The joining 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 violating the integrity of the fastening elements. These are fastenings with nuts, bolts, studs, screws, all connections with and without threads. Those are considered one-piece, when disassembling which, the fastening elements will have to be broken.
These include: welded, glued, riveted, stitched and soldered. Pluggable and one-piece connections are widely used in certain industries. Below we will consider each of the species in more detail.
Detachable connections
Their design consists in drilling holes of a slightly larger diameter than a fastener (screw or bolt). This is done so that both fastened parts have accurate holes. The error in a fraction of a millimeter is compensated, especially for elements with a large number of fasteners. When using bolts and screws for reliability of the joint, they put on a nut and washer.
The first is placed under the second for the immobility of the connection, it prevents the parts from rotating. There is also a snap ring that has two sharp teeth. They rest against the workpiece and the part, thereby preventing spontaneous unscrewing of the nut.
Screws tighten the parts, cutting the thread on their own. When using them, nuts and washers are not needed. Studs are used if another is attached to the massive part. It has a thread at both ends, a hole is drilled under it in the workpiece for more than the length of the stud thread.
One-piece connections
They are:
- welded;
- rivets;
- soldered;
- glue.
These types of integral connections have found application in certain areas of production. Let's consider each of them separately.
Welding
A compound adopted by interatomic bonds between parts of parts when heated is called welded.
Permanent
joints, the welding of which was correctly performed, achieve the necessary strength, reduce cost, and also the mass of the part.
Sources of heating elements can be:
- molten slag;
- gas flame;
- electric arc;
- plasma;
- laser ray.
The metal to be welded is called basic. And the one that is used in the bath is additive.
An area seized in a similar manner is called a weld.
Obtaining one-piece compounds in this way can be of the following types:
- contact welding;
- electric arc manual;
- automatic submerged and semi-automatic;
- arc.
The seam is also divided into:
- butt;
- lap;
- angular;
- T-shaped.
Any of them can be either one-sided or two-sided.
They are divided into intermittent and continuous. There are also differences in the shape of the cross section: normal seam, convex or concave.
Benefits:
- Low cost for such one-piece connections, due to the simplicity of the seam and the low cost of labor.
- Relatively light weight compared to other working methods.
- There is no need to make holes in the part, which gives strength in its section.
- Automation of the welding process implies its tightness.
Disadvantages:
- The appearance of deformation and warping after the work performed, as well as the occurrence of residual stresses.
- Withstands light vibration and shock.
- Difficulty in quality control.
- Workers making permanent connections of parts by welding must undergo training and confirm their qualifications.
Soldering
The parts in the brazing method are held together by the introduction of additional solder metal.
Moreover, 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 no higher than 450 degrees Celsius;
- hard or medium melting. Their melting point is in the range from 450 to 600 degrees;
- high temperature or high melting point. Such metals melt at temperatures above 600 degrees Celsius.
Solders
Depending on the component, they are divided into:
- tin-lead (PIC);
- tin (software);
- zinc (PC);
- silver (PSR);
- copper-zinc (PMC, brass).
Most of the solder work is carried out using tin-lead POS grade material. As a rule, they are produced in the form of wire, ribbons or rods.
Before soldering, the surfaces are well cleaned. So that they do not oxidize, use a special solder flux. This substance prevents the formation of oxides and cleans the surfaces of parts from them, contributes to better spreading of solder. A certain type of flux is suitable for a specific temperature, above which it stops working and burns.
Rivets
These are the joints that are created using a special part - rivets. It has a shaft and a head. The process of obtaining one-piece joints occurs due to the formation of a locking head at the other end of the part; it is obtained by compressing the end of the rod. Such a design is completely motionless and at the same time one-piece. There is no possibility of displacement of parts relative to each other.
Use this mount for parts of small thickness, mainly sheet materials or where the use of high temperatures is unacceptable due to the possible deformation of the parts. When the rivets are near, they form a rivet 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-swept and flat.
pros
The advantages of this compound:
- The ability to withstand large vibrations and impact loads, which is beyond the power of welding.
- Application is possible in materials that are not welded or this process is very long.
- There is no use of high temperatures when connecting.
Minuses
Among them, the following points can be noted:
- Large metal consumption for the work performed.
- Weight gain of the structure.
- High labor input.
- The processability is low.
Glue
To get strong permanent connections, it is enough to connect the parts with the help of an adhesive composition. The action occurs by the formation of bonds at the intermolecular level of the surface of the bonded part and the adhesive film.
The application of this method can be found in structures made of various materials. An adhesive-based mount is used even in bridge building 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, then treat the area with sandpaper.
Gluing parts that will act under shear or rotation load, with a small joint area should not be. This will result in a loss of strength. It is better to glue together those parts that are subject to displacement relative to each other or tensile load.
Advantages of the adhesive method:
- This way you can connect any workpiece and structure, regardless of their shape, weight or materials.
- High corrosion resistance.
- Tightness, which allows you to work with pipelines.
- Does not cause deformation of parts.
- No stress concentration is created.
- Reliability of work in the conditions of vibration loads.
- Low cost of consumables.
- Adhesive permanent joints do not burden the design.
Minuses:
- Low strength, especially with peel load.
- Durability, some types of glue may age.
- Low resistance to thermal stress.
- Many connections must undergo a long exposure before use.
- Mandatory safety measures.
One-piece polyethylene-steel connection
Widespread use for joining pipes of steel and modern polyethylene has received an integral connection polyethylene-steel.
It allows you to securely fasten plastic and metal pipes together, as well as install the necessary fittings for constipation. To make an inextricable design, polyethylene pipes made according to a certain standard are used.
A one-piece steel connection (PE-steel adapter) is obtained by welding a branch pipe of a metal section with a polyethylene one. This method can be used as plugs on gas and water pipelines of trunk networks.
Such one-piece pipe connections are mounted to the gas pipelines of residential buildings. Often you can meet them in boiler plants. The use of steel pipelines in our time is increasingly being superseded by the analog of polyethylene. This is due to the obvious advantage of plastic pipes over metal ones. Therefore, they are used more often. The integral polyethylene-steel connection is so reliable that it does not require any special maintenance.
Its installation takes place directly in the ground without the use of wells. Installation is carried out by butt welding or thermistor. The integral polyethylene-steel connection can be with or without a reinforcing sleeve. This part gives the adapter the ability to withstand high pressure and a continuous load of 1 MPa. An adapter without a coupling can withstand a load of no more than 0.6 MPa. The connection of metal with polyethylene can occur using threads or using various flanges.
So, we examined the main types of compounds, their advantages and disadvantages.