The quality of many products of the furniture, automotive, construction industry and other industrial sectors directly depends on the strong and high-quality fastening of individual parts of the structure. The countersunk head fixing bolt is one of the universal devices that securely connects various elements into a single product.
Bolt Appears
In ancient Russia, bolts were called arrowheads for crossbow arrows, having a variety of shapes. Later, any elongated product of a cylindrical shape began to be called this way. And only with the development of building technologies did the screw connection of parts supplant all other meanings of this word.
Today, threaded bolts are used in a wide variety of areas, both everyday life and industrial production.
Description of countersunk head bolt
This fastener received its name for the peculiar shape of the head. Smooth rod with threaded screwthe thread is crowned with a flat cone-shaped hat with a slot - a turnkey recess or a screwdriver.
The countersunk head bolt enters the entire hole of the fastened product. The head sinks into the material without protruding from its surface. The variety of sizes of countersunk bolts, their ease of use, the strength of the connection and the ability to withstand heavy loads greatly expand their scope.
Classification of bolt fasteners
Thread pitch and depth, screw length, head diameter and many other characteristics are determined by GOST. Countersunk head bolts are divided according to their purpose into several groups:
- Attachments of agricultural machines are fixed with ploughshare countersunk bolts.
- Furniture fasteners are used in the construction and furniture industries.
- Road fasteners fasten elements of metal road barriers and special structures.
- Engineering are used to connect parts in the car, machine and instrument making.
The appropriate grade of unalloyed or alloyed carbon steel and production technology determine the strength of fasteners, expressed in nominal tensile strength and yield strength. According to mechanical strength, countersunk head bolts are divided into 11 classes. The strength marking is applied to the hat and looks like two numbers with a dot between them (for example, 3.6 or 12.9). Uniform labeling simplifiesthe use of similar bolt fasteners in various industries. When calculating the load on the fastener, first of all, the yield point is taken into account, since if it is exceeded, irreversible deformations occur and the use of such a bolt with a countersunk head is prohibited.
Steels and Alloys
Mainly for the production of bolts, low-carbon steel is used, with a content of no more than 0.4% carbon. Subsequent heat treatment to prevent decarburization of fasteners, cold or hot heading process and protective coating can be used to obtain products of various strength classes.
Besides carbon steel, bolts are made from other alloys:
- Alloyed steel grades are obtained by adding nitrogen, chromium, nickel, vanadium, copper and other additives that enhance the strength and corrosion resistance of products. Depending on the required physical or mechanical properties, the amount of alloying additions varies.
- Cold-resistant steels withstand temperatures down to -75 0C.
- Stainless steel is resistant to corrosion in the atmosphere or aggressive environment due to the high content of chromium in its composition.
- Heat-resistant (scaling-resistant, heat-resistant) steel does not collapse in gas environments at temperatures above +550 0C. Nickel, chromium, molybdenum, titanium and silicon are used as additives.
- Heat-resistant alloys withstand high temperatures for a long time without deforming or breaking down. The alloying additions of heat-resistant steels are chromium andsilicon.
Rarely non-ferrous metals are used for the manufacture of countersunk bolts: titanium, brass, copper, aluminum and polymers. High-strength carbon alloys have a low level of corrosion resistance. If it is necessary to obtain fasteners of high strength and resistant to aggressive environments, the finished product is coated with a protective metal, inorganic, enamel or plastic coating using an electrolytic or galvanic method.
How countersunk bolts are secured
To use a bolted connection, it is necessary to prepare technological holes. Since the bolt's distinguishing feature is that it does not have a pointed tip, it will not screw into the material. When fastening parts through, a hole is drilled without a thread as close as possible to the size of the bolt. The fastening is tightened with a nut. The fixation of the bolt in the material is provided by an internal thread. The vertical hole is drilled 0.1-0.2 mm smaller than the bolt diameter and 1 mm shorter. A thread is cut with a hand tap and a bolt is screwed in. The countersunk head is tightened until it stops, flush with the surface of the product.
On the flat surface of the head, the slot can be in the form of a cross, a straight slot, or a hexagonal recess. Depending on the shape of the pull hole, use a flat or Phillips screwdriver or a hex key.
Hex slot
The most widely used in all industrial applications are countersunk head hexagon bolts. Fast and convenientinstallation with an electric or pneumatic tool provides increased strength of the threaded fastening of parts. Conveyor assembly of high-strength mechanisms, components and assemblies is carried out with hexagon countersunk head bolts.
Special L-shaped hex wrenches are compact and easy to use. Precise dimensions and high strength of the hexagons allow you to securely tighten the bolts and, if necessary, easily dismantle the connected parts.
Benefits of bolted connections
- Reliability of fastening is provided by a metric carving and a universal profile. Properly selected strength class of the countersunk bolt and its high-quality tightening provide reliable protection of the product against self-loosening and guarantee high load capacity.
- Made from suitable steel grades, the bolts withstand axial and lateral loads.
- With the help of countersunk bolts, the installation of any structure is faster and easier.
- The cost of assembly work is significantly lower than the cost of, for example, welding. Many building structures or automotive parts today are connected with countersunk bolts, as such work requires significantly less time and physical strength.
In the engineering and automotive industries, a countersunk head bolt with a mustache on the back of the head is used to prevent untwisting. The triangular protrusion provides a stronger fixation of the bolt in the material. Most often, a bolt with a mustache is used for through-connection of parts and works as a stopper when tightening the nut.
Application areas for hidden bolted connections
Countersunk head bolts are widely used in all industries and in everyday life. Precise and durable connection of complex components in instrumentation, vibration-resistant fastening of car and aircraft parts, reliable screeding of iron frames of objects under construction, furniture assembly, building decoration and many other types of connections are provided with countersunk bolts. Manufactured from durable and resistant to aggressive environment steel alloys, hidden fasteners not only provide reliable connections, they attract with convenience and aesthetic appearance.
Flush head recessed into the material does not interfere with the moving parts of various mechanisms. Furniture or decorative interior elements assembled with hidden fasteners without protruding bolt heads have a very attractive appearance.
