Both work.

Why the question? ■

Originally Posted by Shakee

Mr. Nordell,

My question is whether is it possible to run this type of drive system without both VFD or Variable speed fluid coupling?

Regards,

Shakee

Dear Shakeel,

Please specify your requirement.

1.Do you need to run the system in different speeds or for start up only.

2.Proposed drive capacities etc.

Rgds,

Narayanan Nalinakshan. ■

There is not enough information to make any definite recommendations. Lets just throw out some generalities.

Issues that influence the decision:

1. Total Power/Max belt tension

2. Starting/stopping requirement related to 1

3. Load sharing requirements

4. Target tension control (not applicable in the case that you are presenting)

Possible Control systems:

A. Across the line starts, sharing (miss-sharing) according to motor curves and equipment matching

B. Reduced voltage starting

C. Fixed fill type fluid coulplings

- with various levels of delay chambers

D. Variable fill type fluid couplings

E. Wound rotor motors with resistance control

- continuous duty resistance (say to 5%) for load sharing

F. AC variable frequency control

G. DC control

Generally,

A. Does not solve any of the issues but for smaller systems it may be the most economical solution. Sizing up to tolerate miss-sharing may be the cheapest thing to do.

B. Reduced voltage means reduced torque. This does not control start-speed it controls the start effort. It is highly dependent on the conveyor's resistance to motion. It is not typically very smooth. It offers no load sharing control

C. Similar in behavior to B. The fluid levels may be adjusted to achieve some load sharing but only at a specific crossing point of the performance curves.

D. Fluid to the working circuit may be continuously varied in response to speed or tension feed-back

E. Does anyone still do this?

F. Total versatility based on speed control. The full torque range is available at any speed. Great for starting, stopping, load sharing. May be regenerative, producing power for other mine equipment.

G. Same control as F but more expensive and requires more maintenance

Joe Dos Santos ■

Hi Shakee..

For what it is worth, the kind of drive pulley configuration in your diagram went out of favour a long time ago.

This was because any spillage from the transition area can fall onto the belt below, and can get trapped between the belt (still fairly HT) and the secondary drive pulley, and go round and round. Not fool proof .. not self clearing. Can damage the belt.

Not sure what your original question was getting at.

Cheers

Taggart LSL Tekpro ■

Graham, Joe,

I offer an alternative to your stated opinions:

1. Dual head drive arrangement, as pictured, albeit not accurately drawn, is still in vogue to many - no dirty side contact until tension is fully dropped

2. Alternative to the "pictured dual drive" is to add a minimum of 2 pulleys with one on dirty side contact - we try not to have dirty side contact until after tension has fully diminished. The alternative Spriggs configuration, in my opinion is inferior to the picture because it adds extra pulleys and introduces dirty side contact either before any drives or between drives.

3. Reduced Voltage starters can use the configuration - starting time is the limit - can couple starting ramp to reduced voltage circuit to achieve desired starting time vs. velocity

4. Potential for spillage at head transition is a problem regardless of drive configuration. We make a strong effort to control such spillage and agree it must be contained.

5. Wound Rotor Motor Control - still in vogue and may be making a comeback in some quarters. By example, oil sands use it. Some Chilean mines are specing it.

Why? Simple to understand cause and effect. We can argue some can engineer for the anomolies, but, most do not. If you higher the wrong engineer, you get less than anticipated. Caveat Emptor? Permanent slip levels usually less than 2%. Only with large pulley build-up do you need 4-6% permanent slip. ■

Larry,

Thanks. I definitely agree with you on minimizing the number of pulleys and especially avoiding the dirty side contact, especially at the high tension belt. The arrangement that is posted when accurately depicted provides a good wrap distribution for equal drive pulleys or even 2 to 1 (primary to secondary) drive pulleys. The increased wrap is available where needed.

Indeed, reduced voltage steps (many of them) might be tied to tachometer feedback but this is not typical. Most often few steps are set at fixed time intervals and under a light load start the conveyor gallops to the full speed.

Thank you for the update on wound rotor motors. The last time that I used these was on the Majdanpek HAC. The 5% slip may have reflected paranoia with regard to load sharing. I do remember that I thought it was overkill. Your statements confirm this. I must admit that I am surprised that AC VFD hasn't completely nullified WR motors and controls, especially considering the energy losses and heat dissipation requirements for WR motor resistors.

Joe Dos Santos ■