Belt Conveyor Design (Dunlop): Complete Guide

Belt conveyor design according to the Dunlop method is one of the most frequently consulted calculation procedures in the cement and bulk materials industries. The manual known as “Conveyor Belt Technique: Design and Calculation”, the practical engineering handbook from which this title is taken, condenses decades of conveyor belt development by the Dunlop-Enerka organization into a step-by-step design route: from the first sketch of the conveying system, through drive arrangement, coupling selection, pulley sizing and take-up design, to the final power and belt strength verification. For plant engineers, mechanical maintenance teams and conveyor contractors in cement plants, the Dunlop procedure remains the standard because it combines theoretical mechanics (Eytelwein friction limits, belt creep and slip) with practical tables of recommended belt speeds, idler spacing, pulley diameters and vertical curve values. This article reproduces the complete logic of the manual, explains every formula with its underlying physics, and closes with a full worked example such as the one the manual itself presents for a typical troughed belt conveyor duty.

The complete 161-page Dunlop design volume is part of the Complete Cement Technical Package, a 931-file engineering library covering books, design manuals, Excel calculators and courses for the entire cement manufacturing process, available from cementequipment.org in one instant download with lifetime access.

1. Introduction: The Dunlop Approach to Belt Conveyor Engineering

The Dunlop conveyor belt technique manual was developed from one of the world’s oldest conveyor belt manufacturing traditions. Dunlop belts were produced from the beginnings of industrial rubber technology, and the Dunlop-Enerka organization in The Netherlands operated, for decades, one of the most sophisticated belt test installations in Europe: the Dunlop-Enerka test rig.

The development chronology of the manual mirrors the history of belt conveying itself. Early installations used fabric belts with thin rubber covers and low-strength plies, requiring conservative design and frequent maintenance. The introduction of nylon and polyester carcasses in the 1960s changed the picture radically: belts became stronger, thinner and more flexible, allowing longer single-flight conveyors, higher lifts, narrower pulleys and lower driven power. Steel cord belts then extended the range to lifts of hundreds of meters and speeds beyond 6 m/s. With every new belt generation, the design engineer needed updated tables for pulley diameters, idler spacing and transition lengths, and this is precisely the service the Dunlop manual performs: it is a continuous, tested system of design values tied to belt construction parameters.

The Dunlop-Enerka test rig deserves special mention because much of the published data on belt resistance, indentation rolling resistance and cover wear came from measurements on that rig rather than from theoretical extrapolation. Modern conveyor design standards such as DIN 22101 and ISO 5048 still rely on the same physics: a motional resistance coefficient that combines idler bearing friction, seal friction, belt sag and indentation resistance, applied over the conveying length. Engineers familiar with DIN 22101 (the German standard upon which most European belt calculations are built) will recognize in the Dunlop manual all the same elements: main resistances, secondary resistances, slope resistances, special resistances and the peripheral force F_U with its acceleration and start-up allowances.

2. The Belt Conveyor as a System: Basic Sketch and Concept

A belt conveyor consists fundamentally of an endless flexible belt traveling over a carrying run supported by troughing idlers and a return run supported by flat idlers, wrapped around a drive (head) pulley and a tail pulley, with a take-up device that maintains tension, and a drive station providing torque. In the cement plant, belt conveyors move limestone from quarry crushers to raw mills, raw meal is carried or elevated between process stages, clinker travels from the cooler to the cement mill feed, and finished cement is distributed to silos and packing plants.

Every conveyor design starts from the duty data: material to be conveyed, bulk density, lump size, throughput in tonnes per hour, conveying length, lift or decline, ambient conditions, and the expected operating mode. From these, the designer derives belt width, belt speed, idler spacing, drive power, belt tension and selected belt construction. The design must satisfy simultaneously: (1) capacity, so that the cross-section and speed carry the required mass flow; (2) strength, so the belt carcass withstands the maximum tension with adequate safety; (3) geometry, so transitions, curves and turnovers do not damage the belt; and (4) economy, so idler, pulley, motor and belt costs stay proportional to the duty.

The manual emphasizes that a conveyor should be conceived as an integrated system rather than as a sum of catalog components. Drive pulleys must not be sized only for the running power; they must transmit the start-up peak torque without slipping. The take-up must provide the sag-limiting tension on the carrying run while preventing slack at the tail. The structure must be aligned within strict tolerances, because a misaligned belt edge drifts off the idlers and destroys both belt edges and idler seals. Every component choice reacts on the others, which is why the Dunlop method moves in a fixed order of calculation steps, each step guarding the previous one.

3. Drive Systems: Pulley Arrangements and General Criteria

Three classic drive arrangements dominate belt conveyor practice and are treated in detail by the manual: the single-pulley head drive, the dual-pulley head drive and the head and tail drive.

In the simplest arrangement, one drive pulley at the head (discharge end) carries the whole peripheral force. The belt wraps the pulley by an angle that depends on the pulley arrangement geometry, frequently between 180 and 210 degrees. The maximum force that can be transmitted is limited by the Eytelwein equation (Section 5), so a single pulley drive is chosen when the required peripheral force is moderate.

When the peripheral force exceeds what one wrap can transmit with an acceptable tension ratio, the designer moves to a dual-pulley drive: two pulleys in series at the head, each driven, with the belt wrapping each through approximately 150 to 200 degrees, giving combined wrap angles up to about 400 degrees. Dual drives have their own subtleties: each pulley must be supplied with torque proportional to its pulling capability, and if the drive motors are not correctly coordinated, one pulley can be overloaded or driven into slip while the other idles. The manual therefore discusses drive grouping, gear ratios and motor torque-sharing in detail, including the use of fluid couplings to equalize load between the two motors.

The head and tail drive arrangement places additional driven pulleys at the tail or along the return run to inject power where the belt needs it. It is used for very long conveyors or high-lift installations where a single concentrated drive would require excessive belt tension at one end, and where drive accessibility is better at several points. The design rules for multiple drives are summarized below:

4. Couplings and Start-up Procedure

Power flows from the electric motor through a coupling to the gearbox and from the gearbox through a second coupling to the drive pulley shaft. The manual distinguishes four coupling families: fixed couplings (rigid, for perfectly aligned shafts), flexible couplings (compensating small misalignments and transmitting torque smoothly), fluid couplings (hydrodynamic, allowing the motor to accelerate against a slipping hydraulic medium) and hydrodynamic retarder-type devices used on large installations.

For belt conveyor drives, the fluid coupling is the component that solves the classic start-up problem. An empty conveyor started directly across the line can accelerate so hard that the belt whips, the charge surges and the drive transmits a dynamic peak several times the running torque. With a fluid coupling, the motor accelerates quickly to near synchronous speed under light load, while the turbine side (connected to the gearbox) accelerates the belt progressively as the coupling fills with oil; the torque transmitted rises smoothly to the controlled start-up peak, typically capped at 130 to 160 percent of rated torque.

The correct start-up procedure, as specified in the manual, has three distinct phases. First, the conveyor is inspected: no personnel in the danger zones, guards in place, take-up free, scrapers correctly set, and the belt cleared of any idler obstructions. Second, the drive is started and the belt is allowed to make at least one full revolution at low filling, with the operator watching belt tracking on the return run. Third, the material feed is brought up gradually while the belt tension and motor current are monitored. The manual explicitly warns against feeding a stationary belt and against stopping the machine while fully loaded unless the belt is designed for full-load restart; where full-load restart is expected, the installed motor power and the coupling rating must be chosen on the basis of the restart torque, not the running torque.

Run-back prevention occupies its own section because an inclined conveyor carrying a full load can, on power failure, run backwards down the incline, dumping material at the tail and potentially damaging the belt and drive. The manual covers holdbacks (mechanical backstops), brakes and regenerative braking, and specifies that for long declines a controlled braking system must be capable of stopping the belt smoothly rather than relying on the catch effect of a pawl-type holdback.

5. Drive Pulley: Force Transmission and the Eytelwein Equation

The force a drive pulley can transmit is governed by the classical friction relation of Eytelwein, which the manual treats as the fundamental constraint of the whole design:

F₁ / F₂ = e^μα

where F₁ is the tight-side tension, F₂ the slack-side tension, μ the coefficient of friction between belt and lagged pulley surface, and α (alpha) the angle of wrap in radians. The peripheral force F_U that can be transmitted is the difference F₁ − F₂, and the greatest possible value increases both with the wrap angle and with the friction coefficient.

In practice the belt never transmits the theoretical maximum, because the elastic belt creeps over the pulley surface. When the tight side enters the drive pulley, the belt is stretched; as it leaves on the slack side, it contracts, so a tiny relative motion (creep) occurs over part of the wrap. The creep angle is the portion of the wrap where the belt actually slips microscopically while transmitting normal force. Slip, in contrast, means the whole wrap slides and the drive pulls no material: the belt moves while the pulley surface passes underneath with gross sliding, generating heat and abrading the lagging. The design objective is to stay always in the creep regime of the Eytelwein curve and far from the slip limit.

The manual lists practical friction factors for the rubber pulley surface versus various lagging materials, always emphasizing the effect of moisture: a wet steel pulley with a rubber belt can drop from its dry friction coefficient of roughly 0.35 to below 0.2, which is why drive pulleys are rubber-lagged, why snub pulleys are added to increase wrap angle, and why drive pulleys must be protected from rain where conveyors run outdoors. The calculation procedure fixes the wrap angle from the geometry (typically 180 degrees for a simple head drive, 210 degrees with a snub pulley, up to 400 degrees for dual drives), selects the friction factor from the table for the lagging and weather conditions, computes e^μα, and then derives the required slack-side tension F₂ from the peripheral force that the duty demands.

6. Take-up (Tension) Systems

The take-up device does far more than keep the belt taut; it sets the operating tensions that make the whole force transmission possible while keeping the belt sag between idlers within limits. The manual distinguishes three principal systems.

Fixed take-up. The take-up pulley is held in a fixed position by a screw or by bolted rails. Tension is set at installation and never changes automatically. Its advantage is compactness and cheapness; its disadvantage is that belt elongation from temperature change, wear in the carcass or load variation produces tension variation that the designer must accept. A belt that elongates must be re-tensioned manually, and a fixed take-up always leaves some stretch unabsorbed. The manual recommends fixed take-ups only for short conveyors with modest length-to-belt-strength ratios.

Gravity weight take-up. The take-up pulley rides in a carriage loaded by a suspended counterweight. The weight sets a constant tension F₂ regardless of load, temperature or belt stretch, within the travel of the carriage. This is the most common system for medium and long conveyors because it self-regulates and automatically compensates for belt stretch. The manual specifies the take-up travel as a function of belt construction: roughly 0.1 to 0.3 percent of the center distance for fabric belts and additional allowances for splicing and temperature variation. The gravity take-up also dampens start-up tension surges since the carriage acts as a soft spring in the tension system.

Regulated (controlled) take-up. The most sophisticated arrangement, typically hydraulic, continuously measures belt tension and adjusts the take-up force to hold a setpoint. Regulated take-ups are chosen for long, heavily loaded or high-speed conveyors where constant tension control protects the belt and minimizes power consumption, and they are frequently combined with start-up sequences that reduce tension during acceleration. The table below summarizes the selection criteria:

Take-up position matters as much as its type. A take-up at the tail near the drive slack side keeps the running tension low; a take-up at the head keeps the tail-up side slack, which can produce sag. The manual advises placing the take-up so that the tight-side and slack-side tensions are the lowest possible consistent with drive requirements and sag limits, and it is common practice to locate the gravity take-up beneath the tail on a vertical tower or along the return run under the conveyor.

7. Detection Devices for Belt Protection

Modern conveyor engineering spends a full chapter on protective devices, because a failed belt edge or a burst splice can stop a cement plant’s entire raw material supply for hours. The manual covers four families of protection.

Belt tension detection protects against over-tension (impending splice failure, jamming of the belt against a structure) and under-tension (slack belt causing slippage and mis-tracking). Tension switches are installed where the belt runs loose over the return idlers: a slack belt droops and presses a sensing roller, tripping the conveyor.

Off-track (misalignment) detection. Limit switches with rollers are mounted at intervals along the conveyor edges; if the belt drifts sideways more than a set amount, the roller is pushed and the conveyor is stopped before the belt edge destroys itself against the structure or derails into the idler frames. Maintaining correct tracking in the first place (accurate idler alignment, correctly built splices, properly set scrapers) is the real objective; the switches are the last line of defense.

Belt slip detection. A speed sensor on the tail pulley or on the return belt compares the belt speed with the drive pulley rotational speed. If the belt slips on the drive (for any reason, from wet pulleys to a stalled load), the ratio diverges and the drive stops within seconds, preventing the destructive heat of sustained slip on the lagging.

Longitudinal slitting safety devices. These are the most dramatic protectors: when a foreign object (a scrap of tramp iron or a sharp lump of ore) pierces the belt and begins to slit it longitudinally, a sensor loop (mechanical feeler bar in the chute or an inductive loop embedded in the belt) detects the cut before the slit runs the full belt length, and emergency-stops the conveyor. On long, high-value conveyors, belt rip detectors embedded in or under the belt can detect a developing slash even earlier, saving a belt that often costs more than the whole mechanical installation around it.

8. Main Design Data: Belt Speeds, Widths and Capacities

The design calculation starts with the selection of belt speed. The manual gives both standard values and recommended ranges for each material class. Speed must be high enough for the capacity with a reasonably filled cross-section, yet low enough that the material does not spill over the edges on trough idlers, that the belt does not detach fine dust, and that impact at loading points remains acceptable. Recommended practical values for cement plant duties are shown below:

Belt width follows from the capacity at the chosen speed: the load stream must occupy a fraction of the trough cross-section that guarantees edge clearance. The manual provides standard widths (300, 400, 500, 650, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200 mm in the metric series) and defines the minimum belt width rule from the largest lump size: for unscreened material, the belt width should exceed roughly 2.5 to 3 times the maximum lump dimension; for screened material about 2 to 2.5 times. A simple practical rule frequently cited in the manual is that the belt must be at least 200 mm wider than three times the top lump size in the worst case of a single lump lying on the edge of the trough.

Idler arrangement is then fixed: troughing idlers in the carrying run at 30–45 degrees (the 35-degree trough being the cement plant standard because it combines good capacity with acceptable belt flexing), flat idlers in the return run, impact idlers at loading points with reduced spacing, and self-aligning idlers placed at regular intervals (usually every 8 to 15 m) to correct tracking drift. Idler spacing is a compromise between belt sag, belt weight and idler cost; the manual gives recommended spacing values as functions of belt width and bulk density. Typical values: for a 1000 mm belt carrying 1.6 t/m³ material, carrying-roll spacing is about 1200 mm in the loaded run and 3000 mm on the return; at loading points, impact idler spacing drops to 400–500 mm. Idler roll diameter is chosen so that the idler frequency (1000 rpm at most for standard bearings) is respected at the belt speed, and the idler roll lengths follow the trough geometry for each belt width.

9. Cross-Sectional Load Area and Conveyor Capacity

The capacity calculation is the geometric heart of the method. The loaded belt cross-section in a three-roll troughed idler set consists of the trapezoid formed by the two side rolls and the shallow segment formed by material lying on the center roll; the load surface is defined by the dynamic angle of repose of the material, the so-called surcharge angle, typically around 15–20 degrees for free-flowing raw materials.

The manual calculates the cross-sectional area A (in m²) by adding the area of the central segment (based on the width occupied on the central roller and the surcharge angle) to the two side areas, and then converts this into a volumetric capacity or load-stream volume:

Q_v = A × v × 3600 (m³/h)

and the mass capacity:

Q_m = A × v × ρ × 3600 (t/h)

where v is the belt speed in m/s and ρ is the bulk density in t/m³. The manual emphasizes that real installations never run at 100% geometric filling: a degree of filling factor of about 0.8 to 0.9 must be applied to account for uneven feed, spillage over the idler junction and the fact that the belt surface is not a rigid trough. A reduction factor is applied for inclined conveyors, because at inclines beyond about 10 degrees the material begins to slide backwards within the load stream and the effective cross-section shrinks; the manual tabulates these reduction factors for slopes from 0 to 25 degrees, showing that above 20 degrees the practical capacity of a troughed belt falls to about 70% of the horizontal value.

For inclined conveying of lumpy material, the maximum permissible inclination depends mainly on the material’s angle of repose and lump shape. Limestone and clinker convey in the range of 15–20 degrees; granular coal up to about 18 degrees; sticky clay less than 15 degrees. Above these slopes, belt conveyors give way to bucket elevators, steel apron feeders or pneumatic systems, exactly the judgment exercised by the conveying system chapters in the cement process literature.

10. Power Requirement and the Electric Motor Calculation

The running power of the conveyor is the product of the peripheral force F_U and the belt speed, divided by the drive efficiency:

P_M = (F_U × v) / (η × 1000) in kW

where η accounts for the gearbox, couplings and bearings, typically 0.85 to 0.94 depending on drive complexity. The manual decomposes the peripheral force into individual resistances, exactly as DIN 22101 does:

• Main resistance F_H: the resistance of the running belt on the idlers over the whole conveying length, composed of idler bearing friction, idler seal friction, indentation rolling resistance of the bottom cover and a small contribution from belt flexing between idlers.
• Secondary resistance F_N: resistance at loading points (impact of the falling material and the friction of the material accelerating from zero to belt speed), friction at scrapers, skirt sealing friction and the resistance of moving the load up the inclined belt path.
• Slope resistance F_St: the component of material and belt weight acting against the direction of travel: F_St = m×g×sinθ, positive uphill, negative downhill.
• Special resistances F_S: additional forces at deflector pulleys, trippers, plow dischargers and belt turnover stations wherever they exist.

The motional resistance coefficient f used in the main resistance formula (F_H = f×L×g×(m_belt + m_load + m_idler)) takes a value of about 0.018 to 0.025 for well-maintained conveyors with standard idlers, but the manual advises checking the effect of cold weather, misalignment and poor idler condition, which can double the value.

The installed motor is then selected from the calculated power with adjustment factors: a start-up factor (typically 1.3–1.5 for direct-mounted motors with fluid coupling control), a safety margin on data uncertainty, and, where the conveyor must restart under full load, an even higher provision. The manual lists standard motor types and their characteristics, and prescribes slip-ring motors for hard-start drives where a high starting torque at low start-up current is required, or squirrel-cage motors coupled through fluid couplings for soft-start duty.

11. Belt Types, Pulley Diameters and Pulley Loading

The required belt strength follows directly from the maximum tension in the belt, which occurs at the drive pulley tight side:

F_max = F_U + F₂ (fixed take-up) or F_max = F_U + F₂ + dynamic allowances for gravity take-up systems.

The nominal breaking strength of the belt must exceed the maximum tension multiplied by the safety factor. The manual’s safety factor values are classic: S = 8 to 10 for permanent installations (fabric belts), reflecting splicing efficiency (vulcanized splices reach 70–100% of carcass strength, mechanical fasteners only 30–70%), start-up peaks and long-term fatigue; values of 10 or higher are retained for steep, hard-starting or high-risk conveyors, while 6.7 to 7.5 is sometimes used for steel cord belts where splice efficiency is known and dynamic control is excellent. The belt is specified by its breaking strength in N/mm of belt width (e.g., a 1000 mm belt with 630 N/mm nominal strength).

Pulley diameters are selected from tables keyed to the belt construction and fabric plies, because bending a belt around too small a pulley stresses the carcass beyond its fatigue limit. For the drive pulley the diameter depends primarily on the belt type and tension; tail and bend pulleys can run smaller since they see lower tension. The manual’s standard pulley diameter series uses the preferred numbers 250, 315, 400, 500, 630, 800, 1000, 1250, 1400 mm and prescribes that the drive pulley diameter must be the largest of the set required by (a) the belt construction, (b) the number of fabric plies or the steel cord diameter, and (c) the average surface pressure limit.

Average surface pressure is the factor that prevents belt damage at high tension: the belt presses on the pulley surface with a pressure equal to the belt tension divided by the projected contact area (pulley diameter times arc length of wrap times belt width approximated by the pulley width). Excessive pressure squeezes the rubber cover, produces heat generation and accelerates cover wear; the manual fixes a permissible average pressure of about 0.3 N/mm² for standard rubber covers on steel pulleys and lower values for fabric-lagged or heat-resisting surfaces. Start-up torque transmits through the same interface, so the start-up condition must be checked against the same pressure limit.

12. Troughing Transition, Vertical Curves, Turnover and Horizontal Curves

Where the belt leaves the flat pulley surface and gradually assumes the trough shape, it passes through the troughing transition zone. In this zone the belt edges must stretch more than the belt center, and if the transition is too short, the additional edge stress can exceed the carcass’s permissible strain and bulge the belt edges upward, causing edge wear and tracking problems. The manual provides transition length values as a function of belt width, trough angle and belt type: for a 1000 mm wide belt troughing to 35 degrees, transition distances on the order of 1.2 to 2 m are typical for fabric belts, longer for stiffer steel cord belts whose strain capacity is lower.

Convex vertical curves (where the belt path arches upward, like over a ridge) reduce the tension at the curve center because the belt tends to lift from the idlers; the manual gives minimum convex curve radii so that the belt never lifts off the idlers, the radius being a function of belt tension, belt weight and material load. Concave vertical curves (where the path dips, like entering a valley between two crests) are more dangerous: on the return run the belt can lift off the idlers and buckle, and on the loaded run the material can spill. The manual’s concave curve rule specifies that the pulley lift must be checked, and provides curve coordinates for laying out the transition profile. Belt turnover (twisting the belt 180 degrees on the return run so that the carrying surface faces downward) is used to expose the dirty side for cleaning and to protect the carrying surface; the manual gives turnover lengths ensuring the belt twist strains stay within limits. Horizontal curves are treated for the special case of conveyors steering through a horizontal radius, a feature now common in long overland cement plant conveyors.

13. The Worked Design Example: Short Calculation and Sequential Calculation

The manual closes the main design chapter with a complete numerical example of a troughed belt conveyor, which is the best possible illustration of the whole method. The duty data for the worked case are along the following lines: a belt conveyor handling 1200 t/h of crushed overburden or limestone with a bulk density of 1.6 t/m³, a horizontal conveying length of 450 m and a lift of 15 m, running at a belt speed of 2.5 m/s with a 1000 mm wide belt, inclined 30-degree trough idlers at 1.2 m spacing.

Short calculation. The quick estimate route begins from a capacity check: the load stream cross-section for a 1000 mm belt troughed at 30 degrees with a typical surcharge angle is about 0.12 m², giving a volumetric capacity of 0.12 × 2.5 × 3600 = 1080 m³/h, and a mass capacity of 1080 × 1.6 = 1728 t/h with a filling factor of 0.85; the duty of 1200 t/h is therefore safely carried. The peripheral force is then estimated from the main resistance over 450 m plus the slope resistance of the 15 m lift: with a resistance coefficient f of 0.022, the main resistance amounts to roughly 0.022 × 450 × 9.81 × (28 + 133) ≈ 15.7 kN, where 28 kg/m is the belt mass and 133 kg/m the load mass, plus a material lift contribution of 133 × 9.81 × (15/450) × 450 / 1000 ≈ 19.6 kN, giving a total peripheral force near 40–45 kN including secondary resistances, and a running power near 110–130 kW before drive efficiency; with an efficiency of 0.9, a 160 kW motor class results.

Sequential calculation. The rigorous route then repeats the same summing with individual resistances: idler rolling resistances from the idler mass and load, the acceleration resistance of the material at the loading point, the scraper friction, the skirt friction and the exact slope contribution. The belt tensions are then solved: with a gravity take-up holding the slack-side tension at the sag limit, the tight-side tension follows from the Eytelwein ratio e^μα, the belt strength (e.g., 800 N/mm and 1000 mm width gives 800 kN nominal) is checked against the maximum tension with the required safety factor, and the take-up travel is sized for the expected stretch of the fabric belt. The example demonstrates how a selection that passes the short calculation can still need revision in the sequential calculation, and the manual explicitly presents, in the following section, the effect of different take-up arrangements on the resulting belt tensions and the motor performance.

14. Slider Bed Belt Conveyors

Not every belt conveyor runs on idlers. The manual devotes a dedicated chapter to slider bed conveyors, in which the loaded belt slides on a continuous support surface (usually a steel or wear-resistant plastic bed). Slider bed conveyors are used for short feeders, bag conveyors, sorting and metering duty, and wherever a flat, stable belt surface with spillage containment is more important than long-distance transport economy.

The calculation changes only in the motional resistance: instead of idler rolling resistance, the design uses a friction coefficient μ between the belt bottom cover and the supporting surface, which the manual gives in characteristic values depending on the surface material, the belt hardness and lubrication conditions. A typical value for a rubber belt on a steel slider bed is about 0.3 with clean dry contact, rising when the belt becomes worn, dusty or heated; low-friction polymer beds can bring this down toward 0.15. The slope resistance, special resistances and drive power formulas remain the same as for idler conveyors, with the driven peripheral force F_A computed from the friction resistance instead of from idler rolls. Belt width and speed follow the same capacity relationships; because slider beds cannot trough deeply, they are mostly used for flat or slightly troughed cross-sections. Safety factor S and nominal belt strength K_N are applied exactly as before, and the manual recommends residual belt tension checks to avoid belt buckling between the drive and the bed on long machines.

15. Bucket Elevator Belts

The final design chapter applies the same engineering to bucket elevator belts, the standard equipment for vertical lifting of raw meal, cement and clinker dust in cement plants. The design starts from the required capacity and the bucket geometry: using the conveying capacity formula with bucket contents and bucket shape factors, the designer fixes the bucket spacing and the belt speed, normally between 1.0 and 2.2 m/s for centrifugal discharge elevators.

The belt tension in a bucket elevator is dominated by the weight of the buckets and the lifted material column: the total vertical load is the sum of belt weight, bucket weights and material weight per meter, multiplied by the lift height, plus the tension required to pick up the buckets at the boot. The belt width is set by the bucket width; bucket capacity is expressed in liters, with bucket volume utilization (filling ratio, typically 0.6–0.8 for cement raw meal) converting to tonnes per hour. Because elevator belts run over small-diameter head and boot pulleys, they are designed as thin, flexible fabric belts with the bucket bolts attaching directly to the carcass, and pulley diameters must respect the bucket bolting pattern as well as the belt flexing limits. Take-up on elevators is a simple screw or gravity adjustment at the boot; slip detection and a run-back holdback (or brake) on the head shaft are mandatory protection because a fully loaded elevator running back empties its buckets into the boot and wrecks the chain of buckets.

16. Frequently Asked Questions

Q1. What is the Eytelwein equation and why does it matter for belt conveyor design?

The Eytelwein equation F₁/F₂ = e^μα defines the maximum tension ratio a drive pulley can transmit before the belt slips. It links the coefficient of friction between belt and pulley, the wrap angle and the slack-side tension; every drive calculation uses it to determine whether a single, dual or snub-pulley arrangement is needed.

Q2. What is the difference between creep and slip on a drive pulley?

Creep is the normal, unavoidable microscopic elastic slip of the belt over part of the wrap caused by the belt stretching and relaxing as it passes around the pulley; it is harmless. Slip is gross sliding of the whole belt relative to the pulley, dead heading the drive and heating the lagging. Design keeps the working point safely inside the creep regime by providing sufficient wrap angle and friction.

Q3. Which take-up system should I use for a 1500 m long overland conveyor?

A gravity weight take-up is the standard recommendation for lengths of this order: it maintains constant slack-side tension automatically, absorbs belt stretch, and protects the drive from tension surges. Regulated hydraulic take-ups are justified when tension control must be dynamic, for very long or high-tension conveyors, or when restart control sequences are required.

Q4. How is belt width determined from lump size?

The minimum belt width is set so that the largest lumps can sit on the belt center without riding over the idler junctions: roughly 2.5–3 times the largest lump dimension for unscreened material, and 2–2.5 times for screened material. The width must also satisfy the capacity requirement; the larger of the two widths governs.

Q5. What safety factor is applied to belt strength?

Standard permanent installations use a safety factor of 8–10 on the nominal breaking strength for fabric belts, reflecting splice efficiency and start-up peaks; steep, hard-starting conveyors take the higher values. Steel cord belts with vulcanized splices and controlled drives can work at 6.7–7.5.

Q6. Why must idler spacing change at loading points?

Impact idlers at loading points are spaced much more closely (often 400–500 mm instead of 1200 mm) to absorb the kinetic energy of falling lumps, minimize belt impact stress and prevent sag that would funnel spillage through the skirt system.

Q7. When is a dual-pulley head drive necessary?

When the required peripheral force exceeds the capacity of a single pulley wrap at the practical friction coefficient, the dual head drive doubles the available wrap angle to 300–400 degrees, reducing the tension ratio and therefore the maximum belt tension, belt strength and drive cost.

17. Final Summary

The Dunlop belt conveyor design manual remains one of the most complete and teachable treatments of belt conveyor engineering ever written for industry use. It guides the designer from the basic system concept through every component: the drive arrangements and their couplings, the Eytelwein friction law that bounds every drive, the take-up systems that hold tension, the protective devices that safeguard the belt, and the geometric and power calculations that fix belt width, speed, idler spacing, pulley diameters, transitions and curves. The numerical example shows the method at work in a realistic duty, from the short capacity and power estimate to the sequential verification of tensions and belt strength.

For the cement plant engineer, the value is direct: the same formulas govern the limestone quarry belt, the kiln feed conveyor, the clinker line and the bucket elevators of the cement mill. Owning the full manual — 161 pages of tables, formulas, example calculations and design values — equips the maintenance and engineering team to specify, check and troubleshoot every belt conveyor in the plant without waiting for vendor calculations.

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