A shaft-mounted helical gear reducer uses the screw drive shaft as its own output member, removing the need for a mounting base and a low-speed coupling [S1].
An end-mounted (screw conveyor adapter) drive bolts to the trough end flange with CEMA drilling, carries a built-in shaft seal, and has steadily displaced other arrangements over roughly the last 15 years on installed cost and ease of assembly [S2].
Mechanical Configuration and How Each Drive Carries Load
A shaft-mounted reducer is a hollow-bore helical or double-reduction unit that slides onto the driven shaft and is locked with a tapered or split bushing; a torque arm or tie-rod turnbuckle reacts the housing torque to a fixed structure, so the conveyor drive shaft itself becomes the output [S1][S4].
An end-mounted drive sits on a CEMA-drilled adapter flange at the trough end, with a steel motor mount bracket, a removable drive shaft, and integral shaft seals; V-belt tension is set by sliding the motor plate, and the whole assembly can be lifted off by removing the bracket bolts [S1]. Both arrangements typically pair with V-belt primary drive between a TEFC or inverter-duty motor and the reducer input [S6].
Seal Location, Contamination Risk, and Why Discharge-End Mounting Dominates
Adapter-style shaft seals are commonly multi-lip labyrinth arrangements that retain product in horizontal, granular service; the same seals are vulnerable to flood-fed inlets, inclined runs, and dusty materials, and a failure path then runs straight into the gearbox case [S2].
Mounting the drive on the discharge end keeps the seal out of the incoming product stream, lowers the chance of gearbox contamination, and also pulls the screw into tension rather than compression, which resists the natural mid-span bow of long, hanger-supported screws [S2]. For inlet-end duty the design has to add alternative seals and thrust-limiting provisions instead [S2].
Ratio, Frame Size, and Materials Common to Shaft-Mount Units
Screw-conveyor shaft-mount reducers are typically offered in two nominal ratios, 15:1 and 25:1, across box sizes 2 through 6, with hardened AGMA class 11 gearing, FCD45 cast iron housings, double lip plus braided felt seals, and CEMA-conforming drive shafts machined from high-tensile alloy steel [S5]. The bushing is what locks the reducer to the screw shaft, and a properly torqued bushing is what lets the unit carry the rated overhung and torsional load without slip.
Service factor, thermal capacity, backstop selection, and bushing specification are the four sizing decisions that drive repeatability, per recent conveyor engineering guidance [S8]. V-belt or roller-chain secondaries are still used for chain-drive or integral motor-reducer variants, with chain drives needing an overhung-load-rated end bearing [S1].
Decision Matrix: Shaft-Mount vs End-Mount vs Coupled Base
Use the table below as a starting spec sheet, not as a substitute for a manufacturer selection sheet [S1][S2][S3][S5][S8].
Mounting footprint: shaft-mount is the most compact because the conveyor shaft is the output and no baseplate is needed; end-mount (CEMA adapter) is a close second because the flange is integrated; coupled base-mount needs the most floor space and adds a low-speed coupling [S1]. Shaft seal integrity: end-mount with built-in multi-lip seal is the easiest to keep clean in horizontal granular service; shaft-mount lets the specifier choose from a wider range of seal and bearing options, including heavy-duty bearings for higher-than-usual loads [S1][S2]. High-temperature duty: shaft-mount wins because it can be located away from the trough end so damaging heat dissipates before reaching the reducer, and it can be rotated to any clock position around the shaft [S1]. Installed cost and field familiarity: end-mount adapters dominate the market on ease of installation and lower overall cost over the last 15 years [S2]. Alignment and removal: end-mount lifts off by removing bracket bolts; shaft-mount locks with a tie-rod turnbuckle, which is best set in the field, not supported off the conveyor structure [S1].
Use-Case Recommendations
Pick a shaft-mounted reducer with torque arm when the layout is tight, when ambient heat at the trough end is a concern, when heavy radial loads or specialty bearings are required, or when the drive end is inaccessible for a baseplate [S1][S4]. KWS frames its direct shaft-mount design as a compact, cost-effective alternative to traditional belt-driven screw conveyor packages for exactly these reasons [S3].
Pick a CEMA end-mount (adapter) drive for the typical horizontal, granular, moderate-length screw, where the built-in seal, the removable drive shaft, and the bolt-on motor bracket give the shortest install time and the lowest installed cost [S1][S2]. For chain or integral motor-reducer packages, plan an overhung-load-rated end bearing and verify sprocket or pinion geometry against the supplier's shaft-collar and shaft fastening data so the bushing does not become the weak link [S1][S5].
Failure Modes, Couplings, and Maintenance Traps
Heavy, intermittent overloads on a started conveyor will damage drive components unless a fluid, pneumatic, or resilient coupling is fitted between the motor and the reducer input [S1]. A backstop is mandatory on any inclined or vertical screw where reversal under load would walk the product back, and the backstop must be rated for the full reducer output torque, not just the motor nameplate [S8].
The two field failures that show up most often are seal blow-by on inlet-end or flood-fed adapters that contaminate the gearbox, and bushing slip on shaft-mount units that were installed without verifying the bore, the key, and the shaft key fit per the OEM torque sequence [S1][S2][S5]. For plants already running a condition-based program, a one-line vibration and temperature tap on the reducer housing catches both modes early, and the same approach scales to other rotating equipment decisions covered in the CBM vs PdM vs RCM decision matrix.
Trackable signals for the next spec cycle: AGMA class 11 gearing and 15:1 or 25:1 ratios remain the published baseline for screw-conveyor shaft-mount units in 2026, while end-mount adapters continue to absorb the bulk of new builds on installed cost [S2][S5]. Watch the ratio between reducer input service factor and the driven machine's effective service factor at start-up, since that gap is where most published warranty exclusions live [S8].
For the relevant spec sheets and selection criteria, see truck mounted crane.