Vacuum Ovens Information
In vacuum ovens, the heat-treating process takes place inside a vessel that is airtight. This allows a vacuum to be drawn inside the vessel. The entire heat-treating process can take place under vacuum or precisely controlled atmospheres can be introduced. Heat treating under vacuum can:
- prevent surface reactions, such as oxidation or decarburization
- remove surface contaminants such as oxide films and residual traces of lubricants
- add a substance to the surface layers of the work
- remove dissolved contaminating substances from metals by means of degassing
Ovens are built of several kinds of high temperature (refractory) materials to hold the process material and hold in the heat without breaking down during the several months that they usually run. Ovens are lower temperature (usually <1400 ° F) thermal processing units, usually without refractory insulation.
Important parameters to consider when specifying vacuum ovens include temperature range, capacity, and pressure range. The temperature range is the maximum temperature at which the unit may operate and still maintain rated performances. The capacity refers to the capacity of the heated interior space of the unit. Vacuum ranges for vacuum ovens can be rough or low (< 760, > 1 torr), medium (< 1, >10-3 torr), high vacuum (< 10-3, >10-8 torr), ultra-high vacuum (< 10-8 torr), and elevated pressures (> 760 torr).
Configurations of vacuum ovens include tube or muffle, bench or cabinet, vertical, and walk-in or truck-in. A tube or muffle oven is an oven in which the heating is indirect; the material to be heated is contained in a refractory container heated from the outside. Cabinet or bench ovens describe small batch equipment typically mounted on integral stands. Batch ovens are typically suited for processing quantities of a product in a single batch. Vertical units are a space saving configuration, the oven is vertical instead of horizontal. This typically requires greater height clearances. Walk-in or truck-in ovens describe larger size batch equipment, typically with double doors and integral carts, shelves, etc. Batch ovens are typically suited for processing larger quantities of product in a single batch.
Heating sources for vacuum ovens include arc, electric or resistance, and induction. In an arc configuration, an arc between graphite electrodes and the metal generates heat. Both carbon and alloy steels are produced in electric arc ovens, and scrap, rather than molten metal, is used as the base material. In an electric or resistance heated unit the heat source is powered by electricity—typically utilizing existing factory voltages. Induction is a widely used process for the surface hardening of steel. The components are heated by means of an alternating magnetic field to a temperature within or above the transformation range followed by immediate quenching. Controller types can be single set point or programmable.
Common applications for vacuum ovens include preheating, quenching, sterilizing, aging, annealing, baking, brazing and soldering, burn-off, curing, drying, firing and sintering, foundry and melting, heat treating, hot pressing, industrial, and laboratory. Features common to vacuum ovens include a cooling system, shelving, racks, and carts, air filtration, timers, alarms, logging and recorder options, and explosion proof construction.
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