Studs
Stud bolts are metal bolts that are firmly connected to a component with one of their circular intersecting surfaces and thus “stand” on it. Additional components can then be connected to the first using the stud bolts. They are used as fastening parts in many areas of mechanical engineering and electrical engineering. They are available with and without a thread .
Stud bolts with thread
Threaded studs are the most common design today. They are fasteners similar to screws , but do not have a screw head for actuation.
purpose
The purpose of a stud is to connect two or more machine parts. In the case of an expensive machine part, it creates the possibility of flange-mounting another component on a mechanically clean, smooth and partly sealable surface. Often both parts to be connected have to be machined flat and smooth for the purpose of sealing, usually by means of milling . The more expensive part is protected by keeping the studs in it. In this way, the cast part (in this example the cylinder head) is not exposed to the risk that a fastening thread could be damaged by frequent screwing in and screwing out, as can happen with a threaded hole for screws.
Appearance and function
To describe the function of a stud bolt, it is necessary to consider both thread ends.
- One thread is used to screw the stud bolt into a (usually expensive) part of the housing that has been provided with threaded holes for this purpose. This threaded part is often never moved again, or only when the stud bolt is damaged.
- The other end of the thread is used to fasten another part to be flanged on.
In the simplest case, a stud bolt consists only of a continuous piece of threaded rod that is produced by forming (wire drawing of the rod and subsequent thread rolling). Often, however, the threads of the stud bolts are only produced by forming (thread rolling) at both ends; the middle part remains cylindrical, i.e. H. without thread. Mostly the screw-in thread and the fastening thread are of the same size and pitch. Sometimes there is a stepped collar in the middle of the stud.
The screw-in part of the bolt, with which it is screwed into a component, generally remains in the component without the thread moving. The part of the bolt thread protruding from the housing is used to fasten a part equipped with a flange . The flange of the mounted part has holes for the stud bolts. After attaching to the stud bolts, the flange connection is fixed by screwing onto the stud bolts with washers and nuts .
The picture shows the cylinder head of a car engine, in an upside down position, with the combustion chambers on top. Facing the viewer is the flange side, where five stud bolts can be seen, which are used to attach the exhaust manifold . On the exhaust duct on the far left, which leads to the exhaust valve, only the lower stud can be seen, the upper one is missing. Both stud bolts are screwed into the next two exhaust ducts. Both studs are missing on the right exhaust duct. The lower channels are the gas paths for the gasoline-air mixture to the inlet valves.
Blind thread sleeves or counter screws are used to assemble stud bolts . Some studs have a hexagon socket or an external torx so that they can be screwed in and out with a standard tool.
A screw is a steel part whose thread is harder than the thread cut into an aluminum casting. If a screw is now mounted at an angle or offset in an expensive aluminum casting , there is a high risk that the weaker thread in the expensive aluminum casting will be damaged. It is therefore preferred to screw a threaded steel bolt as a stud bolt into the aluminum thread of the expensive part, which then usually always remains in this hole and, with its externally protruding thread, offers a fastening option for flange parts.
In the event of screwing errors, only the threaded part of the stud bolt protruding from the expensive part is at risk. In the event of damage to the bolt thread, however, a stud bolt can often be replaced quite easily. As a rule, stud bolts therefore remain in the more valuable housing part for a long time. However, they can be replaced if, for example, the upper, protruding fastening thread should be damaged. Then the stud bolt is unscrewed with two countered nuts, or it is cut off and drilled out and replaced with a corresponding new part. This change process is risky. The different metallic materials are often responsible for the fact that the connection in the expensive basic housing oxidizes due to electrochemical contact corrosion . The less noble metal of the housing part corrodes. Unscrewing a steel stud becomes a risk, as the thread in the light metal casting can be damaged during removal. To unscrew stud bolts, corrosion dissolving agents should therefore be sprayed on beforehand and allowed to act for several hours.
In such cases of damage to the base thread, a repair thread is often cut into the housing, a thread with a larger bore and the same pitch. A repair threaded pipe with double thread inside and outside is screwed into this larger thread, e.g. B. Helicoil, in which a stud bolt of the original thread size has a new hold.
Tie rods are a special, long design of stud bolts. They are often used in engine technology to connect cylinder heads, cylinders and engine housings in air-cooled engines. Stud bolts or tie rods can also be found in a centrally slender design, similar to expansion bolts .
Ultimately, studs are an inexpensive and proven way of offering durable, often detachable fastening threads on expensive workpieces without endangering a bore thread in expensive cast workpieces by occasionally screwing in screws : the studs are installed once by the manufacturer and then usually remain permanently in the expensive cast part. This shifts the risk of thread damage from the expensive cast part to the steel end of the stud bolt.
Therefore, stud bolts can be found in many applications in electrical engineering , mechanical engineering and vehicle construction .
Stud without thread
For stud bolts without thread, the second component is connected to the first by means of rivets, for example . An example of unthreaded studs is the connection of the fire box to the rest of the standing boiler on steam locomotives.
