Test sieves are a screening medium used to characterize the distribution of particles or separate elements from material. As a sensitive technical instrument, it is essential to take proper care of sieves. If a sieve falls out of specification, it could adversely affect quality standards; however, a well-maintained sieve offers accurate, reliable results. The techniques listed here can be applied to ensure intended operation and extend the life of test sieves.
The Five Practices of Sieve Maintenance
Sieving is an important process in a wide range of industries. Test sieves can be used to separate fine particles in pharmaceutical laboratories or more rugged materials in the mining sector. Users expect the test sieves to function, but might neglect the necessary maintenance. As a result, sieves can become clogged or damaged.
To prevent deterioration, users can implement a strict maintenance regimen of inspection, usage, cleaning, storage, and certification or recertification.
Inspection
Regular inspection is the most proactive method of sieve maintenance. Without it, routine wear-and-tear can alter the condition of the mesh and negatively impact the accuracy of the analysis.
During a visual inspection, users should examine the mesh for irregularities, such as dents or depressions. To assess the surface of the mesh, hold the sieve up to a bright light source. Ensure that the mesh is pulled tight across the length of the sieve.
If the mesh appears to be dented (see Figure 1), users will want to discontinue use of the damaged sieve. Using a dented sieve affects the accuracy of tests due to the openings in the mesh becoming stretched or warped. Similarly, a scratch can result in rips and tears in the mesh, necessitating a sieve change for quality purposes.
Figure 1 – Example of dented mesh.The other component to examine when inspecting a sieve is the condition of the epoxy. Epoxy is the substance used to attach the mesh onto the frame.
A cracked epoxy (see Figure 2) is most often the result of extended usage. Regularly checking the edges of the sieve, especially where the mesh meets metal, is important. In the event of cracks to the epoxy, the sieve will need to be replaced. Cracks will allow more material to escape through the sieve than intended, skewing test results.
Figure 2 – Example of cracked epoxy.Usage
Another proactive method for maintaining sieves is proper usage. Improper usage can damage the integrity of the sieve and impact its accuracy. Some of the most common errors are listed below.
Pushing particles through the sieve. When hand-sieving, users should not place an excessive amount of pressure on the mesh of the sieve. Pressuring the material or particles through the mesh could affect the results of a test.
- Putting too much sample on the sieve. This can cause blinding. Blinding occurs when the aperture of the mesh becomes clogged, preventing particles from flowing through the sieve.
Cleaning
Cleaning is one of the most important practices in maintaining sieves. While it may seem straightforward, it is a more complex and involved process when done correctly, and includes the selection of the ideal cleaning solution and utensils (see Figure 3).
The following steps are a brief overview of the cleaning process:
Turn the sieve over a receiving pan.
- Gently brush the underside of the mesh, using a circular motion
- Gently tap the sieve frame with the brush handle to remove particles that cling to the frame
- Wash sieves in warm water with a mild detergent solution
- Allow adequate time for drying.
Brushes may appear to be interchangeable, but a sieve-specific brush is recommended because harder bristles can damage the wire mesh.
Figure 3 – Cleaning method.Especially for sieves with a finer mesh, an ultrasonic cleaner is also an option. An ultrasonic cleaner is a compact, portable unit that combines a fluid bath with vibrations to dislodge contaminants from the sieve’s frame and smaller media.
Below are several practices to avoid when cleaning sieves:
Don’t use a dishwasher to clean them
- Don’t use air pressure to clean them
- Don’t force particles through the openings while cleaning
- Don’t use acidic solutions while cleaning
- Don’t use an oven to dry them
- Don’t attempt to repair the sieve.
Storage
Storing sieves in ideal conditions is the easiest maintenance technique. Sieves should be stored in a clean, controlled, and dry environment. Exposing sieves to fluctuating temperatures or a wet environment could threaten the condition of the epoxy and mesh and result in a failed test.
Certification
Sending test sieves for certification or recertification is the surest method of quality assurance. A test sieve certification (see Figure 4) is a statement or verification that a sieve meets or exceeds written standards. Certifications should be conducted based on aperture and schedule.
Figure 4 – Test sieve certification.Guidelines for test sieve recertification
During certification, the sieve is visually inspected for deformities and irregularities. Afterward, the sieve is placed under a microscope in order to determine if the wires are clogged or stretched and verify the wire diameter. If the sieve passes all these tests, it is returned to the user with a verification of performance.
Conclusion
While test sieves are sensitive tools and vulnerable to deterioration, there are practices that can prolong their life and allow them to continue to provide accurate results. Proper inspections, usage, cleanings, and storage minimize wear-and-tear. Sending sieves for recertification is the best practice for ensuring they remain in specification.
Candace Blaker is particle analysis equipment manager, W.S. Tyler, 8570 Tyler Blvd., Mentor, OH 44060, U.S.A.; tel.: 800-321-6188; e-mail: [email protected]; wstyler.com