title
top
R&D
profile
products
heat
stainless
MO
nickel
FAQ
contact
faq

Q&A_title

1. Q What kind of materials (symbols) are used for electical heating wires ?
A Ni-Cr series alloys and Fe-Cr-Al series alloys are mainly used.


2. Q What is the advantage or disadvantage depending on the materials ?
A We will briefly show you them in Table 1.

Table 1
Series
Advantages Diadvantages
Ni-Cr series alloys
Good resistant to oxidation at high temperature in air.
Durable strength at high temperature.
Good weldability.
Low resistivity (compared to Fe-Cr-Al series).
Poor resistant to sulphuric gases or substances.
Possibility of green rot decay.
Fe-Cr-Al series alloys
High resistivity
 
Good resistant to oxidation at high temperature in air.
Low strength at high temperature
(compared to Ni-Cr series)
Poor resistant to corrosion at room temperature in air.


 
3. Q For what sort of applications are they usually employed?
A They are widely employed as a most important element in domestic appliances as well as heaters in industrial heating devices.


4. Q What do you mean the maximum operating tempearture of NCHW1 is 1150°C in your catalogue ?
A This is not the temperature of surroundings but the surface temperature of heating element itself of which diameter is 3 mm.


5. Q Teach us the ways to know the expectant life of heating elements.
A Life value of wires is tested in accordance with JIS C2524. Briefly speaking, it is an accelerated test method, employing a test piece of 0.5mm in wire diameter. Heating and cooling cycle consists of 2 minutes with power on and 2 minutes with power off.


6. Q Teach us the relation among the diameter, conductor resistance and resistivity of wire.
A The relation is given as , where, conductor resistance is R (Ω/m), resistivity is ρ (µΩ·m ) , diameter is d (mm) . A simple and fundamental equation, but this is a very convenient, easy-to-use formula applicable to all the round metallic wires.


7. Q What is the coefficient of resistivity with temperature ?
A This is an increasing tendency of resistance with temperature.
Generally speaking, they are big increase in pure metals, meanwhile relatively small increase in high alloys such as heating wires. If accurate wattage is necessary, test the finished device (wires which was set in the apparatus) to determine proper allowance for rise in resistance with temperature.

 
8. Q Teach us the simple way to draw more power of heater.
A On such an occasion, it can be done by reducing a length of the element or by increasing a diameter of the element.


9. Q What is the matter that needs attention in designing a heating device, especially from the view point of durability or thermal expansion of element in hot ?
A Well, trying to design elements so that they will be free to expand or contract is very important matters.


10. Q Teach us the ways of jointing elements and terminals in case of domestic heating appliances.
A Welded, brazed or spot-welded joints are preferable. But a pressed or pressure jointing methods can also be applyed if they are thoroughly tested prior to production.


11. Q Can I ask for a more information ?
A Yes. Please contact us when you need any assistance. Our technical knowhows and experiences will be useful in solving your problems.


©SILVER KOHKI CO.,LTD.All Rights Reserved