From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Comparing the cushioning and damping qualities of foamed latex and chemical blown sponge.
| Identifier | ExFiles\Box 132\3\ scan0231 | |
| Date | 9th January 1939 guessed | |
| - 4 - Another important factor in cushioning is adequate damping to prevent resonance buildup under the varying conditions of road surface and speed of car. The passage of air through the inter-connected cells of foamed latex combined with the natural hysteresis loss of rubber provides exceptional damping qualities. The curves in Fig. #4 show a typical comparison in the damping action of foamed latex and steel. The comparison in both damping and conforming ability have been general since requirements in static deflection, cost, or appearance, may dictate varying thicknesses of foamed latex and numerous combinations with other materials. The data provided on these two principal cushioning qualities are intended to show that, regardless of the combination, the addition of foamed latex if properly made, will improve the conforming and damping qualities of the cushion structure in total. The degree of result obtained will naturally depend on the thickness of foamed latex used, the type of supporting structure, and the trim application. Life The question of service life is always important when considering new material applications. In foamed latex, both the materials used and the method of processing are conducive to long life. Mechanical whipping of the liquid latex before cure produces a finely divided inter-connected cell structure. The right half of the section in Fig. #5 shows the mold cavity completely filled with this structure before the curing or vulcanizing operation. In this operation, the mold is submerged in hot water and the liquid penetrates the vented cavity replacing the air in the cell structure as shown in the left-hand section of Fig. #5. By this method, the heat is transmitted by a good conductor throughout the section, resulting in a uniform cure regardless of thickness or shape of the piece. In contrast, is the curing operation of chemical blown sponge as shown in Fig. #6. The uncured slab of solid stock shown in the right-hand view has been milled with softeners until very plastic so that resistance to expansion is reduced to a minimum. Chemical agents, also added, form a gas at vulcanization temperatures and expand the stock until the mold cavity is filled. As the blowing action progresses, it is increasingly difficult to transmit heat from the platen surfaces to the center of the stock, since both the rubber and the confined gas are relatively poor heat conductors. A uniform cure which is very important to the permanent resiliency of rubber is difficult to obtain for this reason. The cells of the final structure, as shown in the left-hand section of Fig. #6, are not connected and a skin is formed next to the mold surface. Ventilation through the structure is not possible. Accelerated flex testers, as pictured in Fig. #7, have been used to check the flex life of numerous passenger car cushion constructions in conjunction with actual test fleet service. The results of both types of test, as well as actual service history on other types of equipment, indicates a life in excess of normal car life with uniform performance throughout the period. | ||