Vacaero

Manufacturers of heat treating and brazing vacuum furnaces and controls, complete hot zone and vacuum furnace retrofits, thermal spray coatings, plasma, HVOF and paint coating services.

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Archives for June 2017

Preventive Maintenance Extends Hot-Zone Life

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Stretching the service life of a hot zone-one of the most expensive consumables in a vacuum furnace-is of prime importance to the furnace owner. Proper care and maintenance can slow down hot-zone deterioration, which directly translates to cost savings. Hot-zone service life is directly related to the type of heat treating process used in a vacuum furnace and to the severe thermal stresses imposed by continuous vacuum-furnace cycles. Distortion and contamination are the main factors causing a breakdown of hot-zone components. Distortion is inevitable because thermal cycling is inherent to the process. However, periodic inspection and remediation of hot-zone components together with thorough component cleaning can extend service life.

Two main types of hot zone construction used in vacuum furnaces today are an all-metal zone and a carbon-felt zone. An all-metal zone consists of several layers of sheet metal, such as molybdenum, stainless steel, and tantalum, separated by channels. The choice of material depends on operating conditions. For example, a zone that will be subjected to an operating temperature of 2400°F (1315°C) could consist of two inner layers of molybdenum backed by three layers of stainless steel. A hot zone intended for use at temperatures to 2600°F (1430°C) generally is made entirely of molybdenum. Reflective heating is used in an all-metal zone; that is, radiation from heating elements is reflected off the inner layer of molybdenum back to the parts being treated. Heat is contained in the hot zone through the use of channels, which create gaps between each sheet metal layer. Each gap creates an area of insulation with each successive layer being cooler.

Space Simulation Chambers – Part 1

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Manufacturers of materials, components, and machines for spacecraft and satellites deployed in space must vigorously test them prior to putting them into service. For example, linear actuator mechanisms on satellites have failed to function properly (extend or retract) because of a loss of tolerance due to the conversion of retained austenite to martensite and subsequent growth of the part due to volume expansion. Had this test not been performed in a simulation chamber at -62ºC (-80ºF) here on Earth, a solar array or communications antenna would not have deployed when the satellite was in orbit and its mission would have been compromised.

In order to ensure thermal and vacuum readiness of these systems prior to lift off, they must be subjected to the extreme vacuum and temperature of space to ensure they can withstand and perform under these harsh conditions without failure. Space simulation (aka space test) chambers are used to perform this testing. The challenging conditions encountered in space and the development of the space simulation chamber are the focus of our discussion.

Getter Materials

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Experience has shown us that sensitive materials in the presence of minute quantities of unwanted gaseous contaminates can destroy the integrity and shorten the life expectancy of components. It is natural to ask ourselves what can be done to further protect the work in a vacuum environment after the pumps have done their part in reducing the chamber pressure to as low as is economically feasible in a production environment? This task falls on getter materials.

A getter is simply a reactive material that is deliberately placed inside a vacuum system for the purpose of improving the efficiency of that vacuum by scavenging unwanted contaminates. Essentially, when gas molecules strike the getter material, they combine with it chemically or by adsorption so as to be removed from the environment. In other words, a getter eliminates even minute amounts of unwanted gases from the evacuated space.