Cut and Dry
Y ou could make the argument that dryers are the most confusing raw materials handling component. There are a vast number of drying technologies -- hot air, desiccant, desiccant wheel, infrared, et ce...
You could make the argument that dryers are the most confusing raw materials handling component. There are a vast number of drying technologies — hot air, desiccant, desiccant wheel, infrared, et cetera — and dryer solutions often have to be customized to fit a plant’s specific needs.
Canadian Plastics decided to examine some of the questions you should ask when thinking about purchasing a new dryer for your plant. These questions — ranging from central versus press-side systems to energy efficiency — can help you decide whether the dryer you pick is the best suited for your application.
According to equipment suppliers, the type of material the processor is running is one of the first questions they should ask. If you are running multiple materials, use your most challenging material as a point of reference.
“Different materials require different things from a dryer, particularly when it comes to temperature setpoints,” noted Conair. “PET, for instance, needs to be dried at 350F, while some PETG dries at 140F. If you are running PETG, you may need a precooler in the system.”
Brian Davis, general manager of Maguire Canada, also notes that you need to make sure your dryer has the right equipment if you are running high heat applications. Additionally, he notes that knowing the moisture content of your resin — both before and after drying — is a huge factor.
“When it comes in from a supplier, you are probably looking at 0.05 moisture content, and these resin dryers are usually outfitted to remove a half per cent of moisture,” he explained. “Knowing your initial moisture content is critical, as is storing unused resin correctly.”
Conair recommends that processors also take stock of whether their material gives off volatile compounds during drying, because they need to specify a volatile trap to prevent desiccant contamination. And if the material being used is sensitive to overdrying, Conair suggests a temperature setback feature to keep the process stable.
In addition, Conair notes that regrind, particularly film fluff or bottle flake, has a much lower bulk density than virgin resin.
“With low bulk density regrind in the hopper, material may not have sufficient residence time in the hopper for proper drying,” the company said. “If regrind has a high level of dust and fines, you might want to consider a secondary dust collection system.”
THE CENTRAL QUESTION
Once you narrow down your choices based on material usage, the next big question is whether to opt for a central or beside-the-press system.
“You always have to ask the question whether you want to have a central drying system versus a press-side drying system,” noted Joe Corturillo, engineering manager for Wittmann Canada. “It depends on how much the throughput of the machine will be, and what material changeovers, mold changes and recipes you use. Central systems are usually for larger throughputs where several machines are running the same resin. It allows you to cut down costs and not have as many dryers on your actual plant floor.”
Molders who are working with very expensive resins with highly critical cleanliness can benefit from a centrally installed system as well. “A central drying system is very useful for them because it helps them manage and control where the resins are,” noted Bob Crawford of Universal Dynamics.
“They are kept contaminant free, which really becomes a value point for a central drying system,” he continued.
Suppliers note that processors working with more than one material can still take advantage of a central drying system by employing hoppers. “If you do multiple material changeovers, having one dryer with multiple hoppers does lend itself to quick machine startup,” explained Wittmann’s Corturillo. The company supplies a range of hopper sizes for different throughputs, noting that the resin can be predried and readied for processing.
Smaller beside-the-press units are often best suited for short runs with reuse of regrind. “These dryers are normally supplied with a closed-loop conveying package to move the dried material to the press,” added Dri-Air Industries, Inc. president Charlie Sears. “This eliminates the contamination of the dried material with wet ambient air.
Corturillo of Wittmann also notes that beside-the-press units are particularly suited when working with a self-contained work cell, because the closed loop nature allows for greater control over the variables. “If it’s a cell, there is no outside interference of ambient conditions and you can do a lot more fine tuning,” he said.
Dri-Air recommends a hopper bank when trying to serve a group of small molding machines.
“A typical hopper bank includes hoppers sized for a standard run with the ability of pre-drying material for the next job, reducing the idle time for the press,” said Sears. “A properly designed system allows the control of the drying temperature for each hopper and valves to shut the hopper off for cleaning.”
QUESTIONS OF EFFICIENCY
By now, most processors don’t need to be prompted to ask questions about a unit’s energy efficiency. With the recent climb of energy costs, an efficient new dryer can go a long way in reducing your footprint.
Unfortunately, nearly every supplier in the industry now claims to have the most energy efficient units on the market. For this reason, it is recommended that you put the dryers to the test before making a choice.
“Almost every dryer manufacturer claims their dryer is the most energy efficient,” said Sears. “While this cannot be true, an in-house trial is suggested where several dryers are concerned.”
The energy efficiency of your new dryer may depend on the type of base technology you opt for. For instance, Sears notes that it is generally accepted that compressed air dryers are less energy efficient due to the cost of compressed air and the potential cost of adding air compressors to several dryers.
“These dryers are ideal for occasional use or where few molding machines are used,” he said.
Thoreson-McCosh’s dryers, meanwhile, feature an indexing triple desiccant bed design. According to the company, this particular design allows for greater absorbing capacity and more efficient drying.
“This design also allows the dryer to use the residual regeneration heat that is recovered from cool down to preheat the process air flow, making the unit extremely energy efficient,” noted Brad Lemieux, sales manager for Canadian representative En-Plas Inc. “With this system, heat that would normally be wasted is now reclaimed and used in the drying process.”
Novatec, Inc. recently argued that its NovaWheel desiccant wheel dryer uses significantly less energy than a conventional dual-bed dryer. According to tests undertaken by the company, the energy cost per hour for the Nova- Wheel dryer was 35 per cent less for ABS and 14 per cent less for polycarbonate when compared to a Novatec dual-bed dryer.
“The energy efficiency of the wheel dryer is the result of having three times the amount of pure desiccant per minute than in a twin-tower dryer,” said Novatec sales manager Mark Haynie. “On average we estimate that a new NovaWheel unit will use 25 per cent less power than a conventional system.”
Suppliers of desiccant bed drying systems believe their units give their users a much bigger bang for their buck. Motan Inc. recently went on the offensive, addressing claims of energy efficiency made by a competitor.
Motan argued that their desiccant dryers dry material with an average of 38 per cent lower energy consumption than their competitor’s wheel dryer. The company also said that their bed units have lower energy consumption because of longer regeneration cycle times and the relatively low weight of the insulated desiccant canisters.
Additionally, processors should be on the look out for “smart” technologies that improve the unit’s efficiency. Wittmann boasts abo
ut the SmartFlow valves on its drying hoppers, which control the air flow level in each hopper automatically.
“If the throughputs of this hopper were to start to go down because you are shutting the machine off, we would start closing off that air flow and putting it into hoppers that are using that air flow,” said Corturillo.
Controlling the air flow based on temperature in this way also prevents overdrying, and may allow processors to use more hoppers than the theoretical drying capacity would suggest.
At your SERVICE
Maguire’s Davis recommends that you also ask questions about the supplier’s service and training capabilities.
“They tend to promise the world, but what support do they have both in installation and training of the operational and maintenance staff,” he asked. “Also, what types of spare parts are carried, and where are they dispatched from?”
Conair (Pittsburgh, Pa.); www.conairnet.com; 800-654-6661
Hamilton Avtec Inc. (Mississauga, Ont.); www.hamiltonavtec.com; 905-568-1133
Dri-Air Industries, Inc. (Windsor, Conn.); www.dri-air.com; 860-627-5110
Plastics Machinery Inc. (Newmarket, Ont.); www.pmiplastics.com; 905-895-5054
Maguire Canada Inc./Novatec (Vaughan, Ont.); www.maguirecanada.com; 866-441-8409
Motan Inc. (Plainwell, Mich.); www.motan.com; 269-685-1050
Dier International Plastics Inc. (Unionville, Ont.); www.dierinternational.com; 905-474-9874
D Cube (Montreal Que.); 514-272-0500; www.dcube.ca
Thoreson-McCosh Inc. (Troy, Mich.); www.thoresonmccosh.com; 248-362-0960
En-Plas Inc. (Toronto); 416-286-3030; www.en-plasinc.com
Universal Dynamics, Inc. (Woodbridge, Va.); www.unadyn.com; 703-490-7 000
Patton Plastics Inc. (Mississauga, Ont.); 905-568-1133; www.pattonplastics.com
Resource Polytec Inc. (Vancouver, B. C.); www.resourcepolytec.com; 604-454-1295
Wittmann Canada Inc. (Richmond Hill, Ont.); www.wittmann-canada.com; 888-466-8266