Re: Squeaking Air Locks
It seems that you are getting some powder into your shaft packing. The best way to handle this problem is to use a lantern ring with purge air flow. This will stop the powder from entering the shaft packing.
Amrit Agarwal
Pneumatic Conveying Consultants
polypcc@aol.com ■
Squeaking Air Locks
Is it squeaking or "howling"?
We have found it impossible to silence air locks with SS rotor vanes inside SS body - even a small amount of powder or granular material between rotor tips & body causes an induced resonant "howl".
We try to use aluminum body with SS rotor vanes - totally silent. ■
Squeaking Air Locks
Squeaking can occur if the vane clearance is too tight; usually, when too tight at the endplates. Shimming the non drive endplate out by 0.15mm might solve the problem - don't forget to centralise the rotor, so that there are equal running clearance at each endplate. ■
Squeaking Air Locks
Though the best solution is to provide air purged seals, We should know that Calcium silicate may leave thin layers of powder coating to continuously build up inised the valve. This can be either due to temperature or moisture.
A regular maintenance will avoid this problem or provide design changes to eliminate this . If the noise is due to metal to metal , then Nu-Con has a solution ie.. Moonitored Rotary Valve
any metal to metal contact will give signal to the operator to take corrective action(such as replacing the air seals )
Regards
B V Sarma
Regional Sales Manager
Nucon Ltd. Ph +64-9-579-2044. Ext. 216
P.O.Box 12-264 Fax +64-9-579-1121 Mobile +64-21-579111
Penrose Website www.nucon.com
Auckland
New Zealand
Take a look at our Website at www.nucon.com ! ■
Re: Squeaking Air Locks
We have experienced high pitched squealing or howling in many applications, and it can be caused by several effects. Powder in the shaft seals, and coating on the surface of the housing bore are both possible causes.
The other posted replies provide good starting points. Have you inspected the valves for these possible causes?
We have seen, with certain polymer powders a squeezing effect where the particle size of the powder is slightly larger than the gap clearance between the rotor and housing. There is no caking or build-up, but the squeezing effect causes the rotor blades to vibrate at a resonate frequency. The result is very annoying and will eventually cause fatigue type cracks to form on the rotor blades. In some cases, the blades eventually break off from the shaft. This problem can be solved by reinforcing the rotor construction with braces between the rotor blades, or by using a closed-end rotor. Be careful about the closed-end rotor, however, since powder intrusion between the rotor and side-plates, if not constructed with some expertise, can create a dead zone where the powder will eventually build-up.
Increasing the gap clearances can help, but not in all cases. Unless someone comes forward with some specific experience, I'm afraid, you might have to experiment with different treatments. Lab testing in a professional setting may save you from trial and error tactics in your plant. Good Luck.
Bob ■
Squeaking Airlocks
The various advice you have received is all excellent. In addition it may be worth while to consider a scraper blade. This could however lead to air escaping past the rotary seal in cases where it feeds in product into a pneumatic blowline and thus pressurise the vessel feeding the product. With certain raw materials this could also cause bridging. If you experience bridging please let me know and I will expalin a very simple and cheap way round this that we have found ■
Re: Squeaking Air Locks
Noise fro the airlock is normally caued by product build up in the bore and on the end covers.We would normally fit chamfered blades, with 2 set to a closer tolerance,or replace 2 of the blades with scraper blades which have serated edges,and are set closer than the standard blades. These have the effect of cleaning the bore and end covers stopping product build up
If the rotor is singing then stay bars between the rotor blades will stop this happening as well. ■
Squeaking Rotary Air Locks
Bob Reischl got it when he talked about resonance in the rotor vanes.
Again, we found SS rotor in SS body susceptible to this problem.
We confirmed it by removing the complete airlock from the line, setting it up in the shop with inlet facing up & part filling one pocket with a little of our PE powder product.
With the chain disconnected, we spun the rotor by hand
- the resultant "howl" was incredibly loud.
Just this small amount of powder acting on the vanes & end plates was enough to set up the resonance.
Replacing the airlock with SS rotor inside aluminum body
(instead of SS body) totally cured the problem. ■
Rotor Design
All the above points are worth looking at, but there is another one we have found sometimes cures it - to use closed end rotors instead of open end ones.
Often the squeaking is caused, as has rightly been pointed out above, by build up of particles between the rotor tips and body bore. Chamfered blades can help, and scraper blades may also help if this build-up tends to adhere, but an alternative approach is to make the rotor blade itself stiffer so that it does not resonate at such a low frequency. There are various ways of doing this, but one of the simplest is to used rotors which have end plates. This adds a lot of stiffness and often will cure the problem.
Mike. ■
Re: Squeaking Air Locks
The main problem with full end disc rotors on powders is product trapment betwwen end disc and end covers.We would normally use open rotors with stay bars to stiffen the rotor.
Full end discs are used normally on granular products,plastic pellets etc. lf you have to use full end disc on powders then some form of air injection into the end cover would help to remove product between the end disc and end cover ■
Stiffening Rotors
Quite so.
Stay bars are a possibility but might or might not interfere with easy discharge of the material from the pocket, depending on what it is.
Another way to obtain better stiffness is to use a reduced volume rotor which has "floors" in between the blades. This reduces the pocket volume so may need a larger valve or higher speed unless the valve is already oversized, but even if you have the "floors" at quite a large radius the reduction in volume is not much owing to the square relationship between radius and volume - but the gain in stiffness is very great, as deflection of a cantilever is a function of the cube of its length!
Mike.. ■
Re: Squeaking Air Locks
I also have used closed-end rotors to prevent rotor grinding inside the valve body. But some of the fine powder will migrate into the clearance between the rotor-end and the valve body. This powder must be removed to prevent the rotor from stalling. Solution to this problem is to introduce purge gas in the clearance space.
A. T. Agarwal
Pneumatic Conveying Services LLC
polypcc@aol.com ■
Purge Gas
I agree. Also, if using this approach I would recommend an interlock, so that the valve can't run unless purge gas pressure is detected - then it prevents the problem of powder ingress behind the end plates from ever arising.
Mike. ■
Re: Squeaking Air Locks
One more thing, the purge gas pressure must be controlled so that it is about 10% higher than the conveying pressure, assuming a pressure type conveying system. Purge gas flow must also be regulated to maintain a certain velocity across the end clearances to not only prevent powder from backing up, but also to prevent fluidization in the feed hopper. I generally introduce purge gas from 4 locations 90 degrees apart.
Regards,
A. T. Agarwal
Consultant
Pneumatic Conveying Services
polypcc@aol.com ■
Squeaking air locks
we are using calcium silikate as a carrier in our produktion. this causes problems with squeaking air locks.
dos anybody have a simple solution to overcome this problem? ■