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are mainly used to mix different materials using different types of blades to make a good quality homogeneous mixture. Included are dry blending devices, paste mixing designs for high viscosity products and high shear models for emulsification, particle size reduction and homogenization. Industrial mixers range from laboratory to production line scale.

They can operate at different temperatures and pressures for mixing different solutions and can also have internal or external heating systems added to them. Options also exist where spray nozzles, CIP, PLC and pneumatic or electric systems can be used. Systems can come equipped with hydraulic or electronic soft start mechanisms so that they start and stop smoothly.

In addition to performing typical batch mixing operations, some mixing can be done continuously. Using a machine like the Continuous Processor, one or more dry ingredients and one or more liquid ingredients can be accurately and consistently metered into the machine and see a continuous, homogeneous mixture come out the discharge of the machine. Many industries have converted to continuous mixing for many reasons. Some of those are ease of cleaning, lower energy consumption, smaller footprint, versatility, control, and many others. Continuous mixers, such as the twinscrew Continuous Processor, also have the ability to handle very high viscosities.

short mixing times for the industrial production of ready-mix concrete, and more so for precast/prestressed concrete. This has resulted in refinement of mixing technologies for concrete production. Different styles of stationary mixers have been developed, each with its own inherent strengths targeting different parts of the concrete production market. The most common mixers used today fall into 3 categories:

Twin-shaft mixers, known for their high intensity mixing, and short mixing times. These mixers are typically used for high strength concrete, RCC and SCC, typically in batches of 2 – 6 m3 (2.6 – 7.8 cu yd).

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Vertical axis mixers, most commonly used for precast and pre-

stressed concrete. This style of mixer cleans well between batches, and is favoured for coloured concrete, smaller batches (typically 0.75 – 3 m3 or 0.98–3.9 cu yd), and multiple discharge points. Within this category, the Pan mixers are losing popularity to the more efficient Planetary (or coun- ter-current) mixers as the additional mixing action helps in production of more critical concrete mixes (colour consistency, SCC, etc.).

Drum mixers (reversing drum mixer and tilting drum mixers), used where large volumes (batch sizes of 3 – 9 m3 or 3.9 – 12 cu yd) are being produced. This type of mixer dominates the ready-mixed market as it is capable of high production speeds, ideal for slump concrete, and where overall cost of production is important. Drum mixers have the lowest maintenance and operating cost of the three styles of mixers.

All the mixer styles have their own inherent strengths and weaknesses, and all three styles of mixers are used throughout the world to varying degrees of popularity.

1.What are the most common concrete mixers?

2.What mixers are used for precast concrete?

3.What is the most popular type of mixers?

. 4.1

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The stump-jump plough was an Australian invention of the 1870s, designed to cope with the breaking up of new farming land, that contains many tree stumps and rocks that would be very expensive to remove. The plough uses a moveable weight to hold the ploughshare in position. When a tree stump or other obstruction such as a rock is encountered, the ploughshare is thrown upwards, clear of the obstacle, to avoid breaking the plough's harness or linkage; ploughing can be continued when the weight is returned to the earth after the obstacle is passed.

A simpler system, developed later, uses a concave disc (or a pair of them) set at a large angle to the direction of progress that uses the concave shape to hold the disc into the soil – unless something hard strikes the cir-

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cumference of the disk, causing it to roll up and over the obstruction. As the arrangement is dragged forward, the sharp edge of the disc cuts the soil, and the concave surface of the rotating disc lifts and throws the soil to the side. It doesn’t make as good a job as the mouldboard plough (but this is not considered a disadvantage, because it helps fight the wind erosion), but it does lift and break up the soil.

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By processing trees and other vegetation where they stand, mulching machines eliminate many of the steps involved in land clearing such as site prep, cutting/felling/hauling, and site cleanup. This also eliminates the need for multiple machines such as a bulldozer accompanied by some combination of excavators, tree shears, wood chippers or grinders, and hauling equipment. One simpler jobs only one mulching machine is required, reducing fuel requirements and emissions.

Some mulching machines also have the ability to operate on steep slopes and in small or tight areas, in poor ground conditions, and in wet or snowy weather.

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Mulching machines are capable of clearing land of unwanted trees and brush with limited disturbance to soils or desirable vegetation.

Traditional land clearing methods often present an increased risk of erosion by pushing over trees, uprooting the stump and roots, and substantially disturbing soils. In contrast, mulching the vegetation leaves the soil structure intact. The mulched material can be left on the ground and will act as an erosion barrier while returning nutrients back into the soil through decomposition. Over time, grass will naturally grow through the mulch and can be maintained with mowing.

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Land clearing involves the removal of trees and brush on a piece of land. Depending on the size, location, and purpose of the land, the excavation may require professional land clearing equipment. Pushover, cut and grind, and burning are three of the most used land clearing methods.

The pushover method of land clearing often involves the use of major construction equipment. The trees are pushed over and hauled off the land with the roots intact. Once the trees are moved to a central location, they are often processed for sale or ground for use as a mulching material.

The cut and grind method begins with cutting down the trees on the piece of land. These trees are often moved to a processing location, but the stumps are left in the ground. These stumps can be ground into mulching material or pulled out of the grown using a large piece of construction machinery.

Using a controlled burn for land clearing can be one of the most dangerous methods. Burning involves starting a controlled fire and maintaining that fire until all trees and brush are burned to the ground. After the fires are extinguished, the land can be cleared using a bull dozer or other piece of construction equipment.

While some small plots of land may be cleared without the help of a professional, larger plots of land may be more difficult to clear without a team of specialists. This team will often be trained in the fastest and most effective methods of land clearing. They are also more likely to be trained in the local laws and regulations regarding the clearing of land.

One additional option some people choose involves selling the timber located on the plot of land. If the timber is sold before the land is cleared, some timber companies will bring in a team of workers and equipment to clear the land at no cost to the landowner. It is important to

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insure that the timber company will not only clear the land, but clean up the debris after the timber has been removed from the plot.

The landowner should remember that land clearing leaves the surface layer of topsoil open to the elements and erosion. This top layer of dirt can be preserved by planting grass in this soil. While the grass may not be needed on the entire lot, it can be easier to remove a patch of grass for development than to import new dirt, to prevent soil loss.

http://www.wisegeek.com/what-are-the-different-methods-of-land- clearing.htm

digger operator

digger position

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