Conveyor Chain

What is a Conveyor Chain

A conveyor chain is an articulated steel chain whose primary job is to carry product, not to transmit power between shafts. It runs slowly over guide rails or wear strips, drawing slats, aprons, buckets, flights, or pusher dogs along a fixed path. The chain converts the rotation of a drive sprocket into linear movement of material, and because the load sits on or beside the chain rather than being transmitted through it, the geometry is optimized for a wide, flat, attachment-friendly profile rather than for the compact figure-eight plates of a transmission chain.

Structurally, every conveyor chain is built from the same four families of parts: pin links (two pins pressed into two outer plates), roller or bush links (two bushings pressed into two inner plates, with or without rollers), the bearing pins themselves, and the attachments that bolt or weld product-carrying hardware to the chain. The pin articulates inside the bushing, and that pin-and-bushing joint is the single bearing surface where wear and elongation accumulate over the chain's life. A roller, when fitted, rides on the bushing and rolls along the conveyor track to reduce friction.

The distinction from a transmission roller chain matters commercially because the two are priced and stocked separately. A transmission chain to ISO 606 or ANSI B29.1 has a short pitch, hardened figure-eight plates, and is designed to wrap small sprockets at high speed. A conveyor chain has a long pitch, straight sidebars that give a flat surface for bolting attachments, larger rollers that span a guide rail, and is designed to run slowly under high static tension. Double-pitch chain, which doubles the transmission pitch while keeping standard roller and pin components, is the deliberate bridge between the two worlds.

The application scale is broad. Light packaging and pallet conveyors use double-pitch chain in the 19 to 50 mm pitch range carrying a few kilograms per attachment. Bottling, automotive assembly, and food lines use slat and table-top chain. Bulk handling, cement, sugar, forest products, and wastewater plants use heavy M-series and welded steel mill chain at pitches from 100 to 600 mm and breaking loads from tens of kilonewtons to nearly a meganewton, carrying tonnes of material per metre of conveyor. No single chain spans this range; selection is the act of matching pitch, breaking load, roller type, material, and attachment to the duty.

Four engineering metrics determine conveyor chain quality and total cost of ownership: minimum breaking load against the calculated chain pull, wear resistance at the pin-bushing joint, corrosion and abrasion resistance of the wetted or contacting surfaces, and the attachment system that carries the product. A chain that is undersized on breaking load fails catastrophically; a chain that is correctly sized but wears quickly elongates past 3 percent, destroys its sprockets, and forces an unplanned line stop. The chapters that follow address each of these in turn.

Conveyor Chain Types and Classification

Conveyor chains are classified first by construction. The five families below cover almost all industrial conveying duties. Choosing the wrong family is the most common selection error, because a chain of adequate breaking load in the wrong construction may still be unsuitable for the speed, abrasion, or attachment pattern the application demands. The table summarizes the families before the text explains each.

Double-pitch roller chain uses the same pins, bushings, and rollers as standard ANSI transmission chain but with link plates twice as long, so the pitch is exactly double its transmission counterpart. The C-series, C2040 through C2080H, gives a long, straight, flat sidebar that is ideal for bolting small attachments and a large roller for conveying. It is the cheapest entry into chain conveying and is correct for light to moderate loads at low to moderate speed, but its small components limit it to a few kilonewtons of working load.

Solid-pin bush chain, the ISO 1977 and DIN 8167 M-series, is the workhorse of heavy conveying. A bushing is pressed or welded between the inner plates, a solid pin is riveted or welded through the outer plates, and plain or flanged rollers ride on the bushing. The M-series spans a wide strength and pitch range and accepts welded sidebars for higher breaking load. It is specified for apron feeders, drag and slat conveyors, and bulk material handling where the load is high and the speed low.

Hollow-pin chain replaces the solid pin with a hollow tube. The bore lets attachments bolt straight through the chain without welding, and because the link plate pitch is twice that of the equivalent base-series chain, attachments sit at a regular spacing. Hollow-pin chain is the natural choice for slat conveyors, apron feeders, and bucket elevators where flights must be removable for cleaning, repair, or product changeover, and where two strands are joined by cross-rods into a wide carrying bed.

Welded steel mill chain, such as the WH and WR series, is an engineering-class chain with a precision weld around the outside of the barrel that ties the two sidebars together. Every component is heat-treated alloy steel, giving very high breaking load in a compact pitch. It dominates the harsh, abrasive, high-load duties of forest products, lumber mills, sugar, grain, pulp and paper, and bulk material handling. Cast and pintle chain uses cast malleable iron or steel links with no rollers; it handles medium loads at low speed, tolerates abrasive and hot media (malleable iron pintle chain operates to roughly 315 degrees Celsius), and is common on drag conveyors and elevators.

Standards and Strength Classes

Three standards govern most of the conveyor chain market, and a chain should always be specified against one of them rather than by a maker's part number alone. The metric world uses ISO 1977 and the equivalent national DIN 8167 (M-series) and DIN 8165 (FV-series, drop-forged). The ANSI world uses ASME B29.4 for double-pitch chain and ASME B29.15M for steel roller-type conveyor chains. Engineering-class welded steel chain is largely proprietary, dimensioned by maker catalogues that follow common industry practice rather than a single published standard.

ISO 1977:2006 specifies the characteristics of bush, plain-roller, and flanged-roller chains of both solid and hollow bearing-pin types for general conveying and mechanical handling, together with the associated sprockets and attachments. Its strength classes are the M-series, where the number after the M is the chain's minimum breaking load in kilonewtons. The table below lists the M-series classes with their pitch range and nominal minimum breaking load; heat-treated sidebars raise the breaking load above these figures.

The construction column matters because it sets the breaking load and the price. For the smaller classes (roughly M20 to M56), a pressed bush with a riveted pin is standard. For mid classes (around M80 to M160), the pin may be welded or riveted and the bush pressed. For the large classes (M224 and above), both the bush and the pin are typically welded, which is what allows breaking loads to reach 900 kN at 600 mm pitch. Welded sidebar variants of any class raise the breaking load above the nominal kilonewton designation by a meaningful margin.

On the ANSI side, double-pitch chain is built to ASME B29.4. The C-series doubles a transmission pitch while keeping standard pins, bushings, and rollers, which keeps cost low. The table below lists representative C-series sizes by pitch and average tensile strength; the H suffix marks a heavy-series chain with thicker plates and higher strength. These chains are stocked in carbon steel, with stainless variants for washdown and corrosive service.

Engineering-class welded steel mill chain sits above the standardized ranges in strength for its pitch. The WH78 welded steel mill chain, for example, has a 66.27 mm (2.609 in) pitch and an average ultimate tensile strength of about 30,000 lbf (133 kN) when fully heat-treated, weighing roughly 4.2 lb/ft. These chains are dimensioned by maker catalogue (Tsubaki, Rexnord, Webster, Renold) and chosen for the bulk-handling duties where M-series chain would be the metric equivalent.

Materials and Attachments

Two decisions dominate the mechanical specification of a conveyor chain once the strength class is fixed: the material of the links, pins, and rollers, and the attachment system that carries the product. Material sets corrosion and abrasion life; attachment sets how the chain interfaces with slats, flights, buckets, and pusher dogs.

Carbon and alloy steel is the default. Plates are typically medium-carbon steel, while pins and bushings are case-hardened or through-hardened alloy steel to resist joint wear. Welded steel mill chain heat-treats every component for maximum strength and wear life in abrasive bulk handling. For most dry, indoor, lubricated conveying, hardened carbon steel gives the best strength-per-cost and the longest wear life, which is why it dominates the market.

Stainless steel, usually 304 or 316, is specified where corrosion or washdown rules out carbon steel: food and beverage lines, pharmaceutical and chemical plants, and outdoor or wet environments. Stainless chain trades wear life and breaking load for corrosion resistance, because austenitic stainless is softer than hardened carbon steel and cannot be hardened the same way at the joint. Where both corrosion and abrasion are present, makers offer hardened-pin stainless, plated chain, or self-lubricating bushings as a compromise.

The table below maps common service environments to a recommended chain material and the main failure mode to design against. It is a first-pass guide only; confirm specific media, temperature, and abrasion with the maker before ordering.

Attachments are the integrated bent plates or extended pins that turn a plain chain into a carrying chain. The ANSI naming convention is widely used: an A attachment is an L-shaped bent plate on one side of the chain, with one bolt hole (A1) or two (A2); a K attachment is the same bent plate on both sides (K1 and K2); SA and SK are the straight, unbent equivalents; and D attachments are extended pins, D1 for one extended pin per link and D3 for two. M-series chains use the A1, A2, K1, and K2 plate conventions plus bolt-through fixings on hollow-pin chain.

Attachment pitch, the spacing at which attachments repeat along the chain, is set by the product. Flights on a drag conveyor, slats on an apron, buckets on an elevator, and pusher dogs on an accumulation line all dictate how often an attachment must appear: every link, every second link, or every several links. Getting attachment type and pitch right is as important as getting breaking load right, because the wrong attachment forces costly custom fabrication or makes the chain unusable for the intended carrier.

Key Specification Parameters

A conveyor chain datasheet lists many dimensions, but only a handful drive the selection decision. The seven parameters below are the ones to extract and compare across maker quotes: pitch, minimum breaking load, roller type and diameter, chain pull and safety factor, attachment type and pitch, material and surface treatment, and wear-life rating. Each is explained below.

Pitch is the distance between adjacent pin centres and is the master dimension: it sets the sprocket, the attachment spacing, the product carrying interval, and the chain's bending behaviour around the drive. Conveyor pitches run from about 19 mm on light double-pitch chain to 600 mm on the largest M-series. A longer pitch carries the same load with fewer, larger components and lower cost per metre, but it articulates more coarsely around the sprocket and needs more teeth to run smoothly.

Minimum breaking load is the tension at which the chain is guaranteed not to fail, and it is the headline strength number. In the M-series it is encoded in the designation itself (M315 means 315 kN). It is never the working load: the working chain pull must sit far below it, divided down by a safety factor, to allow for shock, startup surge, and progressive wear. Always compare the published minimum breaking load against your calculated chain pull, not the average or ultimate tensile, which manufacturers may quote separately.

Roller type distinguishes bush chain (no roller, the bushing rides the track), plain-roller chain (a cylindrical roller on the bushing), and flanged-roller chain (a roller with side flanges that guide the chain laterally on a rail). Flanged rollers keep wide or heavily loaded conveyors tracking straight; plain rollers reduce friction on simpler runs; bush chain is cheapest where the track is forgiving. Roller diameter and the roller-to-track contact set the rolling friction that feeds back into the chain pull calculation.

Chain pull and safety factor are the working tension and the margin above it. The accepted practice is for ultimate breaking load to be 6 to 10 times the maximum working chain pull, covering shock loads, acceleration at startup, temperature, and the strength loss as the chain wears. A safety factor at the low end of that band is acceptable for smooth, steady, well-maintained lines; the high end is for shock-loaded, abrasive, or safety-critical duty. Undersizing the safety factor is a frequent cause of premature fatigue failure.

Attachment type and pitch, covered in Chapter 4, must appear on the spec line because they determine fabrication. Material and surface treatment, also from Chapter 4, set corrosion and wear life. The seventh parameter, wear-life and elongation rating, is the chain's resistance to joint wear. The industry scrap limit is 3 percent elongation over the original measured length, beyond which the worn chain rides up and skips the sprocket teeth; many maintenance programs replace at 1.5 to 2 percent to protect the more expensive sprockets. A chain rated for higher wear life (through-hardened pins, sealed joints, better lubrication retention) costs more upfront but extends the replacement interval.

Selection Decision Factors

To convert the preceding chapters into a specific chain order, follow the decision sequence below. Most selection mistakes come not from a single wrong number but from deciding pitch or material before the chain pull and family are settled. These eight steps work as a fixed RFQ template.

1. Conveyor type and chain family: First fix the conveyor (slat, apron, drag, bucket elevator, pallet, table-top) because it dictates the family: double-pitch for light packaging, M-series solid or hollow pin for heavy apron and slat, welded steel mill for abrasive bulk, cast/pintle for hot or simple drag duty.
2. Chain pull calculation: Sum product weight, chain weight, friction coefficient between chain and rail, and any incline component, over both the loaded and return runs, to get the maximum working tension at the drive sprocket. This single number drives strength selection.
3. Breaking load and safety factor: Multiply the working chain pull by a safety factor of 6 to 10 (low for smooth steady lines, high for shock or abrasive duty), then pick the smallest strength class whose minimum breaking load exceeds the result. In the M-series this is a direct read from the designation.
4. Pitch and roller type: Choose pitch to match the available sprocket sizes, product carrying interval, and the strength class you selected. Choose bush, plain-roller, or flanged-roller per the track design and lateral guidance needs.
5. Attachment type and pitch: Specify A, K, SA, SK, or D attachments (or bolt-through hollow pin) and the repeat spacing that places flights, slats, buckets, or pusher dogs where the process needs them.
6. Material and surface treatment: Select carbon/alloy steel, heat-treated mill chain, stainless, or plated steel per the corrosion, abrasion, temperature, and washdown environment from Chapter 4.
7. Lubrication and maintenance regime: Decide the lubricant by speed, load, and environment (light oil indoors, dry-film for dust, NSF H1 for food, high-temperature synthetic for ovens), or specify self-lubricating or sealed-joint chain where lubrication is impossible. Lubrication directly sets wear life.
8. Standard and certification: Tie the order to ISO 1977, DIN 8167 / DIN 8165, or ASME B29.4 / B29.15M as applicable, and request the material certificate and published breaking-load datasheet so the delivered chain can be verified against the specification.

One last dimension is often overlooked: serviceability and wear management. Plan how the chain will be inspected for elongation (steel tape or wear gauge across many pitches under tension, never one link), how connecting links and replacement sections will be sourced, and whether the sprockets will be replaced together with the chain when it reaches scrap elongation. Established makers such as Renold, Tsubaki, Rexnord (Regal Rexnord), iwis, John King Chains, Webster Industries, FB Chain, and Senqcia maintain catalogue interchangeability and stock connecting links and attachments, which matters far more after five years of production than at the moment of purchase.