10 Errors in Screening Efficiency That Are Costing You Product Value Every Day

10.03.2026, Remscheid, Germany

Sigurd Schütz, RHEWUM GmbH

The Science of Screening: Why Every Percent More Separation Sharpness Is Worth Real Money

Good screening is not a gut feeling, but applied physics. And applied economics: Precise screening transforms raw material into quality product, reduces rejects, and measurably increases the value of your fractions. Yet very few operators tap into this potential. The result? Suboptimal throw trajectories because the amplitude was set too high, wasted separation sharpness because the frequency doesn't match the particle spectrum. Blinding because hygroscopic materials were underestimated. The following 10 points show what science teaches about perfect screening – and how you can extract more value from every ton of product: From particle-aperture interaction to multi-deck screening with differentiated amplitudes to the industry's most common misconception: What "screening efficiency" really means. No theory. No guesswork. Just physics and 30 years of experience that pays off, provided you consider it:

Error #1: Not Knowing Your Material Properties

For good screening, it's essential to know your product. In addition to particle size distribution as an initial reference point, it's also important to understand other material properties, such as hygroscopicity: Does the product absorb water from the surrounding humidity and change its properties through water absorption? Flowability decreases, caking occurs, it agglomerates into lumps, or similar. Typical examples include lignite, magnesium chloride, and various fertilizers that already change their mechanical properties during storage. Other important questions: Is the product corrosive or sticky?

Error #2: Mismatching Screen Amplitude to Your Product and Separation Goals

Consider this: Screening is comparing the size of the screen aperture with the size of the individual particle. The more often the particle is compared with the aperture, the better the screening. This means that an amplitude that's too large throws the particle too far over the screen media. As a result, the number of encounters between the particle and the screen aperture is lower than it could be – the screening result becomes suboptimal.

Error #3: Underestimating the Impact of Feed Devices

To optimally utilize the available screen media, the product must be distributed evenly across the entire width of the screen media. This ensures the subsequent comparison between screen aperture and particle. Center feeding leads to center discharge. The edges of the screening machine are not utilized, even though the machine can perform better.

Error #4: Using Screen Frequency That Doesn't Match Your Separation Requirements

In addition to screen amplitude, the excitation frequency should also match the desired separation. Too low a frequency prevents the maximum number of comparisons between screen media and bulk material; too high a frequency may lead to a suboptimal number of comparisons, which is important for the perfect screening result. The key is to achieve the optimal throw trajectory of the particle being screened.

Error #5: Using Uniform Amplitudes Across All Decks in Multi-Deck Screeners

A uniform amplitude for all decks wastes potential. It's advantageous in multi-deck screening machines to apply different screen excitations. In the upper screen decks, a larger amplitude is used because of the coarser bulk material; in the lower decks, a smaller one. An identical amplitude for all screen decks is technically an economical solution, but suboptimal, as it doesn't achieve the values needed for a perfect throw trajectory.

Error #6: Ignoring the Impact of Infeed and Discharge Conveying Systems

The performance specifications of screening machines are always based on continuous product feed. Conveying equipment that cannot ensure this, such as bucket elevators, must be taken into account. These can lead to problems because, on the one hand, they feed product in surges to the downstream screening machine. On the other hand, the individual buckets are often filled at an angle, which leads to angled discharge as well. This further complicates the material feed to the downstream screening machine. Remember: Unsteady feed leads to unsteady product flow.

Error #7: Overlooking the Side Effects of Bouncing Balls

When using bouncing balls in horizontal screening machines, they are allowed to "bounce around" involuntarily below the screen media, excited by the vibration of the screening machine. Targeted control of screen amplitude or screen frequency is not possible. The bouncing balls have the positive effect that their chaotic movement below the screen media mechanically keeps possible blockages clear. However, it should be noted that these bouncing balls can also damage the product if it gets caught between the screen media and the bouncing ball. For products that are brittle, this leads to their destruction and the unwanted generation of additional fines. Since the bouncing ball wears down and decreases in size over operating time, traces of the bouncing ball material (usually neoprene or silicone) inevitably end up in the screened product. This can lead to questions in food applications, although the amounts are small and usually in the ppm range.

Error #8: Not Leveraging the Segregation Effect of Your Bulk Material

The segregation effect helps in the separation of bulk materials. Bulk materials with a smaller particle size have a higher bulk density. This means that the finer particles displace the coarser particles upward in the bulk material away from contact with the screen surface. In other words: The fine particles sink through the bulk material down to the screen surface, while the coarse particles migrate upward. This is a helpful effect, as screening machines typically screen from coarse to fine, and the fine particles can thus be separated more quickly.

Error #9: Not Knowing Your Product's Moisture Content

As a general rule for screening machines: Either the product is dry or wet. States – that is, mixtures between solid and liquid – that fall in between, such as pasty, doughy, or sludgy, cannot be processed by screening machines. Of course, there are borderline cases. If you're unsure, test your product on the respective screening machine to really ensure that the later function of the screening machine is guaranteed.

Error #10: Misunderstanding What Screening Efficiency Really Means

A common misconception arises from customer inquiries that screening performance must be greater than 95% or similar. The misconception lies in the term "performance" itself. In the field of screening technology, a distinction must be made:

Purity describes the proportion of the desired product in the specific screen fraction relative to the total amount of that fraction.

Yield refers to the proportion of the recovered product in relation to the amount contained in the feed material.

Efficiency (screening efficiency) results from the fact that product purity and product yield are directly related – it is the product of both values and describes the screening efficiency.

An example: A yield of 90% is achieved with a purity of 85%. Thus, the screening efficiency in this case is 76.5% (90% × 85%). Only the term "performance" is confusing and does not precisely describe the actual performance capability of a screening machine.

Let us analyze together where your screening machine is wasting potential. Our experts examine amplitude, frequency, and material feed – and show you how to extract measurably more value from every ton. Contact our screening technology experts at www.rhewum.com/contact