The water velocity in the water quenching device of rod and wire production line has an important influence on the cooling effect. If the water flow velocity is too low, the cooling effect may be uneven, resulting in slow cooling speed in some areas, which may lead to local overheating or insufficient cooling, affecting the hardness and mechanical properties of bars and wires, and even causing cracks or deformation. On the contrary, if the water speed of the water quenching device is too high, it may cause excessive agitation, lead to unstable water flow, and even fail to achieve uniform cooling, resulting in uneven cold and hot conditions, and may also increase water consumption and energy consumption.
Speed up cooling: the higher water flow speed of water quenching device can make more water contact with the surface of rod and wire in unit time. As a cooling medium, water will take away the heat on the surface of rod and wire. When the speed of water flow increases, the rate of heat transfer is accelerated, thus the cooling rate of rod and wire is significantly improved. For example, in the experiment, when the water velocity is increased from 1m/s to 3m/s, the drop of surface temperature of rod and wire may be doubled in the same time.
Slow cooling (extreme case): However, in some special cases, if the water flow speed of the water quenching device is too fast, it may lead to uneven cooling. For example, high-speed water flow may form local turbulence or vortex on the surface of rod and wire, which makes the water in some areas unable to fully exchange heat with rod and wire, but slows down the cooling speed in these areas. At the same time, the excessive water flow speed of the water quenching device may cause the temperature on the surface of the rod and wire to drop too sharply, resulting in an excessive temperature gradient inside and between the surfaces of the rod and wire, which may cause deformation or even cracking of the rod and wire, thus affecting the product quality.
Uniform cooling and microstructure uniformity: the proper water flow velocity of water quenching device is helpful to realize uniform cooling on the surface of rod and wire. When the velocity of the water flow is appropriate, the water flow can stably scour the surface of the rod and wire, so that the heat can be evenly dissipated from all parts of the rod and wire. This can ensure that the bar and wire can obtain a uniform structure after quenching.
Uneven cooling and tissue difference: If the water flow speed of water quenching device is uneven, for example, the water flow speed in some areas is fast and the water flow speed in some areas is slow due to nozzle blockage or unreasonable design, then the surface of rod and wire will be unevenly cooled. This will make the rod and wire form different structures in different parts.
Improve the surface quality: the appropriate water flow speed of water quenching device can effectively remove the oxide scale and impurities on the surface of rod and wire. In the process of water quenching, the scouring effect of water flow increases with the increase of speed. When the water flow velocity is sufficient, the oxide scale formed on the surface of the rod and wire in the pre-processing process such as high-temperature rolling can be washed away, so that the surface of the rod and wire is smoother. This is very beneficial for bars and wires that need subsequent surface treatment (such as electroplating and painting), because a smooth surface can improve the adhesion of the coating and ensure the quality of surface treatment.
Damage to the surface (extreme case): However, if the water flow speed of the water quenching device is too high, the impact force of the water flow may cause damage to the surface of the rod and wire. For example, high-speed water flow may wash away some metal particles on the surface of rod and wire, resulting in an increase in surface roughness and even the formation of tiny pits or scratches on the surface. These surface defects will not only affect the appearance quality of bars and wires, but also become stress concentration points and reduce the fatigue strength and other properties of bars and wires.