DUNLOP Belting

Conveyor Belt Design Manual

INDEX

INTRODUCTION

Dunlop Africa Industrial Products is the leading designer and manufacturer of industrial rubber products in South Africa. In fact our belting systems can be seen on some highly productive plants all around the globe.

What more can you expect, when you consider that our belts have been designed and fabricated by some of the best engineers in the industry and from only the finest raw materials.

Using the most current technology, many components have taken years of refinement to attain such technological precision. And every belt is guaranteed to provide maximum performance and maximum life.

And with some 750 000 various specifications available, you can expect to find the right belt for your requirements no matter how specialised.

This manual contains all the elements, formulae and tables you need to specify the exact belt. It has been compiled for your benefit, as a quick reference book for easy selection. If however you have an application not covered in the following pages, please contact Dunlop Africa Industrial Products. A team of experienced and helpful engineers will be pleased to assist you.

Our range of excellent products, competitive pricing and impeccable service, has earned Dunlop Africa Industrial Products the reputation of being the market's first choice.

DUNLOP CONVEYOR BELTING RANGE

Dunlop Africa Industrial Products manufactures the most comprehensive range of conveyor belting in South Africa.

Multi-ply rubber covered conveyor belting

• XT textile reinforced conveyor belting with grade N covers

• XT textile reinforced conveyor belting with grade M cut resistant covers 

• Phoenix heat resistant belting 

• Super Phoenix heat resistant belting 

• Delta Hete heat resistant belting 

• Fire resistant belting 

• Rufftop belting

• Riffled concentrator belting

• Grey food belting

• Salmon pink food belting

• Endless belts

• Woodmaster

• Oil resistant belting

Solid woven PVC belting

• Standard solid woven PVC belting

• Nitrile covered PVC belting

Steelcord belting

• Fire resistant steelcord belting

• Steelcord reinforced conveyor belting with cut resistant type M covers

• Steelcord reinforced conveyor belting with type N covers

• Steelcord reinforced conveyor belting with "Ripstop" protection

• Steelcord reinforced conveyor belting with rip detection loops

Flinger belts

• High speed truly endless belting

BELTING CHARACTERISTICS

XT Rubber Conveyor Belting (conforms to SABS 1173-1977)

• From the early days of cotton duck plies, progress has been made in the manufacture of all-synthetic plies offering many advantages.

• The range of strengths has been greatly increased, with improvements in the flexible structure. The modern multi-ply belt is manufactured with a synthetic fibre carcass in a wide slab, then slit to width as required for individual orders.

• A wide range of belt specifications is available with current belt constructions having versatile applications.

• The standard XT belting (Grade N) incorporates covers suitable for the handling of most abrasive materials, having a blend of natural and synthetic rubber.

Cut resistant XT Rubber Belting

• Grade M Belts have covers with high natural rubber content recommended for belts operating under extremely arduous conditions where cutting and gouging of covers occurs.

Phoenix Heat Resistant Belting

• Phoenix Heat Resistant belting covers are styrene butadiene based and are recommended for belts handling materials with temperatures up to 1200C.

Super Phoenix Heat Resistant Belting

• Super Phoenix Heat Resistant belts have chlorobutyl covers and are recommended for belts handling materials with temperatures of up to 1700C.

Delta Hete Heat Resistant Belting

• Delta Hete heat resistant belting with EPDM synthetic rubber covers in a formulation developed to allow conveying materials of temperatures up to 2000C.

Fire Resistant Belting (conforms to SABS 971-1980)

• Fire Resistant XT belting is manufactured with covers containing neoprene and multi-ply carcass constructions to meet the stringent standards for safety in all underground mining industries and is therefore particularly suited to shaft applications.

Woodmaster

• This belt has been especially developed for the Timber Industry. The rubber has been compounded to provide resistance to oil and resin, and is non-staining.

Rufftop Belting

• This is a range of rough top package belting, of two or three ply all-synthetic carcass belts with deep impression rubber covers. The range is ideal for the packaging and warehousing industries and baggage handling installations such as airports and railway stations etc.

Riffled Concentrator Belts

• Riffled conveyor belting has raised edges, is 1 500 mm wide and available in endless form. These belts are uniquely applied at gold mine concentrators.

Food Quality Belting

• Food quality belting is ideal where foodstuffs come into direct contact with the belt surface. This range of belting is manufactured from non-toxic materials and is resistant to oils, fats and staining, and meets the strict hygiene requirements laid down by the food processing industry. The two types available are Grey food belting and Salmon pink belting

Endless Belting

• The complete XT range can be made available as factory spliced endless belts. These belts are recommended for short conveyor installations. (Suitable for lengths up to 50 in.)

Flinger Belts

• Flinger Belts are fitted to flinger conveyors, the primary function of which is to disperse the discharging material over a wide area, thus minimising heap build-up below the main conveyor. The flinging effect is achieved by running the flinger belt at a high speed in a U configuration. Flinger belts are built and cured on a drum to eliminate a spliced join.

Solid Woven (PVC) Belting (conforms to SABS 971-1980)

• Commonly known as 'Vinyplast' solid woven PVC. The construction has inherently high fastener holding qualities. The belting is constructed of polyester and nylon with a cotton armouring, is impregnated with PVC and has PVC covers. These belts have been specially developed to resist impact, tear, rot and abrasion and to meet the most stringent flame-resistant standards.

Nitrile Covered (PVC) Belting

• The nitrile cover on solid woven PVC belts is specially designed to meet the SABS specifications for use in mines, where a fire hazard exists. In general the nitrile cover has good flame-retardant properties and oil, abrasion and heat resistance.

Steelcord Belting (conforms to SABS 1366-1982)

• Steelcord conveyor belting is designed for very long hauls where textile reinforcement would either not achieve the requisite strength or would have too high an elongation at reference load. Resistance to severe shock and exceptional tensile loading is achieved by the wire reinforcement encased between thick top and bottom covers of the highest quality rubber. These belts are designed to conform to or exceed the requirements of stringent standards and offer a long belt life.

Fire Resistant Steelcord Belting (Conforms to SABS 1366. 1982 type F).

• Steelcord belting of fire-resistant quality is made with specially compounded rubbers which render it self extinguishing. Fire-resistant steelcord belting offers great advantages in maintenance-free operation and long belt life for conveyors situated in fiery mines.

Oil Resistant Belting

• Oil resistant belting provides easily cleanable covers of either nitrile or neoprene on all-synthetic fabric plies. Choice of covers gives maximum resistance to mineral and vegetable oils thus permitting the user to convey a wide variety of materials containing mineral and vegetable oils.

ADDITIONAL FEATURES

1. Rip Protector

   As an additional feature rip protection can be incorporated into the belt by means of arranging strong nylon fibres transversely or by inclusion of electronic loops. The textile rip protection can be built into the belt in 2-metre lengths at regular intervals or over the full length of the belt.

2. Shuron Breaker Ply (XT belting)

   For applications where the lump size of the material carried is large and where adverse loading conditions exist, an open weave breaker ply can be incorporated below the top cover as an extra protection for the carcass.

3. Chevron Breaker (XT belting)

   This incorporates steel tyre cord in a 'V shape, as a rip protection, at intervals over the belt length. Particularly recommended for XT belting where arduous conditions are experienced i.e. slag transportation.

4. Belt Edges

   Many conveyor belts track off at some stage of their lives, causing edge damage to a greater or lesser extent. Belts can be supplied with either slit or moulded edges.

   Slit edges:
   All-synthetic constructed carcasses have good resistance to edge chafing, due to modern fibre construction In addition there is minimal penetration of moisture to the carcass and therefore no problem with carrying out hot vulcanised splices or repairs.

   Moulded edges:
   A moulded rubber edge can be provided to protect the carcass from acids, chemicals and oils. In most applications a moulded edge is unnecessary as synthetic fibres will not rot or be degraded by mildew.

SABS SPECIFICATIONS

Dunlop Africa Industrial Products conveyor belting complies with the stringent standards as laid down by the SABS.

1. SABS 1173-1977 - General purpose textile reinforced conveyor belting.
2. SABS 971-1980 - Fire-resistant textile reinforced conveyor belting.
3. SABS 1366-1 982- Steelcord reinforced conveyor belting.

The above specifications cover the requirements of the various conveyor belts and are classified according to the minimum full thickness breaking strength of the finished belting in kilonewtons per metre width.

Further information regarding SABS specifications will be supplied on request.

CONVEYOR BELT DESIGN

Introduction

A conveyor belt comprises two main components:

1. Reinforcement or a carcass which provides the tensile strength of the belt, imparts rigidity for load support and provides a means of joining the belt.
2. An elastometric cover which protects the carcass against damage from the material being conveyed and provides a satisfactory surface for transmitting the drive power to the carcass.

In selecting the most suitable belt for a particular application, several factors have to be considered:

1. The tensile strength of the belt carcass must be adequate to transmit the power required in conveying the material over the distance involved.
2. The belt carcass selected must have the characteristics necessary to:
   1. provide load support for the duty.
   2. conform to the contour of the troughing idlers when empty, and
   3. flex satisfactorily around the pulleys used on the conveyor installation.
3. The quality and gauge of cover material must be suitable to withstand the physical and chemical effects of the material conveyed.

Belt Tensions

In order to calculate the maximum belt tension and hence the strength of belt that is required, it is first necessary to calculate the effective tension. This is the force required to move the conveyor and the load it is conveying at constant speed. Since the calculation of effective tension is based on a constant speed conveyor, the forces required to move the conveyor and material are only those to overcome frictional resistance and gravitational force.

Mass of Moving Parts

For the sake of simplicity the conveyor is considered to be made up of interconnected unit length components all of equal mass. The mass of each of these units is called the mass of the moving parts and is calculated by adding the total mass of the belting, the rotating mass of all the carrying and return idlers and the rotating mass of all pulleys. This total is divided by the horizontal length of the conveyor to get the mean mass of all the components. At the outset the belt idlers and pulleys have not been selected and hence no mass for these components can be determined. Therefore the mass of the moving parts is selected from the tabulated values to be found in Table 10.

Mass of the load per unit length

As is the case with the components the load that is conveyed is considered to be evenly distributed along the length of the conveyor. Given the peak capacity in ton per hour the mass of the load per unit length is given by:

The effective tension is made up of 4 components

• The tension to move the empty belt T_x
• The tension to move the load horizontally T_y
• The tension to raise or lower the load T_z
• The tension to overcome the resistance of accessories T_u

The effective tension is the sum of these four components

T_e = T_x + T_y + T_z +T_u

T_x = 9,8G x f_x x L_c 

T_z = 9,8Q x H

Various conveyor accessories that add resistance to belt movement are standard on most conveyors. The most common are skirtboards at the loading point and belt scrapers. Other accessories include movable trippers and belt plows.

Tension required to overcome the resistance of skirtboards T_us

Tus =	9,8fs x Q x Ls
	S x b

Tension to overcome the resistance of scrapers

T_uc = A x ρ x f_c 

In the case of a belt plow the additional tension required to overcome the resistance of each plow is

T_up = 1,5W

Moving trippers require additional pulleys in the system and therefore add tension. If the mass of the additional pulleys has been included in the mass of moving parts then no additional tension is added. However, if a separate calculation of the tension to overcome the resistance of the additional pulleys is required this can be determined for each additional pulley as follows

Tut = 0,01	do x T1
	Dt

Corrected length L_c

Short conveyors require relatively more force to overcome frictional resistance than longer conveyors and therefore an adjustment is made to the length of the conveyor used in determining the effective tension. The adjusted length is always greater than the actual horizontal length.

L_C = L + 70

The length correction factor is

C =	Lc
	L

All conveyors require an additional tension in the belt to enable the drive pulley to transmit the effective tension into the belt without slipping. This tension, termed the slack side tension T₂, is induced by the take-up system. In the case of a simple horizontal conveyor the maximum belt tension T₁ is the sum of the effective tension Te and the slack side tension T₂

ie: T₁ = T_e + T₂

T₁ is the tight side tension and 12 is the slack side tension

For a more complex conveyor profile that is inclined, additional tensions are induced due to the mass of the belt on the slope. This tension is termed the slope tension 'h and increases the total tension.

Thus T₁ = T_e + T₂ + T_h

The slack side tension is determined by consideration of two conditions that must be met in any conveyor. The first condition is that there must be sufficient tension on the slack side to prevent belt slip on the drive. The second condition is that there must be sufficient tension to prevent excessive sag between the carrying idlers.

Minimum tension to prevent slip Tm

At the point of slipping the relationship between T₁ and T₂ is

T1	= eθ
T2

Since T₁ = T_e + T₂

T2 =	1	Te
	eθ - 1

 

The expression	1	:
	eθ - 1

is called the drive factor k. and the value of T₂ that will just prevent slip is referred to as the minimum to prevent slip T_m and therefore

T_m = k x T_e

Minimum tension to limit belt sag T_s

The tension required to limit sag is dependent on the combined mass of belt and load, the spacing of the carry idlers and the amount of sag that is permissable.

T_s = 9,8S_f x (B + Q) x l_d

The value of the slack side tension must ensure that both conditions are met and therefore T₂ must be the larger of T_m or T_s.

Slope tension T_h

The slope tension is the product of the belt weight and the vertical lift and has its maximum value at the highest point of the conveyor.

T_h = 9,8B x H

Unit tension T

The maximum belt tension T₁ has as its reference width the full width of the belt. Usually this is converted to the tension per unit of belt width as this is the reference dimension for belt strengths.

T =	T1
	W

Absorbed power

The amount of power required by the conveyor is by definition of power equal to the product of the force applied and the speed at which the conveyor belt travels. The force applied is the effective tension and hence the power required at the shaft of the drive pulley/s is

P = T_e x S

STEP BY STEP EXAMPLE OF BELT TENSION CALCULATION

As an example of the application of the formulae the belt tensions for the following conveyor will be determined:

Belt width	900 mm
Conveyor Length	250 m
Lift	20 m
Capacity	400 t/hr
Belt speed	1,4 m/s
Material conveyed	ROM coal
Drive	210 degree wrap. Lagged drive pulley.
Take-up	Gravity
Idler spacing	1,2 m
Idler roll diameter	127 mm

TABLE 1 TABLE OF SYMBOLS

TABLE 2 MATERIAL CHARACTERISTICS

Characteristics

Key:	HA/S - Highly abrasive/sharp
	MA - Mildly abrasive
	NA - Non-abrasive
	VA - Very abrasive

Cover Grade

Code:	N - SASS 1173 NH polyisoprine
	M - Higher natural rubber content SASS 1173
	OR - Oil resistant
	GF - Grey Food
	PHR - Phoenix Heat Resistant
	SPHR - Super Phoenix heat resistant
	W - Wood master
	DHR - Delta Hete heat resistant
	PVC - Polyvinylchloride
	FR - Fire resistant SASS 971

TABLE 2(a) TYPICAL FLOWABILITY

Determination of Conveyor Capacities

The capacity of a troughed belt is a function of:

1. The cross sectional area of the load which can be carried without spillage.
2. The belt speed.
3. The material density.

The cross sectional area is influenced by many factors including the flowability of the material, the angle of surcharge and the incline angle at the load point of the conveyor. To achieve optimum load area the loading chutes must be designed to ensure the most advantageous initial load shape and this can only be achieved if:

1. The load is placed centrally on the belt.
2. The material is delivered in the direction of belt travel and at a speed approaching that of the belt.
3. The angle of incline at the load area must be less than 1 ~O,

To ensure that the optimum load shape is maintained along the entire belt length:

1. The idler pitch should be such as to limit sag to acceptable levels.
2. The belt must be trained properly.
3. The lump size in relation to belt width must be within the recommended limits.
4. The belt must give adequate support to the load.

Under ideal conditions the cross sectional load area is:

A_t = (A_b + A_s) / 10⁶

Where

A_b = (0,371W + 6,3 + M x cosβ) (M x sinβ)

As =	(	0,186W + 3,2 + M x cosβ	)2 (	πα	-	sin2α	)
		sinα		180		2

M = 0,3145W - 3,2 - B_c

W - Belt width (mm)
B_c- Edge distance (mm)
β - Iroughing angle (degree)
α - Material surcharge angle (degree)
A_t - Cross sectional load area (m²)

The belt capacity in ton/hour is
Capacity = 3,6A_t x D x S

Where

D - Material Density (kg/m³)
S - Belt speed (m/s)

TABLE 3 CAPACITIES OF TROUGHED BELT CONVEYORS IN TON/HOUR

TABLE 4 RECOMMENDED MAXIMUM BELT SPEEDS FOR NORMAL USE (METRES PER SECOND)*

* These speeds are intended as guides to general practice and are not absolute.
+ Moderately abrasive materials.
++ Very abrasive materials.

Note: In the case of belts loaded on inclines of 100 or more it may be necessary to reduce the above speeds in order to achieve maximum capacity.

TABLE 5 RECOMMENDED IDLER SPACING

TABLE 6 FRICTION FACTORS

TABLE 7 SAG FACTOR

TABLE 7(a) RECOMMENDED PERCENTAGE SAG

TABLE 8 ESTIMATED BELT MASS B

Note:

The values given in the table are estimated values for use in the calculation of maximum belt operating tension necessary to make the correct belt selection. When the belt specification has been determined, the mass should be checked more accurately from Table 17. If the actual mass of the specification differs considerably from the approximate value obtained from the table the tension calculation should be rechecked using the more accurate belt mass.

TABLE 9 TYPICAL MASS OF ROTATING PARTS OF IDLERS (kg/m)

TABLE 10 MASS OF MOVING PARTS G

TABLE 11 DRIVE FACTOR k

Notes:

1. When calculating the driving tension required for dual drive units, the drive factor selected must correspond to the total angle of driving wrap.
   

2. The drive factors quoted for gravity or automatic take-up systems are minimum values based on the relationship between angle of wrap and coefficient of friction between belt and drum at the point of slip. In the case of screw take-up units, an adjustment has been made to the drive factor to allow for the extra tension which may be induced in the belt either:
   

   1. to compensate for the effect of belt elongation when the material is loaded.

   2. due to the difficulty in measuring the amount of tension applied.
      

3. In those cases where an electrically or hydraulically loaded winch type take-up is used, where the induced tension can be preset and controlled, the drive factor should be selected to correspond with a gravity take-up system.

CONVEYOR BELT SELECTION

Belt carcass selection criteria
In selecting the optimum belt construction for a given application it is necessary to consider the following:

Tensile strength
The belt class required is that which has an operating tension greater than or equal to the calculated maximum unit tension T. (Table 12).

Load support
Choose the lowest class which meets the tensile strength requirement. Looking at Table 14, determine which load category best describes the load being conveyed i.e. A, B, C, D or E category load. The value obtained at the intersection of the belt specification row and the load category column gives the maximum width at which that belt specification can be used.

Number of plies for troughability
The maximum number of plies allowable, in order to ensure that the empty belt will conform to the contour of the troughing idlers, must be checked referring to Table 15. For a particular belt class the value shown at the intersection of the belt width column and troughing angle row, is the maximum number of plies that should be used.

Minimum pulley diameters
If the size of the pulleys is already determined, the belt construction provisionally selected from the previous considerations can be checked against the relevant pulley diameters for suitability. For a new installation, the pulley diameters should be equal to or larger than those given in Table 13 (It should be noted that, in this context, the diameters quoted refer to the minimum pulleys around which the particular belt construction will flex satisfactorily. The conveyor designer should also take into account the gearbox ratio and required belt speed when selecting the drive pulley diameter.)

Gauge of covers required
The correct gauge of cover necessary to give protection to the belt carcass from material impact and wear must be determined by consideration of the size and density of the material to be handled. (Table 19).

Additional Information

Belt modulus
Refer to Table 20 for belt modulus.

Belt mass
The mass of a particular belt construction can be determined by adding the carcass mass found in Table 17 to the combined mass of covers found in Table 18. This will give the mass per unit area. To calculate the mass per unit length multiply by the belt width in metres.

Belt thickness
The belt thickness can be obtained from the information given in Table 16.

TABLE 12 MAXIMUM RECOMMENDED OPERATING TENSIONS

TABLE 13 RECOMMENDED MINIMUM PULLEY DIAMETERS (mm)