Four Disadvantages of screwed joints: 1) Screwed joints are weaker than welded joint 2) Screwed joints weakens( due to holes) the parts that are to be joined. 3) Stress concentration in the threaded portion of screw makes them weak. 4) Locking arrangement is required in case of vibrations
bolts of uniform strength: if a shank dia.is reduced to a core dia.as shown in fig. the stress become same through out the length of the bolt. Hence impact energy is distributed uniformly throughout the bolt length, thus relieving the threaded portion of high stress. The bolt in this way becomes stronger and lighter. This type of bolt is known as bolt of uniform strength.Another method of obtaining the bolt of uniform strength is shown in fig.in this method, instead of reducing the shank dia.an axial hole is drilled through the head down to
Strength equation of double parallel fillet weld= throat area x allowable shear stress P= 2x 0.707x Sw x lwx Ʈ =1.414 x Sw x lwx Ʈ (1mark) Strength equation of single transverse fillet weld
P =throat area x allowable tensile stress P= 0.707x Sw x lw x σ
Horizontal component of 45 KN, WH= 45Sin 600 =45x 0.866=38971N and vertical component of 45 KN, Wv,= 45xcos600 =45x0.5=22500N Direct tensile load in each bolt,Wt1= WH /5=38971/5=7794.20N Turning moment due to WH about G TH = WHx 25=38971x25=974275N (anticlockwise) direct shear load on each bolt =Ws=Wv/5 =22500/5=4500N Turning moment due to Wv about edge of the bracket, Tv= Wvx175=22500x175=3937500N-mm( clockwise( clockwise) Net turning moment =3937500-974275=2963225N---------(I) total moment of the load on the bolts @ th tilting edge = 2w x(L1) 2 + 2w x(L2) 2 =2xwx(50)2 + 2xwx(150)2 = 50000
Definition w.r.t. bolts 1) Major dia.- dia. Of imaginary cylinder parallel with the crest of the thread ,it is the distance from crest to crest largest dia. of an external or internal thread 2) Minor dia.-dia. Of imaginary cylinder which just touches the roots of an external thread or smallest dia.of an external or internal screw thread 3) Pitch-distance from a point on one thread to the corresponding point on the next thread. 4) lead- distance between two corresponding points on the same helix
Consideration in design of key: 1) Power to be transmitted. 2) Tightness of fit 3) Stability of connection 4) Cost 5) Crushing failure of key: 6) shearing failure of key 7) Material of key ,shaft should be same but key should be weaker than shaft .
i) Cylinder head of the engine. (ii) Machine foundation. (iii) Assembly of fan, couplings. Any two examples (iv) Connect two bogies of the train with the turn buckle. (v) Structural bridges, pressure vessels, fly press (vi) Assembly of crank shaft and connecting rod.
Simple band brake:
Given: Length of lever l = 40 cm = 0.4m, diameter d = 40 cm = 0.4, µ = 0.25, b =0 .08 m ϴ = Angle of wrap = 5/8 x 360 = 225 x π /180 = 3.93 rad Braking torque = (T1 –T2) x r T1/T2 = e µϴ = e 0.25 x 3.93 = 2.67 Taking moments about fulcrum P x l = b x T1 500 x 0.40 = 0.08 x T1 T1 = 2500 N T2 = 2500 / 2.67 = 936.3 N Braking Torque = (2500 – 936.3) x 0.2 = 312.74 N-m
