Hello everyone. Today, let's talk about injection molding machines. As anyone in this industry knows, within the hydraulic system of an injection molding machine, there is one element that is particularly delicate: copper-containing components.
Where is copper found in an injection molding machine?
The hydraulic system of an injection molding machine is not made entirely of steel. Several key locations contain copper:
The copper distribution plate in plunger pumps: Many imported injection molding machines utilize plunger pumps, and the internal distribution plates are made of copper alloy.
The copper coils and silver-plated parts in servo valves: Precision injection molding machines use servo valves to control flow rates, and the valve spools often feature a silver-plated layer.
The copper tubing in heat exchangers: Oil coolers-specifically the heat exchangers used for oil cooling-are constructed with coiled copper tubing.
Copper gaskets found in certain fittings and connectors.
If these components become corroded, the consequences range from minor issues-such as leaks or unstable pressure-to severe failures that bring the entire machine to a complete standstill.
What effect does zinc-containing oil have on copper?
Most standard anti-wear hydraulic oils are of the "zinc-containing" type. Their additive packages contain Zinc Dialkyldithiophosphate (ZDDP), which indeed provides excellent anti-wear protection; however, the zinc ions within this additive have a troublesome side effect: they trigger an electrochemical reaction with copper and silver.
Simply put, the zinc "displaces" the copper and silver from the metal surfaces. The copper and silver are gradually eaten away, forming black deposits of silver sulfide and copper oxide that adhere to the surface of the components. Initially, this manifests merely as discoloration; over time, pitting and grooving appear, eventually leading to the failure of sealing surfaces and the seizing of valve spools.
This process is known as "silver corrosion" or "copper corrosion." It is not a phenomenon that occurs overnight; however, after six months to a year of operation, if you disassemble the system for inspection, you will find the copper components coated in a thick layer of black residue-and running your hand over the surface reveals that it is riddled with pits.
Why is ashless oil safe?
Ashless anti-wear hydraulic oils contain no zinc, or-at most-an extremely low concentration (typically less than 0.03%). Instead, they utilize ashless additives based on sulfur, phosphorus, and nitrogen compounds to provide the necessary anti-wear properties.
These specific additives do not trigger displacement reactions with copper or silver. Consequently, when using ashless hydraulic oil, the surfaces of copper components remain clean and pristine-free from discoloration, blackening, or pitting. Requirements from Injection Molding Machine Manufacturers
Today, leading injection molding machine brands-such as Haitian, Chen Hsong, Engel, and KraussMaffei-explicitly state in their operating manuals that their hydraulic systems contain copper and/or silver components. Consequently, they recommend the use of ashless anti-wear hydraulic oil. Some high-end models go even further, strictly mandating: "Ashless oil *must* be used; failure to do so will void the warranty."
This isn't the manufacturers being finicky; rather, they have simply grown weary of dealing with repairs. Dismantling an injection molding machine's piston pump to replace a set of copper distribution plates-including labor costs-can easily run into the thousands of dollars. For larger machines, the cost can reach tens of thousands. By simply using the correct oil, this entire expense can be completely avoided.
A Real-World Comparison
Consider two injection molding facilities operating identical Engel machines under identical working conditions:
Facility A used standard zinc-based hydraulic oil. Two years later, the copper distribution plates within the piston pump suffered severe corrosion; this led to unstable system pressure and resulted in product defects such as flashing (excess material). The subsequent repairs cost $28,000.
Facility B used ashless hydraulic oil right from the start. After the same two-year period, an inspection revealed that the surfaces of the copper components remained bright and pristine-looking as good as new. Aside from routine oil changes, they did not spend a single penny on repairs.
In Summary
If your injection molding machine contains copper or silver-plated components, do not try to save a few dollars by using zinc-based hydraulic oil. While ashless oil may cost slightly more upfront, the repair costs you save will amount to ten times that difference. Focus on the big picture-the overall long-term economics-rather than just the minor short-term costs.
