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Conveyor Belt Conveyor Belt Basics

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작성자 NEWZEN 댓글 0건 조회 178회 작성일 19-07-03 14:38

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Conveyor Belt Basics

 

FORWORD

“CONVEYOR BELT BASICS” has been prepared to assist those who are just becoming familiar with conveyor belting. We do attempt to use “layman’s language” you’re your convenience. However, we are dealing with a highly complex and highly technical subject. The Belting Industry, like so many other industries, does have its own unique vocabulary. This vocabulary is very descriptive and is a convenience in the long run.

 

To assist you in understanding unfamiliar terms, a “GLOSSARY OF INDUSTRY TERMS” accompanies this text.

 

If you have any question relative to conveyor belting, please feel free to contact a HS Distributor, Your Deputy General Manager at 82 55 371 3621.

 

. Conveyor Belt Basics

1. Components

Conveyor belts generally are composed of three main components:

 

1.     Carcass (Strength Member).

2.     Top Cover (Carrying Cover), and

3.     Bottom Cover.

 

2. Carcass

The reinforcement you usually find on the inside of conveyor belt is normally called the “carcass”. In a sense, the carcass is the conveyor belt since it must:

 

A.     Provide the tensile strength necessary to move the loaded belt.

B.     Absorb the impact of the impinging material being load onto conveyor belt.

C.     Provide the bulk and lateral stiffness required for load support.

D.    Provide a adequate strength for proper bolt holding and/or fastener holding.

 

Carcass is normally rated by the manufacturer in terms of “maximum recommended operating tension” permissible per ply. 

                   

Similarly, the manufacturer rate the finished belt in terms of” maximum recommended operating tension” per inch of width (which is the total of the preceding, multiplied by the number of piles in the belt construction). 

The manufacturer determines maximum recommended operating tension per inch of width by a consideration of:

 

1.     Stretch characteristics of the belt.

2.     Fastener/bolt holding capability

3.     Load characteristics.

4.     Stiffness.

5.     Impact resistance of the belt construction.

6.     Customer perception. 

 

There is relationship between the maximum recommended operating tension per inch of width of the belt and the ultimate tensile strength (breaking strength) of the belt. However, this relationship is relatively unimportant since modern day conveyor belts seldom “break”.

 

. Carcass Design

1.    Multi-Piles + Rubber =  BELTOP

The most common carcass design is made up of layers or “piles” of woven fabrics bonded together. This “conventional piled” belt construction, like HS BELTOP, generally employs a plain weave carcass which is built up into as many layers as is required to provide the necessary belt strength …bound together with rubber, Usually.

 

The rubber between the two piles is called a “skim”. Skims are important contributors to internal belt adhesion, impact resistance, and play a significant role in determining belt “load support” and “troughability.”

 

Improper or marginal “skims” can adversely affect belt performance in general and can lead to ply separation and/or idler junction failure.

 

In the “plain weave”, the “wrap yarns” (lengthwise yarns) and the “fill yarns” (crosswise yarns) pass over and under each other. This means that both members are “crimped” (Essentially, each assumes a sine-wave-like configuration.) This fact, plus the basic characteristics of the fiber used give the belt its stretch characteristics.

 

Conventional plied carcass belts have been used for decades. Consequently, they are the most common belt design used today. Most Conveyor Engineers and Millwrights are familiar with constructions and their characteristics. Virtually, all belting mechanics know how to “splice” conventional plied belts. This familiarity with the belt’s characteristics and the “ease of endlessing” gives the conventional plied belting design its broad customer acceptance.


Conventional plied belting constructions, employing all synthetic carcasses and rubber covers appropriate to the end use, like BELTOP, are particularly recommended for:

 

1.     Hard Rock Mining:

 

(A)   Aggregate,

Sand,

Ore,

(B)   Soft Minerals,

(C)   General Purpose Applications,

(D)  Vulcanized Splices, and

(E)   Forest Products.

 

In the days when cotton and similar materials were widely used as carcass components in plied belts, a breaker strip was added into the top cover for heavy abuse construction to help absorb the loading impact. The switch to modern synthetic carcass materials (like polyester and nylon) has essentially eliminated the need for the breaker strip. Today, breaker strips are seldom found in current plied belt constructions.

 

 

2. Single-Ply + Rubber = Monocon

The straight warp carcass design, yields a carcass construction wherein the basic lengthwise (wrap) yarns are essentially     uncrimped. These are the main load-carrying tension yarns. Fill yarns are then laid transversely and alternately, above and below the main tension yarns. This construction gives greater dimensional stability to the belt, and does employ a “beam” effect for better load support.

 

The yarns used are much thicker than yarns in conventional fabrics. Further, they are locked together by means of another series of lengthwise yarns, known as the binder warp system. The binder warp system locks the tension and fill cords tightly together, creating a belt which is unusually tough and which has exceptional tear and impact resistance, as well as unusual fastener and bolt holding ability.


The Monocon belting series lends itself particularly to applications requiring exceptional impact and abuse resistance, high load carrying capacities, and extended life, coupled with very low stretch. HS Monocon is ideal for mechanical fasteners of vulcanized splice applications.

 

 Monocon is recommended for:

 

1.     Hard Rock Mining,

 

(A)   Aggregate,

Sand,

Ore,

(B)   High Impact Applications,

(C)   Soft Minerals, and

(D)  General Purpose Applications.

 

3. Single-Ply + PVC =  VINYL TOP

The single-ply, straight warp carcass concept can also be coupled with PVC as the elastomer, rather than rubber. In the case of HS VINYL TOP, a single-ply, straight warp, all synthetic, carcass construction is essentially encased within a solid block of a high performance PVC elastomer..

 

The VINYLTOP belting series also introduces a solid woven carcass design into the higher tension HS VINYL TOP  belting products. The solid woven design can be considered an extension of the straight warp concept. Polyester filament yarns, as well as spun polyester staple yarns, are coupled in a highly complex fabric construction, which is somewhat similar to the straight warp. However, because of the high performance requirements of these constructions, more than one layer of basic warp yarns are used. The whole is interlocked and tied into one single mass by means of a uniquely designed binder warp system. Spun polyester staple yarns protect the two faces of the carcass construction and combined with the high performance PVC, form the working surface of the belt itself.

 

HS VINYLTOP, a single-ply conveyor and elevator belting construction which incorporates an all polyester carcass with a high performance PVC elastomer, has found wide acceptance in:

1.     A broad range of Industrial Applications,

2.     Agricultural equipment,

3.     Food processing,

4.     Grain handling (conveyor and elevator),

5.     Underground mining, such as coal, potash, and other soft minerals, and

6.     Forest products.

 






 

 

 Monocon belt constructions employ the straight warp carcass principal, coupled with appropriate rubber covers. Reduced weight and gauge with improved strength are offered.

The Monocon I (WL I) belting series yields a range up to 400 # PIW.

 

The HS Monocon belting series extends the desirability of the straight warp minimum stretch concept to the higher tension ranges by using two plies of straight warp carcass. Monocon represents the state of the art in minimum-ply conveyor belting, with a range of 400 # PIW to 1500 # PIW.


 

4. Steel Cord + Rubber

Steel cord-type constructions utilize a single layer of steel cords as tension members; and either use plies of woven fabric to reinforce the cords crosswise, or merely encase the cords in rubber. Steel cord belts are generally found in high tension application ranging from 600 PIW to 5,000 PIW and/or where extremely low stretch is a necessity. Steel cord belts must be manufactured to width, are difficult to splice, and are subject to deterioration because of rusting of the steel components.

 

5.Single Ply Kevlar + Rubber

A single ply carcass construction made of Kelvar (A new “space age” fiber material stronger than steel.) can be coupled with rubber to provide a belt construction which is superior to the steel cord approach. Higher strength is coupled with lower weight and freedom from rust deterioration. ARATOP is the high tension belt of the future.

 

6. Strength Designations

In the past, when cotton was the primary fabric for carcass construction, all fabric were designated by the weight of a piece of fabric 42” ´ 36”. As new carcass materials were developed that varied in strengths and weights, new methods of designation were required. As a general rule, current fabrics in use are designated by the working tension or strength of the fabric, shown in pounds per inch of width (PIW) ie., 80, 110, 150, 200 and 250 pound fabrics.

 

When dealing with carcass fabrics, we work with two separate strength measurements. The first is the Maximum Working Tension or Strength of the belt. This is the highest tension occurring in any portion of the belt on the conveyor system, under normal operating conditions. This is the strength measurement used to determine the proper belt for the system. The second measurement is the Ultimate Tensile Strength of the belt. The Ultimate tensile strength of a belt is the point at which that belt will rupture and fail due to excessive tension.

 

The difference between the maximum working tension and the ultimate tensile stre1ngth of the belt is often referred to as the “service factor”. On top quality domestic polyester belting, this service factor is 8-10 to 1. Most HWASEUNG R&A belting has a 10 to 1 service factor. This means that if the maximum working tension is 220 pounds PIW the ultimate tensile strength would be 2200 pounds PIW. Belting utilizing nylon constructions generally has a service factor of 15 to 1 and more. This higher service factor is necessary to overcome some of the instabilities inherent in nylon; particularly, its excessive stretch.


Cotton

 

 

 

 

 

Rayon

 

Natural Cellulose

 

 

 

 

 

Regenerated Cellulose

 

Only natural fiber used to any great extent in belting Manufacture. Increases in strength when wet. High Moisture absorption – consequently, poor dimensional Stability. Susceptible to mildew attack. At one time Represented 80% of the raw fiber input into belt man-ufacture. Currently, something less than 5%.

 

Slightly stronger than cotton, but tensile strength is lowered by water. Chemical resistance similar to cotton. High moisture absorptionconsequently, poor dimen-sional stability. Susceptible to mildew attack. Used very little in belt manufacture currently.

Glass

 

 

 

Nylon

 

 

 

 

 

 

Polyester

 

 

 

 

 

 

 

Steel

 

 

 

 

 

Kevlar

Glass

 

 

 

Polyamide

 

 

 

 

 

 

Polyester

 

 

 

 

 

 

 

Steel

 

 

 

 

 

Aramid

Very high strength compared to rayon. Low elongation. Mainly used in high temperature applications. Poor flex life. Limited use in belt manufacture currently.

 

High strength, high elongation, good resistance to abra-sion, fatigue and impact. While moisture absorption not as high as cotton, it will absorb up to 10% of its own weight in moisture Consequently, poor dimensional stability. High resistance to mildew. At one time, nylon represented 40% of the raw material input into belt man-ufacture. Today, it is something less than 20%…and shrinking.

 

High strength, exceptionally good abrasion and fatigue Resistance. Extremely low moisture absorption…cones-quently good dimensional stability. Unaffected by mildew. Polyester usage in the manufacture of belting has grown from 0% in 1960 to something in the range of 70-75% today.

 

Used where high strength and extremely low stretch are a necessity. A small amount of woven steel carcass is found in today’s market. However, more steel is used in steel cable-like belting constructions. Use limited because of tendency to rust and the “manufacture to width requirement.

 

Kevlar (the material used in flak jackets and buller-proof vests) has twice the strength of steel, with stretch char-acteristics roughly halfway between steel and polyester. It is significantly lower in weight than steel and will not rust. Kevlar appears to be the high tension material of the future. It is expensive and is currently considered experimental.

 

7. Covers

Covers are used in conveyor belt constructions in order to protect the base conveyor belt carcass and, if possible, to extend its service life. In addition, covers do provide the finished belt with a wide variety of desirable properties, including the following:

A.  Textures,

     To increase traction

     To increase inclinability

     To control product

B.    Ease of cleanability,

C.    A specific coefficient of friction,

D.    A specific color,

E.    Cut resistance, and

F.    Enhanced impact resistance, etc.

 

Cover type, quality and thickness are matched to the service life of the belt involved. A specific

cover formulation used in an individual belt construction, is determined by the material to be carried and the environment in which the belt will operate.

 

Historic belt constructions were highly susceptible to moisture and chemical attack because of their cotton (and nylon) carcass components. Accordingly, it was common to extend the belt covers over the edges of the belt in what is known as a “molded edge” construction. This type of manufacture is expensive because of the additional labor and machine time involved.

 

Modern day belt constructions, with their high adhesion levels and synthetic carcass, are considerably less susceptible to moisture and chemical attack, and do not require edge protection. They make possible the “slitedge belt distribution” program currently used in the Belting industry. Costs are minimized since an 84” slitedge belt can be manufactured about as quickly (if not more so) as a 24” molded edge construction. Further, the labor involved is somewhat less.

Georgia Duck uses an extremely wide variety of polymers for our cover needs, including: Polyvinylchloride, Natural Rubber, various Synthetic Rubbers, and urethaneto meet individual customer needs. Quality competitors offer covers made of similar polymers although their individual “recipe” may be somewhat different. 

 

Individual cover formulations are usually blends consisting of one principal polymer and assorted modifiers, such as other polymers, anti-oxidants, accelerators, curatives, pigments, extending and reinforcing fillers, plasticizers, etc.

 


be a compromise, which seeks to meet the customer’s criteria and still remain cost effective. For many applications, the blending of polymers adds properties that could not be obtained in a single polymer compound.

 

In addition to selecting proper compounds for cover material, it is also necessary to determine the proper cover thickness. The thickness of a cover is influenced by the amount of abuse and wear the belt will receive.

 

 The severity of the wear depends on the nature of the material and on the size, weight, and shape of the lumps conveyed. Sharp edges, particularly on large pieces, can quickly cut a cover badly. On the other hand, if loading conditions are ideal, with the material being loaded in the direction of travel of the belt, and with only a slight impact onto the belt, even very sharp material may not seriously cut or wear the belt surface.

 

The following table provides a good “rule of thumb” for selecting minimum covers on PVC and Grade rubber belt constructions.

 

Wearability of rubber-like compounds can be characterized by a “PICO” abrasion test. This test assigns “wearability levels” or “abrasion numbers” to various elastomers. The higher the number,

the more durable the elastomer. For example, Grade rubber normally will test out at a PICO rating of 135, while a Grade rubber will yield a PICO of 100, and PVC a PICO of 50.

 

Fillers and additives added to a given recipe can affect the PICO adversely. It is not uncommon, for example, for and oil resistant, MSHA, rubber elastomer to yield a PICO in the 50’s or 60’s.

Recommended cover thickness

Class of material                  Examples

Minimum top cover

 

Light or non-abrasive          Soft minerals, salt,

                                 Bituminous coal, potash ore

A. favorable    B. adverse

    conditions      conditions   

Standard HS VINYILTOP     HS VINYILTOP plus*

Rubber

 

1/16˝           1/18˝

Fine and abrasive              Sharp sand, clinker

1/8˝            3/16˝

    Heavy, crushed, to 3”          Sand, gravel, crushed stone

1/8˝            3/16˝

 Heavy, crushed, to 8”          ROM coal, rock, ores

3/16˝           1/4˝

 Heavy, large lumps            Hard ores, slag

 1/4˝             3/8˝+

*Consider “Thicker” HS VINYILTOP construction to get benefit of additional “Binder Warp” cover yarns.

Minimum bottom cover

1/16˝            1/8˝

Specific conveyor belt applications seldom require the belt cover to satisfy one or two conditions. More usually, a broad variety of required and desired properties are encountered. The specific cover formulation is quite likely to  

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