Corrugated Roller Advanced Heat Treatment Process

The corrugating roll adopts alloy steel 42CrMo and 50CrMo forgings with good quenching performance, but the special geometric shape and size of the roll surface brings great difficulty and quality instability to the heat treatment, so it has been the focus of domestic and foreign counterparts. The main problem.
It is well known that corrugating rolls with excellent heat treatment quality should be sufficiently hardened to achieve the desired depth of hardened layer, uniform hardness without soft tape, and no cracking. The conditions of full and uniform hardenability and prevention of quench cracking, in addition to the stable composition of the material and adequate and reasonable preparation of heat treatment (such as quenching and tempering, repeated removal machining and welding stress), also require quenching in the cooling process, the temperature phase The cooling rate distribution must be in the quenching allowable cooling rate zone to realize the "water quenching and cooling" cooling rate distribution, that is, the high-medium temperature cooling stage has a water-like cooling rate to avoid the non-martensite structure. Change area. In the low-temperature stage, the cooling rate should be as low as possible, especially when the temperature is about 300°C, the cooling rate should be as slow as oil to avoid deformation and cracks.
The new process has undergone process reforms for traditional heat treatment methods.
First, by adjusting the material, stabilizing and reducing the chemical composition range, adjusting the heating method and heating temperature to move the cooling rate allowable area.
The second is to move the cooling curve by selecting a quench medium with superior performance and adjusting the cooling mode so that it enters the allowable cooling rate zone.
So far, domestic medium-frequency quenching of alloy steel generally uses polyvinyl alcohol solution as a quenching medium. Polyvinyl alcohol began to be used as an additive for water in the mid-1950s. It is currently used in China. Due to its fear of freezing in winter, it is susceptible to deterioration and odor in other seasons, and it is easy to block and inject pores during use, making maintenance and maintenance difficult. Effective service life is short. At the same time, it is difficult to accurately detect and control the concentration because the use of low levels (usually used in the range of about two to three-thousandths of a thousandth, and a one-thousandth of a change in its concentration can cause a large difference in performance), so most Only by the operator's experience to control (such as: see how much foam and feel the viscosity by hand, etc.), it can not guarantee a stable quenching quality. As it is not conducive to concentration management, it has been rarely used abroad.
The new process introduces SZ water-based quenching liquid and quenching process for the quenching of corrugating rollers and other alloy steels, effectively ensuring the stability of quenching quality. SZ water-based quenching liquid is Polyalklene Glycols quenching agent.
It has insolubility and can be quenched and cooled faster than water by adjusting to a certain concentration. When the workpiece is quenched, the sprayed quenching liquid will adhere to the desolvable polymer film on the working surface. The film can effectively destroy the vapor film formed on the workpiece by the water, thus increasing the high temperature cooling rate of the water and making the workpiece different. The cooling rate of the part tends to be uniform, and the presence of this layer of polymer film also reduces the low temperature cooling rate of water, reducing the risk of quench deformation and cracking. At the same time, the concentration of quenching media is easy to detect and control, ensuring the stability of the process. Secondly, within a certain range, the temperature of the quenching medium is controlled by changing the stirring conditions to ensure that the cooling characteristic curve of the quenching medium falls within the permissible cold speed zone, so that the quenched workpiece achieves quenching with high hardness and uniformity, no cracking, and guarantees stability The hardened layer is deep. Because the layers in each process are strictly controlled, the amount of deformation of the quenched workpiece can be stably less than 0.15 mm.
Why some grooves in a pair of corrugating rollers (including the guide plate slot, vacuum suction and suction slot) are easy to quench cracking and there are obvious soft bands, so the quenching tends to appear soft.
This is because medium frequency induction quenching is an instant heating of the induction coil at a constant speed. With the upward movement of the induction coil during quenching, the lower end of the slot teeth are blocked by the slot to block the magnetic field and upward transfer of heat, and the power and heat are concentrated and the instantaneous overheating is easily quenched. Cracking teeth. At the same time, the upper end of the slot blocks the heat transfer from the lower part due to the slot, the temperature has not yet reached the phase change temperature but the induction coil has risen and the quenching is not hard, forming a distinct soft band. To reduce the risk of quench cracking, the quenching temperature is often reduced or a relatively low carbon content 35CrMo material is used at the expense of quenching hardness.
Corrugated roller similar to the following 2.5 module pinion, common frequency quenching frequency is generally between 2500 ~ 8000Hz. The corrugating roll with a large diameter is between 2500 and 4000 Hz. Therefore, there is a clear temperature difference between the tooth top and the tooth groove when quenching, which often results in hardened tooth tops and soft tooth grooves after quenching, and concentrates a large tensile stress near the tooth grooves, which can easily cause axial cracking.
The new process took targeted breakthroughs in heat treatment equipment, induction coil, water spray ring, distance between induction coil and water spray ring, clearance between two rings and workpiece, spray angle, heating method, and speed and method of induction coil movement. Improvements have been made to obtain a hardened layer with a depth of more than HRC58 and a depth of 6 to 7 mm, uniform hardness, and a soft groove with a grooved roller, thus ensuring the stability of heat treatment quality.