Page 17 - MetalForming June 2015

Lubricant Percentages
Refractometer Reading
Product 1 Factor 1.6
Product 2 Factor 1.0
Product 3 Factor 0.8
5.0
8.0%
5.0%
4.0%
7.5
12.0%
7.5%
6.0%
10.4
16.64%
10.4%
8.3%
The simplest lubricant mixing method uses a venturi mixer, where water flow creates suction and pulls the lubricant concentrate into the water flow. Down- sides: Ratio of water to lubricant can vary, and it won’t work with more viscous fluids.
venturi action with more viscous fluids. For improved performance, use a positive-displacement mixing pump, which can handle more viscous lubri- cants. In these types of mixers, water pressure drives a piston that pulls the proper amount of lubricant and com- bines it with water to provide a much tighter tolerance on the concentration. To adjust concentration, simply turn the piston to a longer stroke, injecting more lubricant into the water flow. Because all adjustments using this method are performed manually,
human error can play a part.
To remove the human element and
other variation, a programmable, pro- portional mixing system will provide a consistent ratio with the touch of a button. These systems can be used as stand-alone mixers, supplying a sin- gle dilution or two dilutions. They can be changed easily and locked out for adjustment only by proper plant per- sonnel. Another advantage, propor- tional mixing systems can connect to a plant distribution system easily, and incorporated into a pressurized deliv- ery system for each stamping press or individual dies.
Measure and Monitor the Mixes
All of the above-
mentioned options
can produce relatively
consistent mixtures.
Mixing a stamping
lubricant to an overly strong concen- tration brings additional costs and pos- sible residue issues. Too lean of a lubri- cant mix leads to production issues such as premature wear, part galling and poor-quality parts as well as increased die wear. Evaluate all of these mixing systems in order to match the mixing method to your process and capabilities.
Once mixed, fluid often is not checked for the proper ratio of lubri- cant to water. Your lubricant supplier should provide a target range for the optimal performance of a specific stamping fluid. Some plants decide to run at one concentration for the entire manufacturing process, while others find that one lubricant with two ratios work best—one for tougher work, and one for light- to medium-duty jobs. Daily checks of the mix ratio are critical; use check sheets to capture the con- centration for each press or workcell.
Handheld or digital refractometers provide accurate readings of the process fluids. Here, a small amount of the lubricant mixture placed on the device delivers a visual reading on a scale or a displayed number that is unique for each product used. The number does not represent the per- centage of stamping lubricant to water—a common misconception— but is a number that must be com- pared to that specific lubricant to deter- mine the actual percentage.
The formula to determine the actu- al ratio of lubricant and water:
Refractive Index x Product Factor = Lubricant Percentage
For example, a stamping lubricant with a product factor of 1.6. that gives a reading of 10.0 yields a lubricant per- centage of 16 percent. Your lubricant supplier can provide a technical datasheet that gives the product factor.
The only time that the refractometer reading reports the true percentage is when the product factor is 1.0 (see Lubricant Percentages chart above).
Also consider the chemical makeup of your stamping lubricant. Petroleum oil is the major component of water- soluble oil, along with other oil-soluble additives. This will give a higher refrac- tometer reading, which does not nec- essarily indicate product efficacy. By incorporating advanced extreme-pres- sure and lubricity additives into the formula, a product with a lower factor may have a lower refractive index com- pared to another lubricant, but may perform better on tougher jobs. There- fore, the refractive index or factor is not a clear indicator of performance when comparing lubricants.
Thorough Testing, Including Upfront Work, Pays Off
Plan a stamping-lubricant test with metrics determined prior to the test. Complete as much upfront, offline
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To remove the human element and other variation, a programmable, proportional lubricant mixing system will provide a consistent ratio at the touch of a button.