This article's lead section contains information that is not included elsewhere in the article.(August 2024) |
A vacuum furnace is a type of furnace in which the product in the furnace is surrounded by a vacuum during processing. The absence of air or other gases prevents oxidation, heat loss from the product through convection, and removes a source of contamination. This enables the furnace to heat materials (typically metals and ceramics) to temperatures as high as 3,000 °C (5,432 °F ) [1] with select materials. Maximum furnace temperatures and vacuum levels depend on melting points and vapor pressures of heated materials. Vacuum furnaces are used to carry out processes such as annealing, brazing, sintering and heat treatment with high consistency and low contamination.
Characteristics of a vacuum furnace are:
Heating metals to high temperatures in open to atmosphere normally causes rapid oxidation, which is undesirable. A vacuum furnace removes the oxygen and prevents this from happening.
An inert gas, such as Argon, is often used to quickly cool the treated metals back to non-metallurgical levels (below 400 °F [200 °C]) after the desired process in the furnace. [2] This inert gas can be pressurized to two times atmosphere or more, then circulated through the hot zone area to pick up heat before passing through a heat exchanger to remove heat. This process continues until the desired temperature is reached.
Vacuum furnaces are used in a wide range of applications in both production industries and research laboratories. For example, a low-temperature vacuum oven can be used for drying biomass much more efficiently than drying alone. [3] Similarly, microwave-vacuum drying has shown potential for drying foods like cranberries. [4] [5]
At temperatures below 1200 °C, a vacuum furnace is commonly used for the heat treatment of steel alloys. Many general heat treating applications involve the hardening and tempering of a steel part to make it strong and tough through service. Hardening involves heating the steel to a predetermined temperature, then cooling it rapidly in water, oil or suitable medium.
A further application for vacuum furnaces is Vacuum Carburizing also known as Low Pressure Carburizing or LPC. In this process, a gas (such as acetylene) is introduced as a partial pressure into the hot zone at temperatures typically between 1,600 and 1,950 °F (870 and 1,070 °C). The gas disassociates into its constituent elements (in this case carbon and hydrogen). The carbon is then diffused into the surface area of the part. This function is typically repeated, varying the duration of gas input and diffusion time. Once the workload is properly "cased", the metal is quenched using oil or high pressure gas (HPGQ). For HPGQ, nitrogen or, for faster quench helium, is commonly used. This process is also known as case hardening.
Another low temperature application of vacuum furnaces is debinding, a process for the removal of binders. Heat is applied under a vacuum in a sealed chamber, melting or vaporizing the binder from the aggregate. The binder is evacuated by the pumping system and collected or purged downstream. The material with a higher melting point is left behind in a purified state and can be further processed.
Vacuum furnaces capable of temperatures above 1200 °C are used in various industry sectors such as electronics, medical, crystal growth, energy and artificial gems. The processing of high temperature materials, both of metals and nonmetals, in a vacuum environment allows annealing, brazing, purification, sintering and other processes to take place in a controlled manner.
A kiln is a thermally insulated chamber, a type of oven, that produces temperatures sufficient to complete some process, such as hardening, drying, or chemical changes. Kilns have been used for millennia to turn objects made from clay into pottery, tiles and bricks. Various industries use rotary kilns for pyroprocessing and to transform many other materials.
Heat treating is a group of industrial, thermal and metalworking processes used to alter the physical, and sometimes chemical, properties of a material. The most common application is metallurgical. Heat treatments are also used in the manufacture of many other materials, such as glass. Heat treatment involves the use of heating or chilling, normally to extreme temperatures, to achieve the desired result such as hardening or softening of a material. Heat treatment techniques include annealing, case hardening, precipitation strengthening, tempering, carburizing, normalizing and quenching. Although the term heat treatment applies only to processes where the heating and cooling are done for the specific purpose of altering properties intentionally, heating and cooling often occur incidentally during other manufacturing processes such as hot forming or welding.
Brazing is a metal-joining process in which two or more metal items are joined by melting and flowing a filler metal into the joint, with the filler metal having a lower melting point than the adjoining metal.
Powder metallurgy (PM) is a term covering a wide range of ways in which materials or components are made from metal powders. PM processes are sometimes used to reduce or eliminate the need for subtractive processes in manufacturing, lowering material losses and reducing the cost of the final product. This occurs especially often with small metal parts, like gears for small machines. Some porous products, allowing liquid or gas to permeate them, are produced in this way. They are also used when melting a material is impractical, due to it having a high melting point, or an alloy of two mutually insoluble materials, such as a mixture of copper and graphite.
Induction heating is the process of heating electrically conductive materials, namely metals or semi-conductors, by electromagnetic induction, through heat transfer passing through an inductor that creates an electromagnetic field within the coil to heat up and possibly melt steel, copper, brass, graphite, gold, silver, aluminum, or carbide.
Sand casting, also known as sand molded casting, is a metal casting process characterized by using sand—known as casting sand—as the mold material. The term "sand casting" can also refer to an object produced via the sand casting process. Sand castings are produced in specialized factories called foundries. In 2003, over 60% of all metal castings were produced via sand casting.
In materials science, quenching is the rapid cooling of a workpiece in water, gas, oil, polymer, air, or other fluids to obtain certain material properties. A type of heat treating, quenching prevents undesired low-temperature processes, such as phase transformations, from occurring. It does this by reducing the window of time during which these undesired reactions are both thermodynamically favorable and kinetically accessible; for instance, quenching can reduce the crystal grain size of both metallic and plastic materials, increasing their hardness.
Carburizing, or carburising, is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. The intent is to make the metal harder and more wear resistant. Depending on the amount of time and temperature, the affected area can vary in carbon content. Longer carburizing times and higher temperatures typically increase the depth of carbon diffusion. When the iron or steel is cooled rapidly by quenching, the higher carbon content on the outer surface becomes hard due to the transformation from austenite to martensite, while the core remains soft and tough as a ferritic and/or pearlite microstructure.
Case-hardening or carburization is the process of introducing carbon to the surface of a low carbon iron or much more commonly low carbon steel object in order to enable the surface to be hardened.
Metal injection molding (MIM) is a metalworking process in which finely-powdered metal is mixed with binder material to create a "feedstock" that is then shaped and solidified using injection molding. Metal injection molding combines the most useful characteristics of powder metallurgy and plastic injection molding to facilitate the production of small, complex-shaped metal components with outstanding mechanical properties. The molding process allows high volume, complex parts to be shaped in a single step. After molding, the part undergoes conditioning operations to remove the binder (debinding) and densify the powders. Finished products are small components used in many industries and applications.
A foundry is a factory that produces metal castings. Metals are cast into shapes by melting them into a liquid, pouring the metal into a mold, and removing the mold material after the metal has solidified as it cools. The most common metals processed are aluminum and cast iron. However, other metals, such as bronze, brass, steel, magnesium, and zinc, are also used to produce castings in foundries. In this process, parts of desired shapes and sizes can be formed.
Carbonitriding is a metallurgical surface modification technique that is used to increase the surface hardness of a metal, thereby reducing wear.
In metallurgy and materials science, annealing is a heat treatment that alters the physical and sometimes chemical properties of a material to increase its ductility and reduce its hardness, making it more workable. It involves heating a material above its recrystallization temperature, maintaining a suitable temperature for an appropriate amount of time and then cooling.
Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-alloy steels. They are also used on titanium, aluminium and molybdenum.
A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, and they have many uses, including cutting stone, concrete, asphalt, bricks, coal balls, glass, and ceramics in the construction industry; cutting semiconductor materials in the semiconductor industry; and cutting gemstones, including diamonds, in the gem industry.
Diffusion hardening is a process used in manufacturing that increases the hardness of steels. In diffusion hardening, diffusion occurs between a steel with a low carbon content and a carbon-rich environment to increase the carbon content of the steel and ultimately harden the workpiece. Diffusion only happens through a small thickness of a piece of steel, so only the surface is hardened while the core maintains its original mechanical properties. Heat treating may be performed on a diffusion hardened part to increase the hardness of the core as desired, but in most cases in which diffusion hardening is performed, it is desirable to have parts with a hard outer shell and a more ductile inside. Heat treating and quenching is a more efficient process if hardness is desired throughout the whole part. In the case of manufacturing parts subject to large amounts of wear, such as gears, the non-uniform properties acquired through diffusion hardening are desired. Through this process, gears obtain a hard wear-resistant outer shell but maintain their softer and more impact-resistant core.
Induction brazing is a process in which two or more materials are joined together by a filler metal that has a lower melting point than the base materials using induction heating. In induction heating, usually ferrous materials are heated rapidly from the electromagnetic field that is created by the alternating current from an induction coil.
Endothermic gas is a gas that inhibits or reverses oxidation on the surfaces it is in contact with. This gas is the product of incomplete combustion in a controlled environment. An example mixture is hydrogen gas (H2), nitrogen gas (N2), and carbon monoxide (CO). The hydrogen and carbon monoxide are reducing agents, so they work together to shield surfaces from oxidation.
Ipsen International Holding GmbH of Kleve, Germany develops, constructs and manufactures industrial furnaces. Its managing directors are Geoffrey Somary and Houman Khorram.
Materials for use in vacuum are materials that show very low rates of outgassing in vacuum and, where applicable, are tolerant to bake-out temperatures. The requirements grow increasingly stringent with the desired degree of vacuum to be achieved in the vacuum chamber. The materials can produce gas by several mechanisms. Molecules of gases and water can be adsorbed on the material surface. Materials may sublimate in vacuum. Or the gases can be released from porous materials or from cracks and crevices. Traces of lubricants, residues from machining, can be present on the surfaces. A specific risk is outgassing of solvents absorbed in plastics after cleaning.