The repair technology of the nylon spraying of the diesel engine is as follows:
Nylon spraying is a process for heating nylon to melt and cover the surface of parts to restore the wear size of parts. Nylon has high tensile strength and impact toughness, low friction coefficient and special adhesive resistance, good mechanical properties and can be machined by car, grinding, planing, milling and other methods, and the dimension precision of the workpiece and the precision of the workpiece. The geometric shape is easy to guarantee, but the heat resistance is poor. It is only applied to working conditions not higher than 100 C.
In order to meet certain characteristic needs, some materials can be added in nylon powder to improve wear resistance: molybdenum disulfide powder, 5% to 10% (weight ratio), graphite 5% ~ 10%. increase strength: fluoroplastic powder 5%, glass fiber 30% ~ 40%. to increase thermal conductivity: aluminum powder 10%, copper powder 10%. to improve heat resistance: a proper amount of talcum powder, lime powder and so on. Can also be added according to the need. Some pigments are coloured D. All the powders should be kept at 70 C for 2~5 hours before they are used.
The common methods of nylon coating are flame spraying and cold spraying.
1 flame spraying method
The principle of flame spraying is to mix the combustible gas with the compressed air in the spray gun, and to compress the air to blow the nylon powder out of the muzzle, melt through the flame area, and melt the melted nylon powder to the surface of the preheated workpiece and form a coating layer.
(1) flame spraying equipment. Spray gun, the brand of common flame spray gun is sY - sP plastic flame spray gun nozzle low pressure acetylene generator or bottled acetylene, air compressor (including oil and water separator), electric furnace, oven, and work worktable to turn the worktable.
(2) flame spraying process parameters.
Preheating temperature of the workpiece: about 250 degrees C.
Compressed air pressure: (0.3 to 0.4) MPa.
Acetylene pressure: 0.02 MPa.
Spray nozzle distance from the workpiece: 200 millimeter.
Workpiece speed: 10 rotating clock.
The movement speed of spray gun is flexible as required. Flame spraying nylon is suitable for repairing small shaft parts.
(3) key points of the process.
(1) surface treatment: in order to improve the bonding strength of the coating layer, it is best to spray the workpiece in advance to make the workpiece surface hairy, and the whole piece is machined into a rough thread.
Degreasing: oil can be removed by cleaning agent or alkaline solution and acetone.
Workpiece preheating: the size of the visible workpiece is preheated by oven or heated to about 250 degrees by flame.
Spraying: turn on the powder control valve and start with a small amount of powder spray. After the powder is wetted on the workpiece, a large amount of powder will be sprayed to the required size.
Before the surface of the workpiece is not solidified, the workpiece is put into water to cool down to 40 degrees centigrade. The faster the cooling rate is, the better, the nylon layer after water cooling is soft, good toughness, wear-resistant and aging resistance.
2 cold spray method
Cold spray method is to preheat the workpiece to a slightly higher temperature than the melting point (about 250 degrees C), without flame, using only compressed air to spray the powder to the preheated surface of the workpiece, and melt the powder by the heat of the workpiece to form a coating layer.
Because of the lack of flame, the spray gun used in cold spray is relatively simple. The PQ-1 and PQ-2 spray lacquer guns can be reformed. When the system is reformed, the air nozzle is blocked, the one one hole is drilled on the gun, the air channel of the spray gun is connected with the paint tank, the spray nozzle is added with a 90o elbow, and the aeration holes on the cover of the paint can be blocked.
The other equipment required by the cold spray method is the same as the flame spraying. But because of the lack of flame, the workpiece is cooled faster, so if the temperature of the workpiece is reduced and the spray can not be melted instantaneously on the workpiece, it should be immediately stopped and reheated and then sprayed second times.
It is not necessary to use the powder spraying gun for cold spraying nylon powder. When spraying smaller workpiece, it can be dusted with simple tools manually, and it can be applied to the same effect without wasting the powder.
The preheating of the workpiece, such as the lack of necessary heating equipment, can also be heated in a coal furnace. In order to make the temperature rise more evenly, a plate of iron can be placed on the furnace and the workpiece is heated on the plate. The heating temperature of the workpiece can be judged as follows: a little nylon powder to the work piece, such as nylon powder, or small particles that are not melted or semi fused. It means that the temperature of the workpiece is not enough. If the nylon powder melts quickly, does not smoke and does not blister, it indicates that the temperature is suitable and can be quickly removed for powder spraying.
