The M3PHT50 torque arm gearbox is the shaft-mounted member of the size 50 industrial range. Its hollow low-speed shaft slides straight onto the driven machine shaft, and a torque arm reacts the drive torque back to the machine structure, so the unit needs no foundation, no output coupling and no bearing pedestal. Inside, the drive is a three-stage all-helical train on parallel axes with case-hardened and ground gearing in a horizontally split cast-iron housing.
A Torque-Arm Build That Hangs Straight on the Machine Shaft
Shaft-mounted mounting is the shortest route from motor to machine: the conveyor head shaft, mixer shaft or elevator shaft does the job that a base frame and coupling would otherwise do. The torque arm is a simple adjustable rod that absorbs the reaction torque and allows the belt tensioning of the whole drive package - a detail plants appreciate on conveyor duty, where the gear unit can be swung to keep the belt tight. Standard industrial practice sizes the horizontal range from 50 to 90, and size 50 covers the compact continuous drives: conveyors, rotary valves, mixers and small elevators.
M3PHT50 Designation Explained
| M3 | Industrial gear unit family, three helical stages |
| P | All-helical parallel-shaft layout (the R code marks the bevel-helical right-angle build) |
| H | Hollow low-speed shaft, keyed fit or shrink-disc connection (S marks solid shaft) |
| T | Torque-arm mounting - the unit hangs on the machine shaft and reacts through the arm (F marks foot mounting) |
| 50 | Frame size 50, entry point of the horizontal range 50 to 90 |
Read left to right, the code fixes gear arrangement, output connection and mounting in three letters and a number. Because those letters are independent, the same size 50 housing is also ordered as a foot-mounted solid-shaft unit - one dimension ladder, several installation styles.
Proven duty points across heavy industry:
- Shaft-mounted belt conveyor head drives without a separate base frame
- Screw conveyor drive points where the trough end shaft carries the unit
- Bucket elevator head sections driven straight on the elevator shaft
- Paddle and ribbon mixers hung on their own mixer shafts
- Rotary valves and vane feeders under silos and hoppers
- Cooler and dryer drum drives in medium-duty process plants
Choosing Between the PHT and PHF Builds
Both builds share the hollow output; they differ in how the unit is held. The PHF foot build is bolted to a bracket or base and suits drives where a foundation point is convenient. The PHT torque-arm build rides on the machine shaft and suits drives where building a base is awkward or where belt-tensioning movement is wanted. For short, stiff machine shafts the torque-arm arrangement is usually the cheaper and quicker installation, and it removes every alignment task except the motor side. WGT can compare both options against the outline drawing before the order is fixed.
Enquiry, Drawing and Delivery
WGT supplies the M-series catalogue and the size 50 outline drawing as PDF downloads, so the bore diameter, keyway or shrink-disc seat and the torque-arm bracket can be checked against the machine shaft before ordering. Send the driven machine, the motor power and speed, the required output speed, the shaft diameter and the daily running hours; the selection is verified against those inputs, quoted in writing, factory-tested and packed in an export wooden crate under a one-year warranty.
Field Applications
Overland conveyor system
A mining company drives a two-kilometre overland conveyor with heavy-duty helical gear units at the head station. Continuous 24-hour duty, frequent starts under full load and minimal maintenance windows were all part of the specification.
Cement plant bucket elevator
A cement works renewed the gear units on its bucket elevators during a kiln shutdown. The new units bolted onto the old foundations without modification, and the elevator was back in service within the planned window.
![where gear reducers are used in industry]()
Where these units are installed across industry.
Selection Example: Screw conveyor trough-end drive
Take a 22 kW motor at 1460 rpm turning a screw conveyor shaft at 41 rpm. The ratio follows directly: 1460 / 41 = 35.6, so a ratio near i=36 is selected. In this case the hollow bore slides onto the trough-end shaft and the torque arm lets the drive swing for belt or chain tensioning. Once the ratio is fixed, check the required output torque against the rating table with the service factor applied - that is what decides the frame, not the ratio alone.
![gearbox selection guide: speed, torque, service factor]()
How a ratio and a frame size are determined, step by step.
Frame Sizes and Typical Duties
| Model | Centre distance | Output | Typical duty |
|---|
| M3PSF50 | size 50 | solid shaft, foot | conveyors, feeders |
| M3PSF60 | size 60 | solid shaft, foot | crushers, mixers |
| M3PSF70 | size 70 | solid shaft, foot | ball mills, shredders |
| M3PSF80 | size 80 | solid shaft, foot | kilns, heavy conveyors |
| M3PSF90 | size 90 | solid shaft, foot | mill and kiln drives |
| M3RSF50 | size 50 | solid shaft, foot, right-angle | inclined conveyors, elevators |
| M3RSF60 | size 60 | solid shaft, foot, right-angle | screw classifiers, feeders |
| M3RHF70 | size 70 | hollow shaft, foot, right-angle | agitators, drum drives |
| M3PHT80 | size 80 | hollow shaft, torque arm, parallel | shaft-mounted conveyors |
| M3RHT90 | size 90 | hollow shaft, torque arm, right-angle | heavy shaft-mounted drives |
The size number is the key dimension that steps up torque capacity through the range: 50 to 90 in horizontal builds, 10 to 90 in vertical builds. Gearing philosophy is shared across the family.
Shutdown Planned? Order Ahead of the Window
Beat the shutdown window. Engineers can size the unit themselves in the WGT Motor & Gearbox Online Selection System - input speed, torque and duty, get the model instantly.
For planned maintenance windows we reserve production capacity and ship the unit ahead of the shutdown date, so the swap takes hours instead of days. Tell us the window and we work back from it. Looking for a gearbox for agricultural machine? Tell us the duty point and we will confirm the model in writing.
Common Questions from Buyers
Which lubrication system does the unit use?
Small and medium frames run on splash lubrication with mineral or synthetic oil. Larger frames or high ambient temperatures can be ordered with forced-feed circulation and cooling coils; the lubricant grade is stated on the nameplate and in the manual.
How often should the oil be changed in heavy duty?
With mineral oil, plan an initial change after the running-in period and then roughly every 5,000 hours. Synthetic oil stretches the interval to around 10,000 hours. Hot environments, dust or frequent starts shorten the interval - we advise the schedule with the quotation.
Can the unit be rebuilt instead of replaced?
Yes. Bearings, seals and gear sets are available as spare internals, and the horizontally split housing allows inspection and reassembly on site. Many operators overhaul units during annual shutdowns instead of buying new.
