The STG-U Series Hopper Drier is a high-efficiency hot-air drying system purpose-built for drying hygroscopic plastic resin pellets immediately before processing in injection molding, extrusion, and blow molding operations. By combining a temperature-controlled heating chamber with a continuously circulating blower fan, the STG-U series removes surface and internal moisture from raw plastic granules, ensuring optimal melt quality and defect-free finished parts.
A defining advantage of the STG-U series is its direct machine-mount design — the unit can be installed directly above the feed throat of the processing machine, creating a sealed material path from the drying hopper to the barrel inlet. This eliminates the open-air transfer step that causes dried pellets to re-absorb ambient moisture in conventional centralized drying setups, preserving the full drying effect right up to the point of plasticization. The design also saves valuable floor space and reduces material handling labor.
With 14 standard models spanning 8 liters to 1,250 liters of hopper volume — corresponding to loading capacities from 5 kg to 800 kg — the STG-U series covers the full range of production scales, from benchtop laboratory extruders to high-tonnage automotive injection molding cells. Heater power ranges from 1.2 kW to 36 kW, delivering the thermal capacity required for engineering resins with elevated drying temperature demands.
The STG-U series is compatible with a wide variety of thermoplastic resins including ABS, PA (Nylon 6/66), PC, PET, PBT, PMMA, POM, PP, PE, PS, and filled/glass-fiber-reinforced grades. For each material, the combination of adjustable thermostat control (digital PID controller available on request) and uniform hot-air distribution through the perforated cone ensures that every pellet in the hopper reaches the target dew point within the specified residence time.
| Model | Volume (L) | Capacity (kg) | Heater Power (kW) | Motor Power (kW) |
|---|---|---|---|---|
| STG-U8 | 8 | 5 | 1.2 | 0.04 |
| STG-U16 | 16 | 10 | 1.4 | 0.06 |
| STG-U20 | 20 | 12 | 1.6 | 0.06 |
| STG-U25 | 25 | 15 | 1.8 | 0.06 |
| STG-U40 | 40 | 25 | 2.6 | 0.06 |
| STG-U80 | 80 | 50 | 3.9 | 0.12 |
| STG-U125 | 125 | 75 | 4.8 | 0.12 |
| STG-U160 | 160 | 100 | 5.4 | 0.25 |
| STG-U250 | 250 | 150 | 9 | 0.37 |
| STG-U315 | 315 | 200 | 12 | 0.37 |
| STG-U400 | 400 | 250 | 15 | 0.55 |
| STG-U500 | 500 | 300 | 18 | 0.55 |
| STG-U800 | 800 | 500 | 24 | 0.75 |
| STG-U1250 | 1250 | 800 | 36 | 1.1 |
Note on Capacity: Loading capacities are based on bulk density of approximately 0.64 kg/L (typical for general-purpose polystyrene). Actual capacity varies by resin type — lower-density materials such as PP (0.90 g/cm³) and PE (0.92–0.96 g/cm³) will yield lower fill weights, while higher-density materials such as PC (1.20 g/cm³) and filled grades will achieve proportionally higher loading. Contact Chenxing Machinery for material-specific drying time and capacity recommendations.
The STG-U series is engineered for low energy consumption without compromising drying performance. Through a combination of high-density insulation wrapping the hopper body, optimized heater element geometry that maximizes radiant heat transfer to the pellet bed, and a duty-cycle-modulated blower that reduces unnecessary air circulation during soak periods, the STG-U series achieves 27–65% energy savings compared to conventional hopper dryers of equivalent capacity. The insulated hopper shell maintains surface temperatures below 50°C during normal operation, minimizing heat loss to the factory environment and reducing HVAC cooling load in climate-controlled production halls. For high-volume manufacturers running multi-shift operations, the cumulative energy cost reduction typically recovers the equipment investment within 12–18 months of continuous operation.
A critical failure mode in centralized drying systems is the re-absorption of ambient moisture by hot, dried pellets during transfer from the drying station to the processing machine. The STG-U series addresses this by mounting directly onto the feed throat of the injection molding machine, extruder, or blow molder. The dried material exits the hopper through a sealed discharge port directly into the barrel, with zero exposure to ambient air. This closed-loop material path is particularly valuable for highly hygroscopic resins such as PA6 (which can absorb up to 2% moisture within 30 minutes of exposure at 50% relative humidity) and PET (where moisture levels exceeding 0.005% cause hydrolytic degradation and loss of intrinsic viscosity). The direct-mount configuration also eliminates the need for vacuum conveying systems between dryer and machine, reducing both capital expenditure and energy consumption for material transport.
The STG-U series combines a high-capacity heating element with a well-matched blower system to deliver consistent hot air at the required temperature and volume. The perforated hot-air distribution cone at the base of the hopper disperses heated air evenly through the entire cross-section of the pellet column, eliminating cold spots and ensuring that pellets at the hopper periphery receive the same thermal treatment as those at the center. This thermal uniformity enables shorter drying residence times and supports higher material throughput rates. In injection molding applications, properly dried resin exhibits lower melt viscosity, which directly translates to faster cavity filling — increasing injection speed and reducing cycle time. For thin-wall packaging and high-cavitation molds where filling speed is a primary productivity driver, the STG-U series contributes measurably to increased output per machine-hour.
Moisture in plastic resin feedstock is one of the most common yet underdiagnosed causes of molding defects. When residual moisture vaporizes inside the barrel at processing temperatures, it creates gas bubbles that manifest as splay marks, silver streaks, and internal voids in finished parts — defects that are often misattributed to mold design or process parameters. The STG-U series eliminates this variable: by delivering consistently dried resin with moisture content below each material's specified threshold, it directly suppresses moisture-related visual defects and improves surface finish quality. Beyond cosmetics, thorough drying prevents hydrolytic degradation in condensation polymers (PET, PA, PC, PBT), preserving molecular weight and mechanical properties such as tensile strength, impact resistance, and long-term creep performance. For manufacturers supplying regulated industries — automotive, medical, electrical — the STG-U series provides a traceable drying process that supports consistent part-to-part quality and compliance documentation.
| Component | Specification | Details |
|---|---|---|
| Hopper Body | High-grade stainless steel (304) with thick insulation jacket | Double-walled construction with high-density thermal insulation layer; polished interior surface prevents pellet bridging and facilitates material flow; observation window for level monitoring |
| Heating Element | Tubular electric resistance heater | High-watt-density design for rapid temperature ramp-up; positioned for maximum radiant and convective heat transfer to the pellet bed; replaceable cartridge design for easy maintenance |
| Blower / Fan Motor | Continuous-duty induction motor with centrifugal fan | Dynamically balanced impeller for low-vibration operation; matched to hopper volume for optimal air velocity through the pellet column; low-noise design suitable for production-floor installation |
| Perforated Distribution Cone | Stainless steel cone with precision-drilled holes | Ensures uniform hot-air distribution across the entire hopper cross-section; prevents channeling and localized overheating; easily removable for cleaning during material changeovers |
| Temperature Controller | Digital PID thermostat (optional upgrade from standard mechanical thermostat) | Maintains set temperature with ±2°C accuracy; LED display for set and actual temperature readout; optional alarm output for over/under-temperature conditions |
| Material Discharge Valve | Manual slide gate or pneumatic butterfly valve | Positive shut-off for material flow control; seals the drying atmosphere when closed; pneumatic option available for automated production lines |
| Loading Port & Filter | Top-mounted loading port with dust filter screen | Captures fines and dust generated during material conveying; protects blower motor from particulate ingress; removable filter for periodic cleaning |
| Mounting Flange | Universal bolt pattern flange at hopper base | Compatible with standard injection molding machine and extruder feed throat dimensions; adapter plates available for non-standard machine interfaces |
| Over-Temperature Protection | Thermal fuse and manual reset thermostat | Independent safety circuit disconnects heater power if hopper temperature exceeds safe operating limit; manual reset requires operator acknowledgment before restart |
| Level Sensor (Optional) | Capacitive or rotary paddle level switch | Signals low material condition to upstream loader; prevents empty-hopper dry-running that can overheat the distribution cone and cause pellet melt adhesion |
The STG-U Series Hopper Drier is compatible with a comprehensive range of thermoplastic resins commonly used in injection molding, extrusion, and blow molding processes:
| Material | Drying Temperature Range (°C) | Typical Drying Time (h) | Notes |
|---|---|---|---|
| ABS | 70–90 | 2–4 | Moderate hygroscopicity; surface moisture removal sufficient for most grades |
| PA6 / PA66 (Nylon) | 75–90 | 4–8 | Highly hygroscopic; must be dried to < 0.05% moisture before processing |
| PC (Polycarbonate) | 100–120 | 3–5 | Sensitive to moisture; drying below 0.02% required for optical-grade applications |
| PET (Polyethylene Terephthalate) | 140–170 | 4–6 | Requires thorough drying to < 0.005% to prevent hydrolytic IV loss |
| PBT (Polybutylene Terephthalate) | 110–140 | 3–5 | Similar drying profile to PET; hot-air drying suitable for non-reinforced grades |
| PMMA (Acrylic) | 70–90 | 2–4 | Surface moisture removal; extended drying may cause yellowing |
| POM (Polyoxymethylene / Acetal) | 80–100 | 3–5 | Moisture causes hydrolysis and formaldehyde release at processing temperature |
| PP (Polypropylene) | 70–90 | 1–2 | Low hygroscopicity; drying recommended for foamed or thin-wall applications |
| PE (Polyethylene) | 70–80 | 1–2 | Minimal moisture absorption; drying improves surface finish in film and sheet extrusion |
| PS (Polystyrene) | 70–80 | 1–2 | Surface moisture removal for GPPS and HIPS; essential for foamed PS |
| Glass-Fiber-Reinforced Grades | Per base resin + 10–20°C | Per base resin | Filled grades typically require slightly higher temperature and longer time |
| TPE / TPU | 60–85 | 2–4 | Pre-drying recommended to avoid surface defects in overmolding applications |
For material-specific drying protocol recommendations, visit the Application Solutions page.
The STG-U Hopper Drier operates on a forced hot-air convection principle within a closed recirculation loop:
[Ambient Air Intake] → [Heating Chamber] → [Blower Pressurization] → [Perforated Cone Distribution] → [Pellet Bed (upward flow)] → [Moisture-Laden Air Exhaust] → [Optional Filtration & Reheating]
Step-by-Step Operating Workflow:
Material Loading: Plastic resin pellets are loaded into the stainless steel hopper through the top port, filling the hopper to the desired level. The integrated dust filter captures airborne fines and prevents them from entering the blower circuit.
Temperature Setting: The operator sets the target drying temperature on the thermostat or digital PID controller, matched to the specific resin type being processed. The tubular heating element begins to warm the air inside the heating chamber.
Forced Hot-Air Circulation: The blower fan draws ambient air through the heating chamber, where it is raised to the set temperature, then forces it upward through the perforated distribution cone at the base of the hopper. The cone's hole pattern distributes hot air evenly across the entire cross-section of the pellet column.
Pellet Bed Drying: Hot air rises through the pellet bed, transferring heat to the resin granules and carrying away surface and internal moisture. The counter-current flow arrangement — hot air entering at the bottom (where the driest pellets exit to the machine) and exiting at the top (where the wettest incoming pellets are) — maximizes thermodynamic drying efficiency.
Moisture Exhaust: Moisture-laden air exits through vents at the top of the hopper. The constant flow of fresh heated air through the system ensures that moisture is continuously removed rather than recirculated, maintaining a consistently low dew point in the drying atmosphere.
Continuous Discharge to Machine: As the processing machine consumes material from the barrel, dried pellets flow by gravity from the hopper base through the discharge valve directly into the feed throat. A level sensor (when installed) signals the upstream loader to replenish the hopper, maintaining a consistent inventory of drying material.
| Aspect | STG-U Series Hopper Drier | Conventional Hot-Air Hopper Dryer | Desiccant / Dehumidifying Dryer |
|---|---|---|---|
| Drying Principle | Forced hot-air convection | Forced hot-air convection | Closed-loop desiccant rotor dehumidification |
| Energy Efficiency | 27–65% savings vs. conventional (insulated hopper + duty-cycle blower) | Standard efficiency; high heat loss through uninsulated hopper walls | Higher energy consumption due to desiccant regeneration cycle |
| Installation | Direct machine-mount; zero floor space | Machine-mount or standalone; conveyor connection required | Standalone; requires vacuum conveying to machine |
| Moisture Re-Absorption Risk | Eliminated — sealed material path from hopper to barrel | Present — open transfer path after drying | Present — conveying pipeline exposure to ambient air |
| Dew Point Achievable | Ambient dew point (dependent on intake air conditions) | Ambient dew point | -40°C to -50°C (with desiccant rotor) |
| Best Suited Materials | PP, PE, PS, ABS, PA, PC, PMMA, POM, PBT | PP, PE, PS (non-hygroscopic or low-hygroscopic) | PET (preform/ bottle grade), PC (optical), PA6/66 (precision), PPS, LCP |
| Capital Cost | Low — comparable to conventional hopper dryers | Low — basic design with few components | High — desiccant rotor, aftercooler, regeneration heater, filters |
| Maintenance | Minimal — heater element replacement, periodic filter cleaning | Minimal — heater and blower maintenance | Moderate — desiccant rotor replacement, regeneration heater, filter media, dew point sensor calibration |
| Floor Space | None (machine-mounted) | Minimal or none | Significant — standalone unit plus conveying system footprint |
| Material Changeover | Quick — empty hopper, clean cone, reload | Quick — similar process | Slow — purge conveying lines, rotor regeneration, dew point stabilization |
The STG-U series occupies a distinct middle ground: it delivers substantially better energy efficiency and moisture protection than conventional hopper dryers through its insulated hopper construction and direct-mount sealed material path, without the capital cost and maintenance overhead of desiccant dehumidifying systems. For the majority of general-purpose and engineering resin applications — where the drying target is ambient dew point or slightly below — the STG-U series provides the optimal balance of performance, efficiency, and operational simplicity.
The STG-U Hopper Drier operates on hot-air convection, heating ambient air and passing it through the pellet bed. Its drying performance is therefore dependent on the ambient air's absolute humidity. A dehumidifying (desiccant) dryer, by contrast, uses a desiccant rotor to remove moisture from the process air before heating, achieving dew points of -40°C or lower. Choose the STG-U series when you are processing standard engineering resins (ABS, PA6/66, PC for non-optical applications, POM, PBT) in climates with moderate ambient humidity and when production does not require sub-zero dew points. Choose a dehumidifying dryer when processing PET bottle-grade preforms, optical-grade PC, or hygroscopic engineering resins in tropical or coastal high-humidity environments where ambient air moisture content would prevent adequate drying. For many injection molders in temperate climates, the STG-U series provides sufficient drying at significantly lower equipment and operating cost than a desiccant system.
Model selection is driven by two primary factors: your processing machine's hourly material throughput and the resin's required drying residence time. Multiply your hourly throughput (kg/h) by the recommended drying time (hours) for your material — this gives the minimum hopper capacity required. For example, if you process 25 kg/h of ABS requiring 3 hours of drying, the minimum hopper capacity is 75 kg — which corresponds to the STG-U125 model (75 kg capacity). Always add a 20–30% safety margin to account for bulk density variation, throughput fluctuations, and partial hopper fill levels. For multi-material production environments, size for the most demanding drying scenario among your regularly processed resins. Chenxing's application engineers can assist with detailed throughput calculations — contact us with your machine specifications and material list.
Yes, the STG-U series works effectively with glass-fiber-reinforced and mineral-filled resin grades. However, two considerations apply: first, filled materials have higher thermal conductivity than unfilled resins, enabling faster heat transfer through the pellet bed — which is favorable for drying efficiency. Second, filled grades may require 10–20°C higher drying temperatures than their unfilled counterparts to compensate for the reduced polymer volume fraction. The STG-U's heater power is sized to accommodate these elevated temperature demands within each model's volume capacity. Note that abrasive fillers (glass fiber, mineral) will accelerate heater element surface oxidation over extended service life; schedule heater element inspection during annual preventive maintenance if filled materials constitute a majority of your production throughput.
The STG-U series is designed for minimal maintenance with extended service intervals. Routine maintenance tasks include: (a) weekly — clean or replace the top dust filter to maintain proper air intake flow; inspect the observation window for haze or cracking; (b) monthly — check blower motor for abnormal noise or vibration indicating bearing wear; verify that the temperature controller setpoint matches the process requirement; clean any pellet dust accumulation from the perforated distribution cone; (c) quarterly — inspect the tubular heating element for surface oxidation or hot-spot discoloration indicating potential failure; check all electrical connections for tightness and insulation integrity; verify the over-temperature safety cut-off functions correctly by testing at a reduced trip point; (d) annually — replace blower motor bearings if operating in a high-dust environment; perform full insulation integrity check of the hopper body; replace the heating element if resistance has drifted more than 10% from nominal. All maintenance procedures can be performed on the machine-mounted unit without removing the hopper from the processing machine.
Yes. The STG-U series is fully compatible with automated vacuum or pressure conveying loading systems. The top loading port accepts standard conveying line connections, and the integrated dust filter captures material fines generated during pneumatic conveying. When integrating with an automatic loader, install a level sensor (capacitive or rotary paddle type) in the hopper to signal the centralized loader controller when the material level drops below the refill threshold. To maximize energy efficiency in automatic loading configurations, consider the following: (a) set the loader to maintain the hopper at 60–80% fill rather than topping off continuously — this ensures newly loaded cold pellets have adequate residence time in the upper portion of the hopper to pre-heat before reaching the lower drying zone; (b) program a brief loader delay after each refill cycle to allow the hopper temperature to stabilize before resuming production-rate material consumption; and (c) ensure the conveying air is dry and oil-free to avoid introducing moisture into the drying circuit. Chenxing Machinery offers complete integrated solutions combining the STG-U Hopper Drier with vacuum loaders, which can be explored on our auxiliary machines page.
Chenxing Machinery is a specialized plastic processing machinery manufacturer with decades of engineering experience serving injection molders, extruders, compounders, and recyclers across the global plastics industry. Our comprehensive product portfolio covers the entire plastics processing value chain:
Size Reduction Equipment:
SMF Series Disc Grinding Pulverizer — High-efficiency disc grinding for PE, PP, and PVC powder production with throughput up to 600 kg/h
SMP Series Knives Pulverizer — Rotary knife milling technology for rigid and flexible plastics, rubber, and elastomers
NSPC Series Crushing & Grinding Machine — Heavy-duty crusher for post-industrial scrap, rejected parts, and post-consumer waste recycling
Extrusion Equipment:
Conical Twin Screw Extruder — Optimized screw geometry for PVC profile, pipe, and wood-plastic composite (WPC) processing with superior plastication
High-Output Single Screw Extruder — Versatile 33:1–38:1 L/D ratio single-screw design for PE, PP, PS, ABS, and engineering resin pelletizing and profile extrusion
Pelletizing & Recycling Lines:
SJ Series Water Strand Pelletizing Line — Complete compounding and pelletizing system with water bath cooling, air knife drying, and strand cutting
Water-Ring Cutting Recycling & Granulating Line — Integrated hot-die-face water-ring pelletizing for waste plastic film, raffia, and regrind recycling
Profile & Pipe Extrusion Lines:
PVC WPC Profile Extrusion Line — Turnkey extrusion line for PVC window/door profiles, WPC decking, fencing, and wall panels
PPR/PPH High-Speed Pipe Production Line — High-output pipe extrusion for plumbing, industrial, and infrastructure applications from 16 mm to 630 mm diameter
PVC WPC Celuka Foam Board Sheet Extrusion Line — Celuka-process foam board and sheet production for signage, construction, and furniture industries
Auxiliary & Supporting Equipment:
Chillers, Hopper Loaders, Vibrating Screens, Dust Collectors, Shredders, Mold Temperature Controllers — Full-range auxiliary equipment ensuring seamless integration and single-source accountability for your entire production line
For industry news, trade show announcements, and application case studies, visit our Company News page. Every STG-U Hopper Drier we deliver is backed by Chenxing's in-house engineering support team, comprehensive spare parts inventory, and a commitment to responsive after-sales service.
Ready to specify the right STG-U Hopper Drier for your production line? Follow these four steps:
Define Your Requirements — Determine your processing machine's hourly material throughput (kg/h), the primary resins you process, and the available space above the machine feed throat. If you operate multiple machines with different materials, list each machine-resin combination.
Contact Our Team — Email ceo@cxsljx.com or call Nicole at +86 15951187228 with your specifications. Our application engineers will review your requirements and recommend the optimal STG-U model. We respond to all inquiries within one business day.
Receive a Tailored Proposal — You will receive a detailed proposal including the recommended STG-U model with technical specifications, optional upgrades (digital PID controller, pneumatic discharge valve, level sensor), pricing, production lead time, and shipping information. Custom voltage and frequency adaptations (220V/60Hz, 440V/60Hz, etc.) are available for international markets.
Install & Produce — Upon delivery, our technical support team provides remote or on-site commissioning guidance. The STG-U Hopper Drier is designed for rapid installation — simply mount it onto the machine feed throat, connect power, set the temperature, load material, and begin production. Operator training documentation is included with every shipment.