Plastics processors are looking to advanced process cooling equipment to lower operational costs, and in many cases, improve the quality of products and achieve sustainability goals. But it’s more than just a matter of finding a better mousetrap and putting systems to work. Instead, it requires a keen understanding of the processes involved, followed by the design and installation of advanced technology in combination with the right process cooling systems matched to a company’s goals.
Plastics Processing Methods
A number of plastic processing methods rely on engineered process-cooling systems to cool previously heated thermoplastic materials to form the shape for a part or product. The basic methods include:
- Injection molding: Heated material is injected into a mold with two halves and subsequently clamped shut. The part is ejected from the mold when the plastic inside the mold is properly cooled and solidified.
- Blow molding: Much like injection molding, blow molding involves the use of molds. Unlike injection molding, however, the basic process involves the use of compressed air to inflate a heated plastic tube so that it conforms to the interior design of the mold, which is then cooled to set the material to the shape of the mold. From there, the part is removed from the mold. Variations of blow molding are injection, injection stretch, and extrusion.
- Thermoforming: A flat sheet of material is heated to its softening temperature and then forced against the contours of a mold using air, vacuum pressure or mechanical means. The thermoformed part holds its shape after it is cooled. If the mold is aluminum, the mold is often cooled.
- Extrusion: Dry materials are fed into one end of a heating chamber and then forced out of an opening or die at the other end to create the shape of the product. Often, the hot extruded plastic is pulled through a water-fed vacuum tank and any number of water baths to remove heat and sufficiently cool and solidify the product.
When it comes to advanced process cooling, the key regardless of the plastic processing method involved is to first understand the numerous variables of any given operation and the strategies each processor uses to design and manufacture products. Typically, the approach involves a full survey and technical analysis of a facility to establish cooling load requirements; plant floor and outside equipment layouts; and cooling equipment parameters including flow, pressure and temperature requirements.
A Frigel closed-loop fluid cooler can be used with individual Microgel combination chiller/temperature control (TCU) machines to achieve accurate temperature control with minimal temperature variation at each machine/processes.
Clear Goals and Opportunities
The outcome of a thorough planning process is a list of clear objectives and the identification of opportunities for process cooling to help achieve them. While the strategy is developed around the uniqueness of each operation, many plastics processors share common goals. They include:
- Operational efficiencies: Process cooling plays a key role in the efficiencies of plastics processing, whether its decreased cycle times for processes that involve molds, or throughput when the method is extrusion.
- Product quality: Consistency in temperature, pressure and flow is essential to the manufacturing of quality products with the lowest possible cycle time, and with minimal scrap.
- Cost savings: A carefully planned approach to process cooling, combined with newer technology, can result in considerable water and energy savings. Saving water and energy also aligns with sustainability goals. In addition, cost savings can be realized with systems that require less maintenance.
- Simplification: Many processors add process-cooling equipment to the mix over time, which can lead to inefficiencies in training and time needed to service disparate equipment. Often, various machines on the plant floor can also consume limited floor space. Simplification of process cooling can result in a streamlined operation that contributes to the bottom line and more space for processing equipment.
- Environmental stewardship: In addition to controlling costs, progressive processors strive to be environmental stewards.
While there are many similarities in what processors hope to achieve, expert analyses and planning is crucial to the strategy used since each operation is unique.
Traditional Systems and Limitations
When assessing options, many processors have recognized limitations of traditional process cooling systems that often take the form of open-cooling towers and central chillers.
A common approach involves the use of open-cooling towers to feed water-cooled central chillers. Open-cooling towers, however, use an evaporative process to cool water making them notorious water wasters. An open-cooling tower also leaves water exposed to outside elements and surrounding communities are at risk for waterborne illnesses such as Legionella. All the while, the open system requires costly chemical treatment and disposal.
Some processors use air-cooled chillers instead of a cooling tower to avoid dirty water. An air-cooled chiller, however, uses ambient air to remove heat from the refrigerant circuit. That means the higher the ambient air temperature, the higher the compressor condensing temperature. As such, the chiller’s refrigeration compressor must work harder in turn consuming high amounts of electricity to provide chilled water.
Whether it’s an air- or water-cooled chiller, another consideration is that central chillers are designed to only provide water at one water temperature to all machines/processes. Yet the reality is that some equipment or processes might need water at a higher temperature than the chiller provides. A processor must then add a temperature control unit (TCU) to reheat the chilled water for given machines or processes, wasting energy. Some situations call for multiple TCU machines. There are also times when a processor must devote both a TCU and a machine-side chiller to any given machine to deliver the proper water temperatures since, for example, two halves of a mold may require significantly different temperatures, adding even more piping and machines to the mix.
The challenges and limitations of conventional methods used in plastics process cooling opened the door for alternate methods and more sophisticated technology.
One approach introduced by Frigel is known as Intelligent Process Cooling. It involves technically advanced systems configured to match customers’ unique processes and goals.
The Frigel Ecodry 3DK closed-loop fluid cooler, which is housed outside a facility, serves as the primary component of an integrated, closed-loop cooling system. It provides clean water at the right temperature to plastics processes year round.
Central Fluid Cooler Advantages
One newer technology is the company’s closed-loop Ecodry fluid cooler, which is located outside a facility’s plant. It uses heat exchangers and an internationally patented adiabatic chamber to cool water circulated to it from machines/processes within a plant. The adiabatic chamber pre-cools ambient air on hotter days before it enters the unit’s heat exchanger compartment. Cooled water is then re-circulated to machines/processes. A microprocessor-based controller automatically maintains precise cooling temperatures.
As a closed-loop system, it allows users to reduce water consumption by as much as 95 percent when compared with open cooling towers. Using the same clean water continuously also greatly minimizes maintenance issues and eliminates costs associated with water disposal and treatment.
The central fluid cooler also offers “free cooling” because it uses ambient air to cool process water. Free cooling means there is no need for chillers to meet cooling loads when ambient conditions permit. Instead, the system automatically shuts down the chillers to capitalize on free cooling.
The closed-loop system also ensures water cleanliness. Additionally, it avoids the risk of proliferation of harmful bacteria, such as Legionella, due to the absence of stagnant water. Compared with cooling towers, it also results in significantly reduced maintenance and minimization of water treatment chemicals.
Advanced Approach to Machine-side Cooling
Another newer technology is the Frigel Microgel, which combines a chiller and TCU in one machine. A combination chiller/TCU includes a refrigeration system and, depending on the machine, either one or two temperature control zones within the same cabinet. A traditional TCU is without a chiller.
In plastics processing, each combined chiller/TCU is dedicated to its own machine or process and operates independently from the others. A high-flow process pump within the combined chiller/TCU also feeds water to the dedicate machine/process, ensuring a consistent supply of pressure and high turbulent flow where needed. It also provides temperatures from 48°F to 195°F with accuracy of plus/minus 0.5°F.
A combined chiller/dual zone TCU, for example, lets molders independently control both mold halves with one machine to accommodate precise heating and cooling requirements. As such, it eliminates the need for three machines to perform the same task.
For extruders, older extrusion tanks are not equipped with a heat exchanger or recirculation pumps. However, an advanced chiller/TCU can provide the heat exchanger and necessary tank recirculation pump – in addition to the refrigeration system.
The end result is overall efficiencies and more control over process cooling temperatures, leading to repeatability, improved cycle times and reduced scrap in molding. Extruders are able to achieve stable heat profiles, resulting in increased throughput.
Advanced chiller/TCUs can also be paired with the central fluid cooler as part of an integrated closed-loop process cooling system.
Shown Frigel Microgel chiller/TCU combination machines, which supply water to dedicate machines/processes, ensuring a consistent supply of pressure and high turbulent flow where needed. The compact modules also provide temperatures from 48°F to 195°F with accuracy of plus/minus 0.5°F.
Plastics Processors Win
Plastics processors throughout the world have found success with the more advanced approach to process cooling – giving them an advantage in a highly competitive industry where every step in process efficiency adds value.
As an example, an injection molder focused on products for the medical industry replaced an open cooling tower with two closed-loop fluid cooler systems. Additionally, the company replaced separate TCUs with 15 combination chiller/dual zone TCU machines. The central fluid coolers supply water to the chiller/TCUs throughout operation. The system also allows the individual chiller/TCU modules to power down the compressors when the fluid coolers can provide sufficiently cool water, depending on outdoor ambient conditions.
The integrated system gives the molder the ability to control process-cooling temperatures within +/- 3 degrees F versus +/- 5 degrees F with the old system – and do it year-round for improved repeatability and increased throughput of high-quality parts cycle-to-cycle and cavity-to-cavity.
The processor has also eliminated the need for multiple portable chillers and TCUs for each press location. In addition, it now consistently supplies clean water to machines, while consistently saving approximately 95 percent in process cooling water compared to the open cooling tower. Additionally, it virtually eliminated maintenance issues associated with the cooling tower and it no longer discharges chemicals to the municipal wastewater system.
Another example involves a company that uses this technology in the extrusion of drinking straws. The company replaced two five-ton air-cooled chillers with two closed-loop fluid coolers and added combined chiller/TCU units at three tanks. The fluid coolers provide water to the company’s three extruders, as well as chiller/TCU units located at each line.
By installing the system, the company consistently achieves a stable heat profile. Doing so ensures dimensional stability on the extrusion lines, as well as the desired color and clarity of products. The company has also increased throughput by as much as 15 percent and saves tens of thousands per year in water and energy costs when compared to the alternative of a cooling tower/central chiller.
To read similar Chiller and Plastics Technology articles, please visit coolingbestpractices.com/technology/chillers or coolingbestpractices.com/industries/plastics-and-rubber.