Simple plastic rods are used in many devices and apparatuses. One use for molded plastic rods is in battery hydrometers. An elongated transparent plastic rod extends downwardly from the top of the battery into one or more cells of the battery. The rod has attached thereto a cage that encloses or suspends one or more spherical balls within the battery fluid. The hydrometer can monitor both the battery fluid level and the specific gravity of the battery fluid. Incident light rays are transmitted through the transparent rod, and various patterns or colors are transmitted to the viewing surface of the rod on the outer top level of the battery. The patterns or colors indicate whether or not the rod is immersed in battery fluid, indicating the battery fluid level, and whether or not the ball of a predetermined specific gravity is buoyant within the battery fluid, indicating the specific gravity of the fluid. An example of such a cage for suspending balls within the battery fluid can be found in U.S. Pat. No. 6,393,910 “One Piece Battery Charge Indicator Cage,” which is commonly assigned herewith.
It is known that the plastic rod by which the cage is suspended in the battery can be manufactured by injection molding processes. It has been observed that such injection-molded rods are susceptible to inborn stresses that are concentrated at the injection point. The concentration of inborn stresses at the injection point weakens the overall strength of the rod, resulting in much reduced overall break strength. The concentration of stresses in a relatively small area can cause cracks to form easily, which can then propagate quickly. As a result, prior rods have been known to break during shipment or installation, and a cracked or weakened rod may even fail during use.
Another problem with known rods of this type is that a sharp point or edge may be developed at the injection point (gate), with residual material (gate vestige) extending above the surface of the rod. A sharp or pointed gate vestige has the potential of damaging any product or item that comes in contact with it. Removing the sharp point or edge involves a subsequent process to the molding process, which can be time consuming and may significantly increase the cost for the rod.
What is needed in the art is an improved injection process and rod design whereby the overall strength of an injection molded rod is increased, particularly at the injection point, and in which the sharp edge or point that may remain after injection molding is shielded from contact with other items or things.