Dear Stephen,

Pulley diameter depends upon :

1) Carcass type i.e. material of carcass (nature of carcass construction may or may not affect)

2) Carcass thickness

3) Percentage utilization of allowable belt tension.

4) Pulley functional location (whether drive pulley, bend pulley, etc).

Pulley diameters are selected using the tables from published data. You are mentioning Phoenix uniply belt so you can select pulley diameter as below :

1) As per applicable DIN.

2) As per Phoenix publication data.

The pulley diameter selected as per 1) and 2) could be same or they may have some difference. Choose the diameter, which is more between the two. In case, the standard of the country where the installation is to be done is also to be complied, then pulley diameter should also be selected as per the standard of the country. Then, one has to choose highest of the three values.

You will find pulley diameters under caption Pulley-A, Pulley-B and Pulley-C. Pulley A implies drive pulley and pulleys, which are subjected to higher tension in belt (like tripper pulley etc.). Pulley B implies tail pulley, take-up pulley, bend pulley where belt tension is comparatively lower (i.e. return run of usual conveyors). Pulley C refers to snub pulley for deflection of belt up to 30 degree.

Above is general information. Exact procedure and finer details cannot be described here, kindly refer to DIN, ISO standards. You may also obtain applicable specific information from manufacturer of your belt. In order to ensure validity of the guarantee for belt life, concurrence of the belt manufacturer is essential.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916. ■

Dear Stephen,

My earlier reply mentions the method used in application engineering for deciding pulley diameter to suit particular belt.

In case if you are analysing theoretical basics for pulley diameter, it has following approach in broad considerations:

1) Just prior to reaching the pulley, the belt carcass has uniform tensile stress across its thickness. Thus the carcass is in stretched condition.

2) The bending (curvature) of belt carcass on pulley causes outer layer to stretch further and inner layer to contract (i.e. reduction in its stretch)

3) Sr. No. 2 causes drop in safety factor, for outer layer of carcass. Now, belt total (gross) safety factor will have certain margin for permissible drop in safety factor.

The belt manufacturers specify pulley diameter, which will keep this drop within allowable limit.

4) You can work out extra strain and consequent extra stress by using modulus of elasticity of carcass. However, deciding pulley diameter in this manner will require comprehensive information about the belt characteristics, belt safety factors, present-practices in this matter and requirement of various standards.

In general, belt manufacturers are the right people to make recommendation on this issue, who also have to guarantee the belt life in working conditions.

Regards,

Ishwar G Mulani.

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

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 5882916 ■

Dear Stephen,

In general the minimum diameter of the pulley is determined by the type of belt.

The needed diameter is depending on a lot of parameters, like friction between belt and pully, angle of belt on the pulley (mostly 180 till 210 degr), basis tension of the belt, type of tension take up, etc.

If yoy want we can send our PC-calculation program so you can make some calculations yourself.

Jur Lommerts

------------------------------------------------------

Jansen & Heuning Bulk handling Systems

Groningen

The Netherlands

web: www.jh.nl ■

Stephen,

You also need to consider the location and orientation of the pulley system.

Dirty side contact pulleys should be avoided if possible. When necessary, they should be kept reasonably round in shape, avoiding material buildup. They should have sufficient distance between pulleys to avoid telegraphing high belt tension flux that can cause drive power oscillation, splice damage and pulley failure. This usually means a pulley center distance where it takes .5 to 1 second for the same belt point to pass over two adjacent pulleys and whether the tension is 50% to 100% of belt rating for the respective distances.

These comments assume you are requiring long belt and pulley assembly life.

Diameters for fabric belt belts vary with belt ply elasticity and number of plies. As has been noted, your best bet is to obtain mfgrs. recommendations.

Steel cord pulley diameters, rated at a SF=6.7:1, should have a diameter about 150 times the steel cord diameter for belt tensions from 80-100% of belt rating, 125 times cord diameter for 50-80% of belt rating, and 100 times cord diameter below 50%belt rating.

Lawrence Nordell

Conveyor Dynamics, Inc. ■