Common problems and reasons of polyurethane spraying construction
发布时间： 2019-10-29 14:01 Author: Polyurethane foam machine Source: http: //motokone.com
Published: 2019-10-29 14:01
Polyurethane spraying is a high-pressure polyurethane spraying equipment
. Because the materials of the high-pressure spray equipment hit the high speed and rotate violently in the mixing room with small space, the mixing is very sufficient. High-speed moving materials form fine mist droplets at the spray gun mouth, which are evenly sprayed onto the surface of the object. Foamed polyurethane spray is mainly used for thermal insulation and sealing. In the field of thermal insulation and refrigeration, it is easy to use molds, such as large spherical storage tanks, large-diameter special-shaped pipe fittings, and cold storage wall coverings, to achieve on-site foam.
Many problems are often encountered in polyurethane spray construction, so what are these problems? How did it happen?
Here mainly refers to the problem of bubble performance, which is described below:
1. The surface of the foam is rough and uneven. The main cause of this phenomenon is poor atomization, especially domestic air-mixed sprayers are more common. The back pressure of the air compressor and the distance from the substrate can be adjusted appropriately. If necessary, the air-mixed spray head can be lengthened and reduced. Small mouth. Imported high-pressure sprayers can be kept away from the substrate. Another reason is that the foaming time is too fast and the black and white materials (spray-type composite materials are composed of a combination of polyether and isocyanate, commonly known as white materials and black materials) have too large viscosity differences.
2. The foam is soft. Check the ratio of black and white materials, usually caused by too much white material. It is recommended to perform a free foaming test according to the correct ratio. If it is still soft, you can appropriately increase the proportion of black material. If it is still soft, you need to check whether the amine ether (ie, ethylenediamine) should be appropriately added to the raw materials used for white material. The amount of polyether which is a starter).
3. The foam is crispy. The cells at this time are generally coarse, which is caused by the excessive moisture content in the system. If only the surface is crisp, consider whether the difference between the material temperature and the ambient temperature is too large, the material temperature is high, and the ambient temperature is low. Another reason is that the viscosity difference of black and white materials is too large, and there is more black material excess.
4. Low peel strength of foam and substrate. The reasons are as follows: the surface of the substrate is not clean, there is floating ash or oil stain; the substrate is not penetrated, the peeling can see the moisture in the interface; also the substrate temperature is too low, the foaming speed is too fast; "Bottoming" (that is, spraying a thin base layer quickly first), but spraying thicker at one time will also cause excessive tension and peel.
5. The foam is cracking. The cracks can be clearly seen on the site. This phenomenon is mainly caused by the low degree of branching and functionality of the polyether used in the foaming system. Sucrose, mannitol and sorbitol can be added as a starting point Polyether. In addition, the number of spraying layers should be appropriately increased during construction to avoid recurrence.
6. Separation between layers. Non-adhesion occurs at the interface connected by each pass of spraying. The appearance of this phenomenon is related to the system of foaming materials. For example, some flame retardants are not compatible with the foaming system. When foaming, they behave like plasticizers on the surface. Of course, other materials can cause this phenomenon. In addition, too fast or too slow time may cause this phenomenon. It's just not that serious. Sometimes it is caused by the excess of silicone oil surfactant added to the foaming system.
7. Foaming surface. This phenomenon can sometimes appear after spraying is completed, and some only appear after several hours. Seriously, large “bags” will be raised. This is because the type of foaming agent in the foaming material is not compatible with the system. To accumulate the second foaming after the foaming is completed, the foaming agent should be used in combination with polyether and auxiliary agents. The expedient solution to this phenomenon at the construction site is to appropriately increase the number of foaming layers. Reduce heat build-up.
8. The shrinkage of the foam. Sometimes it is a local contraction and sometimes it is an overall contraction. This phenomenon occurs due to the following reasons: the foam density is too small, and the water content is too large, which causes the imbalance of the ratio of black and white materials. It should be noted that the equivalent ratio of the equivalent is imbalanced. 136, so even adding a small amount of water can easily cause imbalance of black and white materials; other reasons are caused by too low temperature; uneven mixing of the machine is also a factor causing local shrinkage.
The above are a few common reasons summarized. If you encounter similar problems, you can refer to them.
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