Varnish in Plastic Injection Molding Machines
This technical article was submitted by Michael Fertig.
Abstract
Metal Treatment MT-10® is an anti-friction lubricant additive formulated to reduce friction-related heat and wear and promote protective boundary-film formation on lubricated metal surfaces. In plastic injection molding hydraulic systems, customers have reported cleaner hydraulic components, smoother valve operation, lower operating temperatures, improved cycle performance, and reduced varnish-related maintenance.
**Updated Hydraulic Guidance:** Since this article was published, Muscle Products Corp. has introduced Hydraulic Treatment HT-10™ for hydraulic systems with advanced or fine-micron filtration. MT-10® remains the preferred choice for many conventional hydraulic systems; for current product-selection guidance, see When to Use Metal Treatment MT-10® vs. Hydraulic Treatment HT-10™ in Hydraulic Systems.
Introduction
The utilization of Muscle Metal Treatment MT-10® in the hydraulic systems of plastic injection machinery has yielded substantial benefits. These advantages include the elimination of varnish from metal surfaces, improved cycle times during the injection process, reduced valve replacement costs, and decreased energy consumption. While incorporating MT-10® into preventive maintenance programs has always been advantageous, the recent global shortage of components makes careful maintenance of existing equipment even more critical than ever.
Problem: Contamination of Hydraulic Fluids
Contamination is a major cause of hydraulic system problems. Industry sources commonly estimate that 70% to 80% of hydraulic and lubrication-system breakdowns are associated with contamination. Common contaminants and degradation products include water, air, solid particles, sludge, and varnish. Sludge and varnish form due to thermal degradation of the oil, caused by factors like oxidation, electrostatic discharge, adiabatic compression from entrained bubbles (micro-dieseling), or contact with hot surfaces. Machine surface temperatures greater than 140°F may begin thermal degradation of the hydraulic oil. A temperature of 180°F can damage most seal compounds accelerating oil breakdown.
Micro-dieseling, where air enters the system and bubbles suddenly compress as the oil passes through the pump, can rapidly raise temperatures as high as 2000°F. Additionally, electrostatic discharge, more prevalent with modern hydraulic fluids due to their composition, can lead to localized heating and ignition of the air-ignitable mixture present, thus contributing to micro-dieseling and oxidative oil degradation. Oxidation is one of the primary causes for decreasing the stability of hydraulic fluid, causing the oil to turn dark and contaminated.
Varnish can be seen as a brownish tint on cylinders and other components. It is soluble in oil and accumulates until the oil reaches its solubility limit (known as the saturating point). At this point, no further varnish can be absorbed by the oil. Any additional varnish will deposit on metal surfaces. Unfortunately, traditional oil analysis tests cannot detect varnish formation, so it’s typically only discovered when the machine shows effects of contamination.
Varnish often accumulates in areas exposed to elevated temperatures or close-tolerance operation, although deposits can occur throughout the hydraulic system. Servo valves, proportional valves, pump components, seals, and heat-exchanger surfaces can be particularly sensitive. Sticky varnish deposits can also trap fine particulate contamination, increasing abrasive wear and interfering with precise component movement.
Common symptoms of varnish buildup:
Restriction and sticking of moving mechanical parts (such as servo valves)
Increased or sudden wear in valves and pump seals
Loss of heat transfer effectiveness
Plugging of small orifices and strainers by sludge or deposits
Common results of varnish buildup and sludge:
Slower clamp speeds
Longer or inconsistent cycle periods
Reduction of production efficiency
Increase in scrap or defective product due to erratic molding cycles
Frequent installation of new, expensive parts
It is important to understand that varnish can develop even in newer or well-maintained plastic injection molding machines when operating conditions promote hydraulic fluid degradation.
Solution: Muscle Metal Treatment MT-10®
Since 1985, Muscle Products Corp. has supplied Metal Treatment MT-10® for industrial lubrication applications where friction, heat, wear, and heavy loading affect equipment operation.
We have sold Metal Treatment MT-10® to customers for use in various brands of plastic injection molding machines, including:
HPM
Van Dorn
Husky
Cincinnati Milacron
Ferromatik
Engel (all electric except hydraulic ejector zone)
In our experience, the key factor isn’t the machine’s make or model, but rather how well a company applies and follows preventive maintenance protocols. Often, machines are run until the oil degrades, leading to increased friction and heat on solenoid valves—resulting in frequent, costly replacements. Under normal economic conditions, wear and deterioration on machine life are factored into production costs, and new machines may be purchased at regular intervals. However, the current global shortage of chips and other components, as well as rising financing costs, make it crucial to prioritize effective preventive maintenance protocols to extend the operating life of the machine. Metal Treatment MT-10® provides a significant advantage in ensuring the longevity of plastic injection molding machines, whether new or old.
MT-10® is a surface-active anti-friction lubricant additive designed to work with the existing hydraulic oil. Under boundary and mixed-film lubrication conditions, its chemistry promotes protective boundary-film formation on lubricated metal surfaces. This helps reduce direct asperity interaction, improve surface lubricity and load carrying, and reduce friction-related heat and wear.
A more technical explanation: Metal Treatment MT-10® is best understood through five surface-level mechanisms of improvement:
Controlled tribochemical boundary-film formation at loaded asperity contacts
Oxirane-based acid scavenging and corrosion inhibition
Pressure- and temperature-activated surface chemistry in mixed and boundary lubrication
Reduced asperity interaction and improved surface smoothness and load sharing
Near-surface conditioning of the contact zone under severe service
Key features and benefits of MT-10®:
Improves metal-surface lubricity and helps protect against friction-related wear
Reduces friction-related heat and wear that can contribute to component deterioration
Improves equipment performance and efficiency by reducing friction
Lowers system operating temperatures
Reduces energy costs and oil consumption
Reduces downtime and maintenance
Treats the metal - not the oil - by improving metal-surface lubricity and promoting protective boundary-film formation
Contains no solid lubricants, chlorinated solvents, or phosphate compounds
Will not build up or change tolerances
Specific benefits of MT-10® in plastic injection molding machines:
Metal Treatment MT-10® has been shown to considerably reduce varnish build up and ensure faster, more reliable machine operation. Once added to the hydraulic fluid, the following benefits have been obtained:
Metal surfaces free of varnish, sludge, and wear-causing solid contaminants
Freer flow of oil through the system
Faster cycle times
Reduced operating temperatures
Reduced workload on the pumps
Smoother operation of the valves
Reduction in vibrations
More consistent and stable controls and functions
Greater operating efficiency leading to lower energy consumption
Less downtime for maintenance
Substantial reduction in valve replacement leading to major financial savings
A significant advantage of applying Metal Treatment MT-10® in hydraulic machinery is its ability to safeguard pumps and valves. Pumps are often susceptible to damage caused by solid contaminants, which MT-10® effectively prevents from adhering to metal surfaces. While this issue is more common in hydraulic systems operating in dirty environments, it remains relevant even for plastic injection machinery. On the other hand, varnish deposits can pose a threat to valves in any machine, even those working under optimal conditions. Modern equipment increasingly features servo valves, which are highly sensitive due to their close tolerances. In fact, excessive varnish buildup can lead to automatic shutdowns in most modern machines, as the valves cannot move safely or rapidly enough. The typical solution involves replacing the affected valve, incurring considerable expenses. Consequently, utilizing MT-10® in plastic injection machines can yield substantial economic benefits for manufacturers.
One example of this is a client who applied Metal Treatment MT-10® in their plastic injection machines in 2018. They have 19 - 500-ton presses, combining Husky G-Line, Index machines, and HyPET. Previously, valve replacement had been a significant cost for them, but since they first applied MT-10® in their units, they have not had to replace one single valve because of varnish or component wear. Read more about this customer success here.
Another key benefit of using MT-10® is reduction in operating temperatures. Heat has a direct relationship to varnish formation. We have seen reductions of up to 104˚F (40˚C) in injection machinery upon introducing MT-10®.
Enhancing equipment efficiency by reducing internal friction is yet another advantage that manufacturers gain from using MT-10®. This benefit becomes evident through measurable energy savings. When observing the effects of applying this product to machinery, it becomes clear that the efficiency gains associated with MT-10® are cumulative. In fact, successive applications of the product often lead to further enhancements in energy consumption. To fully capitalize on these benefits, we strongly recommend continuous monitoring of energy usage in machines treated with MT-10®. By doing so, management can accurately quantify the positive impact of this lubricant additive.
Application of Metal Treatment MT-10®
Metal Treatment MT-10® is compatible with lubrication systems using standard hydrocarbon-based hydraulic oils, for example Mobil DTE 26 or 46. (NOTE: In the case of ester-based lubricants, please contact us for an alternative lubricant additive).
Apply MT-10® the first time at a 3% ratio to the volume of oil in the system (1 oz. per quart of oil). Subsequent applications of MT-10® should be at a 1.5% ratio (0.5 oz. per quart of oil). We recommend each machine be treated once a year. Please note that no benefits have been detected applying higher ratios or more frequent applications.
Once MT-10® is applied to the system, the maintenance team should pay attention to the condition of the oil filters. As the MT-10® cleans the system, the varnish and contaminants will be removed and may begin to clog the filters, especially after the first application. Saturated filters should be replaced. Once MT-10® is incorporated into the machine’s maintenance protocol, it will stay much cleaner.
NOTE: The clients we service usually apply MT-10® to the machine with a portable metered pump that connects to the oil inlet. Application by this method can easily add MT-10® to any plastic injection machine without interrupting production, leading to further cost savings.
Summary
Muscle Metal Treatment MT-10® is of proven benefit in all types of plastic injection molding equipment, improving operational parameters of the machine, reducing downtime and costly repairs of valves and other components. It will also improve energy efficiency. MT-10® can be applied to all machines using standard hydrocarbon-based hydraulic oils and is a safe and cost-effective solution to problems of wear and varnish buildup.