Dear Mr. Reis:

You have raised a three interesting possibilities.

With regard to having individual lubrication reservoirs on idlers, or idler sets, that require lubrication to replace central lubrication systems, it appears that there would be more maintenance problems. An operator would need to inspect, fill,, and repair a reservoir for each idler as opposed to checking one reservoir and pump plus the connecting piping. Currently, most of the systems I've inspected use either sealed-for-life bearings on the idlers or manually lubricated bearings. The latter sounds as if it would be labor intensive, but it isn't since this activity is done while conducting the regularly scheduled preventive maintenance inspections.

The use of training idler sections, equiped with I/O devices, for belt training and load distribution monitoring by the control system is an excellent one. The processors can easily be programmed to handle the information and alert the conveyor operator whenever a problem occurs. The measuring devices are as rugged as the conveyors and should work without problems. Currently such devices are utilized on conveyors for belt mis-tracking. They are placed at strategic points -- such at the lead in sections to the terminal pulleys, loading zones (for multiple load zone conveyors), and weigh scales. Input devices, such as limit switches or photo-eyes can be used to monitor load distribution.

Your third concept of having a means to change out idlers while the conveyor is in motion can be done. Although I am not aware of it being done, I have thought of four different ways to accomplish the task after reading your post yesterday. The major stumbling block is the safety issue. Having maintenance personnel working that close to a high speed belt conveyor that is in motion would be extremely dangerous to both them and the system. One of the methods I thought of would, however, provide protection for both men and equipment. This includes lifting rollers or slider beds to raise the belt off the idlers; a shield to separate the workers from the moving belt; and insertion guides to ensure that the moving belt is not deflected or damaged during the set-up process. Of course, this method is the most expensive and the structural costs may make it too costly for the benefit achieved.

Your ideas suggest that you are willing to take a fresh look at things and I applaud your initiative. Thanks for giving me something to think about that iis out of the ordinary.

Regards, ■

Dear Mr. Reis:

Although I tend to agree with your analysis of the waste in industry, you appear to be ignoring the Fact Of Operating Life (FOOL) factor.

Most large companies operate on two budgets -- a capital budget and an operating budget. As such, they have two different people in charge of each of the budgets. Equipment upgrades fall under the capital budget and all maintenance costs fall under the operating budget. Since the person in charge of the capital budget wants to "look good", he (or she) will resist any additional cost - regardless of its practicality. The maintenance or operations manager will, therefore, be forced to spend extra money in an effort to keep production rates up, without the option of making common-sense purchases. This is why a maintenance manager spends tens of thousands a year for clean-up instead of purchasing a two thousand dollar cleaner that would eliminate the manpower and material loss costs. ■

Dear Sir:

A brief comment on your posting and to other replies.



1. Idler replacement on the fly: Has been done. The 96 km overland for Phosbucraa installed in 1972. Elevated trolley, riding on the stringers, crossing the Sahara desert, had automated, semi robotic manipulators. Newer systems are being developed, for 10-100 km overlands that can drop down the idler set to allow for replacement on the fly. Patent app does not allow further discussion.

2. Idler regreasing is not, or rarely done, on long overlands. More out of ignorance on the method and consequences. Long overlands usually have higher degree banking and shortened center rolls to get the most economics out of the belt width. These systems may use shielded grease deep groove ball bearings to maintain the grease reservoir on the wing roll angle.

3. Older overland conveyors demand less power than new belts. Two reasons are known. A) Belt cover rubber is kneaded, by the idlers over time (our theory), that re-aligns the polymer molecular chains. THis can be measured, in the lab, by rubber viscoelastic properties. The 20 km Channar overland power is continueing to drop over the last thirteen years. The initial power was at a DIN f=0.0105 and in now down to f=0.008. Many belts have been measured by CDI and show degrees of the same response. There is a German DOC of ENG publication from Hanover Univ. on the subject. B) Idlers also show lower drag values( low or non-contact seals) from 10x7 N (carry x return) down to 4x3 N. age of about one year or more.

3. Belt tracking is mainly controlled by the loading action. Proper loading will, in most cases assure good belt alignment. Poor idler frame position, such as may be practices with certain installers, will cause misalignment with an increase in moisture due to the change in contact friciton with the belt. Land settlement can add to misalignment. Idler stringer position can be adjusted as is done to track belts in curves.

4. The science or selection of best overland idler specs is usually not practices. Running economics CAPEX and OPEX shows the need for larger capacity bearings and larger diameter rolls. Larger diameter rolls lower power due to rubber hysteresis and lower seal drag ref to belt speed. The larger rolls and bearings allow for larger idler spacing and so on. There are many belts operating with carry idler spacing exceeding 4m-6m.

We have designed over 350km of overland belts ranging to

ST-7800N/mm, 10000kW, 7m/s, 12000 t/h. The industry is not restrained by technology but by the ignorance of some consultants who must apply their brand on "due dilegence".

There are many innovative method, to improve overland conveyors, that will make it to the market place in the next two years. Keep a look out. The cost of the overland is still falling when measured in $/ton/km.

Wishing you success in the subject.

Lawrence Nordell

President

Conveyor Dynamics, Inc.

1111 West Holly St

Bellingham, WA 98225

ph 360/671-2200

fx 360/671-8450

email nordell@conveyor-dynamics.com

www.conveyor-dynamics.com ■

Re:- Idler replacement on the fly.

I have developed a forklift truck attachment which hoists the belt off an offending roller set in complete safety. Fork truck involvement provides stability during the operation & the attachment has an integral fork which prevents any stray rollers falling onto the return strand. The same fork also prevents personnel from approaching either strand. While it is mechanically simple to change rollers it is rarely safe to do so on a moving belt without very robust equipment & tools to minimise human involvement. Belt Trucker does this without spillage and for a very small cost. Manual operation is quite remote, keeping clear of the pull wires while still working safely. For added safety the device removes only the centre & nearside wing idlers. To remove the far side roller the fork truck should be driven to the other side of the conveyor. The fork truck can also carry all the rollers to & from the workplace, although the 96km belt mentioned in other correspondence would stretch the operating range. An AVI file is available on CD to illustrate the principle & method of idler replacement & of course the price is extremely reasonable.

Re:- Slower Belts

Savings from reducing belt speed must be considered against the material throughput demands. No matter what the belt speed the same thp must be shifted & the slower the belt; the bigger the belt; the bigger the idlers; the bigger the gearbox, the wider the chute. These are vital issues for tendering purposes and the fast belt wins hands down , whatever the maintenance benefits might be, the power consumption of a fast belt will always be less than for a more ponderous slower device with higher rotational inertias. Life expectancy of a correctly selected and installed belt is once again a matter of housekeeping. There is a long forgotten (I've lost my copy) section in the Yokahama Design manual which forecasts belt life expectancy & the underlying reasons. ■

Dear Reis,

The topic raised by you is important and useful. Various types of idlers are available such as grease packed for life, periodic lubrication from grease tubes, belt sway switches for automatic alarm for belt sway etc and so on. But often the issue is somewhat different i.e. during procurement stage decision makers have differing priorities, varying from purchaser to purchaser; and accordingly plants get constructed. Any way, this topic will create rational thinking for doing the things better and easier way.

Regards,

Ishwar G Mulani.

Author of Book : Engineering Science and Application Design for Belt Conveyors.

Email : parimul@pn2.vsnl.net.in ■

I refer to the question relating to Custom Conveyors and specifically the development of new features on idlers.

We have recently installed a 2000 m long decline conveyor complete with quick release idlers over the full length.

These idlers can be dropped away from the belt, the rolls replaced and then the assembly reintroduced back into position, even with the belt running, (however we do not encourage this).

We did a small article on the concept some time back, click on the link below to review the concept.

www.ckit.co.za/right index/tech focus/belt friendly structure/evolution.htm

Trust we are going in the right direction. ■