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How to choose the chain

DESCRIPTION OF THE ACTIONS:

The selecting procedure is characterized by the following basic points:

  1. Determination of type of conveyor to be used
  2. Calculation of total draught (in static conditions)
  3. Calculation of actual working load (in dynamic conditions)
  4. Informal choice of chain
  5. Audit of specific pressures
  6. Audit of actual working load and chain selection

1. DETERMINATION OF THE TYPE OF CONVEYOR TO BE USED

Six categories of conveyors can be distinguished; each category is characterized by the type of friction of the chain on the line (sliding or rolling) and by the way the material is carried (supported or dragging in a channel container).

Categories Chain Material
1 Dragging Supported
2 Rolling (on rollers) Supported
3 Supported by additional rollers Supported
4 Dragging with scraping paddles Dragging
5 Dragging without scraping paddles Dragging
6 Rolling (on rollers) Dragging

Table 1 - Conveyor Categories

 

2. CALCULATION OF TOTAL DRAUGHT T (IN STATIC CONDITIONS)

For each type of conveyor, use the following formulae:

  • Category of conveyors 1-2-3

  • Categoria di trasportatori 4,5,6.

were:

  • k1= Coefficient of chain friction (sliding or rolling) on the line (table 2)
  • k2= Coefficient of friction between the carried material and the channel container (table 3)
  • p= Weight of chain in kilos, per meter, including attachments, rolling shutters,plates, etc.

If the weight of the chain is unknown, make an approximate calculation with the following formulae:

  • α = angle of inclination
  • M = Weight in kilos of the conveyed material per meter of conveyor
  • A = Lenght in meters of the conveyor
  • h = Height in meters of the material that rubs against the borders of the conveying channel
  • c = Friction constant of the material against the borders of the channel (Table 3)
The chain rubs on the lines in:
K1

steel without lubrication
steel with lubrication
hard wood
polyethylene
nylon
plastic laminate

0,33
0,20
0,50
0,15
0,20
0,20 0,40
The chain runs on rollers:
K1=kr*(db/dr)

kr= 0,50 x steel roller with unfinished bore , dry
kr= 0,44 x steel roller with unfinished bore, lubricated
kr= 0,40 x steel roller with finished bore, dry
kr= 0,30 x steel roller with finished bore, lubricated
kr= 0,25 x roller in delrin

 

In the planning stage fix k1=0,20 For a efficient rolling, we suggest : dr>2,5 db

db=bush diameter
dr= roller diameter

Table 2 - Coefficient of friction (k1)

 

The chain conveys:
K2
C
cereals
Ashes
Cement
Wood Shavings
Ice
Sand, Clay, Limestone(dry)
Sand, Clay, Limestone(wet)
Coal
Coke
0,50
0,70
0,65
0,40
0,15
0,60
0,85
0,60
0,65
10
16
5
21
15
3
3
9
16

Table 3 - Coefficient of friction of the materials (k2,c)

 

3. CALCULATION OF THE ACTUAL WORKING LOAD (IN DYNAMIC CONDITIONS)

The total draught calculated according to the previous formulae, is referring to static load conditions and it’s not taking into consideration the following possible causes of dynamic stress:

CL=T * FS * FV * FC/n * 1/FA

where:

CL= Actual working load (Kilos)
T= Chain draught (Kilos)
FS= Service Factor

It takes into consideration the starting and stopping frequencies, as well as the entity of possible overloadings . (table 4)

FV= Speed factor

It takes into consideration the transfer velocity of the chain with respect to the number of teeth of the control and transmission wheels. (table 5)

FC= Loading Factor

It’s the coefficient that takes into consideration, in the event of conveyors with 2 or more chains in parallel operated by the same control unit, the eventual unequal distribution of the load on each chain . (table 6)

FA= Environment Factor

It takes into consideration the environment conditions in which the chain is working and more precisely, temperature, presence of abrasive substances , chemical agents or humidity,etc.

Limited to temperature effect we are pointing out the correction factors of the actual working load . (table 7)

n= Number of rows of chains

It takes into consideration the n° of chains assembled on the conveyor.

Characteristics of conveyor

FS

Uniform Load - constant speed
Load with limited variations - discontinuous functioning
Load with considerable variations - discontinuous and jerking functioning
1
1,3
1,7

Table 4 - Service factor (FS)

 

N° teeth

Speed (m/min.)

 

15

30
45
60
90
120
6
7
8
9
10
11
12
14
16
18
20
24
1,4
1,1
1
1
0,9
0,9
0,9
0,8
0,8
0,8
0,8
0,8
2
1,4
1,3
1,2
1,1
1
1
0,9
0,9
0,9
0,9
0,8
2,9
1,8
1,5
1,4
1,2
1,2
1,1
1
1
0,9
0,9
0,9
4,4
2,3
1,8
1,6
1,4
1,3
1,2
1,1
1
1
1
0,9
/
4
2,5
2
1,7
1,5
1,4
1,3
1,2
1,1
1,1
1
/
/
3,6
2,6
2
1,8
1,6
1,4
1,3
1,3
1,2
1,2

Table 5 - Speed Factor (FV)

 

Type of conveyor

FC

Conveyor with only one chain
Conveyor with 2 or more chains
1
1,2

Table 6 - Loading factor (FC)

 

Operating temperature
FA
-40°C , -20°C
-20°C , -10°C
-10°C , +160°C
+160°C , +200°C
+200°C , +300°C
0.25
0,30
1
0,75
0,50

Table 7 - Environment Factor FA

 

4. INFORMAL CHOICE OF CHAIN

Once the actual working load of the chain is defined, the correct choice of dimensions must take into consideration the admissible stress (strain) for the manufacturing materials.

Informally, already with a working load value of 2/3 of the breaking load of the chain, the materials are stressed over the limit of "permanent buckling".

For this reason, we suggest a breaking load of the chain equal to at least 8 times the actual working load and we are indicating this ratio as "Safety Coefficient".

Particularly hard working conditions, with tensile stress (traction strain) not easily quantified in its variations, require consistent safety coefficients, which can be defined by our technical staff which is always at your complete disposal.

The calculation of the actual working load is not always sufficient to identify the type of chain to be used . For concentrated loads on small conveyor surfaces, we also suggest to check the specific pressure values between rollers-bushes and bushes-pins.

5. AUDIT OF THE SPECIFIC PRESSURES

Another factor which must be taken into consideration for the determination of the chain dimensions is the calculation of the specific pressures between rollers-bushes and bushes-pins.

a) Calculation of specific pressure roller-bush

 

 

 

b) Calculation of specific pressure bush-pin

 

 

 

Where:

P= load supported by each roller (kilos)
CL= actual working load (kilos)
Lr= length of roller (mm)
Dfr= diameter of roller bore (mm)
Lb= Length of bush (mm)
Dp= Pin diameter (mm)

If the specific pressure values found should exceed the admissible value limits , pointed out in table 8 , it’s necessary to choose a chain with larger contact surfaces between rollers-bushes and bushes pins, so as to have a smaller load per surface unit.

Material in contact rollers - bushes
Specific pressure (kilos/mm2)
casehardened steel - casehardened steel 0,98
casehardened steel - hardened and tempered steel 0,85
bronze - casehardened steel 0.60
cast-iron - casehardened steel stainless 0,71
stainless steel - stainless steel 0,40
nnylon - casehardened steel 0,10
Material in contact bushes-pins
Specific pressure (kilos/mm2)
casehardened steel - casehardened steel 2,50
casehardened steel - hardened and tempered steel 2,10
non-treated steel - non-treated steel 1,50
stainless steel - stainless steel 1,20

nylon - stainless steel

0,90

Table 8

 

N.B. The a.m. specifications are valid when the working conditions are ideal and that is; low speed ; absence of extraneous material between the contact surfaces ; correct lubrication. If it’s not possible to respect the a.m. conditions , the specific pressures must be adequately reduced.

6. THE AUDIT OF THE ACTUAL WORKING LOAD AND THE SELECTION OF THE CHAIN

Once the actual working load (CL) and the specific pressures (PSR-PSP) are known, you proceed with the choice of the chain by taking into consideration the breaking load allowed for each type of chain.

This specification is usually indicated by the manufacturer. Once the chain is selected and the exact weight is known, proceed with the audit of the actual working load and consequently, with the choice of the chain. This is done by using the same formulae indicated for the project calculation but with the introduction of the exact values.