Cylinder head into the exhaust valve sealing with high frequency induction quenching process research

by:Hengyang Furnace     2020-10-29
1. Overview of the new engine than power is more and more high, many parts lead to aluminum alloy cylinder block and cylinder head temperature over 200 ℃, then the intensity drops rapidly, unbearable by mechanical load. Therefore, Europe and the United States and other western developed countries first vermicular cast iron used as important materials of cylinder head. Vermicular cast iron nodular cast iron and grey cast iron of comprehensive performance, mechanical properties between gray cast iron and nodular cast iron, with good compactness, heat resistance and wear resistance, the casting performance is better than ductile iron, gray cast iron with close, nearly, its strength and ductile cast iron and grey cast iron is similar to the shock of thermal conductivity and casting ability, but the plasticity and fatigue resistance of gray cast iron have been better. Compact structure to cancel the special valve seat, but the valve seat hole must have a certain wear resistance. Due to the special requirements of high power density, and vermicular cast iron and steel for induction hardening of induction heat treatment process as well as the ordinary heat treatment, is the process of solid state phase transition, so can choose induction hardening or laser surface hardening. Using laser surface hardening, early after laser surface melting treatment group, the eutectic austenite and eutectic cementite mechanical mixing, as a product of the iron carbon phase diagram eutectic transformation. In pure ledeburite cementite is more, so the performance similar to cementite, which extremely hard brittle. And the laser hardening depth is 0. 1 to 0. 8 mm, scanning quenching after heating parts, special parts for cylinder head seat hole laser quenching is difficult to control, there will be local travel, crack, surface concave and convex inequality. Therefore, in view of the above the special requirements of product design, it is necessary to study the high frequency quenching process, solve the problem in the laser quenching is difficult to meet the requirements. 2. Research goal and the difficulties ( 1) Use of existing equipment, with the matching design of special sensors, to make the parts quickly into the exhaust sealed with local heating and cooling, avoid spray liquid cooling, satisfy the requirements of the hardened layer depth and hardness. ( 2) Ensure sealing strip hardened, no flashing, no crack, study the influence of electric parameters on the depth of induction hardening parts and determine the optimal parameters to guide production. ( 3) Iron induction heating due to thermal conductivity is weak, the heating time is longer than steel for, generally in more than a few seconds, and heat preservation for a period of time should be made of refractory tissue into austenite, heating speed can lead to high thermal stress, easy to crack. ( 4) Due to the shape of the part is complex, asymmetric structure, thus making copying and can even heat sensors is more difficult, quenching machine tool precision to drop, the clearance between the parts and sensor can't accurate positioning. Therefore, the realization of mass production and stable quality, should be tested for quenching machine tool improvement. 3. The research content of vermicular cast iron substrate material creep ( The ball) Rate of 85%, pearl size 50% ~ 70%, tensile strength of 445 mpa, or higher elongation> 2%, the hardness of < 249 HBW. Graphite morphology and matrix organization as shown in figure 1, figure 2. Technical requirements for cylinder head into the exhaust valve sealing surface hardness 47 ~ 55 HRC, hardening layer 0. 8 to 1. 5mm。 Figure 1 graphite morphology ( Vermicular shape + a small ball) 100 x organization (figure 2 matrix Pearlite ferrite + + graphite) 500 x according to the cylinder head seal cone Angle and size, design special sensors, the Angle and the size of parts of the work and heating cylinder head seal belt, guarantee the uniformity of heating temperature and the area. By using high frequency heating and quenching process specification based data according to the current frequency of equipments, parts hardening layer and the surface area of the selected current frequency is 200 ~ 250 KHZ. According to quenching area select heating method at the same time. The determination of high frequency current parameters: the existing inductive heating anode no-load voltage Ub = 12. 5 kv, anode load voltage Ua = 12 kv, Uc = 10 kv tank circuit voltage, anode current Iao = 10. A, grid current Igo = 1. 4. Check the high frequency output power: using above electric parameter P = 1/2 gamma nUcIao = 1/2 x 1. 7×1×10×10 =85( 千瓦) Type of gamma - — Anode current utilization coefficient, typically take 1. 7. N— — The oscillation tube number, n = 1. Calculation results show that the above equipment electrical parameters, the output power is greater than the required power, shows that the selected suitable than power, so the final decision to use HT - Ab 100 high frequency equipment. Determine the heating time t: heating time can be carried out by relevant data collect and process test, finally determined for 12 ~ 18 s, due to the heating area is small, big, big heat storage of workpiece, using the method of cold. Due to the artifacts as local parenchyma, accumulated heat is less, so can't be self tempering, the tempering box-type furnace is adopted to tempering temperature is 180 ℃ heat preservation 2 h.
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