Why is Zinc cast in a “Hot Chamber” and Aluminum in a “Cold Chamber”? We explain how melting points dictate the manufacturing process, cycle times, and why Zinc tooling can outlast Aluminum by an order of magnitude.

When you send an RFQ to Sureton, you might notice a subtle detail in our quotation.
For your Zinc (Zamak) parts, we quote a “Hot Chamber” machine.
For your Aluminum (ADC12) parts, we quote a “Cold Chamber” machine.

Is this just technical trivia? No.
This distinction is the single most important factor determining your Cycle Time, Tooling Life, and ultimately, your Unit Cost.

We often see engineers trying to force an Aluminum part into a Zinc process to save money, or vice versa. To make the right decision, you need to understand what is happening inside the machine.

Here is the “Under the Hood” look at the two hearts of die casting.

1. The Temperature Limit: Why We Can’t “Hot Chamber” Aluminum

The difference isn’t about the machine’s temperature; it’s about the Injection System.

Hot Chamber (The “Gooseneck” Method):
Imagine a syringe permanently submerged in a pot of molten metal. When you pull the plunger, it refills instantly. When you push, it shoots metal into the mold.

• The Catch: The injection mechanism (the “Gooseneck” and plunger) is made of tool steel. It sits in the molten bath 24/7.

• The Physics: Zinc melts at ~420°C. Steel can survive this temperature indefinitely without losing strength or dissolving.

Cold Chamber (The Ladle Method):
Aluminum melts at ~660°C.
If we submerged a steel gooseneck into molten aluminum, two things would happen:

1. The steel would anneal (lose its hardness) and soften significantly.

2. The aluminum would chemically attack and dissolve the steel (iron pickup), ruining the machine and the alloy.

Therefore, for Aluminum, we must keep the injection system “Cold” (outside the furnace). We have to ladle the molten metal from the furnace into a separate shot sleeve for every single cycle.

2. The Speed Factor: The Tortoise and the Hare

Because of this mechanical difference, the production speed varies wildly.

Hot Chamber (Zinc/Magnesium):

• Process: The plunger retracts, metal flows in, plunger injects. Repeat.

• Speed: It is a machine gun. Small zinc parts can run at 10 – 15 shots per minute.

• Cost Impact: Extremely low labor cost per part because the output is so high.

Cold Chamber (Aluminum):

• Process: The die opens -> Robot ladles metal -> Plunger pushes metal -> Biscuit solidifies -> Die opens -> Robot extracts part.

• Speed: It is a heavy lifter. A typical cycle is 1 – 2 shots per minute.

• Cost Impact: You are paying for more machine time per part. This is why aluminum parts often have a higher processing cost than zinc, even if the material is cheaper by volume.

3. The Tooling Economics: Why Zinc Molds Endure

This is the number one question we get: “Why can a Zinc mold last for half a million shots or more, while an Aluminum mold might be retired after 100,000?”

The answer is Thermal Shock and Corrosion.

• In Zinc Die Casting: The melt is ~420°C. The mold operates around 180-250°C. The relatively small ΔT and minimal chemical attack mean mold steel degrades slowly. Under good conditions, 500,000 to 1 million shots is achievable.

• In Aluminum Die Casting: The ~660°C melt causes severe thermal cycling and promotes soldering. This leads to heat checking. A well-maintained mold might reach 150,000-200,000 shots, but for complex parts, 80,000-100,000 shots is a common planning benchmark.

Sureton’s Planning Insight: If you are planning a product with a 5-year lifecycle:

• Zinc Example (Long Life): At 200,000 units/year (1M total), you might need just 1-2 molds.

• Aluminum Example (Planned Wear):At the same volume, with a 100,000-shot tool life, you should budget for ~2 production molds plus planned insert refurbishments. This upfront understanding is key to accurate Total Cost of Ownership (TCO) modeling.

4. Pressure and Density

There is one area where Cold Chamber wins: Power.

Because the injection cylinder is separate from the furnace, Cold Chamber machines can be built to be massive. We operate machines up to 3,500 Tons at Sureton.
This allows us to apply immense Intensification Pressure during the solidification phase.

• Result: We can squeeze the aluminum hard enough to compress trapped gas and achieve higher density for structural parts.

• Practical Limitation: The immersed gooseneck design imposes a physical limit on shot size and clamping force. While larger machines exist, most commercial hot chamber production operates well below 600 Tons clamping force. You won’t see a hot chamber machine casting a large automotive component; it’s a fundamental design constraint.

5. Making the Strategic Choice: It’s About Total Cost

You don‘t usually “choose” the process; the material chooses it for you. But understanding the trade-offs is crucial for budgeting.

• For Zinc: Leverage its blazing speed and incredible tool life for high-volume, small-to-medium parts where per-part processing cost is paramount.

• For Aluminum: Leverage its strength-to-weight ratio and ability to be cast into large, complex shapes. While the per-part processing cost is higher, its lower density and material cost often make it the more economical choice for larger, structural components where total weight and raw material expenses dominate.

Summary: Which Process Fits Your Part?

To summarize the practical implications: 

We Speak Both Languages

At Sureton, we don’t favor one over the other. Our facility floor is split: one side hums with the rapid-fire rhythm of Hot Chamber Zinc machines; the other rumbles with the heavy power of Cold Chamber Aluminum giants.

Not sure which alloy or process yields the lowest Total Cost of Ownership (TCO) for your specific part?
Contact us today with your CAD model and annual volume forecast. We’ll perform a comparative analysis that factors in tooling investment, piece-part cost, and material properties to give you a data-driven recommendation.