How reliable are adhesive joints?

Repair 2022
How reliable are adhesive joints?
How reliable are adhesive joints?

The scope of the glue is diverse, it is used in industrial production, construction, repair and modeling. Adhesive joints are used in assembly processes, at the stage of installation of structures and materials. The most commonly used glue is in the paper industry and woodworking.

During their history, adhesives and mixtures have been modified. Thanks to modern technology, adhesives based on synthetic resins have appeared that can bond any materials and surfaces. Synthetic adhesives have increased elasticity, waterproof and seal joints, and also ensure their long service life. An example of the effective use of synthetic adhesives is the installation of PVC pipes for adhesive bonding or the use of synthetic adhesive mixtures for the repair and adjustment of machine tools (glue is used to correct the seating surfaces of frames and housings).

adhesive joints

The main advantage of the adhesive is the high reliability of the connection of various surfaces and parts, achieved without excessive impact on structural elements (drilling, screed, welding).

Whatis glue and adhesive joints?

Adhesive is a mixture or multi-component composition used to connect various structural elements and materials. The adhesive bond is one-piece, a strong bond is formed by the adhesion of surfaces with an adhesive layer. Adhesives are different in composition. The compositions consist of organic and inorganic polymers. The basis of the adhesive composition is classified:

  • hot curing polymers;
  • cold-curing polymers;
  • heat-resistant polymers;
  • thermoset and thermoplastic polymers;
  • polymers used in the normal temperature range.

The development of production technologies and polymer chemistry made it possible to create compositions that provide strong adhesive bonds of materials whose surfaces were previously not amenable to strong adhesion: metal, ceramics or glass. In addition to the polymer base, the adhesive contains various additives to give the adhesive layer the desired properties and characteristics (heat resistance, moisture resistance, strength, plasticity, etc.). Targeted additives can be: hardeners, solvents, dyes, plasticizers, and other fillers.

adhesive strength

The quality characteristics and properties of adhesive joints depend on the choice of adhesive and strict adherence to the gluing technology.

Glue: conditions determining choice

In the choice of glue, the main role is played by the properties and characteristics of the materials intended for gluing, the conditionsperformance of work (humidity, temperature conditions), the estimated service life of the adhesive joint and the load on it. When choosing an adhesive, you should pay attention to the cost, sanitary and hygienic parameters, combustibility. A feature of all adhesive joints is the deterioration of adhesion characteristics over time, therefore, adhesive bonds are destroyed throughout the entire period of operation.

pvc for adhesive bonding

Reducing the strength and elasticity of the adhesive layer occurs due to exposure to temperature fluctuations, humidity and other conditions. So, before gluing a building structure, a technological product or a PVC pipe, the adhesive joint is intensively tested for strength under the influence of predicted operating conditions.

General surface bonding technology

Bonding technology involves preparing surfaces, mixing the components of the adhesive composition (if required), applying a thin layer of glue to the surface and waiting until a rigid hitch is obtained. One of the most important steps is the preparation of surfaces before gluing, this ensures optimal adhesion. When applying adhesive to the surface, attention should be paid to the sufficiency of the film thickness. The assembly of adhesive joints is completed with the curing of the adhesive composition, which must take place in the optimal technological mode.

At the preparatory stage of surface treatment, any contaminants are removed, with the help of special solutions, the surfaces are degreased, they are givenroughness. The best option for preparing surfaces is one in which cohesive destruction (destruction along the binder layer) of adhesive joints is noticeable. For the treatment of surfaces to be glued, both chemical and mechanical methods are used to increase the strength of the joint.

The quality of the glue joint depends on the method of applying the adhesive layer to the surface. The adhesive must be evenly distributed over the surface, the film thickness must be uniform and range from 0.1 to 0.2 mm. The method of applying the adhesive depends on the viscosity of the composition.

adhesive pipe

For an example, consider the features of the choice of glue and the technology of glue installation of a water supply system consisting of PVC pipes.

Choosing glue for PVC pipes

The pipe for glue joint made of polyvinyl chloride is used in engineering communications for laying water supply systems, used in heating systems and sewers. There are several technologies for connecting PVC pipes and fittings. Diffusion welding is most often used, however, the technology of gluing pipes with fittings is also very popular, which also achieves a high strength of the adhesive joint.

The adhesive compositions used for gluing PVC pipes contain the main component polyvinyl chloride, which is diluted with a solvent to obtain the required consistency. The adhesive composition may additionally contain various additives and fillers that increase the waterproofing and hermetic properties of the adhesive. The physical bonding process isthe adhesive composition is applied to the surface of the products, then they are brought together, over time the solvent evaporates, a strong adhesive bond is formed. The use of polyvinyl chloride in the adhesive ensures reliable adhesion of surfaces at the molecular level.

To choose the optimal adhesive composition for PVC pipes, consider the following:

  • clearly know for what purposes glue is purchased;
  • it is important to familiarize yourself with the technology of preparing the adhesive composition, PVC-based adhesives can consist of two components, directly affect the strength of the adhesive joint;
  • setting speed, which for most compositions does not exceed 1-2 minutes (depending on humidity and air temperature);
  • adhesives for PVC pipes have different colors;
  • Viscosity of the ready-to-use formulation.

Technology for mounting PVC pipes with adhesive method

The adhesive solution is thoroughly mixed. If the main components need to be connected independently, it is important to observe the correct proportions. The pipe for the adhesive joint is prepared at the gluing site, the surface is cleaned and degreased. Installation begins with the application of adhesive composition on the surfaces to be glued. The glue is applied with a brush with a uniform distribution over the surface, discontinuity of the film and omissions of individual sections are not allowed. Upon completion of the procedure for wetting the surfaces with an adhesive solution, the pipe segment is combined with the fitting.

pvc glue joint

After fitting the fitting and the pipe, the adhesive joint must be firmly fixed for 15-20 seconds, after which the initial adhesive coupling is formed and the adhesive thickens. It is important to make sure that the structure is fixed in the correct position before gluing, as twisting or other manipulation is not allowed. The adhesive joint must be at rest for 15 minutes until the solvent has completely evaporated.

Sequential gluing of all sections of the plumbing system, consisting of fittings and PVC pipes. After 24 hours from the moment of completion of installation, the adhesive joint is checked for tightness and strength under the load of water pressure.

Reliability of adhesive joints

Requirements for the reliability of adhesive joints are imposed depending on the characteristics of the bonded materials and the operating conditions of the connection. However, there are a number of universal parameters that any connection must comply with.

Basic reliability characteristics for all types of adhesive joints:

  • equal strength of the bonded material with adhesive bonding;
  • solidity of the adhesive seam with glued elements;
  • Stability of adhesion bonds and quality of surface treatment determine the indicators of durability and reliability.

The main sign of the reliability of the adhesive seam is to ensure the strength of the joint equal to or greater than the strength of the monolithic part of the material to be glued. Criteria for the reliability of the adhesive connection, based on the featuresoperation, may be:

  • water resistance: the ability of the adhesive layer to resist the damaging effects of water;
  • heat resistance: the ability of an adhesive bond to maintain strength, solidity and elasticity under high temperatures;
  • biological stability: the ability of the adhesive layer and the entire joint to retain its original properties under the destructive influence of biological processes.
adhesive bonding of materials

Advantages of adhesive joints

The use of adhesive mixtures based on polymers and synthetic melts has significantly expanded the scope of plastics. Synthetic adhesive, which is a solution (melt) of a polymer composition, is a plastic processing product. The main advantage of synthetic adhesive bonding is the preservation of the physical and aesthetic parameters of the bonded materials. Reliable connection of planes over large areas is provided by polymer adhesives. Adhesive joints made of polymer compositions are successfully used both for bonding large areas and for spot bonding of small structural elements.

assembly of adhesive joints

9 Reasons Why Bonding

  1. Adhesives are able to form strong bonds between materials with different physical properties and sizes. Bonding technology is superior to a number of other technologies, including welding, because it is able to connect thin-sheet elements and fragile materials.
  2. Glueallows you to evenly distribute stress over the entire plane, which is difficult to achieve using welded or riveted joints. The use of welded and riveted joints is characterized by a high concentration of point stresses only at the coupling points.
  3. Adhesive joints provide high speed assembly of structures, while being economical. Gluing technology is universal and can replace several ways of connecting elements.
  4. Developed production technology and a variety of adhesive mixtures make it possible to use them at various stages of the production process.
  5. The cost of an adhesive joint and its strength often exceeds the corresponding indicators of alternative options for connecting structures and elements. Joints made with adhesive are lighter than welded or riveted joints.
  6. Adhesive materials have a unique ability to absorb, distribute and transfer stresses over the entire plane between structural elements. The elasticity and deformability of the adhesive layer increases the reliability of the coupling.
  7. Adhesive can successfully bond heat-sensitive materials and elements that are liable to collapse or deform under high temperature.
  8. Glue can act as a sealing material, providing not only a reliable connection of the structure, but also effective resistance to the destructive action of moisture and chemicals. Adhesive seams are good at insulating heat and sound,excellent dielectrics.
  9. There are a large number of adhesive compositions designed for difficult climatic conditions, with their help, particularly reliable adhesive bonds are obtained. The use of special compounds makes it possible to glue structures and elements without heating equipment at low temperatures and high humidity.
adhesive joints application

Disadvantages of adhesive joints

The main disadvantages of adhesive joints, in particular those obtained using synthetic adhesives, is the impossibility of their use in harsh and especially harsh operating conditions.

Connecting structures with glue requires high precision and step-by-step control of their execution. Specialists need to monitor the parameters and modes of bonding, adherence to the technology of curing the adhesive, as well as the rest of the structure during the formation of the hitch. By checking the resulting joints, the specialist is not always able to determine possible bonding defects.

For many industrial adhesives, the curing process involves the use of heating elements. Hot bonding is often not possible when joining large, complex structures.

What is important to know when considering adhesive joints?

  1. All bonding technologies involve careful multi-operation surface treatment, which significantly complicates the process. The curing process of the adhesive joint must take place under conditions of a certain humidity, maintainingconstant pressure and temperature conditions. In addition, the full curing period may take a long time. For some types of industrial adhesives, the bonding step involves heating the adhesive joint.
  2. Adhesive joints are carefully designed, experts analyze tensile and peeling loads, calculate the stresses arising from the difference in thermal expansion coefficients of the glued plane and the adhesive line.
  3. Glue joints, despite their positive properties, have a significant drawback - low heat resistance. The use of glue for assembling structures is limited if the structure is operated at elevated temperatures. In addition, many types of adhesive joints can be destroyed under the influence of mechanical shocks.
  4. Features of gluing elements do not make it possible to fully control the quality of the connection.
  5. Connections obtained by gluing are non-separable, for this reason, the use of glue greatly complicates the process of disassembling or dismantling structures. Under conditions of intensive use in aggressive environments or harsh operation, it is not possible to calculate the durability of the adhesive joint.

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