Non-detachable connections: technological process and classification

The docking of elements and structures can be divided into two main groups: detachable and one-piece connections. The first include those that can be disassembled without disrupting the integrity of the fastening elements. These are fastenings with nuts, bolts, studs, screws, all connections with and without thread. All are considered to be non-detachable, when dismantling, they will have to break the fastening elements.

They include: welded, glued, riveted, sewn and soldered. Split and non-detachable connections are widely used in certain industries. Below, we will look at each of the species in more detail.

Detachable connections

Their execution consists in drilling holes of slightly larger diameter than the fastening element (screw or bolt). This is done to ensure that in both parts to be fastened there are exact holes. The error in a fraction of a millimeter is compensated, especially for elements with a large number of fasteners. When using screws and screws for the reliability of the joint on them, put on the nut and washer.

The first is put under the second for the immovable connection, it does not allow the parts to rotate. There is also a spring ring that has two sharp teeth. They are against the workpiece and the part, thereby preventing spontaneous unwinding of the nut.

Screws pull together the parts, cutting the threads themselves. When they are used, nuts and washers are not needed. Studs are used if another part is attached to a massive part. It has a thread on both ends, under it in the workpiece drill a hole more than the thread length of the stud.

All-in-one connections

They are:

• Welded;
• Riveted;
• Soldered;
• Glued.

Such types of integral joints have found application in certain areas of production. Let's consider each of them separately.

Welding

A compound adopted through interatomic bonds between parts of parts when heated is called welded. All-in-one joints, which have been properly welded, achieve the necessary strength, cost reduction, and mass of the part.

The sources of element heating can be:

• Molten slag;
• Gas flame;
• electric arc;
• plasma;
• laser ray.

The metal that is to be welded is called the base metal. And the one used in the bath is additive.
A site stuck in this way is called a weld seam.

The obtaining of non-detachable connections in this way can be of the following types:

• contact welding;
• Electro-arc manual;
• Automatic submerged and semi-automatic;
• Arc.

The seam is also divided into:

• Butt;
• Lapping;
• angular;
• T-shirt.

Any of them can be either one-sided or two-sided. They are divided into discontinuous and uninterrupted. There are also differences in the shape of the cross section: a normal seam, convex or concave.

Benefits:

1. Low cost for such permanent joints, due to the simplicity of the seam and low labor input.
2. Relatively small mass, in comparison with other methods of work.
3. No need to make holes in the parts, which gives strength in its cross section.
4. Automation of the welding process implies its tightness.

Disadvantages:

1. The appearance of deformation and buckling after the work done, as well as the occurrence of residual stresses.
2. Withstands mild vibration and bumps.
3. Complexity in quality control.
4. Workers carrying out permanent joints of parts with welding must necessarily undergo training and confirm their qualifications.

Soldering

Details in the soldering method are cemented by the introduction of an additional metal solder.
And the melting point of the solder should be less than that of the parts to be joined. According to this criterion, solders are distinguished:

• Especially fusible. The required melting point is only 145 degrees;
• Soft or fusible. Working heating is not higher than 450 degrees Celsius;
• Hard or medium melting. The melting point is in the range of 450 to 600 degrees;
• High-temperature or high-melting. Such metals melt at temperatures above 600 degrees Celsius.

Solders

Depending on the component, they are divided into:

• Tin-lead (PIC);
• Tin (PO);
• Zinc (PC);
• Silver (PSr);
• Copper-zinc (PMC, brass).

Most of the work on solder is made using tin-lead material of PIC brand. As a rule, they are produced in the form of wire, ribbons or twigs.

Before the solder surface is well cleaned. That they are not oxidized, use a special soldering flux. This substance does not allow the formation of oxides and cleans the surface of parts from them, contributing to better spreading of the solder. A certain type of flux is suitable for a specific temperature, above which it ceases to work and burns.

Riveting

These are joints that are created using a special part - rivets. It has a stem and a head. The process of obtaining integral joints is due to the formation of a closing head at the other end, it is obtained by compressing the end of the rod. Such a construction is completely immobile and yet one-piece. In it there is no possibility of displacement of details relative to each other.

Use such fastening for details of small thickness in the basic sheet materials or where application of high temperatures is inadmissible because of possible deformation of details. When rivets stand side by side, they form a riveted seam.

The material of the elements must correspond to the material of the fastened parts, otherwise electrochemical corrosion may occur due to the difference in the coefficients of thermal expansion. The rivet heads are round, hidden, half-buried and flat.

pros

Advantages of this connection:

1. The ability to withstand greater vibration and impact loads, which is not in the power of welding.
2. Application is possible in materials that are not welded or this process is very long.
3. No application of high temperatures during connection.

Minuses

Among them, we can note the following points:

1. Large consumption of metal for the work done.
2. Increasing the weight of the structure.
3. High labor intensity.
4. Processibility of the process is low.

Adhesive

To obtain strong, permanent joints, it is enough to connect the parts with the help of adhesive composition. The action takes place by forming bonds at the intermolecular level of the surface of the glued part and the adhesive film.

The use of such a method can be found in structures of various materials. Mounting on the basis of glue is used even in bridge construction and aviation. The durability of such a connection and its quality will depend on the preparation of the surfaces of the parts and the type of load that will affect them. It is necessary to clean the surfaces of rust and grease stains, after processing the place with sandpaper.

Gluing details on which the shear or rotational load will act, with a small joint area should not be. This will lead to a loss of strength. It is better to glue those parts that are subject to displacement relative to each other or to the tensile load.

Advantages of the adhesive method:

1. You can connect in this way any blanks and structures, regardless of their shape, mass or materials.
2. High resistance to corrosion.
3. Tightness, which allows you to work with pipelines.
4. Does not cause deformation of parts.
5. There is no concentration of stresses.
6. Reliability of work in conditions of vibration loads.
7. Low cost of consumables.
8. Adhesive joints do not weight the design.

Minuses:

1. Low strength, especially when pulling off.
2. Short-lived, some types of glue can grow old.
3. Low resistance to heat load.
4. Many connections must undergo a long exposure before use.
5. Mandatory compliance with security measures.

All-in-one connection polyethylene-steel

A wide application for joining pipes of steel and modern polyethylene has received an all-in-one joint of polyethylene-steel.

It allows you to securely fasten plastic and metal pipes together, as well as install the necessary fittings for locks. In order to make an inseparable structure, pipes made of polyethylene, manufactured according to a certain standard, are used. A steel (PE-steel adapter) is permanently welded by welding a branch pipe of a metal section with a polyethylene one. This method can be used as stubs on gas and water mains of main networks.

Such permanent joints of pipes are mounted to gas pipelines of apartment houses. Often you can meet them in boiler plants. The use of steel pipelines in our time is increasingly replaced by polyethylene analog. This is due to the obvious advantage of plastic pipes over metallic ones. Therefore, they are used increasingly. The non-detachable polyethylene-steel joint is so reliable that it does not require special maintenance.

Its installation takes place directly in the ground without the use of wells. Mounting is carried out by means of butt-welding or thermistor welding. A non-detachable polyethylene-steel connection can be with or without an amplifying clutch. This part gives the adapter the ability to withstand high pressure and a continuous load of 1 MPa. Adapter without clutch can withstand a load of not more than 0.6 MPa. The connection of the metal to the polyethylene can take place by threading or by using various flanges.

So, we examined the main types of connections, their advantages and disadvantages.