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Is it possible to heat dies (molds) with infrared?

Yes. Actually, I have given the shortest answer to this question. I will try to detail this answer in the rest of my article. But first, what is infrared? It would be rational to find an answer to questions such as how it heats.

Infrared die preheating, infra red die preheating, aluminum extrusion, forging

What is infrared?

Infrared (infrared, infrared ray, infrared or IR) is the name given to energetic radiation in the region between 700 nm and 1 mm wavelength, located between the visible light and microwave regions of the electromagnetic spectrum. The micron unit can also be used to measure wavelength.

Infrared, radiation, x-rays
Milton spectrum diagram showing the type of radiation, wavelength, frequency, blackbody emission temperature. Adapted from EM Spectrum3-new.jpg, a NASA image.

How does infrared heat?

In fact, it would be good to talk about the principle of the sun heating us. On a winter day, as long as the warm rays of the sun reach us directly, the cool weather does not bother us.

Infrared radiation crosses the distance between the sun and the earth almost without loss and turns into heat when it hits surfaces. In fact, unlike UV or X-ray radiation, the long-wave infrared range has a particularly positive effect on humans.

In industrial infrared heating, heat is transferred from the source to the part (whatever is heated) by invisible electromagnetic energy. When infrared energy reaches the surface to be heated, the molecules inside the heated substance vibrate intensely and turn into heat energy. The heat then moves through the part by conduction.

In infrared used in industry, analysis of the wavelength absorption characteristics of the material to be heated is the key factor in heater design. The basic infrared theory is that the air between the heat source and the product does not need to be heated. Therefore, wavelength selection is important.

For example,

The maximum absorption emission of oxidized steel is 80% at 3 micron wavelength, 4 micron wavelength this drops to 60% and 5.5 micron wavelength has 45% absorption which increases the reflection energy.

In other words, the energy that cannot be absorbed by the oxidized steel is reflected and considered as waste energy in process heating. A heater that emits a specific wavelength will have positive results such as maximum efficiency and energy savings.

A heater using wavelength energy focused on 1.2344 (H13) steel material can achieve 90% radiation efficiency. This is the key to fast and homogeneous heating.

Why is die preheating necessary?

Preheating the mold in shaping processes such as extrusion, forging, metal or plastic injection is a basic requirement for both a smooth process and a healthy mold.

Molds must be kept at optimum temperature regardless of the forming process. While the hardness of an overheated mold decreases, a mold that is not heated enough cannot show the expected toughness behavior and breaks.

A die that is not at the appropriate temperature has a bad effect on the extrusion speed, forging form and metal injection solidification process.

Preheating is also a critical process when welding is required for mold repair and maintenance. The mold must be heated properly before the welding process in order for the weld to adhere to the substrate material and to prevent interface cracks.

Mold heating can be done in ovens or with open flame torches, depending on the application. However, it would be rational to choose an oven for effective heating.

Die preheating ovens according to heating types:

  1. Heating with natural gas

  2. Conventional electrical resistance

  3. electric infrared

Benefits of infrared die preheating:

  1. Reduced energy consumption by more than 50%

  2. Fast and homogeneous heating

  3. Less oxidized mold surfaces since there is no convection (circulation) fan in the oven

  4. Cold start. Since the heat energy is directed directly to the part, the mold preheating oven does not need to be kept warm

  5. Optimum mold preheating temperature. Preventing overheating

When evaluated considering the total cost of ownership, infrared ovens can pay back in a period of 18-24 months, depending on the mold preheating technology they replace.

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