JPH0221305B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a method for easily recycling a metal tube for adjustment used at the start and end of a powder coating operation in a powder coating metal tube manufacturing process. (Prior art) Metal pipes are widely used for transporting fluids such as gas, oil, water, etc., but for the purpose of corrosion prevention, the outer surface of the metal pipes is coated with powder coating such as polyester resin, epoxy resin, etc., or powder coating such as polyethylene resin. Extrusion coating has become common. Particularly in recent years, the need for powder-coated metal pipes using epoxy resin has been increasing. Such anti-corrosion coating is applied at a metal pipe manufacturing company or a coating specialist company, and then transported to the installation site and used for laying the pipeline. Generally, when applying powder coating to the outer surface of a metal pipe, as shown in Fig. 3, after degreasing and applying a predetermined pretreatment such as shotplast, a fitting 2 with a bevel protection function is attached to the end of the metal pipe 1. , Primer coating is performed while the metal tube 1 is continuously transferred via the aforementioned joint 2 with the conveyor roll 3, and further 230
The powder is heated to around ℃ in a gas or oil combustion furnace or electric induction heating furnace 4, and then discharged from a plurality of electrostatic coating guns to a powder coating chamber 5 which has a high concentration powder coating atmosphere. Introduce. Then, the powder coating is brought into contact with the surface of the metal tube, and after completing the melting and curing reaction, it is cooled in the cooling device 6, and after inspection for pinholes, film thickness, etc. specified by the user, it is finished and packed. It becomes a product. In this case, there are two methods for the conveyance roll 3: one is to place the metal tube on a V-shaped roll and move it straight, and the other is to place the metal tube on a skew turning roll and convey it simultaneously with rotation. The latter is generally adopted due to its ease of design and powder coated chamber design. In addition, the outer shell of the powder coating chamber 5 is designed to accommodate the maximum size of the metal pipe to be coated, and a method is adopted in which the holder of the electrostatic coating gun is moved in and out to ensure the nozzle spacing between the specified metal and the metal to be coated. ing. Powder coatings are made by sucking powder coatings using dry compressed air from a supply tank made fluid with dry air using a ventilator method, and then producing powder coatings such as Teflon, polyethylene, etc.
It is discharged along with pressurized air from an electrostatic gun connected to a nylon or other hose. At this time, the discharge amount is determined by adjusting the pumping air pressure according to the passage area per unit time of the metal pipe to be coated and the specified film thickness. (Problems to be Solved by the Invention) Although powder coating of polyester, acrylic, epoxy resin, etc. is applied to the outer surface of a metal tube by the method described above, there are drawbacks as described below. (a) Because it takes time for the high-concentration atmosphere of powder coating to stabilize in the powder coating chamber during coating work, and because heating and other conditions are determined, the metal pipe is the target of the product. It is necessary to start discharging powder paint using a metal tube for adjustment beforehand. For this reason, the outer surface of the adjustment metal tube is also partially coated with strong powder coating. (b) Similarly, at the end of the painting process, stopping the discharge of powder coating while the final metal pipe to be manufactured is located inside the powder coating chamber is problematic in terms of quality assurance. It is necessary to stop discharging the powder coating while the adjustment metal tube is following. For this reason, powder coating is applied to the outer surface of the adjustment metal tube. (c) The adjustment metal tubes in (a) and (b) above are used not only at the start and end of painting work, but also during rework due to equipment failure.
It is necessary to clean the powder coating chamber (usually once every 3 to 4 hours of continuous operation) and to check the discharge rate each time the coating operation is resumed. (d) Powder-coated adjustment metal tubes are only thin in quality, but have almost the same physical and chemical properties as the product, and adhere strongly to the metal surface. When reusing such a metal tube for adjustment, it is necessary to strip off the coating and regenerate it so as not to cause stains or other effects on the powder coating line. Adjustment metal tubes must be prepared in the same size as the metal tubes that are the target of the product, so when considering manufacturing costs, the total number of tubes must be kept as small as possible, and new ones must be prepared at all times. This must be avoided at all costs in terms of manufacturing costs. (e) For powder-coated adjustment metal pipes, the paint film is removed and regeneration is generally carried out off-line at 110°C to 150°C.
After heating it to ℃, it is removed using a powerful electric brush or metal spatula, but it is difficult to completely remove the coating, so it is necessary to perform shot blasting two or three times before it can be regenerated. Become. (f) Conventional recycling methods have had economical and environmental problems such as transportation of regulating pipes, equipment for removing coatings, heat sources, labor costs, and handling. For this reason, in recent years, there has been a demand for higher efficiency in powder-coated metal tubes, and along with the establishment of manufacturing technology for powder-coated metal tubes, there has been a long-awaited emergence of an efficient and economically superior recycling method for metal tubes for adjustment. . (Objective of the Invention) The present invention provides a method for achieving the recycling of the above-mentioned conventional metal tube for adjustment, which is indispensable for manufacturing powder-coated metal tubes, at a low cost, with high efficiency, and without any adverse effects on the powder coating operation. The purpose is to provide (Means for Solving the Problems) That is, the present invention provides an adjustment metal used at the start of the powder coating operation and at the end of the coating operation in the powder coating process of metal pipes that are continuously transferred while rotating. After wrapping 40 g/m ² - 100 g/m ² of aromatic polyamide, nylon, rayon, or polyester nonwoven fabric on the surface of the pipe so that they overlap each other by 1 mm - 50 mm, apply powder coating, and remove the powder using a knife, etc. For adjustment in the production of powder-coated metal tubes, characterized in that the metal tube for adjustment can be easily recycled by making scratches reaching the surface of the metal tube from the painted surface and peeling off the nonwoven fabric from the surface of the metal tube. A method for recycling metal tubes, which includes heating the conditioning metal tube to a melting temperature compatible with the powder coating to be used, prior to wrapping the nonwoven fabric of aromatic polyamide, nylon, rayon, or polyester. This is a method for recycling metal tubes for adjustment during the production of powder-coated metal tubes. The present invention will be explained in detail below. First, the present inventors investigated the chemical coating method and tape wrapping method, which are known in Japanese Patent Application Laid-Open No. 55-66972, as a method for recycling metal tubes for adjustment, which are indispensable when manufacturing various powder-coated metal tubes. As a result, we found that the chemical application method had an impact on ease of application, drying, and powder coating lines, so we focused on the tape wrapping method, and as a result of various studies on the materials, we found that the aromatic We found nonwoven fabrics made of group polyamides, nylon, rayon, and polyester. According to the experience of the present inventors, tapes made of the above-mentioned materials should be heated at temperatures of 220°C to 260°C immediately before powder coating.
Unlike polyethylene or polypropylene tape, it does not cause welding when wrapped around the outer surface of a metal tube heated to ℃. In addition, when wrapped around the surface of a metal tube, such as paper or aluminum tape, thermal expansion may occur and the wrapped tape may become loose, causing damage during the transportation process, or allowing powder to infiltrate from the overlapped portions of the tape. On the other hand, the tape has the property of shrinking in the range of 2 to 3% when wrapped around the outer surface of a heated metal tube, so the tape does not loosen, and as a result, the tape Powder will not infiltrate from the overlapped part. Therefore, the work of winding the tape becomes extremely easy. Furthermore, since the non-woven fabric has pores, even if air is trapped between the tape and the surface of the metal tube when the tape is wrapped around the surface of a metal object, it can be immediately released from the pores, further improving workability. It was found that it has the characteristic of improving As shown in FIGS. 1 and 2, the width of the tape is determined by the width per revolution of the adjustment metal tube 1' and the product metal tube 1, which are conveyed while rotating on the conveyance skew turning roll 3. It is possible to use a nonwoven fabric tape 7 having a width l that is 1 mm or more larger than the running pitch Lp, and it is preferable that the overlap margin of the tape is in the range of 1 mm to 50 mm. However, if it is less than 10 mm, when wrapping the nonwoven tape 7 around the outer surface of the metal tubes 1 and 1',
It may not be possible to reliably obtain the overlapping allowance, which not only makes adjustment during the winding work difficult, but also may cause the powder paint to adhere directly to the surface of the adjustment metal tube 1', but it is possible. The smaller the overlap, the better. Moreover, if it exceeds 50 mm, the winding operation of the nonwoven fabric tape 7 will be easier, but it will be expensive, so it is not a good idea. Furthermore, the nonwoven tape 7 has a weight of 40 g/m ² to 100 g/m ²
If it is less than 40 g/m ² , the nonwoven fabric tape 7 will be too thin and the molten powder paint will leak from the pores of the tape to the surface of the metal tube for adjustment. There is a risk that it will penetrate into the body, making it difficult to weld and regenerate. Moreover, if it exceeds 100 g/m ² , the regeneration effect will not improve, but it will not only become difficult to perform the winding operation but also increase the cost, which is not preferable. (Example) Next, an example of the present invention will be described in detail. Film thickness 400± on the outer surface of a steel pipe with an outer diameter of 30 inches and a length of 12 m.
When applying 50 μm specification epoxy powder paint, the steel pipe that is the product that has gone through the prescribed pre-treatment process is brought close to the adjustment steel pipe in front of it via a joint, and the pipe is rotated at a pitch of 100 mm per rotation. During continuous transfer, immediately after heating to 230°C in a gas heating furnace, a roll of polyester nonwoven tape with a standard weight of 40 g/m ² and a width of 130 mm is placed parallel to the continuously transferred steel pipe, and the polyester tape at one end is Use polyester tape with heat-resistant glue to attach it to the adjustment steel pipe, pull out the polyester tape using the rotational force of the steel pipe, wrap it around the entire surface of the adjustment steel pipe with an overlap of around 30 mm, and wrap the end of the tape in the same way. is fixed with polyester tape coated with heat-resistant glue, and while the adjustment tube wrapped with polyester tape is positioned inside the powder coating chamber, the powder coating starts to be discharged, and the powder coating is continuously applied to the steel tube. At the end of the powder coating process, polyester tape is also wrapped around the adjustment steel pipe that follows the finished steel pipe.
While the adjustment steel pipe was located within the powder coating chamber, the powder coating discharge was stopped. Table 1 shows a comparison of efficiency and other aspects of the recycling method for the preparation steel pipe powder-coated with the polyester tape thus obtained and the conventional recycling method.

[Table] From Table 1, it can be seen that the present invention is significantly superior in all aspects such as efficiency, cost, and working environment. (Effects of the Invention) As a result of manufacturing powder-coated metal tubes by the method for recycling metal tubes for adjustment of the present invention, firstly, a metal tube that is a target of the product can be arbitrarily used as a metal tube for adjustment. Therefore, in addition to the product metal tube, it is only necessary to secure two metal tubes for adjustment, and the need for adjustment metal tubes, which conventionally required 20 or more, is drastically reduced, and as a result, the tube manufacturing yield is significantly improved. There is no need for personnel to regenerate the second adjustment metal pipe. Thirdly, the cost of regeneration is drastically reduced. Fourthly, cleaning of accumulated paint inside the powder coating chamber can be carried out at any time during work. These advantages are extremely beneficial in reducing the manufacturing cost of powder-coated metal pipes.

[Brief explanation of drawings]

Fig. 1 is a plan view at the start of powder coating work according to the method of the present invention, Fig. 2 is a plan view at the end of the same process, and Fig.
The figure is a cross-sectional view of the powder coating process for metal pipes. 1...Metal tube to be the product, 1'...Metal tube for adjustment, 2...Joint, 3...Skewer turning roll for conveyance, 4...Heating furnace, 5...Painting chamber, 6...Water cooling header , 7...Nonwoven tape.

Claims (1)

[Claims] 1. In the powder coating process of metal tubes that are continuously transferred while rotating, 40% is applied to the surface of the adjusting metal tube used at the start and end of the powder coating operation.
After wrapping aromatic polyamide, nylon, rayon, or polyester nonwoven fabrics of g/m ² to 100 g/m ² so as to overlap each other by 1 mm to 50 mm, powder coating is performed, and the powder coating surface is coated with a knife or the like. Recycling of a metal tube for adjustment during manufacture of powder-coated metal tubes, characterized in that the metal tube for adjustment can be easily recycled by making scratches that reach the surface of the metal tube and peeling off the nonwoven fabric from the surface of the metal tube. Method. 2. Powder coating according to claim 1, characterized in that, prior to wrapping the nonwoven fabric as described in the preceding paragraph, the adjusting metal tube is heated in advance to a melting temperature compatible with the powder coating to be used. A method for recycling metal tubes for adjustment during metal tube manufacturing.