JPS6323774A - Method for lining of fluororesin - Google Patents

Abstract

PURPOSE:To apply lining in a uniform thickness regardless of the difference of a film thickness, by heating the fluororesin charged in a material to be lined in two stages at temp. of the m.p. of said resin or less and at temp. of the m.p. of the resin or more. CONSTITUTION:For example, in applying lining to the inner surface of an elbow 5, a jig 8 is fixed to each of the opening parts of the flange parts at both ends of the elbow 5 in which a predetermined amount of a powdery heat-meltable fluororesin is preliminarily charged and set to a molding machine. Next, the fluororesin is heated at temp. 5-10 deg.C lower than the m.p. of the fluororesin for about 10-40min while the elbow 5 is subjected to 'off-axis' rotation to average heat accumulation and heat transfer due to the difference of the wall thickness of the elbow 5. Continuously, the fluororesin is heated at temp. about 20-30 deg.C higher than the m.p. of the resin for about 20-30min while the elbow 5 is subjected to 'off-axis' rotation to uniformly raising the temp. of the elbow 5 within a short time. By this method, the molten resin can be adhered to the inner surface of the elbow 5 in a uniform thickness as a lining material 10.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a fluororesin lining method in which the fluororesin is melted and adhered to the inner surface of a material to be lined, such as a piping material, while being rotated on a different axis.

In general, metal piping materials such as steel and cast iron, as well as some containers, are coated or lined with a resin material to ensure corrosion resistance and contamination resistance. ing.

In this case, as the resin material, it is most preferable to use a fluororesin, which has extremely excellent heat resistance, chemical resistance, weather resistance, and good non-adhesion and low friction properties.

Therefore, there is a method of providing a fluororesin coating on the inner surface of the base material, but conventional coating methods include powder coating,
Fluid dip coating method, spraying method.

There are electrostatic coating methods, etc. However, with this type of coating, the film thickness is on the order of microns, and the risk of pinhole formation cannot be eliminated, and the coating process is extremely difficult or impossible if the substrate is hollow or has a complicated shape. be.

On the other hand, the sheet lining method is in practical use as a coating method for millimeters, and although this eliminates the problem of pinhole formation, it requires welding, and stress tends to concentrate in the welded area. There is a high chance of damage. Furthermore, this method cannot be applied to hollow bodies such as the reaction tank shown in FIG. 3, single-shaped tubes, and cross tubes. In addition, loose lining is used for straight or unbranched piping materials, but with this, there is a gap between the lining material and the base material, where internal corrosion of the base material progresses due to gas permeation. There are problems.

Incidentally, as a method for coating the inner surface of a hollow body with a resin material, although it is not currently common, a method using rotational molding has been proposed in some cases. That is, as described in Japanese Unexamined Patent Publication No. 50-76153, this is a method in which resin powder is introduced into a hollow object and heated to a temperature higher than the melting point of the resin material while rotating the object. However, this method has a problem in that the thickness of the coating layer varies depending on the thickness of the base material.

For example, when the inner surface of the elbow 5 shown in FIG. 2 is coated with resin, the thin pipe portion 6 is coated thickly and the thick flange portion 7 is coated thinly. The inventor of the present invention found that this is due to the fact that the heat storage characteristics and heat conduction characteristics differ based on the difference in wall thickness, and that the faster the heat conduction of the tube portion 6, the faster the resin starts to melt around it.

Means to Solve the Problems Therefore, the fluororesin lining method according to the present invention is as follows: (i) The material to be lined is charged with a heat-melting type fluororesin and rotated on a different axis; The first heating step involves heating at a temperature approximately 5 to 10 degrees Celsius lower than the melting point of the fluororesin for approximately 10 to 40 minutes, and (i) the material to be lined is allowed to rotate on a different axis, while at a temperature approximately lower than the melting point of the hot-melting fluororesin. 20-3
It is characterized by comprising a second heating step of heating at a temperature 0° C. higher for approximately 20 to 30 minutes.

In other words, in the present invention, by heating the material to be lined to just below the melting point of the fluororesin in the first heating step, heat accumulation and heat conduction caused by differences in the wall thickness of the material to be lined are averaged out. That will happen. Then, in the second heating step, the temperature of the material to be lined is quickly and uniformly raised to a temperature higher than the melting point of the fluororesin, and the fluororesin is lined with a uniform thickness regardless of the difference in wall thickness.

In the following, one embodiment of the fluororesin lining method according to the present invention will be explained in order of steps with reference to FIG. In addition, the first
The figure shows the state at the time when the fluororesin has finished melting and hardening.

[Setting Step] For example, when lining the inner surface of the elbow 5, the jig 8 is fixed to the flange openings at both ends, tied, and set in a molding machine. The molding machine may be a conventionally used rotary molding machine, as long as it is capable of rotating on different axes and is equipped with heating means. In addition, jig 8
Before fixing the
P.F.A.

Add ETFE powder. The amount to be added is determined by the inner area of the elbow 5 and the thickness of the lining layer.

[First Stage Heating Step] Here, while rotating the elbow 5 on a different axis, the temperature is lowered by about 5 to 10 degrees Celsius from the melting point of the molten fluororesin introduced.
Heat for 40 minutes. The melting point is approximately 305 to 31 for PFA.
In the case of ETFE, it is approximately 265 to 270°C.

This process eliminates heat accumulation due to the difference in wall thickness of the lined material.
This is carried out to average heat conduction and to shorten the time required for the lined material to exceed its melting point in the second stage heating step below.

[Second Heating Step] Next, while rotating the elbow 5 on a different axis, heating is performed for approximately 20 to 30 minutes at a temperature approximately 20 to 30° C. higher than the melting point of the hot-melting fluororesin.

As a result, each part of the elbow 5 uniformly rises to the melting point in a short time, and the molten resin adheres to the inner surface of the elbow 5 as the lining material 10. This adhesion state becomes uniform in thickness even in the thin tube portion 6 and the thick flange portion 7 by passing through the first heating step. Also,
The thickness of the lining layer can be up to the millimeter order.

[Cooling/Rough Finishing Process] Next, the resin is cooled to room temperature by forced cooling or natural cooling to harden the resin. Then, the jig 8 is removed, and the excess resin is cut off along the - dotted chain line A, and the cut surface is finished if necessary.

With the above steps, the inner surface of the elbow 5 is uniformly lined with fluororesin to a predetermined thickness. However, a third heating step may be added. This process is performed by rotating the elbow 5 on a different axis and by approximately 20 to 3
Heat for about 30 to 60 minutes at a temperature 0°C higher. The main purpose of this process is finishing, and it is carried out to smooth the inner surface.

In the present invention, the inner surface of piping materials of various shapes other than the elbow 5, such as T-shaped tubes and cross tubes, can be lined.

In addition, as shown in Figure 3, it is ideal for a hollow reaction tank 1 equipped with supply/discharge holes 2.3.4, and if applied to cylinders, it is possible to supply cylinders without worrying about contamination. It is possible.

Note that any primer may be used as long as the lining material 10 is of a close contact type.

Effects of the Invention As is clear from the above explanation, according to the present invention, since the material to be lined is preheated in the first heating step, heat storage and heat conduction due to the difference in wall thickness are made uniform. In the second heating process, the molten fluororesin adheres uniformly to the entire inner surface, making it possible to produce fluororesin with excellent properties such as heat resistance, chemical resistance, and non-viscosity, which was previously impossible. The inner surface of the hollow body can be lined. Furthermore, the lining layer can be formed to any desired thickness down to the millimeter order, and there is no fear of pinholes occurring.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing an intermediate process product of an embodiment of the fluororesin according to the present invention, and FIGS. 2 and 3 are sectional views of a material to be lined. DESCRIPTION OF SYMBOLS 1... Reaction tank, 5... Elbow, 6... Pipe part (thin wall), 7... Flange part (thick wall), 8... Jig, 10... Lining material.

Claims (1)

[Claims] (1) The material to be lined is heated at a temperature approximately 5 to 10 degrees Celsius lower than the melting point of the heat-melting fluororesin for approximately 10 to 40 minutes while being rotated on a different axis with heat-melting fluororesin placed inside the material. A second heating step, in which the material to be lined is rotated on a different axis and heated for approximately 20 to 30 minutes at a temperature approximately 20 to 30° C. higher than the melting point of the hot-melting fluororesin. A fluororesin lining method characterized by: