Cutting, drilling, grinding, milling, sawing, or other processing all lead to dust generation during production, while other processes like welding or plasma cutting also produce small particulates, along with smoke and fumes. Known collectively as industrial or process dust, these contaminants must be properly filtered to ensure the safety and health of factory workers. Certain types of industrial dust can even cause explosions or fires.
Industrial dust not only causes problems with health, it wears down equipment. As important components in an industrial dust collector, rotary valves also need to be protected against abrasion and wear caused by abrasive and corrosive material. To protect rotary airlock valves and other vital components, many factories often coat them to ensure they perform at their peak.
The Importance of Protecting Rotary Valves from Dust
Coating a rotary valve will extend its life, protecting its surface from wear and making it easier to clean. Sticky material like sugar or flour builds up in a valve over time, slowing material flow and limiting productivity. Failing to deal with this build-up will eventually cause issues with quality, sometimes even contaminating the material being processed. In heavy-duty applications such as cement or gravel processing, dust causes abrasion and corrosion. Often material processing causes a sandblasting effect that results in reduced efficiency, leaking material and compliance issues, worn rotors, and other mechanical problems.
Dust Collector Rotary Valves
The hopper must be sealed for a dust collector to perform at its peak. Rotary valves are often used to prevent air and contaminants from leaking from a dust collector. These act as airlocks, isolating the dust hopper while collecting dust so it doesn’t become problematic for production.
Without an air-locking device, air will enter a system under a vacuum or leave a pressurized system, causing contaminants to leak from the dust collector. Rotary valves prevent dust from discharging back into clean air in vacuum systems or blowing dust out in pressurized systems. They help prevent the need for additional maintenance while also allowing the dust bin to be changed without halting production.
Best Coatings for Rotary Valves
The best coatings for a rotary valve depend on the application. Sticky materials like sugar require coatings to keep buildups from occurring and reduce flow rates. For abrasive material, heavier material is needed to keep the rotary valve from wearing. Highly abrasive silica sand necessitates the most robust type of coating. These coatings protect the valve’s endplates, housing, and rotors.
When considering the best coating, consider the following:
- For lighter, not-so-sticky materials such as powdered sugar, hard chrome coatings should be used for endplates and housing, while polytetrafluoroethylene (PTFE) – known by its brand name Teflon – works well as a coating for the rotor.
- For light yet sticky material like flour or granulated sugar, 304 stainless steel rotors with the rest of the valve treated with an extreme temperature resistant coat will keep material from building up in the rotor pockets.
- More abrasive materials like cement coatings made from hard chrome, or a thick heavy-plated chrome, work well for endplates and housing, while rotors made from stainless-steel can be used, as these are more easily replaceable.
- When working with corrosive materials like salt, extreme temperature-resistant coatings offer advantages for many applications, as they’re extremely durable and provide a non-stick surface. In contrast, stainless-steel rotors work well in combination.
- Silica sand and other highly abrasive materials should utilize coatings made from tungsten, which has a high melting point and is remarkably tough; tungsten coatings should be applied to all rotary valve parts, including endplates, housing, and rotor.
With sticky materials, buildup will be heavier, particularly when the material becomes moist. Where powdered sugar tends to slide off coatings rather than stick to them, granulated sugar or flour tends to stick. For this reason, stainless-steel valves often work better than coated cast iron valves for stickier material, which starts to build up and harden, reducing flow rates and lowering productivity.
Other Considerations
It’s essential to track the amount of buildup occurring to determine how abrasion affects the rotary valve. On pneumatic conveying lines under high pressure, more wear will occur, as the air coming through the valve will make the material more abrasive. In addition to using coatings, slowing the valve often limits its wear.
Prater Dust Collector Rotary Valve & Airlock
Prater Industries' series of dust collector rotary valve airlocks offers a cost-effective means for dust mitigation. Our dust collector rotary valves provide numerous advantages, used under dust collectors, cyclones, and hoppers. Prater’s dust collector rotary valves feature:
- Additional tips to prevent air leakage.
- Easy configuration for most applications.
- Eight precisely machined rotors with rugged housings made from cast-iron.
- Larger pockets that offer as much as 50 percent more volume.
- Precisely machined to handle actual operating temperatures.
- Robust cast iron housing and endplates.
Dust collector rotary valves by Prater act as air seals in dust mitigation applications and are appropriate for low-temperature use with a minimal pressure differential. Our rotary valve airlocks are additionally custom-drilled to fit manufacturers’ needs to provide the best seal possible while maximizing material flow.
