In a foundry or die-casting shop, hydraulic lines run close to molten metal, hot dies and furnaces. If a hose bursts, mineral hydraulic oil sprays out as a fine mist that ignites easily on a hot surface. Fire-resistant hydraulic fluids are made to resist that. They do not make a fire impossible, but they make it much harder for a leak to become one.
Fire-resistant hydraulic fluids are classified in ISO 6743-4 as HFA (over 80% water), HFB (water-in-oil emulsions), HFC (water-glycol solutions) and HFD (water-free synthetic fluids). Water-glycol (HFC) is the usual choice for die-casting and foundry hydraulics. Change over only with the machine maker's approval: drain and flush out the mineral oil, check seals, hoses, paint and filters for compatibility, confirm the pump ratings, and monitor water content afterwards.
| Type | What it is | Typical water content | Notes |
|---|---|---|---|
| HFA (HFAE, HFAS) | Oil-in-water emulsions or chemical solutions | More than 80% | Very fire resistant; low lubricity; used in mining face hydraulics and special systems |
| HFB | Water-in-oil emulsion | Around 40% | Less common today |
| HFC | Water-glycol (polyglycol) solution | Typically 35–50% | The usual choice for die-casting and many foundry machines |
| HFD (HFDR, HFDU) | Water-free synthetics such as phosphate esters (HFDR) or polyol esters (HFDU) | None | Higher temperatures and pressures; different seal needs |
Banesto's PAG / water-glycol fire-resistant fluid is supplied in ISO VG 46 and 68 for safety-critical hydraulics near hot metal.
Water-glycol fluids resist ignition well because of their water content, work with many standard hydraulic components once the pump is rated for them, and handle the moderate temperatures of most die-casting circuits. Their weaknesses are lower lubricity than mineral oil, higher density, and the need to keep water content in range.
Ask the machine and component makers to confirm each of these:
Mineral oil does not mix with water-glycol. It reduces fire resistance, forms sludge and can block filters and valves. Keep separate, labelled top-up containers for each machine.
Hydraulic circuits well away from heat and ignition sources, such as presses at the far end of the shop, can usually stay on anti-wear mineral oil such as HLP 68. Our guide to hydraulic oil types explains the grades, and hydraulic oil overheating covers temperature problems in hot shops.
For the full range of foundry and forging lubricants, see our page on foundry and forging lubricants.
Which fire-resistant hydraulic fluid is used in die-casting machines?Usually a water-glycol (HFC) fluid, provided the machine and pump makers approve it.
Can water-glycol be mixed with mineral hydraulic oil?No. The mix loses fire resistance and forms sludge. Flush out mineral oil fully when converting and never top up with it.
Do I need new seals when switching to water-glycol?Often. Nitrile seals usually work, but polyurethane and some other materials do not. Check every seal type with the component maker.
How do I check the water content of water-glycol fluid?With the method the fluid maker recommends, such as a viscosity check or a refractometer reading, at regular intervals.
Planning to convert a die-casting or press hydraulic system? Send us the machine and pump details, and our team will check the fluid choice and the changeover steps with you.