The Problems in Rotational Molding
According to different heating methods of rotational molding machines,there are two common ways:direct firing and hot box.The direct firing way is mainly used to produce large-scale products,which is direct firing heating roll-forming machine;And most of small and medium-size products are manufactured by hotbox heating,the most common machines are hotbox heating roll-type rotational molding machine,hot box heating 2-arm rotational molding machine, 3-4 arm tower rotational molding machine,hotbox heating ‘mantle’ type of rotational molding machine is rapid development in recent years.Rotational molding, also known as rotomold, rotary casting molding,a hollow molding method for thermoplastics.The first is putting the plastic raw material into the mold.Depend on heating ,vertical and horizontal rolling rotation,so that the material by its own gravity and centrifugal force evenly covered with the mold cavity and melt, to be demolded after cooling hollow products.It is neccessary to achieve pressure balance in rotational molding in order to the air can enter and out of the mold,which also can avoid the internal material leaving the mold and water go into mold from the outside.Keeping the same pressure inside and outside of the mold is useful to avoid blowing holes on the mold line and reducing the possibility of warping due to reduced pressure in cooling phase.
Polyethylene rotomoulding is made of silicone oil or silicone resin with excellent heat resistance.To use of organic silicone release agent,it will be uniformly coated to the entire surface of the cavity; if to use of silicone resin release agent, and then evenly coated with a good release agent,then should be slowly warming,so that the solvent will be dissipated, forming a thin layer of resin layer, and at 250 ~ 280 ℃ temperature curing 1 ~ 2h,gain a certain strength of the release layer,then can add material and forming. Silicone oil release agent applied to the mold can only be used once,each molding must be coated every time in the future,but the use of silicone resin release agent has a prominent advantage, that is “semi-permanent” nature that can be used repeatedly. As the rotational mold without external force, so the mold is simple, low cost, easy to manufacture.In addition, the rotomolding equipment also has a large mobility, a rotomoulding machine, either to install a large mold, can also install many small molds;it can forming the different size parts at the same time as long as the rotational molding products used in the same raw material and have same thickness,so rotomoulding process than other molding methods have greater mobility.