Bolt Loosening Methods PDF

Gépelemek 1. DETACHABLE FASTENERS, LOOSENING, BOLT SECURING Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Kötések, csavarkötés | GÉPELEMEK 1. előadás 1 Engineering topics Gépelemek 1. − − − − Bolt joint modell Spring basics Pretensional tria...

Gépelemek 1. DETACHABLE FASTENERS, LOOSENING, BOLT SECURING Authors: Dr. Kerényi György Molnár László, Dr. Marosfalvi János, Dr. Horák Péter, & Dr. Baka Ernő Kötések, csavarkötés | GÉPELEMEK 1. előadás 1 Engineering topics Gépelemek 1. − − − − Bolt joint modell Spring basics Pretensional triangle Load case modells − Non-rotational loosenings − External (force) − Internal (force) − Intermediate (force) − Diversion loosening − Energy loosening − Rotational loosenings (self-slacking) − Bolt securings − Design principles Kötések, csavarkötés | GÉPELEMEK 1. előadás 2 The bolt joint spring modell Gépelemek 1. Bolted connections are one of the most common elements in construction and mechanical design. It consists of an externally threaded fastener (such as a bolt) that captures and holds other parts together and is secured with a corresponding internal thread. There are two main types of bolted connection designs: tension and shear connections Kötések, csavarkötés | GÉPELEMEK 1. előadás 3 The bolt joint spring modell Gépelemek 1. In a tension joint, the bolt and the clamped components of the joint are designed so that the applied tensile load is transmitted through the clamped component through the joint by designing an appropriate balance of joint and bolt stiffness. As well as the deformation of both elements are elastic therefore the joint can be modelled by spring system. The lineary elastic elements can be described by HOOKE”s law: Material constants: E: Young”s modulus ν: Poisson”s ratio Kötések, csavarkötés | GÉPELEMEK 1. előadás 4 Spring fundamentals Gépelemek 1. Elongation of the l lenght beam loaded by F force f : f = Fl AE The F = f (f) function is called spring characteristic, which is at lineary elastic elements the so called stiffness. (s). F N tg  = = s   f  mm  At tensioned beam the stiffness is: AE s= l Kötések, csavarkötés | GÉPELEMEK 1. előadás 5 Pre-tensioned bolt & deformed members Gépelemek 1. Before tightening After tightening Elongation of the bolt & the compression of the members. (exagerrated) Kötések, csavarkötés | GÉPELEMEK 1. előadás 6 Pre-tensioning triangle Gépelemek 1. Characteristic of the bolt & members shown together: Fv: Preload force λ1 : elongation (strain) of bolt λ2 : compression of members Kötések, csavarkötés | GÉPELEMEK 1. előadás 7 Stiffness of bolt Gépelemek 1. The bolt stud has two kind of parts: • grip lenght (l1): Ø d ; • thread lenght (l2): Ø d3. ...then elongation of bolt: Fv l1 Fv l 2 1 = + A1 E1 A2 E1 Stiffness of bolt in general: where d i2 Ai = 4 Fv E1 s1 = = n li 1  i =1 Ai cross sections of i-th part. Kötések, csavarkötés | GÉPELEMEK 1. előadás 8 Stiffness of members Gépelemek 1. The stiffness of the grip is calculated based on a simplified pressure-cone method. This method predicts the pressure distribution throughout the thickness of the grip. The pressure cone for a joint can be visualized in the diagram right. ØD Od2 v h Od1 Bolt with nut Tapped joint ( ) E 2 D 2 − d12  s2 = = 2 h 4 Fv Kötések, csavarkötés | GÉPELEMEK 1. előadás 9 Load case modells Gépelemek 1. The modell is a function of the load case in operation: – Force loosening • external • internal • Interediate – Energy type loosening – Diversion loosening Kötések, csavarkötés | GÉPELEMEK 1. előadás 10 Non-rotational loosening (External force slackening) Gépelemek 1. At external loosening the loosening force is acting below the head of bolt.. The springs are in a parallel circuit in the modell. Kötések, csavarkötés | GÉPELEMEK 1. előadás 11 Non-rotational loosening (External force slackening) Gépelemek 1. Based on the similarity of triangles we can derive the increase of the preload of bolt. (F1) because of the loosening force. Fü s1 F1 = Fü s1 + s2 Reduced force in members: s2 F2 = Fü s1 + s2 The triangle diagram Kötések, csavarkötés | GÉPELEMEK 1. előadás 12 Critical force Gépelemek 1. The critical load at which the joint fully loosens, means... F2 = Fv : s2 Fv = Fkrit s1 + s 2 where Fkrit s1 + s 2 = Fv s2 Kötések, csavarkötés | GÉPELEMEK 1. előadás 13 Critical force Gépelemek 1. How the critical force can be increased??? Fkrit ? − stiffer bolt; − softer members. Kötések, csavarkötés | GÉPELEMEK 1. előadás 14 Critical force ‒ Gépelemek 1. the stiffness increase of the bolt can be achieved by increasing the dimensions of bolt; ‒ To „soften” the members we can have these options: Kötések, csavarkötés | GÉPELEMEK 1. előadás 15 Critical force Gépelemek 1. In case of repetative load on the bolt needs to be redused!, which can be achieved by „softening” the stud of bolt. (e.g.: bolt diameter turned to minor diameter or a drilled stud bolt. We reinforce the structures in the way that we cut-off material from it!! ☺ Kötések, csavarkötés | GÉPELEMEK 1. előadás 16 Non-rotational loosening (Internal force slackening) Gépelemek 1. Loosening force is acting between the members. The springs are in a series circuit in the modell. Kötések, csavarkötés | GÉPELEMEK 1. előadás 17 Critical force Gépelemek 1. In here the increase of the preload F1 = 0 because the operational Fü force is smaller than, the preload Fv force. The critical loosening force: Fkrit = Fv The triangle diagram Until the operational Fü force does not reach the Fv force (preload) NO movement in the joint. Kötések, csavarkötés | GÉPELEMEK 1. előadás 18 Non-rotational loosening (Intermediate force slackening) Gépelemek 1. Loosening force is acting at an interediate position of the members. The springs are in a parallel&series circuit in the modell. Kötések, csavarkötés | GÉPELEMEK 1. előadás 19 Non-rotational loosening (Force type slackenings) Gépelemek 1. Engineering guidelines: 1. The critical Fkrit force is the smallest at a clear internal loosening, and this is the most critical situation from slackening point of view. In this case the critical Fkrit force is independent from the stiffness of the members. 2. The critical Fkrit force increases by applying more stiff bolts & softer members. 3. The load increase in the bolt is the smallest in case of clear internal loosening situation. 4. The load increase in the bolt can be reduced by applying soft bolts & stiff members. Kötések, csavarkötés | GÉPELEMEK 1. előadás 20 Non-rotational loosening (Force type slackenings) Gépelemek 1. Built-in examples External loosening Internal loosening Intermediate loosening Kötések, csavarkötés | GÉPELEMEK 1. előadás 21 Non-rotational loosening (Environmental slackenings) Gépelemek 1. „Diverted” loosening happens if the preload force decreases because... − heat expansion between bolts & members; − relaxation, creep; − surface smoothenings − Corrosion − Etc... In this case we can have a proper construction if both stiffnesses (bolt&members) are little. Kötések, csavarkötés | GÉPELEMEK 1. előadás 22 Non-rotational loosening (Energy slackenings) Gépelemek 1. This type occurs when an external energy (impact) gets into the bolt system. The loosening energy is the below formula W... 𝐹ü = 2𝑊(𝑠1 + 𝑠2 ) Kötések, csavarkötés | GÉPELEMEK 1. előadás 23 Non-rotational loosening (Energy slackenings) Gépelemek 1. The total slackening happens when the external (impact) energy is equal/bigger than the joint energy. (kind of a force type loosening situation) In this case we can have a proper construction if both stiffnesses (bolt&members) are little. Kötések, csavarkötés | GÉPELEMEK 1. előadás 24 Bolt securing methods Gépelemek 1. There are three commonly used bolt locking methods, which include friction locking, mechanical locking and permanent locking. Permanent locking that is called non removable locking includes welding, riveting, bonding, etc, which usually destroys threaded fasteners during disassembly and can’t be reused. Common friction locking methods include washer, self-locking nut, double nut, etc. 1. Double nut When the double nut is locked, two friction surfaces are generated. The first friction surface is between the nut and the fastener, and the second friction surface is between the nut and the nut. 2. Self locking nut Self-locking nuts are generally self-locking by friction. 3. Wedge Nord lock washer Radial serrations on outer surface of the wedge lock washer engage with the surface of the workpiece it contacts. When the locking system is subjected to dynamic load, displacement can only occur on the inner surface of the washer. Kötések, csavarkötés | GÉPELEMEK 1. előadás 25 Bolt securing methods Gépelemek 1. 4. Cotter pin and slotted nut After the nut is tightened, insert the cotter pin into the nut slot and the bolt tail hole and pull open the split pin tail to prevent the relative rotation of the nut and bolt. Slotted nuts are used together with threaded rod bolts with holes and cotter pins to prevent the relative rotation between bolts and nuts. 5. Lock washer After the nut is tightened, bend and stick the lock washer to the side of the nut and the connector to lock the nut. If two bolts need to be tightened by double interlocking, double lock washers can be used. 6. Spring washer The anti loose principle of spring washer is that after the spring washer is pressed, the spring washer will produce a continuous elastic force, which will keep a friction force between the nut and the threaded connection of the bolt, generating a torque to prevent the nut from loosening. 7. Hot melt fastening technology The hot melt fastening technology does not require pre opening and connection can be realized by direct tapping under closed profiles, which is widely used in the automotive industry Kötések, csavarkötés | GÉPELEMEK 1. előadás 26 Bolt securing methods Gépelemek 1. Securing methods protect us from slackening of the nut. Based on effects we can have: ‒ form closing; ‒ force closing; ‒ material „closing” bolt securings. Form closing solutions Kötések, csavarkötés | GÉPELEMEK 1. előadás 27 Bolt securing methods Gépelemek 1. Securing by force closing methods Taper nut Notch nut Washers Tab washer nut Lock nut (Nylock nut) Nord-Lock Prevailing torque nuts Kötések, csavarkötés | GÉPELEMEK 1. előadás 28 Bolt securing methods (Nord-lock patent) Gépelemek 1. These wedge-locking washers use tension instead of friction to assure that bolted joints are steadfast when vibration and dynamic loads occur. Kötések, csavarkötés | GÉPELEMEK 1. előadás 29 Bolt securing methods (Nord-lock patent) Gépelemek 1. Kötések, csavarkötés | GÉPELEMEK 1. előadás 30 Bolt securing methods Gépelemek 1. Bolt securing with added material After tightening glue is applied on the bolted joint elements. Kötések, csavarkötés | GÉPELEMEK 1. előadás 31 Bolt securing methods Gépelemek 1. Pre-coated bolts is a processing technology in which a microcapsule compound containing an adhesive is specially applied to the threads of screws to provide sealing and locking functionality. Reaction initiates by tightening a screw Screws are coated with a dry resin film. When screwed in, their microcapsule breaks and the contained locking ingredients seep out, causing a curing reaction. The screw, lock agent, and sealant are integrated, and an excellent effect can be achieved simply by tightening the screw. PRECOTE system (Metrikont bolt & securing systems) Met Tech bolting techiques Kötések, csavarkötés | GÉPELEMEK 1. előadás 32 Bolt securing methods Gépelemek 1. Securing with 2 kind of threads. One coarse , one fine. Because of the different helix angles the nut does not slacken. Kötések, csavarkötés | GÉPELEMEK 1. előadás 33 Engineering guidelines Gépelemek 1. Thread run-out Internal thread in sheet metall d 1 = 1,15d d) R=0,5t good b) t wrong d h t a) e) c) f) Kötések, csavarkötés | GÉPELEMEK 1. előadás 34 Engineering guidelines Gépelemek 1. Screwing into plastic tubes (screw towers with inserts) a) b) 1,6d c) d wrong Plastic sheets fixing good a) b) 1 2 c) 1 1 wrong Kötések, csavarkötés | GÉPELEMEK 1. good előadás 35 Engineering guidelines Gépelemek 1. a) Parallelism of the mating surfaces is required. c) b) d) e) Kötések, csavarkötés | GÉPELEMEK 1. előadás 36 Engineering guidelines Gépelemek 1. Supporting principle (the crown wheel mating from the front) a) Fa wrong b) Fa good Kötések, csavarkötés | GÉPELEMEK 1. előadás 37