Sleeve bearings are plain bearings which have very few moving parts in their construction. This article explains their applications and comparison with ball bearings.
The Plastic Wars: Difference Between Thermoplastics and Thermosets
The main difference between thermoplastics and thermosets is how they react to heat. But that’s not all. They differ in their properties, uses, and even related pros and cons. This ScienceStruck post tells you more…
Did You Know?
Bulletproof vests are enhanced by the use of the thermoplastic polyethylene. It increases the hardness of the vest, while at the same time keeping it light in weight.
Polymers are substances made up of long chains of individual units of atoms. These materials are widely used, especially due to their heat and chemical-resistant properties, as also their elasticity, toughness, and cheap cost. While polymers can be classified into several categories, such as natural, synthetic, and semi-synthetic, depending on the source of the raw material, they can also be divided into elastomers, fibers, thermoplastics, and thermosets, based on the forces between their molecules.
Normally, there is confusion between thermoplastics (thermosoftening plastics) and thermosets (thermosetting plastics or polymers). The differences between them are details in the following sections.
Thermoplastic polymers are polymers that can be repeatedly heated and molded without effecting any change in their chemical or physical properties.
Thermoset polymers are polymers that once molded and hardened, cannot be reshaped or recycled.
● The molecules have weak, straight-chain bonds between them that can be broken by heating.
● Thermoplastics are prepolymerized by the manufacturer, and don’t require polymerization again during processing.
● They are elastic and flexible in nature.
● They dissolve in organic solvents.
● On heating, they will soften and ultimately melt.
● The melting point of thermoplastics is lower than their degradation point.
● Thermoplastics are in the form of solid pellets before use.
● In solid state, their structure consists of hard crystalline regions together with elastic amorphous regions.
● They have strong chemical bonds between molecules, including cross-linking, due to which they do not separate on heating.
● Thermosets have to undergo a two-stage polymerization during the processing stage.
● They are hard and brittle.
● They do not dissolve in organic solvents.
● On heating, thermoset polymers will char, not melt.
● Their degradation point is lower than their melting point.
● Thermosets are in the liquid state before processing.
● When solid, their structure consists of the thermosetting resin interspersed with reinforcing fiber.
● High impact resistance (10 X thermosets)
● Can be recycled and reused
● Easy repair
● High chemical resistance
● Aesthetically better surface finish
● Uncured thermoplastics do not need refrigerated storage
● Environmentally friendly production (less emissions)
● They can be blended with other thermoplastic materials
● High structural rigidity (more strength)
● Heat and chemical resistance
● Economical raw materials
● Easy fiber reinforcement of liquid raw materials
● High durability
● Attractive finished product appearance
● Ability of thick and thin wall formation
● Highly adaptable design process
● Production process is well-established
● Better wetting and adhesive properties
● Heat and pressure requirement for fiber reinforcement
● High cost
● Heat and UV sensitivity
● Polymer degradation after constant remelting and remolding
● Structural failure on high stress or long-term load application
● Leaching of hazardous chemicals in the long run
● Recycling inability
● Refrigerated storage required by liquid raw materials
● Repair difficulty
● Good surface finish is tough to accomplish
● Lengthy, complex process stages
● Structural failure on high-force impact
● Emission during production process
● Inability to blend thermosets by welding
COMMON EXAMPLES AND USES
● Nylon (Polyamide): Mechanical and automotive parts, clothing, packaging, cupboard hinges, heat-resistant composite manufacture.
● Polyethylene: Drums, gas tank coating, milk bottles, squeeze bottles, jugs, movable machine parts, bullet-resistant vests, laundry detergent containers.
● Acrylic: Battery covers, lightweight glass alternative, vehicle taillight covers, eye lenses, as bone cement in medicine.
● Polypropylene: Toys, sanitary tissues, heat-proof medical equipment, rope, string, plastic seats, laboratory equipment, detergent-proof food containers, automobile components, folders.
● Polyvinyl chloride: Cabinets, fume hoods, tanks, electrical insulation, toys, pipes, fittings, flooring, medical devices.
● Teflon: Flange spacers, gaskets, non-stick cookware, machine parts, gears, wires, lubricant for sliding doors.
● Polyurethanes: Paints, coatings, insulating foams, car parts, print rollers, footwear, sealants, adhesives.
● Epoxy resin: Aircraft components, tooling jigs and fixtures, coatings, adhesives for automobiles, marine vessel parts, electronic components.
● Melamine formaldehyde: Adhesives, coatings, laminates, dinnerware, electrical components, knobs, household items, construction material, furniture-making.
● Urea-formaldehyde: Plywood foam, electrical items, doorknobs, toilet items, adhesives, chemically-inert coatings, paper, plastic molds, decorative articles.
● Polyester resins: Casting materials, non-metallic car body fillers, electrical components, reinforced plastic sheets used in restaurants/kitchens, low-care walls, laser printer toners, bonding materials.
● Bakelite: Precision-made parts, vehicle disc brake cylinders, knobs, plastic ware, electrical products and insulation, plugs and sockets, automotive parts, light bulb supports, kitchenware handles.
There is no ‘better’ choice between thermoplastics and thermosets. Each type has its own uses. In hindsight, thermoplastics are used whenever there is a requirement of elasticity or recycling. On the other hand, thermosets are used wherever the work calls for toughness and heat resistivity.