UPMSP Intermediate Metal Craft: Moulding in Ferrous Metals common mistakes
UPMSP Intermediate Metal Craft: Moulding in Ferrous Metals · Understand the traps and how to avoid them.
Treats PPE as one memorised list - writes 'helmet, gloves, shoes' for every foundry operation, including pouring, where the critical items are a face shield, leather apron, spats/leggings and gauntlets, and never mentions the wet-mould steam explosion hazard.
PPE is learned as a list to be recited rather than as a hazard-specific decision; candidates never practise matching a task (pouring, knocking out, fettling, mulling, core shooting) to its hazards and controls.
What to do instead
Build a three-column table - operation / hazard (hot-metal splash, silica dust, noise, fume, steam from damp sand) / control (specific PPE plus engineering control) - and rehearse the pouring row and the rule that damp or cold-damp moulds, tools and floor must never meet molten metal, until recall is automatic.
Answers sand-property questions with one-direction 'more is better' logic: more clay and more moisture are claimed to improve strength, with no mention of lost permeability or the fall in green strength beyond optimum moisture.
The sand tests (clay content, moisture, permeability number, green and dry compressive strength) are memorised as separate procedures, so the trade-offs between them are never internalised and questions that test the balance are missed.
What to do instead
Be able to sketch the moisture-versus-green-strength curve and the clay-versus-permeability curve from memory, then answer every sand question in three parts: the property being optimised, the property being sacrificed, and the test (with its unit or number) used to measure each.
Applies pattern allowances wrongly - subtracts shrinkage instead of adding it, puts machining allowance on a face that is not machined, and applies draft to faces perpendicular to the draw instead of parallel to it.
Allowances are memorised as a list of names and typical values (for example 10 mm/m shrinkage for cast iron) with no mental picture of the pattern being withdrawn from the sand.
What to do instead
For every pattern question, redraw the part, mark the parting line and draw direction first, then place each allowance on the drawing: shrinkage all over, draft only on faces parallel to the draw, machining allowance only on machined faces, and camber where distortion is expected.
Rams the whole mould with uniform effort, or over-rams next to the pattern 'to get a good impression', and then cannot explain why the mould splits, the sand sticks, or the casting shows a scab.
Ramming is learned as one step in a procedure rather than as a controlled variable, so its effect on permeability, mould strength and defect formation is never connected to the casting result.
What to do instead
Learn the rule 'hard near the pattern, softer towards the box wall, vent before closing', and link ramming explicitly to defects: over-ramming gives blows and scabs, under-ramming gives run-outs and sand wash. Rehearse the sequence in order - bed, ram, vent, lift, repair, blackwash, close.
Describes core making without core prints, core vents or chaplets, and specifies a core sand with the same composition and strength as the moulding sand.
Cores are revised as an isolated chapter, so in the candidate's mental picture the core is never actually located in the mould, supported and vented.
What to do instead
Answer any core question in four fixed steps: how the core is supported (prints, chaplets, core seat), how core gases escape (vent ways led to the mould surface), why the core sand needs higher dry strength and better collapsibility than moulding sand, and how the core is removed after solidification.
Sizes sprue, runner and gates with equal cross-sections, ignores the tapered sprue and the choke, and cannot compute choke area from the pouring-time relationship.
The sprue:runner:gate ratio and the pouring-time formula are memorised as symbols only; candidates have never sketched the pressurised system with metal falling down the sprue and entraining air.
What to do instead
Sketch a pressurised gating system showing the tapered sprue, the choke at the sprue base and the expanding runner and gates, then derive the ratio from that sketch. Practise one numerical problem linking casting mass, pouring time and choke area so the formula is used, not recited.
Quotes pouring temperatures far too high (1600 °C and above for grey iron) and mixes up cupola charge terms - coke ratio, metal charge, flux - or confuses the blast furnace product with the cupola product.
Melting is revised as vocabulary without anchor numbers or a charge-balance picture, so approximate values and material flow are guessed during the exam.
What to do instead
Memorise four anchors (grey iron pouring roughly 1350–1450 °C; cupola coke ratio about 1:8 to 1:12; blast furnace produces pig iron; cupola remelts pig iron plus scrap), and answer every charge question by writing the balance: metal charge + coke + flux = iron + slag + gas.
Diagnoses every internal cavity as 'gas' - calling a shrinkage cavity a blowhole - and names moisture as the cause of every defect.
Defects are memorised by name only; the diagnostic signature (shape, location, surface appearance, when it appears) is never learned, so identification collapses to one default answer.
What to do instead
Build a signature matrix: shrinkage (rough, dendritic, at hot spots and thick sections), blowhole (round, smooth, just under the cope surface), pinhole (tiny, scattered, hydrogen), scab and rat-tail (sand expansion), misrun and cold shut (low pouring temperature, thin sections). In the exam, describe the signature, then the cause, then the remedy.
States that grey cast iron can be hardened and tempered like steel, and says white cast iron is softened by ordinary annealing without describing the malleabilising cycle; also ignores that heavy grinding can leave residual stress or cracks.
Heat-treatment answers are carried over from steel metallurgy without noting that graphite flakes control cast-iron behaviour and that white iron requires a long graphitising treatment.
What to do instead
Learn each treatment by its purpose for castings: stress relieving below the critical range, annealing for softening and relief, normalising, and malleabilising of white iron (long hold, graphite in a ferritic matrix). For fettling, note that overheating during grinding causes burns and cracks, and that chipping and grinding should follow, not precede, stress relief where specified.
Converts shrinkage of 10 mm/m into 10 per cent (it is 1 per cent), mixes N/mm² with kN/m², and calculates moulding-box size without allowing sand thickness around the pattern.
Numerical work is practised without unit checking, and the mm-per-metre convention is not distinguished from a percentage, so the error survives every later step of the calculation.
What to do instead
Write the unit at every step: convert shrinkage to a fraction first (10 mm/m = 1 per cent), then to a multiplier (about 1.01 for external dimensions, about 0.99 for internal). For box size, sketch the pattern on the parting line and add a stated sand thickness (commonly 25–50 mm) on all sides plus cope and drag depth before totalling dimensions.