PROCESSING TECHNOLOGY OF “COLORING AFTER INSERTING” OF PA THERMAL BREAK ALUMINUM PROFILES

The following contents are all translated by Polywell company. The original text is an introduction released by Technoform Group.

As we all know, there are two processing methods for thermal break aluminum profiles: one is to color the aluminum profiles first, and then insert the PA thermal break strips into colored aluminum profiles, (that is, “coloring before inserting”, as shown in Figure 1). This is the processing method we commonly use at present. The other is to insert the PA thermal break strips into aluminum profiles before coloring the whole thermal break aluminum profiles, (that is, “coloring after inserting”, as shown in Figure 2), this method is more commonly used in Europe.

Although the second method just exchange several processing sequences of the first one. It does have significant changes and special requirements in the selection of thermal break strips and some processing techniques.

Figure 1  thermal break aluminum profile with the processing technology of

 “coloring before inserting”

Figure 2  thermal break aluminum profile with the processing technology of

 “coloring after inserting”

1. Selection of the Thermal Break Strips

For the thermal break aluminum profile with the processing technology of “coloring before inserting”, the requirement for the PA thermal break strip is: meet the conventional requirements such as dimensional accuracy and strength. The head of the PA thermal break strip is shown in Figure 3.

        Figure 3  The head of ordinary PA thermal break strip                         Figure 4  The head of PA thermal break strip with hot-melt glue wire

But for the thermal break aluminum profile with the processing technology of “coloring after inserting”, in addition to meeting the above requirements, must also ensure that the strength of them after the coloring process meet the relevant requirements of GB/T5237.6.

The head of the PA thermal break strip must be equipped with hot-melt glue wire, as shown in figure 4.

For ordinary PA thermal break strips, although the PA thermal break strips have high longitudinal shear force after inserting. However, after passing through the color furnace, under the high temperature of about 200℃, the outer collet of the aluminum profile slot will be loose due to the influence of thermal expansion and cold contraction, which cannot tightly bite the PA thermal break strip, resulting in the decrease of the longitudinal shear force. I attached Figures 5 for you to understand.

Figure 5  The occlusion of the outer collet with the thermal break strip before and after coloring

As can be seen from Figure 6, in the case where the notch of the aluminum profile is not knurled, after the thermal break aluminum profile is compounded, the longitudinal shear force is 15N/mm. After surface treatment of coloring, due to the high temperature, the outer collet of the thermal break profile is loose, its longitudinal shear force is basically only 0N/mm.

For thermal break aluminum profiles with poor knurling, after compounding, the longitudinal shear force is 64N/mm, and after surface treatment of coloring, this force is only 18N/mm, a loss of 72%.

For the thermal break aluminum profile with good knurling, after compounding, the longitudinal shear force is 90N/mm, and after surface treatment of coloring, this force is only 47N/mm, a loss of 48%.

For the thermal break aluminum profile with the best knurling, after compounding, the longitudinal shear force is 110N/mm, and after surface treatment of coloring, this force is only 58N/mm, a loss of 47%.

From here, we can see that when we select the ordinary PA thermal break strips which are to produce thermal break aluminum profiles, the shear force loss of the final product is more than 50%, which cannot provide a reliable guarantee for production and use.

Figure 6

In short, for the production of thermal break aluminum profiles by the process of “coloring after inserting”, the PA thermal break strips with hot-melt glue wire should be selected.

The hot-melt wire is solid at room temperature. It's stuck on the PA thermal break strip. During the process of coloring, the hot-melt glue wire begins to melt. The molten hot-melt glue wire will fill the gap between the PA thermal break strip and the aluminum profile. When the coloring is completed, the temperature begins to drop and the molten hot melt glue wire begins to solidify. Because of its strong bonding performance, the PA thermal break strip is bonded with the aluminum profile, so as to make up for the loss of longitudinal shear force caused by the loosening of the outer collet.

Figure 7

It can be seen from Figure 7 that for the thermal break aluminum profile with good knurling, after the compounding, the longitudinal shear force is 89N/mm. After coloring, the longitudinal shear force is 80N/mm, which is lost only 10%. However, for the profile equipped with ordinary PA thermal break strips, the loss is more than 50% after coloring. The huge data gap resulted from the use of different strips indicates the obvious positive effect of the PA thermal break strips with hot-melt glue wire for thermal break aluminum profiles in the process of “coloring after inserting”.

Therefore, when using the technology of “coloring after inserting” to produce thermal break aluminum profiles, it is recommended to use PA thermal break strips with hot-melt glue wire.

2. Drying of the Thermal Break Strips

The main material of the PA thermal break strip is polyamide 66 with 25% glass fiber reinforced. PA66 is a water-absorbing material with the water absorption saturation rate of about 5%. Conducting the process of surface treatment and baking when the water in the PA thermal break strip is saturated will cause the moisture in the PA thermal break strip to evaporate during the baking process, resulting in a large area of bubbles on the surface of the strip or even the rupture of it (as shown in the figure 8 and figure 9).

                                 Figure 8  bubble                                                                                         Figure 9  rupture                   

Therefore, after soaked in each pool, the thermal break aluminum profiles should be dried with compressed air before sprayed with powder to ensure that there is no residue from the pool on the profiles, cavities or gaps; then place the thermal break aluminum profiles in the drying box for a period of time, so that the moisture inside the PA thermal break strip is volatilized. Only in this way can ensure that no bubbles or peeling appear on the surface of strips during the baking process of the aluminum profile.

3. Temperature Control During Baking

The softening temperature of the PA thermal break strip is about 230℃, and the melting temperature is around 250°C. Thus, the temperature of the color furnace must be set between 180-200℃ and the time should be less than or equal to 20 minutes. When the temperature or time is exceeded, the stability of the PA thermal break strip will be affected, resulting in deformation of the thermal break aluminum profile. (As shown in the figure 10)

Figure  10

4. About Fluorocarbon Paint

For the thermal break aluminum profile whose surface treatment is fluorocarbon paint, it is not suitable to use the process of “coloring after inserting”. It can only be produced by “coloring before inserting”. This is because the coloring time of fluorocarbon paint is relatively long (maybe two or three coats, etc.) and the coloring temperature is high (about 220 ℃). These may lead to deformation of thermal break aluminum profile.

In short, for the production of thermal break aluminum profiles by the process of “coloring after inserting”, the PA thermal break strips with hot-melt glue wire should be selected. It is necessary to dry the inserted thermal insulation profiles and control the furnace temperature and baking time.