DESCRIPTION OF THE ACTIONS:
The selecting procedure is characterized by the following basic points:
-Determination of type of conveyor to be used
-Calcolo del tiro totale (in condizioni statiche)
-Calculation of total draught (in static conditions)
-Calculation of actual working load (in dynamic conditions)
-Informal choice of chain
-Audit of specific pressures
-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
 |
Horizontal (se Y/X < k1) T=k1*(2p+M)X+(M*Y) (Kg) Inclined (se Y/X > k1) T=(p+M)*(k1*X*Y) (Kg) |
- Category of conveyors 4-5-6
 |
Horizontal (se Y/X < k1) T=(2k1*p+k2*M+1000*h²/c)*X+(M*Y) (Kg)
Inclined (se Y/X > k1) T=(k1*p+k2*M+1000*h²/c)* X+(p+M)*Y(Kg) |
wgere:
- 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:
- p=0,0015*M for conveyors 1-4-5-6
- p=0,0005*M for conveyors 2-3
- M= Weight in kilos of the conveyed material per meter of conveyor
- X and Y = Horizontal and vertical projection 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 |
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
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*FA/n
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 |
|
|---|---|
| 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) |
|
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 |
|
|---|---|
| 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 |
|
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.
