Common problems in construction of polyurethane coating and its causes

Polyurethane spraying construction often encounter many problems, so these questions have what? How does it happen?
Here mainly refers to the problem of the performance of the bubble, is now divided into the following.
1 foam surface roughness
This introduction phenomenon is the main reason for poor atomization, especially domestic gas mixing type spraying machine is common and may be appropriate to adjust the back pressure of the air compressor and the distance from the substrate, the conditions can be appropriately extended gas mixing nozzle and decrease the diameter of the mouth. Imported high pressure spray machine can be appropriate to stay away from the substrate. The other reason is that the foaming time is too fast and the black and white material viscosity difference is too large.
2 foam soft
Check the proportion of black and white, the general is caused by white material. First proposed in accordance with the correct proportions do a free foaming test, if still too soft, appropriate to raise the proportion of black material; if still soft, check white material the use of raw materials whether should be appropriate to increase the ether amines (ethylenediamine polyether initiator).
3 foam crisp
At this time of the bubble hole is generally relatively thick, the cause is the system of water content is too large. If it is only part of the surface is crisp, considering the material temperature and ambient temperature difference is too large, high temperature material, low temperature environment. The other reason is that the difference between black and white material viscosity is too large, the excess of black material.
4 foam with the substrate of low peel strength
Causes: the substrate surface is clean, dust or oil; the matrix was not in the transparent, the spin off can see the interface of water. Besides, there are the substrate temperature is too low, foaming speed too fast; when spraying no "grounding" (that is, first of all, spray thin bottom), but a to be sprayed with a thicker will cause tension is too large to peel.
5 foam cracking
Site can see apparently split the gap. This phenomenon is mainly lower degree of foaming system by the use of polyether branch degree and functional caused, may be appropriate to add sucrose, mannitol and sorbitol as the initiator of the polyether. In addition to the appropriate increase in the construction of the coating layer, to avoid the phenomenon of hair.
Between 6 layers
The non bonding phenomenon occurred at the interface of each of the coating phases. This phenomenon and the foaming material system, such as some flame retardant agent and foaming system is not compatible, foam at the surface increased as plasticizer that, of course, there are other materials can cause this phenomenon. In addition, when the foam is too fast or too slow, it may cause this phenomenon. But it's not so serious. It is also sometimes due to the addition of silicone oil surface active agent in the foam system.
7 foam surface
This phenomenon sometimes after complete the spraying can appear, some hours later appeared, serious will bulge one large "bag", which is due to the foaming material types of foaming agent and system incompatible, after the completion of the foaming and accumulation of the secondary foaming, should enable foaming agents and additives and polyether matched, at the construction site to meet this kind of phenomenon of expediency is appropriate to increase the foaming layer, reduce the accumulation of heat.
8 foam shrinkage
Sometimes local contractions are sometimes the whole retraction. The phenomenon is due to the following reasons: foam density is too small, which water content is too large, causing black and white material imbalance, attention should be paid to say here is the equivalent ratio imbalance, such as: 1 equiv of water is 9, and the black material is 136, so even with a trace of water is easy to cause the imbalance of black and white material; another reason is because the temperature is too low to cause; mixing machines inequality is caused by a factor of local contraction