Nitriding Treatment Technology in the Process of Printing Iron Cans
1. Jet technology
The jet is a stream of fluid ejected from a nozzle at a high speed, which is widely used in industrial automation control. Today, we are going to introduce the use of the entrainment effect of the jet to be applied to the nitriding treatment in can making.
a. The entrainment of the jet
The so-called entrainment of the jet is that a bunch of fluid is ejected from the nozzle. The canning equipment and the automatic welding seam powder coating machine drive the originally static medium around it to flow together due to the friction between the fluid molecules. .
At this time, the speed of the jet will decrease. This phenomenon is the entrainment of the jet, which is also called suction.
b. Coanda effect of jet
If we set a pair of baffles on both sides of the nozzle, when the baffle is far from the nozzle, the situation does not change, and it is still the same as shown in Figure 1. If the two baffles are approached to the nozzle and the distance between the two baffles and the nozzle is not equal, we can find that when the baffle moves to a certain distance, the jet from the nozzle will change in an instant Direction, and flow on the baffle wall that is close to entrainment. As shown in Figure 2, this phenomenon is called the Coanda effect of the jet. This phenomenon is caused by the pressure difference, due to the entrainment of the jet, in S1
2, the working principle of the nitriding device
Any object with speed, we can say that it has “momentum”. Therefore, for jets, there is of course momentum. If two jets are ejected from the nozzle from different directions, after the two jets meet, they will form a new jet. Its direction is no longer the same as that of any original jet, but deflected by an angle, according to the law of conservation of momentum m3v3=m1v1+m2v2 as shown below, the deflection angle depends on the size of the original two jets. If the momentum of the original two jets is equal, the direction of the new jet after synthesis will be exactly in the middle of the original two jets, that is, ∠α=∠β, if m1v1>m2m2, then ∠β>∠α, the direction of the new jet will be at two It is closer to the direction of the jet with high momentum, and this phenomenon is the momentum exchange of the jet. As shown in Figure 3.
Nitriding device is a jet element made by using the momentum exchange phenomenon of the jet and the Coanda effect of the jet to make nitrogen adhere to the surface of the tank body.
3, nitriding process
Liquid nitrogen→Decompression→Synchronization of forming motor.
Solenoid valve → flow juice → jet element → attached tank body.
4, nitriding flow control
The key of nitriding treatment is to form a layer of gas protection film outside the can body to isolate the welding seam from the air. The formation of the protective film is closely related to the flow rate and flow of nitrogen. The can-making equipment and the automatic welding seam powder coating machine are blocked by the welding wheel, as shown in the figure, causing a small low pressure area on both sides of the welding wheel to drive air flow. When the flow rate is too small, the nitriding effect cannot be achieved. If the flow rate is too high, a vortex will be formed at the welding point and the nitride film will be destroyed. Therefore, it is important to adjust the pressure and flow rate of nitrogen. After repeated practice, it is recommended to use a pressure below 1kg/m2 and a flow rate of 0.6L/min is better.
5. Nitrogen protection compensation
Since there is a certain gap between the can body and the can body during the welding process, the minimum is 1～2mm, and often reaches more than 10mm. Therefore, a control signal is given to the jet, which supplements the air to the wall of the jet, so that the nitrogen does not cover the can body. . Therefore, during the production process, there will be partial oxidation and blackening of the head, which is usually referred to as incomplete nitriding.
In order to prevent this from happening, we recommend using the internal and external nitriding devices together, so that the internal nitriding will provide a compensation airflow for the outside nitriding, so that air cannot enter to ensure the quality of nitriding.