The present invention relates generally to methods and apparatuses for performing an infrared treatment, and more particularly, to methods and apparatuses for performing an infrared treatment on extruded plastic and elastomeric products in an infrared oven.
It is known in the prior art to heat plastic or elastomeric product that comes out of the extruder to cross-link the plastic or elastomeric product to obtain a desired effect that changes the capabilities or properties of the product (e.g., increases the strength of the product, changes the product to a solid, etc.). Furthermore, it is known to perform this heating of plastic or elastomeric product using infrared radiation and to use a wavelength of the radiation that penetrates inside the wall of the product in such a way that the heating takes place at the same time in all the depths of the product.
One prior art method is disclosed in patent publication GB 2283 489. In this patent publication, the material is cross-linked by using infrared radiation in such a way that the temperature obtained by the radiation corresponds to the wavelength demanded by the cross-linkage reaction.
A similar prior art method is presented in the patent publication FI 109706. According to this method, an additional material or additive that is used for modifying either physically or chemically the properties of the plastic material is decomposed utilizing infrared radiation, wherein the wavelength is selected so that the radiation penetrates through the plastic material itself as efficiently as possible, but is also absorbed by the additional material, thereby heating and decomposing the additional material.
The greatest disadvantage of the prior art methods is that the infrared radiation inevitably consists of a distribution of different wavelengths. It is also inevitable that a part of this wavelength distribution follows approximately part of the curve of Gauss, and the wavelength distribution has rays of long wavelengths that do not penetrate into the material. Rather, the long wavelengths get absorbed by the surface of the product, causing inconvenient overheating of the product. Overheating causes the surface of the product to become oxidized or to react in some other unwanted way.
Attempts have been made to solve this problem. For example, U.S. Pat. No. 6,106,761 (“the '761 patent”) addresses these issues by eliminating the infrared rays that correspond to absorption peaks of the material to be heated in order to minimize overheating of a surface of the material. The '761 patent notes that eliminating these rays may be accomplished by filtering out the unwanted rays. The filtering process disclosed in the '761 patent is very difficult to undertake because, when filtering out certain wavelengths, the filter itself gets overheated and becomes a source of infrared energy that sends the same filtered wavelength to the material, thus overheating the material.
One solution that attempts to avoid the overheating caused by filtering is cooling of the surface of the material during the infrared treatment. This can be done, for example, by blowing cool gas, like air, on the material. The greatest disadvantage of this method is that the air also cools the infrared lamps and reduces the capacity of the lamps. Another disadvantage is that dirt and other debris splashes from the material to the lamps and, thus, the lamps get dirty, which again reduces the capacity of the lamps.
It is very important for the irradiated material to be heated uniformly across an entire cross-section of the material. A method and apparatus for performing an infrared treatment, for example, on plastic and elastomeric products, that overcomes all of the previous obstacles and that uniformly heats the product is therefore desired.