Solutions
Success Story: What makes a good bottle?
The plastics molding industry has long been challenged by a single factor that greatly affects quality in a bottle blow molding operation - the presence of condensation during molding. While other factors such as contamination or water in the material can affect quality, condensation caused by high humidity is the number one concern among bottle blow molders. The solution - humidity control.
During the injection molding process, condensation limits the efficiency of the production cycle through increased cycle times, decreases production rates and increases 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 (See Exhibit A). Without a quality preform, you cannot produce a quality bottle.
Constar, a wholly owned subsidiary of Crown Cork & Seal, based out of Philadelphia, PA, is one of the largest blow molders in the United States. Their West Chicago, IL plant recognized the need for humidity control and today, is experiencing how desiccant dehumidification can eliminate production problems caused by condensation.
This plant manufactures a wide variety of plastic bottles for applications ranging from oils and soft drinks to liquor and water containers. Their preform injection molding machines service their blow molding operation using PET, with sizes of the finished bottles ranging from sixteen ounces to sixty-four ounces.
At Constar, high humidity levels during the summer months caused condensation or "mold sweat". Condensation or mold sweat occurred when the dew point of the air surrounding the molds was higher than the temperature of the mold cooling water. This mandated the need to increase the water temperature on the molds and thus, production rates declined.
According to Kerry Schott, Constar's West Chicago Plant Manager, "Once we had temperature problems during the spring and summer months, we had problems all over. Anytime the outside temperature was above 60F, we started to see condensation. You have to control the humidity - this eliminates a lot of problems."
Constar wanted to be able to run their molding equipment at the same consistent high production rates all year long, regardless of the season. They realized that the best way to stop condensation on the cold mold surfaces was to reduce the dew point of the air surrounding the molds. The installation of a desiccant dehumidification system was the solution they were looking for.
Constar chose Kathabar Inc., Somerset, NJ as the key element in this solution. Kathabar, with over 65 years of desiccant dehumidification equipment manufacturing experience, provided Constar with a Kathapac 2500FV conditioner and 6FP regenerator. Kathabar's liquid desiccant system met the need for a system that was easy to maintain and didn't require complicated and costly wheel replacement. The simplicity of design required no aftercool coils and no need for face or bypass dampers. The separate units for process dehumidifying and regeneration ensured performance reliability with no cross leakage between the wet and dry air stream. This Kathabar system required less energy as compared to other forms of dehumidification, while providing low humidity air to their molding operation. An economic value analysis of this operation yielded very favorable energy savings for Constar - over 50% annual savings in total energy over other forms of dehumidification!
Kathabar's system reduced the delivered air to 20% RH, which is a 15F dew point, to maintain the conditioned space at 35F dewpoint. This allowed for the use of 44F chilled water for mold cooling rather than the typical 55F. As a result, parts formed more quickly, hence, a faster cycle time.
The Kathabar system can deliver either individual mold dehumidification by supplying cool, dry air directly over the surface of the mold as it opens, or it can maintain humidity control not just to the mold area but to the entire injection and blow molding processing area. Constar utilizes full room conditioning (See Exhibit B). Room conditioning allows for non-symmetrical, variable size parts and machines to fully benefit from the humidity control. This type of conditioning is typically used in many manufacturing operations where a mixture or multiple injection and/or blow molding operation exists. Room control eliminates individual connecting ducts, hoods and/or cumbersome enclosures around each machine.
With the Kathabar unit, humidity problems at Constar are non-existent. The elimination of condensation can achieve zero defects caused by mold sweat. As far as scrap and waste, Constar is meeting or exceeding their monthly corporate standard.
Maintaining consistent high production efficiencies, Constar is one of the many blow molders realizing the benefits that Kathabar desiccant dehumidification systems can offer to increase production. They also realize other benefits:
- Improved part quality; Elimination of streaks and imperfections.
- Decreased cycle times; Increased profits.
- Lower reject rates; Translated into cost savings through reduced scrap or recycling.
- Increased life of molding equipment; Rust on guide pins and other areas is eliminated. Maintenance costs and retooling costs are reduced.
- Most importantly, molding equipment can run consistently all year long at winter production rates with a Kathabar System.
Constar's liquid desiccant dehumidification system enables efficient and reliable production of a wide variety of plastic bottles for a range of applications. With great reliability, the Kathabar dehumidification system provides the low humidity conditions needed to produce their products and to help Constar maintain their leadership position in the plastic blow molding market.
