Screening machines and classifiers for raw material processing

Anyone processing gravel, sand or other mineral raw materials needs far more than a simple screen. Modern processing plants must handle large volumes of material, reliably separate different grain sizes and, at the same time, ensure consistent product quality.

This is where specialised machines come into play; machines that often appear unremarkable at first glance but, in practice, play a central role for the entire raw materials industry. At bauma, Siebtechnik showcased various solutions for the classification and processing of bulk materials. The focus was on vibrating screens for particle size separation and settling machines for separating materials of different densities.

Siebtechnik develops machines for raw material processing

Siebtechnik’s products are used, amongst other things, in the sand and gravel industry. There, large quantities of raw materials must be processed continuously. Whilst a domestic sieve merely separates small quantities, industrial plants operate at throughput rates of several hundred tonnes per hour. The basic principle remains similar, however. The material is set in motion by specifically generated vibrations. The individual grains are circulated, distributed and separated from one another according to their size. It is the vibration that enables the continuous conveying and separation process. At the trade fair, a significantly larger version was presented alongside a laboratory-scale unit. Industrial screening machines can reach widths of several metres and lengths of eight metres or more. Despite the differences in size, the operating principle is based on the same physical principles.

Vibrating screens adapt to the material

A key difference from simple screening systems lies in the machines’ adaptability. The separation performance can be specifically tailored to different materials. To achieve this, various parameters are adjusted, including the machine’s inclination, the direction of movement or the shape of the vibration ellipse. In this way, the conveying behaviour can be influenced. This becomes particularly important when different crushing plants produce varying particle size distributions. Although the feed material varies, the end product must remain consistent. For this reason, modern screening machines are networked with the upstream crushers and automatically adjusted via control systems. This results in consistent particle size fractions, regardless of changes in the upstream process.

Settling machines separate gravel from wood and lignite

In addition to particle size, material density also plays a decisive role in many applications. This is where settling machines come into play. These systems operate using a pulsating water flow that periodically lifts the material and allows it to settle again. During this process, the components rearrange themselves according to their density. Heavy materials such as gravel sink more quickly. Lighter components such as wood or lignite remain higher up. This results in distinct stratification, which can subsequently be utilised for separation.

Typical applications for such systems include:

• Separation of wood from gravel deposits
• Removal of lignite from mineral raw materials
• Processing of sand and gravel mixtures
• Density separation of various bulk materials
• Quality improvement of mineral products

Control technology ensures consistent product quality

The demands placed on modern processing plants are constantly increasing. Today, operators expect not only high throughput rates but also reproducible results. This is why electronic control systems are becoming increasingly important. Machine parameters are automatically adjusted, process data is monitored and material flows are continuously controlled.

In the raw materials industry in particular, even small fluctuations can have a significant impact on the quality of the end product. The combination of mechanics, process engineering and automation is therefore becoming increasingly important. For operators, this means greater process reliability and better control over the produced particle size fractions.

New screening methods for challenging particle shapes

Future development is increasingly focusing on specialised separation tasks. Elongated or irregularly shaped grains present a particular challenge. Such materials often cannot be classified with sufficient precision using conventional screening methods. Siebtechnik is therefore working on new solutions that combine specialised screen liners with adapted vibration patterns. This involves combining different process technologies to reliably solve even difficult separation tasks. This development shows that, despite its often simple appearance, the processing of raw materials remains a highly complex technical field. The plants presented at bauma illustrate just how far modern processing technology has advanced. Behind the seemingly simple separation of gravel, sand or bulk materials lie sophisticated processes that precisely classify large quantities of material whilst ensuring consistently high product quality.