Condensation has long challenged the manufacturing of quality blow-molded products. While other factors such as contamination or water in the material also affect quality, condensation from high humidity is the primary concern among blow-molders. The solution is humidity control.
During the injection-molding process, condensation limits the efficiency of production due to increased cycle times and the amount of scrap and rework for each machine. When condensation forms on the core rod, water spots can appear, causing defects in the preform. Without a quality preform, manufacturers cannot produce a quality product.
A large U.S. blow-molding company successfully faced down condensation at one of its plants that makes plastic bottles for applications ranging from oils and soft drink containers to liquor and water. The preform injection-molding machines service a blow-molding operation using PET (polyethylene terephthalate), with finished bottle sizes from 16 to 64 oz.
High humidity levels in the summer caused condensation. “Mold sweat” occurs when the dewpoint of the air surrounding a mold is higher than the temperature of the mold’s cooling water. The situation was mitigated with an increase in mold water temperature, which resulted in a decline of production rates. Also, any time the dewpoint of the outside temperature passed 60°F (16°C), condensation appeared.
Based in Somerset, N.J., and owned by Niagara Blower in Buffalo, N.Y., 65-year-old Kathabar Dehumidification Systems provided its customer with a Kathapac 2500 FV conditioner and 6 FP regenerator. Kathabar’s liquid desiccant system eases maintenance and does not require wheel replacement, which a dry desiccant system can. The design’s simplicity means aftercool coils or face or bypass dampers are not required. The separate units for process dehumidifying and regeneration ensure performance and reliability, according to the manufacturer. The system provides low humidity air to the molding operation, saving up to 50 percent in energy costs when compared to alternate technologies, says Kathabar.
Kathabar’s system reduced the delivered air to 20 percent relative humidity, resulting in a 15°F (-9°C) dewpoint, to maintain the conditioned space at a 35°F (2°C) dewpoint. This allowed for the use of 44°F (7°C) chilled water for mold cooling rather than the typical 55°F (13°C). As a result, parts formed faster for an improved cycle time with more consistent quality.
The Kathabar system can deliver individual mold dehumidification by supplying cool, dry air directly over the surface of the mold as it opens, or it can maintain humidity not just to the mold area but to the entire injection- and blow-molding processing areas. The plastics manufacturer uses full room conditioning (figure 1), which means non-symmetrical variable-size parts and machines fully benefit from humidity control. This type of conditioning typically is used in manufacturing operations in which a mix of multiple injection- and blow-molding operations exist. Room control eliminates individual connecting ducts, hoods and enclosures around each machine.
By implementing the Kathabar system, the customer’s humidity problems were eliminates. Preventing condensation resulted in zero defects from mold sweat. Regarding scrap and waste, the company is meeting or exceeding its monthly corporate standard.
With its new system, the blow-molder is now maintaining consistent high production efficiencies. Other benefits from a Kathabar desiccant dehumidification system are:
- Improved part quality such as elimination of streaks and imperfections.
- Decreased cycle times, which increase profits.
- Lower reject rates, which translate into cost savings from less scrap or recycling.
- Increased life of molding equipment. Rust on guide pins and other areas is eliminated. Maintenance and retooling costs are reduced.
- Molding equipment can run year-round at high production rates typically only seen in the winter.