You cannot have two independent takeup masses working for the reasons you just experienced. You may be able to connect them together to obtain proper functionality, but more information is required. The check list may be long based on how your design has evolved. A thorough check of the design details are in order.

1. What is the criteria for the takeup mass: a) drive slip, b) belt sag, c) dynamics, d) other

2. What is the criteria for the takeup travel: a) tension range for loaded and empty belt, b) thermal range, c) permanent belt stretch, d) belt sag allowance, e) belt splice allowance for repair, f) clearances between upper and lower travel stops, g) other conditions which may need inclusion

2. MY opinionn is you need professional advice beyond that which can or shoiuld be offered by the forum members as advice. THere are too many "what if" conditions to be answered that will guarantee success with safety.

3 Who ever recommended your applied design does not understand the basic physics and calls into question the design's proper development. Get help.

4. I can assure you there are more than 30 major questions that need to be reviewed to give your design a OK including mechanical, electrical, structural, electrical, and control w/ instrumentation. ■

Your question has merit. I have been in discussions with other engieers which ponder the same question, without thinking the outcome through as an engineer should.

The first counterweight takeup (TU) will fall first as you see when the two TU's have balanced masses because the pulleys following after the first TU require added belt tension to pull the belt around these following pulleys with their bearing and seal drag resistance. THe higher belt tension, at the second TU, exceeds the mass of the second TU mass which cause the TU to rise.

By increasing the second TU mass by 50 kg, this is apparently sufficient to overcome the pulleys' drag and belt bending with the result it has enough mass to overcome the mass of first TU thereby lifting ithe first TU as the second TU mass falls. ■

Question:

I drove by your Mumbai offce and noticed its was not far from the convention center where the Bulk Solids Asia 2005 conference was held. I did not see or meet anyone from Larsen Toubro.

It would have been a pleasure to meet with you and discuss the nature of such problems.

There were many experts from around the world who took their time to come to India and share their research work and design experiences with you. What happened to L & T attendance? ■

Hello nkkabra..

We quite often use double reaved vertical gravity take-ups. Sometimes because of space restrictions. The last one we did, we needed extra movement as the conveyor had a moving head facility.

We simply use two take-up pulleys on a single take-up box.

That's what you need.

Regards

LSL Tekpro ■

nkkabra:

Presumably, you need two take-up pulleys due to space limitations. Depending on the movement required and travel room, you can change this to either one functioning take-up or keep it as two take-ups.

If there is sufficient space to allow for the required take-up travel by one pully, you can fix one of the take up pulleys (trailing one preferred) so that it cannot move and use the other for the take-up action. This allows you to retain belt in the system for splice/repair needs.

If you need the movement of both pulleys, you can do as both Larry Nordell and Graham Spriggs have advised. That is, tie the two travelling pulleys togeter so that they move as a single unit with a bend pulley between them.

The critical action is to do what Larry Nordell advised - have a conveyor expert conduct a site or engineering evaluation as a first step.

Regards, ■

Dear Shri N K Kabra,

When you have insufficient head room generally one provides horizontal loop gravity take-up. Now, you have already provided dual vertical take-up. In such vertical take-up, there are two take-up pulleys mounted on common frame attached to common counterweight. So, you will have a two take-up pulley and three bend pulleys. Such take-p is working in Malaysian power station for stockyard conveyor equipped with bucket wheel on boom stacker cum reclaimer.

When two take-ups are independent, they will not have exact balanced movements in varied situations, which are very large in numbers; and this can create complication.

Earlier respondents have already explained the situation.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Seems to me U have the following options

Join the counterweight frames together - physically or via a rope/sheave system

Fix one GTU and have one in use - if belt stretch etc permits

Go to the different TU arrangement ie inclined with GTU tower outside belt line

Suggest giving your designer a call as well...

Thanks

James ■

Even though everyone has done a great job in describing what you need, they say a picture is worth a thousand words.

So I am attaching a drawing of a system that we converted from a single take-up pulley to a double take-up when we changed the belt from a cable belt to a ply belt.

We used the existing CWT box and added a smaller on each side of the existing. Remember that you will need to double the weight in your counteweight box from that of a single CWT.

Good luck with your project.

Gary Blenkhorn

Attachments

805 conveyor (ZIP)

■

How do these things get through to manufacture? Does, or can, nobody check drawings anymore? ■