Metal wire straightening mechanism

Abstract

The utility model relates to a metal wire rod straightening mechanism, including first feeding device, first straightening device, second feeding device, second straightening device and third straightening device, first straightening device electric link first feeding device, second feeding device electric link first straightening device, second straightening device electric link second feeding device, third straightening device electric link second straightening device, when metal wire rod wants to carry out straightening operation, by first feeding device through threading portion with metal wire rod spacing and conveying to first straightening device, through first straightening device and carries out the pre straightening of metal wire rod, then through second feeding device and conveys metal wire rod to second straightening device and carries out horizontal straightening operation, finally through third straightening device carries out vertical straightening operation, to complete the whole set straightening operation of metal wire rod, thereby horizontal straightening continues vertical straightening operation, so that metal wire rod straightening effect is better.

Description

Technical fields: This utility model relates to a metal wire processing mechanism, and more particularly to a metal wire straightening mechanism with high precision and excellent straightening effect. Background technology: Most existing metal wire straightening mechanisms still require operation and monitoring by experienced professionals to complete the entire straightening process. In other words, during each straightening cycle, personnel must manually input force parameters, causing the straightening mechanism to operate according to these parameters and produce the finished product. However, different metal wires have different diameters and characteristics. Slight carelessness or inaccurate force applied during operation can affect the overall straightening result, leading to poor straightening performance and reduced product yield.

[0001] Because past technologies for straightening metal wires often used a single axial method, such as a single horizontal axis, the straightening effect was not ideal. Furthermore, relying on human intervention for quality control and technical support throughout the straightening process was not only labor-intensive, but also affected the output quality and efficiency of the entire product line if inexperienced operators were encountered. Therefore, how to accurately and efficiently straighten metal wires and improve the straightening effect has always been a problem that those skilled in the art have been eager to solve. Utility Model Content: In view of the shortcomings of the prior art, this application proposes a solution relating to a metal wire straightening mechanism, comprising: a first feeding device including an extension arm, a first processing device, a drive assembly, an alignment sensor, and a clamp, wherein the first processing device is electrically connected to the drive assembly and the alignment sensor, wherein one end of the extension arm is movably connected to a fixing assembly, and the other end is connected to the clamp; a first straightening device electrically linked to the first feeding device, and including a first motor, a first hydraulic circuit, a first pressure sensor, and a plurality of first tension wheels electrically connected to each other, each of the first tension wheels having a first groove; a second feeding device electrically linked to the first straightening device, and including a second lifting device, a second motor, a second hydraulic circuit, a second pressure sensor, and a plurality of second tension wheels electrically connected to each other, each of the second tension wheels having a second groove; and a second straightening device electrically linked to the second feeding device, and including a third lifting device, a plurality of third tension wheels, and a third motor electrically connected to each other. The device comprises a third pressure sensor and a third hydraulic circuit, each of the third tension wheels having a third groove; a third straightening device electrically connected to the second straightening device, and including a plurality of fourth tension wheels, a fourth pressure sensor, and a fourth hydraulic circuit electrically connected to each other, each of the fourth tension wheels having a fourth groove; wherein, when a metal wire is to be straightened, the metal wire is positioned and conveyed to the first straightening device by the first feeding device, the metal wire is pre-straightened by the first tension wheels of the first straightening device, the metal wire is then conveyed to the second straightening device by the second feeding device for a horizontal straightening operation, and finally a vertical straightening operation by the third straightening device to complete the entire straightening operation of the metal wire, wherein the first straightening device, the second feeding device, the second straightening device, and the third straightening device respectively sense multiple pressure values ​​passing through the metal wire by the first pressure sensor, the second pressure sensor, the third pressure sensor, and the fourth pressure sensor.

[0002] In one embodiment, the metal wire straightening mechanism is characterized in that the first straightening device further includes a limiting platform and a pneumatic cylinder electrically connected to each other.

[0003] In one embodiment, the metal wire straightening mechanism is characterized in that the first straightening device further includes a first lifting device electrically connected to the first hydraulic circuit.

[0004] In one embodiment, the metal wire straightening mechanism is characterized in that the first straightening device further includes a plurality of first optical scale assemblies electrically connected to each of the first tension wheels, the first motor, the first pressure sensor and the first hydraulic circuit.

[0005] In one embodiment, the metal wire straightening mechanism is characterized in that the second straightening device further includes a plurality of second optical scale components electrically connected to each of the third tension wheels, the third motor, the third pressure sensor and the third hydraulic circuit.

[0006] In one embodiment, the metal wire straightening mechanism is characterized in that the second straightening device further includes a plurality of second manual devices electrically connected to the plurality of second optical scale components.

[0007] In one embodiment, the metal wire straightening mechanism is characterized in that the third straightening device further includes a plurality of third optical scale components electrically connected to each of the fourth tension wheels, the fourth pressure sensor and the fourth hydraulic circuit.

[0008] In one embodiment, the metal wire straightening mechanism is characterized in that the third straightening device further includes a plurality of third manual devices electrically connected to the plurality of third optical scale components.

[0009] In one embodiment, the metal wire straightening mechanism is characterized in that it further comprises a storage device, a second processing device, and a feature capture device, wherein the storage device is electrically connected to the plurality of second manual devices and the plurality of third manual devices, and wherein the feature capture device and the second processing device are electrically connected to the storage device.

[0010] In one embodiment, the metal wire straightening mechanism is characterized in that the plurality of first tension wheels, second tension wheels, third tension wheels and fourth tension wheels are made of non-metallic materials. Attached image description: Figure 1 This is an embodiment of the metal wire straightening mechanism in this case, and is intended to illustrate the following: Figure 2 This is an intentional representation of the first feeding device component of the metal wire straightening mechanism in this case; Figure 3 This is a block diagram showing an embodiment of the first straightening device of the metal wire straightening mechanism in this case; Figure 4 The diagram illustrates the construction of an embodiment of the first tension wheel, second tension wheel, third tension wheel, and fourth tension wheel of the metal wire straightening mechanism in this case. Figure 5 This is a block diagram showing an embodiment of the second straightening device of the metal wire straightening mechanism in this case; Figure 6 This is a block diagram illustrating an embodiment of the third straightening device in the metal wire straightening mechanism of this case.

[0011] Figure label: 1. Metal wire straightening mechanism 12 First feeding device 121 Extend your arm 122 First Processing Unit 123 Driver Components 124 Alignment Sensor 125 clamp 13 First straightening device 131 First Motor 132 First hydraulic circuit 133 First pressure sensor 134 First tension wheel 1341 First Trench 135 Limiting Platform 136 pneumatic cylinder 137 First Lifting Device 138 First Optical Scale Assembly 14 Second feeding device 141 Second Lifting Device 142 Second Motor 143 Second hydraulic circuit 144 Second pressure sensor 145 Second tension wheel 1451 Second Trench 15 Second straightening device 151 Third Lifting Device 152 Third tension wheel 1521 Third Trench 153 Third Motor 154 Third pressure sensor 155 Third Hydraulic Circuit 156 Second optical scale assembly 157 Second manual device 16 Third straightening device 161 Fourth tension wheel 1611 Fourth trench 162 Fourth pressure sensor 163 Fourth hydraulic circuit 164 Third Optical Scale Assembly 165 Third manual device 17. Processing device 18 Feature capture devices D Storage device H wire diameter W metal wire Detailed implementation method: To more clearly describe the metal wire straightening mechanism proposed in this utility model, the preferred embodiments of this utility model will be described in detail below with reference to the accompanying drawings.

[0012] Please also refer to Figure 1 and Figure 3This is a schematic diagram of an embodiment of a metal wire straightening mechanism in this case. As shown in the figure, a metal wire straightening mechanism 1 includes a first feeding device 12, a first straightening device 13, a second feeding device 14, a second straightening device 15, and a third straightening device 16. These devices are electrically connected to each other. In addition, the first feeding device 12 further includes an extension arm 121, a first processing device 122, a drive assembly 123, an alignment sensor 124, and a clamp 125. Furthermore, the extension arm 121 and the clamp 125 can clamp the metal wire W and accurately thread it through the first processing device 122 and the alignment sensor 124, ensuring stable transmission without falling off. The straightening device 13 is electrically connected to the first feeding device 12 and includes a first motor 131, a set of first hydraulic circuits 132, a first pressure sensor 133, and a plurality of first tension wheels 134 that are electrically connected to each other. The first hydraulic circuit 132 is used to control the horizontal displacement position of the plurality of first tension wheels 134, which is to provide different stretching and straightening forces to the metal wire W to be straightened. The first pressure sensor 133 senses the different stretching and straightening forces. Each first tension wheel 134 has a first groove 1341. The structure of the first groove 1341 can not only accurately limit the position of the metal wire W, but also reduce the friction of the metal wire W. The first tension wheel 134, actuated by the first motor 131, performs a first-stage stretching and straightening operation on the metal wire W to be straightened. This is called pre-straightening and is horizontal straightening. Continuing on, the first straightening device 13 is electrically connected to and physically linked to a set of second feeding devices 14, and includes a second lifting device 141, a second motor 142, a second hydraulic circuit 143, a second pressure sensor 144, and a plurality of second tension wheels 145, all electrically linked to each other. The second lifting device 141... The second feeding device 14 can adjust its height and accurately clamp the metal wire W with each of the second tension rollers 145. The second hydraulic circuit 143 is used to control the horizontal displacement position of the plurality of second tension rollers 145 and to transmit the metal wire W. The second pressure sensor 144 senses different tension and straightening forces of the metal wire W. Each of the second tension rollers 145 has a second groove 1451. The structure of the second groove 1451 can not only accurately limit the position of the metal wire W, but also reduce the friction of the metal wire W.

[0013] Please continue reading. Figure 1 and Figure 4The second feeding device 14 is electrically connected to and physically linked to a set of second straightening devices 15. The second straightening device 15 includes multiple sets of third tension rollers 152, a third motor 153, a third pressure sensor 154, and a set of third hydraulic circuits 155. In addition to straightening the metal wire W, the second straightening device 15 also plays the role of carrying the material, providing support and achieving the practical benefits of simultaneous feeding and stretching straightening, which is not only highly efficient but also less labor-intensive. Furthermore, the third tension rollers 152 can be unpowered rollers or can be driven by the third motor 153. Each third tension roller 152 has a third groove 1521, and the structure of the third groove 1521 can not only accurately limit the position of the metal wire W but also reduce the friction of the metal wire W. The plurality of third tension rollers 152 are actuated by the third motor 153 to perform a second stage of stretching and straightening on the metal wire W that has been fed by the second feeding device 14 and has undergone the first stage of straightening. The straightening is in the horizontal direction. The third hydraulic circuit 154 controls the horizontal displacement of the third tension rollers 152 to provide different stretching and straightening forces to the metal wire W in the second stage of straightening. In addition, the different stretching and straightening forces of the metal wire W can also be sensed by the third pressure sensor 154.

[0014] Please continue reading. Figure 1 The third straightening device 16 is electrically connected to and physically connected to a set of second straightening devices 15. The third straightening device 16 includes a fourth tension wheel 161, a fourth pressure sensor 164, and a set of fourth hydraulic circuits 163, which are electrically connected to each other. There are multiple fourth tension wheels 161, and each fourth tension wheel 161 has a fourth groove 1611. The fourth tension wheel 161 performs a third-stage stretching and straightening operation on the metal wire W that has been fed by the second straightening device 15 and has undergone the second-stage straightening operation. The straightening is in the vertical direction. The fourth hydraulic circuit 163 controls the vertical displacement of the fourth tension wheel 161 to provide different stretching and straightening forces to the metal wire W straightened in the third stage. In addition, in this stage, the fourth pressure sensor 162 senses the different stretching and straightening forces of the metal wire W.

[0015] Please refer to Figure 1In summary, the first straightening device 13 and the second straightening device 15, through the first hydraulic circuit 132 and the third hydraulic circuit 155, cause the first tension rollers 134 and the third tension rollers 152 to move horizontally, thereby controlling the clamping force of each first tension roller 134 and each third tension roller 152 on the metal wire W. The third straightening device 16, through the fourth hydraulic circuit 163, causes the fourth tension rollers 161 to move vertically, thereby controlling the clamping force of each fourth tension roller 161 on the metal wire W. Since the first straightening device 13 and the second straightening device 15 prioritize horizontal straightening of the metal wire W, the metal wire... The stress W will increase. At this time, the third straightening device 16 will then straighten the metal wire W vertically, which will eliminate the yield strength of the wire and make the straightening effect of the wire better. Furthermore, through the coordinated cooperation of each hydraulic circuit and each straightening device, the straightening force can be more accurate, and there will be no situation where the slightest error leads to a huge difference. At the same time, it can also reduce the over-reliance on manpower and move towards fully automated and intelligent production operations. In addition, the first pressure sensor 133, the second pressure sensor 144, the third pressure sensor 154 and the fourth pressure sensor 162 sense different tensile straightening forces of the metal wire W at different straightening stages.

[0016] It is worth mentioning that in actual applications, the order of the first straightening device 13, the second straightening device 15, and the third straightening device 16 can be alternated or interchanged, or they can be connected in series or reduced as needed. For example, if there are size restrictions in the work area, the first straightening device 13 can be removed, and the first feeding device 12 can directly receive the metal wire W from the front end and feed it to the second straightening device 15. In addition, other feeding machines or feeding fixtures can be added to increase the smoothness of the operation after the devices are connected in series.

[0017] Please see Figure 1 and Figure 3 The metal wire straightening mechanism 1 further includes a first straightening device 13 comprising a set of limiting platforms 135 electrically connected to each other and at least one pneumatic cylinder 136. The pneumatic cylinder 136 is used to perform multi-axial displacement of the limiting platforms 135. Furthermore, the pneumatic cylinder 136 will preferentially actuate at least one set of displacement components (not shown) to cause the limiting platforms 135 to move to the most suitable position in multiple axes. This ensures that the metal wire W will not slip outside the first tension wheel 134 during the operation process. In addition, it also makes the first tension wheels 134 more reliable and accurate when clamping the metal wire W, thereby increasing its stretching and straightening effect.

[0018] Please refer to Figure 1 , Figure 3 , Figure 5 and Figure 6The metal wire straightening mechanism 1 includes a first lifting device 137, a second lifting device 141, and a third lifting device 151, which are electrically connected to a first hydraulic circuit 132, a second hydraulic circuit 143, and a third hydraulic circuit 155, respectively. These devices can be used to precisely control the first straightening device 13, the second feeding device 14, and the second straightening device 15 to adjust the opening and closing positions of each tension wheel according to the feeding position of the wire. In other words, they play an indispensable role in the entire stretching and straightening operation. Through the coordinated cooperation of the first lifting device 137, the second lifting device 141, and the third lifting device 151 with the first tension wheel 134, the second tension wheel 145, and the third tension wheel 152, the overall stretching and straightening effect of the metal wire W can be improved.

[0019] Please refer to this again. Figure 3 In one embodiment, the first straightening device 13 in the metal wire straightening mechanism 1 further includes a first optical ruler assembly 138, which is electrically connected to each of the first tension wheels 134, the first motor 131, the first hydraulic circuit 132, and the first pressure sensor 133. Through the setting of the first optical ruler assembly 137 and its coordinated operation with each component, the force output and sensing of the stretching and straightening are made more accurate.

[0020] Please refer to this again. Figure 5 In one embodiment, the second straightening device 15 in the metal wire straightening mechanism 1 further includes a second optical ruler assembly 156, which is electrically connected to each of the third tension wheels 152, the third motor 153, the third pressure sensor 154 and the third hydraulic circuit 155. Through the setting of the second optical ruler assembly 156 and its coordinated operation with each component, the force output and sensing of the stretching and straightening are made more accurate.

[0021] Please continue to refer to this. Figure 5 In one embodiment, the second straightening device 15 in the metal wire straightening mechanism 1 further includes a second manual device 157 electrically connected to a second optical ruler assembly 156. The second manual device 157 allows the operator to manually input the force parameters for stretching and straightening, and the second optical ruler assembly 156 can output the force parameters precisely and accurately, ensuring that the entire straightening process is accurate and error-free.

[0022] Please refer to this again. Figure 6 In one embodiment, the third straightening device 16 in the metal wire straightening mechanism 1 further includes a third optical ruler assembly 164, which is electrically connected to each of the fourth tension wheels 161, the fourth pressure sensor 162 and the fourth hydraulic circuit 163. Through the setting of the third optical ruler assembly 164 and its coordinated operation with each component, the force output and sensing of the tension straightening are made more accurate.

[0023] Please continue to refer to this. Figure 6 In one embodiment, the third straightening device 16 in the metal wire straightening mechanism 1 further includes a third manual device 165 electrically connected to a third optical ruler assembly 164. The third manual device 165 allows the operator to manually input the force parameters for stretching and straightening, and the third optical ruler assembly 164 can output the force parameters precisely and accurately, ensuring that the entire straightening process is accurate and error-free.

[0024] It is worth mentioning that all the manual devices mentioned here are set up in each straightening device or each feeding device with the same setting logic and principle, so that each device can accurately apply the force required for stretching and straightening by manually inputting the force parameter (also known as the bias parameter).

[0025] Please refer to this again. Figure 5 and Figure 6 In one embodiment, the second straightening device 15 and the third straightening device 16 in the metal wire straightening mechanism 1 further include a storage device D, which is electrically connected to the second manual device 157 and the third manual device 165. Furthermore, when the entire straightening operation is unmanned and automated, the storage device D can store the pre-input force parameter (also known as the bias parameter) information, or after the personnel continuously input the parameter through each manual device, the optimal force parameter (also known as the bias parameter) is stored in the storage device D through learning, feedback and other mechanisms. When the stretching and straightening operation is to be performed, this optimal force parameter (also known as the bias parameter) is retrieved from the storage device D for the straightening operation. There is no need for the personnel to input the force parameter (also known as the bias parameter) at all times, which saves more labor costs and does not lose the accuracy of stretching and straightening.

[0026] It is worth mentioning that, please continue to refer to Figure 5 and Figure 6Continuing from the above, in one embodiment, the storage device D of the second straightening device 15 and the third straightening device 16 in the metal wire straightening mechanism 1 can be electrically connected to the processing device 17 and the feature capture device 18. The feature capture device 18 is used to capture the features of the metal wire W to be straightened, and then the processing device 17 performs calculations, comparisons and processing. Furthermore, the feature capture device 18 can include, for example, an image capture device, a barcode scanner, a laser sensor, etc. The feature capture device 18 can be used to capture features of the metal wire W to be straightened, such as capturing images, capturing barcodes, scanning and modeling, etc. After the feature capture is completed, the processing device 17 performs comparisons, calculations and processing to obtain relevant information about the metal wire W, and further determine which force parameter (also known as the bias parameter) to use for the stretching and straightening operation, so as to realize an unmanned intelligent automatic straightening program, while saving operating costs and making the straightened product more perfect. In addition, storage device D can be a physical hard drive, a database, or cloud storage space. By continuously collecting data, it can more accurately output its strength parameters (also known as bias parameters), thus better reflecting the working environment of big data and the Internet of Things.

[0027] In addition, please refer to Figure 4 In this invention, the first groove 1341, the second groove 1451, the third groove 1521, and the fourth groove 1611 are preferably VR grooves, but can also be V grooves or R grooves individually. Their arrangement is not particularly limited here. The VR groove's wider top and narrower bottom configuration allows for the processing of metal wires W with more different wire diameters H, offering greater processing flexibility than a typical single-type groove. Furthermore, the first groove 1341, the second groove 1451, the third groove 1521, and the fourth groove 1611 in this invention include three different wire diameter H specifications: 20mm–16mm, 16mm–12mm, and below 12mm. These three specifications of grooves can be designed simultaneously on the same tension wheel, or selected according to requirements. When the wire diameter H of the metal wire W to be straightened changes, the operation can proceed directly without replacing the components, thereby improving work efficiency. Furthermore, the plurality of first tension wheels 134, second tension wheels 145, third tension wheels 152 and fourth tension wheels 161 are made of non-metallic materials to achieve the effect of no wear with the metal wire W.

[0028] Finally, the first hydraulic circuit 132, the second hydraulic circuit 143, the third hydraulic circuit 154, and the fourth hydraulic circuit 163 further include proportional pressure valves and proportional flow valves to improve the accuracy of the stretching and straightening output force. The first hydraulic circuit 132, the second hydraulic circuit 143, the third hydraulic circuit 154, and the fourth hydraulic circuit 163 can be controlled by a downstream programmable logic controller (PLC) through the proportional pressure valves and proportional flow valves to optimize the control of the pressure and flow rate of the oil pipes, ensuring precise output of the straightening force without deviation, thus achieving optimal efficiency in the straightening operation.

[0029] The metal wire straightening mechanism of this invention, through the aforementioned technical features, enables the first and second straightening devices to prioritize horizontal straightening of the metal wire W during straightening operations, increasing the stress on the metal wire W. Then, the third straightening device subsequently performs vertical straightening, eliminating the yield strength of the wire and resulting in better straightening performance. Furthermore, the coordinated operation of each hydraulic circuit and straightening device ensures more precise straightening force, preventing significant errors even with minor ones. It also reduces over-reliance on manual labor, moving towards fully automated and intelligent production operations.

[0030] Thus, the above description of a metal wire straightening mechanism of this utility model has been fully and clearly illustrated. However, it must be emphasized that the above detailed description is a specific description of feasible embodiments of this utility model, and the embodiments are not intended to limit the scope of the claims of this utility model. All equivalent implementations or modifications that do not depart from the spirit of the technology of this utility model should be included in the scope of the claims of this application.

Claims

1. A metal wire straightening mechanism, characterized in that, include: A first feeding device includes an extension arm, a first processing device, a drive assembly, an alignment sensor, and a clamp, wherein the first processing device is electrically connected to the drive assembly and the alignment sensor, and one end of the extension arm is movably connected to a fixing assembly, and the other end is connected to the clamp. A first straightening device is electrically connected to the first feeding device and includes a first motor, a first hydraulic circuit, a first pressure sensor and a plurality of first tension wheels electrically connected to each other, each of the first tension wheels having a first groove. A second feeding device is electrically connected to the first straightening device and includes a second lifting device, a second motor, a second hydraulic circuit, a second pressure sensor and a plurality of second tension wheels electrically connected to each other, each of the second tension wheels having a second groove; A second straightening device, electrically linked to the second feeding device, and comprising a third lifting device, a plurality of third tension wheels, a third motor, a third pressure sensor and a third hydraulic circuit electrically connected to each other, each of the third tension wheels having a third groove; A third straightening device, electrically connected to the second straightening device, and comprising a plurality of fourth tension wheels, a fourth pressure sensor and a fourth hydraulic circuit electrically connected to each other, each of the fourth tension wheels having a fourth groove; When a metal wire is to be straightened, the first feeding device positions the metal wire and transports it to the first straightening device. The first tension rollers of the first straightening device then perform pre-straightening of the metal wire. The second feeding device then transports the metal wire to the second straightening device for horizontal straightening. Finally, the third straightening device performs vertical straightening to complete the entire straightening process. The first straightening device, the second feeding device, the second straightening device, and the third straightening device each sense multiple pressure values ​​passing through the metal wire using the first pressure sensor, the second pressure sensor, the third pressure sensor, and the fourth pressure sensor, respectively.

2. The metal wire straightening mechanism according to claim 1, characterized in that, The first straightening device further includes a limiting platform and a pneumatic cylinder that are electrically connected to each other.

3. The metal wire straightening mechanism according to claim 2, characterized in that, The first straightening device further includes a first lifting device electrically connected to the first hydraulic circuit.

4. The metal wire straightening mechanism according to claim 3, characterized in that, The first straightening device further includes a plurality of first optical scale assemblies, electrically connected to each of the first tension wheels, the first motor, the first pressure sensor, and the first hydraulic circuit.

5. The metal wire straightening mechanism according to claim 1, characterized in that, The second straightening device further includes multiple second optical scale assemblies, electrically connected to each of the third tension wheels, the third motor, the third pressure sensor, and the third hydraulic circuit.

6. The metal wire straightening mechanism according to claim 5, characterized in that, The second straightening device further includes a plurality of second manual devices electrically connected to the plurality of second optical scale assemblies.

7. The metal wire straightening mechanism according to claim 6, characterized in that, The third straightening device further includes multiple third optical scale components, which are electrically connected to each of the fourth tension wheels, the fourth pressure sensor and the fourth hydraulic circuit.

8. The metal wire straightening mechanism according to claim 7, characterized in that, The third straightening device further includes multiple third manual devices electrically connected to the multiple third optical scale components.

9. The metal wire straightening mechanism according to claim 8, characterized in that, It further includes a storage device, a second processing device, and a feature capture device, wherein the storage device is electrically connected to the plurality of second manual devices and the plurality of third manual devices, and wherein the feature capture device and the second processing device are electrically connected to the storage device.

10. The metal wire straightening mechanism according to claim 1, characterized in that, The materials of the plurality of first tension wheels, second tension wheels, third tension wheels and fourth tension wheels are non-metallic.

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