A heat treatment process for slender, thin-walled hollow gear shafts

Abstract

The present application relates to a kind of heat treatment processes of slender thin-walled hollow gear shaft, comprising: step 1: the slender thin-walled hollow gear shaft is loaded into special carburizing quenching and tempering fixture clamping, using staggered layer clamping mode full load is sent into continuous production line;Step 2: the slender thin-walled hollow gear shaft is treated by carburizing quenching and tempering process, including the following processes: pre-washing-pre-oxidation-preheating-strong penetration-diffusion-cooling-quenching-post cleaning-tempering, the whole continuous line push disc time period is 15~25min;Step 3: the slender thin-walled hollow gear shaft after processing is treated by straightening process, and is loaded into automatic straightening machine straightening by straightening clamping mode.The present application aims to provide a kind of heat treatment process of slender thin-walled hollow gear shaft, which is reasonable in design, simple in process, easy to load and unload, stable in straightening, and can effectively avoid large deformation in batch carburizing quenching.

Description

Technical Field

[0001] This invention relates to a heat treatment process for a slender, thin-walled hollow gear shaft. Background Technology

[0002] In automotive transmissions, gear shafts, which play a crucial role in power transmission, are indispensable. However, slender hollow gear shafts with a length-to-diameter ratio greater than 7 exhibit significant deformation after carburizing and quenching. Ensuring the dimensional compliance rate of such products after heat treatment is a critical issue. The industry typically employs methods such as lowering carburizing and quenching temperatures, shortening the dwell time at high temperatures, and reducing the quenching cooling rate to minimize deformation. However, our customers have high requirements for surface hardness, core hardness, and carburized layer depth in these workpieces, limiting the scope for adjusting these methods. Currently, the failure rate of heat treatment for these slender, thin-walled hollow gear shafts has reached as high as 60%. After implementing the process method of this invention, the heat treatment compliance rate of the produced slender, thin-walled hollow gear shafts can reach over 99.7%. Summary of the Invention

[0003] The purpose of this invention is to overcome the deformation problems existing in the prior art, and to provide a heat treatment process for slender, thin-walled hollow gear shafts that is reasonably designed, simple in process, easy to load and unload, stable in straightening, and can effectively avoid large deformations in batch carburizing and quenching.

[0004] The technical solution adopted by this invention to solve the above problems is: a heat treatment process for a slender, thin-walled hollow gear shaft, comprising:

[0005] Step 1: The slender, thin-walled hollow gear shaft is loaded into a special carburizing, quenching and tempering fixture and fed into the continuous production line in full load using a staggered clamping method.

[0006] Step 2: The slender, thin-walled hollow gear shaft is subjected to carburizing, quenching and tempering processes, including the following steps: pre-cleaning - pre-oxidation - preheating - strong carburizing - diffusion - cooling - quenching - post-cleaning - tempering. The entire continuous line push plate time cycle is 15~25min.

[0007] Step 3: The processed slender thin-walled hollow gear shaft is straightened by a straightening process and then loaded into an automatic straightening machine for straightening using a straightening clamping method.

[0008] In step 1, the length-to-diameter ratio of the slender, thin-walled hollow gear shaft is greater than 7:1; the ratio of length to maximum wall thickness is greater than 25:1.

[0009] In step 2, the carburizing, quenching and tempering process adopts a pusher-type continuous carburizing, quenching and tempering production line.

[0010] In step 2, the pre-oxidation temperature is selected as 400℃~500℃;

[0011] In step 2, the preheating temperature is selected as 820~900℃, the methanol flow rate is selected as 1.5~2.0L / H, and the nitrogen flow rate is selected as 1.7~2.2m³ / h. 3 / H;

[0012] In step 2, the strong permeation temperature is selected as 920℃±30℃, the methanol flow rate is selected as 1.4~1.9L / H, and the nitrogen flow rate is selected as 1.6~2.1m³ / h. 3 / H; Propane flow rate selected: 0~0.5m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected is 1.0±0.20%;

[0013] In step 2, the diffusion temperature is selected as 900℃±30℃, the methanol flow rate is selected as 1.5~2.0L / H, and the nitrogen flow rate is selected as 1.7~2.2m. 3 / H; Propane flow rate selected: 0~0.5m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.85±0.15%;

[0014] In step 2, the quenching temperature is selected as 810℃~860℃, the methanol flow rate is selected as 1.5~2.0L / H, and the nitrogen flow rate is selected as 1.7~2.2m³ / h. 3 / H; Propane flow rate selected: 0~0.5m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.75±0.15%;

[0015] In step 2, slow-speed quenching oil is selected, the quenching oil temperature is selected as 50℃~150℃, the stirring speed is selected as 300~800rpm, and the cooling time is selected as 5~15 minutes.

[0016] In step 2, the tempering temperature is selected as 140℃~200℃.

[0017] Preferably, the straightening process includes two support positions, two pressing positions, one gear runout detection position, two shaft outer circle runout detection positions, and a process for real-time online detection of whether cracking has occurred.

[0018] Preferably, the straightening clamping method of the straightening process is to use a pair of center points for positioning, add a straightening mandrel inside the hollow shaft hole, and then straighten.

[0019] Preferably, the diameter of the straightening mandrel is 2-3 mm smaller than the inner diameter of the hollow shaft.

[0020] Preferably, the carburizing, quenching, and tempering fixture includes a positioning pin. The bottom of the positioning pin has four arc-shaped reinforcing ribs that support the workpiece in line contact. The diameter of the positioning pin is 0.8~2.0mm smaller than the inner diameter of the hollow hole, and the length is slightly larger than the shaft length. The size of the positioning pin can be determined according to the different heights and inner diameters of the product. The positioning pin, made of heat-resistant steel, supports and positions the workpiece at the high temperature of carburizing, preventing deformation.

[0021] Preferably, the straightening mandrel is made of medium carbon steel with a tempering hardness of 35~45HRC. Its diameter is 0.8~2mm smaller than the inner diameter of the hollow shaft, and its length is 2~4mm smaller than the length of the hollow shaft, so as not to affect the positioning of the workpiece by the center. This can avoid excessive pressing during straightening, which may cause cracks.

[0022] Compared with existing technologies, this invention has the following advantages and effects: 1. This invention optimizes the process parameters for carburizing, quenching, and tempering, effectively reducing the deformation of slender hollow shafts and simplifying subsequent straightening while meeting the technical requirements of the drawings for hardness, layer depth, and metallographic structure; 2. This invention designs a positioning pin, with dimensions determined according to the product's height and inner diameter. The positioning pin, made of heat-resistant steel, supports and positions the workpiece throughout the carburizing, quenching, and tempering heat treatment process, preventing deformation; 3. This invention designs a straightening mandrel, which is inserted into the slender hollow shaft for simultaneous straightening. This avoids excessive reduction during straightening, which could lead to cracks; 4. This invention designs a unique load-bearing plate, allowing for staggered loading of slender gear shafts, significantly increasing single-furnace output; 5. This invention optimizes the straightening process parameters, significantly reducing the defect rate of the straightening process. Attached Figure Description

[0023] Figure 1 This is a flowchart of the heat treatment process of the present invention.

[0024] Figure 2 This is a schematic diagram of the slender, thin-walled hollow gear shaft structure of the present invention.

[0025] Figure 3 This is a schematic diagram of the positioning pin structure of the present invention.

[0026] Figure 4 This is a schematic diagram of the straightening mandrel structure of the present invention.

[0027] Figure 5 This is a schematic diagram of an example of the carburizing, quenching, and tempering process of the present invention.

[0028] Figure 6 This is a schematic diagram of Example 2 of the carburizing, quenching and tempering process of the present invention.

[0029] Figure 7 This is a schematic diagram of the straightening process of the present invention.

[0030] Figure 8This is a schematic diagram of the staggered clamping of the present invention.

[0031] In the diagram: 1. Straightening mandrel; 2. Hollow shaft; 3. Positioning pin. Detailed Implementation

[0032] The present invention will be further described in detail below through embodiments. The following embodiments are explanations of the present invention, and the present invention is not limited to the following embodiments.

[0033] Example 1.

[0034] The heat treatment process of the slender thin-walled hollow gear shaft in this embodiment includes step 1: the slender thin-walled hollow gear shaft is installed in a carburizing, quenching and tempering fixture and fed into the furnace using a staggered clamping method; step 2: the slender thin-walled hollow gear shaft is treated by a carburizing, quenching and tempering process, which includes the following steps: pre-cleaning - pre-oxidation - preheating - strong carburizing - diffusion - cooling - quenching - post-cleaning - tempering, and the entire continuous line push plate time cycle is 20 minutes; step 3: the slender thin-walled hollow gear shaft after carburizing, quenching and tempering processes is treated by a straightening process and is installed in an automatic straightening machine for straightening using a straightening clamping method.

[0035] In step 1, the slender, thin-walled hollow gear shaft has a length-to-diameter ratio of 7.1:1 and a length-to-maximum wall thickness ratio of 25.3:1.

[0036] In step 2, the carburizing, quenching and tempering process adopts a pusher-type continuous carburizing, quenching and tempering production line.

[0037] In step 2, the pre-oxidation temperature is selected as 450℃±5℃;

[0038] In step 2 ( Figure 5 (Zone I), the preheating temperature is selected as 880℃±5℃, the methanol flow rate is selected as 1.7±0.2L / H, and the nitrogen flow rate is selected as 1.9±0.2m³ / h. 3 / H;

[0039] In step 2 ( Figure 5 For zones II and III, the strong permeation temperature is selected as 900℃±5℃, the methanol flow rate as 1.6±0.2L / H, and the nitrogen flow rate as 1.8±0.2m³ / h. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected is 1.0±0.05%;

[0040] In step 2 (zone IV of zone 5), the diffusion temperature is selected as 900℃±5℃, the methanol flow rate is selected as 1.7±0.2L / H, and the nitrogen flow rate is selected as 1.9±0.2m. 3 / H; Propane flow rate selected: 0~0.4m3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.80±0.05%;

[0041] In step 2 (region V of zone 5), the quenching temperature is selected as 840℃±5℃, the methanol flow rate is selected as 1.7±0.2L / H, and the nitrogen flow rate is selected as 1.9±0.2m. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.8±0.05%;

[0042] In step 2, slow quenching oil is selected, the quenching oil temperature is selected as 120±10℃, the stirring speed is selected as 800 / 400rpm, and the cooling time is selected as 8 minutes.

[0043] In step 2, the tempering temperature is selected as 160±10℃.

[0044] The straightening process in this embodiment includes two support positions, two pressing positions, one gear runout detection position, two shaft outer circle runout detection positions, and a process for real-time online detection of whether cracking has occurred.

[0045] In this embodiment, the straightening clamping method of the straightening process is to use a pair of center points for positioning, add a straightening mandrel 1 inside the hole of the hollow shaft 2, and then straighten it.

[0046] In this embodiment, the diameter of the straightening mandrel 1 is 2-3 mm smaller than the inner diameter of the hollow shaft 2.

[0047] This embodiment of the carburizing, quenching, and tempering fixture includes a positioning pin 3. The bottom of the positioning pin 3 is reinforced with four arc-shaped ribs that provide line contact support for the workpiece. The diameter of the positioning pin is 0.8~2.0mm smaller than the inner diameter of the hollow hole, and the length is slightly greater than the shaft length. The size of the positioning pin can be determined according to the different heights and inner diameters of the product. The positioning pin, made of heat-resistant steel, supports and positions the workpiece at the high temperature of carburizing, preventing deformation.

[0048] In this embodiment, the straightening mandrel 1 is made of medium carbon steel with a tempering hardness of 35~45HRC. Its diameter is 0.8~2mm smaller than the inner diameter of the hollow shaft 2, and its length is 2~4mm smaller than the length of the hollow shaft 2, so as not to affect the positioning of the workpiece by the center. This can avoid excessive pressing during straightening, which may cause cracks.

[0049] The surface hardness of the product produced using the process described in this embodiment reaches over 680 HV1, the core hardness reaches 340~400 HV1, and the hardened layer (550 HV1) reaches 0.6~0.9mm. The output per furnace has reached twice the original output, and the defect rate of the straightening process has been significantly reduced. The heat treatment qualification rate of the resulting slender, thin-walled hollow gear shafts reaches 99.8%.

[0050] Example 2.

[0051] The heat treatment process of the slender thin-walled hollow gear shaft in this embodiment includes step 1: the slender thin-walled hollow gear shaft is installed in a carburizing, quenching and tempering fixture and fed into the furnace using a staggered clamping method; step 2: the slender thin-walled hollow gear shaft is treated by a carburizing, quenching and tempering process, which includes the following steps: pre-cleaning - pre-oxidation - preheating - strong carburizing - diffusion - cooling - quenching - post-cleaning - tempering, and the entire continuous line push plate time cycle is 25 minutes; step 3: the slender thin-walled hollow gear shaft after carburizing, quenching and tempering processes is treated by a straightening process and is installed in an automatic straightening machine for straightening using a straightening clamping method.

[0052] In step 1, the slender, thin-walled hollow gear shaft has a length-to-diameter ratio of 7.3:1 and a length-to-maximum wall thickness ratio of 25.4:1.

[0053] In step 2, the carburizing, quenching and tempering process adopts a pusher-type continuous carburizing, quenching and tempering production line.

[0054] In step 2, the pre-oxidation temperature is selected as 450℃±5℃;

[0055] In step 2 ( Figure 6 (Zone I), the preheating temperature is selected as 880℃±5℃, the methanol flow rate is selected as 1.7±0.2L / H, and the nitrogen flow rate is selected as 1.9±0.2m³ / h. 3 / H;

[0056] In step 2 ( Figure 6 In Zone II, the strong permeation temperature is selected as 890℃±5℃, the methanol flow rate is selected as 1.7±0.2L / H, and the nitrogen flow rate is selected as 1.9±0.2m³ / h. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; carbon potential is selected as 1.0±0.05%; in step 2 ( Figure 6 In Zone III, the strong permeation temperature is selected as 890℃±5℃, the methanol flow rate is selected as 1.6±0.2L / H, and the nitrogen flow rate is selected as 1.8±0.2m³ / h. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected is 1.0±0.05%;

[0057] In step 2 ( Figure 6 In zone IV (middle), the diffusion temperature was selected as 890℃±5℃, the methanol flow rate as 1.6±0.2L / H, and the nitrogen flow rate as 1.8±0.2m³ / h. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.95±0.05%;

[0058] In step 2 ( Figure 6 (Middle V zone), quenching temperature selected is 840℃±5℃, methanol flow rate selected is 1.8±0.2L / H, nitrogen flow rate selected is 2.0±0.2m³ / h. 3 / H; Propane flow rate selected: 0~0.4m 3 / H; Process air flow rate is selected as 0~0.5m. 3 / H; Carbon potential selected: 0.85±0.05%;

[0059] In step 2, slow quenching oil is selected, the quenching oil temperature is selected as 110±10℃, the stirring speed is selected as 800 / 600rpm, and the cooling time is selected as 8 minutes.

[0060] In step 2, the tempering temperature is selected as 160±5℃.

[0061] The straightening process in this embodiment includes two support positions, two pressing positions, one gear runout detection position, two shaft outer circle runout detection positions, and a process for real-time online detection of whether cracking has occurred.

[0062] In this embodiment, the straightening clamping method of the straightening process is to use a pair of center points for positioning, add a straightening mandrel 1 inside the hole of the hollow shaft 2, and then straighten it.

[0063] In this embodiment, the diameter of the straightening mandrel 1 is 2-3 mm smaller than the inner diameter of the hollow shaft 2.

[0064] The carburizing, quenching and tempering fixture in this embodiment includes a positioning pin 3. The bottom of the positioning pin 3 is reinforced with four arc-shaped ribs to support the workpiece in line contact. The diameter is 0.8~2.0mm smaller than the inner diameter of the hollow hole, and the length is slightly larger than the shaft length.

[0065] In this embodiment, the straightening mandrel 1 is made of medium carbon steel with a tempering hardness of 35~45HRC. Its diameter is 0.8~2mm smaller than the inner diameter of the hollow shaft 2, and its length is 2~4mm smaller than the length of the hollow shaft 2, so as not to affect the positioning of the workpiece by the center. This can avoid excessive pressing during straightening, which may cause cracks.

[0066] The surface hardness of the product produced using the process described in this embodiment reaches over 680 HV1, the core hardness reaches 360~420 HV1, and the hardened layer (550 HV1) reaches 0.7~1.0 mm. The output per furnace has reached twice the original output, and the defect rate of the straightening process has been significantly reduced. The heat treatment qualification rate of the resulting slender, thin-walled hollow gear shafts reaches 99.7%.

[0067] It should be noted that all equivalent or simple variations made based on the structure, features and principles of this invention are included within the scope of protection of this invention.

Claims

1. A heat treatment process for an elongated thin-walled hollow gear shaft, characterized in that: Step 1: The elongated thin-walled hollow gear shaft is loaded into a special carburizing quenching and tempering clamp, and is sent into a continuous production line in full load with staggered clamping; Step 2: The elongated thin-walled hollow gear shaft is subjected to carburizing quenching and tempering process, including the following processes: pre-cleaning, pre-oxidation, pre-heating, strong penetration, diffusion, cooling, quenching, post-cleaning, and tempering, and the entire continuous line push disc time period is 15-25 min; Step 3: The processed elongated thin-walled hollow gear shaft is subjected to straightening process, and is loaded into an automatic straightening machine through straightening clamping; In the step 1, the length-diameter ratio of the elongated thin-walled hollow gear shaft is greater than 7:1, and the length-to-maximum wall thickness ratio is greater than 25:1; In the step 2, the carburizing quenching and tempering process adopts a push rod type continuous carburizing quenching and tempering production line; In the step 2, the pre-oxidation temperature is selected from 400-500℃; In the step 2, the preheating temperature is selected as 820-900℃, the methanol flow is selected as 1.5-2.0 L / H, and the nitrogen flow is selected as 1.7-2.2 m 3 / H. In step 2, the strong permeation temperature is selected as 920℃±30℃, the methanol flow is selected as 1.4~1.9L / H, the nitrogen flow is selected as 1.6~2.1m 3 / H; the propane flow is selected as 0~0.5m 3 / H; the process air flow is selected as 0~0.5m 3 / H; the carbon potential is selected as 1.0±0.20%; In the step 2, the diffusion temperature is selected as 900℃±30℃, the methanol flow is selected as 1.5-2.0L / H, the nitrogen flow is selected as 1.7-2.2m 3 / H; the propane flow is selected as 0-0.5m 3 / H; the process air flow is selected as 0-0.5m 3 / H; the carbon potential is selected as 0.85±0.15%. In the step 2, the quenching temperature is selected from 810-860 DEG C, the methanol flow is selected from 1.5-2.0 L / H, and the nitrogen flow is selected from 1.7-2.2 m 3 / H; the propane flow is selected from 0-0.5 m 3 / H; the process air flow is selected from 0-0.5 m 3 / H; and the carbon potential is selected from 0.75±0.15%. In the step 2, the quenching oil is selected from slow quenching oil, the quenching oil temperature is selected from 50-150℃, the stirring speed is selected from 300-800 rpm, and the cooling time is selected from 5-15 min; In the step 2, the tempering temperature is selected from 140-200℃.

2. The heat treatment process for an elongated thin-walled hollow gear shaft according to claim 1, characterized in that: The straightening process includes two support positions, two pressing positions, one gear run-out detection position, two shaft outer circle run-out detection positions, and a process for real-time online detection of whether cracking occurs.

3. The heat treatment process for an elongated thin-walled hollow gear shaft as claimed in claim 1, wherein: The straightening clamping method of the straightening process is to use a pair of centers to position, and then to straighten by adding a straightening core rod in the hollow shaft hole.

4. The heat treatment process for an elongated thin-walled hollow gear shaft according to claim 3, characterized in that: The diameter of the straightening core rod is 2-3 mm smaller than the inner diameter of the hollow shaft hole.

5. The heat treatment process for an elongated thin-walled hollow gear shaft as claimed in claim 1, wherein: The carburizing quenching and tempering clamp includes a positioning pin, the bottom of which is supported by four circular arc reinforcing ribs in line contact, and the diameter is 0.8-2.0 mm smaller than the inner diameter of the corresponding hollow hole, and the length is slightly larger than the shaft length.

6. The heat treatment process for an elongated thin-walled hollow gear shaft according to claim 4, wherein: The straightening core rod is made of medium carbon steel with a quenched and tempered hardness of 35-45 HRC, a diameter of 0.8-2 mm smaller than the inner diameter of the hollow shaft hole, and a length of 2-4 mm shorter than the length of the hollow shaft hole.

Images