Fully holographed 3D image of processed stone

using RoxRay Radar

2018 Short description

Ballast, made of crushed stone, is used for road and railway construction and is an important component of concrete. Depending on the application, different requirements are imposed on the ballast's dimension and distribution, that is, the size and shape of the stones and the mixture between large and small stones. The ballast used for example railways should not be too oblong or else it will break under the pressure from the train. Consequently it is important for the manufacturer of the ballast to control these characteristics of the stones. Therefore the manufacturer wants to be able to show some statistics of the shape and the size of the stones. Improvements of the quality can be achieved if these statistics are obtained during the process and used to change the settings of the stonechrusher to get the desired shape and size.

Control of ballast content is currently performed mostly by manual methods such as sieving through different types of raster. These methods are slow, labor-intensive and expensive. This is because automatic instruments have not appeared despite many years of effort. Therefore, there is a need to make reliable measurements in real time at the crusher to control the quality and steer the process.

In earlier collaboration, Cirrus Consulting AB, Chalmers and FOI have developed a radar-based technology that has been tested in a laboratory environment. A patent, currently owned by RocksRay Sweden AB, covers the principles. The technology is based on radar wavelength in the same order as the individual objects to be measured. Measurement data is then processed through proprietary algorithms and the result shows the dimension and distribution of the ballast.

Based on this technology the RoxRay ™ stone radar is being developed. RoxRay ™ is a microwave-based measurement system for three-dimensional real-time measurement of ballast products. Dimensions, their distribution from coarse stone to fine gravel is crucial to the mechanical strength and aging characteristics of the finished product. Since the demand for crushed stone as ballast increases there is a need for better measurement and control systems to streamline production. Market analyses indicate the need for equipment to be placed at crushing plants and in quarries. Over the years regulations on the management of rockery, environmental issues and energy issues have been accentuated.

RoxRay ™ consists of a pulse radar where a transmitter generates a very short microwave pulse (in order of magnitude of nanoseconds), which via an antenna is transmitted to a stream of ballast elements falling from a cross. The signal from individual stone elements is reflected and received by a broadband receiver. The pulse is sampled, digitized and processed using calculation algorithms that classify data and deliver results in the form of desired parameters. The most common of these is the maximum dimension of the element and the so-called L / E's (length / thickness ratio) also called shape index. Even the statistical characteristics of a current of ballast can be calculated, that is, the distribution of stones in different sizes. The radar itself is built into a durable device that is placed a few meters from the stream of stone. Measurement data is transmitted for final processing to a computing computer with appropriate location, such as control room. Control of the crush in real time is an opportunity.

RocksRay Sweden AB is now planning to develop two variants of RoxRay ™

A low frequency system for the first step in the crushing process with the purpose of identifying if the crush produces excessive stones that will cause a stop in the next step.

An intermediate frequency system for measuring the distribution of stones of different sizes after the first fine crushing step (stone sizes approximately 50-90 mm).