Astride type and curved beam shift is a clutch of the motorcycle, shift treadle, change gear shaft, gear positioning plate, shift the locator, change gear fork, drum, main shaft, and countershaft work together to achieve complete, the shift drum is to complete this activity is one of the main features, and its function is to shift treadle drive gear shaft torsion, and then change the gear shaft radial component upon archives positioning plate to the appropriate gear position, by shift locator positioning, change gear positioning plate linkage gear drums, make in the shift drum trip around the fork groove pin moves to the corresponding position, dial the main fork around so the corresponding movement and meshing gear. The common shift drum shape is shown in Figure 1.Change gears drum parts using conditions determines the shift drum should have a certain strength and abrasion resistance, we according to the function and performance requirements, design the heat treatment process of the parts, and in the long-term practice in the process of continuous optimization and improved the heat treatment process of the part, in this to grope for the improvement of experiences to share with you.
FIG. 1 :A shift drum for a motorcycle
2. Main manufacturing process flow of variable drum
A certain type of riding a motorcycle use shift drum, material using JIS FC300 cast iron, according to the shift drum using conditions and technical requirements, set the main technological process: ingredients to smelting, casting to car round, small toe and heel, drilling, tapping and milling slot to marking to quenching tempering, sandblasting, cylindrical grinding, shoulder to cleaning, packing and warehousing.
3. Heat treatment technology of variable drum
Technical requirements of the shift drum after tempering hardness of 40 ~ 55 HRC, according to the shift drum using conditions and technical requirements, we in the early design adopted continuous mesh belt furnace heating, oil cooling quenching and tempering continuous heat treatment production line, as shown in figure 2, the use of models for RCW – 120 roller mesh belt type controlled atmosphere quenching production line, the quenching furnace 55 kw power 12 kw, tempering furnace power; Isothermal quenching oil cooling quenching. Heat treatment process: quenching heating temperature 850~870℃, quenching oil temperature 100~120℃, tempering temperature 170~190℃.
Fig.2: Schematic diagram of the heat treatment line of the motorcycle drum shift used in the early stage
4. Equipment and process improvement
Due to such change can drum product technical requirements for the whole quenching or surface induction quenching, we for the sake of reducing energy consumption and cost savings, a heat treatment equipment, and process improvements, we change the quenching furnace to make labor frequency heating furnace heating, namely USES the power frequency induction heating oil, quenching, mesh belt furnace in tempering heat treatment process route, as shown in figure 3. The specific operating frequency diathermy unit model is KGPS-300, with a power of 300kW and frequency of 50Hz. Other equipment is the same as before improvement. The heat treatment process is as follows: quenching temperature 900~930℃, quenching oil temperature 100~120℃, tempering temperature 170~190℃.
FIG. 3:The heat treatment line of the modified motorcycle drum
5. Improve results
By using the above improved production line of power-frequency heat treatment equipment and heat treatment process to process the variable drum parts, the energy consumption per piece is reduced by about 55% compared with the mesh belt furnace, and the cost per piece is reduced by about 56%, achieving a very good effect of energy saving and cost reduction. Heat treatment quality confirmed by the test: 43 ~ 48 HRC hardness distribution (see figure 4), graphite is typed A (see figure 5), graphite length is 4 ~ 5 level (see figure 5), martensite structure of martensite lath with a fine needle (see figure 6), all qualified, in line with the technical requirements, but the difference between maximum hardness and minimum hardness six HRC, hardness difference is bigger, in order to improve the stability of the heat treatment quality we decided to continue to improve this bad phenomenon.
FIG. 4: Hardness distribution of a variable drum after one improvement
Fig.5: Graphite distribution and length
Figure 6: Martensite tissue after one improvement
6. Cause analysis and improvement measures for large hardness difference
(1) the hardness difference analysis of the causes of large scattered scattered hardness difference is big, the uniformity is poorer, this kind of phenomenon is mainly due to uneven heating or cooling quenching uneven, due to the power frequency diathermy heating parts are relatively even and the clearance between the sensors, current, voltage is constant, the heating time is controlled by relay accurate, under the thermometer monitoring temperature range within + / – 5 ℃, so can rule out the influence factors of uneven heating, then look at quenching cooling systems, due to the artifacts from the outlet of the heating furnace has been falling downward sloping pipeline into inside the tank (see figure 3),When falling into a quench oil is a tilt Angle into the oil, when cooling is also from the bottom to the top, so in the process of cooling, it can’t be all parts of the synchronization of relative cooling at the same time, so the uniformity of quenching cooling is poorer, can determine the hardness uniformity is poor, the main reason for the big difference, so we decided to improve quenching cooling uniformity of the direction of research.
(2) improvement measures to improve the quenching cooling uniformity, we studied the disadvantages of the original quenching cooling system, and to develop the design as shown in figure 7 levels of quenching cooling unit, and the power frequency heating furnace, tempering furnace heat treatment production line, the artifacts to a horizontal direction perpendicular to liquid level is higher than the upper part of the workpiece quenching cooling medium (for a certain concentration of water soluble quenchant PAG and water mixture), heat treatment process for 25 ~ 35 ℃ quenching liquid temperature and quenching liquid pressure is 0.2 ~ 0.4 MPa, 900 ~ 930 ℃ quenching heating temperature, tempering temperature 170 ~ 190 ℃.
FIG. 7:Schematic diagram of heat treatment line of motorcycle gear changing drum after secondary improvement
7. Improve results
After heat treatment with the above improvement measures, the variable drum parts were inspected and confirmed: hardness 45~48HRC (see Figure 8), the difference between the maximum hardness and the minimum hardness was 4HRC, the hardness difference ratio was greatly improved before the improvement, and there was no significant difference between other metallograms and before the improvement, and the improvement achieved the expected effect.
FIG. 8: Hardness distribution of a variable drum after secondary improvement
Through to the drum shape more complex shift system of heat treatment equipment and process improvements, reduce the product differential heat treatment hardness are scattered, improved hardness uniformity, heat energy consumption and cost down significantly, to achieve the expected goal, which made us more aware only in practice do not satisfy the present situation, constantly thinking about whether can be better than the status quo, put forward topic, and study and solve the issue, to make our personal skills and heat treatment professional constantly grow up together.