Safety shoes are a profitable market for shoes with a small but specialized share. The world churns out nearly 20 billion pairs of shoes a year, mostly made by hand, a time-consuming and error-ridden way of making shoes. At present, only 10% of manufacturers use fully automatic or semi-automatic production lines, while in other industries, the degree of automation is much higher, which is a trend that cannot be ignored by footwear producers. Some large shoemakers have realized the benefits and necessity of automating shoe making.

Safety shoes are a profitable market for shoes with a small but specialized share. The world churns out nearly 20 billion pairs of shoes a year, mostly made by hand, a time-consuming and error-ridden way of making shoes. At present, only 10% of manufacturers use fully automatic or semi-automatic production lines, while in other industries, the degree of automation is much higher, which is a trend that cannot be ignored by footwear producers. Some large shoemakers have realized the benefits and necessity of automating shoe making.

The demand for safety shoes continues to grow. There are a number of reasons for this: increased security awareness; More regulations on health and safety in working areas have been formulated; Developing and nearly developed countries are becoming more industrialized, while population and urbanization are growing. Two factors dominate. According to the DSW, there are currently about 7.1 billion people on earth. That number is expected to grow to 9.6 billion by 2050. More than 50 percent of the world's population now lives in cities, and that number could rise to 80 percent by 2050. More than 20 million people live in big cities. In order to provide such a huge city with functional infrastructure, food, water and energy, huge industrial demand is essential. The need for personal safety equipment for these industrial workers has also increased

Safety shoes are high-tech products

Safety shoes must meet the highest requirements of consistent and stable production quality. This requirement can only be achieved through the efficient and automatic production process of safety control. Safety shoe surface materials usually include wear-resistant leather, anti-skid materials such as PU or PUR, rubber (GU) or thermoplastic polyurethane (TPU). Built in steel, aluminum or composite material to protect the toes from injury. Penetration protection made of steel, composite materials or aluminum to prevent nails or other sharp objects from being inserted into the foot. In addition, modern shock absorption makes wearers more comfortable. Sole production is a major and decisive production link independent of the type and use of safety shoes. And this is where desma's injection machine is going to show you.

Continuous injection - uncompromising quality assurance

The first machine to perform the injection was in 1953, when manual vulcanizing buttons were commonly used by shoe factory workers. They place rubber strips or slabs in open sole molds and press them against the border of the upper. In the following years, automation has developed rapidly. In 1960, DESMA officially introduced disc machines equipped with 20 to 10 stations and side mounted automatic connected injection casting units to the market. So far labor-intensive, full of mistakes in the way of artificial glue to the upper shoe soles of the way is gradually abandoned. The working principle of the machine developed is still in use today. The injection casting unit will plasticize the formulated sole material such as rubber strips or plastic particles, and then inject the raw material liquid into the open sole mold. The metal border of the upper is then lowered to a certain depth in the sole mold, so that the upper and the mold cavity of the sole form a complete combination state. The mold cavity is still a liquid sole that solidifies on the upper of the shoe while forming a special shape. This method of continuous injection machine has brought a new revolution to shoe production. It brings efficient automation equipment production line, increases the production of shoes, and reduces the corresponding loss in the production process. However, the production process before and after the injection is still manual. Further research and development has resulted in more productive and flexible machine components, and the use of industrial robots has replaced error-ridden manual work. For example: the application of a remodeling agent that facilitates the shaping of the sole before filling and the roughing of the upper of the shoe before the injection of the upper.

With the continuous update of automation of DESMA turntable machines, in addition to the increase of mold units, according to the requirements of the process, the equipped assembly stations can reach 18,24,30 or even 60. Today desma again presents advanced technology and art techniques, multi-layer and multi-color automatic direct injection molding soles, as well as production of different sizes, order or material changes, all of which can be completed within a rotating cycle of the disc machine. This flexibility provides users with great advantages in production, process and economy. More importantly, they can make timely response and adjustment to the requirements and shorten the delivery time as much as possible.

In addition, with constant processing parameters, automatic production can ensure stable product quality and meet the high standard of almost strict zero error. According to the different materials used in the sole, even the procedure of injection is changed with the technical details. Nowadays, the important materials used in soles are mainly rubber (GU), thermoplastic polyurethane (TPU) and polyurethane (PU).

TPU and rubber injection

Is plasticizing and TPU rubber sole material, and then by pouring technology DESMA DESflow ® padding to open within the sole mould. DESflow ® pouring process is a sole raw material into the mould, compared with the loss of precast produce this method can save more material. The casting time or the truly required glue bar can be adjusted according to the specific size of the mold by the specified casting speed and the use of various nozzle. The glue is filled into the mold cavity, and the upper is lowered into the material, and the mold is closed. The sole material is glued tightly to the upper of the shoe under pressure. The mold opens again after the set processing time. The disc machine circulates to the next step.

PU side injection

The technology of continuous injection of PU is more remarkable and complicated. In this process, shoe manufacturers do not use pre-formulated ingredients, but rather two or more of the liquid ingredients produced by chemical reactions (gradually added and polymerized). In short, the two liquids must be mixed together at the beginning of making the material, then injected into a closed unit and waited for the material to react to produce a PU. So material A is either polyester or polyether (polyhydroxy compound), and material B is isocyanate. Polyester polyols are more resistant to mechanical wear, high temperature and chemical reactions than polyether systems, which is why polyester polyols are more suitable for safe shoe production.

The technology of PU continuous injection focuses on accurately transporting, measuring, mixing and injecting two reactive components into the mold cavity. The molded bottom is then glued tightly to the edge along the contour of the upper. A hole is drilled in the mold surface of the mixing head of the injection unit to fill the nozzle at any time. Desma designed a special mixing head for this process.

In addition, the mechanized synchronous controlled circulation valve is located in the mixing head to transfer liquid components in batches at any time. The distribution circulation valve is opened and the liquid components to be mixed flow through the inlet channel into the mixing chamber. A conical mixing and conveying screw ensures a single closed mixing and is then injected into the mold through a nozzle. The speed of screw rotation can be continuously adjusted from 10,000 to 18,000 times per minute. The screw and the mixing chamber are cooled by liquid to keep the chamber constant temperature. At the later stage of mixing stage, the screw is axial to the nozzle, which greatly reduces the amount of principle in the mixing chamber. The purpose of this procedure is to self-clean the screw and chamber by centrifugal force generated by the high-speed rotation of the screw. The bits of residue attached to the screw can be thrown onto the wall of the chamber.

The material is injected into the chamber to react and bubble into PU, which is then bonded to the upper part of the shoe under the action of pressure. The DESMA PU can also mix other additives and pigments. In addition, users can also record the formulations of production and processing parameters in the database, and then, during the exchange of products or molds, either through the manual BAR code or through the RFID chip, the information is allocated to the corresponding mold fixator. Therefore, it is necessary to ensure correct parameters and stable production conditions in order to ensure that beautiful finished shoes can be obtained at any time.

In the production of safety shoes, continuous injection technology is a mature and reliable manufacturing process. The technology has been successfully used worldwide. With calls for stable footwear quality and lower production costs rising, the company's injection technology is poised to triumph in the market. And this application is especially suitable for all kinds of lightweight and flexible shoes.