Spiral Trough Research Articles

Some design considerations for spiral separators

There are a number of design considerations which influence the selection of a suitable pitch and trough shape for a new spiral separator. The separation requirements impose certain constraints on the total design envelope and mutual interaction between some of the requirements and the conflict between metallurgy and materials handling requirements often defines a narrow range of permissible geometries. Capacity requirements determine the diameter of a spiral trough but fundamental fluid dynamic considerations play a major role in the selection of pitch and trough shape and the paper considers some of the issues in detail. Where the dynamics of the separation lead to excessive accumulation of solids at high slurry densities, various types of flow deflectors have been adopted either to restore fluidity to the material or to assist in securing a better quality of product. Apart from the trough, the design of suitable ancillaries such as feed boxes, auxiliary splitters and product collection facilities can exert a significant influence on both the operation of the spiral and the quality of separation achieved. These features are discussed in the paper and illustrated with examples.

A study of particle separation in a spiral concentrator

Modelling particle separation in a spiral trough is a complex process which requires knowledge of particle transport behaviour under different flow regimes. With the demonstration of the existence of secondary flow and utilizing knowledge of particle behaviour in flowing fluid films, the hydrodynamic model of particle separation in a spiral trough is, to some extent, capable of explaining the behaviour of fluid flow and that of particles at low concentrations. The recent trend in research on spiral technology is to the modelling particle behaviour in flowing films in spiral troughs. While this is essential in terms of developing a fundamental model, a question arises as to how successful such a model is in providing an adequate explanation for particle separation. Distribution of the particles of different sizes and densities across the trough, under plant conditions, has not been much reported in the literature. Therefore, a research project was undertaken to determine the distribution of coal particles across the cross-section of a spiral in a Reichert LD4 coal spiral. The results showed that using different length of spiral may be beneficial for treating coal particles at different sizes.

Fluid flow modelling on spiral concentrators

An artificial binary ore was used to investigate the action of a spiral concentrator. The ore was sized to between 500 and 850 μm. Size sorting effects were observed of a type which indiacted a separating mechanism not related to seetling velocity. The nature of the flow in the inner region of the spiral trough was investigated and found to be laminar according to the Reynolds criterion. Three velocity profiles were evaluated by calculation of slurry properties from the mean velocity. For the laminar profile, a correlation between the volumetric concentration of solids and the calculated viscosity of the slurry followed established trends and an empirical relationship was fitted. Manning flow was found to be unsuitable as an a priori predictor of flow. A new profile based on Bagnold forces was developed from first principles and was found to be usedful as a predictor of flow.

A study of the potential for improved separation of fine particles by use of rotating spirals

In previous work an analysis of the primary flow and secondary circulation on a spiral was developed and an approximate model was derived for the free motion of particles within the slurry. The main features of the fluid and particle motion were subsequently investigated experimentally and found to be in reasonable agreement with predictions based on free motion on a spiral trough. The theoretical basis is briefly reviewed and the current limitations of the model are discussed. The extensions to the theory needed to include an external rotation are then introduced and the results of a range of simulations for both coal and heavy mineral spirals are presented.

A Quantitative Model for the Prediction of Fine Coal Cleaning in a Spiral Concentrator

A useful predictive model is developed for the partition function when fine coal is cleaned on a spiral concentrator. The calculation of the partition function for the spiral is complicated because the behaviour of any particle is strongly influenced by its size as well as its density. In addition two distinct regimes of behaviour are identified depending on whether the particle is in suspension in the flowing water or in the sliding bed on the floor of the spiral trough. Although the (density) cut point is a strong function of the position of the splitter at the foot of the spiral, the range of cut points that can be achieved is limited. This is the chief limitation of the spiral as a device for the production of clean coal. Also the density cut-point was found to be a strong function of particle size with a distinct minimum that varied with the splitter position.

Recent developments in spiral design, construction and application

The paper supports the generally accepted view that modern generation spiral concentrators have a place in the beneficiation process flowsheet of a wide range of minerals, and gives examples of recent installations. These include environmental applications in the areas of contaminated soil cleaning and coal dump reclamation. Comments are made on the significant effect that advances in polymer technology has had on the manufacturing techniques involved and how this has influenced changes in spiral design, construction and application. The current development effort towards eliminating laminate construction for spiral trough manufacture is discussed. Suggestions are made regarding other applications and circuitry in which the equipment could be effectively utilised.

Flow visualisation of secondary currents on spiral separators

This paper describes the results of some simple flow visualisation experiments using two different techniques on a wash water-less mineral spiral, at water flow rates from 2 to 6 m 3/hour. The existence of an inwardly directed secondary current at the base of the spiral trough, as required by the current qualitative theory of spiral operation. was clearly demonstrated. The flow at the trough base deviated by between approximately 2 and 5 degrees from the primary flow direction. No significant difference in the angle of deviation could be seen over the range of flow rates studied.

Research on the Interaction between Power Source and Machinery : Part 3, Vibrating Lift Made by Utilizing the Principle of Self-Synchronization

This paper investigates new types of vibrating lift made by utilizing the principle of self-synchronization of mechanical vibrators. Two unbalanced vibrators whose axes are non-parallel and each driven by two motors, rotate at the same speed and have a definite phase angle as the result of the phenomena of self-synchronization. Accordingly, due to a screw vibration about the axis of the structure, products ride up the inclined way of a spiral trough. Two types of vibrating lift were set up and vibrations of the spiral trough were measured for various values of set parameters of the unbalanced rotors. In addition, the travelling speeds of products in the spiral trough were measured.

On a New Type of Vibrating Lift

This paper investigates in detail the new vibrating lift made by utilizing the principle of the self-synchronization of mechanical vibrators. In a general way products ride up inclined way of the spiral trough of a vibrating lift, propelled by forces generated by two unbalanced rotors connected by the gear and driven by a motor, which are mounted on top of the structure in a horizontal position. This machine is a new type of vibrating lift. The axes of two unbalanced rotors are nonparallel and each driven by two asynchronous motors. One motor is positioned on the right hand side and the other is situated on the left hand side of the structure in a vertical position. In spite of the absence of any connection between two rotors, they rotate at the same speed and have the definite phase angle between them as the result of the phenomena of the self-synchronization under a certain condition. This phenomenon is also called entrainment. Accordingly, by the linear vibration in the direction of the axis of the structure and rotational vibration about the axis of the structure by two unbalanced rotors, products ride up inclined way of the spiral trough.

Efecto del flujo secundario en la separación de metales pesados en una canaleta en espiral

En el presente artículo se reportan los resultados de la investigación experimental llevada a cabo paraevaluar el efecto del flujo secundario en la separación de plomo contenido en una mezcla de agua ysedimentos, usando una canaleta en espiral con sección transversal del tipo FLG con radio interno de0.025m y radio externo de 0.15m y un paso de espiral de 0.185m. Para establecer el procedimientoexperimental se recurrió al método del análisis dimensional y al diseño de experimentos factorialaleatorizado, obteniéndose con dicho diseño un total de 16 corridas experimentales. Las variables derespuesta estudiadas fueron la concentración en peso de plomo en la descarga, la partición de agua, laremoción de sedimentos y la remoción de plomo, las cuales dependen de parámetros adimensionalescomo el número de Dean, la relación de radios y el coeficiente de arrastre promedio de las partículassólidas que incluye el efecto de la granulometría. Con los datos experimentales se obtuvieron ecuacionesempíricas por medio de regresión lineal múltiple para cada una de las variables de respuesta.