What is Copper Casting？Comprehensive Guide

I. What is Copper Casting?

Copper casting is fundamentally a metal forming process. Its core principle involves heating solid copper (Cu) or its alloys to a fully molten state at high temperatures, transforming them into fluid liquid metal. This liquid metal is then poured (poured/cast) into a pre-prepared mold that has a specific cavity shape. After cooling (cooling) and solidification (solidification) within the mold, a solid metal product (casting) matching the shape of the mold cavity is finally obtained.

This process appears simple but is actually a complex system engineering task integrating materials science, thermodynamics, fluid dynamics, and engineering technology. Understanding copper casting requires grasping its following key characteristics and connotations:

Core Objective: Integration of Shape and Performance

• Shape Replication:
  The fundamental advantage of casting is its ability to economically produce parts with extremely complex shapes, internal cavities, or channels. This is difficult or costly to achieve with many other metal processing methods (like forging, machining). The mold is the "negative" of the shape; liquid metal fills it and solidifies, precisely replicating the cavity's shape.

• Performance Imparting:
  Casting is not only about shape but also the process of shaping material properties. By selecting different copper alloys (like brass, bronze, cupronickel), controlling melting quality, optimizing the solidification process, and applying necessary post-heat treatments, castings can be endowed with the required mechanical properties (strength, hardness, toughness), physical properties (electrical conductivity, thermal conductivity), chemical properties (corrosion resistance, wear resistance), and special functions (such as self-lubrication, non-magnetism, anti-biofouling).

Core Process Chain: From Solid to Liquid to Solid

1. Melting:
   Copper and alloying elements are melted in a high-temperature furnace (e.g., induction furnace), followed by refining (deoxidation, degassing, deslagging), alloying (composition adjustment), and temperature control to obtain pure, compositionally uniform, molten metal at a suitable temperature. This is the foundation for ensuring the internal quality of the casting.

2. Mold Making:
   Suitable molds are selected and manufactured based on the casting's shape, size, accuracy requirements, and production volume. This embodies the diversity of casting processes:

   • Disposable Molds: E.g., sand molds (Sand Mold - green sand, resin sand, sodium silicate sand, etc.), investment shells (Investment Mold). After the casting solidifies and cools, the mold is destroyed to remove the casting.

   • Permanent Molds: E.g., metal dies (Permanent Mold/Dies), die casting dies (Die Casting Dies). Can be reused hundreds to tens of thousands of times.

3. Pouring:
   Molten copper is transferred from the furnace to a ladle and smoothly, continuously, and rapidly poured into the mold cavity through a designed gating system (Gating System). Pouring temperature and speed are key control parameters.

4. Solidification & Cooling:
   The liquid metal releases heat within the mold, undergoing a phase change from liquid to solid (solidification), and continues cooling to room temperature. The solidification process determines the casting's internal structure, density (presence of shrinkage porosity), and final properties. Feeding (via risers) and solidification control (e.g., using chills) are the focus of this stage.

5. Knockout & Cleaning:
   Once the casting cools sufficiently (to prevent distortion/cracking), it is removed from the mold (knockout). The gating system, risers, and flash/burrs are removed, and surface cleaning (shot blasting, sand blasting, etc.) is performed. This step yields the final deliverable casting.

6. Post-processing:
   Performed as needed: heat treatment (e.g., annealing, solution treatment + aging), weld repair, machining, surface treatment (e.g., plating, painting) to further enhance properties or achieve final dimensions and appearance requirements.

Material Basis: The Rich Copper Alloy Family

Pure copper (red copper) has excellent electrical and thermal conductivity but limited castability and strength. Therefore, copper casting primarily uses various copper alloys (Copper Alloys), achieved by adding other elements (like Zinc-Zn, Tin-Sn, Lead-Pb, Aluminum-Al, Nickel-Ni, Silicon-Si, Beryllium-Be, Manganese-Mn, etc.) to copper to obtain superior comprehensive properties:

• Brasses (Cu-Zn based alloys):
  Good fluidity, easy to cast, relatively low cost. Adding lead (leaded brass) improves machinability; adding aluminum, manganese, iron increases strength and corrosion resistance (e.g., aluminum brass, manganese brass). Widely used in valves, pipe fittings, gears, decorative parts.

• Bronzes (Originally Cu-Sn alloys, now broadly refers to copper alloys primarily without Zn):

  • Tin Bronzes: Excellent wear resistance, corrosion resistance (especially seawater, dilute acids), low friction coefficient. Used for bearings, gears, art castings.

  • Aluminum Bronzes: High strength, high wear resistance, high corrosion resistance, high temperature resistance. Used for heavy-duty gears, ship propellers, wear parts.

  • Lead Bronzes: Exceptional anti-friction, embeddability, and self-lubrication. Primary material for sliding bearings.

  • Silicon Bronzes: Good strength, corrosion resistance, castability, and weldability. Used for pump/valve bodies, ship fittings.

  • Beryllium Bronzes: Ultra-high strength, high elasticity, wear resistance, non-magnetic. Used for precision elastic components, mold inserts.

• Cupronickels (Cu-Ni based alloys):
  Excellent seawater corrosion resistance, anti-biofouling, attractive silvery color. Used for ship condensers, seawater valves, medical equipment.

• Pure Copper: Primarily used for castings requiring very high electrical/thermal conductivity.

Core Advantages and Applicability

• Complex Shape Manufacturing Capability: Can produce parts with complex internal cavities, curved surfaces, thin walls, and fine details. Often the preferred or only feasible process for many complex structural parts (e.g., artwork, pump housings, valve bodies).

• High Material Utilization: Significant near-net-shape potential, reducing subsequent machining and saving material. Gating/riser scrap can be largely recycled.

• Wide Size Adaptability: Can cast parts ranging from a few grams (e.g., jewelry, electronic parts) to tens of tons (e.g., ship propellers, large statues).

• Excellent Comprehensive Properties: The inherent properties of copper alloys (strength, toughness, wear resistance, corrosion resistance, electrical/thermal conductivity, anti-microbial, aesthetics) are fully realized and utilized through the casting process.

• Batch Production Economy: For batch production, especially using permanent molds (metal dies, die casting dies), the unit cost is competitive.

Distinguishing from Other Copper Processing Techniques

• VS Forging: Forging changes metal shape and refines structure through plastic deformation (hammering, pressing), improving strength/toughness, but struggles with complex internal cavities and usually has lower material utilization than casting. Casting excels at complex shapes.

• VS Machining: Machining achieves shape by cutting away material, offering high precision but significant material waste, especially inefficient/costly for complex parts. Casting is net-shape forming; waste is mainly in gating/risers (recyclable), suitable for complex part blanks.

• VS Powder Metallurgy (PM): PM forms shapes by pressing and sintering metal powders, suitable for porous or special material parts. However, casting is generally superior for large, high-density, high-performance (especially conductive/thermally conductive) copper parts.

• VS Additive Manufacturing (3D Printing): 3D printing builds shapes layer-by-layer, offering extreme design freedom, suitable for small-batch complex parts and prototypes. Casting retains cost and performance advantages for large batches, large parts, and specific material properties (e.g., high density, high thermal/electrical conductivity), but combining the two (e.g., 3D printed molds/cores) is a trend.

II. Core Processes: Technical Analysis of Copper Casting

Copper casting is a complex physico-chemical process involving several key steps:

Alloy Design and Melting Preparation

• Material Selection: Choose suitable copper alloy grade (e.g., pure Cu, brass, bronze, cupronickel, special Cu alloy) based on the casting's end-use requirements (strength, conductivity, corrosion/wear resistance, color, cost).

• Charge Calculation: Precisely calculate proportions of pure copper, alloying elements (e.g., Zn, Sn, Pb, Ni, Al, Si, Be, Mn), and returns (scrap).

• Melting Equipment: Primarily medium-frequency induction furnaces (efficient, energy-saving, precise temperature control, uniform alloy composition, relatively environmentally friendly). Crucible, reverberatory, and arc furnaces have specific applications.

• Melting Process:

  • Charging & Melting: Add metal charges in sequence (usually difficult-to-melt Cu, Ni first, then easily oxidized/volatile Zn, Pb, etc.). Induction furnaces melt metal using electromagnetic induction eddy currents.

  • Covering & Deoxidation: Use covering agents (charcoal, borax, glass) to reduce oxidation and gas absorption (mainly H₂). Add deoxidizers (e.g., phosphor copper, silicon calcium alloys) to remove dissolved oxygen, preventing gas porosity and oxide inclusions.

  • Refining (if needed): Remove impurities (e.g., S, Fe). For high-demand castings, inert gas (e.g., Ar) refining or vacuum melting may be used.

  • Alloying: Add alloying elements when melt temperature is suitable; stir thoroughly for uniform dissolution.

  • Temperature Control: Precisely control tapping and pouring temperatures (typically 50-150°C above alloy liquidus), crucial for fluidity, feeding, and grain size. Monitored using thermocouples and infrared pyrometers.

Mold Making: Shaping the Metal

The mold is the core tooling forming the casting's external contour and internal cavities. Common mold processes for copper casting include:

• Sand Casting: The most widely used and adaptable casting method.

  • Molding Sand: Composed mainly of base sand (silica sand, zircon sand, chromite sand, etc.), binder (clay, sodium silicate, resin, etc.), and additives (coal dust, water, etc.). Requires adequate strength, permeability, refractoriness, collapsibility.

  • Molding Methods:

    • Hand Molding: High flexibility, suitable for prototypes, small batches, large or complex parts. Low efficiency, quality relies on worker skill.

    • Machine Molding: (Jolt-squeeze, shoot-squeeze, static pressure, air impact, etc.) Significantly improves efficiency and mold compaction uniformity. Suitable for batch production.

  • Binder Systems:

    • Clay Green Sand: Low cost, widely used. High green strength, relatively poor permeability/collapsibility.

    • Sodium Silicate Sand: (CO₂ hardened, ester cured) Fast hardening, high strength, good collapsibility (especially ester cured). Hygroscopic, difficult sand reclamation.

    • Resin Sand: (Furan, phenolic, alkaline phenolic no-bake sands) High casting dimensional accuracy, surface finish, strength, good collapsibility. Higher cost, environmental concerns (formaldehyde, phenol emissions).

  • Core Making: Making cores (sand cores) for internal holes or complex cavities. Often made with resin sand, oil sand, sodium silicate sand. Requires adequate strength, permeability, collapsibility, and reliable positioning in the mold (core prints, chaplets).

  • Coatings: Apply refractory coatings (e.g., graphite-based, zircon-based) to mold cavities and cores to improve surface finish, prevent metal penetration, and enhance metal flow.

• Investment Casting (Lost Wax Casting): Preferred for high-precision, high-complexity, high-surface-quality castings.

  • Wax Injection: Inject liquid/paste pattern material (wax or resin-based) into a metal die to make a precise wax pattern.

  • Assembly: Weld multiple wax patterns onto a wax gating system (pouring cup, sprue, runner, ingate) to form a pattern cluster.

  • Shell Building: Repeatedly dip the cluster into refractory slurry (silica sol/sodium silicate + zircon flour, alumina flour, etc.) and stucco (different grit sizes), drying/hardening each layer. Typically 5-9 layers form a shell of sufficient strength.

  • Dewaxing: Heat the shell (steam, hot water, or furnace) to melt out the pattern material, leaving a hollow shell.

  • Firing: Fire the shell at high temperature (800-1100°C) to remove residual pattern material and moisture, increase shell strength/permeability, and preheat it for pouring.

  • Advantages: High dimensional accuracy (CT4-7), good surface finish (Ra 3.2-12.5 μm), can cast extremely complex shapes (thin walls, deep holes, fine details), minimal parting line flash, suitable for hard-to-machine alloys. Disadvantages: Many steps, long cycle time, high cost, size limitations.

• Permanent Mold Casting (Gravity Die Casting):
  Uses reusable molds made of metal (cast iron, cast steel, copper alloy, etc.).

  • Advantages: Faster cooling, denser structure, better mechanical properties; high dimensional accuracy, good surface finish; high production rate (no molding required). Disadvantages: High mold cost, long mold lead time; limitations on part complexity; requires coating and mold temperature control.

  • Application: High-volume production of relatively simple to moderately complex copper alloy castings, e.g., gear blanks, bushings, valve parts.

• Die Casting:
  Forces liquid or semi-solid copper alloy under high pressure (tens to hundreds of MPa) at high speed into a precision metal die cavity, where it rapidly solidifies under pressure.

  • Advantages: Very high production rates; very high dimensional accuracy and surface finish; can produce thin-wall complex parts; dense structure (semi-solid die casting better). Disadvantages: Expensive equipment; very high die cost; prone to gas porosity; generally only suitable for low-melting-point, free-flowing alloys (e.g., some brasses); size limitations.

  • Application: High-volume production of small, thin-wall, high-precision copper alloy parts, e.g., locks, hardware, small gears, electrical connectors.

• Centrifugal Casting:
  Pours molten metal into a mold rotating at high speed, filling the cavity and solidifying under centrifugal force.

  • Advantages: Dense casting structure (especially good for gas/shrinkage porosity sensitive parts); good mechanical properties; simplifies casting of cylindrical/ring-shaped parts (bushings, rings, pipes). Disadvantages: Primarily for specific shapes; poor dimensional accuracy/surface finish on inner diameter (requires machining); segregation may occur.

  • Application: Copper alloy bearing sleeves, bushings, flanges, valve bodies, ring components.

• Continuous Casting:
  Continuously pours molten copper into a water-cooled mold (crystallizer), where it solidifies into a specific cross-section shape (slab, billet, tube) and is continuously withdrawn.

  • Advantages: Very high production efficiency; uniform and dense structure; high material yield; easy automation. Disadvantages: High equipment investment; mainly used to produce billets for subsequent rolling, extrusion, forging.

  • Application: Producing pure copper, brass, bronze slabs, billets, tubes for further plastic forming.

Pouring: Injection of Liquid Metal

Transfer molten copper at the suitable temperature from the furnace to a ladle (manual, crane-lifted, automatic pouring machine) and pour it smoothly, continuously, and rapidly (avoiding interruption) into the mold's gating system.

Key Controls:

• Pouring Temperature: Too high causes shrinkage porosity, metal penetration, coarse grains; too low causes cold shuts, misruns, inclusions. Precisely control based on alloy, part size/wall thickness, mold material.

• Pouring Speed: Affects mold filling stability, air entrapment, cavity venting. Often follows "slow-fast-slow" principle (slow start for venting, fast filling, slow end for feeding).

• Gating System Design: Guides metal to fill the cavity smoothly, orderly, and turbulently; traps slag; vents gases; controls cooling/solidification sequence. Includes pouring cup, sprue, runner, ingate, risers, etc. Design is crucial, directly impacting casting quality.

Solidification & Cooling: Defining the Form

The process where copper loses heat within the mold and transforms from liquid to solid. A complex physical process involving heat transfer, phase change, and volume shrinkage.

Solidification Characteristics:

• Freezing Range: Copper alloys have vastly different solidification ranges (liquidus to solidus temperature difference). Wide freezing range alloys (e.g., some high-lead brasses) tend towards mushy solidification, making feeding difficult and prone to microporosity; narrow freezing range alloys (e.g., aluminum bronzes, some manganese bronzes) tend towards directional solidification, making feeding relatively easier.

• Shrinkage: Copper alloys undergo liquid shrinkage, solidification shrinkage, and solid shrinkage during cooling. Solidification shrinkage is the main cause of shrinkage cavities and porosity; solid shrinkage determines final dimensions and distortion tendency (requires considering shrinkage allowance in mold design).

• Feeding: To compensate for solidification shrinkage and prevent cavities/porosity, risers (reservoirs of molten metal located above thermal centers or last-to-freeze sections) are commonly used. Riser design (location, size, shape) and insulating/exothermic measures are key to effective feeding.

• Directional Solidification: Controlling the cooling direction (e.g., using chills, insulating risers) to make the casting solidify progressively from areas farthest from the riser towards the riser, ensuring the riser solidifies last and can effectively feed the casting.

• Cooling Rate: Affects grain size, dendrite arm spacing, microsegregation, second-phase distribution, thereby influencing final mechanical/physical properties. Metal mold/die casting cools fast, resulting in fine structures; sand/investment casting cools slower.

Knockout, Cleaning & Post-Processing

• Knockout: After the casting cools sufficiently (to prevent distortion/cracking), remove it from the mold (vibration, shakeout machines).

• Removing Gates/Risers: Remove the gating system and risers from the casting by knocking, sawing, grinding, flame cutting, hydraulic shearing.

• Surface Cleaning:

  • Shot/Sand Blasting: Use high-speed steel shot/sand to impact the surface, removing adhered sand, scale, burrs, achieving a clean surface and work-hardening the skin.

  • Chemical Cleaning: Pickling (remove scale), alkaline cleaning (remove core sand residues), etc. Environmental and safety considerations are important.

  • Grinding & Finishing: Remove flash, burrs, gate/riser stubs manually or mechanically; dress the surface.

• Heat Treatment (as required):

  • Stress relieving (annealing).

  • Improving microstructure uniformity and mechanical properties (solution treatment + aging, especially for beryllium copper, aluminum bronze).

  • Improving dimensional stability (stress relieving).

• Weld Repair (optional): Repair permissible casting defects (e.g., small pores, microporosity).

• Final Inspection & Coating: After passing quality inspection, apply surface treatments (e.g., passivation, electroplating, painting) as needed for corrosion resistance or aesthetics.

III. Types of Copper Castings

Numerous copper alloys are used for casting, with diverse properties. Main categories include:

• Pure Copper (Red Copper):

  • Grades: e.g., C11000 (Electrolytic Tough Pitch Copper - ETP).

  • Characteristics: Extremely high electrical (~100% IACS) & thermal conductivity, excellent ductility, good corrosion resistance (especially in atmosphere, fresh water). Poor castability (moderate fluidity, prone to oxidation/gas absorption, high shrinkage).

  • Casting Applications: Primarily castings requiring very high electrical/thermal conductivity, e.g., large electrical components, molds (e.g., continuous casting molds), art castings. Commonly sand cast, centrifugally cast.

• Brasses (Copper-Zinc Alloys): The most widely used cast copper alloys.

  • Plain Brasses: Cu-Zn binary alloys (e.g., C85800, C86100). Strength increases with Zn, ductility peaks then decreases. Good castability (good fluidity, moderate shrinkage).

  • Special Brasses: Add other elements to improve properties:

    • Leaded Brasses: Add Pb (e.g., C83600, C84400, C85700). Significantly improve machinability and wear resistance, enhance self-lubrication. Widely used in valves, pipe fittings, gears, bearings, locks, clock parts. The mainstay of cast brasses. Under environmental trends, lead-free free-machining brasses (adding Bi, Se, Te, etc.) are developing.

    • Tin Brasses: Add Sn (e.g., C87500, C87600). Increase strength, hardness, and seawater corrosion resistance (dezincification resistance). Used for marine parts, pump bodies.

    • Aluminum Brasses: Add Al (e.g., C86200, C86300). Significantly increase strength, hardness, wear resistance, and corrosion resistance (especially seawater erosion-corrosion). Used for heavy-duty gears, worms, bearings, ship propellers.

    • Manganese Brasses: Add Mn (e.g., C86500, C86700). High strength, high toughness, excellent seawater/steam corrosion resistance, good damping. Used for marine propellers, heavy-duty bearings, gears, pump bodies, valves.

    • Silicon Brasses: Add Si (e.g., C87500, C87800). Good castability, moderate strength, high corrosion resistance (especially high-velocity water), easy brazing. Used for pipe fittings, pump housings, faucet valve bodies.

    • Iron Brasses: Add Fe (often with Mn, Al, e.g., C86300, C86500). Refine grains, increase strength and wear resistance.

• Bronzes (Originally Cu-Sn alloys, now broadly Cu alloys without Zn or with Zn as minor):

  • Tin Bronzes: Cu-Sn binary or multi-alloys (e.g., C90300, C90500, C90700, C91000, C91300).

    • Characteristics: Excellent wear resistance, corrosion resistance (especially seawater, dilute acids), low friction coefficient (anti-galling), good castability (good fluidity, low shrinkage, segregation tendency). Strength/hardness increase with Sn content, ductility decreases. Historically most important casting alloy.

    • Applications: Bearings, bushings, gears, worms, wear sleeves, valve parts, pump bodies, art sculptures, bells. High-tin bronzes (>10% Sn) for high-performance wear parts.

  • Aluminum Bronzes: Cu-Al binary or multi-alloys (often with Fe, Ni, Mn, e.g., C95200, C95400, C95500, C95800).

    • Characteristics: Among the highest strength and hardness cast copper alloys; excellent wear resistance, corrosion resistance (especially seawater, sulfuric/organic acids); good impact/fatigue resistance; high temperature oxidation resistance (up to 500°C); spark-resistant. Castability acceptable (good fluidity, but higher shrinkage, prone to oxidation/gas absorption).

    • Applications: Heavy-duty gears, worms, bearings, bushings, valve seats, pump impellers, ship propellers, mining machinery parts, chemical equipment corrosion-resistant parts, spark-resistant tools.

  • Lead Bronzes: Cu-Pb binary or multi-alloys (often with Sn, e.g., C93200, C93400, C93500, C93700, C93800, C94300).

    • Characteristics: Contain large amounts of insoluble lead particles (5-25%), providing excellent embeddability and conformability (wear/anti-friction), anti-galling, and self-lubrication, especially suitable for low-speed, high-load bearings. Relatively low strength/hardness.

    • Applications: Primary material for sliding bearings (bushings, shells), used in engines, heavy machinery, railway vehicles.

  • Silicon Bronzes: Cu-Si binary or multi-alloys (often with Zn, Mn, Fe, e.g., C87300, C87500, C87800).

    • Characteristics: Good strength, corrosion resistance (especially seawater), castability, and weldability; non-magnetic; spark-resistant. Good fluidity, low shrinkage.

    • Applications: Pump housings, valve bodies, pipe fittings, ship fittings, chemical equipment, art castings, explosion-proof tools.

  • Beryllium Bronzes: Cu-Be binary or multi-alloys (often with Ni, Co, e.g., C82000, C82200, C82500).

    • Characteristics: Highest strength level among cast copper alloys (after solution+aging); excellent elasticity, fatigue strength, wear resistance, corrosion resistance, thermal conductivity, non-magnetic; good castability (good fluidity). High cost, beryllium is toxic requiring strict protection.

    • Applications: Precision elastic components (springs, diaphragms), high-wear parts (plastic mold inserts, spark-resistant tools), aerospace/electronics components, high-performance switch contacts.

• Cupronickels (Copper-Nickel Alloys):

  • Plain Cupronickels: Cu-Ni binary alloys (e.g., C96200, C96400).

    • Characteristics: Excellent corrosion resistance (especially seawater, organic acids, alkalis); good strength, toughness, hot/cold workability; attractive silvery color; anti-biofouling. Acceptable castability.

    • Applications: Ship condenser tube plates, seawater pump/valve parts, chemical equipment corrosion-resistant parts, medical devices, coins, decorative parts.

  • Complex Cupronickels: Add Fe, Mn, Cr, Al, etc. (e.g., C70600 - CuNi10Fe1Mn, C71500 - CuNi30Mn1Fe).

    • Characteristics: Further increase strength, corrosion resistance (e.g., high-velocity seawater erosion, stress corrosion), heat resistance.

    • Applications: High-performance ship condenser tubes (often used together), heat exchangers, high-temperature/high-pressure valves, offshore platform equipment.

IV. Application Areas: The Vast Realm of Copper Castings

Leveraging their comprehensive performance advantages, copper castings permeate all aspects of modern society:

• Industrial Equipment & Machinery Manufacturing:

  • Valves & Pipe Fittings: Faucet bodies, gate/globe/ball/butterfly/check valve bodies, bonnets, discs (Commonly Leaded Brass, Silicon Brass, Aluminum Bronze).

  • Pumps: Pump housings, impellers, wear rings for centrifugal/gear/screw pumps (Commonly Aluminum Bronze, Tin Bronze, Manganese Brass).

  • Bearings & Bushings: Plain bearings (Leaded Bronze, Tin Bronze, Aluminum Bronze), thrust bearings, bushings (Widely used in various mechanical transmission systems).

  • Gears & Worms: Small/medium gears (Leaded Brass), heavy-duty high-load gears and worms (Aluminum Bronze, Manganese Bronze).

  • General Machinery Parts: Fittings, bushings, flanges, connectors, housings, wear plates.

• Transportation:

  • Marine: Propellers (High Manganese Aluminum Bronze, Nickel Aluminum Bronze), seawater pump valves, condenser tube plates (Cupronickel), stern tube bearings (Lignum Vitae + Cupronickel/Bronze), piping system fittings, outfitting parts.

  • Automotive: Carburetor parts (traditional), radiator caps, oil pump parts, lock cylinders, bearing cages, synchronizer rings (Special Brasses, Bronzes).

  • Railway: Locomotive/rolling stock bearing shells (Leaded Bronze), brake system parts, pantograph contact strips (Copper alloy powder metallurgy).

  • Aerospace: High-performance bearings, gears, hydraulic valves, conductive components (Often Beryllium Bronze, special Aluminum Bronzes, etc.).

• Construction & Plumbing:

  • Piping Systems: Pipe fittings, elbows, tees, caps (Heavily use cast Leaded Brass, Lead-Free Brass).

  • Plumbing Hardware: Faucet bodies, handles, showerheads, drain components (Primarily use cast Brass, surface plated with Cr, Ni, etc.).

  • Architectural Decoration: Door handles, hinges, locks, plaques, art railings, roof ornaments (Bronze, Brass).

• Power & Electronics:

  • Conductive Components: Switch contacts, clamps, busbar connectors (Pure Copper, high-conductivity copper alloy castings).

  • Heat Sink Components: Heat sink bases, heat pipe parts (Pure Copper, Copper alloys).

  • Electronic Packaging: Some housings, bases (Special Copper alloys).

  • Motors & Electrical Appliances: Motor end shields, rotor bars (Pure Cu castings rare, mostly wrought), appliance housings.

• Art & Culture:

  • Sculpture: Large urban sculptures, statues, animal figures (Commonly Tin Bronze, Silicon Bronze, sand or investment cast).

  • Bells & Chimes: Church bells, carillons, art bells (High Tin Bronze).

  • Religious & Decorative Objects: Censers, candlesticks, trophies, plaques, reliefs (Bronze, Brass).

  • Musical Instrument Parts: Saxophone bodies, trumpet bells (Brass), cymbals (Special Bronze).

• Other Fields:

  • Hardware & Tools: Wrenches, hammer heads (some copper alloy castings), spark-resistant tools (Beryllium Bronze, Aluminum Bronze).

  • Wear Parts: Mining machinery liners, rolls (Aluminum Bronze).

  • Consumer Goods: Locks, zipper pulls, eyeglass frames (mostly zinc die cast, also brass), decorative items.

V. Copper Casting Quality Control: Defects and Inspection

The casting process is complex with many influencing factors, making defects inevitable. Common defects and causes:

• Cavity-Type Defects:

  • Gas Porosity: Gas dissolved in the metal (mainly H₂) precipitating during solidification, or gas generated by mold/core entrapped in metal unable to escape. Appears as spherical or pear-shaped cavities with smooth walls. Prevention: Thorough deoxidation/degassing, improve sand permeability, ensure gating vents properly, control pouring temp.

  • Shrinkage Cavity/Shrinkage Porosity: Formed when metal solidification shrinkage is not adequately compensated. Cavity: large concentrated void; Porosity: fine dispersed voids. Prevention: Rational riser/chill design for directional solidification; ensure sufficient feeding pressure; control alloy composition (avoid wide freezing range).

  • Slag Inclusion (Inclusions): Slag, oxides, sand particles entrained with metal into cavity, or mold/gating surface spalling. Irregular cavities containing slag. Prevention: Thorough deslagging during melting; slag trapping during pouring (ladle lip, filters); keep gating system clean.

• Surface Defects:

  • Metal Penetration (Burning-on): Metal penetrates sand pores or reacts chemically with sand, causing sand to firmly adhere to casting surface. Mechanical penetration (physical), Chemical penetration (forming low-m.p. compounds). Prevention: Use finer sand, refractory coatings; control pouring temp; optimize sand properties (compaction, refractoriness).

  • Scab/Buckle: Mold surface buckles/cracks under heat, metal penetrates forming metal-sand lumps. Prevention: Increase sand hot strength (e.g., add clay, bentonite); avoid excessive surface drying; lower pouring temp.

  • Cold Shut/Misrun: Metal streams fail to fuse completely (Cold Shut), or fail to fill cavity (Misrun). Common in thin sections, areas far from gate. Appears as seams or missing fillets. Prevention: Increase pouring temp/speed; improve fluidity (alloy, superheat); increase ingate area; improve venting.

• Shape & Dimension Defects:

  • Distortion (Warpage): Casting warps during solidification/cooling due to restrained shrinkage (mold, core, part geometry) or uneven stress. Prevention: Optimize design (uniform walls, stiffeners); improve mold/core collapsibility; use bracing; control knockout time; stress relieve.

  • Mold Shift/Core Shift: Misalignment of cope/drag or cores during mold assembly, causing dimensional/shape deviation. Prevention: Improve pattern/core box accuracy; strengthen mold/core locating (dowel pins); ensure accurate molding/assembly.

• Crack-Type Defects:

  • Hot Tear: Intergranular cracks occurring at high temperature during final solidification or just after, due to restrained shrinkage (mold, core, part design). Crack surfaces oxidized. Prevention: Improve mold/core collapsibility; optimize design (avoid hot spots, sharp corners); lower pouring temp; control harmful elements (e.g., S).

  • Cold Crack: Transgranular cracks occurring when casting cools to lower temperature (elastic state), due to casting stresses (thermal, transformation, mechanical restraint) exceeding material strength. Cracks straight, surfaces clean. Prevention: Optimize design to reduce stress concentration; improve collapsibility; control cooling rate (e.g., slow cool); stress relieve.

Quality Inspection Methods:

• Visual Inspection (VT): Most basic method, checks surface defects, contour integrity.

• Dimensional Inspection: Checks key dimensions using calipers, gauges, Coordinate Measuring Machine (CMM).

• Liquid Penetrant Testing (PT): Detects surface-breaking defects (cracks, pores, porosity).

• Magnetic Particle Testing (MT): Only applicable to ferromagnetic materials (some Cu alloys with high Fe). Detects surface/near-surface defects.

• Radiographic Testing (RT - X-ray/γ-ray): Detects internal defects (porosity, shrinkage cavities/porosity, inclusions, cracks), visually shows defect shape/size/location. Common method.

• Ultrasonic Testing (UT): Detects internal defects, measures thickness, sensitive to planar defects (cracks). Requires skilled operation/interpretation.

• Pressure Testing: Hydrostatic or pneumatic testing of pressure-containing castings (e.g., valves, pump bodies) to check leakage.

• Metallographic Analysis: Samples examined microscopically to assess grain size, phase composition, inclusions, defect nature, verify heat treatment.

• Mechanical Property Testing: Tensile, hardness, impact tests to verify material properties meet requirements.

• Chemical Composition Analysis: Spectrometry, etc., to verify alloy composition.