Equipment design features
According to the performance characteristics of graphite materials, in the design of impervious graphite chemical equipment (hereinafter referred to as graphite equipment), the following aspects should be noted:
1 should try to give full play to the characteristics of high compressive strength of graphite materials. The graphite element is subjected to a compressive stress state to avoid or reduce tensile stress and bending stress;
2 The channel orientation of the heat exchanger must conform to the optimal heat conduction direction brought about by the graphite anisotropy. Since the thermal conductivity of the graphite article perpendicular to the extrusion axis is 25% smaller than the direction parallel to the axis, when designing the heat transfer element, the direction of the heat transfer heat flow should be as far as possible along the axis of the graphite extrusion;
3 As a heating device, when resin-impregnated graphite, pressed graphite and its binder are combined with metal materials or other materials to manufacture heating equipment, excessive temperature stress is caused due to the difference in thermal expansion coefficient, and the viscosity should be minimized. Connected structure. In the design of the tubular heat exchanger, it is especially necessary to select the material and structural form reasonably;
4 The main graphite parts of the equipment should also avoid the use of structures with bonded joints. Due to the difference in thermal expansion coefficient between the cement and the graphite material, the bonding joint will generate temperature stress at a higher operating temperature, and it may cause embrittlement under the action of the medium temperature and time, causing the part to break. At present, the largest size of artificial graphite blanks used in manufacturing equipment in China: square section is 400mm X 400mm, cylindrical section is generally φ60Omm, and the maximum is φ1800mm, and the required graphite parts often exceed the maximum size of graphite blanks. At this time, it is inevitable to use a bonding structure. At this time, the glue joint of the graphite parts should be tight and uniform, and the slit width is generally not more than 1mm;
5 Metal material joints, such as bolts and stud bolts, should not be screwed directly onto the graphite element;
6 The geometry and equipment structure of the parts should not be too complicated;
7 graphite joints should not protrude too far from the outer wall of the equipment to avoid damage during transportation or use;
8 should consider the lifting position of the equipment, generally should not be directly hoisted on the impervious graphite components;
9 Due to the heterogeneity of the graphite material, a large safety factor is used in the calculation of the strength, generally taking 9 to 10 (the former West German AD specification N2 is 9 and Japan is usually 10), and the basic materials and process guarantee conditions are good. When considering, you can consider using n=9).
Processing and manufacturing process
The manufacturing process of impervious graphite equipment and its components varies with the structure of the equipment. The mechanical properties of impervious graphite are similar to those of cast iron. They are less hard than cast iron and can be added by metal cutting tools or woodworking tools. Such as car, planing, milling, drilling, sawing, grinding and other processing. Due to the poor strength and brittleness of graphite itself. Generally, two impregnations and two additions are used to increase the strength and ensure the processing accuracy.
For the processing and manufacturing of impervious graphite equipment, relevant standards such as “Graphic Chemical Technology Conditions” (HG 2370) shall be implemented to strictly control the construction links to ensure the construction quality.
Graphite materials are hard but brittle and extremely fragile. Therefore, the graphite material and any of its components and products should be handled lightly during any handling process, and it is strictly forbidden to throw it away. During the machining process, when clamping is required, the force should be uniform. Avoid local stress. During the machining and assembly process. It is strictly forbidden to hit with a gold hammer. In the case where it is necessary to knock, it should be beaten with a rubber raft.
Despite this, the overall level of China's graphite equipment industry is still not high, because most of the main materials for the current production of graphite equipment are still electrode graphite, and there are not many varieties of immersion agents. The internal graphite particles of the electrode graphite are coarse (the particle size is about 6 to 10 mm). High void ratio (generally around 20%), poor mechanical properties, resulting in poor performance and quality of graphite equipment. Therefore, how to develop chemical-specific graphite, improve the mechanical and physical properties of graphite materials, develop new varieties of high-performance impregnant, improve the processing and manufacturing process of graphite equipment, and improve the performance and quality of graphite equipment are the goals and priorities of our future work.