Butterfly Mixer Model Selection: PM150 to PM900 Sizing Guide

What the Butterfly Blade Changes About Mixing

On a butterfly machine the two shafts do genuinely different jobs. The high-speed disc shears product at its rim, where the velocity difference between disc edge and bulk material does the dispersing work. The butterfly blade is a low-speed impeller with two or more swept wings that push product up the wall and down the center, and outward as well. Because it sweeps a large diameter slowly, it moves volume instead of shearing it.

That division of labor is the whole point. A single-shaft disperser in a 500 L batch of stiff paste forms a doughnut of moving material around the disc while the rest of the tank sits still. Adding a slow, wide impeller on a second drive breaks that pattern: the blade folds the outer batch into the shear zone and the disc never runs in a channel it has already cleared.

The alternative layout is the concentric double shaft, where the low-speed anchor rides a hollow shaft around the high-speed shaft so both turn on the same centerline. Concentric construction scrapes the wall on the drive axis and suits products that need continuous wall contact. A butterfly twin-shaft mixer puts the shafts side by side instead, which gives a larger swept diameter for the same tank and keeps the seal geometry simpler, at the cost of needing wall scrapers as a separate feature.

PM Series Model Range

Four models cover the band. The numbers below are the standard build; motor ratings are given as ranges because the final selection follows the product rather than the tank.

Tank figures are total capacity. Usable working volume depends on product density and the fill level you run, which we confirm against your formula.

Reading Tip Speed and Turn-Down

Tip speed is the number that connects a spec table to a product. Disc tip speed is the circumference of the disc times its revolutions per minute, divided by 60: at 1450 rpm the PM150's 200 mm disc runs at about 15.2 m/s, the PM500's 250 mm disc at 19.0 m/s, the PM600's 280 mm at 21.3 m/s and the PM900's 330 mm at 25.1 m/s.

Run the same arithmetic on the low-speed side and the picture clarifies. The PM150's 500 mm blade at 60 rpm gives about 1.6 m/s; the PM500's 800 mm blade at 90 rpm gives 3.8 m/s; the PM600's 900 mm blade at 120 rpm gives 5.7 m/s; the PM900's 1100 mm blade at 120 rpm gives 6.9 m/s. The gap between the two tip speeds widens as you move up the range, which is exactly why the bigger frames handle stiffer product: the low-speed blade gains both torque and swept speed to fold the mass back into the disc.

Both drives are variable across the published ranges, so a single machine can run a low-shear fold at 30 rpm and then open up to full disc speed for the dispersion stage. Treat those two set points as separate recipe steps rather than one compromise speed.

Butterfly, Concentric, Helical or Triple Shaft

Viscosity figures are normal service bands, not hard limits. A pilot trial on your own formula settles the boundary case.

Which PM Model and Configuration Fits

Blade, Scraper and Vacuum Details

The butterfly wings are welded to the hub at a fixed angle of attack and braced back to the shaft, which is why the assembly can be rebuilt after years of service rather than replaced as a unit. PTFE wear strips bolt onto the outer edge of each wing when wall scraping is specified, and a matching bottom strip covers the lower sweep. Clearance between strip and vessel shell is set at assembly; a strip worn past its service thickness is a bolt-on replacement, not a re-weld.

When the machine is ordered with a vacuum cover, the disc shaft passes through a mechanical seal rather than a simple gland, and the cover carries the drop port for additives, a sight glass and the vacuum connection. Keeping the vessel closed during the dispersion stage is what removes entrained air from a filled adhesive before it reaches the packing line.

Where Butterfly Mixers Sit in Adhesive and Putty Lines

In an adhesive plant the butterfly frame usually carries the filler-loading stage: resin and solvent go in first, filler is added under the low-speed fold, and the disc breaks the agglomerates once the batch is wetted out. Putty production follows the same pattern at a heavier solids loading, where the butterfly blade's large swept area keeps calcium carbonate in motion without demanding disc speed the product cannot take. Where a plant also runs higher-viscosity sealant, the same line often pairs a butterfly unit with a concentric double-shaft mixer or a triple-shaft machine for the stiffest grades.

Buyers comparing frame types across several product families usually end up at the same fork: a butterfly machine for the middle of the range, a planetary or triple-shaft machine for the top, and a disperser for everything below. Plants running both ends of that spread often ask us to size the mid-range machine for the stiffest product they expect in three years, which is cheaper than adding a second frame later.

For a worked example of how viscosity bands, electrical standard and packing requirements combine in one export project, see our high viscosity mixer guide for Colombian plants.

Four Sizing Mistakes That Lead to a Rebuild

Choosing tank volume first. A 1,000 L tank fitted with a 250 mm disc and an 800 mm blade is a PM500 doing a 1,000 L job. Volume should follow the blade and disc diameters you need, not the other way around.

Under-specifying the blade drive. The low-speed side is where stiff batches stall. The same 500 L frame is offered with a 7.5 to 15 kW blade drive for exactly this reason, and the upper end of that range exists for products that thicken as they wet out.

Ignoring lift height. The 700, 950 and 1100 mm lift figures have to clear your tank rim and any docking collar. A machine that cannot raise its shafts above the rim cannot be cleaned between batches.

Treating vacuum as an afterthought. Adding a vacuum cover later means changing the seal arrangement, the shaft geometry at the cover penetration and the port layout. It is a design decision, not an accessory.

Manufactured In-House in Wuxi

POLYC builds in a 9,000 m2 plant in Wuxi where machining, dynamic balancing of the shafts, hydraulic assembly and tank welding happen under one roof. Keeping those steps in-house is what allows the anchor-and-disc geometry, the scraper clearance and the lift alignment to be controlled as one assembly rather than as parts from several suppliers.

Technical FAQ

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