Plastics manufacturing is a cooling water intensive process with production efficiency and product quality directly tied to effective water treatment. Increased cycle time, high defect rates, unscheduled downtime, mold damage, and high maintenance costs can all result from water system problems including corrosion, deposits, and biofouling.
However, effective water treatment requires more than just chemical additions. Cooling water system design and operational factors also play a big role. Serious and costly waterside problems can be avoided or reduced by applying simple principles:
A galvanic couple occurs when two different metals are directly connected in a water system. This creates an electrochemical “battery” that causes one metal to be corroded with the corrosion byproducts migrating to form deposits elsewhere in the system. A common example is a copper quick disconnect fitting on an aluminum mold. The piping arrangement dramatically increases the potential for aluminum to corrode. To avoid galvanic corrosion, dissimilar metals should be joined using a dielectric union.
Effective filtration to remove suspended solids greatly reduces the potential for fouling deposits that reduce heat transfer and block flow. Mold cooling water loops should employ submicron (<0.5 micron) filtration with automatic backwash to ensure reliable solids removal. Chem-Aqua High Performance Filters (HPF) are designed to efficiently remove problem causing suspended solids with minimum routine maintenance.
A dead leg is equipment or piping where low flow or stagnant water conditions exist. These non-circulating areas are prime locations for biofouling, and can result in serious corrosion, heat transfer, and blockage problems. Common dead legs include capped extensions for future piping expansion and intermittently operated equipment such as mold control units. Bacteria will “hide out” in stagnant areas during biocide additions and continuously re-inoculate the cooling system. Where dead legs cannot be eliminated, consider the installation of by-pass lines or cross connections so that flow can be maintained at all times, even when a machine or section of the plant is off line.
High pressure air compressors employ heat exchangers that can experience low water flow and high skin temperatures. These conditions make it difficult to control scale formation in the small diameter heat exchanger tubes. The resulting heat transfer loss can reduce air compressor and plant capacity. To avoid problems related to scale deposits in these critical systems, it is recommended that a recirculating closed loop rather than an open cooling tower be used for cooling. This will dramatically reduce the potential for operational problems.
Chem-Aqua is a global leader in custom-designed programs for cooling, boiler, and process water systems. Our success has been built upon our Total System Approach, providing solutions for water treatment problems and improving water system efficiencies. Learn more about how Chem-Aqua can help you manage and protect your water systems at www.chemaqua.com.
Written by: Matt Schnepf, PE, CWT