Vacuum carburizing and quenching of thin-walled ring gears and arc gears

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Large thin-walled ring gears and arc gears are prone to deformation such as oval, warping and swelling after long-term vacuum carburizing and vacuum quenching. Once the deformation is out of tolerance, it is difficult to correct and repair, resulting in out-of-tolerance or even scrapped in post-grinding or fine-milling gear processing. For mass production, special tooling is mostly used to control deformation, but for sporadic single-piece small batch production, special tooling with long manufacturing cycle and high cost is not suitable. To this end, we take technological measures such as increasing the reserved processing volume and strictly controlling the vacuum carburizing and quenching flat-pack furnace method, and control the deformation of vacuum carburizing and quenching for large thin-walled ring gears and arc gear parts.

1.Structure and technical requirements of thin-walled ring gear and arc gear

The thin-walled ring gear material is 20CrNi2Mo, and the wall thickness of the ring gear is only 129.795mm. Technical requirements: vacuum carburizing and quenching of teeth, minimum carburizing layer depth 6mm, tooth surface hardness 58 ~ 60HRC, core hardness 33 ~ 38HRC.

The arc gear material is 17Cr2Ni2Mo, the wall thickness of the thin part is only 85mm, and the height of the lower end face of the big end tooth pitch is only 127.59mm. Technical requirements: vacuum carburizing and quenching of the teeth, the hardness of the tooth surface is 54~58HRC, the hardness of the core is 30~35HRC, and the effective hardened layer depth is 3~7.5mm.

2.Process analysis and deformation control

From the structure of the thin-walled ring gear and the arc gear, it can be seen that both parts are large-scale thin-walled ring parts, and the carburized layer is required to be deep. Seep carbon is a chemical heat treatment of high temperature and long-term heating. For such large-scale thin-walled ring parts, the body strength and rigidity are low. After long-term heating and carburizing at high temperature (930C ± 10C) and quenching and cooling treatment, it is easy to produce oval, warped Deformation failure such as bending and swelling, resulting in out-of-tolerance processing of subsequent grinding or fine-milling teeth, or even scrapping.

The flat-mounted furnace method of the flat disc type tooling support ring gear and the lower end face of the arc gear is adopted. Before vacuum carburizing, the lower end face is flat and solid, and the reserved non-carburized surface is painted with anti-seepage paint, together with Tooling furnace carburizing. For the symmetrical two end faces of the large ring gear, turn over and re-support the pad before vacuum quenching; for large thin-walled arc gears, replace the flat-machined tooling before vacuum quenching and re-support the lower end face of the pad, single-piece quenching, and strictly monitor the vacuum carburizing and quenching process process. The flat-mounting method of the flat-plate tooling support ring gear and the lower end face of the arc gear is used for carburizing in the furnace, and the ring gear is turned over before vacuum quenching to re-support the cushion, which can offset or reduce the falling deformation of the unsupported part of the cushion. Before vacuum quenching Replacing the flat-processed tooling support pad arc gear can avoid warping deformation of the thin-walled arc gear due to tooling deformation. For deformation control of large thin-walled ring gears and arc gears that are easily deformed in small batches, the machining allowance of non-carburized inner holes or end faces should be increased before vacuum carburizing.

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