Achieving consistent stock lubrication with less oil

Figure 1 LVLP systems use precision spray valves and air pressure of 5 to 10 pounds per square inch (PSI) to apply a uniform film of lubricant over the stock surface.

When it comes to stock lubrication, metal stampers often choose to flood their strip or sheet with oil rather than risk tool damage from inadequate lubrication.

While this approach ensures that stock is thoroughly coated, it does so at the cost of high oil consumption, rejects from slug pulling, hazardous-waste generation, regulatory compliance issues, pressroom safety issues, and other problems related to excessive lubrication.

What matters even more than the volume of oil applied, however, are the consistency of application and the uniformity of the coating, so that the exact amount of oil needed to prevent tool damage is spread evenly across the entire stock surface, with no dry spots to pull a punch or other areas so drenched that slugs are pulled back onto the stock.

Low-volume, low-pressure (LVLP) lubrication systems can offer stampers a way to maintain the most appropriate lubrication level for each job while reducing oil consumption.

How LVLP Lubrication Works

LVLP systems use precision spray valves and air pressure of 5 to 10 pounds per square inch (PSI) to apply a uniform film of lubricant over the stock surface (see Figure 1). Using low air pressure prevents bounce and mist and allows the lubricant to be applied with high transfer efficiency.
A typical LVLP system comprises spray valves, a valve controller, and a lubricant reservoir.

The spray valves are compact and designed to fit inside the press between the stock feed and the die. A single valve can coat stock from less than 1 in. up to 6 in. wide, depending on the coating width and how far the valve is positioned above or below the stock.

Figure 2 Valve operation is regulated with a pneumatically operated controller that can handle up to eight valves.

Valve operation is regulated with a pneumatically operated controller that can handle up to eight valves (see Figure 2). This configuration provides single-sided coverage of stock up to 48 in. wide, or top and bottom coverage of stock up to 24 in. wide. For wider stock, additional valve/controller systems can be used.

During operation, lubricant is forced through flow controls installed in the valve controller and out to the valves mounted in the press. When the press begins stamping, a three-way air solenoid simultaneously activates the lubrication system. As the valves open, LVLP air at 5 to 10 PSI creates a pressure drop at the valve nozzle and causes a fine, even film of lubricant to be deposited on the stock.

Because LVLP lubrication uses such low pressure, it's not suitable for processes that require fat-based, water-soluble oils or lubricant viscosities higher than 500 SUS (Saybold Universal Seconds). It also is not suitable for applications in which high volumes of oil are needed to cool or quench stamped parts.

The precision flow controls allow each valve's output to be adjusted independently and provide extremely fine control over the amount of oil applied. The lubrication level needed to prevent tool damage and produce well-defined stampings can be established in a few minutes, and coverage remains consistent throughout the job without further adjustment.

As a safeguard to keep the press from operating without lubricant, the valve controller is wired into the press circuit so that lubrication begins automatically when the press is turned on and stops when it shuts down. This ensures lubrication while the press is running and prevents dripping and puddles when it is stopped.

If lubricant pressure drops below a preset level, the system automatically stops the press before the tool can be damaged.

Effects of LVLP Lubrication

Oil Consumption. Because LVLP lubrication remains consistent, coverage is achieved without applying more oil than necessary. Some stampers have lowered lubricant consumption by as much as 90 percent, allowing them to switch to higher-performance lubricants while still saving money.

Housekeeping. Because lubricant is applied at low pressure and with high transfer efficiency, oil stays on the stock, and pressroom mist and puddles are nearly eliminated. Maintenance and housekeeping time is reduced, as is the consumption of absorbent materials, which in turn decreases the amount of hazardous waste that must be stored and disposed of.

Regulatory Compliance. Reduced oil usage means decreased volatile organic compounds (VOCs) and hazarous waste. This aids compliance with environmental regulations and avoidance of potential fines.

Tool Maintenance. Consistent lubrication levels can double the time between tool sharpenings. When sharpening does become necessary, the tool is in good condition for the operation.

Cleaning and Disposal. LVLP lubrication leaves little residue, so stampings often do not have to be cleaned. If cleaning is required, the amount of sludge generated remains small, helping to simplify washwater disposal.

Scrap Prices. Metal recyclers pay less for oily scrap. LVLP lubrication typically leaves scrap clean enough to command the best prices.S

Ron Hawkins is a metal forming applications specialist at EFD Inc., 977 Waterman Ave., East Providence, RI 02914-1378, 800-556-3484, fax 401-431-0237, www.efd-inc.com.