application notes kanthal super …. automation srl application note-kantal super molibdenum v 1 2...

USER’S MANUAL V1 - Rev. 01/2002

CD Automation S.r.l. Via F.lli Cervi, 42/44 20020 Cantalupo di Cerro Maggiore (M) - Italy Tel +39 0331 533512 – Fax +39 0331 533516 e-mail: [email protected] web: www.cdautomation.com

APPLICATION NOTES

KANTHAL SUPER MOLIBDENUM

DI SILICIDE MoSi2

C.D. Automation srl Application Note-Kantal Super Molibdenum V 1

www.cdautomation.com 1

KANTHAL SUPER MOLIBDENUM DI SILICIDE MOSI2

It’s an electric heating element material for use in industrial and

laboratory furnaces. It can be used in air to heat furnaces to a

temperature as high as 1850 °C.

These resistance has a particular feature

• The resistivity of Kanthal super element increases sharply with

temperature and when is cold can have a current that is up to 17

times, the nominal current if is not limited. It has a strong positive

coefficient of resistance 17:1 from ambient to working temperature

• Thus a current limit thyristor unit with phase angle must be used like:

• CD 2200 – CD 3200: for one phase loads

• CD 3000E – MULTIDRIVE: for three phase loads

• As Kanthal Super elements

do not increase in resistance

with use, there is no need

for a voltage reserve, and

should one fail, it may be

replaced without affecting

the others in circuit.



• These Kanthal Super elements are fragile at ambient temperature

and soft when are working at high temperature.

• MoSi2 elements are manufactured in the form of giant hair pins. The

force between the arms due to current flowing is proportional to the

square of current. When cold, if current is not limited, the force can

reach 100 times the normal one damaging the elements.

• It’s also necessary to use Phase Angle plus current limit to reduce

the thermal shock that can damage the furnace building materials.

• Due to this reasons also if we size a thyristor unit or a contactor to

supply cold elements we can damage them and the furnace building

materials. In the past when where not used thyristor units was

necessary to use multi-tapped or continuously variable transformers

and, in this case, human errors in forgetting part of the start

procedure was possible. With thyristor every think is done

automatically.



IMPORTANT

With MoSi2 elements due to the very low cold resistance the inrush current

is very quick so we suggest:

• Soft start (setted ≅ 2 sec)

• Current limit

• Phase Angle Firing

CD Automation Thyristor unit can accept an external current limit profiling

signal. This is an important feature because is possible to have a density

of circulating current up to 1200°C and after a linear decreasing up

1700°C.

For example it’s possible to use:

20W/cm2 from O : 1200°C

10W/cm from 1200 : 1700°C

This external signal can be given by a temperature controller with

retransmission of Process Variable.

The controller can be configured by front to have

From 0 : 1200°C → 10V Retransmission

From 1200 : 1700°C → 5V Retransmission

This output from controller can be connected on the external current

profiling of CD Automation Thyristor Unit.

This feature is also known as Dallas profiling.



L2 or N

L1

FiringCircuit

Main Supply

CurrentLinitProfiling

1200

CurrentLimit

V

1400



Sometimes the elements MoSi2 must be supplied at low voltage via a

transformer that can be one or three phase, depending on load

configuration.

There are no particular problems for thyristor units and when a

transformer is coupled with MoSi2 and the thyristors are connected on

primary, use the same precaution mentioned above for the MoSi2 powered

directly.

If a three phase transformer is used the voltage on the three phase must

be keepad balanced and this will lead certainly to an imbalance of

currents.

Power factor is low when the voltage is low with cold resistance and

increase with resistance value of element.

application notes kanthal super …. automation srl application note-kantal super molibdenum v 1 2...

Documents