Rotomolding, called as rotational moulding or rotary forming, is a kind of plastics molding process technology with long history. It’s reported that the pioneer technological core of rotomolding probably derives from Qing Dynasty. But plastic rotomolding originated from England, with the first rotomolding patent coming out in 1887 and the first commercial rolling molding machine coming into being in 1934. It developed a lot in 1950’s in Europe, and gradually spread into America and Japan and so on. At first, it was just supplement to injection molding and blow molding process. As mature of polyethylene power technology, rotomolding increasingly became a competitive molding method in plastic molding process. From then on, rotomolding has been developing all over the world.
A. Status and development abroad
In recent years,
rotomolding grows quickly in North America and developed countries in Europe, the development speed of which is higher than the average speed of plastic industry. The development of the whole rotomolding is comparatively prefect, besides rolling machine factories and rolling plastic products manufacturers, there are a number of other professional auxiliary plant such as plastic mold factories, mold release agent factories, rotomolding special paint factories, mill factories, insert factories, mixing equipment manufacturing factories suitable for rotomolding, and lots of plastic special row material supply plants an so on. Plastic equipment of manufacturing in developed countries becomes more and more excellent, keeping growing in the direction of higher and higher automation control level.
Nowadays, rotomolding can not only produce simple small single products, but also can produce complex multi-layer large and super large products, including all kinds of container products, cars, planes and other power tool accessories, military supplies, ship and human organs and so on.
In view of the heating mode of rolling machine, at present there are two categories most commonly used, say, direct fire and hot box heating. Production of large goods mostly adopts direct fire, namely direct heat swing type rolling machine. Small and medium-sized products usually produced by hot box heating, and the most common types are hot box and two arm swing rolling machine, three to four arm thermal heating box and “oyster” type rolling machine has developed quickly in recent years.
Developed countries not only better the type of rolling machine, but also vigorously improve the control level of rolling machine. It should be especially introduced that a rotomolding process diagnosis system was opened up successfully. Now the system after improvement is nearly perfect, which includes temperature test and control display. The part of temperature measurement sealed on a thermal insulation can be installed into the mould frame box, inside the mold, radio real-time thermocouple temperature can be sent to the monitoring computer out of hot box. And computer will show the mould temperature/time curve. Compared the curve with the hot oven temperature/time curve, plastic mold and mold heat transfer in the heating process and the material heated condition can be displayed visually. Operators can take advantage of it to optimize heating and cooling cycle, improve and guarantee the quality of products plasticizing, maximize the strength of products, reduce production cost, and more accurately evaluate the mould and new raw material.
Rotomolding companies abroad generally have many sets of different sizes or different kinds of rolling machine. For instance, a company in the United States has 7 rolling molding machine, and mold maximum turning diameter is 4 m; a company has 9 sets of rolling molding machine, and mold maximum turning diameter is 4.3 m; a company has 10 sets, and mould maximum turning diameter is 3.3 m.
B. Status and development at home
Plastic industry in China began in the late 70 s with a late starter. Most rotomolding companies do not know enough about deeper knowledge of plastic technology .Plastic processing professional textbooks of higher institutions introduce very little.
From the perspective of the use of domestic roll-plastic equipment, the used rolling machine is mostly swing, shuttle, tower, and other models are less; domestic manufacturing of roll machine model is almost the same; domestic rotomolding companies each own roll rolling machines in small numbers, most owning one or two.
On the whole, the gap between the development of rotomolding industry in China and developed countries is large. But rolling molding machine manufacturing, plastic mold manufacturing factory in development appear gradually. Plastic material is developed successfully and roll plastic varieties is also increasing. Rapid development of rotomolding industry in recent years has attracted more and more attention from abroad, and international communication is becoming more and more.
Rotomolding industry development in our country depends on continuous new product development of plastic products and expanding application field, continuous improvement of rolling machines’ manufacturing technology and related technology. Rotomolding industry association will also be a powerful push to all aspects of the rotomolding industry of our country in the future, which of course needs continuous joint efforts. Rotomolding industry in China should have good prospects for development.
