Hot Air Heaters for High Temperature
Special heater for silver brazing
Hot air heaters with long service life that can stably generate hot air of 1652ºF (900ºC).
The structural difference with the normal product is that this product uses a ceramic heating tube that reduces the surface load of the heating element by about 1/3 improving the heat exchange, and a special nozzle with less entrainment of external air in the nozzle.
The photo below is of a 100 V - 350 W heater based on this concept. The dimensions of the metal case are, external diameter ø19 mm, length approximately, 185 mm, and inner diameter ø5 mm, and there are multiple nozzles of ø1 mm.
When the air flow is set to 10 L/min, and the heater consumes a power of 300 W, hot air of approximately 1652ºF (900ºC) can be obtained. The heating element temperature at this time is about about 2012ºF (1100ºC)
The difference between the hot air temperature and the heating element temperature is only 392ºF (200ºC). This difference is 572ºF (300ºC) in case of normal hot air heaters indicating that the improvement in heat exchanged.
A hot air temperature sensor (K thermocouple)can be incorporated in this heater in the same way as other hot air heaters. However, consumption of the sensor at this temperature is severe and probably will expire in a relatively short period of time.
This sensor is used for setting the initial conditions, if the sensor will not be used after setting and the heater is operated then it can be used as it is.
However, if the temperature has to be monitored continuously during operations or the hot air temperature has to be controlled using a temperature controller, then an external sensor has to be inserted near the hot air outlet without using the built-in sensor or the material of the built-in thermocouple has to be changed to R (platinum-based). Changing to R increases the cost, but production is easy.
||Inner diameter of the main nozzle is ø5 mm. The diameter of the surrounding sub-nozzles is ø1.0 mm.
The low-speed high-temperature air blown from the sub-nozzle wraps the mainstream flux coming from the main nozzle, and prevents cold outside air from mixing with the mainstream flux.
Therefore, the mainstream flux cannot be cooled by the outside air and travels far while remaining hot.
If the sub-nozzles are not present, back flow of air from the outside up to the inside of the nozzle takes place, cooling the hot air. A large temperature distribution was found to occur when measuring inside the nozzle of the older products because of this local back flow.
|Silver brazing special heater 100 V - 300 W type, metal case ø19 mm x 185 mm 10 L/min, built-in temperature sensor approximately 1742ºF (950ºC)
Hot air temperature in the nozzle reaches more than 1652ºF (900ºC). Silver solder has a working temperature of 1202ºF (650ºC) and melts easily under this condition.
Generally used silver solder has a working temperature of 1382ºF (750ºC) and barely melts. Therefore, when working with this heater, pasty silver solder with a working temperature of 1202ºF (650ºC) is preferred.
As this is a heating wire with low surface load, the hot air temperature rises slowly after the power supply is turned ON. The time required is approximately 10 minutes. If you permit the application of over voltage using a temperature controller during the temperature increase process, the increase will be faster bit may reduce the service life to some extent.
| Slightly larger silver brazing special heater
Metal caseø22 mm x 300mm
Setting conditions Air flow rate : 22 L/min 98 V-562 W
Temperature of built-in temperature sensor 1778ºF (970ºC)
Heating element temperature 2066ºF (1130ºC)
Maximum hot air temperature at a distance 10 mm from the nozzle is about 1652ºF (900ºC)
|Silver brazing special heater of a little high power 100 V - 600 W type.
Main nozzle is approximately ø8 mm, and diameter of sub-nozzles is approximately ø1.5 mm. The main nozzle is not present separately, and is formed by the circular space formed by wrapping multiple sub-nozzles made of ceramic on the periphery.
This heater is large in size and ø1.6 mm built-in K thermocouple can be used. Therefore, the life of the built-in thermocouple is expected to be fairly long.
|This video shows the process of silver brazing. The silver brazing is of base type of working temperature 1202ºF (650ºC). A cutter blade was used as the base material.
The heater used was 100 V - 300 W type. When silver brazing small objects using silver solder paste of 1202ºF (650ºC), this heater will meet the requirement adequately.
|The wire mesh is being heated in this video. The place where the hot air comes in contact with the wire mesh is red hot. The distinct red-hot spot is at 1472ºF (800ºC) or more, the pale red-hot location is approximately 1292ºF (700ºC). (100 V - 300 W type is used) The red hot spot of the wire mesh can be seen even when the wire mesh is placed further away from the nozzle. The heater provides a good hot air flow, and hot air of 1472ºF (800ºC) is reaching a distance of 50 mm or more.
|The wire mesh can be heated using the 100 V - 600 W type in the same way as above.
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