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Hot Dip Galvanizing Q&A: G60 vs. G90, G140, G185

Q. I am looking for info regarding zinc galvanizing. I need to know what the terms G-90 and G-140 mean regarding galvanizing. Also, if anyone has relevant experience comparing these two terms to plated alkaline zinc with yellow chromate it would help me tremendously.

John R. Hill

- Sparta, Michigan

A. G-90 and G-140 are coating designations for Galvanized Steel. For example, G-90 designates a zinc coating of .90 oz/square foot, while G-140 designates a zinc coating of 1.40 oz/square foot. These coating weights are a total for both sides of the strip. The complete list of coating designations can be found in ASTM A525 "Specification for General Requirements for Steel Sheet, Zinc Coated (galvanized) by the Hot Dip Process". I don't know how these compare to the other types of zinc plating you mentioned.

Patrick Patton

- Westlake, Ohio

A. Hi John. Hot-dip galvanized zinc coatings are usually much heavier than electroplated zinc coatings. Most "commercial" zinc electroplating is .0002" thick (5 µm) or even less, and 8 µm is probably the most common in the automotive industry.
Pre-galvanized G-90 coil, at .90 oz/square foot for both sides would be .45 oz/square foot on each side, equivalent to about 0.00076 (19 microns); that thickness can be achieved by zinc electroplating, but that is quite thick and quite unusual. Hot-dip coatings on discrete parts (post fabrication galvanizing) might be say 85 microns, sometimes even thicker. Thus as a simplification but a visualization tool, we might say that pre-galvanized coatings run about 3-5X as thick as most zinc electroplating, and post-fabrication hot-dipped parts have about 10X the zinc thickness of most parts electroplated with zinc.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. What is the most common hot dipped galvanized used? Is it G60 or G90? Please let me know.

Thank you!

CÈsar Marciales

- El Segundo, California

A. The G-60 is the most common galvanized metal and determines the amount of galvanize on the metal. The G-90 would be more galvanized coating than say G-60. If it is for outdoor use or in a high moisture environment I would always specify G90, just because it seems to make a difference over time.

I hope this helps,

Steve Sarten

steel company - Lenoir City, Tennessee

A. In an outdoor area G90 will last longer; it's like painting a car: the more coats the longer the steel will be protected ... but in this case it's more zinc applied to the steel.
G90 100-150 yrs.
G60 50-100
G30 <50

DANNY TIDWELL

METAL WORKS - GAINESVILLE, FLORIDA

Thanks, Danny, we appreciate the input! But your numbers sound extremely optimistic to me. What is their derivation please? Thanks.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. Evaluation of G60 vs G90 galvanizing with respect to cold formed metal framing (studs in exterior wall construction) and interior metal stud or other architectural components. Also for use in sheet metal work directly exposed to the elements. Any guideline as to when to spec one over the other? Industry standard and any significant difference in cost?

Thank you.

Dale Hurttgam

architect/engineer - Southfield, Michigan

A. Hi Dale. We appended your question to a thread where Steve S. suggests at least G90 for outdoor use. G90 has 50% more zinc, so it costs more of course, but the relative cost differential depends on the steel sheet thickness of course. G90 is probably the minimum for outdoor use, and for hangers, etc., in contact with today's very corrosive pressure treated wood, G185 is often recommended.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Need HOT-DIPPED G30, G60 and G90

RFQ: I want to know where hot dipped G30, G60 and G90 could be provided? Thanks.

Qiao vendy

- wuxi, jiangsu, China

Ed. note: Sorry, this RFQ is old & outdated, so contact info is no longer available. However, if you feel that something technical should be said in reply, please post it; no public commercial suggestions please ( huh? why?)

Multiple threads merged: please forgive chronology errors :-)

Is JIS SGCC Z08 equivalent to ASTM SGCC G30

Q. Dear Peers,

My name is Roger Ho come from a metal stamping factory, recently we got a big problem. In our factory is according to the JIS standard to purchase the raw material, but one of our customers requests us purchase the raw material according to the ASTM standard. Could you please advise me if JIS standard SGCC Z08 is equal to ASTM standard SGCC G30? If not, please advise me the right standard.

Thanks & Regards,

Roger-Ho

metal stamping - Hong Kong, China

A. I'm sorry you experienced this problem. It can be difficult to compare JIS to ASTM standards. The problems are lack of printed standards, language and conversion tables.

I highly recommend you secure copies of each respective standard and compare them. ASTM standards may be purchased on line, for a small fee. IMO, JIS standards are more difficult to get a copy of.

When you don't have a copy of a specific standard, please inquire of your customer and/or your vendor. They can be very helpful. Lean on your quality standards, merely explain you need a copy of the specification, in order to perform "contract review". Your quality process should compare the specifications of your "sales order" to that of your "purchase order", to insure you meet your customer's requirements.

I suspect SGCC Z08 is a Hot Dip Regular Spangle Galvanize.
You will also need to determine if any surface treatment is required, such as chromate treatment and/or oil.

I don't remember ASTM having as SGCC specification. However G30 would refer to the coating weight. Please get copies of the respective standards and compare all the product variables to determine if Z08 is comparable to G30 and both specifications are Hot Dipped Galvanize.

From my experience a G30 coating is an extremely light coating for a hot dip process. At least in the USA, it's difficult for any hot dip process to produce a G30 coating.

Some vendors would sell you a G60, in place of a G30. You would have more zinc coating than is necessary. However, JIS standards may specify a min and max coating weight. So a sheet with a heavy coating weight may met an ASTM std., but not a JIS standard.

A heavy coating or even a non-uniform coating would make any welding more difficult. A welding process "set up" for a G30 coating weight may produce inadequate welds if a vendor furnishes a heavier coated strip.

Most continuous hot dip lines produce G60 and G90 coatings on a cold rolled substrate. A G60 coating refers to a total of 60 grams per square foot. Approximately 30 per side. Some JIS specifications may call for a hot rolled substrate. Some steel mills REFUSE to use any hot rolled substrate.

You must also understand that JIS is a general industry standard. All Japanese auto manufacturers have more detailed specifications based on the general standard.

Toyota has their own engineering standard. Honda relies on their Honda Engineering std. (HES). As does Nissan and Fuji Heavy Industries.

The ASTM standards are also general industry standards. Every ISO certified, steel vendor that sells to an ASTM specification should be able to give you a copy of the specification cited on the purchase order.

Unfortunately I don't have copies of the specifications you cited, but recommend you focus on the process (hot dip vs electro.,) coating weight, and surface treatment. required.

Good luck.

Terry Magyar

ex - Berwick Steel - Columbus, Ohio

-- this entry appended to this thread by editor in lieu of spawning a duplicative thread
Q. WHAT DOES IT MEANS G90 GALVANIZED STEEL FINISH, IT REFERS TO G90 IS THE THICKNESS? OR THE PROCESS? WERE CAN I HAVE MORE INFORMATION ABOUT THIS MATTER, IT IS ELECTROLYTIC OR HOT GALVANIZED.

VICTOR MEDINA

MANUFACTURES OF FLOOR BOXES - MEXICO,

A. Hi Walter. We appended your question to a thread which answers it. G90 is an ASTM thickness (actually a weight) designation for hot dip galvanized sheet.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. What is the abbreviation of SGCC material

s.basker sivaraman

Design and development - pondicherry, India  

A. Hi Basker. It means hot dip Galvanized Coil. Perhaps "Standard Galvanized Commercial Coil".

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. Is there a specification difference between G60/G60 and 60G/60G? Basically, are there 2 different specs, or do 60G and G60 mean the same thing?

Kurt Dutcher

Stamping - Chelsea, Michigan

A. Hi Kurt. They do not mean the same thing!

G60 is a hot dip galvanizing specification for .6 oz total weight of zinc per square foot (approx. 0.0005" thickness per side), whereas there is a different spec for electrogalvanizing wherein 60G60G means each side is plated to a weight of 60 g/m2. If we take this then as a total of 120 g/m2, a 60G60 finish is roughly 2/3 the thickness of a G60 finish. Still, I don't think you should take a chance on quoting without clarification because, unfortunately, without specific context short alphanumerics like 60G can mean virtually anything. Good luck.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. I am looking for pass/fail criteria for humidity tested SGCC plated metal sheets.
In case that such a criteria is a negotiable issue with the customer, still, what is acceptable and used by the big enterprises?
Could you provide links to such specs?

Moshe Shoval

manufacturing quality engr. - Tel Aviv, ISRAEL

A. Hi. The applicable standard is probably JIS G3302. You'll have to buy this from a clearinghouse as it will not be free.

Sorry, although I'm sure the humidity test hours would be dependent on the thickness specified, I can't answer the question.

Regards,

Ted Mooney

, P.E.

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Need American drywall screws with G90 galvanizing

Q. I can't find an American made drywall screw with a G90 coating. Can anyone point me in the right direction?

Dan Wing

- LaCrosse, Wisconsin, USA

A. Both Simpson and East Coast Fasteners sell drywall screws that are mechanically galvanized. G90 is 0.9 oz/sq ft, and the deposit thicknesses are in that range. Mechanical galvanizing is a good choice for these fasteners due to the risk of hydrogen embrittlement.

Tom Rochester

CTO - Jackson, Michigan, USA

Plating Systems & Technologies, Inc.

Q. WHAT IS THE DIFFERENCE BETWEEN GALVANISED STEEL AND STAINLESS STEEL... HOW CAN I DIFFERENTIATE G90 AND G115 ? WHAT WOULD BE THE ASTM VALUE OF G90 AND G115.

MOHAMMAD ALAM

- DUBAI CITY, UNITED ARAB EMIRATES

A. Hi Mohammad. Galvanized steel is plain low carbon steel which has been dipped into a vat of molten zinc to acquire a coating of zinc on it.

Stainless steel is an alloy of steel plus chromium, and often nickel, plus trace ingredients. The most essential difference is that galvanized steel is plain steel with a coating on it which offers sacrificial corrosion protection, whereas stainless steel is homogeneous through and through and is inherently more corrosion resistant than plain steel because of its chromium and other metals.

As Tom says, G90 is 0.9 oz/sq. ft. Per the previously referenced specification ASTM A525, G115 would be 1.15 oz/sq. ft.

Regards,

Ted Mooney

, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

A. G90 means 90 GSM, that is 90 grams per square meter total weight inclusive both sides of coil or sheet

akil alva

Hitech - Ras al khaima UAE

A. Hmm...
1. Patrick and Tom say G90 means .90 oz per square foot (which equates to a thickness of about .00076" of zinc per side).
2. Terry says it means 90 grams per square foot (which equates to about .00267" per side) -- but I think he is wrong.
3. Akil says it means 90 grams per square meter (which equates to about .000248" per side) -- and I am sure he is wrong.

Me & Goldilocks agree with Patrick & Tom because that thickness sounds just right and the other two sound too thick and too thin :-)

Regards,

Ted Mooney

, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Thickness of coating

Q. Hi.
I need to know how to recognize and inspect galvanized sheet metal, and to find out if it is a G90 or G60, etc., galvanized sheet metal.

nabila aoun

- lebanon

A. Hi Nabila. The first step is to obtain a copy of ASTM A525 because if a coating is supposed to be G90 or G60, and claims to be, you'll need to know exactly what is entailed in that claim, so you know what to inspect for. The fabricators of the sheet metal coil stock probably use automated X-ray fluorescence instruments to determine/control the thickness, but they are very expensive, and you should be able to do a simple weigh/strip/weigh process if a destructive test is okay. Perhaps you can even test the thickness magnetically as a rough check. Good luck!

Regards,

Ted Mooney

, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Standards for Pregalvanized steel

Q. Dear sir,
Could you tell me, how to get whole information of pre galvanised steel Specification (as per thickness) with standards?
If any body has whole information or soft copy of book related to JIS G3302 and IS 513 standard for pre-galv steel, please share.

Thanks & Regards,
Mangesh

Mangesh Taware

If you want to learn more, please visit our website prepainted steel coil for household appliances.

student - Pune, Maharashtra & India

A. Hi cousin Mangesh. JIS standards are copyrighted and you must buy them through an authorized source, we cannot share them here or assist anyone in sharing them. Indian Standards are also copyrighted but, realistically, if you Google you will find IS 513 widely available on line, although it seems to refer to the steel itself rather than the galvanizing process.

You will find some older online books on the topic at https://books.google.com/advanced_book_search
if you click the 'Google ebooks only' button and scan the results for "Free Google eBook".

The galvanizing associations like galvanizeit.org, galvanizing.org.uk, galvanizing.org.nz, gaa.com.au, and egga.com have white papers available but it may take some time to find what you are looking for ... and you still can't quote to or certify to standards you don't have. Good luck.

Regards,

Ted Mooney

, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

⇦ (tip: readers rarely show interest in abstract questions, but people's actual situations usually prompt responses)  

Q. Hi Sir,
What's the difference between G60U and G60UL?

Doug Sir

- Long Beach, California

A. Hi. The "U" is definitely related to Underwriter Laboratories, per attached bulletin from US Steel.
Please put your question in context though: where are you hearing or seeing 'G60U'; and where are you hearing or seeing 'G60UL'? In the abstract, 'G60UL' could have been accidentally made up right on the spot by someone who knew that 'G60U' involved Underwriter Laboratories and decided to further clarify it for themself by replacing the U with UL :-)
Luck & Regards,

Ted Mooney

, P.E. RET

Striving to live Aloha

finishing.com - Pine Beach, New Jersey

Q. Hi there,
I'm quoting a job that requires zin G - finish to withstand 720 hours salt spray test with which I'm not familiar. The drawing is calling out a G185. I've only ever quoted G90. Any suggestions for which finish would withstand 720 hr salt spray testing?

Michael Nicoletta

- Toms River, New Jersey

A. Hi Michael. For many years G90 was the expected and often specified thickness of galvanizing for outdoor exposure. However, with the transition away from chromated copper treatments for pressure-treated wood, it was discovered that the replacements are far more corrosive than the old treatment ... approximately 2X. So it has become standard to use G185 (galvanizing twice as thick) for applications like joist hangers and associated hardware which used to be okay with G90.

Galvanizing is a sacrificial coating which gradually dissolves to protect the underlying steel, and one theory is that doubling the thickness doubles the life. Some standards called for G90 to resist 375 hours of salt spray, so presumably some people think G185 will last 750 hours. ASTM B117 salt spray testing is universally recognized as a horribly irrelevant test for galvanized coatings, but on the other hand is the saying "if you can't measure it, you can't control it", so the test gets specified anyway :-)

So it is vitally important to demand that your specifier be quite exacting about what the requirements are -- to 5% rust, 10% rust, cut edges, stamped holes, etc., in accordance with what standard ... or contract disputes are possible down the road. Any pre-galvanizing lasting a realistic 720 hours in salt spray testing sounds quite unlikely to me :-(
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

This is very informative and super helpful. I can't thank you enough for sharing your expert opinion. We mostly work in the stamping of cold rolled steel (1050, 1080), copper, brass, stainless, etc. As of lately we've been quoting the HSLA hot dipped which is new territory. We've made parts out of aluminum for this customer in the past, but this is the first time they asked for a salt test spray spec on the Galv. It's nice for us to be able to expand -- though there is a learning curve. I reached out to vendors who in turn reached out to Mill Metallurgists without gaining a definitive answer. You're the closest I can get to a solid answer. Thank you for the support and feedback - I just shared with my Team members.

Now we're working on the formability aspect of the part made from HSLA F Grade 80.

Kindest regards,

Michael Nicoletta

- Toms River NJ

A. Ted has already answered, and I'm just echoing his point.
Salt spray testing is quite inappropriate for galvanized products and will give totally misleading results.

Geoff Crowley

Crithwood Ltd.

Bathgate, Scotland, UK

This is very informative and super helpful. I can't thank you enough for sharing your expert opinion. We mostly work in the stamping of cold rolled steel (1050, 1080), copper, brass, stainless, etc. As of lately we've been quoting the HSLA hot dipped which is new territory. We've made parts out of aluminum for this customer in the past, but this is the first time they asked for a salt test spray spec on the Galv. It's nice for us to be able to expand -- though there is a learning curve. I reached out to vendors who in turn reached out to Mill Metallurgists without gaining a definitive answer. You're the closest I can get to a solid answer. Thank you for the support and feedback - I just shared with my Team members.Now we're working on the formability aspect of the part made from HSLA F Grade 80.Kindest regards,

Thank you Geoff - I greatly appreciate the support.
The hot dipped galv is new territory. So, I can use all of the advice I can get.

Michael Nicoletta

- Toms River New Jersey

A. As the other replies in this thread say, salt spray tests are quite inappropriate for galvanized coatings.
Those that specify salt spray for zinc based coatings clearly don't understand the mechanism of zinc based corrosion protection or of what salt spray testing does.

SS tests give no indication of the expected life of zinc coatings.

Geoff Crowley

Crithwood Ltd.

Bathgate, Scotland, UK

Q. I am looking for some recommendations on what type of galvanizing to spec (G60 or G90 or G140.....) for a structure that is close to the ocean (about 1500 feet). Need to specify galvanizing specs for steel purlins so they can last for 20 years. Any guidance or articles will be appreciated.

A Dar

- Honolulu, Hawaii

A. Hi A,
Because G90 is widely available, and Hawaii is more corrosive than most places, I would not consider G60 ... only G90 as a minimum.
G140 seems to be used on rooftop solar power installations so that would seem to be a lot for interior use supporting a roof.

Guarantees are tricky things and I'm not guaranteeing anything, but G90 seems generally appropriate to me, as long as there are no special circumstances like contact with pressure treated wood or more noble metals.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Q. Aloha Ted - Thank you for your response. I did not quite understand your comment regarding the G140 spec. Could you elaborate on it a little bit more.

A Dar

- Honolulu, Hawaii

A. Hi again. G140 is heavier and better than G90, and if cost is no object there is no reason not to spec it.
But G140, to my understanding, is usually used for exterior applications (facing the weather), like the framing for roof-mounted solar collectors. So it doesn't seem to me that you would need that heavy a coating for an interior application like roof purlins.
Luck & Regards,


Ted Mooney, P.E. RET
Striving to live Aloha
finishing.com - Pine Beach, New Jersey

Got it! Thank you for sharing. Mahalo

A Dar

- Honolulu, Hawaii

1. What is the main use of hot-dip galvanized sheet?

Answer: Hot-dip galvanized sheet is mainly used in industries such as construction, household appliances, automobiles, machinery, electronics, and light industry.

2. What are the three types of galvanizing methods currently used in the world?

Answer: There are three types of galvanizing methods: electroplating zinc, hot-dip galvanizing and coating zinc.

3. What are the two types of hot-dip galvanizing according to different annealing methods?

Answer: They can be divided into two types: in-line annealing and off-line annealing, also known as protective gas method and flux method respectively.

4. What are the commonly used steel grades for hot-dip galvanized sheets?

Answer: Product categories include general commodity coils (CQ), structural use galvanized sheets (HSLA), deep drawing hot-dip galvanized sheets (DDQ), bake-hardened hot-dip galvanized sheets (BH), dual-phase steel (DP), TRIP steel (transformation-induced plasticity steel) etc.

5. What are the three forms of cooling towers usually used for cooling?

Answer: There are two kinds of cooling methods - air-cooled and water-cooled.

6. What are some common defects in hot-dipped zinc coatings?

Answer: The main defects include peeling off, scratches, passivation spots, zinc particles, thick edges, air knife marks/scratches/scrapes/exposed steel surface/inclusions/mechanical damage/poor base metal properties/wavy edges/cambering/out-of-size/embossing/zinc layer thickness out-of-specs/roll printing etc.

7. How many forms do zinc plating furnaces have? 

Answer：There are three forms including vertical furnace，horizontal furnace，and vertical-horizontal combined furnace。

8.What is length tolerance for a piece of galvanized steel sheet?

Answer: The length tolerance should not have a negative value, and the maximum allowable deviation is +6mm.

Galvanized Steel Coil

9. What are the main reasons for zinc layer shedding?

Answer: The main reasons for zinc layer shedding include surface oxidation, silicide compounds, dirty cold rolling emulsion, oxidizing atmosphere in NOF section and high dew point of protective gas, unreasonable air-fuel ratio or low hydrogen flow rate during production process; oxygen infiltration into furnace; too low entry temperature of strip; low furnace pressure in RWP section or air intake at door；low temperature in NOF section，incomplete evaporation of oil/grease，low aluminum content in zinc pot，too fast line speed，insufficient reduction reaction time and short residence time of strip in molten zinc bath etc.

10. What are the causes of white rust and black spots?

Answer: Black spots are formed by further oxidation of white rust. The main causes of white rust formation include poor passivation film quality or uneven thickness; insufficient drying after passivation treatment; residual moisture on the surface before coating application or during coiling operation；moisture absorption due to poor ventilation conditions during storage/transportation；long-term storage under unfavorable environmental conditions such as exposure to acid/alkaline/salt media etc.

11. How long can finished products be stored? Why?

Answer: Finished products can be stored for up to three months to avoid excessive oxidation caused by prolonged storage.

12.What is the length tolerance for hot-dip galvanized steel sheets？

Answer：The length tolerance should not have a negative value, and the maximum allowable deviation is +6mm。

13.What is big flower pattern？What is small flower pattern？

Answer：Big flower pattern refers to normal spangle which can be produced through normal production process with crystal nucleus diameter no less than 0.2 mm while small flower pattern refers to spangle with crystal nucleus diameter less than 0.2 mm which is difficult to identify by naked eyes.

14.What is the protection principle of hot-dip galvanized coating?

Answer: Zinc can form a corrosion-resistant film on its surface in corrosive environments, which not only protects the zinc layer itself but also protects the steel base.

15.What is the passivation principle of hot-dip galvanized sheet?

Answer: Passivation treatment with chromate solution can form a passivation film on the surface of galvanized sheet. The chemical reaction formula is as follows: Zn + H2CrO4 - ZnCrO2 + H2

The trivalent chromium in passivating solution has low solubility and chemical activity, acting as a skeleton while hexavalent chromium easily dissolves in water and plays a role in re-passivating when scratches occur on passivated film, thus having healing effect. Therefore, within certain limits, passivation film can prevent direct erosion of steam or humid air into galvanized sheet and protect zinc layer.

16. What are the methods for testing the corrosion resistance of hot-dip galvanized sheets?

Answer: There are three methods for testing the corrosion resistance of hot-dip galvanized sheets: salt spray test, wet test, and immersion test.

17. Why is rust prevention treatment necessary for hot-dip galvanized products?

Answer: When hot-dip galvanized sheets are exposed to humid air, especially when the air contains acidic substances such as SiO2, CO2, NO2 and NO, a loose white rust will quickly form on the surface of the zinc coating. The main components of this white rust are ZnO and Zn(OH)2. This kind of white rust not only affects aesthetics but also brings great difficulties to future use.

18. What are the reasons for white rust formation?

Answer: The reasons for white rust formation include putting hot-dip galvanizing together with other corrosive media such as acid-base or salt; damage to passivation film or anti-film; poor passivation or oiling effect; poor ventilation in storage warehouse causing humidity; water splashing on galvanized sheet during transportation; transportation at low temperature and storage at high temperature resulting in condensation.

19. How do you calculate coating thickness?

Answer: The formula for coating thickness is Dz = Gz (Sz * dz), where Dz represents coating thickness in mm, Gz represents weight per square meter of coating in g/m² , Sz represents area covered by coating in mm² , dz represents density of zinc. This formula can be simplified as Dz = 0.000139Gz.

20.What causes zinc particles to appear?

Answer: Problems with raw materials mainly involve cleanliness and iron content levels within them；the temperature being too high which causes slag floating up from bottom；Aluminum content being too high affecting solubility level of iron.

21.What does it mean when a hot-dip galvanized sheet is smooth?

Answer: With the continuous expansion of the use of hot-dip galvanized sheets, in modern strip steel continuous hot-dip galvanizing units, the following objectives can be achieved by smoothing the strip:

① Improve the flatness and straightness of thin plates. At the same time, zinc particles on surface can also be flattened to make it smooth. This is particularly advantageous for deep drawing and other high-precision applications in future.

② The smoothing roller used has been pre-treated with shot blasting, so that after being smoothed, there is a certain roughness on the surface of plated plate. It can improve coating adhesion and store a certain amount of grease which will benefit lubrication during deep drawing processing;

③ For plated plates that will undergo painting treatment later on, even if their surfaces are controlled to have small zinc flowers but these small zinc flowers still show through paint layer. Therefore, for some high-demanding galvanized sheets, their surfaces need to go through further smoothing treatment so as to obtain a more uniform silver-white appearance;

④ Through smoothing process，yield point can be lowered，making yield platform disappear or less obvious，which could prevent slip lines from appearing when stretching or deep drawing processing takes place in future thus improving its deep drawability.

Galvanized Steel Coil

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- Email: jameson@fadasteel.com

Hope you can forward this message to your purchasing manager or related directors if you are not the intended one.

Thank you and best regards,

Mr Jameson / Sales Manager / FADA STEEL CO., LTD

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