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What is a drying furnace? A simple explanation of its structure and applications.
A drying furnace is used to dry moisture or paint that has adhered to workpieces and is widely used in various industries such as manufacturing, food and chemical.
There are many types of drying furnaces, and the optimal method must be chosen depending on the workpieces and their intended use. In this article, we will provide an overview of drying furnaces, their components, and important points to consider.
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What is a drying furnace?
A drying furnace is a type of furnace that circulates heated air inside to evaporate and dry the moisture attached to workpieces.
In addition to the moisture on the workpieces themselves, it is also used to dry paints or solvents that have been applied to the workpieces during the manufacturing process.
Furnace drying applications extend beyond industrial use to include food, pharmaceuticals, and wood.
While temperature control within the furnace is a necessary feature, making it similar in design and control to a heat treatment furnace, the primary difference is that since the purpose is drying, it is not necessary to raise the furnace temperature to the levels required for heat treatment.
Drying furnaces are generally set to temperatures below 200°C, and temperature settings are adjusted depending on the application. A fan circulates the air inside the furnace to dry the workpieces.
Types of drying furnaces
Drying furnaces are classified according to their structure, manufacturing methods, and heat sources used. The characteristics and mechanisms of each type are explained below.
Classification by structure
Drying furnaces can be classified into two types based on the drying method: direct and indirect drying methods.
Direct drying furnace
In a direct drying furnace, a heater is installed inside the furnace, and the heated furnace atmosphere is directly applied to the workpieces to dry them.
Since the workpieces are heated directly, this method offers high energy efficiency, and since the heater is not separate, the installation space can be reduced.
However, a disadvantage is that temperature fluctuations may occur inside the furnace, and when drying multiple workpieces at the same time, the temperature may not be uniform.
Indirect drying furnace
In an indirect drying furnace, the drying chamber and the combustion chamber are separated. The heater in the firing chamber heats the furnace atmosphere, which is then directed into the drying chamber.
The heated air is distributed throughout the furnace, resulting in a more uniform temperature distribution, which reduces the likelihood of uneven drying of the workpieces.
In addition, the risk of fire is minimized because there is no risk of sparks or flames reaching flammable materials such as paint.
On the downside, separating the combustion chamber requires more installation space and it takes longer for the furnace temperature to rise, which reduces thermal efficiency.
Classification by production method
Drying furnaces can be classified into two types based on the production method: batch type and continuous type.
Batch-type
A batch-type furnace dries workpieces placed on trays at one time, and when the process is complete, the trays are replaced with new ones.
Because the heating conditions can be adjusted for each batch, this method is suitable for small-scale, multi-variant production.
The structure is typically box-shaped and called a muffle furnace, equipped with doors and a conveyor system to change the trays.
However, because the doors must be opened to change trays after each process, heat is lost and additional energy is required for reheating, reducing thermal efficiency.
Continuous-type
A continuous-type drying furnace uses a conveyor to continuously move workpieces through the furnace, where they pass through a chamber maintained at a constant temperature for a set period of time to complete the process.
Because the workpieces are processed at a constant temperature, this method is suitable for mass production. Unlike batch furnaces, heat is not lost after each process, providing a higher thermal efficiency advantage.
Classification by energy source
The energy used by drying furnaces is mainly divided into electricity and fuel gas.
Electric type
An electric type drying furnace uses heating elements as the heating device, and the furnace atmosphere is heated by resistance heating to dry the workpieces.
By controlling the electric current, the temperature can be precisely regulated, which offers the advantage of fine temperature control.
In addition, there is no need for an exhaust system because there are no exhaust gases, making it an environmentally friendly option.
On the downside, the cost per unit of energy tends to be higher than gas, resulting in potentially higher energy costs.
Combustion type
A combustion drying furnace uses a burner to combust energy sources such as fuel gas to heat the furnace atmosphere and dry the workpieces.
Fuel gas is the primary fuel used, but liquid fuel, gaseous fuel, infrared, and steam are all options as well.
Combustion provides high-temperature hot air for rapid drying.
While controlling gas flow and air volume can sometimes be challenging, the use of gas allows for more efficient management of energy costs.
Areas of application for drying furnaces
Drying furnaces are used for a wide variety of workpieces and materials.
In the chemical industry, they are used to dry plastic raw materials, resin lenses, functional films, and more.
In the automotive industry, drying furnaces are used after the body painting process and play an important role in determining the appearance.
They are also used for a wide variety of workpieces, such as ceramics, battery materials, semiconductor components, tableware, and tiles.
In addition to industrial use, drying furnaces are used in the food industry to dry vegetables and fruits, and in the pharmaceutical industry to dry drugs for crystallization or solidification.
| Applications | Materials |
|---|---|
| Drying | Ceramics Metal Glass Electronic components Metal |
| Painting ・ Coating | Metal Plastic Glass |
| Curing | Resin Silicon |
| Sterilization | Medical equipment Pharmaceuticals |
| Preservation | Food Spices |
Structure of a Drying Furnace
A drying furnace consists of the following components.
Heating Device
The heater in a drying furnace is used to heat the atmosphere to dry the workpieces.
The heat source typically consists of heaters in electric furnaces and burners in combustion furnaces.
Electric heaters use resistance heating, where the electric current generates radiant heat to warm the surrounding air.
The temperature can be controlled by adjusting the current, which makes it easier to control compared to gas furnaces.
On the other hand, gas burners mix fuel, such as city gas, with air and burn it to heat the air.
Temperature control is done by adjusting the flow of fuel and air, and technical expertise is required for precise temperature management.
Circulation fan
The circulation fan is used to maintain a uniform temperature within the furnace.
It creates convection of the heated atmosphere inside the furnace to deliver even heat, prevent drying inconsistencies, and reduce variation.
It is typically installed from the top or bottom, but side installation is also possible.
It is important to install the fan in a position that does not obstruct the flow of the furnace atmosphere, which requires attention to installation space, wiring, and piping.
Exhaust system
The exhaust system is used to draw in any harmful substances or fumes generated during the drying process and expel them outside through ducts. There are several types of exhaust systems, including local exhaust systems, fume fans, and heat-resistant exhaust systems, depending on the application.
Whether it is a gas-type or electric-type drying furnace, it is recommended to install an exhaust system if harmful substances or smoke are produced during the drying process.
Installation may also be required for safety reasons or to comply with work environment regulations.
Control system
A control system is a general term for devices used to control various functions. The main control devices are listed below.
Temperature control system
Adjusts the output of the heater to match the set temperature inside the furnace.
Fan control system
Controls the circulation of atmosphere inside the furnace to maintain uniform temperature distribution.
Exhaust control system
Properly exhausts harmful substances and smoke to maintain a safe working environment.
Automation control system
Automates the process and simplifies the operation, resulting in improved work efficiency.
Control systems are equipped with safety functions depending on the application, such as overtemperature protection, fault monitoring, and interlocks to ensure safety.
Maintenance of drying furnaces
Regular maintenance of a drying furnace is essential for effective operation and long life. It includes tasks such as cleaning the inside of the furnace and measuring the furnace temperature.
The most important maintenance methods are described below:
Cleaning
Removal of scale, foreign matter, and scattered paint.
Inspection and calibration
Inspect and calibrate sensors and gauges.
Parts replacement
Regular replacement of consumables and parts due to wear, deterioration, or malfunction.
It is recommended that maintenance be scheduled in advance, based on the manufacturer’s recommended replacement intervals and the frequency and conditions of use, to prevent the equipment from becoming inoperable.
CO2 Reduction in drying furnaces
In recent years, manufacturers have been asked to reduce the CO2 emissions generated in their own factories, as well as the CO2 emissions generated in the generation of electricity.
A typical countermeasure includes:
Heat recovery
CO2 emissions can be reduced by reusing the heat emitted from the drying furnace.
Improve energy efficiency
Introducing insulation materials and energy-saving devices that reduce heat loss can help reduce CO2 emissions.
Heat shielding sheets and heat resistant coatings
By reducing heat radiation and stabilizing the temperature inside the furnace, energy-saving effects can be expected.
The drying furnace uses electricity, gas, and other energy sources for heating, making it a focus area for CO2 reduction efforts.
Technological developments are advancing in methods such as exploring the use of electricity from renewable energy sources such as solar power, switching to fuels that do not emit CO2 when burned, and methods to separate and capture CO2 from emitted gases.
Frequently Asked Questions
Q. Are there any laws regarding drying furnaces?
Drying furnaces are subject to regulations under the Fire Safety Act,
It is required to have a partition between the heat source and the workpieces, and ventilation is required to prevent accumulation of substances such as paint inside the furnace.
In addition, the installation of a drying furnace may require notification to and inspection by the local fire department.
Q. What is a vacuum drying furnace?
A vacuum drying furnace is a type of furnace that creates a vacuum inside to lower the boiling point of liquids and increase efficiency.
The furnace is a sealed environment and the air inside is evacuated by a vacuum pump. It is common to use a vacuum pump with 2 to 5 times the suction capacity of the drying furnace, and rotary or diaphragm oil pumps are typically used.
Q. How should I select the specifications for a drying furnace?
The specifications of a drying furnace should be selected based on the nature of the workpieces and the required processing quantity, and by calculating the amount of heat required. The furnace should be selected to match the required heating capacity.
In addition, the heat required varies depending on the preheating time to evaporate the moisture and the drying time to remove the moisture, so it is important to keep these factors in mind.
Designing furnace specifications tailored to your company’s needs is essential.
Summary
Drying furnaces are used in many industries, including manufacturing, food, chemical, and pharmaceutical, and are essential equipment for optimizing the performance and properties of workpieces.
As a manufacturer of industrial furnaces, Sun Furnace can provide you with a customized atmosphere gas generation system for your application based on our experience in manufacturing more than 1,500 industrial furnaces. We also offer free technical consultations, so please feel free to contact us.
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