Tinplate used for can-making materials is primarily for containers such as three-piece cans, DI cans, DRD cans, aerosol cans, crown caps, easy-open lids, various miscellaneous cans, and basket-style drums. Tinplate undergoes processes including coating baking, bending, stamping, flanging, and welding. Therefore, tinplate production quality, can-making quality, and can-filling conditions are all critically important.

Common defects in tinplate applications and their causes are analyzed as follows:

(1) Storage and Transportation
Defects during storage and transportation and their causes are summarized in Table 2-17.

(2) Enamel Baking:The defects and their causes during enamel baking are shown in

Defects	Cause Analysis and Countermeasures
Defects	During storage and transportation, ingress of water or moisture may occur. Waterproof measures should be implemented, with indoor storage that is moisture-proof, ventilated and protected against condensation. Preventive measures should be applied during template production and whenever open and handle the materials.
Scratches on the Tin Coating	Cause and Countermeasures: improperly secured bundles and vibrations during transport, especially over long distances, can cause impacts, tilting, or rolling of steel coils on the ground. Countermeasures: Increase the oil coating appropriately and use vertical packaging.

Table 2-18

2-18 Defects and Causes in Enamel Baking

Defects	Cause Analysis and Countermeasures	Defects	Cause Analysis and Countermeasures
Pinholes	Control the oil-coating amount and ensure the tinplate surface, coating, and enamel equipment are clean	Small Black Spots	Ensure the tinplate surface is clean, free of small white spots or burn marks. Make sure the coating contains no impurities. Keep enamel equipment, rollers, and belts clean to prevent defects during baking. Avoid debris falling into the oven.
Poor Adhesion	Ensure the tinplate surface is clean. Select an appropriate surface roughness. Avoid excessively thick tin layer that affects adhesion. Use proper baking process (temperature and time)	Misalignment of Colors	Ensure minimal dimensional deviation and cutting angle of the tinplate. Maintain flatness of the tinplate.

(3) Defects in cylindrical body welding and their causes are listed in Table 2-19。

Table 2-19 Defects in Cylindrical Body Welding and Their Causes

Defects	Cause Analysis and Countermeasures	Defects	Cause Analysis and Countermeasures
Buckling	Due to aging, the yield plate of the tinplate is too large. The tinplate has been repeatedly baked. It has been stored for too long. Canning equipment is not properly adjusted.	Welding performance	Tinplate thickness accuracy; surface finish; tin layer; and alloy layer. Thickness should be stable. Adjust welding current and overlap. IF steel has poor welding performance.
Poor bending	Tinplate performance is uneven; with poor flatness and inconsistent thickness. Canning equipment is not properly adjusted.	Expansion cracking	Select the appropriate hardness and diameter expansion process. Note that the circumferential direction of the barrel is the rolling direction.
(4) Stamping Processing Defects and their causes in stamping processing are shown in Table 2-20. Table 2-20 Defects and their causes in stamping	Cause analysis and measures	Defects	Cause analysis and measures
Stamping cracks	Abnormal tinplate hardness and performance; Incorrect stamping die design and adjustment; Poor lubrication.	18L barrel bottom cracked	When the contents are heavy, they are subjected to repeated vibrations during long-distance transportation, which may cause cracking due to fatigue damage. The hardness of the tin plate and the shape design of the bottom cover reinforcement ribs can reduce vibration of full barrels. BA plate is better than CA plate.
Slip Line	It is easy to produce when the processing degree is small. It has no effect on the actual application, but affects the appearance. IF steel is better than low-carbon aluminum killed steel.

(4) Canned acidic foods Defects and their causes in canned acidic foods are shown in Table 2-21.。

Table 2-21 Defects in Canned Acidic Foods and Their Causes

Defects	Cause Analysis and Countermeasures
	Production	Surface properties	Corrosion resistance
Material: poor corrosion resistance	Material: L steel	Pure steel	ISV: ≤20μg/3in²
	Pretreatment: strong acid	Surface cleaning	PLV: ≤10s
			T-CS: ≤9 level
	Lanthanum plating: low speed, high tin layer	≥11.2g/m²	ATC: ≤0.12pA/cm²
	Soft melt: high alloy layer	(1.2±0.2)g/m²
	Passivation: High current	60c/ft?
	Passivation: High current	60c/ft?
	Oil film: High oil coating	5·m·g·/·m·2·
Canning: Severe scratches; tin layer damage; loose seals	Severe surface scratches. Check that the tin layer on the reinforcement is not damaged. The overlap length and selectivity of the crimp seal should comply with standard specifications.
Canning: Severe oxidation ring	Insufficient exhaust; low vacuum; excessive residual oxygen; and excessive headspace.
Contents: Various corrosion factors; including natural, added, and external factors; may cause abnormal corrosion on the inner surface of the can.	The type of acid; pH; nitrate ions; sulfur; and anthocyanins vary depending on the variety and origin. Suitable tinplate materials should be selected. Nitrates; sulfur; and chloride ions added or introduced during water; sugar; and food processing; should be minimized.

(5) Internally painted cans Defects and their causes in internally painted cans are shown in Table 2-22.

Table 2-22 Defects in Interior Paint Cans and Their Causes

Defects	Cause analysis and measures	Defects	Cause analysis and measures
The coating quality is not up to standard	The surface quality should be guaranteed, with no severe scratches or exposed metal marks. The coating thickness should be guaranteed. Adhesion and corrosion resistance tests should be conducted according to standards. Defects and current testing should be conducted when necessary.	Scratches and damage to the coating	During canning, quality inspections should be performed, especially around the neck and flange. Coating damage should be prevented. Internal spraying should be performed if necessary.
		Canning	Reduce residual oxygen
		Contents	Minimize various corrosion factors as much as possible.