Vacuum Sintering Furnaces | High-Temp ...

Small or complex parts are difficult to produce by casting or machining. Components that require sintering are often delicate, intricate, and easy to botch. Vacuum sintering is an efficient way to join parts with minimal waste.Vacuum sintering produces consistent, bright parts with no seams, joints, or fillers. Powdered metal, metal injection molding, 3D printing, and other similar technologies can benefit greatly from the superior quality and flexibility of vacuum sintering.

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Benefits of a Vacuum Sintering Furnace

• Clean, bright parts
• Incredible design flexibility
• Quick turnaround
• Superior quality
• Fewer defects
• Easy maintenance
• Maximum productivity

How Vacuum Sintering Works

Sintering starts with debinding.

The debinding process removes binder materials that can contaminate the furnace and the final product. Binding materials are originally necessary for each separate part compaction, but become unnecessary and undesirable during the sintering process.

Vacuum sintering requires a high vacuum for clean, quality parts. The temperature must be high enough for the metals to combine smoothly, but not so high that they liquefy. Cooling speed will depend on the material.

Temperature and pressure limits can be chosen during the engineering phase, and controlled manually or automatically during processing.

Vacuum furnaces can be built to perform both debinding and sintering. Combining these processes in one furnace saves time and money. No part transfer, secondary machinery, or resources wasted on a repetitive process.

Vacuum furnaces are perfect for higher temperature sintering applications. Highly customizable controls allow for manual or automatic temperature changes depending on the needs of your specific project. The temperature is uniform, ensuring consistent part quality across the board.

1. Conventional vacuum sintering furnace

A conventional vacuum sintering furnace has an outer wall forming a cavity which receives the parts to be sintered.

Heaters are positioned within the cavity, which can increase the temperature to 800°C.

To create a vacuum in the cavity, a vacuum pump is connected to it. Various layers of insulation are installed around the cavity to maintain the temperature.

The figure below shows the the construction of a conventional vacuum sintering furnace.

Vacuum Sintering Furnace: Patent Image

For more information refer to this patent.

2. Continuous production vacuum sintering furnace

A continuous production vacuum sintering furnace has following units:

• Conveyer unit
• Multiple vacuum sintering systems

The conveyor unit transfers the sintering compact to each sintering system individually. This is shown in the diagram below:

Continuous Production Vacuum Sintering Furnace: Patent Image

Each of the sintering systems in the above figure contains:

• Sintering furnace
• Vacuum control unit
• Temperature control unit

Individual unit in a continuous production vacuum sintering furnace: Patent Image

The furnace is connected to vacuum control unit via a valve. The valve is also connected to an air supplying system for breaking the vacuum and a pressure sensor for measuring the pressure (vacuum) inside the furnace.

The entire sintering process can be divided in sintering steps and can be assigned to the systems in a sequential order, where each sintering system can continue to work where the previous one has left.

All the pressure and temperature conditions provided by the corresponding vacuum sintering systems do not interfere with each other.

More information about such a furnace can be found in this patent .

3. Rotating vacuum sintering furnace

A rotating vacuum heat treatment has following units:

• Vacuum unit
• Gas cooling device
• Vacuum furnace

Rotating Vacuum Sintering Furnace: Patent Image

The vacuum furnace is covered by a insulating layer. Multiple heaters are located inside the insulating layer.

The rotating cylinder is located in the central part of the furnace surrounded by the heaters. The sintering materials are loaded in the rotating cylinder.

For cooling the furnace, a nozzle is present on the insulating layer which is connected to the gas cooling device through pipes. The cooled gas is sprayed to the rotating cylinder via the nozzle.

The cylinders are supported by multiple rollers and these rollers is driven by the supporting axle to rotate.

A power supply is present outside the insulating layer for driving the rollers.

This furnace setup is suitable for producing neodymium-iron-boron rare earth permanent magnetic materials.

For more information refer to this patent.

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Image from Wikipedia Commons

What is sintering?

Sintering is a process in which heat and pressure are used to create bulk items from a powder. The temperature used in sintering are relatively low and below the melting point of the material being sintered.

Sintering can be used with a variety of materials such as metals, ceramics, plastics, and semiconductors. The particles in the sintered powder can range in size from nanometers to micrometers.

How does sintering work?

The process of sintering comprises diffusion of atoms across the particles boundaries, effectively fusing them together and resulting in a solid piece.

Temperature and pressure are generally applied to cause this diffusion to take place. However, the temperature during the sintering process always stays below the melting point of the material.

In contrast to melting, the powder used in sintering never reaches a liquid phase. This makes sintering a great choice for materials that have a high melting point, such as tungsten and molybdenum.

Types of Sintering

Depending on whether pressure is applied during the process, sintering can be classified into two types:

1. Pressureless sintering (PLS)

2. Pressurized sintering

Pressureless Sintering

Pressureless sintering is conducted without any application of external pressure. This allows uniform densification of sintered material contrary to conventional hot pressing methods.

Pressureless sintering can further be classified into reaction sintering and atmospheric sintering.

Reaction sintering involves reaction between the green components to form the sintering bond.

Atmospheric sintering are done in a specialized atmosphere such as that of inert gases. Few examples of pressureless sintering methods includes thermal plasma sintering, microwave sintering and milliwave sintering.

Pressurized Sintering

Pressurized sintering can be further classified as solid compaction sintering and gas compaction sintering.

Few examples of pressurized sintering are hot pressing, hot isostatic pressing, super high-pressure sintering, spark plasma sintering and high pressure gas reacting sintering.

The figure below shows a taxonomy of sintering processes.

A taxonomy of sintering process

There are several different types of sintering, each with their own unique characteristics and applications.

1. Cold Isostatic Pressing (CIP) Sintering: CIP sintering is a process where powders are placed in a sealed container and then subjected to high pressure. This process is often used to create dense, homogenous parts with complex shapes.
2. Spark Plasma Sintering (SPS): SPS is a process where a spark is used to heat powders in a sealed container. This process is often used to create high-density parts with high strength and excellent electrical conductivity.
3. Hot Isostatic Pressing (HIP) Sintering: HIP sintering is similar to CIP sintering, but the powders are heated to a high temperature before being subjected to high pressure. This process is often used to create high-density, homogenous parts with excellent mechanical properties.
4. Field-Assisted Sintering: Field-assisted sintering uses an electric field to compact powders. This process is often used to create high-density, homogenous parts with excellent mechanical properties.
5. Microwave Sintering: Microwave sintering uses microwave energy to heat powders. This process is often used to create high-density, homogenous parts with excellent mechanical properties and is faster than traditional sintering methods.

Reactive Sintering

Reactive sintering is a process that involves the addition of a reactive element to the powders being sintered. During the sintering process, the reactive element reacts with one or more of the other elements in the powder, forming a new compound that bonds the powders together. This process results in the formation of a solid object with unique properties that are not possible to achieve through traditional sintering methods.

There are several types of reactive sintering, each with their own unique characteristics and applications. Some common types of reactive sintering include:

1. Self-propagating High-temperature Synthesis (SHS): SHS is a reactive sintering process where a mixture of powders is ignited, and the reaction proceeds through a self-sustaining exothermic reaction. This process is often used to create high-density, homogenous parts with excellent mechanical properties.
2. Reactive hot pressing (RHP): RHP is a process where powders are placed in a sealed container and then subjected to high pressure and high temperature. This process is often used to create high-density, homogenous parts with excellent mechanical properties.
3. Reactive liquid-phase sintering (RLPS): RLPS is a process where a liquid phase is added to the powders being sintered. The liquid reacts with the powders, forming a new compound that bonds the powders together. This process is often used to create high-density, homogenous parts with excellent mechanical properties.

Reactive sintering can be used to create parts with unique properties, such as high strength, excellent electrical and thermal conductivity, and improved wear resistance. It is used to sinter a wide range of materials, such as ceramics, metals, and alloys. Applications of reactive sintering include aerospace, biomedical, and electronic industries.

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