PIROWATT Cartridge heaters0 pages

Application: Heating of Moulds PIROWATT High Power Cartridge Heaters Figure 1 GENERAL CHARACTERISTICS These heaters are characterised by a high specific power and a high reliability: These qualities are essential in the applications for which they have been conceived. These heaters can reach specific powers as high as 50 W/cm2 and operating temperatures up to 750 °C. PIROWATT cartridge heaters power supply cables are embedded into the heater head (see Figure 1) without junctions or stiff parts: this manufacturing solution has eliminated all the problems and allows to limit the non-heating ("neutral") section to a 3 - 4 mm. These heaters undergo final acceptance testing as required by EN 60335-1 specification and are manufactured to comply with VDE 0720 specifications. APPLICATIONS These heaters are used in the heating of moulds, plates, injection nozzles and hot-channel injection nozzles. They can be employed, inserted into appropriate slots, in the heating of all metallic masses, provided that the operating temperature does not exceed 750 °C. TECHNICAL DATA (see Figure 1) 1. METALLIC SHEATH made of stainless steel suitable for high temperatures. The sheath surface is ground and the bottom is water-tight and corrosion resistant 2. ELECTRICAL INSULATION made of highly concentrated pure magnesium oxide 3. RESISTIVE WINDING made of Nickel/Chrome 80/20 4. POWER SUPPLY provided by a couple of pure nickel conductors, with a silicone-impregnated fibreglass insulation. DIMENSIONS PIROWATT cartridge heaters are available on stock in several dimensions which differ in diameter and/or length (see table below). For all heaters the dimensional tolerances are fro00°82for the nominal diameter and ± 1.5 % (with a maximum of 2 mm) for the length. The nominal length is the real cartridge length. POWER PIROWATT heaters are normally manufactured with a specific power of about 25 W/cm2 but it is possible to manufacture them up to 50 W/cm2. PIROWATT heaters heating power is constant even if they belong to different production lots: the nominal power is guaranteed with a tolerance of ± 10 %. Thanks to this characteristic it is possible to insure an overall stability of the heating system also after the replacement of several heaters. COUPLING SLOT PIROWATT heaters shall be inserted into appropriate slots which have been machined inside the mass to be heated. A Slots surface finishing shall be very good for the coupling to be optimum: the presence of scores or grooves creates stagnant air pockets which, even if very small, insulate thermally the heater causing locally a strong increase of the temperature and a reduction of the heater life (see also Figure 2). 105 o 10* 10^ 10' 0,5 1 1,5 2 _Wire Diameter (mm)_ Figure 2: Nickel/Chrome 80/20 winding lifetime (in hours) as a function of the operating temperature and of the _wire diameter_ The cartridge heater, when hot, expands by few cents of a mm. Hence the tolerances on the slot dimensions is less important than the surface finishing quality. The best result is obtained with an H7 reamer. ELECTRICAL CONNECTION The connection to the power supply (monophase) is normally via a couple of nickel cables. Upon request, special cable terminals (see section "Special Constructions") can be provided. c/) c CD 2 O O 4 PIROWATT