Tham khảo tài liệu 'process engineering equipment handbook episode 2 part 8', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Metallurgy Metallurgical Repair Metallurgical Refurbishment M-37 deceptively simple and is often misused. Surface preparation is particularly important because defects can easily be masked by overpeening. In the analysis of service-exposed components such as discs and blades a judicious compromise is often required on the surface preparation. Light glass bead cleaning is often effective in removing surface deposits with minimal loss in sensitivity however care must be taken not to overpeen the surface. Where optimum sensitivity is required such as in rotating blades the parts should be chemically etched after glass bead cleaning to remove metal peened over the discontinuities. LPI is designed to locate only discontinuities that are open to the surface. When a penetrant is applied to the surface of a component it is drawn into surface discontinuities by capillary forces. After the excess penetrant has been removed from the surface the penetrant trapped by the defects is drawn back out by capillary action and forms a detectable outline of the defect. Over the years many penetrants have been developed that vary in sensitivity and application. As indicated in the enclosed information sheets from the manufacturers the penetrants are divided into water washable and post-emulsifiable solvent remover types. Commonly used penetrants include ZL-17B or Ardrox 970-P10 water washable and ZL-22A solvent type . Care must be taken to ensure that the correct combinations of penetrants removers and developers are used. In addition a test should never be repeated using a different penetrant type because complete masking of the defects will occur. Field inspections are particularly challenging because the inspection conditions are generally not ideal and often the operator does not have all the equipment desired. Although some compromises are often required the inspector must ensure that the sensitivity and validity of the test are not jeopardized. Laser techniques. These can be used
