The maintenance of magnetic particle flaw detectors is a meticulous and persistent task. The effectiveness of magnetization is ensured through standardized cleaning of the magnetic head; By scientifically preparing and managing magnetic suspensions, the sensitivity and clarity of defect display are ensured. Only by internalizing these two key points into daily habits and recording them can operators fully utilize the performance of magnetic particle flaw detectors and provide solid and reliable technical support for industrial safety and quality control.
1、 Magnetic head cleaning: ensuring effective transmission of magnetic field lines
The magnetic head is the part in direct contact with the measured workpiece, and its cleanliness directly affects the transmission efficiency of magnetic field lines. If there are oil stains, rust, or non-conductive substances on the surface of the magnetic head, gaps will form, causing an increase in magnetic resistance and preventing some magnetic field lines from effectively entering the workpiece, which may result in missed detections.
Cleaning steps and key points:
1. Daily cleaning: After each use, be sure to use a clean cotton cloth or soft brush to remove metal powder, dust, and oil stains attached to the surface of the magnetic head. For stubborn stains, dip a small amount of anhydrous ethanol or acetone and gently wipe, avoiding the use of highly corrosive solvents.
2. Regular deep cleaning: Conduct deep cleaning once a week or every two weeks according to the frequency of use. Check if the contact surface of the magnetic head is flat, free from oxidation or damage. If necessary, use fine sandpaper (such as 800 grit or more) to lightly polish and restore its flatness and conductivity, but be careful to avoid excessive wear.
3. Rust prevention maintenance: After cleaning, a thin layer of rust prevention oil or Vaseline can be applied to the surface of the magnetic head to prevent rusting during storage. Before the next use, this protective layer should be removed to avoid affecting conductivity.
4. Inspection of connection parts: At the same time, check whether the connection between the magnetic head and the cable is firm, whether the terminals are loose or oxidized, and ensure stable current transmission.
Keeping the magnetic head clean and in good contact is the first step to obtaining clear and reliable magnetic trace display.
2、 Preparation of Magnetic Suspension: Suspension Uniformity and Concentration Control
Magnetic suspension is a suspension liquid composed of magnetic powder, carrier liquid (usually water or oil), and additives mixed in proportion, and its properties directly affect the aggregation effect of magnetic powder at the leakage magnetic field.
Key points and precautions for preparation:
1. Precise concentration control: The concentration of magnetic suspension is the core parameter. Low concentration, insufficient magnetic powder quantity, and difficulty in displaying minor defects; Excessive concentration can lead to poor background contrast and easily mask related magnetic traces. It should be prepared strictly in accordance with the proportion recommended by the equipment manufacturer or process standards (such as GB/T15822 or ASTME709). Usually, the concentration of fluorescent magnetic powder is 0.5-2.0g/L, and the concentration of non fluorescent magnetic powder is 10-25g/L. Regularly calibrate using sedimentation tubes or concentration measuring instruments.
2. Selection and treatment of carrier fluid:
*Oil based carrier fluid: It has the advantages of rust prevention and good wetting, but it is expensive and flammable. High flash point (usually>94 ° C) and low viscosity odorless kerosene should be selected.
*Water based carrier fluid: economical and environmentally friendly, but it must be supplemented with wetting agents, rust inhibitors, and defoamers. When preparing, the additive should be fully dissolved in water before adding magnetic powder and stirring to prevent the magnetic powder from clumping.
3. Dispersion and stirring: When preparing, mechanical or manual stirring should be used to ensure that the magnetic powder is evenly dispersed without clumping or precipitation. For reusable magnetic suspension systems, it should be ensured that the magnetic suspension in the storage tank is continuously stirred before spraying.
4. Regular performance verification: Magnetic suspensions may experience performance degradation due to volatilization, contamination, and magnetic particle loss. It is necessary to check its concentration, wettability (through a "water break test"), and pollution level before daily work. If the carrier liquid is found to be turbid, with suspended solids or magnetic particle precipitation, it should be replaced in a timely manner.
5. Safety and Environmental Protection: The preparation and waste liquid treatment must comply with relevant environmental regulations. Especially for oil-based carrier liquids, waste liquids should be treated as hazardous waste.