KWS Split Gland Seals are used to prevent bulk materials from leaking from a screw conveyor, screw feeder, drag conveyor or bucket elevator. Externally mounted, KWS Split Gland Seals consist of a two-piece split outer housing, single ring of packing, and a plunger.
The packing material is 1/2-inch square braided rope that fits tightly inside the outer housing and around the shaft diameter. The plunger is used to compress the packing and create a seal between the shaft and housing. Compression force may be adjusted by tightening or loosening the two exposed nuts on the outer housing.
Wide Variety of Packing Materials -inch square braided rope packing is available in many different materials. Graphite impregnated packing is used in most industrial and low to medium temperature applications. Teflon packing provides chemical resistance for use in the chemical industry. Ceramic fiber packing is used for high temperature applications.
Ease of Maintenance Braided rope packing can easily be replaced in minutes without disturbing the adjacent pillow block bearing or drive by retracting the split outer housing to allow full access to the rope packing.
Very Cost Effective KWS Split Gland Seals offer an advantage over more complicated mechanical seals on the market due to lower initial purchase price and reduced maintenance costs. Additional savings are also realized due to reduced maintenance down time when replacement of the rope packing is required.
We are using a chain bucket elevator to convey a powder that is very fine at -325 mesh and at an elevated temperature of approximately 450-degrees F. Our dust collector pulls a negative pressure on the elevator but we still leak material out of the tail shaft. The boot section is tensioned by a gravity take-up and there is a graphite/felt seal sheet that moves with the tail shaft.
Over time, this seal elongates with movement and thats when the material starts to leak. My question is twofold. Would it be detrimental to the life of the elevator if I switched to a lock down style take-up to eliminate the movement? If so, is there a new seal design that has solved this age-old problem?
Your questions are very valid. Leakage at the tail shaft of a bucket elevator is very common when handling very fine bulk materials at high temperatures. As you described, the take-up has a sliding seal arrangement to allow for thermal expansion and chain stretch. Locking down the take-up will put undue stresses and forces on the chain and shafts of the elevator, causing premature failure and therefore, is not recommended. Modifying the take-up or the seal would be a much better solution.
Since you have an internal gravity take-up in the elevator, the take-up can be modified or redesigned with sleeve-type bearings that are internal to the boot section of the bucket elevator. These sleeve bearings are very common and are typically a cast material that is very hard and tough.
In this case, the tail shaft needs to be hardened in the bearing area to match the bearing. This design is used in thousands of industrial applications including the cement and minerals processing industries. The boot section will be totally enclosed with no tail shaft projections through the side walls. The leakage will be totally eliminated with this design.
A second option is to use a take-up on the head section of the bucket elevator. The head shaft can be designed to adjust vertically to take up thermal expansion and chain slack. The tail shaft would be fixed and have packing gland seals to prevent product leakage. This modification would be more costly and time consuming than modifying the internal gravity take-up.
The most cost effective option for minimizing product leakage at the boot section is to use seal materials that are better suited for the application. There are new seal designs on the market, but most do not function well at high temperatures. However, high temperature seal materials are available that can withstand temperatures well over 450-degrees F.
Most of these materials are ceramic fibers and can be woven for rope packing for packing gland seals. In your application, a packing gland seal utilizing high temperature rope packing would be the most economical replacement for the graphite/felt seals. The packing gland seal has been around for a hundred years, but is still probably the best option for your application.
Home Free Articles and White Papers on Maintenance Engineering and Plant Engineering Problems and Solutions for Industrial Process Plant and Production Equipment Bucket Elevator Shaft Seal Design Quadruples Head and Tail Pulley Bearing Life
Bucket Elevator Shaft Seal Design Quadruples Bearing Life. Dust ingress into bearings is one of the great causes of premature bearing failure on bucket elevators. By selecting the right bearing housing and position, combined with this special dust seal arrangement, you can get quadruple the bearing life. The article provides the full details of the low pressure dust leak seal design along with a sketch of the successful set-up.
Below is a sketch of a dust seal arrangement that tripled the bearing life of the bearing in the housing. It went from 12 months at best to over 4 years without a failure. Combining the end cover sealed bearing housing mounted off the elevator frame with this separate dust seal arrangement where the shaft entered the frame, it more than quadrupled bearing life.
You will need to make the seal housing that mounts to the bucket elevator, or to any low shaft velocity low pressure dust leak situation, from commercially available carbon steel. The secret behind its success is that the primary seals are in a separate housing to the bearing and provide multiple and redundant sealing before the dust can escape the bucket elevator.
Disclaimer: Because the authors, publisher and resellers do not know the context in which the information presented in this article is to be used they accept no responsibility for the consequences of using the information contained or implied in any articles.
P.S. If you have maintenance engineering advice on industrial equipment maintenance, especially defect elimination and failure prevention of plant and equipment, or have made successful equipment reliability improvements, please feel free to send me your articles to post on this website. You can contact me by email at [email protected]