Steam turbine condenser (heat exchanger) tube sheets are usually made of low carbon steel or low alloy steel, but for some tube sheets that require corrosion resistance and high mechanical properties, copper-nickel alloy material BFe30-1- 1. The chemical composition and mechanical properties of this material are shown in Tables 1 and 2, respectively.
| Applicable Products | Ni+Co | Fe | Mn | Cu | Zu | Si | Pb | S | C | P | Sn | Total impurity |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| GB5234-85 | 29.0~32.0 | 0.5 to 1.0 | 0.5 to 1.0 | 0.5 to 1.2 | base | <0.3 | <0.15 | <0.01 | <0.05 | <0.006 | <0.03 | <0.7 |
| Variety | status | d b (MPa) | d 10 (%) | Supply material hardness (HB) |
|---|---|---|---|---|
| Plate | M | >375 | >23 | 60～70 |
| Y | >535 | >3 | 100 |
Second, the choice of tool materials
High-speed cutting of BFe30-1-1 material with high nickel content. The material of the cutting part of the tool should be made of tungsten-cobalt (YG) alloy, so that the tool can get better wear resistance, high cutting efficiency and good thermal conductivity. . At the same time, in order to avoid the vibration during the high-speed cutting of the tool and the chipping caused by the inaccurate tool, the material of the cutting part of the tool is preferably YG6X.
Third, the tool structure and geometric angle design
- Selection of rake angle g If the rake angle g is large, the cutting force can be reduced, the plastic deformation of the cutting zone, the temperature and the friction reducing force can be reduced, and the generation of the knife can also be suppressed. For processing difficult materials such as BFe30-1-1 copper-nickel alloy, the rake angle should be chosen larger because of their greater viscosity and toughness. Therefore, g=5° is selected.
- Back angle and choice of land The reaming of cemented carbide reamer relies mainly on extrusion, so the choice of land f is important. If f is chosen to be narrower, it will not be squeezed, so that the surface of the hole wall is not only light and there are rills; if f is selected too wide, the cutting force will increase, causing vibration and even distortion of the arbor. When the edge belt f=0.2～0.25, when the copper-nickel alloy tube plate hole is processed, a better extrusion effect can be obtained. The choice of the back angle of the tool to ensure that the blade has sufficient strength, usually 10 °.
- Choice of blade inclination angle l In order to prevent the surface of the hole from being scratched or pulled by the upward chip removal during the reaming process, the tool should adopt a large blade inclination angle, that is, l=15°-20°. The larger blade inclination not only makes the chip removal downward, but also increases the actual rake angle of the tool, which also achieves a light cutting effect. The structure and geometry of the tool are shown in Figure 1.
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- Cutting amount
- Process margin
- Cooling lubricant
Low-speed reaming of copper-nickel alloy materials with a hard alloy reamer can achieve better processing results, but the production efficiency is low. If medium speed reaming is used, the surface quality of the hole is affected by the fact that the knife is often generated during the cutting process. Therefore, the processing of copper-nickel alloy materials should be high-speed reaming, and the cutting amount is:
V=80m/min～100m/min;
S = 0.6 mm / r ~ 1.2 mm / r.Since the cemented carbide reamer is mainly squeezed during work, the residual amount of the hinge should be larger than the reaming allowance of the high speed steel. The reaming allowance for the copper-nickel alloy material is t=0.1d (d is the reaming diameter).
When the tool is reamed at high speed, it generates a lot of cutting heat. If the cutting heat cannot be taken away in time, it will affect the surface quality of the hole and reduce the service life of the tool. When high-speed reaming of double-layer alloy materials, it is advisable to use a higher concentration emulsion and should be sufficiently cooled. If possible, it is best to use an extreme pressure emulsion of extreme pressure additives because it forms a film between the wall of the hole and the edge of the blade, which acts as a lubricant to suppress the occurrence of tool marks.
In the processing of steam turbine condenser tube plate, the high-speed reaming of cemented carbide reamer is used, the cutting efficiency is increased by 10~15 times compared with the use of high-speed steel reamer, the tool life is increased by 50%-200%, and the machining precision of the hole is stable. Secondary, the surface roughness is Ra3.2 ~ Ra1.6.
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