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Home > Fluids

Water-Based Lubricants

Jenifer Ineman,

Product Manager of Metal Processing Additives at The Lubrizol Corporation

Water-based lubricants--soluble oils, semi-synthetics and synthetics--offer better cooling capability than oil-based lubricants, but less lubricity. With safety and environmental concerns at the forefront, water-based metal-stamping lubricants have experienced increased popularity. Here’s a rundown of their characteristics and capabilities.

Water-based metalworking Fluid Types

© The Lubrizol Corporation, all rights reserved.

As opposed to oil-based lubricants, where oil serves as the carrier for performance additives, water-based lubricants rely on water as the carrier. Because oil-based lubricants have good anti-weld (non-stick) properties and high lubricity, they often get the call for operations where press speeds are low, pressures are high and part material is tough. Water-based lubricants, on the other hand, which offer improved cooling capability over oil-based lubricants, are ideal for high-speed stamping. Water-based lubricants typically are supplied as concentrates designed for dilution at the metal-stamping plant.

With safety and environmental concerns such as lubricant disposal at the forefront, water-based metal-stamping lubricants have experienced increased popularity. But being an aqueous system, a water-based lubricant brings special challenges, which can be addressed through the use of performance additives. Challenges include: 1) corrosion control; 2) potential for microbial growth that can lead to unpleasant odors, shortened lubricant service life and health and safety issues; and 3) limited ability to provide lubrication.

Categories of water-based metal-stamping lubricants include soluble oil, semi-synthetic and synthetic. These categories have been based traditionally on the amount of mineral oil in the formulation, but recent evolution in fluid design has blurred the lines, and fluid categories are less definitive than in decades past.

Soluble Oil

Soluble Oil

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Soluble-oil lubricants typically contain 50 percent or more of mineral oil in concentrate, and form milky macro-emulsions when diluted with water. Soluble oils are capable of serving most metal-stamping operations and functioning with various materials. Product quality of soluble oil ranges from basic performance to highly enhanced performance through EP additives, lubricity additives and biocides.

Soluble oils bring many advantages to a metal-stamping process. They offer good cooling and lubricity characteristics and good performance at low concentrations. The oily film inherent in the use of soluble-oil lubricants provides rust prevention. Other positives associated with soluble oils include detergency and cascade-able product performance levels, meaning that concentrations can be fine-tuned based on application needs. But soluble oils bring disadvantages as well. Hard-water sensitivity can result in soap scum, emulsion instability and rust problems. Use with soft water can result in foaming. Other disadvantages include susceptibility to microbial attack and disposal issues.

Synthetic

Synthetic

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Free of mineral oil, full synthetic lubricants can be further divided into two varieties: true solution (think sugar in coffee) and emulsion (think mayonnaise). True-solution synthetic varieties provide extremely high cooling performance but minimal lubricity. Emulsion synthetics carry water-insoluble materials as microscopic droplets in the water. These are sometimes referred to as neo-synthetic lubricants, and offer improved lubricity performance similar to semi-synthetic lubricants.

Generally, synthetic lubricants offer clean operation and long fluid life, with minimal lubrication potential. Their chief use is in high-speed operations where cooling is more important than lubrication, and generally limited to use with typical easier-to-form steel alloys.

Semi-Synthetic

Semi-Synthetic

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Semi-synthetic lubricants offer performance ranging between soluble-oil and synthetic lubricants. In concentrate, semi-synthetic lubricants contain some mineral oil, but at lower levels than with soluble oil, and typically form clear micro-emulsions when diluted with water.

Semi-synthetics are ideal lubricants for multi-operation service on multiple materials, and can be provided in a broad range of qualities to serve a broad range of cost and performance expectations. But such capabilities make semi-synthetics the most complex and technically challenging water-based lubricants to formulate. Even so, more and more metal stampers are opting for semi-synthetics due to their performance characteristics and flexibility.

Synthetic vs. Soluble Oil: Advantages and Disadvantages
Synthetic fluids offer a host of advantages over soluble oils. Chief among them:
  • Resistance to bacterial degradation
  • Good work visibility due to clear solutions
  • Good stability and good water tolerance
  • Cleanliness
  • Low foaming
  • Good wetting
  • Excellent cooling capability.
Disadvantages of synthetics compared to soluble oils include:
  • Reduced lubricity due to a lack of petroleum oil
  • Hard crystalline residues
  • High alkalinity
  • Skin irritation
  • Peeling paint
  • Difficulty related to waste treatment.

Discussion Questions:

  • Does you operation employ water-based lubricants over oil-based? Why or why not?

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