Carbon fibre-reinforced carbons (C/C for short) are used in modern vacuum or protective gas furnaces in the form of heating elements or charging systems. They are characterised by thermal shock resistance, absence of distortion, low mass and strength increase with rising temperature. These features enable users to operate their plants more effectively, minimise reject rates and therefore reduce the cost of production. C/C is thus a key element in many process optimisation steps and helps companies to improve their competitiveness. by Alexander Racek, SGL CARBON GmbH

The heat treatment of landing gear is a complex operation requiring precise control of time, temperature, and carbon control. Understanding the interaction of quenching, racking, and distortion contributes to reduced distortion and residual stress. Arguably, landing gear has perhaps the most stringent requirements for performance. They must perform under severe loading con­ditions and in many different envi­ronments. They have complex shapes and thick sections. Alloys used in these applications must have high strengths between 260 to 300 ksi (1,792 to 2,068 MPa) and excellent fracture toughness (up to100 ksi in.1/2, or 110 MPa×m0.5). To achieve these design and per­formance goals, heat treatments have been developed to extract the optimum performance for these alloys. By D. Scott MacKenzie, Houghton International Inc. Valley Forge, PA

For heat treating purposes, "quenching" can be defined as the rapid cooling of a metal to impart some desired property such as hardness.

Different metals and alloys require different quenching rates to achieve their optimum properties. Regardless of equipment design, gas quenching in vacuum furnaces involve the same basic principles. The gas quenching process normally consists of the following sequence of events. First, the power to the heating elements is shut off. Next, the furnace chamber and quench loop are backfilled with a non-reactive gas, commonly nitrogen or argon. READ MORE

There are several factors to be considered in preparing workpieces for vacuum heat treating or brazing. Cleanliness of the workpieces and baskets or fixtures is very important.

They must be free of oil, dirt, machining lubricants or other contaminants prior to being loaded into the furnace. Some lubricants contain sulphur compounds which can adversely affect the alloys being heat treated. Inadequate cleaning can also cause staining and discoloring of the end product or result in poor braze alloy flow. Contaminants with high vapour pressures will evaporate during heating causing loss of vacuum. The vapours may eventually condense on colder surfaces in the furnace only to re-vaporize to cause contamination problems in subsequent runs. READ MORE

VAC AERO’s Oakville Furnace Manufacturing Division continues to be busy. Contracts have recently been completed for customers in the Philippines, U.K. and the United States. Final commissioning activities are almost complete for installations in Russia and Korea. New orders have been received from customers in Poland, the United States and Canada. VAC AERO’s newest interactive…

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When heat treating or brazing in vacuum, the vapour pressure of the constituents in the materials being processed can be a very important consideration. 

The vapour pressure of a material is that pressure exerted at a given temperature when a material is in equilibrium with its own vapour.  Vapour pressure is a function of both the material and the temperature.  Figure 1 shows approximate vapour pressure curves for a variety of metals and compounds.  The area to the left of each curve represents the conditions of temperature and pressure under which the material exists as a solid.  The area to the right of each curve represents those conditions under which the material exists as a gas (or vapour).

VAC AERO’s Boucherville, Quebec facility has long held thermal spray and inorganic paint approvals for a variety of coating applications. Recently, the facility has become approved for a complementary grinding capability that allows it to act as a one-stop shop for applying and finishing chrome oxide coatings and paint used on turbine shafts and seal runners….

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In vacuum processing, metal surfaces remain very clean and free of oxides. When these near-perfect surfaces are in contact with other surfaces, certain elements have a tendency to interact between the surfaces through solid state diffusion. Therefore, a major consideration when selecting both hearth and load fixturing materials for vacuum heat treating is the possibility of solid state diffusion between different materials in contact at high temperatures. Solid state diffusion of certain elements can cause the formation of a lower melting point alloy called a eutectic. For example, solid state diffusion between carbon and nickel can begin to occur at temperatures as low as 1165ºC (2130ºF) and cause local melting, also known as eutectic melting.

The air we breathe contains a number of elements that can react with metals under the proper conditions. Moisture, oxygen, carbon dioxide and hydrogen are present in significant amounts in our atmosphere. Each can react to varying degrees with many different metals. While many of these reactions occur to only a small extent at room temperature, they are often greatly accelerated in the presence of heat. Consider the example of a piece of polished metal held over a heat source. It will eventually turn blue or black as the elements in the atmosphere react with the hot metal.