Heitgalvanhúðuð húðun veitir framúrskarandi tæringarvörn fyrir undirlagið úr stáli, en frágangur þess er ekki alltaf sléttur eða einsleitur eins ogmálverk, dufthúðeðaskurðaðgerð. In general, galvanized coatings are specified by zinc coating thickness for corrosion resistance, and it's not specified by its appearance. However, the buyer can always specify what are the non-confirmative appearances, and below are the typical examples.
1. Welding spatters Slag
Suðuaðferðir sem framleiða ekki gjall, eins og MIG-suðu, eru ákjósanlegar. Ef húðuð suðurafskaut eru notuð skal fjarlægja allar gjallútfellingar vandlega af suðunni. Það er ekki hægt að fjarlægja suðugjall með venjulegri súrsun og allar leifar valda því að svartir blettir myndast við heit-galvaniseringu. Suðugos, gjall og svitahola skal alltaf fjarlægð áður en formeðferð galvaniserunar hefst, annars lítur yfirborð galvaniserunar mjög gróft út.
2. Sýrugildra
Steel structures should be designed to avoid narrow crevices or gaps. If lap welds must be used, they should be welded around the entire joint. In case of double-sided fillet welds, the weld must be continued over the ends of the steel material to prevent the penetration of acid into any conceivable crevice. Plus, it is important to avoid the formation of pinholes. If the gap between contact surfaces is larger than 100 cm², venting holes must be provided to avoid the risk of explosion. Since molten zinc is more viscous than acid, it will seal the opening during hot-dip galvanizing. Afterwards, the acid will create holes in the coating, and then the rust-colored liquid will run on to the surface and spoils the appearance. Therefore, once acid has penetrated a crevice, it is impossible to be removed.
3. Frárennslisbroddar
Drainage spike is a very common defect, and it can be greatly avoided by setting up a hanging angle close to 45 degree ,which can minimize drainage at the bottom of the workpiece. Hanging steel works with a horizontal angle is forbidden, which will cause excessive drainage spikes. Grinding of drainage spikes shall be handled carefully, and overgrinding shall be prohibited.
4.Dross Bólur
Dross pimples are small zinc-iron crystals formed from iron reacting with molten zinc during galvanization process. Dresses are heavier than zinc, and they settle on the bottom of the zinc kettle where they are periodically removed every 2 weeks or 10days. If the dross is stirred up and mixed into the molten zinc, it will often get trapped in the zinc coating leaving marks like pimples on the galvanization surface. An excessive amount of pimples can indicate a poor coating, and the zinc kettle shall be cleaned soon before another shift starts.
5. Öskulitun
Sometimes, ash is trapped inside areas and sticks to the outer side of the coating as the steelwork is lifted from the zinc bath. Ash may cause a light brown stain, a dull or dark surface appearance after removal. It has negative impact upon the performance of the galvanized coating, and it's possible to be repaired by zinc paint if its size is small.
6.Rönd, hnúður og hlaup
Hryggir og línur þykkari en nærliggjandi galvaniseruðu húðunin stafa af mismunandi hraða hvarfs sinks við stályfirborðið vegna álagssvæða á stályfirborðinu eða tilvistar suðusvæða eða suðumálms með breyttri málmvinnslu á móðurmálmnum. Þetta tilvik sést oftast á stálrörum ogrúlluformaðir stálprófílar. There is no impact on coating performance, but it does have appearance issue. Please also be reminded that it's a bad practice to remove the lumps by angle grinder vigorously, and this could remove the whole zinc coating leaving the steel uncoated.
7.Hengingarmerki
Hanging marks are almost impossible to avoid, but it's possible to adjust the hanging angle to minimize the hanging marks. And, it's also possible to use manual grinder to remove marks with care, and then repair them by zinc rich paint.
8. Galvanization Flaking
Flaking is the separation of the entire zinc coating, including the iron zinc alloy layers from the underlying steel. It is also known as delamination or chipping and should not be confused with peeling where only the top pure zinc layer separates from the underlying zinc alloy layers. Flaking usually occurs in thicker than normal galvanized coatings (200 μm or more), especially when these coatings receive impact forces during handling. Excessively thick coatings generate high stresses at the interface of the steel and galvanized coating which causes the zinc to become flaky and separate from the steel surface. Flaking typically occurs near the edges and creates bare spots in the protective zinc coating and it should be repaired to ensure ongoing corrosion protection. If the area of flaking is small, it can be repaired; however, if the flaking area is larger than allowed by the specifications, the part must be rejected and re-galvanized. Flaking can be avoided by minimizing the immersion time in the galvanizing kettle and cooling of the galvanized steel parts as quickly as possible, and if possible using a different steel grade. Steels with phosphorous content greater than 0.025 percent can experience flaking after galvanizing, even when the silicon levels are satisfactory.
9. Flögnun og eyðing
Delamination or peeling creates a rough coating on the steel where the zinc comes off. Many large galvanized structures and steel profiles take a long time to cool in the air, and the zinc coating continues to form zinc-iron layer after they have been lifted from the zinc bath. This continued coating formation leaves a gap between the top two layers of the galvanized coating. If there are many gaps formed, the top layer of zinc can separate from the rest of the coating and peel off the part. If the remaining coating still meets the minimum specification requirements, then the part is acceptable. If the zinc coating that remains on the steel does not meet the minimum specification requirements, then the part must be rejected and re-galvanized.
10.Berir blettir
Berir blettir, óhúðuð svæði á stályfirborði, eru yfirborðsgalli sem getur komið fram vegna ófullnægjandi undirbúnings yfirborðs. Berir blettir geta stafað af suðugjalli, sandi sem er felldur í steypur, umfram ál í galvaniserunarketilnum eða lyftibúnaði sem kemur í veg fyrir að húðin myndist á litlu svæði. Til að forðast beina bletti verður galvaniserinn að tryggja að yfirborðið sé hreint og ryðlaust eftir formeðferð. Hægt er að laga litla bletti með ríkulegum sinkúða. Ef stærð berra blettsins eða heildarfjöldi bletta er yfir kröfum sem tilgreindar eru í ISO 1461, þarf stálvinnustykkið að fara í gegnum alla formeðferðina og galvaniseringuna aftur.
11.Motling
A mottled surface appearance is caused by uneven cooling rates of newly hot-dip galvanized articles after withdrawal from the zinc bath. During air cooling of the articles, the zinc-iron coating formation reaction, consuming the outer free zinc layer in the process, can continue for a short time as long as the steel stays about 550 Fahrenheit degree. Due to the fact that the galvanizing reaction continues on the interior portion and consumes the free zinc layer, but not the exterior potion of the steel, and this causes a nonuniform appearance of the zinc coating. However, this difference in appearance does not affect the corrosion protection of the galvanized coating, and this mottling surface is acceptable per ISO 1461 specifications. Therefore, to speed up the cooling process, quenching is recommended. But, the galvanizers shall be reminded that some designs might not be suitable for quenching as they have a tendency for warpage or distortion during quenching process.
After galvanizing, the steel cools from a temperature of approximately 840 F to ambient temperature. If the steel is quenched, cooling takes place rapidly, but not all galvanizers have quench baths and quenching is not recommended on some designs due to the potential for warpage/distortion of the steel. When the newly galvanized steel is allowed to cool naturally (without quenching), it can take several hours for the steel to come down to ambient temperature. Thinner steel cools faster while thicker steel takes longer to cool. Sometimes an individual piece of steel will have different cooling rates.
12.Daumur frágangur
The most common reason for dull appearances is the chemistry of the workpiece, and the main elements of steel chemistry which most strongly influence the final appearance are silicon and phosphorous. Both elements are catalysts to coating growth, and the thicker coating is responsible for the differing appearance. In addition to producing thicker coatings, highly reactive steels tend to have a matte gray or mottled appearance instead of a typical bright coating.
13. Léleg viðgerð á galvaniserun
Galvaniserunarviðgerðir eru einhvern veginn jafn mikilvægar og galvaniserunarvinnan sjálf og það eru fá algeng mistök sem ber að forðast.
√ Overgrinding, removed the zinc coating completely
√ Notaðu úðara með lágt sinkinnihald til að gera við
√ Sinkviðgerðarþykkt uppfyllir ekki nauðsynlega þykkt
Fabmann hefur strangt framleiðsluferliseftirlit á sínum staðyfirborðsmeðferð málms, and we have very experienced quality engineers who have profound knowledge about pretreatment of hot dip galvanization, galvanization and galvanization repair. That's why we can provide premium quality for wide range steel products like vélbúnaður fyrir bryggjufestingu, sérsniðnar rekki, styrktar hornfestingar, rúlluformaðir stálprófílar, merki pósta svigaogbúrfestingar fyrir fiskeldi to our clients.
