YIWU JINBAO HEATING PRODUCTS FACTORY

FURNACE ELEMENTS

SURFACE LOAD
The electrical and thermal load on the surface of a resistance wire or strip is expressed in W/cm2 or W/Sq. in. and has a bearing on the Temperature the element will reach and its length of life. When determining a suitable size of wire or strip, the surface load value therefore plays an important part.

When two elements of the same rating or wattage are compared, the one using the wire that carries a higher surface load can be made from a smaller quantity of wire, but will have a shorter life than the element using a wire of a lower service load. In other words, initailly there is saving of material on the case of higher surface load, but the element have to be replaced more often in view of its shorter life.

The actual permissable surface load is greatly dependant on the design of the heating elements, the ceramic supports and the furnace, but also on the operation of the furnace (atmosphere, frequency of switching etc.), so that it is impossible to give figures of generally validity.

The above mentioned factors are of even greater importance to the permissable surface of heating elements for domestic and industrial equipment. Although the figure of 5-6 w/cm2 (32-39 W/Sq. In) may be taken as normal, hotplate elements, for example, can be loaded considerably higher, and similar differences apply to domestic irons, ovens, grill elements, water heaters, soldering irons, immersion heating elements, air heaters, space heaters, etc.

Heating appliances vary so much in design and in their use of different construction materials that no attempt has been made to specify any figures.

By choosing construction materials such as high quality embedding cemments, insulators, high Temperature-resistant metal parts, which ensure an effective transfer of heat from the heating element to the medium being heated, the surface loading may be many times higher than is normally permissable with inferior materials, in view of the excellent heat resisting properties of the NIKROTHAL and KANTHAL alloys.