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

Большинство винтов характеризуются спиральным гребнем и обычно используются в качестве крепежа; винты с квадратной резьбой часто используются в машинах для передачи мощности или движения между деталями.
Рассмотрим домкрат с винтом с квадратной резьбой, несущий груз. Когда к рукоятке прикладывается усилие, винт поворачивается, и груз поднимается.
Винт можно считать цилиндрическим валом с наматываемым на него наклонным квадратным гребнем.
Расстояние между гребнями двух соседних резьб является шагом, а расстояние, на которое винт продвигается за один оборот, известно как его ход.
Когда нить разворачивается на один оборот, она напоминает наклонную рампу с углом. Угол наклона резьбы называется углом опережения и выражается в терминах среднего радиуса резьбы и свинца.
Поскольку сила трения между поверхностями не зависит от площади контакта, винт представлен в виде блока над резьбой домкрата.
Угол между силой реакции и нормалью к резьбе — это угол трения.

<ol>
	<li>Хиббелер, Р.К. (2016). Инженерная механика: Статика. Четырнадцатое издание, Нью-Джерси: Пирсон. С. 432.</li>
	<li>Мериам, Д.Л., Крайге, Л.Г. и Болтен, Д.Н. (2016). Инженерная механика: статика и динамика. Восьмое издание, Сингапур: John Wiley & Sons. С. 354-355.</li>
	<li>Бир, Ф.., Джонстон, Э.Р., Мазурек, Д.Ф., Корнуэлл,.Д. и Селф, Б.. (2016). Векторная механика для инженеров. Одиннадцатое издание, Нью-Йорк: McGraw-Hill Education. С. 450-451.</li>
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Силы трения на шурупах

Frictional Forces on Screws

Шурупы характеризуются спиральной ребристостью, известной как резьба, намотанной вокруг цилиндрического вала. Они широко используются в качестве крепежных элементов для соединения объектов или для передачи силы и движения в машинах. Одним из видов шурупов, особенно полезных для передачи силы, является квадратная резьба.

Домкрат с квадратной резьбой - это механическое устройство, которое используется для подъема тяжелых нагрузок путем приложения силы к его ручке. При приложении силы шуруп поворачивается, поднимая нагрузку. Шуруп можно рассматривать как цилиндрический вал с наклонной квадратной кромкой или резьбой, намотанной вокруг него. У этой резьбы есть особенности, которые определяют ее функциональность.

Расстояние между двумя соседними резьбами на шурупе называется шагом. Это измерение является критическим, поскольку оно определяет, насколько плотно резьба упакована. Другой важной характеристикой шурупа является его ход, который относится к расстоянию, на которое шуруп перемещается при одном полном обороте.

Когда резьба шурупа раскручивается на один оборот, она напоминает наклонную плоскость с определенным углом наклона. Этот угол наклона, известный как угол подъема, может быть выражен в терминах среднего радиуса резьбы (среднего расстояния от центра шурупа до центральной линии резьбы) и хода. Угол подъема является важным параметром, так как он влияет на эффективность шурупа и количество силы, необходимой для его поворота.

Для понимания механики квадратной резьбы шурупа полезно рассмотреть трения, действующие на шуруп. Поскольку трение между двумя поверхностями не зависит от площади контакта, шуруп можно представить в виде блока над резьбой домкрата. Угол между реакционной силой (силой, которую резьба оказывает на блок) и нормалью к резьбе (направлению, перпендикулярному поверхности резьбы) называется углом трения. Этот угол определяется материалами в контакте и используемой смазкой.

Трение между шурупом и нагрузкой, которую он несет, играет важную роль в эффективности и функциональности квадратной резьбы шурупа. Тренияльные силы должны быть преодолены, чтобы повернуть шуруп и поднять нагрузку. Однако эти силы также обеспечивают устойчивость, предотвращая поворот шурупа и падение нагрузки, даже когда сила удалена с ручки. Эта самозакрепляющая функция особенно полезна в приложениях, где шуруп должен удерживать нагрузку на месте без непрерывной силы подачи.

Благодаря их высокой эффективности и самозакрепляющимся возможностям, квадратные резьбовые шурупы часто применяются в машинах для передачи силы или движения между деталями. Примеры таких применений включают домкраты, зажимы, тиски и различные прессы. Эти шурупы спроектированы для выдерживания тяжелых нагрузок и обеспечивают плавное, контролируемое движение.

Винты характеризуются спиральным гребнем, известным как резьба, обернутая вокруг цилиндрического вала. Они обычно используются в качестве креплений для удержания предметов ...

Education

JoVE Core

Mechanical Engineering

Машиностроение

Unit 1

Раздел 1

Friction

Трение

KEY TERMS AND CONCEPTS

ОСНОВНЫЕ ТЕРМИНЫ И ПОНЯТИЯ

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

Dry Friction in Crates and Everyday Motion

Dry friction appears when two solid surfaces touch and try to move past each other. Students can see it when they walk, slide a box across a table, or rub their hands together. Even though it is common, the forces behind it are not easy to see. A simple crate on a rough horizontal floor helps explain the idea. When an external force pushes the crate sideways, two main forces act on it. The normal force acts perpendicular to the surface and helps balance the crate’s weight, while the frictional...

static friction

Static Friction at the Point of Slip

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kinetic friction

Sliding Friction Between Moving Surfaces

Kinetic friction is the sliding friction that acts when two surfaces move against each other. It opposes relative motion and acts parallel to the contact surface, in the opposite direction of travel. In the truck and car example, the car first stays still because static friction holds it in place. When the truck’s force becomes greater than the limiting static frictional force, the friction at the contact surface drops to a lower value. The car then begins to slide, and its speed increases. At...

characteristics of dry friction

Static and Kinetic Dry Friction

Dry friction is the resistance between two solid surfaces that move against each other without lubrication or any fluid. A common example is a gardener pushing a wheelbarrow across the ground. The wheel and the ground create dry friction that slows the motion. Before the wheelbarrow starts to move, static friction acts at the contact surface. Static friction is the force that opposes motion before slipping begins, and it helps keep the wheelbarrow stable. It is present only when there is no...

types of friction problems

Dry Friction in Crate, Ladder, and Frame Problems

Dry friction problems often focus on crates, ladders, and frames that are close to slipping. Dry friction is the force that resists relative motion, or the tendency for motion, between two surfaces in contact. In many physics and engineering problems, this force helps keep an object still or defines the point where motion is about to begin. One common case has no clear impending motion. A force may be applied to a crate, but the crate stays at rest. The friction force between the floor and the...

friction: problem solving

Friction on a Banked Road

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wedges

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frictional forces on screws

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...

upward impending motion

Screw Jack Force and Friction Analysis

A square-threaded screw jack lifts heavy loads by turning handle force into a twisting moment. Its upward motion depends on overcoming static friction between the screw threads and the jack. To study this motion, the thread can be treated as if it were a block on the groove of the jack after the thread is completely unraveled. A free-body diagram helps show the forces acting on this simplified system. The force at the handle creates a horizontal force that pushes the movable thread up the...

self-locking screw

Screw Jack Self-Locking Behavior

A square-threaded screw jack can hold a heavy load because of its self-locking behavior. This feature makes the device more reliable when it is used to lift large weights or apply a strong force. If the screw keeps its position after the turning moment is removed, the jack is self-locking. Self-locking happens because friction changes the way the forces act on the thread. The friction force reverses direction, and the reaction force moves to the other side of the thread’s normal. In this case,...

screw: problem solving

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frictional forces on flat belts

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flat belts: problem solving

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pivot bearings

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Pivot bearings support axial loads on a rotating shaft. A bearing helps two parts move relative to each other while reducing friction and wear. In this design, the pivot is placed at the end of the shaft to carry the axial thrust. The pivot surface can be flat, conical, or truncated, depending on the application. In a flat pivot bearing, the axial load is spread over the bearing area. The pressure is uniform and can be found by dividing the load by the area. To study the forces more closely,...

collar bearings

Friction Torque in Collar Bearings

Collar bearings support axial loads on rotating shafts, and their friction helps determine the torque needed to start motion. They are used in many machines and may have a single collar or multiple collars, depending on the application and load needs. For a single collar bearing under an axial load, the contact area is the ring-shaped region between the external radius and the internal radius of the collar. If the bearing is assumed to support the load evenly, the uniform normal pressure is...

journal bearings

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Journal bearings support rotating shafts and axles while helping keep them stable. They are used in machines such as engines, turbines, and pumps. Their job is to reduce friction, wear, and vibration. A journal bearing works by keeping a thin film of lubricant between the bearing surface and the rotating shaft. This film limits direct contact and lowers frictional force. The video uses a rope winch with dry or only partly lubricated journal bearings to show the idea. As the spool turns...

bearings: problem solving

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rolling resistance

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rolling resistance: problem solving

Lawn Roller Force Calculation

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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

JoVE Core Mechanical Engineering offers concise, easy-to-understand animated videos covering key topics such as equilibrium, forces, truss analysis, and structural mechanics. Explore their real-world applications, and witness these concepts in action through scientist-led experiments.

mechanical engineering

Square-Thread Screw Mechanics and Friction

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