Adhesives

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Adhesives

  1. 1. MET FACULTY OF ARCHITECTURE, MORADABAD SESSION 2010-11 PRESENTATION ON ADHESIVES BY VISHVENDU PANDEY
  2. 2. ADHESIVES AN ADHESIVE IS A SUBSTANCE WHICH IS USED TO JOIN TWO OR MORE PARTS SO AS TO FORM A SINGLE UNIT. THE APPLICATION OF ADHESIVE HAS THE FOLLOWING ADVANTAGES OVER THE CONVECTIONAL METHODS OF BOLTING, RIVETING AND WELDING :  A WIDE VARIETY OF COMBINATIONS IN JOINING IS POSSIBLE.  IT CAN BE USED FOR BONDING THE SURFACES OF GLASS, METAL, PLASTICS AND WOOD.  IT CREATES A MASSIVE EFFECT.  IT IS POSSIBLE TO PREVENT CORROSION BETWEEN DIFFERENT METALS JOINED BY ADHESIVE.  IT PRODUCE ADEQUATE STRENGTH.  THE PERMEABLE JOINT CAN BE MADE IMPERMEABLE FOR WATER AND GAS BY THE APPLICATION OF ADHESIVES.  THE PROCESS OF APPLYING ADHESIVE IS EASY, ECONOMICAL AND SPEEDY.
  3. 3. DISADVANTAGES:  IT IS NOT POSSIBLE TO ADOPT ANY ADHESIVE FOR ALL SUBSTANCES. DEPENDING UPON THE PROPERTIES OF SUBSTANCES TO BE JOINED, SUITABLE ADHESIVE HAS TO BE SELECTED.  THE ADHESIVE SUBSTANCE DOES NOT BECOME STRONG IMMEDIATELY AFTER ITS APPLICATION. IT REQUIRES SOME TIME TO ATTAIN THE DESIRED STRENGTH.  THE ADHESIVE SUBSTANCE GENERALLY DOES NOT REMAIN STABLE AT HIGH TEMPERATURE FOLLOWING FACTORS DETERMINE THE QUALITY OF AN ADHESIVE :  ITS DEGREE OR INTENSITY OF STICKING.  ITS DURABILITY.  ITS RESISTANCE TO HEAT.  THE STRENGTH OF BOND DEVELOPED AFTER DRYING OR SETTING.  THE REQUIRED TO DEVELOP THE REQUIRED BOND ETC.
  4. 4. PROPERTIES ADHESIVES SHOULD HAVE HIGH TENSILE STRENGTH. THE IMPORTANT PHYSICAL PROPERTIES OF ADHESIVES ARE COHESIVE STRENGTH, ADHERENCE, FLUIDITY AND WET ABILITY OF THE SUBSTRATE.  COHESIVE STRENGTH : ADHESIVE SHOULD HAVE MORE COHESIVE STRENGTH THAN EITHER OF THE SURFACES BEING HELD TOGETHER. USUALLY THE ADHESIVE BECOMES MORE BRITTLE AS ITS COHESIVE STRENGTH IS INCREASED.  ADHERENCE : FOR AN ADHESIVE TO HOLD TWO SURFACES TOGETHER THE FORMER SHOULD FORM A STRONG BOND AT EACH OF THE INTERFACES BETWEEN THE SURFACE AND THE ADHESIVE, AND THE ADHESIVE MUST HAVE STRONG COHESIVE STRENGTH. SINCE ADHESIVE FAILURE OCCURS IN THE WEAKEST BOND, FAILURE CAN OCCUR AT EITHER INTERFACE, AS ALSO FOR COHESIVE FAILURE. FAILURE MAY ALSO OCCUR INSIDE THE ADHESIVE ITSELF. IN PRACTICE THE BOND FAILURE AT THE INTERFACE IS RARE. REGARDLESS OF THE QUALITY OF THE ADHESIVE CLEAN SURFACES ARE NECESSARY TO GET THE BEST RESULT.
  5. 5. FLUIDITY : WHEN THE LIQUIDS ARE STIRRED, THEY BECOME TEMPORARILY MORE FLUID BECAUSE OF ALIGNMENT OF THEIR TINY CRYSTALS. THE FLUIDS THICKENS AS SOON AS STIRRING IS STOPPED. THIS PROPERTY, CALLED THIXOTROPY OF ADHESIVE AND PAINTS HELPS TO PREVENT A SAG OR RUN WHEN THESE COATINGS ARE APPLIED ON VERTICAL SURFACES. IF THE VISCOSITY OF A LIQUID INCREASES WITH INCREASE IN TEMPERATURE, AN ADHESIVE SHOULD BE APPLIED WHILE HOT.  WETTABILITY: ADHESIVE MUST WET THE SURFACE THOROUGHLY AS IT SPREADS. IT MUST BE ABLE TO FLOW INTO THE SURFACE CREVICES DISPLACING DIRT, MOISTURE AND TRAPPED AIR. FOR THIS PURPOSE THE SURFACE TENSION OF ADHESIVE CAN BE LOWERED BY ADDING A SURFACTANT WETTING AGENT.
  6. 6. ADHESIVES ORGANIC ANIMAL PROTIEN GLUES BLOOD ALBUMIN GLUES CASEIN ADHESIVES STARCH ADHESIVES SYNTHETIC PHENOLIC RESINS RESORCINOL RESINS UREA RESINS MELAMINE RESINS
  7. 7. ORGANIC ADHESIVES  ANIMAL PROTEIN GLUES : THESE GLUES ARE OBTAINED BY BOILING THE WASTE PIECES OF SKINS, BONES, TRIMMINGS ETC OF ANIMALS WITH HOT WATER. ANIMAL GLUES DEVELOP STRONG AND TOUGH JOINTS AND ARE EASILY APPLIED, BUT THEY ARE AFFECTED BY DAMP AND MOIST CONDITIONS. ANIMAL GLUES ARE AVAILABLE IN THE FORM OF FLAKES, PEARLS, CAKES, CUBES, GRANULES AND IN THE FORM OF JELLY. THIS IS USED IN THE MANUFACTURE OF PLYWOOD, LAMINATED TIMBERS ETC  BLOOD ALBUMIN GLUES : THIS TYPE OF GLUE IS MADE BY DRYING RAW BLOOD. THIS GLUE IS OF BETTER QUALITY AND IS AFFECTED LITTLE BY DAMP AND MOIST CONDITIONS. THIS TYPE IS USED FOR MAKING FURNITURE.  CASEIN ADHESIVES : THESE ARE PREPARED FORM CASEIN PRECIPITATED FROM SKIMMED MILK. IT HAS BEEN SPECIFIED THAT THESE ADHESIVES SHOULD FULFILL THE FOLLOWING FINENESS REQUIREMENTS.
  8. 8. FOR WET MIX GLUE----SHOULD PASS THROUGH I.S. SIEVE 60 WHEN SHAKEN FOR 10 MINUTES. FOR DRY MIX GLUE----SHOULD PASS THROUGH I.S. SIEVE 25. THESE GLUES POSSESS HIGH RESISTANCE TO MOISTURE WHEN USED FOR JOINING PURPOSES. HOWEVER, THEY ARE NOT RESISTANT TO MOULDS AND BACTERIA. STARCH ADHESIVES : THESE GLUES ARE MADE FROM VEGETABLE STARCH. THEY POSSESS GOOD STRENGTH ON DRYING BUT ARE NOT MOISTURE RESISTANT . SYNTHETIC ADHESIVES OR GLUES SYNTHETIC GLUES ARE BASED ON SYNTHETIC RESINS. BROADLY SPEAKING, THEY ARE OF TWO TYPES : THERMO-SETTING GLUES AND THERMO-PLASTIC GLUES. THESE GLUES HAVE REVOLUTIONIZED THE METHOD OF GLUING FOR PLYWOOD AND OTHER WOOD WORKS. THESE GLUES ARE APPLIED IN THE LIQUID AND DRY FORM. THERMO-SETTING GLUES ARE PERMANENT, ONCE THEY ARE SET. WHERE AS THERMO-PLASTIC GLUES CAN BE MADE PLASTIC AGAIN BY REHEATING.
  9. 9. ADHESIVES ARE GENERALLY CLASSIFIED AS:  THERMOPLASTIC ADHESIVES  THERMOSETTING ADHESIVES THERMOPLASTIC ADHESIVES: THERMOPLASTIC ADHESIVES ARE FUSIBLE, SOLUBLE, AND POOR HEAT AND CREEP RESISTANT. THEY ARE NORMALLY USED FOR LOW/MEDIUM LOAD ASSEMBLIES UNDER RESONABLE SERVICE CONDITIONS. THEY HAVE GOOD RESISTANCE TO OILS BUT POOR RESISTANCE TO WATER. THERMOPLASTIC ADHESIVES INCLUDE POLYVINYL ACETATE, POLY VIMYL ALCOHOL, POLYACRYLA
  10. 10. ALL THESE GLUES FROM SYNTHETIC RESINS ARE STRONG, WATERPROOF AND THE SETTING TIME CAN BE REGULATED BY VARYING THE KIND AND AMOUNT OF THE HARDENER. THEY ARE RESISTANT TO FUNGAL ATTACK AND POSSES NON-STAINING QUALITIES. PHENOLIC RESINS : THE GLUES OF THESE RESINS ARE AVAILABLE IN FILM, POWDER AND LIQUID FORMS. THEY REQUIRE HEAT AND PRESSURE TO FORM A PERMANENT STRONG BOND. THEY ARE USED IN THE MANUFACTURE OF RESINS BONDED PLYWOOD. RESORCINOL RESINS : GLUES OF THESE RESINS ARE DARK VISCOUS LIQUIDS. THEY BECOME HARD IN SHORT TIME AT LOW TEMPERATURES. THEY ARE RESISTANT TO HEAT, MOISTURE, FUNGI AND BACTERIA. UREA FORMALDEHYDE RESINS: GLUES OF THESE RESINS ARE AVAILABLE IN THE FORM OF SYRUPS AND POWDERS. THEY ARE EXTENSIVELY USED IN JOINERY WORK TO FORM WATER-RESISTANT GLUE JOINTS.
  11. 11.  MELAMINE RESINS: GLUES OF THESE RESINS REQUIRE HEAT AND PRESSURE FOR SETTING. THEY ARE USED IN THE MANUFACTURE OF PLYWOOD.  RUBBER-BASED SOLVENT CEMENTS: THESE ARE THE ADHESIVES MADE BY COMBINING ONE OR MORE RUBBERS OR ELASTOMERS IN A SOLVENT, RUBBER–BASED ADHESIVES ARE USED IN A WIDE VARIETY OF APPLICATIONS, SUCH AS CONTACT ADHESIVES FOR PLASTIC LAMINATES LIKE COUNTER TOPS, CABINETS, DESKS, AND TABLES  EPOXIES: THESE ARE THE ADHESIVE SYSTEM MADE BY A COMPLEX CHEMICAL REACTION. VARIOUS RESINS ARE MADE SYTHETICALLY BY REACTING TWO OR MORE CHEMICALS. EPOXY ADHESIVE CAN BOND A VARIETY OF SUBSTRATES WITH HIGH STRENGTH, THEY HAVE BEEN USED TO REPLACE SOME TRADITIONAL METALWORKING METHODS OF JOINING LIKE NUTS AND BOLTS, RIVETS, WELDINGS ETC.
  12. 12. THERMOSETTING ADHESIVES ARE ESSENTIALLY INFUSIBLE , INSOLUBLE, AND SHOW GOOD CREEP RESISTANCE. THEY ARE USED FOR HIGH LOAD ASSEMBLIES AND SEVERE SERVICE CONDITIONS SUCH AS HEAT, COLD, RADIATION, ETC. THERMOSET ADHESIVES ARE GENERALLY MORE EXPENSIVE TO PURCHASE AND TO USE,THAN THE OTHER ADHESIVE TYPES. THEY ARE THE ADHESIVES MOST USED FOR STRUCTURAL,LOAD BEARING APPLICATIONS. SOME OF THE TOUGHENED VARIANTS PROVIDE EXCEPTIONAL PROPERTIES DIRECTLY COMPARABLE WITH WELDED AND RIVETED ALTERNATIVES.

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