Skirtboard Friction Factors, CS

Posted in: , on 22. Sep. 2009 - 20:36

As CEMA implies, the skirtboard friction factor is an imperical value that is tabulated in Section 6 of the book. Very often I refer to this table, and about half the time, the material my client needs to convey is not listed. I can, of course, make a guess at what material is most similar and estimate the value to use. I imagine that many experts on this forum have a similar experience and would like to see a more comprehensive table. Thankfully, we can use this forum as a means to share the values that we have determined are appropriate for various materials, and hopefully CEMA members can incorporate the values into future editions.

I'll start the thread out with the values we know from Table 6-7 of CEMA. Please add the values that you use for other materials not listed.

Alumina, pulv. dry - 0.1210

Ashes, coal, dry - 0.0571

Bauxite, ground - 0.1881

Beans, navy, dry - 0.0798

Borax - 0.0734

Bran, granular - 0.0238

Cement, Portland, dry - 0.2120

Cement clinker - 0.1228

Clay, ceramic, dry fines - 0.0924

Coal, anthracite, sized - 0.0538

Coal, bituminous, mined - 0.0754

Coke, ground fine - 0.0452

Coke, lumps and fines - 0.0186

Copra, lumpy - 0.0203

Cullet - 0.0836

Flour, wheat - 0.0265

Grains, wheat, corn or rye - 0.0433

Gravel, bank run - 0.1145

Gypsum, 1/2" screenings - 0.0900

Iron ore, 200 lbs/cu ft - 0.2760

Lime, burned, 1/8" - 0.1166

Lime, hydrated - 0.0490

Limestone, pulv, dry - 0.1280

Magnesium chloride, dry - 0.276

Oats - 0.0219

Phosphate rock, dry, broken - 0.1086

Salt, common, dry, fine - 0.0814

Sand, dry, bank - 0.1378

Sawdust, dry - 0.0086

Soda ash, heavy - 0.0705

Starch, small lumps - 0.0623

Sugar, granulated dry - 0.0349

Wood chips, hogged fuel - 0.0095

And one new entry to get it started

Municipal sludge - 0.200

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Re: Skirtboard Friction Factors, Cs

Posted on 22. Sep. 2009 - 08:29

When faced with a new product I ask for a representative sample. I can then use this to compare against products I already know and select factors accordingly. There's also the consideration that one companies "Material X" may be totally different to another companies "Material X" yet sharing the same name

Another consideration is the effect of one part of a power calculation on the overall power. If it's just a small part then errors in a factor may not be worth worrying about too much.

I do have experience with one belt conveyor where an underestimate in skirt friction resulted in overloading the drive. A factor had been selected from CEMA and applied to a conveyor with continuous skirts. Unfortunately, when the conveyor was made and the skirts fixed in position, they were jammed hard down on the belt resulting in burning of the belt top cover. A little common sense also needs applying along with published factors

As an aside, how is this factor measured?