WHY HF WELDING ?
The two technologies that can be used for the welding of PVC, PU coated fabrics are
1. High Frequency Welding
2. Hot Air/Hot Wedge Welding
| HOT AIR/WEDGE WELDING | HIGH FREQUENCY WELDING | CONCLUSION | This is achieved by blowing hot air or using a heated wedge to heat the interface between the two layers to be welded to a temperature of approximately 300°C. The hot air gun/heated wedge has to be moved along the length of the fabric to be welded whereby the heated fabric gets into a semi-molten state and is pressed by a set of rollers trailing the heated point. | HF Welding consists of a weld bar of suitable length and breadth which first clamps the fabric to be welded. The fabric is then energised with a high frequency electric field which produces heat within the fabric itself to bring it to a semi-molten state. This takes typically 5 to 10 seconds after which the fabric is allowed to cool under pressure. The cooling time is typically 2 to 5 seconds. | Any plastic when heated without pressure tends to shrink. Hot air/wedge welding hence results in shrinkage. Cooling under pressure in HF welding results in negligible shrinkage, hence no wrinkles appear. |
| Speed of movement of the hot air gun/heated wedge is directly linked to the temperature of hot air/wedge. If the speed of movement is lower there is a possibility of over-melting or burning. Higher speed of movement would result in poor welding. | HF welding parameters are heat time, cool time, power level and pressure on fabric. These can be précised controlled by the machine. | HF Welding is a lot less operator dependent than hot air/wedge welding. |
| By the very nature of the process, hot air/wedge tools have to run continuously without stops during welding. Welding along contours will involve moving the fabric precisely in the required direction. This requires skilled operation. In cases of complicated contours it may not even be possible. | Since HF Welding is an intermittent process, the fabric can be conveniently moved to achieve any contour that is required. Curved dies can be used to achieve welds in any contour. | Welding in curves can be easily achieved with HF Welding. |
| Hot air/wedge tools need heaters to be replaced periodically. | HF welders need no such spares. | Virtually no need for spares for HF welders. |
| By their very design hot air/wedge welding has to be carried out with the fabric spread out on the floor, thus making it more inconvenient and prone to fatigue. | HF welders have tables/platforms for welding of the fabrics. | HF welders are more convenient and user friendly. |