The application of honing tools in the hole processing of steam turbine products

- Feb 15, 2021-

Precision dimension control in the processing of mechanical products has always been an important and difficult point, which involves many aspects such as processing equipment, processing technology flow, processing technology parameters, etc., and steam turbine products are a complete set of assemblies, and their design precision is related to power generation. The overall vibration, power and even efficiency of the plant unit are closely related, so it is very important to control the processing of parts and components and ensure product quality.

1 Conventional hole processing method

There are many methods of inner hole surface processing, commonly used methods such as drilling, reaming, reaming, and boring. Drilling is the most commonly used method of hole processing, but it can only be used as a roughing method. The achievable dimensional tolerance level is IT13~IT11. The roughness of the hole after processing is relatively high, and due to the limitation of processing tools, there may be drills during processing. Disadvantages such as easy tilting and large axial force of the drilling hole. Generally, semi-finishing processing is required with reaming and reaming. The dimensional tolerance level after reaming and reaming is IT11~IT10, and the surface roughness value is Ra12.5. ~6.3 μm, can also be used as the final machining of holes with low precision. Boring is the further processing of holes that have been drilled, cast or forged with a boring tool. It can be performed on a lathe, boring machine or milling machine. Boring is one of the commonly used hole processing methods, which can be divided into rough boring, semi-fine boring and fine boring.

In the production of steam turbine products, some assembly and flow dimensional accuracy requirements are very high, and it is difficult for conventional equipment to guarantee the accuracy requirements. This puts high requirements on equipment, tools, and operating methods. Therefore, in order to meet the requirements of steam turbine product holes According to the processing requirements, non-standard honing tools are specially developed for the processing of these holes according to the product characteristics.

2 Honing tools for machining large inner holes of valves

The importance of valves in the operation of steam turbines is self-evident. How to achieve precise size processing and ensure air tightness has a great impact on the efficiency of the unit. The efficiency of the steam turbine unit and the steam pressure are closely related to the accuracy of the valve. In the processing of some valve inner holes, conventional boring methods cannot meet the requirements of dimensional accuracy, especially for roughness requirements, which need to reach the accuracy level of Ra0.6 μm, which puts forward a high level of processing tools and process methods. Claim.

In view of this requirement, after the technicians have verified the size characteristics and technical requirements of the product, they plan to use the honing method for processing and design a special honing tool. The design idea is to install the workpiece on the worktable of the radial drill, connect the honing tool to the radial drill, and drive the rotation of the honing tool through the rotation of the spindle of the radial drill. The honing tool is designed and installed with oil stone and oil stone guiding device. The up and down movement of the honing spindle is used to honing the bored valve inner hole.

After processing by the honing tool, due to the accuracy of the honing method, the processed hole can well meet the requirements of the dimensional accuracy and roughness of the valve inner hole.

3 Honing tool for concentric machining of rotor and intermediate shaft to wheel hole

In a multi-rotor steam turbine unit, the steam turbine rotor and the rotor connect two rotors together through an intermediate shaft. The three connections are connected by flange bolts. Therefore, the connecting holes must ensure sufficiently high concentricity. The processing requirements for the concentric flange holes of the three parts are very high, and because this kind of processing needs to be carried out at the installation site of the unit, the processing is very difficult.

    The process technicians first use on-site boring equipment to boring the wheel hole, and then use a non-standard honing tool to honing the inner hole. The honing tool uses a hand drill as the power part to drive the rotation of the overall honing tool after processing by this tool , The roughness of the hole after processing can reach Ra0.6 μm, the accuracy can meet the requirements of installation, and the on-site operation is very convenient.