Fasteners, Effects - Bolt Joints PDF

Gépelemek 1. FASTENERS, EFFECTS ▬ BOLT JOINTS Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Kötések, csavarkötés | GÉPELEMEK 1. előadás 1 Joints Gépelemek 1. A connection where a joint fixes or limits the relative movement between machine el...

Gépelemek 1. FASTENERS, EFFECTS ▬ BOLT JOINTS Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Kötések, csavarkötés | GÉPELEMEK 1. előadás 1 Joints Gépelemek 1. A connection where a joint fixes or limits the relative movement between machine elements or boundary parts. The joint task (function): fixing & limiting the relative motion of machine elements in certain directions while transffering power or force. Kötések, csavarkötés | GÉPELEMEK 1. előadás 2 Grouping of joints Gépelemek 1. By phisical principle: – Force closing (friction force) – Form closing – Material closing (welding, soldering, glueing) By assembly: – Detachable – Un-detachable By elements: – Direct connection – Traction (in-between) element connection Kötések, csavarkötés | GÉPELEMEK 1. előadás 3 Design of joints Gépelemek 1. 1. 2. Definition of load case & constraints Definition of mating surfaces (force transition surfaces: pressured surface, weakest cross section) according to the flow of flux. 3. Calculation the load per unit area (average pressure, stress) 4. Comparison to ultimate strenght (allowable stresses) → n = … (safety factor) 5. Analysis of extraordinaries – E.g..: stress calculation in useful section; calculation of ring stress; etc- Kötések, csavarkötés | GÉPELEMEK 1. előadás 4 Elements of bolted joints Gépelemek 1. Hexagon head bolt Hexagon nut Hexagon head bolt Stud bolt Hexagon nut Spring washer Spring washer Spring washer + connected parts Kötések, csavarkötés | GÉPELEMEK 1. előadás 5 Materials of bolts Gépelemek 1. The most common bolt ISO standards are: ISO 898-1:2013 - This standard specifies the mechanical and material properties of bolts, screws and studs made of carbon steel and alloy steel used in bolting assemblies. It also specifies the methods for verifying these properties. ISO 898-2:2009 - This standard applies to bolts, screws and studs made of austenitic or austenitic-ferritic stainless steel used in bolting assemblies. It specifies the mechanical and material properties of these fasteners, as well as the methods for verifying these properties. ISO 3506-1:1997 - This standard applies to stainless steel bolts, screws and studs used in bolting assemblies. It specifies the mechanical and material properties of these fasteners, as well as the methods for verifying these properties. ISO 3506-2: Corrosion-resistant stainless steel fasteners ISO 965-1: General table of tolerances ISO 1042: Chemical analysis of steels Kötések, csavarkötés | GÉPELEMEK 1. előadás 6 Some types of bolts Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 7 Materials of bolts Gépelemek 1. • The bolts are made from the following materials: 3.6; 4.6; 4.8; 5.6; 5.8; 6.8; 8.8; 10.9; 12.9 és 14.9. first number is 100-fold of the tensile strenght in MPa, second number is 10-fold of the quotient of yield strenght/tensile strenght. (e.g. In 5.6 group the material has a minimum of 500 Mpa tensile strenght, and yield strenght is 300 MPa.) • The nut strenght groups are the following: 5; 6; 8; 10; 12; 14. The number represents the 100 fold investigated stress which requires a mnimum tensile strenght of the bolt in Mpa which can be paired with the nut. Kötések, csavarkötés | GÉPELEMEK 1. előadás 8 Materials of bolts Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 9 Manufacturing of bolts Gépelemek 1. The bolts are manufactured by plastic forming • upsetting the head & body • head forming • thread rolling Kötések, csavarkötés | GÉPELEMEK 1. előadás 10 Manufacturing of bolts Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 11 The bolt joint Gépelemek 1. This joint is simultaneously force & form closing The fastening procedure: Tightening torque (spanner torque) Bolt joint Clamping force (tension force) Kötések, csavarkötés | GÉPELEMEK 1. előadás 12 Types of threads (operation) Gépelemek 1. 1. Mounting thread 2. Transmission thread 3. Transport thread 1. Mounting (Fastening) thread is probably the type of thread that most of you think of first. They are tight threads, as we find in nuts and bolts. 2. Transmission (movement) threads, on the other hand, are thread types that convert rotary motion into linear motion. 3. Nowadays, we find Transport threads in agricultural machines and in water conveyance in the form of screws. Generally 2 major types mounting (sharp or vee) threads: ISO European & Whithworth (UK-US standard) Kötések, csavarkötés | GÉPELEMEK 1. előadás 13 Types of threads (geometry) Gépelemek 1. 1.Classification based on Gender 1. Internal Thread 2. External Thread 2.Classification based on Designation 1. Connection 2. Sealing 3. Fastening 4. Special 5. Motion 3.Classification based on Handedness 1. Right handed 2. Left handed 4.Classification based on Pitch 1. Coarse Pitch 2. Fine Pitch 5.Classification based on Profile 1. Trapezoidal 2. Round 3. Triangular 4. Scalene 5. Square 6.Classification based on Start 1. Single-Start 2. Multi-Start 7.Classification based on Surface Shape 1. Cylindrical 2. Conical 8.Classification based on Scope 1. Pipe thread 2. Workshop thread Kötések, csavarkötés | GÉPELEMEK 1. előadás 14 General nomenclature Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 15 General nomenclature Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 16 Forces on threads Gépelemek 1. I. the connection between the fastening torque & tension force Operational forces when tightening a sharp threaded nut: • Mv : tightening torque • Fv : tension force • Fk : tightening perimetral force • ρ : spatial friction cone half angle • β : thread angle • α : helix angle • d2 : pitch diameter Kötések, csavarkötés | GÉPELEMEK 1. előadás 17 Forces on threads during fastening Gépelemek 1. Thread angle: 𝑝 𝛼 = arctg 𝑑2 𝜋 Friction force which hinders motion: Because of wedge effect where p is the pitch 𝐹𝑆 = 𝜇𝐹𝑁 where 𝜇 = tg𝜌 𝐹𝑁 ′ 𝐹𝑁 = 𝛽 cos 2 Introducing apparent half cone angle: 𝜇 ′ ′ 𝜌 = 𝑎𝑟𝑐𝑡𝑔𝜇 = 𝑎𝑟𝑐𝑡𝑔 𝛽 cos 2 Essential perimetral force for nut tightening Fk 𝐹𝑘 = 𝐹𝑣𝑡𝑔(𝛼 + 𝜌′ ) Kötések, csavarkötés | GÉPELEMEK 1. előadás 18 Forces on threads during loosening Gépelemek 1. Calculation of loosening perimetral force: − If the joint is self-locking, is then the perimetral force: 𝛼 ≤ 𝜌′ 𝐹𝑘 = 𝐹𝑣𝑡𝑔(𝛼 − 𝜌′ ) − If the joint is not self-locking 𝛼 > 𝜌′ then the nut twists off the bolt on its own. Kötések, csavarkötés | GÉPELEMEK 1. előadás 19 Tightening torque Gépelemek 1. The tightening torque is calculated from the perimetral force on the thread: 𝑀𝑣 = 𝐹𝑣 𝑑2 𝑡𝑔(𝛼 ± 𝜌′ ) 2 The frictional torque derived from the friction on the bearing surface of the nut during tightening: 𝑑𝑎 𝑀𝑎 = 𝐹𝑣𝜇𝑎 2 where da : middle diameter of bearing surface of the nut μa : friction coefficient on bearing surface of the nut Total tightening torque of the nut: 𝑑2 𝑑𝑎 ′ 𝑀 = 𝐹𝑣 𝑡𝑔(𝛼 ± 𝜌 ) + 𝜇𝑎 2 2 Kötések, csavarkötés | GÉPELEMEK 1. előadás 20 Klein diagram Gépelemek 1. The figure shows the tightening torque versus tension force at the two boundary values of friction coefficient. The required torque can be achieved with a certain deviation (e.g.: ± 3 %) , therefore the minimum & maximum tension force can be calculated. Kötések, csavarkötés | GÉPELEMEK 1. előadás 21 Load carrying capacity of the joint Gépelemek 1. Bolt joint as a form closing joint Load capacity of bolt by tension force. (based on study of joints) Kötések, csavarkötés | GÉPELEMEK 1. előadás 22 Load carrying capacity of the joint Gépelemek 1. 1. Load case of the bolt: is Fv tension force 2. Mating surfaces: a. load transmission surface (Ap ) b. veakest cross section (Aτ ) 𝐷 2 − 𝑑32 𝐴𝑝 = 𝜋𝑖 4 𝐴𝜏 = 𝑑3 𝜋𝑚 where i : thread number of the nut m: height of the nut Kötések, csavarkötés | GÉPELEMEK 1. előadás 23 Load carrying capacity of the joint Gépelemek 1. 3. Determination of the load per unit area: 𝑝𝑎𝑣𝑒𝑟𝑎𝑔𝑒 = 𝐹𝑣 𝐴𝑝 𝜏𝑎𝑣𝑒𝑟𝑎𝑔𝑒 = 𝐹𝑣 𝐴𝜏 4. Comparing to boundary state (as a safety factor): 𝑝𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝑛= 𝑝𝑎𝑣𝑒𝑟𝑎𝑔𝑒 𝜏𝑎𝑙𝑙𝑜𝑤𝑎𝑏𝑙𝑒 𝑛= 𝜏𝑎𝑣𝑒𝑟𝑎𝑔𝑒 Kötések, csavarkötés | GÉPELEMEK 1. előadás 24 Load carrying capacity of the joint Gépelemek 1. 5. Analyzing extraordinaries: a. Load distribution on the thread Solutions for the load distribution smoothing Kötések, csavarkötés | GÉPELEMEK 1. előadás 25 Load carrying capacity of the joint Gépelemek 1. 5. Analyzing extraordinaries: b. Stress in the threaded bolt after tightening the nut Stress from tension force: 𝐹𝑣 𝜎= 𝐴𝜎 where 𝑑12 𝜋 𝐴𝜎 = 4 Stress on the threads from tightening torque: 𝑀𝑣 𝜏= 𝐾𝑝 where 𝑑13 𝜋 𝐾𝑝 = 16 The equivalent stress based on Mohr”s theory: 𝜎𝑟 = 𝜎 2 + 4𝜏 2 Kötések, csavarkötés | GÉPELEMEK 1. előadás 26