PP Intake Manifold
Plastic intake manifolds are now used in most motor vehicles. They are lighter and less costly than their metal counterparts and offer a high degree of design freedom as well as numerous opportunities to integrated additional functions. Until now, glass fiber-reinforced polyamides (PA) have dominated the market. However, the mechanical properties of these materials vary greatly with the moisture level in the surroundings. Increasing dimensions to offset such changes leads to greater material consumption and higher part weight.
For this reason, in March 2009 Volkswagen AG began to equip gasoline engines with displacements of 1.4 and 1.6 liters with PP intake manifolds. The material chosen was the PP compound Xmod from Borealis with a glass fiber content of 35%. These PP manifolds are comparable to PA manifolds in terms of long-term thermal stability and chemical resistance as well as bursting pressure and vibration resistance. Thanks to the lower density of the material (1.18 g/cm3 ), the part weight is reduced to about 2 kg. As a result, the PP intake manifolds are about 15% lighter than similar PA parts. With a 5 dB lower noise level in operation, the PP manifolds exhibit outstanding acoustic properties in spite of the material savings. The stable property profile in surroundings with a variable moisture level represents an additional major benefit.
In contrast to PA, the PP need not be dried prior to processing. Injection molding cycle times are similar for both materials. Melt and mold temperatures are lower, which minimizes equipment wear and tear. The subsequent vibration welding remains unchanged. The lower material usage, the good vibration characteristics and the lower material price of PP compared to that of PA translate into production costs that are as much as 20 % lower overall.