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Specialize in Cutting Doorways and Windows in Concrete Foundations”
Are You in Kingston Massachusetts? Do You
Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 781-519-2456
We Service Kingston
MA and all surrounding Cities & Towns
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In
purchasing a new plant, care must be exercised in selecting machinery that will
not only be satisfactory for the first job, but that will fulfill the general
needs of the purchaser on other work. All parts of the plant, as well as all
parts of any one machine, should be easily duplicated from stock, so that there
will not be any great delay from any breakdown or worn-out parts. The design of
a plant for handling the material and concrete, and the selection of a concrete
mixer, depend upon local conditions, the amount of concrete to be mixed per
day, and the total amount required on the contract. It is very evident that on
large jobs it pays to invest a large sun in machinery to reduce the number of
men and horses; but if not over 50 cubic yards are to be deposited per day, the
cost of the machinery is a big item, and hand labor is generally cheaper. The
interest on the plant must be charged against the number of cubic yards of
concrete; that is, the interest on the plant for a year must be charged to the
number of cubic yards of concrete laid in a year.
The
depreciation of the plant is followed by taking the cost of the entire plant
when new, and then appraising it after the contract is finished, and dividing
the difference by the total cubic yards of concrete laid. This will give the
depreciation per cubic yard of concrete manufactured. The best concrete mixer
is the one that turns out the maximum of thoroughly mixed concrete at the
minimum of cost for power, interest, and maintenance. The type of concrete
mixer with a complicated motion gives better and quicker results than one with
a simpler motion. There are two general classes of concrete mixers continuous concrete
mixers and batch concrete mixers. A continuous concrete mixer is -one into
which the materials are fed constantly, and from which the concrete is
discharged constantly. Batch concrete mixers are constructed to receive the
cement with its proportionate amount of sand and stone, all at one charge; and,
when mixed, it is discharged in a mass. No very distinct line can be drawn
between these two classes, for many of these concrete mixers are adapted to
either continuous or batch mixing. Generally, batch concrete mixers are
preferred, as it is a very difficult matter to feed the concrete mixers
uniformly unless the materials are mechanically measured. Continuous concrete
mixers usually consist of a long screw or pug mill that pushes the materials
along a drum until they are discharged in a continuous stream of concrete.
Where
the concrete mixers are fed with automatic measuring devices, the concrete is
not regular, as there is no reciprocating motion of the materials. In a paper recently
read before the Association of American Portland Cement Manufacturers, S. B.
Newberry "For the preparation of concrete for blocks in which thorough
mixing and use of an exact and uniform proportion of water are necessary,
continuous mixing machines are unsuitable; and batch concrete mixers, in which
a measured batch of the material is mixed the required time, and then
discharged, are the only type which will be found effective." There are
three general types of concrete mixers: gravity concrete mixers, rotary concrete
mixers, and paddle concrete mixers. Gravity concrete mixers are the oldest type
of concrete mixers.
They
require no power, the materials being mixed by striking obstructions which
throw them together in their descent though the machine. Their construction is
very simple. Fig. 122 illustrates a portable gravity concrete mixer. This
concrete mixer, as will be seen from the figure, is a steel trough or chute in
which are contained mixing members consisting of pins blades. The concrete mixer
is portable, and requires no skilled labor to operate it. There is nothing to
get out o order or cause delays. It is adapted for both large and small jobs.
Operation of Portable Gravity is usually fed by measure, and Concrete mixer, by
this method will produce concrete as fast as the materials can be fed to their
respective bins and the mixed concrete can be taken from the discharge end of
the device.
Are You in Kingston Massachusetts? Do You
Need Concrete Cutting?
We Are Your Local
Concrete Cutter
Call 781-519-2456
We Service Kingston
MA and all surrounding Cities & Towns
