There are many reasons why off-center gates happen, and processors should be aware of all of them to quickly find the ones causing the problem. Bottle with an off-center gate. The lower of the red circles shows the center of the bottom insert of the mold. The higher one shows where the gate ended up after blowing. Preform mandrel with three segments. The segments hold the preforms concentric as they travel through the ovens. Typical setup on a continuous-motion linear machine with passive rotation. The belt can be adjusted to push against the gears, but should not push hard enough to cause side-stress against the bearing. When the preform is stretched into the blow mold, the vestige of the injection molding process, mostly referred to as a gate, must be placed and held in the center of the bottom insert of the mold. If this does not happen, the side to which the gate is pushed becomes thicker, and, consequently, the other side will be thinner. This is simply the effect of shorter and longer paths of the preform wall to reach the blow mold wall. With bottles becoming lighter and thinner as a result of cost-cutting measures as well as environmental concerns (“carbon footprint”), ...