Galling is a process that can occur when stainless steel thread lock together and fuse due to friction. Galling can occur when an individual apply too much torque to a stainless steel bolt. When galling occurs, the metal surface of the stainless steel bolt and the stainless steel nut fuse together, making it difficultly to separate the two components.
To prevent galling from occurring, individuals should use the correct amount of torque when tightening the bolt and use lubrication on the threads of the stainless steel component. The charts that demonstrate the amount of force that an individual should use on a stainless steel bolt to avoid damaging the threads is known as torque charts. There are different grade of stainless steel bolts.
How to Tighten Stainless Steel Bolts and Stop Galling
For instance, environments where exposure to moisture are high but where the stainless steel bolts will not be exposed to saltwater use A2-70 stainless steel bolts. A2-70 stainless steel bolts are suitable for indoor environment or food preparation areas because the bolts resist corrosion in these areas. A4-80 stainless steel bolts contains molybdenum.
These bolts are better suited for marine environments because the molybdenum content allows the bolt to more better resist corrosion caused by saltwater exposure. A4-80 bolts should be used in areas near saltwater while A2-70 bolts is best used in indoor environments. Additionally, locations that require high strength use 17-4 PH stainless steel bolts.
These bolts are used in aerospace application because of their high tensile strength. The torque that must be applied to a bolt also depend on whether the threads are dry or lubricated. If the threads are dry, more force will be required to allow the bolt to properly engage with the threads of the other component with which the bolt will be used.
If the threads are lubricated, the bolt will require less force to engage. For instance, a half inch bolt will require 47 foot-pounds of torque if the threads are dry but will only require 35 foot-pounds of torque if the bolt threads are lubricated. An anti-seize lubricant should be used on the threads since it will prevent the bolts from gallant and make the bolts easier to remove once the bolted components have been secured.
Based off the design of the bolt head, individuals can determine how the bolt will be accessed once secured and how the bolt will look when it is secured to an object. For instance, hex-head bolts allow for the bolt to be secured with a wrench and have high strength. Socket cap heads has a drive located on the head of the bolt.
These bolts are used when there is limited access to the bolt head. Button heads have a low profile while flat heads will be flush with the material it is secured to. Additionally, the grade of the bolt can be determined based on the markings on the bolt head.
For instance, if a circle is marked on the bolt head, that indicates that it is an A2-70 stainless steel bolt while radial line on the bolt head indicate that the bolt is an A4-70 stainless steel bolt. To properly tighten a bolt, certain procedure should be followed. For instance, if the bolt has a flange that includes multiple bolts, those bolts should be tightened in a star pattern to ensure that the load is evenly distributed on the flange.
Additionally, the bolts should be tightened in stages. The bolts should be tightened to 30 percent of the required torque, then to 60 percent and finally to 100 percent of the required torque. Using a click-type torque wrench will allow individuals to apply the correct amount of torque to the bolt since these wrenches provides precision in the amount of torque that is applied.
Additionally, the bolts should be checked again after heating and cooling cycle because the bolts may settle in these environments. Depending on the industry in which bolts are used, the type of stainless steel bolt that is used may change. For instance, marine industries will require the use of A4-80 stainless steel bolts because of the saltwater exposure.
Food processing facility will use A2-70 stainless steel bolts because they are easy to clean and the corrosion resistance is enough for food processing facilities. Chemical plants will require the use of A4-80 or duplex stainless steel bolts because these steels can better resist corrosive chemical. Each industry requires a specific type of bolt.
If the bolts are tightened with too much torque, they may yield. However, if there is too little torque used on the bolts, the bolts may loosen due to vibration from the processing equipment.
