The Flaw Detection Methods For Forged Parts, Steel Castings And Crankshafts

Magnetic particle inspection for forged steel parts

• The characteristics of flaw detection of forged steel parts: The forging process and forming methods are generally divided into two categories: free forging and die forging.The process flow is: blanking-heating-forging-(trimming)-flaw detection-machining-heat treatment-flaw detection-(surface heat treatment-flaw detection)-surface treatment-finished product delivery.Among them, the forging process is prone to defects such as cracks, folding and white spots; heat treatment will produce quenching cracks; machining will produce grinding cracks and correction cracks; surface heat treatment will also produce cracks.
• Flaw detection method selection: Generally, a fixed magnetic particle flaw detector is used for circumferential and longitudinal magnetization. If the remanence and coercivity of the material meet the requirements, it is recommended to use the remanence method for flaw detection.
• Magnetic particle inspection of crankshaftFlaw detection method: directly energize circumferential magnetization, check forging cracks, folding, grinding cracks, quenching cracks, and hair lines. The segmented coil is magnetized longitudinally, and the transverse cracks are inspected, including forging cracks, grinding cracks, correction cracks, quenching cracks, etc. Pay special attention to the observation of the corners and the edge of the oil injection hole during flaw detection.

Magnetic particle inspection of steel castings

• The characteristics of magnetic particle inspection of steel castings: steel castings are generally complex in shape, and the types and positions of defects are relatively regular. The main defects are casting cracks, porosity, shrinkage cavities, inclusions, pores and cold partitions.
• Choice of flaw detection method: Castings are generally small in size, which is convenient for flaw detection on a fixed flaw detector. All castings must undergo circumferential and longitudinal magnetization inspections. The continuous method is used for flaw detection before heat treatment, and the residual magnetic method is generally used for flaw detection after heat treatment. Check for pores and inclusions under the surface, and DC flaw detection should be used. For network cracks, it is best to use fluorescent magnetic particle inspection.
• Cam magnetic particle inspectionFlaw detection method: The blank is tested by continuous method, and after heat treatment, the residual magnetic method is used for flaw detection. The wheel part is inspected by the rod-through method, and the shaft part is magnetized circumferentially by the direct energization method, and then longitudinally magnetized by the coil. Focus on checking the cracks at the root.

Magnetic particle inspection of in-service and maintenance parts of special equipment

• The characteristics of magnetic particle inspection of in-service and repaired parts: mainly found fatigue cracks and stress corrosion cracks. The location of the crack is directly related to the force. The inspection conditions of in-service and repaired parts are poor, and the fatigue cracks are small. If conditions permit, use fluorescent magnetic particle inspection as much as possible. For bolt holes, the rod-through method should be used, and technologies such as endoscopes should be borrowed. Small bolt holes can also be inspected by rubber casting method.
• Bolt magnetic particle inspection: Bolts are fasteners, which are subjected to tensile force and are prone to transverse fatigue cracks. Therefore, longitudinal magnetization of the coil should be used. The residual magnetization method and the lower concentration of fluorescent magnetic particle inspection have the best effect.

Special workpiece magnetic particle inspection:

• Compression spring flaw detection: First, directly energize to check the longitudinal defects on the steel wire; then use the rod-through method to check the lateral flaws on the steel wire. Note: The spring should be turned continuously when demagnetizing.
• Flaw detection of the tension spring: First, pull the spring apart (use a tension machine if necessary) and support it with an insulating rod, so that the spring coils are separated from each other, and then directly energize to check the longitudinal defects on the steel wire. Then, insulate each coil of the spring (remove the support rod), and use the rod-through method to detect the lateral defects on the steel wire.

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