Factors influencing the choice of adhesive

The basic function of the adhesive is to coat the surfaces of the adherends to connect the adherends.

One, bonding assembly

The entire processing process of the bonding assembly has more or less an impact on the choice of adhesive com" href="http://">coating online coatingol.

Second, the nature of the material to be adhered

The physical and chemical properties of the material to be adhered and the degree of surface preparation required before bonding are another important factor to consider when selecting an adhesive.

Third, the strength of the adhered material

Low-strength materials, such as fabric, felt or some wood-like materials, may be more fragile than adhesives, so joint failure occurs in the material content.

Fourth, the thickness of the adhered material

Low-strength materials, such as fabric, felt or some wood-like materials, may be more fragile than adhesives, so joint failure occurs in the material content.

Five, the thickness of the adhered material

Another factor that cannot be ignored is the form of the adhesive.

Six, the force of the bonded body

Adhesive changes from a flexible, undried material to a tough, hard solid, and its cohesive strength properties vary greatly, with an amplitude of about several thousand N/cm2.

In some cases, the adhesive may only be needed for temporary bonding.

The type and magnitude of the stress provided by the adhesive is largely determined by the joint design.

The thickness of the joint film to select a suitable adhesive to meet the required strength is of special significance.

The conditions of the external stress on the bonded body must be specified in detail.

7.

When the adherend is incompatible with the adhesive, it will cause the bonding failure of the adhesive.

Whenever possible, a detailed description of the nature of the adhesive must be provided at the same time as the sample of the adhesive.

Eight, the requirements of the bonding process

The condition of adhesive bonding is also an important criterion for choosing the correct adhesive.

Typical factors involved in the bonding process include: the form of the adhesive, the preparation and application methods of the adhesive, the storage period of the adhesive, the pot life of the adhesive, the necessary means or equipment for the use of adhesive, the variability of the bonding process, and the application of glue The allowable time between bonding and bonding (superimposition), the drying time and temperature of the adhesive layer, the curing temperature and use temperature of the adhesive layer, the rate of change of the bonding strength at different temperatures, special requirements and preventive measures, such as odor, easy Flammability and toxicity, etc.

The selection method of the adhesive applied to the workpiece is not only determined by the physical properties of the adhesive, but also by the size and shape of the part, the number of components to be coated and the size of the part.
The form of the adhesive ranges from thin liquid to paste and solid.
But for different forms, different methods of use must be adopted.
For example: spraying, brushing or rolling for thin liquid form; while for paste-like adhesives, use a glue applicator or a spatula glue applicator.

For the adherend, the adhesiveness of the adhesive is usually important.
For the parts that have been coated with glue to be assembled, the nailability or adhesion plays a decisive role.
During assembly, the adhesion time range determines the time interval between the application of the adhesive and the assembly.
Therefore, the adhesive properties will determine the necessary use conditions of the adhesive (ie, the form of the adhesive, the mass transfer rate, the mixing time and the application method).
In contrast to thermoplastic adhesives, thermosetting adhesives are generally less tacky.
Adhesion varies greatly, depending on the structure and aggregation morphology of the adhesive molecules.
Latex adhesives become sticky only when the liquid dispersion medium (carrier) is removed (volatized); solvent-based rubbers become sticky even when they contain a considerable amount of solvent.
Both glues show very good adhesion.
For some adhesive parts, the curing temperature of the adhesive affects the choice of adhesive.
Many thermosetting adhesives need to be heated and pressurized to form an adhesive, and it is impossible to achieve these conditions during processing.
Cold-curing adhesives are usually used.

The choice of adhesive can also be determined by the geometry and arrangement of the parts of the adhesive.
Generally, loose-fitting parts require gap adhesives; on the contrary, tight-fitting parts need low-viscosity adhesives.

9.
Conditions of use

For each type of assembly, when selecting an adhesive for it, the strength that the adhesive must maintain under the conditions of use must be taken into account during the entire expected life.
Therefore, in order to specify a suitable adhesive, the designer must understand all the conditions that need to be met.

Usually, the important thing is the strength and durability requirements, and these related factors have been mentioned in the stress situation of the bonded body.
Different types of adhesives have a wide range of responses to different stresses and rates of application.
Thermoplastic adhesives are not suitable for structural applications because they tend to break when supporting lower loads and soften when heated.
Thermoplastic adhesives cannot withstand long-term vibration stress, although they show greater strength than thermosets in short-term continuous tests.
Thermoplastic rubber adhesives usually have high peel strength, but their tensile strength and shear strength are relatively low.
In contrast, thermosetting resins are often used as the basic component of structural adhesives.
The structural adhesive becomes a relatively hard adhesive layer at room temperature and retains most of its strength.
Therefore, generally speaking, the application of thermosetting structural adhesives is desirable when high strength and high destruction stability are required.
Adhesives with thermosetting resin or rubber/resin as the main component are also suitable for supporting vibration loads, but their strength is relatively poor for supporting peeling stress or splitting stress.
Under impact loads, color resilience adhesives will prove more satisfactory than using brittle thermosetting adhesives.

Another important factor worth considering is the effective temperature range required by the adhesive.
Usually the use temperature of the adhesive part refers to the temperature of the glue layer, not the ambient temperature.
The temperature of the adhesive member is often lower than the ambient temperature, especially when the adhesive member is intermittently or briefly exposed to a heated environment.
At high temperatures, all adhesives lose strength to varying degrees, and part of the 540 adhesive softens or decomposes into useless things.
There are many types of thermosetting and thermoplastic adhesives that can be used below 70°C; but at 120°C, only a few thermoplastic adhesives have a service life of adhesives

Generally, the adhesive is required to have a service life, that is, the service life of the adhesive.
In fact, it is required that the bonding validity or life of the adhesive should be longer than that of the adhesive.
For example, the adhesive used to bond the whetstone to the metal seat must maintain a satisfactory bond until the whetstone is exhausted.

Of course, in some cases, short service life is another requirement for adhesives.
In assembly, it is sometimes necessary to temporarily stick the parts with adhesive so that they can be installed by other means; or use adhesive to "clamp" the workpiece on the worktable during processing, such as for glass, stone, magnetic head or The situation during polishing of metals, etc.
The bonding of porcelain powder before sintering and the bonding of foundry sand materials are two other examples of temporary bonding.
There are also special requirements for the bonding of casting sand, that is, after the casting is shaped, the bonding will fail, and the sand will disintegrate and no longer attach to the casting.
Wax, lacquer, shellac, etc.
are often used as temporary adhesives.

X.
Requirements for storage of adhesive parts

People usually pay attention to the use conditions of the bonding parts, but the storage conditions of the bonding parts can be ignored.
The correct method is to pay attention to the abnormal extreme temperature and impact (impact) load of the adhesive during transportation and storage when selecting the adhesive.
For example, a jet engine works in a hot state, and may be stored in an environment below -40°C or transported under such conditions.
If the storage and transportation conditions are ignored when selecting the adhesive, the adhesive will be damaged before use.

11.
Cost

Consider the bonding process as a whole, choosing the proper properties of the adhesive is more important than the cost of the adhesive.
In addition to the price of the adhesive, the production efficiency of the selected adhesive and other factors must also be considered.
Using only the lowest cost adhesive, regardless of the following related factors, may not achieve good economic results:

(1) The total efficiency of bonding (related to the bonding area and the number of components);

(2) The ease of equipment required for application or processing (equipment includes molds, fixtures, pressurizers, heating furnaces, applicators, etc.
);

(3) The time required for the process (including assembly time, preparation time of the adhered component, curing time, etc.
);

(4) The labor cost of assembling and inspecting the adhered components;

(5) The quantity of waste materials compared with other connection methods.

Usually, it is better to use the fast positioning adhesive with a simple bonding process, as long as no complicated assembly fixtures or molds are used, even if the price of the adhesive is high, it is also cost-effective.