seals for dry wall mud

[mecoman]

Hi,

Looking for sealing options for sealing dry wall or sheet rock mud in a cylindrical ribbon mixer pulling a vacuum. Product is wet and making wallboard aka sheetrock. Approx. 5" shaft at 20-25 rpm, batch operation, wet slurry.

TIA

 

[SealSolutions]

We have seen similar service of this application on moyno pumps as well as rotary lobe pumps, the system was a split mechanical seal. The split seal worked very well with a rifled bushing in the stuffing box that removed the high solids and allowed the seal faces to flex with the high product solids . If you need to contact the firm that works with the seals they are a Chesterton Distributor in Mulberry FL

 

[mecoman]

SealSolutions,

Is the rifled bushing cut like a gun barrel internally? ALso, any water applied to the bushing or seal?

Thanks,
MECOMAN

 

[longeron]

Solids in vacuum service?

I can think of a couple of possible solutions:

Perhaps a dual pressurized seal might be in order.
The dual seal with a pressurized reservoir would help to ensure proper lubrication of the seal faces with nice clean fluid instead of air and solids. Depending upon how worried you are about diluting the gypsum this might work better than a Plan 32 because the volume of fluid required to keep the faces clean would be significantly reduced. A rotating metal bellows platform might also be a good idea.

Another option is a set of segmented bushings. Two bushings with a gas injected between them at a higher pressure, say air or nitrogen, or maybe even steam would contain the gypsum, would not clog, not have any moving parts, and could be much less expensive to install. I know that this method has been used in grinders, dough mixers, and a number of other applications with similar media.

To be sure, I'd take these ideas and run them past your trusted vendor with specifics about the mud including solids concentration and viscosity, dimensions for the seal chamber and nearest obstruction, as well as your budget constraints.

 

[flexibox]

A dual pressurized seal is the best choice and guarantees a clean fluid film at the seal, however be aware when the machine is stopped! do not allow the product to solidify at the inboard of the seal. If you can provide a clean water flush (prior to start up) to the inboard dynamic seal do so or you run the risk of seal hang up. In the event of a seal failure then you will dilute the product with water and if this is a batch production you have to consider if the high dilution will throw the product off spec.
I believe that because of the low speed the use of a Single seal Silicon vs Silicon Carbide, external springs with a static water quench will work (Plan 02 & 62 water quench) The quench will wash away any powder formation due to normal seal leakage and prevent potential air drawn in due to the vacuum. Using lip seals as the secondary seal will be the seals biggest weakness as they are not reliable in these applications. I have assumed horizontal side entry mixer.
If you have a top entry mixer a single seal is not well suited due to dry running.