ejection mechanisms (for most pieces). Rotational molding can be used as a feasible alternative to blow molding with products such as plastic bottles and cylindrical containers. This substitution is efficient on only a smaller scale, as blow-molding's efficiency depends on large runs. Another advantage lies in the molds themselves. Since they require less tooling, they can be manufactured and put into production much more quickly than other molding processes. This is especially true for complex parts, which may require large amounts of tooling for other molding processes. Rotational molding is also the process of choice for short runs and rush deliveries. The molds can be swapped quickly or different colors can be used without purging the mold. With other processes, purging may be required to swap colors. Due to the uniform thicknesses achieved, large stretched sections are nonexistent, which makes large thin panels possible (although warping may occur). Also, there is little flow of plastic (stretching) but rather a placing of the material within the part. These thin walls also limit cost and production time. Another cost advantage with rotational molding is the minimal amount of material wasted in production. There are no sprues or runners (as in injection molding), and no off-cuts or pinch-off scrap (as in blow molding). What material is wasted, as scrap or from failed part testing, can usually be recycled. Limitations Rotation-molded parts are subject to restrictions that are different from those of other plastic processes. As it is a low-pressure process, sometimes designers face hard-to-reach areas in the mold. Good-quality powder may help overcome some situations, but usually the designers have to keep in mind that it is not possible to make sharp threads that would be possible with injection molding. Some products based on polyethylene can be put in the mold before it is charged with the main material. This can help to avoid holes that otherwise would appear in some areas. This could also be achieved using molds with movable sections. Another limitation lies in the molds themselves. Unlike other processes in which only the product needs to be cooled before being removed, with rotational molding the entire mold must be cooled. While water-cooling processes are possible, there is still a large down time of the mold, increasing both financial and environmental costs. Some plastics will degrade with the long heating cycles or in the process of turning them into a powder