Patent Application
20070062617
The invention relates to a method for lowering the coefficient of friction of the surface of metal bands with a coating, especially of tin-plated or chromium-plated steel bands, which are moved with a band speed through a coating installation, as well as to a device for applying a metallic coating onto a steel band, especially a bond tin-plating installation or band chromium-plating installation.
In the production of tinplate, especially in electrolytically operating band tin-plating installations, and in the production of black plate with electrolytic chromium (ECCS), the metal-coated and chemically or electrochemically passivated steel plate (tinplate with tin metal and chromium metal+chromium III hydroxide or ECCS electrolytic chromium coated steel with chromium metal+chromium III hydroxide) is greased after the coating process in order to lower the coefficient of friction of the coated steel plate, in order to make it able to be better processed during subsequent processing. For this purpose, for example, in the production of tinplate in band tin-plating installations, the tin-plated and passivated steel sheet metal band is greased electrostatically after a drying process with dioctyl sebacate (DOS), acetyl tributyl citrate (ATBC) or butyl stearate (BSO), typically with a deposition of 2-6 mg/m2.
Methods for lubricating the surface of coated metals, e.g., tinplate, are described in U.S. Pat. Nos. 2,579,778 and 3,826,675, with an aqueous lubricant emulsion with a pH value between 2 and 6 produced from a weakly ionizable organic acid being used in U.S. Pat. No. 2,579,778, and citric acid ester being used in U.S. Pat. No. 3,826,675.
In band tin-plating installations in which the steel sheet-metal band passes through with a band speed of less than 150 m/min, DOS can be deposited as an emulsion in a mixture of, e.g., 0.8 g/L DOS with 0.08 g/L lauryl ethoxylate in an immersion process after passivation and after rinsing the tin-plated steel sheet-metal band in an immersion tank. The DOS emulsion that adheres to the sheet-metal band surface due to the passage of the tin-plated steel sheet-metal band through the immersion tank is then pinched off and dried with a band drier. However, in fast-running band tin-plating installations, in which the steel sheet-metal band passes through the installation at band speeds of 300 to 600 m/min, the aforementioned DOS emulsion has proven to be disadvantageous because of problems occurring with the distribution of the height of the DOS deposition over the band width, when the pinching rollers, with which the emulsion captured in the immersion tank was pinched, had been in use for a long time and exhibited wear, especially erosion at their edges.
Therefore, an objective of the invention is to provide a method for lowering the coefficient of friction of the surface of metal bands with a coating, especially of a tin-plated or chromium-plated steel sheet-metal band, in which the metal band passes through a coating installation at a high speed and is coated there with the metal coating, with the method being able to be performed with the highest possible throughput and especially at a high band speed.
The objectives of the invention are obtained by a method for towering the coefficient of friction of the surface of metal bands with a coating, especially of tin-plated or chromium-plated steel bands, which are moved with a band speed through a coating installation characterized ill that after the coating process, an aqueous solution of a tenside is sprayed onto the coated metal band moved at the band speed. The objectives of the invention are also achieved with a device for applying a metallic coating onto a steel band, especially a band tin-plating installation or band chromium-plating installation, with a deposition device for electrolytic deposition of a thin metal layer on the steel band passing through the deposition device at a band speed, a passivation device for passivation of the deposited metal layer, a rinsing bath for rinsing the coated and passivated steel band, and a processing device for reducing the coefficient of friction of the surface of the coated steel band, through which the steel band coated with the metal layer passes at the band speed, characterized in that the greasing device comprises at least one tube arranged at a distance from the coated steel band, with the tube having a plurality of boreholes in the tube jacket, through which an aqueous solution of a tenside is sprayed onto the coated steel band passed through the greasing device.
According to the method of the invention, an aqueous solution of a tenside is sprayed onto the moving metal band, especially a steel band, after the coating process, for example, after the electrolytic tin-plating in a band tin-plating installation or the electrolytic chromium-plating in the production of ECCS. Here, the tenside solution is sprayed onto the metal band surface in amounts that are so small that only a thin tenside layer composed of a few molecular layers is adsorbed onto the metal band surface. Here, the sprayed tenside solution is then preferably pinched by means of pinching rollers and then dried. After the pinching of the tenside solution and the drying, a tenside film with a coating of, e.g., ca. 0.1-10 mg/m2 remains on the surface of the metal band.
The tenside preferably involves a non-ionogenic tenside, which is sprayed onto the surface of the coated metal band in an aqueous solution with a concentration of 0.01-20 g/L. However, other tensides, especially anionic-active or cationic-active and also amphoteric tensides, can also be used.
For spraying the aqueous tenside solution onto the metal band surface, an arrangement with a tube with a plurality of boreholes in the tube jacket has proven to be advantageous. Here, the tube with the boreholes is arranged at a distance from the metal band surface and charged with the aqueous tenside solution. This solution emerges through the boreholes and is led in the form of spraying streams onto the moving metal band. Preferably, on each side of the metal band, at least one such tube with boreholes is arranged, through which the tenside solution is sprayed onto the metal band surface opposite the boreholes. The tubes arranged on both sides of the metal band preferably are at a distance of 5-15 cm from the metal band surface. The fluid streams emerging from the boreholes of the tube intersect the surface of the coated metal band preferably at a right angle or especially at an angle in the range from −15° to +15° with respect to the normal, and are pinched by one or more pinching rollers arranged behind the intersection point in the advancing direction of the band.
In one preferred embodiment of the method according to the invention, the spraying of the tenside solution is performed within a vertical tank, which has an open outlet. In the vertical tank, the excess tenside solution, especially the solution pinched off by the pinching rollers, is collected and can flow via the outlet into a storage tank underneath the vertical tank and from there can be supplied for reuse.
With the method according to the invention, the coefficients of sliding friction of tinplate and ECCS are reduced to values required by the specific application.
Below, the invention is explained in more detail with reference to an embodiment, with reference being made to the enclosed drawings. These show:
The section of a band tin-plating installation shown schematically in
Then the tin-plated steel band S is led through a quenching tank 1 via a deflection roller U. In the quenching tank 1, there is deionized water (VE water) with a temperature of 70-95° C. Then the steel band S is led through the passivation device 2 via deflection rollers U at the band speed v, which typically equals between 200 and 600 m/min. The passivation device 2 comprises one to two passivation tanks 2a and optionally 2b, in which is located a passivation fluid, for example, a 10-25 g/L sodium dichromate solution with 50-70° C. bath temperature. The passivation can be performed electrolytically or without current. For the electrolytic passivation, the tin-plated steel band S is polarized as a cathode in the passivation device via a current roller SR and in this way is electrolytically passivated. For the most part, steel plates are used as anodes in the passivation bath.
Then the tin-plated and passivated steel band S is led into a rinsing bath 3 via deflection rollers U. The rinsing bath 3 comprises, in the example in
It is also possible to use the rinsing tank 3a and 3b without spraying tubes as opposite current sinks, with the deionized rinsing water being filled into the rinsing tank 3b and being led from there into the rinsing tank 3a via an overflow. However, the amount of rinsing water necessary for this rinsing arrangement is greater than for the (additional) use of spraying tubes described above.
After the rinsing, the steel band S is led through a processing device 4 at band speed v via deflection rollers U for reducing the coefficient of friction of the surface of the coated steel band S. In the processing device 4, the coefficient of sliding friction of the tun-plated, passivated, and rinsed steel band S is reduced to the values required for later use and processing. The processing device 4 comprises a vertical tank 5, which has in the base a permanently open outlet 6. In the upper region of the vertical tank 5, tubes 11 with a plurality of boreholes in the tube jacket are arranged on both sides of the passing steel band S.
This arrangement is shown in detail in
Behind the tubes 11 in the advancing direction v of the band (thus, above the tubes 11 in
The spacing between the tubes 11 and the tin-plated steel band S equals between 1 and 50 cm and lies preferably at 5 to 15 cm. Each tube 11 has at least one borehole or opening, but preferably, as shown in
The tubes 11 are charged with an aqueous solution of a tenside. The aqueous tenside solution emerges through the boreholes into the tubes 11 and strikes the moving, tin-plated steel band S in fluid streams. According to the distance of the tubes 11 from the steel band S and the position of the boreholes relative to the movement direction of the steel band S, the fluid streams strike the steel band surface either at a right angle or at a falling or rising angle. Preferably, the distance between the tubes 11 and the steel band S is set and the position of the boreholes relative to the movement direction of the steel band is selected so that the fluid streams intersect at a right angle onto the steel band surface or at least within an angular range of ±45°, preferably within an angular range of ±15°, with respect to the normal (perpendicular) band surface.
With the pinching roller pairs 12a, 12b arranged approximately 50 to 100 cm behind the tubes 11 in the advancing direction, the tenside solution sprayed onto the steel band surface is pinched off, so that a tenside layer with only a few molecular layers, possibly only a one-molecule tenside layer, remains on the tin-plated steel band surface.
The excess tenside solution and especially the solution pinched by the pinching rollers 12 from the tin-plated steel band S collects in the vertical tank 5 and flows via the outlet 6 into a storage tank 4 under the vertical tank 5, from where the tenside solution can be supplied for reuse via a pump 8, in that the tenside solution collected in the storage tank 4 is transferred to a tenside application tank 9 and finally pumped back into the tubes 11.
After passing through the processing device 4, the tin-plated steel band S finally passes into a drying device 10, which is formed by, for example, a hot-air drier, via deflection rollers U.
With the previously described processing device 4, tin-plated steel bands were treated with various tenside solutions in different concentrations and tested in terms of their coefficients of sliding friction.
For greasing the tinplate surface, a plurality of surface-active substances are suitable, especially cationic, anionic, non-ionogenic, and amphoteric tensides. Preferably, tensides are used that have meet legal requirements for food use according to FDA §178.9310, FDA §178.3400, and the EG guidelines 2002/72/EG and 1935//2004/EG. For non-approved tensides, an expensive toxicological test and approval is necessary if the steel sheets processed according to the invention are to be used for creating food packages. In addition to the legal approval for food use, also required are good wettability and adhesion of the paint used for coating with the tinplate surface post-treated with tenside, i.e., the tenside used must be tailored to the paints used. Due to the described application via spray tubes 11, the formation of foam by the tensides that are used does not cause interference in the post-processing of the coated steel band.
Comparison tests with the tenside lauryl ethoxylate with 3 EO were performed in a band tin-plating installation that showed the suitability of the described method for large-scale application. This tenside is legally approved for food use according to FDA §178.9310.
It was sprayed in an aqueous solution in concentrations of 1-8 g/L after the passivation and rinsing in the described band tin-plating installation made from two tubes 11 on each band side onto the tin-plated steel band S, with the two tubes 11 each having five boreholes with a 2.5 mm diameter at a distance of 25 cm from each other in the direction horizontal to the band surface. The two tubes 11 were arranged ca. 80 cm in front of a pinching roll pair 12a in the advancing direction of the band at a distance of 10 cm from the steel band surface. The fluid streams extended approximately horizontally from the boreholes in the tubes 11 onto the galvanized steel surface. The fluid streams striking the band surface were visible in the light of a lamp and one could see that the fluid pinched off by the pinching rollers 12 was distributed uniformly over the width of the pinching rollers 12, detached in the form of droplets, and finally fell into the vertical tank 5. The tin-plated steel band samples treated in this way were then analyzed with a Leco C-analyzer at a maximum oven temperature of 400° C. Here, in the scope of the analysis variation, tenside deposits with equal height over the width of the steel band were measured, which corresponded to 3=1.5 mg/m2 lauryl ethoxylate.
In further tests, by varying the band speeds v, the tenside used, and its concentration and various surface roughness values of the tinplate band surfaces treated in this way, tenside film deposits of 3±1.5 mg/m were detected. From this it results that the tenside-containing solution. was pinched up to a no longer detectable fluid film of less than 0.5 mL/m2 of the tinplate surface. In contrast, for tenside-free rinsing water, the fluid film on the tinplate surface is pinched off only up to a residue of 5-10 mL/m on the band surface.
The tenside coating remaining on the tin-plated steel band surface after use of the method according to the invention is composed of the tenside deposit adsorbed onto the band surface, and the coating, which is produced from the thickness of the pinched fluid film and its tenside concentration. In comparison to tinplate rinsed conventionally (that is, with tenside-free rinsing water), the tinplate treated according to the method of the invention has significantly lower energy needs for drying in the drying device connected after the processing device. The energy expense for drying the tinplate band can be reduced even more if the passivation fluid is heated in the passivation tanks 2a, 2b and/or the rinsing water is heated in the rinsing tanks 3a, 3b (for example, to temperatures of 50-70° C., the rinsing water also to temperatures up to 80° C.).
The adsorption time of the tenside solution sprayed onto the band surface according to the method of the invention is sufficiently short to guarantee a uniform adsorption of the tenside film onto the tinplate surface before the pinching rollers 12 pinch the excess tenside solution. Due to the short adsorption time, it is presumably not necessary to spray the fluid onto the tinplate surface as uniformly as possible via fine spray nozzles. Instead, it is sufficient-as provided according to the invention-to spray the tenside solution relatively coarsely onto the wet tinplate surface. The advantage of spraying the tenside solution in the form of thin fluid streams distributed over the width of the steel band is that the risk of forming foam in the tank, in which the excess, especially the pinched tenside solution, collects is significantly lower than that when using spray tubes with nozzles, which would spray the tenside solution in a fine mist onto the tinplate surface. The larger borehole diameters of the spray tubes tend to accumulate less foreign matter than do the smaller diameters of the spray nozzles required for the same application.
The tinplate bands examined in the comparison tests were examined with a three-ball tribometer in terms of their coefficient of sliding friction before and after the treatment according to the invention. Here, the following coefficients of sliding friction were determined for electrochemically passivated tinplate with 2.8 g/m2 tin deposit and stone-finish surface:
The tenside deposit does not reduce the sliding friction of the tin surface as much as does the DOS deposit. However, the sliding friction is good so that scratches and scrapes are not created on the tinplate surface when the tinplate rings break apart and the tables in the next post-processing stage can be cleared of packages without a problem.
However, in contrast to conventional electrostatic greasing of the tinplate surfaces with esters such as DOS, in the tinplate bands treated according to the invention, no tin dust caused by production has been observed. In contrast, especially for tinplate greased with DOS, a dust layer due to production is often observed, which is problematic, because it can be removed only through suitable, complicated, and careful measures during the installation. The reason for the freedom from dust in the method according to the invention can be traced possibly to the rinsing effect of the tenside solution in the application after the passivation and rinsing, as well as to the better adhesion of the tinplate to the surfaces of the non-driven deflection rollers in the second loop tower of the band tin-plating installation. Due to the low slippage of the tinplate with the deflection rollers in the loop tower, in contrast to greasing with conventional substances such as DOS, obviously no tin particles are rubbed off.
Another advantage over greasing tinplate conventionally, for example, with DOS, ATBC (acetyl tributyl citrate) or BSO (butyl stearate oil), is the ability for perfect (pore-free) painting of the tinplate surfaces treated according to the invention after typical storage times (for example, more than 12 months). This advantage can be explained presumably in that the adsorbed tenside molecules do not coagulate into droplets, as is often the case for DOS greasing with >4 mg/m2 in the edge region of the tinplate tables. Paint, which cannot completely dissolve these droplets in the wet film on the tinplate surface, then tends toward formation of pores in the paint layer.
The method according to the invention can also be applied in band tin-plating installations with horizontal rinsing cascades. In these horizontal rinsing cascades, rinsing water is sprayed through spray registers with nozzles onto both band surfaces for each rinsing stage up to 40 m3/h. The rinsing water is then pinched off and flows back into a storage tank under the corresponding rinsing stage, from where it is pumped back into the horizontal rinsing stage. In these horizontal rinsing cascades, the method according to the invention can be used when the spray registers before the last pinching roller pair is replaced by the aforementioned tubes with boreholes, with which the aqueous tenside solution according to the invention is sprayed onto one or both band surfaces. For two-sided spraying of the tin-plated steel band, the tenside solution is sprayed first through a tube arranged above the top side of the band. Second, the aqueous tenside solution is sprayed onto the bottom side of the band, by spraying the tenside solution through a tube with boreholes on the pinching roller adjacent to the bottom side of the band. In this way, the aqueous tenside solution is transported through the gap between the steel band and the pinching roller adjacent to the bottom side of the band, where the fluid mixes with the water film on the bottom side of the band and the band surface is “greased” in this way with the tenside film. Here, the pinched off tenside solution also flows back into a storage tank-as in the described embodiment of the band tin-plating installation with a vertical tank - and can then be reused.
The method according to the invention applied in the processing device 4 of the described band tin-plating installation can be used very generally for reducing the coefficient of friction of metal bands with a metallic coating, e.g., also special chromium-plated steel bands (ECCS).
In the laboratory, black plate sheets with a stone finish surface with 17×20 cm area were
The tin-plated sample was
A: lauryl ethoxylate with 3 EO
B: C12-14 carboxylic acid ethoxylate with 9 EO
C: C10-12 alkane sulfonic acid, Na salt,
D: polyethylene oxide (average molecular weight 6000 Dalton)
The samples were removed from the paint centrifuge and dried with hot air.
On the samples with the various tenside coatings, the following tests were performed:
The painting adhesion was tested after the sterilization test through a cross-cut adhesion test and tesa test according to EN ISO 2409.
The tinplate samples greased with the various non-ionogenic tensides also had low organic deposits with ≦5 mg/m2 like tinplate samples greased electrostatically with dioctyl sebacate in a band tin-plating installation (desired deposit in the tinplate production at industrial scale: 4±2 mg/m2 DOS).
The tin oxide deposits and the chromium deposits of the tinplate samples passivated in sodium chromate solution were within the desired range of commercial tinplate production.
With μ=0.13-0.24, the sliding friction of the tinplate samples greased with tenside or DOS lay significantly under the sliding friction of ungreased tinplate with μ=0.4. The tinplate samples with sliding friction in the range of μ=0.13-0.24 have the same good sliding ability in further processing through painting and shaping in production.
The paint adhesion of the tinplate sample painted with 5 g/m2 paint PPG 3907-301/A and sterilized in various solutions was just as good for the greasing with tenside as for the greasing with DOS.
*cross-cut adhesion test according to DIN EN 2409.
Reference sample, tinplate, electrostatically greased with DOS (mg/m2)
Reference sample, tinplate, electrostatically greased with DOS
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2005 045 033.4 | Sep 2005 | DE | national |
