What Is an Air Micrometer?
An air micrometer is a comparative measuring instrument that employs air pressure differences to measure objects. It is predominantly used for measuring the inner diameter of holes or the outer diameter of round rods. Notable for its high precision, an air micrometer can perform non-contact measurements with an accuracy of up to 1μm, which is advantageous for precision-required tasks as it applies no contact pressure and avoids damaging the measured object.
While cylinder gauges and 3-point micrometers are alternatives for measuring inner diameters, air micrometers offer quicker measurements and reduce operator-induced errors.
Uses of Air Micrometers
Air micrometers are primarily used in scenarios requiring high dimensional accuracy, such as measuring the inside diameters of bores in automotive engine parts or the outside diameters of shafts like camshafts and crankshafts. They are also versatile enough for other measurements, including thickness and fine wire dimensions.
1. Thickness Measurement
Used in the production of plate-shaped products and thin films, the thickness of an object is measured by positioning the instrument between the object and the head.
2. Measurement of Fine Wire
This technique applies to metal wire, raw silk, and chemical fibers, measuring changes in cross-sectional properties.
3. Geometric Tolerance Measurement Regarding Bore Inside Diameter
Specialized measuring heads enable geometric tolerance assessments, such as straightness in axially long holes and taper and squareness in different cross sections.
4. Hole Center-To-Center Distance (Pitch) Measurement
By using multiple taper tubes and combining nozzles, the pitch of holes can be measured accurately.
Principle of Air Micrometers
Air micrometers use air flow rate or back pressure to measure object shapes and displacements. For inside diameter measurements, a measuring head slightly smaller than the hole’s diameter is placed inside the hole. Clean, constant-pressure air supplied through a compressor, regulator, and filter is then blown out through a nozzle in the measuring head. The air amount varies with the gap between the object and the head, moving a float in a tapered tube, which is then compared against a master component to determine the hole’s diameter.
Features of Air Micrometer
Air micrometers offer precision measurement with less susceptibility to oil and dust, thanks to their non-contact nature. They allow for recording exact measurements rather than mere pass/fail judgments. However, they are specific to the parts they measure, offering limited versatility and a relatively narrow range of measurable tolerances.