上游充通大率 Shanghai Jiao Tong University Multiple Screw Threads2(多线螺纹) Screws s can be multiple-threaded by having two or more threads cut beside each other Double--threaded screw(双线螺纹) >lead is equal to twice the pitch,/=2p .Triple-threaded screw (三线螺纹) >lead is equal to 3 times the pitch, =3p .Advantage of multiple threads:They have >Smaller thread height >Increased lead for fast advancement of nut. .Standardized products all have single thread 16
16 Multiple Screw Threads 2（多线螺纹） •Screws can be multiple-threaded by having two or more threads cut beside each other •Double-threaded screw（双线螺纹） lead is equal to twice the pitch，l=2p •Triple-threaded screw （三线螺纹） lead is equal to 3 times the pitch, l=3p •Advantage of multiple threads: They have Smaller thread height Increased lead for fast advancement of nut. •Standardized products all have single thread
上潘充通大学 Shanghai Jiao Tong University Multiple Screw Threads2 End views Side views 1 start Single thread 旺 (a) () I Developed pitch cylinders for single-and double-start threads. 2s:arts Double thread I=n *p,n-number of threads tan 1 3s:arts Triple tread Multiple screw thread showing relation between lead L and pitch p for screws with 1.2. and 3 starts
17 Multiple Screw Threads 2 l=n p, n—number of threads m d l tan
上海充通大学 Shanghai Jiao Tong University Thread Profiles2 (b) Unified and SI profile Trapezoidal 0250 025p 统一标准米制螺纹 梯形螺纹 am0.32476p b=021651p 274 145 Whitworth Acme 0.25p 025p 惠氏螺纹，英制螺纹 英制梯形螺纹 a=032016pT=0.13733p (b) 45° Modified Square Stub Acme 0.25p 0.15p 025p 10.15p 修正矩形螺纹 短英制梯形螺纹 Square 0.3d00p Buttress Thread .25 0.25p 03627p 矩形螺纹 锯齿形螺纹 UE1D OU a=0.1631pb=0.0828p c=090720 ( (网 Figure 6.2.1 (a)Unified and M protile;(b)Whitworth:(c)modified square;(d)square:(e)trapezoidal; (f)Acme:(g)stub Acme:(h)buttress thread forms. 18
18 Thread Profiles 2 Unified and SI profile 统一标准米制螺纹 Whitworth 惠氏螺纹，英制螺纹 Modified Square 修正矩形螺纹 Square 矩形螺纹 Trapezoidal 梯形螺纹 Acme 英制梯形螺纹 Stub Acme 短英制梯形螺纹 Buttress Thread 锯齿形螺纹
上浒充通大学 Shanghai Jiao Tong University Thread Profiles2 .Of 8 thread profiles,square thread has greatest strength and efficiency It eliminates any radial component of force between screw and nut. However,it is more difficult to manufacture because of the perpendicular face >Normally takes two steps to manufacture. .Acme and Buttress profiles have low thread angles which make them easier to manufacture,and are not greatly less efficient.The buttress thread is desirable when force is to be transmitted in only one direction 19
19 Thread Profiles 2 •Of 8 thread profiles, square thread has greatest strength and efficiency It eliminates any radial component of force between screw and nut. However, it is more difficult to manufacture because of the perpendicular face Normally takes two steps to manufacture. •Acme and Buttress profiles have low thread angles which make them easier to manufacture, and are not greatly less efficient. The buttress thread is desirable when force is to be transmitted in only one direction
上海充通大学 Shanghai Jiao Tong University Thread Profiles2 .When power is to be transmitted, >Square and Acme threads are normally used (a) (b) 20
20 Thread Profiles 2 •When power is to be transmitted, Square and Acme threads are normally used Fig. 8-3