*6.2.6 Torque augmentation*

When the mechanical assembly is done with fasteners on a flange, it is expected that the assembled fastener should maintain in the assembly the 100% of the tightening

**125**

*6.2.7 Galling*

**Figure 9.** *Wide tension scatter.*

*Liquid Thread Locking Solution for Machinery Assembly Industry*

torque applied according to the standard guideline. However, in reality, it is not. When "10 N m" tightening torque was applied to tighten fasteners, it takes around "7 N m" to loosen the assembly. It means that around 30% of tightening torque is lost during the assembly to overcome the friction generated between male and female threads and between bolt head and substrates. This explains that the assembly maintains only 70% of the tightening torque. Therefore, when there were parameters to loosen the fastener, it would have a high possibility to be susceptible to such loosening factors and finally loosen. A proper measure should be addressed to prevent this failure. At the same time, it is important to understand that the torque augmentation becomes thin as the bolt size, and its tightening torque becomes bigger because the gap between threads is getting bigger, and it is not an ideal condition for anaerobic adhesive to polymerize and lock the thread in place. As shown in **Figure 10**, the lines of torque augmentation for bolt and nut assembly of "without anaerobic adhesive" and "with adhesive" are not parallel; they will meet at some point. In the situation of big bolt and nut, thread locking is not a main point as a very high tightening torque is applied. When the break loose torque for bolt and nut assembly was measured with and without anaerobic adhesive, the result is very identical meaning there is not much torque augmentation due to too high tightening torque and big gap between threads. Therefore, thread "seizing" or "galling" is more important point which they have to use an extreme high-temperature and high-pressure

lubricant product to prevent the thread seizing and galling (see **Figure 10**) [1].

When a bolt and nut were tightened with a tightening torque, it has to overcome the friction generated between threads and bolt head or nut to part the surface. As shown in **Table 1**, a comparison test has been done to see the difference between "Unified National Coarse" (UNC) thread and "Unified National Fine" (UNF) thread. Coarse thread has more bolt tension than fine thread, and fine thread has more thread and head friction than coarse thread. But on the other hand, coarse thread has more torque loss than fine thread. The distribution of tightening torque is shown in **Table 1** [2].

Galling is a wear caused by friction and the buildup of heat between two sliding thread surfaces. When a relatively big size bolt and nut are assembled or loosened for repair, a very high heat is generated; this heat fuses and melts the two sliding thread surfaces and causes the galling. The same issue occurs when a low thermal conductivity of metal is used as a fastener for assembly or disassembly. A care must be taken when stainless steel fasteners are used as they have the lowest thermal conductivity. **Figure 11** shows thermal conductivity of major fastener metals [1].

*DOI: http://dx.doi.org/10.5772/intechopen.85090*

*Liquid Thread Locking Solution for Machinery Assembly Industry DOI: http://dx.doi.org/10.5772/intechopen.85090*

**Figure 9.** *Wide tension scatter.*

*Adhesives and Adhesive Joints in Industry Applications*

nut fasteners because each bolt generates a different bolt tension even though it was tightened equally according to the standard tightening guideline. The same size bolts are made by the same supplier and same spec. All end up having a different bolt tension after tightening. Then the flange pressure becomes high at one side of bolt assembly, and the flange pressure becomes low at other sides of bolt assembly, and then, one side has higher stress, and the other side has lower stress. It is suppose that five bolts were used to assemble a flange assembly. The same tightening torque was used to tighten each bolt. But a different bolt tension (or flange surface pressure) is achieved for each bolt because each bolt has a different surface roughness on the threads. This different surface roughness on the thread surface generates a different remaining bolt tension after some portion is consumed by the friction on the thread, and consequently, through the flange sealing area with a low flange surface pressure, the leak occurs. This can cause a long-term reliability issue of sealing, and

it must be addressed properly to prevent such failure (see **Figure 9**) [1].

When the mechanical assembly is done with fasteners on a flange, it is expected that

the assembled fastener should maintain in the assembly the 100% of the tightening

**124**

**Figure 7.**

**Figure 8.**

*Reason for assembly failures.*

*Empty space in a threaded assembly.*

*6.2.6 Torque augmentation*

torque applied according to the standard guideline. However, in reality, it is not. When "10 N m" tightening torque was applied to tighten fasteners, it takes around "7 N m" to loosen the assembly. It means that around 30% of tightening torque is lost during the assembly to overcome the friction generated between male and female threads and between bolt head and substrates. This explains that the assembly maintains only 70% of the tightening torque. Therefore, when there were parameters to loosen the fastener, it would have a high possibility to be susceptible to such loosening factors and finally loosen. A proper measure should be addressed to prevent this failure. At the same time, it is important to understand that the torque augmentation becomes thin as the bolt size, and its tightening torque becomes bigger because the gap between threads is getting bigger, and it is not an ideal condition for anaerobic adhesive to polymerize and lock the thread in place. As shown in **Figure 10**, the lines of torque augmentation for bolt and nut assembly of "without anaerobic adhesive" and "with adhesive" are not parallel; they will meet at some point. In the situation of big bolt and nut, thread locking is not a main point as a very high tightening torque is applied. When the break loose torque for bolt and nut assembly was measured with and without anaerobic adhesive, the result is very identical meaning there is not much torque augmentation due to too high tightening torque and big gap between threads. Therefore, thread "seizing" or "galling" is more important point which they have to use an extreme high-temperature and high-pressure lubricant product to prevent the thread seizing and galling (see **Figure 10**) [1].

When a bolt and nut were tightened with a tightening torque, it has to overcome the friction generated between threads and bolt head or nut to part the surface. As shown in **Table 1**, a comparison test has been done to see the difference between "Unified National Coarse" (UNC) thread and "Unified National Fine" (UNF) thread. Coarse thread has more bolt tension than fine thread, and fine thread has more thread and head friction than coarse thread. But on the other hand, coarse thread has more torque loss than fine thread. The distribution of tightening torque is shown in **Table 1** [2].

#### *6.2.7 Galling*

Galling is a wear caused by friction and the buildup of heat between two sliding thread surfaces. When a relatively big size bolt and nut are assembled or loosened for repair, a very high heat is generated; this heat fuses and melts the two sliding thread surfaces and causes the galling. The same issue occurs when a low thermal conductivity of metal is used as a fastener for assembly or disassembly. A care must be taken when stainless steel fasteners are used as they have the lowest thermal conductivity. **Figure 11** shows thermal conductivity of major fastener metals [1].

**Figure 10.** *Torque augmentation.*


#### **Table 1.**

*Distribution of tightening torque.*


#### **Figure 11.**

*Thermal conductivity of metals (Btu/hr-ft-F).*

#### *6.2.8 Cost*

Those conventional fasteners require additional items such as flat washer, spring washer, star washer, and tab washer, and some of them were designed especially such as nut with nylon insert, castellated nut, and tooth flanged bolt.

**127**

**Figure 12.**

*Anaerobic cure mechanism.*

*Liquid Thread Locking Solution for Machinery Assembly Industry*

They are much more expensive than using a plain bot and nut. It would be ideal to have a way to lock the normal bolt and nut in a way we want but with a minimal

This chapter explains everything about anaerobic liquid thread locking adhesive such as its curing mechanism and benefits that can help assembly industries. This is a liquid single-component product that fills all voids to unitize the bolt and nut, and it cures to a thermoset plastic and creates material closure. It also maintains friction by

When adhesive is applied onto one side of metal substrate, then adhesives contact with metal ion (Fe++, CU++) for some anaerobic initiator to be broken into free radicals which are unstable, but the presence of air to contact adhesive is stronger; therefore, it remains as a liquid. As a next step, when the other mating part comes in contact with the first part with adhesive in between, then more anaerobic initiators contact more metal ions to be broken into more free radicals, and at the same time, oxygen contact is blocked by both substrates, and then, those unstable free radicals react with a monomer nearby which becomes unstable, too, and then, it reacts with other monomers nearby, and gradually, all the monomers react and become polym-

In case of inactive metal substrates that contain low metal ions such as Cu++ or Fe++ and have a slow reaction with photoinitiator and slow cure, an acceleration method such as primer or heating can be used to speed up the curing. Anaerobic

The gap in the threaded fasteners after assembly has always been the issue ever since it has been developed and used. It has led various unwanted situations that had to be corrected and improved with additional cost and time. Liquid thread locking adhesive is one component that fills all the inner space of assembled threaded fasteners and cures to a tough thermoset plastic. It is called as "Conquest of Inner space." It is surprising to know that the inner space in the threaded assembly has had issues. The liquid thread locking adhesive solves various issues that mechanical fasteners

adhesives become a very reliable thermoset plastic after cure [2].

adhesion, resists a vibration, and prevents bolt and nut from loosening.

*DOI: http://dx.doi.org/10.5772/intechopen.85090*

**7. Liquid thread locking adhesive**

**7.1 Anaerobic curing mechanism**

erized (cure) (see **Figure 12**) [3, 4].

**7.2 Liquid thread lockers and benefits**

cost addition.

They are much more expensive than using a plain bot and nut. It would be ideal to have a way to lock the normal bolt and nut in a way we want but with a minimal cost addition.
