troughed_ design guidelines and standards

8/12/2019 Troughed_ Design Guidelines and Standards

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18/6/2014 Troughed: Design Guidelines and standards

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Beginners Guide Print

Design Guidelines and Standards

Some of the fundamental conveyor design parameters and standards are included here to acquaintthe learner with the norms of the technology.

Once the learner has progressed to the stage of detailed design and engineering of troughed beltconveyors, then the appropriate sections in this Handbook should be consulted for a morecomprehensive explanation of terms and design information.

a) Troughed Belt Conveyor Capacities

Material surcharge angles vary between 0 degrees and 35 degrees and greater however, for thepurposes of an indication of belt conveying capacities, the chart below assumes that the materialsurcharge angle is 20 de grees and has a bulk density of 1000 kg/m3.

The graph indicates the theoretical capacity of a conveyor at a belt speed of 1 m/s and three differentidler trough angles nam ely 20, 35 and 45 degrees.

BG19

The capacity of a troughed belt can also be viewed/calculated on the Ckit " Load & Capacity" calculator.

b) Belt Speeds

A number of factors should be considered when determining the correct conveyor belt speed. Theseinclude the material particle size, the inclination of the belt at the loading point, degradation of thematerial during loading and discharge, the width of the conveyor structure, belt tensions and powerconsumption.

The following tables provide an indication of the recomm ended be lt speeds for different materials.

Max. Belt Speed

c) Standard Belt Data

Troughed conveyor belting usually complies to the following standard dimensions and ratings.

- Belt widths

Standard Belt Widths

450 mm 600 mm 750 mm 800 mm 900 mm1000 mm1050 mm1200 mm1350 mm1400 mm1500 mm1650 mm1800 mm2100 mm2400 mm

3000 mm

- Belt classes :-

Steel Cord Belt Rating Fabric Belt Rating Fabric Belt Plies*
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ST 500ST 630ST 800ST 1000ST 1250ST 1600ST 2000ST 2600ST 3000ST 3150ST 4000ST 5000

EP 160EP 200EP 250EP 315EP 400EP 500EP 630EP 800EP 1000EP 1250EP 1600EP 2000EP 2500EP3150

2 ply3 ply4 ply5 ply6 ply

'*' Click hereto view standard number of plies for different belt classes

- Belt covers :-

Cover

Grade

Tempe rature Service Conditions

MNormalTemp.

Heavy Duty ServiceSuperior in abrasion resistance, cut and gouge resistance.Suitable for conveying large sized lumps, sharp and ruggedmaterials.

NNormalTemp.

Normal Duty ServiceSuperior in abrasion resistance but inferior to grade M in cut-and-gouge resistance.

B (G)NormalTemp.

General Light Duty ServiceSuitable for conveying mode rately abrasive materials and sma ll sizedmaterials.

SANormalTemp.

Super abrasion resistanceSuitable for conveying materials tending to cause fast wear on belts.

HRSBelt Surface:max . 100CMaterial:max . 200C

Superior in heat resistance and also in cut, abrasion and tearresistance.Suitable fo r conveying the following materials:Hot sintered o re, hot pa llet, hot clinke r, hot chemical, fertilizer, etc.

HRE

Belt Surface:max . 150CMaterial:max . 400C

Highly exellent in heat resistance and also superior in abrasionresistance,cut and tear resistance.No cracks will resu lt. So suitable for hot m aterials.Typical applications :Hot clinker, hot cement, hot powder, hot sintered ore, hot chemical,fertilizer, etc.

OHRMaterial:max . 100C

Oil & Heat ResistanceHaving oil resistance suitable for conveying hot materials.Recomm endable for conveying the m aterial containing some mineraloil.

ORNormalTemp.

Oil ResistanceExcellent in o il resistance, lubricating oil, animal fa t, mineral oil, oiltreated coal, phosphate involved oil, vegetable oil, fish oil, corn oil,etc

FRNormalTemp.

Fire ResistanceResistant to flame propagation. Extremely low burning rate.Suitable for underground operation.

d) Types of Idlers

There is an array of idlers available in the market for use on conveyors in different applications.

Some examples of the different types of idlers available a re provided below. For more de tails on thetypes and design of idlers available, refer to the idler section on the contents bar.
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e) Idler Spacing

The spacing or pitch of idlers has a direct bearing on the sag of the belt between the idler sets. Theidlers on the carrying side of a conveyor must support both the belt and the load carried by the beltwhile on the return side, the idlers must only support the empty return belt. It follows therefore thatthe idlers on the carrying side must be positioned at smaller intervals than on the return side.

Excessive sag in the belt between idlers results in a higher absorbed power for the conveyor andtherefore the pitch of the idlers in conjunction with the tension in the conveyor should ensure that thesag is limited to between 1,5% and 3%.

The designer must also consider the load which the idlers mustsupport and the effe cts of this load on the design rating of the idlers'sha ft and bea rings. Spa cing idle rs too far apart will resu lt inex cessive load ing of the idlers which will reduce the life e xpe ctancy ofthe idlers.

f) Conveyor Drive Units

The location, layout and configurations of drive units on a conveyor depends on the size of the driverequired, the tensions in the belt under various operating conditions, the physical space available forthe drive unit, access to the drive for maintenance, and so on.

Some examples of drive arrangements and locations a re provided below.
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In selecting the appropriate drive for a conveyor it is common practice to standardise on commerciallyavailable drive sizes and configurations. This is important from a cost point of view as well as theclients spares holding requirements and the required delivery period.

Generally speaking drive assem blies comprising motor, high speed coupling, gearbox/reducer and lowspeed coupling are rated for the following duties. Reducers have different reduction ratios and theSuppliers should be consulted for specific information.

0.25 kW0.37 kW0.55 kW0.75 kW1.1 kW1.5 kW2.2 kW3.0 kW4.0 kW

5.5 kW7.5 kW11 kW15 kW

18,5 kW22 kW30 kW37 kW

45 kW55 kW75 kW90 kW

110 kW132 kW160 kW185 kW200 kW

225 kW250 kW315 kW400 kW450 kW500 kW550 kW600 kW

g) Pulleys

The width and diameter of the pulley to be used are determined by the width of the conveyor belt, thebelt rating or class and the required conveyor belt speed.

Some standardisation in pulley diameters and widths exists although pulley shaft diameters andlengths are usually selected for each specific conveyor.

An indication of pulley dimensions and commonly used terms is provided in the following table.

h) Take-up Assemblies

Take-up assemblies are required on all conveyors to maintain the required tension in the conveyorunder all operating conditions.

The location of the take-up, orientation of the take-up and design of the take-up depends on factorssuch as the length of the conveyor, the available headroom for the take-up and the mass of thecounterweight.

Some examples of take-up assemblies are provided below.
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i) Loading Stations

The layout and design of the loading point is often critical to the successful operation of the conveyorin as much as the alignment of the belt along the conveyor is concerned and whether or not spillageoccurs at the loading point.

A number of standard loading point configurations exist which are shown in the following diagrams.The choice of loading point design is often dependent on for example, the height through which theloaded material falls before impacting onto the belt, whether or not the material is dusty or wet, tominimise the damage caused to the belt at the impa ct point.

j) Belt Cleaning Devices

Whenever material is transported on a conveyor a certain small percentage of product is notdischarged as the belt passes around the head pulley. In instances where the material conveyed is wetand sticky, more material can be expected to carry over onto the return side of the conveyor.

The problem with carry over is that the residual material is gradually removed from the belt as the

return belt passes over the return idlers and as the material dries along the return strand. Small heapsof product can be seen forming beneath each return idler and these piles of material can grow rapidlyand have a high cleanup cost over the life of the Plant.

For this reason be lt scrapers are use d at the head end of the conveyor and belt ploughs are em ployedahead of the tail pulley. In extreme cases belt turnovers are used which physically turn the return beltupside down along the returned strand thereby preventing the dirty side of the belt coming into contactwith the idlers.

Three main types of belt cleaning devices are used namely primary scrapers, secondary scrapers andbelt ploughs. Pictures of each of these devices are provided below together with an indication of whereeach of these items may be found on a conveyor. For additional information consult the appropriatesection in this Handbook.
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k) Field Instrumentation

Conveyor belts are designed to operate reliably and continuously for many years. During

comm issioning and a fter ma intenance the performance of the conveyor is usually monitored a nd oncethe initial setting up has been completed, it can be expected that the conveyor will operate safelyunder normal operating conditions.

In practice however, abnormal conditions develop for example, material fed onto the conveyor maymisalign due to gradual buildup in the feed chute resulting in a misaligned belt which could rundangerously close to the structure and which could damage the belt. Catastrophic failures also occurfrom time to time examples of which include a belt splice failure on an inclined conveyor.

These abnormalities may occur when the conveyor is not being monitored and if left unattended,serious damage to the equipment and possibly to pe rsonnel could arise.

Field instruments are therefore used on conveyors and serve to warn the operator that an abnormalcondition is developing and will trip the conveyor should be problem become serious enough.

Most conveyors are fitted with the following instrumentation (click on the thumbnail for the full image):-

Item Description Function when actuayed

1 Misalignment detector Trip be lt if serious ly misa ligned BG29a

2 Unde r spe ed switch Trip drive and fe eding conve yor BG29b

3 Blocked chute detector Trip drive and receiving conveyor BG29c

4 Pull wire and switch Trip drive and feed conveyor BG29d

5 Emergency stop Trip drive and feed conveyor BG29e

6 Rip detector Trip drive and feed conveyor BG29f

7 Thermal Plug Trip drive and feeding conveyor BG29g
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