英文原文 SHAFT AND GEAR DESIGN Abstract The important position of the wheel gear and shaft can t falter in traditional machine and modern machines The wheel gear and shafts mainly install the direction that delivers the dint at the principal axis box The passing to process to make them can is divided into many model numbers useding for many situations respectively So we must be the multilayers to the understanding of the wheel gear and shaft in many ways Key words Wheel gear Shaft In the force analysis of spur gears the forces are assumed to act in a single plane We shall study gears in which the forces have three dimensions The reason for this in the case of helical gears is that the teeth are not parallel to the axis of rotation And in the case of bevel gears the rotational axes are not parallel to each other There are also other reasons as we shall learn Helical gears are used to transmit motion between parallel shafts The helix angle is the same on each gear but one gear must have a right hand helix and the other a left hand helix The shape of the tooth is an involute helicoid If a piece of paper cut in the shape of a parallelogram is wrapped around a cylinder the angular edge of the paper becomes a helix If we unwind this paper each point on the angular edge generates an involute curve The surface obtained when every point on the edge generates an involute is called an involute helicoid The initial contact of spur gear teeth is a line extending all the way across the face of the tooth The initial contact of helical gear teeth is a point which changes into a line as the teeth come into more engagement In spur gears the line of contact is parallel to the axis of the rotation in helical gears the line is diagonal across the face of the tooth It is this gradual of the teeth and the smooth transfer of load from one tooth to another which give helical gears the ability to transmit heavy loads at high speeds Helical gears subject the shaft bearings to both radial and thrust loads When the thrust loads become high or are objectionable for other reasons it may be desirable to use double helical gears A double helical gear herringbone is equivalent to two helical gears of opposite hand mounted side byside on the same shaft They develop opposite thrust reactions and thus cancel out the thrust load When two or more single helical gears are mounted on the same shaft the hand of the gears should be selected so as to produce the minimum thrust load Crossed helical or spiral gears are those in which the shaft centerlines are neither parallel nor intersecting The teeth of crossed helical fears have point contact with each other which changes to line contact as the gears wear in For this reason they will carry out very small loads and are mainly for instrumental applications and are definitely not recommended for use in the transmission of power There is on difference between a crossed heli cal gear and a helical gear until they are mounted in mesh with each other They are manufactured in the same way A pair of meshed crossed helical gears usually have the same hand that is a right hand driver goes with a right hand driven In the design of crossed helical gears the minimum sliding velocity is obtained when the helix angle are equal However when the helix angle are not equal the gear with the larger helix angle should be used as the driver if both gears have the same hand Worm gears are similar to crossed helical gears The pinion or worm has a small number of teeth usually one to four and since they completely wrap around the pitch cylinder they are called threads Its mating gear is called a worm gear which is not a true helical gear A worm and worm gear are used to provide a high angular velocity reduction between nonintersecting shafts which are usually at right angle The worm gear is not a helical gear because its face is made concave to fit the curvature of the worm in order to provide line contact instead of point contact However a disadvantage of worm gearing is the high sliding velocities across the teeth the same as with crossed helical gears Worm gearing are either single or double enveloping A single enveloping gearing is one in which the gear wraps around or partially encloses the worm A gearing in which each element partially encloses the other is of course a double enveloping worm gearing The important difference between the two is that area contact exists between the teeth of doubleenveloping gears while only line contact between those of single enveloping gears The worm and worm gear of a set have the same hand ofhelix as for crossed helical gears but the helix angles are usually quite different The helix angle on the worm is generally quite large and that on the gear very small Because of this it is usual to specify the lead angle on the worm which is the complement of the worm helix angle and the helix angle on the gear the two angles are equal for a 90 deg Shaft angle When gears are to be used to transmit motion between intersecting shaft some of bevel gear is required Although bevel gear are usually made for a shaft angle of 90 deg They may be produced for almost any shaft angle The teeth may be cast milled or generated Only the generated teeth may be classed as accurate In a typical bevel gear mounting one of the gear is often mounted outboard of the bearing This means that shaft deflection can be more pronounced and have a greater effect on the contact of teeth Another difficulty which occurs in predicting the stress in bevel gear teeth is the fact the teeth are tapered Straight bevel gears are easy to design and simple to manufacture and give very good results in service if they are mounted accurately and positively As in the case of squr gears however they become noisy at higher values of the pitch line velocity In these cases it is often go od design practice to go to the spiral bevel gear which is the bevel counterpart of the helical gear As in the case of helical gears spiral bevel gears give a much smoother tooth action than straight bevel gears and hence are useful where high speed are encountered It is frequently desirable as in the case of automotive differential applications to have gearing similar to bevel gears but with the shaft offset Such gears are called hypoid gears because their pitch surfaces are hyperboloids of revolution The tooth action between such gears is a combination of rolling and sliding along a straight line and has much in common with that of worm gears A shaft is a rotating or stationary member usually of circular cross section having mounted upon it such elementsas gears pulleys flywheels cranks sprockets and other power transmission elements Shaft may be subjected to bending tension compression or torsional loads acting singly or in combination with one another When they are combined one may expect to find both static and fatigue strength tobe important design considerations since a single shaft may be subjected to static stresses completely reversed and repeated stresses all acting at the same time The word shaft covers numerous variations such as axles and spindles Anaxle is a shaft wither stationary or rotating nor subjected to torsion load A shirt rotating shaft is often called a spindle When either the lateral or the torsional deflection of a shaft must be held to close limits the shaft must be sized on the basis of deflection before analyzing the stresses The reason for this is that if the shaft is made stiff enough so that the deflection is not too large it is probable that the resulting stresses will be safe But by no means should the designer assume that they are safe it is almost always necessary to calculate them so that he knows they are within acceptable limits Whenever possible the power transruission elements such as gears or pullets should be located close to the supporting bearings This reduces the bending moment and hence the deflection and bending stress Although the von Mises Hencky Goodman method is difficult to use in design of shaft it probably comes closest to predicting actual failure Thus it is a good way of checking a shaft that has already been designed or of discovering why a particular shaft has failed in service Furthermore there are a considerable number of shaft design problems in which the dimension are pretty well limited by other considerations such as rigidity and it is only necessary for the designer to discover something about the fillet sizes heat treatment and surface finish and whether or not shot peening is necessary in order to achieve the required life and reliability Because of the similarity of their functions clutches and brakes are treated together In a simplified dynamic representation of a friction clutch or brake two in ertias 11 and 12 traveling at the respective angular velocities Wl and W2 one of which may be zero in the case of brake are to be brought to the same speed by engaging the clutch or brake Slippage occurs because the two elements are running at different speeds and energy is dissipated during actuation resulting in a temperature rise In analyzing the performance of these devices we shall beinterested in the actuating force the torque transmitted the energy loss and the temperature rise The torque transmitted is related to the actuating force the coefficient of friction and the geometry of the clutch or brake This is problem in static which will have to be studied separately for eath geometric configuration However temperature rise is related to energy loss and can be studied without regard to the type of brake or clutch because the geometry of interest is the heat dissipating surfaces The various types of clutches and brakes may be classified as fllows 1 Rim type with internally expanding shoes 2 Rim type with externally contracting shoes 3 Band type 4 Disk or axial type 5 Cone type 6 Miscellaneous type The analysis of all type of friction clutches and brakes use the same general procedure The following step are necessary 1 Assume or determine the distribution of pressure on the frictional surfaces 2 Find a relation between the maximum pressure and the pressure at any point 3 Apply the condition of statical equilibrium to find a the actuating force b the torque and c the support reactions Miscellaneous clutches include several types such as the positive contact clutches overload release clutches overrunning clutches magnetic fluid clutches and others A positive contact clutch consists of a shift lever and two jaws The greatest differences between the various types of positive clutches are concerned with the design of the jaws To provide a longer period of time for shift action during engagement the jaws may be ratchet shaped or gear tooth shaped Sometimes a greatmany teeth or jaws are used and they may be cut either circumferentially so that they engage by cylindrical mating or on the faces of the mating elements Although positive clutches are not used to the extent of the frictional contact type they do have important applications where synchronous operation is required Devices such as linear drives or motor operated screw drivers must run to definite limit and then come to a stop An overload release type of clutch is required for these applications These clutches are usually spring loaded so as to release at a predetermined toque The clicking sound which is heard when the overload point is reached is considered to be a desirable signal An overrunning clutch or coupling permits the driven member of a machine to freewheel or overrun because the driver is stopped or because another source of power increase the speed of the driven This type of clutch usually uses rollers or balls mounted between an outer sleeve and an inner member having flats machined around the periphery Driving action is obtained by wedging the rollers between the sleeve and the flats The clutch is therefore equivalent to a pawl and ratchet with an infinite number of teeth Magnetic fluid clutch or brake is a relatively new development which has two parallel magnetic plates Between these plates is a lubricated magnetic powder mixture An electromagnetic coil is inserted somewhere in the magnetic circuit By varying the excitation to this coil the shearing strength of the magnetic fluid mixture may be accurately controlled Thus any condition from a full slip to a frozen lockup may be obtained Introduciton of Machining Have a shape as a processing method all machining process for the production of the most commonly used and most important method Machining process is a process generated shape in this process Drivers device on the workpiece material to be in the form of chip removal Although in some occasions the workpiece under no circumstances the use of mobile equipment to the processing However the majorityof the machining is not only supporting the workpiece also supporting tools and equipment to complete Machining know the process has two aspects Small group of low cost production For casting forging and machining pressure every production of a specific shape of the workpiece even a spare parts almost have to spend the high cost of processing Welding to rely on the shape of the structure to a large extent depend on effective in the form of raw materials In general through the use of expensive equipment and without special processing conditions can be almost any type of raw materials mechanical processing to convert the raw materials processed into the arbitrary shape of the structure as long as the external dimensions large enough it is possible Because of a production of spare parts even when the parts and structure of the production batch sizes are suitable for the original casting Forging or pressure processing to produce but usually prefer machining Strict precision and good surface finish Machining the second purpose is the establishment of the high precision and surface finish possible on the basis of Many parts if any other means of production belonging to the largescale production Well Machining is a low tolerance and can meet the requirements of small batch production Besides many parts on the production and processing of coarse process to improve its general shape of the surface It is only necessary precision and choose only the surface machining For instance thread in addition to mechanical processing almost no other processing method for processing Another example is the blacksmith pieces keyhole processing as well as training to be conducted immediately after the mechanical completion of the processing Primary Cutting Parameters Cutting the work piece and tool based on the basic relationship between the following four elements to fully describe the tool geometry cutting speed feed rate depth and penetration of a cutting tool Cutting Tools must be of a suitable material to manufacture it must be strong tough hard and wear resistant Tool geometry to the tip plane and cutter angle characteristics for each cutting process must be correct Cutting speed is the cutting edge of work piece surface rate it is inches per minute to show In order to effectively processing and cutting speed must adapt to the level of specific parts with knives Generally the more hard work piece material the lower the rate Progressive Tool to speed is cut into the work piece speed If the work piece or tool for rotating movement feed rate per round over the number of inches to the measurement When the work piece or tool for reciprocating movement and feed rate on each trip through the measurement of inches Generally in other conditions feed rate and cutting speed is inversely proportional to Depth of penetration of a cutting tool to inches dollars is the tool to the work piece distance Rotary cutting it to the chip or equal to the width of the linear cutting chip thickness Rough than finishing deeper penetration of a cutting tool depth Wears of Cutting To01 We already have been processed and the rattle of the countless cracks edge tool we learn that tool wear are basically three forms flank wear the former flank wear and V Notch wear Flank wear occurred in both the main blade occurred vice blade On the main blade shoulder removed because most metal chip mandate which resulted in an increase cutting force and cutting temperature increase If not allowed to check That could lead to the work piece and the tool vibration and provide for efficient cutting conditions may no longer exist Vicebladed on it is determined work piece dimensions and surface finish Flank wear size of the possible failure of the product and surface finish are also inferior In most actual cutting conditions as the principal in the former first deputy flank before flank wear wear arrival enough Tool will be effective the results are made unqualified parts As Tool stress on the surface uneven chip and flank before sliding contact zone between stress in sliding contact the start of the largest and in contact with the tail of zero so abrasive wear in the region occurred This is because the card cutting edge than the nearby settlements near the more serious wear and bladed chip due to the vicinity of the former flank and lost contact wear lighter This resultsfrom a certain distance from the cutting edge of the surface formed before the knife point Ma pit which is usually considered before wear Under normal circumstances this is wear cross sectional shape of an arc In many instances and for the actual cutting conditions the former flank wear compared to flank wear light Therefore flank wear more generally as a tool failure of scale signs But because many authors have said in the cutting speed of the increase Maeto surface temperature than the knife surface temperatures have risen faster but because any form of wear rate is essentially temperature changes by the significant impact Therefore the former usually wear in high speed cutting happen The main tool flank wear the tail is not processed with the work piece surface in contact Therefore flank wear than wear along with the ends more visible which is the most common This is because the local effect which is as rough on the surface has hardened layer This effect is by cutting in front of the hardening of t he work piece Not just cutting and as oxidation skin the blade local high temperature will also cause this effect This partial wear normally referred to as pit sexual wear but occasionally it is very serious Despite the emergence of the pits on the Cutting Tool nature is not meaningful impact but often pits gradually become darker If cutting continued the case then there cutter fracture crisis If any form of sexual allowed to wear eventually wear rate increase obviously will be a tool to destroy failure destruction that will no longer tool for cutting cause the work piece scrapped it is good can cause serious damage machine For various carbide cutting tools and for the various types of wear in the event of a serious lapse on the tool that has reached the end of the life cycle But for various high speed steel cutting tools and wear belonging to the non uniformity of wear has been found When the wear and even to allow for a serious lapse the most meaningful is that the tool can re mill use of course In practice cutting the time to use than the short time lapse Several phenomena are one tool serious lapse began features the most common is the sudden increase cutting force appeared on the work piece burning ring patterns and an increase in noise The Effect of Changes in Cutting Parameters on Cutting Temperatures In metal cutting operations heat is generated in the primary and secondary deformation zones and this results in a complex temperature distribution throughoutthe tool workpiece and chip A typical set of isotherms is shown in figure where it can be seen that as could be expected there is a very large temperature gradient throughout the width of the chip as the workpiece material is sheared in primary deformation and there is a further large tempera