Review Questions
14.1 How is the rubber industry organized?
Answer. The rubber industry is organized into three parts: (1) rubber growing plantations produce natural rubber, (2) the petrochemical industry produces synthetic rubber, and (3) fabricators take the NR and SR and produce finished rubber goods.
14.2 How is raw rubber recovered from the latex that is tapped from a rubber tree?
Answer. The rubber is usually recovered as follows: (1) the latex is collected into tanks and diluted to half natural concentration; (2) formic or acetic or other acid is added to the solution which causes the rubber to coagulate; (3) the coagulum is then squeezed through rolls to drive off water;
and (4) the resulting sheets are dried in smokehouses for several days. The resulting raw rubber is called ribbed smoked sheet.
14.3 What is the sequence of processing steps required to produce finished rubber goods?
Answer. The typical sequence is: (1) production of the raw rubber, (2) compounding, (3) mixing, (4) shaping, and (5) vulcanization.
14.4 What are some of the functions of the additives that are combined with rubber during compounding?
Answer. The additives and functions are: vulcanizing chemicals, reinforcing fillers, extenders to reduce cost, antioxidants, coloring pigments, plasticizers to soften the rubber, and blowing agents to make foam rubber.
14.5 Name the four basic categories of processes used to shape rubber.
Answer. The categories are: (1) extrusion, (2) calendering, (3) coating, and (4) molding.
14.6 What are some of the operations used to coat rubber onto a fabric to produce reinforced rubber?
Answer. Calendering, skimming, dipping, and spraying; see Article 14.1.4.
14.7 What does vulcanization do to the rubber?
Answer. Vulcanization causes cross-linking of the rubber molecules; this strengthens and stiffens the rubber while extensibility is retained.
14.8 Name the three basic tire constructions and briefly identify the differences in their construction.
Answer. (a) diagonal ply, (b) belted bias, and (c) radial ply. Diagonal ply and belted bias both have their carcass plys running in a diagonal direction relative to the tire circumference; radial ply has its carcass plies running in a radial direction; belted bias and radial ply tires use belts, which are additional plies around the outside circumference of the tire; whereas diagonal ply tires do not have these belts.
14.9 What are the three basic steps in the manufacture of a pneumatic tire?
Answer. The three steps are: (1) preform the components, (2) building the carcass and adding the rubber for the sidewall and treads, and (3) molding and curing.
14.10 What is the purpose of the bead coil in a pneumatic tire?
Answer. The bead coil provides a rigid support for the tire when it is mounted onto the wheel rim.
14.11 What is a TPE?
Answer. TPE stands for thermoplastic elastomer; it is a thermoplastic polymer that behaves like a rubber.
14.12 Many of the design guidelines that are applicable to plastics are also applicable to rubber.
However, the extreme flexibility of rubber results in certain differences. What are some examples of these differences?
Answer. Three examples: (1) no draft is needed on the part for mold removal; (2) holes should be molded into rubber parts rather than machined, whereas holes can be machined or molded in a plastic part; and (3) screw threads are not normally used on rubber parts.
Multiple Choice Quiz
There are a total of 11 correct answers in the following multiple choice questions (some questions have multiple answers that are correct). To attain a perfect score on the quiz, all correct answers must be given, since each correct answer is worth 1 point. For each question, each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the number of answers required reduces the score by 1 point. Percentage score on the quiz is based on the total number of correct answers.
14.1 The most important rubber product is: (a) footwear, (b) conveyor belts, (c) pneumatic tires, or (d) tennis balls.
Answer. (c)
14.2 The chemical name of the ingredient recovered from the latex of the rubber tree is which one of the following? (a) polybutadiene, (b) polyisobutylene, (c) polyisoprene, or (d) polystyrene.
Answer. (c)
14.3 Of the following rubber additives, which one would rank as the single most important? (a) antioxidants, (b) carbon black, (c) clays and other hydrous aluminum silicates, (d) plasticizers and softening oils, or (e) reclaimed rubber.
Answer. (b)
14.4 Which one of the following molding processes is the most important in the production of products made of conventional rubber? (a) compression molding, (b) injection molding, (c) thermoforming, or (d) transfer molding.
Answer. (a)
14.5 Which of the following ingredients do not contribute to the vulcanizing process (more than one)?
(a) calcium carbonate, (b) carbon black, (c) stearic acid, (d) sulfur, and (e) zinc oxide.
Answer. (a) and (b)
14.6 How many minutes are required to cure (vulcanize) a modern passenger car tire? (a) 5, (b) 15, (c) 25, or (d) 45.
Answer. (b)
14.7 When is the tread pattern imprinted onto the circumference of the tire? (a) during preforming, (b) while building the carcass, (c) during molding, or (d) during curing.
Answer. (c)
14.8 Which of the following are not normally used in the processing of thermoplastic elastomers (more than one)? (a) blow molding, (b) compression molding, (c) extrusion, (d) injection molding, or (e) vulcanization.
Answer. (b) and (e)
14.9 Screw threads are not normally molded into rubber parts: (a) true or (b) false.
Answer. (a) Screw threads are not normally designed into rubber parts because of the extreme flexibility of rubber.