Hi Paul,

The closest to a shaftless pulley that I know of are the internal motor pulleys, and these still have shaft stubs for attachment to pillow blocks.

I do not believe tha there is a market, since the shaft/pulley shell concept appears to be a very economical solution for gearing, cost containment, and belt protection purposes. The shaft provides strength and the pulley shell provides an expanded surface area to avoid rupture of the belt carcass.

Regards, ■

Dear Mr. Attiwell

Shaftless pulleys have been designed and are in service around the world. PWH's (now defunct) Dr Deitrich did his DOC of ENG on the subject in the 1970's. Precision Pulley have provided this design to the North American market. I believe Prof Hager had a recent DOC of ENG (Univ of Hanover) student work on a version using swagged ends. Krupp, Takraf and others have worked and installed versions ie. EL ABRA in Chile. This installation is not considered a success by some - many failures in end disk and shell in fatigue.

They have their place and benefits in shipping and site handling.

Lawrence Nordell

President

Conveyor Dynamics, Inc.

1111 West Holly St.

Bellingham. WA 98225

USA

ph 360/6761-2200

fx 360/671-8450

email nordell@conveyor-dynamics.com

www.conveyor-dynamics.com ■

Sorry:

I forgot to mention the conveyor specs for EL ABRA

1. Belt: 1600mm ST-6800 N/mm Speed = 5.9m/s, SF = 5.5:1

2. Power: 3x2500 = 7500 kW

3. Capacity 7800 t/h

Lawrence Nordell

President

Conveyor Dynamics, Inc.

1111 West Holly St.

Bellingham, WA 98225

USA

ph 360/671-2200

fax 360/671-8450

email: nordell@conveyor-dynamics.com

www.conveyor-dynamics.com ■

The shaft is sized for strength and to limit angular deflection at the pulley hub. The latter typically governs in sizing the shaft. The CEMA shaft calculation are based on free shaft deflection. In fact the moment between the pulley hubs is carried by the center of the shaft and by the pulley (in sectional bending) according to their relative stiffness. How much bending to each can be easily determined by the "momement distribution" method. Some years ago there were many failures of shrink type locking hubs, at high tension pulleys where the end discs were relatively rigid. This led to revision of deflection criteria that was equivalent to treating the shafts as cantilevered stubs ignoring the center of the shaft, hence a flurry of activity in development of stub-shaft pulleys.

The writer has designed and built large diameter rolls with shrunk stub shafts for very heavy rock-belt feeders. These were very successfull under the most severe impact loads. It is important to machine the shafts of each roll in one set-up after final assembly of the stubs in the roll hubs. This will insure perfect alignment of the stubs.

Joe Dos Santos

Email: jds@dossantosintl.com

www.dossantosintl.com ■

Precision supplies a standard line of stub shaft pulley designs ranging from 2.5 inches to 14 inches shaft diameter. It is called the EZ Mount pulley, and can be viewed on our web site.

EZ Mounts have been supplied in the North American market for over 10 years with great success. As with all products, it is important to properly select components based on loading, speed, environment, etc. If you desire we have the staff to assist in this area.

The EZ Mount has proven to be a popular way to minimize spares inventories. It is possible to design one pulley for each diameter and face combination and a set of shaft stubs for it to fit into all areas that size of pulley is used at the site. We have staff to assist in creation of standardization schemes and site surveys.

It has also been used in areas where getting a complete pulley and shaft assembly into a constrained area is difficult. The stub shaft construction makes it possible to install components rather than a complete assembly.

If you or anyone else has an interest in this product feel free to contact us at your convenience. ■

In the 80's the UK Natioanl Coal Board had a large, solid forged drive drum on the head of one of the spine drift belts at Gascoigne Wood, Selby, North Yorkshire. This little gadget was about 2m diameter, belt speed 0-9m/s and the belt was about 1.2m width. Pole piece assemblies were bolted onto the drum & the whole thing then finished up as the rotor for a rather large DC motor. REI did the design; Anderson Strathclyde were the builders & INA supplied the bearings. There was a lecture on the installation in the mid 80's, by INA. Eventual belt centres were expected to be 14km but I don't know if this was ever acheived.

Feasibility considerations would be that the belt tension would have to outweigh the drum mass. (otherwise the bearings are just holding up the drum;; the bearings are the cost item) After that we must consider the manufacturing cost. Forging a solid part would be just as economical as rolling a big heavy plate and then undertaking costly welding and inspection. A shaftless assembly would be machined in one shot whereas a shafted job needs the shaft to be machined as well as the drum having to be dressed and bored. All this points to a shaftless drum being a lot cheaper if it properly made.

But... Anderson Mavor in South Africa (Refinery Road, Germiston or whatever it is called these days) used to regularly make cast iron drums for Anglo American. It never occured to anybody to cast webs inside and bearing bosses outside. Ask them, they might just do it. How's that for a price drop without the eternal drag of weld fatigue? ■

We have manufacture stub shaft pulleys for years.

Extruded tubing stock with ribbed double wall is available of the shelf up to 8" in diameter. I immagine that larger diameters can be extruded as well.

With today's automation state, welding the end caps is not difficult or expensive. The bearings are still the high cost item on the assembly.

If the idler turns without slippage of the belt, the wear on the idler surface will be very small allowing the use of light weight rigid extrusions for the fabrication of idler drums.

Antonio Reis

www.vitrom.com ■