Integrated processing technology of medium-high strength aluminum alloy 3C back cover product

Abstract

The invention relates to the technical field of aluminum alloy preparation, and discloses an integrated machining process of a medium-high-strength aluminum alloy 3C back cover product. All procedures of semi-finished products before extrusion-CNC machining are integrated and unified, and as integrated production, intermediate extra transportation actions are completely removed. According to the integrated production mode, the production efficiency is improved, the production cost is reduced, the material loss is reduced, and the resource utilization rate is improved. Meanwhile, as forging and pressing are conducted immediately after extrusion, strength improvement caused by natural aging can be avoided, the forging and pressing effect is improved, CNC machining can be replaced with forging and pressing, and the production efficiency is further improved. And secondly, according to the technical scheme, through alloy component optimization, the strength improvement speed of subsequent artificial aging of the material is greatly increased, so that a continuous aging furnace can be integrated on a production line, and it is guaranteed that the material is subjected to rapid aging to meet the strength requirement. The rapid aging mode not only improves the production efficiency, but also ensures the quality and performance of the product.

Description

Technical Field

[0001] The present invention relates to the technical field of preparation of aluminum alloy products, and in particular to an integrated processing technology for medium- and high-strength aluminum alloy 3C back cover products. Background Art

[0002] Aluminum alloy is widely used in precision machinery manufacturing and electronic equipment manufacturing due to its advantages of light weight, high strength and easy processing, such as the manufacture of tablet computers and laptops. The aluminum alloy shell of computer products is a key component, and its processing accuracy and strength directly affect the overall performance and service life of the computer.

[0003] In the prior art, the processing of aluminum alloy profile products for computers usually requires multiple processes such as extrusion, aging, sawing, surface grinding, CNC, etc. CNC processing is usually carried out using a whole piece of aluminum plate, and the middle needs to be hollowed out, which can realize the processing of complex shapes, but the processing efficiency is low, which will cause a lot of loss and scrap, and the processing cost is high. Secondly, if the forging forming method is used, because the material strength is high after natural aging, it cannot be forged or the forging effect is poor. Thirdly, in the current process, the aging time is long, and multiple processes are connected, such as extrusion, aging, sawing, double-sided grinding, etc. The material flow will cause a lot of handling and labor cost waste. Finally, the existing process cannot realize the integration and unification of all processes of semi-finished products before extrusion-CNC processing, and requires additional transportation actions in the middle, resulting in low production efficiency and high production costs. Summary of the invention

[0004] The purpose of the present invention is to provide an integrated processing technology for medium- and high-strength aluminum alloy 3C back cover products that integrates all processes from extrusion to semi-finished products before CNC processing, thereby improving production efficiency, reducing production costs, and thereby providing at least a beneficial choice or creating conditions for solving one or more technical problems existing in the prior art.

[0005] To achieve the above objectives, the present invention adopts the following technical solutions.

[0006] An integrated processing technology for medium- and high-strength aluminum alloy 3C back cover products is achieved by using an extruder and quenching equipment, a straightening machine, a material storage cooling bed, a punching / sawing equipment, a preheating equipment, a forging equipment and a continuous aging equipment that are sequentially connected to form a continuous production line.

[0007] The specific steps are as follows: Step 1: configure the aluminum alloy material composition, calculated by weight percentage, the Mg element content is 0.5%-0.7%, the Si element content is 0.5%-0.7%, wherein Mg / Si is in the range of 1.0-1.15, the Cu element content is 0.3%-0.5%, the total content of Mg+Si+Cu elements is in the range of 1.4%-1.8%, the Fe element content is less than 0.15%, the Mn element content is 0.05%-0.15%, Fe / Mn is in the range of 0.8-1.2, the Zn element content is 0.1%-0.2%, the La element content is 0.05%-0.15%, and the balance is Al.

[0008] Step 2: Extrusion molding, melting the aluminum alloy material components prepared in step 1, casting them into aluminum rods, and then extruding them to obtain aluminum alloy profiles.

[0009] Step 3: Online cooling and quenching: the extruded aluminum alloy profile is subjected to online cooling and quenching.

[0010] Step 4: Straighten and stretch, the straightening and stretching amount is 2.0-5.0%.

[0011] Step 5: Sawing / punching. First, cut off the head and tail waste by sawing / punching, and then punch or saw to obtain the single piece required for forging.

[0012] Step 6: Preheating: send the cut single pieces into the preheating equipment and heat them to 160-180℃.

[0013] Step 7: Forging. The preheated single piece is sent into the forging equipment for forging. The profile is turned up on the four sides by forging to form a disc shape.

[0014] Step 8: Continuous aging: the forged product is sent into a continuous aging furnace for aging. The aging time is 1-3 hours and the aging insulation temperature is 170-190°C.

[0015] More preferably, the extruder and quenching equipment and the straightening machine, as well as the straightening machine and the material storage cooling bed are all transmitted through a cooling bed belt.

[0016] More preferably, the material storage cooling bed and the punching / sawing equipment are transported via rollers.

[0017] More preferably, the punching / sawing equipment and the preheating equipment, the preheating equipment and the forging equipment, and the forging equipment and the continuous aging equipment are all transported by a robot or a conveyor belt.

[0018] More preferably, the continuous production line further comprises an automatic packaging device, and the automatic packaging device is connected to the discharge end of the continuous aging device via a robot or a conveyor belt.

[0019] More preferably, the continuous equipment is a crawler-type multi-layer continuous aging furnace with a furnace length of 10-20 m and a crawler moving speed of 0.1-0.3 m / min in the furnace.

[0020] More preferably, in the second extrusion molding step, the extrusion temperature is 510-540° C. and the extrusion main cylinder speed is 2-10 mm / s.

[0021] More preferably, in the online cooling and quenching step of step three, the cooling rate is greater than 300°C / min.

[0022] More preferably, in step five, punching or sawing, 2-10 pieces are punched or sawed at the same time as a batch to obtain a single piece.

[0023] More preferably, in step seven, the forging step, the forging die and the fixture are both maintained at 150-180°C.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects.

[0025] 1. Improve production efficiency: The present invention integrates all the processes of extrusion-CNC processing of semi-finished products as an integrated production, completely eliminating the additional transportation actions in the middle, greatly improving production efficiency, reducing labor costs and material flow time, and improving the efficiency of the entire production line.

[0026] 2. Reduce production costs: Due to the process optimization of the present invention, the loss and scrap of CNC processing are reduced. At the same time, due to the integration of all processes, the intermediate transportation and labor costs are reduced, so the overall production cost is significantly reduced.

[0027] 3. Improve processing quality: Since the present invention performs forging processing immediately after extrusion, it avoids the improvement of strength due to natural aging, improves the forging effect, and significantly improves the processing quality. At the same time, by optimizing the alloy composition, the strength improvement speed of the material after subsequent artificial aging is greatly improved, thereby ensuring that the material is quickly aged to meet the strength requirements.

[0028] 4. Improve material utilization: Traditional aluminum alloy computer back cover profiles use a whole piece of aluminum plate for deep processing, which has a high material loss rate. The process flow of the present invention is optimized, which reduces material loss and improves material utilization.

[0029] 5. Easy to realize the processing of complex shapes: Although forging processing requires the material to have higher plasticity and lower strength, due to the optimization of the process flow of the present invention, the strength of the material after natural aging is controlled, so that complex shapes can be processed, improving the accuracy and performance of the product.

[0030] Some other beneficial effects of the present invention will become more obvious from the following description or be understood in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Shown is a schematic structural diagram of an integrated processing device for medium- and high-strength aluminum alloy 3C back cover products in the present invention.

[0032] Description of Figure Numbers.

[0033] 1: Extrusion machine and quenching equipment, 2: Straightening machine, 3: Storage cooling bed, 4: Punching / sawing equipment, 5: Preheating equipment, 6: Forging equipment, 7: Continuous aging equipment, 8: Automatic packaging equipment. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0035] Reference Figure 1 As shown, an integrated processing device for medium- and high-strength aluminum alloy 3C back cover products includes an extruder and quenching equipment 1, a straightening machine 2, a material storage cooling bed 3, a punching / sawing equipment 4, a preheating equipment 5, a forging equipment 6, a continuous aging equipment 7 and an automatic packaging equipment 8 which are sequentially connected to form a continuous production line. The extruder and quenching equipment 1 and the straightening machine 2 are conveyed by a cooling bed belt, the straightening machine 2 and the material storage cooling bed 3 are conveyed by a cooling bed belt, the material storage cooling bed 3 and the punching / sawing equipment 4 are conveyed by a roller, and the punching / sawing equipment 4 and the preheating equipment 5 are conveyed by a manipulator or a special conveyor belt; the preheating equipment 5 and the forging equipment 6 are conveyed by a manipulator or a special conveyor belt, the forging equipment 6 and the continuous aging equipment 7 are conveyed by a manipulator or a special conveyor belt, and the continuous aging equipment 7 and the automatic packaging equipment 8 are conveyed by a manipulator or a special conveyor belt.

[0036] It should be noted that the various devices constituting the above-mentioned continuous production line are conventional devices known to those skilled in the art. In addition to the connection methods exemplified above, the transition connection methods between adjacent devices may also adopt other transition connection methods that are currently known or may be realized in the future.

[0037] The following introduces an integrated processing technology for medium- and high-strength aluminum alloy 3C back cover products using the above-mentioned integrated processing device, and the specific steps are as follows.

[0038] Step 1: configure the composition of aluminum alloy materials. By weight percentage, the Mg element content is 0.5%-0.7%, the Si element content is 0.5%-0.7%, wherein Mg / Si is in the range of 1.0-1.15, the Cu element content is 0.3%-0.5%, the total content of Mg+Si+Cu elements is in the range of 1.4%-1.8%, the Fe element content is less than 0.15%, the Mn element content is 0.05%-0.15%, Fe / Mn is in the range of 0.8-1.2, the Zn element content is 0.1%-0.2%, the La element content is 0.05%-0.15%, and the balance is Al.

[0039] In this step, by controlling the elements of Mg, Si, Cu, and Fe, adding elements such as Mn, Zn, and La, optimizing the Fe phase structure, avoiding the appearance of needle-like phases, and increasing the strength increase rate of the material during artificial aging, the continuous aging furnace can also be integrated into the production line to ensure that the material is quickly aged to meet the strength requirements. This rapid aging method not only improves production efficiency, but also ensures product quality and performance.

[0040] Step 2: Extrusion molding. The aluminum alloy material components prepared in step 1 are melted and cast into aluminum rods, and then extruded to obtain aluminum alloy profiles; the extrusion temperature is 510-540℃, and the extrusion main cylinder speed is 2-10mm / s to ensure the quality and precision of the profiles.

[0041] Step 3: Online cooling and quenching. The extruded aluminum alloy profiles are subjected to online cooling and quenching, with a cooling rate greater than 300°C / min, to ensure the stability of the internal microstructure of the material and improve the strength and hardness of the material.

[0042] Step 4: Straightening and stretching. Through straightening and stretching, ensure that the material straightness meets the requirements, avoid affecting the forging process due to material bending, and at the same time increase the internal dislocation density of the material through a large stretching amount, and promote the rapid improvement of the strength of the material during subsequent aging. The specific stretching amount is 2.0-5.0%.

[0043] Step 5: Sawing / punching. Cut off the head and tail waste by sawing / punching, and punch or saw in batches of 2-10 pieces. The cutting length is the single piece length required for forging, which improves production efficiency and material utilization.

[0044] Step 6: Preheating: Send the cut profiles into the industrial frequency preheating equipment and quickly heat them to 160-180℃.

[0045] Step 7: Forging. The preheated profile is automatically sent to the forging equipment for forging. During the forging process, the forging die and fixture are kept at 150-180℃. The profile is turned up on the four sides through forging to form a disc shape.

[0046] Step 8: Continuous aging. The ground products are sent to the crawler-type multi-layer continuous aging furnace for aging through the conveyor track or manipulator. The furnace is 10-20m long, the material crawler moving speed in the furnace is 0.1-0.3m / min, the material heating + insulation time in the furnace is a total of 1-3h, and the insulation temperature is set to 170-190℃.

[0047] Step 9: Packaging. The profiles after continuous aging are first cooled by a fan, and then packaged and loaded by an automatic robot.

[0048] Through these steps, the present invention can realize the integrated processing of high-strength aluminum alloy computer back cover products, effectively solving the problems of high material loss rate, low processing efficiency, poor forging effect, etc. in traditional processes.

[0049] In the present invention, since all the processes of the semi-finished product before extrusion-CNC processing are integrated and unified as an integrated production, the extra transportation action in the middle is completely eliminated. At the same time, because the forging process is performed immediately after extrusion, the increase in strength due to natural aging can be avoided, and the forging effect can be improved. At the same time, the temperature of the forging process is specially designed, and the strength of the material during forging can be reduced as much as possible without affecting the subsequent aging performance improvement, which greatly improves the deformation effect of forging, and forging can be used instead of CNC processing.

[0050] In the present invention, by integrating the continuous aging furnace into the production line, the forged material is directly sent into the aging furnace for heat preservation, ensuring that the material is quickly aged to meet the strength requirements, avoiding the waste of transportation and labor costs caused by the connection of multiple processes, and improving production efficiency.

[0051] The present invention realizes efficient and low-cost processing of aluminum alloy computer back cover profiles by optimizing the processing technology. This efficient and low-cost processing method not only meets the market demand for high-performance and high-quality aluminum alloy computer back cover profiles, but also provides new ideas and methods for the development of the field of material processing technology. In general, the present invention has broad application prospects, large market demand, and good commercial value.

[0052] The technical advancement of the present invention is further illustrated by Examples 1-4 and Comparative Examples 1-10.

[0053] Table 1. Alloy composition ratios of Examples 1-4 and Comparative Examples 1-10.

[0054] Mg Si Mg / Si Cu Mg+Si+Cu Fe Mn Fe / Mn Zn La Example 1 0.54 0.53 1.02 0.45 1.52 0.08 0.09 0.89 0.15 0.07 Example 2 0.69 0.61 1.13 0.39 1.69 0.09 0.08 1.13 0.14 0.06 Example 3 0.52 0.52 1.00 0.47 1.51 0.09 0.10 0.90 0.14 0.09 Example 4 0.62 0.62 1.00 0.31 1.55 0.07 0.08 0.88 0.13 0.10 Comparative Example 1 0.43 0.41 1.05 0.46 1.3 0.08 0.07 1.14 0.17 0.10 Comparative Example 2 0.61 0.61 1.00 0.32 1.54 0.07 0.07 1.00 0.14 0.11 Comparative Example 3 0.61 0.61 1.00 0.32 1.54 0.07 0.07 1.00 0.14 0.11 Comparative Example 4 0.55 0.54 1.02 0.07 1.16 0.09 0.09 1.00 0.14 0.07 Comparative Example 5 0.64 0.57 1.12 0.44 1.65 0.07 0.07 1.00 0.15 0.00 Comparative Example 6 0.63 0.58 1.09 0.47 1.68 0.09 0.10 0.90 0.02 0.14 Comparative Example 7 0.59 0.54 1.09 0.38 1.51 0.08 0.08 1.00 0.02 0.00 Comparative Example 8 0.59 0.54 1.09 0.38 1.51 0.08 0.08 1.00 0.02 0.00 Comparative Example 9 0.59 0.54 1.09 0.38 1.51 0.08 0.08 1.00 0.02 0.00 Comparative Example 10 0.59 0.54 1.09 0.38 1.51 0.08 0.08 1.00 0.02 0.00

[0055] Table 2. Process parameters and product performance of Examples 1-4 and Comparative Examples 1-10.

[0056] Straightening amount% Aging temperature ℃ Aging time h Tensile strengthMpa Yield StrengthMpa Elongation% Example 1 4.7 175 2.5 321 297 11.5 Example 2 3.6 185 1.5 323 295 12.4 Example 3 4.4 180 2 326 301 12.2 Example 4 3.9 180 2 321 300 12.4 Comparative Example 1 4.1 180 2 313 287 13.9 Comparative Example 2 0.5 180 2 320 285 13.2 Comparative Example 3 4.8 160 3 314 265 14.5 Comparative Example 4 3.8 180 2 311 291 12.9 Comparative Example 5 4.5 180 2 325 264 9.5 Comparative Example 6 4.2 180 2 327 268 14.2 Comparative Example 7 3.8 180 2 323 273 13.3 Comparative Example 8 0.3 180 2 315 266 14.1 Comparative Example 9 0.5 180 5 320 295 12.2 Comparative Example 10 0.5 180 8 325 308 9.7

[0057] It should be noted that, except for the process parameters listed in Table 1 and Table 2, other process parameters are the same by default.

[0058] It can be seen from Table 1 and Table 2 that under the alloy formula and process conditions of the present invention, the product can take into account tensile strength, yield strength and elongation. When the content of Mg, Si, and Mg+Si+Cu is lower than the lower limit of the present invention, the tensile strength and yield strength of the product will be significantly reduced (Comparative Example 1); when the straightening amount is lower than the lower limit, the yield strength of the product will be significantly reduced (Comparative Example 2); when the aging temperature is lower than the lower limit, the tensile strength and yield strength of the product will be significantly reduced (Comparative Example 3); when the content of Cu, Mg+Si+Cu is lower than the lower limit of the present invention, the tensile strength and yield strength of the product will be significantly reduced (Comparative Example 4); when the La content is lower than the lower limit of the present invention, the yield strength and elongation of the product are significantly reduced (Comparative Example 5); when the Zn content or the content of Zn and La is lower than the lower limit of the present invention, the yield strength of the product is significantly reduced (Comparative Examples 6-8); when the content of Zn and La, and the straightening amount are lower than the lower limit of the present invention, even if the artificial aging time is extended, the technical effect of the present invention cannot be achieved (Comparative Example 9, Comparative Example 10).

[0059] In addition, under the premise that other processes are consistent with Example 1, as the preheating temperature decreases, the forging tearing ratio will increase sharply. The specific comparison results are shown in Table 3.

[0060] Table 3. Comparison of the influence of preheating temperature on forging effect.

[0061] Preheating temperature ℃ Forging flange height (mm) Forging tear ratio Example 1 170 9.5 0% Comparative Example 2-1 Room temperature 25 7.4 100% Comparative Example 2-2 80 8.5 90% Comparative Examples 2-3 100 8.8 80% Comparative Examples 2-4 120 9.1 60% Comparative Examples 2-5 140 9.3 30%

[0062] It should be noted that when comparing the effects of preheating temperature on forging effects, except for the preheating temperature, other parameters are the same by default.

[0063] It should also be noted that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0064] The above embodiments only express several implementation methods of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. The parts not described in the specific embodiments are all prior art or common knowledge.

[0065] It should be noted that, in the description of the present invention, the content of the present invention can be more easily understood by referring to the detailed description of the preferred implementation method of the present invention and the embodiments included. Unless otherwise specified, all technical and scientific terms used in the present invention have the same meanings as those of ordinary skill in the art to which the present invention belongs. When there is a conflict, the definitions in this specification shall prevail.

[0066] In the present invention, the term "prepared from..." is used synonymously with "comprising". The terms "comprising", "including", "having", "containing" or any other variation thereof, as used in the present invention, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus comprising the listed elements is not necessarily limited to only those elements, but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.

[0067] In the present invention, when an amount, concentration, or other value or parameter is expressed as a range, a preferred range, or a range limited by a series of upper preferred values ​​and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pairing of any range upper limit or preferred value with any range lower limit or preferred value, regardless of whether the range is disclosed separately. For example, when a range of "1 to 5" is disclosed, the described range should be interpreted as including a range of "1 to 4", "1 to 3", "1 to 2", "1 to 2 and 4 to 5", "1 to 3 and 5" etc. When a numerical range is described in the present invention, unless otherwise stated, the range is intended to include its end values ​​and all integers and fractions within the range.

[0068] In addition, the indefinite articles "a" and "an" before the elements or components of the present invention have no restrictions on the quantity requirements (i.e. the number of occurrences) of the elements or components. Therefore, "a" or "an" should be interpreted as including one or at least one, and the elements or components in the singular form also include the plural form, unless the number is obviously intended to be in the singular form.

Claims

1. An integrated processing technology for medium-high strength aluminum alloy 3C back cover products, characterized in that: This is achieved by using extruders and quenching equipment, straightening machines, material storage cooling beds, punching / sawing equipment, preheating equipment, forging equipment and continuous aging equipment that are connected in sequence to form a continuous production line. The specific steps are as follows: Step 1: configure the aluminum alloy material composition, by weight percentage, the Mg element content is 0.5%-0.7%, the Si element content is 0.5%-0.7%, wherein the Mg / Si is in the range of 1.0-1.15, the Cu element content is 0.3%-0.5%, the total content of Mg+Si+Cu elements is in the range of 1.4%-1.8%, the Fe element content is less than 0.15%, the Mn element content is 0.05%-0.15%, the Fe / Mn is in the range of 0.8-1.2, the Zn element content is 0.1%-0.2%, the La element content is 0.05%-0.15%, and the balance is Al; Step 2: extrusion molding, melting the aluminum alloy material components prepared in step 1, casting them into aluminum rods, and then extruding them to obtain aluminum alloy profiles; Step 3: Online cooling and quenching: the extruded aluminum alloy profile is subjected to online cooling and quenching; Step 4: Straightening and stretching, the straightening and stretching amount is 2.0-5.0%; Step 5: Sawing / punching, first cut off the head and tail waste by sawing / punching, and then punch or saw to obtain the single piece required for forging; Step 6: Preheating: send the cut single piece into the preheating equipment and heat it to 160-180℃; Step 7: Forging: The preheated single piece is sent into the forging equipment for forging. The profile is turned up on the four sides by forging to form a disc shape; Step 8: Continuous aging: the forged product is sent into a continuous aging furnace for aging. The aging time is 1-3 hours and the aging insulation temperature is 170-190°C.

2. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: The extruder and quenching equipment are connected to the straightening machine, and the straightening machine is connected to the material storage cooling bed through a cooling bed belt.

3. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: The material storage cooling bed and the punching / sawing equipment are transported via rollers.

4. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: The punching / sawing equipment and the preheating equipment, the preheating equipment and the forging equipment, and the forging equipment and the continuous aging equipment are all transported through a robot or a conveyor belt.

5. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: The continuous production line also includes automatic packaging equipment, which is connected to the discharge end of the continuous aging equipment through a robot or a conveyor belt.

6. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: The continuous equipment is a crawler-type multi-layer continuous aging furnace with a furnace length of 10-20m and a crawler moving speed of 0.1-0.3m / min in the furnace.

7. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: In the second extrusion molding step, the extrusion temperature is 510-540° C., and the extrusion main cylinder speed is 2-10 mm / s.

8. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1 is characterized in that: In step three, the online cooling and quenching step, the cooling rate is greater than 300°C / min.

9. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1, characterized in that: In step five, punching or sawing, 2 to 10 pieces are punched or sawed at the same time as a batch to obtain a single piece.

10. The integrated processing technology of a medium-high strength aluminum alloy 3C back cover product according to claim 1, characterized in that: In step seven, the forging step, the forging die and the fixture are maintained at 150-180°C.

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