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Precision dimensional control in the processing of mechanical products has always been a focus and difficulty, which involves many aspects such as processing equipment, processing processes, and processing parameters. The steam turbine product is a complete set of assembly parts. The precision of its design is closely related to the overall vibration, power and even efficiency of the power plant unit. Therefore, it is very important to control the processing of parts and ensure product quality.

1 Conventional hole processing methods

There are many methods for processing the inner hole surface. Commonly used methods include drilling, reaming, boring and other methods. Drilling is the most commonly used hole processing method, but it can only be used as a rough machining method. The achievable dimensional tolerance level is IT13~IT11. The roughness of the hole after processing is relatively high, and due to the limitations of the processing tools during processing, there may be shortcomings such as the drill bit is easy to tilt and the drilling axial force is large. Generally, it is necessary to cooperate with enlarging and reaming for semi-finishing. After enlarging and reaming, the dimensional tolerance level is IT11~IT10, and the surface roughness value is Ra12.5~6.3 μm, it can also be used as the final processing of holes with low precision. Boring is the further processing of drilled, cast or forged holes using boring tools. This can be done 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-finish 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 ensure the accuracy requirements. This places high demands on equipment, tools, operating methods, etc. Therefore, in order to meet the requirements for hole processing of steam turbine products, non-standard honing tools are specially developed based on product characteristics for the processing of these holes.

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 dimensional processing and ensure air tightness has a great impact on the efficiency of the unit. The efficiency of the steam turbine unit and the pressure of the steam are closely related to the accuracy of the valve. Therefore, in the processing of some valve inner holes, conventional boring methods cannot meet the dimensional accuracy requirements, especially the roughness requirements, which need to reach the Ra0.6 μm accuracy level, which puts forward high requirements for processing tools and process methods.

In view of this requirement, after verifying the dimensional characteristics and technical requirements of the product, the craftsmen plan to use the honing method for processing and design special honing tools. The design idea is to install the workpiece on the radial arm drill workbench, connect the honing tool to the radial arm drill, and drive the rotation of the honing tool through the rotation of the radial arm drill spindle. The honing tool is designed to install a whetstone and a whetstone guide device. As the honing spindle moves up and down, the bored valve inner hole is honed.

 

through thisHoningAfter the tool is processed, due to the accuracy of the honing method, the processed hole can well meet the dimensional accuracy and roughness requirements of the valve inner hole.

3 Honing tools for concentric machining of wheel holes on rotors and intermediate shafts

In a steam turbine unit with multiple rotors, the steam turbine rotor and the two rotors are connected together through the intermediate shaft. The three connections are connected by flange bolts. Therefore, the connecting holes must ensure high enough concentricity. The processing requirements for the concentric flange holes of the three components are very high, and because this kind of processing needs to be performed at the unit installation site, the processing is very difficult.

 

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