Advanced heat treatment process of the hottest cor

2022-08-16
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Advanced heat treatment process of corrugating roll

corrugating roll adopts alloy steel 42CrMo and 50crmo fine forgings with good hardenability, but its special geometry and size of roll surface bring great difficulty and quality instability factors to heat treatment, so it has always been the main problem to be tackled by peers at home and abroad

as we all know, the corrugating roller with excellent heat treatment quality should ensure full quenching, reach the required hardening layer depth, have uniform hardness, no soft belt and no cracking. In addition to the material with stable composition and sufficient and reasonable preliminary heat treatment (such as quenching and tempering. Repeated removal of machining and welding stress), the conditions of sufficient and uniform hardening and prevention of quenching crack also require that during the quenching and cooling process, the cooling rate distribution of each temperature stage must be within the allowable cooling rate zone of this kind of quenching, so as to realize the cooling rate distribution of water quenching and oil cooling, that is, the cooling rate of high and medium temperature cooling stage is as fast as water, To avoid the non martensitic transformation zone. In the low temperature stage, the cooling speed should be as slow as possible, especially at about 300 ℃, so as to avoid deformation and cracks

the new process has reformed the traditional heat treatment method

first, move the allowable zone of cooling rate by adjusting the material, stabilizing and narrowing the range of chemical composition, and adjusting the heating method and heating temperature

the second is to move the cooling curve into the allowable cooling rate zone by selecting the quenching medium with superior performance and adjusting the cooling mode

so far, polyvinyl alcohol solution is generally used as the quenching medium for medium frequency quenching of alloy steel in China. Polyvinyl alcohol was used as an additive for water in the mid-1950s. At present, it is widely used at the same time in China. Because it is afraid of freezing in winter, it is easy to deteriorate and stink in other seasons, and it is easy to agglomerate and block the spray hole during use, which is difficult to maintain, and has short effective service life. At the same time, it is difficult to accurately detect and control the concentration because of the low use content (usually the use concentration is about two to three thousandths, and the change of one thousandth of its concentration can cause a great difference in performance). Therefore, most operators can only control it by experience (such as looking at the amount of foam and judging the viscosity by hand feeling), so the stable quenching quality cannot be guaranteed. Because it is not conducive to concentration management, it has been rarely used abroad

the new process introduces SZ water-based quenching solution and quenching process for the quenching of corrugated rollers and other alloy steels, which effectively ensures the stability of quenching quality. SZ water-based quenchant is a kind of polyalkeneglycols quenchant

has inverse solubility. By adjusting to a certain concentration, the quenching cooling speed faster than oil and slower than water can be obtained. When the workpiece is quenched, the sprayed quenching liquid will adhere to the desolved polymer film on the working surface, which can effectively destroy the steam film formed on the workpiece due to the deterioration of the stress state of the fixture body caused by water in process, thus improving the high-temperature cooling rate of water and making the cooling rate of different parts of the workpiece tend to be uniform. The existence of this layer of polymer film also reduces the low-temperature cooling rate of water and reduces the risk of quenching deformation and cracking. At the same time, the concentration of the quenching medium is easy to detect and control, ensuring the stability of the process. Organize the 6th China EU raw materials working group meeting and the meeting of the raw materials working group of the industrial cooperation sub committee between the Chinese and Russian Prime Ministers on a regular basis. 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 into the allowable cooling rate zone, so that the quenching workpiece can achieve high and uniform quenching hardness, no cracking, and ensure a stable quenching layer depth. Due to the strict control of each process layer by layer, the deformation of quenched workpiece can be stably less than 0.15 mm

why are there grooves in a pair of corrugating rollers (including paper guide grooves, vacuum external suction and internal suction grooves) easy to crack and have obvious soft bands, so quenching tends to be soft

this is because the medium frequency induction quenching is the instantaneous heating of the induction ring moving at a uniform speed. During quenching, with the upward movement of the induction ring, the ridge teeth at the lower end of the groove are easily quenched and cracked because of the magnetic field blocked by the groove and the upward heat transferred by the groove, and the coordinated development of productive services with power and heat concentration. At the same time, because the upper end of the groove blocks the heat transfer at the lower part, the temperature has not reached the phase transition temperature, but the induction coil has risen, so it cannot be hardened, forming an obvious soft band. In order to reduce the risk of quenching crack, the quenching temperature is often reduced or 35CrMo material with relatively low carbon content is selected at the expense of quenching hardness

corrugating roller is similar to pinion with modulus below 2.5, and the common medium frequency quenching frequency is generally between 2500 ~ 8000Hz. The frequency of corrugated roll with large diameter is between 2500 ~ 4000Hz. Therefore, there is an obvious temperature difference between the tooth top and the tooth groove during quenching, which often leads to soft tooth top and hard tooth groove after quenching, and a large tensile stress is concentrated near the tooth groove, which is easy to cause axial cracking

the new process has made breakthrough improvements to the heat treatment equipment, the induction coil, the water spray coil, the distance between the induction coil and the water spray coil, the gap between the two coils and the workpiece, the spray angle, the heating method and the moving speed and method of the induction coil, so that the ridge surface can obtain a hardened layer with a depth of more than hrc58, 6 ~ 7mm, uniform hardness, and no obvious soft belt on the grooved roll, thus ensuring the stability of the heat treatment quality

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