During construction, all welded joints in a vacuum furnace are inspected for hermetic integrity and should remain intact for the life of the furnace.

However, there are also a number of demountable connections that can be separated and reconnected for component changing or repair access reasons. These connections are generally sealed with a gasket sandwiched between two flanges. Though different gasket materials are used depending on the vacuum level required, most seals in a standard vacuum furnace incorporate an o-ring made of natural or synthetic rubber. Buna-N, silicone and Viton o-rings are readily available in many sizes. READ MORE

This is the second in a series of four articles on Vacuum Furnace Maintenance. (read part 1)

As with any piece of equipment, proper maintenance at regular intervals is essential for long service life and trouble free operation.

The mechanical components in a vacuum furnace require standard maintenance practices (ie. cleaning, lubrication, etc.). However, successful use of a vacuum furnace depends on the purity and reliability of its vacuum. Additional maintenance activities are required to ensure good vacuum levels in the system. Leaks in joints and contamination of furnace internals will greatly affect operating vacuum levels and the quality of the processing.  Leaks are the most time-consuming and troublesome of the maintenance items. READ MORE

This is the first in a series of four articles on Vacuum Furnace Maintenance due to appear over the next three months.

There are a number of factors that influence the development of a brazing cycle. These include such things as base metal and braze alloy composition, mass of the assembly and joint design. 

However, each cycle is comprised of a number of common segments. The illustration below shows the typical profile for a vacuum brazing cycle. During the initial pumpdown, water vapour adsorbed by the parts and furnace is driven off. For most brazing applications, a pumpdown before heating to a vacuum level of 8 x 10-4 torr or better is recommended. A vacuum safety interlock should be programmed into the cycle to ensure this level is reached. After pumpdown, the initial heating rate should not exceed 15ºC (30ºF) per minute. Faster rates may cause paste braze alloy to spall off or distortion of the assembly. Heating continues to a stand off temperature at about 25ºC (50ºF) below the solidus temperature of the braze alloy. The load is then soaked at this temperature to ensure temperature uniformity and to allow vacuum levels to recover. A soak time of 30 minutes is usually sufficient, though the incorporation of a second vacuum safety interlock in the braze cycle program may be desirable. READ MORE

This is the last in a series of four articles on Vacuum Brazing Tecniques. (read part 1) / (read part 2) / (read part 3)

Most base metals typically brazed in vacuum furnaces have a natural oxide “coating” that can inhibit the flow of brazing filler metals. 

The oxides of the less reactive metals like iron, nickel and cobalt tend to dissociate (break down) under low pressure and high temperature. Therefore, alloys such as the 300 and 400 series stainless steels, carbon steels and many tool steels can be successfully brazed in vacuum at relatively high pressures (1 to 50 microns). READ MORE

This is the first in a series of four articles on Vacuum Brazing Tecniques due to appear over the next three months.

All furnace equipment used for heat treating should be properly instrumented and periodically tested for uniformity.

The temperature uniformity within the furnace must be regularly surveyed. The frequency of surveying is largely dependent on the type of equipment in use and its previous history in accuracy and reliability. Exact survey frequencies should be determined from applicable processing specifications. However, quarterly temperature uniformity surveys are fairly standard. The purpose of the uniformity survey is to determine the range of temperatures present at different locations in the furnace under normal operating conditions. A furnace is normally qualified through an initial comprehensive survey. READ MORE

In any heat treating cycle, there are two important considerations concerning temperature: the temperature of the furnace hot zone which is generating the heat input, and the temperature of the actual workload.

Heating by direct radiation, the main heating mechanism in vacuum, tends to be a slower process than other heating mechanisms such as convection or conduction. As a result, there are times in the heat treating cycle, particularly during heat up, when the load will be at a lower temperature than the furnace hot zone. This is known as temperature lag. READ MORE

Good fixturing and loading practices are essential elements in achieving proper heat treating results and long equipment life.

Fixture materials and design must be appropriate for the processing application.  Maintenance of fixtures is equally important.  The possibility of reactions between the workpieces and baskets or fixtures must also be considered.  High temperature sintering of the workpieces to themselves or the fixtures can occur.  Eutectic melting can also occur when certain chemical compositions come into contact at high temperature.  Selection of a fixture material is influenced by cost, service environment and compatibility with the workpiece and furnace hearth. READ MORE

OAKVILLE, Ontario, (July 17, 2008) –  VAC AERO has been awarded an order for two large vacuum furnaces from Bodycote, the world’s largest supplier of thermal processing services. The equipment is destined for Bodycote’s facility in Berlin, Connecticut. Both vertical, bottom-loading furnaces have work zone areas 72" diameter by 72" high, VAC AERO’s unique graphite felt and…

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The Ultimate Cleaning Treatment For Superalloy Repair.

All gas turbine engines require regular overhaul to ensure continued safe operation. During engine overhaul, decisions must be made on whether to replace deteriorated individual parts and assemblies with new components or to repair them. The ultimate decision depends on both technical and commercial criteria. That is, is there a technically sound repair available and, if so, is it economically favorable compared to the cost of a replacement component? Sometimes lack of availability of replacement components may override purely economic criteria. READ MORE 

Once a good fixture design has been developed, careful consideration should next be given to the loading of the workpieces.

Heating in a vacuum depends mostly on the transfer of energy through radiation from the elements to the load.  For uniform heating and cooling, it is important that the workpieces are not shielded by one another.  Pieces within the load should be evenly spaced to ensure even exposure to radiation.  The size, shape and high temperature strength of the workpiece should also be considered during loading.  Alloys with complex shapes and relatively low strength at heat treating temperatures may distort during processing.  In some cases, it may be necessary to support these components with specially designed fixtures. READ MORE