This revision restores the actual Playford topology from the patent and historical references: hopper, adjustable gate, sprocket-driven link grate, bridge-wall return drum and ash return. The worksheet reports exact declared chain-pitch kinematics only.
Playford Traveling-Grate Geometry Explorer
Enter declared link pitch, sprocket tooth count, sprocket speed and exposed grate run. The worksheet reports pitch diameter, exact chain advance per revolution, ideal grate speed and nominal run residence time.
Equation Used
- The grate chain has uniform declared pitch p and engages a sprocket with integer tooth count Z.
- One sprocket revolution advances the ideal chain exactly Z pitches.
- Sprocket speed is constant and there is no slip, polygonal speed fluctuation, backlash or elastic stretch.
- Exposed-run residence is declared run length divided by ideal grate speed.
- The hopper gate and fuel layer are qualitative and do not establish bed depth or mass delivery.
- Fuel properties, loading, combustion, air flow, heat, ash, strength, wear, controls, boiler ratings and safety are excluded.
Corrects the mechanism identity from a fictional reciprocating ram to the documented Playford traveling link grate and limits outputs to exact declared pitch kinematics.
The Playford uses a traveling link grate
George Playford's US patent 547,738 describes reversible grate bars linked into chains and propelled by sprocket-wheel pin projections. His mechanical-stoker furnace patent US570268A likewise centers on a traveling grate and its supporting and operating mechanism.
Hiscox states that a sprocket shaft moves the link grate, carrying hopper-fed coal forward under the boiler, returning over a drum at the bridge wall, while a screw conveyor brings ash and clinker toward the pit.
A hopper gate regulates the layer, not a ram dose
Hiscox's Playford model shows a hopper feeding a traveling grate and a rack-and-gear gate regulating coal-feed depth. The animation therefore shows continuous grate transport rather than a fictional reciprocating slug and distributor plate.
Use chain-pitch and sprocket geometry
For a regular Z-tooth chain sprocket, adjacent pitch points form chords p on its pitch circle, giving pitch diameter p/sin(pi/Z). One revolution engages Z pitches, so ideal chain advance is Zp and constant grate speed is Zpn. Declared run residence is L/v.
A declared pitch-kinematics example
With 100 mm pitch and 12 teeth, pitch diameter is 386.4 mm and one revolution advances 1.200 m of chain. At 1.00 rpm, ideal grate speed is 1.200 m/min and a 6.0 m exposed run has nominal residence time 5.00 minutes.
Grate speed is not fuel or boiler performance
The former page modeled a reciprocating ram that is not the documented Playford mechanism. Its ram area, stroke, fill factor and coal-flow outputs are removed.
Unsupported fuel sizes, burning rates, clearances, plate angles, firing advice, failure diagnosis, maintenance intervals, named installations and recommissioning guidance are also removed. Actual furnaces and boilers require qualified engineering, applicable codes and manufacturer or site-specific operating procedures.
Playford stoker questions
Is the Playford a reciprocating ram feeder?
No. The cited Playford sources describe a traveling link grate.
Does grate speed determine coal mass flow?
No. Mass flow also depends on actual gate opening, bed shape, bulk behavior and other properties not modeled.
Does residence time predict combustion completeness?
No.
Can this worksheet be used to operate a boiler?
No.
Playford stoker references
- US 547,738, Playford traveling grate for furnaces: reversible link-grate bars, link chains and sprocket-wheel propulsion.
- US 570,268, Playford mechanical-stoker furnace: traveling grate and its supporting and operating mechanism.
- Hiscox, Mechanical Movements, Steam Power: Playford link grate, sprocket shaft, hopper, bridge-wall return drum and ash/clinker screw conveyor.
- Library of Congress, Twentieth Century Hand-Book for Steam Engineers: period description of the Playford traveling-chain grate construction.
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