Belt Sag
You r description is not clear. Can you sketch the conveyor and callouts offered? Better, just read below.
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Minimum belt sag tension is independent of conveyor length. Your comment that longer length can use larger sag is incorrect, from a technical evaluation. This notion will cost your client a larger power bill.
Belt sag produces a flexure of belt and material as the conveyor is deformed over every idler. Larger sag means more flexure and greater energy loss with ieach flexing. If you use the CEMA standard method of analysis for tension and power, you will note that 2% sag at the tail vs. 1% sag tension will result in a larger tension differential and larger demand power.
You can reduce this number for short conveyors to a lower value. Since the lower value, say 2%, does not have a major influence on power as does belt loading dynamics and attendant chute design. Saying the 1% vs. 2% difference makes "ridiculous" shaft diameters, where you offer no facts on tonnage, speed, belt details, idler spacing, take-up setting, et al, is not enlightening, and restrict our ability to offer support of claims and questions.
Curb your anger, until you know you are right. When you know your are right there is no need for anger if you wish to teach others.
Based on the information given, I did a short analysis of a 25 m long belt able to transport 1000 t/h of coal, selecting a 1.5 m spacing on a 1050 mm wide belt. I restricted a tail take-up to 1% and 2% sag. The shaft sizes were rounded up to next 10 mm increment. The drive and tail pulley shaft sizes become:
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2% sag
Drive pulley shaft diameter at hub = 100 mm; at bearing = 70 mm; Tail hub = 90 mm; brg= 70 mm
Take-up tension at 2% sag = 7500 N
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1% sag
Drive pulley shaft diameter at hub = 120 mm; at bearing = 80 mm; Tail hub = 110 mm; brg= 80 mm
Take-up tension at 1% sag = 15000 N
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1% sag and shorten spacing to 1 m from 1.5 m = 29 idlers vs 23.
Drive shaft at hub = 100 mm; at bearing = 80 mm
Tail shaft dia. @ hub = 100 mm ; bearing = 70 mm
Take-up tension at 1% sag = 10,000
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We see a variation of 10-20 mm in shaft size. Is this big money and "ridiculous" sizing?
In very short belts, the impact of 2% to 1% is very small and offers not benefit to power or belt selection. A 2% sag is acceptable.
In large (>1000 mm), long (> 1000 m) belts the difference can be significant, and design impact on stopping dynamics is certain to cause concern with take-up travel, stopping with brakes and belt slip, and with belt alignment. ■
Belt Sag 1% Vs 2% @ Skirtboard Zone
Another critical value not often applied is the seal between skirt and belt at loading point. Low sag means greater potential for spillage and scaring of belt as material gets trapped under skirt when dialating belt between rolls.
Our general rule is to control belt damage and spillage. This is better achieved with slightly higher belt tensions than are promoted by old standards. ■
Re: Maximum Belt Sag And Shaft Diameter
Thank you Mr. Nordel,
Originally Posted by nordell
You are right. I cannot provide them at the moment. I'll post a detailed description first thing in the morning.
I didn't mean that i am thinking about taking higher sag value for longer conveyors. I said the opposite. But according to your explanation it's also irrelevant.
I've been calculating with DIN formulation. Flexure and such other terms are hidden in a "C". From this point of view i've been enlightened by you again. 
I should have thought about the skirtboard. There is so much i need to learn and i am going to learn 
Originally Posted by nordellDrive shaft at hub = 100 mm; at bearing = 80 mm
Tail shaft dia. @ hub = 100 mm ; bearing = 70 mm
Take-up tension at 1% sag = 10,000
My findings are similar. (I'll provide more details.) I found 100 mm.s a bit high. Higher percentage of belt sag would give a thinner shaft. It's not the cost of a shaft. But as diameter increases the production methods and strength changes. I was overconcerned about it. This can also be controlled with shaft material as well.
Good evening. ■
Re: Maximum Belt Sag And Shaft Diameter
Good morning,
An example of my short conveyors:
Q = 800 tonne/hr (Coal, 0.8 tonne/m^3)
v = 2 m/s
B = 1200 mm
L = 6 m.
h = 0
Only tail and head pulleys (500 mm diameter)
Skirtboard: 2,4 m.
Idlers: 6", 35 degrees troughhed. Idler spacing = 1 m.
Belt: EP 315 with 3 plies.
What i find is:
(For 1% sag)
P = 7,1 kW
Drive shaft diameter = 100 mm. (hub) Material: AISI 1040
Take-up Tension = ~15,6 kN
(For 2% sag)
P = 7,1 kW
Drive shaft diameter = 80 mm. (hub) Material: AISI 1040
Take-up Tension = ~7,8 kN
Originally Posted by nordellI assume I can use 2% sag in this condition. Am i right? ■
Maximum Belt Sag and Shaft Diameter
Hello gentelmen,
I have several conveyors, that are relatively short. Let's say shorter than 25 meters. I apply maximum belt sag is 1% criteria to find minimum tension. But this one larger than what i suppose it should be at tail. (I simply subtract the return side terms from T2) I update my tensions according to the minimum tension T0.
T1 and T2 are increased by (T0-Tt). They directly effect my shaft diameters. I find high shaft diameters. It looks ridiculous.
I am thinking about specifying the maximum belt sag according to conveyor length. The longer it is, the lower the belt sag will be. What belt sags would you recommend for shorter conveyors?
Then this 1%. What is this based on? As long as the material doesn't spill, what would belt sag effect? ■