The following bolt that will be discussed are the M36 bolts. M36 bolts is often used in the construction of heavy structure, such as wind turbines and press frames for heavy industrial application. Furthermore, due to the size of these bolt, they are able to handle significant amount of force that is placed upon those structures.
If any of these bolts should fail, the cost and danger of such a failure will be significant as well. In order to avoid choosing incorrect specification for the M36 bolts that are to be used in these structures, a thread pitch chart can be used to determine the correct pitch and preload that should be used for those bolt. The thread pitch chart contain information regarding three different types of threads for the M36 bolts: coarse, fine, and extra fine threads.
M36 Bolts Thread Pitch and Installation
Each of these types of threads allow for the bolts to have different amounts of stress areas, as well as different minimum engagement length for the bolts. Coarse threads allow for the structure to be assembled more quickly, as the threads is less likely to become damaged during installation. Fine threads allow for those structures to be able to handle more tension, but do not have the same forgiveness towards any damaged threads.
The decision of which type of thread pitch should be used for the M36 bolts can be made based off the type of load that the structures will experience; whether they will be primarily experiencing loads in shear, or whether the structures need to be able to maintain a specific load upon the joints where the M36 bolts are used. Information regarding the torque that should be used for those bolts is present on the thread pitch chart itself, as well as information regarding the fact that the torque for those bolts may change based upon the condition of the threads. For instance, if the bolts has dry threads, if they have molybdenum coating on their threads, or if they are hot dip galvanized, the torque that is applied to the bolts will change.
The use of lubricants will change the amount of friction against the M36 bolts, and any change in friction will impact the amount of effort that is required from the wrench to be placed into the bolts to achieve the intended tension for the structure. Thus, the torque for these bolts is not a single, specific number, but is instead a relationship between the M36 bolts themselves, the coating that is used on those bolts, and the tool that is used to place that torque upon the bolts. In addition to these structures and their requirement for the M36 bolts to allow the bolts to provide the necessary preloads for those structures, the thread pitch chart also contains information regarding the method in which those bolts are to be installed into the structures.
For instance, if the M36 bolt is to be used in a structure that requires the bolts to be slip-critical, the chart will show the difference between installing the bolts to a snug tight installation as opposed to installing the bolts to their fully tensioned state. Additionally, the method for installing the bolts will impact the way that the bolts are installed into the structures; whether they are to be installed with the turn-of-nut method, or whether they are to be installed with direct tension indicator washers. These installation methods will differ according to the accessibility of the structures, as well as the whether the individuals who install the M36 bolts will be able to check the installations at a later date.
In addition to these requirements for installing the M36 bolts, the chart also contains information regarding the specific requirements of hot-dip galvanizing those M36 bolts. Hot-dip galvanizing will add zinc to the M36 bolts. The addition of this zinc will increase the thickness of the M36 bolts, which may prevent standard nuts from being able to fit within the bolts.
Thus, oversize nuts may be required for hot-dip galvanized M36 bolts. Another factor that may impact hot-dip galvanized M36 bolts is the possibility of hydrogen embrittlement of the high-strength bolts. Hydrogen embrittlement may lead to the M36 bolts begin to crack several week after they are installed into the structures.
The requirements for the tooling that is necessary to install these M36 bolts will also increase with the size of the bolts. Tools like impact wrenches or hydraulic torque tools may be required to install the M36 Grade 10.9 bolts. Using a tool that is not rated for the output requirement of these bolts will lead to installation error in the creation of the necessary preloads.
The same can be said for using a standard chrome socket with an impact gun; the high torque of the impact gun may crack the standard chrome socket into pieces. The thread pitch chart for M36 bolts is another useful tool that removes the necessity of remembering the minor diameter and the K factors of the various types of coatings. The chart allow individuals to install the M36 bolts based upon the manufacturer’s specification for those bolts.
Additionally, using the chart allows individuals to move forward with the knowledge that the numbers that are printed on the chart have been calculated for the specific situation of installing M36 bolts into various structures. Thus, using the thread pitch chart for M36 bolts not only ensures that the joints created with the bolts will hold, but also ensures that the joint will not need to be created again at a later date.
