Name: screw torque and self-locking
Uploaded: 2023-09-22T11:49:29.000Z
Duration: 1 min 21 s
Channel: JoVE

Si consideri un albero di vite a filettatura quadrata con un raggio medio di 20 millimetri e un passo di 10 millimetri a contatto con un ingranaggio a piastra con raggio medio di 35 millimetri. Il coefficiente di attrito statico tra la vite e l'ingranaggio è 0,3.
Valutare la coppia di resistenza sull'ingranaggio a piastre che può essere sovradimensionata quando all'albero viene applicato un momento torsionale di otto newton-metro.
Inizialmente, calcolare l'angolo di attrito statico utilizzando il coefficiente di attrito statico e determinare l'angolo di attacco sostituendo i valori di piombo e raggio medio.
Per un movimento imminente verso l'alto, la forza assiale sviluppata nell'albero può essere determinata sostituendo i valori corrispondenti.
La coppia di resistenza sull'ingranaggio a piastre è uguale al prodotto della forza assiale dell'albero e del raggio medio dell'ingranaggio.
Sostituendo i valori, è possibile determinare la coppia di resistenza che può sovrastare il momento torsionale applicato.
In questo caso, l'angolo di attrito statico è maggiore dell'angolo di attacco. Quindi l'albero è autobloccante anche se il momento viene rimosso.

<ol>
	<li>Hibbeler, R.C. (2016). Ingegneria Meccanica: Statica. Quattordicesima edizione, New Jersey: Pearson. Pagine 434-437.</li>
</ol>

vite: risoluzione dei problemi

In ingegneria meccanica, l'interazione tra un albero filettato a vite e una ruota piana, comporta l'analisi della coppia resistente sulla ruota piana che può essere sopraffatta quando viene applicato un determinato momento torsionale all'albero. Per comprendere meglio questo concetto, consideriamo una situazione generica con un albero filettato a vite con un dato raggio medio e passo e una ruota piana con un raggio medio specifico. Viene anche fornito il coefficiente di attrito statico tra la vite e la ruota.

Per valutare la coppia resistente sulla ruota piana, che può essere sopraffatta quando viene applicato un certo momento torsionale all'albero, il primo passo consiste nel calcolare l'angolo di attrito statico utilizzando il rispettivo coefficiente di attrito. L'angolo di attrito statico, indicato come θ, è l'angolo la cui tangente è uguale al coefficiente di attrito statico.

Successivamente, l'angolo di passo viene determinato sostituendo i valori del passo e del raggio medio. È uguale al rapporto tra il passo e la circonferenza dell'albero.

La forza assiale, indicata come F, è la forza che agisce lungo l'asse dell'albero che fa ruotare la ruota piana. Per un moto imminente in una determinata direzione, la forza assiale sviluppata nell'albero può essere determinata utilizzando una formula che coinvolge il momento torsionale, l'angolo di attrito statico, l'angolo di passo e il raggio medio.

<img alt="Equation 1" src="/files/ftp_upload/14321/14321_PT_Equation_1v2.svg" style="text-align: center; height: 30px;" />

La coppia resistente sulla ruota piana, è uguale al prodotto della forza assiale dell'albero per il raggio medio della ruota. Sostituendo i valori, è possibile determinare la coppia resistente che può sopraffare il momento torsionale applicato.

Inoltre, se l'angolo di attrito statico è maggiore dell'angolo di passo, l'albero è autobloccante anche se il momento viene rimosso.

Infine, è possibile determinare se l'albero è autobloccante attraverso una serie di calcoli che coinvolgono l'angolo di attrito statico, l'angolo di passo, la forza assiale e la coppia resistente. Questa analisi è fondamentale per comprendere il comportamento meccanico di alberi e ingranaggi in diverse applicazioni ingegneristiche.

Vite: Risoluzione dei problemi

Nell'ingegneria meccanica, l'interazione tra un albero a vite filettato e un ingranaggio a piastre comporta l'analisi della coppia di resistenza sull'ingranaggio a piastre che ...

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Ingegneria Meccanica

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Screw: Problem Solving

screw torque and self-locking

Screw torque and self-locking are analyzed by looking at a threaded screw shaft and a plate gear. The shaft has a mean radius and a lead. The plate gear also has a mean radius. The coefficient of static friction between the screw and the gear is part of the setup.

The first step is to find the static friction angle, φ. This angle is defined by the coefficient of static friction. Next, the lead angle is calculated from the lead and the mean radius of the shaft. It gives the screw geometry needed for the torque analysis.

The axial force, F, acts along the axis of the shaft and drives the plate gear to rotate. For impending motion in a chosen direction, this force is found from a formula that uses the torsional moment, static friction angle, lead angle, and mean radius. The resisting torque on the plate gear is then the axial force multiplied by the gear’s mean radius.

By substituting the given values, the resisting torque can be determined and compared with the applied torsional moment. The same calculations also show whether the shaft is self-locking. If the static friction angle is greater than the lead angle, the shaft stays locked even after the moment is removed.

Screw Torque and Self-Locking

dry friction

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screw: problem solving

Screw torque and self-locking are analyzed by looking at a threaded screw shaft and a plate gear. The shaft has a mean radius and a lead. The plate gear also has a mean radius. The coefficient of static friction between the screw and the gear is part of the setup. The first step is to find the static friction angle, φ. This angle is defined by the coefficient of static friction. Next, the lead angle is calculated from the lead and the mean radius of the shaft. It gives the screw geometry...

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key terms and concepts

Learn how to calculate axial force, resisting torque, and self-locking for a threaded screw shaft and plate gear using friction and lead angle.

Screw Torque and Self-Locking | JoVE K12

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mechanical engineering

Screw Torque and Self-Locking

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