Ploughing


The basket centrifuge exists in many different versions. The slurry is fed through a pipe or a rotating feed cone into the basket. The cake is discharged manually by digging it out, or some versions allow the cloth to be pulled inside out by the center causing the cake to discharge the axis of rotation has to be horizontal in this case. The latter method is particularly suitable for crystalline or thixotropic materials. Alternatively, the cake can be ploughed out by a scraper which moves into the cake after the basket slows down to a few revolutions per minute. The plough directs the soHds toward a discharge opening provided at the bottom of the basket, through which the cake simply falls out. The speed of the bowl varies during the cycle, ie, filtration is done at moderate speed, dewatering at high speed, and cake discharge by ploughing at low speed. The frequent changes in speed lead to dead times which limit the capacity.  [c.413]

Although this shearing of asperity junctions often accounts for 90% or more of the total friction force, other factors may contribute. A lifting force may be needed to raise asperities over the roughness of the mating surface. Scratching by dirt and wear particles, or by sharp asperities, may introduce ploughing resistance. Internal damping, surface charges, and chemical films also play a role.  [c.233]

Application of Nitrogen Fertilizer in Autumn. Winter-sown crops were assumed for many years to need a small amount of nitrogen fertilizer in the seed-bed in autumn to help them through the winter . Concern about naturally occurring nitrate in the soil in autumn brought this practice into question, and the effect of autumn-applied nitrogen on nitrate losses from the soil during autumn and winter was investigated in the Brimstone Farm experiment. The results were striking. For every kilogram of nitrogen applied in autumn, an extra kilogram of nitrogen was leached as nitrate. It was probably not the fertilizer nitrogen that was leached but soil nitrogen that would have been taken up by the crop if the fertilizer had not been there. These results and others have led to a decline in the application of nitrogen in autumn in recent years. A few farmers say that they have started the practice again, and the reason illustrates the complexity of the nitrate problem. The burning of cereal straw in autumn is now banned, and farmers have either to plough it into the soil or find a use for it elsewhere. Many plough it in, but when it is ploughed into soil it immobilizes mineral nitrogen. Straw has a nitrogen to carbon ratio that is too low for the microbes to be able to use it satisfactorily, so they use mineral nitrogen from the soil to help them metabolize it. This mineral nitrogen thus becomes immobilized in organic matter and is not available to crops at the beginning of autumn. The amounts involved are not huge—one tonne of straw immobilizes about 10 kg of nitrogen—but farmers are aware of this phenomenon and they are sensitive to the appearance of their crops. They like them to look green. It will be a pity if the need to plough in straw causes a resurgence in the use of nitrogen fertilizer in autumn, but the author is not aware that this is happening on a wide scale. Immobilization may well be beneficial, of course, where the farmer applied too much fertilizer nitrogen in the spring.  [c.14]

The clay plays an important role in soil structure because its particles can adhere to each other strongly. This is a mixed blessing. Aggregation of soil particles to form crumbs is vital for the proper functioning of some soils and this process depends on clay and organic matter to provide the adhesion and stabilization of the particles. On the other hand, a soil that contains a large proportion of clay may be so strongly held together that it lets very little water through except in the layer that has been ploughed. We can obtain a picture of the transmission of water and nitrate through soils by considering the behaviour of three general types sandy soils, aggregated soils, and heavy clay soils.  [c.18]

Could the ploughing of grassland in, say, 1945 really contribute to the nitrate problem in 1995 For this to be likely, we would need to be looking at some very long-term processes. Nitrate moves very slowly in some of the rocks that form our aquifers, at 0.8 m per year in imsatiirated chalk, for example, so nitrate entering the top of a chalk aquifer in 1945 will have just arrived at a water surface 40 m below in 1995. Forty metres is a fairly likely depth to the water surface, so this slow transport could mean that nitrate from the ploughing-up is still contributing to nitrate concentrations in deep aquifers. However, is the ploughing-up making an appreciable contribution to nitrate leaving the soil now  [c.19]

Figure 7 The estimated eontribution of nitrate from ploughed-up old grassland to eoneentrations of nitrate-nitrogen leaving soils in England and Wales in 1945. The EC limit is 11.3gm of nitrate-nitrogen. (Taken from Whitmore et Figure 7 The estimated eontribution of nitrate from ploughed-up old grassland to eoneentrations of nitrate-nitrogen leaving soils in England and Wales in 1945. The EC limit is 11.3gm of nitrate-nitrogen. (Taken from Whitmore et
One of the relationships iised to obtain Figure 7 was that between the amount of organic nitrogen in the soil, kg ha and the time, t yr, from the ploughing out of the permanent grassland. This was an exponential relationship derived by fitting to field data.  [c.20]

Table 3 Effects of ploughing out of old permanent grassland at various dates. Estimated contribution in 1995 to nitrate-nitrogen in soil and, if leached, to the nitrate concentration in drainage from the soil (assumed to be 250 mm per year) Table 3 Effects of ploughing out of old permanent grassland at various dates. Estimated contribution in 1995 to nitrate-nitrogen in soil and, if leached, to the nitrate concentration in drainage from the soil (assumed to be 250 mm per year)
Year of ploughing Contribution in 1995 to  [c.21]

Ploughing of sugar crystals at very low speeds of 50 r.p.m. or so. This is achieved by a 48- or a 56-pole motor. A further reduction in speed is obtained by conventional electrodynamic or d.c. electric braking.  [c.169]

Shelf Driers The shelf drier has hollow shelves, usually of welded steel, with connections for incoming steam and outgoing drips to each shelf, a number of shelves are superimposed in a square or rectangular box. The material is spread on the shelves directly or on trays that are placed on the shelves, and the heating is through the metal wall of the shelf. In the atmospheric shelf drier an exhauster may be connected to the top of the shell. The rotary shelf drier has stationary, horizontal circular shelves and a rotating vertical central shaft with arms carrying paddles or ploughs. The shelves are hollow, and usually of steel, with steam and drip pipe connections they have alternating central and circumferential openings, through which the material makes its way downward, traveling over the entire width of each shelf. Sloughs are set to sweep inward or outward, as the shelf may require. At the lowest shelf, the material is discharged at the circumference into barrels or a conveyor. A light steel casing fits around the shelves and permits the removal of gases, which may develop by an exhauster connected to the top of the compartment. Rotary shelf driers are built in all sizes.  [c.141]

Cambridge, Mass.,) and R. P. Feynman (California Institute of Technology, Pasadena) fundamental work in quantum electrodynamics, with deep-ploughing consequences for the physics of elementary particles.  [c.1302]

Tractors, combined harvesters, ploughs, harrows, etc. are large and complex machines with many parts. Some of these are sheet metal and others are castings, and all are mainly steel. The assembled product is finished in a uniform single house colour of the manufacturer, even though the parts may be painted with different systems in different finishing shops.  [c.630]

Friction. An analysis of friction mechanisms suggests that a frictional force is likely to consist of several components such as adhesion-tearing, ploughing (or abrasion), elastic and plastic deformation, fracture, shearing of a friction film (gla2e) (21), and asperity interlocking, all occurring at the sliding surface. Relative contributions of these mechanisms presumably depend on the normal load and sliding speed as well as the temperature. (Material properties ate known to depend on these vafiables). In the case of automotive friction matenals, the coefficient of friction is usually found to decrease with increasing unit pressure and sliding speed at a given temperature, contrary to Amontons law (22—24). This decrease in friction is controlled by the composition and microstmcture of friction matenals.  [c.273]

The lampblack process has the distinction of being the oldest and most primitive carbon black process stiU being practiced. The ancient Egyptians and Chinese employed techniques similar to modem methods collecting the lampblack by deposition on cool surfaces. Basically, the process consists of burning various Hquid or molten raw materials in large, open, shallow pans 0.5 to 2 m in diameter and 16 cm deep under brick-lined flue enclosures with a restricted air supply. The smoke from the burning pans passes through low velocity settling chambers from which the carbon black is cleared by motor-driven ploughs. In more modem installations the black is separated by cyclones and filters. By varying the size of the burner pans and the amount of combustion air, the particle size and surface area can be controlled within narrow limits. Lampblacks have similar properties to the low area od-fumace blacks. A typical lampblack has an average particle diameter of 65 nm, a surface area of 22 m /g, and a DBPA of 130 mL/100 g. Production is small, mostly in Western and Eastern Europe. Its main use is in paints, as a tinting pigment where blue tone is desired. In the mbber industry lampblack finds some special appHcations.  [c.547]

During this century, much old permanent grassland has been ploughed up to make way for arable crops, particularly cereals. This process began in the 1930s and accelerated during World War II, but it continued after the war and through the 1960s. By 1982 the area of permanent grass was one-third of what it had been in 1942. Enlarging the area of arable land may have increased the use of nitrogen fertilizer, but the reason the ploughing-up is relevant to this review is that at least part of the increase in the concentrations of nitrate in natural waters that has been blamed on nitrogen fertilizer may have resulted from the ploughing-up.  [c.19]

Some old permanent grassland at Rothamsted was ploughed in December 1959 and lost about 4tha of organic nitrogen as a result of the activities of microbes and other soil organisms during the next 20 years. Much of this nitrogen was found as nitrate in the water in the chalk below, when a team from the Water Research Centre took cores from the chalk. These data, together with information on losses of organic nitrogen from grassland ploughed up in Tincolnshire, were iised to estimate, through a simple model, the potential contribution of the ploughing to nitrate concentrations in drainage from soils in England and Wales. The results were expressed in maps such as that in Figure 7, which shows its contribution to nitrate concentrations in various parts of the country in 1945. If the EC nitrate limit of 50gm had been in force then, it would have been disobeyed widely.  [c.19]

This relationship was used here to estimate what contribution the ploiighing-iip of old grassland in 1945 and at subsequent ten-year intervals could be making to nitrate-N in soil now in 1995 and, if it were leached, what contribution it then would make to the nitrate concentration, assuming 250 mm of through drainage per year (Table 3). The contribution of the 1945 ploughing is almost negligible, but that in 1965, if leached, would contribute more than one-third of the nitrate needed to reach the EC s limit. Any ploughing done in 1973 would contribute all the nitrate needed to reach the limit. If these calculations are correct, the war-time ploughing is now a spent force, but the considerable area of grassland ploughed up in the 1960s is still making some contribution to the nitrate in and leaching from the soil.  [c.20]

The physically timed bomb comprises nitrate that is moving slowly but inexorably through the unsaturated zones of chalk and other slow-response aquifers, as described earlier. This nitrate will eventually reach the water from which supplies are drawn for public use. This is a very long-term process, but it has been simulated quite successfully using a hydrological modek that makes allowance for mobile and immobile categories of water in the chalk similar in principle to those identihed in many soils. The ploughing-up of grass is a key component in this model.  [c.23]

Regenerative braking When the process is complete and the residue molasses are purged, an oversynchro-nous braking is applied by changing the motor from spinning (4 or 6 poles) to ploughing (48 or 56 poles). This brake energy is then fed back to the mains (see Section 6.20.1 (B)).  [c.169]


See pages that mention the term Ploughing : [c.408]    [c.14]    [c.18]    [c.19]    [c.142]    [c.196]    [c.231]    [c.388]   
Agricultural Chemicals and the Environment (1996) -- [ c.20 , c.21 ]