The technique of glass making too is based on similar lines. People learned to make the first glass containers about two thousand years ago. Molten glass was collected on the ends of hollow iron pipes and then expanded by blowing through the pipes. Slowly, people learnt to blow molten glass into moulds. Glass bottle making machines were introduced in the thirties.

The first plastics blow molding machine was designed in the early forties; the first plastic bottles were manufactured using polythene.

In the early seventies, environmentalists began arguing on the grounds that glass and plastic bottles added to pollution. This led to the setting up of numerous recycling centers where people could return bottles for reuse in other bottles. Most of the recycled plastic is used to manufacture lower quality plastic than those used to make bottles.

There are four main ingredients used to manufacture glass:

1. Silica sand,
2. Soda ash,
3. Limestone
4. Recycled glass (cullet).

Small quantities of other materials give glass its colour.

The Process
· All the materials are first weighed then mixed, and then poured into large
furnaces. The temperature in the furnace ranges from about 1100 – 1590
degrees Celsius. This melts all the ingredients into Molten (liquid) glass.
Computers monitor the whole process.

· From the furnace, the Molten glass goes to a bottle-making machine. A
measure of molten glass (this is called a GOB) is delivered to the machine to
make a bottle or jar.

· The bottles then pass through electronic inspection machines, which
automatically detect faults Rejected damaged bottles, are returned to the raw
materials area and recycled for making new glass.

· The bottles are then packed onto pallets. Each pallet can contain as many as
5000 bottles. The pallet is then covered in a large plastic envelope that has
been shrunk until tight. This makes sure the pallet is stable, ready for
transportation to the manufactures for filling.

Bottle Making (Molding Process)

Annealing is done by reheating the glass and gradually cooling it. Such a process removes the stresses and strains in the glass after shaping. This is an important step and if not done may cause the glass to shatter as a result of the build up of tension caused by uneven cooling. After the bottles have cooled to room temperature, they are inspected and finally packaged.

Plastic bottles may be made from polyethylene, polypropylene or polyvinyl chloride. Large cold drink bottles are made of polyethylene terephalate (PET). These bottles are designed in such a way that the gases used to carbonate the soft drinks are unable to escape.

There are three different methods used for processing plastic bottles – extrusion blow molding (in which the parison is tube shaped), injection blow molding (in which the parison is prepared by injecting molten plastic through a small hole) and injection stretch blow molding (in which the plastic is blown into the mould while it is simultaneously being stretched by a metal rod).

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MINING DIAMONDS
Of all the diamonds mined in the world each year, less than half are gem quality; the rest fall into two other main categories known as near-gem quality and industrial quality diamonds. Gem quality diamonds display a high standard of excellence in quality and are used in jewellery. The clarity of these diamonds ranges from flawless through to visible inclusions. Near-gem quality diamonds represent those stones of a quality between gem and industrial, that in fact can be used as either depending on the individual stone. These stones have clarity grades ranging from visible inclusions through to industrial. Industrial quality diamonds are low quality or badly included stones and are suitable only for industrial use; for example, they are used in dentist's drills and earthmoving equipment.

Diamonds are recovered by way of pipe or alluvial mining.

Pipe Mining:
Pipe mining refers to the extraction of diamonds from volcanic pipes. Typically, a very large area has to be covered. An average of 250 tons of ore must be mined in order to produce a one-carat gem uality polished diamond. In most countries, a diamond pipe mine is composed of kimberlite, or blue ground. Initially kimberlite is dug from the surface of the pipes in rough opencast mining. Once the surface deposits have been exhausted, shafts are sunk into the ground at the edge of the pipes, and tunnels are driven into the eeper parts of the pipes.

In open cut mining, the ore is dislodged by blasting and then loaded by excavators into 120-ton dump trucks. The ore is then transported to the processing plant where the diamonds are extracted. The processing techniques are purely physical and involve crushing, scrubbing, screening and gravity separation of the diamond-bearing ore. Final diamond recovery is achieved by the use of x-ray sorting machines. The machines can detect and remove diamond material because the diamonds fluoresce under x-ray.

Alluvial Mining:
This process involves the extraction of diamonds from riverbeds or ocean beaches. Millions of years ago, at the time the diamond pipes were formed, some diamonds were weathered out of the pipes and carried great distances long rivers and even into oceans. In order to extract these diamonds from beaches, a wall is built to hold back the surf. Up to 25 meters of sand is bulldozed aside to reach the diamond-bearing level. Once reached, the diamond-bearing earth is removed and transported to screening plants.

Screening Process:
Once a mining operation yields ore, the diamonds must be sorted from the other materials. This process relies primarily on diamond's high density. An old but effective method is to use a washing pan, which forces heavy minerals like diamond to the bottom and waste to the top. Cones and cyclones use swirling heavy fluids mixed with crushed ore to achieve density separations. With 99 percent of the waste in the ore removed, further separations may use either a grease table or an x-ray separator. Final separation and sorting is done by eye.
Crushed ore is mixed with a muddy water suspension, called puddle, and all is stirred by angled rotating blades in the circular washing pan. Heavier minerals settle to the bottom and are pushed toward an exit point, while lighter waste rises to the top and overflows as a separate stream of material. The surface of diamond is highly unusual in that it resists being wetted by water but sticks readily to grease. Here, wet gravel washes across 3 inclined surfaces covered with beeswax and paraffin. Diamonds stick to the grease while wetted waste minerals flow past. The operator routinely scrapes the material that adheres to the table into a grease pot, using a trowel. The grease in the pot is melted and the diamonds are removed in a strainer. More automated systems use a rotating grease belt and craper.

Cones (left) and cyclones (right) use heavy-media separation. Diamond-bearing concentrate is mixed with a fluid near the density of diamond. Separation occurs in cones and cyclones by swirling the mixture at low and high velocities respectively. In the cone, rotational mixing permits lighter minerals to float to the top and run out as overflow, while diamonds and dense minerals sink to the bottom and are sucked out ith a compressed air siphon.

In the cyclone, fast rotation of the suspension drives heavy minerals to the conical wall, where they sink to the bottom and are extracted, while float waste minerals are sucked from the center of the vortex. Cyclones are about 99.999% efficient at concentrating diamonds and similarly dense inerals from the original ore. The x-ray separator system acts on a thin stream of particles from the concentrate accelerated off a moving belt into the air, where they encounter an intense beam of x-rays. Any diamond fluoresces in the x-rays, activating a photomultiplier that triggers a jet of air, deflecting the diamonds (blue) into a collector bin.

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Depending on the depth of the coal layers (seams), extraction is achieved by means of open-cast (down to a depth 500m) or underground mines.

An opencast operation has the appearance of an enormous hole, organised a bit like a stadium with terraces, along which machines dig into the seams. But what a stadium! The biggest opencast mines are several kilometres in length and hundreds of meters in depth. In underground mines, the coal is extracted by means of vertical or inclined shafts. At each level where coal is present, these shafts are linked together by a vast network of galleries (10 to 20 m² in cross-section). These networks can be made up of several dozens of kilometres of galleries. The coal is extracted by enormous machines (the coalcutters). It is transported to the surface where it is separated from the sands and clays by flotation (the coal floats and the other mineral materials, known as “steriles”, sink to the bottom). Extraction by opencast mining is more productive and less expensive than underground mining. As a result it is more profitable. Working conditions are also a significantly less dangerous. Unfortunately, opencast mining is less environmentally friendly; the countryside is disfigured and the surface activity tends to pollute the atmosphere within the locality.

The majority of coalmines in the world are underground.

Methods of extraction of coal:

- Opencast mining: the soil layers located above the first coal layer (the overburden) are removed. Then extraction can begin. When the hole is sufficiently large, digging continues as far as the subsequent coal layer, where the coal is extracted in the same way, simultaneously with continued extraction of the first layer, and so on. Each of the coal layers is called a “discovery”. The mine gradually becomes a giant amphitheatre, the terraces of which are made up of the layers of coal being extracted. It is more a terracing activity than mining. Giant excavators dig out the coal. Their buckets can contain up to 300 tons of rock. The production from an opencast or strip mine starts 2 to 5 years after the initial work. The technique is less expensive, more profitable and less dangerous than extraction by underground mining. Nevertheless it is little used in Europe, where the coal is generally too deeply buried.

- Underground mines: to reach the coal-bearing rocks, vertical shafts are dug, into which lifts and other systems for links with the surface are installed. At the levels of the coal-bearing seams (layers), digging takes place horizontally, following each seam for as long as possible. Several techniques are used:
In each seam exploited, regularly spaced large pillars of coal are left in place to support the roof: this is called the “room and pillar method”;
Or two parallel tunnels are dug and a machine (a giant rasp or undercutter) goes backwards and forwards between these tunnels, extracting coal at each step: it is the “long coal face” or “long wall” method, which allows recovery of a little more coal than the preceding method. As the coalface moves forward, the roof is allowed to collapse behind (miners talk about “thundering”). The main disadvantage is that the effects of these roof collapses are sometimes felt on the surface, and the buildings and roadways located above the mine suffer the consequences of subsidence: they crack and sometimes even disappear into a hole! To solve this problem, the deliberate collapsing of the roof can be replaced by a filling procedure: the «sterile» rocks replace the extracted coal. But that is more expensive;
In mountainous regions, the galleries can be dug horizontally, directly into the side of the hill, whereas, on the plains, infrastructures are necessary to bring the coal-bearing rocks to the surface. Pumping and drainage equipment is essential although if the mines are in the mountains the evacuation of water usually happens naturally. Conveyors or trains of large wagons transport the extracted coal to the vertical shafts. Finally the coal is taken up to the surface by means of a bucket conveyor driven by very powerful electric motors.

MACHINERIES USED:

Machines make mining easier, quicker, and sometimes safer. Here are some of the machines used in mining:

* Surface Mining:

- Wheel loaders: These are used when a lot of mining materials need to be moved at one time.

- Excavator: Most surface mines have one of these. This machine is used to do the digging. Usually this machine dumps the materials that it dug up into a dump truck.

- Dump Trucks: These are used to take away or move materials. You can see how big it is compared to the driver. Sometimes these are called monster trucks because they are so big.

- Crawler-tractor [bull dozer]: Sometimes these are called dozers. Instead of rubber tires, these have chains. Chain tractors are used on land where rubber tires won't work too well--like in mud or on mountain slopes. Dozers push dirt from one place to another. When mines close and they begin to fix the land that has been changed, dozers push dirt and materials where they need to go.

- Motor grader: These are used to make the ground level when they are clearing off the land for mining or fixing it when they are done.

* Underground mining:

- Articulated Dump Trucks: These are used to move large amounts of material in the mine. They can turn easier inside mines than most trucks can.

- Continuous miner: This machine is used to cut out long sections of the inside walls of the mine. They use this machine instead of blasting and drilling. Click here for pictures.

- Longwall mining equipment: This is used to cut out the coal in layers. Part of the machinery will hold up the roof, too. Click here for a picture.

- Shuttle car: These were used to take out the coal or minerals from the mine. They look a little like our buttons on the left, but not colorful. The ore or coal was loaded into these to be taken out of the mine. Trucks are used for this in up-to-date mines.

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Process Description
Figure 9.7-1 is a flow diagram of a typical cotton-ginning process. Each of the five ginning steps and associated equipment is described below.

Unloading System -
Module trucks and trailers transport cotton from the field to the gin. A pneumatic system removes the cotton from the trailers, and either a pneumatic system or a module feeder removes the cotton from modules. A combination conveyer and pneumatic system conveys the cotton to a separator and feed control unit. Prior to this first separator point, some gins use a stone and green boll trap for preliminary trash removal. The screen assembly in the separator allows air to escape but collects the cotton and allows it to fall into the feed control unit. The conveying air flows from the separator to a cyclone system, where it is cleaned and discharged to the atmosphere.

Seed Cotton Cleaning System -
Cotton is subjected to three basic conditioning processes--drying, cleaning, and
extracting- before it is processed for separation of lint and seed. To ensure adequate conditioning, cotton gins typically use two conditioning systems (drying, cleaning, and extracting) in series.

Seed cotton dryers are designed to reduce lint cotton moisture content to 5 to 8 percent to facilitate cleaning and fiber/seed separation. A high-pressure fan conveys seed cotton through the drying system to the first seed cotton cleaner, which loosens the cotton and removes fine particles of foreign matter (e. g., leaf trash, sand, and dirt). In the second cleaner, large pieces (e. g., sticks, stems, and burs) are removed from the cotton by a different process, referred to as "extracting". Different types of extractors may be used, including bur machines, stick machines, stick and bur machines, stick and green leaf extractors, and extractor/feeders. These machines remove burs, sticks, stems, and large leaves, pneumatically conveying them to the trash storage area. The cotton is pneumatically conveyed to the next processing step. Typically, all conveying air is cleaned by a cyclone before being released to the atmosphere.

Overflow System -
After cleaning, the cotton enters a screw conveyor distributor, which apportions the cotton to the extractor/feeders at a controlled rate. The extractor/feeders drop the cotton into the gin stands at the recommended processing rates. If the flow of cotton exceeds the limit of the extractor/feeder systems, the excess cotton flows into the overflow hopper. A pneumatic system (overflow separator) then returns this cotton back to the screw conveyor distributor, as required. Typically, the air from this system is routed through a cyclone and cleaned before being exhausted to the atmosphere.

Ginning and Lint Handling System -
Cotton enters the gin stand through a "huller front", which performs some cleaning. Saws grasp the locks of cotton and draw them through a widely spaced set of "huller ribs" that strip off hulls and sticks. (New gin stands do not have huller ribs.) The cotton locks are then drawn into the roll box, where fibers are separated from the seeds. After all the fibers are removed, the seeds slide down the face of the ginning ribs and fall to the bottom of the gin stand for subsequent removal to storage. Cotton lint is removed from the saws by a rotating brush, or a blast of air, and is conveyed pneumatically to the lint cleaning system for final cleaning and combing. The lint cotton is removed from the conveying airstream by a condenser that forms the lint into a batt. The lint batt is fed into the first lint cleaner, where saws comb the lint cotton again and remove part of the remaining leaf particles, grass, and motes. Most condensers are covered with fine mesh wire or fine perforated metal, which acts to filter short lint fibers and some dust from the conveying air.

Battery Condenser And Baling System -
Lint cotton is pneumatically transported from the lint cleaning system to a battery condenser, which is a drum covered with fine mesh screen or fine perforated metal that separates the lint cotton from the conveying air. The lint cotton is formed into batts and fed into a baling press, which compresses the cotton into uniform bales.

Most gins use a double-press box for packaging the cotton into bales. The lint drops into one press box and fills it while a bale is being pressed and strapped in the other box. Approximately 480 lb (217 kilograms [kg]) of cotton is pressed into a bale before it is wrapped with a cover and strapped. Modern gins are presently equipped with higher-tonnage bale presses that produce the more compact universal density cotton bales. In 1995, 96 percent of the U.S. crop was pressed into universal density bales at the gins. The finished cotton bale is transported to the textile mill for processing into yarn. Motes are sometimes cleaned and baled also.

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