An Evolution in Spray Lubrication Performance

July 27, 2023

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While many metal formers have, over the years, updated their press-line lubrication systems, some still employ outdated spray-lubrication systems—in some cases custom-fabricated inhouse—to coat blanks and coil stock. These setups, using old-school air-over-oil circuits, can leave press shops in a foggy haze, unhealthy and unsafe. Too, delivering lubricant with such setups often leads to inconsistent coverage and overspray, depositing seemingly less lube on the stock than on the press and other equipment, and the floor. The result: significant safety concerns, premature wear of press bearings and other apparatus due to oil-mist infiltration, and unnecessary and avoidable costs related to excess lubricant consumption and associated costs for cleanup.

Smart stamping companies seek better control of their press-line lubrication processes, to provide precisely monitored and tightly controlled application. The benefits are endless—reduced consumption leads to multiple cost-savings opportunities, while precise application in targeted areas of a blank or coil, and the opportunity to intermittently apply lubricant using pulsed spray patterns, ensure uniform coverage and optimize stamped-part quality and consistency.

Replacing Aged Spray Systems

Generally, stampers have two options when replacing aging spray systems—roller coaters or automated airless spray systems employing hydraulic nozzles. Here we focus on the latter, where replacing air-over-oil circuits with precision-controlled airless setups eliminates the use of compressed air, dramatically reduces the number of required spray nozzles and reduces lube consumption, all while decreasing the volume of airborne oil. In addition, worker comfort and health improves, and labor and other costs associated with the cleanup and disposal of waste lubricant diminishes.

Spraying Systems lubrication Full Coverage

To lead our discussion on airless spray technology, we bring in two engineers from Spraying Systems Co., Glendale Hts., IL, to share their expertise: Andrew Day and Sam Scully. Day and Scully immediately note a few trends impacting lubricant application in stamping operations—the drive to reduce lubricant consumption; the move from oil-based lubricants to non-petroleum wax-based formulations; and the growing applications for stamping aluminum-alloy parts, particularly for the automotive market.

“Aluminum in particular is more susceptible than steel to the consequences of over- and under-lubrication,” says Day. “Therefore, we see stampers requiring more precise control over their lube systems when stamping aluminum. And, heavier wax-based lube formulations can be more difficult to spray. In both cases, we often recommend preheated airless systems to achieve predictable and repeatable lubricant viscosity at the nozzle.”

Precisely controlled spray systems, say Day and Scully, enable application of lubricant when and where it’s needed on a blank or coil, and help to ensure that the lubricant doesn’t go where it’s not needed. “Stampers increasingly want to vary the application rate and spray pattern, depending on the size and complexity of the blanks,” says Scully, “and want to spray the right amount of lube in the right locations. This minimizes consumption and improves system performance and part quality. Too much lubricant on any one area of a blank can create parts with cosmetic issues—rippling or hydraulic marks on the material, for example. And, insufficient lube can lead to tears.”

Airless Spraying with Hydraulic Nozzles

Spraying Systems Zone Control Day and Scully report instances where converting to airless spray systems can cut lubricant use in half, not only reducing costs for the lube and for cleanup of overspray, but also avoiding damage to the press and other nearby equipment as excess oil mist infiltrates machine bearings and other components.

One potentially overlooked variable in the lubricant-application formula is the stamping environment—in particular the temperature and humidity at the press. Day and Scully, both engineers working to support every customer’s unique projects, work backward from the application specifics and the process variables involved to help devise optimized lubrication systems and their individual components.

“We might, for example, be working with a stamper that’s mopping lubricant onto blanks, or overspraying with an air-over-oil setup,” says Day. “So, we might be selecting anywhere from a simple nozzle header to air-atomizing nozzles, or to completely airless hydraulic nozzles. And, when it comes to managing fluctuations in heat and humidity, we typically recommend a heated airless system that consistently preheats the lubricant to within a specified range. This critical, yet often overlooked, step makes lubricant viscosity a fixed and known constant regardless of the pressroom environment, rather than a variable parameter.”

“We used to hear stampers say that when the temperature drops during winter months and the lubricant becomes more viscous, we just crank up the air pressure,” adds Scully. “But today air-assist is almost a last resort. While many stampers now understand the benefits of heating their lubricant to a constant temperature regardless of the pressroom environment, we feel as if more stampers should be doing this…we recommend it more than it is done in practice.”

PWM Systems

In addition to heated, airless spray systems for optimizing lubricant delivery, Day and Scully point to increased use of pulse-width modulated (PWM) spraying systems for helping stampers maintain a constant application rate (volume per square inch) onto blanks and coil stock, particularly important when travel speed through the press varies.

“PWM control, or what we call precision spray control (PSC), allows real-time adjustments to flow rate based on press-line speed,” Day notes, “made possible using hydraulic spray nozzles. And, because PSC setups can adjust lubricant flow rate without changing pressure, we can dial in the proper pressure at the beginning of the process and then ensure a constant application rate regardless of travel speed of the stock through the press.”
In terms of what’s new or coming soon to further enhance PSC systems, Day and Scully both point to in-process monitoring and closed-loop feedback control of spray-system performance—to ensure proper lubricant application and to enable predictive maintenance of system components, rather than preventive.

“For several years, we’ve been able to apply process controls by monitoring pressure in the fluid lines,” explains Day. “Now, when using high-speed PWM valves we can add a sensor package on each valve to monitor when it opens and closes and ensure that it’s cycling properly. With spray times measured in milliseconds, there’s no other way to monitor valve actuation.”

Explaining how such sensor data might be applied in practice on a stamping operation, “we’d typically be looking for consecutive faulty pulses,” Day adds, “rather than just one or two bad cycles. We then can track the percentage of overall pulses that are bad and compare the data against a preset limit. This would avoid nuisance stops, while ensuring that we always have lubricant on the part where it’s supposed to be.”

Concludes Day: “Stampers today quickly can get these PSC lubrication systems set up, programmed and running, with parameters set to optimize lube delivery and consumption, and to ensure repeatable performance in the press and optimize part quality. Now, with newer process controls and sensored feedback loops, we can ensure that the systems perform as prescribed on day 100 just as they did on day one.” MF

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