1. First, remove the sludge from the surface of the broken screw end with a center punch. Make the center punch mark the center of the broken surface. Then, use an electric drill with a 6-8 mm drill bit to drill a hole at the center of the marked hole. Make sure the hole is drilled through completely. After the hole is drilled through, remove the small drill bit and replace it with a 16 mm drill bit. Continue to enlarge and drill through the hole of the broken bolt.

2. For welding rods with a diameter of 3.2 millimeters or less, use a medium to small current to perform overlay welding in the drilled hole of the disconnected bolt, starting from the inside to the outside. The starting point of the overlay welding should be at half the length of the entire disconnected bolt. When starting the overlay welding, do not arc for too long to avoid burning through the outer wall of the disconnected bolt. Continue the overlay welding until the upper surface of the disconnected bolt is reached, and then add a cylindrical shape with a diameter of 14-16 millimeters and a height of 8-10 millimeters.

3. After the welding is completed, use a hammer to strike the end face of the welded part to cause the broken bolt to vibrate along its axis. Due to the heat generated by the previous arc, the subsequent cooling, and the vibration at this time, the threaded connection between the broken bolt and the body will become loose.

4. Carefully observe. Once you notice a small amount of rust leaking from the fracture surface after the tapping process, then attach the M18 nut to the welded column head and weld the two together.

5. After welding, it will be slightly cool. At this point, quickly put the梅花扳手 (a special tool with a curved handle) on the nut and twist it back and forth. Alternatively, while twisting, you can also use a small sledgehammer to strike the end face of the nut. This way, the broken bolt can be removed.

6. After removing the broken bolts, use the appropriate tap to re-machine the threaded holes inside the frame to remove the rust and other debris from the holes.

Testing method

The surface inspection of screws is divided into two types. One is the inspection before the screws are electroplated after they are produced, and the other is the inspection after the screws are electroplated. In other words, it is the inspection of the screw surface after it has been hardened and treated. After the screws are produced and before electroplating, we conduct inspections on various aspects such as size and tolerance to see if they meet national standards or customer requirements. After the screw surface treatment, we inspect the electroplated screws, mainly checking the color of the electroplating and whether there are any defective screws. In this way, when we send the screws to the customer and the customer receives them, they can pass the inspection smoothly. Inspection after screw treatment:

1. Appearance quality requirements

The inspection of the screw's appearance involves checking it from various aspects such as the appearance and the electroplating layer.

2. Inspection of the thickness of the screw coating layer

1. Measurement method

The measuring tools include micrometers, vernier calipers and gauge blocks.

2. Magnetic method

The measurement of coating layer thickness by magnetic method is a non-destructive measurement carried out using a magnetic thickness gauge on the non-magnetic coating layer on a magnetic substrate.

3. Microscopy method

The microscopic method is called the metallographic method. It involves placing the corroded fasteners on a metallographic microscope equipped with a magnifying eyepiece, then measuring the thickness of the coating on the fracture surface.

4. Time-keeping fluid flow method

The timed liquid flow method involves using a solution that can dissolve the coating to flow over the local surface of the coating. The thickness of the coating is calculated based on the time required for the local coating to dissolve completely. Other methods include the coating drop method and the anode dissolution coulometric method.

III. Inspection of the Adhesion Strength of the Screw Coating Layer

There are many methods for evaluating the adhesion between the coating and the base metal. Generally, the following methods are used.

1. Friction polishing test; 2. File method test; 3. Scratch method; 4. Bending test; 5. Thermal shock test; 6. Extrusion method.

IV. Inspection of Corrosion Resistance of Screw Coating

The methods for testing the corrosion resistance of coatings include: atmospheric exposure test; neutral salt spray test (NSS test); acetic acid salt spray test (ASS test), copper accelerated acetic acid salt spray test (CASS test); as well as corrosion paste corrosion test (CORR test), solution drop corrosion test, immersion test, inter-impregnation corrosion test, etc.