Other than mineral-based oils and dry plunger pellets utilized to lubricate the interface between the plunger sleeve and plunger tip of high-pressure die-cast machines, some die-casters have turned into using water-based lubricants.
Such a preference for water-based lubricants are normally driven by a die-casters’ desire for either one of the following factors, or a combination thereof,
- The improvement in casting quality, especially regarding stains and porosity, as ‘water-based oils are deemed ‘cleaner’ than oils,
- Enhanced safety, considering that ‘water-based’ fluids are less of a fire-hazard compared to oils and the wax-based dry plunger lubricants, and,
- A cleaner, less oily work environment, since oil spillages are reduced using water-based lubricant as compared to oil-based fluids
Water-based plunger lubricants are primarily composed of water of course, but still, it includes emulsified mineral-oils, extremely pressured additives, as well as suspended solids, micro-particle sized solid lubricants such as PTFE or graphite. Water does not provide any friction reduction function, but importantly, it serves as a carrier to ‘deliver’ the mineral-oils, additives, and solid lubricants into either the plunger sleeve, plunger tip, or both. By using water as a carrier, as opposed to mineral oils (that serve a dual function of being a carrier and a lubricant), spillages or wastage are reduced to a minimum, minimizing casting contamination and improving the cleanliness in the casting area.
Indeed, fire-resistance or retardance is improved owing to the water component, though it is still not uncommon to witness the water-based lubricant in a plunger sleeve flash-up upon contact with molten aluminum, albeit briefly since there are still mineral oils in the formulation.
Water-based lubricants for plunger systems are either dripped with mineral oils, but it may also be atomized or sprayed.
It has its disadvantages that a die-caster must consider before making a final selection of which technology to utilize for the plunger lubrication of his high-pressure die-cast machines.
- Poor wetting – a significant amount of water will evaporate upon contact with either a hot sleeve or hot tip, and thus a water-based lubricant will not ‘spread readily’ into the frictional areas. This may lead to premature wearing. An accurately-aimed nozzle or dispenser, or several nozzles working in tandem, can mitigate this scenario.
- Clogging of nozzles or lubrication lines – as an emulsion, the oil-phase of a water-based lubricant, given time, or improper storage conditions, can separate, forming gel-like substances that destroy the homogeneity of the lubricant. Such de-emulsified by-products can accumulate along certain sections of the lubrication lines, causing lubrication blockages. A controlled environment for storing water-based lubricants, and an efficient FIFO inventory management system is, therefore, a must, in order to ensure that the water-based lubricants are as homogenous and fresh as possible.
The author hopes that a clear summary of the various available options for plunger lubrication has been presented, in aid of the die-casters’ selection process.