Installation (cylindrical, conical, "lying") pins

Pins and pin joints consist of parts that are connected using pins.

Pin connections are used to fix the relative position of parts (Fig. 1; a, b, c, d), when transmitting relatively small torques (Fig. 1; e, f). A common example is the fixation of the relative position of the gearbox body and cover with two conical pins (Fig. 1, b), which ensures that their relative position is maintained during joint machining, assembly and disassembly of the gearbox.

Rice. 1. Pin connections

The advantages of pin connections: their simplicity, manufacturability and low cost. The disadvantage of some pin connections is the weakening of the shaft cross-section by the hole and the associated stress concentration.

The main types of standard pins are shown in Fig. 1.

In addition to the above designs, there are many other pins that are used in mechanical engineering. These include: conical and cylindrical with a notch on the outer surface, spring, cylindrical and conical pins with internal thread (the thread on the pins serves either to secure them or to remove them from the hole during disassembly); conical adjustable pins, hardened cylindrical pins and cylindrical rivet pins (these pins have grooves and are used instead of nails or screws, etc.).

Cylindrical pins are usually placed on the workplace with a guaranteed interference fit K7/m6 or with a transition fit H7/m6, and in moving joints - with riveted ends (Fig. 1, e).

The hardness of unhardened pins is at least 145 HB and hardened ones - 58...62 HRC.

Conical pins are made with a taper of 1:50, ensuring their self-braking. Ordinary conical pins (Fig. 1, b) are placed at through holes, when they can be knocked out from the opposite side. For blind holes, conical pins with threads are installed for pulling out (Fig. 1, c). Conical with a thread at the end (Fig. 1, d) and adjustable pins are installed in connections experiencing dynamic loads, shocks and impacts, as well as in connections moving at high speed. After installing the adjustable pins on the workplace, their ends are slightly spread apart.

Pins are made from steel St4, St5, Steel 35, 40 and 45. It is recommended to make drilled pins from spring steel (steel 65G). If necessary, use pins with heat treatment of 45..65 HRC. Roughness of the landing surface Ra = 0.8…0.4 µm. Plastic pins are used to connect plastic parts.

Where are they used?

Such connections are generally used to transmit only very small loads. Sometimes pins are used to secure parts together. There are also special shear 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 pin connections is prosthetics in dentistry. Using such elements, artificial teeth are attached.

Cotter pins

A cotter pin is an elastic product made of metal; it is a wire rod of a semicircular cross-section, bent in half and with an eye formed at the bend. The length of such a product is measured from the short end of the rod to the point where the eye is formed.

Cotter pin DIN 94 Cotter pin length

Cotter pins are used mainly with castle nuts, bolts and pins with holes (pins) when it is necessary to connect and fix lightly loaded parts, as well as to protect against unscrewing. To install the cotter pin, you need to insert it into the intended through hole and bend the ears.

Other types of cotter pins:

Spring DIN 11024 (needle) in two versions: D with a double loop and E with a single loop.

Execution D Execution E

The figure below shows a diagram of installing a spring cotter pin into a hole on the shaft:

The TsKI assortment also includes a ring cotter pin and a cotter pin with a ring (pin) DIN 11023.

Ring cotter pin Ring cotter pin

Types of pins

When assembling various types of components, two main types of similar products are used:

• cylindrical;
• conical

Cylindrical pins, in turn, can be:

• spring split;
• perforated (with grooves).

Additional design elements of the pins may include threaded holes or protrusions. They are used for removing products from blind holes.

According to the functions performed in the assembly, three groups of pins are distinguished:

• installation;
• guides;
• fastening.

Pin connection: GOST

In most cases, when assembling assemblies, standard pins are used, manufactured in compliance with GOST standards. They are different for each specific type of product. Thus, the production of simple-shaped pins is regulated by GOST 3128-70 (cylindrical) and GOST 3129-70 (conical). Such parts are usually made from steel grade 45. But GOST allows the use of material grades A12, 10 kp, 20 kp, etc. for this purpose. Expanded products are made from spring steel. Sometimes pins of different types are made from non-ferrous metals.

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

The designation of these products includes:

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

The type is indicated only if it is clearly defined by the standard. In the “dimensions” field, the diameter of the product and its length are indicated. Sometimes tolerance fields are also entered here.

Contraindications

In some cases, the pin design is contraindicated. The possibility of installing pins for dental prosthetics is determined by the doctor after studying the medical history, conducting an examination of the damaged tooth and assessing the condition of the oral cavity.

In most cases, inflammatory processes in the oral cavity immediately become an obstacle to placing a pin. In this case, pin structures are installed after treatment.

Direct contraindications to the installation of pins are:

• absence of a tooth crown in the frontal part;
• narrowness of the root canals: width less than two millimeters;
• impossibility of giving a cylindrical shape to the root canal;
• insufficient root height;
• the presence of cysts and granulomas in the oral cavity;
• blood clotting disorders, including during menstruation in women;
• pregnancy;
• mental disorders;
• any dental diseases of an inflammatory nature in the acute stage;
• complete destruction of the tooth crown.

What is

Connections of this type are of the detachable type. When creating them, the parts of the assembly are first drilled. Moreover, it must be joint. That is, the parts are first stacked with each other in the same way as they will be located in the unit later during its operation. After this, the actual drilling takes place.

At the next stage, the pins themselves are inserted into the resulting holes. 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 will be subjected to repeated assembly/disassembly during operation, conical pins rather than cylindrical pins are provided for it. This allows you to extend the service 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 original performance qualities. That is, the connection may simply not be too strong.

The pins work during operation:

• for cutting (along the joint surface);
• to crumple.

It is based on these characteristics that calculations are made to determine their suitability for use in a particular unit. The working surfaces of both the pins and the parts being connected can be subject to collapse.

CONTROL METHODS

5.1. The appearance of the pins is checked by inspection without the use of magnifying devices, in a room with illumination of at least 300 lux.

It is allowed to use a magnifying glass with a magnification of 2.5 - 3´.

5.2. The diameter of the circumscribed circle of the notched pins is checked with ring gauges.

5.3. Threads are checked using limit gauges in accordance with GOST 24997.

5.4. The remaining pin sizes are checked using universal methods and means.

5.5. Hardness control - according to GOST 2999.

5.6. The roughness of the working surfaces of the pins is checked by the organoleptic method by comparison with roughness samples in accordance with GOST 9378 or instruments.

5.7. Quality control of coatings - according to GOST 9.302.

Advantages and disadvantages

In the manufacture of various types of assemblies, in addition to pin connections, wedge, key, and spline connections can be used. All of them are of the detachable type. Threaded connections of this type using screws, studs and bolts, profiles, and terminals are also very often used. Each of these types has both its advantages and disadvantages.

The advantages of pin connections include primarily:

• simplicity of design;
• ease of assembly/disassembly;
• precise centering of the parts to be connected.

Such connections have basically only one drawback. In any case, a hole drilled for the pin will weaken the part in the future. Terminal connections, for example, do not have such a disadvantage.

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

Tooth restoration using a pin: indications and contraindications

If a tooth can be saved, then it is worth fighting for. You can always make it in time with dentures or implantation, but time is running out to save your natural tooth. In this regard, it is important to seek dental care in a timely manner. Let's consider cases when the extension procedure is appropriate and when it is not.

Indications

• Cases when the tooth is destroyed by half or more, but the root is intact. Even if the crown is destroyed, but the root is intact, then extension onto a pin is possible.
• Damage in which the degree of dentin damage does not allow filling. For restoration work, a support in the form of a pin is required to minimize and distribute the chewing load.
• Cases when a tooth needs to be restored for further dental prosthetics. In this case, the restoration is carried out with the aim of using the tooth as a support for the prosthesis.

Contraindications

• The roots of the teeth are destroyed. In this case, there is no stable support for the pin, and installing the structure is risky.
• Inflammatory diseases of the oral cavity. In particular, we are talking about inflammatory pathologies of the gums (gingivitis, periodontitis).
• Cysts, granulomas or tumors in the area of ​​the tooth to be restored.
• Thinning of the walls of the root canals. If during diagnostics it is clear that the wall thickness is 2 mm or less, then pin restoration is not performed.

Alternative options

If tooth augmentation is contraindicated for a patient, this does not mean that a beautiful smile can be given up. Dentistry offers a number of alternative methods, among which the following are often used:

• Implantation – installation of an implant on the jaw bone. Then an abutment and crown are installed on the healed implant. The Center for Israeli Dentistry performs all types of implantation - one-stage, two-stage, All-on-6 and All-on-4 implantations.
• Installation of dental inlays is a microprosthetic option often used to restore lateral teeth. Often such inlays are used for advanced stages of caries or injuries. The production of the inlay is carried out by a dental technician, who makes the design based on a computer model of the patient’s dentition.
• Metal-ceramic crowns are a metal dental prosthesis coated with ceramics. The advantage of metal ceramics is strength, durability (up to 12 years) and aesthetics.

Alternative options for dental restoration are discussed with your doctor. The dentist will recommend the best option based on medical indications, patient preferences, and financial capabilities.

Features of using cylindrical pins

The assembly of pin connections when fastening machine parts is usually performed using smooth products. In the same way, the usual fixation of structural elements of the machine during its operation is usually carried out. In this case, two smooth pins are most often used.

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

In static connections, cylindrical products are installed with interference. In moving ones, they are mounted with the obligatory riveting of the ends. Spring cylindrical pins are usually mounted in lightly loaded connections. The tension when using them is created by reducing the diameter of the hole. Installation types of pins in fit connections are installed with an interference fit with one of the parts. On the other hand, they are mounted with a H7/h6 or H7/js6 fit.

Types of pins in dentistry

Dental pins vary in material, elasticity, fixation method and shape. The doctor selects a suitable design after a thorough examination, conducting the necessary studies and interviewing the patient. To make sure that there are no contraindications to installing the rod and that the width and depth of the canals are sufficient, the doctor must conduct an X-ray examination.

By material

• The anchor pin is the most popular in dentistry. This is due to the fact that it helps restore teeth with the maximum degree of crown destruction. The condition of the tooth root is extremely important: the pin can only be installed if it is intact and healthy. The product is made from an alloy of various metals: stainless steel, brass, palladium, titanium and even gold. Due to their high strength, lightness and low cost, titanium pins are most often used in dentistry. The main advantage of the anchor pin is the reliable retention of the restored part of the tooth and the possibility of further installation of dentures.
  Disadvantages include susceptibility to corrosion, difficulty in removal and visibility. Anchor pins can be installed either passively or actively.
• Fiberglass pin is the second most popular. Its difference lies in its high elasticity, hypoallergenicity and easy removal. The structure is made by dipping fiberglass into a plastic mold in such a way that an equivalent load is created on the hard tissues of the tooth. Visually, the fiberglass pin is almost invisible (see photo), since its color matches the enamel pigment. The disadvantage of the product is the 15 percent probability of destruction of dental tissue.
• Carbon fiber dental pins are very elastic, which reduces the load on the tooth root and prevents canal fracture. The structure of the material is close to the dentin layer of a natural tooth, making the product strong and durable.
• Parapulpal rods are made of a metal alloy and coated on the outside with polymer. They are used primarily for reinforcing filling material with a tooth cavity. They are inserted into hard tissues without penetrating the pulp. On the one hand, this eliminates the possibility of bacteria penetrating inside and developing inflammation, on the other hand, it limits the range of applications.

By elasticity

• Elastic pins better protect the tooth from fractures and impacts.
• Inelastic ones are preferred for supporting restorative structures, prostheses and bridges.

Pin Shape

When choosing the shape of the rod, the doctor proceeds from the individual shape of the root canal. The following rod shapes have been developed:

• conical;
• cylindrical;
• cylindrical-conical;
• screw.

Installation methods

• Active. The rod is screwed into the root of the tooth using a thread and is used as a support for a full crown.
• Passive. The rod is inserted and fixed into the root canal using special cement; it does not need to be screwed in. The strength of the structure is lower, but this method is more gentle on tooth tissue.

Conical products

Pins of this variety are made with a taper of 1:50. This ensures their subsequent self-denial in the nodes. Such products are used to transmit torque and to connect covers with 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 connection. If the hole is not through, a tapered pin with a thread is installed into it for pulling out.

Adjustable products of this type are used in connections that may be subject to shocks and shock loads during operation of the mechanism. In addition, they are installed in those units in which parts move at very high speeds. The ends of such pins are usually separated after installation.

Features of installation in the node

The parts are drilled for connection with a pin, as already mentioned, in the assembly. In some cases, these elements are additionally fixed to avoid falling out. This is done, for example, when installing dismountable connections. In this case, additional fixation is provided with a ring of 0.5-0.8 mm wire.

In non-separable connections, the pins are usually cored. 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 units subject to vibration or operating under conditions in which the temperature changes sharply. In such connections, conical pins must be secured additionally.

Selection and calculation of pin connections

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

• t av=4T/dxd2pcs.<.

Here T is the torque and is the permissible shear stress. The last parameter is looked at in special tables. The connection is checked for collapse with a thin hub using the formula:

• Q av=2T/d(Dd)d pcs.<.

Here /d(Dd)d pcs. — conditional crushing area, — permissible bearing stress for steel.

Repair

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

The actual repair of pin connections is, of course, carried out in compliance with certain standards. In most cases, defective pins are discarded 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.