If you are considering Fusion Granular Fabrication (FGF) or pellet-based printing due to its lower cost and the wider range of materials versus filament printers, there are components that you need to consider to put the system together. These include drying the pellets and conveying the dried pellets to the Extruder.
Drying the resins properly is critical – as most of the resins that you will be printing are engineering grade resins such as Nylons, ABS, PEEKS, Urethane. These resins are hygroscopic and absorb moisture inside the pellet. A properly designed drying system will remove the trapped moisture providing you with a high quality, consistent print with strong mechanical properties.
Moisture that is not removed from the pellets will be visible in your print bead shown by bubbles, blisters, streaks, and inconsistent beads. This is due to the trapped moisture in the pellet turning to vapor (1600 times its size) as the plastic melts. Removing this trapped moisture is key for a high-quality structurally sound print.
There are several types of dryers available: Hot Air, Compressed Air and Desiccant.
Hot Air: these are the least expensive dryers to purchase as basically they are just a heater, blower, and hopper to contain the resin. While these are lower in cost than other types of dryers they have significant drawbacks – for one as they are not removing any moisture in the air used in the drying process, as they just heating the resin, removing surface moisture, but not the moisture trapped inside the pellet. Also, as they are a single pass system where the heated air is directly vented into your plant, they discharge lots of hot air, dust, and fibers into your work environment.
Compressed Air: Compressed air dryers use your shop air to dry the resin. There are two types, membrane and non-membrane – membrane use a membrane to remove the moisture in your shop air, non-membrane dryers just release the compressed air to atmosphere – which drops the dewpoint but is dependent upon the quality of your shop air. As the dewpoint of these dryers are usually in the + 10 category we do not recommend non-membrane type dryers. Advantages to membrane type compressed air dryers include no cooling water required for both low temperature (under 120F) and high temperature (350F) applications, and can be very small in size with little maintenance. Disadvantages include the need for compressed air and operational costs. While smaller dryers (under 10 pounds per hour only use 2.5 CFM, larger sizes use significant amounts of compressed air – (50 pound per hour dryer, 12 CFM). You should also consider the availability and the quality of your compressed air, is it available when you need it to pre dry material? If you feel compressed air technology is right for your application, please click here for small on- the-Extruder dryer or small portable off- the-Extruder dryer click here
Desiccant: These have multiple beds or a wheel that sends dry air to the hopper while the other bed or wheel section is regenerated. The regeneration process is the process that bakes the moisture out of the desiccant after it is used to dry the process air to dry the material. Desiccant dryers are efficient and better suited for most FGF pellet-based applications due to their lower operational costs, flexibility and in most cases do not require any compressed air. Desiccant dryers can be categorized into two types: wheel and stationary.
Dri-Air uses a stationary design as its 50% more efficient than wheel dryers, provide lower dewpoint air and discharges 85% less regeneration air into your work environment. We achieve these benefits as we use a single blower for drying and regeneration, wheel dryers have two blowers one for regeneration and one for process. Lower dewpoints are achieved as we use dry air for regeneration while wheel dryers use ambient air. Regenerating with dry air provides lower overall dewpoint as the dewpoint of the air determines the dryness of the air after regeneration. Low dewpoints are ideal for the most challenging resins and humid plant environments. Another benefit to our stationary design is that in most applications, cooling water is not required.
To see our portable dryers click here (HPD- Link)
Material conveyance: Now that you spent time and money in drying the resin, you next need to convey the dried resin to the Extruder – this is a very important aspect of the process, after all there is no point in drying the resin then conveying the resin with air that can contaminate the resin with moisture!
There are several methods for conveying the resin, compressed air and closed loop dry-air conveying systems.
Compressed air systems use an air accelerator to amplify your shop air and blow the resin to the extruder. Advantages include low purchase cost, a single material hose, small compact receivers on the Extruder and are ideal for low throughput applications (under 10 pounds per hour). Disadvantages are that it uses compressed air and is dependent upon the quality of your compressed air which can contaminate the dried material. They are also limited in the distance they can convey the material (around 20’). Another disadvantage is with carbon or glass filled resins that can clog the filters which then severely reduces the conveyance performance.
You can see our CAL compressed air loaders here
Dry air or closed loop systems are a sealed system that conveys the resin with dry air to prevent your dried material from reabsorbing moisture. While these are more expensive then compressed air systems the advantages of conveying with dry air translate to better print quality. They can also handle filled resins as they have better filters, and convey higher throughputs up to 1000 pounds per hour and convey much longer distances 150’ when properly designed. You will also want to make sure the system includes a line purge or clean out cycle – this purges the line clear so there are no left-over materials in the conveyance line.
We incorporate our closed loop systems into the base of our portable dryers making it a all in one, compact package – you can see our portable dryers here
Need assistance in designing your pellet delivery and drying system? Please reach out to us at 860-627-5110 and ask for Herb Wischow or Jason Sears or email us at Sales@dri-air.com