Meeting these challenges requires more than advances in machine design. It demands tighter control of the process itself, and at the center of all die casting operations is the hydraulic system. Fire-resistant hydraulic fluids, once chosen primarily for their safety profile, are increasingly recognized as enablers of process control, reliability and productivity.

Performing Under Pressure

Firstly, hydraulic fluids must deliver consistent pressure. This is partly achieved through a high viscosity index — ensuring the fluid’s viscosity and therefore pressure and flow remain consistent even as temperatures rise during long production runs.

Air entrainment and foaming present further concerns for pressure management, as they increase compressibility within the hydraulic system. Die casters should therefore opt for a product with fast air release to avoid introducing variability into the pressure curve that governs both injection and intensification phases. This is particularly important for large or thin-walled parts, to ensure complete cavity filling and support structural integrity.

Smooth Operations

Good lubricity is another key requirement for smooth die casting operations. Without adequate lubrication, hydraulic cylinders can exhibit stick-slip behavior, leading to jerky, unpredictable movements that reduce process stability and are unacceptable for the injection step. More generally, poorly lubricated metal-to-metal contact — particularly in pumps — leads to wear, scuffing, and ultimately equipment failure. This unchecked friction also results in excess heat generation, which doesn’t just represent energy losses in the system but also promotes premature aging of the fluid — reducing service life and increasing costs.

Stability and Cleanliness

The harsh conditions of die casting operations can cause premature aging and degradation in a lower quality hydraulic fluid, resulting in insoluble compounds and varnish. High cleanliness is critical to avoid sticky valves or sluggish actuators that compromise timing and repeatability. High shear strength is also essential in maintaining fluid viscosity and pressure in the longer term, given the mechanical forces experienced by the fluid as it is pushed through narrow clearances at high speeds and pressures over 200 bar. In brief, the longer a hydraulic fluid remains within its specification, the better the machine responses will align with the programmed profiles.

The two most widely used technologies are water-glycol HFC types and water-free polyol ester HFDu fluids. Historically, HFC fluids have been the go-to for die casters as their 35-45% water content provides a superior level of fire resistance. But it’s this high-water content that adds complexity: the fluid concentration must be closely monitored and maintained to guarantee adequate lubricity and corrosion protection. It also needs noting that not all HFC fluids are formulated equal. Die casters should look for product with robust anti-wear and corrosion protection properties, as well as fast air release and low foam potential to reduce the risk of cavitation that’s inherent with high water concentration. Overall, with the right management, high quality HFC fluids can provide reliable performance. Particularly with older installations more prone to leakage, or operations experiencing frequent fires, HFC is a logical choice.

Today we estimate that between 80 and 90% of high-pressure die casting operations in Europe are running on HFC fluid, but with current market trends, the need for better process control, productivity, and equipment reliability is intensifying. As a result, we’re seeing many customers becoming more interested in HFDu synthetic ester technology for its improved lubrication and long-term stability. With zero water content, HFDu protects equipment to the same level as traditional mineral oil, but unlike mineral oil, HFDu has a high fire point and auto ignition temperature to reduce chance of fire. Plus, its self-extinguishing nature keeps any fire incidents under control, which is recognized by insurers and often reflected in premiums — look for products with Factory Mutual (FM) approval. For large-scale and giga casting applications where state-of-the-art equipment is in use — and the consequences of process instability are extremely costly — synthetic ester HFDu fluids are being increasingly relied upon to drive quality and minimize total cost of ownership.

Boosting Overall Equipment Effectiveness

Both HFC and HFDu fluid types benefit from universal maintenance best practices. Routine fluid analysis is essential in providing insights such as viscosity, acid number, contamination levels, and overall fluid condition. This data forms the backbone of a predictive maintenance program to keep fluids — and equipment — operating within specification.

For HFC-type fluids, generally we recommend sampling at least every three months; for HFDu, it’s every six months. It’s important to make sure the sample is representative of the fluid circulating under normal operating conditions, and that the sample is always taken from the same point in the system, as this supports effective trend monitoring.

A good service partner should supply not just the results of the fluid analysis but also recommendations for corrective actions, such as concentration adjustment (in the case of HFC) or filtration (both HFC and HFDu), which should be implemented in a timely manner. Maintaining oil cleanliness through filtration is critical in high pressure systems to protect pumps, valves and servos from particulates that could shorten component life or undermine performance. Typically, an ISO 4406 cleanliness code of 18/16/13 or better is required — always check the OEM specification.

An often-overlooked tactic to improve overall equipment effectiveness of hydraulic systems is ensuring seal compatibility. This should always be checked with your fluid supplier, as degradation of the elastomer can lead to leakage and failures that both reduce reliability and increase fire risk.

A Strategic Asset for Success

For high-pressure die casters in the modern market, hydraulic fluid is not a consumable but a strategic asset. The right fluid choice paired with robust maintenance practices directly influences equipment reliability, productivity, operator safety, and ultimately the quality of every casting produced. As the industry pushes into giga casting, more complex geometries, and ever-tighter tolerances, high quality fire-resistant hydraulic fluids provide control and confidence to operate at the limits of technology without compromising safety. In short, the future of die casting will be forged not just in molten metal, but also in the hydraulic systems and fluids that power them.