Appearance
A roller burnishing tool with 6 rollers and 0.15 mm interference on a 50 mm bore in medium-carbon steel will produce a surface finish of Ra 0.1–0.2 µm — a 10× improvement over the previous machined surface. The same tool with 0.25 mm interference on the same bore will cause peeling — the surface work-hardens beyond its ductility limit and flakes off. The difference between a successful burnishing operation and a scrapped workpiece is often a few hundredths of a millimeter in interference, determined by the relationship between roller geometry, workpiece material properties, and the applied pressure.
Roller Burnishing Tool Design
Roller Configuration by Bore Diameter
| Bore Diameter Range (mm) | Recommended Roller Count | Roller Diameter (mm) | Roller Width (mm) | Roller Configuration | Best Application |
|---|---|---|---|---|---|
| 10–25 | 3 | 5–8 | 6–10 | Single row — straight | Small precision bores — hydraulic valves |
| 25–50 | 6 | 8–12 | 10–16 | Single or double row | General hydraulic cylinders |
| 50–100 | 6–9 | 12–18 | 14–22 | Double row — staggered | Medium to large cylinders |
| 100–200 | 9–12 | 16–25 | 20–35 | Double or triple row | Large hydraulic cylinders |
| 200–400 | 12–18 | 20–35 | 30–50 | Triple row — staggered | Heavy equipment cylinders |
Interference Selection by Material
| Workpiece Material | Recommended Interference (mm per side) | Elastic Recovery (mm) | Expected Ra Improvement Factor | Surface Hardness Increase |
|---|---|---|---|---|
| Low-carbon steel (1018, 1020) | 0.08–0.15 | 0.02–0.04 | 5–8× | 20–40% |
| Medium-carbon steel (1045) | 0.08–0.15 | 0.02–0.05 | 6–10× | 20–50% |
| Alloy steel (4140, 4340) annealed | 0.06–0.12 | 0.02–0.04 | 5–8× | 15–35% |
| Alloy steel hardened (35–45 HRC) | 0.03–0.08 | 0.01–0.03 | 3–5× | 5–15% |
| Stainless steel (304, 316) | 0.10–0.20 | 0.03–0.06 | 4–6× | 30–60% |
| Gray cast iron | 0.05–0.12 | 0.01–0.03 | 3–5× | 10–20% |
| Ductile iron | 0.06–0.12 | 0.02–0.04 | 4–6× | 15–25% |
| Aluminum (6061, 7075) | 0.10–0.25 | 0.03–0.08 | 5–10× | 30–60% |
| Brass — bronze | 0.08–0.20 | 0.02–0.05 | 4–8× | 20–40% |
Operating Parameters
Recommended Burnishing Parameters
| Material | Burnishing Speed (m/min) | Feed Rate (mm/rev) | Lubricant Type | Lubricant Viscosity (cSt at 40°C) | Number of Passes |
|---|---|---|---|---|---|
| Low-carbon steel | 80–150 | 0.1–0.3 | Oil-based or emulsion | 20–40 | 1–2 |
| Medium-carbon steel | 60–120 | 0.1–0.25 | Oil-based | 30–50 | 1–2 |
| Alloy steel — annealed | 60–100 | 0.08–0.2 | Oil-based (EP additives) | 30–60 | 1–2 |
| Stainless steel | 40–80 | 0.08–0.15 | Oil-based (chlorinated EP) | 40–80 | 2–3 |
| Cast iron | 80–150 | 0.1–0.3 | Emulsion or light oil | 15–30 | 1 |
| Aluminum | 100–200 | 0.15–0.35 | Kerosene or light oil | 10–20 | 1 |
| Brass — bronze | 80–150 | 0.1–0.25 | Emulsion or light oil | 15–25 | 1 |
FAQ
How does roller count affect burnishing performance?
Roller count affects the distribution of burnishing pressure around the bore circumference and the stability of the tool during the burnishing process. A higher roller count distributes the burnishing force more evenly, producing a more uniform surface finish and reducing the tendency for the tool to deflect or chatter. However, higher roller count also increases the total contact area between the rollers and the bore surface, requiring higher axial force to advance the tool. For small bores under 25 mm, 3–6 rollers are typical — fewer rollers are needed because the smaller circumference limits the space available for roller mounting, and the lower contact force is adequate for the smaller surface area. For large bores over 100 mm, 9–18 rollers provide the necessary even pressure distribution and tool stability. The rule of thumb is to use the minimum roller count that provides stable, chatter-free burnishing — excessive roller count increases tool cost and maintenance without proportional quality improvement.
What happens if burnishing interference is too high?
Excessive burnishing interference causes surface over-stressing that damages the bore surface. The most common consequence is surface peeling or flaking — the work-hardened surface layer becomes too brittle and separates from the base material, creating a rough, damaged surface that cannot be salvaged. In severe cases, the roller pressure can exceed the material's yield strength in compression, causing the bore diameter to increase beyond the intended size rather than decreasing (as the material plastic flows outward rather than being compressed into the surface valleys). Excessive interference also dramatically increases tool wear — the rollers and their bearing surfaces experience loads beyond their design limits, causing premature roller fatigue, spalling, or bearing failure. The interference must be selected based on the workpiece material's yield strength and ductility — harder materials tolerate less interference, while softer materials can accept more interference before damage occurs.
What is the relationship between pre-burnish surface finish and final finish?
The pre-burnish surface finish (the machined surface before burnishing) directly affects the achievable final burnished finish. Roller burnishing works by compressing surface peaks into valleys — if the pre-burnish surface has deep valleys or tears, the burnishing process cannot fully close these defects, leaving residual surface irregularities. The general relationship is: the final burnished finish is approximately 1/5 to 1/10 of the pre-burnish Ra value, provided the interference is correctly set for the material. A pre-burnish surface of Ra 1.0–1.5 µm (typical for skiving or fine boring) will produce a final burnished finish of Ra 0.1–0.2 µm. A pre-burnish surface of Ra 2.5–3.5 µm will produce only Ra 0.3–0.6 µm after burnishing. For hydraulic cylinder applications requiring Ra ≤ 0.2 µm, the pre-burnish surface finish should be Ra ≤ 1.6 µm.
What lubricant is required for roller burnishing?
Roller burnishing requires a lubricant with sufficient film strength to prevent metal-to-metal contact between the rollers and the workpiece surface at the high contact pressures (typically 1000–3000 MPa at the roller-bore interface). For steel and alloy materials, oil-based lubricants with extreme-pressure (EP) additives are recommended — typically ISO VG 32–68 grade with sulfur-phosphorus EP additives. For stainless steel and other difficult-to-burnish materials, chlorinated EP additives provide superior film strength at the high contact temperatures generated during burnishing. For cast iron, a light oil or high-viscosity emulsion is adequate. For aluminum, kerosene or light oil prevents the aluminum from adhering to the rollers. The lubricant must be clean — contamination particles larger than 10 µm can be pressed into the bore surface by the rollers, creating surface defects. Coolant filtration to 10–20 µm is recommended before the lubricant reaches the burnishing tool.
When should roller burnishing tools be replaced or reconditioned?
Roller burnishing tools should be inspected for wear after every 5,000–20,000 burnished bores, depending on material and interference. Rollers should be replaced when visible surface deterioration appears — spalling (small pits or craters on the roller surface), flaking (larger surface fragments breaking away), flat spots (from lengthy dwell at the bore end), or diameter reduction (more than 0.01 mm below the original size). Roller bearing surfaces should be inspected for wear or damage at the same interval — rough-running rollers indicate bearing wear requiring replacement. The tool body and cone assembly should be inspected for damage and cleaned thoroughly. Complete tool rebuilding — replacing all rollers, bearings, and seals — should be performed at intervals of 50,000–100,000 bores or when individual roller replacements exceed 50% of the total rollers in the tool.
Disclaimer: The roller burnishing parameters and selection guidelines provided in this article are general guidelines based on industry-standard practices. Actual burnishing results depend on workpiece material condition, pre-burnish surface quality, machine rigidity, coolant type, and tool condition. Burnishing parameters should be verified through application testing under actual production conditions. The authors and publisher assume no liability for any damages or losses arising from the use of this information — always follow original equipment manufacturer guidelines for your specific equipment. Content is for informational purposes only and does not constitute professional engineering advice. Verify all parameters with qualified personnel before implementation as of 2026.