I. Scope of Application and Core Requirements
Applicable Objects
This standard applies to glass food jars with an inner neck diameter ≥30mm and a nominal capacity of 50mL to 5000mL, used as packaging containers for food.
Thickness Specifications
Bottle body thickness: Shall not be less than 1.0mm to ensure mechanical strength during transportation and use.
Bottle bottom thickness: Shall not be less than 2.0mm to enhance impact resistance and pressure resistance.
Uniformity requirements: Although no direct specification is given for thickness variation, the thickness distribution must be uniform, ensured by multi-point measurement (e.g., selecting 4 points on the same circumference of the bottle body, and measuring the center and edge of the bottle bottom).
II. Measurement Methods and Instrument Requirements
Principle: The thickness is converted into mechanical displacement or electrical signal through direct contact between the thickness gauge probe and the bottle body.
Accuracy requirements: A thickness gauge with a graduation value of no more than 0.02mm is required. It is recommended to use equipment with higher accuracy (such as the Link Testing Electronics CHY-B2 electronic wall thickness tester, with a graduation value of 0.001mm) to meet stringent testing requirements.
Calibration requirements: Calibration should be performed using a standard thickness gauge block (error ≤±0.005mm) certified by national metrology, ensuring that the instrument display value deviates from the standard block by ≤0.001mm.
Calibration: Calibrate the instrument using a standard block, adjusting the probe pressure (5-10N is recommended for glass to avoid deformation).
Bottle body measurement: Select 4 points evenly distributed on the same circumference in the middle of the bottle body (avoiding the bottle shoulder and bottom transition areas), and repeat the measurement 3 times at each point, taking the average value.
Center area: Measure the thinnest point, which should be ≥1.8mm (referencing industry experience).
Edge area: At the connection with the bottle body, the thickness should be ≥2.0mm and ≥1.2 times the thickness of the center area.
Data recording: Record the thickness value of each point, calculate the average value, maximum value, minimum value, and thickness difference (maximum value - minimum value).
III. Key Control Points for Operation
Bottle Body: For regular bottle shapes, select 4 points (front, back, left, and right). For irregularly shaped bottles, select points according to design requirements.
Bottle Bottom: Must cover the central and edge areas to avoid missing weak points.
Temperature must be stable at 20±5℃ to avoid errors caused by thermal expansion and contraction (e.g., for PET bottles, a 10℃ temperature change results in a thickness deviation of approximately 0.01mm).
The bottle surface must be clean and free of oil stains to prevent interference with probe contact.
Glass Jars: The pressure of the capacitive thickness gauge should be set to 5-10N to ensure tight contact without damaging the bottle.
Plastic Bottles (if measurement is required): The pressure needs to be reduced to 3-5N to avoid compression deformation.
IV. Data Processing and Result Determination
Minimum Thickness: Must be ≥1.0mm (bottle body) or 2.0mm (bottle bottom).
Thickness Variation: Although not explicitly defined in the standard, industry practice requires that the thickness variation of glass bottles be ≤0.05mm, and for plastic bottles ≤0.1mm.
Thickness Ratio: The ratio of the maximum to minimum thickness of the same bottle bottom should not be greater than 2:1 (refer to company standards).
If the thickness of any measurement point is below the standard lower limit, or the thickness variation exceeds the industry threshold, the instrument needs to be recalibrated and retested to confirm whether it is a bottle defect.
QB/T 4594 clearly specifies the thickness indicators and measurement methods for glass food canning jars, providing technical support for the safety of food packaging. Link Testing's test instrument meets the standard requirements in terms of both accuracy and functionality. Companies with related needs can learn more about their products to make quality inspection more efficient and compliant.
For more details please visit www.linktesting.org
