Calculation And Experimental Study Of The Surface Comprehensive Heat Transfer Coefficient About Heavy Rail In Quenching Process

Rail quenching is one of the metal heat-treatment measures. Spray cooling is one wayto control the cooling speed. The surface comprehensive heat transfer coefficient, as animportant parameter in spraying, can accurately control the cooling speed and assure thequality of the heavy rail.Combining with the actual situation of heavy rail production technology, the paperdesigned and assembled spray cooling experimental device, researched relation betweencooling curves of heavy rail and different water flow, air pressure and the height of thenozzle. The experimental study shows that: the average cooling rate of the heavy rail alsoincreases with the increase of the water flow between0.6m3/h and1.8m3/h; with theincrease of pressure between0.18MPa and0.30MPa, the average cooling rate of the heavyrail firstly decreases and then increases; with the increase of the distance between nozzlesand head of the heavy rail between100mm and300mm, the average cooling rate of theheavy rail decreases.Based on the heat transfer theory and the finite element theory, the finite elementmodel of heat transfer of heavy rail was established. The Two-point method, Three-pointmethod and Whole method were put forward. Surface comprehensive heat transfercoefficient during the process of heavy rail spray was calculated respectively. Theexperimental study shows that cooling curves obtained by Two-point method and Three-point method is a big difference from the experimental value while the cooling curvegotten by Whole method has small error range and is closer to the experimental value.Whole method is a better method in calculating surface comprehensive heat transfercoefficients.It could be obtained by comparing surface comprehensive heat transfer coefficientunder different experimental conditions that with the increase of the water flow from0.6m3/h to1.8m3/h, the surface comprehensive heat transfer coefficient of heavy railincreases between600C and900C, while firstly rising and then dropping between200C and600C and changing not obviously in other temperature; with the increase of thepressure from0.18MPa to0.30MPa, the surface comprehensive heat transfer coefficient ofheavy rail decreases firstly and increases subsequently between600C and900C, whilereduces firstly and increases subsequently, then reduces, finally increases between200Cand600C and changes not obviously in other temperature; with the increase of thedistance between the nozzle and head of the heavy rail from100mm to300mm, thesurface comprehensive heat transfer coefficient of heavy rail reduces between300C and900C and changes not obviously in other temperature.Temperature-displacement finite element model of rail was established. Temperatureand axial stress during heavy rail spray cooling were calculated. By comparing thetemperature and stress under different experimental conditions, when heavy rail is sprayedunder the experimental condition that the water flow is1.2m3/h, the pressure is0.24MPaand the distance between the nozzle and head of the heavy rail is300mm, its organizationand axial stress can meet the requirements, and the experimental condition is a betterexperimental scheme.