BAe Aerostructures converts to steel shot peening

Citation

(1999), "BAe Aerostructures converts to steel shot peening", Aircraft Engineering and Aerospace Technology, Vol. 71 No. 1. https://doi.org/10.1108/aeat.1999.12771aab.010

BAe Aerostructures converts to steel shot peening

BAe Aerostructures converts to steel shot peening

Keywords Blasting, Peening, Wheelabrator Tilghman

British Aerospace Military Aircraft and Aerostructures Ltd at Chadderton has installed a wheel-blast peening machine using cast steel shot. The facility partly replaces a glass bead peening facility that uses air blast technology which has been in operation at Chadderton for the last 15 years.

The Wheelabrator machine is being used to metal shot peen aircraft stringers and chords for the US aircraft industry under a ten-year contract and represents a substantial investment by BAe towards improvements to increase production capacity at Chadderton.

The wheel blast machine from USF Wheelabrator Tilghman in Halifax was selected on grounds of cost and processing capability. Similar machines using air blast technology were found to be excessively costly for the same result (Plates 5 and 6).

The specification required the facility to peen aluminium alloy extrusions of T, H, Z and J sections for the purpose of fatigue life enhancement and improved resistance to stress-corrosion cracking of the machined surfaces. The facility was required to peen each surface on each face to a saturated intensity of 0.004in. to 0.010in.A (0.1mm to 0.25mm) at 100 per cent coverage.

Plate 5 Peening system from USF Wheelabrator Tilghman, at British Aerospace, Chadderton

Plate 6 Inside the acoustic chamber surrounding the USF Wheelabrator Tilghman peening machine at British Aerospace, Chadderton

Almen gauge testing of representative aluminium alloy sections was carried out to an accuracy of 1/10,000th of an inch (0.0025mm) before shipping the facility from the Wheelabrator Tilghman factory. All testing was witnessed by BAe and carried out in accordance with BAe requirements. The steel shot is controlled and inspected to meet and exceed the requirements of MIL-S-851 Type 1 and screened to the tolerances in MIL-S- 13165.

The peening machine is of the roller conveyor type, manually loaded and unloaded, with 15 metres of conveyor at the input and output ends. It has a peening envelope of 12in. × 12in. (300mm x 300mm) and will theoretically accept components of any length.

Peening is achieved by six 12in. (300mm) diameter rotary blast wheels, rated at 7.5kW (10hp) and driven by potentiometer controlled inverters, giving a wheel speed range of 1,200 to 3,000rpm. The wheels are positioned in the peening cabinet to achieve 100 per cent coverage at saturation of all areas on the component to be peened.

Shot flow to the wheels is maintained at a constant rate by six potentiometer controlled magna-valves, enabling various shot feed rates to be achieved. At maximum rating the machine is capable of throwing approximately 3,600lb (1,600kg) of shot per minute.

Various Archimedes screws transport used shot from the peening cabinet to the elevator for recycling. It is then passed through various meshes and screens to remove large debris before passing through an air-wash separator that removes fines and dust. Finally the shot passes through a classification system that removes broken and misshapen shot.

The facility stands in an acoustic chamber that limits external noise to below 80db. It is also supplied with a reverse pulse jet type dust collection system which limits the particulate emissions to the shopfloor atmosphere to below recommended levels.

BAe's specialist peening engineer at Chadderton, Paul Fletcher, commented: "The facility designed by Tilghmans is now processing production components previously blasted using glass bead peening methods. The facility has enabled processing throughput to be increased by at least six-fold, with peening carried out in a more controllable and sustainable manner than the old process. The facility was also designed, manufactured, installed and commissioned to the satisfaction of all parties within agreed timescales and costs."

Details are available from USF Surface Preparations Ltd. Tel: +44 (0) 1422 330603; Fax: +44 (0) 1422 348575.