ISO 21256-2:2020

Overview

ISO 21256-2:2020 establishes a standardized laboratory test method for evaluating the removal of machine-oil stains from non‑corrosive machined metal surfaces using fine bubble water. The standard compares cleaning performance with and without fine bubbles by measuring residual oil with an infrared oil content meter, enabling objective assessment of fine bubble technology for detergent‑free cleaning in industrial settings.

Key topics and technical requirements

• Scope & principle: Measures residual machine oil after cleaning with plain water versus fine‑bubble‑enhanced water; performance quantified by an oil cleaning index.
• Test oil and reagents: Test oil specified as triolein (or an agreed substitute). An extraction solvent and laboratory‑grade water (per ISO 3696) are required; Annex B provides example IR spectrum for calibration.
• Test pieces: Machined metal coupons with defined dimensions and surface roughness (lapped to Ra 50–100 nm), prepared and coated with a uniform oil surface density (50–150 μg/cm²), then fixed by heating.
• Apparatus & setup: A defined cleaning tank and fine bubble generator (ON/OFF capability). The document specifies tank dimensions, flow outlet diameter, nozzle/test piece positioning, and a typical test rig layout.
• Operating parameters: Typical conditions include water temperature < 40 °C, cleaning flow rate ~8.0 ± 0.2 L/min, cleaning duration 5.0 ± 0.1 min, and a water volume ≈15 L - all prescribed to ensure repeatability.
• Measurement & calculation: Residual oil is extracted from the test surface with solvent and quantified using an oil content meter (infrared spectroscopy). The oil cleaning index compares baseline, plain‑water, and fine‑bubble results using formulas given in the standard.
• Reporting: Test report must document conditions (date, temperature, flow rate, material, fine bubble parameters) and measured surface concentrations.

Applications and users

ISO 21256-2:2020 is practical for:

• Manufacturers of cleaning equipment and fine bubble generators
• Metalworking and machining shops evaluating post‑process cleaning
• Test laboratories performing comparative cleaning validation
• R&D teams optimizing eco‑friendly, detergent‑free cleaning systems
• Quality assurance and procurement teams assessing cleaning performance and sustainability benefits

Fine bubble cleaning is positioned as an ecological alternative to solvent or detergent‑based processes, offering resource savings and reduced chemical use.

Related standards

• ISO 20480‑1, ISO 20480‑2 (fine bubble terminology and attributes)
• ISO 3696 (water for analytical laboratory use)
• ISO 15510 (material designation referenced for test pieces)
• ISO 6353‑3 (surface cleaning preparatory guidance)
• Other parts of the ISO 21256 series (see ISO website for the series listing)

Keywords: ISO 21256-2:2020, fine bubble technology, cleaning test method, machine oil stain, oil cleaning index, triolein, oil content meter, industrial cleaning, detergent‑free cleaning.