Bonding and Sealants - Types of adhesives
The adhesive in liquid state should have less surface tension than the substrate. The substrate must be sufficiently rugged, surface roughness must be of the order of a micron. The viscosity and adhesive application conditions should be such that the roughness of the substrate is completely wet. If aggressive half is expected to be ensured the ability of covalent bonds as these contribute to the stability of atoms combined.
Structural Adhesives: those who bear burdens greater than the weight of the adhesive. Eg sections of aircraft wings, basic body parts of vehicles. Adhesives support: they must support only the weight of the members. Eg tile adhesives, etc. Adhesives, Sealants: preventing fluid passage of a board through sealants for body joints, for windshield, etc. Stability to heat: Thermoplastic adhesives are those, which soften and flow when heated and solidify when cooled. Thermoset Adhesives: do not soften when heated, may char if they are heated to high temperatures but do not flow.
According to Chemical Composition: Sources animals include various types of glues animal protein for the longest time used for the bonding of wooden objects, obtained from hides and bones) and tails of casein (milk protein: practically insoluble in water, are used in the stuck packet of cigarettes and paper tapes, labels and moisture resistant packaging industry. Plant Sources: based adhesives include starches (carbohydrates: hot water so the paste) or dextrin (depolymerization of starch) maize is the major source of adhesives based on carbohydrates, used in the manufacture of cartons Corrugated, corrugated and other paper products have poor cohesiveness and poor water resistance. Also, the natural rubber and asphalt adhesives. Synthetic: based on materials developed by the chemical industry. According to the curing methods: Solidification (sealants or paraffin wax base).
Evaporation of solvent (rubber based cements and white tails). By chemical reaction: Being stronger than most modern adhesives, animal glues are still used in the restoration of wood and traditional joinery, as well as some painting techniques. Once thickened in water and heated water-bath, used in hot and gel on cooling. In carpentry, water solubility makes reversible, thus rectifying the same glue. In painting, are used both for priming canvases and boards as the development of tempera paintings, and of course in traditional techniques of gilding to the queue.
Animal glues are distinguished by their different degrees of adhesiveness and elasticity, but in any case, we should aim to prepare castings with the minimum concentration required in order to avoid risks of tension or stress in the glued materials. As an example, 40 grams of rabbit skin glue in a quart of water is sufficient to prepare a canvas primer and 60 g in one liter of water to make a painting in tempera, queue for water in water gilding are often used 70 g per liter. For gluing pieces of wood, however, we recommend glue or glue swell cartilage in water, then add more water while it heats up the solution of a loose drain a wooden spoon. The adhesives or glues are those substances capable of joining other substances by surface contact.
They can be classified according to type in: adhesives, inorganic and organic adhesives, among the latter are the natural and synthetic. The cold glue adhesive is organic, synthetic, specifically emulsion is a milky-looking liquid that has tiny suspended particles of oil or resin, polyvinyl acetate or polyvinyl acrylate (PVA) more additives which serve to give special characteristics such as adhesiveness, open time, drying time, color, smell and pH (acidity). The additives used are varied and depend on the specific product characteristics, but overall, the most commonly used are: plasticizers, colorants, buffer type solutions and resins.
Adhesives in general: Most adhesives allow bonding to fill tiny holes and cracks that exist normally on any surface, even very smooth. Adhesives are economic, distribute the tension on the junction, resist moisture and corrosion and eliminate the need for rivets and screws. Its effectiveness depends on several factors, such as resistance to shrinkage and detachment, the malleability, the adhesive force and surface tension, which determine the degree of penetration of glue on the tiny depressions on the mating surfaces. Adhesives vary the purpose for which will be used. Currently, these targets include the growing use of adhesives in surgery and dentistry. Natural adhesives have been replaced in many applications by synthetic, but are still used in large quantities starches, gums, cellulose, bitumen and natural rubber cements.
Among the organic adhesives derived from natural proteins are the tails (sticky solids) made of collagen, a component of bones and connective tissues of mammals and fish, the tail of the blood albumin, used in industry wood veneer, and a tail made of casein, a milk protein, which is used for gluing wood and paint. Among the glue is vegetable starches and dextrin derived from corn, wheat, potatoes (potatoes) and rice, which are used to glue paper, wood and fabric, certain gums such as gum arabic, agar and algin, when are wet adhesion to provide certain products such as seals, stamps and envelopes gummed cellulose adhesives, used to paste leather, fabric and paper, rubber cement, and resins such as tar and putty. Synthetic adhesives, whether used alone or as modifiers of natural adhesives, have better performance and wider application range of natural products.
Most of them contain polymers, which are large molecules composed of a large number of simple molecules that form strong networks linking chains and surfaces in a firm bond. Thermosetting adhesives, which become hard and solid heat resistant by the addition of a catalyst or heat application, are used to glue metal parts for aircraft and space vehicles. Thermoplastic resins, which may soften with heat, are used to glue wood, glass, rubber or rubber, metal and paper products. Elastomeric adhesives, rubber cements as natural or synthetic, are used to stick to rigid materials, flexible materials.
Types of adhesives
Wet Adhesives: The wet adhesive applied to only one of the pieces to be joined and immediately it is attached to the second piece. The pieces must be fixed, and that adherence occurs only once the solvents have evaporated. In the case of so-called solvent-free adhesives, the carrier material is water. Materials open pores favor the drying of wet adhesives. Contact Adhesives: Contact adhesives are applied at both joints. After drying time, which may vary according to each solvent, the pieces are brought together to exert strong clamping pressure. The pieces are immediately connected and the workpiece can be quickly put to the effort. Reactive adhesives: Reactive adhesives are adhesives that cure by chemical reaction rate, physical or catalytic.
According to the type of reaction can consist of one or two components. The adhesives are single component adhesives, depending on the type, they react by humidity, ultraviolet light or atmospheric oxygen (aerobic adhesives) or, in absence of air, for example, metal ions (anaerobic adhesives). In the case of single component adhesives, the glue is applied on one side of the seam. The reaction begins immediately upon contact with the second active component present in the environment or on the bonding surface. The two-component adhesives are adhesives, by type, consisting of liquid components, paste or powder. Generally, the ingredients should be mixed exactly in the mixing ratio indicated. For use is only available a limited period (time from liquid).
Curing begins immediately. The curing time also depends on the type of glue and room temperature. The gluing must be fixed until it is fully hardened. Hot melt glue: The hot melt adhesives can be applied in the form of cartridges, bar, powder, granular, network or movie. They contain no solvents, usually not required or dosing mixing processes. The hot melt adhesives are melted by heat. This can occur in the same joint (eg ironing strips glued) or using a glue gun whereby the hot glue is applied on the parts to be joined. The thermo adhesive melt at temperatures between 110 ° C and greater than 220 ° C (in other systems).
Stickers: The stickers are products that retain their power permanently adhesive. These permanent adhesive materials can be applied where there is no intention of long-term bonding, but later you want to take off again. The stickers find application mainly in adhesive tapes and bands, banded and double-sided adhesive pads, as well as notes, self-adhesive labels and plastic sheets.
Hot Cola: It is derived from collagen, a protein that forms the cartilaginous tissue of joints. Its use is very old. It is probably the oldest glue has been used. It has been found even use the furniture found in Egyptian tombs, and has been used continuously in the development of instruments to the "discovery" of plastic and vinyl glue. Began to fall into disuse product of haste (cheaper) in mass production and its use requires certain precautions and care for optimum results in your strength and stability.
Much of this optimization in the aggregate in small amounts of some substances (vary according to function requiring) that enhance properties such as hardness, elasticity, impermeability, resistance, etc.. For its use and application uses a "last place" which is a small container that fits under pressure into a larger one containing water. This goes straight to the fire, which keeps the queue at a temperature not to exceed one hundred degrees centigrade (essential for it not to burn), its application is hot which increases the dilation of the pores of the wood, which also usually slightly favoring heat absorption. Hardness should also be stressed by drying, which favors understand driving frequencies.
The means of adhesive bonding is a technique to collect materials in recent years proved it can replace or complement to conventional methods such as the joints with nails, or other programs, in numerous applications. The strength and durability of structures connected on airplanes frameworks and assemblies has been demonstrated through the years, but the extent of this experience to other practical uses this still comparatively diminished or restricted by other joining methods. To be clear, screws, nails and programs still dominate the field of marine structures and domestic, also many products mass production involving metal fittings depends on mechanical joints 50 years ago as the only commercially important adhesives were those that were obtained from animals or other natural products whose use dates back centuries. Currently and since 1900 the adhesives from plants and trees have found a wide range of applications, especially on porous materials like paper. Adhesives "Casein" were widely used in World War I military aircraft, but found to have limited resistance in humid environments and the effect of fungal growth. The progressive and rapid increase in the use of adhesives in the industry was mainly due to the development of synthetic resins, which have the limitations of natural products and whose benefit is that unions can generate metals and other materials without porosity.
The first major synthetic resin was the "Phenol" which was widely used to connect tin or tin plates. The Second World War saw the development of epoxy resins for bonding of metal structures on aircraft, and since then many kinds of synthetic resins and rubbers have been developed. Unions by means of adhesives are considered of great importance for the binding of metals and a wide range of materials and are used to an endless number of purposes. This increased use of adhesives has taken place in non-structural applications such as general engineering products, like shoes and packing industry.
(Natural adhesives, epoxies, solvents, adhesives, cell adhesion, due to their advantages in numerous applications, glues or adhesives offer new possibilities for low cost buildings. These should be considered as a complementary method to other methods of attachment, and can be used in conditions of need and economic benefit to marginalized sectors. For example, the weight of a product is vital for a product designer and can easily affect the cost of it, so the use of adhesives complemented the use of screws and nails significantly reduces the size and quantity of the same, reducing her see the weight. At present, the engineering design guidelines seek to familiarize the designer with a variety of applications on the use of adhesive materials and bonding processes, keeping in mind that their effectiveness goes hand in hand with knowledge of their advantages and limitations and involves new concepts of design and production.
Advantages and disadvantages of bonding with adhesives
Benefits achieved by the use of adhesives: Depending on the type of adhesive used, the design of joints, method of application and function you need to fulfill, the bonding will be able to offer the following advantages:
The ability to bond a wide range of materials, whose qualities may vary in composition, deformation and expansion coefficients, elastic modulus, thickness, etc..
The elimination of those irregular surfaces and contours surface generated by the methods of attachment such as bolts and nails, providing a better looking finish in the process of assembly. The manufacture of complex shapes where conventional methods binding are not applicable A more uniform distribution of stress over the area adhesive application, with the minimization of stress areas concentrated as those generated by the screws and nails. With often able to use thinner materials without the loss of resistance, saving weight and cost. Weight reduction through the elimination of metal fittings such as bolts, screws and nails. The possibility of joining heat-sensitive materials, generating bonding by means of pressure.
The advantage of the sealing and insulation properties of unions by means of adhesives against moisture and chemicals. Adhesive layers can act as insulation against electricity, heat, sound and even more can reduce or prevent galvanic corrosion between metals that are similar. The reduction in production costs in the process of manufacturing and assembly, through the reduction of material requirements, reduced weight and elimination of other operations such as drilling with drill, in the case of the screw, the elimination of the hammering, in the case of nails, etc. Perseverance service adhesive joints over time are unknown in severe weather conditions. The heat, radiation, chemicals and bio-degradation can cause destruction of the adhesive.
Adhesives Materials And Their Properties
The adhesives can be classified in many ways, considering that each different type of formula can be defined in terms of:
A. - The materials to be joined.
B. - The physical form of the adhesive.
C. - Methods of adhesion.
D. - The mechanical properties exerted at the junction.
E. - Its durability and service.
They may also be classified in terms of major chemical components that make up and although that is the less information classification given to the designer, is the most commonly used. The classification of adhesives according to the range of materials that are able to bind is not fully applicable to plastics and rubbers due to changes in adhesion properties that can be found within specific members in each class, for example, an adhesive that is suitable for copper is not necessarily suitable for steel will. The tables included in their lists of different materials bonded with adhesives or similar recommendations identified by its chemical composition, have a limited use or value and can be misleading.
Physical form of adhesive materials
The adhesive materials are available in a wide range of physical forms, and for a particular type of application choices or decisions are primarily dictated by considerations of assembly, cost of design and capabilities of the manufacturing industry. The adhesive film/foil piece is a newly developed, been increasing use in structural construction. This type of adhesive is available either in the form of a pressure sensitive material or one that depends on liquid solvents or heat to the material so there will grip. In the practice of structural construction works, the combination of heat and pressure methods for drying are generally required. In general, adhesive film / foil produce uniformity in the thickness and distribution of adhesive in the joint area, restricting it to a specific area and allocated. High performance liquid and low density: Most formulas that exist in this state, or dispersions are aqueous solvents or postings. These are simple applied with the possibility of having a viscosity control by the user.
Pasta or Nursery The material in this way is appropriate for mass production applications where they are needed vacuum features filled sink. A wide variety of consistencies are obtainable from this material. Film/Print: This material is restricted in use to smooth surfaces and uniform and is characterized by easy and quick to low waste as well as in the uniform thickness and distribution of adhesive. Powder Material on this form must be mixed with liquids or are heat should be applied to allow the dust to reach its liquid state. Some types contain latent catalysts that are active during the drying process at high temperatures. In general, powders are economic forms of adhesives, with extensive life. Granules, scepters, bucket, and other solid forms. These are convenient ways for easy application and drying for particular functions.
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