I do nnot think there is an answer to your problem as a weigh hopper has its own weight and if you add product build up from fines that only adds to it so there is really no constant-this laymans opinion. ■

Feed hopper size for loss in weight feeders is based on the feed rate and number of refills/hr.

During normal operation, weight of material in the feed hopper reduces continuously from its maximum weight in the feed hopper to its minimum at which point the refill cycle is initiated. During the refill cycle the weigh feeder operates in a volumetric mode or at the feed rate at which the refill cycle starts. If the feed hopper is too big, it results in a long time to fill the feed hopper to its original maximum weight. To reduce this time, the size of the hopper is reduced but this means that the feed hopper must be refilled more often. The number of refill cycles/hour typically varies from 6 to 10 because of other constraints such as time required to open and close the refill device such as a slide gate valve.

Using the feed rate and the number of refills, feed hopper size can be calculated easily.

Regards,

Amrit Agarwal

Consulting Engineer

Pneumatic Conveying Consulting Services

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■

Really!

How many emtpyings per hour are envisaged? ■

6 to 10 refills/hour is a very good rule of thumb for sizing feed hoppers. In addition to the working volume, also include 30% buffer volume above the screw and 30% open volume for the angle of repose.

Please also consider the flowability of the material. If the material is easy to handle (i.e. plastic pellets) you can safely go above or below the rule of thumb.

If the material is easily fluidized (i.e. talc, flour) you should increase the buffer volume to allow the material to deaerate. Otherwise you can experience wide swings in bulk density or even flushing from the feed screw.

If the material is compressible and difficult to hopper (i.e. TI02) you should reduce the working volume to minimize headload.

Bottom line....always test before purchasing a feeder.

Delmar Schmidt

Melfi Technolgies

dschmidt@melfitechnologies.com ■

In the above response I forgot to add one more variable that comes into play when sizing feed hoppers for LIW feeders. This variable is the empty weight of the hopper itself. Unless the feed hopper is counter-balanced, this weight must be measured by the weigh scale of the LIW feeder in addition to the weight of the material in the feed hopper. If this weight is too high, it will affect the accuracy of the feed rate measurement because the sensitivity of the weigh scale has an upper limit.

Regards,

Amrit T. Agarwal

Consulting Engineer

Pneumatic Conveying Consulting Services

Email: polypcc@aol.com

Ph and Fax: 304 346 5125 ■