Maintenance procedures and safe working conditions are essential in maintaining vacuum furnaces as is proper preparation of components to be heat treated prior to charging to the furnace.

VAC AERO International operates more than a dozen vacuum furnaces in its own heat treating facilities. In addition, it has manufactured hundreds of vacuum furnaces for sale to the global market. Through these activities, the company has gained extensive experience in the care and maintenance of vacuum furnace equipment.

The assembly is a five-piece, tubular structure manufactured entirely from 4330V steel. It consists of a hollow tube approximately 1500mm long by 120mm in diameter, two fittings (upper and lower) that are TIG welded to each end of the tube and two backing rings that bridge the gaps between the fittings and the tube during the welding operation. For many years, VAC AERO has been performing welding and heat treating operations on a landing gear component for a popular turboprop aircraft. Because of the part design, the welding operation in particular is complex and challenging and often involves substantial re-work. In order to minimize the rate of re-work...read more. by Jeff Pritchard CEO, VAC AERO International Inc.

In recent years, the operating temperatures of land-based gas turbine engines have increased to improve efficiency.  As a result, greater demands are placed on the materials used in the manufacture of the engine components.

In particular, hot section turbine blades must function in a very severe operating environment.  The blades are usually manufactured from advanced nickel-based superalloys but these materials on their own are still not durable enough.  To enhance their durability, they are protected from hot corrosion and high temperature oxidation through the use of special coatings.  The coatings form adherent oxide layers that inhibit the blade material from directly interacting with potentially damaging elements within the combustion gases like oxygen, sulphur and other contaminants.  A popular approach involves coating the blades with an MCrAlY bond coat topped with a thermal barrier coating (TBC) overlay. READ MORE

Vacuum level as indicated by vacuum gauge readings is not always a true indication of the actual conditions within a vacuum furnace. It is possible to have two identical furnaces operating at the same pressure but producing entirely different results on heat treating.

The reason for this can be explained by the relative leak tightness or leak rate of each furnace. Most furnaces are equipped with pumping systems sufficient to overcome reasonably significant leaks. On the furnace with the higher leak rate, air would be leaking continuously into the furnace resulting in a higher residual oxygen content than in the leak tight furnace. The higher oxygen content would adversely affect the heat treating results. Therefore, leak rate checks as prescribed by the furnace manufacturer should be performed at regular intervals to prevent this problem. READ MORE

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

Whenever the door to a vacuum furnace chamber is open, humidity from the air will enter the chamber and condense in a very thin film on the chamber walls or be absorbed into the hot zone materials.

When the chamber is subsequently evacuated (before heating) and the furnace internals are exposed to this lower pressure, “outgassing” of the entrapped moisture will occur. If sufficient moisture has been entrapped (such as in very humid environments), the outgassing effect will slow the pumpdown process and may even give the appearance of a malfunction in the pumping system. Eventually, the outgassed moisture will be pulled out of the chamber by the pumping system and evacuation rates will improve. This same effect will be apparent when oily or contaminated workloads are placed in the furnace. It may be more pronounced in furnaces with graphite-based hot zone insulation materials. READ MORE

This is the third in a series of four articles on Vacuum Furnace Maintenance. (read part 1) / (read part 2)

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)

Clean, oxide-free surfaces are essential to achieve sound brazed joints. 

Uniform capillary action will occur only when all grease, oil, dirt and oxides have been removed from both the braze alloy and base metal prior to brazing. The length of time that cleaning remains effective depends on the material involved, atmospheric conditions, storage techniques and the amount of handling that may be involved. It is recommended that brazing be performed as soon as possible after the material has been cleaned. The selection of a cleaning technique depends on the nature of the contaminant, the base metals involved and the joint design. The same cleaning practices used for vacuum heat treating (ie. manual cleaning, vapour degreasing, etc.) are applicable to vacuum brazing. READ MORE

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