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1、Loading machines For materials handing in construction,use is made of loaders.Practice has shown that excavators are less effective in the capacity of loads in quarries and storages of nonmetallic materials than loaders.By the kind of loads handled,loaders are classified as forklift loads and scoopi
2、ng loaders for loose materials.Sooping loaders are divided into single-bucket and continuous-action Multi-bucket loaders.Single-bucket loaders are general-purpose machines suited engineering and in applications requring continuous working process. Depending on the kind of running gear,crawler and an
3、ailable.Crawler loaders have a high passblibity and develop a great thrust efftort. Wheeled loaders feature a high manoeuvrability and high traveling speeds making no damage to the road pavement and the storage areas.Unloaders are used for unloading sand, gravel, crushed stone, cement form railway c
4、ars.Power and pneumatic unloaders are used,power for unloading materials from flat cars or gondola cars(open wagons)and pneumatic for unloading cement.The main working member of fork-lift loaders is the fork serving to load and unload piece loads. These loaders have different change attachments. Whe
5、n equipped with buckets or grabs, they are used for loading loose and small-piece materials, and the boom attachment makes these loaders suited for hoisting loads to a small heighe and sometimes for erection work in construction.Fork-lift loaders are operated on hard-pavement areas,therefore they ar
6、e mainly used in storehouse and as factory materials-handing equipment.They are made on the basis of a truck therefore they are also called truck loaders.they are powered by internal combustion engines or electric motors with storage batteries. Engine powered truck are used for large warehouse and s
7、tock-handing application, for general yard work and fpr loading and unloading of vehicles. Torque converter transmission provides smooth operation; power steering and all-weather cabs are options available.Single-bucket loaders have a crawler tractor or a wheeled truck as a carrier mounting. The loa
8、der permits mechanization of loading construction and erection and work with the aid of change attachments,of which the main one is the bucket. The loading equipment is available in three modifications: front-end,overloading, and half-swing,jib-type. The front-end attachment provides also side unloa
9、ding.The overloading modifiactaion permits back unloading.Presently front-end loader with the positive displacement hydraulic drives for the attachment are most widely used.The output of multi-bucket loaders is 40 to 60 percent higher than of single-bucket machines at the same power rating,it is exp
10、edient to use them in brickyards,prefabricated concrete products plants,railway stations with large volumes of loading-unloading operatins and also for loading loose materials.In addition,they are suited for size grading of loose materials,for which purpose they are provided with special vibrating s
11、creens.Multi-bucket loaders are very efficient in unloading flatcars with side dumping of the handle material.These loaders can be applied in the production lines of prefabricatde ainstruction products plants and also in road building.In the latter case they are used for loading sand and gravel into
12、 drying drums and mixers.The working member of the loader is a screw feeder consisting of tow right-hand and left-hand screws,which are arranged on both sides of a bucket elecator.When the feeder rotates,the loaded material is delivered to the buckets to make the scooping easier.A scraper is secured
13、 underneath the screw feeder.The elevator of the multi-bucket loader usually dischanges the material onto belt conveyers that deliver it to tiansport facilities.Some loaders discharge the handle material into tranport facilities through hoppers or chutes. 装载机在建筑施工中，材料的装卸是用装载机和写在机进行的。实践证明，在采石场和非金属材料的
14、仓库作业中，挖掘机的装在效率要比装载机高。根据所装载材料的种类，装载机可以分为叉式装载机，用于装在整块物料；铲斗式装载机，用于装载松散物料。铲斗装载机分为单斗装载机和连续作业多斗装载机。单斗装载机式通用机械，适用于多种条件下作业。多斗装载机用于大型仓库、公路工程以及需要连续作业的工作。按照行走装置的类型，可以分为履带行走装载机和轮胎式装载机。履带行走式装载机具有良好的通过性，能产生很大的推进力。轮胎装载机机动性能良好。行走速度快，对公路路面和存活地面从不产生破坏作用。装载机用来卸掉火车车厢里的砂子、砾石、碎石和水泥。卸载机分为机动卸载和气动卸载机。既定卸载机用于从平板货车或敞蓬车上卸货；气动卸
15、载机用于卸水泥。叉车的主要工作装置是用于装卸整件货物的叉子。这些装载机有不同的换装部件。当装上铲斗或抓斗时，可用语装卸松散和小块物料，叉架机构使这些装载机能适于把货物举升到一个不大的高度，有时也适于建筑安装工程。因为叉车在硬路面上作业，因此，主要用于仓库并作为工厂物料的装卸设备。这些装载机是根据卡车的原理制造的，所以也叫卡车装载机，他们以内燃机或带有蓄电池的电动机为动力。以发动机为动力的卡车用于大型仓库和材料搬运工作，用于一般的堆放场和车辆装卸。液力变距传动系统使运动平稳。还可以选配动力转向及全天候驾驶室。单斗装载机以履带拖拉机或轮胎拖拉机作为行走机架。该装载机可使装载作业、建筑施工、安装工程
16、实现机械化。在这些换装装置中，主要附件是铲斗。装载设备有三种不同的形式，即前卸式、翻转式和侧卸式。前卸式机构只允许从装料的一侧卸料；侧卸式机构是侧面卸料；翻转式机构则从后面卸料。目前，具有变量液压驱动的工作装置的前卸式装载机使用得最为广泛。多斗装载机的产量比同一额定功率的单斗装载机的产量高40%60%。多斗装载机适于砖厂、混泥土预制品厂及装卸量大的火车站，也同样适用于装载松散物料。此外，该机还适用于对松散物料的颗粒分级，为此，可以安装一个专用的振动筛。用多斗装载机为侧边卸料的平板车卸料，其效率很高。多斗装载机可用于混凝土预制品厂的生产线中，也可用于筑路。在筑路中，用于将砂子和砾石装入烘干筒和搅
17、拌机里。该装载机的工作机构是两个左右螺旋杆组成的螺旋给料器，安装在斗式提升机的两侧。当给料器旋转时，物料被送入各个铲斗内，使得装料比较容易。刮板固定在螺旋给料器的下方。多斗装载机的提升机把物料卸在传送带上，再由传送带将物料运送到设备中。有些装载机用漏斗或料槽把物料送进运输设备中。 Pneumatic Motors and ToolsCompressde air can be used for a wide variety of operations,such as:to drive air motors and air hammers,to operate air cylinders,to a
18、tomize liquids,to convery materials,to displace and agitate liquids,to serve as a cushion,to create a vacuum,to accelerate combustion,and to serve as a coolant and lubricant.An electric motor is a device in which electrical energy is converted into mechanical energy.A fluid motor is a device for con
19、verting fulid energy into mechanical energy.In this chapter,the main features of pneumatic motors and pneumatic tools are discussed.GENERAL TYPES OF AIR MOTORSAir motors may be divided into tow general type: (1) the rotary type and (2) the reciprocating type. The combination of a piston and cylinder
20、 is an example of the reciprocating type of motor.Two example of the rotary motor are the vane-type and gear-type motors.A rotary vane-type motor is illustrated.The rotating member,with its sliding vanes,it is trapped between the vane(which ride on the inside of the housing)and pushes to the outlet.
21、Thus the compressed air drives a rotating member.A gear-type motor is illustrated.A pair of meshed gears rotate inside a housing,As the gears rotate,the air is trapped between the gear teeth and housing,and pushes from the inlet to the outlet.Thus the compressed air drives the gears.CHARACTERISTICS
22、OF AIR MOTORS An air motor operates safely in an explosive atmosphere,and has a low installation cost,a rapid acceleration,and a high starting troque.It is compact,and its cariable speed can be changed.A typical curve for torque versus speed(rpm)for a rotary-type air motor is illustrated.Air-motor s
23、peed can be caried,in small steps,from zero a maximum by varying the air flow to the motor.The air flow rate to the motor can be varied by means of a valve in the inlet compressed-air line.The pressure at the air motor inlet can be contolled with an adjustable pressure regulator in the air inlet lin
24、e;thus torque can be controlled by means of the pressure regulator.An air motor can be arranged to be recersible in speed direction,by means of a four-way valve.As shown,the speed decreases as the load increase.Air motor can be stalled without any damage being done.A curve for horsepower versus spee
25、d for a rotary-type air motor is shown.The power output is at a maximum between zero and maximum speed.Power output is proportional to the product of torque times angular or rotational speed(rpm).The speed,torque,and direction og rotation of an air motor can be controlled and adjusted to job require
26、ments.For example,reversible air motors are used to turn or screm studs into castings,when assembling engines.The air pressure to the air motor is regulated,so that the air motor stalls when the stud is driven to the correct tightness.In this instance,the air motor starts off at high speed(very low
27、torque),is quickly loaded so that it stalls,and is then reversed.An air motor has no tendency to heat when it is overheating;the motor can withstand repeated stalling and reversing without damage or overheating.An air motor can accelerate(or speed up)rapidly,because the compressed air energy can be
28、released at a high rate.Air motors are available commercially in sizes ranging from 1/10 horsepower to 50 horsepower,and in speed ranging from 20 rmp to 75,000 rmp.GENERAL FEATURES OF PNEUMATIC TOOLSPneumatic tools represent a large number of air-operated machines that are usually transported to a w
29、ork area,rather than transporting the work to the tool(as in machining some metals by machine tools).In many instances,the tool is either held entirely by the hands or guided and controlled by hand.The tool may be portable.In a manufacturing plant,the compressor.On an outdoor construction job,the co
30、mpressor may be portable.In a manufacturing plant,the compressor may be stationary.Air from the compressor system is fed by means of distribution piping through a filter,a pressure regulator,and a lubricator.Air from the lubricator may be fed through a flexible hose to the pneumatic tool.Pneumatic t
31、ools are usually supplied with compressed air at about 90 pounds per square inch,gauge.There are three hroad classifications of pneumatic tools(1)rotary,(2)piston,and(3)percussion.In a typical rotary pneumatic tool,the air enters the tool handle,passes through a manually operated control valve,passe
32、s through the end plates,and enters a chamber of a vane-type air motor.The air pushes the rotor form the inlet to the outlet.At the outlet,the air is discharged into the atmosphere.The typical rotary air motor possesses three to five blades,rotates at speeds of 4000 to 25,000 rpm,and develops up to
33、3 horsepower.A spindle fastened to the rotor drives a set of planetary reduction gears to supply the desired output shaft.The output shaft may be equipped with a chuck for holding a drill,grinder,or some other tool.The piston-type air motor is used for tools when higher horsepower and slower speeds
34、are desired,as in hoists and heavy-drills.The percussion or hammer-type air motor is found in chippers, riveters,and pavement breakers.In this type of machine,the air usually passes through an exhaust valve,and then is exhausted into the atmosphere.The piston is moved back and forth.On the driving s
35、troke,the inertia of the piston provides a hammer blow or impact to a drill,a chisel,or a bit.Compressed air permits the use of tools are relatively compact,light in weight,flexible,portable,and easy to operate.Pneumatic tools are used on a very light assembly work and on heavy-duty constrution jobs
36、.The speed and direction of rotation of air motors can be controlled quickly,and they can be adjusted to serve requirements by means of a control valve which throttles the flow of compressed air to the motor.pneumatic motors do not have a tendency to become hot when they are overheated.An air motor
37、presents no spark hazard in explosive atmospheres;therefore,it can be used in oil refineries and other plants that the problem of example of explosive atmospheres.Air motors are used under wet and humid conditions,because there is no electric shock hazard.Among the many applications and users of pne
38、umatic tools are: agricultural equipment manufacturers, aircrafe manufacturers, ammunition depots, automotive shops and plants, bakeries, boiler shop, can factories, cement plants, coal mines, construction work, cotton mills, cut-stone plants, dairies, distilleries, forge shops, foundries and steel
39、mills, furniture factories, many kinds of industrial plants, laundries, machine shop, mining, oil refineries, paper mills, quarries, railroads, road building, rubber factories, sawmills, shipyards, and boat-builders, smelters, structural work, and waterworks.PNEUMATIC TOOLSFrom the point of view of
40、application of pneumatic tools, two main classes of tools should be considered (1)air-operated portable tools, and (2)air-operated rock drills.Portable toolsThis class of pneumatic tools include grinders, buffers, and sanders. A rotary vane-type air motor is usually used for tools of this type. They
41、 are available in a wide range of speed and power.Drill-A rotary vane-type air motor is usually used for drills, reamers, tappers, and stud setters. Drills and reamers are used for steel, wood, and other materials. Some tools are reversible, with rotation possible in either direction, and tools are
42、nonreversible. Drill speed can be caried by throttling the air supply to the drill. Portable drills powered by a vane-type rotary air motor are used also for drilling any mineral substance that can be penetrated by an auger or a tungsten carbied bit-for example, coal, chalk, shale, and hardpan.Screw
43、drivers-A rotary vane-type air motor is usually used for screwdrivers, nut srtters, impact wrencher, and nibblers. Millions of nut, bolts, and screws, are driven daily by pneumatic tools in the large production plants making products,such as automobiles,refrigerator,radios,and various appliances.pne
44、umatic impact wrenches are used to remove or to tighten nuts by torsional or rotary impact,and pneumatic nibblers,and shears are used for cutting and sheathing steel metal. Hammer-In the penbmatic chipping hammer,a piston delivers a series of blows to a forming tool or chisel at the end of the hamme
45、r;the piston is air operated. The two type of percussion tool are the valve type and the vaveless type. In the valve type,a avlve arrangement is used to contral the flow of air both to and from the two ends of the hammering piston. In the valveless type, the valve action is performed by the piston .
46、 sand rammers are actually pneumatic hammers; they are used for packing sand molds.Hoists hoists that are by compressed air are used in in many application, especially in machine shops and fundries. Pneumatic hoists are used outdoors and where fumes and explosive gases are present. An air motor is v
47、ariable in speed, reversible in direction,and can withstand stalling form an overload without damage.Rock drills and paving breakers The second class of air-operated tools include various types of rock drills and pavement breakers.the hammers drills is commonly used air-operated tool in mining and g
48、enera excavation work. A piston can be fund inside the air cylinder, and a-drill steel in used. The drill steel is provided with a shank on one end and a bit at the other end . the freely moving piston hammers or strikers rapid blows on the shank of the drill steel.Paving breakers are hand-operated
49、pneumatic tools that have a wide variety of uses in industrial plants and in general construction work. One type of tool is valveless;another type is valve operated.One class of pneumatic tools is sometimes designated as pneumatic specialty tools. They include:staybolt riveters, paint mixers, screw spike drives,wire-wrapping decices, spinner riveters, shank grinders, reciprocating filing machines, valve g