Volume 17 - Nondestructive Evaluation and Quality Control Part 14

Tham khảo tài liệu 'volume 17 - nondestructive evaluation and quality control part 14', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Wet Technique. The magnetic particles selected are nonfluorescent and suspended in a liquid vehicle. The magnetizing equipment is capable of inducing a magnetic flux of suitable intensity in the desired direction by both the circular and the longitudinal methods. Direct current from generators storage batteries or rectifiers is used to induce the magnetic flux. Circular magnetization is obtained by passing the current through the forging being examined or through a central conductor to induce the magnetic flux. Longitudinal magnetization is obtained by using a solenoid coil or magnet to induce the magnetic flux. The magnetic particles are nontoxic and exhibit good visual contrast. The viscosity of the suspension vehicle for the particles must be a maximum of 5 X 10-6 m2 s centistokes at any bath temperature used. The magnetic particles are limited to 28 to 40 g to oz of solid per gallon of liquid vehicle. The liquid used as a vehicle for the magnetic particles may be a petroleum distillate such as kerosene. Tap water with suitable rust inhibitors and wetting and antifoaming agents can be substituted for the petroleum distillate. The water should contain about antifoam agent rust inhibitor and wetting agent. Inspection is carried out by the continuous method. For this method the magnetizing circuit is closed just before applying the suspension or just before removing the forging from the suspension. The circuit remains closed for approximately to s. For circular magnetization an ammeter is used to verify the presence of adequate field strength. For verifying adequate field strength in longitudinal magnetization a field indicator is useful. Typical current levels utilized to provide an adequate field strength are 4 to 12 A mm 100 to 300 A in. of diameter of the surface being examined although current levels of up to 30 A mm 750 A in. of diameter have been used. The magnetizing force for longitudinal magnetization is 2000 to 4000 ampere-turns

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