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Quotes - Engineering - SalesCompressed Air Dryers for Injection Molding
An injection molding machine uses compressed air at the mold and around it: core-pull and ejector-assist valves, air poppets under deep parts, valve-gate actuators on hot-runner manifolds, sprue pickers and robots with venturi vacuum cups, hopper loaders, and blow-off nozzles at the parting line. None of them consumes much on its own; a floor of 20 presses on a 100 hp rotary screw draws 400 to 450 SCFM with everything running.
Water in that air lands on the tooling. A mold running on 45 to 55°F chilled water is the coldest surface in the building, so wet air blown across it condenses on the cavity, leaves water marks and splay on the next shot, and rusts core pins, ejector plates and vent lands. Valve-gate actuators bolted to a 450°F manifold flash any water in their supply to steam, and venturi vacuum generators lose pull as their nozzles scale.
A refrigerated dryer at the compressor room holding a 38°F pressure dew point stops all of this, because 38°F is below the chilled-water temperature of every mold in the plant. It is sized to the compressor, not the presses: a 75 hp screw delivering 330 SCFM into a 100°F room takes a 400 SCFM dryer, a 150 hp screw at 650 SCFM the 800 or 850 size. Only molds run below 40°F, and clean-room cells with a class 2 specification, call for desiccant drying.
Molding plants run three shifts with the compressor loaded most of the time, so the non-cycling DXR Series is the usual choice. A plant that idles presses between jobs, or holds pressure overnight on one shift, gets its cycling premium back with the TMC Series or FLXA Series. Either way a 1 micron prefilter and a 0.01 micron oil-removal afterfilter bracket the dryer and keep compressor oil off clear lenses and medical parts.
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Chilled-water range on most production moldsMold water at 45 to 55°F sits above the 38°F a refrigerated dryer delivers, so blow-off air crossing the cavity has nothing left to condense on it.
What wet air does on a molding floor
The defects and failures that trace back to the air line
- Water marks, splay and haze where condensate on the cavity meets the melt
- Rusted core pins, ejector plates and vent lands on molds that run cold
- Valve-gate and core-pull cylinders sticking as water washes out their lubricant
- Robot vacuum cups dropping parts as venturi nozzles scale and corrode
The dryer specification for a molding plant
What to ask for and what to leave out
- 38°F pressure dew point, ISO 8573-1 class 4, sized to the compressor's delivery at the compressor room temperature
- 1 micron prefilter ahead of the dryer, 0.01 micron oil-removal afterfilter behind it; a carbon filter for medical and food-contact parts
- Non-cycling for three-shift plants, cycling where presses idle for hours at a time
- Zero-loss drains on the receiver, separator, dryer and filter bowls
Dryers that fit a molding plant
Flow ratings at 100 psig and 100°F inlet. A 25 to 50 hp screw lands in the 65 to 250 SCFM band; a 75 to 150 hp plant uses the 300 to 850 SCFM sizes.
| SERIES | TYPE | FLOW RANGE | MAX INLET | MAX PRESSURE |
| DXR Series | Non-Cycling | 10 to 4,200 SCFM | 131°F | 203 psig |
| FLXA Series | Cycling | 75 to 2,000 SCFM | 120°F | — |
| TMC Series | Thermal Mass Cycling | 30 to 635 SCFM | 140°F | 210 psig |
| NXC Series | Cycling | 20 to 2,000 SCFM | 158°F | 232 psig |
| AES Series | Digital Scroll Cycling | 600 to 10,000 SCFM | 120°F | 232 psig |
| GFN Series Filters | Compressed Air Filter | 6 to 1,500 SCFM | — | 232 psig |
| NGF Series Filters | Compressed Air Filter | 20 to 1,500 SCFM | — | 250 psig |
| ND Series Zero-Loss Drains | Condensate Drain | Call for sizing | — | 290 psig |
A molding plant's air is ready when these are in place.
- Receiver ahead of the dryer at a gallon per SCFM of delivery
- Dryer sized from the compressor nameplate, corrected for the room
- Carbon stage after the afterfilter for medical and optical parts
The receiver does half the dryer's work
A refrigerated dryer is rated for a steady flow at 100°F. Hopper loaders, air poppets and blow-off nozzles do not draw steadily; they pull in bursts that can run 50 percent above the compressor's delivery for a few seconds at a time. A receiver of at least a gallon per SCFM ahead of the dryer flattens those bursts and drops out most of the aftercooler condensate, so the dryer's separator sees droplets rather than a slug. Where loaders and robots were added without receiver volume, the dew point climbs during every loader cycle, and adding receiver capacity is cheaper than adding dryer capacity.
- Size the receiver at a gallon per SCFM of compressor delivery, ahead of the dryer
- Fit a zero-loss drain on the receiver so it does not fill with water between drain cycles
- Add receiver volume before adding dryer capacity when the load has become burstier
Where the dryer and filters go
The order is compressor, aftercooler, receiver, prefilter, dryer and afterfilter, with the loop header around the press floor after that. The receiver ahead of the dryer matters more in a molding plant than most, because hopper loaders and air poppets pull air in short bursts that would otherwise pass through the dryer as flow spikes above its rating. A plant that grew press by press often has two compressors in different rooms; give each its own dryer rather than one large dryer on a header fed at two temperatures.
Sizing from the compressor
Read the compressor's delivery from its nameplate rather than the horsepower rule, then correct for the room. A 75 hp screw at 330 SCFM in a 110°F mezzanine compressor room needs 330 divided by 0.88, or 375 SCFM of dryer, so the 400 SCFM model. Sizing from the sum of press nameplates undercounts loaders, robots and leaks; the flow and SCFM page walks through the arithmetic.
Hot runners, loaders and clean rooms
Valve-gate actuators sit on a manifold at melt temperature, so the air reaching them must be dry enough that nothing flashes to steam inside the cylinder, and a 38°F dew point does that. Hopper loaders and venturi generators are the largest air users on the floor and the most sensitive to scale, so keep the 0.01 micron afterfilter close behind the dryer where the air is coldest. A clean-room medical cell that must meet a class 2 dew point gets a point-of-use desiccant unit and its own filter train off the plant header, with the refrigerated dryer still doing the bulk of the work upstream.
Cycling or non-cycling
A three-shift plant with the compressor loaded 70 percent of the hours has little to gain from a cycling dryer; the non-cycling unit is cheaper and simpler. A plant that shuts half its presses on weekends, or a custom molder whose load swings with the job mix, sees the refrigeration compressor of a cycling dryer resting most of that time, and the power saved pays the diffrence in a year or two. The cycling versus non-cycling page has the comparison.
Molding floor air, from compressor to cavity
Better to give each compressor its own dryer. Two rooms usually run at two temperatures, so the air reaching a shared dryer arrives at different inlet conditions and the warmer stream sets the capacity you actually get. A dryer at each compressor is sized to that room's heat and that machine's delivery, and one can be serviced while the other keeps half the presses running. Join the two streams downstream, where both are already dry.
The line falls at about 40°F. A refrigerated dryer holds a 38°F pressure dew point, so molds on 45 to 55°F water stay above it with margin and nothing condenses on the cavity. Run the chiller below 40°F to shorten cycle times and blow-off air across that cavity can deposit water, at which point a point-of-use desiccant unit on the cold-mold cells is the answer, with the plant dryer still carrying everything else.
The loaders pull air in bursts that drive flow through the dryer above its rating for a few seconds, and at that velocity the separator lets water through. Plants that added loaders and robots press by press often never added receiver volume to match. A receiver of at least a gallon per SCFM of compressor delivery, placed ahead of the dryer, flattens those bursts, and it costs far less than a bigger dryer bought to cover a peak that lasts seconds.
For the press pneumatics, no: the 1 micron prefilter, the 0.01 micron afterfilter and an activated carbon stage after it cover oil for medical and optical parts. What changes the answer is a clean-room cell whose specification names a class 2 dew point. That cell takes a point-of-use desiccant unit with its own filter train off the plant header, fed with air the refrigerated dryer has already taken down to 38°F, so its regeneration stays modest.
It can, and quickly. The actuators bolt to a manifold near 450°F, so condensate in their supply flashes to steam inside the cylinder, pushes past the seals and leaves scale on the piston rod, and the gate opens late or not at all. A short shot or heavy gate vestige on one cavity is the usual sign. A 38°F dryer at the compressor removes the water; taking each actuator drop off the top of the header keeps slugs left in the pipe away from it.
Mezzanines trap heat, and a refrigerated dryer is rated at 100°F ambient. At 110°F it delivers about 88 percent of its rating, so divide the compressor's nameplate SCFM by 0.88 to find the dryer capacity required. For a 75 hp screw at 330 SCFM that works out near 375 SCFM, which means the next model up. Ventilating the mezzanine can save that step, but only if the room has been measured on a summer afternoon.
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