When selecting extrusion equipment, in addition to considering the thermal effects of extrusion speed on the extruded metal, it is also necessary to ensure that the press has adequate rigidity and guiding precision, as well as a reliable overload protection device.
When extruding with a friction press, due to differences in the guiding precision of the equipment, guiding devices need to be added to the mold. For friction presses without ejection devices, ejection devices should also be added.
When extruding with a universal crank press, in order to increase the strength and rigidity of the equipment, the worktable base plate should be made of cast steel, and the holes on the table should be reduced in size. Due to the parts remaining on the mold after extrusion, there is a significant clamping force between the extruded parts and the mold, resulting in a high ejection force required, approximately 10% to 20% of the nominal pressure, thus the die ejection device of the press should be strengthened. In addition, the extrusion pressure and stroke should be verified according to the load curve permissible for the press slider. That is, throughout the entire range of the extrusion stroke, the extrusion pressure should be less than the limit value of the stroke-pressure curve allowable for the press, and cannot be determined based on the nominal pressure.
The accuracy and extrusion stroke of a general press are insufficient, and the pressure exerted at the midpoint of the stroke is only about one-third of the nominal pressure. Therefore, when extruding, it is best to use a specialized industrial aluminum profile extrusion machine as the extrusion equipment. The characteristics of a lever-type industrial aluminum profile extrusion machine are a short stroke, a high number of strokes, and a long pressurization time, making it suitable for extruding parts with short working strokes. The tension lever-type and crank-type industrial aluminum profile extrusion machines are suitable for extruding longer parts. The hydraulic industrial aluminum profile extrusion machine can operate at nominal pressure throughout the entire stroke, and the extrusion speed and stroke can be adjusted, making it suitable for extruding longer parts.
The selection of extrusion equipment should consider the following points:
(1) Choose the type of extrusion equipment based on the determined production plan and the requirements of the production process. Select corresponding supporting extrusion equipment according to the production plan, such as for pipe production, bar and profile production, or the production plans for online coiling of billet, etc. Select extrusion equipment that is compatible with the process requirements; for easily oxidizable copper and copper alloys, a water-sealed extrusion method can be used; for the extrusion forming of various coated materials, a hydrostatic extrusion method can be used; and for products that need to achieve lengths of thousands to tens of thousands of meters in coiled form, the Conform continuous extrusion process can be employed, etc.
(2) Choose extrusion equipment based on the variety, specifications, performance, and quality requirements of the product. For instance, when selecting the tonnage of the extruder, first determine the range of specifications for the extruded product or intermediate blank and consider the required degree of deformation to establish the size range of the ingot and the necessary size range of the extrusion cylinder, thus determining the appropriate tonnage of the extruder. Additionally, the type of extruder should be determined based on different varieties, specifications, and quality requirements.
(3) Select extrusion equipment based on the process performance, structural characteristics, and the reasonable matching of various equipment. Different performance and structural characteristics dictate the different uses of extruders. When choosing extrusion equipment, it is essential to consider the reasonable configuration and balance among the main equipment to maximize the equipment's capabilities and achieve higher production efficiency. Generally, downtime due to the primary equipment's capability lagging behind is not allowed.
(4) The degree of mechanization and automation of the extrusion equipment must be considered. To improve production efficiency, reduce labor intensity, lower consumption, decrease costs, and enhance the quality of extruded products, the demands for the mechanization and automation of extrusion equipment are increasingly high. Therefore, whenever conditions allow, it is advisable to adopt advanced technological equipment when selecting extrusion equipment. Selection should be based on verified advanced technologies and reliability through investigation and production practice, ensuring that conditions in the enterprise allow for implementation, and cannot be adopted blindly. Moreover, the chosen extrusion equipment should also allow for future development; neglecting this could lead to obsolescence and passivity, especially in the case of introduced extrusion equipment.
(5) It is essential to consider the economic effectiveness of the extrusion equipment in the selection process:
1) When standard extrusion equipment and commonly used extrusion equipment are available, it is advisable to choose standard and common equipment whenever possible. Particularly, when introducing extrusion equipment, consideration should be given to the localization of spare parts, which benefits the enhancement of economic efficiency, usability, and reduction of installation time.
2) In the absence of reference standards and commonly used equipment, factors such as ease of manufacturing and low cost should be considered to propose reasonable technical parameters for the extrusion equipment based on process requirements.
3) Consider the construction design conditions of the factory and the existing conditions of water, electricity, wind, and gas, as well as the average temperature and humidity conditions of the factory buildings in winter and summer, to propose reasonable design requirements for the extrusion equipment.
When selecting an extrusion machine based on the principles for choosing extruders, it is essential to consider both the selection and design of the hydraulic system and the control method. If the working time of the extruder accounts for 70% to 80% or more of the entire extrusion cycle, and the extrusion speed does not vary much, using high-pressure pumps for direct drive is more economical. For fast extrusion speeds, short time usage, and large extruders or units, using water pump accumulators for drive is more economical. Many modern advanced extrusion machines use hydraulic systems with high-pressure oil pumps for direct drive, eliminating the need for a pump station system and reducing investment costs. The control system of the extruder uses programmable logic control (PLC) systems to achieve program control. In addition to using PLC systems, modern extruders also incorporate monitoring of extrusion data, fault diagnosis, eccentric monitoring of extruded products, data production control, and report printing. The reliability and ease of maintenance of the control system are high, and it easily adapts to future functional expansions with flexibility.
An important aspect to consider when selecting an extruder is the auxiliary system of the extruder, which together with the extruder constitutes a complete production means. During the operation of the extruder, approximately 30% to 70% of the work time is consumed on auxiliary operations. This is often due to the imperfect structure of the auxiliary machines, which can affect the production efficiency of the extruder and the quality of the extruded products, while also increasing the labor intensity of the operators. Therefore, carefully considering the selection and design of auxiliary devices is crucial for improving the quality of extruded products and enhancing the automation level of the production line. The auxiliary devices of the extruder mainly include the feeding mechanism of the heating furnace and the sealing device of the furnace door; the feeding device of the extruder; the mold base device (for changing molds); the separation mechanism for the extruded gasket and excess material and copper skin; devices for cleaning, repairing, cooling, and lubricating the extruder molds; and the discharging mechanism of the extruder.
