Characteristics of adhesives and adhesive joints, Mechanical Engineering

Characteristics of Adhesives and Adhesive Joints

While an adhesive joint is created this has to show individual or several of given properties.

(a) Mechanical strength against peel and shear.

(b) Hardiness or resistance to impact.

(c) Resistance to moisture and heat and other environmental degrading actions.

(d) Resistance to various fluids and chemicals.

(e) Capability to spread consistently on surfaces to be jointed - wetting property.

A huge number of adhesives are available commercially. A lot of them have been identified earlier. Properties of a few are demonstrated in Table no.4.

                    Table no.4: Typical Properties of various Commercial Adhesives

Characteristics

Acrylic

Cyanoacrylate

Polyurethane

Epoxy

Shear Strength (MPa)

26

19

15.4

15.4

Peel Strength (N/m)

5250

500

14000

500

Impact Resistance

Good

Poor

Excellent

Poor

Service Temperature range, (oC)

- 70 to 120

- 55 to 80

- 160 to 80

- 55 to 120

Surfaces bonded

Smooth, nonporous

Nonporous metals or plastics

Smooth, nonporous

Most surfaces

Curing hot

No

No

Yes

Yes

Resistance to solvent

Good

Good

Good

Excellent

Resistance to moisture

Good

Poor

Fair

Excellent

Odor

Strong

Moderate

Mild

Mild

Toxicity

Moderate

Low

Moderate

Moderate

Flammability

High

Low

Low

Low

Availability

Two part liquid or paste

One part liquid

Two part liquid or paste

Two part liquid or paste

Application

Metals, plastics, wood

Metals, plastics, glass

Plastics, metals, rubber

Metals, plastics, glass, rubber, ceramics

Nevertheless adhesives have convenience of joining related and unrelated metallic and non-metallic materials of various shapes and size the application is restricted because of special care and skill desired for design of bonding and joint methods. Service temperatures are highly prohibited. Curing time is now another significant factor to be considered for this may range from some seconds at higher temperature to lots of hours at room temperature. Thermosetting adhesives need long curing time.

Designer should ensure about the joints are subjected to compression, shear or tension but not subjected to peeling force. Individual lap, double lap, tapered lap as scarf and butt as strap joints and peeling action are illustrated in figure given below. The production of such joints will need special fixtures, presses, autoclaves, ovens and tooling for curing. Various industries have developed that special skills and high level of conveniences for producing adhesive joints. Automotive, building products, appliances industries and aerospace employ these joints extensively. Attaching rear vision mirror to windscreen of car, laminated wind shield glass, aircraft bodies, automotive brake lining assemblies, helicopter blades, are some illustrations where adhesive bonding is employed.

 

                                     339_Peeling Action.png

                                                       Figure: Peeling Action

Posted Date: 2/27/2013 5:53:54 AM | Location : United States







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