Mechanical Design Handbook

PEEK is an abbreviation for polyetheretherketone, a high performance engineering thermoplastic. It is another engineering plastic which is widely used in machine components since it has very good mechanical strength and dimensional stability, excellent thermal and chemical resistance properties and outstanding resistance to abrasion and dynamic fatigue. Its yield strength is about 92 MPa. Its density is about 1.32 g/cm3 which is 1/6 of steel. It is a strong and stiff thermoplastic material that is often used in applications where performance at high temperatures is required. PEEK has outstanding chemical resistance as well as resistance to hot water and steam. PEEK is insoluble in all common solvents and is extremely resistant to attack by a very wide range of organic and inorganic chemicals. PEEK can be used continuously to 250°C (for short term, it can operate at 300°C) and in hot water or steam without permanent loss in physical properties. It also has high abrasion and cut th

P oly t etra f luoro e thylene ( PTFE ) is another engineering plastic using in machine parts. PTFE is a non-stick substance. The trade name of the DuPont company for PTFE is Teflon . PTFE is used as a non-stick coating for pans and other cookware. It has exceptional resistance to high temperatures, chemical reaction, corrosion, and stress-cracking. Working temperature of PTFE is between -200 o C and 260 o C. Since it has very low friction (PTFE's coefficient of friction is 0.05 to 0.10) and good resistance to chemical reaction, it's normally used in bearings, pipes or containers of chemical substances. It's also used for sealing purpose at high temperature environment. The tapes for thread sealing in pipes are also made from PTFE. Though it can work well until 260 o C, but its strength is not always high since it may expand and deform at high temperature. PTFE is easy to machine, low cost and long lasting. PTFE parts are often used in mechanisms that rotate or slide. It d

PA is the abbreviation of Polyamide . The commercial name of polyamide is Nylon . Nylon is an engineering thermoplastic which is commonly used in textiles, automotive, carpet and sportswear due to its extreme durability and strength. It has tensile strength about 80 MPa which is higher than POM . Solid nylon is used for mechanical parts such as machine screws, gears , cams, bearings, guides, rollers, and other low- to medium-stress components previously cast in metal. Nylon is frequently used as a replacement for bronze, brass, aluminium, steel and other metals, as well as other plastics, wood, and rubber. Engineering-grade nylon is processed by extrusion, casting, and injection molding. Nylon price is approximately 2 times of the price of POM (Polyacetal). Working temperature when using Nylon should be within - 50 o C to 160 o C. Nylons are available in various colors such as white, blue, black, etc. One important property of Nylon that should be noted when use it to make machine

Normally, we use steels to make machine components. But in some applications, engineering plastics are also commonly used in machine parts since their unique properties e.g. lighter weight, easy for machining, great quantities can be made quickly by injection, etc. General properties of engineering plastics: Light weight - The density of engineering plastics is usually about 1-2 g/cm 3 . We often use them in the portable machines that we often move them, or use in the parts that the user has to hold by hand. No rust - We normally use engineering plastics without surface treatment to prevent rust. However, engineering plastics do not withstand the corrosion from oxygen or ultraviolet, so we need to consider this point when using plastic for long time. Low electrical conductivity - We use plastics to prevent users from direct contact with electrical parts for safety reason. Low thermal conductivity - Engineering plastics are good for insulation. We can prevent some heat

Screws and bolts are the most common types. The difference between screws and bolts is only the intended use. Screws are intended by screwing into tapped holes; bolts are intended for use with nuts. Sometimes screws are supplied with a captive washer under the screw head. They are also called SEMS. A SEMS screw is a generic term used to describe a screw pre-assembled with a free-spinning lock washer. It is a permanent assembly with the washer held in place by the major diameter of the screw thread being larger than the hole of the washer. The SEMS screw is simple, easy to use and available in many different styles making it well suited for many applications. SEMS save assembly time and eliminate the possibility that a screw will be installed without its specified washer. Normally, a bolt can also serve as a screw by using it with a tapped hole rather than a nut. A stud is threaded on both ends. It is usually screwed permanently into a tapped hole. Threads on the two ends may or