如果螺栓擰緊的程度沒有極限,擰緊后要退半圈嗎?

　　擰螺栓的時候真的要擰緊后再退回來半圈嗎?不然。我們說了,擰螺栓的時候一旦突破了極限,進入了屈服階段,螺栓就會永久變形,此時再退回半圈已經(jīng)沒有作用了。相反,退回之后的螺栓會失去一部分韌性,反而會更易折斷。

　　如果螺栓擰緊的程度并沒有突破極限,那么退回半圈就更是沒有必要,那只會讓螺栓松動。

　　很多人在固定機械設(shè)備時,會把螺栓擰到不能擰動為止,這種方式好嗎?也不完全是。那也有人說,螺栓在擰緊后再退半圈,這樣才能更加的緊固,這種說法對嗎?有什么科學依據(jù)嗎?其實生活中有很多信奉者的人都會這樣認為,其中的科學依據(jù)又在哪里呢?

　　一個擰好的螺栓受到兩個力的作用,一個是向下的,一個是向上的。螺栓順著螺紋旋轉(zhuǎn)而下,在與螺紋接觸的過程中產(chǎn)生了一個向下的軸力。

　　與此同時,還有一個與向下的軸力相對應的向上的力了,這個力來自于螺帽與下方平面接觸所產(chǎn)生的向上的分布力。一個擰緊的螺栓應該保證這一上一下兩個力是相互平衡的。由于螺栓的功用,制造螺栓的材料具有兩個方面的要求,一個就是剛性,另一個則是韌性,二者缺一不可。

　　但是所有的韌性材料都有著一個共性,那就是對于應力的承受是有一個極限的。在力學上對于這個極限是用應力應變曲線來表示。我們沒有必要說得過于深奧。我們只需要知道在擰螺栓的過程中,螺栓作為一種彈性零件,其彈性是會發(fā)生作用的。

　　隨著螺栓被逐漸擰緊,螺栓的彈性作用會接近一個極限,一旦突破了這個極限,螺栓就會從彈性階段進入到屈服階段。

　　螺栓一旦進入到屈服階段,就會產(chǎn)生永久的變形,這種變形是不可逆的,也就是說螺栓會失效。在現(xiàn)實生活中,當我們不斷擰緊螺栓時會出現(xiàn)脫扣的現(xiàn)象就是這種原因造成的,而且一旦脫扣,就不可能再次擰上,因為螺栓已經(jīng)永久變形了,可見,螺栓并不是擰得越緊越好。

　　那什么時候螺栓在擰緊后可以再退回半圈呢?

　　要知道,沒有擰緊的螺栓會在使用過程中因振動的原因越來越松。所以無論螺栓是否擰緊突破了極限,退回半圈都是有害無益的。當然,有一種情況例外,那就是有墊片的時候。有些東西會給螺栓配備墊片。

　　那么這薄薄的環(huán)形小金屬片的作用到底是什么呢?其實這個金屬片的作用就相當于一個彈簧,目的也是要增加彈性。增加彈性的目的是為了讓整個組件更加堅固。但是,墊片作為一種彈簧組件,其承受力同樣也是有限的。所謂彈簧,就是擠壓之后,會變形,而由于自身彈性的關(guān)系,在壓力消除之后又會恢復,但是彈簧的恢復力是有極限的。

　　當墊片所承受的壓力過大,以至于超過極限的時候,其彈簧作用就會消失,那么這個墊片的存在也就是多余的了。

　　而為了能夠保持墊片的彈性作用,讓整個組件更加堅固,在擰緊螺栓之后,我們可以退回半圈,以便于保持墊片的彈性,這更有利于整個組件的堅固。不過前提是必須要確保螺栓并沒有因為過緊而變形。

　　那么我們怎么才能夠確保螺栓不會擰得太緊呢?在進行精密儀器制造的時候,我們要使用可以測量力道的扭力扳手,而在日常生活中,這樣做就有些多此一舉了。在日常生活中,擰螺栓主要還是靠經(jīng)驗和手感,另外不要被強迫癥左右,不要一直擰、一直擰。不管有沒有墊片,螺栓并不是擰得越緊就越好。對于沒有墊片的螺栓而言,擰緊后再退半圈的操作是錯誤的。

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　　The bolt is not tightened as much as possible. Do you need to back off half a turn after tightening?

　　Do you really need to screw down the bolt and back half a turn? Otherwise. We have said that once the bolt breaks through the limit and enters the yield stage, the bolt will be permanently deformed. At this time, another half turn back has no effect. On the contrary, the returned bolt will lose part of its toughness and be more likely to break.

　　If the tightening degree of the bolt does not exceed the limit, it is unnecessary to return half a turn, which will only loosen the bolt.

　　When many people fix the mechanical equipment, they will screw the bolt to the point where it can't be screwed. Is this a good way? Not exactly. It's also said that bolts should be tightened and then back half a circle. Is that right? Is there any scientific basis? In fact, there are many believers in life who think so. What's the scientific basis?

　　The tighter the bolt, the better? Or half a turn back?

　　A screwed bolt is affected by two forces, one is downward and the other is upward. The bolt rotates down the thread, creating a downward axial force in contact with the thread.

　　At the same time, there is an upward force corresponding to the downward axial force, which comes from the upward distribution force generated by the contact between the nut and the lower plane. A tightened bolt should ensure that the upper and lower forces are balanced with each other. Due to the function of bolts, the materials for manufacturing bolts have two requirements, one is rigidity, the other is toughness, both of which are indispensable.

　　But all ductile materials have a common feature, that is, there is a limit to the stress bearing. In mechanics, the limit is expressed by stress-strain curve. We don't need to be too deep. We only need to know that in the process of screwing the bolt, as an elastic part, its elasticity will take effect.

　　As the bolt is tightened gradually, the elastic action of the bolt will approach a limit. Once the limit is broken, the bolt will enter the yield stage from the elastic stage.

　　Once the bolt enters the yield stage, it will produce permanent deformation, which is irreversible, that is to say, the bolt will fail. In real life, when we tighten the bolt continuously, the phenomenon of tripping will occur. Once the bolt is tripped, it is impossible to screw it on again, because the bolt has been permanently deformed. It can be seen that the bolt is not tightened as tightly as possible.

　　When can the bolt be returned half a turn after tightening?

　　It is necessary to know that the bolts that are not tightened will become looser and looser due to vibration during use. So whether or not the bolt is tightened beyond the limit, half a turn back is harmful and useless. Of course, there is an exception, that is, when there is gasket. Some things will gasket the bolts.

　　So what's the function of the thin ring-shaped small metal sheet? Actually, the function of the metal sheet is equivalent to a spring, and the purpose is to increase the elasticity. The purpose of increasing flexibility is to make the whole component more robust. However, as a spring component, the bearing force of gasket is also limited. The so-called spring, after extrusion, will deform, and because of its own elastic relationship, it will recover after the pressure is eliminated, but the recovery force of the spring is limited.

　　When the pressure on the gasket is too large to exceed the limit, the spring effect will disappear, so the existence of the gasket is redundant.

　　In order to maintain the elastic function of the gasket and make the whole assembly more solid, after tightening the bolt, we can return half a circle to maintain the elasticity of the gasket, which is more conducive to the firmness of the whole assembly. However, the premise is to ensure that the bolt is not deformed due to over tightening.

　　So how can we make sure that the bolts are not too tight? When making precision instruments, we need to use a torque wrench that can measure the torque. In daily life, this is a little redundant. In daily life, screw bolt mainly depends on experience and hand feeling. In addition, don't be around obsessive-compulsive disorder, and don't screw bolt all the time. No matter whether there is gasket or not, the tighter the bolt is, the better. For the bolt without gasket, it is wrong to screw it down for another half turn.