Tutor profile: Steven M.

How are plastics created?

Plastics are derived from petroleum oil. A single molecule consisting of carbon, hydrogen, and oxygen, is polymerized, or made into a long strand. This polymer can be many thousands of singe molecules, of monomers. The length determines some physical characteristics. Additives give the polymer other characteristics, such as UV protection, fire retardant, and strength.

This plastic engine bracket is failing in the field. The outer dimensions cannot be changed, not the material. What can be done to fix this problem?

The answer is that the failure point is at a seam where during the molding process two flow fronts meet and form a weak joint. There are two alternatives. The first one is to modify the molding process to eliminate the seam. This can usually be done by increasing the liquid plastic temperature so it remains liquid until after the two flow fronts meet. And the injection speed can be increased to again make the flow fronts meet before they start to solidify. The second choice is to create a channel at the seam so the seam will flow into this channel. It can later be trimmed off. This remedy would only be used if the molding parameters cannot be changed because it requires a design change to the mold. This requires down-time and an additional cost by adding the trim operation.

What is the best material is best to use for an engine cover?

A 33% Glass Fiber reinforced 4/6 polyamide would give the necessary strength, heat resistance and chemical resistance for an under-hood environment. In addition, this material is injection moldable, and the price point and availability are all suited to meet the necessary.