In order to understand mechanics, we need know your “abc”. That is why this time we bring you a blog with a difference, We review some of the fundamentals of mechanics. Are you ready? Here we go.
When we start talking about the basics of mechanics we have to clarify some concepts, such as, for example, the difference between shaft and stem. A shaft is a cylindrical bar that rotates on itself, while a rod has a forward and backward movement.
The scale that measures the hardness depends on the type of material. In the case of elastomeric and thermoplastic materials the hardness scale is used. shore type A, which starts from zero numbering, corresponding to very soft materials.
The type D shore scale is intended for more rigid materials, such as polyurethane or hard plastics.
Roughness and tolerance are often confused with each other, but the two concepts are not related.
We hope this article has been of interest to you. If you have any questions, please contact us at our specialists in the field.
Index
Concepts of the fundamentals of mechanics
Shafts and rods
When we start talking about the basics of mechanics we have to clarify some concepts, such as, for example, the difference between shaft and stem. A shaft is a cylindrical bar that rotates on itself, while a rod has a forward and backward movement.
Diameter, an essential parameter to be taken into account
To define the diameter of an axle or a shank, it is necessary to imagine a cross section in the part. The figure resulting from this cut is a circumference; from this we obtain the diameter of the parts.
Units of measure
Continuing with these concepts, let's talk about units of measurement. The international measurement system is the MKS. This system has the meter (m), the kilogram (kg) and the second(s) as basic units, associated with three fundamental magnitudes, such as the mass, the length, and the time. From these, complementary units are obtained, such as, for example, the millimeter (mm) which is the most common unit in mechanics and avoids the use of too many decimal places. However, in Anglo-Saxon countries the inch is used,and is divided into halves (½”), fourths (¼”), eighths (⅛”)... and so on.The speed
The speed is a concept developed by Galileo Galilei (16th century) in the study of the motion of bodies, and is defined as the distance traveled by an object in a given time. The speed is expressed in meters per second (m/s). In the Anglo-Saxon system, feet per second (ft/s) is used. To know at what speed a shaft rotates, the number of revolutions or revolutions per minute (rpm) is counted, also known as the famous "revolutions per minute" (r.p.m.). rpm's. This speed is known as angular velocity. If we talk about speed in mechanics it is necessary to comment on the concept of the linear or peripheral speed, defined as the velocity at the periphery of the axis or tangential to the axis. It is expressed in meters per second.Force and motion
The force is defined as that action that causes changes in the movement or the structure of an object and its unit is the Newton (N). This unit owes its name to the 17th century English mathematician Sir Isaac Newton, who, through study, ruled the three laws of motion; inertia, the fundamental law of dynamics and the principle of action and reaction.Newton's second law
This law of the British mathematician states that force is the product of a mass times an acceleration. Therefore, we could define weight as the force exerted by the Earth's gravity on any object on Earth. Thus, the units of force, charge, voltage y weight are the same.The pressure
The pressure is an essential parameter for understanding mechanics and hydraulics. It is the the effect of a force acting on a surface. This is defined using the Pascal as the unit of measurement. Even so, it is an impractical unit, which usually has multiples of the Pascal. megapascal (MPa) y hectopascal (hPa). Other definitions of pressure are also used to define pressure units such as atmosphere and bar. These define a kilogram of force applied over the area of one square centimeter. The Anglo-Saxon system uses “psi” (pounds square inches), ie, one pound of force applied over the area of one square inch. A pressure can be relative o absolute.- - In the case of a pressure relative, means that is linked to a reference and we take, for example, the atmospheric pressure at sea level. From that point, we will have various levels of pressure expressed positively or negatively. The adjective “manometric” is often added to pressure because the device that measures pressure is called a manometer.
- - In the case of being absolute, The pressure reference is zero, i.e. absolute vacuum, and it is as if the body were outside the earth's atmosphere, in space.
Hardness, a mechanics foundation to be taken into account
Another basic concept when talking about the fundamentals of mechanics is the hardness. It is defined as the resistance of a material to physical change, e.g., scratching, abrasion or penetration.
The scale that measures the hardness depends on the type of material. In the case of elastomeric and thermoplastic materials the hardness scale is used. shore type A, which starts from zero numbering, corresponding to very soft materials.
The type D shore scale is intended for more rigid materials, such as polyurethane or hard plastics.
Roughness
Any sealing solution (flat gasket, O-ring, collar, retainer, wiper...) will be in contact with the sealing surface. The performance of the sealing solution chosen will be influenced by the surface finish of the sealing surface. This has a series of of irregularities that define its roughness. Roughness is a determining factor in watertightness. If a surface has a very low roughness, such as a mirror, the sealing gasket may become slippery.. On the contrary, in case of high roughness, the seal can wear prematurely. Thus, experience tells us that the surface roughness is key to the life of the joint and it is recommended that it has a roughness between a maximum and minimum value.ISO Scale
Due to the wear and tear of the components used in the parts manufacturing process, the manufactured parts will never be the same. For this reason, it is important to accept a certain tolerance in the replicated part. At these levels, the scale used to express tolerance is the following thousandth of a millimeter or micron. In the case of angles, the following are used minutes o seconds. Therefore, the ISO standard indicates tolerances that fall within the normal range and are expressed in letters, which define the tolerance, and numbers, its amplitude.
Roughness and tolerance are often confused with each other, but the two concepts are not related.