What Is a Wall Thickness Gauge? A Guide to Measuring Container Thickness and Dimensions
A wall thickness gauge measures how thick the wall of a container is, at one point or along its whole profile. For PET bottles, preforms and glass bottles, the thickness of the wall and the way the material is distributed decide how well the container resists pressure, top load and impacts, and how much material it uses. Thickness and dimensional gauges are basic tools in the quality control laboratories of container manufacturers and fillers.
How does a wall thickness gauge work?
Three measuring principles are used on containers:
Mechanical contact: two measuring tips touch the inner and outer surfaces of the wall, and a dial or digital indicator shows the distance between them. The AT2E BTG-D for glass bottles and PTG-A / PTG-D for preforms are manual gauges of this type, read on an analog or digital indicator. It is simple and fast, but the tips must reach both sides of the wall.
Magnetic (Hall effect): a small steel ball is placed inside the container and a probe touches the outside of the wall. The probe holds the ball against the inner surface, and a Hall effect sensor measures the distance between the probe tip and the ball. This is the principle of the AT2E AMTG-2.
Optical: a camera measures the outer profile and dimensions of the container without contact, and a laser confocal sensor measures the wall thickness. The AT2E PBMS systems combine a telecentric lens and light with a high-resolution camera for the dimensions, and the laser confocal principle for the thickness.
Main applications
PET preforms: wall thickness, finish dimensions and concentricity before blow molding.
PET bottles: wall, shoulder and base thickness after blow molding, to check how the material is distributed.
Glass bottles: wall thickness of glass containers, where thin zones reduce the resistance to pressure and impact.
Height and diameter: overall height of bottles and cans, outer diameter and circumference.
Base clearance: the height of the dome in the bottom of PET containers.
Key concepts: material distribution, resolution and accuracy
Material distribution: a PET bottle is blown from a small, thick preform. The same preform can give a bottle with an even wall, or a bottle with thick and thin zones, depending on the blow molding settings. One reading is therefore not enough: laboratories measure the wall at several heights and positions around the bottle.
Resolution: the smallest step the gauge can display. The AMTG-2 displays 0.01 mm or 0.001 mm in metric mode, and 0.001 in or 0.0001 in in inch mode.
Accuracy: how close the reading is to the true thickness. On the AMTG-2, it depends on the steel ball used: a 5.00 mm ball measures up to 10 mm with an accuracy of 1 % ±0.003, while a 1.59 mm ball, for thin walls up to 2 mm, has an accuracy of 3 %. On the PBMS systems, the dimensional measuring accuracy is ±0.01 mm, and the optional thickness modules cover 0.04 to 1.4 mm for bottles and 0.3 to 8 mm for preforms.
Non-destructive measurement: magnetic and optical gauges do not damage the container, so the same sample can go on to other tests.
A magnet on a fridge door
Everyone has felt a fridge magnet pull harder as it gets closer to the door. A magnetic thickness gauge uses the same physics: the magnetic field at the probe changes with the distance to the steel ball, and the Hall effect sensor converts that field into a distance. Since the ball sits directly against the inner wall, that distance is the wall thickness.
This method has two practical advantages. Only the outside of the wall needs to be reached with the probe, and the shape of the sample has little influence on the accuracy, as long as the ball can sit freely against the inner wall. This is why the AMTG-2 can measure in corners, small radii and some irregular shapes. It only works on non-magnetic materials, such as plastic, glass, ceramic or aluminum, because a magnetic wall would disturb the field.
Calibration of a thickness gauge
A thickness gauge is calibrated against reference blocks of known thickness:
Measure a set of calibration blocks that covers the measuring range.
Compare each reading with the certified value of the block, and record the deviation.
Adjust the gauge if a deviation exceeds the acceptable limit, then measure the blocks again.
The AMTG-2 allows a multi-point calibration with up to 21 points, and its standard kit includes calibration blocks: 9 for the 0 to 4 mm range, up to 21 for the 0 to 10 mm range. The more points cover the range, the better the gauge follows the true thickness from thin to thick walls.
AT2E thickness and dimensional gauges
AT2E thickness and dimensional gauges range from hand tools to fully automatic systems:
PBMS-AUTO: fully automatic preform and bottle measuring system with AI recognition and automated handling; dimensions, finish inner diameter and perpendicularity, and wall thickness with the optional thickness modules.
PBMS-Lab: automatic laboratory version of the PBMS, with the same optical and laser confocal measurement; measuring accuracy ±0.01 mm.
AMTG-2: magnetic (Hall effect) thickness gauge for non-magnetic materials, up to 10 mm (0.39 in), with a 7" touch screen.
BTG-D: digital wall thickness gauge for glass bottles, 0 to 10 mm (0 to 20 mm optional), resolution 0.01 mm.
PTG-A / PTG-D: preform thickness gauge with analog or digital indicator, 0 to 10 mm, for preforms 20 to 65 mm in diameter.
HG-1: height gauge for bottles and cans, 0 to 300 mm (0 to 11.8 in), accuracy ±0.04 mm.
BCG: base clearance gauge for the dome height in the bottom of PET containers, 0 to 10 mm.
CM CircoMeter: circumference from 60 to 950 mm and diameter from 20 to 300 mm.
Conclusion
The wall is where the material of a container does its work. A gauge suited to the material and the shape, whether contact, magnetic or optical, and regular checks on reference blocks give reliable thickness values that help production teams adjust blow molding and forming, and reduce material use while keeping the required strength.
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AT2E is an ISO 9001 certified company (AFNOR Certification).
Request a quote: info@at2e.com
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