DEAR SHANE

please clarify about live/ dead shafts. I understand you mean stationary shaft and rotating shaft .

I came accross pulleys having stationary shaft for some conveyors of underground mines

I feel difference of these pulleysare as follows

1.0 Hub and End Disc welding failure is eliminted in stationary shaft pulley

2.0 As wide PB are avoided support centres are reduced means pulley having same shaft dia can take more load

3.0 Sttionary shaft pulley can not be provded for drive pulleys

4.0 Pulley greasing while conveyor is moving is difficult in stationary shaft

A R SINGH ■

Hello Shane

Van Gorp list some of the advgantages of "dead shaft pulleys".

You can get their brochure with that information at.

http://www.vangorp.biz/pdf/vg-catalog.pdf

Regards, Gary ■

The main reason they are specified is to save space, which is not listed by Van Gorp. The bearing housing is removed from the support base thereby reducing the supporting width. this is found on take-up, tail and bend pulleys where space is at a premium.

I do not understand Van Gorp's claim that this concept reduces bearing size. Bearing size is selected bases on bearing dynamic capacity and L-10 hours life. ■

Good point Larry - You are right. They may be taking the idea that if you can reduce the shaft size you can reduce the bearing size. Good question to ask the rep next time he visits me.

Thanks,

Gary ■

I can only think that the smaller bearing size is the result of a smaller shaft not being subject to so much fatigue loading.

There is a further variant on pulley shafting where the take up pulley is live but mounted across bearings in the rope sheaves. This design obliterates the clumsy take up trolleys etc & affords vastly improved maintenance access & adjustment. ■

Nordell, I would think that their claim is that with the live shaft, the pillow blocks are wider, thus a larger bearing centers. With the dead shaft, you can reduce the spacing. ■

Dear Shane,

The earlier respondents have already written on most of the points. The in-board bearing permits more deflection of shaft as compared to keyed pulley or pulley fitted with taper lock assembly. The other important advantages are absence of fatigue loading, and thereby some reduction in shaft diameter, and compact arrangement to suit mounting in winch take-up of shift-able conveyors, or for use in mines etc., as mentioned in earlier replies.

Regards,

Ishwar G Mulani.

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

Author of Book : Belt Feeder Design and Hopper Bin Silo

Advisor / Consultant for Bulk Material Handling System & Issues.

Email : parimul@pn2.vsnl.net.in

Tel.: 0091 (0)20 25882916 ■

Other Pros and Cons are:

Pros:

1. Removal of the bending moment at the end disk and hub assembly. The hub located bearing removes most of this shaft deflection bending moment that otherwise would need to be designed into the end disk and into the end disk to shell connection. I believe this fact and point two below are of far greater economic benefit than the reduction of shaft diameter and costs resulting from the reduction in size between hub and stationary support.

2 By using a hub bearing, there is no compression locking pressure such as is found with the Ringfeder type attachment between pulley and shaft. This will further reduce the pulley material costs of hub, end disk and shell.

Cons:

Having said the above, this style of pulley is not widely embraced. The key factors for this are:

3. Inspection and repalcement are more difficult. The bearing cannot be readily inspected when running with typical plant tools such as hands and ears.

4. Special probes are required to monitor the bearing thermal and noise levels.

5. External bearings can be replaced without removing the pulley with the conventional bearing housing design. ■

Shane,

When assessing dead shaft pulleys it is critically important that there be as little as possible flex in the shaft under operating conditions. I have had experience with shafts that flex in a loop take up of longwall belts, it seems that seals dont like flex, lube excapes and then bearings fail. Changeing these pulleys is difficult and expensive. Think about a flexing shaft inside a non flexing shell and the dynamics are quite interesting.

When we upgraded our shafts from 90 to 105 mm the problems went away.This upgrade reduced the deflection of the shaft and saved the seals. A simple fea will give % reduction in deflection with any upgrade.

These types of pulleys are difficult to maintain and if possible (from a maintenance perspective) I would stick to external bearings. ■

Dead Shaft Advantages:

1.Less Expensive

2.Lower Rolling Inertia

3.Free Spinning

Live Shaft Advantages:

1.Elevated Temperatures

2.Harmful Environments

3.Higher Allowable Loads ■

Hi all..

Read somewhere in this thread that you can not use the concept for drive pulleys.

Well the Joki (spelling?) is exactly that. It has a stationary shaft, and an internal motor/gearbox inside the shell. It is sold by Melco here in South Africa which is actualy Rulmeca.

Excellent for saving walkway space.. Not so good for motor cooling, nor for the pocket and maintenance.

A great idea for very small installations though.

Cheers

LSL Tekpro ■

Dear All,

Many have raised the benefit of the dead shaft having less fatigue stress that may also allow a smaller bearing size.

I disagree, when the bearing shaft size reduction is less than 25-30% of the shaft diameter at the hub. Most shaft turndowns, of small to medium bearing sizes, are selected based on bearing L-10 life if the rating is at 60,000 hours or so and not on shaft bending or stress fatigue. This has been my experience. ■

I am familiar with some dead shaft pulleys, including the Joki motorized pulley. I don't know what type of bearings they use on the dead shaft. I'll guess they are spherical roller bearings. On this basis I'll try to formulate the basis for claiming that smaller shafts and thus bearings are possible.

Let's start with some generalities about Pulley assemblies with live shafts:

1. Shaft deflection at the hub is limited in order to not fatigue the end disc by flexing it

2. Consequently shafts are larger than required for strength and for shaft fatigue

3. Typical turn down allowances result in grossly over-sized bearings. Indeed, many will use conical turn downs in order to reduce the bearing sizes

In this light then, with a dead shaft, the claim of smaller bearings rings true as:

1. There are no shaft deflection limitations. A spherical roller bearing can accommodate any possible shaft deflection in this case and no flexing fatigue will be transferred to the end disc

2. The shaft is sized solely for its static stress allowable without regard to fatigue as the load will not vary greatly in most cases and will certainly not reverse

3. It does not take a large bearing to support the load, that is why most bearing selections, in the previous case are grossly over-sized

All that remains is to run the numbers, to demonstrate this. If Van Gorp is making the claim it is because they have run the numbers and have implemented the results.

It will be nice to have someone from Van Gorp to chime in to confirm this since they are making the claims.

Joe Dos Santos ■