DE2251604C3 - Process for hot-dip galvanizing a metal object - Google Patents

Description

SwodnfLTR 'ÄiÄ charcoal the molten zinc against ^ OxydaUon Matic hydrocarbon group means. the ambient air ^ creates a reduction in the end

3. The method according to claim 2, characterized in that the oxidation of the zinc surface is characterized by the fact that the sulfur-containing fluid prevents methyl 25, ι ^ ι, οηηί HiK the presence of mercaptan, CH ₃ -S- H, is used. It is got in professional circles t, ^ H _e 7 b ^ f earlyi

4. The method according to claim 2, characterized in that an aluminum housing in zinc bath \ c "Je, j ™ he records that the sulfur-containing fluid tolerates dimethyl usual processes od ^" .s ^ - ^. ™ ".. disulfide, CH ₃ - S - S - CH ₃ , is used. (M ac hu »Met JJj = ^" * ™ 8J;

5. The method according to one of claims 1 to 4, 30 3rd edition 1948 pp. 191 to 194 u J w. Which is characterized in that an aluminum as hard zinc formation should inhibit ("BIech" 1967 No. 1, alloy containing zinc melt ^^^ SJS ^^ oSS ^ & is used. Scnau rur oicuivciaiu _QA % ■, i _Q7 n Mr S ¹ ^ 8 ^ hpi

lung e. V. Düsseldorf «, Vol. 21, 1970, No. 5, ί>. 8 i), at

35 the use of such a, in particular fat-soaked, hollow carbon body layer on the zinc bath

The invention relates to a method of being used as a stripping layer that led to the galvanized Hot-dip galvanizing of a metal object, e.g. B. wire, wires or other galvanized objects tes or tape. having bad looks, which gives rise to prejudice

One of the problems that arises concerns the 40 against the presence of aluminum in the zinc bath Control of the zinc layer, which resulted when wetting the in this way of working and the professional circles covered of the metal was tempered by the molten zinc, in these cases zinc baths without aluminum is taken. It is important to use a regular one in order to get the final look you want the and to secure a glossy appearance on the surface of the zinc coating layer. Create layer. It is necessary to take an excessive 45 Among Other Known Means of Influencing would take away from zinc to avoid it having an effect on the meniscus was also the surface of the yerwen of the object during solidification indicated the formation of a layer of rounded grains can not hold suitably what are inert to the trickling down of the molten zinc and aut Zinks down and then to freeze the bath swim, taking the place where the leg Droplet form or to other surface 50 acted object from the molten zinc bath from irregularities leads. In addition, it is necessary, under a non-oxidizing atmosphere, to avoid the entrainment of zinc oxide that will hold. This is the protection against oxidation Forms on the surface of the zinc melt, so as not to get through the material on the zinc bath an acceptable surface appearance to be floated layer, but rather by the non-oxy-rich. 55 ding atmosphere causes while the grains

However, in order to increase the productivity of the galvanizing system only to increase the meniscus, it is always preferable to use high pressure and to produce the wiping effect. It is speed to work. The wires or ribbons make it possible to run heavier grains of larger dimensions at high conveying speeds through the use, so that the meniscus can be printed more effectively after zinc-plating bath and come out of it even with high 60 down. Preferably used speed off. However, due to the roundish grains, in order to achieve a softer and more regular viscosity of the molten zinc the amount of more moderate wiping effect grows. However, the zinc that is carried along increases in size and more rounded shape at the exit speed, which increases the risk of underneath grains penetrating the environment for regularities in the zinc coating. Conse- 6 ₅ molten zinc, so that the contact with this method, the appearance of the excess is with respect alone is not possible, a better compromise zugsschicht requirements imposed to the maximum between the Oberflächengüte- and Fördcrgeschwin-conveying speed is a limit. to achieve skill requirements. For this reason

3 4

So far, a sufficiently thick layer is important. It was also recognized that the ^Ve grains sufficiently small dimensions good results were not simply due to the fact • 7iisanimenwirken with sufficient current that _H2S his shield ⁱⁿ nichtoxvdierendem gas to a good protection function against the ingress of oxygen from the ^V0 V _n forth the ambient air to achieve, and five ambient air in a better way than the nichtoxy- § we will not ή it possible rocketing higher velocity gas to which it was mixed, exercising. To galvanize Hin-SKn than before. against was found to be the reason of the limited

Pine solution to this problem is given, the conveying speed ter to the presence of a SENR u · Z \ while retaining the use of back feeds one by a small residual film of ZnO, oer. eraser end gas-impregnated layer of io can not be avoided, and that even this all ^"1 HLSE. grains consists in that the nichtoxy- thin film ^r even for the limited Fördergeschwin, bark gas deficient introduced into the granular layer resistance and for the coating Good A small proportion of hydrogen sulfide is responsible, so that an additional agent contains verms \ (Australian patent 421751 must be used, not to better prevent the formation of nP PS 7 29 567) This process is intended to protect a higher level of ZnO but allow the ZnO to Reaup-niereeschwindigkeit and found to be still present adorn the same time, fuhs η that glefchwohl a sufficiently good and was and its oxygen atom m «n other dänzendes appearance of the zinc coating is obtained. molecule, not in the form of ZnO. The reason for this positive result is clear

? u SnSn was supposed to confirm this result * »in which a layer of grains and a gas non-oxidizing to the reducing nature of the hydrogen sulphide were used this and also to the formation of a very thin top, but a small amount of M ^^ g Schenfilm! of zinc sulfide contained on the outer surface. It was possible to find a nwkjche JZzi nk? can be attributed to the fact that the object increases in the uläss.gen conveying speed to i J because this film has an effect on the upper a ₅ . Moreover, it was a g ^{b "cozy} Plane 'nspannung de molten zinc has the pulled-out from the color of the zinc coating on GegenJ ^ * ° J ^ J £ ÄLkbid subject with- the ^ e -" ^ ££ ^8e NT'" t ^W, however, hydrogen sulfide not always of still desirable liquid entrained with the article, partly because of the toxic effect of zinc 30 to form a very thin prims msta

s 3 _{Ä Ä}

ÄwEHf «- SfSf-ÄSHss

hydrogen is reached, but the unfavorable conditions of this high <£ ^er ^ _{liquid zinc}

gleiterscheinungcn of hydrogen sulphide ^Hau J ^avoided ^ ^{Γ £} ^ '\ | _{of the} object firmly

will. This is to those who Hochgeschwindigke.ts- on the surface de Geg _e ^ _{def skin}

Galvanizing plants have to have a bigger hold. At oruna ° _nreg el-like, and at

Selection to be given to the hand so that each, na> h ₅ os ndjedodj d «e M g ^^ _{and enables}

the local requirements of security, costs, some btuien, wira _{Djes tnU}

Pushing possibilities, zinc bath construct.on etc. g ^^^^ toAustrittoenfaku. on,

the most favorable choice can be made in each case mainly borrowed in α he in _transition between the

^^ SS ^ ÄKS ^ Ä «and the surface of the

the respectively favorable _transition between

^^ SrS ^ n -nÄKeSn ^ S ₅ Ä « _S and the surface of the

Eat Dräites or Band, from according to which the opposite aridesta _{berdts ge} _

subject matter from the molten zinc bath through to ^ ^0, j / _A ^e _if "X _w i _rdda forth accordance with the invention

borrowed type with the use of a layer of esi is ^ sentncn chemical react.on

α ä ™

The atmosphere around the object removes the zinc from the ZnO with the formation of zinc mercaptide and binds it the oxygen released in this way to the hydrogen contained in its molecule. Hence the Film that forms on the outer surface of the zinc is of little importance whether it is an oxide another metal or another zinc compound as long as the zinc oxide disappears.

The substances that can be used in order to be able to react with the zinc oxide in this way are limited to those substances which, from an energy standpoint, have a tendency to break certain bonds in their own molecule and the Zn - O bond to break such To cause recombination that a lower enthalpy level is established. For this type of substance, however, it is also necessary to be of such a nature that these reactions take place in the limited time of the object emerging from the molten zinc bath and the formation of the absorbed zinc layer. This formation occurs effectively in the meniscus which forms the transition surface between the surface of the zinc bath and the surface of the zinc carried along by the article. The reactions must therefore be able to take place in a fraction of a second. Finally, it is advisable to avoid the use of substances which are disadvantageous or dangerous for other reasons, e.g. B. Too strong acids that attack the plant or the grains, or those substances that lead to the formation of toxic reaction products. Thus, although HCl can certainly react sufficiently quickly with the zinc oxide in the non-oxidizing gas, too many precautionary measures would have to be taken to avoid any corrosion of the system as a result of the use of HCl.

It is clear that the reaction proceeds faster if the substance used is a mobile one Molecule is and where the bond to be broken is easily accessible to the access of the neighboring molecules.

It is not possible to state all substances that can be used to reduce zinc oxide. It is however, possible in any case, a suitable reducing medium in each case taking the following into account Select rules:

a) The additive in the gas introduced into the granular layer is all the more suitable for removing the ZnO, the greater the affinity of certain parts of the molecule of the substance for zinc or oxygen in comparison with the affinity that binds these parts in the molecule of the substance.

b) The additive in the gas introduced into the granular layer reacts faster, the more the to initiate the reaction to be broken bond in the molecule is spatially exposed.

c) The lower its molecular weight, the more suitable the additive in the gas introduced into the granular layer is for rapid reaction. _{However, since H 2} S has already been specified for this purpose, the sulfur-containing gases claimed among others in the present invention _{do not include H 2} S, but must have a molecular weight of more than 34.

When looking for a gas that should be suitable, one should therefore not search for the least probable extend, d. H. a highly exothermic Gas with a high molecular weight and with bonds which, although weak, internally gul against every access is protected.

In accordance with these criteria, fluids containing chlorine and, in particular, sulfur-containing fluids come into play closer examination. Sulfur-containing fluids do in fact contain sulfur, which is present in the molecule through affinity bonds is bound, which are generally weaker than the affinity for zinc. In addition, if the Sulfur to a part of the molecule that has a high affinity for zinc or oxygen, e.g. B. to a hydrogen atom, is bound, the chances of a quick response are even greater.

For example, the methyl mcrcaptan molecule CH ₃ -S 11 contains a CH ₃ -S-TeU, which has a strong affinity for zinc, and in particular an 11-Tcil, which has a strong affinity for the oxygen of ZnO, so that the S - Η- Bond is broken quickly. The methyl mercaptan reacts according to the following equation:
2CHa-SH I-Zn -O- * Zn (S-CIi ₁ )., I-H ₂ O

It should be noted that this first reaction is followed by a slower decomposition reaction which leads to the formation of zinc sulfide, although it is difficult to time these two reactions separate and watch them separately.

Other sulfur-containing gases also meet these criteria, such as B. dimethyl disulfide

(CIl ₁

S-CIi ₁ ),

in which the valence bond between the two sulfur atoms is weaker than the affinity for zinc is. However, dimethyl disulfide is in itself a liquid that must be mixed with the non-oxidizing gas must be evaporated. However, the invention is not directed to a gaseous additive to the non-oxidizing one Gas restricted. A liquid in the form of an aerosol can also enter the non-oxidizing device Gas can be injected. According to a general definition, the ZnO-reducing material in the non-oxidizing gas be in the form of a fluid.

Similar to the methyl mercaptan already mentioned, these are, however, suitable within the scope of the invention more expensive - ethyl mcrcaptan, propyl mcrcaptan and generally substances of the formula R - S - R, in which R represents an aliphatic or aromatic hydrocarbon group, e.g. B. thiophenol. Also are suitable similar to the mentioned dimethyl disulfide, diethyl and Dipropyl disulfide and generally substances of the formula R - S - S - R '. wherein R and R 'are an aliphatic c or an aromatic hydrocarbon group, thus also substances with an aliphatic and an aromatic hydrocarbon group are included are. There are also sulfides of the general formula R-S-R ', such as dimethyl sulfide, dialhyl sulfide etc. can be used, but they are more stable than the aforementioned disulfides and contain only 1 active Sulfur atom per molecule, which is why they form the disulfide lag behind. One can also consider polysulfides of the formula R _ s - S ■ - ... S- R, insofar as they are not too unstable. Ammonium sulfide (NH |) oS is also suitable for reducing zinc oxide. Instead of the sulfur-containing substances explained above, they are suitable for removing the zinc oxide basically also those substances in which the sulfur atom has been replaced in particular by the chlorine atom, however, their use is generally unfavorable because at the same time corrosion factors on the

zinc plant occur. It is possible for professionals to check the suitability of other substances taking into account the criteria mentioned above.

It should also be mentioned that instead of a zinc bath, one with aluminum as an alloy component can be used.

The Iirlinding is explained in more detail using an example in which the covering of four steel wires which run parallel through the bath and emerge perpendicular to the bath surface.

Here, the wire is first subjected to a customary pretreatment that is suitable for any zinc coating treatment. Treatments of this type are sufficiently well known in specialist circles and are e.g. B. in the book by Heinz Bablik, "Galvanising, (hotdip)" Edition E & FN Spon Ltd - London 1950, described. In the selected example, four wires with a diameter of 2.05 mm are unwound in parallel at a constant speed and first run through a bath of molten lead, in which the grease and other impurities on the surface of the wire are burned away. The wires then enter an HCI pickling bath. After rinsing in a bath of whirled up cold water, the wires are placed in a bath known as a "flux bath", in which they are _{moistened in an aqueous bath of zinc chloride and ammonium chloride (ZnCl 2} -NH ₁ CI) and then dried. This treatment favors the adherence of the zinc to the surface of the wire.

Immediately after flux treatment and drying the wires are still parallel and with constant movement in a bath of molten material Zinc introduced. The composition and temperature are as usual. In the example chosen, pure zinc with the inevitable residues of iron and lead at a temperature of approx 450 C used. There is a horizontal one in the bathroom Leadership role. These wires pass under the pulley and then rise vertically to vertically to step out of the bathroom. There is a floating layer on the surface of the bath Cilaskuggets that are round and approximately 3 to 4 mm in diameter. The layer is preferably limited to the part of the surface where the wires exit and to prevent see the balls all over the surface of the Spread zinc, the glass beads are preferred held together within a frame that surrounds the layer over its entire depth and the said Part of the bathroom covers, the wires so through the layer of glass cover within of the frame.

In addition, the zinc transfer solution is with a or several gas inlet pipes equipped, on the one hand with a source of non-oxydicrcndcm Gas are connected and on the other hand at the lower part of the layer of GlaskUgeleh.cn near the point where the wires exit the bath, end and let out the gas. F.in or more pipes can be used here that penetrate the bath of the Kegelehcn and to near the Ausiülsstcllc of the DrIIhIc reach where they have mouths through which the non-oxidizing gas enters the mass of the Kllgeleheti is injected. Obviously, if one uses a frame to hold the balls together, that, in general, every gas incinerator should direct the gas into the interior of the frame and that in particular The tubes should extend into the inside of the frame to keep the wires from the bathroom in one leak in a non-oxidizing atmosphere.

A reducing gas can be used as a non-oxidic gas Gas, such as B. propane, methane or natural gas or natural gas, use, but it is clear that in general any other non-oxidizing gas can also be used. If a poisonous or combustible gas is used, it is evident that the plant with

ίο a suitable drainage and / or incineration system of the gases escaping from the layer of beads or a system to prevent it should be that this gas escape from this layer. For example, the top part of the layer von Kügelehcn be provided with one or more suction pipes, which together with air the from Suck off the lower part of the rising gases and this mixture outside or first to one Discharge the burner. It is also possible to convert the gases emerging from the layer of beads into one Passing the opening over the layer and burning it there in the open air, but this does not eliminate the The need to remove the combustion gases if they are toxic.

The required gas flow rate depends on the thickness of the layer of beads, the dimensions of the beads, the gas introduction system and the viscosity of the gas. The minimum value for this flow rate can be determined for each individual system. A clear indication of this minimum value is given in terms of the entrainment of globules which are stuck in the zinc, which rises with the wire. This is the normal consequence of excessive oxidation of the zinc film on the wire. Preferably, two to three times this minimum flow rate will be assumed in order to prevent any possibility of accidental undesirable oxidation without incurring the wasteful expense associated with an excessively high flow rate. In the chosen example of the four wires with a diameter of 2.05 mm, a layer 15 cm deep was used, which was held together in a frame of 400 a ⁸ ; using 3 to 4 mm diameter beads, it was possible to easily prevent bead entrainment at flow rates of propane introduced into the lower part of the layer of 200 to 700 l / h without any adverse effect

so to prevent flow velocity on the appearance of the zinc film on the wire. A flow rate of 400 l / h was preferably used here.
Obviously the diameter of the balls has an influence on the various functions of the layer. First of all, the balls partly serve to protect the wire against the ingress of ambient air. The use of a smaller diameter of the balls results in a layer which offers greater resistance to the flow of air and reduces the risk of oxidation and the resulting sticking of the balls on the wire. On the other hand, the smaller globules stick to the zinc more easily without being exposed to the

r> 5 kung of their own weight. The usage a smaller diameter thus has two consequences with regard to the risk of being entrained of the spheres in opposite directions

7 (10 830/219

works. In the case of glass beads, this leads to a minimum diameter of approximately 2.5 mm. The minimum value depends on the specific gravity of the material of the beads, the temperature of the zinc, the depth of the layer and the flow rate of the non-oxidizing gas, since these values influence their tendency to stick in the zinc or to fall out of it. The maximum diameter is determined by the wiping action that is to be generated by the beads. If the beads have a diameter that is too large relative to the wire diameter, this wiping effect disappears. Another reason for limiting the diameter of the beads is that if the diameter of the beads is too large, the layer becomes too accessible to the ambient air, which leads to the requirement for an extraordinarily high flow rate of the protective gas. In the example given, for pure zinc at about 45O ⁰ C, a 15-cm layer and flow rates of the propane of 400 l / h and wires with 2.05 mm diameter glass beads may advantageously from about 2.5 to 6 mm and preferably from 3 up to 4 mm in diameter can be used.

The depth of the layer is not critical. Its only function is to push the meniscus down and prevent the ingress of oxygen. The appearance of the wire changes during the tests according to this example not if the depth of the layer is varied from 10 to 30 cm. Preferably a thick layer 30 cm deep is chosen to dampen the vibrations in the wire.

Nevertheless, in order for the method to be suitable for operation at high wire feed speeds, it is again necessary to add a fluid to this non-oxidizing gas, in this case propane, which can reduce the zinc oxide which could still form in the area of the meniscus. In the present example this fluid is a gas, namely methyl mercaptan (CH ₃ - S - H). It can be introduced directly into the layer, but it is preferred to mix it with the non-oxidizing gas before it enters the layer of beads. The amount of methyl mercaptan is of little importance provided that some minimum amount is present. For example, a flow of 5 l / h is sufficient to mix in a flow of 200 to 600 l / h propane. This makes it possible to zinc coat the four wires in this example at a speed of 50 m / min; however, when the methyl mercaptan flow was shut off, the film immediately grew in thickness and became irregular in its surface and took on an unacceptable appearance.

It is not necessary that the atmosphere pass through the entire layer of beads is non-oxidizing atmosphere with methyl mercaptan. Rather, this is sufficient for the area in which the Object exits, d. H. at the point of exit

»5 meniscus and to a level where oxidation of the hot zinc no longer has any influence on the distribution of the zinc. A height of 5 to 30 cm, d. H. optionally the entire depth of the layer of beads will be sufficient.

The results of some tests are given below, for example: wire diameter: 2.05mm; Killed steel wire with 0.033% C; Zinc Temperature: 45O ⁰ C; Immersion length in zinc: 1.80 m; Grains of glass beads.

KUgelchen diameter

3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 3 to 4 6th 6th

Depth of

Spherical

layer

cm

10
20th
35
20th
20th
20th
20th
25th
25th
35
10
35
35
25th
25th
5

15th 30th 20th 20th 10 10

Propane salt

l / h

300

300

300

100 300 300 300 100 300 100 300 500 500 100 100 100 700 700 300 500

Throughput CH ₃ -SH

l / h

10

10

10

10

10

10

15 20 20

5 5 5

10 10 10 conveyor m / min

Secluded Appearance or Weight Bemer kings * g / m » E. E. - E. - E. . E. 350 A. 330 A. 430 D. 530 D. 340 C. 320 C. 350 B. 350 B. 360 B. 470 D. 340 C. 330 C. 330 C. 500 D. 350 B. 450 to 500 D. _ D.

♦ = appearance or remarks

A = t smooth and perfect surfacec

D = smooth and acceptable surface C
D.
B.

40
40
40
20th
20th
25th
25th
40
40
43
43
40
40
40
40
40
40
40
40
40
40
25th

low unrcgclmllOlgkcltcn the thickness of the animal Zlnkschichl The surface is irregular and unacceptable. The balls stick in or on the zinc

It is clear that the invention is neither on the said material nor on the shape of the layer of Grains located on the surface of the molten zinc provided that that these grains are sufficiently inert and heat-resistant to zinc at the bath temperature and are rounded

and are small enough to have a mild and sufficient wiping effect on the wire exiting the zinc bath and that the grains are not too small to prevent them from being entrained with the zinc as it solidifies on the wire.

Claims (1)

It is known that a robust layer of wood claims: ^^^ "^^ 1. Procedure for hot-dip galvanizing of a meta »- by ^ if necessary ^ object. For example, wire or tape, like 5 leaves. ^D f ^, zenL zinc and makes it so which the object from the molten zinc bath erBens. from yscnm to cr- by a H '^' J ^^ end of the coating layer arranged on its surface Layer of zinc iner- high compared to molten, and the b ^ _{k that the M} th, rounded grains emerge and nozzle from Y ^ Mrnj Es «^ mi ubng _wetting meniscus occurs under a steep nichtoxyd.erenden, a sulfur to the m.tge "™ ^ ks _rgangsste | len between felhaltiges fluid as a reducing agent containing hillside ^ de-itself * »« ^s object and the Atmosphere is maintained, since you rc hg e- Jr Otoflache de s aust _s ^ _{The greater def} ke η η ζ ech η et that as a sulfur-containing fluid Oberllacne aes * - ¹ "™" infolee of entrainment one with an additional weight over 34 (H ₂ S) S ^ ÄÄS dddd Gt d zinc one with a Mehrgewih ( ₂ ) S ^ ÄÄS is used that in the presence of the zinc 15 of the L nksaur ur ^U11 "J". _k . _erö ß _he Oxide film on the bath surface and on the appearance of the object can be all the more coarse ^ temperature is unstable and the zinc oxide is below d, e ^ J ^ S ^ Metiskuf nTcn A Ä1. marked by this