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Determination of machining plan of open impeller
The foreword: The impeller is the core component of an industrial pump, and its configuration varies significantly depending on operating conditions. A fully open impeller, which lacks a cover, has blades that are directly exposed to the stationary wear plate (fixed to the pump body and cover). When handling media containing fibers, high viscosity, crystallization, or particles, the small gap between the impeller and the wear plate can cause significant wear due to the relative movement, leading to scraping and removal of material. This makes fully open impellers unsuitable for many applications. The structure of a fully open impeller centrifugal pump is shown in Figure 1.
Figure 1: Structure of a fully open impeller centrifugal pump
1. Pump housing
2. Front wear plate
3. Open impeller
4. Rear wear plate
5. Pump cover
Second, the machining clamping method for open impellers: Dalian Dark Blue Pump Co., Ltd. produces EAPK series pumps (design pressure 5.0MPa, center-supported) and ESHK series pumps (design pressure 2.5MPa, foot-supported), both featuring open impellers without front covers or mouth rings. These pumps are equipped with wear-resistant plates, making them suitable for handling media with particles. They are widely used and represent one of the company's flagship products. Figure 2 shows the structure of the ESHK series impeller.
As a core component, the impeller’s machining accuracy directly affects the pump’s performance. Poor machining can lead to uneven gaps between the blades and the wear plate, resulting in reduced head and efficiency. Therefore, ensuring precise machining is critical. During processing, the traditional approach involved welding a clamping ring to the blade, followed by grinding. However, this method was time-consuming, energy-intensive, and required expensive welding rods, especially for high-corrosion-resistant alloys. Skilled workers suggested modifying the model to include an import process hub, enabling easier lathe processing.
After discussions between the technical center, machining shop, and foundry, the plan to machine and open the impeller was finalized. Two main clamping options were considered:
Option 1: Welding a clamping ring on the blade.
- The pattern may not be fully machined, requiring spot welding.
- The model remains fixed.
- Machinists must find their own waste ring and weld it to the blade.
- Advantages: Stable clamping, good processing quality.
- Disadvantages: Time-consuming, not ideal for mass production, and can damage the microstructure of high-corrosion alloys.
Option 2: Casting a process boss at the inlet.
- The casting process includes a boss added to the impeller inlet.
- Provides a permanent clamping solution.
- Disadvantages: Increases blank weight and material cost, and may cause chatter on large impellers.
Option 3: Casting a process ring around the impeller.
- Similar to Option 2 but with a larger clamping diameter.
- Offers better stability and processing quality.
- Disadvantages: Further increases material cost and processing time.
Third, the conclusion: After analysis, the technical center and relevant departments reached a consensus on the clamping scheme based on the impeller’s nominal diameter:
1. For open impellers with a nominal diameter ≤ 250 mm, use the first option (imported wheel + casting process boss).
2. For diameters > 250 mm, the second option (welding clamp ring) is generally used.
3. In special cases, such as poor welding performance or corrosion resistance issues, an integral process ring may be cast on the outer circumference.
Options 1 and 2 are the most commonly used. Practical application has proven that the selected clamping program effectively solves the long-standing issue of machining difficulties on lathes, delivering excellent results.