How Does VOLM Ensure Machining Precision for a BB3  Long Shaft

Challenge

The shaft is one of the most critical components in a centrifugal pump. It connects the impellers, bearings, seals, motor, and other key parts. Therefore, its dimensional accuracy, geometric accuracy, positional accuracy, and surface roughness are all essential to the pump’s performance and service life.

The BB3 multistage pump shaft discussed in this case features:

• Shaft length: 1950 mm.

• Impeller section diameter: 68 mm.

• Structure: Multiple shoulders, grooves, keyways, and stepped sections.

• Configuration: 7-stage impeller arrangement.

This type of shaft is characterized by a slender structure, high machining precision requirements, and complex geometry, making manufacturing particularly challenging.

So how does VOLM achieve an almost perfect reproduction of the drawing requirements?

Micron-Level CNC Machining Ensures Shaft Tolerances Within 0.01 mm

The shaft contains many different structures, each designed to fit with specific components. For example, the sections matched with the impellers must precisely fit the impeller bores in both dimension and geometry. Excessive tolerance deviation would make accurate assembly impossible.

At VOLM, we use world-class CNC machine tools for shaft machining. For turning operations, we use Korean Doosan machines, while keyway and groove milling are performed using Japanese Kuraki equipment.

With these high-precision machines, shaft tolerances can be controlled within 0.01 mm, ensuring:

• Precise matching between the shaft and all related components;

• Stable pump flow rate and head performance;

• Low vibration and noise;

• High safety and reliability. 

Nearly 20 Years of Grinding Experience Ensures Radial Runout and Surface Finish

After machining on imported CNC equipment, the shaft undergoes an additional grinding process mainly for two purposes:

• To control shaft radial runout within 0.01 mm, further ensuring concentricity;

• To reduce surface roughness to below Ra 0.4.

Grinding a slender shaft is extremely demanding. Improper operation can easily cause shaft bending. Moreover, the shaft contains many stepped sections with varying diameters at different positions. Compared with grinding a simple cylindrical shaft, this type of shaft is significantly more complicated to process.

At VOLM, our grinding work is carried out by highly skilled craftsmen with nearly 20 years of experience. They rely on exceptional expertise to manually control grinding depth and timing with precision. Throughout the process, professional measuring instruments are also used to continuously monitor shaft dimensions and runout conditions in real time.