Search results

Cleaning metals used in helicopter manufacture. As a result of a search for a generalised method of cleaning metals used in helicopter construction, and which would be safe in all areas, Westland Helicopters Ltd, Yeovil, now uses two Oakite cleaners throughout the factory. Both are alkaline and are supplied in bulk by Oakite Ltd. Both have had to meet stringent AQD approved internal specifications for metal treatment which include requirements that chemical reaction with, or attack by, the cleaner on the metal surface and that tolerances of 0.0001 inch (0.025mm) must be maintained, especially on magnesium.

Vacuum blasting has come a long way in the last ten years from heavy industrial units to lightweight all purpose tools giving very high work output under severe conditions. Demands of Health and Safety regulations are now placing pressures on specifiers and contractors to clean up their shot blasting operations. To meet these requirements vacuum blasting equipment manufacturers have developed products to compete more favourably with open blasting, such a product is “Blast N' Vac” being widely used in the construction and off‐shore oil industry. Using a range of heads coupled to an air vacuum pump, a system can be specified to operate around 60 metres from the base equipment. With a BNV‐5 workhead and a nozzle of 7.5mm. concrete and brickwork can be grit blasted leaving a clean even surface or by using heavier grits and higher pressures concrete facings can be removed prior to re‐coating. Rates of work vary depending on type of surface being treated but previously where rates came out at about half that of open blasting the new range of heads have closed that gap to around two thirds. If one now takes in the pollution and cleaning up factors it makes vacuum blasting a more viable alternative. Operator fatigue has always been the major factor in vacuum blasting tools but again with Blast N' Vac, BNV‐3 & 5 workheads only weighing 3 lbs. and 3½ lbs. respectively, coupled to lightweight blast and vacuum hoses give the operators less effort in the blasting operations so leading to a more satisified and efficient blaster.

Economics of surface coatings on metals are discussed with emphasis on surface preparation, especially when large scale coating operations are conducted. Relative cost and other parameters affecting the choice between manual and machine blasting are considered, including the area cost of surface preparation, health and safety factors, incidental pollution, and other variations. Advantages of high build surface and multi‐purpose primer application are related along with comparisons of cost between initial and manual recoating of structures after erection. Importance of proper coating maintenance is emphasised. Economic case histories are given, including large scale surface preparation of tank plates and piping, differences between sand abrasive and centrifugal blasting, factors related to intercoat adhesion, cost of Zn rich with epoxy or alkyd topcoats, and the high cost of repainting when scaffolding is necessary. Regulations on surface preparations, ecological controls, and safety are discussed. Two coat simplified systems are recommended, along with automatic and semiautomatic surface preparation when the size of the job makes either one possible. Tabulated data on area costs of various modes an locations for surface preparation and coating costs for various metal configurations are provided.

Blasting is an economical method for rock breakage in open-pit mines. Backbreak is an undesirable phenomenon induced by blasting operations and has several unsuitable effects such as equipment instability and decreased performance of the blasting. Therefore, accurate estimation of backbreak is required for minimizing the environmental problems. The primary purpose of this paper is to propose a novel predictive model for estimating the backbreak at Shur River Dam region, Iran, using particle swarm optimization (PSO).

For this work, a total of 84 blasting events were considered and five effective factors on backbreak including spacing, burden, stemming, rock mass rating and specific charge were measured. To evaluate the accuracy of the proposed PSO model, multiple regression (MR) model was also developed, and the results of two predictive models were compared with actual field data.

Based on two statistical metrics [i.e. coefficient of determination (R²) and root mean square error (RMSE)], it was found that the proposed PSO model (with R² = 0.960 and RMSE = 0.08) can predict backbreak better than MR (with R² = 0.873 and RMSE = 0.14).

The analysis indicated that the specific charge is the most effective parameter on backbreak among all independent parameters used in this study.

Introduction Blast cleaning is a tried and tested method of cleaning metal surfaces and preparing them for painting, or for such sophisticated modern finishing processes as are necessary to resist corrosion in the atmosphere, under water or in other aggressive environments. Although the process has been in use for a long time, and the earliest sand blasting operations can be dated back to the middle of the last century, blast cleaning is certainly not limited to the realms of intermediate technology.