If I understand you right, you seek to lower momentary high tensions. Any recommendation requires qualifications. A better answer should be tailored to a specific need.

One way to reduce dynamic tensions is to use a drive inertia control such as a flywheel. The added inertia reduces drive transients during starting and stopping.

The leading question is -- what is causing the dynamic tension magnitudes which in the end should point to your answer. It can be related to:

a) belt profile

b) belt sag

ic) dler spacing

d) fluid coupling decoupling the drive mass during a shutdown,

e) control of the takeup tension and displacement

f) location of the drive motors and other facrtor.

Trying to generalize on such a question seems to have very limited value. ■

What about controling the tensions through belt speed regulation which is what a flywheel does. Other speed regulators can do the same - such as inverter regualtion during starting and stopping with longer accel and decel times.

A difficulty for many readers will be what are the circumstances you wish to apply? If no conditions, then there is a larger body of answers but they would meander in mind and spirit with total lack of focus. ■

Depending on what you know or can investigate about the belt, it may be prudent to rebuild the splices. I have studied this problem in some depth. It depends on the belt cover conditions and the age status of compounds and cables. If the belt is worn through to the cables, toss it. If you have +3 mm left and the cables are not highly corroded, it can be done. We advocate testing a sample to evaluate the core gum. Even if it cannot hold a resplice, there is a treatment to obtain a splice that can last +5 years. ■

Shane,

I think there needs to be further clarification. I suspect that you are talking about a fabric reinforced belt as a steel cord belt should not have the same % decrease as is possible with a fabric belt unless the cords have been subject to some sort of severe abuse. Also is this an underground application? Larry has given some broad options but others could include just starting the belt a lot slower so you limit tension peaks on start up.

Col Benjamin ■

Shane,

From your description, it appears that you are discussing a fabric carcass belt where there is a suspected loss of tensile strength.

Non-Capital Cost Options to reduce Dynamic Tensions include:

1) Load Management (i.e., only start the belt when empty and gradually increase the load rate to the desired load level).

2) Tension Adjustment (Adjust the tension to reduce belt sag - although this places extra tension on the belt it helps to reduce start-up surges)

3) Reduce the carrying capicity of the belt (Depending on the tonnage requirements this may be more costly than introducing capital cost options such as soft-start fluid couplings or a belt replacement). Hopefully, your facility has sufficient downtime available to transport the same tonnage over an extended period.

4) Lifting of tension grabbers, such as cleaners and skirting during start-ups (this option is time consuming and potentially dangerous - as care must be taken to place them back properly once the belt has started without causing damage to the belt or endangering personnel).

Other than these, you are looking at Capital Cost options, as suggested by Mr. Nordell.

The questionw that I have for you are, how much tension drop are you talking about & how do you know that the belt's tension capacity has dropped?

Regards, ■

What investment is client willing to make?

Aside from adding a motor and pulley assembly, or the other noted methods, why not a fixed fill level fluid coupling or primary voltage SCR regulated starter. These are very low cost options. THis is what I eluded to in the comment on speed regulation.

Campaigning ore may do it but limits to total investment on the facility. ■

Dear shane

without kmowing exect details of conveyor it is difficult to solve the problem.

Have you actualy tested the belt tensile strength and in case it is reduced to what extent it is reduced

How much margin is in your motor in case your consumed power is less than installed power there is achance of increasing speed and reducing tension rating to the extent of installed power.This can be done by incresing pulley dia or changing gear box ratio.

It may be possible to reduce starting tension by providing flywheel.Delayed starting can also be achieved by VFD CONTROL or by delay filling of oil in fluid coupling.

we are not aware about the speed capacity , length , type of belting , type of drive unit , details of coupling etc In case these details are available proper reply can be given

A R SINGH ■

Shane,

Increasing the winch tension to reduce belt sag does add to the initial tension at start-up but the reduction in belt sag minimizes the large snap-tension effect - so you end up with a net reduction in start-up tensions. The danger is found in going too far in the effort to reduce sag - a belt that is too tight (i.e. no sag between the idlers (I normally look at the return run because of the extra spacing and lower or no troughing). If too much tension is applied you will gretaly increase the risk of splce separation / belt breakage and find that the belt is more sensitive to mistraining influences.

Ideally, sag should be reduced to approximately 0.75 - 1.00 %.

Going with a Soft-Start is probably your best bet.

Regards, ■