 
1. Basic Knowledge of Hot Air Heating
1-0. Overview
Hot air heaters such as SAH and CLH series supply compressed air from the atmospheric air outside (0.05 to 0.5 atm), electrically heats and blows the air.
The below diagram is the basic structural diagram of SAH and CLH series. There are models of different shapes and sizes but the basic structure is almost the same. There are other PAH series using platinum heating element.
SAH Series Hot Air Heater (Standard Hot Air Heater)
SAH series Features of Hot Air Heaters
In SAH series, heating element and heat vapors are in direct contact. The outer diameter is compact but the surface area is extremely large due to the high density heating element. The difference between the temperature of heated gas and heating element is about 572ºF (300ºC) ((392ºF (200ºC) to 482ºF (250ºC) for SAHD series) and the heat transmission efficiency is very good. The passing gas can be heated to approximately 1652ºF (900ºC).
Accuracy of the Built-in Temperature Sensor
The built-in hot air temperature sensor (optional) is not accurate enough to be used as a reference for hot air temperature. Set the hot air temperature using a standard thermometer and use it for reference in case the built-in sensor temperature is used during that time. The reproducibility of temperature is comparatively good and can be used as an operating standard. The operating temperature of the reference thermometer must be reset without fail when the heater is replaced.
Service Life of the Built-in Temperature Sensor
Normally K thermocouple is used as a temperature sensor. Using a thermocouple of sufficient thickness may not be possible depending on the size of the heater. Wire with diameter of 0.039 in (ø1.0 mm) can be used for a metal case of ø0.5 in (ø13 mm) type and 0.019 in (ø0.5 mm) for metal case of ø0.314 in (ø8) type.
Since the structure is such that the temperature sensor passes through the center of the heating element, the sensor is exposed to almost the same temperature as the heating element. In many cases, there is no problem with the service life of the thermocouple but on using the SAH heater at very high temperatures, the service life of the built-in temperature sensor may be reduce. Specify R type (platinum type) built-in temperature sensor in such cases. The option code added to the model number is /+S(R).
The lead wire of the temperature sensor is thin and can easily be bent with a small R. If the sensor is installed in moving parts of automatic machines causes additional bending, then the deformation is concentrated at one location resulting in frequent fatigue burn-out. If the amount of deformation is huge then the fatigue burn-out can occur after several hundred times of use. Fatigue burn-out may occur by repeated usage of thousands and tens of thousand times even if the amount of deformation is not very high. In case of automatic machine, there is a possibility of fatigue burn-out within a few days depending on the machine tact.
For applications attached to such moving parts, relay terminals should be provided in the moving parts and lead wires from the heater should be temporarily connected to the terminals. Flexible cables should be connected from the terminal to the external fixed part, so that fatigue burn-out is not caused. Any conductor material can be used if the cable is at room temperature. Compensating wire must be used since the error in temperature measurement increases if this part becomes hot. Fatigue burn-out can occur with temperature sensor leads. This can also happen with power supply lead wires.
CLH Series Hot Air Heater (Clean Heater)
CLH series Features of Clean Hot Air Heaters
CLH series has heating elements and sensors sealed in quartz glass capsules. The heating element and sensor do not come in direct contact with the heated gas. This prevents dust generated from oxides from mixing in the heated gas.
The efficiency of heat transfer is less compared to the SAH type since the passing gas is heated with a heating element through the quartz capsule in this system. Therefore, the maximum temperature of hot air is approximately 932ºF (500ºC).
This heating element must be used in an oxidation atmosphere and outside air is supplied inside the capsule by respiratory action through the above “Heat-resistant rubber tube”. The increase in the pressure due to thermal expansion of capsule internal gas is released through this rubber tube.
Accuracy of the Built-in Temperature Sensor
The built-in hot air temperature sensor (optional) is not accurate enough to be used as a reference for hot air temperature. Structurally, the measurement error will be higher than the built-in sensor incorporated in normal hot-air heaters. Set the hot air temperature using a standard thermometer and use it for reference in case the built-in sensor temperature is used during that time. The reproducibility of temperature is comparatively good and can be used as an operating standard. The operating temperature of the reference thermometer must be reset without fail when the heater is replaced.
Service Life of the Built-in Temperature Sensor
Normally K thermocouple is used as a temperature sensor. Using a thermocouple of sufficient thickness may not be possible depending on the size of the heater. Wire with diameter of 0.019 in (ø0.5 mm) can be used for a metal case of ø0.5 in (ø13 mm) type.
Since the structure is such that the temperature sensor passes through the center of the heating element, the sensor is exposed to almost the same temperature as the heating element. In many cases, there is no problem with the service life of the thermocouple but on using the CLH heater at very high temperatures, the service life of the built-in temperature sensor may be reduce. Specify R type (platinum type) built-in temperature sensor in such cases. The option code added to the model number is /+S(R).
The lead wire of the temperature sensor is thin and can easily be bent with a small R. If the sensor is installed in moving parts of automatic machines causes additional bending, then the deformation is concentrated at one location resulting in frequent fatigue burn-out. If the amount of deformation is huge then the fatigue burn-out can occur after several hundred times of use. Fatigue burn-out may occur by repeated usage of thousands and tens of thousand times even if the amount of deformation is not very high. In case of automatic machine, there is a possibility of fatigue burn-out within a few days depending on the machine tact.
For applications attached to such moving parts, relay terminals should be provided in the moving parts and lead wires from the heater should be temporarily connected to the terminals. Flexible cables should be connected from the terminal to the external fixed part, so that fatigue burn-out is not caused. Any conductor material can be used if the cable is at room temperature. Compensating wire must be used since the error in temperature measurement increases if this part becomes hot. Fatigue burn-out can occur with temperature sensor leads. This can also happen with power supply lead wires.
Type Name Notation Method of SAH and CLH Series
Example of Model Name SAH100v-350w/10BH/+S
Explanation of model name → See below. For details, refer to “Model Name Notation” on the left menu in the website
SAH- - - - SAH type hot air heater
100v-350w - Rated voltage and power
10- - - - - - Display 10 series. ø0.5 in (ø10 mm) series is the outer tube diameter of the heating tube. Normally ø0.5 in (ø13 mm) is used as the metal case compatible with this.
B- - - - - - - Shape of hot air outlet. B type is a pencil shaped throttle nozzle.
H- - - - - - Indicates H series. H series is a standard hot air heater, with metal case. Air inlet is threaded pipe
+S- - - - - - Temperature sensor (K thermocouple) indicates that it is built-in type
Usage of a Simple Hot-air Heater (Example)
Figure 1: Actual connection diagram (example of the simplest usage method)
The figure above is an example of an actual connection diagram. Links to videos of actual heating is in the top menu of Fintech website under “Hot Air Heating Videos”, please refer to the videos.
A pressure of 0.5 kg/cm2 (50 kPa) or higher is suitable as the compressed gas source for the above figure. Setting conditions may be restricted if the pressure is less than this and achieving the required gas flow rate may not be possible. 0.2 kg/cm2 (20 kPa) may serve the purpose in most uses and sometimes lesser pressure may be sufficient but pressure not more than 0.05 kg/cm2 (5 kPa) is perhaps not practical. Therefore sirocco fans cannot be used.
Even an inexpensive electromagnetic blower can output 0.2 kg/cm2 (20 kPa). Rotary blowers can output 0.5 kg/cm2 (50 kPa). Compressors can output above 5 kg/cm2 (500 kPa).
Even if the pressure are higher than necessary, there is no problem as pressure can be easily reduced using flow adjustment valves. The high pressure gas source (such as air from compressors) is preferred because of the convenience, but a large amount of energy is required to increase the pressure of air to a value higher than necessary and the loss is said to be very high from the perspective of energy economy.
Only about 3.17 gal/min (12 L/min) of air can be obtained with a compressor for every 100 W. While 21.13 gal/min (80 L/min) can be obtained with an electromagnetic blower or a rotary blower for every 100 W.
For various air sources, please refer to Air Sources in the top menu of Fintech website.
The procedure to operate air heaters is as given below from (1) to (3).
(1) Supply compressed gas
(2) Apply voltage so as to obtain the necessary hot air temperature
(3) Point the nozzle to the heated object and heat
The following sections will explained based on these steps.
 
1-1. Supply Compressed Gas
The type of gas and usability is as follows. Please consult us for gases other than these.
Type of gas |
Usability |
Attention point, others |
SAH |
CLH |
Air, oxygen |
|
|
Should not contain large amounts of oil mist, and water. |
Nitrogen, argon |
0 |
|
All inert gases can be used. However, SAH tends to have a shorter service life than air |
Hydrogen |
|
|
Ignites on exposure to air at temperatures above 1112°F (600ºC) |
Green gas |
|
|
A small amount of hydrogen mixed with nitrogen gas. Deoxidization |
Water vapor |
~ x |
|
Difficult in the case of SAH (electric leakage due to water droplets) |
City gas, LPG |
|
|
Due to thermal decomposition and adherence of carbon to the heating element |
* Electric heating wire used in an air heater is most durable in an oxidizing environment
Since the electric heating wire comes in direct contact with the gas in SAH type, heat transfer effectiveness is high and a high temperature of 1472ºF (800ºC) can be obtained.
* There is no direct contact between electric heating wire and gas in CLH type. There are few restrictions on the gas being used as a result but the size is slightly large and a hot air temperature of up to 932ºF (500ºC) can be obtained.
Required pressure and flow rate required
Generic data cannot be provided since the pressure required varies greatly depending on the flow rate being used, type of gas, nozzle size, and structure of the air heater, but the value can be set somewhere in the range of 0.05 to 0.5 kg/cm2 (5 to 50 kPa).
Empirical data is available for some types → Please refer to Characteristics of Air Heater in the top menu of Fintech website.
Sources of compressed gas that can supply pressure above necessary values are compressors, electromagnetic blowers, and rotary blower → For various air sources, please refer to Air Sources in the top menu of Fintech website.
The required flow rate varies significantly based on the object to be heated and purpose. The flow rate in the range of 5.28 to 13.2 gal/min (20 to 50 L/min) is sufficient if we consider a standard air heater SAH series 100v-350w type and simple methods are used for heating the objects.
If a large amount of hot air is required at a low temperature (752ºF (400°C) and below), then rated voltage or over-voltage (up to 200%) may be applied to obtain a high flow rate. Power is about 4 times with 200% voltage. The wire will be cut almost instantly if the air stops even for a short period of time due to some problem in this method and is not recommended. Applying rated or lower voltage is safe.
If air at high temperature is required, then set the flow rate to about 3.96 to 5.28 gal/min (15 to 20 L/min) and apply a voltage close to the rated voltage (100v). If even higher temperature is required, then further reduce the flow rate (by several gal/min (L/min)) and reduce the voltage accordingly.
If the pressure of air is blowing away the object, then select a model with a slightly bigger nozzle, use a flow rate ranging between a few to a few tens gal/min (L/min) and also reduce the voltage. In case of 1 point soldering, use a nozzle of ø0.157 in (ø4 mm) to ø0.236 in (ø6 mm) to supply gas at 1.32 to 2.64 gal/min (5 to 10 L/min) and supply a voltage of 50% to 80% (Hot air temperature of about (1112ºF (600°C)).
As a method to prevent objects from being blown away, two air heaters are used by placing them in a V-shaped arrangement pointing at one position. An area without air is created at the zone where the two blasts merge reducing the possibility of objects being blow away. This method is also used in soldering.
Using a specialized nozzle for soldering and removing the solder of IC is effective. If standard air heaters cannot meet the requirements, then a customized air heater can be specially ordered or air heaters such as the ones with a screw at the tip can be used by optimally designing only the nozzle.
Air heater SAH burns out in a short duration of time if the air supply is stopped while applying the rated voltage. Past experience has shown that this is a frequently occurring problem. Therefore, using a flow or pressure switch for interlocking is recommended.
The above example is that of SAH type. The required pressure in CLH type is less compared to the SAH type. (approximately 0.05 kgf/cm2 (5 kPa))
* To obtain a stable flow rate
Stabiliz3 the flow rate which in turn stabilizes the temperature of hot air reducing variations in heating. Also, the value of flow rate has to be managed to increase the reproducibility of work. For these reasons, pressure regulators and flowmeters are a must. These must be selected according to the type of gas being used.
 
1-2. Apply Voltage
After supplying compressed gas, check that the gas is released normally from the nozzle and apply the voltage till the required hot air temperature is reached. Several tens of seconds are required for the hot air temperature to completely stabilize. Ensure that the hot air temperature does not exceed the required value by taking this delay into consideration.
* Precautions to prevent damage from burning due to excess increase in temperature
Air heaters with built-in hot air temperature sensor can be managed safely by maintaining temperatures within (1472ºF (800°C)). However, since the service life is limited at 1472ºF (800°C), temperature of 1292ºF (700°C) and below is safe for using the heater over a long period of time.
If the temperature of the heating element exceeds 2192ºF (1200°C) even for a short period is dangerous. For air heaters with no built-in hot air temperature sensor, temperature of the heating element has to be monitored for using the heaters near the high temperature limit. Non-contact measurement method such as pyrometers are suitable for measuring the temperature. A simple method is to visually compare the exothermic color of the standard heat source.
To manage the high temperature limit of the heating element in an air heater by measuring the temperature of hot air, problems may occur if air heaters without built-in sensors are used and hot air temperature is measured externally using a thermometer. The maximum value of hot air temperature is the value near the extremes of the heating element. Depending on the type of the nozzle, the air gets cooled inside the nozzle and a lower value is recorded near the outlet of the nozzle.
Also, if hot air is released into the air, air gets mixed causing a sudden drop in temperature. For air heaters with no built-in hot air temperature sensor, temperature of the heating element has to be monitored near the maximum temperature limit (1472ºF (800°C)). Therefore, if voltage is applied so as to attain maximum temperature based on the value of temperature measured near the nozzle outlet, then the heating element may get overheated and melt.
Managing air heaters having a built-in hot air temperature sensor with the hot air temperature from the sensor is relatively safe.
1-2-1. Voltage Adjustment Method
Voltage may be connected directly from the line power supply. In this case, always keep the flow of the gas at 3.96 to 5.28 gal/min (15 to 20 L/min or more (for 350 W type). However, regulating the voltage is more convenient in many cases. Voltage regulator is used to adjust the voltage. There are two broad types of voltage regulators. A winding type (Product name - Bolt slider, Slidac etc.) and semiconductor type (Product name - SCR slider, Varitap etc.).
For regular use, winding type is recommended. The reason is durability and ability to boost voltage above the supply voltage. Normally, winding type can regulate in the range 0 to 130% of the power supply voltage. In contrast, the semiconductor type (controlled by SCR or Triac) can regulate up to 0 to 95%.
Advantages of the semiconductor type are light weight, high power, low cost, easy auto control etc. The winding type can used if these functions are not required. Voltage has to be measured carefully with the semiconductor type. Accurate values may not be displayed depending on the type of the voltmeter. (Accurate measurement is possible if a digital meter is of the “True RMS value type” and an analog meter is of the “Moving iron type”).
Power supply voltage requires stabilization in applications that demand highly accurate heat control. Install an AC regulated power supply before the voltage regulator for such cases.
Stabilization of voltage is an ideal condition but is costly. Therefore, in most cases a commonly practiced method is to use an air heater having a temperature sensor that is controlled using a temperature regulator and power controller so as to maintain a constant temperature. → “Voltage, Controller”
Semiconductor type voltage regulators usually change the effective voltage by phase control, but many temperature regulators etc. control the heater by switching the semiconductor relay (SSR) between ON and OFF. However, the air heater is controlled using SSR responds quickly, so the following precautions are necessary. → Refer to the following reasons.
1-2-2. Using a Temperature Controller
When using an air heater attached with a temperature sensor and when controlling the hot air temperature with a temperature controller, the following precautions are required.
1) The measured temperature of the hot air will be less even though the temperature of the heating element is high when the air flow rate becomes extremely low, and relying on this value will cause the heater to burn out. To use a temperature controller, please ensure that the minimum necessary air flow rate (about several gal/ min (L/min)) can be ensured. (Monitor with flow switch etc.)
2) Since the response speed of the heating element in air heaters is extremely high, consideration that is different from an ordinary electric furnace control etc. is necessary.
* Simple ON-OFF based control should never be used.
* Cycle control is possible in some cases.
Cycle time of 1 sec may be used in some cases, but cycle control is basically difficult. Since the heater responds quickly, the heater changes to the blinking state even in one second period. The service life of the heating element in the air heater significantly reduces under severe changes in temperature, and the service life may reduce to extent of 1/100.
The control amount decreases when cycle control is performed with a cycle of one second. In other words, by adding a voltage regulator in addition to the temperature controller, the ON state of the temperature controller is sufficiently extended and the OFF state becomes almost nil and the temperature change of the heating element is almost eliminated.
Or shorten the control cycle. Many temperature controllers have a control period of 1 second or more, but temperature controllers with 0.5 seconds or less are available depending on the model. If the control cycle is 0.5 seconds or less (recommended duration is 0.3 seconds), there is almost no problem.
* Voltage control (phase control by SCR, triac, etc.) is most preferable, but even cycle control
is not almost inferior if the control period is 0.3 seconds.
Even in this case please pay attention to PID value etc. (Recommended value P = 10, I = 10, D = 1). The response speed is different from electric furnace etc. (several hundred times). Phase control is preferable for heaters, but is not necessarily a preferable load for power supply side. There is also a problem of noise generation. For the above reasons, recommending either cycle control or phase control is confusing! However, temperature controllers with shorter control cycles has become easy to obtain, and selecting cycle control can be considered a good option in the future.
 
1-4. Calculation Method to Determine the Hot Air Temperature for Selecting the Model
If hot air temperature heated with air heaters is T[ºC], air flow rate is F[L/min.], and power of air heater consumed by air heater is P[w],
50 x P
T ≒-------------[°C] - - - - Expression for obtaining hot air temperature
F
P 0.02 x F x T [w] - - - - Formula for finding required power
50 x P
F ≒-------------[L/min] - - - - Equation for finding the air flow rate that can be heated
T
If the flow rate F is increased in the above equation, hot air temperature T decreases, and if F is decreased, hot air temperature rises. Since the coil will overheat and rupture when the hot air temperature exceeds 1472ºF (800°C), ensure that the setting is always 1472ºF (800°C) or less.
If F has been fixed, heater power consumption P will have to be changed to obtain the target hot air temperature T. If the selected P is higher than the rated power of the air heater, the model of the air heater has to be changed and a model with higher output power has to be selected.
If the selected P is smaller than the rated power of the selected air heater, then the power consumption can be reduced by decreasing the supply voltage. The method of controlling the voltage is as described above.
* Thermal efficiency has been ignored in the above calculation formula. However, heat loss has to be considered. Normally, thermal efficiency is in the 80% to 90% range, but because thermal losses are high, air temperature is higher with low flow rates due to which thermal efficiency reduces, thermal efficiency may also become 50% to 60% in the case of low flow rates. In contrary, in the case of a large flow rate, the thermal efficiency even become 90% or more.
* Regarding the capacity of the air heater, Fintech has manufacturing experience in the range of 30 w to 70,000 w. Also, Fintech can manufacture any custom specifications provided such specifications are feasible.
 
1-5. Service Life of Air Heaters
The service life of the air heater can vary significantly depending on the usage method, and assigning a specific value and offering warranty is not possible. The most accurate method to predict service life is by measuring the maximum temperature of the heating element in use condition with a non-contact thermometer such as a pyrometer and estimate the heating element life from the following graph with the temperature.
Also, since the heating element temperature is approximately 572ºF (300ºC) higher than the hot air temperature, heating element temperature can also be estimated from the hot air temperature. This temperature difference varies depending on the flow rate and is a very rough estimation. Based on this, the heating element temperature will be around 2012ºF (1100ºC) when the hot air temperature is 1472ºF (800ºC) and the approximate service life will be 1000 hours, if the hot air temperature is 1292ºF (700ºC) or less, the heating element temperature will be around 1832°F (1000ºC) or lower and value of service life approaches infinity and this indicates that service life need not be considered.
However, this is a generalized statement and results will be significantly different depending on individual conditions. Voltage control method will also have a significant effect as described above. Vibration, shock, and impurities (water, oil, metal powder) contained in air also affect the service life.
The service life of heaters cannot be predicted easily as many factors are involved. The expected service life with respect to the hot air temperature that is used is as given below. This value also varies with the thickness of the heating wire. This service life is for heating wire diameter of approximately 0.019 in (0.5 mm). For air heaters with thinner (lower rated current value) wire, value service life reduces further.
However, it is rare for burn-out to occur with normal consumption in practice, in many cases burn-out occurs due to overheating caused by control errors while using the heaters.
Figure 2: Relationship between heating element temperature and service life
The heating element temperature is approximately 572ºF (300ºC) higher than hot air temperature. Therefore,
Hot air temperature 1562ºF (850ºC) → Heating element 2102°F (1150ºC) → Service life of approximately 300 hours from the above chart
Hot air temperature 1472ºF (800ºC) → heating element 2012ºF (1100ºC) → Service life of approximately 1000 - 2000 hours from the above chart
Hot air temperature 1292ºF (700ºC) → Heating element 1832ºF (1000ºC) → Almost semi-permanent life from the above figure Almost
However, the difference between hot air temperature and heating element temperature also varies depending on the flow rate, generally the difference increases as the flow rate increases. To obtain air that is as hot as possible with the required service life, maintaining the difference as small as possible is preferable, and high temperature hot air can be expected to be obtained if the air flow rate is set low.
With the example of usage for high temperatures, voltage actually applied is limited to about 60% of the rated voltage (approximately 1/3 the rated value in terms of electric power). If the air flow rate is reduced accordingly, high temperature hot air of about 1652ºF (900ºC) can be obtained at the heating element temperature of 2012ºF (1100ºC).
In this way, service life of SAH heater is mainly determined by the heating element temperature. However, guarantying the service life as a manufacturer is difficult.
 
2 to 5 below explains the usage methods at various levels. Simple minimum necessary configuration to advanced control methods have been defined.
2. Usage with a Simple Configuration
The power supply (rated voltage) can be directly connected to the air heater as a simple usage method. However, in this case, the heater will burn within around 10 seconds if air does not flow with a minimum flow rate.
Figure 3: Example of use with direct power supply connection
Use the following formula to find out the minimum flow rate Fmin.
Fmin. = 0.05 × power [L/min]
For example, when 100 V is added to a heater of 100v-350w, the minimum flow rate is Fmin = 0.05 × 350 ≒ 18 L/min
However, if a flowmeter or a thermometer is not present as shown above, usage in a high temperature range close to the limit of SAH should be avoided. For this reason, allow a sufficiently large flow rate to flow, wait for about 30 seconds after the start of energization and close the “Flow rate adjustment valve, then use once 1/3 the tip of the heating element glows in deep red heat (hot air temperature 1112°F (600ºC)). To use at a higher temperature (operation in the direction of reducing the air flow rate), please use the method given in the following paragraphs.
Presence of water or oil in the supplied air will have a negative effect on the flowmeters and air heaters. Be sure to use air from which oil and moisture have been removed.
 
3. Usage with a Simple Configuration (Using Compressor Air)
Figure 4: Application example of compressor air
Checking of air flow rate should be possible and requires flowmeter. Float type flowmeters such as the one in the above figure is widely used. The indicated value will be change depending on the pressure, and has to be used at the specified pressure. Digital type of flowmeters (mass flowmeters) are also available other than the float type.
In case of the above figure, use a flowmeter with a specified pressure of about 200 kPa (2kg/cm2) and adjust such that the pressure is constantly applied by the pressure regulator. The flow rate is adjusted with the flow control valve provided on the outlet side of the flowmeter.
This flow control valve may be incorporated in the flow meter. There are some models in which the valve is installed towards the inlet side. Since these valves are not suitable, valves must be purchased by specifying “Outlet side valve”, operating pressure, and type of gas used.
This method requires compressed gas source of a high pressure and can be applied when compressor air is used. In case you have already been purchased the flowmeter that is not of the required pressure, please use the following connection method (4. Using a low-pressure rotary blower etc. as the air source).
Monitoring the hot air temperature is useful to ensure reproducibility of work and to prevent overheating of the heater. Therefore, please use models provided with temperature sensors. Also connect a thermocouple thermometer (standard K thermocouple).
For details, refer to Air Sources in the top menu of Fintech website. For thermocouples, refer to “Thermocouple” in the top menu of Fintech website.
Presence of water or oil in the supplied air will have a negative effect on the flowmeters and air heaters. Be sure to use air from which oil and moisture have been removed.
 
4. Usage with a Simple Configuration (Using a Low Pressure Rotary Blower)
Figure 5: Application example of low pressure air source
Pressure regulators cannot be used when the air source obtained is only about 50 kPa by using electromagnetic and rotary blowers etc. In this case, the flow control valve is placed in front of the flow meter as shown above. Or the flow control valve is not used. Flowmeter without pressure indicator- that is, use the type for normal pressure.
In this method, controlling flow rate by controlling the air source itself with the flow control valve is preferred if possible. The flow rate is controlled by supply voltage in the case of electromagnetic blowers and inverters are used for blowers such as rotary blowers that use motors. For details, refer to Air Sources in the top menu of Fintech website.
A blower of exact size that can produce the required amount of air can be used so that the flow control valve is not needed or too much narrowing is not required
The reason for this is that narrowing the flow control valve increases the pressure of the air source and result in a negative effect on the blower of the air source (failure or reduced service life).(Electromagnetic blowers do not have pressure switches such as the ones provided in compressors and pressure rises abnormally so if air outlets are blocked.)
A pressure difference is generated between the entrance and exit when the valve is narrowed down, and temperature of the gas passing through the valve reduces due to adiabatic expansion likely forming water droplets due to condensation. The water droplets adversely affects the flowmeter and air heater.(Since devices such as air dryers are not attached to the low pressure air sources, care is required to prevent water droplets from being formed.
If the flow rate cannot be adjusted with the air source and flow has to be narrowed down significantly, please install a release valve as shown below and discard the excess air. This will enable to avoid damage to the blower and prevent water droplets from being formed.
Supplementary explanation drawing of Figure 5 Example for air release valve installation
5. Highly Stable Configuration (Using Temperature Controller)
Figure 6: Highly stable usage (using a temperature controller)
Controlled hot air at constant temperature can be obtained by connecting temperature and power controllers to air heaters with sensors.
The flow rate adjustable compressed gas source can be of the configuration shown in Figures 3 to 5 and mass flow controller can also be used if there is no cost constraint. Since hot air of constant temperature can be obtained even when the flow rate is changed, power consumption can be reduced by controlling the flow rate during standby.
High power will be continuously applied to the heater if air flow rate is reduced to zero and sensor of the air heater does not function, this will cause burning within several tens of seconds. Ensure that a minimum flow rate is always maintained. This flow rate is approximately 0.792 gal/min (3 L/min) for standard 10 series and 1.58 gal/min (6 L/min) for 15 series.
Temperature controllers are sold by companies manufacturing control equipment. For details, refer to Power Supply, and Controller Sources in the top menu of Fintech website.
The method using SCR power controller is shown in the above figure, there are also other methods such as using a SSR (solid state relay). In this case, temperature controller is changed to cycle controlling type (with control period of 5 seconds or less) and power is controlled by the ratio of on-time to off-time by repeating the on-off cycles 2 or more times per second.
Please refer to “Power supply and controller” as the details are introduced in this section.
Presence of water or oil in the supplied air will have a negative effect on the air heaters. Be sure to use air from which oil and moisture have been removed.
 
6. Configuration for ON-OFF of Air with Solenoid Valve
[Figure 7] To turn air ON/OFF with a solenoid valve
When air supply is turned ON/OFF with the solenoid valve, a flow rate control valve (L adjustment) is provided in parallel to the solenoid valve as shown in the above diagram to ensure the minimum flow rate even when the solenoid valve is OFF.
A solenoid valve is provided at the upstream side of the control valve (H adjustment). If this is reversed, air of high pressure will be supplied to the air heater at the moment when the solenoid valve is turned ON adversely affecting the heater.
For the above configuration, when the solenoid valve is OFF and hot air temperature is the same as the ON condition, then only the flow rate decreases and the setup enters the standby state. When the solenoid is turned ON, hot air of a predetermined temperature can be obtained quickly.
When ON, if the time taken for the temperature of air to increase does not matter, then please turn OFF the power supply to the heater while the solenoid valve is turned OFF. Even the condition of the L control valve not being closed completely is okay because the minimum flow rate is zero, but after the solenoid valve has been turned OFF depending on the usage conditions, heat from the heat generating portion may be transmitted to the base side of the heater (air inlet side) and in some cases temperature of the lead wire etc. may cross the limit. To prevent this back flow of heat, a small amount of air flow has to be maintained even after turning OFF the power supply to the heater.
As explained in the previous section, SSR can be used instead of the SCR power controller (Temperature controller uses cycle control with a control period of 0.5 seconds or less)
Presence of water or oil in the supplied air will have a negative effect on the flowmeters and air heaters. Be sure to use air from which oil and moisture have been removed.
 
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