Metal heat treating furnace is an essential tool in the manufacturing industry, used to alter the physical and chemical properties of various metals. Heat treating is a thermal process that involves heating and cooling metal to achieve specific properties such as increased hardness, ductility, or resistance to wear and corrosion. This process is used in a wide range of industries, including aerospace, automotive, construction, and medical.

The type of furnace used for heat treating depends on the specific properties required for the metal being treated. For example, aluminum alloys are heat treated to temperatures up to 1000°F, while metallic alloys must be heat treated within given specifications like AMS 2770G, DPS 1.700, BAC 5621, MIL-H-6088, NADCAP. Furnaces can be designed for batch or continuous production and can be customized to accommodate various structural sizes. The furnace design must also take into account factors such as heating rate, cooling rate, and atmosphere control to ensure the desired properties are achieved.

Proper heat treating can significantly improve the performance and longevity of metal components. It is critical to work with a knowledgeable and experienced heat treating provider to ensure that the proper furnace and process are selected for the specific application. With the right furnace and process, manufacturers can achieve consistent and repeatable results, ensuring high-quality products and satisfied customers.

Fundamentals of Metal Heat Treating

Heat Treating Principles

Metal heat treating is a process of heating and cooling metals to alter their physical and mechanical properties. The three main principles of heat treating are heating, holding, and cooling. Heating the metal to a specific temperature changes its microstructure. Holding the metal at that temperature for a specific time allows the microstructure to change uniformly. Cooling the metal at a controlled rate determines its final properties.

Types of Metal Heat Treatment

There are several types of metal heat treatment, including annealing, normalizing, quenching, tempering, and case hardening. Annealing is a process of heating the metal to a specific temperature and holding it there for a specific time to soften it. Normalizing is a process of heating the metal to a specific temperature and holding it there for a specific time to refine its grain structure. Quenching is a process of cooling the metal rapidly to harden it. Tempering is a process of heating the metal to a specific temperature and holding it there for a specific time to reduce its brittleness. Case hardening is a process of adding a hard outer layer to the metal.

Goals of Heat Treatment

The goals of heat treatment are to improve the metal’s strength, toughness, hardness, ductility, and wear resistance. The specific goal depends on the type of metal, its intended use, and the desired properties. For example, a metal used for cutting tools requires high hardness and wear resistance, while a metal used for structural components requires high strength and toughness.

In summary, metal heat treating is a process of heating and cooling metals to alter their physical and mechanical properties. The three main principles of heat treating are heating, holding, and cooling. There are several types of metal heat treatment, including annealing, normalizing, quenching, tempering, and case hardening. The goals of heat treatment are to improve the metal’s strength, toughness, hardness, ductility, and wear resistance.

Furnace Types and Design

When it comes to metal heat treating furnaces, there are two main types: batch furnaces and continuous furnaces. Each type has its own unique design and is used for different purposes.

Batch Furnaces

Batch furnaces are designed to heat a specific amount of material at one time. This type of furnace is ideal for small to medium-sized batches of material that require heat treatment. Batch furnaces are often used for annealing, hardening, and tempering processes.

One common design for batch furnaces is the box furnace. This type of furnace is made up of a metal box with heating elements on the top, bottom, and sides. The material to be heat treated is placed inside the box and heated to the desired temperature. Box furnaces are versatile and can be used for a variety of heat treatment processes.

Another type of batch furnace is the car bottom furnace. This type of furnace is designed for larger batches of material and is often used for stress relieving and annealing processes. The material is placed on a large metal plate that is then moved into the furnace. Once the material is heated to the desired temperature, the plate is removed from the furnace and allowed to cool.

Continuous Furnaces

Continuous furnaces are designed to heat a continuous stream of material. This type of furnace is ideal for large-scale production processes that require a constant flow of material to be heat treated. Continuous furnaces are often used for processes such as annealing, hardening, and tempering.

One common design for continuous furnaces is the conveyor furnace. This type of furnace uses a conveyor belt to move the material through the furnace. The material is heated as it moves through the furnace and is then cooled as it exits. Conveyor furnaces are efficient and can be used for a variety of heat treatment processes.

Another type of continuous furnace is the rotary furnace. This type of furnace is designed for high-temperature applications and is often used for processes such as calcining and sintering. The material is placed inside a rotating drum and heated to the desired temperature. As the drum rotates, the material is heated evenly and is then cooled as it exits the furnace.

In summary, batch furnaces are ideal for small to medium-sized batches of material, while continuous furnaces are designed for large-scale production processes. Both types of furnaces have unique designs and are used for different purposes in the heat treatment of metals.

Heat Treating Processes

Metal heat treating is a group of industrial processes used to alter the physical and sometimes chemical properties of a material. The most common application of heat treatment is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass.

Hardening

Hardening is a heat treatment process used to increase the hardness of the material. The process involves heating the material to a specific temperature and then cooling it rapidly, often in water or oil. The rapid cooling creates a hard, brittle material that is often used for cutting tools, gears, and other applications where hardness is important. Hardening is commonly used for steel and other ferrous alloys.

Annealing

Annealing is a heat treatment process that softens the metal, enhancing its ductility and making it more workable. It is suitable for metals like steel, aluminum, copper, silver, or brass. The metal is heated to a specific temperature and then cooled slowly, often in the furnace. This slow cooling allows the formation of a new microstructure, which makes the metal more ductile and easier to work with.

Tempering

Tempering is a heat treatment process used to reduce the hardness of the material and increase its toughness. The process involves heating the material to a specific temperature and then cooling it slowly. Tempering is often used after hardening to reduce the brittleness of the material. Tempering is commonly used for steel and other ferrous alloys.

Normalizing

Normalizing is a heat treatment process used to improve the strength and toughness of the material. The process involves heating the material to a specific temperature and then cooling it in still air. Normalizing is often used to refine the grain structure of the material, which improves its strength and toughness. Normalizing is commonly used for steel and other ferrous alloys.

Heat treating processes are essential to the manufacturing of many industrial materials. Each process has its unique benefits and is used depending on the desired properties of the material.

Furnace Components

When it comes to heat treating furnaces, there are several crucial components that ensure their proper functioning. These components include heating elements, control systems, and insulation materials.

Heating Elements

The heating elements are responsible for generating the heat required for the heat treating process. These elements are typically made of materials such as Kanthal, molybdenum disilicide, or silicon carbide. The choice of material depends on the temperature required for the process. For instance, Kanthal heating elements are designed to operate at up to 1850°C (3360°F) and are ideal for use in case hardening and sintering furnaces [1].

Control Systems

Control systems play a vital role in ensuring that the furnace operates at the desired temperature and that the heat treating process is carried out accurately. These systems consist of temperature controllers, thermocouples, and other sensors that monitor the temperature inside the furnace. They also include safety features such as emergency shut-off switches and alarms that alert operators in case of any malfunctions.

Insulation Materials

Insulation materials are used to prevent heat loss from the furnace and to maintain a consistent temperature inside the chamber. These materials are typically made of ceramic fibers, refractory bricks, or insulating castables. The choice of insulation material depends on the temperature, the type of furnace, and the heat treating process. For example, ceramic fibers are ideal for use in high-temperature furnaces, while insulating castables are suitable for low-temperature applications [2].

In summary, the heating elements, control systems, and insulation materials are all crucial components of a heat treating furnace. They work together to ensure that the furnace operates at the desired temperature and that the heat treating process is carried out accurately and efficiently.

References:

1. Heating elements for heat treatment furnaces — Kanthal®
2. Industrial Heat Treatment Furnace Guide – Abbot Furnace

Temperature Control

Temperature control is a crucial aspect of metal heat treating furnaces. The temperature control system must maintain the desired temperature within a specific range to achieve the desired metallurgical results. Two common types of temperature sensors used in heat treating furnaces are thermocouples and pyrometers.

Thermocouples

Thermocouples are the most commonly used temperature sensors in heat treating furnaces. They work by measuring the voltage produced by the temperature difference between two different metals. The thermocouple is made up of two different metals, usually nickel and chromium, which are joined together at one end. The other end of the thermocouple is connected to a temperature controller, which measures the voltage produced by the thermocouple to determine the temperature inside the furnace.

Thermocouples are relatively inexpensive and provide accurate temperature measurements. They are also durable and can withstand high temperatures, making them ideal for use in heat treating furnaces.

Pyrometers

Pyrometers are another type of temperature sensor used in heat treating furnaces. They work by measuring the temperature of an object without making physical contact with it. Pyrometers use infrared radiation to determine the temperature of an object based on the amount of radiation it emits.

Pyrometers are more expensive than thermocouples but provide more accurate temperature measurements. They are also non-contact sensors, which means they do not come into contact with the object being measured, making them ideal for use in heat treating furnaces where contamination must be avoided.

In conclusion, both thermocouples and pyrometers are essential tools for temperature control in metal heat treating furnaces. The choice between the two depends on the specific application and budget.

Atmosphere in Furnaces

Metal heat treating furnaces require a specific atmosphere to achieve the desired results. The atmosphere can be either protective or reactive, depending on the type of heat treatment process.

Protective Atmospheres

Protective atmospheres are used to prevent oxidation and decarburization of the metal surface during heat treatment. These atmospheres are typically composed of inert gases such as nitrogen, argon, and helium. Protective atmospheres can also be created by using a reducing gas such as hydrogen or a hydrocarbon gas such as methane or propane.

Nitrogen is the most commonly used protective atmosphere gas due to its low cost and availability. It is often used for annealing and normalizing processes. Argon and helium are more expensive but are sometimes used for specific applications where their unique properties are advantageous.

Hydrogen is a common reducing gas used for protective atmospheres. It is often used for bright annealing and brazing processes. Hydrocarbon gases such as methane and propane can also be used as reducing gases, but they are less common due to their higher cost and potential safety hazards.

Reactive Atmospheres

Reactive atmospheres are used to alter the chemical composition of the metal surface during heat treatment. These atmospheres can be composed of gases such as oxygen, carbon monoxide, and carbon dioxide.

Oxygen is the most reactive gas and is often used for processes such as carburizing and nitriding. Carbon monoxide and carbon dioxide can also be used for carburizing processes, but they are less common due to their potential safety hazards.

It is important to carefully control the atmosphere composition and flow rate during heat treatment to ensure consistent and predictable results.

Material Handling

Metal heat treating furnaces require a reliable material handling system to ensure the safe and efficient transfer of workpieces in and out of the furnace. Two key components of material handling are the loading and unloading mechanisms and conveyance systems.

Loading and Unloading Mechanisms

Loading and unloading mechanisms are responsible for moving the workpieces into and out of the furnace. The type of loading and unloading mechanism used will depend on the size and weight of the workpieces, as well as the type of furnace being used. Some common loading and unloading mechanisms include:

• Manual loading and unloading: Small furnaces may require manual loading and unloading, where an operator manually places the workpieces into the furnace and removes them once the heat treatment process is complete.
• Overhead cranes: Overhead cranes are often used for larger furnaces and heavy workpieces. These cranes use a hoist and trolley system to move the workpieces into and out of the furnace.
• Robotic loading and unloading: Robotic loading and unloading systems are becoming increasingly popular in modern heat treating facilities. These systems use robots to load and unload the workpieces, improving efficiency and reducing the risk of injury to operators.

Conveyance Systems

Conveyance systems are responsible for moving the workpieces from one stage of the heat treatment process to another. The type of conveyance system used will depend on the specific heat treatment process being used, as well as the size and weight of the workpieces. Some common conveyance systems include:

• Belt conveyors: Belt conveyors are often used to move workpieces from the loading area to the furnace and from the furnace to the quench tank. These conveyors are typically made of heat-resistant materials and can be customized to fit the specific needs of the heat treating process.
• Roller conveyors: Roller conveyors are commonly used in continuous heat treating processes, where workpieces are moved through the furnace on a continuous basis. These conveyors use a series of rollers to move the workpieces along the conveyor.
• Pusher conveyors: Pusher conveyors are used in batch heat treating processes, where workpieces are loaded into the furnace in batches. These conveyors use a pusher mechanism to move the workpieces through the furnace.

In conclusion, a reliable material handling system is essential for the safe and efficient operation of a metal heat treating furnace. The loading and unloading mechanisms and conveyance systems used will depend on the specific needs of the heat treating process and the size and weight of the workpieces being treated.

Safety and Maintenance

Safety Protocols

When it comes to heat treating furnaces, safety is of utmost importance. There are several safety protocols that must be followed to ensure the safety of the workers and the equipment.

Firstly, workers must wear appropriate personal protective equipment (PPE) such as heat-resistant gloves, safety glasses, and protective clothing. They should also be trained to handle the equipment safely and be aware of the potential hazards of the process.

Secondly, the furnace should be equipped with safety features such as emergency shut-off switches, temperature and pressure gauges, and ventilation systems. The furnace should also be inspected regularly to ensure that these safety features are functioning properly.

Thirdly, the quenching process should be carefully monitored to avoid the risk of explosions or fires. The quench oil should not exceed a maximum of 0.1% water content, and the flash point should be checked to ensure that no extraneous contamination of a low flash point material has been introduced into the quench tank.

Maintenance Procedures

Regular maintenance of the heat treating furnace is essential to ensure its longevity and optimal performance. Here are some maintenance procedures that should be followed:

• Periodic furnace maintenance: The furnace should be inspected and maintained regularly to ensure that it is functioning properly. This includes checking the heating elements, thermocouples, and insulation.
• Cleaning the furnace: The furnace should be cleaned regularly to remove any debris or residue that may have accumulated. This can be done using a vacuum or compressed air.
• Lubrication: The moving parts of the furnace should be lubricated regularly to prevent wear and tear. This includes the bearings, chains, and gears.
• Calibration: The temperature and pressure gauges should be calibrated regularly to ensure their accuracy.

By following these safety protocols and maintenance procedures, the heat treating furnace can be operated safely and efficiently for years to come.

Frequently Asked Questions

What factors influence the cost of a metal heat treating furnace?

The cost of a metal heat treating furnace is influenced by several factors, including the size of the furnace, the type of heat source, the temperature range, the level of automation, and the manufacturer. Generally, larger furnaces with higher temperature ranges and more advanced automation features will be more expensive. Additionally, furnaces that use more advanced heat sources, such as induction heating, will also be more expensive than those that use more traditional heat sources.

How do you determine the best furnace for metal heat treating applications?

When determining the best furnace for metal heat treating applications, several factors should be considered, including the type of metal being treated, the required temperature range, the desired level of automation, and the available budget. It is also important to consider the reputation and experience of the manufacturer, as well as the quality of customer support and after-sales service.

What are the different types of furnaces available for heat treating metals?

There are several types of furnaces available for heat treating metals, including box furnaces, car bottom furnaces, vacuum furnaces, and continuous furnaces. Box furnaces are the most common type and are suitable for a wide range of applications. Car bottom furnaces are ideal for large and heavy parts, while vacuum furnaces are used for high-precision applications that require a controlled atmosphere. Continuous furnaces are used for high-volume production.

Which manufacturers are considered leaders in the production of metal heat treating furnaces?

There are several manufacturers that are considered leaders in the production of metal heat treating furnaces, including Ipsen, Lindberg/MPH, and Surface Combustion. These manufacturers have a reputation for producing high-quality furnaces that are reliable, efficient, and easy to use.

What is the typical price range for a quality heat treat furnace?

The typical price range for a quality heat treat furnace can vary widely depending on the size, type, and features of the furnace. Generally, smaller box furnaces can be purchased for a few thousand dollars, while larger, more advanced furnaces can cost tens or even hundreds of thousands of dollars. It is important to consider the long-term value and return on investment when making a purchasing decision.

Can metal heat treating be effectively performed at home, and if so, how?

Metal heat treating can be effectively performed at home using a variety of methods, including gas and electric furnaces, torches, and even charcoal fires. However, it is important to have a basic understanding of the principles of heat treating and to take appropriate safety precautions, as the process can be dangerous if not done properly. It is recommended that those who are new to heat treating seek guidance and instruction from a qualified professional before attempting to perform heat treating at home.