hardness of mill scale

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Metal hardness is a characteristic that determines the surface wear and abrasive resistance. The ability of a material to resist denting from impact is related to hardness as well as a materials ductility. Various degrees of hardness may be achieved in many metals by tempering, a heat treatment process used in cold rolled and cold worked metals.

As the grain structure of the metal undergoes cold forming, the grains are stretched and altered. The surface becomes harder, resisting deformation from contact. Tempering heats the worked metal to temperatures at which the grains begin to dissolve.

There are series of standard tempers available. These tempers and their availability in a particular alloy vary, depending on the nature of the grains as they recrystallize. The temper designation is actually determined by this grain size, rather than the yield strength of the metal.

The below chart is useful for determining which metals will be impervious to scratching and dinging, as it relates to the Rockwell scale and ductility. The Rockwell scale is a hardness scale based on indentation hardness of a material. The Rockwell test determines the hardness by measuring the depth of penetration of an indenter under a large load compared to the penetration made by a preload.

There are a number of ways to harden architectural metal, through the mill, or during the fabrication process. Each of the hardening mechanisms are introducing crystal lattice irregularities into the metal crystal structure, causing dislocation of the metals structure to become more difficult. The result is a harder, less ductile metal surface.

Work hardeningrefers to the straining or cold-hardening of a metal surface. As metal is bent or strained repeated, the plasticity of the metal reduces, becoming work-hardened and less ductile.Usually refers to strain-hardening behavior of the metal as it is worked at room temperature. Certain metals alloys such as nickel-titaniumdo not undergo strain hardening but actually has a characteristic of strain relieving as it returns to the original shape.

Solid Solution Strengtheningrefers to a metal in the alloying process, in which an alloying constituent is inserted into a solid material. One or more elemental constituents are able to enter into a heated but solid solution. The metal is then rapidly quenched to capture the element in solid solution.

Age hardeningis a process which occurs rapidly in the first few days after casting, then much slower over the next several weeks. This process is often referred to as natural age-hardening. Another artificial version of this process can be used by heating the metal for a short period of time at a high temperature. The result is that it will stabilize the properties, further strengthening the alloy. This process is known as artificial age-hardening, or precipitation hardening.

Anodization, a process specific to aluminum, has a hardening effect. The final step in creating anodized aluminum is toharden and seal the surface by use of deionized boiling water or metal salt sealers. Sealing is required to close the pores of the oxide film and provide uniformity to the exception of the alloying constituents.

Case hardeningrefers to asurface heat treatment process used to produce a hard, wear-resistant surface on metal. Methods of case-hardening include carburization, cyaniding, nitriding, flame hardening, and electroinduction hardening.

Temperingis a heat treatment process used in cold rolled and cold worked metals. As the grain structure of a metal undergoes cold forming, the grains are stretched and altered. The surface becomes harder, resisting deformation from contact. Tempering heats the cold worked metal to temperatures at which the grains begin to dissolve into one another.There are series of standard tempers available. These tempers and their availability in a particular alloy vary, depending on the nature of the grains as they recrystallize. The temper designation is actually determined by this grain size, rather than the yield strength of the metal.

Back-blastinga metal surface is a way of flattening metal, which also tends to greatly increases the surface hardness. It is advised to back-blast a material after forming operations, because the material will become harder to work and form after blasting the surface.

what exactly is mill scale and what is done about it

Q. My name is Frank Rea. I am a coatings consultant, predominately for steel structures. Arguments with contractors about mill scale are common. In order to discuss this issue knowledgeably I would like to know: What is the chemical composition of mill scale? Does it vary by process? Are there primary constituents that must be present for a substance to be classified as mill scale. thank you

A. Mill scale consists primarily of magnetite, Fe3O4, of characteristic blue-gray "steely" color. An extremely thin outer film of hematite, Fe2O3, is invisible to the naked eye. The inner portion of the magnetite contains fine metal grains and sometimes, residual black FeO (see below), which contribute to the roughness of descaled metal. Mill scale is found on all hot-rolled steel products unless processed in a protective atmosphere or descaled (e.g., for galvanizing). At hot rolling temperatures, an inner layer of wstite, FeO, exists between the steel and magnetite. "At elevated temperatures, FeO constitutes about 85% of the scale thickness, Fe3O4 about 10 to 15% and Fe2O3 about 0.5 to 2%. During slow cooling [below 1040 F] of hot-rolled coils of hot-rolled strip [and heavy shapes], most of the FeO is transformed to Fe and Fe3O4, and the latter oxide is predominant after cooling."

The alloying metals form cations within the mill scale at about the alloying proportions* due to the almost instantaneous oxidation of freshly exposed metal at high temperature. Fe3O4 contains both Fe+2 and Fe+3, and is sometimes written FeOFe2O3. Ni+2 substitutes for Fe+2, Al+3 and Cr+3 substitute for Fe+3. Thus, (Fe,Ni)O(Fe,Al,Cr)2O3. Cations of other valences, e.g., Si+4 and Ti+4, are accompanied by cation vacancies to maintain overall electrical neutrality. With very slow cooling, small grains of Si- and Ti-containing oxides may precipitate within the scale. *unlike general heating or heat treatment scale, where Al, Cr, etc. preferentially oxidize. Steel mills descale sheet and plate by passage through scalebreaker rolls, which flexes the metal enough to fracture the scale. This allows pickling acid (HCl) to attack the more soluble (partially transformed) inner wstite layer.

Finishing.com honored Ken for his countless carefully researched responses. He passed away May 14, 2015. Rest in peace, Ken. Thank you for your hard work which the finishing world continues to benefit from.

Q. My name is Dr P K Maitra, (formerly G M ,Q/A & head R&D, BALCO), in past I have communicated & interacted through Finishing.com. I have read the letter No 38657 of Mr KEN VLACH Dec 20-2005, & appreciated the efforts being done by Finishing.com & through this platform I want to ask & reply or propagate the information for future compilation for valuable readers.

---- Ed. note: Thanks for the kind words, Dr. Maitra. You are welcome to attributed fair use, of course, and to mention my name ... but unless individual responders reply to your offer, we certainly can't speak for them regarding their permission to use their name in a different forum or media.

Q. I am particularly concerned about the effects of Mill Scale if left in place and painted over. Does it have any long term negative effects on the steel or subsequent paint or coating surfaces. Secondly if left in place and painted how can in be removed in the field.

A. In response to the question on whether or not mill scale on hot rolled steel is detrimental, I would submit that is very much so as it is anodic to the steel. Meaning that once moisture enter the picture the steel corrode (rust) and not the mill scale. Which is why the most protective coating products designed for immersion and other tough environments require an SSPC SP-5 white metal degree of cleaning as this process removes all mill scale.

A. When you are applying a coating to a steel surfaces in order to produce sufficient adhesion against corrosion it is necessary to remove all contaminants off the surface. Mill scale is porous and poorly adherent scale of magnetite, it will only give limited short term protection to steel against corrosion. If you are coating any steel surface against corrosion it is necessary to blast clean (with garnet or similar) to a finish of Sa2.5 blast standard before coating. Regards Vijay

Q. As per some friends, the mill scale can be used in production of steel production, put in the trench when steel liquid get out, thus it will automatically smelt in the liquid, and no wastage, steel still proper, want to know if it is the best way to use mill scale?

Q. If you are installing heavy, rotating equipment what are the policies for the base plates, regarding mill scale. I have been taught that it is poor engineering practice to install equipment on a mill scale surface. Can anyone corroborate my thinking.

Ted, The base plates support a Gas Turbine weighing 370 tonnes. If the Mill Scale is on the plates, under vibration, the scale breaks down to dust and effectively leaves a void. The underside of the plate is coated with scale also and sits on a cementitious grout. The grout is water based which could result in the Mill Scale separating from the plate.

Hi, Les. I never designed in that field and can't comment on codes or standard practices for heavy gas turbines, but I do agree with you in general that steel structures require removal of mill scales, and that same opinion has already been offered here by Burt Olhiser and Vijay Vijayaraghavan. Good luck.

It is easy to understand why the oxides form in a specific sequence in a mill scale. The highest oxide (the one with maximum proportion of oxygen) forms on the surface as it is directly exposed to air (the source of oxygen) and the lowest oxide forms next to the base metal (the source of Fe). However, the lowest oxide, FeO, is said to form only above 570 C. Therefore, its presence could be indicative of the scale being mill scale, which might be easy to confirm if FeO is retained at room temperature, without further oxidation to a higher oxide, for sufficiently long time. If only mill scale was dense, adherent and continuous it could have provided necessary protection against corrosion but unfortunately it is not. Moreover, it is cathodic (and not anodic like zinc) to iron and hence will corrode much faster at locations of discontinuity due to unfavorably large area ratio of cathode to anode. In such a case, a bare metal surface might be better than a discontinuous mill scale (or any other cathodic coating) as the former will corrode more uniformly as against the possible severe localised corrosion of the latter.

Comments on applying finishes over mill scale gave me a sculptor's idea. I don't fight Mother Nature, I leave my outdoor steel sculptures to develop a handsome rust finish. So, if I was to remove some of the mill scale selectively, in a decorative pattern, the finished piece might develop a pattern as parts rust differently. However, would the mill scale and non-mill scale rust soon catch up with each other and soon look the same? I posted an earlier question with no response - whether applying a rust converter in a selected pattern on a rusted surface would also allow you to add visual interests or does the rust margin creep under and push off the converted rust?

A. Hi Vk. Murarka, Just some ideas to your question for de-oiling mill scale: There are really many different processes. One method is using water to separate the oil content from the solid by high shear agitation. I refer you to the following US patent for details: US Patent 5047083, "Process for de-oiling mill scale". Another patent suggests a mixing the mill scale with calcined lime followed by a burning process to form pellets. Please see US patent 4326883. Regards,

Q. Hello: I want to briquette Mill Scale Dust removed from a Shot Blasting Operation. Can these briquettes be used as material to be remelted for Industrial Steel Manufacturing in EAF type of process? What are the pros and cons?

All about mill scale . . . Mill scale immediately starts at the steel making stage of casting hot metal steel grades and steel alloys when the metal is in a liquid stage. The mill scale chemistry will be the exact makeup of the steel and/or steel alloys being made. It is the outer skin of the casting and is formed by the rusting of the iron as it is exposed to the humidity and Oxygen of the air. Steel makers allow this to occur as it will form a protective coating from further rusting to occur for a period, normally 1 mm per year under normal ambient conditions. Sometimes it is forced to occur by a light spray of moisture. As indicated it will slow the development of further rusting but will not stop it and an additional 1mm per year will be expected on normal high carbon steel. Any crack or hole in the mill scale to reach the base metal will continue the rusting effect. Salt air will hasten rusting. ---- I am continuing my response on mill scale, if I may . . . In addition to the explanation on where mill scale comes from and how it forms -- mill scale is sold on the commercial and international exchange mainly to the Chinese steel makers that use low quality iron ores either domestically mined or purchased. The Chinese steel makers then mix the mill scale with the low quality iron ore and prepare it for feed to a sinter plant, whereas the iron ore is mostly less than 60% Fe and the mill scale is around 70% Fe. How much they add is dependent on their steel making processes. Mill scale can be used in other iron ore preparation for steel making but it may require crushing and grinding it to very specific sizes and too expensive or it can be briquetted and used directly. If it is used directly the further preparation and processes to use it would have to be scrutinized to ensure that it would be efficient and economic to do so. It would be beneficial to use it as it is the highest quality iron oxide available. Mill scale production is equal to 1% of all cast steel in the world. Today on an annual basis with1.4 billion tons of steel cast worldwide, that means there is produced around 10 million tons of mill scale per year. Today only about 1/2 million to 1 million tons or so are commercially exchanged. It should be noted to remember that all mill scale will include the exact makeup of the cast metal or steel and alloys. Meaning that if there are any other ingredients in the steel, carbon, any alloy or additive it will also be in the mill scale. Another question I noted was about finishing: it absolutely must be removed prior to any use of the steel and/or finishing. As it starts out to be a protectant it is also the beginning of rusting and over time the steel must be protected from itself. From the casting metal it is removed before further processing, rolling or drawing as the mill scale will damage other equipment in the processes and can cause early failure of any component. ---- Further to my previous 2 blogs on mill scale, I seem to find more information in my aged brain, therefore, I wish to explain what it looks like after it is removed from the steel and what to do with it. In a rolling mill where the steel will be stretched and squished the mill scale will first be removed mostly by water jets, or by sand blasting in some shops or by vibrating rolls in others and the mill scale will fall into a pit below the equipment where it will also be joined by rolling mill lubricants and bearing oils and water. From there it will be pumped to a holding pond, where companies like Harsco will be paid by the steel mill to clean out the pond once in awhile and get rid of the mill scale. In the U.S. in the past, and only a few short years ago it was dredged up and let drip dry and sold to a bidder, normally a cement plant who bought it for a very low amount and processed it to use in cement making since they require a little amount of iron in their processing and mill scale hit the mark. However a few years ago the EPA found that some of the ingredients, mostly from the lubricants from the rolling mill oils, caused the mill scale to be a hazardous material. The cement plants looked for other sources of the iron and mill scale became a personna non-grata. As the international market place for mill scale was taking off with China purchasing it as previously indicated, it is now an out to send the hazardous waste there and let them deal with it. This is not very neighborly, to say the least, so a few companies have come up with alternatives. One is to compress the mill scale into giving up the oils and lubricants and water to an acceptable level for the feed to the sinter plant where the mill scale is mixed with other iron ores and hydrocarbons from coke plants and bake it at 2500 F. The squished out oils and lubricants by the way are recycled to be used once again. As far as recycling it to make other steel, the answer is yes it is being done at steel mills that employ a sinter plant. There are 7 in the U.S. and almost all steel mills in Europe, China and other places like India employ them with the use of the blast furnace to make steel. Other plants that use the EAF (electric arc furnace) cannot use them as it would take an ungodly amount of energy to extract the iron from the mill scale unless it were put through a major amount of preparation and chemical reduction first. There is also the consideration of what are the elements that are in the mill scale. Remember, I indicated that every bit of mill scale represents the product being made at the steel mill whether it is construction grades of steel like rebar or high quality alloys and stainless for example. Therefore if a steel mill wants to make rebar and they buy mill scale from the open market and it comes from an alloy shop what do they do with the other elements and how do they get it out? That costs money and lots of it for the procedures and the equipment and the chemicals to eliminate the unwanted stuff. So, further processing and experimentation and trials and tribulations must be done to be able to recycle and use all of the 10 million tons per year and growing. Thomas J Coyne jr T.C.Inc. - Estacada, Oregon, USA July 2014 Wow! Finishing.com has received thousands of helpful postings, but this is one of the most thorough and exhaustive ever. Thanks! Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey March 21, 2016 Q. Hi All, I am currently doing a study on mill scale uses. My understanding is that a majority of mill scale is used in sintering. Are there other feasible uses as well (in cement and other such industries) And by feasibility I mean are companies from other industry verticals (apart from reuse in sinter for steel production) using mill scale in large amounts. Any expert opinion around this would be greatly appreciated Sanjeev Kumar The Smart Cube - Noida, India October 26, 2016 Q. - How can you mimic a finish that resembles mill scale on sheets of hot rolled material that has been de-scaled? I would like to first say that I am very impressed with the knowledge here! I am an architect and builder in Las Vegas. I also have a background in metal working and have studied metallurgy fairly in depth. I have never seen such concise (and correct) descriptions and explanation about mill scale and "what it is" before reading these entries! Great job! Anyways, as for my question: Here in the Southwestern United States, a trend in architectural aesthetics is a heavy industrial look using hot rolled steel where the mill scale is left intact and you can see the heat marks left by the rollers in the factory. One reason this is popular is because the extremely low humidity in our dry desert climates allows for these types of finishes to be left without a sealer and will never oxidize (rust) further. So the project gets an industrial aesthetic that requires no maintenance or upkeep and the cost for these types of looks is very low. You just put up sheets of hot rolled material and you're done. These architectural details are often full sheets of hot rolled steel used as wall paneling, fireplaces, bar-dies, etc. If anyone is interested, I can direct you to some photos on our website or social media pages to show you examples of this. My question is this: What is the best way to fake or apply a finish that closely resembles black mill scale on a hot rolled sheet? I am currently working on a project for an architect client who is using hot rolled sheets on a residential project. I ordered sheets of hot rolled steel from a large company in the midwest to be perforated (punched) in such a way where the different sized perforations make an image in the steel. The problem is that they ordered a "clean" hot rolled material where the mill scale has been removed. We are out of time on this project so I can't wait for them to receive the correct material and start over. I am hoping I can have them proceed with the punching and when I receive the material, just apply a chemical or something that would closely resemble mill scale. Thank you in advanced for your time and effort! Nathan Weber Make Studios - Las Vegas , Nevada - USA February 5, 2017 A. Nathan, There are a few things you can try on a few small samples to see which you like best. You can apply a faux finish such as paint but it's tricky and the paint could stand out over time. Some people take used motor oil, spread or spray it thinly over the material and light it on fire. After it cools off you can clean and scrub. Don't try this at home kids! Blake Kneedler Feather Hollow Eng. - Stockton, California May 4, 2017 Q. Hi, I am researching ways to measure the thickness of mill scale formed on hot rolled steel coils. Can anyone suggest a way to make a Bakelite mold without disturbing the oxide scale so that I can use the mold to measure the thickness of oxide scale? In addition to the above problem, can you also suggest a way to cut the steel to the size of the molding machine without disturbing the oxide scale? "Disturbing" here is defined as breakage of oxide scale or reduction in thickness of scale due to mechanical vibration or by heat. Dinakaran Murugadass - Chennai, Tamilnadu and India June 1, 2017 A. I have a substantial restoration business in NYC restoring old "wrought iron" doors, windows, and architectural metal work. We are constantly refinishing old Fenestra-style windows and doors, chemically stripping them, and repainting. From our experience stripping thousands of windows and hundreds of doors, the mill finish is generally intact, and protects the steel. The only time it is not, is when the caulking fails and traps moisture, or air conditioners drip steadily on hot rolled steel causing it to fail. Without question in my mind, the mill finish is more durable than the typical oil alkyd paints made since lead paint was banned. We always leave it intact, unless the client doesn't want it. The blue black finish can be imitated with nigrosene powder and top coated with acrylic lacquer, but that will be more susceptible to rusting than the mill finish. Peter Triestman Olek, Inc. - historic metal restoration - Newark, New Jersey, US Effect of mill scale on refractories November 1, 2018 Q. Hi I am Muhammad Bilal, working in a steel-making industry as a refractory trainee engineer. I just want to know that what are the effects of mill scale on refractories either acidic or basic, and what effects it may cause useful or adverse, on all refractories, monolithic and bricked ones, too. Thank You. Please give me a detailed answer. Hafiz Muhammad Bilal Agha Steel Industries - Karachi, Pakistan finishing.com is made possible by ... this text gets replaced with bannerText Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Mill scale immediately starts at the steel making stage of casting hot metal steel grades and steel alloys when the metal is in a liquid stage. The mill scale chemistry will be the exact makeup of the steel and/or steel alloys being made. It is the outer skin of the casting and is formed by the rusting of the iron as it is exposed to the humidity and Oxygen of the air. Steel makers allow this to occur as it will form a protective coating from further rusting to occur for a period, normally 1 mm per year under normal ambient conditions. Sometimes it is forced to occur by a light spray of moisture. As indicated it will slow the development of further rusting but will not stop it and an additional 1mm per year will be expected on normal high carbon steel. Any crack or hole in the mill scale to reach the base metal will continue the rusting effect. Salt air will hasten rusting.

I am continuing my response on mill scale, if I may . . . In addition to the explanation on where mill scale comes from and how it forms -- mill scale is sold on the commercial and international exchange mainly to the Chinese steel makers that use low quality iron ores either domestically mined or purchased. The Chinese steel makers then mix the mill scale with the low quality iron ore and prepare it for feed to a sinter plant, whereas the iron ore is mostly less than 60% Fe and the mill scale is around 70% Fe. How much they add is dependent on their steel making processes. Mill scale can be used in other iron ore preparation for steel making but it may require crushing and grinding it to very specific sizes and too expensive or it can be briquetted and used directly. If it is used directly the further preparation and processes to use it would have to be scrutinized to ensure that it would be efficient and economic to do so. It would be beneficial to use it as it is the highest quality iron oxide available. Mill scale production is equal to 1% of all cast steel in the world. Today on an annual basis with1.4 billion tons of steel cast worldwide, that means there is produced around 10 million tons of mill scale per year. Today only about 1/2 million to 1 million tons or so are commercially exchanged. It should be noted to remember that all mill scale will include the exact makeup of the cast metal or steel and alloys. Meaning that if there are any other ingredients in the steel, carbon, any alloy or additive it will also be in the mill scale. Another question I noted was about finishing: it absolutely must be removed prior to any use of the steel and/or finishing. As it starts out to be a protectant it is also the beginning of rusting and over time the steel must be protected from itself. From the casting metal it is removed before further processing, rolling or drawing as the mill scale will damage other equipment in the processes and can cause early failure of any component. ---- Further to my previous 2 blogs on mill scale, I seem to find more information in my aged brain, therefore, I wish to explain what it looks like after it is removed from the steel and what to do with it. In a rolling mill where the steel will be stretched and squished the mill scale will first be removed mostly by water jets, or by sand blasting in some shops or by vibrating rolls in others and the mill scale will fall into a pit below the equipment where it will also be joined by rolling mill lubricants and bearing oils and water. From there it will be pumped to a holding pond, where companies like Harsco will be paid by the steel mill to clean out the pond once in awhile and get rid of the mill scale. In the U.S. in the past, and only a few short years ago it was dredged up and let drip dry and sold to a bidder, normally a cement plant who bought it for a very low amount and processed it to use in cement making since they require a little amount of iron in their processing and mill scale hit the mark. However a few years ago the EPA found that some of the ingredients, mostly from the lubricants from the rolling mill oils, caused the mill scale to be a hazardous material. The cement plants looked for other sources of the iron and mill scale became a personna non-grata. As the international market place for mill scale was taking off with China purchasing it as previously indicated, it is now an out to send the hazardous waste there and let them deal with it. This is not very neighborly, to say the least, so a few companies have come up with alternatives. One is to compress the mill scale into giving up the oils and lubricants and water to an acceptable level for the feed to the sinter plant where the mill scale is mixed with other iron ores and hydrocarbons from coke plants and bake it at 2500 F. The squished out oils and lubricants by the way are recycled to be used once again. As far as recycling it to make other steel, the answer is yes it is being done at steel mills that employ a sinter plant. There are 7 in the U.S. and almost all steel mills in Europe, China and other places like India employ them with the use of the blast furnace to make steel. Other plants that use the EAF (electric arc furnace) cannot use them as it would take an ungodly amount of energy to extract the iron from the mill scale unless it were put through a major amount of preparation and chemical reduction first. There is also the consideration of what are the elements that are in the mill scale. Remember, I indicated that every bit of mill scale represents the product being made at the steel mill whether it is construction grades of steel like rebar or high quality alloys and stainless for example. Therefore if a steel mill wants to make rebar and they buy mill scale from the open market and it comes from an alloy shop what do they do with the other elements and how do they get it out? That costs money and lots of it for the procedures and the equipment and the chemicals to eliminate the unwanted stuff. So, further processing and experimentation and trials and tribulations must be done to be able to recycle and use all of the 10 million tons per year and growing. Thomas J Coyne jr T.C.Inc. - Estacada, Oregon, USA July 2014 Wow! Finishing.com has received thousands of helpful postings, but this is one of the most thorough and exhaustive ever. Thanks! Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey March 21, 2016 Q. Hi All, I am currently doing a study on mill scale uses. My understanding is that a majority of mill scale is used in sintering. Are there other feasible uses as well (in cement and other such industries) And by feasibility I mean are companies from other industry verticals (apart from reuse in sinter for steel production) using mill scale in large amounts. Any expert opinion around this would be greatly appreciated Sanjeev Kumar The Smart Cube - Noida, India October 26, 2016 Q. - How can you mimic a finish that resembles mill scale on sheets of hot rolled material that has been de-scaled? I would like to first say that I am very impressed with the knowledge here! I am an architect and builder in Las Vegas. I also have a background in metal working and have studied metallurgy fairly in depth. I have never seen such concise (and correct) descriptions and explanation about mill scale and "what it is" before reading these entries! Great job! Anyways, as for my question: Here in the Southwestern United States, a trend in architectural aesthetics is a heavy industrial look using hot rolled steel where the mill scale is left intact and you can see the heat marks left by the rollers in the factory. One reason this is popular is because the extremely low humidity in our dry desert climates allows for these types of finishes to be left without a sealer and will never oxidize (rust) further. So the project gets an industrial aesthetic that requires no maintenance or upkeep and the cost for these types of looks is very low. You just put up sheets of hot rolled material and you're done. These architectural details are often full sheets of hot rolled steel used as wall paneling, fireplaces, bar-dies, etc. If anyone is interested, I can direct you to some photos on our website or social media pages to show you examples of this. My question is this: What is the best way to fake or apply a finish that closely resembles black mill scale on a hot rolled sheet? I am currently working on a project for an architect client who is using hot rolled sheets on a residential project. I ordered sheets of hot rolled steel from a large company in the midwest to be perforated (punched) in such a way where the different sized perforations make an image in the steel. The problem is that they ordered a "clean" hot rolled material where the mill scale has been removed. We are out of time on this project so I can't wait for them to receive the correct material and start over. I am hoping I can have them proceed with the punching and when I receive the material, just apply a chemical or something that would closely resemble mill scale. Thank you in advanced for your time and effort! Nathan Weber Make Studios - Las Vegas , Nevada - USA February 5, 2017 A. Nathan, There are a few things you can try on a few small samples to see which you like best. You can apply a faux finish such as paint but it's tricky and the paint could stand out over time. Some people take used motor oil, spread or spray it thinly over the material and light it on fire. After it cools off you can clean and scrub. Don't try this at home kids! Blake Kneedler Feather Hollow Eng. - Stockton, California May 4, 2017 Q. Hi, I am researching ways to measure the thickness of mill scale formed on hot rolled steel coils. Can anyone suggest a way to make a Bakelite mold without disturbing the oxide scale so that I can use the mold to measure the thickness of oxide scale? In addition to the above problem, can you also suggest a way to cut the steel to the size of the molding machine without disturbing the oxide scale? "Disturbing" here is defined as breakage of oxide scale or reduction in thickness of scale due to mechanical vibration or by heat. Dinakaran Murugadass - Chennai, Tamilnadu and India June 1, 2017 A. I have a substantial restoration business in NYC restoring old "wrought iron" doors, windows, and architectural metal work. We are constantly refinishing old Fenestra-style windows and doors, chemically stripping them, and repainting. From our experience stripping thousands of windows and hundreds of doors, the mill finish is generally intact, and protects the steel. The only time it is not, is when the caulking fails and traps moisture, or air conditioners drip steadily on hot rolled steel causing it to fail. Without question in my mind, the mill finish is more durable than the typical oil alkyd paints made since lead paint was banned. We always leave it intact, unless the client doesn't want it. The blue black finish can be imitated with nigrosene powder and top coated with acrylic lacquer, but that will be more susceptible to rusting than the mill finish. Peter Triestman Olek, Inc. - historic metal restoration - Newark, New Jersey, US Effect of mill scale on refractories November 1, 2018 Q. Hi I am Muhammad Bilal, working in a steel-making industry as a refractory trainee engineer. I just want to know that what are the effects of mill scale on refractories either acidic or basic, and what effects it may cause useful or adverse, on all refractories, monolithic and bricked ones, too. Thank You. Please give me a detailed answer. Hafiz Muhammad Bilal Agha Steel Industries - Karachi, Pakistan finishing.com is made possible by ... this text gets replaced with bannerText Q, A, or Comment on THIS thread SEARCH for Threads about ... My Topic Not Found: Start NEW Thread

Further to my previous 2 blogs on mill scale, I seem to find more information in my aged brain, therefore, I wish to explain what it looks like after it is removed from the steel and what to do with it. In a rolling mill where the steel will be stretched and squished the mill scale will first be removed mostly by water jets, or by sand blasting in some shops or by vibrating rolls in others and the mill scale will fall into a pit below the equipment where it will also be joined by rolling mill lubricants and bearing oils and water. From there it will be pumped to a holding pond, where companies like Harsco will be paid by the steel mill to clean out the pond once in awhile and get rid of the mill scale. In the U.S. in the past, and only a few short years ago it was dredged up and let drip dry and sold to a bidder, normally a cement plant who bought it for a very low amount and processed it to use in cement making since they require a little amount of iron in their processing and mill scale hit the mark. However a few years ago the EPA found that some of the ingredients, mostly from the lubricants from the rolling mill oils, caused the mill scale to be a hazardous material. The cement plants looked for other sources of the iron and mill scale became a personna non-grata. As the international market place for mill scale was taking off with China purchasing it as previously indicated, it is now an out to send the hazardous waste there and let them deal with it. This is not very neighborly, to say the least, so a few companies have come up with alternatives. One is to compress the mill scale into giving up the oils and lubricants and water to an acceptable level for the feed to the sinter plant where the mill scale is mixed with other iron ores and hydrocarbons from coke plants and bake it at 2500 F. The squished out oils and lubricants by the way are recycled to be used once again. As far as recycling it to make other steel, the answer is yes it is being done at steel mills that employ a sinter plant. There are 7 in the U.S. and almost all steel mills in Europe, China and other places like India employ them with the use of the blast furnace to make steel. Other plants that use the EAF (electric arc furnace) cannot use them as it would take an ungodly amount of energy to extract the iron from the mill scale unless it were put through a major amount of preparation and chemical reduction first. There is also the consideration of what are the elements that are in the mill scale. Remember, I indicated that every bit of mill scale represents the product being made at the steel mill whether it is construction grades of steel like rebar or high quality alloys and stainless for example. Therefore if a steel mill wants to make rebar and they buy mill scale from the open market and it comes from an alloy shop what do they do with the other elements and how do they get it out? That costs money and lots of it for the procedures and the equipment and the chemicals to eliminate the unwanted stuff. So, further processing and experimentation and trials and tribulations must be done to be able to recycle and use all of the 10 million tons per year and growing.

Wow! Finishing.com has received thousands of helpful postings, but this is one of the most thorough and exhaustive ever. Thanks! Regards, Ted Mooney, P.E. Striving to live Aloha finishing.com - Pine Beach, New Jersey

Q. Hi All, I am currently doing a study on mill scale uses. My understanding is that a majority of mill scale is used in sintering. Are there other feasible uses as well (in cement and other such industries) And by feasibility I mean are companies from other industry verticals (apart from reuse in sinter for steel production) using mill scale in large amounts. Any expert opinion around this would be greatly appreciated

Q. - How can you mimic a finish that resembles mill scale on sheets of hot rolled material that has been de-scaled? I would like to first say that I am very impressed with the knowledge here! I am an architect and builder in Las Vegas. I also have a background in metal working and have studied metallurgy fairly in depth. I have never seen such concise (and correct) descriptions and explanation about mill scale and "what it is" before reading these entries! Great job! Anyways, as for my question: Here in the Southwestern United States, a trend in architectural aesthetics is a heavy industrial look using hot rolled steel where the mill scale is left intact and you can see the heat marks left by the rollers in the factory. One reason this is popular is because the extremely low humidity in our dry desert climates allows for these types of finishes to be left without a sealer and will never oxidize (rust) further. So the project gets an industrial aesthetic that requires no maintenance or upkeep and the cost for these types of looks is very low. You just put up sheets of hot rolled material and you're done. These architectural details are often full sheets of hot rolled steel used as wall paneling, fireplaces, bar-dies, etc. If anyone is interested, I can direct you to some photos on our website or social media pages to show you examples of this. My question is this: What is the best way to fake or apply a finish that closely resembles black mill scale on a hot rolled sheet? I am currently working on a project for an architect client who is using hot rolled sheets on a residential project. I ordered sheets of hot rolled steel from a large company in the midwest to be perforated (punched) in such a way where the different sized perforations make an image in the steel. The problem is that they ordered a "clean" hot rolled material where the mill scale has been removed. We are out of time on this project so I can't wait for them to receive the correct material and start over. I am hoping I can have them proceed with the punching and when I receive the material, just apply a chemical or something that would closely resemble mill scale. Thank you in advanced for your time and effort!

A. Nathan, There are a few things you can try on a few small samples to see which you like best. You can apply a faux finish such as paint but it's tricky and the paint could stand out over time. Some people take used motor oil, spread or spray it thinly over the material and light it on fire. After it cools off you can clean and scrub. Don't try this at home kids!

Q. Hi, I am researching ways to measure the thickness of mill scale formed on hot rolled steel coils. Can anyone suggest a way to make a Bakelite mold without disturbing the oxide scale so that I can use the mold to measure the thickness of oxide scale? In addition to the above problem, can you also suggest a way to cut the steel to the size of the molding machine without disturbing the oxide scale? "Disturbing" here is defined as breakage of oxide scale or reduction in thickness of scale due to mechanical vibration or by heat.

A. I have a substantial restoration business in NYC restoring old "wrought iron" doors, windows, and architectural metal work. We are constantly refinishing old Fenestra-style windows and doors, chemically stripping them, and repainting. From our experience stripping thousands of windows and hundreds of doors, the mill finish is generally intact, and protects the steel. The only time it is not, is when the caulking fails and traps moisture, or air conditioners drip steadily on hot rolled steel causing it to fail. Without question in my mind, the mill finish is more durable than the typical oil alkyd paints made since lead paint was banned. We always leave it intact, unless the client doesn't want it. The blue black finish can be imitated with nigrosene powder and top coated with acrylic lacquer, but that will be more susceptible to rusting than the mill finish.

Q. Hi I am Muhammad Bilal, working in a steel-making industry as a refractory trainee engineer. I just want to know that what are the effects of mill scale on refractories either acidic or basic, and what effects it may cause useful or adverse, on all refractories, monolithic and bricked ones, too. Thank You. Please give me a detailed answer.

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful. If you are seeking a product or service related to metal finishing, please check these Directories: Jobshops CapitalEquipment Chemicals &Consumables Consult'g, Train'g& Software About/Contact-Privacy Policy-1995-2021 finishing.com, Pine Beach, New Jersey, USA

water hardness scale for water softener: the ideal number

Maybe youre wondering if your home water is too hard? Millions of Americans wonder about their water, and there are tons of myths circulating online about what hard water is and how to calculate their water hardness scale.

Luckily for us calculating your water softener hardness number is a relatively easy thing to do. In this article, well go into what hard water actually is, give some tips on how to tell if its too hard, and discuss what the ideal water hardness is.

You may understand the effects of hard water if youve ever washed your hands with hard water and used soap immediately afterward. If water is excessively hard, you can feel a thin film remaining on your hands. This film, called soap scum, is created from the reaction of high levels of calcium in the water with the soap.

Another place hard water leaves its markliterallyis when doing dishes in a dishwasher. If youve ever done the dishes and taken out the glasses with spots or unsightly stains on them, this is a sign of too-hard water existing on your appliances.

Though hard water is not a health risk, it is something of a hassle when it leaves unattractive splotches on your dishware. It requires you to use extra soap to remove the product of the soap-calcium reaction in hard water.

Dishwashers, coffee machines, electric tea kettles, clothes washers, and any other device that heats water and passes it through its machinery can all experience buildup of calcium carbonate. These solid deposits can reduce the longevity of your appliance and alter the taste of your water.

If youve ever heard of people running vinegar through their coffee machines every once in a while, hard water is the reason. When passed through your appliance, the vinegar easily breaks down the calcium carbonate to keep your coffee tasting like coffee.

That said, though, there are other effective ways to get these minerals, and it may not be worth it to sacrifice the life of your appliances just for a few extra milligrams of calcium and magnesium a day.

Understanding your water hardness is extremely important when considering buying a water softener because you dont want to underpay and buy a water softening system that doesnt cut the mustard. Simultaneously, you dont want to buy a lion to deal with a mouse problem water softener systems that process harder water cost more (sometimes a lot more).

PPM is the most basic of the three measurements. PPM tells you the number of hard water minerals in a million drops of water. For example, if you have 1 PPM, one out of every one million molecules of your water will actually be a dissolved mineral.

GPG is also extremely common for measuring water hardness. A grain is a unit measurement leftover from the bronze age, when determining the weight of cereal grains was significant for ensuring fair trade amongst different nations. A grain, equal to about 64.8mg, is theoretically the weight of one cereal grain.

All that said, we still measure water hardness in grains, and a measurement in GPG essentially tells you how many grains (or quantities of exactly 64.8mg in weight) of hard minerals you have per gallon of water.

1 GPG is equal to 17.1 PPM, so to calculate your grains per gallon from parts per million, simply divide GPG by 17.1. If you have a measurement in GPG and want to get PPM, reverse this equation and multiply PPM by 17.1.

Measuring water hardness itself requires some special equipment. You can most likely find information about your water hardness level online or from your neighbors. If this isnt a possibility, or if you live in a rural area, you can hire a specialist to come to check your water for you or buy a water hardness test kit online.

The question of when water is hard is a hard (no pun intended) one to answer. While some water softener manufacturers consider water hard at 1 GPG or more, the United States Geological Survey puts the number at which water is considered hard at 3.5 GPG.

That said, we call it the water hardness scale, so there are different tiers of hardness, as indicated by the colors in the map above. From 0 60 milligrams per liter (0 3.5 GPG), the USGS considers water soft. According to this measurement, 61 to 120 milligrams per liter (3.5 7 GPG) is moderately hard water, 121 to 180 milligrams per liter (7 10.5 GPG) is hard water, and 181 milligrams per liter and above (10.5 GPG +) is very hard water.

Appliances will have a good, long life and soap scum should not be noticeable at 3.5 GPG or less. That said, at 3.4 GPG there are still many milligrams of dissolved minerals that can contribute to calcium carbonate buildup.

The ideal water hardness level depends to a large degree on your individual taste. The US Geological Survey tells us that water goes from being moderately hard to hard with a hardness of 121 milligrams per liter or above.

Similarly, the Minnesota Department of Health recommends anyone with above 7 GPG (~120 milligrams per liter) to soften their water to improve the longevity of their applications and the taste of their water.

Others online will recommend anyone with 3 GPG or above to get a water softener. Those who recommend getting a water softener at between 3 GPG and 7 GPG tend to make the claim that water at even 3 GPG of hardness will still leave splotches on dishes. There are also plenty of erroneous claims on the internet about moderately hard water drying out the skin and making the color of your laundry dull.

The ideal water hardness is best for you: if you dont notice bad tasting water or encounter any of the symptoms of hard water (soap scum, splotchy dishes), then you shouldnt worry whether your water is too hard. If, however, your water tastes bad or you notice calcium carbonate deposits in your oft-used appliances, you should consider treating the water.

The water hardness scale for water softener is a handy way to decide what kind of water softener you need if, in fact, you decide to use a water softener to treat your hard water. In this article, weve covered some facts about water hardness, discussed what is considered hard water, and made recommendations about ideal water hardness.

Remember that the most important measure of water hardness is your own senses! If you see mineral buildup in your appliances or taste water that isnt right, you should definitely consider treating it.

water hardness scale chart: do you have hard water? | waternity lab

Internationally recognized water hardness scale recognizes 4 water hardness classes from soft, moderately hard, hard, to very hard. In the US, the unit of water hardness is usually parts per million (ppm) or grains per gallon (GPG).

The immediate effects of using hard water might be apparent on your skin or on your dishes, faucets. Hard water with a high concentration of calcium and magnesium ions causes white stains pretty much everywhere.

You might not like it but fighting hard water is a smart long-term decision. Pretty much the only way that is very effective at softening water and eliminating all the problems that come with it is installing a water softener. You can find a list of the best water softeners here.

janka hardness scale - logs end

The Janka Hardness Scale is determined by a controlled test, performed to measure the force necessary to embed a .444 inch (11.28mm)steel ball to half its diameter in wood. The resulting data is expressed in pounds-force, or lbf. This industry standard assessment is designed to gauge the various wood species hardness, determine its suitability as flooring, and illustrate its tolerance to normal wear, tear and dents.

When selecting hardwood floors, consider your home or office layout and traffic patterns. If you have children or animals, very soft wood like pine may not be desirable. All wood species below Red Oak on the Janka scale areexpected to dent or wear more easily, but offer warmth and charm as they age. Extremely dense and exotic woods, however, are reputed for being exceptionally hard. While these species may offer benefits in high-traffic homes and offices, they can be challenging to install or require temperature controlled environments.

difference between hot rolled steel vs cold rolled steel | tampa steel

So you want to use rolled steel in your project. What type of rolled steel should you use? The terms cold and hot rolled refer to the industry names for steel formed at different temperatures. Here are the differences between these terms, and the advantages that come with each kind of steel.

In metalworking, rolling is a process of forming the metal into a final shape by passing through special machines that use heavy cylinders to flatten the metal into sheets. Its very similar to rolling out dough with a rolling pin!

The rolling process is a key feature of most steel mills. Passing the metal material through pairs of roll stands that are grouped into rolling mills is how most steel factories shape metal into finished products. The rolling process can be used to create structural steel (l-beams, angle stock, channel stock), bar stock, and rails. There are many types of rolling like ring rolling, roll bending, roll forming, profile rolling, and controlled rolling that can be used depending on the desired shape.

Steel mills start with a large mass of metal called a billet, which looks like a fairly long beam of metal. These billets are sent for pre-processing, where theyre passed through rollers and flattened into a sheet. After its flattened, the metal is white hot. This superheated metal is kept at a high temperature, and then sent through finishing rolls where it will be smushed into its correct, final thickness!

The last steps will depend on what type of product this hot rolled steel is going to become. For sheet metal, thats about all of the processing it has to go through! After its pressed to its final thickness, its rolled onto a coil and left to cool. If this steel is going to become bars, plates, or beams, then the metal is sectioned off sent for additional processing.

The reason why hot rolled steel has these markings on it is that the temperature is so high that it does not allow recrystallization. Recrystallization is a process where grains that have been damaged, as they are through the steel rolling process, are replaced with a new set of grains. This can only happen when the metal is cool, so any metalworking process that involves forming the metal in temperatures above the recrystallization point is considered hot rolled. The key to rolling steel is to closely monitor the temperature while its being worked to be sure that its remaining above the recrystallization temperature, otherwise the material will need to be reheated before being worked any further.

Matter expands when its really hot, and contracts when it cools. Because of this factor, the dimensions of hot rolled steel are not exact and can always change slightly as it settles after its cooled.

The difference between hot rolled and cold rolled steel is this recrystallization point. Cold rolling is done when the metal is able to form new grains as the old ones are deformed by rolling and bending the metal.

Typically, mills take hot rolled steel after its mostly or completely cooled and work it to its final dimension by either rolling it, extruding it, or drawing the metal over a mandrel. For this reason, its usually referred to as cold finished in the industry instead of cold rolled.

When you cold work the steel, you can reduce its strength so a final step called annealing is added. In metalworking, annealing means heating the metal to 1,333-1,400F which is just at the upper limit of the recrystallization point for steel. The metal is then allowed to cool very slowly, normally by leaving the metal inside the furnace and just switching the furnace off so its not brought to room temperature too quickly. Doing this allows the metal to create a uniform microstructure, and reset its grain from the deformed heated grain back to something more closely resembling an unheated microstructure. This process allows for metal that is very strong, but not too hard so its still easily malleable.

Cold rolled steel is going to be stronger overall than hot rolled steel. Note that cold rolled steel has grains, while hot rolled steel does not. This is important because cold rolled steel is going to be strongest when its laid with the grain, and is significantly weaker against the grain. Because hot rolled steel has no grain, there is no difference in strength depending on its orientation.

Another big factor in whether to use hot or cold rolled metal will depend on what construction processes youre planning on using to affix the metal, and what function its going to play in your project.

If youre planning on machining your materials further for your project then be very cautious with cold rolled steel. Cutting it the wrong way can cause warping, or otherwise damage the structural integrity of the metal if youre not careful! This is a big contrast to hot rolled metal, which does not experience any sort of warping when machined because of its lack of grain. If youre planning on welding, both hot and cold rolled metals will weld just fine but keep in mind that cold rolled metal will take on the appearance, and some of the other characteristics of hot rolled metal after being welded.

Is the metal going to be visible, or not? The finish of cold rolled steel will be overall better than hot rolled, because of the mill scale that develops when its heated. Although, some people do like the look of hot rolled metal and have incorporated it on the exterior for design purposes.

This article illuminates the basic differences between hot and cold rolled steel. For more in-depth information, consult with experts in the steel field. The team of friendly professionals at Tampa Steel and Supply has decades of experience and can help answer any questions regarding rolled steel or other steel and metal concernsfrom stainless steel sheets and pipes to sheet metal and aluminum tubing. Pick up the phone today to get a head start on your steel related projects.

janka scale - janka hardness - janka lumber scale

The Janka Test is a measure of the hardness of wood. The Janka Test was developed as a variation of the Brinell hardness test. The test measures the force required to push a steel ball with a diameter of 11.28 millimeters (0.444 inches) into the wood to a depth of half the balls diameter. The diameter was chosen to produce a circle with an area of 100 square millimeters. The Janka hardness values have been indicated below for your reference.

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