Varinishing process is the process of applying enameled wire paint to metal conductors to form a uniform paint layer with a certain thickness.
1) Viscosity When the liquid flows, the molecules collide with each other to make one layer of molecules move with another layer of molecules. Due to the mutual force, the latter layer of molecules hinders the movement of the previous layer of molecules, thus showing activity. The stickiness is called viscosity. Different coating methods and different wire specifications have different requirements for the viscosity of the paint. The viscosity is mainly related to the molecular weight of the resin. The higher the molecular weight of the resin, the higher the viscosity of the paint. It is used to coat thick lines, because the mechanical properties of the paint film obtained with a higher molecular weight are better. The low viscosity is used for coating thin lines, the molecular weight of the resin is small and it is easy to coat evenly, and the paint film is smooth.
2) Surface tension There are molecules around the molecules inside the liquid, and the gravitational force between these molecules can reach a temporary equilibrium, while a layer of molecules on the surface of the liquid is attracted by the liquid molecules on the one hand, and its force is directed to the depth of the liquid. On the other hand, it is attracted by the gas molecules, but the gas molecules are less than the liquid molecules, and the distance is farther, so the molecules on the surface layer of the liquid are strongly attracted by the liquid inside, so that the surface of the liquid shrinks as much as possible, forming a bead shape. A sphere has the smallest surface area in a geometry of the same volume, and if the liquid is not acted upon by other forces, it will always be spherical under surface tension.
According to the effect of surface tension on the surface of the paint liquid, the uneven surface has different curvatures everywhere, and the positive pressure at each point is unbalanced. Before entering the enameling furnace, the paint liquid in the thick part flows to the thin part under the action of surface tension, so that the The paint liquid is uniform, and this process is called the leveling process. In addition to the leveling effect, the uniformity of the paint film is also affected by the effect of gravity, which is the result of the combined force of the two.
After the lacquered wire comes out of the felt, there is a rounding process. Because the wire is coated with paint and passed through the felt, the shape of the paint liquid is olive-shaped. At this time, under the action of surface tension, the paint liquid overcomes the viscosity of the paint liquid itself and turns into a circle in an instant. The rounding process of the paint liquid is shown in the figure:
1—The painted wire is in the felt 2—The moment it comes out of the felt 3—The paint liquid is rounded due to surface tension
If the size of the wire is small, the viscosity of the paint is small, and the time required for rounding is also less; if the size of the wire is increased, the viscosity of the paint is also increased, and the time required for rounding is also larger. In high-viscosity paint, sometimes the surface tension cannot overcome the internal friction of the paint liquid, resulting in uneven paint layer.
After the lacquered wire exits the felt, there is also a problem of gravity during the rounding process of the lacquer layer. If the rounding time is very short, the sharp corners of the olive shape will disappear quickly, the influence of gravity will be very short, and the paint layer on the wire will be relatively uniform. If the rounding time is longer, the sharp corners at both ends will exist for a longer time, and the gravity action time will also be longer. At this time, the paint liquid layer at the sharp corners has a tendency to flow downward, which will thicken the paint layer in local areas and cause the surface The tension in turn causes the paint liquid to be pulled into a spherical shape and become particles. Since the effect of gravity is very prominent when the paint layer is thick, each layer of paint should not be applied too thickly.
When the thin thread is coated thickly, it shrinks under the action of surface tension to form wavy or bamboo-shaped wool.
If there are very fine burrs on the wire, under the action of surface tension, the burrs are not easy to be painted, but also easy to lose and thin, resulting in pinholes of the enameled wire.
If the round wire itself is oval, under the action of additional pressure during painting, the paint layer will be thinner at the two ends of the long axis of the ellipse and thicker at the two ends of the short axis, resulting in significant unevenness. The out-of-roundness of the round copper wire should meet the requirements.
When air bubbles are generated in the paint, the air bubbles are the air wrapped in the paint liquid during the stirring and feeding process. Due to the small specific gravity of the air, it rises to the external surface by buoyancy, but due to the surface tension of the paint liquid, the air cannot be absorbed. It breaks through the surface layer and stays in the paint liquid. This paint liquid with air bubbles is coated on the surface of the wire and enters the enameling furnace. After heating, the air expands sharply, and when the surface tension of the paint liquid is reduced due to heat, it rushes out of the surface. The surface of the enameled wire is not smooth.
3) Wetting phenomenon The mercury droplets shrink into an oval shape on the glass plate, and the water droplets spread out on the glass plate to form a thin layer with a slightly convex center. The former is a non-wetting phenomenon, and the latter is a wetting phenomenon. Wetting phenomenon is a manifestation of molecular force. If the gravitational force between liquid molecules is smaller than the gravitational force between the liquid and the solid, the liquid will wet the solid, and the liquid can be uniformly coated on the surface of the solid; if the liquid molecules If the gravitational force between the liquid and the solid is greater than the gravitational force between the liquid and the solid, the liquid cannot wet the solid, and the liquid will shrink into a clump when it is coated on the surface of the solid. All liquids each wet some solids and not others. The angle between the tangent of the liquid surface and the tangent of the solid surface is called the contact angle. The contact angle is less than 90° when the liquid wets the solid, and when the contact angle is greater than or equal to 90° the liquid does not wet the solid.
If the surface of the copper wire is bright and clean, it can be coated with a layer of paint. If the surface is stained with oil, the contact angle between the two interfaces of the wire and the paint liquid will be affected, and the paint liquid will change from wet to non-wet to the wire. If the copper wire is hard, the irregular arrangement of the molecular lattice on the surface will have a small gravitational force on the paint, which is not conducive to the wetting of the copper wire by the paint liquid.
4) Capillary phenomenon The phenomenon that the liquid that wets the pipe wall rises in the pipe, and the liquid that does not wet the pipe wall descends in the pipe is called capillary phenomenon. This is due to the effect of wetting and surface tension. Felt painting is the use of capillary phenomenon. When the liquid wets the pipe wall, the liquid rises along the pipe wall to form a concave surface, which increases the surface area of the liquid, and the surface tension shrinks the surface of the liquid to a minimum. Under this force, the liquid level tends to be horizontal, and the pipe The liquid in the tube rises along with it, and the liquid in the tube stops rising until the effect of wetting and surface tension pulling upwards and the weight of the rising liquid column in the tube reach a balance. The thinner the capillary, the smaller the specific gravity of the liquid, the smaller the wetted contact angle, the greater the surface tension, the higher the liquid level in the capillary rises, and the more pronounced the capillary phenomenon is.