1. faster idler speed and lower bearing life.

2. friction is still friction.

3.The idlers need to be sized in relation to the head, tail and drive pulleys. ■

Conveyor Dynamics, Inc. (CDI) has conducted research into the theory and practice of idler roll influence on power consumption. Many of the points are published in Bulk Solids Handling, IIR Australia,and BELTCON South Africa:

1. "The Channar 20 km Overland A Flagship of Modern Belt Conveyor Technology", vol 11, no. 4, November 1991

This was the first introduction of our work on viscoelastic mechanics and its application to overland conveyors (10.4 km; 10.1 km) with specific results.

2. "The Power of Rubber - Part I", vol 16, no. 3 July-September 1996

This has a definitive chart on idler roll diameters contribution to the viscoelastic rubber influence on the power equation. This does not include the variables of idler seal drag, bearing and bearing lubrication with rotation speed and temperature to the overall drag factors.

3. "Improving Belt Conveyor Efficiencies: Power, Strength,& Life with Overland Case Studies", 4th annual Optimizing Conveyor Performance in Mining Conference", Australiasian Mining & Energy Taskforce, Perth & Sydney, Australia, April 1998

4. "ZISCO Installs World's Longest Troughed Belt, 15.6 km Horizontally Curved Overland Conveyor" BELTCON 9, 1997.

5. " Overland Conveyors Designed for Efficient Cost & Performance" BELTCON 12, July 12

Has many comparisons and sensitivity analysis on idler spacing et al.

There are other articles. The above givens reasonable insight.

In principle, larger idler rolls provide improved performance for:

a) lower power from lower idler indention into belt covers as given in the articles

b) lower power from reducer idler drag from large radius against bearing and seal drag radii.

c) reduces idler noise and improves control of belt edge flap

d) improves belt and idler life with lower pressure and lower RPM

e) and on and on......... ■

Lyle,

I am curious. What is the "artificial friction factor"? I have never heard of the term before. "Artificial" implies not "Natural". Is this so, or just your perception?

The cited articles, already given above, also have bibliographies on many authors with their classical mechanics approach to resolving energy consumption of idler rolling into a viscoelastic material, mainly rubber, as well as subsidiary losses.

More recently, Prof. Craig Wheeler, and historically Prof Hager's and Prof. Spaans many Ph. D. and/or DE students with combined 100 years of research on this very subject will to be challenged by the term "artificial". ■

There are terms that describe pseudo or apparent friction factors:

1. Phenomenological or implied friction like the DIN "f" factor which is based on many observations. It is without scientific foundation, except in its statistics. An example is the published work in DIN 22101 factor “f”, I believe first given in 1942.

2. CEMA's Ky and Kx drag terms are also phenomenological based derived from many field and laboratory tests in the 1940's and 1950's that culminated in the first edition publication in 1966. Kx is more specific in treating seal drag and bearing race drag. Still neither has any scientific fundamentals that you would find a SKF text on their bearing products.

3. Precismeca published simple idler drag terms dependent on (load, velocity; temperature, with adjustments for lump size and type of alignment) for all of their idler considerations that boiled down to one number like DIN “f”.

However, true fundamentals are being researched that break the drag loss into many factors that describe 20 or more large families of data, which are based on science, that are more accurate and correlate with observations.

I guess pseudo can be tagged with “artificial”. ■

Sometimes, you can increase the counterweight mass. This reduces the belt sag between idlers that in some cases will result in lower demand power. However, it will not reduce max belt tension.

More often, the decrease in belt width, from elongation, is produced by excessive acceleration force. Sadly, fluid coupling mfgrs. do not give all details of their product. When they claim 135-140% starting torque, this is more an average and not peak. The peak torque of typical fluid couplings, without special drain control, tends to 150-160% or more. This ocurrs for a very short but measurable duration.

Another point, with fluid couplings, is they tend to be misfilled which have varying responses that are not intuitive (i.e. less fill can deliver more motor torque, when more fill stalls the motor before reaching full speed). The motor must cover the pump (fluid coupling) performance curve to be effective. ■

Yes, reduction in idler spacing can reduce belt tension and demand power. The condition must be studied to give meaningful recommendations. There is an optimum idler spacing, give all other factors are fixed. ■

This maybe true for traction and drain type fluid couplings.

Scoop control couplings (Fluidrive SCR or ST range) can however achieve 140% starting torque without any excess peaking. Also with a good quality actuator, and reliable feedback system, starting torques towards 120% can be achieved.

Agree filling can be an issue, but again with the Fluidrive SCR this is not such a problem. These types of coupling are also very easy to balance on multi motor drives. With the ST couplings it is not possible to overfill the working circuit, as the pump is of a constant fill type with the scoop tube controlling the circuit oil level.

Typically 6% of the load power requirement was added to the coupling absorbed power, for motor calculation however this has been shown to be excessive, anywhere between 1.5 and 2% is more realistic. ■