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Notes on the Selection and Care of Chains

Chain Selection

 There are many chains, differing in style, materials and heat treatments, within industry

The most important consideration to be made is in the correct selection of chain to suit a particular application.

The correct chain choice will ensure that there are no breakages, or problems to be encountered during service, assuming that the applicational details remain constant.

Such problems are not only very expensive, but also very disruptive to the production process.

If breakage does occur, and the correct chain has been chosen from the strength standpoint, then it could be due to the other major causes of breakage, which are abrasion and corrosion.

These two effects can cause thinning of the main load bearing components of pin and bush, down to such an extent that eventually, the components will not withstand the forces acting upon it, and breakage occurs.

Abrasion can be a problem in many areas, and of course, depends upon the cleanliness of the product being handled, or the environmental conditions, which in turn could give rise to serious problems.

Severe corrosion can again be experienced in many applications, and then this would lead to the possibility of consideration in using a corrosion resistant material such as stainless steel. However, the grade of stainless steel normally used for the articulating components, allows for a heat treatment process to be undertaken, but this leads to a compromise situation between hardness, for wear resistance, and corrosion resistance. Coupled to this, is the necessity for the stainless steel components to be kept wet for lubrication purposes, or the wear rate in dry conditions is faster than for standard materials.

Therefore, because of the increase in cost, the applicational conditions must be suitable for the use of stainless steel components, and an acceptable increase in performance noted, to offset the extra expense. 

Some applications could experience a combination of both abrasion and corrosion, so consideration of the applicational conditions and requirements must be borne in mind when the final chain selection is made.

Styles of chain should also be a consideration, and these can start at the simple cast chain designs, through the steel bushed chains and onto the steel roller chains. The steel roller chains are generally considered for applications of high loading and/or with long conveyor centres, where the lower frictional demands results in a lower strength chain being required.

Chains are sometimes chosen by their U.T.S. (Ultimate Tensile Strength) rating, but this basis of selection does not always give the best results.

Chains should be chosen by their stated Allowable Chain Pull figure.

This figure can also be called the maximum theoretical loading that is to be applied to the chain, ensuring that the pressure created between the chain pin and the chain bush does not exceed generally accepted levels.

When this figure is taken in combination with the appropriate working condition and speed correction factors, then it allows for the best means of correct chain size selection, to achieve good wear life.

The attached charts should give some guidelines to the differing chain styles generally used within industry, and show some of their advantages and disadvantages, and may assist in making the correct selection.

Chains of varying styles do overlap in terms of rated working loads, so understanding the best design requirements for the application is also necessary.

Further areas that can greatly assist in trouble free running are in a good inspection and maintenance procedure, and also consideration of good gearing characteristics with the mating sprockets.

 

General Guidelines For Chain Styles

 Steel Conveyor Roller Chains

 

Advantages

Disadvantages

Standard Materials

Smaller in size than cast or

forged chains for a given

working load

 

 

 

 

Rolling friction decreases the chain strength and conveyor power requirements

 

Very adaptable for differing attachments

Articulating components

suffer from any corrosive

conditions

(Induction hardened pins have been found to resist corrosion better than non-induction hardened pins)

With Lubricated Pin

 

Helps in resisting corrosion

Corrosion resistance is not assured

 

Increase in maintenance costs, because of increase in labour time required

 

Adequate lubrication is dependant upon human factor

 

Contamination of product by the grease may not be acceptable

 

Stainless Steel Articulating Components

Best solution for corrosive resistance

 

 

 

Negligible maintenance costs

Lubrication essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

 General;

Possible that any new chains could be based on existing components. Therefore, there may be no costly tooling.

Material quality is assured.

Rolling friction decreases the required chain strength over sliding friction. Therefore, a lighter chain is required for a given duty.

Steel chains are more adaptable for attachments and modification.

Flanged rollers, to be used as guides, can be fitted if required, to lessen the need for wear strips or guide plates.

Chain rollers have shoulders on the side faces to lessen the tendancy of packing between the roller and the sideplates.

 

Steel Bushed Chains (Non-Roller Design)

 

Advantages

Disadvantages

Standard Materials

Simple design(Minimal articulating components

 

 

Generally, attachments available as for the steel roller range

Sliding friction could increase the chain strength and conveyor power requirements

 

Articulating components suffer from any corrosive conditions

Centre Link Fitted with Stainless Steel Bush and with Stainless Steel Pin

Articulating area is corrosion resistant

Lubrication essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

General;

Possible that any new chains could be based on existing components. Therefore, there may be no costly tooling.

Material quality is assured.

Non roller type chain, and therefore friction values are higher than for a roller type chain. Stronger and larger chains may be required for a given duty.

Simple design with minimal components, could be most cost effective answer for a particular application.

  

Combination Chain (Cast Centre Link with Steel Outer Sideplates)

 

Advantages

Disadvantages

Standard Materials

Simple design (Minimal articulating components)

Generally, larger sizes than steel chains are required for a given duty, when using standard bearing area loading

 

Sliding friction could increase the chain strength and conveyor power requirements

 

Greater general casting tolerances than for steel chains

 

Attachment modifications generally restricted to outer sidebars (modifications to centre casting could mean expensive pattern costs)

 

Articulating components suffer from any corrosive conditions

Corrosion Resistant Centre and Stainless Steel Pins

Helps in resisting corrosion

Corrosion resistance not assured

 

essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

Centre Link Fitted with Stainless Steel Bush and with Stainless Steel Pin

Articulating area corrosion resistant

Lubrication essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

 

Larger size chain may be required for equivalent strength, in order to accommodate the bush

General;

Non roller type chain, and therefore friction values are higher than for a roller type chain. Stronger and larger chains may be required for a given duty.

Modifications to the centre link may be difficult, and could lead to expensive pattern changes.

Simple design with minimal components could be most cost effective solution.

 

Block Link Chains (With Cast or Forged Centre Link)

 

Advantages

Disadvantages

Standard Materials

Simple design (Minimal articulating components)

Generally, larger sizes than steel chain are required for a given duty, when using standard bearing area loading

 

Heavy

 

Sliding friction could increase the chain strength and conveyor power requirements

 

Greater general casting tolerances

 

Attachment modifications restricted to outer sidebars (Modifications to centre casting could mean expensive pattern costs)

 

Articulating components suffer from any corrosive conditions

Centre Link Fitted with Bush

Larger working loads available from equivalent strength chains, due to higher permitted bearing area loading

Larger size chain may be required for equivalent strength, in order to accommodate the bush

 

Still liable to corrosion attack

Centre Link Fitted with Stainless Steel Bush and Stainless Steel Pin

Articulating area corrosion resistant

Lubrication essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

 

Larger size chain may be required for equivalent strength, in order to accommodate the bush

General;

Non roller type chain, and therefore friction values are higher than for a roller type chain. Stronger and larger chains may be required for a given duty.

Modifications to the centre link may be difficult, and could lead to expensive pattern changes

 

Standard Cast Malleable or Cast Steel Chains

 

Advantages

Disadvantages

Standard Materials

Simplest design – only links and pins

Generally, larger sizes than steel chain are required for a given duty, when using standard bearing loading

 

Sliding friction could increase the chain strength and conveyor power requirements

 

Greater general casting tolerances

 

Attachment modifications could mean expensive pattern changes

 

Articulating components suffer from any corrosive conditions

Link Fitted with Bush

Larger working loads available from equivalent strength chains, due to higher permitted bearing area loading

Larger size chain may be required for equivalnt strength, in order to accommodate the bush

 

Still liable to corrosion attack

Link Fitted with Stainless Steel Bush and Stainless Steel Pin

Articulating area corrosion resistant

Lubrication essential (However, lubricant is only necessary to keep components wet. Therefore, steam or water spray aimed at chain is ideal)

 

Larger size chain may be required for equivalent strength, in order to accommodate the bush

General;

Non roller type chain, and therefore friction values are higher than for a roller type chain.

Stronger and larger chains may be required for a given duty.

Modifications to the link could lead to expensive pattern changes.

The simplest chain design.

 

Conclusions;

The sizes and the working loads of chains required are dependant upon the duty involved, and therefore there could be no standard chain suitable for all applications.

Roller chains have a frictional value less than for non roller chains, and for a given duty, a smaller chain may be possible because of the lower strength requirements.

In the long term, stainless steel components are the most economical in corrosive conditions. The only stipulation is that the components must be kept wet by either lubrication, or with water or steam.

Modifications are much easier with steel chains.

For an equivalent  size chain, the allowable working loads are greater for a steel chain, because of their greater allowable bearing area loading.

Greater strength can usually be obtained from a steel chain, because of the greater material and heat treatment choices available.

Steel chains generally offer the greater degree of material integrity and accuracy.

Cast chains are the most simplistic, but the choice and attachment availability is limited.

Steel bushed chains have few components, have material and heat treatment choice and attachment availability as for the steel roller chains, but being of a non roller design, may require higher strength and create greater conveyor power requirements.

 

Maximising Chain Life

As soon as the new chain is installed and is operating, wear commences and during the first few days chain stretch will occur as the chain adjusts to the sprockets, after that, initial period a slower rate of wear,(pitch elongation) normally transpires.

Understanding chain wear and appreciating basic principles of good installation, operation and maintenance will result in good maximum chain life.

We hope the following information will help you to deal with any chain and sprocket operational problems that may arise.

 

Chain Wear

Excessive wear is easy to detect, as the chain when travelling around the sprocket will appear as if it were about to “ fall off”.  The chain may be noisy in operation and it is necessary to continually adjust chain tension until only the removal of one or several links will permit the chain to continue in operation.  To avoid breakdowns it is important to establish a regular chain inspection, which should include measuring and recording the chain pitch before excessive wear results in lost down time.

Chain wear is the result of either mechanical type (abrasion of mating chain components), or outside influences such as corrosion or other application factors.

In service, chain wear is generally noticed in two areas: -

 

Pitch Elongation:  (or Chain stretch)

This is caused by wear between the pin diameter and the bush inside diameter.

When this elongation goes beyond acceptable parameters, then sprocket malgearing, and even jumping of sprocket teeth may result.

Ewart sprockets are designed to accept 5% pitch elongation (although larger sprockets may not – due to the unacceptably high tooth required), and therefore, it would be recommended that chain be replaced when the chain pitch extends 3-4% above the stated catalogue pitch.

Also, it must be remembered that due to the necessary design difference between straight, and cranked (offset) sidebar chains, then pitch elongation is seen in differing forms.

Cranked sidebar chains wear evenly on every pitch, whilst straight sidebar chains are seen to wear unequally between inner and outer chain pitches, as far as sprocket gearing is concerned.

But generally, say for 6” pitch chains, when measured over a number of pitches, if the average dimension per pitch is 6.18” (3%) then replacement should be considered.

 

Component Wear

Generally chain pins are produced from through hardened material (together with or without induction hardening), whilst chain bushes are produced from case hardening material.

Whilst case depths can vary due to component size and wall thickness, the general rule that case depths of 0.030” – 0.040” are most common could be used.

Therefore, as wear would be very much accelerated once the case has worn away, replacement would be necessary once 0.030” has worn from either chain bush inside or outside faces.

For the chain pin, replacement should be considered once 10% of the original diameter has been worn away.

Chain rollers can be case hardened, and again case depths of 0.030” – 0.040” are normal, but Ewart’s can offer their standard range of chain rollers to be of a through hardening material, in order to achieve a more consistent wear rate, without any noticeable difference in the rate of wear.

Replacement should be considered if inside or outside diameter shows wear of 0.060” – 0.080”, or if flat spots on the outside diameter are noted, or if excessive clearance with the chain bush is noted.  This could be so severe that sidebars can be seen dragging on the guideways.

Sidebars do not normally require replacing, unless either damaged, or suffering with severe corrosion.

However, it should be recognised that the pin and bush components have interference fits with the sidebar holes, and therefore, component diameters should not be reduced to make the fit easier.  Indeed, if components are found to rotate in the sidebar after fitting, then it must be concluded that damage has occurred, and replacements must be made.

Ewarts, like most major chain manufacturers, do not recommend replacing components, but we must be realistic enough to appreciate that it is a common occurrence.

Also, we must realise that customers’ also rotate components, in order to present a new bearing surface to the direction of thrust.

We therefore cannot recommend a certain number of times that components can be replaced or rotated, as this depends upon the care taken to replace the first time.  It is possible that a second set may be possible, but this can only be judged at the time, and would be dependent upon component fits.

 

Sprockets

Sprockets are designed to enable correct gearing with the chain, so therefore new chain should only be used in conjunction with new sprockets, or at least sprockets still in good condition.

Worn sprockets can cause premature failure of new chain, and therefore ignoring sprocket condition, and replacement, could be false economy.

It should be remembered, that most sprocket tooth profiles are equal on both sides of the tooth, and therefore, when one face is worn, they could be turned to allow a new unworn face to be presented.

When taking receipt of new sprockets, it is a good idea to test that the chain wraps itself cleanly around the sprocket, and also to check that if sprockets are ordered matched, to ensure that keyways are machined in line with respect to the sprocket teeth.

Generally chain and component life is dependent upon correct chain selection, controlling the working environment, and carrying out good maintenance procedure.

Chain selection, loading and speed are all very much inter related, but a major consideration would be to keep chain speed to as low as practicable, as high speed can be as much a cause of rapid chain wear as other factors.

Correct sprocket design is extremely important, because the whole of the conveyor / elevator installation depends on the chain / sprocket interaction, by converting either rotational force into pulling power, or pulling power into rotational force.

In order to successfully achieve this transference of force, then the chain and sprockets must be compatible with the correct gearing characteristics, as poor gearing could lead to either inferior chain performance, or premature chain failure.

A correctly designed sprocket tooth form should absorb the working chain tension, whilst accommodating a reasonable amount of chain wear, and should also allow for trouble free engagement and disengagement of the chain.

Ewart’s sprockets are designed to accept up to 5% pitch elongation, although the larger the sprocket, the less likely this figure is to be in fact, due to the tooth height that would be necessary. This is why Ewart recommend that the chain be replaced after 3% pitch elongation.

As can be appreciated, it is false economy to ignore the sprocket tooth condition, as indeed it is with correct alignment, and matching of the sprockets in general. Sprockets maintained in good condition will assist in achieving both improved chain performance, and in giving improved chain life.

In order to assist in achieving these aims, Ewart’s produce their plate sprockets in material to B.S. 970 grade 080A42 (Centre plate), and B.S. 4360 grade 43A for the bosses. The material choice then allows for the centre plate tooth profile to be flame hardened to a value of 350 BHN. (37.5 Rc) surface minimum, and to a depth of 1/8”, although actual results show that hardness values of 40 Rc + are generally achieved.

Chain and sprockets work together in order to give a correctly matched installation, and forgetting the sprocket condition could lead to disappointment in chain performance.

  

Extending Chain Life

This is unachievable without preventative maintenance, incorporating regular and systematic inspection of chain, sprockets and the conveyor system.

When inspecting chain drives or conveyors, look for the following conditions and take corrective action if required:

1 - Chain Cleanliness

Chains have to be protected from abrasive or corrosive materials.

2 - Chain Travel Direction

Correct installation. 

Cranked offset roller chains( narrow head of link leading ensures reduced wear).

Cranked non-roller (open end leading).

3 - Lubrication.

Reduces wear between moving parts.  Not all chains are suitable for lubrication especially in dirty, abrasive atmosphere.

4 - Poor Fit of Chain on Sprockets.

5 - Excessive Chain Stretch/Elongation

Chain has tendency to jump sprocket teeth.

6 - Excessive Wear on Outside of Links.

Marks on sidebars, or chain pins suggestion fouling of chain on conveyor structure.

7 - Discolouration of Chain

May indicate corrosion.

8 - Chain Surge ,Irregular Movement

Caused by many factors, sprockets, method of conveyor loading, alignment, conveyor structure faults, take up tension, “seized rollers”

9 - Chain Twist

Alignment problems, caused by uneven wear, tension.

10 - Loose Chain Components and Chain Attachments

Check pin cotters, chain bushes.

11 - Incorrect Chain Tension

Excessive tension promotes faster chain wear.

12 - Conveyor Structure, Chain Wear Strips

Poor condition – more chain wear.

13-Sprockets

a - Wear on sides due to misalignment

b - Tooth wear (indicated by hooked teeth)

c - Broken teeth

d - Irregular movement of sprockets on shafts

e - Drum/traction wheel slippages

If you require more detailed information on any of the above, contact us and we will be pleased to assist in any of your chain problems

 

CONVEYORS

General comments on Chain Maintenance

Chains, whether sliding or rolling, require guide rails for support, and these require positioning correctly to allow for the correct chain travel into it’s correct gearing arrangement with sprocket.

Generally, the top chain strand should be positioned, so as to allow for the chain to be lifted into it’s gearing position, whilst the bottom strand should be allowed to drop slightly from it’s gearing position.

Both the top and bottom strand guides should take into account the chain being at the lowest point of it’s gearing position.

That is, the top strand when the pitch chord is in a horizontal position, and the bottom strand when it is coincidental with the sprocket Pitch Circle Diameter.

Once the guides are in a satisfactory location, then problems in the conveyor operation require consideration of other areas.

The following charts cover areas suggested to be checked during the maintenance programme, in order to assist in the smooth running of the conveyor, and therefore, obtaining the maximum chain life.

 

Check List Explanation;

1/ Worn wear strips can increase friction, and induce out of square and uneven loading on the articulating components.

Badly grooved and worn wear strips can allow the chain sidebars to drag, and again friction is increased.

Increasing friction then places extra loading on the chain and it’s components, and this increases the wear rate.

2/ Unmatched sprockets ( or incorrectly fitted sprockets ) can place unequal loading on the chains, and again increase the wear rate.

3/ Wear strips giving the chain incorrect alignment with the sprockets, could lead to gearing problems, uneven loading, increased wear rate, and even chain breakage.

4/ Distorted or loose slats/ aprons can allow trash to fall onto the return strand.

This trash can then become trapped within the chain, which in turn can cause roller seizure and sliding , and hence increased loading and wear.

If the trash were to affect the pin/bush areas, then increased articulating loading would result, and again increased loading and wear.

In the case of carrier applications especially, trapped trash can yield corrosive juices into the chain parts, and then there is the complication of the onset of corrosion.

Air or steam jets could be positioned close to, and before the tail sprocket/drum, to ensure the chain is clean prior to articulating around the sprocket.

Whilst air is preferable, steam is sometimes more readily available, but has the disadvantage of possibly starting the corrosion process, but then could be followed by a drip feed lubrication system onto the chain.

To try and prevent trash from entering, consideration could be given to the installation of a metal deflector canopy over the conveyor return strands.

5/ Thoroughly cleaning the chains periodically, prevents any possible material build up and could prevent the possible onset of corrosion.

6/ Fouling of any side panels by pin heads would cause uneven loading , and therefore, uneven chain wear.

7/ Any scrapers should not foul the deck plates, as not only would this lead to extra loading on the chains, but would apply extra forces on the scraper/chain attachment points, and this could lead to distortion and breakage.

8/ Scraper ends should not foul the side structure, as again this could cause uneven loading on the chains, or extra loading on the chain/attachment points.

9/ Ensure as much as possible that conveyed material is evenly spread across and along the conveyor system, to even out the loading on the running gear.

 

Other Areas for consideration;

A/  Ensure that the chains used in the application are still suitable, when any increase in capacity occurs.

B/ Any change in the chains used within a particular application, may require modifications to the conveyor structure to suit.

C/ Lubrication can be supplied for pins and bushes if required.

If the points raised are addressed, then decreased downtime and increased chain life may result.

 

Suggestions for Conveyor Chain Maintenance

1/ Head and tail shafts are to be square and parallel

2/ Double strand chains are to have the sprockets matched and fitted as pairs

3/ Check wear strips for wear and replace as necessary

4/ Check wear strips to ensure correct chain alignment with sprockets

5/ Check that chain pin heads are not fouling any side plates

6/ For scraper conveyors, check that the scrapers are not fouling any side structure, or

     the deck plates

    Also, check that stub shafts and tail shafts do not restrict scraper articulation

    Check that with wear on roller chains, the chain sidebars do not foul the wear strips

7/ On slat / apron conveyors, check for distorted or loose slats and rectify or replace

8/ Remove trash or material ingress from chain where possible

9/ Check that material is evenly loaded across conveyor

10/ In  the case of a horizontal or nearly horizontal conveyor, there is no natural tension in the return  strand of chain at the point where it leaves the driving sprocket, so that applied tension is required to keep the chain down on the teeth of the drive sprocket. This is usually done by means of tensioning screws arranged to adjust the position of the sliding bearings in which the tail shaft is carried. Care should be taken that the applied tension is not too great, and that it is merely sufficient to keep the chain correctly seated on the driving sprocket.

 

 Checks for Drive Chains

1/ Head and tail shafts to be square and parallel

2/ Check that the chain is not fouling any structure

3/ Check chain tension

4/ Lubricate with good quality oil

5/ Note that a cranked roller chain design runs with the narrow end of the link leading

  

Chain Pull and Power Calculations

 The maximum chain pull and power requirements may be calculated using the formula for the appropriate conveyor layout.

The power calculated will be the power required at the headshaft.

For the motor horse power requirements, the theoretical power calculated at the headshaft should be multiplied by 1.5, to cover losses in the drive system.

Where the material is conveyed between fixed skirts, the calculated value of P must be increased by an additional allowance calculated from the formula shown.

 

Symbols

 

P

 Chain Pull

Lb f

 

 

 

Pt

Total Chain Pull

Lbf

 

 

 

C

Conveyor Capacity

Tons / Hr

 

 

 

M

Material Weight per Conveyor Unit Length

 

 

 

 

 

 =      37.3 x C

Lb / Ft

 

                    S

 

 

 

 

W

Weight of Chain + Slats / Scrapers, Etc. per Unit Length

Lb / Ft

 

 

 

S

Conveyor Speed

Ft / Min

 

 

 

L

Horizontal Centre Distance

Ft

 

 

 

H

Vertical Centre Distance

Ft

 

 

 

A

Horizontal Section of Partially Inclined Conveyor

Ft

 

 

 

B

Horizontal Distance of Conveyor Incline

Ft

 

 

 

CD

Conveyor Material Depth  =  5376 x C

ins

 

                                              CW x MD x S

 

 

 

 

CW

Conveyor Width

ins

 

 

 

fc

Chain Friction - Loaded Strand

 

 

 

 

fr

Chain Friction - Return Strand

 

 

 

 

fm

Material Friction

 

 

 

 

MD

Material Density

Lb / Cu.Ft

 

 

 

 

 

 

Average values for the coefficient of friction can be taken from the list below.

They apply to clean, moderate temperature working conditions.

 

Chain sliding                                                                 = 0.33

Rolling – up to 2.1/2” dia. Roller dry                           = 0.20

Rolling – up to 2.1/2” dia. Roller lubricated                = 0.15

Rolling – 2.1/2” – 3.1/2” dia. Roller dry                      = 0.16

Rolling – 2.1/2” – 3.1/2” dia. Roller lubricated           = 0.12

Rolling – 3.1/2” – 6” dia. Roller dry                            = 0.12

Rolling – 3.1/2” – 6” dia. Roller lubricated                 = 0.08

 

Horizontal Conveyors

 

         

 

 

                                      P = MLfm + WLfc + 1.2WLfr

 

 

 

 

 

    Horse Power (at Headshaft)    =   1.2SP

 

 

                                                             33000

 

 

 

 

 

 Inclined Conveyors

                                 P = MLfm + MH + W(Lfc + H) + {1.2W(Lfr *- H)}

 

                        Horse Power (at Headshaft) = 1.2S[P - {W(H -* Lfr)}]

                                                                                       33000

Partially Inclined Conveyors

 

P = MLfm + MH + W(Lfc + H) + 1.2WAfr + {1.2W(Bfr *- H)}

 

 

 

 

Horse Power (at Headshaft) = 1.2S[P - {W(H - *Bfr)}]

                                               33000

 

 

 

NOTE;

Where the term * in the chain pull and power formula give a negative value, they should be regarded as zero.

Consequently, the whole term designated thus {  } is zero.

 

Additional Chain Pull

                                         =    MD x  L x CD2        Lb

                                                                                        1000

   

 

 

 

 

 

This additional chain pull should be added to Chain Pull P before calculating the power required at the headshaft.

When calculating a specific chain pull, apply the appropriate service factor and speed factor from the following tables to obtain the equivalent chain pull.

If this figure should exceed the allowable pull listed for any pre-selected chain, then a higher rated chain is required.

 

 

         

Chain Service Factors

CONDITION OF LOADING

GENERAL WORKING CONDITIONS

CLEAN , MODERATE WORKING TEMPERATURE

FAIRLY DUSTY ,MODERATE WORKING TEMPERATURE

EXPOSED TO WEATHER, ABRASIVE,MILDLY CORROSIVE, HIGHER TEMPERATURES

WORKING  HOURS  PER  DAY

0 - 10

Over 10

0 - 10

Over 10

0 - 10

Over 10

UNIFORM  OR  STEADY

1.0

1.2

1.2

1.4

1.4

1.7

INFREQUENT  MODERATE SHOCK

1.2

1.4

1.4

1.7

1.7

2.0

INFREQUENT  HEAVY  SHOCK

1.5

1.8

1.8

2.2

2.1

2.5

FREQUENT  HEAVY  SHOCK

1.8

2.2

2.2

2.6

2.5

3.0

 

Speed Correction Factors

Cast and Combination Chains

No. TEETH ON  DRIVING SPROCKET

SPEED OF CHAIN IN FT / MIN

10

20

30

40

50

60

70

80

90

100

8

0.9

1.0

1.1

1.1

1.2

1.3

1.3

1.4

1.4

1.4

10

0.9

0.9

1.0

1.0

1.1

1.1

1.2

1.2

1.2

1.3

12

0.9

0.9

0.9

1.0

1.0

1.0

1.1

1.1

1.1

1.1

16

0.8

0.9

0.9

0.9

0.9

1.0

1.0

1.0

1.0

1.0

20

0.8

0.8

0.9

0.9

0.9

0.9

1.0

1.0

1.0

1.0

24

0.8

0.8

0.8

0.9

0.9

0.9

0.9

0.9

0.9

0.9

Steel Chains

No. TEETH ON DRIVING SPROCKET

SPEED OF CHAIN IN FT / MIN

10

20

30

40

50

60

70

80

90

100

8

0.8

0.9

0.9

1.0

1.0

1.1

1.1

1.2

1.2

1.3

10

0.8

0.8

0.9

0.9

1.0

1.0

1.0

1.0

1.1

1.1

12

0.7

0.7

0.8

0.8

0.9

0.9

0.9

1.0

1.0

1.0

16

0.7

0.7

0.7

0.8

0.8

0.8

0.9

0.9

0.9

0.9

20

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.8

0.8

0.9

24

0.7

0.7

0.7

0.7

0.8

0.8

0.8

0.8

0.8

0.8

 

Material  Weight Bulk Density Examples 

 

MATERIAL

AVERAGE WEIGHT

LB. / Cu. Ft.

 

 

MATERIAL

AVERAGE WEIGHT

LB. / Cu. Ft.

Alum. Lumpy

50 - 60

Coke, Sized

23 - 32

Ashes, Dry – ½” and under

35 - 40

Coke, Mixed

25 - 35

Ashes, Wet – ½” and under

45 - 50

Coke, Breeze

25 - 35

Ashes, Dry – 3” and under

35 - 40

Cottonseed, Undelinted

18 - 25

Ashes, Wet – 3” and under

45 - 50

Grains

38 - 45

Bagasse

10

Gravel, Dry, Screened

90 - 100

Bagasse, Wet

40

Ice, Crushed

35 - 45

Beans, Whole

45 - 50

Lime, Ground

55 - 65

Cane, Chopped

18 - 20

Lime, Pebble

55 - 60

Cane, Shredded

20

Sand, dry

90 - 110

Cement, Portland

75 - 85

Sand, Damp

110 - 130

Cement, Clinker

75 - 80

Sand, Foundry, Shakeout

85 - 95

Coal, Anthracite Nuts

50 - 55

Sand, Foundry, Prepared

90 - 100

Coal, Anthracite, run of mine

50 - 55

Sawdust

10 - 13

Coal, Bituminous, Sized

45 - 55

Stone, Dust

75 - 85

Coal, Bituminous, run of mine

45 - 55

Stone, Screened Lumps

85 - 90

Coal, Bituminous, Slack, Dry

40 - 50

Stone, Lumps and Fines

85 - 90

Coal, Bituminous, Slack, Wet

50 - 60

Wood, Chips

12 - 20

 

  

CONVEYORS WITHIN THE PROCESS INDUSTRY

The following data covers the use of acetal and malleable iron crate conveyor chains within the process industries.

The maximum chain pull and power requirements can be calculated using the following formula, utilising the appropriate factors, as necessary.

Bends should be placed as far away from the head shaft as possible.

When using 50mm or 1700 chains with turnwheels, calculate as for a straight conveyor, and multiply the result by 1.12n  ( where n = number of turns ) 

Symbols

Units

CP

C

W

M

S

Fc

Ft

D

B

N

Fp

L

Chain Pull

Conveyor Centres

Chain Weight per Metre of Conveyor

Product Weight per Metre of Conveyor

Conveyor Speed

Friction ( Chain / Conveyor Bed )

Temperature Factor

Duty Factor

Bend Factor

Number of Bends

Friction ( Product / Chain )

Length of Accumulation

Kgf

M

Kg / M

Kg / M

M / Min

-

-

-

-

-

-

M

     

NOTE:

If there are NO bends on the conveyor circuit, then make B and N =1

If there is NO accumulation on the conveyor, then make Fp and L =1

 

CP = [ { C x Fc ( M + 2W ) + ( M x Fp x L ) } x B x N x Ft x D ]

 

HP ( KW ) = [ { ( CP x 2.204 ) x ( S x 3.281 ) } x 1.5 x 0.746 ]

                                                         33000                                         

 

FRICTION FACTORS ( Fc )

Chain

Conveyor Bed

Factor

Dry

Wet

Dry

Wet

Stainless Steel

Stainless Steel

Polyethylene

Polyethylene

0.22

0.13

0.27

0.10

 

FRICTION FACTORS (Fp )

PRODUCT

FACTOR

METAL CANS

PLASTIC CARTONS

CARDBOARD

WAX BOARD

0.18

0.20

0.30

0.35

 

BEND FACTOR ( B )

TURN ANGLE ( DEGREES )

FACTOR

30

45

90

180

1.2

1.4

1.5

2.0

 

TEMPERATURE FACTOR ( Ft )

TEMPERATURE RANGE ( DEG. C )

FACTOR

- 40 TO  - 20

- 20 TO  - 0

     0  TO + 60

+  60 TO + 90

+ 90 TO + 105  ( Dry Applications )

+ 90 TO + 105  ( Wet Applications )

0.8

 0.9

1.0

1.5

2.0

2.67

DUTY FACTOR ( D )

DUTY

FACTOR

STEADY

STOP / START  -  OCCASIONALLY

STOP / START  -  6 PER HOUR

STOP / START  - 12 PER HOUR

STOP / START  -  FREQUENTLY

1.00

1.25

1.50

1.75

2.00

  

CHEMICAL RESISTANCE CHART FOR ACETAL MATERIAL

            CHEMICAL

RESISTANCE CODE AT 23 DEG. CENT.

Acetic Acid – 20%

Acetone

Ammonia

Beer

Beverages, Soft Drinks

Benzine

Bleach

Bromine Water

Carbon Tetrachloride

Chlorine

Citric Acid

Formaldehyde

Formic Acid

Glucose

Hydraulic Fluid

Hydrochloric Acid

Hydrocyanic Acid

Hydrogen Peroxide – 3%

Iodine

Kerosene

Milk

Motor oil

Nitric Acid

Oils ( Vegetable and Mineral )

Phosphoric Acid – 25%

Soap Water

Sodium Hydroxide – 10%

Sodium Hypochloride ( Bleach )

Sulphuric Acid – 3%

Sulphuric Acid – 10%

Vinegar

Water ( Fresh and Salt )

 

B

B

A

A

A

A

C

C

A

C

B

A

C

A

A

C

C

A

A

A

A

A

C

A

C

A

A

C

A

C

B

A

A = LITTLE ATTACK                                                          B = SLIGHT ATTACK

C = BAD ATTACK, DO NOT USE IN THIS ENVIRONMENT

 

DRIVE CHAINS

Chains for power transmission can be of either steel or malleable construction, and where the loading and the speed are not excessive (say 400 Ft / Min ), then a malleable chain may be preferred.

Cranked sided chains should be arranged to travel thus;

 A/ Roller end leading – Roller Chains

B/ Open end leading – Non Roller Chains

( See diagrammatic sketches for detailed explanation )

Chains for drives generally operate at higher speeds than for conveyors and elevators, and therefore, shorter pitch chains are necessary.

Power is the product of force and speed, so that when the speed is very low, the pull in the chain will be relatively very high.

For higher speeds, the chain pitch should be as short as possible, whilst the longer pitches are generally used for lower speeds, and thus heavier loading.

The smaller sprocket should be as large as is practicable, but preferably not less than 12 teeth.

For preference, a chain drive should be arranged as nearly horizontal as possible, and vertical drives should be avoided.

The slack side of the chain should be properly tensioned, as too much tension will cause undue wearing of both the chain and the sprockets. But, too little tension may allow a chain to jump the sprocket teeth, or could cause damage by allowing the links to ride up the teeth, and if the speed is high, then shock loads due to whipping may result.

A steeply inclined drive should be fitted with some means of adjusting the tension in the slack side. Such drives need tighter chains than for horizontal installations, but for the best results, tension should still be as low as possible, not being more than is necessary to keep the chain on the sprocket.

 

 

A jockey sprocket engaging with the slack side of the drive near to the driving sprocket forms a convenient method of applying slack side tension.

  

Direction of Travel

 

Roller Chains

 

Non Roller Chains

The following formulae may be found useful in determining the chain required for a particular application.

The calculated chain pull should be less that the allowable pull figures to be found in the chain tables.

 

Chain Pull

P = HP x 33000             where  V = No.teeth x RPM x chain pitch (ins)

                                  V                                                           12

Symbols

Units

P

 

HP

 

V

Chain Pull

 

Motor Horse Power

 

Chain Speed

Lbf

 

--

 

Ft / Min

     

 

Slack Side Tension

For a drive approximately horizontal, the deflection or sag in the slack side may be determined by the following.

 

Symbols

Units

D

H

S

 

Pc

W

Deflection or Sag

Horizontal Span

Excess Chain or Difference between Actual Slack Side Length and   the Horizontal Span 

Catenary Pull

Weight per Foot of Chain

Ins

Ins

Ins

 

Lbs

Lbs

     

    ____

D = Φ 0.375 H S

An approximation of a suitable amount of allowable sag may be taken as 2% of the sprocket centres.

 

Catenary Pull 

It should be remembered that the less the amount of sag , the greater will be the catenary pull.

In approximately horizontal drives of moderate centres, an excess of chain equal to one pitch will result in a catenary pull of sufficient magnitude to keep the chain on the sprocket teeth, at the standard pressure angles, even though the friction between chain and sprockets would be very low, as in a well lubricated steel roller chain.

The catenary pull in the slack side of an approximately horizontal drive may be found from the following.                          

Pc = W ( H 2 +  8D2 )

96D

Length of Chain

The length of chain needed for a given drive may be found from;

Symbol

Units

L

C

N

n

Required Length

Sprocket Centres

Number of Teeth on Large Sprocket

Number of Teeth on Smaller Sprocket

Pitches

Pitches

-

-

     

 

 

 

The above formula will obviously give the theoretically correct chain length, but will not be to the exact pitch length. The next nearest exact pitch length should be used in the application, and the difference between these two figures can then be used in the formulas quoted before.

 

 

 

 

 

 

 

 

 

 

 

 

 

ELEVATORS

Chains can be utilised in differing designs of elevator, which can generally be categorised into the following styles.

 

A/ Centrifugal Discharge – uses either single or double chain strands ( double strand would be preferable for buckets 16” long and over.

These are probable the most common form of elevator, and handle a wide range of materials.

They should not be used for light fluffy materials, or those that would resist dredging or digging.

They operate at generally higher speeds than the other designs( say 180 – 250 Ft / Min. ) and the discharge of material is a result of centrifugal force.

 

B/ Positive Discharge or Dump Type  - uses double chain strands.

These operate at much lower speeds, and are ideal for handling light, fluffy, fragile and sluggish materials.

These elevators must use double strands of chain, which are attached to the ends of the buckets. This then allows the descending chains to engage on deflector sprockets positioned below reatively large head sprockets.

During the passage of the bucket from the head shaft to the deflector sprocket, they become inverted and the material falls by gravity into the discharge chute.

 

C/ Continuous Non Overlapping – uses either single or double chain strands ( double strand would be preferable for buckets 18” long and over.

These also operate at slower speeds ( say 100 – 120 Ft / Min ), with the buckets being of a special design and fitted continuously on the chain.

The discharge of the material is then by hitting and sliding off the back of the preceeding bucket. The depth of the bucket then determines the pitch of the chain required.

They are most suitable in handling light, friable materials, and those containing large lumps.

 

Chain Pull – Vertical Bucket Elevator

 

The maximum pull in the chain on a vertical elevator is at the top of the ascending strand, and is the sum of the following;

The weight of the ascending strand(s) of chain

The weight of the buckets on it

The weight of the material in them

An allowance for the dredging action of the buckets through the material in the boot.

 

Note;

 

 The dredging allowance is independent of the height of the elevator, but does depend on the weight of the material being handled, and the size of the bucket, so the following equations are to be used for the allowance to be made.

 

Symbols

Units

A

Ac

W

S

Allowance for Spaced Bucket Elevators

Allowance for Continuous Bucket Elevators

Weight of Contents of each Bucket

Bucket Spacing

Lbs

Lbs

Lbs

Ins

     

 

 

It will be noticed that the allowance for the continuous bucket elevators is less than that for spaced bucket elevators. This is because there is little or no dredging in continuous bucket elevators if they are properly fed.

                        A = 360 x W

                                 S

 

OR             Ac = 120 x W

                                  S

 

Once the above Chain Pull has been calculated, then this figure should be multiplied by the appropriate service and speed factors ( to be found in the Conveyor Section ), in order to arrive at the Effective Chain Pull.

The selected chain should then have an allowable chain pull, equal to or in excess of, this calculated Effective Chain Pull.

 

 

Power to Drive – Vertical Elevator

 

It will be appreciated that the weight of the chain and buckets on the ascending strand will be balanced by the same weights on the descending strand, and therefore, the Horse Power is only required to lift the material in the buckets and to overcome dredging.

 

Symbol

Units

D

Wm

N

A or Ac

Pitch Circle Diameter of Sprocket

Weight of Material in the Buckets on the Ascending Strand

Speed of Sprocket Shaft

Dredging Allowance ( see above)

Ins

Lbs

Revs / Min

Lbs

     

 

HP = D ( Wm + A ) N

                                                     2 x 63025

 

The figure found above is for the horse power required at the top shaft, and the size of the driving motor should have an allowance to account for losses in the reduction gearing system and frictional losses.

A figure of twice the theoretical horse power at the top shaft may be required to allow for the starting power needed.

 

 

Chain Pull -  Inclined Bucket Elevator

 

As for the vertical elevator above, the chain maximum pull occurs as the ascending chain enters the top sprocket. It is equal to the static pull acting in the line of the chain, plus the force required to overcome friction by either skidding or rolling with the guides. Also, as for the vertical elevator, an allowance should be made for dredging.

 

 

 

 

Symbol

Units

W

Ψ

μ

A or Ac

Total weight of chain, skidders, and contents of the buckets

Angle of inclination

Coefficient of friction between skidders and guides

Allowance for dredging ( see above )

Lbs

Degrees

-

Lbs

     

 

P = W ( sin Ψ + μ cos Ψ ) + A  Lbs

Again, as for the vertical elevator, the above requires the application of the service and the speed correction factors to arrive at the Effective Chain Pull figure.

 

Power to Drive – Inclined Elevator

 

The power required at the top shaft to drive an inclined elevator can be found by the following.

 

Symbol

Unit

D

P1

P2

 

A or Ac

N

Pitch Circle Diameter of Sprocket

Pull at the top of the ascending strand of chain

Wg = Weight of chain, buckets and skidders on descending strand

 = Wg ( sin Ψ - μ cos Ψ )

Allowance for Dredging ( see above )

Speed of Sprocket Shaft

Ins

Lbs

Lbs

 

Lbs

Rev / Min

     

 

Spaced Bucket Elevator

 

                        H P = D ( P1 – P2 + A )N

                                                       2 x 63025

 

Continuous Bucket Elevator

 

                        H P = D ( P1 – P2 + Ac ) N

                                      2 x 63025

 

As before, this figure should be increased to find the drive motor size.

 

 

 

 

 

Chain Tension in Elevators

 

The bottom shafts of elevators are normally carried in sliding bearings, which are generally operated by tension screws.

Sometimes this tension gear is misused, so the following comments may be found useful.

It is essential that an elevator chain, together with the buckets, are constrained to a proper path through the boot and not allowed to wander to either side, nor be forced upwards by the material in the boot. The bottom sprocket serves this purpose, if its position is adjusted so that it nestles comfortably in the loop of the chain. It should not be forced hard down so as to add tension to both the ascending and the descending strands of chain. Such applied tension is unnecessary to the correct working of the elevator, and could actually cause considerable harm by increasing wear on both the chain and the top sprocket. The natural tension at the top of the descending strand of a vertical or a steeply inclined elevator is far greater than is necessary for correct gearing at the top sprocket.