UNIT-2 equipment for production of aggregates & concreting • Equipment for Production of Aggregate and Concreting • Crushers • Feeders • Screening Equipment • Handling Equipment • Batching and Mixing Equipment • Hauling, • Pouring and Pumping Equipment • Transporters. 1 Aggregate production:• Aggregate of various sizes are required for most of the construction activities for construction of roads, buildings , tunnels, dams , & other concrete structure. • Production of aggregate involves:1. Drilling & Blasting 2. Loading 3. Transporting 4. Unloading 5. Crushing 6. Screening 7. Storing 2 Capacity of crusher depend upon:• • • • Size of stone Size of field Size of finishing product Uniformity of crusher In aggregate production, crusher are usually classified as primary , secondary or tertiary crusher. 3 • Primary crushers reduces the size of a boulder to relatively small size, which are usually non- uniform in size. • Then the crushed boulder goes to the secondary crusher where it crushes into finer & more uniform product. • Tertiary crusher provide third degree size reduction & use to produce fine aggregate. Crushing plants use step reduction , because the amount of size reduction accomplished is directly related to the energy applied. when there is a large difference between the size feed material & the size of crushed product, a large amount of energy is required. 4 • If there was concentration of this energy in a single step process ,excessive fine will be generated & normally there is only a limited market for fine. • As stone passes through a crusher the reduction in size can be expressed as a reduction ratio. • The ratio of crushed feed size to product size. 5 8/12/2013 Types of crusher:1. Jaw crusher:- (primary crusher) This machine operates by allowing stone to flow into the space between 2 jaws one of which stationary & other is moveable. The distance between two jaw & the dimension of the stone travels downward under the effect of gravity & the motion of the moveable jaw until the Ultimately passes through a lower opening. 6 • The moveable jaw is capable of exerting a pressure sufficiently high to crush the hardest rock. • The jaw plates are made up of manganese , steel, which can be removed or replaced. 7 2. Gyratory crusher :- (primary crusher) • The crushing unit consists of cast iron or steel frame with an eccentric shaft driving gear in the lower part of the unit. • In the upper part there is cone shaped crushing chamber line with hard steel or manganese steel plate called the concave, the crushing member include a hard steel crushing head mounted on a vertical steel shaft. • The shaft & the crushing head to gyrate as the shaft rotates, thereby the width of space between the concave & the crusher head. • As the rock which is feed in the top of the crushing chamber moves downward . 8 • It undergoes a reduction in size until it finally passes through the opening at the bottom of the chamber. • The ratio of reduction for gyratory crusher usually range from 3:1 to 10:1 . 9 3. Cone crusher:- (2nd ry & 3rd ry crusher) • Cone crusher are used as secondary or tertiary crushers, they are capable of producing large quantities of uniformly fine crushed stone. • The cone crusher differs from gyratory crusher in this respect:1. It has a shorter cone. 2. It has a smaller receiving opening. 3. It rotates at higher speed, about twice that of gyratory crusher. 4. It produces more uniformly size stone. 10 • In this type of crusher , the manganese steel conical head is mounted on vertical shaft which form as one of the crushing surface. • The other surface is the concave which is attached to the upper part of the crusher frame. • The bottom of the shaft is on eccentric bushing to produces gyratory effects on the shaft rotates. 11 4. Roll crusher:- Roll crushers are one of the secondary & tertiary crushers this crusher consists of heavy cast iron frame, equipped with two counter rotating rollers, mounted on separate horizontal shaft. • The crushed rock from the primary crusher is feed through the gap between the two rollers for crushing further. • Usually one roller has one fixed axis while the other can be adjusted to give the required setting. • The crusher is compact , light weight & low in cost. 12 Roll crusher - 5. Hammer mill:• Hammer mill is most widely used , impact crusher can be used for primary & secondary crushing. The basic parts of unit include:1. Casing 2. Hammer 3. Repulsion plate 4. Rotor As the stone to be crushed is feed into the mil the hammer which reduces at high rpm strikes the particles, breaking them against the repulsion plates which further reduces their size. • The size of the hammer mill may be designed by the size of the feed opening. • The capacity will vary with size of the unit, the kind of stone crushed , size of material feed to the mill & the speed of the shaft. • Hammer mills will produce a high proportion of fines & can not handle wet material. 6. Rod mill & Ball mill:• They are tertiary crusher. • A rod mill consists of a circular steel shell, the interior of the shell is lying on the inside of the hard wearing surface • A shell consist of a number of steel rods, the length of these rods are slightly less than the length of the shell. • Crushed stone is feed through the inlet & fine aggregate of the size of the sand is discharged at the other end. • If the rods are replaced by the steel balls to provide the impact required to grind the stone. • The crusher is known is as ball crusher, the size of the ball generally used is 50mm in diameter. • using rod mills rather than ball mills for larger mining projects including greater efficiency, better grinding performance and lower energy costs Rod mill & Ball mill Crushing cycle:- • Depending upon the hardness of the rock and how much the ore must be crushed, it is not unusual for a mine to have more than one stage of crushing. The diagram below illustrates a three stage crushing cycle for feeding a ball mill. The primary stage uses a gyratory crusher to reduce the ore to fragments less than 150 mm (6") in maximum dimension . A secondary cone crusher further reduces fragments to 12 mm (0.5") or smaller greater. • Ore pieces greater than 12 mm from the secondary crushing stage are sent through a tertiary crushing stage that employs two cone crushers where they are crushed to the desired size. In both the secondary and tertiary stages, screens are used to classify fragments based on size. • • • • 7. feeder:Compression type crushers are designed to use particle interaction in the crushing process & under feed compression crusher produces a larger percentage of oversize material. The capacity of the compression & impact type crushers will be increased if the stone feed is at a uniform rate. Using a feeder a head of crusher eliminates most surge feeding problems that reduces crushing capacity. The installation of such a feeder may increase the capacity of a jaw crusher as much as 15%. • These are many types of feeders:1.Apron feeder 2.Vibrating feeder 3.Plate feeder 4.Belt feeder 1.APRON FEEDER:- A feeder consist of over lopping pans that form a continuous belt is a referred to an apron feeder. • VIBRATING FEEDER:- A vibrating feeder eliminates fine from materials entering the crusher. A vibrating feeder requires less maintenance than apron feeder. • 3.PLATE FEEDER:- By means of rotating eccentric , a plate can be made to move back & forth of the horizontal plane & used to uniformly feed material to the crusher. 4.BELT FEEDER :-Belt feeder is used for smaller size of material usually sand or small size aggregate. Surge Piles:• A stationary crushing plant can include several types & size of crusher is probably followed by set of screens & a belt conveyor to transport the stone to next crushing or to storage. • A plank be designed to provide a temporary storage for stones between the successive stage of crushing. • This plank has the advantage of eliminating or reducing the surge effect that frequently exists when the crushing screening & handling operation are conducted as a linear operation. • Temporary storage ahead of the crusher is known as surge pile. surge can be used to keep at list a portion • Of plank in operation at all times within reasonable limits. • The use of surge piles ahead of crusher, permits the crusher to fit uniformly at most satisfactory rate regardless of variation in the output of other equipment ahead of crusher. • The use of surge piles has unable some planks to increase final output production by as much as 20%. 9.Screening aggregate:• In screening process the particle size smaller than screen cloth opening size will pass through the screen & over sized particle will be retain. • Screen opening can be described by either of two terms:1. Mesh:- The term mesh refers to the number of openings per inch. 2.Clear opening:- It is a term that refers to the distance between the inside edges of parallel wires. a) Revolving screens b) Vibrating screen a) Revolving Screens:- Revolving screen have several advantages over other type of screens. • Specially when they are used to wash & screen gravel & sand. • The operating action is slow & simple & repair , maintenance cost are low. • If the aggregate to be washed ,if it contains silt & clay, a scrubber can be installed near the entrance of the screen water can be spread on the aggregate as it move to the screen. b) Vibrating Screen:- The vibrating screen consist of one or more layer of open mesh wire , mounted on one above the other in a rectangular metal box. • The vibration is obtained by means of eccentric shaft or counter weight shaft. • A unit may be horizontal or inclined with slight slope from the receiving to discharge end. 10. Classification Machines:• When the specifications for sand & other fine aggregate require the materials to meet size gradation. • There are mechanical & water flow machines that classify sand into a multiple no. of individual sizes. 1. Sand and water are feed to this classifier at one end of the unit tanks as the water flows through the outlet end of the tank. The sand particle settle to the bottom of the tank coarse ones first & fine one last. 2. Another machine for handling sand is the screw type classifier this unit can be used to produce specification sand. A sand screw is erected. • So that the material must more up the screw to the discharge in case of screw ,the motor is at discharge end , sand & water feed into hopper, as the spiral screw rotate, the sand is moved up the tank to the discharge outlet under motor. • Undesirable material is flushed out of the tank with overflowing water. 11.Log washer:• When natural deposits of aggregate such as sand , gravels or individual pieces of crush stone, contains deleterious materials as the part of matrix or as deposits on the surface of aggregate . • It will be necessary to remove these materials before using the aggregate. • One method of removing the material is to pass the aggregate through a machine called log washers. • This unit consists of a steel tank with 2 eccentric motor, driving shaft to which replaceable paddles are attached. • The aggregate is feed into the unit at lower end while a constant supply of water flows into the elevated end. • As the shaft rotate in opposite direction , the paddle move the aggregate towards the upper end of the tank while producing a continuous scrubbing action between the particles. • The stream of water will remove undesirable material & discharge it from tank at the lower end. • Where as the processed aggregates will be discharged at the upper end. 12. Concrete production plant:- 1. Batching :a. Manual b. Semi –Automatic c. Fully- Automatic 2.Mixing :a. Ready mix concrete b. Central mixing 3. Placing concrete:a. Buckets b. Manual or Motor propelled buggies c. Chutes & drop pipes d. Belt conveyor e. Concrete pump 1. Batching :• Batching is nothing but proportioning the ingredients of concrete such as cement , sand , aggregates & water for particular mix of concrete by weighing each item separately. • Batchers are available in 3 categories:• Manual :-manual batching is used for small jobs. • Semi- automatic:- the charging & discharging for batchers are activated manually but are automatically terminated. • Fully- automatic:- In fully automatic batching , single starts switch activated the batching sequence, the weight & volume of which have previously programmed into the system. 2. Mixing concrete:• There are two types of concrete mixing operation in use:1.Ready mix concrete:-(central location , truck mixer) 2.Central Mixing:-( Remote location, stationary mixer) 1.RMC:- Project is at a remote location or is relatively large, the concrete is batch in a central batch plant and transported to the job site in transit mixer. • Truck is often referred to as ready mix concrete truck. • Concrete is proportioned at central location & transported to site in fresh state, this type of concrete is termed as ready mix concrete or truck mix concrete. • Concrete is completely mixed in a truck mixer with 7200 revolutions a speed sufficient to mix the concrete completely . 2.In central mix:- in central mix, concrete is completely mixed in stationary mixture then transported to the project by a truck. 3.Placing Concrete:• Once the concrete arrives at the project site, it must be moved to its final position without segregation and before it has achieved initial set . • This movement may be accomplished in several ways, depending on the horizontal , vertical discharge of movement. Various ways of placing concrete are:1. Buckets 2. Manual or Motor Propelled Buggies 3. Chutes & drop pipes 4. Belt conveyor 5. Concrete pump 1. Bucket:• Buckets permit placing of concrete at lowest practical slump. • Care should be exercised to prevent the concrete from segregation , as a result of discharging from high , above the surface or allowing fresh concrete to fall past obstruction. • Gates should be designed so that they can be opened & closed during the discharge of concrete. 2. Manual or Motor propelled Buggies:• Hand buggies & wheel barrows are usually capable of carrying from 4 to 9 cubic feet of concrete as suitable for many projects. • Hand buggies & wheel barrows are suitable for distance less than 200 feet . • Where as power driven or motor driven buggies with capacity up to 14 cubic feet can travel up to 1000 feet economically. 3. Chutes & Drop pipes:• Chutes are often used to transfer concrete from a higher elevation to lower elevation. • They should have a round bottom & slope should be steep enough for the concrete to flow continuously without segregation. 8/12/2013 49 • Drop pipes are used to transfer concrete vertically down. • The top 6-8 feet of the pipe should have a diameter at least 8 times the max aggregate size and may be tapered so that , the lower end is approximately 6 times the max aggregate size. 50 4. Belt Conveyor:• Belt conveyor are used for rapid movement of fresh concrete but must have proper belt size & speed to achieve desired rate of transportation particular attention must be given to point, where concrete leaves on one conveyor and either continuous on another conveyor. 51 14. Concrete Pump:• The pump is an externally simple machine, it transfer concrete by applying pressure to a column of fresh concrete in a pipe. • The concrete can be moved through the pipe, if a lubricant outer layer is provided and if the mixture is properly proportioned for pumping. • Generally pumps have moved concrete more than 500 feet & 1000 feet vertically. • Types of pumps are described below:1. Piston pump 2. Pneumatic pump 3. Squeeze pressure pump 52 1.Piston pump:• Most of the piston pumps contain 2 pistons with one retracting during the forward stroke of the other to give a more continuous flow of concrete • Inlet valve is open while outlet valve is closed & concrete is drawn into cylinder by gravity & piston suction. • As the piston is moves forward inlet valve closes , outlet valve opens & concrete is pushed into pump line. 53 2.Pneumatic Pump:- • It uses compression to push concrete through a pipe lines & can be used for placing concrete in accessible places. • It consists of a pressure vessel with opening at top & conical bottom . • The bottom has opening on both sides which are connected to discharge pipe and other to compressed air pipe. • When the air pressure is applied , the concrete moves through the discharge pipe 54 3. Squeeze pressure pump:• In case of squeeze pressure pump, hydraulically powered roller rotate on the flexible hose , within the drum & squeeze the concrete out of drum. • The vacuum keeps the steady supply of concrete in the tube in the receiving hopper. Concrete Vibrators:• Compaction of concrete is important to improve the characteristics of concrete. • Vibrators are used for compaction of concrete after placement. • These are 2 types of vibrators:1. Internal vibrators 2. External vibrators • Internal vibrator:- Of all the vibrators, the internal vibrator is most commonly used. This is also called ‘Needle Vibrator’. This essentially consist of a power unit , a flexible shaft and a needle. The power unit may be electrically driven or operated by petrol engine.. • The diameter of needle varies from 20mm to 75mm and its length varies from 25cm to 90cm. • They are portable and can be shifted from place to place very easily during concreting operation. 8/12/2013 External vibrator(form work vibrator):• Formwork vibrators are used for concreting columns, thin walls ,or in the casting of precast units. • The machine is clamped on to the external wall surface of the formwork. The vibration is given to the formwork so that the concrete in the vicinity of the shutter gets vibrated. • This method of the vibrating concrete is particularly useful and adopted where reinforcement , lateral ties and spacers interfere too much with internal vibrator. • Use of formwork vibrator will produce a good finish to the concrete surface. 8/12/2013 • Since the vibration is given to the concrete indirectly through the formwork, they consume more power and the efficiency of external vibrator is lower than the efficiency of internal vibrator. 8/12/2013 Concrete mixer:• The concrete mixers are used for mixing all the ingredients to concrete to make mix of specified consistency, the advantage of using concrete mixer is fast mixing & proper mixing. • The important factors which govern the productions are:1.Correct setting of machine. 2.Proper clearing of blades & inner surface drum. 3.Sequence of material charged into the drum. 4.Time of mixing & speed of mixing drums. These are 2 main type of concrete mixers:1) Drum type 2) Pan type 1. Drum type:A) Tilting mixer:- The tilting mixer are useful for large construction work. mixing of concrete in tilting mixer occurs from end to centre & upon itself. The tilting mixers are easier to clean & can discharge the mix quickly with minimum segregation. 58 B) Non-tilting mixer:-Non-tilting Type Mixer (NT) consists of a cylindrical drum that rotates about a horizontal axis and does not have the tilting facility. The vanes are fixed inside the drum surface. • The drum is provided with two central openings at the opposite ends. Feeding of the ingredients is done by front opening and discharging of mixed concrete by rear opening. • For discharging the mixed concrete, the inclined chute is introduced into the drum at rear opening end with the help of a lever. This type of concrete mixer is shown in Figure. 59 It has been observed that in this type of mixers the rate of discharge is slow and chances of segregation are more as compared to tilting type mixers. The capacity of these mixers is generally higher than that of the tilting type mixers. 8/12/2013 2.Pan type mixer:• The pan type mixer consists of open pan with rotating star of blades, moving in the direction opposite to that of star & with less speed. • These mixers are very efficient in working specially with stiff mixes, but due to its big construction it is difficult to maintain & transport. • In some models blade may be stationary & only blades moving. 60 Slip form paver:• Slip form pavers performs the function of spreading, vibrating, striking off , consolidating & finishing the concrete pavement. • It leads to use of minimum hand work. • These name slip form is derived from the fact that the slide form of the machine , slide forward with the paver & line the slab edges unsupported. • Slip form paving has definitely prove as a speedy and an economical method for producing smooth & durable concrete pavement. • Slip form pavers is a major equipment are capable of spreading the concrete dump in front of the machine by dumpers, compacting the concrete through number of powerful vibrators. • The pavers carried out the smooth finishing operation to the highest accuracy and then texture with the Nylon brush operating across the lane . • The equipment also drops the tie bar at the predetermined interval & push them through & places them at predetermined depth and recompact the concrete to cover up the gap that are created by dowel bars. • Generally , no bleeding takes place because the stiff consistency of concrete is designed by for placing by slip form pavers. • All the above operation are continuously carried out and the slip form paver crawls continuously on track wheel. • The speed of the construction i.e. the speed of continuous movement of paver is around 1m per minute. 65
