What is a pin connection?

2024 Author: Howard Calhoun | [email protected]. Last modified: 2024-01-15 14:07

Like keyed connections, pin connections are most often used in assemblies to transfer torque between a shaft and a workpiece. Their main feature is that they allow you to set the elements with high accuracy. Connections of this type are made using special parts - pins.

Where used

Such connections are used to transmit mostly only very small loads. Sometimes pins are used for mutual fixation of parts. There are also special shear elements of this type used as fuses. In addition to shaft assemblies, these products are very often used to connect covers and housings.

Another purpose of pin connections is prosthetics in dentistry. With the use of such elements, artificial teeth are fastened.

Varieties of pins

When assembling various kinds of nodes, two main types of such products are used:

• cylindrical;
• tapered.

Cylinder pins, in turn, can be:

• spring split;
• notched (with grooves).

Additional elements of the design of the pins can be threaded holes or protrusions. They are used to extract products from blind holes.

Three groups of pins are distinguished according to the functions performed in the node:

• installation;
• guides;
• fasteners.

Pin connection: GOST

In most cases, when assembling units, standard pins are used, manufactured in compliance with GOST standards. For each specific type of product they have their own. 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 grade 45. But GOST allows the use of material grades A12, 10 kp, 20 kp, etc. for this purpose. Perforated products are made of spring steel. Sometimes pins of different types are made from non-ferrous metals.

Of course, the nominal dimensions of these elements are regulated by standards. GOST also provides for permissible deviations of the latter. This allows you to assign typical pin fits to holes in bushings, shafts, covers, and housings.

The symbol for these items includes:

• word "pin";
• product type;
• its dimensions;
• designation of the standard.

The type is specified only if it is unambiguously defined by the standard. In the field "dimensions"the diameter of the product and its length are noted. Sometimes tolerance fields are put down here.

What is

Connections of this variety belong to the detachable type. When creating them, the assembly parts are first drilled. And it must be cooperative. That is, the parts are pre-folded with each other in such a way as they will be located in the node in the future during its operation. After that, the actual drilling is performed.

The pins themselves are inserted into the holes obtained at the next stage. 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 assembly will be subjected to repeated assembly / disassembly during operation, not cylindrical, but conical pins are provided for it. 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 disassembly and assembly, the assembly may lose its inherent operational qualities. That is, the connection may simply not be too strong.

The pins work during operation:

• on a cut (along the joint surface);
• to the crush.

It is on these grounds that calculations are made for their suitability when used in a particular node. The working surfaces of both pins andparts to be joined.

Advantages and disadvantages

In the manufacture of various kinds of nodes, in addition to pin connections, wedge connections, keyed, slotted connections can be used. All of them are of the detachable type. 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 both advantages and disadvantages.

The advantages of pin connections include in the first place:

• simple design;
• ease of assembly/dismantling;
• precise centering of parts to be joined.

The disadvantage of such connections is basically only one. A hole drilled under the pin will in any case further weaken the part. Terminal connections, for example, do not have such a minus.

At the same time, the sockets for the pins must be processed very carefully. Otherwise, the product may subsequently bend. The need for precise machining of the hole increases the cost of manufacturing the assembly part.

Features of roll pins

The assembly of pin connections when fastening machine parts is usually performed 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.

Punched products of this type can also be used to fix the position of parts. Their main advantage, incompared to smooth ones is that they do not require reaming holes. In the absence of additional fasteners, such elements are also more reliable in terms of falling out. As with the use of conical pins, when using grooved cylindrical pins, assembly / disassembly of the connection can be carried out repeatedly during operation.

In static connections, cylindrical products are installed with an interference fit. In moving ones, they are mounted with the obligatory riveting of the ends. Spring roll pins are usually mounted in lightly loaded connections. Preload during their use is created by reducing the diameter of the hole. Mounting types of pins in fitting connections are installed with an interference fit from one of the parts. On the other hand, they are mounted with a fit 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-rejection at the nodes. Such products are used for torque transmission and for connecting covers to housings almost as often as cylindrical ones.

Simple tapered pins are usually installed in through holes. In this case, during installation, they are simply driven in from the opposite side of the connection. If the hole is not through, a taper pin with a pull-out thread is installed in it.

Adjustable products of this type are used in such connections that, during the operation of the mechanism, can be subjected to shocks and shock loads. In addition, theirinstalled in those nodes in which the parts move at a very high speed. The ends of such pins are usually bred at the end of installation.

Features of installation in the node

Drill parts for pin connection, as already mentioned, assembled. In some cases, these elements, in order to avoid falling out, are additionally fixed. This is done, for example, when installing collapsible connections. Additional fixation in this case is provided with a ring of wire 0.5-0.8 mm.

In non-separable connections, the pins are usually punched. But in some cases, products with drilled ends can also be used. After assembly, such pins are flared.

When using conical products, in some cases, the self-rejection condition may not be met. This happens quite often, for example, in nodes that are subject to vibrations or operate under conditions in which the temperature changes dramatically. In such connections, the conical pins are supposed to be fixed additionally.

Selection and calculation of pin connection

The dimensions of the products used to transmit torque depend primarily on the diameter of the shaft (within d pcs.<0.3d). For shear strength, the pin is selected using the following formula:

t avg=4T/dxd2pcs.<[t avg].

Here T - torque, [t cf] - allowable shear stresses. The last parameter is looked at in special tables. For collapse with a thin hub, the connection is checked according to the formula:

Q avg=2T/d(D-d)d pcs.<[Q avg].

Here/d(D-d)d pcs. - conditional crushing area, [Qav] - allowable crushing stress for steel.

Repair

In addition to crushing or shearing, defects such as hole wear and cracks in the parts themselves can also occur in this type of connection. It is not allowed to operate the nodes further if any of the four problems appear. Repair of the node must be carried out necessarily. In any case, the node with the defect will work for a very short time.

Actually, the repair of pin connections, 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 weld old holes and drill new ones in their place.