Rotary melting process
The rotational molding process ( English rotational molding , rotomoulding ) is a manufacturing process for parts made of plastic . Other terms include rotational sintering and rotational casting . The process was developed in the USA in the early 1940s and is one of the oldest processes for shaping plastics.
distribution
In relation to the total production volume of plastic articles, the rotary melting process is a niche technology. This is very common in the USA and for some years now the number of users in Europe and Asia has been increasing. Certain plastic products can best be made with this process.
description
Every plastic product needs its own shape. This is made of steel or aluminum . The mold is mounted on a mold carrier. Then the two-part or multi-part mold is opened and filled with powdered raw material (e.g. polyethylene , polypropylene ). The mold carrier is moved into the oven together with the mold. The mold is slowly set in biaxial rotation under controlled heating from 190 ° C to a maximum of 320 ° C. The raw material melts in the mold, increasingly leans against the inner wall of the mold and builds up the wall thickness of the plastic part in layers. As soon as this process is complete, the mold carrier and the mold are moved out of the oven and into the cooling chamber. After the controlled air or water cooling , demolding takes place. The finished plastic molded part is removed from the opened mold. A production cycle takes about an hour, which means that a maximum of one plastic part can be produced in one hour per mold. Depending on the size of the mold in relation to the size of the heating room (furnace), one or more molds can be mounted on the mold carrier, heated and cooled down together.
The development of directly heatable molds is currently in progress.
advantages
Due to the almost pressureless production (low pressure process), the products are almost stress-free and therefore very tolerant of pressure and impact. The other properties of the products are determined by the raw material. Rotationally sintered containers are mainly made from polyethylene today. These containers are, for example, very robust and, due to the raw material, resistant to many chemicals. They are used in plant construction with chemicals, water and food, as well as for storage and transport.
Types of production equipment
The arrangement of the baking oven / melting furnace describes the shape of the production plant, which is called the rotary melting plant. In the carousel system (star system), the mold loading station, the oven, the cooling chamber and the product removal station are arranged around a central axis.
In the shuttle system, these workstations are arranged horizontally in a linear manner.
Special features of the procedure
Due to the long production time, the rotary melting process is only sensible and economical for small and medium-sized parts series.
In the rotation melting process, a seamless hollow body is always produced. Other bodies can only be achieved by separating the completed rotational molding. This must be taken into account when designing rotationally sintered plastic parts and when manufacturing the corresponding rotational molds. This results in interesting design options that are increasingly being used for new products with future-oriented designs.
Applications for rotationally melted products
- Industrial containers and collecting trays
- Fuel tanks
- Device housing
- Canoes, kayaks, boats, floats
- Lamp housing for inside and outside
- Garden furniture and other furniture made of plastic
- Mobile toilet cubicles and dog houses
- Truck wheel aprons and other commercial vehicle parts
- Sports and play equipment
Web links
- Report in Cadcam 6/2003 (PDF file; 1.12 MB)