What are trommel screens?

Trommel screens belong to the family of screening machines. They are also known as trommel screens or trommel screening plants as well as drum screens or rotary trommel screens. Trommel screening machines are used to screen different screening materials, i.e. they separate them according to size. This process is also known as classification or grading screening.

They consist of a long cylindrical trommel that rotates on its own axis and is equipped with screen perforations or screen plates. As the material rotates, smaller particles should fall through the perforations and larger material should be transported out of the trommel.

Although trommel screens are relatively well known in practice due to their long history, they offer the user significant disadvantages when screening recycling materials. These include, in particular, the low separation efficiency and low screening quality, the associated high maintenance and cleaning costs and the inferior feeding of recycling materials to downstream sorting devices such as magnetic sorters or sensor sorting devices.

As your manufacturer for screening machines with optimum screening results, we offer you first-class alternatives to replacing trommel screens. We would be happy to advise you!

Christian Lake | Sales Manager
Thomas Harres | Technical Sales
Markus Döbbelt | Technical Sales
Marc Steffen | Technical Sales
Marcel van Reimersdahl | Technical Sales
Klaus Hauhoff | Technical Sales
Dominik Becker | Technical Sales
Simon Dall | Team Lead Internal Sales
Martin Hurson | Technical Sales
Hermann Kahle | Sales Manager Asia
Frederik Stening | Manager Application Technology
Niklas Lohscheller | Technical Manager After Sales
Tom Willing | Team Lead Spare Parts
Andreas Ahler | Managing Director

Open this in UX Builder to add and edit content

Gewerbemüll

What are trommel screens used for?

Typical applications of trommel screeners

Trommel screening machines are used for screening stones and soil, recycling materials and waste, among other things. Typical applications include the screening of household waste, compost, biomass and scrap metal.

Maintenance and cleaning effort

How much maintenance is required for trommel screens?

The maintenance requirements for a trommel screen can be significant, particularly due to its susceptibility to blockages. Regular inspections, cleaning and possibly repairs are required.

Stark verschmutzte Trommelsiebanlage.

Advantages of trommel screens

  • Relatively simple technology
  • Suitable for less demanding material processing
  • Medium throughput rates
  • Mobile use easily possible
  • Minimal construction and installation work required, therefore easy to install
Detailblick in ein Trommelsieb. Man erkennt, dass Langteile sehr leicht durch den Siebbelag fallen können. Das ist schlecht für die Sortierqualität.

Why should trommel screens not be used when it comes to high sorting quality and profitability?

Incorrect separation reduces sorting results

Trommel screening machines and mobile trommel screeners have difficulties achieving a high sorting quality due to their inadequate separation efficiency. In recycling processes in particular, where the precise separation of materials is crucial, trommel screens can quickly reach their limits. With the low sorting quality and the high cleaning effort, the lower profitability of the entire recycling process must also be taken into account.

Working principle of trommel screens

How do trommel screens work?

The operating principle of a trommel screening machine is based on the permanent rotation of the trommel around its own axis. The material to be screened is fed into the trommel. A slight downward incline transports the screening material during the screening process from the material feed to the material discharge at the end of the screening trommel. Particles that fit through the perforations of the screening trommel are pressed outwards and screened off. Larger particles, on the other hand, remain in the screening trommel until they are fed to the next processing step at the end of the trommel.

Funktionsprinzip Trommelsiebanlage

Disadvantages of trommel screens

  • Low screening quality
    The main criticism levelled at trommel screens is the poor screening quality and insufficient separation efficiency when screening and classifying. Due to the design and operating principle of the trommel screener, there is a high proportion of faulty particles in practice. This means, for example, that long particles that are problematic for the downstream sorting equipment end up in the fine fraction. Or take the example of compost screening, where unwanted long particles for the desired premium product pass through the trommel screen into the fine fraction.
  • Carryover of fines
    Due to the rotation principle of the trommel screen, the fines are unfortunately carried over into the coarse fraction or screen overflow. This is the case, for example, when film waste is screened. Due to their physical material properties, these tend to become entangled during rotation. This prevents clean separation of the fines that become entangled.
  • Entanglement of the recycling materials
    Also due to the technical design, tangling of the material occurs in practice when screening inhomogeneous and windable materials. The constant turning of the recycling materials in the trommel causes them to bind together and become ‘braided like a plait’. These plaits contaminate the trommel and cannot be further processed and utilised in the subsequent recycling process.
  • Clogging of the screening surfaces
    Trommel screens are also very vulnerable to clogging, which impairs the screen quality and increases the cleaning effort. Unlike 3D screens, for example, long particles are not prevented from getting stuck in the screen deck. Instead of being transported to the end of the screen, they tend to get stuck and further reduce the screen quality.
  • Increased maintenance and cleaning effort
    Due to the disadvantages of trommel screens mentioned above, their maintenance and cleaning requirements are generally much higher than those of a recyclable material screen. Daily, multiple cleanings and thus downtimes are usually the result (see user example of compost screening)
Trommelsiebanlagen bieten oft eine schlechte Siebqualität, da Langteile einfach ins Zielkorn gelangen können und zugleich wertvolle Recyclingmaterialien verschleppt werden können.

Lower results with downstream sorting

Why can downstream sorting devices such as sensor or magnetic sorters sort worse if the target fraction contains unwanted long parts and incorrect grain?

Sensor-based sorting devices and magnetic sorting technology are sensitive, high-performance sorting devices whose sorting quality and return on investment depend largely on the quality of the material fed in.

The following applies: the better the screening quality of the material supplied, the better the performance of the sorting technology. In short: BEST SCREENING = BEST SORTING.

The working principle of sorting devices such as sensor or magnetic sorting devices is based on the specific properties of the material to be sorted. These include, for example, the density, the colour spectrum or its magnetic properties. These sorting devices only do a good job if these characteristics are easy to detect.

However, if unwanted impurities occur in the target fraction, e.g. due to missing particles, long parts or sand and dirt, it is almost impossible for sorting devices to achieve reliable separation.

If long parts are carried over into the fine fraction when using trommel screens, the sorting devices often have the problem that they cannot distinguish cleanly between shapes, lengths and materials. This leads to an unwanted but unavoidable mixing and contamination of the material due to the trommel screening technology used.

Experts in sorting technology confirm that long parts significantly degrade the sorting quality.