A fastener is a type of hardware used to attach two objects together through a mechanical process. Examples of fasteners include rivets, nuts and bolts, studs, screws, washers, eyebolts, and nails. Bolted connections most commonly use threaded metal bolts with nuts to hold two components firmly together. Alternatively, screws engage with matching threads in the object itself without needing an additional nut for a secure union.
BOLTS LENGTH CALCULATION
L = 2(t + t + d) + s + 2(p) where: l = calculated stud bolt length. T = total flange thickness. T = plus tolerance for flange thickness. D = heavy hex nut thickness (equals bolt dia) s = flange face standoff. P = maximum end point height (1.5 x pitch of thread).
Fasteners are objects used to tightly fasten two items or surfaces together. This process, which is also called bolting, typically involves the use of bolts and nuts of a specific grade that is strong enough to properly compress the item in between the two surfaces. Sheet gasket materials, due to their microporous nature, must be particularly compressed in order for them to form a proper seal.
Torque loss can be caused by the tendency of the gasket to relax after it has been compressed and/or by elongation of the bolts. This loss can be minimized in several ways:
1. Use of a denser gasket: in general, the denser the gasket material, less creep relaxation will occur.
2. Use of conical washer: the elastic effect of a conical washer helps compensate for some of the loss in gasket resilience. Torque loss can be caused by the tendency of the gasket to relax after it has been compressed and/or by elongation of the bolts.
This loss can be minimized in several ways:
1. Use of a denser gasket: in general, the denser the gasket material, less creep relaxation will occur.
2. Use of conical washer: the elastic effect of a conical washer helps compensate for some of the loss in gasket resilience.
3) Greater bolt load: the use of stronger bolts or more bolts can also help in the reduction of torque loss.
4) Use of a thinner gasket: the thinner the gasket, the less is flexible mass less will be the relaxation. However, if the surface is pitted or marred it may not be feasible to switch to a thinner gasket.
When fastening bolts and components together, it is important to consider the effects that temperature can have on these elements. Temperature can cause bolt elongation, related creep relaxation of gasket material and thermal degradation – leading to a loss in flange load. Additionally, at higher temperatures, different coefficients of expansion between the bolts and their respective components can create potential forces which may affect their performance. Properly torquing all bolts is essential in order to ensure a secure seal.
BOLT TORQUING PROCESS
Bolt torquing is the process of tightening a bolt to a specific level of tension or torque. Proper torquing is important to ensure that the bolted joint is secure and can withstand the intended load. Here are the steps involved in the bolt torquing process:
- Clean the bolt and nut: Before torquing, make sure that the threads of the bolt and nut are clean and free of debris. This will help ensure that the torque is applied evenly and accurately.
- Determine the torque specification: The torque specification is the amount of force that should be applied to the bolt to achieve the desired level of tension. This specification can be found in the bolt manufacturer’s specifications or in industry standards.
- Apply lubrication (if required): Some bolt specifications may require the use of a specific lubricant to achieve the desired level of torque. If lubrication is required, apply it evenly to the threads of the bolt and nut.
- Tighten the bolt: Use a torque wrench to tighten the bolt to the specified torque value. Tighten the bolt in a gradual, even manner, alternating between the nut and bolt head to ensure even tension. Stop tightening when the desired torque value is reached.
- Verify the torque: After torquing, use a torque wrench to verify that the bolt has been tightened to the specified torque value. If the torque is too low or too high, adjust as needed until the correct torque is achieved.
- Mark the bolt: To ensure that the bolt has been properly torqued and to prevent tampering, mark the bolt head with a permanent marker or paint.
- Retorque (if required): Some bolt specifications may require a re-torque after a certain period of time or after the bolt has been subjected to load. Follow the manufacturer’s recommendations for re-torquing.
Following these steps can help ensure that bolts are properly torqued and can provide a secure and reliable connection. It’s important to always refer to the manufacturer’s specifications and follow industry standards when torquing bolts.
Torque the bolts to 30% of torque value using bolt sequence. Then torque bolts to 60% of torque value using bolt sequence. Then torque bolts to 100% of torque value using bolt
sequence. Make a final rotation around flange at 100% of torque value.
BOLTS MATERIALS SELECTION
Bolts are critical components in many mechanical systems, and selecting the right materials is important to ensure their performance and durability. Here are the steps and considerations for selecting bolt materials, along with a summary of bolt grades:
- Determine the application requirements: The first step in selecting bolt materials is to determine the application requirements, including factors such as load capacity, temperature resistance, corrosion resistance, and environmental conditions.
- Consider the bolt grades: Bolt grades are a classification system used to indicate the strength and hardness of the bolt material. The most common grades for carbon steel bolts are Grade 2, Grade 5, and Grade 8, which have minimum yield strengths of 33000 psi, 85000 psi, and 120000 psi, respectively.
- Choose the appropriate material: Based on the application requirements and bolt grades, you can choose the appropriate material for the bolts. Common materials used for bolts include:
- Carbon steel: Carbon steel bolts are the most commonly used type of bolt and are available in a variety of grades. They are typically used in low to medium strength applications.
- Alloy steel: Alloy steel bolts are made from a mixture of steel and other materials, such as chromium, nickel, or molybdenum. They are used in high-strength applications and have higher corrosion resistance than carbon steel bolts.
- Stainless steel: Stainless steel bolts are highly corrosion-resistant and are often used in applications where the bolts will be exposed to moisture or corrosive chemicals.
- Titanium: Titanium bolts are lightweight and highly corrosion-resistant, making them ideal for applications where weight is a concern, such as aerospace and medical devices.
- Consider coatings: In addition to the material, you may also want to consider coatings for the bolts to provide additional corrosion resistance or lubrication. Some common coatings include zinc plating, galvanizing, and black oxide.
When selecting bolt materials, it’s important to consider not only the strength and hardness of the material, but also factors such as corrosion resistance, temperature resistance, and environmental conditions. Consulting with a materials specialist or engineer can help ensure that you select the appropriate materials for your application.
TYPES OF COATINGS OF BOLTS
There are several types of coatings that can be applied to bolts to provide additional corrosion resistance, lubrication, or other properties. Here are some common types of bolt coatings and their specifications:
Zinc plating: Zinc plating is a common coating for bolts that provides good corrosion resistance and a bright, attractive appearance. The plating thickness can range from 5-10 microns, and the coating can be either clear or yellow chromate. Zinc plating is often used in indoor and non-corrosive environments.
Galvanizing: Galvanizing is a process of coating bolts with a layer of zinc to provide excellent corrosion resistance, even in harsh environments. The coating thickness can range from 5-80 microns, depending on the application requirements. Galvanizing can be either hot-dip or electroplated, and the coating can be either clear or colored.
Black oxide: Black oxide is a conversion coating that provides a black, non-reflective surface on bolts. The coating provides good corrosion resistance and can also act as a lubricant. Black oxide can be applied to a variety of materials, including carbon steel, alloy steel, and stainless steel.
Teflon coating: Teflon coating is a non-stick, low-friction coating that can be applied to bolts to reduce friction and wear. The coating can be either PTFE or FEP, and can be applied in thicknesses ranging from 0.1-1.0 mils. Teflon coating is often used in applications where bolts will be exposed to high temperatures or corrosive chemicals.
Ceramic coating: Ceramic coating is a high-temperature coating that provides excellent corrosion and wear resistance, as well as thermal insulation. The coating can be applied to a variety of materials, including steel, titanium, and aluminum. Ceramic coatings are often used in aerospace, automotive, and industrial applications.
When selecting bolt coatings, it’s important to consider factors such as the application requirements, environmental conditions, and material compatibility. Consulting with a coatings specialist or engineer can help ensure that you select the appropriate coating for your application.
PREVENT BOLTS FROM CORROSION
Bolts are often used in environments that are prone to corrosion, such as those that are exposed to moisture, saltwater, or chemicals. Corrosion can weaken the bolt and lead to premature failure, which can be dangerous in certain applications. Here are some ways to prevent bolts from corrosion:
- Material selection: Choosing the right material for the bolt can go a long way in preventing corrosion. Stainless steel bolts are particularly resistant to corrosion and are often used in harsh environments.
- Coatings: Applying a coating to the bolt can provide an additional layer of protection against corrosion. Zinc plating, galvanizing, and black oxide are some common coatings that can be applied to bolts.
- Lubrication: Applying a lubricant to the bolt can help prevent corrosion by creating a barrier between the bolt and the environment. Lubricants such as grease, oil, or anti-seize compounds can be applied to the threads of the bolt.
- Sealants: Sealants such as thread sealant or silicone can be applied to the bolt to prevent moisture or other corrosive substances from penetrating the threads.
- Cathodic protection: Cathodic protection is a technique used to protect metals from corrosion by connecting the metal to a sacrificial anode. This can be achieved by using a zinc or aluminum anode connected to the bolt.
- Environmental control: Controlling the environment in which the bolt is used can also help prevent corrosion. For example, storing bolts in a dry location or using a protective cover can prevent exposure to moisture.
- Maintenance: Regular maintenance can help prevent corrosion by ensuring that bolts are clean and free of debris. Regular inspections can also identify any signs of corrosion or other damage, allowing for timely repairs or replacements.
By implementing these measures, bolts can be protected from corrosion and can provide a secure and reliable connection. It’s important to consult with a corrosion specialist or engineer to determine the most appropriate measures for your specific application.
Types of fasteners
Types of fasteners along with their details and applications:
- Bolts: A type of threaded fastener that has a head and a threaded shank. They are commonly used to secure two or more objects together, and are available in a variety of materials, finishes, and sizes.
- Screws: A threaded fastener that is inserted into a pre-threaded hole. They come in many different types, including wood screws, sheet metal screws, and machine screws, and are used in a variety of applications.
- Nuts: A type of fastener that is threaded on the inside and used with a bolt or screw to secure two or more objects together. They are available in many different materials, finishes, and sizes.
- Washers: A thin, flat ring that is placed between a nut or bolt head and the object being secured. They distribute the load of the fastener over a larger area, which can help prevent damage to the object being secured.
- Rivets: A type of fastener that is inserted through two or more objects and then deformed to secure them together. They are commonly used in applications where welding is not possible.
- Cotter pins: A pin that is used to secure a nut or bolt in place. They are commonly used in automotive and industrial applications.
- Retaining rings: A type of fastener that is used to secure a shaft or other object in place. They are commonly used in automotive and industrial applications.
- Studs: A type of threaded fastener that has no head and is used to secure two objects together. They are commonly used in automotive and industrial applications.
- U-bolts: A type of bolt that has a U-shape, with threaded ends on each side. They are commonly used to secure pipes and tubes.
- J-bolts: A type of bolt that has a J-shape, with a threaded end on one side and a hook on the other. They are commonly used to secure objects to a wall or ceiling.
- Eye bolts: A type of bolt that has a loop or eye at the end, which can be used to attach ropes or cables. They are commonly used in industrial and marine applications.
- Hook bolts: A type of bolt that has a hook at the end, which can be used to hang objects. They are commonly used in construction and industrial applications.
- Anchor bolts: A type of bolt that is embedded in concrete or masonry and used to secure objects to a foundation or wall. They are commonly used in construction and industrial applications.
- Lag bolts: A type of bolt that has a wood screw thread and a hex head. They are commonly used to attach wood to other materials.
- Machine screws: A type of screw that has a straight shank and a flat or rounded head. They are commonly used in machinery and electronics.
- Sheet metal screws: A type of screw that has a sharp point and a flat or rounded head. They are commonly used in sheet metal and other thin materials.
- Wood screws: A type of screw that has a tapered shank and a pointed tip. They are commonly used to attach wood to other materials.
- Self-tapping screws: A type of screw that cuts its own threads as it is screwed into a material. They are commonly used in sheet metal and other thin materials.
- Thread-cutting screws: A type of screw that cuts threads into a material as it is screwed in. They are commonly used in metal and other hard materials.
Thread-forming screws: A type of screw that forms threads in a material as it is screwed in. They are commonly used in plastic and other soft materials.