Like key, pin connections are most often used in assemblies to transmit torque between the shaft and the part. Their main feature is that they allow you to install elements with high accuracy. Connections of this type are carried out using special parts - pins.
Where are used
Such connections are used to transfer mainly only very small loads. Sometimes pins are used for mutual fixation of parts. There are also special cut-off elements of this type used as fuses. In addition to assemblies with shafts, such products are very often used to connect covers and housings.
Another purpose of the pin joints is prosthetics in dentistry. Using these elements, artificial teeth are fastened.
Varieties of pins
When assembling all kinds of nodes, two main types of similar products are used:
The cylindrical pins, in turn, can be:
Additional design elements of the pins may be threaded holes or protrusions. They are used to remove products from blind holes.
According to the functions performed in the node, three groups of pins are distinguished:
installation;
guides;
fixing.
Pin connection: GOST
In most cases, when assembling nodes, standard pins are used, made in compliance with GOST standards. For each particular type of product, they are different. So, the manufacture of simple-shaped pins is regulated by GOST 3128-70 (cylindrical) and GOST 3129-70 (conical). Such parts are usually made of steel of grade 45. But GOST allows the use of material of the grades A12, 10 kp, 20 kp, etc. for this purpose. Perforated products are made of spring steel. Sometimes pins of different types are made of non-ferrous metals.
Of course, the nominal sizes of these elements are also regulated by standards. GOST also provides for the permissible deviations of the latter. This allows you to assign typical pin seating to holes in bushings, shafts, covers and housings.
The symbol for these products includes:
In this case, the type is indicated only if it is uniquely determined by the standard. In the "dimensions" field, the diameter of the product and its length are indicated. Sometimes tolerance fields are also affixed here.
What is a
Connections of this variety are classified as detachable. When they are created, drilling of the parts of the assembly is first performed. Moreover, it must be joint. That is, previously the parts are folded together with each other in such a way as they will be located in the unit in the future during its operation. After that, the actual drilling is performed.
The pins themselves are inserted into the resulting holes in the next step. Cylindrical elements of this type are installed very tightly. That is, the pin always has a slightly larger diameter than the hole prepared for it.
In the event that the unit during operation will be subjected to repeated assembly / disassembly, conical pins are provided for it, not cylindrical. This allows you to extend the life of the structure. Since the cylindrical pins are inserted into the holes of the parts very tightly, after disassembling and assembling the assembly may lose its original operational qualities. That is, the connection may simply become not too strong.
The pins work during operation:
It is on these grounds that calculations are made on their suitability when used in a particular site. The working surfaces of both pins and parts to be joined may be crushed.
Advantages and disadvantages
In the manufacture of various kinds of nodes can be used, in addition to pin, and wedge connections, key, slotted. All of them belong to the type of detachable. Very often threaded connections of this variety are also used with the use of screws, studs and bolts, profile, terminal. Each of these types has its own advantages and disadvantages.
The pluses of the pin connections include in the first place:
The disadvantage of such compounds are basically only one. In any case, the hole drilled under the pin will weaken the part in the future. Terminal connections, for example, lack such a minus.
At the same time, the pockets for the pins must be processed very carefully. Otherwise, the product may subsequently bend. The need for precise hole machining increases the cost of manufacturing a part assembly.
Features of using cylindrical pins
The assembly of the pin joints when fastening machine parts is usually carried out using smooth products. In the same way, the usual fixation of the structural elements of the machine during its operation is usually performed. In this case, two smooth pins are most often used.
To fix the position of the parts can be used and perforated products of this type. Their main advantage, compared to smooth ones, is that they do not require reaming holes. In the absence of additional fastenings, such elements are also more reliable in terms of loss. As with the use of conical, when using perforated cylindrical pins, assembly / disassembly of the connection can be carried out repeatedly during the subsequent operation.
In static joints, cylindrical products are fitted with an interference fit. In the moving ones they are mounted with the obligatory riveting of the ends. Spring cylindrical pins are usually mounted in lightly loaded joints. Preload when using them is created by reducing the diameter of the hole. The mounting types of pins in the fittings are fitted with an interference fit on one of the parts. On the other hand, they are mounted with a landing H7 / h6 or H7 / js6.
Conical products
The pins of this variety are made with a taper of 1:50. This ensures their subsequent self-trapping in nodes. Such products are used to transmit torque and to connect covers to housings almost as often as cylindrical ones.
Simple conical pins are usually installed in through holes. In this case, during installation they are simply driven in from the opposite side of the joint. If the hole is not through, a conical pin with thread for pulling out is installed in it.
Adjustable products of this type are used in such joints, which during the operation of the mechanism may be subjected to shocks and shock loads. In addition, they are installed in those nodes in which the parts move at a very high speed. The ends of such pins at the end of installation are usually parted.
Features of installation in the node
Drill the parts for connection with a pin, as already mentioned, in the assembly. In some cases, these elements are additionally fixed to prevent loss. This is done, for example, when installing collapsible joints. In this case, additional fixation is provided by a 0.5-0.8 mm ring of wire.
In a non-separable connection, the pins are usually core. But in some cases, drilled ends may also be used. After assembly, such pins are flared.
When using conical products in some cases, the condition of self-rejection may not be fulfilled. This happens quite often, for example, in nodes subjected to vibrations or functioning under conditions in which the temperature changes sharply. In such joints, the conical pins must be secured additionally.
Pin selection and calculation
The dimensions of the products used to transmit torque depend primarily on the shaft diameter (within d pcs. <0.3d). According to the shear strength, the pin is selected using the following formula:
Here T is the torque, [t cf] is the allowable shear stress. The last parameter is looked in special tables. On crushing with a thin hub, the connection is checked according to the formula:
Here / d (Dd) d pcs. - conditional area of collapse, [Q cf] - allowable stress of collapse for steel.
Repairs
In addition to wrinkling or shearing, defects of this type can also cause defects such as hole wear and cracks in the parts themselves. Operate the nodes further if any of the four problems occurs. Repair of the unit must be carried out necessarily. In any case, the node with the defect will work for a very short time.
Actually, the repair of the pin joints itself, of course, is carried out in compliance with certain standards. In most cases, defective pins are disposed of and replaced with new ones. However, GOST still allows, for example, to expand worn holes for another larger pin. It is also allowed to brew old holes and drill new ones in their place.