+ 86 13588290489

Tots els pobles
EN

Notícies

Notícies populars

Què és el cargol

Temps: 2020-07-10 Comentari: 41

A screw, or bolt, is a type of fastener, typically made of metal, and characterized by a helical ridge, known as a male thread (external thread) or just thread, wrapped around a cylinder. Some screw threads are designed to mate with a complementary thread, known as a female thread (internal thread), often in the form of a nut or an object that has the internal thread formed into it. Other screw threads are designed to cut a helical groove in a softer material as the screw is inserted. The most common uses of  Screws  are to hold objects together and to position objects.

Un cargol tindrà gairebé sempre un cap en un extrem que conté una forma especialment formada que permet girar-la o accionar-la amb una eina. Les eines habituals per accionar cargols són els tornavisos i les claus. El cap sol ser més gran que el cos del cargol, cosa que impedeix que el cargol sigui conduït més profund que la longitud del cargol i proporcionar una superfície de suport. Hi ha excepcions; per exemple, Cargols de carro have a domed head that is not designed to be driven; set screws often have a head smaller than the outer diameter of the screw; J- Bolts  have a J-shaped head which is not designed to be driven, but rather is usually sunk into concrete allowing it to be used as an anchor bolt. The cylindrical portion of the screw from the underside of the head to the tip is known as the shank; it may be fully threaded or partially threaded.[1] The distance between each thread is called the "pitch".

The majority of screws are tightened by clockwise rotation, which is termed a right-hand thread; a common mnemonic device for remembering this when working with screws or bolts is "righty-tighty, lefty-loosey." Screws with left-hand threads are used in exceptional cases. For example, when the screw will be subject to counterclockwise torque (which would work to undo a right-hand thread), a left-hand-threaded screw would be an appropriate choice. The left side pedal of a bicycle has a left-hand thread.

More generally, screw may mean any helical device, such as a clamp, a micrometer, a ship's propeller or an Archimedes' screw water pump.


Diferenciació entre cargol i cargol
Un cargol amb femella quadrada
Un cargol estructural amb rosca i rosca hexagonal.

There is no universally accepted distinction between a screw and a bolt. A simple distinction that is often true, although not always, is that a bolt passes through a substrate and takes a nut on the other side, whereas a screw takes no nut because it threads directly into the substrate. Machinery's Handbook describes the distinction as follows:

Un cargol és un element de subjecció roscat externment dissenyat per a la inserció a través de forats de les peces muntades i que normalment es pretén estrenyre o alliberar torçant una femella. Un cargol és un element de subjecció roscat externment que es pot inserir en forats de les parts muntades, aparellar-se amb un fil intern preformat o formar el seu propi fil, i apretar-lo o alliberar-lo torçant el cap. Un tancament roscat externment que no es pot girar durant el muntatge i que només es pot apretar o alliberar torçant una femella és un pern. (Exemple: Cargols de cap rodó, Perns de rastreig, cargols de llaurar.) Un cargol de rosca exterior que té forma de rosca que prohibeix el muntatge amb una femella amb un fil recte de longitud de pas múltiple és un cargol. (Exemple: Cargols de fusta, Cargol de cargol.) [2]

Aquesta distinció és coherent amb ASME B18.2.1 i algunes definicions del diccionari per a cargol [3] [4] i cargol. [5] [6] [7]

The issue of what is a screw and what is a bolt is not completely resolved with Machinery's Handbook distinction, however, because of confounding terms, the ambiguous nature of some parts of the distinction, and usage variations.[8][not in citation given] Some of these issues are discussed below:
Cargols de màquina

ASME standards specify a variety of "Machine Screws"[9] in diameters ranging up to 0.75 in (19.05 mm). These fasteners are often used with   Nuts  as well as driven into tapped holes. They might be considered a screw or a bolt based on the Machinery's Handbook distinction. In practice, they tend to be mostly available in smaller sizes and the smaller sizes are referred to as screws or less ambiguously as machine screws, although some kinds of machine screw can be referred to as stove bolts.
Cargols hexagonals

La norma ASME B18.2.1-1996 especifica els cargols de capçal hexagonal que tenen una mida d'entre 0.25 i 3 mm de diàmetre. Aquests elements de fixació són molt similars a Perns hexagonal. They differ mostly in that they are manufactured to tighter tolerances than the corresponding bolts. Machinery's Handbook refers parenthetically to these fasteners as "Finished Perns hexagonals".[10] Reasonably, these fasteners might be referred to as bolts, but based on the US government document Distinguishing Bolts from Screws, the US government might classify them as screws because of the tighter tolerance.[11] In 1991 responding to an influx of counterfeit fasteners Congress passed PL 101-592[12] "Fastener Quality Act" This resulted in the rewriting of specifications by the ASME B18 committee. B18.2.1[13] was re-written and as a result they eliminated the "Finished Hex Bolts" and renamed them the "Hex Cap Screw"-a term that had existed in common usage long before, but was now also being codified as an official name for the ASME B18 standard.
Cargols de cargol i cargols de capçal

These terms refer to fasteners that are designed to be threaded into a tapped hole that is in part of the assembly and so based on the Machinery's Handbook distinction they would be screws. Here common terms are at variance with Machinery's Handbook distinction.[14][15]
Cargol retardat
Cargols de retard, també anomenats perns de retard
Una vista lateral

Els cargols de retard (també anomenats cargols de retard, encara que es tracta d’un nom incorrecte) són bàsicament cargols de fusta grans. Els cargols de retard de cap quadrat i els de cargol hexagonal estan coberts per les normes ASME B18.2.1, i el cap sol ser un hexagonal extern. Un pern de retard típic pot variar de diàmetre des de 1 mm fins a 4 mm i longituds de 6.35 a 1 mm o més, amb els fils gruixuts. d’un cargol de fusta o de cargol de xapa (però més gran).

Els materials solen ser substrats d'acer al carboni amb un recobriment de galvanització de zinc (per a la resistència a la corrosió). El recobriment de zinc pot ser brillant (galvanitzat), groc (galvanitzat) o galvanitzat en calent de color gris opac. Els perns de retard s’utilitzen per ajuntar l’emmarcament de la fusta, per endarrerir els peus de la maquinària als terres de fusta i per a altres aplicacions de fusteria pesada. L'adjectiu de lag va provenir d'un primer ús principal d'aquests elements de fixació: la fixació de lags com ara barres de barril i altres parts similars. [16]

These fasteners are "screws" according to the Machinery's Handbook criteria, and the obsolescent term "lag bolt" has been replaced by "lag screw" in the Handbook.[17] However, in the minds of many tradesmen, they are "bolts", simply because they are large, with hex or square heads. In the United Kingdom and Australia, lag screws are known as coach screws.
Normes governamentals dels EUA

The US government made an effort to formalize the difference between a bolt and a screw because different tariffs apply to each.[18] The document seems to have no significant effect on common usage and does not eliminate the ambiguous nature of the distinction between screws and bolts for some threaded fasteners. The document also reflects (although it probably did not originate) significant confusion of terminology usage that differs between the legal/statutory/regulatory community and the fastener industry. The legal/statutory/regulatory wording uses the terms "coarse" and "fine" to refer to the tightness of the tolerance range, referring basically to "high-quality" or "low-quality", but this is a poor choice of terms, because those terms in the fastener industry have a different meaning (referring to the steepness of the helix's lead).
Qüestió històrica

Els antics estàndards USS i SAE definien els cargols de tap com a fixacions amb varetes que estaven roscades al cap i els cargols com a fixacions amb varetes parcialment sense roscar. [19] La relació d’aquesta regla amb la idea que un cargol per definició pren una rosca és clara (perquè s’esperava que la secció sense rosca de la canya, que s’anomena empunyadura, passés pel substrat sense enfilar-s’hi). Ara és una distinció obsoleta.
Vocabulari controlat versus llenguatge natural

The distinctions above are enforced in the controlled vocabulary of standards organizations. Nevertheless, there are sometimes differences between the controlled vocabulary and the natural language use of the words by machinists, auto mechanics and  Others . These differences reflect linguistic evolution shaped by the changing of technology over centuries. The words bolt and screw have both existed since before today's modern mix of fastener types existed, and the natural usage of those words has evolved retronymously in response to the technological change. (That is, the use of words as names for objects changes as the objects themselves change.) Non-threaded fasteners predominated until the advent of practical, inexpensive screw-cutting in the early 19th century. The basic meaning of the word screw has long involved the idea of a helical screw thread, but the Archimedes screw and the screw gimlet (like a corkscrew) preceded the fastener.

La paraula cargol també és una paraula molt antiga i es va utilitzar durant segles per referir-se a barres metàl·liques que passaven pel substrat per subjectar-les a l’altra banda, sovint mitjançant mitjans no roscats (arrauliment, soldadura de forja, fixació, falca, etc.). ). La connexió d’aquest sentit amb el sentit d’un cargol de porta o de ballesta és evident. Al segle XIX, els cargols subjectats mitjançant rosques eren sovint anomenats cargols en contradicció amb els cargols de tancament.

In common usage, the distinction (not rigorous) is often that screws are smaller than bolts, and that screws are generally tapered while bolts are not. For example, cylinder head bolts are called "bolts" (at least in North American usage) despite the fact that by some definitions they ought to be called "screws". Their size and their similarity to a bolt that would take a nut seem linguistically to overrule any other factors in this natural word choice proclivity.
Altres distincions

Bolts have been defined as headed fasteners having external threads that meet an exacting, uniform bolt thread specification (such as ISO metric screw thread M, MJ, Unified Thread Standard UN, UNR, and UNJ) such that they can accept a non-tapered nut. Screws are then defined as headed, externally threaded fasteners that do not meet the above definition of bolts.[citation needed] These definitions of screw and bolt eliminate the ambiguity of the Machinery's handbook distinction. And it is for that reason, perhaps, that some people favor them. However, they are neither compliant with common usage of the two words nor are they compliant with formal specifications.

Una possible distinció és que un cargol està dissenyat per tallar el seu propi fil; no necessita accés ni exposició al costat oposat del component al qual es fixa. Aquesta definició de cargol es reforça encara més amb la consideració dels desenvolupaments de fixacions, com ara Tek Screws per a revestiments de sostre, autoperforats i cargols autorroscants per a diverses aplicacions de subjecció metàl·lica, cargols de barres de sostre per reforçar la connexió entre la barra de sostre i la biga, cargols de coberta, etc. D'altra banda, un cargol és la part mascle d'un sistema de subjecció dissenyat per ser acceptat per un endoll (o femella) pre-equipat del mateix disseny de rosca.


anterior: Rebló

Següent: cap