tailieunhanh - Hydroblasting and Coating of Steel Structures Episode 3

Tham khảo tài liệu 'hydroblasting and coating of steel structures episode 3', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 28 Hydroblasting and Coating of Steel Structures for efficient coating removal Kaye et al. 1995 . The duration of the jetting stage is tj 2 tp Field 1999 . Multiple Drop Impact The number of impinging water drops is critical to the material removal process. The situation can be generalised by the relationship shown in Fig. . This function can sufficiently be described by mc N0 ar ND - No b . The following three regions can be distinguished in Fig. region I ND Nd for very small numbers of impinging drops no material removal occurs the number of drops is not sufficient to visibly damage the material. The critical drop number Nd can be considered to be an incubation number. region II No No. bl 1 a linear relationship with a progress of 1 exists between drop number and removed material. Any additional drop impact removes an equivalent mass of material. region III Nd Nd 0 bl 1 the progress of the function drops and Nd . The erosion efficiency declines which can be explained by drop break-up due to the roughened surface also the impact is no longer normal to the whole of the surface. 0 Vỏ 20 40 60 80 Number of impacting drops in 106 Figure Drop number influence on mass loss measurements Baker et al. 1966 . Fundamentals of Hydroblasting 2 9 Parameter Influence on the Coating Removal Parameter Definition Target parameters for coating removal Basic target parameters include coating thickness hc mass removal mc and cleaning width wc . They are illustrated in Fig. a . For the erosion by a stationary waterjet these parameters are related through the following approximation mc tt 4 w2. hc pc. For a given cleaning width a certain coating mass must be removed to completely penetrate the coating with a given thickness. A maximum mass removal is desired. The energy efficiency of the cleaning process is given by the specific energy Es E mc. This parameter should be as low as possible its physical unit is kj kg. The cleaning rate