Surfactants Suitable for Metalworking Fluids

Surfactants Suitable for Metalworking Fluids
The core properties (lubrication, cooling, cleaning, and rust prevention) of metalworking fluids (cutting fluids, grinding fluids, cleaning agents, etc.) are highly dependent on the synergistic effect of surfactants. By regulating interfacial tension, optimizing dispersion stability, and enhancing compatibility, surfactants address the four core pain points in metal processing: friction and wear, chip residue, corrosion and rust, and system failure. Below is an in-depth analysis from two aspects: the core requirements of metalworking fluids for surfactants and the functions of compatible surfactants.
I. Core Requirements of Metalworking Fluids for Surfactants (Based on Processing Scene Pain Points)
During metal processing (cutting, grinding, stamping, cleaning), metalworking fluids need to cope with issues such as high-temperature and high-pressure friction, contamination by metal chips and oil stains, workpiece corrosion, and system stratification failure. Therefore, the requirements for surfactants focus on the following six aspects:
1. Low Foaming/Easy Defoaming Property (Core Process Requirement)
Pain Point: Most metal processing relies on high-pressure spraying and high-speed stirring (e.g., cutting fluid circulation systems, cleaning machines). Severe foaming of surfactants can lead to:
① Uneven spraying of metalworking fluids, insufficient cooling/lubrication, resulting in tool wear and workpiece surface burns.
② Foam overflow causing waste of metalworking fluids and pollution of the workshop environment.
③ Cavitation in the circulation system, affecting equipment life.
Key Requirements: Strong dynamic defoaming ability (rather than static low foaming), rapid bubble breaking under high shear and high-temperature conditions (e.g., the temperature in the cutting zone can reach 300-800℃), good defoaming durability, and no failure with the cyclic use of metalworking fluids.
Applicable Scenarios: High-speed cutting, grinding, high-pressure spray cleaning, and other high-disturbance processes.
2. Excellent Wettability and Permeability
Pain Point: The surface of metal workpieces (especially precision parts and deep hole/blind hole structures) is prone to residual air and oil stains, making it difficult for metalworking fluids to wet quickly, leading to:
① Failure to form a lubricating film, resulting in dry friction between tools and workpieces.
② Failure of cooling medium to reach the cutting zone, causing workpiece deformation due to local high temperature
③ Inability of oil stains to detach from the metal surface during cleaning.
Key Requirements: It can significantly reduce the surface tension of metalworking fluids (ideal value ≤35 mN/m) to achieve "rapid spreading + deep penetration", and efficiently wet the metal surface (common processing materials such as steel, aluminum, copper) even in narrow gaps and complex cavities.
Applicable Scenarios: Deep hole drilling, precision grinding, and cleaning of complex parts.
3. Strong Emulsifying and Dispersion Stability
Pain Point: Two types of pollutants are generated during metal processing:
① Oil-based pollutants (cutting oil, rust preventive oil residues, oil films generated by tool wear);
② Solid pollutants (metal chips, abrasive grains, dust).
Failure to effectively emulsify/disperse can lead to:
① Oil sludge and chip sedimentation, clogging the circulation system;
② Secondary scratches on the workpiece surface by abrasive grains, reducing processing accuracy;
③ Stratification and deterioration of metalworking fluids, shortening their service life.
Key Requirements:
① Emulsifying ability: It can stably disperse oil-based substances into micron-sized droplets (≤5μm) to form a uniform oil-in-water (O/W) or water-in-oil (W/O) system
② Dispersion ability: It can adsorb on the surface of solid particles to form electrostatic repulsion or steric hindrance, preventing particle agglomeration and sedimentation
③ Stability: No demulsification or stratification within a wide temperature range (-1060℃) and a wide pH range (710.5, the common alkaline system for metalworking fluids).
Applicable Scenarios: Emulsifiable cutting fluids, metal cleaning agents, and grinding fluids.
4. Synergistic Lubrication and Friction Reduction
Pain Point: During metal processing (especially heavy-load cutting and cold stamping), the contact pressure between tools and workpieces can reach hundreds of MPa. The lubrication ability of base oil alone is insufficient, which is prone to tool breakage and workpiece scuffing.
Key Requirements: Surfactants need to cooperate with extreme pressure agents (such as sulfur, phosphorus, and chlorine-based additives) to form a "physical adsorption film + chemical reaction film" on the metal surface, reduce the friction coefficient (ideal value ≤0.15), reduce adhesive wear and diffusion wear, and not affect subsequent processes such as workpiece coating and electroplating.
Applicable Scenarios: Heavy-load cutting (e.g., cutting of carbon steel forgings), cold stamping forming, and stainless steel processing.
5. Compatibility and Chemical Stability
Pain Point: Metalworking fluids are complex systems containing various additives such as base oil, extreme pressure agents, rust inhibitors, and preservatives. If surfactants are incompatible with other components, it will lead to:
① Precipitation of additives, loss of function
② Abnormal fluctuation of pH value of metalworking fluids, causing metal corrosion.
③ Discoloration and odor of the system, and microbial growth.
Key Requirements:
① Good compatibility with non-ionic, anionic, and cationic additives (no precipitation, no stratification).
② Resistance to acid, alkali, high temperature, and hard water (calcium and magnesium ion concentration ≤200ppm).
③ Biological stability: Not easily degraded by bacteria and fungi, extending the service life of metalworking fluids.
Applicable Scenarios: Full-formula metalworking fluids (cutting fluids, grinding fluids, forming fluids).
6. Environmental Friendliness and Low Irritation
Pain Point: Traditional surfactants (such as branched alkylbenzene sulfonate) have poor biodegradability and are irritating to the skin and respiratory tract of operators, which do not meet the requirements of modern industrial "green production" and may cause occupational health problems.
Key Requirements:
① Environmental friendliness: Biodegradability ≥90%, in line with EU REACH, RoHS and other standards, no heavy metals, formaldehyde and other harmful substances.
② Low irritation: Skin irritation ≤ grade 2 (acute dermal irritation test), mild odor, no volatile harmful gases.
Applicable Scenarios: Environmentally friendly metalworking fluids, food machinery processing fluids (need to meet FDA standards).
II. Core Functions of Surfactants and Their Compatibility with Metalworking Fluids
Not all surfactant functions are compatible with metalworking fluids. Core functions need to be selected based on the above requirements. The following is the compatibility logic of key functions:

III. Typical Compatible Surfactant Types

Based on the above requirements and functions, the common surfactant types in metalworking fluids include:
1.Non-ionic Surfactants: Acetylenic Diol derivatives (Vanconol LFS-1900 series) have low dynamic surface tension and excellent defoaming properties, which are suitable for high-speed processing and high-pressure spraying scenarios. They also have low foaming, wetting, emulsifying, and dispersing functions, and good compatibility, making them the preferred type for metalworking fluids.
2.Other Non-ionic Surfactants: Such as fatty alcohol polyoxyethylene ethers and alkylphenol polyoxyethylene ethers (APEO has been gradually restricted), which have good compatibility but insufficient performance under dynamic high-speed conditions.
3.Anionic Surfactants: Such as sodium dodecylbenzene sulfonate (LAS) and sodium fatty alcohol ether sulfate (AES), which have strong emulsifying and cleaning abilities but high foaming, and need to be used with defoamers. They are suitable for medium and low-load processing scenarios.
4.Special Surfactants: Silicone surfactants have long-lasting defoaming effects, but attention should be paid to their compatibility with other components.
Summary
The core demand of metalworking fluids for surfactants is essentially "solving interface problems"—by optimizing the interface interactions between metalworking fluids and metal surfaces, pollutants, and additives through core functions such as low foaming, wetting, emulsifying, dispersing, and lubricating, ultimately achieving the goals of "improving processing accuracy, extending tool life, reducing comprehensive costs, and meeting environmental requirements".
In actual formula design, priority should be given to surfactants with "low foaming + high wetting + strong stability" (such as Vanconol LFS-1900 series), and they should be synergistically matched with other additives according to specific processing technologies (load, temperature, materials) to maximize the performance of metalworking fluids.