Copper Sand Casting Process
What is the copper sand casting process?
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| C6pper Sand Casting |
Copper sand casting is the process of making a copper casting by pouring molten copper metal alloy into a mould made up of silica sand to manufacture complex castings from sm+all to large sizes.
Copper moulding is a very important process for making copper products having application in automotive, marine, electronics, electrical, industrial, heat exchangers and construction as copper is resistant to corrosion, has high mechanical strength, durability and good thermal conductivity.
This process is widely used due to copper's unique properties, such as:
- High thermal conductivity (385 W/m·K).
- High electrical conductivity.
- Excellent corrosion resistance.
- Good wear resistance and fatigue strength.
Because of these properties, copper sand casting is extensively used in electrical systems, heat exchangers, marine applications, and industrial components.
What is copper sand casting also called?
This process is also known as the following:
- Copper sand moulding process.
- Copper alloy sand casting.
- Sand mould casting of copper.
Copper Sand Casting Step-by-Step Process
The copper sand casting process consists of six major steps:
- Pattern and core making.
- Sand mould preparation.
- Melting and pouring of copper molten metal in the mould cavity.
- Solidification of molten metal in a mould.
- Shakeout, runner, riser and casting removal process.
- Cleaning, inspection, finishing and secondary manufacturing operation.
Copper casting differs from aluminium and steel casting due to:
- Higher melting temperature.
- Higher density and fluidity.
- Higher oxidation tendency.
- Greater heat transfer rate.
STEP 1: Pattern Making And Core Making
a) Pattern Making
Patterns made from wood, metal, wax and plastic are used to create a mould cavity, which determines the final shape of the copper casting.
Important pattern considerations in copper casting:
- Shrinkage allowance (1.5% – 2%) depending on the type of alloy.
- Machining allowance for finishing operations.
- Draft allowance for easy pattern removal from the sand.
- Distortion allowance for complex geometries.
Pattern materials include:
- Wood (low cost, short production runs are best for large size casting).
- Metal (high accuracy, long production runs).
- Plastic and wax (precision applications).
Patterns must be dimensionally accurate because copper casting has a limited tolerance compared to precision casting methods.
b) Core Making
Cores are used in the copper sand casting to produce:
- Internal cavities in casting.
- Hollow sections.
- Complex internal passages.
- Support casting during the solidification process to reduce sand mould collapsibility.
Requirements of cores in copper casting:
- High refractoriness to withstand molten copper temperature.
- Good permeability to allow gas escape when molten metal is poured into the sand mould.
- Adequate strength to resist erosion of sand/refractory material.
Core materials:
- Silica sand with binders.
- Resin-bonded sand.
- Oil sand.
Core support systems:
- Chaplets.
- Core prints.
Improper core design may lead to:
- Core shift.
- Gas defects.
- Internal porosity.
STEP 2: Sand Mould Making Process
The sand mould is prepared using:
- Silica sand.
- Clay. (binder)
- Additives (coal dust, wood flour, sawdust etc.).
Types of sand moulds:
- Green sand mould.
- Dry sand mould.
- Skin-dried mould.
Gating System Design
The gating system plays a critical role in copper casting due to:
- High density. (8.97 g/cm³)
- High fluidity.
- Sensitivity to turbulence and oxidation.
Gating elements:
- Pouring basin.
- Sprue.
- Runner.
- Gate and ingate.
- Riser.
Design considerations:
- Smooth flow of molten metal in the gate, runner and riser.
- Minimised the turbulence of molten copper during the metal flow.
- Prevention of oxide inclusion.
- Proper feeding during the solidification process.
A well-designed gating system ensures:
- Reduced sand casting defects during the casting process.
- Improved mechanical properties and strength of casting.
- Uniform filling of the mould cavity during the pouring operation.
STEP 3: Melting And Pouring Of Copper
The first step in the copper moulding process is to melt copper ingots in the induction or crucible furnace. The properties of the final casting are the same as those of the copper ingots used in this process.
The melting point of the copper is around 1080, while the pouring temperature is 1200. The pouring temperature is kept higher than the melting temperature to compensate for the heat loss during the travel of the molten metal.
Melting of Copper alloy.
Copper and its alloys are melted in:
- Induction furnaces. (preferred for clean melting)
- Crucible furnaces.
- Fuel-fired furnaces.
Important parameters:
- Melting temperature: 1083°C (pure copper) to 1200°C+ (alloys)
- Superheat: typically 50–150°C above liquidus.
- Melt cleanliness is critical.
Metallurgical Challenges
1. Oxidation
Copper reacts with oxygen to form copper oxide (Cu₂O), which leads to:
- Reduced ductility.
- Inclusion defects.
2. Gas Absorption
Hydrogen absorption can lead to:
- Porosity.
- Blow holes.
Melt Treatment Before Pouring Melting Metal In Casting
To improve casting quality:
- Degassing using inert gases. (argon, nitrogen)
- Fluxing to remove impurities.
- Deoxidation using phosphorus or lithium. (in some alloys)
Pouring Operation
Molten copper is poured into the mould via the gating system. Sand mould used in the copper casting process is made from a mixture of silica sand, binders and moisture.
Copper has less fluidity during the pouring operation, which requires a careful gating system as compared to the aluminium casting process.
Key factors:
- Controlled pouring rate.
- Avoid turbulence and air entrainment.
- Maintain proper temperature.
Mould Preheating
Moulds are often preheated (200–400°C) to:
- Improve fluidity.
- Reduce thermal shock.
- Prevent premature solidification.
STEP 4: Solidification Of Copper Casting
Solidification begins at the mould walls and progresses inward.
Characteristics of copper solidification:
- Rapid heat transfer due to high conductivity.
- Requires controlled cooling.
Types of Shrinkage
a) Liquid Shrinkage
Occurs during phase change from liquid to solid and is controlled using risers.
b) Solid Shrinkage
Occurs after solidification during cooling and is controlled using allowances.
Grain Structure Formation and Directional Solidification
Grain Structure Formation is achieved by:
- Fine grains near the mould wall. (chilled zone)
- Columnar grains in the intermediate region.
- Equiaxed grains in the centre.
Directional Solidification is achieved by using:
- Chills (metal inserts)
- Proper riser placement
This ensures:
- Reduced shrinkage defects
- Improved mechanical properties
STEP 5: Shakeout And Removal
After solidification, the mould is broken, and the casting is removed. Operations include the removal of runners and risers and sand casting cleaning. Sand can be reused, and the gating material is recycled.
STEP 6: Cleaning, Inspection, and Finishing
Cleaning (Fettling)
- Sandblasting the casting to make the surface smoother and improve the surface finish.
- Grinding of casting components.
- Cutting of riser, runner and unwanted elements.
Inspection
- Visual inspection.
- Radiographic testing.
- Ultrasonic testing.
- Dimensional checks.
Secondary Manufacturing
- CNC machining.
- Turning, milling.
- Polishing and coating.
Copper Sand Casting Defects And Problems
1. Porosity
Cause: Hydrogen gas.
Solution: Proper degassing
2. Oxide Inclusions
Cause: Oxidation during melting
Solution: Fluxing and controlled pouring
3. Misruns
Cause: Low fluidity or temperature
Solution: Increase pouring temperature
4. Shrinkage Cavities
Cause: Improper feeding
Solution: Proper riser design
Why Copper Casting is Better Than Other Sand Casting Processes
Copper vs Aluminium Sand Casting
Advantages of Copper:
- Higher electrical conductivity (critical for electrical applications)
- Better wear resistance
- Higher temperature resistance
- Superior corrosion resistance in aggressive environments
Aluminium Advantages:
- Lower density (lightweight)
- Lower cost
- Easier to cast
Comparison Table (Copper vs Aluminium vs Steel alloy Metal)
Property |
Copper Alloys | Aluminium Alloys | Steel Alloys |
|---|---|---|---|
| Density | 8.6 – 8.9 g/cm³ (High) | 2.6 – 2.9 g/cm³ (Low) | 7.6 – 8 g/cm³ (High) |
| Thermal Conductivity | 200 – 400 W/m·K (Very High) | 120 – 180 W/m·K (High) | 15 – 50 W/m·K (Low) |
| Electrical Conductivity | 80 – 100 W/m·K (Excellent) | 35 – 60 W/m·K (Moderate) | 3 – 15 W/m·K (Low) |
| Corrosion Resistance | Excellent | Good | Moderate |
| Mechanical Strength (MPa) | 200 – 400 N/m² (Medium) | 150 – 300 N/m² (Low–Medium) | 400 – 1000 N/m² (High) |
| Machinability | Good | Excellent | Moderate to Difficult |
| Melting Temperature | 1085 °C | 670 °C | 1400 – 1510 °C |
| Casting Fluidity | Good | Excellent | Moderate |
| Shrinkage (Casting) | Moderate | High | Moderate to High |
| Cost | High | Low | Medium |
Advantages of Copper Sand Casting
- Excellent electrical and thermal conductivity.
- High corrosion resistance.
- Suitable for complex geometries and good machinability.
- The copper sand casting process is harder to manufacture than aluminium, but it is much easier than stainless steel. Because the temperature control in the copper sand casting is delicate, if the temperature is incorrect, it will cause casting defects such as misrun, cold shuts and poor surface finish.
- Heat loss in the copper sand casting process is rapid. Formation of oxides is at a higher risk in copper sand casting because copper reacts with oxygen, leading to inclusions and weak parts.
- Can this casting process require a higher shrinkage allowance as compared to the other casting processes? The energy required for this casting process is higher.
- Moulds that are used in this process require higher refractory properties.
- This casting process can create flexible, complex castings. There is no limitation of size; small to medium to large components can be manufactured.
- This process is cost-effective for small to large production runs.
Disadvantages of Copper Casting
- High cost of material.
- Difficult to cast (oxidation and gas issues).
- Requires precise process control.
- Limitations of this process are that it has a poor surface finish as compared to die casting.
- The dimensional accuracy of this process is very low, requiring post-processing. which means the casting needs to go through secondary operations to improve its surface finish.
- The grain structure in this casting process is coarser due to slower cooling.
Applications Of Copper Sand Casting
- Electrical connectors and components.
- Heat exchangers.
- Marine hardware.
- Industrial valves.
- Decorative and architectural parts.
Copper Sand Casting Conclusion
Copper sand casting is a metal casting process in which molten copper or copper alloys are poured into a refractory sand mould to produce copper cast components with the desired geometry, mechanical properties, and dimensional accuracy in a foundry.
Copper sand casting is a technically advanced and highly specialised casting process used for manufacturing high-performance components.
Compared to aluminium and steel:
- It provides superior conductivity and corrosion resistance
- But requires higher cost and better process control
With advancements in:
- Furnace technology
- Gating system design
- Simulation-based casting
The quality and efficiency of copper casting have improved significantly.
Future developments include:
- Automated foundry systems
- Advanced copper alloys
- Integration with CNC machining and additive manufacturing