Sulfide Additives: Extreme Pressure Additives in Metal Working and Lubrication

In metalworking processes, including cutting, grinding, and other metal forming processes, due to the high speed and high pressure, friction between cutting tools and workpieces often involves extreme pressure and high temperatures.

Engineers always need to add metalworking fluids with certain chemicals to prevent bad effects from these extreme-pressure frictions, prevent excessive wear, heat, and even sintering. These chemicals, which isolate metal surfaces under boundary lubrication conditions to resist wear and sintering, are known as extreme pressure anti-wear additives.

 

Sulfur-containing extreme-pressure / anti-wear (EP/AW) chemicals are currently one of the most widely used additives in lubricants and metalworking fluids. The most commonly used sulfur agents include sulfurised animal and vegetable oils, sulfurised olefins, zinc dialkyl dithiophosphate, derivatives of dimercaptothiadiazole (DMTD), as well as polysulfides.

 

 

1. Sulfurized Fatty Esters

Sulfurized Fatty Esters are currently widely used type of sulfur-containing extreme pressure additives with good performance. They are produced by reacting natural or synthetic fatty acid esters with sulfur. In addition to providing extreme pressure properties, they also exhibit good lubricity. Common products include sulfurised lard and sulfurised cottonseed oil.

 

2. Sulfurized Olefins

Properties: Produced by reacting α-olefins, isobutylene, and other compounds with sulfur. Sulfur content can be very high (over 40%), resulting in excellent extreme pressure performance, especially under high loads. They are primarily used in ferrous metal processing applications requiring extremely high extreme pressure performance, such as high-pressure tapping and broaching.

Sulfurized isobutylene has been a key additive in gear oil blending for over 40 years. It remains an essential core extreme pressure and anti-wear agent in mainstream gear oil formulations worldwide. Internationally renowned lubricant additive companies such as Lubrizol, Mobil, and Rhein Chemie all produce sulfurized isobutylene and use it as an extreme pressure additive in gear oils, hydraulic oils, and metalworking fluids.

3. ZDDP

Zinc dialkyl dithiophosphate (ZDDP), commonly classified as an antioxidant and corrosion inhibitor (AW), is widely used in lubricants and metalworking fluids. Because ZDDP contains two active elements, sulfur and phosphorus, it exhibits certain extreme pressure properties.

 

4. DMTD

 

Dithiothiadiazole (DMTD) derivatives, a highly effective multifunctional additive, are the primary copper corrosion inhibitor. Because DMTD contains both sulfur and nitrogen in its molecule, it also possesses extreme pressure and anti-wear properties.

 

5. Polysulfide

 

Polysulfides are typical extreme pressure additives used in metalworking fluids and lubricants.

 

Chorus offers Dialkyl Pentasulfides (Chorus S32) and Dialkyl Trisulfides (Chorus S20), which are widely applicable to various metalworking fluids, providing excellent extreme pressure and anti-wear protection and compatibility with a variety of formulations.

 

ITEM	Chorus S32	Chorus S20
Chemical Name	Dialkyl Pentasulfide	Dialkyl Trisulfide
Sulfur Content	High (due to 5 sulfur atoms in the molecule)	Relatively Lower (due to 3 sulfur atoms in the molecule)
Main Advantage	Excellent extreme pressure and anti-wear performance, especially for severe conditions	Excellent extreme pressure and anti-wear performance, and wide adaptability
Inactive or active Sulfur	Active Sulfur	Inactive Sulfur
Copper Corrosion	Poor	Excellent
Applicable Systems	Pure oil-based, soluble oil	Pure oil-based, Emulsifiable oil
Typical Applications	metal working and lubricant additive for non-copper parts	Lubricants for copper processing, gear oils, extreme pressure esters, cold rolling oils, etc
Environmental & Safety	Low odor, Chloride-free, Unsaturated hydrocarbon-free	Low odor, Chloride-free, Unsaturated hydrocarbon-free
Summary	Inactive Sulfur, High performance but corrosive to copper	Active Sulfur, Suitable for systems with copper

Sulfur-containing extreme pressure and anti-wear agents are generally not used alone. They are usually combined with other additives for a synergistic effect. For example, sulfur-based EP additives offer good anti-welding (EP) properties but poor anti-wear performance, while phosphorus-based EP agents provide excellent anti-wear performance but relatively poor extreme pressure resistance. Thus, they complement each other's shortcomings. These additives are widely used in engine oils, hydraulic fluids, gear oils, compressor oils, and metalworking fluids.

For application guidance on suitable extreme pressure and anti-wear agents, please feel free to consult the sales engineers of Chorus Company.