How to weld PE and PP? Which welding effect is better between PE and PP?

Customers often ask, how to weld PE and PP? Which welding effect is better between PE and PP? The following blog will give some suggestions and conclusions.

How to weld PE and PP?

1. Welding of polyethylene (PE) plastics

This plastic welding is basically the same as the PVC plastic welding operation.
Because of its high melting temperature, the temperature of the welding torch should also be increased accordingly to make it fully melted. The viscosity of PE after melting is small, so the air volume should not be too large, so as to avoid the phenomenon of overflowing and blowing. At the same time, due to the large shrinkage of PE plastic, the area heated by the hot air flow of the welding torch is larger (that is, the amplitude of the up and down swing of the welding torch is increased), so as to avoid local shrinkage and cracks (especially when welding thick plates). When using polyethylene plastics, a quick welding tip can be used to apply pressure. If you press the electrode by hand (pendulum welding), you must wait until the welding area cools down to opaque before letting go. If the welding torch gas source can use nitrogen, it can avoid oxidation and improve the welding quality.

2. Welding of polypropylene (PP) plastics

This type of plastic welding, but should pay attention to the following situations:

(1) The isotactic structure and high crystallinity of PP determine that it will soften and become plastic only when its temperature is close to the melting point and reaches the crystalline melting temperature region. This is one reason why PP has better heat resistance. However, this narrow plastic temperature range also brings difficulties to the hot forming process of the sheet. At this time, the temperature amplitude of the welding torch has an influence on it.

(2) When PP is welded with a hot air torch. Compared with PE, its welding temperature is slightly higher (about 200~270℃, which can be appropriately increased if there are auxiliary parts), and the air volume is somewhat smaller due to the lower viscosity after melting. PP is easy to be oxidized at high temperatures. It is better to use inert gas (such as carbon dioxide and nitrogen, etc.) under conditions. Ordinary air can also be used, but the quality is slightly lower. The speed of manual welding is slightly slower than that of PVC, about 100~120mm/min (without auxiliary parts). The hot air welding coefficient of PP can generally reach more than 90%.

Which welding effect is better between PE and PP?

Several factors affect the welding effect:

1. Hardness: the higher the hardness, the better the welding effect.

2. Melting point, the higher the melting point, the higher the welding energy and welding temperature required.

3. Purity, the higher the purity, the better the welding effect. Impurities will appear when the cycle is in use, and the effect will be worse.

Due to the above factors, combined with the respective physical properties of PE and PP, as well as practical experience. The conclusion is as follows, PE has low welding strength and good toughness, and PP has high welding strength and good rigidity.