A grinding disc convenient to disassemble and replace

Abstract

The utility model relates to a powder grinding and pulp grinding equipment technical field especially relates to a convenient to detach and replace's millstone, including grinding shell, the inside of grinding shell is provided with two groups of opposite setting driven shaft, two groups the driven shaft opposite one end shaft body all are equipped with the locking hole, two groups the driven shaft opposite one end shaft body periphery is equipped with the millstone that is mirror image each other, install the locking piece in the locking hole, the driven shaft is along its radial direction and is connected with a plurality of ring around driven shaft equidistance setting's quick -witted connection pin of sliding connection, the utility model discloses a quick -witted connection pin is arranged on the shaft body of driven shaft along the radial direction, and sets up with the locking piece of driven shaft detachable for limiting the radial displacement distance of quick -witted connection pin, realizes millstone and drive shaft between through quick -witted connection pin and carries out quick clamping or unlocking, has simplified the structural component needed to install millstone, not only has improved millstone installation and the convenience of dismounting, also reduced the operation difficulty of replacing millstone, saves time cost.

Description

Technical Field

[0001] This utility model relates to the technical field of grinding and pulping equipment, and in particular to a grinding disc that is easy to disassemble and replace. Background Technology

[0002] Grinding and pulping equipment is a processing device used to mechanically crush and grind solid particles or soaked particles of raw materials such as soybeans, peanuts, sesame seeds, and grains, after adding water, to form corresponding powders or slurries. It is widely used in the deep processing of food and agricultural by-products. Grinding and pulping equipment generally consists of a transmission mechanism, a grinding chamber, and grinding discs. The transmission mechanism provides rotational power, the grinding chamber contains the material and the grinding discs, and the grinding discs are the key grinding execution components. They usually consist of two grinding discs, one moving and one stationary, arranged opposite each other. The moving grinding disc is driven by the transmission mechanism and cooperates with the stationary grinding disc to form a high-pressure friction and shearing zone, which crushes, presses, and grinds the material entering it into powder or slurry mixture.

[0003] As a consumable component of grinding and pulping equipment, the grinding disc operates under high load and high friction conditions for extended periods, making it prone to wear, deformation, or blockage. Regular disassembly, cleaning, or replacement is necessary. Existing grinding disc structures often employ a keyway connection with the drive shaft, secured by bolts, nuts, pressure plates, or retaining rings. This type of connection requires specialized tools for fastening and disassembly, involving numerous steps and complex operations. When cleaning or replacing the grinding disc, multiple fasteners often need to be disassembled individually, resulting in significant time consumption. Repeated assembly and disassembly over a long period can also cause wear between components, leading to misalignment and affecting connection reliability. This can result in uneven grinding disc operation, inconsistent contact with other grinding discs, and ultimately, reduced grinding accuracy and efficiency. Utility Model Content

[0004] The purpose of this invention is to provide a grinding disc that is easy to disassemble and replace, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A grinding disc that is easy to disassemble and replace includes a grinding shell. Inside the grinding shell, there are two sets of driven shafts arranged opposite each other. Each set of driven shafts has a locking hole on one end of the shaft. The outer periphery of the two sets of driven shafts is provided with a grinding disc that is mirror image of each other. A locking element is installed in the locking hole. The driven shaft is slidably connected to a number of quick-connecting pins that are equidistantly arranged around the driven shaft. One end of the quick-connecting pin passes through the shaft body and engages with the grinding disc. The inner ring of the grinding disc is provided with a groove that corresponds to the quick-connecting pin. The other end of the quick-connecting pin abuts against the side wall of the locking element provided in the locking hole.

[0006] Preferably, the locking hole is a stepped hole, including a connecting hole and a limiting hole that are progressively deeper along the axis of the driven shaft, with the diameters of the limiting hole and the connecting hole increasing sequentially. The locking component includes a limiting shaft, which is disposed in the limiting hole and its outer circumference abuts against a quick-connect pin. The other end of the limiting shaft is integrally connected to a bolt, and the bolt is threadedly connected to the connecting hole.

[0007] Preferably, the limiting hole is provided with a plurality of radially penetrating guide grooves at equal intervals around its inner wall, and the plurality of quick-connecting pins are respectively slidably disposed in the plurality of guide grooves.

[0008] Preferably, the guide groove has a limiting groove at one end located radially outside the driven shaft, and the groove area of ​​the limiting groove is larger than the groove area of ​​the guide groove.

[0009] Preferably, the quick-connect pin is fixedly connected to a first limiting ring in the limiting groove, the shape of the first limiting ring corresponds to and matches the limiting groove, and one end of the quick-connect pin passes through the guide groove and is provided with a second limiting ring inside the limiting hole.

[0010] Preferably, a sealing ring is slidably connected to the outer periphery of the driven shaft, one end of the sealing ring is fixedly connected to the grinding disc via a flange, and a first sealing ring is provided between the sealing ring and the driven shaft, and a second sealing ring is provided on the connecting end face between the sealing ring and the grinding disc.

[0011] Preferably, the driven shaft is provided with a snap-fit ​​block on the end of the shaft away from the grinding disc, and the grinding shell includes a first cover and a second cover arranged opposite to each other. The first cover and the second cover are movably hinged together, and the two sets of driven shafts arranged opposite to each other are respectively arranged inside the first cover and the second cover.

[0012] Preferably, the driven shaft located at one end of the first cover passes through the first cover and is engaged with a drive shaft by a snap-fit ​​block, and the drive shaft is provided with a feeding paddle that extends spirally along its axial direction on its outer periphery.

[0013] Preferably, the driven shaft located at one end of the second cover is engaged with an adjusting shaft via a snap-fit ​​block, and the adjusting shaft has an external thread on its outer periphery and is threadedly connected to the second cover via the external thread.

[0014] Preferably, the end of the adjusting shaft away from the end connected to the corresponding driven shaft is provided with a drive handle, and the adjusting shaft is located on the shaft between the second cover and the drive handle and is connected to a backstop ring by an external thread.

[0015] Compared with the prior art, this utility model provides a grinding disc that is easy to disassemble and replace, and has the following beneficial effects: 1. This utility model achieves quick engagement or unlocking between the grinding disc and the drive shaft by setting a quick-connecting pin radially on the driven shaft and setting a locking component detachable from the driven shaft to limit the radial displacement distance of the quick-connecting pin. This simplifies the structural components required for installing the grinding disc, improves the convenience of installing and disassembling the grinding disc, reduces the difficulty of replacing the grinding disc, and saves time and costs.

[0016] 2. This utility model, by setting a supporting and cooperating structure between the locking component and the quick-connecting pin, enables the grinding disc to form a connection structure with balanced force and stable support after assembly. The locking component provides rigid restraint to the inner end of the quick-connecting pin in the assembled state, preventing it from loosening or shifting due to vibration, impact, or thermal expansion and contraction during the grinding process. This ensures that the grinding disc remains coaxial and stable at high speed, avoiding vibration and noise caused by loose connection. Furthermore, it keeps the grinding gap between the two grinding discs constant during a single grinding process, thus ensuring that the fineness of the material after grinding remains consistent. Attached Figure Description

[0017] Figure 1 This is a three-dimensional structural diagram of the present invention; Figure 2 This is a partial cross-sectional three-dimensional structural schematic diagram of the present invention; Figure 3 This is a three-dimensional structural diagram of the connection state between the grinding disc and the driven shaft of this utility model. Figure 4 This is a partial cross-sectional three-dimensional structural diagram of the connection state between the grinding disc and the driven shaft of this utility model. Figure 5 This is a three-dimensional structural diagram of the grinding disc of this utility model; Figure 6 This is a partial cross-sectional three-dimensional structural diagram of the driven shaft and quick-connect pin of this utility model in connection. Figure 7 This is a partial cross-sectional three-dimensional structural schematic diagram of the driven shaft of this utility model; Figure 8 This is a three-dimensional structural diagram of the locking component of this utility model; Figure 9 For the present utility model Figure 4 A magnified schematic diagram of the structure at point A in the middle.

[0018] In the diagram: 1. Grinding shell; 101. First cover; 102. Second cover; 2. Driven shaft; 201. Locking hole; 2011. Connecting hole; 2012. Limiting hole; 202. Guide groove; 2021. Limiting groove; 203. Snap-fit ​​block; 3. Grinding disc; 301. Snap-fit ​​groove; 4. Adjusting shaft; 401. Drive handle; 402. Anti-reverse ring; 5. Sealing ring sleeve; 501. First sealing ring; 502. Second sealing ring; 6. Drive shaft; 601. Feeding paddle; 7. Quick-connect pin; 701. First limiting ring; 702. Second limiting ring; 8. Locking element; 801. Bolt body; 802. Limiting shaft. Detailed Implementation

[0019] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present utility model. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments.

[0020] In the description of this utility model, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this utility model 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 this utility model.

[0021] Example, refer to Figure 1 - Figure 9A grinding disc that is easy to disassemble and replace includes a grinding shell 1. Inside the grinding shell 1 are two sets of oppositely arranged driven shafts 2. Each set of driven shafts 2 has a locking hole 201 on one end of its shaft. Mirror-shaped grinding discs 3 are arranged on the outer periphery of the opposite ends of the shafts. The two mirror-shaped grinding discs 3 cooperate to grind or slurry materials. A locking element 8 is installed in the locking hole 201. Several quick-connecting pins 7 are equidistantly arranged around the driven shaft 2 along its radial direction. One end of each quick-connecting pin 7 passes through the shaft and engages with the grinding disc 3. The inner ring of the grinding disc 3 has a groove 301 corresponding to the quick-connecting pin 7. The other end of each quick-connecting pin 7 abuts against the side wall of the locking element 8 in the locking hole 201. After the quick-connecting pin 7 engages with the grinding disc 3, the locking element 8 abuts against the non-engaged end of the quick-connecting pin 7, forming a support structure for the quick-connecting pin 7 and restricting its movement stroke, thereby maintaining the stability of the engagement structure between the quick-connecting pin 7 and the grinding disc 3. When it is necessary to disengage, the support structure between the locking element 8 and the quick-connecting pin 7 is removed, allowing the quick-connecting pin 7 to slide relative to the guide groove 202, thus releasing the engagement structure between the quick-connecting pin 7 and the grinding disc 3. This eliminates the need for complex tools and cumbersome steps in the disassembly and replacement of the grinding disc 3. Simply adjusting the connection state between the locking element 8 and the driven shaft 2 is sufficient to quickly complete the disassembly and installation of the grinding disc 3. This design offers high versatility and can be used to assemble grinding discs 3 of different specifications and models.

[0022] Furthermore, the locking hole 201 is a stepped hole, including a connecting hole 2011 and a limiting hole 2012 that are progressively deeper along the axis of the driven shaft 2. The diameters of the limiting hole 2012 and the connecting hole 2011 increase sequentially. The locking component 8 includes a limiting shaft 802, which is disposed in the limiting hole 2012 and abuts against the quick-connect pin 7 on its outer circumference. The other end of the limiting shaft 802 is integrally connected to a bolt 801, which is threadedly connected to the connecting hole 2011 to fix the locking component 8 to the locking hole 201, thereby ensuring that during assembly, the locking component 8 is securely connected to the locking hole 201. The limiting shaft 802 is held in the limiting hole 2012, so that the outer periphery of the limiting shaft 802 is in abutting state with the quick connecting pin 7, so that the other end of the quick connecting pin 7 can pass through the driven shaft 2 and engage with the corresponding slot 301 of the grinding disc 3, forming a stable connection structure. When replacing the grinding disc 3, by unscrewing the locking part 8, the end of the quick connecting pin 7 located inside the limiting hole 2012 loses support, so that the quick connecting pin 7 can slide freely along the guide groove 202 toward the end away from the slot 301, so that the engaging structure fails, and the grinding disc 3 can be disassembled for replacement or cleaning.

[0023] Furthermore, the limiting hole 2012 is provided with several guide grooves 202 that are radially penetrating the driven shaft 2 at equal intervals around its inner wall. Several quick-connecting pins 7 are respectively slidably disposed in several guide grooves 202 to constrain the movement path of the quick-connecting pins 7, thereby ensuring that the quick-connecting pins 7 are engaged with the grooves 301 of the inner ring of the grinding disc 3, thereby realizing quick assembly and connection. In use, the grinding disc 3 with different grinding groove depths can be replaced according to the particle size of the material to be processed or the fineness of grinding.

[0024] Furthermore, the guide groove 202 is provided with a limiting groove 2021 at one end located radially outside the driven shaft 2. The groove area of ​​the limiting groove 2021 is larger than the groove area of ​​the guide groove 202, which is used to limit the movement stroke of the quick connecting pin 7 in the guide groove 202, thereby preventing the quick connecting pin 7 from moving excessively in the guide groove 202, which would interfere with the normal assembly of the grinding disc 3.

[0025] Furthermore, the quick-connect pin 7 is fixedly connected to the first limiting ring 701 in the limiting groove 2021. The shape of the first limiting ring 701 corresponds to and matches the limiting groove 2021. This is to prevent the quick-connect pin 7 from moving along the guide groove 202 into the limiting hole 2012 when the locking element 8 is not installed in the driven shaft 2. This would prevent the grinding disc 3 from engaging with the grinding disc 3 during assembly, thus affecting the assembly. One end of the quick-connect pin 7 passes through the guide groove 202 and is located inside the limiting hole 2012. A second limiting ring 702 is provided inside the limiting hole 2012 to prevent the quick-connect pin 7 from coming out of the guide groove 202 when the grinding disc 3 is not connected.

[0026] Furthermore, a sealing ring 5 is slidably connected to the outer circumference of the driven shaft 2. One end of the sealing ring 5 is fixedly connected to the grinding disc 3 via a flange. A first sealing ring 501 is provided between the sealing ring 5 and the driven shaft 2 to fill the gap between the sealing ring 5 and the driven shaft 2. A second sealing ring 502 is provided on the connecting end face between the sealing ring 5 and the grinding disc 3 to fill the gap between the sealing ring 5 and the grinding disc 3, thereby preventing fine materials after grinding from entering the interior of the component through the assembly gap between the components and corroding the component.

[0027] Furthermore, a snap-fit ​​block 203 is provided on the end of the driven shaft 2 away from the end connected to the grinding disc 3 for connecting an external transmission structure. The grinding shell 1 includes a first cover 101 and a second cover 102 arranged opposite to each other. The first cover 101 and the second cover 102 are movably hinged together. The two sets of opposite driven shafts 2 are respectively arranged inside the first cover 101 and the second cover 102. During the grinding process, the first cover 101 and the second cover 102 close to form a closed cavity structure, so that the material is ground by the grinding disc 3 in the closed cavity. After grinding, the powdery or slurry material is discharged outward through the outlets arranged radially at the bottom of the first cover 101 and the second cover 102. After grinding, the first cover 101 and the second cover 102 are separated to facilitate the cleaning and replacement of the internal driven shaft 2 and the grinding disc 3, and to prevent the residue remaining after grinding from deteriorating in the gaps of the driven shaft 2 and the grinding disc 3, affecting the next use.

[0028] Furthermore, the driven shaft 2 located at one end of the first cover 101 passes through the first cover 101 and is engaged with the drive shaft 6 by the snap-fit ​​block 203. The drive shaft 6 has a feeding paddle 601 extending spirally along its axial direction on its outer periphery. The first cover 101 is connected to an external grinding mill. The feeding paddle 601 is used to push the material discharged from one end of the grinding mill into the grinding shell 1 for grinding by the grinding disc 3. In use, the drive shaft 6 is used to drive the driven shaft 2 connected to it to rotate. The driven shaft 2 drives the grinding disc 3 to rotate through the quick-connect pin 7. The grinding disc 3 located in the second cover 102 is stationary. The two grinding discs 3 cooperate to grind the material.

[0029] Furthermore, the driven shaft 2 located at one end of the second cover 102 is engaged with the adjusting shaft 4 via the snap-fit ​​block 203. The outer periphery of the adjusting shaft 4 is provided with an external thread and is threadedly connected to the second cover 102 via the external thread, so that the adjusting shaft 4 can rotate relative to the second cover 102, thereby controlling the length of the adjusting shaft 4 itself screwed into the second cover 102, thereby pushing the driven shaft 2 to drive the grinding disc 3 closer to the grinding disc 3 on the side of the first cover 101.

[0030] Furthermore, a drive handle 401 is provided at the end of the adjusting shaft 4 away from the end connected to the corresponding driven shaft 2. The drive handle 401 drives the adjusting shaft 4 to rotate relative to the second cover 102, thereby pushing the grinding disc 3 to move along the axial direction of the adjusting shaft 4. This is used to adjust the distance between the two grinding discs 3, thereby controlling the fineness of the grinding. A retaining ring 402 is connected to the shaft of the adjusting shaft 4 located between the second cover 102 and the drive handle 401 by an external thread. After the adjusting shaft 4 is adjusted to the correct position, the retaining ring 402 is rotated to move along the axial direction of the adjusting shaft 4 to a state of abutment against the second cover 102, thereby restricting the adjusting shaft 4 and preventing the adjusting shaft 4 from moving backward under the force during the grinding process, which would cause the distance between the two grinding discs 3 to be too large, making it impossible to effectively grind the material.

[0031] Working principle: First, two sets of driven shafts 2, which are arranged opposite to each other, are installed in the first cover 101 and the second cover 102 respectively. The driven shaft 2 in the first cover 101 is connected to the drive shaft 6 of the grinding mill through its corresponding snap-fit ​​block 203. The drive shaft 6 is connected to an external motor, thereby driving the driven shaft 2 to rotate the corresponding grinding disc 3. The driven shaft 2 in the second cover 102 is connected to an adjusting shaft 4 through the snap-fit ​​block 203, so that the distance between the two grinding discs 3 can be adjusted by manual rotation to control the fineness of grinding.

[0032] When performing grinding operations, first select a suitable grinding disc 3 according to the type of material and the required grinding fineness. Install the grinding disc 3 on the shaft of the driven shaft 2, so that the groove 301 of the inner ring of the grinding disc 3 corresponds to the guide slide groove 202. Then, by screwing in the locking part 8, the limiting shaft 802 pushes the quick connecting pin 7 to slide outward along the guide slide groove 202, so that one end of the quick connecting pin 7 abuts against the groove 301 to form a locking structure. At this time, the limiting shaft 802 is in the limiting hole 2012 and abuts against the inner end of the quick connecting pin 7, thereby supporting the quick connecting pin 7 and forming a stable connection structure between the grinding disc 3 and the quick connecting pin 7, preventing it from loosening due to vibration or torque during operation, so that the grinding disc 3 remains stable during high-intensity grinding.

[0033] After assembly, the first cover 101 and the second cover 102 are closed to form a closed grinding chamber. The material is pushed into the grinding chamber by the pusher paddle. The drive shaft 6 drives the driven shaft 2 and the corresponding grinding disc 3 connected to it to rotate at high speed, while the grinding disc 3 on the other side of the driven shaft 2 remains stationary. The two grinding discs 3 cooperate with each other to perform efficient grinding or slurry treatment on the material entering the chamber. The ground material is discharged through the outlet at the bottom of the grinding shell 1.

[0034] When it is necessary to adjust the grinding fineness, the drive handle 401 on the adjustment shaft 4 is rotated to move the adjustment shaft 4 axially relative to the second cover 102, causing the grinding disc 3 in the second cover 102 to move closer to or further away from the grinding disc 3 in the first cover 101, thereby changing the distance between the two grinding discs 3 to control the grinding precision. After grinding, in order to clean or replace the grinding disc 3, the operator only needs to unscrew the locking part 8 to release the support structure between the locking part 8 and the quick connecting pin 7. Under the action of gravity, the quick connecting pin 7 slides along the guide groove 202 and disengages from the slot 301 of the grinding disc 3, and the grinding disc 3 can be easily removed. Disassembly can be completed without the use of tools, which is convenient for cleaning the grinding disc 3.

[0035] The above description is only a preferred embodiment of the present utility model, but the protection scope of the present utility model is not limited thereto. Any equivalent substitutions or changes made by those skilled in the art within the technical scope disclosed in the present utility model, based on the technical solution and the inventive concept of the present utility model, should be included within the protection scope of the present utility model.

Claims

1. A grinding disc that is easy to disassemble and replace, comprising a grinding shell (1), characterized in that: The grinding shell (1) is provided with two sets of driven shafts (2) arranged opposite to each other. Each set of driven shafts (2) has a locking hole (201) on one end of the shaft body opposite to each other. The outer periphery of the shaft body opposite to each other is provided with a grinding disc (3) that is mirror image of each other. A locking element (8) is installed in the locking hole (201). The driven shaft (2) is slidably connected with a number of quick-connecting pins (7) arranged equidistantly around the driven shaft (2) in the radial direction. One end of the quick-connecting pin (7) passes through the shaft body and engages with the grinding disc (3). The inner ring of the grinding disc (3) is provided with a groove (301) corresponding to the quick-connecting pin (7). The other end of the quick-connecting pin (7) abuts against the side wall of the locking element (8) in the locking hole (201).

2. The easily disassembled and replaceable grinding disc according to claim 1, characterized in that, The locking hole (201) is a stepped hole, including a connecting hole (2011) and a limiting hole (2012) that are progressively deeper along the axis of the driven shaft (2). The diameters of the limiting hole (2012) and the connecting hole (2011) increase sequentially. The locking member (8) includes a limiting shaft (802), which is located in the limiting hole (2012) and its outer circumference abuts against the quick-connecting pin (7). The other end of the limiting shaft (802) is integrally connected to a bolt (801), and the bolt (801) is connected to the connecting hole (2011) by a thread.

3. A grinding disc that is easy to disassemble and replace according to claim 2, characterized in that, The limiting hole (2012) is provided with a number of radially penetrating guide grooves (202) around its inner wall, and a number of quick connecting pins (7) are respectively slidably disposed in the number of guide grooves (202).

4. The easily disassembled and replaceable grinding disc according to claim 3, characterized in that, The guide groove (202) is provided with a limiting groove (2021) at one end located radially outside the driven shaft (2), and the groove area of ​​the limiting groove (2021) is larger than the groove area of ​​the guide groove (202).

5. A grinding disc that is easy to disassemble and replace according to claim 4, characterized in that, The quick-connecting pin (7) is fixedly connected to the first limiting ring (701) in the limiting groove (2021). The shape of the first limiting ring (701) corresponds to and matches the limiting groove (2021). One end of the quick-connecting pin (7) passes through the guide groove (202) and is located inside the limiting hole (2012) with a second limiting ring (702).

6. A grinding disc that is easy to disassemble and replace according to claim 1, characterized in that, A sealing ring (5) is slidably connected to the outer periphery of the driven shaft (2). One end of the sealing ring (5) is fixedly connected to the grinding disc (3) through a flange. A first sealing ring (501) is provided between the sealing ring (5) and the driven shaft (2), and a second sealing ring (502) is provided on the connecting end face between the sealing ring (5) and the grinding disc (3).

7. A grinding disc that is easy to disassemble and replace according to claim 1, characterized in that, The driven shaft (2) is provided with a snap-fit ​​block (203) on the end of the shaft that is away from the grinding disc (3). The grinding shell (1) includes a first cover (101) and a second cover (102) that are arranged opposite to each other. The first cover (101) and the second cover (102) are movably hinged together. The two sets of driven shafts (2) that are arranged opposite to each other are respectively arranged inside the first cover (101) and the second cover (102).

8. A grinding disc that is easy to disassemble and replace according to claim 7, characterized in that, The driven shaft (2) located at one end of the first cover (101) passes through the first cover (101) and is engaged with the drive shaft (6) by the snap-fit ​​block (203). The drive shaft (6) has a feeding paddle (601) extending spirally along its axial direction on its outer periphery.

9. A grinding disc that is easy to disassemble and replace according to claim 8, characterized in that, The driven shaft (2) located at one end of the second cover (102) is engaged with the adjusting shaft (4) by the snap-fit ​​block (203). The adjusting shaft (4) has an external thread on its outer periphery and is threadedly connected to the second cover (102) through the external thread.

10. A grinding disc that is easy to disassemble and replace according to claim 9, characterized in that, The adjusting shaft (4) has a drive handle (401) at the end away from the corresponding driven shaft (2). The adjusting shaft (4) is located between the second cover (102) and the drive handle (401) and is connected to a backstop ring (402) by an external thread.

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