Conveyor Tracking Help

[sraomberts]

Got a good one for you guys. I am designing a conveyor to carry a shredded loose tobacco product, replacing an existing flimsy conveyor that has tracking and drive issues. The current system allows product to get under the belt, leading to buildup on the rollers and causing the belt to slip.

In my redesign, I’ve created a robust, washdown-compliant conveyor featuring:

• A polished stainless-steel running bed with bent-up edges that sandwich the belt between the skirting to prevent product from getting under the belt.
• Crowned pulleys at the head and tail for improved tracking.
• A snub roller to increase belt wrap around the drive pulley.
• Over 3" of belt tensioning adjustment, a significant improvement over the current 3/4" of existing tensioning.

I’ve done some research on conveyor belt tracking and have prior experience designing simpler conveyors. For this project, I’ve designed the following belt path and roller configuration. Ideally, I would use a head drive, but since the conveyor feeds into a machine, that’s not an option. As a result, I’m using a tail drive and tensioning the belt from the back just before the drive roller.

For those experienced in conveyor design and fabrication, I have a couple of questions:

1. Am I overthinking this?
2. Will the take-up pulley between the two fixed idler rollers have any effect on tracking?
3. Are my crowned pulleys even doing anything in this configuration?
4. On the head end, is the additional tracking adjustment necessary for the idler pulley that uses a self-aligning bearings with 5 degrees of articulation?

Hopefully, this all makes sense. Thanks in advance for your input!

 

[3DDave]

I would look at a smooth trough and use a drag conveyor to scoot the material along. They keep the material from reaching places the material is not wanted.

 

[sraomberts]

I would look at a smooth trough and use a drag conveyor to scoot the material along. They keep the material from reaching places the material is not wanted.

I originally thought about doing just that. Unfortunately I cant as the product is either dry or incredibly wet and sticky depending on flavor. Since this conveyor is used for metering the client wants a smooth level layer of product that can be scraped off at the end.

 

[dvd]

Depending on the characteristics of the tobacco, you could end up with problems from your tobacco rolling up and pinching the belt under the skirtboards - make sure you have an increasing clearance gap as the belt travels downstream to avoid a pinching point.

You could consider a flexwall belt conveyor and eliminate the skirtboards -

 

[MintJulep]

Vibratory conveyor.

 

[Compositepro]

I would strongly consider a vibratory conveyor. Much cleaner and simpler. No seals, and less chance for material to stick since it does not stay in continuous contact with the conveying trough. The trough can be lined with ptfe film.

As to the belt conveyor, use the head pulley alignment for belt tensioning as well.
Crowned rollers need adequate lead-in distance to work. It is the distortion of the belt shape in the approach to the roller that causes tracking over the center of the crown.

 

[3DDave]

I agree that this is very short-coupled for the tracking roller to do much to affect tracking. Being a long belt I would expect tracking adjustments on both ends.

Here's a short and very simplified explanation; I apologize if it seems overly basic:

If the belt isn't tracking where it needs to be then it may require tweaking to both end rollers. In power transmission the pulleys are often wide enough that tracking by crowning is sufficient to not leave the desired path tolerance.

This is mentioned here - https://www.dornerconveyors.com/resource/belt-conveyor-tracking-v-guided-vs-crowned-roller

This method works by the taper sections of the roller steering the running conveyor belt to the center to the roller. This is however not exact. Due to the tolerance of the belt splice, the accuracy of the belt conveyor frame, and weave of the belting the conveyor belt will drift back and forth across the face of the roller. On larger rollers a drift of +/- ½? can be expected.

I think your path tolerance is far smaller than that.

 

[MintJulep]

The trough can be lined with ptfe film.

Some tobacco companies don't allow PTEF in any equipment because if small pieces break or wear off and contaminate the product they released toxic products of combustion.

Ironic isn't it?

 

[Compositepro]

Good point. But the the main thing is that non-stick liners can be easily applied. There are many alternatives. Also, the trough can be quickly replaced with another for off-line cleaning.