The Development of Large Rubber Fender
Fender is a kind of energy buffer device used on the port dock or ship. It is used to slow down the shock of ships and wharfs or ships and ships when berthing or mooring, so that ships and wharfs are free from damage.
Rubber fender has the characteristics of good elasticity, high energy absorption, convenient maintenance, long service life and large quantity of fixed production, which is widely used in Japan, Europe, America and Southeast Asian countries.
The size range of rubber fenders is large. Conventional size products can be easily selected to match the vulcanization equipment, but large vulcanization equipment required for large size products which will cost high investment. Especially in the small batch of products, the investment to buy large vulcanization equipment is not cost-effective. The large rubber fender is made by the vulcanization mechanism of ordinary flat belt.
1. Type of rubber fender and overall performance requirements
The type of rubber fender mainly includes shear type, rotary type, compression type, pneumatic type and water pressure type. Compression rubber fender has the characteristics of simple structure, easy manufacture and easy installation, which is the most widely used variety at home and abroad. Compression type rubber fender can be subdivided into D type rubber fender, cylindrical rubber fender, arch rubber fender, cell rubber fender and I type rubber fender. D type rubber fender and cylindrical rubber fender are early varieties. Arched rubber fender appeared in the 1960s and is widely used now. Cell rubber fender is a new type developed for large ships in recent years. The characteristics of the cell rubber fender are the large size products, and in front of the rubber body are equipped with metal, plastic or wooden impingement plate. This kind of fender is widely used in wharf, pier wharf and other large wharf in open sea. Most of the rubber fenders are all rubber products, but large fenders often have reinforcing layer, and the connection with the quay wall is also strengthened by steel plate, so the firm combination of steel inlay and rubber is one of the problems that must be reasonably solved. With the development of large ships and wharves, the requirement of rubber fender performance is higher and higher. In addition to high absorption energy, low reaction force and small pressure on the hull, it is required to have the characteristics of wear resistance, oil resistance, seawater erosion resistance and high bonding strength, while considering reducing the cost.
2. Formula design
The reaction force and pressure of the rubber fender depend on the type and hardness of the rubber material, the harder the hardness, the higher the reaction force and pressure. Hardness and constant tensile stress are the main factors that determine the performance of products. Since the rubber fender is thick products, rubber material vulcanization flat is better. NR was widely used in rubber fenders. With the development of polymer application technology, SR was also used. For example, NR/SR combination is adopted for the inner rubber fender, CR with good weather and oil resistance is adopted for the outer rubber fender.
3. Mold design
3.1 Determination of shrinkage of rubber
The size of rubber material shrinks after vulcanization cooling; resulting in the size of the finished product is smaller than the mold cavity size, so we should consider the shrinkage of rubber material in the mold design. There are many factors that affect the shrinkage of rubber materials, mainly including the thermal expansion of rubber materials, the structure of products, the wall thickness of broken surfaces, whether there are embedded parts, the rubber content of rubber materials, vulcanization temperature, rubber types and hardness and vulcanization conditions. Since there are many influencing factors, there are many formulas to calculate shrinkage rate, including 3 commonly used formulas, which are respectively the formula to calculate according to the product and mold cavity size, the empirical formula to calculate according to the type A hardness of vulcanized rubber shole and the general formula to calculate according to the vulcanization temperature.
3.2 Mold design and tooling configuration
According to the model and batch of the products, the mould was designed with combination structure, and a series of mould with vulcanization heating system was developed, which was economical and practical. For the products with large length, the segmenting vulcanization process is used to vulcanize the large rubber fender of the ordinary flat belt vulcanizing machine. It is an important task to develop a mold equipment system with both pressurizing and heating properties. In this work, the heating system configured with electric heat pipes is adopted, and the thermodynamic temperature field parameters optimized by FEM analysis are adopted to conduct the structural arrangement of the heating system, resulting in significant energy saving effect.
4. Manufacturing technique
4.1 The treatment of inlaid reinforcing plate
At present, there are mainly 4 kinds of methods used to bond steel plate with rubber, including rigid adhesive method, phosphorus sulfide direct adhesive method, isocyanate adhesive method and commercial adhesive method. After comprehensive comparison of advantages and disadvantages, it is concluded that although the material is unstable and harmful to human body, the adhesive strength of isocyanate is very high and suitable for rubber fender.
The steps for treating isocyanate adhesive method are as follows.
(1) Sand blasting is carried out on the steel plate first, followed by pickling with dilute hydrochloric acid, and acetone is used to remove the surface grease after drying. The surface area of sandblasted and acid-washed metal increases and the surface activity is concentrated.
(2) The synthetic isocyanate adhesive is brushed on the treated metal surface 4 hours before vulcanization and left for 2 hours.
(3) Then coated with high hardness adhesive material glue on the surface coated with adhesive, forming adhesive strength strengthening layer.
(4) Apply a high hardness adhesive film about 8 mm thick to the surface to be adhered.
(5) Affix the buffer film made by mixing high hardness rubber and molding rubber.
4.2 Molding
According to the structure of rubber fender, mixing film is pasted into prefabricated parts. All kinds of film must be made into a certain shape according to specifications before forming, the thickness of the outer rubber and the bottom rubber film should also be controlled.
Since the shrinkage rate, adding excessive rubber during preforming can make the product compactness, which plays an important role in ensuring the size accuracy of the product and improving the quality of the product.
Attention should be paid to the positioning of the Mosaic block when adopting the mould with movable Mosaic block. For the rubber fender with embedded parts, in addition to ensuring the normal positioning tolerance of embedded parts during mold design, attention should be paid to ensure the correct position of embedded parts during molding.
4.3 Vulcanization
Rubber fender is a large rubber products, should use a large vulcanization pressure, the vulcanization pressure used in this work is 20 ~ 40MPa, far more than the general vulcanization pressure of rubber products. At the same time, since the product thickness is large, so it is appropriate to use low temperature long time curing. The temperature is controlled in 140~160℃. The curing time was determined by the curing characteristic curve.