Views: 32 Author: Site Editor Publish Time: 2019-09-23 Origin: Site
The size and shape of the parts that have just been injected change significantly within a few minutes after leaving the moulding machine due to the incomplete solidification, and they are finalized in the cold state. Experience shows that the welding process of parts is different in both cold and hot states.
The parts that have just been injected retain considerable heat, which is beneficial to the subsequent plastic welding process. It must be noted that the welding parameters of the parts are different in both cold and hot states. Using the same parameters and not paying attention to the temperature of the parts will lead to significant changes in the consistency of the welding effect during the production of the parts, such as inadequate welding strength, more spills, or surface scalds.
For common PC materials, welding in hot state has good effect. Because (1) PC is the strongest thermal conductivity in thermoplastics, it is usually difficult to keep enough heat in the weld for a long time to complete welding; (2) Because PC needs relatively high temperature to flow, if the parts are already hot, the heat required for flow will be less; (3) There is one material around the weld. Fixed temperature will slow down the cooling rate of the weld and help to reduce the stress in the welding area.
Of course, not all materials behave like PCs, such as PP and PE. This kind of material is relatively soft and its thermal conductivity is relatively low. Therefore, they usually have better welding effect in cold state, i. e. under the condition of better stiffness. On the other hand, for easily absorbent materials such as PA, more welding energy is needed after absorbing water, and the release of water vapor will produce more spills, which will affect the weldability of parts. Therefore, parts of absorbent materials should be heated and dried before welding. Or keep the parts in sealed bags after injection to insulate the moisture in the air.
Many factors must be considered when welding hot parts. At the same time, before the full production, the temperature of the parts should be defined and tested to determine the welding parameters, so as to obtain stable and good welding effect.