Tyre Maintenance of Mine Machinery

The performance of machinery and their availability plays a major role in the productivity and output of a mine. For this reason, every aspect of the machines should be properly maintained. The tyres of these machines are what keeps the machine in contact with the ground and bears the weight of the machine. While tyres for mining machinery are designed to withstand a beating, incorrect maintenance can reduce lifetime of the tyres, or ultimately lead to catastrophic accidents. Therefore, the proper maintenance of the tyres is as important as the maintenance of any other component of the machine.

Handling large tyres of the gigantic mine machinery is not an easy task. Even a simple task such as changing the tyre is difficult and results in a considerable amount of downtime. Therefore the best strategy in this case is preventive maintenance. This means checking tyre inflation daily, ensuring that valve caps are on, checking tread depth and removing stones and other debris lodged between the treads.

changing tyres is a difficult task

When it comes to daily maintenance, the first thing that comes to mind is the inflation pressure. Both over-inflation and under-inflation are detrimental to the tyre, and therefore, it must be ensured that the inflation pressure lies within the accepted limits. It should be noted that when running the machine the tyre pressure increases by about 10-20 percent. Therefore, this must be taken in to account when setting inflation pressure bounds. Tyres kept in good condition with the proper inflation will last longer and perform better.

External conditions of the mine also affect the tires. The road condition for example is what determines how fast the tyres will wear out. While it is not practical to maintain spotless roads, roads should be kept clear of scattered rocks and sharp pits as driving over these can cause a crack in the rubber, and subsequent running will cause it to propagate and destroy the tyre. Therefore clearing fallen debris off the roads and maintaining the road surface is also a part of tire maintenance. Wet rubber cuts better. therefore it is best to avoid wet road conditions. While most haul roads in mines are watered regularly to minimize dust, it must be ensured that the roads don't get too wet.

Bad road conditions can cause cracks to develop

The handling of the machines and their usage are two other areas that need to be considered. Driving too fast, especially in the case of dump trucks can cause several types of tire damage. In the case of heavy machinery used in mines, a combined parameter combining both speed and weight is assigned to tyres. This parameter is called the TKPH rating (Ton Kilometer per Hour). The TKPH rating should be considered when selecting and using tyres. When loading dump trucks, they should be loaded symmetrically so that the load is distributed over tyres equally. asymmetric loading can cause uneven wear and later result in more severe damages. It should also be noted that shear forces generated when steering the trucks while stationary at the loading points could cause ruptures in the tyres.

When dealing with damaged tyres, it is always best to attend to it them at the start of the problem. Neglecting small faults like cracks and running with them can cause these small faults to quickly propagate and result in serious and irreversible damage. When a crack appears it can be removed altogether by cutting around it. This however has to be done with proper equipment and knowledge of the tyre. When replacing tyres, it is always best to replace it with a tyre of similar amount of wear.

In summary, daily maintenance goes a long way in increasing the lifetime of the tyre. Inflation pressure must always be within the specified limits. The road surfaces, loading and dumping points should be free of fallen debris and excessive water, because wet rubber gets cut better. payload weight and hauling speed must be controlled. The TKPH rating assigned to the tyre must be adhered to. Proper handling of the machinery such as symmetric loading, avoiding steering while stationary and avoiding excessive tyre spinning will reduce the likelihood of damages. when repairing, the first stages of the problem is always easy to cure.

Jet Skiing at Unawatuna

Unawatuna is known for its pristine beaches and is one of the most popular tourist destinations in Sri Lanka. For thrill seekers going on holiday to Unawatuna, The Unawatuna Water Sports Club offers a wide range of water sports. On my recent visit to Unawatuna I tried Jet skiing. Having ridden a jet ski on a river before, this was a totally different experience. The waves and undulations of the sea makes it much more exciting.

Located in front of the Cormoran Beach Club, the friendly staff at Unawatuna Water Sports Club will guide first timers. A safety jacket is provided and an instructor will accompany you if needed. The Jet Skis at Unawatuna Water Sports Club are easy to operate as you only have to accelerate and steer. It only takes a while for you to master the controls and start skiing like a pro.

In addition to Jet Skiing, Unawatuna Water Sports Club also offers, Surfing, Sailing, Banana Boat Rides, Doughnut Rides and Kayaking.

Turquoise Water in a Limestone Mine

Clear turquoise water is often associated with tropical beaches. An open cast mine is probably the last place one would expect to find clear blue or turquoise water. The pictures below were taken at the Aruwakkalu Limestone mine in Puttalam Sri Lanka.

When limestone is excavated from the base of the quarry, and when the excavated pit reaches the ground water table, water starts seeping in. It is this water that has a spectacular turquoise colour. The reason for this colour is not the blue reflection of the sky like in the case of seas and lakes. It is due to the scattering of light by minute Calcite crystals.

Limestone is essentially Calcium Carbonate and the water in the limestone pit contains a large amount of it dissolved. Once the water gets saturated by calcium carbonate, it starts to crystallize and forms very tiny crystals which remain dispersed in the water. This crystalline form of calcium carbonate, is known as Calcite. These micro Calcite crystals scatter light selectively giving it a turquoise colour.

Since Calcium Carbonate is alkaline, this water has a high pH value. Therefore, as inviting as it looks, taking a dip in this water is not advisable. Prolonged exposure to water with a high pH can cause skin and eye irritations.

The Intricacies of Mud Crack Formation

Patterns found in nature are most often astoundingly complex while also being elegant and aesthetically pleasing. Snowflakes for example consist of extremely delicate, symmetric structures of frozen ice and are always different from each other. Yet these infinite patterns are influenced by only two main controlling factors, temperature and humidity. A  more obvious example of patterns in nature are mud cracks. Although they are not as delicate and complex as snowflakes, they also exhibit some patterns that are interesting to observe. What follows are some facts I gathered from a small study about mud cracks and some  photographs taken during my training period at the Aruwakkalu limestone mine.

Mud cracks are formed quite obviously, when  mud dries up. So the main factor controlling mud crack formation is moisture content. Unlike in glass and many other materials, cracks in mud do not originate at single point and then propagate. If the rate of drying is uniform across a surface of a layer of mud, cracks will start appearing simultaneously across the surface. Mud starts to dry from the exposed surface. So when the moisture content of the surface layer starts to drop, the mud particles come close to each other as the space occupied by water is emptied. This results in the contraction of the surface layer. This causes stresses to build up on the surface layer and ultimately results in the formation of cracks. First the main cracks divide the exposed surface into a series of "islands" then, secondary cracks may occur within these islands.

primary and secondary cracks

Since drying starts from the surface, the bottom layers still contain some water and still remain expanded. Therefore the width of the crack is lesser in bottom layers, like a cut made from the surface. As the moisture content further reduces and the bottom layers also dry up, the crack propagates to the bottom layers and the gap widens. 

If the moisture content in a single layer of mud differs at the top of the layer and the bottom, the amount of contraction also differs. The top portion will contract more than the bottom portion. This will result in an upward curving of the layer like in a bimetallic strip. If the wet mud has been standing for a long period, stratification of different layers will take place. Stratified layers can be observed when a portion of the cracked mud is viewed sideways. Stratified layers can have a bigger difference in contraction rates, and if the layers are strongly adhered to each other, a more prominent curving of the layers will be seen.

stratification and upward curving of layers

If the layers are not strongly adhered, instead of curving upwards, the layers will separately contract producing a step like effect of the cracks. 

step like contraction

Although the mechanics of mud crack formation has no immediate practical application, crack formation in other substances is studied extensively. Crack formation on thin surface layers in electronic circuits can lead to peeling off of printed components and cause problems. Therefore a lot of effort is put into preventing the formation of such cracks. A very fine network of small cracks can be seen on the surface of old paintings on close inspection. This fine set of cracks is called "craquelure".  The characteristics of these cracks depend on the type of pigments, oil and also the ambient conditions at the time of painting. For this reason, these cracks are used to authenticate old paintings. 

Creating a 3D Terrain Model using Surfer

A three dimensional model of a particular land feature can be very useful for visualization. A 3D model which can be manipulated in a digital environment is even more useful, especially if volume calculations need to be performed. A good software package for this purpose is, "Surfer". It has a relatively simple user interface and is easy to learn.

Essentially what Surfer requires to create a 3D surface model is a set of spot heights along with their northing and easting coordinates. The data can be imported into Surfer by many ways, of which using a MS Excel file or an ASCII text file are simplest. The software will interpolate the data points and create a surface. The algorithm used for interpolation can be changed according to the requirement.

Obtaining spot heights of the area can be done by performing a level survey. If high accuracy is not required, a quick and easy method of obtaining spot heights is to overlay a grid with known coordinates over a topo sheet with contours. Using the contours, the heights of the vertices of the grid can be determined. Since the northing and easting of the grid are also known, it can be fed into Surfer via MS Excel Another method of creating a 3D model using Surfer is to directly import a DEM (Digital Elevation Model) into the software. DEMs can be downloaded from the USGS website.

A simple volume calculation based on spot heights obtained by the gridding method is illustrated below.

First, the grid was drawn over the contour map in the AutoCAD environment. In this example, the contour interval is 2 m, and the grid spacing has been selected as 3 m.  

The spot heights were found by using the contours closest to the vertices of the grid and the data was entered as x, y and z coordinates into an MS Excel sheet.

Using Surfer, the excel sheet was input and a grid file was created. (Grid>Data). The gridding method used for this example is "Kriging". Other methods can be used depending on the requirement.

A 3D surface was created using the grid file previously created.

This 3D surface can be used for volume calculations as well. For example, Consider that the trough indicated in the above terrain model needs to be filled with water, up to the 8m contour level and it is required to calculate the volume of water required.

This means we need to calculate the volume between the modeled surface and the plane z=8. To do this, the volume calculation dialog box was opened (grid>volume..) and the upper surface was given as z=8 and for the lower surface, the grid file was selected. The calculated positive volume indicates the volume of water required to fill the trough. In this example the calculated volume is, 696.73 cubic meters. 

Optimization of production of a Mine

The main objective of a mine is to extract a mineral deposit in an economical manner and to maintain a continuous output. In order to do this, the operations performed in and out of the mine must complement each other. While intensive planing and monitoring of all unit activities is required to achieve this, the following steps will help to optimize production and reduce cost thereby increasing efficiency.

Calculate and plan production targets and compare with actual production.

In order to determine whether a mine is operating efficiently, first targets should be established. To do this, drilling and blasting cycles and hauling capabilities can be factored in initial calculations. To set more specific production targets, modelling software can be used. The important thing is to compare the actual data with these targets and to take corrective action when the production does not meet the target.

Maintain a buffer stock of material

While in normal conditions, production can be carried out without interruption, due to various reasons the rate of production can decrease or in worst cases, halt altogether. Interruptions due to bad whether in open pit mines is a good example for this. To cope up with these delays it is essential to have a stockpile of material ready to be dispatched. This stockpile will act as a buffer until production resumes and the mine will produce the expected output throughout.

Proactive maintenance of machinery

Several approaches can be taken in the case of maintenance of mine machinery. in order to minimize losses due to downtime and faulty operation it is best to employ a preventive or proactive maintenance strategy. When doing maintenance work, it is vital to get operator feedback as it will help to diagnose problems better. Another very important fact to be considered when acquiring a new fleet of machines to a mine is to obtain all the machines of one particular brand. This ensures inter machine compatibility. It also saves time and resources in ordering, acquiring and using of spare parts.

Streamline work and physical movement

A mine is a place of continuous movement. To increase efficiency, these movements must be streamlined and effective. This means that access paths and haulage ways must be as short as possible with sufficient room for maneuvering. The mine layout itself must be orderly and separate operations should not disturb each other(except in unavoidable circumstances such as blasting). These reduce cycle times of the mine and increase production.

Safety

This is a factor overlooked in most mines. However safety plays a major role in the overall efficiency of the mine. A mine with a lot of accidents suffers a lot of downtime and it will reduce production. Proper safety procedures will enable continuous operation and will also enhance working conditions, both of which will ultimately result in an increase in efficiency.

Global Tidal Variations Explained

Tides are periodic variations of the ocean surface caused by the gravitational attraction of the moon and the sun. On a fundamental level, tides can also be considered as waves. Since these tidal waves have extremely long wavelengths, they are essentially shallow water waves(Shallow water waves are waves which travel over depths lower than 1/20th their wavelength). This means that the speed of the tidal wave is proportional to the depth. The depth of the ocean basin, the time of year and month, latitude and earth's rotation affect the type and magnitude of tides. While the exact relationship between all these variables can be somewhat complex, certain scientific theories and models help simplify and explain the behavior of tides.

Depending on the occurrence of high and low tides, tidal patterns are classified into three types. These are,
1. Diurnal tides
2. Semi-diurnal tides
3. Mixed Tides.
If the tidal wave shows 1 crest and 1 trough within a period of 1 lunar day(24hrs and 50mts), then it is called a diurnal tide. If it shows two crests and two troughs or vice versa in one lunar day, it is called a semi-diurnal tide. Mixed tides are a mixture of these two, often with significantly different amplitudes.

While tidal variations can be attributed to the gravitational attraction of both the sun and moon, the effect of the moon is significantly larger. "The Equilibrium theory of tides" attempts to explain these variations with the following assumptions.
-the ocean is indefinitely deep
-no land masses are present
-no inertial forces
With these assumptions, the key tide generating forces are, gravitation and centripetal force. These two forces act differently on different locations on the earth. While the gravitational force directs to the center of the moon, the centripetal forces at different locations are parallel to each other. This is because, centripetal force is the force that keeps an object in circular orbit, and the different locations have their own circular orbits parallel to each other.

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

The gravitational attraction provides the required centripetal force to keep the earth in orbit. However, the gravitational attraction and the required centripetal force are unequal at different locations on the earth. These two are equal only at the center of the earth. The difference between these two forces creates a resultant force which acts as shown in the diagram. It is this resultant force that is responsible for the generation of tides. This is also why, tidal bulges appear on both sides of the planet, because the resultant forces at the two sides of the earth are oppositely oriented. 

The orbital plane of the moon is inclined by approximately 28.5 degrees to the earth's axis of rotation. This causes the tidal bulges also to orient as shown below. The earth rotates through these tidal bulges. This explains the occurrence of diurnal and semi-diurnal tidal patterns explained above. By inspecting the diagram below it can be seen that high latitude locations receive diurnal tides, equatorial regions receive semi-diurnal tides and mid latitude locations receive mixed tides. 

Source : Trujillo,Alan P.Essentials of oceanography / Al Trujillo, Harold Thurman. 10th ed.

This shows how the equilibrium theory explains the occurrence of the diurnal and semi-diurnal tides. This means that, tidal patterns on earth should be related to latitude. According to the above diagram it is also seen that tidal heights should also vary with latitude, with the highest tidal heights in mid latitude regions. However, the following tide map of the world shows that no such connection between tidal characteristics and latitude can be observed. This is where the equilibrium theory of tides fails.

-world tidal patterns- Source : Invitation to oceanography / Paul R. Pinet. — 5th ed.

The equilibrium theory of tides does not take into account the depth variations of the ocean basins. It also neglects the effect of the earth's rotation. To overcome these issues, another theory, "The Dynamic Theory of Tides" was proposed. Proposed in the 18th century by Pierre Simon Laplace, it attempts to explain tidal variations with the Coriolis Force.

To illustrate this theory, consider a large rectangular ocean basin in the northern hemisphere. when the water level rises in the upper portion of the basin due to the tidal action, the Coriolis force deflects the mass of travelling water towards the right. this causes the water to build up in the upper right corner of the basin. The resulting pressure gradient causes the water to flow downwards, but is again deflected to the right by the Coriolis force. This cycle continues, and it results in a counterclockwise oscillation of the water mass. The nodal point where the water does not oscillate is known as an "Amphidromic Point."

Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

If the ocean basin is situated in the southern hemisphere, the Coriolis force will deflect the water towards the left side, and the resulting oscillation would be clockwise. While ocean basins found on earth are not ideal basins like the above explained, several Amphidromic Points can be identified in the earth's oceans through tidal action. This amphidromic system of tides better explains the tidal variations depicted in the above tidal map. Since the amphidromic system is an oscillatory system, tides can undergo resonance. If the natural period of the ocean basin equals the period of the tides, tidal resonance will occur creating a massive tidal wave. An example of this is the Bay of Fundy where tidal ranges of over 17metres have been observed.

Global Amphidromic Points - Source : Invitation to oceanography / Paul R. Pinet. — 5th ed

The depth of ocean basins also affect tidal heights. As explained above, tides being shallow water waves, have speeds that are proportional to depth. This means that a lower depth would cause the tidal wave to slow down, and due to the conservation of energy, the amplitude of the wave would increase, thus creating a higher tide. Taking all these factors into consideration, tides can be accurately modeled and predicted.

This understanding of tidal action opens up means of using it as an energy source. In places where a high tide variation is present, tidal energy can be tapped into by building dams to trap the incoming tidal flood current, and then channeling them through turbines like in a hydro-power plant. Power plants of this type are already in operation around the world, an exmaple is the La Rance tidal power plant at St. Malo, France. Tidal power plants do not pose a significant threat to the environment and are therefore are a good alternate source of renewable energy.