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Königstrasse 10 C 70173 Stuttgart |
Phone: +49 (0) 711 222 54 491 Fax: +49 (0) 711 222 54 200 |
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Königstrasse 10 C 70173 Stuttgart |
Phone: +49 (0) 711 222 54 491 Fax: +49 (0) 711 222 54 200 |
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DuraWatt: cartridge heaters
Maxiwatt compressed cartridges
High watt density cartridges.
They provide a great uniform distribution of heat, and are hermetically manufactured, which increases considerably the long life of the resistance as well as prevents the oxidation of the heater wire even at high temperatures. Over 8000 measurements in high density available.
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Internal complements
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Technical data
Heat intensity Not exceeding 258W/inch2 (advisable) Power Depends on the dimension Escape of current (when cold) <=0.1mA to 242 v. Insulation (when cold) 5 Min Ohms 500 Watts minimum Dielectric strength 1500v. 1/sec Working temperature 750ºC max. Length tolerance +/-1.5% Diameter tolerance -0.00079 to -0.0024 inch Cut of connection tolerance +/-0.59 inch Power tolerance (w) + 5 % - 10 % Cold areas Depends on length and diameter 0.20-0.98 inch
Manufacture
Durawatt cartridge heaters are made of means of compression for all their components, with the purpose of lengthening their working life.
The conductor wire is wound spirally on hard ceramic body into which the conductor lead is inserted, with no connection (sometimes, a connection may occur on the outside of the cartridge). Ceramic discs and heads are inserted to obtain insulation and protection. Everything is coated with checked pure granulometric magnesium oxide to ensure a total full cartridge.
Later a process of compression and another of correction the surface is carried out until the required measurement is calibrated. Finally, a strict quality control is carried out to guarantee the best performance of the cartridge.
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| The unique manufacture system of Maxiwatt allows to achieve the perfect concentricity possible and in conjunction with its electronic system of the space between the spirals, guarantees the same temperature around the whole perimeter and length of the cartridge, thereby obtaining an uniform and long lasting temperature. |  |
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Use
They are able to resist the toughest working conditions, such as vibration, moisture, fluid, spills, frequent expansion and where temperatures of between 400ºC and 750ºC are required, or temperatures within a limited space.
Applications
Specifications: to be considered
When solids, gases and fluids are to be heated by elecric energy the process is generally carried out by conduction. It is only possible to transmit heat quickly by conduction if the producer of the heat (the cartridge) is in direct contact with the receiver of the heat (any solid, gas or fluid).
When heating occurs, the molecules expand and move faster, producing a distribution of heat to the colder body until their temperatures level is equal.
If there is mould on which to drill in order to house a cartridge heater, and where the mould is not means to be in direct contact with the whole cartridge heater, the transmission of heat by conduction would occurs, due to the fact the air molecules would not transmit the energy required to heat the mould. The heat would not be distributed but would remain within the cartridge heater, producing overheating of the same, which would cause a reduction of the dielectric strength between the heating wire, the power conductors, and the weakening of the metal shield, resulting in a shortcircuit. Is therefore, very important the adjustment of the cartridge with the mass to be heated.
Power
When dealing with high-density cartridge heaters, the exact amount of the required power must to be considered for a correct functioning and useful life of the cartridge heater.
Maxiwatt cartridge heaters are designed in a way that considers the natural aging of the heater wire and its nature, matching with the nominal power of the cartridge heater.
The coincidence of the real power at rated power is made through a selective process which only chooses only those cartridge heaters having a power tolerance corresponding to 7% of the rated power.
Powe at. Cold state Hot State Power at. D. Y Long. 230 V. Ohms Value Ohms Value 230V. Variation 10x80 315 W 167.94 174.15 303.76 W -3.7 10x100 400 W 132.25 136.34 388.00 W -3.1 10x130 500 W 105.80 108.55 487.33 W -2.6 12.5x80 400 W 132.25 136.21 388.37 W -3 12.5x100 500 W 105.80 108.02 489.72 W -2.1 12.5x130 800 W 66.13 67.32 785.80 W -1.8 16x80 630 W 83.97 85.64 617.97 W -2 16x100 1000 W 52.90 53.69 985.29 W -1.5 16x130 1100 W 48.09 48.52 1090.27 W -0.9 20x100 1000 W 52.90 53.44 989.90 W -1 20x130 1250 W 42.32 62.65 1240.33 W -0.8
Stainless steel 321: cover
The stainless steel 321 cover provides the highest quality to the manufacture of cartridge heaters. The materials which can be used in their manufacture are limited due to the strain caused by constant expansion due to the cooling and heating of the cartridge heater, the lack of a metal cover, which causes oxidation, and abrasive action. Stainless steel has been shown to be the most suitable material for the construction of cartridge heaters.
Comparison of stainless steels.
Power at. Cold state Hot State Power at. D. & length 230 V. Ohms Value Ohms Value 230V. Variation 0.394x3.150 315 W 167.94 174.15 303.76 W -3.7 0.394x3.937 400 W 132.25 136.34 388.00 W -3.1 0.394x5.118 500 W 105.80 108.55 487.33 W -2.6 0.492x3.150 400 W 132.25 136.21 388.37 W -3 0.492x3.937 500 W 105.80 108.02 489.72 W -2.1 0.492x5.118 800 W 66.13 67.32 785.80 W -1.8 0.630x3.150 630 W 83.97 85.64 617.97 W -2 0.630x3.937 1000 W 52.90 53.69 985.29 W -1.5 0.630x5.118 1100 W 48.09 48.52 1090.27 W -0.9 0.787x3.937 1000 W 52.90 53.44 989.90 W -1 0.787x5.118 1250 W 42.32 62.65 1240.33 W -0.8
Total insulation
Insulation is made with pure Magnesium oxide, and this material is the most suitable and used for insulating the heating wire and the conductor lead against the current of the sheath of the cartridge. When the space between the heating wire and the protecting sheath is too short, an insulator is required, this should be composed of the best qualities: purity, high thermal resistance, maximum melting point, uniform and exact compression, perfect thermal conductivity, etc, so that the best insulation is obtained.
Control of the working temperature is essential. It must never exceed the working limits of the cartridge. It is very important to store the cartridge in a dry place because magnesium oxide is very hygroscopic. Just a few drops of water particles are enough to weaken considerably the insulating capacity of magnesium oxide.
Ni-Cr 80/20 heater wire
The most important element for ensuring the long life of the cartridge heater is the heating wire used in its manufacture. Maxiwatt uses the best to be found anywhere in the market. After extensive research and years of experience it has been shown that a heating wire made of Ni-Cr 80/20 is both efficient and resistant to the formation of metallic coating brought at out by oxidation. As the austenitic combination of nickel and chromium lacks iron, it is the most recommended for the heater wire.
Specific weight 8.3 Thermic conductivity 20ºC 0.35-0.0031 Specific heat 20ºC 0.11 Melting point 1400ºC Resistence to traction 65-80 Elasticity limit 30-35 Brinell hardness 130-150 Lengthening in % over 7,874 mm of lenght 25-30 Contraction in approximately % 60-75
Maximum temperature of continuous working 1200ºC Specific existence 20ºC Chmx (min. 2/m) 1,09
+/-5%Linear expansion coefficient x 10-6 20-250ºC=15
20-1000ºC=18Composition Ni80 Cr20 Density g/cm3 835 Structure austenitic
Conductor lead
For the induction of electricity a nickel cable (sheathed by fibreglass) is used. It is coated with silicone and fire-proof glazing. The cable wires are turned. Sometimes, the charge of the cartridge prevents the use of this type of connection. At the end, special procedures are used: threaded outlets with bolts, opposite outlets, etc.
The different types of connection are shown on protections section
