Why can’t stainless steel screws and nuts be used together?

We all know that self-tapping screws do not require nuts because they are born with cool and anti-loose skills. But you have heard that stainless steel screws cannot be used with nuts. This is why? 

Why is your stainless steel fastener locked
Precautions and methods to avoid locking
Common problems and solutions in the use of stainless steel screws

News 22416 20190222 - Why can't stainless steel screws and nuts be used together?

The reason why this is said is that, when the low temperature pipe flange is assembled, if it is fastened with stainless steel bolts and nuts, it is very easy to bite after a period of time. This is because after the screwing, the overall structure of the thread and the bolt will be slightly deformed, resulting in a tighter bite; or after a long time, the screw and the screw hole will be “fused”. At this point, if you want to remove the bolts and nuts again, you will need more force to overcome the friction of the threaded joints and overcome the energy generated by the deformation of the material and the destruction of the intermolecular polymerization. In short, it will become particularly difficult. 

In order to avoid the situation that is difficult to disassemble, we can use the following methods.

  1. You can change the material of the nut to a copper nut to avoid fusion. 
  2. Apply some grease to the screw before screwing the nut. 
  3. Anti-bite agent can be used to prevent corrosion, sintering, rust and wear of parts at high temperatures. 

In addition to stainless steel bolts can not be used with nuts, we often encounter stainless steel fastener lock-up problems in daily use, what is going on? 

Why is your stainless steel fastener locked? 

Stainless steel fasteners are often used for fastening on more expensive machine parts due to their aesthetics, durability and corrosion resistance. 

However, metal fasteners in fasteners often rust due to various reasons. Some fasteners may become completely locked when rust occurs, resulting in the failure of the fastener itself to operate, that is, it cannot be disassembled or continued. Lock the fasteners. The complete locking of the fasteners may only occur in just a few seconds… 

Today, yaang will give you a trick to let everyone use the probability of locking down to the lowest level! 

News 22416 20190222 2 - Why can't stainless steel screws and nuts be used together?

First of all, we need to know why stainless steel fasteners are locked: 

  1. If the product is not selected correctly, make sure that the mechanical properties of the product meet the requirements before use. In addition, the length of the screw is selected properly, and the nut is tightened to expose the nut one to two pitches. 
  2. Rough tooth or foreign matter If there is solder joint, other metal chips are caught between the teeth, which often leads to locking. 
  3. If the force is too strong or the locking speed is too fast, use a torque wrench or a socket wrench as much as possible. Avoid using a spanner wrench or an electric wrench. Because the electric wrench often causes the locking speed to be too fast, the temperature rises rapidly and locks up. 
  4. The direction of the force direction angle nut must be screwed perpendicular to the axis of the screw, do not tilt. 
  5. The use of flat and elastic washers can effectively prevent the problem of too tight locking. 

News 22416 20190222 3 - Why can't stainless steel screws and nuts be used together?

Precautions and methods to avoid locking:

  1. Correct selection of products: Before use, confirm whether the mechanical properties of the product can meet the requirements of use, such as the tensile strength of the screw and the guaranteed load of the nut. The length of the screw should be properly selected to tighten the nut and expose the nut 1-2 teeth. 
  2. Check whether the thread is rough before use, whether there is iron filings or dirt between the threads, these things often lead to lock. 
  3. Lubricate the fasteners before use. Spa: It is recommended to use butter, molybdenum disulfide, mica, graphite or talcum powder for lubrication. At present, it is commonly used to do lubrication to prevent lockup. 
  4. Pay attention to the use of methods: 
    • A. The speed of the screwing should be appropriate. Do not use it too fast. Use a torque wrench or a socket wrench as much as possible to avoid using an adjustable wrench or an electric wrench. Too fast will cause the temperature to rise rapidly and cause lockup. 
    • B. The direction of the force applied, the nut must be screwed perpendicular to the axis of the screw. 
  5. The use of gaskets can effectively prevent the problem of over-tightening. 
  6. lock or bite often occurs in stainless steel, aluminum alloy and titanium alloy fasteners, these metal alloys have anti-corrosion properties, will produce a thin layer of oxide on the metal surface when the surface is damaged To prevent further rust. When the stainless steel fasteners are locked, the pressure and heat generated between the teeth will damage the oxide layer, causing blockage or shearing between the metal threads, and adhesion will occur. When this phenomenon continues, the stainless steel fasteners will be completely locked and will no longer be able to be removed or remain locked. Usually a series of blocking_clip_adhesive_locking actions occur in just a few seconds, so correct understanding of the use of such fasteners can prevent this phenomenon. 

Some friends will wonder why stainless steel fasteners sometimes have lock-up problems, but carbon steel fasteners do not often have similar phenomena? This should be seen from the two materials of stainless steel and iron. Stainless steel standard parts are softer and have better ductility. The hardness of the stainless steel standard parts is compared with the hardness of the standard parts of the iron, which is softer than the standard part 8.8 of the iron. Stainless steel has good ductility, but its hardness has a certain gap with carbon steel. 

Seeing this, I think everyone should know more about the reasons for the lock of stainless steel fasteners. Remember the method to prevent the phenomenon of lock-up! 

News 22416 20190222 4 - Why can't stainless steel screws and nuts be used together?

Common problems and solutions in the use of stainless steel screws

Stainless steel screws are very large in our daily life, but they are not widely known in daily use, such as common anti-loose, rust, breakage, etc. Once these problems occur, they are replaced. Screws, if they cause damaging damage to equipment components, how to avoid these problems, the following are some of the common problems and ways to prevent them. 

First, stainless steel screws anti-loose problem 

Simply put, stainless steel screws are used on the material of the product so that the stainless steel screws do not fall lightly. Screws are required to be more tightly connected to the product material. For stainless steel screw-proof solutions, there are two solutions: 

  1. Using the resilience of special materials, such as engineering resin materials, it has a good rebound. Attach it to the stainless steel screw pattern. Mechanically rub it with the nut, or the material product. Produces vibration and absolute resistance. Completely solve the screw loose problem. 
  2. Apply a layer of glue on the stainless steel screw thread, so-called dispensing. This glue is called a drop-resistant glue. This glue has high adhesion, non-toxic and other good properties. This glue is applied to stainless steel screws and after drying, the adhesion is super strong. The stainless steel screw thread can be screwed on the nut or the super-tightening effect can be produced after the threaded hole of the product is engaged. Plays a super good anti-loose effect. 

Second, stainless steel screw rust problem 

  1. The attachment of dust or dissimilar metal particles, in the humid air, the condensate of the attached material and the stainless steel screw, and the two are connected into a micro-battery, which triggers an electrochemical reaction and the protective film is destroyed. Chemical corrosion. 
  2. The surface of the stainless steel screw adheres to the organic juice (such as melon, noodle soup, glutinous rice, etc.), in the case of water and oxygen, constitutes an organic acid, and the organic acid corrodes the metal surface for a long time. 
  3. The surface of stainless steel screws adheres to acid, alkali and salt substances (such as alkali water and lime water splashing on the wall), causing local corrosion. 
  4. In polluted air (such as the atmosphere containing a large amount of sulfide, carbon oxide, nitrogen oxide), in the case of condensed water, sulfuric acid, nitric acid, acetic acid liquid point is formed, causing chemical corrosion. 

All of the above can cause corrosion of the stainless steel screw surface protective film and cause rust. Therefore, in order to ensure that the stainless steel screw surface is permanently bright, it is not rusted. We have to clean the surface. Passivation, hot rust and other coating treatment. 

Remind everyone: When using stainless steel screws in daily work and life, be sure to pay attention to the above four points to prevent stainless steel screws from rusting. 

News 22416 20190222 5 - Why can't stainless steel screws and nuts be used together?

Third, stainless steel screw break problem 

But in general stainless steel screws are rarely broken. However, in certain cases, the stainless steel screws will still break. So what are the main reasons for the broken stainless steel screws? 

  1. The quality of raw materials used in stainless steel screws, stainless steel screw wire quality is not good. There are a lot of impurities, impure, resulting in insufficient hardness of stainless steel screws. 
  2. The production of stainless steel screws process problems. For example, the stainless steel screws with eccentricity and the Q value are too deep and the R position is too small during the manufacturing process. 
  3. When the customer uses stainless steel screws, the force is too large. It is generally recommended to do a torque test on a stainless steel screw to see what the minimum breaking force is, and then adjust the corresponding torque. If the screw torque is required to be high, the screw should be heat treated. At present, the stainless steel 410 material can be heat treated, heat treated stainless steel 410 screw, surface hardness HV580-680, core hardness: HV350-450. 
  4. See if the pre-hole is suitable, the pre-hole will break when the small screw is broken. 

Source: China Fasteners Manufacturer – Yaang Pipe Industry Co., Limited (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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