THE UNIQUE PROPERTIES
- MOLY-D elements may be used up to a surface temperature of 1800 °C(3270 °F) in oxidizing atmospheres.
- Long service life and ease of replacement contribute to high furnace utilization and low maintenance costs.
- New and old elements can be use together and in series.
- Can dissipate high power loading.
- Can be use continuously or intermittently.
- Provide rapid furnace temperature ramping.
QUALITY AND PRODUCT SUMMARY
- Maximum Element Temperature --
1700 °C(3090 °F)
- General Applications -- Most types of industrial furnaces for heat treating, forging, sintering, glass melting and refining, and for use in radiant tubes.
- Maximum Element Temperature --
1800 °C(3270 °F)
- General Applications -- Laboratory furnaces,testing equipment,and high temperature sintering production furnaces.
MOLY-D(Molybdenum Disilicide Heating Element) heating elements are manufactured by powder metallurgy. They consist of molybdenum disilicide with additives that prevent recrystallization. Since MOLY-D is completely stable up to 1800 °C, it surpasses other heating element types for high temperature performance.
The resistance of MOLY-D to oxidation lies in the formation of an impermeable quartz, or glass-like protective layer which re-forms when heated if damaged in operation.
MOLY-D has a low specific electrical resistivity with a positive resistance-temperature characteristic as shown in figure 1.
It can be used at a very high watt loading compared to metallic heating elements.
Please refer to figure 2, for watt loading at various element temperatures. Because of its high temperature oxidation resistance, MOLY-D electrical resistance remains constant at constant temperature over its useful life. This permits the use of old and new elements together in the same furnace, even if series-connected.
Figure 1, Resistivity of MOLY-D elements MD-31 and MD-33
SERVICE LIFE & EXCHANGE
* The resistance of MOLY-D heating elements are not aged.
Main reason of uncontributed life service is tha mechanical breakage, when they are cooler in short time or sometimes power of electromagnetic.
* It is possible to exchange elements during operating.
This element is not aged. Please exchange only broken elements. This is our recommended characteristic and advantageous to MOLY-D heating elements.
As shown in Table A,below,maximum element temperature depends on the atmosphere within the furnace chamber. In air this is 1800 degrees centigrade.
Since element surface temperature exceeds furnace ambient in relation to the watt loading, careful attention must be given to these parameters for satisfactory element performance.
MOLY-D heating elements normally operate between1300 and 1750 Cent. (2372-3182 Fahr.). MOLY-D may be used below 1300 Cent. (2372 Fahr.) particularly for furnace atmospheres harmful to silicon carbide heating elements (e.g., sulfur dioxide, water-steam,etc.).
MOLY-D should not be used between the temperature range of 400 and 700 Cent.(752-1292 Fahr.), where a destructive low temperature oxidation may occur called pest.
MOLY-D heating elements are designed for use in oxidizing atmospheres. In addition, neutral atmospheres such as nitrogen, inert gases, CO and CO2 are not harmful to MOLY-D. Maximum element surface temperatures in various gaseous enbironment are given in Table A.
|MAXIMUM RECOMMENDED ELEMENT TEMPERATURES IN ATOMOSPHERES|
|Dry Hydrogen,dewpoint -80 Cent. (-112 Fahr.)||1150||2100||1150||2100|
|Moist Hydrogen,dewpoint 20 Cent. (68 Fahr.)||1450||2640||1450||2640|
|Cracked and partially converted ammonia(〜8%H2)||1400||2550||1400||2640|
ELEMENT TYPE AND DIMENSIONS
MOLY-D heating elements may be made in a variety of configurations. Most common is a two shank (U-shaped) element having terminal end twice the diameter of the heating section.
Please refer to Table B for sizes currently available. Since the cross sectional area of the terminal ends is four times that of the heating section, the exposed terminal ends operate at a low enough temperature to require no supplemental cooling if proper design criterial are used.
Maximum heating lengths at various element temperatures are shown in figure 3.
Four-shank-elements in the 6/12 and 9/18 diameters are also available. They are normally used in furnaces with a low chamber height where the elements would be mounted horizontally.
TABLE B SIZE AND GRADES AVAILABLE SIZE Heating
Grade 3/6 3 6 25 *MD-31
4/9 4 9 25 *MD-31
6/12 6 12 50 *MD-31
9/18 9 18 60 *MD-31
18/36 18 36 80 *MD-31
*Grade MD-31 - maximum element temperature 1700 Cent. **Grade MD-33 - maximum element temperature 1800 Cent.
Figure 3, Maximum recommended heating zone lengths at element temperatures for vertically suspended 6/12 & 9/18 elements.
Note : 3/6 and 4/9mm MD-33 elements are not normally manufactured with a Hot Zone(Le) longer than 400mm(15.8 in.).
Two-shank elements with straight terminals are defined by :
- Heating zone diameter, mm
- Terminal diameter, mm
- Terminal length, Lu, mm (in.)
- Heating zone length, Le, mm(in.)
- Center distance between shanks, A, mm(in.)
- The grade (MD-31 or MD-33)
Example in metric : MD 6/12 Lu=254, Le=560, A=50, Grade MD-33
Example in inches : MD 6/12 Lu=10, Le=22, A=1.97, Grade MD-33
TWO-SHANK BENT ELEMENTS
Elements with a bend are available in all sizes. Bends can be made in the Le or Lu at 45 or 90 degrees angles.
MADE TO INDUSTRY STANDARDS
MOLY-D heating elements are manufactured to industry established resistance values.
The same spacing, power ratings and voltages, used with other molybdeum disilicide elements can be used.
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