Analysis on the development trend of rubber track technology
Section 1 Status of product technology development
The belt structure of a general rubber crawler has the following parts: iron core, driving crawler; steel core, bearing traction; pattern (1 ug), grounding portion; wheel side, supporting the roller portion.
As a molded product, the rubber crawler is vulcanized in a mold. Its production method: joint vulcanization, jointless vulcanization, wherein the jointless vulcanization is divided into integral mold vulcanization and segmental vulcanization.
At present, most of the manufacturing plants in the world use joint curing, that is, a long belt is pre-formed, and then the ends of the long belt are jointed. The number of sections of the track is in principle not limited by the mould and can be used for large or small quantities. There are a few manufacturers that use a one-piece mold to produce a rubber track without joints. The biggest limitation is that the number of sections (length) of the rubber track cannot be adjusted.
Some factories in our country use segmented vulcanization to produce rubber crawlers. This process inevitably has multiple vulcanizations in the manufacture of a rubber track, which is prone to quality defects.
Section 2 Product Process Features or Process
The rubber track is composed of a metal transmission carrier, a strong layer traction member, a traction member protection layer and a rubber elastic body. The metal transmission carrier acts as a power transmission guide and a lateral support; the strength layer traction member is a longitudinal tensile body of the rubber track, which bears the traction force and maintains the stability of the track pitch; the traction member protection layer protects the traction member from the external force. The rubber elastomer tightly combines the other components into one unit, providing walking capability and overall cushioning, shock absorption and noise reduction.
The materials for the transmission carrier are mainly ductile iron, cast iron forged steel, aluminum alloy and alloy steel sheet stamping and forming assembly, etc. Some low-strength crawlers can use plastic. In addition to the most common steel cords, the traction elements can also be galvanized steel wire, stainless steel wire, fiberglass, aramid or other high-strength low-stretch synthetic fiber ropes or cords. The material of the traction layer protection layer is nylon mesh cloth, canvas, curtain and film filled with different fibers. Most of the rubber compounds are NR, polyurethane elastomer or NR/SBR and NR/BR based on NR.
The premise of rubber track design is to understand the relevant mechanical vehicle type, wheel structure, power, speed, use and working conditions. The design range includes the driving method, calculation of bearing and traction strength, selection of structural material types and models, layout of section structure, pattern shape and height, and compounding of rubber compound.
The drive carrier shall be designed to withstand the ability to withstand bending, wear, shear, torsion and lateral support during use without cracking and breaking. The strength layer traction member is designed to ensure the tensile strength of the track and to maintain the stability of the track pitch. The calculation of the material strength should take into account the mechanical and chemical corrosion damage caused by overloading and the use of medium and external forces and the environment. The setting of the safety factor cannot be lower than 12. In the structural hierarchy of the traction material, a reasonable combination of different fiber materials should be considered. Improve the longitudinal flexibility, durability and reduce product quality of the track while ensuring tensile strength and pitch stability.
The selection and arrangement of the protective layer not only can enhance and protect the traction layer of the strong layer, but also have the ability to absorb shock and cushion, and can resist the biting, smashing, puncture and cutting damage of the belt by external force.
The outer rubber pattern of the track has parallel, single ladder, double ladder, triangular butterfly, snowflake, serrated and smooth surface without pattern. The selection and height design of the blocks should be based on the conditions of terrain and traction, and of course the cost should be considered. The height of the general track pattern is: 20-40mm for the agricultural machinery, 18-40mm for the earthmoving machine, 35-50mm for the handling machine, 40-70mm' for the bulldozer, and 15-30mm for the snow removal machine. The configuration of the pattern should avoid stress concentration, improve the growth resistance of the crack and reduce the early damage of the rubber caused by the crushing of the gravel into the pattern.
The design of the compound formulation includes the outer flange adhesive, the inner layer of the glue and the filler. The outer flange rubber varies with the use conditions and load capacity of the crawler belt, but the formula design has some common features: first, the use of after-effect vulcanization system, second, the use of anti-aging agent is large, and the use of multiple varieties of physical and Chemical anti-aging agents are used together.
3. Manufacturing process
The manufacturing process of rubber crawler belt mainly includes two methods of secondary vulcanization joint method and ring forming section vulcanization method. In order to develop the annular forming segment vulcanization process, China has developed a track ring vulcanizer.
The secondary vulcanization joint method is more traditional, and the basic process of manufacture is to form a strip with a laminated rubber steel cord and a reinforcing tape and a film. The metal transmission member is processed to be rubberized to obtain a rack, and then separately loaded into a mold and vulcanized into a strip on a flat vulcanizing machine. The length of the mold depends on the length of the belt. In order to facilitate the joint, both ends of the belt should have unvulcanized heads. After the two heads are overlapped, a ring shape is formed.
The annular forming stage vulcanization process uses a squeezing vulcanizer and is vulcanized into an endless belt using a short set of dies. The length of the belt is not limited by the mold, and the mold for the joint machine and the joint is omitted. The strip is subjected to tension during both forming and vulcanization. The strip blank is wound and formed on a double drum forming machine to form an endless strip blank and then placed on the vulcanizer, sequentially loaded into the rubberized rack, and vulcanized into strips. Due to the lack of joint overlap of the traction layer of the strong layer, the increase of the bending rigidity at the joint and the wire piercing which may occur at the joint are avoided, and the length of the produced track does not need to be replaced when the length of the track is changed, which is advantageous for reducing the cost.
Section III Analysis of future development trends of domestic and foreign technologies
Rubber track greatly expands the application range of crawler and wheeled transport machinery, overcomes the constraints of various unfavorable terrain conditions on mechanical operations, and its application in tractors, various agricultural and engineering and transportation machinery will be further expanded. . Its development trend is to improve the life on the basis of improving the structure, adopting new materials and new technologies, and developing towards lightweight, large-scale, high-strength, multi-variety, multi-functional and adjustable, to further meet the various harsh climates. Requirements for use in terrain conditions and use of large tonnage construction machinery transport vehicles. With the development and improvement of science and technology, rubber crawlers will evolve from wearing parts to functional parts, and the great improvement in service life is completely achievable.