more suited to arc or laser seams. Common Pitfalls: Confusing seam welding with spot welding capability; attempting thick stacks that cause expulsion, burn-through, or poor nugget overlap. Final Answer: 0.025 to 3 mm

Question 17

Cold working of metals — effects on mechanical properties In manufacturing and materials engineering, cold working (plastic deformation below the recrystallisation temperature) tends to alter several properties. Which of the following increases due …

Accepted Answer

Introduction / Context: Cold working, also called work hardening or strain hardening, is plastic deformation carried out at a temperature below the metal’s recrystallisation temperature. It is widely used to strengthen sheets, wires, and fasteners without adding alloying elements. Understanding which properties increase or decrease is vital for selecting subsequent heat treatments and predicting service behaviour. Given Data / Assumptions: Deformation is below recrystallisation temperature (typically room temperature for steels and many non-ferrous alloys). No intermediate anneal is applied during the cold work. Microstructure accumulates dislocations and internal stresses. Concept / Approach: Work hardening raises the dislocation density. Dislocations interact and impede further motion, so a higher applied stress is required to continue plastic flow. Consequently, yield strength, tensile strength, and hardness increase. Ductility and impact toughness usually decrease, and electrical conductivity may decline in some alloys. Springback also increases due to a higher yield/elastic modulus ratio. Step-by-Step Solution: Identify property changes due to dislocation accumulation.Yield strength increases because more stress is needed to initiate plastic flow.Ultimate tensile strength increases as the entire stress–strain curve shifts upward.Hardness increases because resistance to indentation correlates with flow stress.Therefore, the correct comprehensive choice is “all of these”. Verification / Alternative check: Tensile tests on cold-rolled steels or drawn copper wires show higher proof stress and UTS after deformation; hardness numbers (e.g., Vickers or Rockwell) also rise proportionally to cold work percent. Why Other Options Are Wrong: Tensile strength / Yield strength / Hardness individually: each is true but incomplete. The question asks what increases, and multiple properties increase together. Impact toughness: generally decreases due to reduced ductility and notch resistance. Common Pitfalls: Assuming all properties improve with cold work. In reality, ductility and toughness fall, and residual stresses may necessitate stress-relief or annealing steps. Final Answer: all of these

Question 18

Hand tools — direction of cutting for a hacksaw blade For a standard hand hacksaw used in fitting and bench work, during which stroke does the blade perform the effective cutting action?

Accepted Answer

Introduction / Context: A hand hacksaw is a basic shop tool for cutting metals. The orientation of the teeth determines whether cutting occurs on the push (forward) or pull (return) stroke. Proper setup reduces effort, improves accuracy, and extends blade life. Given Data / Assumptions: Standard hand hacksaw frame and blade with teeth pointing away from the handle. Correct blade tension and typical tooth set for metal cutting. No special draw-saw or pull-saw variant is considered. Concept / Approach: In the usual configuration, hacksaw teeth point forward (away from the handle). The blade therefore cuts on the forward (push) stroke when the operator drives the teeth into the work. The return stroke lifts pressure to avoid dulling and to clear chips. Some specialised frames or user preferences can reverse the blade for pull cutting, but that is not the common workshop practice. Step-by-Step Solution: Check tooth direction: points forward.Apply feed pressure on forward stroke; relax on return.Thus, cutting action is on the forward stroke. Verification / Alternative check: Observation of chip formation and sound confirms that the blade bites during the push stroke while the return stroke is largely idle. Why Other Options Are Wrong: Return stroke: incorrect for the standard setup. Both strokes: true for some double-cut tools, not for a conventional hacksaw. Depends only on force direction: tooth orientation is decisive. Teeth do have set; this affects kerf width and clearance, not the cutting direction. Common Pitfalls: Over-pressing on the return stroke causes blade chatter and premature tooth wear. Maintain light pressure while returning. Final Answer: forward stroke

Question 19

Foundry pattern colour code — marking surfaces to be machined In standard foundry practice, which colour is used on the pattern to indicate surfaces that will be machined after casting (so extra machining allowance is provided)?

Accepted Answer

Introduction / Context: Pattern colour coding communicates allowances and special requirements to moulders and machinists. Correct colours avoid costly errors like insufficient stock for machining or missed core prints. Given Data / Assumptions: Conventional Indian/British foundry colour codes. Solid wood or metal patterns with painted areas. Objective: identify machining allowance areas. Concept / Approach: Surfaces intended for machining are painted red on the pattern. Core prints are often painted yellow; surfaces that must not be machined may be left natural or painted other designated colours depending on local standards. The red marking ensures that the moulding process includes extra stock on those faces to permit finishing operations such as turning, milling, or drilling. Step-by-Step Solution: Recall standard code: red = machining allowance.Identify the option matching this code.Select “red colour”. Verification / Alternative check: Many foundry manuals and training charts depict patterns with red faces where machining will occur and yellow on core prints. Why Other Options Are Wrong: Yellow: typically for core prints. Black/Blue/Green: not the standard for machining allowance in most systems. Common Pitfalls: Confusing core print colour with machining colour; this leads to missing or misplacing cores or allowances. Final Answer: red colour

Question 20

Arc welding processes — use of consumable electrodes Which one of the following welding processes definitely employs a consumable filler wire/electrode as part of the process?

Accepted Answer

Introduction / Context: Welding processes are distinguished by the type of electrode (consumable vs. non-consumable) and shielding method. Recognising which processes use consumable wire helps in selecting appropriate power sources, feeders, and shielding arrangements. Given Data / Assumptions: Standard industrial practices and naming conventions. “Consumable” means the electrode melts and contributes filler metal to the joint. SAW uses a continuous wire under a granular flux blanket. Concept / Approach: Submerged arc welding (SAW) always uses a consumable wire electrode fed continuously. The arc and molten pool are covered by flux, preventing oxidation. TIG (GTAW) and many plasma processes use non-consumable tungsten electrodes; any filler is added separately. Traditional carbon arc welding uses carbon/graphite electrodes that are non-consumable relative to the weld filler (though they erode, they are not intended as filler). The misleading option for “MIG with non-consumable electrode” is self-contradictory; MIG/GMAW is also a consumable process, but the option is written to be false. Step-by-Step Solution: Identify processes: SAW, TIG, carbon arc, plasma.Match each to electrode type.Select the process that definitely uses a consumable electrode: SAW. Verification / Alternative check: Process datasheets for SAW specify wire feed units and flux delivery; TIG lists tungsten electrodes with separate filler rods. Why Other Options Are Wrong: Carbon arc: non-consumable carbon electrode. TIG: non-consumable tungsten electrode. MIG with “non-consumable” and plasma with “non-consumable”: phrased to be incorrect here. Common Pitfalls: Assuming all arc processes feed wire; many high-quality processes (TIG, plasma) use non-consumable electrodes with optional filler. Final Answer: submerged arc welding (SAW)

Workshop Technology Questions