From Double Seaming to Airtight Assurance

Metal × Tech: A Perfect "Weld"

This is a complex system involving materials science, precision machinery, thermodynamics, and food engineering.

The global can sealing technology market is worth over $20 billion. Through the perfect "weld" of metal and technology, canned food gains the ability to be preserved for long periods. From double seaming to airtight assurance – it's not just a lid…

Millimeter Precision Double Seaming

The seal of a modern metal can relies on a precision plastic forming process called double seaming. It is not a simple snapfit, but a permanent sealing connection formed by mechanically deforming the can body and lid through plastic deformation.

01 First Operation Seaming

During the presealing stage, the lid curl and body flange are initially interlocked by a seaming roll, forming a preliminary interlocking structure. At this stage, the seam tightness and width must be precisely controlled. Typical seam thickness is 1.14–1.52 mm, and seam width is 2.92–3.20 mm.

02 Second Operation Seaming

A second set of precision rolls applies higher pressure to the preliminary structure, compressing the five metal layers (two from the lid, three from the can body) into the designed geometry. This process controls seam compactness and ensures that the overlap rate meets the national standard requirement of ≥50%.

Nanoscale Protective Barrier Sealing Compound

The sealing compound is the most easily overlooked yet critical component of the can sealing system. During seaming, the compound preapplied in the lid groove undergoes viscoelastic flow under heat and pressure, filling microscopic gaps between the metal layers to form a physical barrier.

This high performance composite is precisely formulated from 8–12 components, including a synthetic rubber base (butyl rubber / polyisobutylene), tackifying resins, fillers, antioxidants, rheology modifiers, etc. The proportion of each component must be controlled within ±0.5%. It is the last – and most invisible – guardian of airtightness.

A Different Path: Glass Container Sealing

01 Twist off Closure

A metal cap lined with an elastic sealing gasket uses vacuum shrinkage after hot filling to create a negative pressure seal. The cap threads must meet the sealing torque requirements of JIS Z 1806 or GB/T 24616.

02 Press on / Pry off Closure

A tinplate cap is mechanically pressed onto the bottle finish, achieving an airtight seal via a PVB liner inside the cap. Opening requires destroying the cap’s integrity. Commonly used for acidic food packaging.

03 Crown Cap

After corrugation forming, the cap seals against the bottle finish’s contact line. Mainly used for positivepressure packaging systems such as carbonated beverages.

The Engineering Balance of Design Opening Mechanics

The force required to open the can is a critical engineering trade‑off in seal design. International standards specify that the opening torque for conventional cans should be controlled between 1.2 and 2.5 N·m. This range is carefully calculated:

Too low (<1.2 N·m) → transport vibrations may cause accidental opening.

Too high (>2.5 N·m) → exceeds the average hand strength, requiring a tool.

To optimise the opening experience, modern easyopen ends are designed using finite element analysis. Computer simulations precisely calculate the relationship between scoring depth and remaining material strength, ensuring both easy opening and resistance to rupture during transport.

FullProcess Quality Monitoring System Five Quality Gates

01 AI Vision Monitoring

High speed cameras capture each seam at 1,000 frames per second. AI algorithms analyse seven key dimensions in real time, rejecting any outoftolerance product within 0.5 seconds.

02 Destructive Sampling

Every hour, random samples are taken for destructive measurement. A precision profile projector measures the overlap length, with an allowable error of ±0.02 mm.

03 Micro Leak Detection

In addition to the standard 0.7 bar air test, high end production lines use a helium mass spectrometer leak detector capable of detecting extremely small leaks down to 10⁻⁸ Pa·m³/s – near absolute verification of airtightness.

04 Accelerated Aging Test

Harsh temperature cycles (-10°C to 40°C) simulate accelerated aging, testing the long term performance degradation of the sealing compound.

05 Real Can Tracking

Retained samples from each batch are monitored for 24 months under real storage conditions, generating complete curves of microbiological, sensory, and physicochemical changes.

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