PA66 fiber melt spinning temperature control forming device

Abstract

The application discloses a PA66 fiber melt spinning temperature control forming device, one side of a melt spinning device is provided with a spinning box, the top of the spinning box is horizontally provided with a circular spinning plate; the upper part of the inside of the wind box is provided with a cooling cavity; the side of the cooling cavity close to the hollow part of the wind box is embedded with a first air blowing plate, the outer side of the first air blowing plate is circularly and uniformly provided with a plurality of first air blowing holes; the outer side of the cooling cavity is provided with a driving assembly; the lower part of the first air blowing plate is provided with a hole air volume adjusting assembly; the upper part of the first air blowing plate is provided with a no-air-zone fine adjustment assembly. While adopting the ring air blowing cooling mode, the application can adapt to spinning melts with different viscosities, different spinning speeds and different thicknesses, can adjust the aperture of the air blowing plate in a targeted manner, does not need to stop and replace parts with corresponding sizes, does not need to change the total air volume, prevents regional temperature difference, and ensures that the PA66 melt spinning has the best quality.

Description

Technical Field

[0001] This invention relates to the field of fiber spinning melt molding equipment technology, and in particular to a PA66 fiber melt spinning temperature control molding device. Background Technology

[0002] Melt spinning of PA66 fibers is a core process that uses polyhexamethylene adipamide (PAD) chips as raw material. Through drying, melting, extrusion, cooling, drawing, and winding, the polymer melt is directly produced into continuous filaments. PA66 has a melting point of approximately 262–263℃ and can stably melt into a fluid at 280–300℃. The dried chips are melted and pressurized using a screw extruder, then precisely delivered to the spinneret via a metering pump, and extruded through micropores to form a melt stream. This stream rapidly solidifies in a cooling airflow, and then is drawn to highly orient the molecular chains, ultimately yielding high-strength, high-modulus PA66 fibers. The regular molecular chains of PA66 allow for rapid crystallization and high orientation during stretching, which is why it can be made into high-strength, high-elasticity fibers. However, this also requires rapid cooling of the melt after extrusion from the spinneret to fix its orientation structure and prevent excessively rapid crystallization that could lead to fiber brittleness or adhesion. Traditional cooling methods for PA66 melt use annular airflow cooling. Air is blown radially from all sides towards the filament bundle, ensuring consistent wind speed and temperature for each filament. The symmetrical air pressure at the perimeter allows the filaments to fall stably in the center with minimal sliver drift or wobbling. The airflow directly adheres to the filament bundle, resulting in high heat exchange efficiency and rapid solidification of the melt stream. However, this annular airflow cooling method has the following problems: the orifice diameter on the blowing plate in traditional annular airflow devices is fixed and cannot be adjusted; the airflow from each orifice is constant, making it impossible to adapt to different spinning speeds. At higher spinning speeds, a larger airflow is needed to provide a stronger cooling effect, while at lower spinning speeds, a smaller airflow is needed to provide a gentler cooling effect. However, traditional ring blower devices require replacing the blower plate with the corresponding aperture when switching spinning speeds, which requires shutting down and disassembling the entire device, which is time-consuming, labor-intensive, and inefficient. If the blower plate is not replaced directly, when the spinning speed is increased, the total airflow needs to be increased to compensate for the insufficient airflow. Increased air pressure will cause the spun yarn to vibrate and may easily cause regional temperature differences, affecting the quality of cooling and forming, and increasing the energy consumption cost of the equipment. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a PA66 fiber melt spinning temperature control molding device. This invention can adapt to spinning melts of different viscosities, spinning speeds and thicknesses, and can adjust the aperture of the blower plate accordingly. It does not require stopping the machine to replace parts of the corresponding size, nor does it require changing the total air intake, thus preventing regional temperature differences and ensuring the best quality PA66 melt spinning.

[0004] This invention is achieved through the following technical solution: This invention discloses a PA66 fiber melt spinning temperature control molding device, including a horizontally arranged melt spinning equipment. A spinneret box is provided on one side of the melt spinning equipment, with its upper and lower ends connected. A circular spinneret plate is horizontally arranged on the top of the spinneret box, and the top of the spinneret plate is connected to the discharge end of the metering pump of the melt spinning equipment. An annular air blowing device is provided inside the spinneret box. The annular air blowing device includes an annularly arranged air box connected to the spinneret plate at its upper part, with its upper and lower ends connected and the spinneret plate located in a circular hollow area inside the air box. The upper part inside the air box is equipped with a... The lower part of the chamber is a completely separated cooling chamber; the side wall of the cooling chamber near the hollow part of the air box has an opening and is fitted with a first air blowing plate arranged in a ring. The outer side of the first air blowing plate is evenly distributed with several first air blowing holes in a circle; the outer side of the cooling chamber is provided with a driving component, which can generate cooling air and transmit it through several first air blowing holes to the PA66 melt extruded by the spinneret and cool it with airflow; the lower part of the first air blowing plate is provided with a hole airflow regulating component that can adjust the air outlet area of ​​each first air blowing hole; the upper part of the first air blowing plate is provided with a windless zone fine-tuning component that can fine-tune the windless zone coverage of the first air blowing plate.

[0005] Furthermore, the drive assembly includes air inlet channels symmetrically arranged on both sides of the air box. One end of the air inlet channel passes through the side of the air box and communicates with the interior of the cooling chamber. The other end of the air inlet channel passes through the spinneret box and is located outside the spinneret box. Each air inlet channel is equipped with a fan at the end outside the spinneret box that can deliver air into the cooling chamber. The fan is connected to an external controller, a wind speed control module, and a temperature control module.

[0006] Furthermore, a ring-shaped air blower is fitted on the outer side of the first air blower plate. The side of the air blower facing the first air blower plate is open and fully covers the first air blower plate. The outer side of the air blower plate is connected to the side ends of the two air inlet channels.

[0007] Furthermore, a filter screen is provided at the connection between the fan and the air inlet channel.

[0008] Furthermore, the airflow adjustment assembly includes first electric push rods symmetrically arranged at both ends of the lower part of the air box. The output ends of the two first electric push rods are arranged facing upwards and are slidably connected to the bottom of the cooling cavity. A second air blower is arranged in a ring on the outer side of the first air blower. The second air blower has the same length as the first air blower and the outer side of the first air blower is in contact with the inner side of the second air blower.

[0009] Furthermore, the second blower plate is uniformly provided with a plurality of second blower holes in a circular shape. The diameter of the first blower holes and the second blower holes are the same. The positions of the plurality of second blower holes and the plurality of first blower holes correspond one-to-one and form a through hole. The second blower plate is located inside the blower tube, and the two ends of the bottom of the second blower plate are respectively connected to the output ends of the two first electric push rods.

[0010] Furthermore, the windless zone fine-tuning component includes a ring-shaped shielding sleeve fitted on the upper outer side of the second blower plate. The inner side of the shielding sleeve is in contact with the outer side of the second blower plate, and the bottom of the shielding sleeve is located above the uppermost second blower hole on the second blower plate. Two second electric push rods are symmetrically arranged at both ends of the lower part of the air box. The output ends of the two second electric push rods are arranged facing upward and are slidably connected to the bottom of the cooling cavity. The output ends of the two second electric push rods are respectively connected to the two ends of the shielding sleeve.

[0011] Furthermore, one side of the spinneret box is open and rotatably connected to an inspection door that closes the opening.

[0012] The present invention has the following advantages: (1) In this invention, before cooling the melt, the diameter of several first air holes on the first air blowing plate is adjusted according to the current viscosity of the melt, the orifice diameter of the spinneret, and the spinning speed of the melt flowing downwards. The higher the spinning speed, the larger the orifice diameter; the lower the spinning speed, the smaller the orifice diameter. The height of the windless zone at the top of the first air blowing plate is finely adjusted by the windless zone fine-tuning component. The coarser the melt, the higher the height of the windless zone, and the faster the melt contacts the cooling air. The finer the melt, the lower the height of the windless zone. The slower the contact with the cooling air, the better the cooling air output and the height of the windless zone of the ring blowing device are perfectly matched with the melt of the current type. At this time, the melt is extruded through the spinneret by the metering pump of the melt spinning equipment. The melt is extruded through the micropores of the spinneret to form a melt stream. The control drive component works outside the melt stream to form a ring-shaped cooling air field. The stream solidifies rapidly in the cooling air field and is then stretched to make the molecular chains highly oriented, ultimately obtaining high-strength, high-modulus PA66 fiber. Attached Figure Description

[0013] Figure 1 This is a three-dimensional structural diagram of the present invention; Figure 2 This is a three-dimensional structural diagram of the spinneret box, spinneret plate, and ring blower in this invention; Figure 3 This is a partial structural diagram of the spinneret box, spinneret plate, and ring blower in this invention; Figure 4 This is a three-dimensional structural diagram of the ring blower and spinneret in this invention; Figure 5This is a side sectional view of the ring blower device in this invention; Figure 6 This is a partial side sectional view of the ring blower device in this invention; Figure 7 This is a partial top view of the ring blower device in this invention; Figure 8 This is a three-dimensional structural diagram of the orifice airflow regulating component and the no-wind zone fine-tuning component of the present invention; Figure 9 This is a schematic diagram of the unfolded structure of the first and second air-blowing plates in this invention; Figure 10 This is a three-dimensional structural diagram of the first and second air-blowing plates in the present invention when they are completely overlapped. Figure 11 This is a three-dimensional structural diagram of the first and second air-blowing plates in this invention when they are staggered. Figure 12 for Figure 11 Enlarged view of point A in the middle.

[0014] In the diagram: 1. Melt spinning equipment; 2. Spinneret box; 3. Spinneret plate; 4. Circular air blowing device; 41. Air box; 42. Cooling chamber; 43. First air blowing plate; 44. First air blowing hole; 45. Drive assembly; 451. Air inlet channel; 452. Fan; 453. Air blowing tube; 46. Orifice air volume adjustment assembly; 461. First electric push rod; 462. Second air blowing plate; 463. Second air blowing hole; 47. No-wind zone fine adjustment assembly; 471. Shielding sleeve; 472. Second electric push rod; 5. Inspection door. Detailed Implementation

[0015] The embodiments of the present invention are described in detail below. These embodiments are implemented based on the technical solution of the present invention, and provide detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. In the description of the present invention, words such as "front", "rear", "left", and "right" that indicate orientation or positional relationship are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0016] Example 1

[0017] Example 1 discloses a PA66 fiber melt spinning temperature control molding device, such as Figures 1-12As shown, the device includes a horizontally arranged melt spinning apparatus 1. A spinneret box 2 is located on one side of the melt spinning apparatus 1, with its upper and lower ends connected. A circular spinneret plate 3 is horizontally arranged on the top of the spinneret box 2, and the top of the spinneret plate 3 is connected to the discharge end of the metering pump of the melt spinning apparatus 1. An annular air blowing device 4 is located inside the spinneret box 2. The annular air blowing device 4 includes an annularly arranged air box 41 connected to the spinneret plate 3 at its upper part. The upper and lower ends of the air box 41 are connected, and the spinneret plate 3 is located in a circular hollow area inside the air box 41. A cooling chamber 42, completely separated from the lower part of the air box 41, is located in the upper part of the air box 41. The cooling chamber 42 is located near the air box. 41. One side wall of the hollow section is provided with an opening and a first air blowing plate 43 arranged in a ring is embedded therein. The outer side of the first air blowing plate 43 is provided with a number of first air blowing holes 44 evenly distributed in a circle. The outer side of the cooling chamber 42 is provided with a driving component 45, which can generate cooling air and transmit it through the number of first air blowing holes 44 to the PA66 melt extruded by the spinneret 3 and cool it with air force. The lower part of the first air blowing plate 43 is provided with a hole air volume adjustment component 46 that can adjust the air outlet area of ​​each first air blowing hole 44. The upper part of the first air blowing plate 43 is provided with a windless area fine adjustment component 47 that can fine adjust the windless area coverage of the first air blowing plate 43.

[0018] Furthermore, in this embodiment, the drive assembly 45 includes air inlet channels 451 symmetrically arranged on both sides of the air box 41. One end of the air inlet channel 451 passes through the side end of the air box 41 and communicates with the interior of the cooling chamber 42. The other end of the air inlet channel 451 passes through the spinneret box 2 and is located outside the spinneret box 2. Each air inlet channel 451 is provided with a fan 452 at the end outside the spinneret box 2, which can deliver air into the cooling chamber 42. The fan 452 is externally connected to a controller, a wind speed control module, and a temperature control module. Furthermore, a ring-shaped air blower 453 is sleeved on the outer side of the first air blower plate 43. The side of the air blower 453 facing the first air blower plate 43 is open and fully covers the first air blower plate 43. The outer side of the air blower 453 is connected to the side ends of the two air inlet channels 451. Furthermore, a filter screen is provided at the connection between the fan 452 and the air inlet channel 451; like Figures 3 to 7As shown, in this embodiment, the fan 452 is controlled by the controller to deliver cooling air into the cooling chamber 42 for cooling the melt. Through the air inlet channel 451 and the annular blower 453, the cooling air can be evenly delivered to several first blower holes 44 on the first blower plate 43, so that the air volume of each first blower hole 44 is uniform, thereby improving the quality of the melt stream cooling and forming. The wind speed control module and temperature control module can adjust the wind speed and temperature of the cooling air to adapt to different progresses of melt cooling and forming. While filtering the cold air through the set filter screen, the wind speed can be homogenized to ensure that the cold air enters the cooling chamber 42 at a uniform flow rate, avoiding the problem of uneven wind force from the source.

[0019] Furthermore, the airflow adjustment assembly 46 includes first electric push rods 461 symmetrically arranged at both ends of the lower part of the air box 41. The output ends of the two first electric push rods 461 are arranged facing upwards and are slidably connected to the bottom of the cooling cavity 42. A second air blower 462 is arranged in a ring on the outer side of the first air blower 43. The second air blower 462 has the same length as the first air blower 43 and the outer side of the first air blower 43 is in contact with the inner side of the second air blower 462. Furthermore, the second blower plate 462 is provided with a plurality of second blower holes 463 in a circular and uniform manner. The diameter of the first blower hole 44 and the second blower hole 463 is the same. The positions of the plurality of second blower holes 463 and the plurality of first blower holes 44 correspond one-to-one and form a through hole. The second blower plate 462 is located inside the blower tube 453. The two ends of the bottom of the second blower plate 462 are respectively connected to the output ends of the two first electric push rods 461. like Figures 8 to 12As shown in this embodiment, the aperture of the first air hole 44 on the first air blowing plate 43 needs to be adjusted for different spinning speeds and melt types. Initially, the first air hole 44 and the second air hole 463 on the first air blowing plate 43 and the second air blowing plate 462 are in a corresponding state, and the aperture of the through hole formed by the two is the same as the aperture of the first air hole 44, which is also the maximum air output aperture, to cope with the highest spinning speed. When the spinning speed decreases, the aperture of the through hole formed by the first air hole 44 and the second air hole 463 needs to be reduced. At this time, the two first electric push rods 461 are controlled by the external controller to drive the second air blowing plate 462 to rise along the outside of the first air blowing plate 43, so that the first air hole 44 at each position is adjusted. The second blower plate 462 is offset from the first blower hole 44, and the overlapping through-hole portion between them is reduced, thereby reducing the space through which the cooling air can pass and thus reducing the air volume. This makes the cooling air effect gradually gentler. The higher the stroke of the second blower plate 462, the smaller the overlapping through-hole between the first blower hole 44 and the second blower hole 463, and the smaller the air volume. Conversely, the air volume can be increased by driving the second blower plate 462 down. The specific adjustment can be made according to the current spinning speed. Through the above operations, it is possible to adapt to spinning melts with different viscosities and spinning speeds, and to adjust the hole diameter of the blower plate accordingly. There is no need to stop the machine to replace the corresponding size parts or increase the air pressure, so as to ensure the best quality PA66 melt spinning effect.

[0020] Furthermore, the windless zone fine-tuning component 47 includes a ring-shaped shielding sleeve 471 sleeved on the upper outer side of the second blower plate 462. The inner side of the shielding sleeve 471 is in contact with the outer side of the second blower plate 462. The bottom of the shielding sleeve 471 is located above the uppermost second blower hole 463 on the second blower plate 462. Two second electric push rods 472 are symmetrically arranged at both ends of the lower part of the air box 41. The output ends of the two second electric push rods 472 are arranged upward and slide vertically through the bottom of the cooling cavity 42. The output ends of the two second electric push rods 472 are respectively connected to the two ends of the shielding sleeve 471. like Figure 6 and Figure 8As shown, in this embodiment, the shielding sleeve 471 is positioned at the top of the second blowing plate 462 in the initial state and does not block the uppermost second blowing hole 463. At this time, the windless zone is at its highest level to accommodate the thickest melt stream. When cooling melt streams of different diameters is required, the height of the windless zone needs to be adjusted accordingly. The two second electric push rods 472 are controlled by an external controller to drive the shielding sleeve 471 to descend, cooling the uppermost rows of second blowing holes 463 from top to bottom. By blocking the airflow, the second air-blowing hole 463 is blocked, and the through hole formed by the first air-blowing hole 44 and the second air-blowing hole 463 is also blocked. Cooling air cannot pass through the through hole, thus forming a windless zone. The finer the diameter of the melt stream, the more rows of the second air-blowing hole 463 need to be blocked. The specific descent height is determined according to the diameter of the melt stream of the current product. This allows for the adaptation to spinning melts of different thicknesses, and targeted fine-tuning of the height of the windless zone without stopping the machine to replace parts of the corresponding size, thus ensuring the best quality PA66 melt spinning effect.

[0021] Furthermore, one side of the spinneret 2 is open and rotatably connected to an inspection door 5 for closing the open area; like Figure 1 and Figure 2 As shown, in this embodiment, by providing a flip-open inspection door 5 on one side of the spinneret box 2, simply flipping the inspection door 5 will open one side of the spinneret box 2, making it convenient to inspect or replace the various components inside the spinneret box 2, thus improving the maintainability and convenience of the device.

[0022] In this embodiment, during operation: before cooling the melt, based on the current melt viscosity, the orifice diameter of the spinneret 3, and the spinning speed of the melt flowing downwards, the orifice airflow adjustment component 46 adjusts the orifice diameter of several first blowing holes 44 on the first blowing plate 43. The higher the spinning speed, the larger the orifice diameter; the lower the spinning speed, the smaller the orifice diameter. The no-wind zone height on the upper part of the first blowing plate 43 is finely adjusted by the no-wind zone fine-tuning component 47. The coarser the melt, the higher the no-wind zone height, and the faster the melt contacts the cooling air; the finer the melt, the lower the no-wind zone height, and the slower the melt contacts the cooling air. This ensures that the cooling air output volume and no-wind zone height of the annular blowing device 4 are perfectly matched to the current type of melt. At this time, through melting... The metering pump of the spinning equipment 1 extrudes the melt through the spinneret 3, forming a fine melt stream through the micropores on the spinneret 3. The control drive component 45 operates outside the fine melt stream to form an annular cooling air field. The fine stream solidifies rapidly in the cooling air field, and then is stretched to make the molecular chains highly oriented, ultimately obtaining high-strength, high-modulus PA66 fibers. This device can adapt to spinning melts of different viscosities, spinning speeds, and thicknesses, and can specifically adjust the aperture of the blower plate and finely adjust the height of the windless zone. It does not require stopping the machine to replace parts of the corresponding size, nor does it require increasing the air pressure, thus preventing regional temperature differences and ensuring the best quality PA66 melt spinning effect.

[0023] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A PA66 fiber melt spinning temperature control forming device, characterized in that, The device includes a horizontally arranged melt spinning equipment (1), a spinneret box (2) is provided on one side of the melt spinning equipment (1), the upper and lower ends of the spinneret box (2) are connected, and a circular spinneret plate (3) is horizontally arranged on the top of the spinneret box (2), and the top of the spinneret plate (3) is connected to the metering pump outlet end of the melt spinning equipment (1). The spinneret box (2) is equipped with an annular air blowing device (4). The annular air blowing device (4) includes an air box (41) connected to the upper part of the spinneret plate (3) in a circular arrangement. The upper and lower ends of the air box (41) are connected through each other, and the spinneret plate (3) is located in the circular hollow part inside the air box (41). The upper part of the air box (41) is provided with a cooling chamber (42) that is completely separated from the lower part of the air box (41). The cooling chamber (42) has an opening on one side wall near the hollow part of the air box (41) and is fitted with a first air blowing plate (43) arranged in a circular shape. The outer side of the first air blowing plate (43) is evenly provided with several first air blowing holes (44). A drive assembly (45) is provided on the outside of the cooling chamber (42). The drive assembly (45) can generate cooling air and transmit it through several first air holes (44) to the PA66 melt extruded by the spinneret (3) and cool it with air force. The lower part of the first air blowing plate (43) is provided with an air volume regulating component (46) that can adjust the air outlet area of ​​each first air blowing hole (44). The upper part of the first air blowing plate (43) is provided with a windless area fine-tuning component (47) that can fine-tune the windless area coverage of the first air blowing plate (43).

2. The PA66 fiber melt spinning temperature control forming device as described in claim 1, characterized in that, The drive assembly (45) includes air inlet channels (451) symmetrically arranged on both sides of the air box (41). One end of the air inlet channel (451) passes through the side of the air box (41) and communicates with the interior of the cooling chamber (42). The other end of the air inlet channel (451) passes through the spinneret box (2) and is located outside the spinneret box (2). Each air inlet channel (451) is provided with a fan (452) at the end outside the spinneret box (2) that can deliver air into the cooling chamber (42). The fan (452) is connected to an external controller, a wind speed control module and a temperature control module.

3. The PA66 fiber melt spinning temperature control forming device as described in claim 2, characterized in that, The outer side of the first blower plate (43) is fitted with a ring-shaped blower tube (453). The blower tube (453) is open on the side facing the first blower plate (43) and fully covers the first blower plate (43). The outer side of the blower tube (453) is connected to the side ends of the two air inlet channels (451).

4. The PA66 fiber melt spinning temperature control forming device as described in claim 3, characterized in that, A filter screen is provided at the connection between the fan (452) and the air inlet channel (451).

5. The PA66 fiber melt spinning temperature control forming device as described in claim 4, characterized in that, The airflow regulating component (46) includes first electric push rods (461) symmetrically arranged at both ends of the lower part of the air box (41). The output ends of the two first electric push rods (461) are arranged facing upwards and the output ends pass through the bottom of the cooling cavity (42) and slide up and down with it. A second air blower (462) is arranged in a ring on the outer side of the first air blower (43). The second air blower (462) has the same length as the first air blower (43) and the outer side of the first air blower (43) is in contact with the inner side of the second air blower (462).

6. The PA66 fiber melt spinning temperature control forming device as described in claim 5, characterized in that, The second blower plate (462) is provided with a plurality of second blower holes (463) in a circular shape. The diameter of the first blower hole (44) and the second blower hole (463) are the same. The positions of the plurality of second blower holes (463) and the plurality of first blower holes (44) correspond one-to-one and form a through hole. The second blower plate (462) is located inside the blower tube (453). The two ends of the bottom of the second blower plate (462) are respectively connected to the output ends of the two first electric push rods (461).

7. The PA66 fiber melt spinning temperature control forming device as described in claim 6, characterized in that, The windless zone fine-tuning component (47) includes a ring-shaped shielding sleeve (471) fitted on the upper outer side of the second blower plate (462). The inner side of the shielding sleeve (471) is in contact with the outer side of the second blower plate (462). The bottom of the shielding sleeve (471) is located above the uppermost second blower hole (463) on the second blower plate (462). Two second electric push rods (472) are symmetrically arranged at both ends of the lower part of the air box (41). The output ends of the two second electric push rods (472) are arranged facing upward and slide through the bottom of the cooling cavity (42) and are connected to it vertically. The output ends of the two second electric push rods (472) are respectively connected to the two ends of the shielding sleeve (471).

8. The PA66 fiber melt spinning temperature control forming device as described in claim 7, characterized in that, The spinneret (2) is open on one side and is rotatably connected to an inspection door (5) to close the open area.

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