Plastic resin hopper dryers · Hot-air vs desiccant dehumidifying, resin maker's temperature, time, dew point and moisture limit, hopper size vs throughput
A hopper dryer holds plastic pellets above an injection moulding machine or extruder and passes heated air through them to remove moisture before processing; desiccant (dehumidifying) versions also dry the air. Ask three things first: the resin's required drying temperature, time, dew point and residual moisture, the throughput that sets hopper size, and whether hot-air drying is enough or a dehumidifying dryer is needed.
Hot-air hopper dryers and desiccant dehumidifying hopper dryers for plastic pellets at moulding and extrusion machines. Central drying systems, crystallisers for PET, vacuum dryers and dryers for food or chemical powders are outside this page.
01
Covestro explains that Makrolon polycarbonate is hygroscopic and absorbs moisture during transport and storage, so residual moisture must be removed before moulding to make tough, transparent, defect-free parts; a desiccant-type dehumidifying dryer is used, holding pellets in a hopper while hot dry air circulates and the removed moisture is captured in desiccant beds that are regenerated on a schedule. Its standard conditions are four hours at 250 °F (120 °C) with circulating-air dew point below −20 °F, and residual moisture must be below 0.02% to avoid moisture-related defects and degradation. [1]
Editorial note: these figures apply to the Makrolon grades in Covestro's sheet; other resins have their own published conditions, which should be taken from each resin maker's processing data rather than from a generic chart.
Give the supplier the resins to be dried and their makers' drying temperature, time, dew point and target moisture, the machine throughput in kg/h, number of machines, whether regrind is used, available power and air supply, and whether the dryer mounts on the machine throat or stands beside it.
02
Jiusheng describes its hot-air hopper dryers as heating to 120 °C with standard hoppers of 12, 25, 50, 75, 100, 150 and 200 kg and larger 300–600 kg units with over-temperature alarms. [2] Kunya's stainless hopper dryer uses electric hot-air circulation with a stirring screw, temperature control within ±2 °C, motors of 5.5–30 kW and drying in as little as 3 hours. [3]
Editorial calculation: a hopper must hold at least throughput × drying time, so a machine using 25 kg/h of polycarbonate that needs 4 hours of drying needs at least 25 × 4 = 100 kg of resin under drying conditions at all times. Covestro's process uses a dehumidifying dryer to reach its dew point requirement; ask any hot-air hopper dryer supplier what dew point and residual moisture its dryer achieves before using it for such resins. [1] [2]
03
A Canadian patent assigned to dryer maker Novatec Inc. (CA2412772C, priority 2000) sets out the air-supply options a hopper dryer buyer chooses between. It puts the recommended dew point of air for drying plastic pellets below 0 °F, in a range of about −20 °F to about −50 °F or lower, and gives about four hours as the residence time of plastic pellets in the hopper. It describes the conventional desiccant system as a closed loop in which a molecular-sieve desiccant such as zeolite dries recirculated air, a heater between desiccant and hopper raises it to drying temperature, and the desiccant has to be regenerated with heated air, either by taking a single unit off line or by alternating two units. [4]
The patent's alternative feeds plant compressed air, which it says may already have a dew point of +40 °F to +50 °F after a refrigerant dryer, through a membrane dryer giving −10 °F to −20 °F, then expands it through an orifice to atmospheric pressure at −40 °F or lower, and recirculates hopper air at about 5 recirculated volumes to 1 compressed volume to cut compressed-air use. [4]
Editorial calculation: −20 °F is −28.9 °C, −40 °F is −40 °C and −50 °F is −45.6 °C. Covestro's below −20 °F requirement for Makrolon sits at the warm end of that range, while refrigerated compressed air at +40 to +50 °F (4.4 to 10 °C) is far wetter than that range, so ask for the dew point the quoted dryer delivers at the hopper inlet, including for hot-air models. [4] [1]
| Air source | Dew point stated | What to ask the supplier |
|---|---|---|
| Recommended for plastic pellets | Below 0 °F; about −20 to −50 °F or lower. [4] | Dew point at hopper inlet, °F or °C. |
| Plant air after refrigerant dryer | +40 to +50 °F. [4] | Not sufficient alone for hygroscopic resins. |
| Membrane dryer output | −10 to −20 °F; −40 °F or lower after expansion. [4] | Compressed-air consumption, SCFM. |
| Desiccant (molecular sieve) loop | Very low dew point; needs regeneration. [4] | Single or twin bed; regeneration method. |
| Makrolon PC requirement | Below −20 °F, 4 h at 250 °F. [1] | Residual moisture result below 0.02%. |
04
The suppliers linked to this page list hopper dryers or their parts; their cards link to the pages reviewed.
Ask any supplier for dryer type (hot air or desiccant), hopper capacity, maximum temperature and control accuracy, air flow, achievable dew point, heater and blower power, insulation, filters, over-temperature protection, and the moisture result on your resin.
05
This is a functional reference built from the sources cited; it is not one maker's specification.
| Part | Role | Fix in the order |
|---|---|---|
| Hopper | Hold resin for the drying time. [1] [2] | Capacity; insulation. |
| Heater and blower | Heat and circulate air. [3] | Power; air flow. |
| Desiccant beds (dehumidifying type) | Dry the circulating air. [1] | Dew point; regeneration. |
| Temperature control and alarm | Hold set point. [3] [2] | Accuracy; alarms. |
| Stirrer (option) | Mix and avoid hot spots. [3] | Type. |
06
A hopper dryer quotation needs values for your resin and machine. The table explains each field, gives published values where a reviewed source states them, and says what to obtain from the supplier.
| Field | What it means and published values | Ask the supplier for |
|---|---|---|
| Hopper Capacity (kg) | e.g. 12–600 kg; ≥ throughput × drying time. [2] | Capacity. |
| Drying Temperature (°C) | e.g. 120 °C for Makrolon PC. [1] | Maximum and control. |
| Air Flow Rate (m³/min) | Circulating air. | Flow. |
| Dew Point (°C) | e.g. below −20 °F for Makrolon PC. [1] | Achievable dew point. |
| Power Consumption (kW) | Heater and blower. | Total power. |
| Drying Time (hours) | e.g. 4 h for Makrolon PC. [1] | Time at your throughput. |
| Temperature Accuracy (°C) | e.g. ±2 °C. [3] | Accuracy. |
| Heating Power (kW) | Heater rating. | Power. |
| Operating Voltage (V AC) | Plant supply. | Voltage. |
| Frequency (Hz) | Plant supply. | 50 or 60 Hz. |
| Material | e.g. 304 stainless inner tank. [3] | Material. |
| Weight (kg) | Mass. | Mass. |
| Dimensions (L×W×H) (mm) | Footprint and height. | Size. |
| Noise Level (dB(A)) | Blower noise. | Level. |
07
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Resin: [type; maker's temperature; time; dew point; moisture] Throughput: [kg/h per machine; regrind] Dryer: [hot air or desiccant; hopper size] Mounting: [on machine throat or floor] Utilities: [power; voltage; frequency]
These companies list hopper dryers or their parts.
Lists hot-air hopper dryers and plastic dryers with chillers.
Product scope checked 2026-10-11
Lists stainless plastic hopper dryers with extruders.
Product scope checked 2026-10-11
Lists plastic hopper dryers with pipe extrusion lines.
Product scope checked 2026-10-11
Lists hopper dryer parts and stands with mould clamps.
Product scope checked 2026-10-11
Lists plastic dryers with recycling equipment.
Product scope checked 2026-10-11
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
Covestro gives four hours at 250 °F (120 °C) for Makrolon, with circulating air below −20 °F dew point and residual moisture under 0.02%. [1]
Editorially, at least throughput × drying time; for example 25 kg/h × 4 h = 100 kg under drying conditions. [1]
Jiusheng lists 12–200 kg standard hoppers and 300–600 kg units, heating to 120 °C. [2]
Sources checked 2026-10-11. Covestro is a resin maker publishing processing conditions; a Novatec patent describes drying-air dew points and air-supply options; Jiusheng and Kunya are suppliers linked to this page.
Ask for use case, specification boundaries, supplier type, and RFQ preparation information for this product.
Compare manufacturer profiles with relevant product and process capability.