Thickness Testing Machine | Thickness Gauge | Introduction to thickness gauges !
Thickness testing machine are used to determine the thickness or size of a material. In fact, there are several different types of thickness gauges; each works in a different way depending on the intended application for the meter.
This article will discuss the common types of thickness gauges; and their use; and will present information on the relevant technical specifications for these types of devices.
I. Types of thickness testing machine
The term Thickness Gauge has a number of potential meanings and can refer to one of the following main categories:
- Material Thickness Gauge
- Coating Thickness Gauge
- Wire and metal thickness gauge
Measure material thickness by mechanical method; a calibrated instrument is closed around the sample until it makes contact with both sides of the material; like Micrometer’s process.
Measure the thickness of the coating applied to the surface – these are called coating thickness gauges.
Simple mechanical device; used to measure wire and sheet metal thickness or metal thickness gauge.
II. Material Thickness Gauge
If both sides of the material with the measured thickness can be accessed; material thickness gauge can be used. These measuring instruments are available in several types, including:
- Mechanical Thickness Gauge
- Digital thickness gauge (electronic)
- Pocket thickness gauge.
Mechanical thickness gauge (analog):
- Mechanical thickness gauge with steel gauge contacts and handle and lever. When the lever is released after the material is inserted between the contact pins; pins close to the surface of the material; and the measured thickness value is indicated on the analog dial by the position of the hand relative to the graduated scale on the dial.
- The edges of the contact pin are usually rounded so that pressing the pins against the surface of the material will not damage or mark the surface.
Digital thickness gauge (electronic):
- Electronic (digital) thickness testers function the same as Analog thickness gauges; but replace the digital display for the needle screen. The reading thickness value can be viewed directly on the digital reader; without having to interpret the measurement from the needle position relative to the scale on the dial.
Pocket Thickness Gauge:
- Smaller versions of analog and digital thickness gauges are known as pocket thickness gauges or pocket dial thickness gauges..
- Instead of using the whole hand to operate the meter; the user holds the tool between the thumb and forefinger.
- These units are intended to perform quick thickness checks of materials such as paper, film or other types of flat stock. Pocket sized thickness gauge available with analog display (dial & hands); or electronic (digital) display.
Dimensions and specifications:
- The dimensions and specifications for the thickness gauge are outlined below. Note that there will be some changes in the specifications; depending on the type of dial thickness gauge considered. The parameters shown below are intended to provide an overview of what to look for and consider when looking for a dial thickness gauge. The size of the thickness gauge can refer to the thickness measuring range; but other parameters such as measuring range are also a relative indicator of size.
- For analog gauges, a mechanical dial indicator is used. For digital (electronic) meters, the display types are usually LCD or LED.
Contact type (anvil & spindle):
- Common contact pins are flat steel with parallel surfaces, with radial edges. A number is rounded; while others are blade-shaped. Other materials include ceramic facets for longer wear.
- Measure the diameter of the contact pin.
Thickness measuring range:
- Indicates the range of values for which the gauge can provide material thickness readings; eg: 0 to 0.0500 inch.
Measuring range – (also known as pharyngeal or throat depth):
- This value is an indication of the distance the gauge can be inserted from the edge of the material; before the edge of the material hits the back of the frame.
- The depth of the throat can be fractions of an inch or can be much larger. Such as 12 throws or 16 steel. When the thickness gauge throat increases to a large value; the strength of the frame must be increased to avoid deformation of the frame from its weight causing problems with the accuracy of the thickness measurement.
Clearing the throat:
- There are also models like calipers; called caliper type thickness gauge. For these; Throat clearance is the maximum separation when the unit’s jaw is open.
The resolution of the meter:
- An indicator of the fineness or fineness to which a thickness gauge can provide a measurement.
- A ruler that ranges from 0 to 0.0500 inches can have a 0.0001 resolution; which means it can resolve values down to a tenth of an inch.
- Is a measure of the gauge’s ability to reflect the actual thickness of the material; expressed as a value of +/- or a percentage of full-scale reading (e.g. +/- 0.0002).
- Amount of force (for metric units, in Newtons) applied to a material in close contact with the material for thickness measurement. For softer materials such as plastic or fabric; it may be necessary to take into account the magnitude of the measuring force.
- Thickness value can be displayed as metric or unit (English).
- For digital thickness testers, indicate the specific type of battery installed in the device.
III. Coating Thickness Gauge
- In some cases; it is important to measure the thickness of the material that has been applied to another surface; such as coatings or paints applied to pipes.
- With such cases; a material thickness gauge will not be sufficient as there is only one side of the coating or paint; and therefore the material thickness gauge as described earlier cannot take the measurement.
- Coating thickness gauges (sometimes called paint gauges) provide a coating thickness measurement; to ensure that the coating complies with the required standards.
There are generally two types of coating thickness gauges:
- The simpler of these is a destructive measurement process; where the thickness tester measures through the dry coating down to the surface; and thus directly set the coating thickness. The obvious problem with this method is that it requires damaging the integrity of the overlay to get a read. There is also a wet coating gauge that measures the thickness of the coating before it is cured
- The second type of coating thickness gauge uses a non-destructive process to determine coating thickness. There are several technologies used for these thickness gauges, one common being ultrasonic waves.
Ultrasonic Thickness Gauge:
- The ultrasonic thickness gauge contains an ultrasonic transducer that emits a pulse of sound wave energy into the coating. When the sound wave hits a material boundary; in this case, the boundary between the bottom of the mantle and the substrate. There is a reflection occurring, sending a pulse back to the transducer. By measuring the time required to detect the return pulse; coating thickness tester can set the thickness of coating or paint.
- This method works on a wide range of materials; including metals, plastics, composites, fiberglass and ceramics…
The advantages of this measurement method include:
- The measuring device only requires access to one side of the material; making it ideal for pipes, tubes, hollow castings; and other cases with limited access
- It does not destroy
- It offers a wide measuring range
- It provides quick results
- It is very easy to use.
Dry Film Thickness Gauge:
- When the coating thickness is measured as non-magnetic; but is applicable to magnetic substrates such as iron or steel. There are several types of magnetic thickness gauges that can be used to determine the thickness of a coating application.
A magnetometer is called a type 1 magnetometer:
- Use an estimate of the force required to pull the magnet away from the coated base to estimate the coating thickness.
- These thickness gauges contain a permanent magnet and a calibration spring with graduated scale.
- The thicker the coating, the less force is required to remove the magnet; The thinner the coating, the greater the force required. Therefore, the away drag force can be used to estimate the coating thickness.
Magnetic meter type 2:
- Works by measuring changes in the magnetic field generated from the probe when that device is placed on a coating (again used in the case of a non-magnetic coating resting on a magnetic base).
- Variation of magnetic field strength; will vary as a function of the distance between the magnetic substrate and the probe on the coating surface. Many of these devices use constant pressure transducers so that operator pressure on the coating is not a factor in coating thickness estimates..
- There is also a reverse coil magnetic tensile thickness gauge; has the same function as the magnetic tensile tester described above.
Other coating thickness gauges and tools:
- Three additional instruments that can be used to measure coating thickness are the magnetic induction instrument, the electromagnetic instrument and the eddy current thickness tester. The first of these three functions by measuring the change in flux density at the surface of a magnetic transducer when it is brought close to the surface of a coated steel surface. The measured flux density values can be used to estimate the thickness of the coating applied to the surface..
- Eddy current thickness gauge works on non-conductive coatings; applied to non-ferrous metal surfaces. These units generate high frequency alternating current which generates an alternating magnetic field. When the field approaches the surface; alternating magnetic field induces eddy currents on the surface; which in turn leads to the creation of the opposite magnetic field. The opposite field can be detected by the eddy current thickness gauge; and is used to estimate the coating thickness.
- Material thickness gauges and coating thickness gauges require calibration on standard material test pieces to ensure that the readings provide and maintain accurate values. For example, with an ultrasonic coating thickness gauge, the speed of sound energy will depend on the material it is traveling through.
- The table below shows the speed of sound in meters per second for different materials. This property must be stored and used to establish the pulse propagation time (and hence the material thickness).
Magnitude of the speed of sound for different materials
3040 – 6420
|3600 – 4200|
3200 – 3700
|3560 – 3900|
3950 – 5000
|3850 – 5130|
1160 – 1320
|4880 – 5050|
3300 – 5000
- Similarly, material thickness gauges are often sold with calibration blocks that can be used to calibrate the gauge by placing material of known thickness between contact pins or clamp arms to confirm the price reading value.
IV. Wire and metal thickness gauges
- Wire and sheet metal thickness gauges are metal models in which precise holes and slots have been cut.
- These thickness testers can allow users to easily assess sheet metal quantities for steel or iron and wire sizes for steel, aluminum, brass and copper wire. Gauges include American Standard Iron and Steel Gauge, American Wire Gauge (AWG) and American Steel Wire Gauge.
- The gauges allow the user to read the respective measurements directly from these samples and also access decimal equivalent sizes. Although referred to by the term thickness gauge, they differ in meaning from the other types of gauges mentioned in this article in that they validate more than one material to a standard size, as opposed to measuring a value whose magnitude is unknown.
***Videos of material thickness gauges, and surface coating thickness gauges are available at: Gmga Measuring Youtube.
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