As precision forged components, stainless steel balls are manufactured from stainless steel wire through multiple processing steps. Their common materials should be selected based on application scenarios: Type 201 is suitable for general rust-proof applications; Type 304, with excellent corrosion resistance, is mostly used in food and pharmaceutical contact fields; Types 316 and 316L can withstand acid-alkali environments; while Types 420 and 440C focus on high-hardness and wear-resistant scenarios. Below is the standard production process adopted by steel ball manufacturers, where parameters of each link must be strictly controlled to ensure product quality:
- Wire Drawing Process:
Continuous wire drawing machines are used for progressive drawing of stainless steel wires. The diameter of the wire is controlled within an accuracy range of ±0.02mm according to the final ball diameter requirement. During the drawing process, emulsion is required for lubrication and cooling to prevent the wire from oxidation or deformation due to frictional overheating. This process provides a raw material foundation with uniform dimensions for subsequent cold heading forming.
- Cold Heading (Forging) Process:
The qualified drawn wires are cut into fixed-length segments and then fed into automatic stainless steel ball cold heading machines. The machine is equipped with customized hemispherical steel dies, and hydraulic drive is used to achieve die closing and pressure application (pressure range: 8-12MPa), enabling one-time forging of the wire segments into preliminary spherical blanks. After cold heading, the roundness error of the blanks must be inspected to ensure it does not exceed 0.1mm, avoiding difficulties in correction during subsequent processes.
- Ball Polishing Process:
Cold-headed ball blanks are batch-fed into ball polishing machines. Two cast iron grinding discs with fine file patterns on the surface are symmetrically installed inside the machine. Through the relative rotation of the discs (rotational speed: 200-300r/min) and the application of a pressing force of 5-8MPa, the surface of the ball blanks is subjected to filing and grinding. The main function of this process is to remove the outer ring protrusions, surface burrs, and fine impurities generated during cold heading, initially smoothing the surface of the blanks and reducing the machining allowance for the subsequent soft ball processing.
- Soft Ball Processing:
The ball blanks after polishing are transferred to soft ball machines for precision processing. The equipment also uses cast iron grinding discs, but the file pattern density on the disc surface is higher (approximately 120 meshes), and the rotational speed is increased to 300-500r/min. Through 15-20 minutes of low-speed pressing, filing, and grinding, on one hand, the diameter of the ball blanks is accurately controlled to the preset specification (tolerance: ±0.05mm); on the other hand, the surface roughness is optimized to Ra1.6-3.2μm. This lays a high-precision foundation for the subsequent heat treatment and hard grinding processes, while reducing the surface stress concentration of the ball blanks.
- Heat Treatment Process:
The ball blanks after soft ball processing are evenly stacked in a heat treatment furnace and undergo a three-stage “carburizing-quenching-tempering” treatment according to the process curve. In the carburizing stage, the blanks are held at 900-950℃ in a protective atmosphere for 2-4 hours to form a 0.8-1.2mm thick carburized layer on the surface of the blanks; then rapid oil quenching is adopted (cooling rate: ≥50℃/s) to increase the surface hardness to HRC58-62; finally, tempering is performed at 180-220℃ for 2 hours to eliminate quenching internal stress, balance the hardness and toughness of the steel balls, and ensure their crushing load reaches over 2000N (with slight differences depending on the material).
- Hard Grinding Process:
A black oxide scale will form on the surface of the ball blanks after heat treatment, which needs to be fed into grinding machines for hard grinding. The machine uses white corundum grinding discs (granularity: 80-100 meshes) and is equipped with an emulsion cooling system to grind the ball blanks under pressure (3-5MPa). This process not only completely removes the oxide scale but also corrects the ball diameter accuracy to IT10 grade tolerance (≤0.01mm) and controls the roundness error within 0.005mm. Finally, the surface roughness is reduced to Ra0.4-0.8μm, meeting the usage accuracy requirements in different scenarios.
