Case Studies

The following actual case histories describe various operating systems encountered in military metalworking/plating applications, the present filtration installed and a filtration recommendation to achieve the required fluid cleanliness.

A. Grinding

Fluid: Water based coolant
Filtration System: None
Current Contamination Level: >50,000 particles/ml > 5 µm.
Flow Rate: Variable, 3.7-18.9 lpm (1-5 gpm)

Recommendation: Installation of a graded pore disposable filtration system to reduce the coolant's contamination level in order to improve product surface finish, hold product tolerances and extend the interval for recharging the system's coolant.

The following illustration depicts the extremely high particle count level that needs to be reduced to achieve both product specifications and longer coolant life.

Water Based Grinding Coolant's Contamination Level

[ illustration ]


 

Number of Particles Per Milliliter
In the Noted Size Ranges
1 µ - 5 µm 145,472
5 µ - 15 µm  36,966
15 µ - 25 µm   9,750
25 µ - 50 µm   3,180
50 µ - 100 µm     510
> 100 µm  
SAMPLE: Serviced Water Based Coolant
VOLUME: 5 ml
MEMBRANE DISK
DIAMETER:
25 mm
MAGNIFICATION: 100X
SCALE: 14.6 µm/division

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B. Zinc Phosphate Bath Solution - Parkerizing

 

Fluid: Zinc Phosphate coating fluid (MIL-P-50002 type II specifications)
Filtration System: None
Current Contamination Level: 12 Kg/5700 liters in ten days
Flow Rate: Dip tank (no flow), parts are lowered into bath by cranes

Recommendation: Installation of a kidney loop backwash filtration system incorporating high temperature (205°F) and low pH (2.4) compatible cylindrical filter elements in order to extend the 14-day service life of the bath which is directly related to the removal of the sludge plugged steam heating coils for cleaning. The following illustration depicts the contamination of the bath solution in service for ten days. The chemistry of the Parkerizing bath requires that a portion of the contaminant remain in the bath to establish equilibrium. Since the recommended filtration system is required to reduce the contaminant level significantly to achieve an extension of the bath's service life, to meet the criteria for bath equilibrium, metal fibers or a portion of the backwashed contaminant can be reintroduced into the bath.

Contaminant Observed in 1.0 ml of Zinc Phosphate Coating Fluid Bath in Service for Ten Days

[ illustration ]

MEMBRANE: 0.8 mm
MEMBRANE DISK
DIAMETER:
25 mm
MAGNIFICATION: 100X
SCALE: 100 µm per line on
optical photomicrograph

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C. Chromate Conversion Bath Solution - Alodine

 

Fluid: Alodine Bath Solution
Filtration System: None
Current Contamination Level: 1 Kg/5700 liters in two months
Flow Rate: Dip Tank (no flow)
Recommendation: Installation of a kidney loop backwash filtration system incorporating low pH (2.6) compatible cylindrical filter elements in order to extend the six-month service life of the bath which is directly related to the removal of the sludge that builds up. The following illustration depicts the level of contamination of the bath in service for two months.

Contaminant Observed in 1.0 ml of Alodine Bath in Service for Two Months

[ illustration ]

MEMBRANE: 0.8 mm
MEMBRANE DISK
DIAMETER:
25 mm
MAGNIFICATION: 100X
SCALE: 100 µm per line on
optical photomicrograph

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Conclusion

Depending on the metalworking/plating application, a Backwashable Filtration System or Graded Pore Filtration can be employed to reduce the level of contamination of a fluid. This reduction can prolong the useful service life of the coolant/plating fluid, thus preventing pollution and minimizing waste stream volumes in addition to decreasing the number of machined or plated parts rejected. Though many filtration technologies are available, the one chosen should have a short payback period, provide the required fluid cleanliness, not be a significant waste stream contributor itself, require low maintenance and not require the use of an abrasive filter aid, such as diatomaceous earth, to achieve the desired metalworking coolant or plating bath cleanliness.

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