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Conveyor Belt Coveyor belt Basics

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작성자 NEWZEN 댓글 0건 조회 294회 작성일 19-07-05 12:24

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Conveyor Belt Basics

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

 

 
 

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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).

 
 

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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.

 

 

 
 

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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.

 

 

 

 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.

 

 

 
 

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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.

 

 

 
 

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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.

 

 

        
 

Materials-Fibers        Carcass  materials used in belt manufacture in recent years are listed in the  following table: (Please note their characteristics and current position in  the market place.)

 
 

 

 

Common name             Composition                          General Comments

 
 

 

 
 

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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.

 
 

 

 
 

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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.

 

 

 

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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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˝

 
 

:..

 
 

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Ⅲ.  Methods of Belt Manufacture

 

The major  methods of conveyor belt manufacture are:

 

1.       Millable elastomeric technique,

 

2.       Liquid elastomeric technique, and

 

3.       Extrusion/lamination.

 

 

 

1.      Rubber

 

Rubber and  rubber-like elastomers are millable in nature. That is to say, they have the  consistency of “chewing gum”. The first step in this type manufacturing  approach is to warm the elastomer to the point where it can be combined with  carcass plies. Elastomers of this type have an exceedingly high insulation  characteristic. Accordingly, it is very difficult to get heat into the  elastomer by conduction means. Normally, the elastomer is “worked” of  “milled” in a warming mill. The action here is very similar to the action of  a housewife in kneading bread. The point is, mechanical energy is converted  to heat energy and the elastomer warmed to and appropriate temperature.

 

 

 

The warmed  elastomer is now rolled into a thin film by calendaring, This thin film,  called the “skim”, is now placed between plies of carcass material. The  “calendar”, which is nothing more than a large, high pressure roller, forces  the warmed uncured elastomer into and onto the carcass material, which had  been previously treated for a adhesion purposes. The carcass plies and  elastomer skims are stacked onto each other as required … the covers are  applied in a similar manner. Calender rolls are adjustable, allowing the  uncured elastomer to be rolled into various thicknesses as required by the  top and bottom cover specifications. For thicker covers, the process may  require more than one pass through the calender.

 

 

 

This “green”  belt (meaning uncured) is dusted with a “dusting powder” and interleaved with  a release sheet as it is rolled up on the take-up. The object here is to  prevent the uncured covers from sticking to each other.

 

 

 

From the  calendar, the uncured belt is taken to a vulcanizing press, where appropriate  heat, pressure, and time will vulcanize the rubber-like elastomer and create  a finished belt. Single-ply, minimum-ply, and multi-ply belt constructions  are all handled in essentially the same manner.

 

 

 

Vulcanizing  presses used can be either flat bed or rotary.

 

 

 

A flat bed  press is designed to cure a section of belt for a specified amount of time  under specific pressure and temperature conditions. This type of press is  usually used for heavy covered and thick belts. They are also used there  specialty covers, such as cleats or chevrons, are molded into the cover  during vulcanization. The flat press can be equipped with one or more curing  decks, or curing units..