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 8.000 measurements in high density available.

• Long-life
• High temperatures
• Maximum watts capacity 40w/cm2

Internal complements

Technical data

Heat intensity	Not exceeding 40W/cm2 (advisable)
Power	Depends on the dimension
Escape of current (when cold)	<=0.1mA to 242 v.
Insulation (when cold)	5 mΩ at 500 Watts
Dielectric strength	1500v. 1/sec
Working temperature	750ºC max.
Length tolerance	+/-1.5% (min 1 mm)
Diameter tolerance	-0.02 to -0.06 mm
Cut of connection tolerance	+/-15 mm
Power tolerance (w)	+ 5 % - 10 %
Cold areas	Depends on length and diameter 5-25mm

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.

Welded watertight base (Tig) to resist pressure up to 60 kg/cm2. Calibrated stainless steel AISI 304/316/321/ INCOLOY. Ceramic disc insulator. Checked pure granulometric magnesium oxide. Nickel-chromium 80/20 heater wire. Melting point 1400º C. Ceramic core. Hard ceramic head. Conductor lead. Hard refractory paste. Conductor without connections.

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.

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

• Moulds
• Smelting of materials
• Heating of fluids
• Heat welding, etc

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.

	Power 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.

Steel	Steel	Steel	Steel
NORMA DIN	X5 CrNi 169	X10 CrNiTi 185	X5 CrNiMo 182	INCOLOY
NORMA AISI	304	321	316
FE	>72	>72	>67	>6/10
C	<=0.07	<=0.1	<=0.07	<0.2
Cr	17/20	17/19	16.5/18.5	14/7
Ni+Co	9/11.5	9/11.5	12/14.6	82
Mn	<=2.0	<=2.0	-	<=1
Mo	-	-	2.5/3.0	-
Si	<=1.0	<=1.0	<=1.0	<=1.0
P	<=0.045	<=0.045	<=0.045	<=0.5
S	<=0.03	<=0.03	<=0.03	<=0.03
Cu	<0.2	<0.2	-	<0.7
Ti	-	0.5	-	-

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 200 mm of lenght 25-30 Contraction in approximately % 60-75

Maximum temperature of continuous working 1200ºC Specific existence 20ºC (Ohm x mm2/m) 1,09 +/-5% Linear expansion coefficient x 10-6 20-250ºC=15 20-1000ºC=18 Composition 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