Common quality problems and their causes in the darkening process of square bolts
1) The Square Bolt have white spots on the black surface
It may be: the surface of the fastener is not cleaned and there are booties;
There are too many black fillers on the fasteners, which are in close contact with each other, so that the blackening fluid cannot evenly contact the surface;
The oxide on the surface of the hot-pressed fastener was not completely removed.
2) The oxidation film on the surface of the square bolts is reddish and rusty
It may be: the proportion of blackening liquid is not properly prepared;
There are floating rusts before the surface becomes black;
The surface contains phosphating residues.
3) Poor adhesion of surface oxide film, easy to fall off
It may be: the surface of the fastener is not cleaned and there are oil stains;
The temperature of the blackening liquid is too high;
The rust on the surface of the fastener is not completely cleaned;
The blackening time is adjusted too long, so that the oxide film on the surface of the fastener is too thick and falls off.
4) After the surface of the square bolt is blackened, there is a foreign body, which affects the screwing performance.
It may be: after the fastener is tempered, there is oxide scale on the surface, which is caused by falling into the blackening liquid during the blackening process;
A large amount of black liquid agglomerates are formed on the mesh belt furnace, which sticks to the thread surface in the workpiece;
Foreign matter is mixed in the blackening solution.
5) The surface of the fastener after blackening will rust in a short time
It may be: the fasteners are not dried in time after drying or they are not completely dried, and they are coated with rust preventive oil, so that the surface has water molecules;
The surface of the fastener is black and uneven, and there are floating rust on the surface to continue corrosion;
There may be water in the rust-proof oil tank used for a long time, and the water should be drained in time and regularly.
Selecting a professional Hex Bolt Manufacturer can effectively prevent the bolts from blackening and bring you a better use process.