Hydraulic Piston Rod, why do induction hardening?
Hydraulic piston rod do quenching and tempering treatment, why still do induction hardening ？
Hydraulic Piston Rod induction heat treatment can make the surface of the product obtain high hardness and wear resistance, while the interior still maintains the original good plasticity and toughness. It is currently the most widely used and fastest-growing surface heat treatment method with its unique advantages. Mainly lies in:
1. High heating speed and high thermal efficiency: heating by the induction current generated by the parts can reduce the heat loss, and the thermal efficiency can reach more than 60%, and the temperature can reach hundreds of thousands of degrees centigrade in a few seconds;
2. High quality of heat treatment: due to the short heating time, there is almost no internal oxidation and decarburization; and because only the surface of the parts is heated, the core temperature is lower and the strength is reduced less, so the quenching deformation is small;
3. Stable product quality, easy to realize automatic and intelligent production.
Induction heating principle of hydraulic piston rod
Its principle is electromagnetic induction: alternating magnetic field can cause alternating electric field, conversely, alternating electric field can also cause alternating magnetic field. Generally speaking, an alternating current is applied to a coil, and then a conductor is placed in the coil, and the induced current will be generated in the conductor to start heating.
when the coil is connected with alternating current, according to the principle of electromagnetic induction, an alternating magnetic field will be generated around the coil, and the conductor (metal part) placed in the magnetic field will produce the induced electromotive force E (V), that is:
E = 4.44fnφ × 10-8
F -- current frequency
Φ -- amplitude of magnetic flux
N -- the number of turns of the loop
When heating a metal part, the loop is the part itself, and N = 1.
Under the action of the induced electromotive force, the conductor produces eddy current, i.e. the induced current I (a): 1
I = E / Z, where Z is the impedance of the part itself.
According to the Joule Lenz law, the heat Q (J) produced by the eddy current is as follows:
Q = I2Rt
Where, R -- Resistance of metal parts (Ω)
T -- heating time (s)
This is the whole process of induction heating.
Skin effect of induction heating and Proximity effect
Skin effect
Skin effect is also called skin effect or surface phenomenon. When the conductor passes through direct current, the current density at each point of the conductor cross-section is uniform; but when the conductor passes through alternating current, the skin phenomenon will occur, that is, when the high-frequency current passes through the conductor, the current on the conductor cross-section is not evenly distributed, but mainly concentrated on the surface of the conductor.
The principle is as follows: when the current to the left is applied into the conductor, the right-hand helix rule can be used to generate magnetic lines of force entering and leaving the profile. If the current in the conductor increases at this time, the eddy current in the conductor in the direction shown in the figure will be generated due to the electromagnetic induction effect, which will increase the current on the surface of the conductor and offset the central line current. The result is that the current will gather on the surface of the conductor.
The calculation formula of skin effect depth is
Proximity effect
Proximity effect is that the distribution of alternating current in the body is affected by the alternating current in the adjacent conductor. The specific performance is as follows:
1,When two parallel conductors pass in the opposite direction and the same size of current, the current will concentrate on the side of the conductors close to each other
2,When two parallel conductors are connected with the same direction and the same size of current, the current will concentrate on the farthest side of the conducto
Its principle is similar to skin effect. As shown in the following figure, the two conductors A and B flow through the current IA and IB in the same direction. When the current suddenly increases in the direction of the arrow in the figure, according to the electromagnetic induction effect, the sudden magnetic flux produces eddy current in conductor B as shown in the figure, which increases the current on its lower surface and reduces the current on the upper surface. Similarly, we can know the effect of conductor B on conductor A.
Skin effect and proximity effect coexist
Therefore, it is suggested that the hydraulic piston rod should be treated with high frequency before hard chromium plating. The hydraulic piston rod is more durable