In the production of aluminum cookware, the bottom pressing (or “re-bottoming”) process is crucial for creating durable, warp-resistant pots and pans with excellent heat distribution. A common question from manufacturers is: What tonnage (pressure) machine is required for the bottom pressing of aluminum stretched pots? The answer isn’t a single number, as it directly depends on two key factors: the size and the pattern (design) of the bottom plate. This article explores this relationship and provides guidance for selecting the right equipment.
Understanding the Bottom Pressing Process
Bottom pressing involves using a hydraulic or mechanical press to permanently bond a separate, often thicker, plate (usually aluminum or stainless steel) to the base of an aluminum-stretched pot body. This creates a multi-layer, compound bottom. The machine must apply sufficient pressure to ensure complete adhesion across the entire interface without leaving air gaps, while also forming any desired thermal expansion pattern.
Key Factor 1: Required Pressure Calculation
The required press force (in tons) is fundamentally a function of Area and Pressure per Unit Area.
- Formula: Required Force (Tons) = Pressing Area (cm²) × Unit Pressure (Tons/cm²)
- Pressing Area: This is the total surface area of the bottom plate that needs to be bonded, approximately equal to π × (Radius of the pot bottom)².
- Unit Pressure: This is the specific pressure needed for effective bonding and forming. For aluminum pot bottom pressing, this typically ranges from 2 to 4 tons/cm², depending on the material thickness and the complexity of the pattern. Deeper, more intricate patterns require higher unit pressure.
Example: For a standard 30cm diameter pot (bottom radius ~15cm), the pressing area is roughly 706 cm². Using a unit pressure of 2.5 tons/cm²:
Required Force = 706 cm² × 2.5 tons/cm² = 1765 tons, or approximately 1800 tons.
Therefore, for common household pot sizes (20cm-32cm diameter), machines in the range of 1500 to 2500 tons are widely used.
Key Factor 2: The Link with Pattern (Design) and Size
- Size of the Bottom Plate:
- Direct Correlation: The larger the bottom diameter, the larger the pressing area. As per the formula above, this directly increases the total tonnage requirement. A 36cm pot requires significantly more force than a 20cm pot for the same pattern.
- Pattern (Design / “Flower Pattern”):
- Pattern Depth and Complexity: The bottom plate often features a stamped pattern (like concentric circles or a honeycomb grid). This isn’t just for aesthetics; it manages thermal expansion and improves heat transfer. Deep or complex patterns require higher pressure to fully form the metal into the mold (die) without spring-back, ensuring a crisp, complete impression.
- Surface Contact & Adhesion: A complex pattern slightly reduces the immediate contact area but increases the need for precise, high-pressure forming. Insufficient pressure will result in a poorly defined pattern and weak bonding at the raised edges.
How Pattern and Size Work Together:
- A large bottom plate with a simple, shallow pattern might be served by a machine at the lower end of the tonnage range for its size.
- A small bottom plate with a very deep, intricate pattern may require a machine with higher tonnage than expected for its size to achieve perfect pattern definition.
- A large bottom plate with a deep, complex pattern represents the most demanding scenario, requiring a high-tonnage machine (often 2500 tons or more) to handle both the large area and the forming difficulty.
Conclusion & Recommendations
Selecting the correct bottom pressing machine is a balance between pot size and bottom plate design. As a rule of thumb:
- For small to medium pots/pans (up to 28cm) with standard patterns, a 1500-2000 ton press is often adequate.
- For larger or commercial-sized pots (30cm and above), or for any pot with a deep/complex pattern, a 2000-3000+ ton press is recommended.
Actionable Tip: Always consult with your die/mold manufacturer and press supplier. Provide them with the exact diameter, material thickness, and a sample or drawing of your bottom plate pattern. They can perform precise calculations and recommend the optimal machine tonnage, ensuring quality production, strong bonding, and a perfectly formed bottom every time.
Post time: Feb-05-2026
