Rubber roller production process and technical progress

In recent years, technologies such as injection, extrusion and winding have been continuously developed, and the rubber roll forming vulcanization equipment has gradually led to the mechanization and automation of rubber roller production. The performance of the rubber roller has a great impact on the whole machine. The process operation and production quality are extremely strict. Many of its products have been classified as fine products. The selection of rubber and plastic materials and the control of product dimensional accuracy are the key. The rubber surface of the rubber roller is not allowed to have any impurities, blisters and air bubbles, and it is not allowed to have scars, defects, grooves, cracks and local sponges and soft and hard. To this end, it is required that the rubber roller must be absolutely clean and fine-tuned throughout the production process to achieve uniform operation and standardization of technology. The combination of rubber plastic and metal core, bonding and injection molding, and vulcanization grinding have become high-tech processes.

For many years, rubber roller production has become a difficult point for the mechanization and automation of process equipment due to the unfixedness of the products and the diversity of size specifications. So far, most of them are still intermittent unit type production lines. Recently, some large professional manufacturers have begun to realize continuous production from the rubber compound to the molding and vulcanization process, which has doubled the production efficiency and greatly improved the working environment and labor intensity.

First, the preparation of rubber

       For rubber rollers, rubber compounding is the most critical aspect. The rubber compounding materials range from natural rubber and synthetic rubber to more than 10 kinds of special materials. The rubber content is 25%-85%, and the hardness is soil (0-90) degrees, which spans a wide range. Therefore, how to mix these rubber compounds has become a big problem. The conventional method is to carry out the kneading process in the form of a plurality of master batches using an open mill. In recent years, companies have increasingly switched to intermeshing mixers to produce rubber compounds in a batch-mixed manner.

After the rubber compound is evenly mixed, it is filtered with a filter machine to eliminate impurities in the rubber compound. Then, a calender, an extruder, and a laminating machine are used to form a film or strip without bubbles and impurities for molding the rubber roll. Before the molding, these films and strips should be subjected to strict visual inspection to limit the parking period, keep the surface fresh and prevent adhesion and deformation. Because most of the rubber roller is a non-molded product, once the surface rubber has impurities and air bubbles, sanding may occur when the surface is ground after vulcanization, which will cause the entire rubber roller to be over-repaired or even scrapped.

Second, molding

The rubber roller is mainly formed by coating a rubber on a metal core, and has a wrapping method, an extrusion method, a molding method, a pressure injection method, and an injection method. At present, the main domestic machinery or manual paste molding, the majority of foreign countries have achieved mechanical automation. The large and medium-sized rubber rollers are basically produced by profile extrusion, and are continuously molded by extrusion film or continuous extrusion molding of extruded rubber strips. At the same time, the micro-machine automatically controls its size and appearance during the molding process, and some can also be formed by the extrusion machine at right angles and irregular extrusion.

The above molding method not only reduces labor intensity but also eliminates bubbles which may be generated. In order to prevent the deformation of the rubber roller during vulcanization and prevent the generation of bubbles and sponges, especially for the rubber roller which is formed by the wrapping method, a flexible press method is also used on the outside. Usually, a plurality of layers of cotton or nylon cloth are wrapped around the outer surface of the rubber roller, and then fixed and pressurized with steel wire or fiber rope. Although this process has already been mechanized, it has to be removed from the dressing after vulcanization to form a “cecal” process, which complicates the manufacturing process and is extremely limited due to the use of the wrapping cloth and the winding rope. waste.

For small and micro rubber rollers, manual production methods such as manual placement, extrusion, injection, injection and casting can be used. In order to improve production efficiency, the molding method has been mostly used, and the precision is much higher than the non-molding method. Injection molding of solid rubber, injection, and pouring of liquid rubber have become the most important production methods.

Third, vulcanization

At present, the vulcanization method of large and medium-sized rubber rollers is still vulcanization tank vulcanization. Although the flexible pressurization mode has been changed, it still does not deviate from the heavy labor burden of reciprocating transportation. The heat source for vulcanization is steam, hot air and hot water. The main stream is still steam. The rubber roller which has special requirements due to the contact of the metal core with water vapor is indirectly steam vulcanized, and the time is extended by 1 to 2 times, and is generally used for the rubber roller of the hollow iron core. For special rubber rollers that cannot be vulcanized with vulcanization tanks, hot water vulcanization is sometimes used, but the treatment of water pollution needs to be resolved.

In order to prevent the rubber and the metal core from different shrinkage due to the difference in heat conduction, delamination occurs between the rubber roller and the rubber core. Generally, the vulcanization is mostly carried out by a slow temperature rise and pressure, and the vulcanization time is much longer than the curing time required for the rubber itself. . The large rubber roller achieves uniform vulcanization inside and outside and makes the metal core and rubber have similar thermal conductivity. The residence time in the tank is often as long as 24~48h, which is about 30~50 times of the normal vulcanization time of the rubber.

Small and micro rubber rollers have now been mostly converted to flat vulcanizing presses, which have completely changed the traditional vulcanization method of rubber rollers. In recent years, the injection molding machine has been installed, vacuum vulcanization is applied, and the mold can be automatically opened and closed. The degree of mechanization and automation is greatly improved, and the vulcanization time is short, the production efficiency is high, and the product quality is good. Especially when the rubber injection molding vulcanizer is used, the two processes of molding and vulcanization are combined into one, and the time can be shortened to 2 to 4 minutes, which has become an important direction for the development of rubber roller production.

At present, liquid rubber represented by polyurethane elastomer (PUR) has developed rapidly in the production of rubber rollers, and has opened up a new way for materials and process revolution. It uses a cast form to remove complex molding operations and bulky vulcanizing equipment, which greatly simplifies the production process of the rubber roller. However, the biggest problem is that due to the necessity of using molds, for large rubber rolls, especially for individual products, the production cost is greatly increased, which brings great difficulties for promotion and use.

In order to solve this problem, in recent years, there has been a new process of PUR rubber roller without mold manufacturing. It uses polyoxypropylene ether polyol (TDIOL), polytetrahydrofuran ether polyol (PIMG) and diphenylmethane diisocyanate (MDl) as raw materials, reacts rapidly after mixing and is quantitatively poured onto the metal core of slowly rotating rubber roller. Step by step to achieve side-casting and solidification, and finally form a rubber roller. This process not only has a short process, high mechanization and high degree of automation, but also eliminates the cumbersome molds. It can produce rubber rollers of various specifications and sizes according to requirements, which greatly reduces the cost. It has become the main development direction of PUR rubber rollers. .

In addition, miniature fine rubber rollers used in the manufacture of office automation equipment using liquid silicone rubber have also developed rapidly around the world. They are divided into two categories: heat curing (LTV) and room temperature curing (RTV). The equipment used is also different from the above PUR to form another type of casting. Here, the most critical issue is how to control and reduce the viscosity of the compound to maintain a certain pressure and extrusion speed.

Fourth, surface treatment

Surface treatment is the last and most critical process in the production of rubber rollers. The surface grinding state directly affects the performance of the rubber roller. At present, the grinding methods are various, but mainly mechanical turning and polishing. For this reason, the grinding method, the grinding tools and the abrasives used are very important, and each enterprise regards it as a technical decision and maintains an undisclosed attitude. The biggest problem is how to solve the heat generation of the rubber during grinding and to maintain the optimum deflection of the surface after grinding.

In addition to grinding the surface of the rubber roller, it must be thoroughly cleaned to remove the rubber powder adhering to the surface. The higher the surface is required to be further polished, and some coated with resin coating, latex paint and magnetic powder. , electrostatic powder, etc. At the same time, it is also possible to plate a desired plating layer or perform a chemical oxidation treatment to achieve functions such as light sensitivity, corrosion resistance, magnetization and conductivity.

With the continuous development of the rubber roller, the coating technology of the rubber roller surface has also been rapidly improved, and the conventional method of changing the rubber roller performance by completely covering the rubber has been started. Specifically, it is a coating method that changes and imparts new properties to the rubber roller. For example, a device such as a calender or a knife coater is used, and an oil shield layer is added to achieve the purpose of improving oil resistance. Although the shape and material of the rubber roller are the same as before, the function has changed greatly, and some have become Functional rubber roller, this surface treatment technology will have a promising future.

In summary, the rubber rollers used in today's production have formed a product line with a unique process. Although the domestic products are still dominated by traditional products, the technical content is constantly improving. Many products have entered the high-tech field, and the added value has gradually increased, which is becoming another economic highlight in industrial rubber products.