The main tasks of the sheet heating unit in vacuum molding.
In the vacuum molding of plastic, when the sheet is heated, there are two classic problems that need to be solved:
the uniformity of heating in area and thickness of the sheet, taking into account the decrease in intensity from the edges to the center;
adjustable irregularity for tasks requiring obviously uneven heating of the sheet.
What are the main parameters of the vacuum molding machine affect the uniformity of heating or the ability to adjust the heating in accordance with your technical problem?
type of heating elements;
wavelength of infrared radiation of heating elements;
placement of heating elements in the area;
distance from heating plate to plastic sheet;
availability and technical characteristics of reflectors;
availability of power adjustment of each heater;
availability of temperature control of heating elements;
additional options to ensure uniform heating.
As you can see, there are 8 main factors that ultimately affect the quality of your product and, as such, the fundamental possibility of its production.
Since some of the points are a trade secret and a lengthy development process, in this article we will answer only a few items from the list above.
The main types of heaters in the vacuum molding of plastic.
In the vacuum molding of plastic, five basic types of heaters are used.
infrared ceramic heaters
infrared quartz heaters
European halogen lamps
Let's go through each type of heater and analyze its suitability for use in vacuum forming equipment. But first, I want to note that plastic has the largest molecular absorption of infrared radiation at a wavelength of 1 to 4 µ.
The pros and cons of various types of heaters on vacuum forming machines.
Open tenes have a very long wavelength, more than 6 µ, which is reflected in the heating of the plastic in thickness. They have a ceramic base and do not have a reflector. Their radiation is difficult to dissipate. Such heaters are not safe to install and use. Their only advantage is low cost. Today, they are not used by any manufacturer of vacuum molding machines, which in other ways did not prevent them from being installed in old machines made before 2000.
Can not be used in any vacuum molding machines, outdated heating technology.
In contrast to shadows, QGT lamps are too short in wavelength, less than 1 µ. This leads to a very bad warm-up of transparent and colored plastic. The poor quality of the spiral and the cheap materials from which the lamps are made do not allow the sheet to be heated evenly. A big mistake when installing such lamps is the lack of individual aluminum reflectors. Since KGT lamps have very directional radiation, it is important to disperse it skillfully, and the so-called “chandelier” where all the lamps are installed, cannot cope with this. Almost all plastic molding machines from the CIS and China are made without installing individual reflectors. As a result, such lamps are used only on home-made or low-cost machine tools and are suitable for molding simple products from dark plastic without high technical and aesthetic requirements to them.
Low heater cost
Short time to reach operating temperature
Can be turned off when idle
A good indicator of warming up of dark plastic in thickness
Technologically can not be used to heat the transparent and colored plastic
Demanding on infrared radiation scattering methods
Cannot be used in industrial vacuum forming machines.
Infrared ceramic heaters.
The wavelength of infrared radiation of ceramic heaters is from 3 to 6 µ. These heaters felt great in plastic molding until recently, since they have an average wavelength and dissipate heat very well even without installing reflectors. Many machines were equipped with such heaters, for a long time it was one of the relatively cheap, but at the same time sufficiently high-quality methods of uniform heating of plastic sheet. However, from their drawbacks, it is possible to distinguish a not very deep heating of the plastic in thickness, high power consumption with the inability to turn off in the rear position and a large inertia, which increases the changeover time and the machine to reach operating temperature. They show themselves well in many tasks, are often used in low-cost machine tools, but are not economically profitable with large molding cycles and thick-walled products.
High area heat dissipation
High plastic warming up thickness
Heat up any type of plastic
Relatively quickly reach the operating temperature (about a minute)
Can be turned off when idle
The relatively high cost of the heater and installation
Heavy enough that imposes technical conditions on the heating design
Halogen heating, earlier, was subject to the problems that we have already described in the section on KGT lamps, namely: short wavelength and problems in the molding of transparent and colored plastic. But today, halogen lamps from manufacturers such as PHILIPS (installed on machines of the P series) or OSRAM are free from these disadvantages. Modern technologies for the production of lamps have corrected many technical issues. The wavelength of such lamps is often stable and amounts to 1.2 µ. This allows you to penetrate deeper into the plastic than other types of heaters. Special additives to the thread of frying, spraying, innovative quartz glass, internal reflector, all this allows such heaters to perfectly heat both transparent and colored plastic. But their use imposes a number of technical requirements: each lamp must have its own individual aluminum reflector, the placement of heaters must be performed by a special method for uniform heating of the entire area of the sheet, the power change can be performed by the phase-pulse method, which is very expensive. The lamps themselves are also not a cheap pleasure in relation to other types of heaters. What is the result? Halogen heating in terms of productivity and depth of heating is the most efficient method of heating used in vacuum molding. At the same time, the cost of its installation is high, so it is often used in industrial vacuum molding machines (we have the P series) with full automation of the process, where reducing the molding cycle by 20% saves the client a lot of money.
Good area heat dissipation
The best indicator of plastic warming up in thickness
Heat up any type and color of plastic
Instantly reach operating temperature
Can be turned off when idle
Very demanding on the correct design of the reflector
Very demanding on the right location above the plastic
High heater cost
High cost of implementing heater power control
Summing up, it can be said that in professional and industrial vacuum molding plants, two types of heaters are now mainly used: quartz and halogen. Ceramic infrared heaters can be used if there are no serious requirements for the technical and economic model of production. KGT lamps are installed and used on installations of the budget segment and on self-made vacuum molding machines.
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