Introduction
A dust leak should be traced to its path and driving condition before a new shaft seal is selected. Check shaft movement, joint fit, process pressure and ventilation as well as the seal itself. Fine-powder transfer from silos to weigh hoppers or mixers needs a defined containment target and a means of verifying it in service.
An enclosed cement screw conveyor can reduce exposure, but the enclosure does not establish zero leakage. Dust can harm health, contaminate equipment and waste product. Combustible dust requires a separate assessment: ordinary cement dust must not be treated as coal dust simply because both occur in cement plants. This guide compares sealing arrangements and the mechanical and maintenance conditions that determine their performance.
Root causes of dust leakage
Contact seals can deteriorate under abrasive contamination, unsuitable adjustment, temperature or shaft motion. Radial runout, axial movement and angular misalignment must stay within the selected seal’s limits. A seal is not a bearing; worn packing does not itself provide or remove the shaft’s structural support. Check the bearings and mounting that control shaft position.
Housing joints, cover gaskets and access doors can leak when mating faces are distorted, fasteners are loose or the gasket is damaged. Airflow from filling, aeration, purge or connected equipment can create pressure differences across those paths. High speed may influence material and air motion, but is not proof of a pressure fault by itself.
Poor vent performance may increase pressure, whereas absence of seal purge is a fault only if that seal requires purge. Adding purge indiscriminately can introduce more air that the system must handle. Check receiver vent filters, duct restrictions and pressure at relevant operating states. EPA’s fabric-filter guidance identifies differential pressure and other operating indicators as useful monitoring parameters; filter condition needs its own assessment.
Temperature changes and moisture can affect seal compatibility and deposits. Examine cracking, hardening, swelling or abrasive grooves with the actual seal material and service history. Replace a failed component only after checking the cause that could damage its replacement.
Comparing shaft sealing technologies
Gland packing is an adjustable contact arrangement and may suit a duty with suitable material, shaft finish and maintenance access. Over-tightening can increase friction and heat; insufficient or worn packing can leak. Lantern rings and grease or gas barriers are options only when designed for the process and contamination limits. One unsuccessful installation does not establish that all packing fails in cement service.
Labyrinth seals create a restrictive path with defined clearance; brush seals use bristles and have their own contact and movement limits. Contact lip seals and mechanical face seals are further options where their pressure, temperature and surface requirements fit. A seal’s name alone does not demonstrate suitability for dry abrasive powder.
A non-contacting air-purged design can avoid rubbing at the intended sealing interface. It still needs the specified shaft geometry, movement range, clean dry air and pressure relationship to the process. It is not automatically standard equipment for every cement screw, does not tolerate unlimited motion and is not maintenance-free as a complete system.
Inpro/Seal’s published retrofit describes coal-handling screws in a cement plant, not a trial with ordinary cement powder. The case reports packing problems and replacement with Air Mizer seals; importantly, scored shafts still needed sleeves for the required sealing geometry. Treat it as a supplier’s application example, not a universal lifetime, certification or cost guarantee for VOGO equipment.
Split designs can simplify replacement where shaft removal is difficult, provided the selected design fits the available space and assembly requirements. Compare access, consumables, air demand and failure response as well as purchase cost. The shaft seal selection guide develops the specification for pressure, movement and leakage acceptance.
The role of an enclosed housing
A U-trough with properly designed covers and gaskets can contain powder; it should not be equated with an open trough. A tubular shell can reduce long cover joints and provide a compact path, but still has flanges, hatches, shaft penetrations and connections to seal. Either form needs appropriate supports and alignment. A tube does not automatically prevent sag or pressure buildup.
VOGO’s cement screw catalog lists selection diameters Ø89–Ø407 mm, length bands extending to “below 15 m” and a reference capacity range of 1.3–170 t/h. These are catalog selection data, not one configuration’s guaranteed output or pressure rating. Confirm diameter, length, inclination, material condition and drive for the actual duty.
Correct fill and speed can help stable operation, but cannot replace a ventilation and pressure review. Coordinate inlet, receiver and any added air, and define pressure limits for covers, joints and flexible connectors. Bearings and supports must preserve the seal geometry through the expected load and temperature range.
Maintenance for seal reliability
Inspect leakage patterns, seal condition and shaft movement at scheduled intervals based on service experience. For purged designs, verify supply quality, flow and the required pressure differential, not just a pressure reading upstream of a blocked line. Define an alarm or stop response to purge failure according to the design. Wet air can create deposits or other compatibility problems.
Trend end- and hanger-bearing temperatures at comparable operating conditions. A rise can indicate lubrication, alignment, loading or contamination problems; it does not identify dust ingress on its own. Investigate alongside vibration, noise and inspection findings. Avoid touching moving or hot components to assess condition.
During isolated replacement, inspect the shaft or sleeve for grooves, dimensions and runout. Repair or replace it using an approved method. A non-contacting seal does not automatically bypass a damaged surface: it may still depend on tight and consistent geometry. Verify the installed seal and any sleeve joint against the supplier’s instructions.
Inspect static gaskets, covers and flange joints, tightening fasteners to the specified method rather than crushing seals through indiscriminate retightening. Check mating surfaces and supports if leaks recur. After repair, verify containment under representative operating conditions and retain records. Maintenance supports performance; it does not by itself certify compliance with every applicable emissions requirement.
Conclusion
Control leakage by treating seals, shaft support, joints and ventilation as one system. Select a technology for the actual powder and operating conditions, then verify and maintain its performance. Use VOGO’s conveyor datasheet with the required leakage target, layout and duty data to review the proposed configuration.
