Coating drums have become an increasingly utilized tool in industrial process settings, giving producers the opportunity to coat their granular products for improved handling, performance, and even storage characteristics.
The relative newness of these machines, however, leaves some operators and maintenance personnel struggling to identify and resolve problems. The following covers the most common issues experienced with coating drums, as well as how to resolve them.
Coating Drum Process Problems
Mechanically, the issues coating drums experience are no different from other rotary drum equipment, but the unique internals of a coating drum can present a few novel challenges in the process. Most often, these problems reveal themselves as inconsistencies in the product discharging from the drum.
Inconsistent product could mean that the product exiting the drum is inconsistently coated, clumps have formed, or another type of anomaly is occurring. In any case, the path to resolution starts with confirming feedstock uniformity.
Feedstock Uniformity
Coating drums are designed to work around specific granule properties; when these parameters fall out of spec, it is not uncommon to see issues with the product. As such, before inspecting the internals, operators should always first rule out that an inconsistent feedstock is causing the issue.
How to Resolve an Inconsistent Feedstock
Resolving an inconsistent feedstock is highly dependent on the specific material at hand and the processing conditions. Operators must pinpoint the type and source of variation and then work to resolve it by making the necessary process adjustments.
Clogged Nozzles
When one or more nozzles in the spray system become clogged, the process does not receive the required amount of the liquid additive, leading to an inconsistent output.
How to Resolve Clogged Nozzles
Nozzles may become clogged for a number of reasons: a drop in pressure, improper nozzle selection, or a problem with the additive preparation system. As such, maintenance personnel must typically clean or replace the affected nozzle(s).
Caking
Caking on the Coating Drum’s Interior Walls
Caking can be a common problem for coating drum operators; material may stick to the drum’s interior, causing a number of issues, such as changes in the ratio of liquid additive to product, material breaking away in clumps, and more.
Caking on the Sparger
The liquid additive/spray distribution system, or sparger, can also become caked in material. In addition to the typical issues associated with caking, a caked sparger is especially problematic when the material being processed is corrosive, as caking encourages corrosive wear on the mechanical components and support structure of the sparger. If not properly managed, this can cause the support system to fail, leading the sparger to break off in the drum, which presents its own set of problems.
How to Resolve Caking
Resolving Caking on the Coating Drum’s Interior Walls
Caking on a drum’s interior is often largely resolved with the addition of a drum liner. Liners are available in a variety of materials, including stainless steel, ceramic, rubber, and more. Rubber liners are the most common and discourage buildup by flexing as the drum rotates, sloughing off any material that has stuck to the liner. In addition to preventing buildup, liners also help to protect the drum shell from corrosive and abrasive wear.
Caking on the drum’s interior can also be resolved by retrofitting the unit with knockers, which impact or “knock” a wear band on the drum’s exterior to dislodge any caked-on material within.
Resolving Caking on the Sparger
When it comes to the sparger, caking is unfortunately not always preventable. When this is the case, operators should clean out the drum as production allows to minimize caking and monitor sparger condition.
In other cases, caking may be the result of poor nozzle placement, improper nozzle selection, or inadequate drum speed, all of which can be remedied. Operators can thus troubleshoot the issue and experiment with different process conditions to resolve the issue.
The addition of a “top hat,” or metal plate positioned over the length of the sparger, can be useful in protecting the sparger from caking by shielding it from falling product and additive.
Troubleshooting Coating Drum Process Problems
Operators may not always be able to readily view what’s actually happening in the coating drum, making identifying the source of a problem difficult. When this occurs, or when operators have reached the extent of their ability to troubleshoot a problem in the coating drum process, FEECO recommends one of two approaches: testing in a facility such as the FEECO Innovation Center, or conducting a process audit.
Testing in the FEECO Innovation Center
The FEECO Innovation Center is equipped with a pilot-scale coating drum with viewing access, allowing experts to simulate process conditions, test different variables, and systematically evaluate an issue (or assess potential changes to production). A number of different variables can be tested, including:
- Coating drum speed and slope
- Internal arrangements
- Spray nozzle type
- Spray nozzle location
- Coating/liquid additive type, concentration, and feed rate
- Coating/liquid additive preparation
- Product feed rate
- Product feed conditions
Conducting a Process Audit
Calling in the OEM or a qualified service expert to conduct a process audit can be an invaluable approach to issue resolution. A process expert will be able to assess the unit in its live production environment, systematically working to identify and resolve the issue at hand.
This gives operators, maintenance personnel, and plant managers a chance to ask questions and become more familiar with their process and equipment, so they are able to better troubleshoot in the future.
A process audit can also provide valuable benchmark data for future troubleshooting and maintenance planning.
Coating Drum Mechanical Problems
Rotary drums are generally highly reliable, but they can experience mechanical issues on occasion. As with other types of rotary drums, the two most common mechanical issues coating drums see are:
Misalignment
Misalignment may occur as a result of normal wear and tear, or because of an underlying issue. Most often, misalignment is identified through a vibrating or chattering noise, or through specific wear patterns on tires (riding rings) and/or trunnion wheels. In addition to added stress on all drum components, misalignment can also cause excessive contact and potential wear of the thrust roller. As such, misalignment should be resolved as quickly as possible.
How to Resolve a Misaligned Coating Drum
A misaligned coating drum can only be realigned by an experienced professional. This typically involves the use of a laser alignment system, which takes coordinates of the machine and translates them into a 3D image that allows technicians to identify and make the necessary adjustments.
Tire and Trunnion Wear
Wear or damage to tires and trunnions may be the result of misalignment, inadequate lubrication, or any number of other causes of tire and trunnion wear. This is easily identified by looking for any type of anomalies in the surface of tires and trunnions – typically trunnions will experience wear before tires will, so these should be checked first.
Tire and trunnion wear left untreated can cause a variety of issues, including misalignment, as well as excessive damage to tires and trunnions. Abnormally worn tires or trunnions also have the potential to cause excessive contact with the thrust roller, which can result in wear.
How to Resolve Worn Tires or Trunnions
Worn tires and trunnions also require the help of outside expertise. If wear is minimal, an external service provider will bring in specialized equipment to recondition tire and trunnion surfaces to like-new condition. Severe damage will unfortunately require component replacement.
Conclusion
Coating drums have become an integral tool in industrial processing, helping producers to control the behavior and performance of their products and materials. And while they are a tremendously valuable production tool, operators can experience issues with them from time to time.
By working with a coating drum expert such as FEECO International, however, producers can readily troubleshoot and resolve both process and mechanical issues such as inconsistent product, misalignment, and trunnion and tire wear. FEECO offers process experts, as well as an experienced Customer Service Team to inspect, assess, and repair any issues, with testing and process audits available. For more information on our coating drum testing and service capabilities, contact us today!