High Pressure Die Cast Machines, or HPDCMs, require a good amount of hydraulic oils to run the machine. The hydraulic fluid is utilized to generate significant pressure or force, measured in tons, to ensure that the fixed and the moving halves of the die-molds used for casting is clamped shut, without the possibility of opening, upon the injection of molten metal into the die cavity. Any failure to keep the die-molds shut during injection can be catastrophic as dangerous molten metal can seep or spray out, harming personnel, or potentially causing fires in the workplace.
The hydraulic fluids also function to lubricate the hydraulic pump, which is of a significant value to either repair or replace. A good hydraulic oil therefore needs to reduce the friction and wear of any rotating and/or sliding frictional components inside the pump, such as the rings and vanes. Toshiba and Toyo Die Cast Machines, as a guide, recommend lubricants with either an ISO VG 46 or 68 viscosity, a Viscosity Index of at least 90, and the presence of anti-wear additives, which act to prevent metal-to-metal friction and wear should the viscosity of the fluid be insufficient due to pressure and temperature changes. Such minimum standards or specifications, if satisfied by the correct selection of the hydraulic oil, can ensure a good working lifetime for the hydraulic pump.
Pump troubles do occur nonetheless despite the use of correctly specified hydraulic fluids. It can be attributed to various factors, but two possible conditions stand out:
1) The lubricant is highly contaminated with either solids or water, degrading the lubricating properties of the oil. In fact, an NAS Class 9 contamination grade is the maximum level allowable for hydraulic oil in HPDCM’s, while water should be kept a minimum — < 0.1%. Control of the filtration system and systems leaks are essential.
2) Correct specification lubricant is already degraded, due to the failure of the maintenance personnel to follow or adhere to the recommended drain and change oil intervals. Going past the recommended oil usage interval creates a condition inside the pump wherein oxidized, out-of-spec fluid is being circulated, causing wear, as well rust and corrosion to the metal components. A good rule-of-thumb is to drain and change the fluid once every 12 months.
The different choices of hydraulic fluids for High Pressure Die Cast Machines shall be presented in the succeeding segments of this paper.