MXPA03006198A

MXPA03006198A - Process for continuously and chromate free coating a pipe in a fluidized bed.

Info

Publication number: MXPA03006198A
Application number: MXPA03006198A
Authority: MX
Inventors: Scholten Heinz
Original assignee: Degussa
Priority date: 2002-07-23
Filing date: 2003-07-10
Publication date: 2004-12-03
Also published as: EP1384523A1; DE10233345A1; CN1488447A; CA2435690A1; CN100509178C; BR0302592A; JP4360856B2; ES2246443T3; DE50300986D1; ATE302069T1; KR20040010311A; EP1384523B1; JP2004105949A

Abstract

A process for coating pipes comprises vortex sintering using a powdery, meltable polymer as the coating material. The pipe is first cleaned. A primer is then applied and burnt in using a middle frequency induction spool. Vaporized solvent is removed using a radial ventilation unit, and the pipe is pre-heated using an induction spool. A process for coating pipes comprises vortex sintering using a powdery, meltable polymer as the coating material. The pipe is first cleaned. A primer is then applied and burnt in using a middle frequency induction spool. Vaporized solvent is removed using a radial ventilation unit, and the pipe is pre-heated using an induction spool. Powder is prevented from clumping together by air shower members and guide plates. A further induction spool smooths out incompletely melted areas, and an air shower is used to pre-cool the pipe surface. Final cooling takes place in a water bath.

Description

CONTINUOUS PIPE COATING, CHROMATIC EXEMPT, BY SINTERIZED IN PLUIDIZED BED Until now, coated tubes for the automotive industry are produced using chromium VI compounds (chromates). Chromates are used to achieve very good adhesion values in the extrusion process used to date. For this, chromed tubes are used, also the aluminum tubes are chromed; The steel tubes are first aluminized before chroming. However, since 2003, the automotive industry requires chromium-free tubes. The aim of the invention was to provide a new process that would allow continuous, chromium-free tube coating. Processes for the continuous coating of tubes are already known. For example, in the magazine "Kunststoffe", Year 57, Magazine 1, pages 21 to 24, a procedure is described with which tubes are coated with PVC by sintering in a fluidized bed, however, in said magazine there is no mention of good adhesion values or homogeneous coat thickness distributions. With the above, can not meet the fundamental demands of the automotive industry. The disadvantages of the prior art, in particular the adhesion values and the layer thickness distribution, even in the case of thin layers (120 -150 μt?), Could be overcome by a method according to the claims. Preferably, the equipment works automatically and continuously and serves to externally coat tubes by sintering in a fluidized bed. It consists of the following parts: 1) the pre-treatment facility to clean the generally greasy tubes in the condition in which they are delivered; 2) primer adhesion tank to apply the adherent between the steel surface and the plastic layer (spray or immersion equipment); 3) the medium frequency induction coil 1 to dry the primer and, if a solvent primer is used, to evaporate it, - 4) the radial fan to evacuate the evaporated solvent more quickly, - 5) the induction coil of average frequency 2 to preheat the tube; 6) the fluidized bed sintering tank with integrated medium frequency induction coil 3, to apply the coating. Since the coating has a dielectric loss factor that is too small, it does not heat up, while the preheated steel tube that passes is heated very quickly to the desired temperature. In sintering in a fluidized bed, the layer thickness is determined decisively by the preheating temperature and the immersion time. In the case of a passing pipe, the foregoing implies that the layer thickness can be modified by the power of the generator and the speed of advance. Both parameters can be regulated independently of each other in the control desk; 7) the insertions in the fluidised bed sintering tank, which consist of an air shower above the pipe, in order to avoid accumulations of dust, and the direction sheets of the flow under the pipe, in order to avoid shortage of dust and the resulting pores in the lower part of the tube. Only by means of the special inserts can a homogeneous layer thickness be guaranteed both radially and axially; 8) the medium frequency induction coil 4 to smooth the coating not completely melted; 9) the fusion path, required to melt and smooth the adhering coating when the medium frequency induction coil tube 4 comes out. The layer is still hot and soft when passing and, therefore, can be easily injured. For this reason, in this phase the tube can not be transported in rollers; 10) the air sprinkler to precool the surface of the tube. The temperature of the tube surface is thus regulated below the melting point of the coating; 11) cooling with water. The tube passes through a water gutter, in which the layer continues to cool and harden, so that at this point the tube can be moved again in rollers. Depending on the desired layer thickness, the induction coils at points 5, 6 and 8 can be operated in various combinations and powers. The following possibilities of the use of the coils are available: 5 and 8, 5 and 6, 5, 6 and 8, 6, 6 and 8. The tubes are respectively heated by means of medium frequency induction. Approximation formulas are provided for the requirement of electrical energy, the performance of the coating of such equipment and the requirement of dust. With the method, pieces of tube can be attached to a desired length to obtain an endless tube and coated externally in the horizontal passage process with plastic powder. Suitable coating materials are fluidizable polymers, fuses, or mixtures thereof. Especially suitable are polyamide powders, in particular based on polyamide 11 and polyamide 12. In the foregoing, powders produced in accordance with German Patent DE 29 06 647 (Hüls AG), under the trade name of VESTOSINT (Degussa AG), thanks to its production in the precipitation process, achieve a particularly round grain shape. A commercial adhesive is first applied to the surface of the tube. In the foregoing, all customary types for polymers, in particular those for polyamides, are suitable as the primer. They can be applied in solution, suspension or powder. VESTOSINT is particularly suitable for adhesives intended especially for VESTOSINT. If an adherent with solvent is used, with a solids content of approximately 8%, the layer thickness of the ventilated primer is between 5 and 8 μp ?. With the method according to the invention, uniform layer thicknesses of 50 to 1 000 μp can be achieved. Layer thicknesses of 50 to 300 μt are preferred, and variations of + 30% can be achieved with the method according to the invention. A commercial adhesive (for example, VESTOSINT Haftvermittler WS 5) is first applied to the surface of the tube. The layer thickness of the ventilated primer is usually between 5 and 8 μp ?. If an adherent with solvent is used, it usually has a solids content of about 8%. The tubes produced with the process according to the invention are especially suitable as hydraulic and brake lines for, for example, the automotive industry. The process according to the invention is described in more detail below.

Preheating by medium frequency induction The medium frequency induction heating was selected because it is a heating method which, in the step procedure, can be regulated comfortably and, in addition, is very fast, with which it has the additional advantage that the coil of induction that heats the passing tube, can be arranged directly in the fluidized powder, thereby avoiding thermal losses. At 101000 Hz and a tube wall thickness of 2 mm, heating at 300 ° C lasts 1 s. At lower frequencies, the heating is even faster thanks to the greater penetration depth, at 2'000 Hz the time would be only 0.73 s for the same conditions. The induction coil is made as a helical tube and through it passes cooling water; Like the dust, it stays cold. The generator set consists of the machine generator, which generates the high frequency, the control cabinet with control desk, the condenser battery and the induction coil. In a simplified way, the equipment can be visualized as a transformer, in whose primary side high frequency electric power is fed and whose secondary side consists of a single turn, the work piece. The very high current density resulting in the secondary circuit results in rapid heating. In the case of the workpieces that pass, only those with constant cross section and uniform wall thickness, for example, rotating symmetry objects such as wires, tubes, rods and the like, are considered.

Energy requirement and coating performance The speed of passage (advancement) of the tubes depends on the diameter of the tube and the wall thickness, that is, the weight of the tube per unit length, as well as the power of the generator. Of course, also the degree of efficiency of the generator and the necessary heating of the tube play an essential role. Since these last two parameters, however, can be considered constant or, at least, with little variation, the corresponding numerical averages can be assumed. The necessary power of the generator is: At N = G x cc (1) 860? where N is the power of the generator in kW, G is the weight of the tube that passes in kg / h, cp is the specific heat of the steel (~ 0.12 kcal / kg grd.), At is the increase in temperature required of the tube Y ? is the degree of total efficiency of the generating equipment (approximately 0.6 to 0.75). The number 860 results from the conversion 1 kW = 860 kcal / h. If equation (1) is cleared according to G and replaced? = 0.7 and At ~ 240 ° C, an empirical formula is obtained that can be used well for the maximum steel quantity heatable in kg / h with a certain generator power (applicable for the present conditions and for similar conditions): G «20N (2) With an average frequency generator of 36 kW, it could be heated to 240 ° C, therefore, approximately 720 kg / h of steel tube. This calculated value was checked in the example. For approximate calculations, as a reference value for the power requirement (with the present conditions and for similar conditions) applies: W N & 50 (3) kg / h Of course, these empirical formulas are not correct in dimension, since magnitudes subject to dimension (for example, specific heat cp) were used with their numerical values. Even so, these equations of incorrect dimensions have proved to be very useful in terms of operation. If you combine the formulas for the weight of the tube that goes with the formula for the required generator power, for steel tubes with a specific weight y = 7.85 kg / dm3, you get a simple ratio for the highest step speed (advance ) of a tube, which is possible with a given generator power. If, for example, tubes of various diameters and wall thicknesses are often coated on a tube coating equipment, the following formula quickly provides a reference value for the highest step velocity. For other conditions, the numerical factor should be modified slightly: N vmax 18 (4) (da-s) x s In the above, the step speed vmax must be indicated in m / rain, the power of the generator N in kW, the external diameter of the tube gives in mm and the wall thickness of the tube s also in mm.

Example: The tube coating equipment (Figure 01) consists of: 1) the pre-treatment facility to clean the generally greasy tubes in the condition in which they are delivered; 2) primer (adhesion) tank to apply the adherent between the steel surface and the plastic layer (spray or immersion equipment); 3) the medium frequency induction coil 1 to dry the primer and evaporate the solvent; 4) the radial fan to evacuate the evaporated solvent more quickly; 5) the medium frequency induction coil 2 to preheat the tube; 6) the fluidised bed sintering tank with integrated medium frequency induction coil 3, to apply the polyamide 12 layer. Since the PA powder has too small a dielectric loss factor, it does not heat up, while the tube Preheated steel that passes is heated very quickly to the desired temperature. In sintering in a fluidized bed, the layer thickness is determined by the preheating temperature and the immersion time. In the case of a passing tube, the foregoing implies that the layer thickness can be modified by the power of the generator and the speed of advance of the tube. Both parameters can be regulated independently of each other in the control desk; 7) the insertions in the fluidised bed sintering tank, which consist of an air shower above the pipe, in order to avoid accumulations of dust, and the direction sheets of the flow under the pipe, in order to avoid shortage of dust and the resulting pores in the lower part of the tube. Only by means of the special inserts can a homogeneous layer thickness be guaranteed both radially and axially; 8) the medium frequency induction coil 4 to smooth the non-fully fused polyamide layer; 9) the fusion path, required to melt and smooth the polyamide cladding adhered to when the medium frequency induction coil tube 4 comes out. The layer is still hot and soft when passing and, therefore, can be easily injured. For this reason, in this phase the tube can not be transported in rollers; 10) the air sprinkler to precool the surface of the tube. The temperature of the tube surface is thus regulated below the melting point of the polyamide; 11) cooling with water. The tube passes through a water channel, in which the layer continues to cool and harden, so that at this point it can be moved again on rollers. The results of a series of tests on the equipment described are summarized in Table 1. For examples 1 to 7, polyamide 12 precipitation powder of the VESTOSINT 2157 type from Degussa AG was used respectively. In none of the indicated examples a pre-treatment by chrome-plating took place.

Tests of continuous coating of tubes with PA 12 Coil I Primer drying I Coil II Tube preheating Coil III Fluidized bed sintering tank Coil IV Smoothing Coil V Drying primer V Tests on tubes with primer a) TL 222 anticorrosive coatings on brake pipes (surface protection requirements) D-Zn / PA version Corrosion resistance: test duration 500 h with scratch marks according to DIN 53 167; Wb submigration < 2 mm Corrosion resistance: duration of the test 500 h after the stone impact test according to PV 1213; no corrosion of the base metal. Resistance to corrosion: duration of the test l'OOO h; no corrosion of the zinc, no corrosion of the base metal as well as no detachment of the PA layer. Resistance to chemical agents: according to TL point 5; there was no bubble formation or softening of the plastic layer. After venting 24 hours and then rolling around a 16 mm mandrel (360 °), no visible cracks or leaf-like detachments of the PA coating appd. b) Adhesion tests in primed tubes after storage in water, knife tip test: Tubes without streak mark Dry test, one day after coating: very good adhesion.

Dry test, one day after coating in a rolled tube (around 16 mm mandrel): very good adhesion. 3 days of storage in water, very good adhesion directly after extracting. Tubes with scratch marks Dry test, one day after coating: very good adhesion. 3 days of storage in water, very good adhesion directly after extracting. 1 Cleaning equipment 2 Drive 1 3 Primer station 4 Induction 1 (coil I - priming drying) 5 Induction 2 (coil V - priming drying) 6 Radial fan 1 7 Radial fan 2 8 Drive 2 9 Induction 3 (preheat) 10 Support roll 1 11 Fluidised bed sintering tank including induction 4 12 Drive 3 13 TUBE 14 Blow nozzle 15 Support roller 2 16 Water tank 17 Support roller 3 18 Support roller 4 19 Drive 4 20 Drive 5 (track output) 21 Hacker

Claims

1. A process for coating tubes, without chromate, by sintering in a fluidized bed, with the help of fusible, pulverulent polymers, as a coating, characterized in that: 1) the tubes are cleaned in a pretreatment facility, 2) a primer is applied over the tube, 3) with a medium frequency induction coil, the primer is dried and, if a solvent primer is used, it evaporates, 4) a radial fan is used to evacuate the evaporated solvent more quickly, 5) uses a medium frequency induction coil to preheat the tube, 6) with a fluidized bed sintering tank with integrated medium frequency induction coil, a coating is applied, 7) by insertions in the fluidized bed sintering tank, which consist of air sprinkler above the tube, dust accumulations are avoided, and flow direction sheets under the tube, shortage of dust is avoided and the resulting pores in the lower part of the tube, 8) with a medium frequency induction coil, the non-fully melted coating is smoothed, 9) in a melting path, the bonded coating is melted and smoothed, 10) with a air sprinkler, the surface of the tube is previously cooled, 11) by cooling with water, the coating is further cooled and hardened.

2. A method according to claim 1, characterized in that the three induction coils at points 5, 6 and 8, depending on the layer thickness of the coating, are used as follows: use of the induction coils 5 and 8, or use of the induction coils 5 and 6, or use of the induction coils 5, 6 and 8, or use of the induction coil 6, or use of the induction coils 6 and 8.

3. A procedure according to any of the preceding claims, characterized in that polyamide is used as the coating. . A process according to any of the preceding claims, characterized in that polyamide 11 or polyamide 12 is used. 5. A process according to any of the preceding claims, characterized in that polyamide 12 of precipitation powder is used. 6. A process according to any of the preceding claims, characterized in that a commercial adhesive is applied in the form of a suspension, solution or powder. 7. A process according to any of the preceding claims, characterized in that the polymer layer is from 50 to 1 000 μt? and the average variation does not exceed 30%. 8. A process according to any of the preceding claims, characterized in that the polymer layer is 50 to 300 μp? and the average variation does not exceed 30%. 9. A method according to any of the preceding claims, characterized in that the polymer layer is 50 to 300 μtt? and the average variation does not exceed 20%. 10. A chromate-free coated tube, characterized in that a primer layer was applied to the tube and a fusible, fluidizable polymer was applied in the fluidized bed sintering process.