Taper bushes for pulp and paper conveyors, dryer sections, and reel drives are specified in the same four-digit series used elsewhere in heavy industry (1008 through 5050), with bore ranges from 9 mm to 125 mm and keyways cut to BS 4235 Part 1:1972 / ISO recommendations [S1]. The selection job in a mill is not the bushing itself, it is matching the bush family, bore, and material to the duty environment: wet, steamy, chemical-laden, and frequently above 80 deg C around dryer cans.
Pulp and paper drives run three principal bush families: Taper Lock (8 degree taper, flangeless, hex-socket screws), QD (Quick Disconnect, separate flanged bushing), and split-taper / ST / XT variants. Taper Lock is the most common mill-floor pattern because the hub is flangeless, the screws sit inside the hub, and the 8 degree taper gives a high clamp without deforming the shaft [S1][S5]. QD is found on legacy multi-groove sheaves and some timing-belt drives; split-taper (ST) and extra-taper (XT) bushings show up on older conveyor and dryer-section pulleys where the hub was originally machined for a Martin or Emerson pattern [S3][S4][S5].
Match the Hub Before You Match the Bore
The single most common error in mill stores is buying a bushing that fits the shaft but not the pulley. QD and Taper Lock hubs are not interchangeable: taper angles, bolt patterns, and mounting geometry differ, and there is no adapter [S3]. A Taper Lock hub shows a visible axial split and draw-screws on the flange face; a QD hub has a flat face with 2 or 3 cap-screw holes around a smooth tapered bore and no slit in the hub body [S3]. If the existing pulley carries a part number, the bush series is fixed by that number; only the bore can be changed.
For new pulleys specified into a paper machine, the practical rule is: standardise on Taper Lock, metric bore, ferritic grey cast iron FG-200, and stick to a 1:12 wedge geometry. The Taper Lock has a nominal 8-degree taper angle equaling 1 11/16 inch per foot, or 14.06% taper, split through the entire bushing, and uses blind hex socket-head screws on the tapered outside diameter to drive the bushing into the bore of the component, thus compressing the inner diameter of the bushing to the keyed shaft and allowing a locking without any shaft deformation [S5]. For higher torque draws (calender drives, couch rolls, refiners) move up the series: 2517, 3020, 3535, 4040, 4545, 5050, with face widths from 45 mm to 127 mm and large-end diameters from 85.5 mm to 177.5 mm [S1].
Bore and Keyway: BS 4235 Part 1:1972 is the Baseline
PIX PowerWare bushes are manufactured with all bores and keyways to BS 4235, Part 1:1972, with finished bores and keyways offered in both metric and imperial sizes [S1]. The four-digit series itself does not fix the bore; it fixes the outside geometry (large-end diameter, face width, screw size). The bore is selected inside the published window for that series, for example 2517 covers 16 mm to 60 mm, 3020 covers 25 mm to 75 mm, 3535 covers 35 mm to 90 mm, 4040 covers 40 mm to 100 mm, 5050 covers 70 mm to 125 mm [S1][S7].
When matching the bushing to a shaft collar or lock nut already in the drive train, always cross-check the series face width against the hub bore depth; a 2517 bushing has a 45 mm face, a 2525 has 65 mm, and the deeper face gives more contact area but requires a deeper pocket in the pulley hub [S1]. For imperial shafts the same 2517 will accept 5/8 inch to 2-1/2 inch; for metric shafts the 2517 takes 16 mm to 60 mm [S1][S3].
Comparison: Taper Lock vs QD vs Split-Taper for Paper-Mill Service
Lining the three families up against four paper-mill decision criteria gives a clean selection matrix: Taper Lock is the default for new builds and for shaft sizes 9 mm to 125 mm because it is flangeless, uses 1/4-20NC to 1 1/2-6NC hex-socket screws, and accepts the widest bore range inside a single series; QD is specified only when the existing sheave is QD-pattern, since QD and Taper Lock hubs are not interchangeable and no adapter exists [S3][S5]. Split-taper (ST) and extra-taper (XT) are retained for replacement on older conveyor and dryer-section pulleys originally bored for Martin or Emerson patterns, but they are no longer the preferred spec for new equipment [S4][S5].
On torque capacity the four-digit series tells the story: a 5050 bushing uses 1 1/4-7NC screws on a 6.72 inch bolt circle, while a 1008 uses 1/4-20NC screws on a 1.33 inch bolt circle, a 20x increase in screw size between the smallest and largest standard series [S5]. On material, Taper Lock is normally supplied in FG-200 grade ferritic grey cast iron, with stainless steel available for food-grade and white-paper machine areas where corrosion from chlorinated water and peroxide bleaching is a concern [S1][S5]. For wet-end and broke-handling conveyors where wash-down is routine, stainless or a coated ductile option is worth specifying; for the dry end above 80 deg C, standard FG-200 is adequate.
Series-to-Application Map for Paper Machines
The small-frame end of the range covers the high-speed, low-torque end of the drive: 1008 (9 to 25 mm bore), 1108 (9 to 28 mm), 1210 (11 to 32 mm), 1215 (11 to 32 mm), 1310 (14 to 35 mm), 1610 (14 to 42 mm), 1615 (14 to 42 mm) are typical for felt-roll idlers, small fan drives, and approach-flow pump couplings [S1]. Mid-range 2012 (14 to 50 mm), 2517 (16 to 60 mm), 2525 (19 to 60 mm), 3020 (25 to 75 mm), 3030 (35 to 75 mm) take the main conveyor, agitator, and stock-pulper drives. Heavy-end 3525, 3535, 4040, 4545, 5050 cover dryer-section drive shafts, calender stacks, reel drum drives, and the refiner input shafts, where bore windows reach 35 to 125 mm and face widths reach 65 to 127 mm [S1][S7].
In paper-mill conveyors, the 2517 and 3020 are the workhorse sizes, paired with C-section V-belts or timing belts on the head and tail pulleys. Roller chain drives on the same conveyors use matching hub patterns but the locking assembly inside the sprocket is typically a Taper Lock of the same 2517 or 3020 series, not a separate wedge element. For chain conveyors carrying wet laps or rolls, the same series applies but the bushing material should be upgraded to stainless or zinc-plated ductile to resist the moist, acidic broke chest environment.
Installation, Removal, and the Mistakes That Kill Pulleys
Install sequence for a Taper Lock: clean shaft and bore, slide bushing into hub, align screw holes, hand-start the hex-socket screws, then torque them progressively in opposing pairs to the value stamped on the bushing or listed in the maker's table; under-torque lets the wedge slip, over-torque strips the screw threads in the cast iron body [S3][S7]. The 1:12 taper generates the clamping force, so screw torque is the only variable you control. For removal, slacken all screws, then tighten two adjacent screws one full turn at a time to walk the bushing back out of the bore; never use a pry bar on the hub [S3][S7].
Two paper-mill failure modes are worth flagging. First, a Taper Lock bushing under sustained vibration (press section, calender) will fret the keyway and the shaft shoulder if the screws are not re-torqued after the first 8 to 24 hours of run-time. Second, a QD bushing installed dry on a vertical or inverted shaft will creep; a light film of light-grade oil on the tapered interface of a Taper Lock helps removal later, but the taper must be wiped clean of oil before final clamp-up on a QD bushing or it will not grip. The fit philosophy is different between families, and a rule that works for one will fail the other [S3].
Standards, Sourcing, and What to Watch Next
Reference standard for general Taper Lock dimensions and tolerances is MPTA-B9i-2013, with the bore and keyway to BS 4235 Part 1:1972, conforming to ISO recommendations [S1][S5]. The PIX, BTL, SKF, and B&B Manufacturing product ranges all share the same 1008 to 5050 numbering, so cross-vendor interchange is normal for the bushing itself; the hub pattern, however, is matched to the pulley maker, not the bushing maker [S1][S9]. QD is a registered trademark of Emerson Electric, Taper Lock of Reliance Electric, ST of Martin Sprocket & Gear, and XT of Emerson Electric; the trademarks signal hub-pattern origin, not quality grade [S5].
Watch for two signals over the next quarters: more stainless and coated-ductile Taper Lock options reaching 2517 to 3535 size ranges for broke and wet-end service, and CAD-native selection tables replacing printed catalogues at distributors, with downloadable STEP files for hub-and-bush assemblies [S6]. For a deeper look at the wedge-clamping principle behind these figures, see the taper-lock wedge clamping reference on the engineering desk.