Quick answer. Select an IBC mixer for polyurethane adhesive from viscosity measured at the actual mixing temperature and shear rate, then verify that its impeller produces both near-wall circulation and upward flow from the IBC floor. For filler-containing PU glue, gearbox output torque, impeller clearance and restart capability after a 24–72 hour stop matter more than motor kilowatts alone. A production trial should confirm top, middle and outlet solids uniformity before the mixer is approved.
A nominal 1000 L IBC is commonly about 1200 × 1000 × 1160 mm externally, but the HDPE liner has rounded corners, a sloping floor and dimensions that vary by supplier. Those features create low-velocity zones that a small central propeller may never sweep.
PU adhesive also changes viscosity with temperature, shear and storage time. A value such as “20,000 mPa·s” is incomplete unless the test temperature, spindle, speed and conditioning history are recorded.
Start with PU Adhesive Rheology and Filler Settling
Most filled polyurethane adhesives behave as non-Newtonian liquids. Their apparent viscosity can fall as shear rate rises, while thixotropic grades rebuild structure after mixing stops. One viscosity number therefore cannot predict startup torque, running torque and storage stability at the same time.
Request a viscosity curve at several speeds rather than a single Brookfield reading. ASTM D2196 covers apparent viscosity, shear thinning and thixotropic behavior of non-Newtonian materials using rotational viscometers over approximately 0.1–50 s⁻¹.
ISO 2555:2018 describes apparent-viscosity measurement with a single-cylinder rotational viscometer over 0.02–60,000 Pa·s. The method applies to Newtonian and non-Newtonian liquids, and ISO explicitly ties the result to the imposed velocity gradient.
Why viscosity alone does not prevent settling
Filler settling is driven by particle diameter, density difference and agglomeration as well as liquid viscosity. For an isolated spherical particle in a Newtonian liquid at low Reynolds number, the Stokes estimate is v = Δρgd²/(18μ).
Consider an illustrative calcium-carbonate particle with a density of 2700 kg/m³ in a resin phase of 1150 kg/m³. At a 50 μm diameter and 5 Pa·s viscosity, the calculated settling velocity is about 0.00000042 m/s, or 1.5 mm/h; over 24 hours, that is roughly 36 mm.
If the diameter doubles to 100 μm, the calculated rate increases fourfold to about 6.1 mm/h because velocity is proportional to diameter squared. Agglomeration can therefore turn nominally fine powder into a much faster-settling population.
The calculation is a screening tool, not a batch guarantee. Concentrated fillers interact, PU adhesives may possess yield stress, and the square IBC walls modify flow. Research on particle settling in yield-stress fluids shows that increasing yield stress can slow or suppress particle motion, but shear can break the structure that provided static suspension.
This explains a common production failure: a tote appears stable during storage, then filler migrates after several minutes of local agitation. The mixer has yielded the material around the blade without establishing circulation through the corners and bottom layer.
| Data required from the adhesive | Minimum test detail | Why the mixer supplier needs it |
|---|---|---|
| Apparent viscosity | Values at 5, 10, 20 and 50 rpm; report spindle and 20–25°C temperature | Separates low-speed startup behavior from viscosity under mixing shear |
| Density | kg/m³ at the same temperature used for viscosity testing | Sets batch mass, shaft loading and power-per-unit-mass calculations |
| Filler distribution | Median size plus coarse tail such as D90, in μm | Large particles or agglomerates dominate settling risk |
| Filler density and loading | kg/m³ and wt% | Defines density mismatch and the solids mass that must be lifted |
| Yield stress or low-shear curve | Pa, with test method and conditioning time | Indicates storage suspension and required restart torque |
| Temperature range | Minimum startup, normal mixing and maximum permitted °C | PU viscosity may change sharply with temperature; overheating can shorten pot life |
| Maximum idle period | Hours or days before restart | Defines the sediment-bed restart test |
Compare Impellers for a 1000 L Adhesive Agitator
A frame agitator moves viscous material close to the walls and can generate more bulk turnover than a narrow propeller at the same low speed. In a rectangular IBC, however, a simple flat frame still leaves corner zones unless its width, vertical members and bottom profile follow the liner geometry.
A rigid 650–800 mm frame cannot pass through a typical 150 or 225 mm IBC top opening. The practical choices are a folding impeller, segmented assembly inside the tote, a removable/open-top liner, or transfer into a purpose-built mixing tank.
| Mixer geometry | Best starting viscosity range | Flow pattern in a 1000 L IBC | Filler-settling limitation | Procurement check |
|---|---|---|---|---|
| Small marine propeller | Below about 1,000–3,000 mPa·s | Strong local axial jet; limited wall coverage | Can leave a compacted floor layer once viscosity rises | Require sampling from the outlet, not only beside the shaft |
| Pitched-blade turbine | About 1,000–15,000 mPa·s | Combined axial and radial circulation | Performance falls if blade diameter is too small relative to the tote width | Specify deployed diameter, blade angle and rotation direction |
| Gate or frame impeller | About 10,000–80,000 mPa·s | Near-wall sweeping at low speed | A flat bottom member may miss filler in the sloped outlet sump | Match the lower frame profile to a measured liner drawing |
| Double frame with axial element | About 20,000–100,000 mPa·s | Wall sweep plus vertical turnover | Higher startup torque and greater shaft bending load | Request loaded-current and restart-torque records from a full-tote trial |
| Helical ribbon in a mixing vessel | Above about 50,000–100,000 mPa·s | Strong top-to-bottom displacement | Usually incompatible with a closed standard IBC opening | Compare a dedicated vessel and transfer pump against an IBC-mounted design |
These ranges are RFQ screening bands, not universal limits. A shear-thinning adhesive reading 80,000 mPa·s at 5 rpm may run at far lower viscosity around the impeller, while a settled mineral bed can still demand several times the normal running torque.
Reactive PUR hot-melt adhesive requires a separate assessment. Molten processing temperatures may fall around 80–140°C depending on the formulation, and a standard HDPE IBC liner or ordinary ambient-temperature mixer should not be assumed suitable. Use the adhesive TDS, container temperature rating and heated-equipment design as the controlling documents.
Size the Frame, Speed, Motor and Gearbox
Begin with the actual IBC liner drawing and filled mass. A 1000 L adhesive at 1250 kg/m³ weighs 1250 kg before the pallet, cage and mixer are counted; floor capacity and handling equipment must be rated for the complete assembly.
For a frame mixer, record the deployed impeller width, height, bottom clearance and minimum corner clearance in millimetres. A useful trial target is to position the lower element close enough to mobilize the floor layer—often 50–100 mm above the lowest surface—without contacting a liner that bows during filling or transport.
The cage is a transport frame, not automatically a mixer support. The mounting bridge must transmit motor weight, shaft thrust and startup torque into a verified structure without loading the thin manway neck or allowing the rotating frame to strike the HDPE wall.
Use torque, not motor power alone
Ideal shaft torque follows T = P/(2πN), where P is shaft power in watts and N is rotational speed in revolutions per second. A 7.5 kW drive at 60 rpm corresponds to about 1190 N·m before gearbox losses; at 30 rpm, the same power corresponds to about 2390 N·m.
That does not mean the gearbox can deliver either value continuously. The quotation should state rated output torque, peak permissible torque, service factor, thermal rating, gearbox efficiency and allowable radial load at the shaft extension.
| Illustrative 1000 L screening case | Speed | Nominal motor | Ideal calculated torque | Engineering question |
|---|---|---|---|---|
| Moderately filled, 5–20 Pa·s | 40 rpm | 4.0 kW | About 955 N·m | Can it restart after the specified idle period? |
| High-viscosity, shear-thinning PU | 30 rpm | 7.5 kW | About 2390 N·m | What is the gearbox’s continuous output rating? |
| Heavy sediment or very low-speed frame | 20 rpm | 11 kW | About 5250 N·m | Will shaft deflection and frame stress remain within design limits? |
These examples show why “11 kW” is not a complete specification. A buyer also needs the gearbox ratio, impeller dimensions and measured current during startup, steady mixing and deliberate restart after settling.
Tip speed provides another useful check: u = πDN. A 0.70 m deployed frame at 30 rpm has a tip speed of about 1.10 m/s. Raising speed to 60 rpm doubles tip speed and increases shear, but it may pull air through the surface, heat the adhesive or accelerate moisture exposure.
Specify a variable-frequency drive when the motor and hazardous-area assessment permit it. A controlled sequence can begin at low frequency, watch motor current, then ramp to the validated mixing speed; the minimum speed must still provide motor cooling and gearbox lubrication required by the manufacturers.
Do not accept a vortex as proof of complete mixing. A visible surface funnel can coexist with unmoved filler at the IBC outlet, particularly when the shaft carries a narrow impeller.
Write the RFQ Around a Full-Tote Acceptance Test
The purchase specification should name the adhesive condition that creates the greatest mechanical load. For filled PU glue, that is often a cold restart after 24, 48 or 72 hours rather than continuous mixing immediately after filling.
Provide the mixer vendor with a representative fluid or arrange a trial using the actual adhesive. Water testing confirms rotation and leaks, but its viscosity near 1 mPa·s at room temperature says little about a PU adhesive at 20,000–80,000 mPa·s.
- Define working volume in litres and batch mass in kilograms; do not use “one IBC” as the only quantity.
- State minimum startup temperature, normal temperature and maximum allowed product-temperature rise in °C.
- Give apparent viscosity at multiple speeds, density, filler wt%, D50/D90 particle size and expected idle time.
- Require deployed impeller dimensions, shaft material, wetted seal materials, gearbox output torque and rated motor current.
- Specify continuous or intermittent duty in minutes per cycle and cycles per shift.
- Require a guard around couplings and rotating shafts, plus an interlock if the frame can operate with the lid open.
- Define cleaning chemistry and confirm compatibility with PU residue, solvent, seal elastomers and the IBC liner.
Measure homogeneity where production experiences failure
Collect samples from the top, geometric middle and bottom outlet after mixing. Test density or solids content with the same documented method, and record sample time because rapid settling can distort a slow sampling sequence.
A buyer might set an acceptance limit such as each location remaining within ±2% relative of the three-sample mean after 15 minutes of mixing. That figure is an example purchasing threshold, not an industry standard; the correct limit must follow the adhesive’s coating weight, mix-ratio and bond-performance tolerance.
Run a restart challenge after the agreed idle period. Record peak current in amperes, time to reach the target speed, mixing time to uniformity, final temperature and any unmixed residue removed from the outlet or liner floor.
For two-component PU systems, agitate only the component that requires suspension unless the process design says otherwise. Mixing A and B in a storage IBC initiates reaction, increases viscosity and can generate enough cured material to destroy the impeller or block the bottom valve.
For MDI-containing products supplied to EU industrial or professional users, check the SDS and total diisocyanate concentration. REACH Annex XVII, Entry 74 requires safe-use training after 24 August 2023 unless the combined diisocyanate concentration is below 0.1% by weight.
Solvent-containing adhesives need a documented area classification and ignition-risk assessment. OSHA requires ventilation where specified flammable liquids are pumped or dispensed and addresses bonding against static sparks in 29 CFR 1910.106. An ordinary motor, switch or VFD must never be described as explosion-protected without the applicable equipment marking and certificate.
Manufacturer-direct sourcing is most valuable when adhesive and mixing requirements are handled together. PUGLUE can review substrate, application viscosity and packaging through its polyurethane adhesive product category, then provide the selected grade’s TDS and sample for line validation.
For custom or private-label supply, put the approved viscosity test condition, filler uniformity limit and packaging configuration into the purchase specification. Batch COA values should use the same method as the approved sample; otherwise two numerically similar viscosity results may describe different flow behavior.
Ask for SDS, TDS, COA format and any market-specific declaration before the commercial order. Certification scope must identify the actual adhesive or equipment supplied; a logo in a brochure does not establish that a particular formulation, motor or complete mixer assembly is covered.
FAQ
Q: What viscosity can a 1000 L frame mixer handle?
There is no single ceiling. Frame and gate mixers are commonly screened for adhesives around 10,000–80,000 mPa·s, but impeller dimensions, shear thinning, filler loading and gearbox torque determine the usable limit. Require a restart trial at the lowest operating temperature.
Q: How long should PU adhesive be mixed in an IBC?
Set time from measured uniformity rather than a generic timer. Sample the top, middle and bottom outlet at intervals such as 5, 10 and 15 minutes, then select the shortest time that meets the agreed solids or density deviation without excessive temperature rise or air entrainment.
Q: Will continuous slow agitation stop PU glue filler settling?
Only if the impeller creates circulation through the IBC floor, corners and outlet zone. Slow rotation that shears material near the shaft can disturb a yield-stress structure while leaving the bottom bed unmoved, producing more segregation rather than less.
Q: Is a 7.5 kW mixer automatically better than a 4 kW mixer?
No. At 30 rpm, 7.5 kW represents about 2390 N·m of ideal torque, but actual capability depends on gearbox losses, thermal rating, service factor, shaft strength and impeller load. Compare rated output torque and trial current, not motor power alone.
Q: Can the mixer be clamped directly to the IBC cage?
Only after the cage and mounting bridge have been checked for mixer weight, thrust, vibration and startup reaction torque. The plastic manway must not carry these loads, and the impeller needs clearance for liner movement.
Q: What information should be sent for a factory quotation?
Send the IBC drawing, working volume, adhesive density, multi-speed viscosity data, temperature range, filler type and wt%, D50/D90 size, idle period, electrical supply and hazardous-area classification. Add the required top/middle/outlet uniformity and restart test so competing quotations cover the same duty.