3.1 Introduction | unit 3 design of belt conveyor system for material handling

MSD

UNIT 3

DESIGN OF BELT CONVEYOR SYSTEM FOR MATERIAL HANDLING

3.1 Introduction

The development of material handling system to move materials from one stage to another stage is very important. Materials handling includes moving, packaging and storing all the materials used by the production unit. Material handling is one of the important management and also in production.

Materials are received and is moved into the plant and transferred to the storeroom. When materials are needed it is moved along the path of manufacturing. Plant layout and, material handling are closely inter-related; it has to be adjusted according to the layout of the plant.

3.2 System Concept

A general definition of the system is a complex unity formed of many diverse parts subjected to a common purpose.

The characteristics of system are called subsystems.

Material handling can also be considered to be a system whose subsystem is

Method or design to be adopted

Maintenance required for the equipment

Transportation made by the suppliers, distributors etc...

Types of material handling equipment to be used.

The system concept of material handling means the different types of material handling needed at different parts of an industry. The use of this will reduce overall cost.

It should operate at low initial cost and operating cost

The system should not create problem to the product cycle

Future development should be easy

The system should be selected so that it should achieve maximus output.

3.3 Objectives of Material Handling System

The basic objectives of material handling system are:

Reduce the manufacturing cycle time

Transport of loads in planned quantity

Safe transport of the load without damages

Contribute toward a better control of the flow of goods

Gain higher productivity at lower manufacturing cost

Safe operation

Achieve decreased storage requirement

3.4 Unit load and Containerization

The types of load handled by a material handling system can be of two types

 Bulk load

A bulk load is the form of particles, powders or lumps of homogeneous materials, which cannot be counted by numbers.

Example are coal, iron ore, sand, cement, clay etc...

 Unit load

Unit loads are those loads which can be counted by numbers or units

Examples are machine, building block, containers etc...

Containerization

In a high productivity cycle, handling small sized packets or units is inconvenient and uneconomical.

In such cases, containers of different sizes and shapes are used for handling such materials. Many a time, certain quantities of bulk material can be placed in a container which can then be handled as unit load. This process of converting a bulk load into a unit load is called as containerization.

3.5 Consideration of Containerization

Limit the number of containers sizes and shapes

Design the container based on the requirements of the material to handle

Container size taking into account the area or space available of handling material.

Containers design for stacking arrangement. This reduces storage costs.

The containers should be properly coated or painted

Colour code for the containers by functions.

Wooden or plastic containers are rust free, but have limitations on their life, cleanliness and can also be hazardous in case of fires

Steel containers are sturdy and have a long life

Wire mesh and steel containers are preferred over wooden or plastic containers.

3.6 Belt Conveyors

In this conveyor, the active side of belt remains flat supported by cylindrical rollers or flat slider bed

A belt conveyor consist of two end pulleys, with a continuous loop of material that rotates about them

The pulleys are powered, moving the belt and the material on the belt forward. The belt span is supported by idlers spaced along the length

Flat belts are conveniently used for conveying parts between workstation or in assembly line in mass production of goods.

3.7 Flat belt conveyors

In this type of conveyor the side belts remain flat supported by cylindrical rollers. These are used for shorter length and suitable for unit loads such as boxes, packages etc. and in manufacturing, assembly operation. These are used for conveyors between workstation and in assembly line for mass production.

3.8 Troughed belt conveyors

In this conveyor wide flat belt is supported on troughed carrying rollers or shaped supporting surface so that the two edges of the active side of the belt are elevated from the middle part to form a trough, it provides a greater carrying capacity than a flat belt of equal width for conveying bulk materials. Such type of conveyors are used in handling bulk material of different classes.

3.9 Capacity of Conveyor

Capacity of belt conveyor (Q):

The material which is carried out by conveyor system is called capacity of the conveyor.

Q = C x b2 x V m3/sec

where, b = Storage material width in m = (0.9 B – 0.05)

B = Width of the belt in m

Q = Capacity of conveyor m3/sec

M = Mass capacity of conveyor

V = Speed of belt

Horizontal belt conveyor capacity :

Q = C x b2 x V

Q = C(0.92B – 0.05)2 V m3/sec

where C = Surge factor

Capacity of inclined Belt Conveyors :

Q = K x b2 x V m3/sec

Q = K (0.9B – 0.05)2 V m3/sec

Q = K (0.9B – 0.05)2 V x 3600mi3/sec

Mass capacity of inclined conveyor

M = ρQ

K = Flow ability Factor

ρ = Density of material

Conveyor belt speed :

The running conveyor belt travels at speed which is called as conveyor speed

The speed depend on

The size of lump

The belt width

Type of material

The weight of material is fine and light in order to prevent slippage

The wider belts are operated at higher speeds

The different conveyor belts speed for different material is given in the table below

Standard belt width used for the conveyor belts are:

400, 450, 500, 600, 750, 800, 900, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400 mm.

3.10 Rubber Covered Belt

Synthetic rubber is in use for belts. Combination of synthetic and natural rubber have been found satisfactory. Synthetics are superior under special circumstances eg, neoprene for flame resistance and resistant to petroleum based oils, Buna N for resistance to vegetable, animal and petroleum oils, and butyl for resistance to heat.

Fabric Ply Belts :

The most common carcass design is made up of layers or piles of woven fabrics bonded together. The fabric is made from a variety of materials. Some of these are listed below with characteristics.

Material	Characteristics
Cotton(Natural Cellulose Composition)	This is the only natural fibre carcass used excessively in conveyor belts. Its strength increases when it is wet but the absorption of moisture results in poor dimensional stability. It is also susceptible to mild dew attacks.
Rayon (Regenerated Cellulose Composition)	Slightly stronger that cotton, but tensile strength is lowered by water. High absorption reduces the dimensional stability. Chemical resistance is similar to cotton and is Susceptible to mildew attack.
Glass	Very high strength compared to rayon. Low elongation, mainly used in high temperature applications. It has poor flex life and has a limited use.
Nylon (Polyamide)	High strength, high elongation, good resistance to abrasion, fatigue and impact. Moisture absorption not as high as cotton but it reduces the dimensional stability.
Polyester	High strength, exceptionally good abrasion and fatigue resistance. Extremely low moisture absorption and is unaffected by mildew and is used extensively for conveyor belts (70 to 75% of all conveyor)
Kevlar (Aramid)	Aramid has twice the strength of steel, with stretch characteristics roughly half wave between steel and polyester. It is significantly lower in weight that steel and will not rust. The belts made from this are extremely expensive and are used only in special circumstances.

3.11 Conveyor Pulley

The conveyor arrangement uses the following types of pulleys

Driving Pulley (Head and Tail pulley)

Snub Pulley

Idlers

Driving pulley (Head and Tail pulley)

Drive pulley is located at the discharge terminal of the conveyor. It provides driving force for the conveyor. In order to increase pulley life and traction, it often has larger diameter than other pulleys.

They are manufactured in a wide range of size and consist of a continuous rim and two end discs fitted in the hub. The rim is supported by stiffening discs welded to it to support large loads.

The pulley may be straight faced or crowned due to such arrangements the crown helps in keeping the belt cantered

Crown height is 0.5% of pulley width and not less than 4 mm.

Snub Pulley

These are used to increase the angle of wrap of the belt and overall for all the necessary changes in belt direction in the areas of counterweight tensioner, mobile unloader etc.

The choice of the optimum conveyor system and its project design and rationalization depends on full knowledge of the construction characteristics and the forces involved that apply themselves to all the system components.

16) BELT TAKE UP ARRANGEMENT

 Idlers

Idlers

The efficiency of belt conveyor is mainly dependent on idlers. For higher efficiency of conveying systems, the idlers must be accurately made and provide a rigid framework. This will maintain a permanent, well balanced smooth running alignment.

There are, in general, three kinds of belt carrying idlers used in handling of bulk materials. The type of idlers affects the cross-sectional load on the belt.

Flat belt idlers: are used for granular materials having an angle of repose of not less than 35°. Flat belt idlers are preferred for low capacity requirements.

Toughing idlers with 20° through: are used for conveying all kinds of bulk materials.

Troughing idlers with 35° and 45° through: are used for transportation of small particles and lightweight materials like grain, cotton seed etc.

There are two basic types of belt conveyor idlers:

 Carrying idlers which support the loaded run of the conveyor belt; and

 Return idlers which support empty return run of the conveyor belt.

Carrying Idlers

 Carrying idlers

Usually troughed with 3 equal size rollers on a frame in mining applications

Some suspended catenary systems have 5 rollers

Toughing angles are usually 20, 35, 45 degrees

Deeper trough more volume

Requires thinner belt to lay in trough which limits strength.

Return Idlers

Usually Flat and one piece

Sometimes two-piece V for belt training

Spiral roll to self and belt clean

Rollers

3.12 Belt Tension Take-up System

Main functions of take up are:

Ensuring adequate tension of the belt leaving the drive pulley so as to avoid any slipping of the belt.

Permanently ensuring adequate belt tension at the loading point and at any other point of the conveyor to keep the troughed belt in shape and limit belt sag between carrying idler

Compensating for operating belt length variation due to physical factors (instantaneous tensions, permanent elongation, outside temperature, temperature of conveyed material, dampness, etc.)

Making available, if needed, an adequate extra length of belt to enable re-joining without having to add an extra piece of belt.

Two types of belt take up devices are generally used:

 Fixed take-up devices that are adjusted periodically

 Automatic take-up devices (constant load type)

Fixed take-up devices that are adjusted periodically

In this type of take-up devices, the take-up pulley remains fixed between successive periodic adjustments.

Take-ups of this type generally used are:

Screw take-up — in this system the adjustment is manually effected by means of two screws acting upon the pulley bearings and which are tightened simultaneously or successively. The screw is normally of non-extendable type and sliding surfaces are suitably protected against ingress of dirt. In this system, the applied tension is not fully determinable. This generally leads to excessive tension of belt (when tension is insufficient, belt slips and quickly deteriorates). This excessive tension is unavoidable and shall be taken into account when determining the size of the belt, designing the mechanical components and calculating the adjustments. For this reason, these devices are used only in case of short conveyors of up to 60 m length s and under light duty cycle condition

Winch take-up — in this system, the tension is adjusted by means of a mechanical motorized device which does not automatically compensate for belt length variations. A tension indicator may be included between winch and pulley. This system also requires careful checking of tension and leads to excessive belt tension in order to avoid too frequent take-ups. However, it may be used for long conveyors and under heavy duty conditions provided that these conveyors are equipped with belts having very low elongation coefficient under the effect of load and over a long period, for example, steel cord belt s which are use d almost exclusively.

 Automatic take-up devices

In this system, take-up pulley is mounted on slides or on a trolley and travels freely while a constant tension is automatically maintained to ensure normal conveyor operation in all cases. The most frequently used type is gravity weight operated take-up device. Hydraulic, pneumatic or electrical take-up devices of

Various types are also used. All types of automatic take up devices shall include a system for adjusting belt tension. Automatic take-up has following features:

It is self-adjusting and automatic.

Greater take-up movement is possible.

It is suitable for horizontal or vertical installation.

It is preferred for long center conveyors.

It can be located at drive end (preferred for low tensions).

In case of underground mines, provision of loop at drive end may be made to cater for take-up and small extension of belt conveyor lengths.

3.13 Power Requirements of Belt Conveyors

The power requirement of belt conveyor is

Power required to lift the load at height ‘h’

Power required to overcome frictional resistance at different points

Let, Q = Conveyor capacity m3/sec

ρ = Mass density of material kg/ m3