Screening machines

Drum screening

Trommel screens are used for the simple classification of screened materials. As a manufacturer of screening machines, we recommend modern screening technology as an alternative for optimal screening results.

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Simple screening technology with significant drawbacks

What are drum screening machines?

Drum screens belong to the family of screening machines. They are also referred to as drum screens, drum screening systems, screening drums, or rotary tube screens. Drum screens are used for the screening process for various materials, thereby separating them by size. This process is also known as classification or classification screening.

They consist of a long, cylindrical drum that rotates around its own axis and is equipped with screen perforations or screen plates. As the material rotates, smaller particles are allowed to fall through the perforations, while larger material is discharged from the drum.

Although drum screens are relatively well known in practice due to their long history, they present users with significant disadvantages during screening of recycled materials. These include, in particular, low separation efficiency and poor screening quality, the resulting high maintenance and cleaning costs, and the substandard feed of recycled materials to downstream sorting equipment such as Magnetic sorters or sensor sorters.

As your manufacturer of screening machines that deliver optimal screening results, we offer you top-quality alternatives for replacing drum screen systems. We’d be happy to advise you on this!

Typical Applications of Drum Screening Systems

What are trommel screens used for?

Drum screens are used, among other things, for screening rocks and soil, recycled materials, and waste. Typical applications include screening municipal solid waste, compost, Biomass, and scrap metal.

Maintenance and Cleaning Effort

How much maintenance do drum screens require?

Maintenance requirements for Drum screens can be significant, particularly due to their susceptibility to Blockages. Regular inspections, cleaning, and possibly repairs are necessary.

Advantages of Drum Screening

What are the advantages of trommel screens?

The key advantages of drum screens include the following:

a relatively simple technique
suitable for less demanding material processing
average throughput rates
Easy to use on the go
Requires minimal construction and installation support, making installation straightforward

Poor selectivity reduces sorting performance

Why shouldn’t drum screens be used when high sorting quality and profitability are the goals?

Due to their insufficient separation efficiency, drum screens and drum screening systems have difficulty achieving a high sorting quality. Especially in Recycling processes where precise separation of materials is crucial, drum screens can quickly reach their limits. Given the low sorting quality and the high cleaning costs, the reduced profitability of the entire Recycling process must also be taken into account.

How Trommel Screens Work

How do trommel screens work?

The operating principle of a drum screen is based on the continuous rotation of the drum around its own axis. During screening, the material to be screened is fed into the drum. Due to a slight downward slope, the material is transported during the screening process from the feed end to the discharge end of the screening drum. Particles that pass through the perforations in the screening drum are thus pushed outward and screened out. Larger particles, on the other hand, remain inside the screening drum until they are fed to the next processing step at the end of the drum.

Disadvantages of Drum Screening

滾筒篩有哪些缺點？

滾筒篩的主要缺點包括以下幾點：

篩分品質不佳
對滾筒篩分機的主要批評在於，其在篩分與分級過程中的篩分品質不佳，且分離精度不足。
由於滾筒篩的結構設計與運作原理，實際操作中會產生較高的過篩率。這意味著，例如，對後續的分類設備而言，有害的長條狀物體會混入細顆粒分級中。又或者以堆肥篩分為例：在生產所需的高級產品時，不希望出現的長條狀雜質會透過滾筒篩進入細粒分級或篩分通道中。
細顆粒物質的攜帶現象
由於滾筒篩的旋轉原理，細顆粒物難免會被帶入粗顆粒分級或篩分溢流中。例如，在對薄膜廢料進行篩分時便是如此。由於其材料的物理特性，這些材料在旋轉時容易相互糾纏。這會妨礙其中纏繞的細微顆粒被徹底分離。
回收材料的糾結
同樣由於技術結構的緣故，在實際操作中，對不均質且易纏繞的物料進行篩分時，常會發生物料纏結的情況。透過持續旋轉回收材料，這些材料會相互結合，並被「編織成辮子般的狀」。這些纏結物一方面會污染滾筒，另一方面在後續的回收過程中無法進一步處理，也無法加以利用。
篩網表面堵塞
此外，滾筒式篩分機極易發生堵塞，這不僅會影響篩分品質，還會增加清潔工作量。與3D 篩分等工法不同，長條狀工件不會因此而卡在篩網層中。這些顆粒非但沒有被輸送至篩網盡頭，反而容易卡在篩網中，進而進一步降低篩分品質。
維護與清潔工作量增加
鑑於前述滾筒式篩分機的缺點，其維護與清潔工作量通常遠高於回收物料篩分機。通常會導致每天需進行多次清潔，進而造成停機（參見「堆肥篩分」應用案例）

Worse results in the subsequent sorting

Why do downstream sorting devices, such as sensor or Magnetic sorter, perform less effectively when the target fraction contains unwanted long pieces and mis-sized particles?

Sensor-based sorting machines and magnetic sorting technology are sensitive, high-performance sorting machines whose sorting quality and return on investment depend significantly on the quality of the feed material.

The rule is: The better the quality of the material fed into the screen, the better the performance of the sorting technology. In short: Best Screening = Best Sorting.

The operating principle of sorting devices, such as sensor-based or magnetic sorters, is based on the specific properties of the material being sorted. These include, for example, density, color spectrum, or magnetic properties. These sorting devices only perform effectively if these properties are easy to detect.

However, if unwanted contaminants enter the target fraction—for example, due to mis-sized grains, long pieces, or sand and dirt —it is nearly impossible for sorting machines to achieve precise separation.

So if the use of trommel screens results in long pieces being carried over into the fine fraction, the sorting machines often face the problem that they cannot clearly distinguish between shapes, lengths, and materials. This results in unintended—but, due to the Screening technology used, unavoidable—mixing and contamination of the material.

Sorting technology experts confirm that long pieces significantly impair sorting results.

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