TECHNICAL FIELD OF THE INVENTION

The present invention relates to a coated tube, in particular relates to a coated tube applied for the fluid carrying pipeline system in a vehicle, such as the vehicle brake pipe and fuel pipe with composite coatings.

BACKGROUND OF THE INVENTION

Attributing to the working environment of equipment, its metal members may suffer from corrosion under certain circumstances to influence normal use of a local system or the whole equipment. For instance, as for steel wires, steel strands, pipes and tubes, plates and strips etc. used under adverse circumstances, in particular the tubes applied in the vehicle pipeline system should have better corrosion resistance or should be treated by corresponding protective measures and should be adopted for ensuring their service life.

In the automobile manufacturing industry, most of the vehicle brake pipes and fuel pipes used in the early time in China are copper tubes which are very expensive. In the middle 1980s, the BUNDY pipe welding technology (TI Automotive, Bundy Pipeline System Co., Ltd.) was introduced from abroad to China. Hereby, a copper-plated strip of low carbon steel is rolled and welded to form a double layer welded tube, or a low carbon steel strip is rolled to form a monolayer welded tube via upset butt welding. Such double layer welded tubes and monolayer welded tubes have been widely applied for vehicle brake systems and vehicle fuel pipeline systems to replace the expensive copper tubes.

With the development of new materials and new production processes, Zinc-Aluminium alloys, regarded as a corrosion-resistant coating material, have been applied for steel-based parts possessing properties of both Aluminum (which separates the steel from the environment to function as a barrier protective layer) and Zinc (which is regarded as sacrificial anode to have an electrochemic protective function). Especially, as compared with the traditional hot-dip galvanization coating, the Zinc-Aluminium alloy provides better anti-corrosion ability in various atmospheric environments. In the 1980s, a new Zinc-Aluminium coating material i.e. the called Galfan (coating of an alloy combining zinc, 5% aluminum plus rare earth metal) was successfully developed and commercialized in foreign countries. The Galfan, which has been applied widely in recent years, possesses excellent corrosion-resistant performance and good processing and welding properties. On this basis, some manufacturers of automotive have conducted advantageous exploration and research to obtain practicable vehicle pipes, such as brake pipes and fuel pipes etc.

For instance, the Chinese utility model patent CN2932004Y discloses a tube having a nylon coating for brake and fuel pipes of a vehicle, wherein a double layer coil-welded tube is successively adhered with four layers of coatings which are zinc or Galfan alloy, passive film, adhasive and nylon. The key point of the utility model is adopting the nylon coating having a larger thickness to provide friction resistant ability and sand or stone impact resistance ability and to have the function of protecting the inner layer of the tube. Simultaneously, the application of the nylon material per se reinforces the total corrosion resistance of the tube. According to one optional solution of the utility model, if zinc is adopted for the first layer of coating, especially in the joint area at the end of the tube, when the nylon coating is stripped off, the tube becomes a common zinc galvanized tube which cannot meet the corrosion-resistant requirements of the vehicle pipeline. According to another optional solution of the utility model, the Galfan alloy is adopted for the first coating, wherein the alloy material per se can improve the corrosion resistance, but this effect is limited by the existing production technology level. Deficiencies such as plating leakage, pin holes etc. occur easily, and thus there is still the problem of corrosion of the tube. With regard to the vehicle pipeline parts, the application of the Galfan alloy together with the nylon cannot achieve the satisfying effects all the time, which will be further explained in the following text.

The TI Automotive provides a called Nygal coating tube applied for the vehicle brake and fuel pipeline system, which tube is formed by coating a base tube (a monolayer welded tube or a double-layer tube) with a layer of Galfan alloy coating and a layer of nylon coating. Generally, the thickness of the Galfan alloy (Zn-5% A1) coating is equal to or larger than 3 microns, and the average weight of the alloy coating is 50-60 g/m ² . Then, the nylon primer (1-2 micron(s)) is coated, and then the PA (Nylon) coating (>120 microns) is extruded, and finally, the brake or fuel pipe with the Galfan alloy coating and the nylon coating is formed. It is found out in practice that the above-mentioned coating tube still has the following deficiencies:

-The Galfan alloy coating, as most of the alloy coatings, formed by a hot-dip process contains pin holes, which directly influences the corrosion-resistance property of the coating. Generally, red rust is generated in the Galfan alloy coating in 100-160 hours in the neutral salt spray test;

-The corrosion resistance of the Galfan alloy coating is directly correlated with the thickness of the coating. The thicker the coating is, the better its corrosion resistance is. However, under the condition of the existing processing and equipment, it is hard to produce the Galfan alloy coating with an increased thickness. Hence, the corrosion resistance is limited. In particular, the corrosion resistance of the tube at the end is limited. Due to the nylon coating being stripped off when the joint structure is processed, the corrosion resistance of the joint structure depends directly on the thickness of the zinc layer or the Galfan alloy coating (or in other words, the total amount of the zinc element as the sacrificial anode).

- Attributing to the fact that pin holes can be easily formed after the Galfan alloy coating process in the following cooling and drying processes it is possible that trace moisture may remain in the pin holes. Under such circumstances, coating the nylon primer or the nylon coating will readily result in bad adhesion force. Hence, the requirements of the following treating process conditions are extremely strict; otherwise, the tubes possessing enough composite strength cannot be produced.

SUMMARY OF THE INVENTION

The object of the present invention is to provide a coated tube, in particular a coated tube for a fluid carrying pipeline system in a vehicle, wherein the deficiencies of the existing technologies mentioned above are overcome, and requirements of the application performance and service life of the pipeline system of top vehicles, such as the braking pipe and the fuel pipe, can be satisfied. The coated tube shall be provided with an improved corrosion resistance property and composite strength between laminates, and simultaneously, its good processing and forming property and mechanical loading performance shall be maintained. In addition, the production of the coating tube shall be based on the existing processes, equipments and conditions, so that it is easily and economically feasible.

To be specific, the present invention provides such a coated tube wherein the coated tube comprises: a base tube; and a zinc-aluminum alloy coating, a nylon primer coating and a nylon coating coated and arranged outwards from inside on the base tube, characterized in that a pre-plating zinc layer is added and provided between the base tube and the zinc-aluminum alloy coating, and a sealant coating is coated between said zinc-aluminum alloy coating and said nylon primer coating.

The core concept of the technical solution of the present invention lies in comprehensively considering and rationally arranging the coatings and the configuration of the coatings in the coated tube to form a new composite coating structure having outstanding properties. In order to increase the thickness of the sacrificial anodes coating, i.e. increasing the total amount of the zinc element, a pre-plating zinc layer is arranged between the base tube and the zinc-aluminum alloy coating, so as to form a double layer sacrificial anode coating which provides better electrochemical corrosion protection. The coating has a double layer structure that can be produced on a hot dipping production line (for instance, the hot dipping production line for the brake or fuel pipeline of vehicles). Besides, coating the sealant coating on the zinc-aluminum alloy coating eliminates effectively the pin hole forming on the surface of the hot-dipped coating to avoid remaining of moisture after the succeeding drying process and to facilitate the attachment of the following layer of nylon primer, such that adhesion of the nylon coating is improved.

Advantageously, the thickness of the pre-plating zinc layer is 1-2 micron(s).The thickness of said nylon primer coating can be 1-2 micron(s), and the appropriate thickness of said nylon coating is equal to or larger than 120 microns, so as to satisfy the requirements of wear and impact resistance of brake or fuel pipeline in particular for top vehicles. PA 11 or PA 12 can be selected as the nylon material.

In order to realize the object of the present invention, according to one aspect of the present invention, a coated tube is provided, comprising a base pipe and an alloy coating outside the base pipe, characterized in that said coated tube further comprises a thin seal coating outside the alloy coating, and an epoxy resin coating outside the thin seal coating.

According to one embodiment of the present invention, said epoxy resin coating can be an aluminum-rich epoxy resin coating having a thickness that is equal to or more than 3 microns.

According to one embodiment of the present invention, the average weight of said aluminum-rich epoxy resin coating can be equal to or more than 10 g/m ² .

According to one embodiment a polypropylene (PP) coating is added and provided outside said nylon coating or the coated tube comprises a polypropylene coating located outside the epoxy resin coating. Preferably, the polypropylene coating is formed by extruding PP to enclose the nylon coating or to enclose the epoxy resin coating.

According to one embodiment of the invention said polypropylene coating has a thickness of at least 0.825 mm.

According to one embodiment of the present invention, the thickness of said polypropylene coating can be 0.9 to 1.1 mm.

According to one embodiment of the present invention, said seal coating can be a sealant coating having a thickness ranging from 0.5 micron to 1 micron, comprising such as a mixture of polyvinyl alcohol and phosphate or a polyvinyl butyral resin coating. Functional components can be incorporated into the sealant coating if necessary.

According to one embodiment of the present invention, said alloy coating can be a Galmeg coating having a thickness equal to or more than 3 microns. The Galmeg coating is a special specified alloy developed by Bundy Pipeline System Co., Ltd., TI Automotive (China), which comprises Zn-(5-7%)Al-(2.5-3.5%)Mg and several special rare earth elements (0.03-0.50%). Such an alloy material is known from the invention patent applications CN101875255A and CN101876015A.

According to one embodiment of the present invention, the average weight of the Galmeg coating can be 50-60 g/m ² .

According to one embodiment of the present invention, said base pipe can be a welded double-layer pipe or a welded monolayer pipe.

According to one embodiment of the present invention, said coated tube can have an end provided with a joint structure.

According to one embodiment of the present invention, said coated tube comprises profiled portions, such as a flaring portion and a curved portion, at the end.

The technical solution according to the present invention can achieve advantageous technical effects, including at least a reduction or elimination of pin holes formed in the hot-dipped plating of the coated tube and an improvement of the corrosion resistance, wear resistance and impact resistance of the coated tube and thus prolong the service life of the coated tube.

For instance, by means of adopting a sealant, the pin holes on the surface of the hot dipped coating are eliminated effectively; usage of the Galmeg coating in combination with the seal coating improves the anti-corrosion property effectively; furthermore, due to the seal coating, the effects of pin hole forming is at least weakened or effectively eliminated, such that the coating of the aluminum-rich epoxy resin coating is simpler and more feasible, and the adhesion of the coatings of the coated tube is significantly improved. Furthermore, the extruded outer polypropylene coating improves the corrosion resistance, wear resistance and impact resistance of the coated tube and thus prolongs the service life of the coated tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Technical solutions of the present invention will be further explained in the following text with reference to the preferred embodiments shown in the enclosed figures. Respective enclosed figures are only schematic and are not drawn strictly according to the actual proportions or sizes, wherein

Figure 1 shows a schematic view of the cross section of the known Nygal coating tube in the prior art;

Figure 2 shows a schematic view of the cross section of the coating tube of the present invention in a first embodiment;

Figures 3-7 show schematic views of the end structures of the tube according to Figure 2 in a plurality of application examples of the coated tube of the present invention;

Figure 8 is a schematic view of the cross section of a coated tube of a second embodiment of the invention and

Figures 9-12 show the schematic view of end structures of the coated tube according to the second embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Figure 1 (the prior art) shows a schematic view of the called Nygal coating tube of the TI automotive. This tube is formed by coating a layer of a Galfan alloy coating 3 and a layer of nylon coating 6 on a base tube 1 (a monolayer welded tube or a double layer tube). Generally, the thickness of the Galfan alloy (Zn-5%A1) coating is equal to or larger than 3 microns, and the average weight of the alloy coating is 50-60g/m ² . Subsequently, the tube 1 is coated with a nylon primer 5 (1-2 micron(s)), and then a PA (nylon) coating 6 (> 120 microns) is extended on the tube 1 to finally form the brake or fuel pipe with the Galfan alloy coating and the nylon coating.

The following explanations with respect to the present invention are only schematic and do not constitute limitations to the disclosure of the present application as well as usage of the present invention.

Figure 2 shows a schematic view of the cross section of a coated tube of the present invention. The coated tube comprises a base tube 1 constituted by a double layer welded tube or a monolayer welded tube, and a pre-plating zinc layer 2, a zinc-aluminum alloy coating 3, a sealant coating 4, a nylon primer coating 5 and a nylon coating 6 and a polypropylene coating 7 coated outwardly from inside on the base tube 1.

According to the preferred embodiments of the present invention, it is suitable to select the Galmeg alloy, developed by the TI Automotive (China), Bundy Pipeline System Co., Ltd., for said zinc-aluminum alloy coating, and the polyvinyl butyral resin coating for said sealant coating. The manufacturing process of the coated tube is as follows: uncoiling the base tube 1 , treatment before hot galvanizing by induction heating, hot-dip plating zinc, cooling, drying, induction heating, hot-dip plating Galmeg, cooling, drying, coating the sealant coating, thermosetting, coating the nylon primer, thermosetting, extruding PA (nylon), thermosetting, cooling, drying, curling the composite coating tube. In order to obtain improved protective properties of the coated tube, the following processing procedures are further carried out: uncoiling the composite coated tube, straightening, extruding PP (polypropylene), cooling, straightening, testing the joint, straightening, on-line shearing, fixing the lengths of the straightened tube with the polypropylene coating.

Accordingly, for instance, on the hot dip plating production line of the vehicle brake pipeline or fuel pipeline, the tube is first pre-plated with a zinc plating having a thickness of 1-2 micron(s) outside the base tube, and then the Galmeg coating (the thickness is equal to or larger than 3 microns, and the average weight of the coating is 50-60g/m ² ) is applied to the tube. The thickness or the coated amount of the Galmeg herein, as mentioned in the prior art, is still at the level that can be readily achieved by the existing processing and equipment. However, after the double superposing of the pre-plating zinc layer and the Galmeg coating, the thickness of the sacrificial anode protective coating is increased so as to achieve an improvement of the anti-corrosion property.

On the Galmeg coating there is deposited polyvinyl butyral resin to form a thin layer of sealant coating having a thickness of 0.5-1 micron to effectively eliminate the pin holes on the surface of the hot dipped coating. Due to the elimination of the pin holes, it is not easy for moisture to remain after the subsequent drying in the coating, so that the attachment of the next layer of nylon primer, such that adhesion of the nylon coating can be simplified.

Experiments indicate that the red rust does not appear in the hot dip plating zinc and Galmeg coating in combination with the sealant (polyvinyl butyral resin) coating during a neutral salt spray test for 600-1600 hours. It can be seen that the coating structure formed by the associated application of the hot dip plating zinc, the Galmeg coating and the sealant effectively improve the anti-corrosion property.

On the basis of the hot dip plating zinc, Galmeg coating and sealant (polyvinyl butyral resin) coating, the nylon primer and the nylon (PA) coating having a thickness that is equal to or larger than 120 microns are further coated to finally form a composite coated tube. It is shown in the experiments that after the neutral salt spray test for more than 12000 hours, there is no red rust generated on the surface of the composite coated tube, and the surface of the tube is still bright. It can be seen that the anti-corrosion property is significantly improved. Besides, viewed from the whole aspect, adhesion of respective coatings is good, and wear resistance and impact resistance are improved largely, such that the requirements of the brake pipe or fuel pipe for top vehicles can be satisfied.

On the basis of the composite coated tube, the polypropylene (PP) is further applied as a coating having a thickness of at least 0,825 mm to form a reinforced composite coated tube. With the polypropylene coating, there is provide a new type of coated tube showing better wear resistance, impact resistance and corrosion resistance adopted for stricter use conditions to satisfy requirements of the brake pipe or fuel pipe performance for top vehicles.

After removing of the polypropylene coating (if necessary, after further removing of the nylon coating), said composite coated tube can satisfy the subsequent processing requirements (forming processes such as flaring, bending etc.) of brake pipes, fuel pipelines of a vehicle, such that the required deformation processing and manufacturing precision can be achieved. Figures 3-7 show schematic views of end structures of the tube in a plurality of application examples of the coated tube of the present invention. Certainly, the specific configurations and sizes (unit: mm) in the figures as shown below are only schematic and have no limitation function.

6.35DW EPSILONII Z183 Figure 5

7.94SW J1/300C/R2 SAE QC Figure 6

9.53SW R2 X-B PS-7254 Figure 7

The tube produced hereby satisfies requirements of application performance and service life of the pipeline systems of top vehicles such as the brake pipes or fuel pipes. Particularly, the weak areas at the end portions also possess outstanding anti-corrosion property.

Furthermore, the tube can satisfy the stricter requirements from the aspects of wear resistance, impact resistance and protective performance of the tube for top vehicles or vehicles used under adverse environments.

Figure 8 shows a schematic view of the cross section of a coated tube of the second embodiment of the present invention.

As shown in Figure 8, the coated tube according to the second embodiment of the present invention is generally designated by the reference sign 10. The coated tube comprises a base pipe 11 and an alloy coating 12 formed outside the base pipe 11. Said coated tube further comprises a thin seal coating 15 outside the alloy coating 12, an epoxy resin coating 17 located outside the thin seal coating 15 and a polypropylene coating 19 located outside the epoxy resin coating 17.

For example, the coated tube can be obtained by the following steps: Firstly, the Galmeg alloy for example made of the TI company is provided for the hot-dip plating production line for the vehicle brake pipeline and/or fuel pipeline, and the Galmeg coating is coated outside the base pipe (which can be a welded double-layer pipe or a welded monolayer pipe) to produce the Galmeg coated tube. As mentioned above, the Galmeg coating is a special alloy developed by the TI company and comprises Zn-(5-7%)Al-(2.5-3.5%)Mg and several special rare earth elements (0.03-0.50%). Reference can be made to the invention patent applications CN101875255A and CN101876015A of the applicant of the present application. Then, a sealant (the mixture containing polyvinyl alcohol and phosphate, or polyvinyl resin) can be employed to form a rather thin layer of seal coating over the Galmeg coated tube. Subsequently, the aluminum-rich epoxy resin coating can be applied over the seal coating surrounding the Galmeg coating. Then, a polypropylene coating can be extruded surrounding the aluminum-rich epoxy resin coating and closing in the seal coating and the Galmeg coating.

The aforementioned coated tube can be produced by means of the following process: uncoiling the base pipe; conducting induction heating before hot-dipping; hot-dip plating the Galmeg coating enclosing the base pipe; cooling and drying; applying a seal coating enclosing the Galmeg coating; drying or conducting thermosetting treatment; applying the aluminum-rich epoxy resin coating outside the seal coating; then thermosetting, cooling and drying sequentially; and finally coiling. After that, the prepared tube is uncoiled and straightened, wherein the PP coating is extruded, and the steps of cooling, straightening, testing the joint, straightening, on-line shearing are conducted sequentially to provide a straight pipe with a certain length.

The Galmeg coating can have a thickness equal to or more than 3 microns, and the average weight of the coating can be 50-60g/m ² .

The thickness of the seal coating formed by a sealant can be 0.5-1 micron.

The aluminum-rich epoxy resin coating can have a thickness equal to or more than 3 microns, and the average weight of the coating can be equal to or more than 10g/m ² .

The thickness of the polypropylene coating can be 0.9 to 1.1 mm.

Due to the sealant being applied to form a rather thin layer of seal coating (this layer of seal coating can have a thickness of 0.5-1 micron) over the Galmeg coating, forming of pin holes on the surface of the hot-dipped coating are at least reduced or eliminated.

A neutral salt spray test for 500-1500 hours shows that the red rust is not generated for the Galmeg coating together with the seal coating. Thus it can be seen that the combination of the corrosion resistant alloy and the sealant of the present invention effectively improves the anti-corrosion property.

The aluminum-rich epoxy resin coating is applied over the seal coating which is applied on the Galmeg coating, wherein the pin holes are effectively eliminated due to the seal coating, such that the aluminum-rich epoxy resin coating can be applied in a simpler and more feasible way, and the adhesion of the coatings of the coated tube are significantly improved.

No red rust is generated on the surface of the coated tube after a neutral salt spray test for more than 3500 hours, as indicates that the anti-corrosion property is improved obviously.

By further extruding the PP coating, better chemical corrosion resistance, wear resistance and impact resistance can be obtained, and the service life of the product can be significantly prolonged.

This kind of coated tube can be used for the brake and fuel pipeline systems of middle and top-grade vehicles.

This kind of coated tube can satisfy requirements of subsequent processing, flaring, curing and forming of the vehicle brake and/or fuel pipeline. For instance, an end of the coated tube can be provided with a joint structure which can includes a flaring portion.

Figures 9-12 show schematic views of the end structures of the coated tube of the present invention.

Examples of the end processing are listed in the following table. However, the present invention is not limited to this.

PIPE SIZE APPROVED STANDARD FLARING CODE FLARING FORM

4.75DW SAEJ533b Z183 Figure 3 4.75DW DIN74234-F Z822 Figure 4

6.35DW Ford Copperhead Z606 Figure 5

6.35SW BC2 TDC Figure 5

7.94SW Ford Copperhead Z183 Figure 6

The embodiments of the present invention have been explained with reference to the drawings. An ordinary person skilled in the art should understand that the specific features as mentioned above are merely illustrated as examples and are not intended for limiting the present invention. Furthermore, it is obvious for an ordinary person skilled in the art to use the features as mentioned above separately or in combination in any possible manner to constitute new technical solutions, or make other alterations, wherein all of them fall into the scope of the present invention.