Corrugated board temperature measurement artifact

According to China Packaging News, achieving proper paper temperature throughout the corrugated production process is critical to the production of smooth, well-bonded paperboard. For instant measurement of paper or board temperature, there is no better instrument than a handheld infrared (IR) pyrometer. Moreover, for machines without automatic temperature control, non-contact pyrometers are the only practical means of controlling temperature. Safety is another important advantage of using infrared pyrometers. Because it does not need to touch the moving parts and there is no danger of burns, the temperature can be measured. Infrared guns are now well-established instruments in cartons. They are extremely useful tools that are easy to use and inexpensive. But their function is often misunderstood.

How do they work

As we all know, when iron is heated to a very high temperature, it will be incandescent to almost white, so there is a word called "white hot metal" energy emitted from the metal to become visible light. When the temperature drops, the metal will appear yellow and then red. When the temperature drops again, it is no longer dazzling but still radiates energy like light. This light has a lower frequency than red light and is invisible to the human eye. So it is called infrared. Hot objects radiate energy in the form of infrared radiation.

Infrared guns do not measure temperature directly; they simply measure infrared radiation. This distinction is important because although the total amount of infrared radiation emitted by an object is proportional to its temperature, it is very different from the emissivity of its surface.

Know that any particles or vapors like dust and smoke can affect the accuracy of the readings.

How the surface affects the reading

Emissivity is the effectiveness of a surface emitting energy in the form of thermal radiation (infrared rays), expressed as a percentage. A "black body" (all objects that absorb radiant energy) is a theoretical standard with an emission coefficient of 100%. The total amount of infrared radiation on any particular surface will vary depending on its color and surface smoothness. The brightest surface radiation is the smallest and the coarse dark surface radiation is the largest.

To illustrate how much the surface influences the infrared pyrometer readings, we can take a piece of steel piece with a flat black paint on one side and a bright one on the other. A contact pyrometer measured both sides at a temperature of 350°F. The infrared gun confirms this temperature on the black painted side, but on the bright side, the reading is much lower (below 200°F) because of the lower emissivity of the reflective surface. Therefore, before using infrared guns, use flat black paint as an ideal “equalizer” to check the temperature of any metal surfaces such as hot plates and preheaters.

If you know the correct emissivity of the target object, the emissivity of some infrared guns can be adjusted. The emissivity of non-adjustable infrared guns is generally set at 95%, just like flat black paint. Fortunately, the emissivity of the leather card is also 95%, so it is very convenient to use in the carton factory.

Using infrared pyrometer

Although infra-red pyrometers are sometimes referred to as laser thermometers, the laser is actually not involved in the measurement of temperature and is just a target orientation instrument to show where the infrared gun is pointing.

The infrared gun averages the temperature within the image circle it is aiming at. If you aim at the edge of the web, you can get an average of the web and the surface temperature behind it. Also, the farther away from the infrared gun, the larger the dot, and the infrared gun sweeps out a cone. In order to reduce this effect, the infrared gun should be as close to the paper as possible and preferably kept the same distance while ensuring safety.

The aim of the infrared gun is to be at right angles to the target as much as possible, because if it is at an oblique angle, the dots will be elliptical and increase in size. Therefore, machine readings cannot be separated. Be aware that any particles or vapors like dust and smoke can affect the accuracy of readings. Keep the lens clean, otherwise it will affect the accuracy. Remember that using an infrared gun around a machine that uses steam as a single-sided machine will condense water vapor on the lens. Like all precision electronic equipment, it is necessary to prevent the infrared gun from falling.

For diagnosing problems with corrugated board machines, ensuring that the machine is within the required temperature range, infrared pyrometers are a valuable tool.

Side note

Thermal imaging cameras work in the same way as infrared guns. They collect temperature through a large number of grid-like sensors. These collected temperatures form a temperature map. Each temperature is assigned to a color, and the color typically represents a gradual change from light yellow to very hot to red representing moderate heat and blue to a lower temperature. The color dots “draw” a temperature map, just like the pixels on the computer screen together form an image.

Simple tool

For diagnosing problems with corrugated board machines, ensuring that the machine is controlled within the required temperature range, infrared pyrometers are valuable tools. Effective use of this simple tool can increase the reliability of the measurement. A deeper understanding of how it works helps to use it accurately.