Pignons de chaîne en acier soudé WR78 / WH78 | Plaque A 7–20 dents — Acier doux et trempé QT400

Pignons de chaîne en acier soudé 1

La Corée toujours puissante WR78/WH78 welded steel chain A-plate sprockets cover 7 to 20 teeth at 2.609-inch pitch — compatible with both WR78 offset sidebar chain and WH78 welded steel mill chain. Available in mild steel or QT400 hardened steel, and in solid, split-to-bolt, or split-for-welding construction. Non-metallic idler bodies in brass, nylon, or UHMW with grease grooves and grease fittings are available for applications requiring lubrication-free or corrosion-resistant idler positions.

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WR78 and WH78 Welded Steel Chain — Construction, Differences, and Sprocket Compatibility

Welded steel chain is a category of heavy-duty engineering chain where the chain links are formed by stamping and welding thick steel plates — fundamentally different from both pintle chain (cast iron links) and roller chain (assembled pin-bushing-roller construction). The welded construction creates a chain with no separate inner/outer plate components: each link is a single continuous welded steel element, giving these chains exceptional resistance to the lateral bending and impact loads encountered in bucket conveyor, drag conveyor, and heavy agricultural applications.

 Pignons de chaîne en acier soudé 1

The WR78 and WH78 designations cover two closely related chains at the same 2.609-inch pitch:

WR78 — Offset Sidebar Welded Steel Chain
WR78 is constructed with offset sidebars — each link's sidebar is bent at an angle that causes adjacent links to interlock at their crossing points. The offset geometry provides a tighter, more compact chain construction that is resistant to twisting under off-axis loads. The "R" indicates the standard (regular) construction. WR78 is the most common specification for agricultural drag conveyors, grain elevators, and light industrial drag chain applications.
WH78 — Mill and Heavy Welded Steel Chain
WH78 uses a heavier sidebar cross-section than WR78 — the "H" indicates heavy construction. Same 2.609-inch pitch, same barrel diameter (0.875 inches), same tooth face (1.000 inch), making WH78 directly compatible with the same sprockets as WR78. WH78 is specified when the application requires higher breaking load — cement plant raw material conveyors, steel slag handling, and industrial applications where impact loading exceeds the WR78 rating. Both chains use identical sprockets: any sprocket listed as WH78-A also works with WR78.

The A-plate sprocket style has no hub projection — the sprocket is a flat disc with the tooth profile cut into the outer edge and a through-bore in the centre. This is the standard configuration for welded steel chain drives where the sprocket is keyed to the shaft and retained with collars or shaft shoulders.

For detailed WR78 welded steel chain specifications including breaking loads, attachment configurations, and compatibility with XHD construction variants, technical reference data is available on request from Korea Ever-Power before ordering.

Three Construction Options — Solid, Split-to-Bolt, Split-for-Welding

WR78/WH78 A-plate sprockets can be manufactured in three structural configurations, each suited to a different installation and maintenance scenario:

Solid Construction — Standard, Maximum Strength
The standard A-plate is machined from a single solid billet. Maximum structural integrity and tooth root strength. Required for high-shock applications and drives where the sprocket must transmit high torque through a keyway. Replacement requires shaft removal if the shaft end is not accessible — the sprocket must be slid off the shaft end.
Split-to-Bolt — Two Halves, Field Replaceable Without Shaft Removal
The sprocket is machined in two halves that bolt together around the shaft. Allows complete sprocket replacement without removing the shaft from its bearings — identical maintenance advantage to the split sprockets described in the 81X series page. Split-to-bolt construction is precision-matched: the two halves are machined together as a matched set and must be replaced as a pair. Slightly higher cost than solid; justified by the maintenance time savings on busy conveyor lines.
Split-for-Welding — Two Halves, Welded Onto Shaft Stub
The sprocket is supplied as two halves for field welding onto a fabricated shaft stub or conveyor drive component. This construction is used in custom-fabricated conveyor equipment where the shaft is not a standard machined component — the sprocket halves are positioned and welded to the fabricated shaft during equipment assembly. Not suitable for retrofit replacement; only for new fabrication or major reconstruction.

WH78 A-Plate Sprocket Specifications — 7 to 20 Teeth

All dimensions in inches. Pitch is 2.609 inches for all sizes (same as 81X series). Barrel diameter and tooth face are consistent across the range (0.875″ and 1.000″ respectively). Maximum bore increases with tooth count from 2.1875″ (7T) to 5.9375″ (20T).

Welded Steel Chain Sprockets Dimension

Sprocket # Dents Pitch (in) Pitch Dia. Style Shroud Dia. Barrel Dia. Tooth Face Alésage maximal Poids
WH78-A7 7 2.609″ 6.01″ Plaque A 4.150″ 0.875″ 1,000″ 2.1875″ 7.5 lb
WH78-A8 8 2.609″ 6.82″ Plaque A 5.040″ 0.875″ 1,000″ 2.4375″ 9.0 lb
WH78-A9 9 2.609″ 7.63″ Plaque A 5.920″ 0.875″ 1,000″ 2.6875″ 11.0 lb
WH78-A10 10 2.609″ 8.44″ Plaque A 6.776″ 0.875″ 1,000″ 2.9375″ 14.0 lb
WH78-A11 11 2.609″ 9.26″ Plaque A 7.640″ 0.875″ 1,000″ 3.4375″ 17.0 lb
WH78-A12 12 2.609″ 10.08″ Plaque A 8.500″ 0.875″ 1,000″ 3.4375″ 20.0 lb
WH78-A13 13 2.609″ 10.90″ Plaque A 9.350″ 0.875″ 1,000″ 3.9375″ 23.0 lb
WH78-A14 14 2.609″ 11.72″ Plaque A 10.180″ 0.875″ 1,000″ 4.9375″ 27.0 lb
WH78-A15 15 2.609″ 12.55″ Plaque A 11.030″ 0.875″ 1,000″ 4.9375″ 31.0 lb
WH78-A16 16 2.609″ 13.37″ Plaque A 11.860″ 0.875″ 1,000″ 4.9375″ 35.0 lb
WH78-A17 17 2.609″ 14.20″ Plaque A 12.710″ 0.875″ 1,000″ 4.9375″ 38.0 lb
WH78-A18 18 2.609″ 15.02″ Plaque A 13.550″ 0.875″ 1,000″ 4.9375″ 41.0 lb
WH78-A19 19 2.609″ 15.85″ Plaque A 14.380″ 0.875″ 1,000″ 4.9375″ 44.0 lb
WH78-A20 20 2.609″ 14.20″ Plaque A 12.710″ 0.875″ 1,000″ 5.9375″ 47.0 lb

Material Selection — Mild Steel vs. QT400 Quench-and-Tempered Steel

WR78 WH78 welded steel chain sprocket material mild steel QT400 hardened

WR78/WH78 A-plate sprockets are available in two material grades with significantly different performance characteristics:

Propriété Mild Steel QT400 (Quench and Tempered)
Yield strength 250 MPa (36,000 psi) 400 MPa (58,000 psi) minimum
Tooth face hardness 120–160 HB (as-machined) 300–360 HB (through-hardened)
résistance à l'abrasion Modéré Excellent
Machinability (bore machining) Easy — standard tooling Moderate — harder tooling required
Best application Light-to-medium agricultural, low abrasion Industrial abrasive, high-speed, high-load
Délai de mise en œuvre From stock 3–4 weeks production

QT400 is specified for cement plant, steel slag handling, and industrial conveyor applications where the higher hardness is needed to resist abrasion from the conveyed material contacting the sprocket tooth face. For standard agricultural grain drag conveyors and light industrial material handling, mild steel provides adequate service life at lower cost.

Non-Metallic Idler Bodies — Brass, Nylon, and UHMW with Grease Fittings

WR78/WH78 idler positions (non-driving take-up sprockets) can be supplied with non-metallic bodies in brass, nylon, or UHMW-PE instead of steel. These configurations include grease grooves machined into the barrel contact surface and standard grease fittings for periodic lubrication. The non-metallic body reduces the friction coefficient at the chain-to-sprocket contact, which is particularly valuable at idler positions where the chain contacts the sprocket without transmitting torque — minimising the drag that a steel-on-steel contact would otherwise impose on chain tension.

Brass idler bodies are specified for wet or corrosive environments where steel would corrode. Nylon bodies are used where weight reduction matters. UHMW bodies (with the lowest friction coefficient) are the preferred specification for idler positions in cement and aggregate applications where abrasive dust contacts the sprocket — UHMW resists abrasive wear better than nylon at these contact conditions. All three materials are available with the standard WR78/WH78 tooth profile and any bore size within the sprocket's maximum bore limit.

Where WR78/WH78 Welded Steel Chain Sprockets Are Used

🌾 Agricultural Drag Conveyors

WR78 welded steel chain sprocket agricultural drag conveyor grain handling

Korean grain storage facilities and feed mills use WR78 chain on drag conveyors and grain chain conveyors where the chain pulls flight paddles through a U-trough. The WH78-A9 and WH78-A10 are common for standard grain drag applications; larger tooth counts for the slower return sections. Mild steel sprockets are adequate for most seasonal grain handling duty.

🏭 Cement and Aggregate Handling

WH78 welded steel chain sprocket cement aggregate handling QT400

Korean cement plants use WH78 chain on clinker and raw material drag conveyors where the abrasive material in contact with the chain requires QT400 hardened sprockets. The split-to-bolt construction is increasingly specified at head shaft positions to allow sprocket replacement during scheduled maintenance windows without dismantling the entire conveyor head assembly.

⚙ Custom Fabricated Conveyor Equipment

WR78 welded steel chain sprocket split-for-welding custom fabricated conveyor

Korean conveyor equipment fabricators building custom drag and bucket conveyors for industrial clients use split-for-welding WH78 A-plate sprockets where the shaft is a fabricated component rather than a machined shaft. The weld-in construction is integral to the conveyor design, allowing the sprocket to be sized and positioned precisely during fabrication. Both WR78 and WH78 chain compatibility ensures the client's existing chain is supported.

Pourquoi choisir la chaîne et le pignon Korea Ever-Power ?

Korea Ever-Power WR78 WH78 welded steel chain sprocket manufacturing

Korea Ever-Power Chain and Sprocket Co., Ltd. supplies WR78/WH78 A-plate sprockets with full material and construction options:

✦All 14 standard tooth counts (7T–20T) in mild steel stock; QT400 hardened to order 3–4 weeks
✦Three construction types — solid, split-to-bolt, split-for-welding; specify construction when ordering
✦Non-metallic idler bodies — brass, nylon, UHMW with grease grooves and fittings available to order
✦Precision hobbed option — high-speed applications requiring tighter tooth profile tolerance can be specified as precision hobbed at order
✦Custom bore to maximum bore — keyway to ASME B17.1 or customer drawing; split-to-bolt matched-pair bore machined simultaneously for concentric tooth profile

Foire aux questions

Can WH78-A sprockets be used interchangeably with 81X sprockets since both have 2.609-inch pitch?
No. 81X chain is an ANSI engineer class roller chain with a 2.609-inch pitch but a different roller diameter and link geometry from WR78/WH78 welded steel chain. The sprocket tooth profile is designed for a different chain cross-section. An 81X sprocket's tooth form does not correctly seat the WH78 chain barrel (0.875-inch diameter), and a WH78 sprocket's barrel seat does not match the 81X chain's roller geometry. The identical pitch is coincidental — the chain and sprocket systems are not interchangeable. Always verify the chain designation before ordering sprockets.
What is the "shroud diameter" in the specification table?
The shroud diameter is the outside diameter of the smooth cylindrical surface between the tooth tips — it is the diameter that the chain links ride over as they approach the tooth engagement zone. In welded steel chain, the chain link's inner guide rail contacts this shroud surface as the chain wraps onto the sprocket, centring the chain laterally on the sprocket face. The shroud diameter must be smaller than the chain link's inner gauge dimension to allow correct chain seating. This dimension is important when designing the conveyor trough to ensure the sprocket clears the trough walls at the chain inlet.
When should I use QT400 instead of mild steel?
QT400 is the correct specification when any of these conditions are present: the conveyed material is abrasive (stone, aggregate, clinker, slag, coarse grain with grit contamination); chain speed is above 60 fpm; operating hours exceed 2,000 per year; or the drive requires maximum tooth engagement precision (precision hobbed QT400 for high-speed applications). For seasonal agricultural grain handling below 50 fpm, mild steel is cost-effective. If you are unsure, describe your operating conditions and Korea Ever-Power will recommend the correct material before your order.

Avis clients

Verified feedback from Korean customers.

Kim Jong-hwan, Conveyor Engineer, Cement Plant, North Chungcheong (early 2025)

"WH78 chain drag conveyors throughout our cement plant. Switched to QT400 hardened WH78-A10 and WH78-A12 sprockets from Korea Ever-Power two years ago after mild steel units were wearing out in 7–8 months in our clinker dust environment. QT400 sprockets are currently at 16 months with acceptable tooth wear. The material specification recommendation from Korea Ever-Power before our order was correct."

Park Hyun-jin, Agricultural Equipment Fabricator, Jeonbuk (2024)

"We build custom grain drag conveyors for Korean feed mills and storage cooperatives. WR78 chain with mild steel WH78-A9 and WH78-A11 A-plate sprockets. Korea Ever-Power supplies split-for-welding construction for our fabrication work — we weld the sprocket halves to our fabricated shaft stubs during assembly. Consistent dimensional accuracy across multiple orders over 14 months."

Oh Tae-jun, Maintenance Engineer, Aggregate Processing Plant, Gangwon (Q3 2024)

"We installed split-to-bolt WH78-A12 sprockets on our head shaft positions. The previous solid construction required 3+ hours to replace per sprocket due to shaft removal. Split-to-bolt installation reduced that to 35 minutes per position. Korea Ever-Power confirmed the matched-pair machining for the split halves — the bore concentricity is correct on all installed units."

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