Development Bottleneck and Breakthrough in Current Status of Rubber Injection Molding in China

With the development of the rubber industry, the molding technology of rubber products has also undergone different stages of development: molding stage, injection stage, injection stage, and injection molding and injection transfer on the basis of injection.

Injection molding has become the main method of rubber processing. With regard to the characteristics of rubber itself, injection molding has become the mainstream method of molding rubber products with its unique advantages. The injection process is through the heating of the plasticizing cylinder and the mixing and shearing of the plasticizing screw, which raises the temperature of the compound to the state of the best fluidity, and then injects the compound at a higher injection pressure. In a mold-locked (vacuumed) cavity, pressure is applied and the temperature is increased to cure the rubber. Throughout the process, the three factors of time, pressure and temperature determine the efficiency and quality of production.

First, injection molding can improve product quality. By holding the mold first and injecting pressure afterwards, it is possible to continuously and steadily deliver the pressure required for the molding of the product so that the product can be vulcanized under controlled pressure, temperature and time. Injection molding can improve the compactness and functionality of the product (especially the functionality of the cushioning product).

Second, injection molding can greatly increase production efficiency. Through the plasticizing function of the injection unit, the fluidity of the rubber material is greatly increased, so that the mold cavity is filled at a relatively high temperature and immediately begins to be vulcanized. By a reasonable parameter setting, the injection process can shorten the vulcanization by 30 to 50% compared with the molding process. time.

Third, the injection molding process can significantly reduce the labor intensity of workers, reduce the waste of plastic and power consumption.

The present situation and development bottleneck of injection molding Compared with the current development status of rubber injection molding in foreign countries, domestic rubber injection technology is still in its infancy. Although there are injection molding machines available for production, the related process research work is insufficient. A typical example is that most of the production process does not set the holding pressure, but only fills the cavity through the injection pressure, which results in the easy generation of “cakes” in the flow channel and the generation of flashes on the product.

The development of rubber injection molding is inseparable from the tripartite cooperation of equipment factories, mold suppliers and product factories to jointly promote the application and development of injection molding. However, at present, these three links are basically independent and lack integration. From the injection molding machine itself, the current domestic market capacity is about 450 million yuan, with an annual growth rate of about 30-40%. At present, the Chinese market has more than 20 rubber injection "brands" of large and small sizes, most of which have evolved from the original Taiwanese aircraft or continental aircraft. Usually, injection machine manufacturers find an investor, copy a company’s drawings or make minor changes to manufacture, use low prices or rely on personal relationships with equipment procurement personnel to compete in the market, lack innovation and R&D capabilities. This has led to a lack of technological innovation in the equipment, let alone research on the rubber injection process.

The common problems of domestic rubber injection machine technology are mainly reflected in several aspects:

The first is that most of the models adopt a lower system pressure of 21/22 MPa and nominally 300 tons. Actually, they can only provide a clamping force of 2600 KN and the clamping force is insufficient. The corresponding pumps and valves are all of cheaper Japan or Taiwan and other brands are prone to oil leakage and damage, and their service life is not long. Hydraulic valves, etc. also use separate valves and tubes, which are prone to failure and difficult to maintain.

Second, the structural design of the fuselage is irrational. The mold opening space is insufficient. The mold must be removed before the mold can be opened externally. The design of the guide column is unreasonable, and the lock nut is easy to loosen, resulting in unbalanced hot plate and easy to cause flashing. "cake" and so on.

The third is the backward advanced injection unit, each mold needs to shoot about 20 ~ 30g of plastic material, and the temperature of the plasticizing cylinder is relatively low; cleaning and changing the rubber material is very tedious and needs to be disassembled.

Actually, the most fatal weakness of many machines is instability, and various problems often arise that affect customer use and production.

In addition, the associated molds and cold runners have insufficient capacity, which are mainly manifested in the relatively primitive structure of the molds and concepts, the inaccurate processing and manufacturing precision, and the unreasonable surface treatment or simply not doing so.

The domestic lack of professional rubber mold manufacturers, most of them are professional to do plastic molds, with some rubber molds, lack of understanding and research on rubber molds, lack of innovation. There has always been a concept in China that rubber molds are simple, easy, and low in price. In fact, it is precisely this erroneous concept that has spurred the development and growth of domestic rubber injection molding processes.

In addition, the lack of professional injection molding process personnel, as well as the production plant. At present, there is a serious shortage of relevant personnel involved in process research in domestic product factories. Recruitment of process engineers from a foreign-funded company with a monthly salary of RMB 12,000 can be found. In foreign countries, the craftsman of the product factory can make clear requirements for the machine and mold, and adjust and correct the process according to the machine capacity and mold. However, there is a shortage of domestic technicians with this capability. Most craftsmen only know the design. Three factors are set for temperature, pressure and time, but the research and deep understanding of the injection molding process are not enough.

Characteristics of New Type Rubber Injection Machines In recent years, domestic suppliers of rubber injection machines have also actively explored and launched new rubber injection machines to meet market needs. The servo-hydraulic drive system first introduced at the CHINAPLAS2011 exhibition by the Gladiator Company was well received by the industry.

Fighter rubber injection machine adopts European synchronous injection molding technology, and has carried out revolutionary innovation and research and development in the structure of the closing unit, the structure of the injection unit and the related electronic control systems and functions. In the fuselage structure, a sturdy and highly redundant design scheme is adopted to ensure the strength and durability of the fuselage; a high mold opening space allows the mold to be placed and demolded without removing the mold.

The hydraulic system uses a Rexroth 25Mpa variable pump (energy-saving up to 40%) and a full Rexroth valve, connected by an integrated valve plate and Parker high-pressure piping, ensuring sufficient mold-locking capacity and high reliability. At the same time, the use of a first-in, first-out injection unit can increase the plasticizing temperature as much as possible, shorten the vulcanization time, increase production efficiency, and eliminates the need for ejection of a material head per mold.

In addition, the problems of cleaning and maintenance of the injection unit were taken into account in the initial design, so the production process was more human and easier to operate.