Tension control for elastic ropes in rope and belt hot pressing machines must first be established during the pre-pressing pretreatment phase. The key is to calibrate the initial tension based on the elastic rope's material properties. Elastic ropes inherently exhibit stretch-and-rebound properties. Excessive initial tension can lead to overstretching before hot pressing, resulting in severe springback deformation when the tension is released after hot pressing. However, too low initial tension can lead to wrinkling during the hot pressing process, impairing the shaping effect. Therefore, before hot pressing, a tension calibration mechanism is used to adjust the initial tension based on the rope's elastic modulus (i.e., its ability to recover after stretching). This ensures the rope is in a stable state of "slightly stretched but not stretched." This ensures smooth entry into the hot pressing zone while preventing residual internal stress caused by the initial tension. This ensures stable tension during subsequent hot pressing, minimizing the risk of deformation.
The design of the tension adjustment mechanism in rope and belt hot pressing machines is crucial for dynamically controlling elastic rope tension and preventing deformation. This type of mechanism typically consists of an active feed roller assembly and a tension sensor. The roller's speed and pressure are adjusted in real time based on the elasticity of the cord. As the elastic cord enters the hot press, the tension sensor continuously monitors the tension changes. If the tension decreases due to elastic contraction, the roller assembly will appropriately increase the feed speed or roller pressure to replenish the tension and maintain stability. If the tension increases due to slight elongation during the hot press, the roller assembly will slow down or reduce the pressure to prevent excessive tension accumulation. This dynamic adjustment prevents irreversible stretching or contraction of the elastic cord caused by sudden increases and decreases in tension during the hot press, ensuring that the cord is always hot-pressed under constant tension, minimizing the risk of deformation.
Coordinated control of the tension in the hot press and the hot press action further minimizes deformation of the elastic cord. When heated, the elastic modulus of the elastic cord changes. If the tension at this time is mismatched with the hot press timing, uneven force can occur during the hot press. Therefore, rope and belt hot pressing machines require a coordinated "tension-hot pressing" logic. The hot pressing head only lowers and begins hot pressing once the rope enters the hot pressing zone and reaches the set tension. This prevents deformation caused by pressure before the rope stabilizes. During the hot pressing process, the tensioning mechanism maintains constant tension to offset slight thermal expansion and contraction. For example, the rope may briefly expand after heating, and the tensioning mechanism fine-tunes to maintain the original tension, preventing the resulting relaxation and wrinkling. After the hot pressing is complete, the hot pressing head slowly lifts, and the tensioning mechanism briefly maintains a stable tension to prevent elastic rebound caused by a sudden loss of pressure. This allows the shaped rope to stabilize before proceeding to the next steps.
A tension feedback and real-time adjustment system can address tension fluctuations caused by batch-to-batch variations in elastic rope and prevent deformation. Elastic ropes from different batches can have slightly different elastic moduli due to variations in production processes. Even ropes made of the same material may have slightly more elasticity than others. Using fixed tension parameters can easily cause deformation of highly elastic cords due to insufficient tension, while stretching of less elastic cords due to excessive tension can occur. Therefore, rope and belt hot pressing machines require a tension feedback system. Sensors collect real-time tension data during the hot pressing process and compare it to a preset standard tension value. If tension deviates, the system immediately adjusts the speed and pressure of the feed rollers or the angle of the tension rod to bring the tension back within the standard range. This real-time feedback adjustment can mitigate batch variations in cord, ensuring that each section of elastic cord is hot-pressed at the appropriate tension, minimizing deformation caused by material inconsistencies.
The gradual release of tension after hot pressing is crucial to preventing elastic cords from rebounding and deforming after they have been shaped. After hot pressing, elastic cords still retain a certain amount of internal tension. Rapidly releasing the tension at this point will cause the cord to rebound rapidly due to its elastic nature, disrupting the shaped form (e.g., shortening in length or thickening in cross-section). Therefore, after hot pressing, the rope and belt hot pressing machine slowly reduces the tension using a tension release mechanism. This is achieved by, for example, gradually slowing the speed of the feed rollers or slowly resetting the tension rod, allowing the rope tension to drop to zero at a steady rate. This slow tension release is also coordinated with cooling and shaping. During this gradual tension release, the hot-pressed rope passes through a cooling zone, allowing the shaped structure to stabilize as the tension slowly decreases. This prevents springback caused by the sudden release of tension and ensures that the rope's shape is maintained over time.
Tension control requires customized adaptation for ropes with different elasticity levels to avoid deformation caused by a "one-size-fits-all" tension parameter. Elastic ropes vary greatly in elasticity. For example, high-elasticity ropes (such as those containing spandex) have strong rebound properties after stretching, while low-elasticity ropes (such as cotton ropes with a small amount of elastane) have weak rebound properties. For highly elastic cords, tension control should adopt a "low tension + slow adjustment" strategy—using a low, constant tension to avoid overstretching, while also slowing tension adjustment to prevent springback caused by tension fluctuations. For low-elasticity cords, tension can be appropriately increased to ensure the cord sets smoothly during hot pressing without exceeding its elastic limit and causing permanent deformation. This differentiated adaptation allows tension control to precisely match the cord's elastic properties, mitigating deformation risks through material adaptation.
The integrated matching of tension control and hot pressing parameters is a comprehensive guarantee for preventing deformation in elastic cords. Deformation in elastic cords is closely related not only to tension but also to hot pressing temperature and time. For example, excessively high temperatures soften the cord's elastic fibers, making improper tensioning more likely to cause overstretching. Excessively low temperatures prevent the cord from fully setting and causing springback after tension release. Therefore, rope and belt hot pressing machines require coordinated adjustment of tension parameters and hot pressing parameters: when the hot pressing temperature is set high, tension should be appropriately reduced to prevent deformation of the softened elastic fibers due to excessive tension. When the hot pressing time is long, tension should be maintained while extending the duration of tension to ensure that the rope and belt maintain a stable shape within the sufficient setting time. By comprehensively matching tension and hot pressing parameters, a synergistic effect of "tension controls shape, hot pressing fixes shape" is achieved, comprehensively preventing deformation of elastic ropes and belts after hot pressing.
