Name: square-thread screw mechanics and friction
Uploaded: 2023-09-22T11:49:29.000Z
Duration: 1 min 17 s
Channel: JoVE

La plupart des vis sont caractérisées par une crête hélicoïdale et sont couramment utilisées comme fixations ; les vis à filetage carré sont souvent utilisées dans les machines pour transmettre la puissance ou le mouvement entre les pièces.
Considérez un vérin avec une vis à filetage carré portant une charge. Lorsqu’une force est appliquée au niveau de la poignée, la vis tourne et la charge est soulevée.
La vis peut être considérée comme un arbre cylindrique avec une crête carrée inclinée enroulée dessus.
La distance entre les crêtes de deux filetages adjacents est le pas, et la distance à laquelle la vis avance en un tour est connue sous le nom de son avance.
Lorsque le fil est déroulé d’un tour, il ressemble à une rampe inclinée avec un angle. L'angle d'inclinaison du filetage est appelé angle d'attaque et est exprimé en termes de rayon de filetage moyen et d'avance.
Étant donné que la force de frottement entre les surfaces est indépendante de la surface de contact, la vis est représentée par un bloc sur le filetage du vérin.
L’angle entre la force de réaction et la normale au fil est l’angle de frottement.

<ol>
	<li>Hibbeler, R.C. (2016). Mécanique du génie : Statique. Quatorzième édition, New Jersey : Pearson. p. 432.</li>
	<li>Meriam, J.L., Kraige, L.G. et Bolten, J.N. (2016). Mécanique de l’ingénierie : statique et dynamique. Huitième édition, Singapour : John Wiley & Sons. P. 354 et 355.</li>
	<li>Beer, F.P., Johnston, E.R., Mazurek, D.F., Cornwell, P.J. et Self, B.P. (2016). Mécanique vectorielle pour les ingénieurs. Onzième édition, New York : McGraw-Hill Education. P. 450 et 451.</li>
</ol>

forces de frottement sur les vis

Frictional Forces on Screws

Les vis se caractérisent par une crête hélicoïdale connue sous le nom de filetage enroulé autour d'un axe cylindrique. Elles sont couramment utilisées comme éléments de fixation pour maintenir des objets ensemble ou pour transmettre de la puissance et du mouvement dans les machines. Un type de vis particulièrement utile pour transmettre de la puissance est la vis à filet carré. Un cric avec une vis à filet carré est un dispositif mécanique utilisé pour soulever des charges lourdes en appliquant une force sur sa poignée. Lorsque la force est appliquée, la vis tourne, soulevant la charge. La vis peut être considérée comme un axe cylindrique avec une crête ou un filetage carré incliné enroulé autour de celui-ci. Ce filetage présente des caractéristiques spécifiques qui définissent sa fonctionnalité. La distance entre deux filets adjacents sur une vis est appelée pas. Cette mesure est cruciale car elle détermine la proximité des filets. Une autre caractéristique essentielle d'une vis est son avance, qui désigne la distance que la vis avance en une rotation complète. Lorsque le filetage d'une vis est déroulé d'une rotation, il ressemble à une rampe inclinée avec un angle spécifique. Cet angle d'inclinaison, connu sous le nom d'angle d'avance, peut être exprimé en termes du rayon moyen du filetage (la distance moyenne entre le centre de la vis et la ligne médiane du filetage) et de l'avance. L'angle d'avance est un paramètre crucial, car il affecte l'efficacité de la vis et la quantité de force requise pour la faire tourner. Pour comprendre la mécanique d'une vis à filet carré, il est utile de considérer les forces de frottement qui agissent sur la vis. Étant donné que la force de frottement entre deux surfaces est indépendante de la surface de contact, la vis peut être représentée comme un bloc sur le filetage du cric. L'angle entre la force de réaction (la force exercée par le filetage sur le bloc) et la normale au filetage (la direction perpendiculaire à la surface du filetage) est appelé l'angle de frottement. Cet angle est déterminé par les matériaux en contact et la lubrification utilisée entre eux. Le frottement entre la vis et la charge qu'elle porte joue un rôle crucial dans l'efficacité et le fonctionnement de la vis à filet carré. Les forces de frottement doivent être surmontées pour tourner la vis et soulever la charge. Cependant, ces forces fournissent également la stabilité, empêchant la vis de tourner et la charge de tomber même lorsque la force est retirée de la poignée. Cette fonctionnalité auto-verrouillante est particulièrement utile dans les applications où la vis doit maintenir la charge en place sans une force d'entrée continue. En raison de leur efficacité élevée et de leurs capacités d'auto-verrouillage, les vis à filet carré sont souvent utilisées dans les machines pour transmettre de la puissance ou du mouvement entre les pièces. Des exemples d'applications de ce type comprennent les crics, les pinces, les étaux et diverses presses. Ces vis sont conçues pour supporter des charges lourdes et fournir un mouvement doux et contrôlé.

Forces de frottement sur les vis

Les vis sont caractérisées par une crête hélicoïdale connue sous le nom de filetage enroulé autour d’un arbre cylindrique. Ils sont couramment utilisés comme attaches pour maintenir des objets ...

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Mechanical Engineering

Génie mécanique

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Friction

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square-thread screw mechanics and friction

Square-threaded screws use a helical thread to turn force into lifting motion. They are common fasteners, but they are also useful for transmitting power and motion in machines. A jack with a square-threaded screw lifts heavy loads when force is applied at the handle and the screw turns.

A screw can be viewed as a cylindrical shaft with an inclined square ridge wrapped around it. The distance between two neighboring threads is called the pitch. The lead is the distance the screw advances in one full revolution, and the lead angle is the angle of that advance when the thread is unwrapped into a ramp.

The lead angle depends on the mean thread radius, which is the average distance from the center of the screw to the centerline of the thread, and on the lead itself. This angle matters because it affects screw efficiency and the force needed to turn the screw. To study a square-threaded screw, the frictional forces acting on it must also be considered.

Because friction does not depend on contact area, the screw can be modeled as a block moving over the thread of the jack. The angle between the reaction force from the thread and the normal to the thread surface is called the angle of friction. It depends on the materials in contact and on any lubrication used between them.

Friction between the screw and the load must be overcome to raise the load. At the same time, that same friction helps keep the screw from turning back when the handle force is removed. This self-locking feature is useful when the load must stay in place without continuous force.

Square-threaded screws are valued for high efficiency and self-locking behavior. They are used in jacks, clamps, vises, and presses. These machines rely on the screw to hold heavy loads and produce smooth, controlled motion.

Square-Thread Screw Mechanics and Friction

square-thread-screw-mechanics-and-friction

dry friction

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key terms and concepts

Learn how square-threaded screws lift heavy loads, use pitch and lead, and stay self-locking through friction in jacks, clamps, vises, and presses.

Square-Thread Screw Mechanics and Friction | JoVE K12

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Square-Thread Screw Mechanics and Friction

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