Question & Answer

What is sheet molding compound (SMC)?

Why are particles and flakes members of the same basic class of reinforcing material?

In the context of fiber reinforcement, what is a mat?

What is the difference between a roving and a yarn?

What are the principal polymers used in fiber-reinforced polymers?

There are 10 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. Each correct answer is worth 1 point. Each omitted answer or wrong answer reduces the score by 1 point, and each additional answer beyond the correct number of answers 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 which one of the following: (a) footwear, (b) conveyor belts, (c) pneumatic tires, or (d) tennis balls?

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?

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?

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?

14.5 Which of the following ingredients do not contribute to the vulcanizing process (two correct answers): (a) calcium carbonate, (b) carbon black, (c) stearic acid, (d) sulfur, and (e) zinc oxide?

14.6 How many minutes are required to cure (vulcanize) a modern passenger car tire: (a) 5, (b) 15, (c) 25, or (d) 45?

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?

14.8 Which of the following are not normally used in the processing of thermoplastic elastomers (two correct answers): (a) blow molding, (b) compression molding, (c) extrusion, (d) injection molding, or (e) vulcanization?

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?

What is a TPE?

What is the purpose of the bead coil in a pneumatic tire?

What are the three basic steps in the manufacture of a pneumatic tire?

Name the three basic tire constructions and briefly identify the differences in their construction

What does vulcanization do to the rubber?

Name the four basic categories of processes used to shape rubber

What are some of the additives that are combined with rubber during compounding?

What is the sequence of processing steps required to produce finished rubber goods?

How is raw rubber recovered from the latex that is tapped from a rubber tree?

How is the rubber industry organized?

The problem in a certain thermoforming operation is that there is too much thinning in the walls of the large cup-shaped part. The operation is conventional pressure thermoforming using a positive mold, and the plastic is an ABS sheet with an initial thickness of 3.2 mm. (a) Why is thinning occurring in the walls of the cup? (b) What changes could be made in the operation to correct the problem?

A rotational molding operation is to be used to mold a hollow playing ball out of polypropylene. The ball will be 1.25 ft in diameter and its wall thickness should be 3/32 in. What weight of PP powder should be loaded into the mold in order to meet these specifications? The specific gravity of the PP grade is 0.90, and the density of water is 62.4 lb/ft³ .

An extrusion operation is used to produce a parison whose mean diameter = 27 mm. The inside and outside diameters of the die that produced the parison are 18 mm and 22 mm, respectively. If the minimum wall thickness of the blow-molded container is to be 0.40 mm, what is the maximum possible diameter of the blow mold?

A blow-molding operation is used to produce a bottle with a diameter of 2.250 in and a wall thickness of 0.045 in. The parison has a thickness of 0.290 in. The observed die swell ratio is 1.30. (a) What is the required diameter of the parison? (b) What is the diameter of the die?

A parison is extruded from a die with outside diameter = 11.5 mm and inside diameter = 7.5 mm. The observed die swell is 1.25. The parison is used to blow mold a beverage container whose outside diameter = 112 mm (a standard size 2-liter soda bottle). (a) What is the corresponding wall thickness of the container? (b) Obtain an empty 2-liter plastic soda bottle and (carefully) cut it across the diameter. Using a micrometer, measure the wall thickness to compare with your answer in (a)

The extrusion die for a polyethylene parison used in blow molding has a mean diameter of 18.0 mm. The size of the ring opening in the die is 2.0 mm. The mean diameter of the parison is observed to swell to a size of 21.5 mm after exiting the die orifice. If the diameter of the blow molded container is to be 150 mm, determine (a) the corresponding wall thickness of the container and (b) the wall thickness of the parison.

An injection molded polyethylene part has a dimension of 2.500 in. A new material, polycarbonate, is used in the same mold. What is the expected corresponding dimension of the polycarbonate molding?

The foreman in the injection molding department says that a polyethylene part produced in one of the operations has greater shrinkage than the calculations indicate it should have. The important dimension of the part is specified as 112.5 ±0.25 mm. However, the actual molded part measures 112.02 mm. (a) As a first step, the corresponding mold cavity dimension should be checked. Compute the correct value of the mold dimension, given that the shrinkage value for polyethylene is 0.025 (from Table 13.1). (b) What adjustments in process parameters could be made to reduce the amount of shrinkage?