Chain Conveyor

What is a Chain Conveyor

A chain conveyor is a continuous material-handling machine in which one or more endless chains, driven by toothed sprockets, transport material or unit loads along a fixed path. The defining feature is positive engagement: the sprocket teeth mesh with the chain pitch, so the load advances in exact step with the drive shaft without the slip a friction belt can suffer. That positive drive is what lets a chain conveyor index a part to a precise station, climb a steep incline without back-slip, and transmit the very high pull that bulk and heavy-unit handling demands.

Functionally a chain conveyor has four elements. First, the chain itself, a flexible tension member built from interlocking links with pins, bushings and (often) rollers that mesh with the sprockets. Second, the carrying medium attached to the chain: flights or scraper bars for bulk, overlapping pans for apron units, slats for unit loads, or the integral plate of a flat-top chain. Third, the sprockets and drive, a geared-motor turning a head sprocket while a tail sprocket and take-up keep the chain tensioned. Fourth, the frame and trough or track that guide and support the running chain and contain the material.

Chain conveyance is one of the oldest powered handling methods. Bucket-and-chain water lifts predate the industrial era, and by the late nineteenth century welded and cast detachable mill chain moved grain, coal and castings through American and European works. The twentieth century split the field into two streams: precise short-pitch roller chain derived from transmission practice, codified for the inch world by ANSI B29.1 and the American Chain Association, and large-pitch steel conveyor chain for bulk duty, codified in metric form by ISO 1977 and the German DIN 8167 and DIN 8165 series. CEMA, the Conveyor Equipment Manufacturers Association, standardized the North American mill-chain families still quoted today.

The application scale is enormous. A single tabletop chain in a bottling hall may carry a few kilograms of containers at a gentle pace, while an apron feeder under a primary crusher in a copper mine carries lumps up to several cubic metres and delivers up to 6,000 t/h. En-masse grain conveyors move 100 to 500 m3/h with almost no kernel breakage. Because the load, abrasion, temperature and timing requirements vary by orders of magnitude, there is no universal chain conveyor: selection is the act of mapping a specific duty onto a specific chain pitch, breaking load, carrying medium and material grade.

The chain conveyor also occupies a distinct niche against the alternatives. A belt conveyor is cheaper, quieter and faster for light, cool, free-flowing bulk and parcels, but its elastomer or fabric surface fails under heat, sharp edges and heavy point loads. A screw conveyor is compact and fully enclosed for short bulk runs, but it degrades friable material and cannot carry units. A pneumatic conveyor moves fine powder through pipe over complex routes, but it consumes far more energy per tonne. The chain conveyor wins precisely where those alternatives struggle: hot, heavy, abrasive, lumpy or corrosive material, steep inclines, and any duty needing positive timing. Reading the family boundaries this way prevents the common error of forcing one conveyor type onto a duty that another handles for less money and less maintenance.

Four engineering realities decide whether a chain conveyor is the right choice and which family fits: the nature of the load (bulk solid versus discrete unit), the duty severity (abrasion, impact, temperature, corrosion), the required pull and therefore chain size, and the maintenance regime the site can sustain, since steel chain demands lubrication and periodic wear measurement. Get these four right and a chain conveyor outlasts a belt by years in punishing service; get them wrong and the chain elongates, jumps sprockets and stops the line.

Chain Conveyor Types

Industrial chain conveyors split into four working families, distinguished by how the load sits on the chain and whether the material is bulk or discrete. Choosing the wrong family is the costliest early mistake: a slat conveyor will never move free-flowing powder, and a drag conveyor cannot index a packaged carton. The table below compares the four families on the variables that drive the decision.

Drag and en-masse conveyors pull bulk material along an enclosed trough using flights or skeletal bars attached to the chain. In a classic scraper drag, the flights drag a layer of material across the trough floor and fill roughly 40 to 50 percent of the cross-section. In an en-masse conveyor the flights are sized and spaced so the whole charge moves as a coherent mass: inter-particle friction carries the material above the chain, filling 80 to 90 percent of the housing and so delivering the same throughput in a far smaller, fully enclosed cross-section with low breakage. En-masse units handle grain, sugar, flour, fly ash and biomass at 100 to 500 m3/h, and their slow 0.1 to 0.5 m/s speed minimises both product degradation and chain wear.

Apron conveyors and apron feeders carry heavy, lumpy, hot or sharp material on overlapping steel pans (aprons) bolted to one or two strands of heavy roller chain. They are the workhorse under crushers and stockpiles in mining, quarrying, cement and steel. Reported capacities run from about 10 t/h on small units to 4,000 to 6,000 t/h on the largest, with pan widths from roughly 0.3 m to 4.5 m (1 to 15 ft) and several standard chain sizes. A general field guide sizes pan width at about twice the maximum lump size to prevent bridging. Because the pans absorb direct dump impact, apron feeders survive duty that would shatter a belt.

Slat conveyors fix rigid slats (steel, aluminium or hardwood) crosswise between two chain strands to make a moving flat surface for discrete unit loads. They suit heavy, hot or oily parts such as engine blocks, castings, drums and pallets, and assembly lines where parts must be carried at a controlled pace through paint, wash or cure stations. Slats give a stable platform that a belt cannot under point loads, and the steel chain tolerates the heat and solvents of finishing lines.

Flat-top and tabletop chain conveyors use a single articulating chain whose top plates form the carrying surface, so containers ride directly on the chain. Pin pitches of 25.4, 31.75, 38.1 and 63.5 mm are common, in stainless steel for wet, hygienic, higher-load lines and in engineering plastic (acetal, PP, PE) for dry, quiet, corrosion-free running. They are the backbone of beverage and food container handling, where side-flexing plastic versions also negotiate curves and merges that rigid two-strand conveyors cannot. Speeds reach roughly 0.75 m/s, and because the chain runs dry on a wear strip, the line is easy to wash down and free of lubricant contamination, a decisive advantage in food, pharmaceutical and clean packaging plants.

Two boundary cases sit at the edges of these four families. Drag-chain cable carriers (energy chains) protect and guide moving cables and hoses on machine tools and robots; they share the name but are an enclosure, not a material conveyor, and should not be confused with bulk drag conveyors during a parts search. Tubular drag conveyors enclose a chain of solid discs in a pipe and route gently around bends in three dimensions, bridging drag and pneumatic practice for fragile or dusty powders. Knowing these edge cases keeps a specification from drifting into the wrong product category.

Conveyor Chain Construction and Grades

The chain is the heart of the machine, and its construction determines breaking load, wear life and how attachments mount. By construction, industrial conveyor chain falls into four broad groups: bush chain, roller chain, hollow-pin chain, and cast or welded mill chain. The table below compares them on the engineering variables that drive selection.

Bush chain (DIN 8165, FV) omits the outer roller: the bushing rides directly on the sprocket tooth. This double drag-link chain of inner and outer links is economical and tolerant of dirt, which suits slow scraper and light bulk duty where the absence of a roller is acceptable. DIN 8165 and the closely related DIN 8167 (the M-series bush and roller conveyor chains) define the metric pitches and dimensions that ensure links and complete chains are interchangeable for repair.

Metric M series solid-pin roller chain is the mainstream heavy conveyor chain, conforming to ISO 1977 and DIN 8167. The designation encodes the minimum breaking load in kilonewtons: M20 is rated 20 kN, and the series runs through M40, M56, M80, M112, M160, M224, M315, M450, M630 up to M900 at 900 kN, with pitches spanning roughly 40 mm to 600 to 630 mm. Larger pitch and breaking load suit heavier, slower bulk and apron duty; the engineer selects the smallest chain whose breaking load gives an adequate safety factor over the calculated working pull.

Hollow-pin chain (MC series) replaces the solid pin with a tube, so attachments, cross rods, slats or pans can be fixed through the pin from the outer plates without splitting the chain. It shares the ISO 1977 and DIN 8167 strength grades of the solid-pin M series and is favoured wherever slats, buckets or aprons must be bolted across two strands, because it simplifies assembly and field replacement of carrying elements.

ANSI attachment chain (ANSI B29.1, ISO 606) is transmission-style short-pitch roller chain fitted with bent (K) or straight (A) attachment plates. Standard inch pitches are 12.7 mm (ANSI 40, 1/2 in), 19.05 mm (ANSI 60, 3/4 in), 25.4 mm (ANSI 80, 1 in), 31.75 mm (ANSI 100, 1-1/4 in), 38.1 mm (ANSI 120, 1-1/2 in) and 50.8 mm (ANSI 160, 2 in). Attachment codes are standardized: A1 and A2 plates carry holes in the link-plate plane, K1 and K2 plates bend perpendicular to it with one or two mounting holes. This chain drives lighter slat, flat-top and packaging conveyors.

Material grade is the second axis. Carbon-steel chain (heat-treated alloy pins and bushings) is the default for strength and abrasion. Stainless grades (304, 316) resist corrosion in wet, hygienic and chemical lines at some loss of strength. Surface treatments such as nickel plating, zinc and dacromet extend life in mild corrosion, while engineering-plastic chains (acetal, PP, PE) run dry and quiet for light food duty. For abrasive bulk, hardened or through-hardened pins and bushings, sealed or self-lubricating joints, and induction-hardened tooth surfaces on the sprockets all extend service life.

Capacity, Chain Pull and Standards

Two calculations decide a chain conveyor specification: how much it must carry (capacity) and how hard it must pull (chain tension, which sets the chain size and motor). Both are straightforward once the duty is defined, and both trace to published methods rather than guesswork.

Capacity for bulk conveyors is the loaded cross-section area multiplied by chain speed and a fill factor, then converted to mass by the material bulk density. Because en-masse conveyors fill 80 to 90 percent of the housing against 40 to 50 percent for plain scraper drags, an en-masse unit reaches a target throughput in a smaller, enclosed cross-section. For apron feeders a long-standing field formula is T = 5 w d s / c, where T is tons per hour, w is the effective pan width in feet, d is the material bed depth in inches, s is the speed in feet per minute, and c is the cubic feet of broken material per ton. For unit-load slat and flat-top conveyors, capacity is simply parts per minute, governed by part pitch and line speed, and bulk density is irrelevant.

Chain pull is the sum of three components, a structure the KWS drag-conveyor method makes explicit. Empty horsepower (HPE) moves the chain, flights and sprockets and equals chain weight per unit length times length times speed times a friction factor, divided by 33,000 (in US units). Live horsepower (HPL) overcomes material friction in the trough on the same form using material weight per unit length and a material friction factor. Lift horsepower (HPH) raises the material through any vertical height and equals material mass rate times height divided by 33,000. The three sum and divide by drive efficiency to give total power, and the chain working pull follows from power and speed.

Friction factors are duty-specific and often confirmed by test, but the ranking is stable: steel chain sliding on a polymer (UHMW) wear bar has a far lower friction factor than steel on steel, which is why lined troughs cut both power and wear. A service factor of 1.0 to 1.5 is then applied to the calculated pull for shock, loading frequency, environment and operating hours, and the chain is selected so its minimum breaking load gives a safety factor of roughly 8 to 10 over the service-factored working pull.

The table below maps the governing standards so a specification can cite the right document. Always confirm the exact pitch, breaking load and attachment code against the maker catalog, because catalog values are the contractual numbers.

Key Specification Parameters

Reading a chain conveyor and chain spec sheet is a core procurement skill. A vendor proposal may list dozens of lines, but eight parameters truly drive the decision: chain pitch, minimum breaking load, attachment code, chain and conveyor speed, capacity, carrying-element width, material and surface grade, and drive power. Each is explained below, with the comparison table for the key chain numbers.

Chain pitch is the centre-to-centre distance between adjacent pins and the master dimension of any chain. It must match the sprocket exactly, and it sets the resolution of indexing and the chordal speed variation. Larger pitch lowers cost per metre and tolerates lumpy duty, but raises chordal action, so low tooth counts (below 17) on large-pitch chain produce a pulsing speed that a high-precision line cannot accept.

Minimum breaking load is the rated ultimate tension. Manufacturers may quote minimum, average and ultimate tensile values; the minimum is the design figure. The working pull must stay well below it, with a safety factor of roughly 8 to 10 after the service factor, because fatigue, shock and corrosion all erode real-world strength below the static rating.

Attachment code defines how the carrying medium fixes to the chain: A1 and A2 plates in the link plane, K1 and K2 bent plates perpendicular to it, plus extended pins, cross rods and shrouds. The code must be specified at order because retrofitting attachments to plain chain is rarely practical.

Chain and conveyor speed trade throughput against wear and noise. Drag conveyors run slow (0.1 to 0.5 m/s) to limit degradation and chain wear; flat-top container lines run faster (up to roughly 0.75 m/s). Speed also drives chordal vibration and the lubrication interval.

The remaining parameters follow from duty. Capacity (t/h or m3/h for bulk, parts/min for unit loads) must include a margin for surge. Carrying-element width (pan, slat or chain width) sizes to the load and, for apron feeders, to about twice the maximum lump. Material and surface grade (carbon, 304/316 stainless, nickel-plated, hardened) match corrosion, temperature and abrasion. Drive power follows from the chain-pull calculation, sized with headroom for start-up and the highest fill condition.

Selection Decision Factors

To turn the preceding chapters into a specific machine, follow the decision sequence below. Most selection failures come not from one wrong number but from deciding chain size before the load and duty are pinned down. These eight steps form a reusable RFQ template.

1. Load type and family: First decide bulk solid versus discrete unit. Bulk routes to drag, en-masse or apron; units route to slat or flat-top. This single choice eliminates most of the catalog.
2. Material and duty profile: Characterise bulk density, lump size, abrasiveness, moisture, temperature and corrosivity, or for units the weight, footprint and surface. These set fill factor, friction factor and material grade.
3. Capacity and speed: Fix required throughput (t/h, m3/h or parts/min) and derive chain speed from cross-section and fill, keeping bulk drag conveyors in the 0.1 to 0.5 m/s band to limit wear.
4. Chain pull and chain size: Compute empty, live and lift power, apply a 1.0 to 1.5 service factor, and select the M-series or ANSI chain whose minimum breaking load gives a safety factor near 8 to 10 over the working pull.
5. Carrying medium and attachment code: Choose flights, pans, slats or flat-top plate, then the matching attachment code (A1/A2, K1/K2, hollow-pin cross rod). Size pan or slat width to the load and, for feeders, to twice the lump.
6. Frame, trough and wear protection: Specify trough liner (UHMW or hardened steel) to cut friction power and wear, take-up type for chain elongation, and enclosure for dust or hygiene. Match sprocket material and hardness to the chain.
7. Drive, controls and standards: Select geared-motor and VFD for the worst-case start and fill, and cite the governing standards (ISO 1977, DIN 8167/8165, ANSI B29.1, CEMA) plus any plant safety and hygiene codes in the specification.
8. Total cost of ownership: Add lubrication, periodic wear measurement, chain and sprocket replacement, and downtime to the purchase price. A chain run dry or never gauged reaches the 2 to 3 percent elongation replacement limit far sooner than a lubricated, monitored one.

One dimension is routinely overlooked at the buying stage: serviceability and wear management. Steel chain elongates as the pin-and-bushing joints wear, and most makers set replacement at 2 to 3 percent elongation over nominal pitch, measured with a wear gauge or tape across a span of links. Plan for scheduled lubrication (the single biggest lever on chain life), connecting-link and spare-pan inventory, and accessible take-ups. Renold, Tsubaki, John King Chains, SKF and SEDIS for chain, and FEECO, KWS, CDM Systems, MEKA, McLanahan, AUMUND and HAZEMAG for complete conveyors and apron feeders, all maintain spare-part and service networks; confirm local availability before committing, because a stalled chain line stops the process behind it.