The cost of your molded part is dependent upon many things, including; material price, material specific gravity, material properties, part design and processing.

Material Costs
· Comparative pricing was obtained from Plastics News 10/11/99
· Pricing basded on annual volumes of 2,000,000 lbs. PBT, PET based on annual volumes of 1MM pounds.
· Comparative property data was obtained from Modern Plastics Encyclopedia 1998. When property ranges were given, the center value of the range is used. Modulus reported as conditioned to equilibrium with 50% relative humidity.

Material Performance / Product Design

In design conversions from metal or engineering thermoplastics, nominal wall thickness can be adjusted to maintain equivalent "stiffness" in the part. Using the simple beam analog, we gain an understanding of how the modulus of the material dictates the required wall thickness of the part.

For equivalent deflection ^§BMC = ^§Other Plastic: The terms F, L, and b will be the same for the given application. Canceling terms where appropriate, the equation can be reduced to:

By inserting the respective flexural moduli in the expression, the ratio of the required thickness of a BMC part versus another material can be easily calculated.

Keep in mind that the modulus value (E) is temperature dependent, therefore the modulus that prevails under actual end use conditions must be applied. Understanding that BMCs are thermosetting, they inherently demonstrate excellent modulus retention well above the glass transition temperature. Thermoplastics, such as those illustrated, have substantial modulus loss as the temperature is increased, particularly above the glass transition of the material.

How does this help you?

If the part needs to perform at extreme temperatures, the modulus ratio of BMC to these other plastics will be even greater at that temperature. Thus, you can expect less deflection under load. Or, for the same amount of deflection, you can use less (BMC) material.

Processing

BMC can be processed by injection, compression, or transfer molding. Injection molding proves to be the most economical for high volume application. Press size and cycle time are the main cost elements. Press size is determined by the projected area of the part, number of cavities needed, and a material constant (based on the clamp tonnage required to keep the mold closed during injection). Let the technical staff at BMC demonstrate how you can save money in material cost, part design and processing, while increasing the performance of your product.