The surface load density of silicon carbide rod refers to the electric power borne by the unit surface area of the heating part of the rod in use, that is, the surface load

Under the same furnace temperature, if the unit surface load density of the rod is large, the service life of the rod is short,

Therefore, do not overload use. The relationship between load density and furnace temperature and rod surface temperature is as follows:

Proper selection of surface load density is an important way to reasonably use silicon carbide rod and prolong the service life of rod body. The following is the reference value of the maximum surface load density allowed by the silicon carbide rod body under different furnace temperatures at the rated service temperature of the surface.

2. Selection of silicon carbide rod specification and calculation of required number:The selection of silicon carbide rod specification shall mainly meet the requirements of electric furnace structure and size, furnace power, furnace temperature and temperature field distribution. When using, it shall be noted that it is conducive to external wiring and power regulation. The required number of silicon carbide rods can be calculated as follows: after the specification is determined, the load-bearing power of each rod is:

P1 = f * w (W)

F - surface area of heating part of each rod (cm2)

W - allowable load density of heating part under calculated heating temperature (w / cm2)

Quantity required:

P - furnace power U - voltage of series branch terminal (V) U - voltage borne by each rod (V)

Voltage borne by each rod: R - nominal resistance value of a single rod.

3. Selection of power supply equipment and connection mode of silicon carbide rod:

It is better to select the equipment with large voltage regulation range and stable and continuous voltage regulation, such as magnetic voltage regulator, thyristor AC / DC voltage regulator, etc. If the step-by-step voltage regulating transformer is selected, the transformer with small voltage level difference and many voltage regulating gears shall also be selected. The connection mode of silicon carbide rod elements can be series or parallel, and it is better to use in parallel. When used in series, the number of branches in series should not be more than 3.

5. Precautions for use and maintenance of silicon carbide rod

1. Before the installation and use of the silicon carbide rod, check the resistance (Ω) value marked on the cold end. If the handwriting is unclear, it must be retested. The test method is to energize the silicon carbide rod and heat it to the high temperature of 1050 ℃, the measured voltage and current, and the resistance calculated by Ohm's law. The test principle is shown in the figure below.

2. When the silicon carbide rod is used, each group of rods shall be subject to high-temperature resistance distribution, and the allowable difference of electrical value of resistance distribution is: ≥ φ 12mm bar resistance distribution, the tolerance of resistance value is ≤ 0.2 Ω, ≤ φ The resistance of 8mm rod is distributed, and the tolerance of resistance value is ≤ 0.5 Ω.

3. When the rod passes through the rod holes on both sides (or up and down) of the furnace wall, it shall rotate 360 degrees freely to prevent forced installation and knocking. Before installing the rod, it can be trial installed with an iron pipe with the same diameter as the rod.

4. The use of silicon carbide rod must be equipped with voltage regulator or silicon controlled voltage regulator, voltage, ammeter and automatic temperature control instrument. In the process of use, the resistance increases gradually due to the oxidation of the rod. In order to keep the furnace temperature normal, the service voltage should be increased. When the voltage is increased to the maximum limit of the voltage used and still can not meet the requirements, the furnace can be stopped to change the wiring mode of the rod and continue to be used.

5. When the new furnace starts power transmission, in order to prevent rod breakage, 1 / 2 of the rated power of the electric furnace shall be used for air transmission for a period of time. After everything is normal, the voltage shall be gradually increased, and the temperature shall be increased according to the heating specification of the electric furnace, so as to avoid breaking the silicon carbide rod due to high power.

6. The new furnace or electric furnace (kiln) that has not been used for a long time must be dried before use. When drying the furnace (kiln), try to use the old rod or other heat source as much as possible.

7. It is forbidden to overload the use of silicon carbide rod. If the rod is broken for some reason or uneven heating is found, and the part is incandescent or dark red, it indicates that the aging of the rod body is inconsistent, and the resistance difference between the sections is too large. The furnace should be shut down for maintenance and replacement. It is best to replace all new rods. If some new rods or single rods are replaced, the load will be unbalanced and the furnace temperature will be uneven due to the improper matching between the resistance of the new rod and the resistance of the used rod. Due to the large resistance difference, the rod temperature is also related, which will seriously affect the service life.

8. If water is discharged during the heating process when firing the device or material factory, the resistance furnace (kiln) used shall be provided with an exhaust hole to eliminate the water or other waste gas in the furnace (kiln), so as not to affect the service life of the rod.

9. Pay attention to moisture during the storage of rods. In case of deterioration and deliquescence at the aluminum spraying place at the rod end, the aluminum can be sprayed again after surface treatment. If there is no aluminum spraying condition, wrap several layers of aluminum foil in the aluminum spraying section of the rod.

10. The silicon carbide rod is hard and brittle. Don't be careful during transportation, unpacking, installation and replacement. Handle with care and avoid mechanical beating to avoid rod breakage