Cost-effective heat-treatment of aerospace fabrications

Citation

(2003), "Cost-effective heat-treatment of aerospace fabrications", Aircraft Engineering and Aerospace Technology, Vol. 75 No. 3. https://doi.org/10.1108/aeat.2003.12775cab.002

Cost-effective heat-treatment of aerospace fabrications

Cost-effective heat-treatment of aerospace fabrications

A large Carbolite oven designed to meet the construction and temperature uniformity requirements of major aircraft manufacturers has been installed by RSM Fabrications to provide in-house heat-treatment of aluminium alloy fabrications (Plate 2).

The equipment has replaced a smaller Carbolite oven supplied 5 years ago which was no longer able to cope with the quantity of material now produced by the company in its Hampshire factory, even though it was operating almost continuously 7 days a week. The range of products manufactured by RSM Fabrications has also expanded considerably over the last 5 years. In addition to manufacturing pipe and duct sub-assemblies for commercial and military aircraft, the company now also produces a wide variety of sheet metal air-frame fabrications. Many of these were too large for the 500 m × 50 m × 500 mm chamber of the original oven and had to be heat-treated by external subcontractors.

Plate 2 Carbolite oven at RSM Fabrications

The new equipment, which has a chamber measuring 1,500 mm wide × 1,200 mm high × 1,500 mm deep, is now typically operated for 8 h a day – less than 25 per cent of the time needed with the smaller unit, bringing significant savings in energy costs. A further advantage is said to be a substantial reduction in sample testing, as only one sample is required for each load processed.

The oven has an operating temperature range from 100 to 600°C, provided by a series of incolloy sheathed rod elements positioned behind the side duct sheets and isolated from the working area to prevent heat radiating directly on to any part of the load. An air circulation system with two heavy-duty fans, which give a powerful horizontal air flow through the chamber, produces temperature uniformity better than ±3°C.

The equipment is used for solution heat treatment at 475-530°C, annealing at 360-450°C and precipitation hardening at 120-175°C. Process times range from 20 min for annealing to 14 h for the longest precipitation hardening programmes.

The materials processed are generally between 0.4and 3 mm thick and can range from 10 mm diameter washers to 1,000 mm × 1,000 mm sheets with profiled details. For ease of handling and to ensure the products are held securely throughout the process, a stainless steel basket is used, which fits on tracks in the base of the chamber.

At the end of a heating cycle the basket is pulled manually on to a platform immediately in front of the oven, which lowers it automatically into a water quench tank below. This arrangement reportedly allows quenching to be performed within the 10 s required by the aerospace industry for solution heat treatment of aluminium alloys.

A PID instrument which can store four programs, each with up to 16 segments, controls time and temperature functions. The control system also includes an over-temperature protection system and a chart recorder.

Details available from: Carbolite. Tel: +44 (0) 1433 620011; Fax: +44 (0) 1433 621198; E-mail: info@carbolite.com; Web site: www.carbolite.com