Types and rules for using paint thickness gauges
Content
When buying a used car, it can be difficult for the buyer to correctly assess its condition. Behind the beautiful wrapper can hide serious defects and damage resulting from an accident, which the seller may be silent about. A special device - a thickness gauge - will help to reveal the deception, assess the real state of the body and find out the thickness of its paintwork.
What is a thickness gauge
The thickness of the paintwork (paintwork) is measured in microns (1 microns = 000 mm.). For a better understanding of these quantities, imagine a human hair. Its average thickness is 1 microns, and the thickness of an A40 sheet is 4 microns.
The thickness gauge measures the distance from the metal to the gauge using electromagnetic or ultrasonic waves. The device detects the wavelength and shows the result on the display.
Thus, it is possible to determine the repainted and putty parts after repair, knowing the thickness of the paintwork of a particular model. The average value for modern cars is in the range of 90-160 microns. An error is allowed in different places of the body by 30-40 microns, the error of the device itself should also be taken into account.
Types of devices
There are a large number of types of thickness gauges. There are separate models for measuring the thickness of concrete, paper, rolled tubes or sheets. Four main types are used to measure paintwork:
- magnetic;
- electromagnetic;
- ultrasound;
- eddy current.
Magnetic
Such devices have the simplest design. There is a magnet in a small case. Depending on the thickness of the coating, the attractive force of the magnet will change. The results obtained are transferred to the arrow, which shows the value in microns.
Magnetic thickness gauges are inexpensive, but they are inferior in measurement accuracy. Shows only approximate values and only work with metal surfaces. The cost of the device can start from 400 rubles.
Electromagnetic
An electromagnetic thickness gauge works in a similar way to a magnetic thickness gauge, but uses electromagnetic induction for measurements. The accuracy of such meters is higher, and the cost is quite acceptable, about 3 thousand rubles. Therefore, these devices are more common among motorists. Their main disadvantage is that they can only work with metal surfaces. They do not measure the coating on aluminum or copper parts.
Ultrasonic
The principle of operation of these thickness gages is based on measuring the speed of passage of ultrasonic waves from the surface to the sensor. As you know, ultrasound passes through different materials in different ways, but this is the basis for obtaining data. They are versatile because they can measure paint thickness on a wide variety of surfaces, including plastic, ceramic, composite and metal. Therefore, such devices are used at professional service stations. The disadvantage of ultrasonic thickness gauges is their high cost. On average, from 10 thousand rubles and more.
Eddy current
This type of thickness gauge has the highest measurement accuracy. LKP measurements can be carried out on any metal surface, as well as on non-ferrous metals (aluminum, copper). Accuracy will depend on the conductivity of the material. An EM coil is used, which creates vortex magnetic fields on the surface of the metal. In physics, this is called Foucault currents. It is known that copper and aluminum conduct current better, which means that these surfaces will have the most accurate readings. There will be an error on the hardware, sometimes significant. The device is perfect for measurements on an aluminum body. The average cost is 5 thousand rubles and more.
instrument calibration
The instrument must be calibrated before use. This is very easy to do. Along with the device, the set includes reference plates made of metal and plastic. The instrument usually has a "cal" (calibration) button. After pressing the button, you need to attach the thickness gauge sensor to the metal plate and reset it to zero. Then we put a plastic one on the metal plate and measure it again. The thickness of the plastic plate is already written on it. For example, 120 microns. It remains only to check the results.
Small deviations of a few microns are allowed, but this is within the normal range. If the device shows the correct value, then you can start measuring.
How to use the thickness gauge
Find out the factory thickness of the car paintwork before measuring. There are many data tables on the Internet. Measurements should be started from the front wing, gradually moving along the perimeter of the body. More carefully check the areas prone to impacts: fenders, doors, sills. Apply the sensor to a clean and level body surface.
A reading above 300 µm indicates the presence of putty and repainting. 1-000 microns indicate serious defects in this area. The surface was straightened, putty and painted. The car may have been in a serious accident. After some time, cracks and chips may appear at this place, and corrosion will begin. By identifying such areas, past damage can be assessed.
This is not to say that a car with paintwork repair does not need to be bought. For example, a reading above 200 µm often indicates removal of scratches and small chips. This is not critical, but it can significantly bring down the price. There is an opportunity to bargain.
If the indicators are significantly lower than the factory ones, then this indicates that the master overdid it with abrasive polishing when removing scratches. I removed a layer of paintwork that was too thick.
You also need to understand what type of device you have in your hands. The electromagnetic thickness gauge does not work on plastic. It will not work to measure the paintwork on the bumper. You will need an ultrasonic device. You also need to know if there are aluminum parts in the body.
You don't have to buy a new appliance if you don't use it often. The thickness gauge can be rented for a fee.
The thickness gauge allows you to assess the condition of the paintwork of the car body. Different types of instrument have different accuracy and capabilities. For their own needs, an electromagnetic one is quite suitable. If you need a more complete examination of the body, then you should contact the professionals.
