【正文】 ds (Table 51) Connecting threads (聯(lián)接螺紋 ): Plain thread, Gas thread (管螺紋 ) Transmission threads (傳動螺紋 ): Rectangular thread, trapezoidal thread (梯形 )。 Ψ(Helix angle, 升角 )。 5— 1 Thread Righthand and lefthand threads: A righthand thread is one that advances into a nut when turned clockwise (figure a). A lefthand thread is on the advances into a nut when turned counterclockwise (figure b). A thread is always considered to be righthanded unless specified otherwise. A lefthanded thread is always labeled (LH) on a drawing. (I) Main parameters of threads: Single and Multiple Threads: A single thread is posed of one ridge (脊 ) and the lead is equal to the pitch (齒距 ) (figure a). A double thread is posed of two ridges and the lead is equal to twice the pitch (figure b). A triple thread is posed to three ridges and the lead is equal three times the pitch (figure c). Three diameters： ｄ (Major Dia.(大徑 )－ Standard Dia.(標準直徑 )) ； ｄ 1(Minor Dia. (小徑 )) ； ｄ 2(Pitch Dia. (中徑 )) Two heights： p(pitch, 螺距 )；Ｓ (Lead, 導程 ) ； ｎ (Number of threads, 螺旋線數 )。Part I Connections Types Static connection→Releasable connections such as thread, key and pin connections。 Nondetachable connections such as weld, bonding and riveting c onnections Motion connection→Kinematic pair 167。 Ｓ＝ n p。 a— (Thread angle, 牙型斜角 )。 Sawtooth thread (鋸齒形 ) 1. Connecting (triangular) threads Plain thread(普通螺紋 ): α＝ 60176。 →tight (Metric system, 米制） →α＝ 60176。 β＝ 15176。 βw＝ 3176。 └Rectangular thread (R) α＝０ 176。 ) Working surface Feed screw of a machine tool Forcing press (壓力機 ) I． Fundamental types of the threaded connection* 167。 Round nut with grooves Gasket (墊片 )－ Flat gasket(平墊片 ) ； Spring shim (彈簧墊片 )； Bevel washer (斜墊片 )； Spherical washer (球形墊片 ) According to GB/T , ponents of threaded connections includes three accuracy classes, ., Aclass, Bclass and Cclass. Aclass has the highest degree of accuracy, it is applied for important thread connections requiring exact fit and vibrationproof； Bclass is used to thread connections subjected to heavy loads or fluctuating loads and those needing frequent adjustment or dismounting. ； Cclass is often used to ordinary thread connections. 167。 5— 4 antiloose of thread connection Tightened→ψ≤ ?v(selflock) →antiloose？ If impact, vibration and variable loads happen, friction may disappear, so that selflock by friction is unreliable, therefore, antiloose is necessary Friction antiloose: Maintain longitudinal and lateral pressure between contact area of threads→ resistance moment will not disappear Mechanical antiloose→Constrain the screw pair by the metal elements being easy to replace Undetachable antilose→weld, riveting and bonding Antilose method ： Prevent screw pair from relative turning I Strength calculation of loose bolt conn. (noＦ 0) Tight bolt conn.: have pretightening force and operating tension Loose bolt conn.: no pretightening force, only operating tension ? ?? ??????FddF44121???167。 mbbCCC?—— Relative stiffness of the