Manufacturing of refrigerators involves injecting isocyanate into the body of the appliance as thermal insulation. After injection, the substance transforms from liquid to foam. An appliance manufacturer found high levels of isocyanate contamination in the anti-wear hydraulic fluid of its hydraulic injection system. Personnel discovered that small amounts of isocyanate were adhering to the cylinder’s piston rod and drawn into the cylinder when the rod retracted. This un-dissolved material remained in the fluid as particulate contamination. Furthermore, some of the isocyanate dissolved in the fluid, causing varnish deposits and gels to form.
The conditions resulted in multiple problems:
- Excessive product defects occurred in the refrigerators.
- Productivity was compromised from all the downtime required to shut down the operation to perform corrective maintenance.
- The maintenance labor and expenses to repair or replace pumps, motors, and control valves from premature failure added substantial cost to the operation.
- The component malfunctions had a domino effect because the electric motors driving the hydraulic pumps had to operate at 150% rated power in an effort to keep the operation going. This not only reduced service life of the electric motors and the pumps, but exacerbated the varnish problem because more varnish formed from elevated fluid temperatures.
To slow the buildup of varnish, the fluid was changed every two weeks. This action treated one of the symptoms but did not address the cause. Plant personnel then ordered fluid analysis to be conducted to find out just how bad the problem was, and what could be done to solve it. The results revealed another problem.
A Call to Action
Fluid analysis revealed high levels of particulate contamination—22/21/16, according to ISO 4408. Analysts also tested for contamination from the varnish and found the fluid had an MPC∆E (indicative of the presence of varnish) value of 33.1 according to ASTM D7843. These results showed that the fluid condition did not meet requirements of the injection machine’s manufacturer. The manufacturer required particulate contamination to be no more than 21/18/15, according to ISO 4408. The OEM also required ASTM MPC∆E levels to be less than 15.
Plant personnel consulted with Hy-Pro Filtration, Anderson, Ind., for a solution. Hy-Pro representatives recommended its FSW off-line filtration system. This off-line circuit—often referred to as a kidney loop—connects to a hydraulic system’s reservoir, pumps the dirty fluid through high-efficiency filters, and returns the clean fluid to the reservoir. Representatives also recommended increasing the size of hydraulic pumps and motors to keep components operating within specifications, normalize fluid temperature, and reduce the system’s susceptibility to varnish buildup.
Results of these actions revealed that ISO 4408 cleanliness dropped to 18/15/10—a 93.5% reduction of particles 4 µm and larger. In addition, the ASTM MPC∆E value fell from 33.1 to 5.2— an 84% reduction. The number of defective units has also decreased substantially, so did downtime, maintenance costs, and the need for frequent oil changes.
All combined, these cost reductions add up to a total annual savings of $211,698 for the OEM. Based on a continuous flow rate of 0.2 gpm, the FSW system has reduced annual particulate contamination circulating in the fluid from 16 lb. to only 1 lb.