One of the problems you might face during welding is mill scale which can make the weld look rough and attractive. So how about we have a little discussion regarding mill scale removal and its solutions?
When it comes to welding, you have to be careful with each step and each part to get a problem-free and effective weld. You will encounter different problems in your working area while doing a specific type of weld.
Mill scales will not only make the weld appear attractive but also they can cause the weld to be weaker and weaker. And if not taken care of properly, they might cause other problems as well related to weld.
So let’s make sure that our weld and the base metal must be clean from mill scales.
What are mill scales?
Before we go deep into our discussion, first we will let you know what mill scales are. This way you will have an exact idea about it if you don’t know what mill scales are or if you are new to welding.
Mill scale is the formation of the iron oxide layer in a dark grey color on the surface of hot steel.
However, if you are using cold steel for your work, then you will not encounter any problems related to mill scales. But cold steel is expensive as compared to hot steel. Also, it is not suitable for all types of welding work.
Is it necessary to remove mill scales?
Now, this is the question that should come to your mind: “Why do we have to remove mill scales?” or “What happens if we don’t remove mill scales from the metal?”
To answer these questions, here are a few things which you need to know:
- Mill scale can result in porous metal. It will cause pr\orosity on both the upper and lower sides of the welding metal and the weld itself.
- Before painting the welded surface, mill scales should be removed to get a clean and smooth finishing.
- If mill scales are not removed before welding, then prepare yourself to do a lot of cleanup after the welding. However, to save your time and effort, make sure to remove them before welding.
- The last thing is that mill scales have a higher melting point in comparison with base metal.
What if I weld metal without removing mill scales?
This is the second question that we are going to answer you right now. Well, in the case of a thin coating of mill scales, some welders recommend welding using the MIG welding technique.
For this purpose, they use a steel MIG wire having manganese and silicon in it. This wire acts as a deoxidizing agent. Besides this, it is also permissive to impurities that are present on the surface of base metal in a light coating.
This method will cause all the impurities to gather up and collect on the surface of the base metal. After the weld is cooled down, these contaminants are removed by cleaning the surface.
However, doesn’t matter if you are using the MIG welding technique or any other method to weld metals, removing scale mills should always come first.
Removing mill scale
Now coming toward the main topic of today, there are several ways to remove mill scales from the metal. Also, some of these methods are applied before welding and some after welding.
Each method has its effectiveness. You need to select the method which you think will give you the 100% result you want.
Methods for mill scale removal
Among all the different methods, we will discuss the three most effective ways to remove mill scales:
- Using a grinder to remove mill scales
- Use of white vinegar
- Using muriatic acid
Using a grinder to remove mill scales
This is the most traditional method to remove mill scales. For removing mill scales on a small level, MIG welders very often use a grinder to make the surface free from these impurities.
But using a grinder to remove mill scales is not easy and effective if you are not using the right tool for it. If you are using sanding disc wheels or flap disc wheels to remove a heavy layer of mill scales, then it will leave you frustrated.
These two wheels are not recommended for heavy mill scale removal. That is why the choice of equipment is very important.
Why use the grinding method?
- Here, you don’t have to deal with any type of acid for mill scale removal.
- Grinding can be done indoors and in open areas as well.
- Choosing the right type of grinding wheel is the key point of this method. Once you have the right equipment, removal of mill scales is quite convenient and easy.
After grinding mill scales
When you are using grinding methods, keep in mind that his way metal is highly likely to rust when exposed to air as compared to other methods.
For this reason, after the welding is done, applying a light coating of oil on the surface is advised. This oil coating should be removed when you are going to paint the metal.
Use of white vinegar for mill scale removal
Removing the mill scale using white vinegar is more effective and smooth in comparison with grinding.
It is very similar to the method where we use muriatic acid to remove mill scales. But as we know that vinegar is less acidic, it is quite safe and convenient to use.
All you need here is a suitable tank that is capable of containing vinegar. Make sure that your container is strong enough that the vinegar will not penetrate through its walls during the time of mill scale removal.
In addition, you will need a lid to close the mouth of the container. A lid is required to keep the sharp smell of vinegar contained within the tank.
Preparation and safety measures while using vinegar
As we know that vinegar is less acidic, it doesn’t mean that we don’t have to be careful. Make sure your hands are covered properly with gloves. In case you are working bare-handed, there is a chance that the acid will seep into any cut or scratch on your hand.
Also, wear safety goggles to protect your eyes. Because you will not want to have an unpleasant experience of vinegar splashing into your eyes.
Dipping the metal in white vinegar
Here all you have to do is take a container that can contain vinegar. Pour vinegar into the container. Put the metal piece in it. Lastly, close the lid.
Now, wait for 24 hours because vinegar needs time to work properly. If you are putting more than one piece of metal, then make sure you change the sides of the metal at a given time. This way vinegar can thoroughly come in contact with every part of the metal.
After that, you can remove the metal from the vinegar container and wash it with water to clean it. Then dry it in the air or use a blow dryer for quick drying. If you still see some mild mill scales on the surface, then use a grinder to grind them off the surface.
Spraying white vinegar on the metal surface
For large metal pieces, it will be difficult to find a container so they can fit in. you might not find it at all. Here the best solution is to spray the vinegar on the metal surface.
Either you can use a spray bottle to spray the vinegar. Or a more effective way is to soak some clothes or towels in vinegar and place it on the metal surface. Leave the soaked towels there for 24 hours.
After that, clean the surface will water and dry it off.
Why use white vinegar?
- First of all, there is no chemical requirement here.
- Secondly, it can be easily done indoors as long as you have something to cover the mouth of the tank to contain the sharp smell of vinegar.
After using white vinegar
Now that the mill scales are removed and the surface is exposed to air, it will start to rust. So apply an oil coating to protect it from rusting.
Using muriatic acid for removing mill scales
Here comes the most effective and quickest way when it comes to remove thick and heavy layers of mill scales. You will need a container with a lid big enough that you can dip your metal in the container having acid in it.
It contains 20-32% hydrochloric acid. It is highly acidic so a lot of care is required while handling such an acid. This acid can be easily found in pool supply stores because it is also used to clean pools.
Preparation and safety measures while using muriatic acid
Here you are dealing with a strong chemical so extra care is required. Your whole body should be covered to make sure you are safe from any splashes of the acid.
Wear acid-resistant gloves and safety goggles to protect your hands and eyes. You will also need a respirator here because the fumes coming from the acid are very hazardous. You will certainly not want to breathe it in and fill your lungs with acid, right?
Dipping the metal in Muraitic acid
Here all you have to do is to put the acid in the container. Dip your metal in it. Check it after 10 to 15 minutes. A maximum time of 30 minutes is more than enough for the removal of all types of impurities.
After that, take it out of the acid and clean it thoroughly with water.
Spraying muriatic acid on the metal surface
Here you need a spray bottle capable of containing the acid in it. You will have to work outdoors in this case to avoid splashing of acid. Besides, this method is used when the metal you are working on is very big and cannot fit in any container.
Spray the acid on the metal surface and check it after 10 to 15 minutes. Remove it after 30 minutes. The rest of the procedure is the same as above.
After using muriatic acid
After the removal of mill scales, muriatic acid should be disposed of properly to ensure safety. Also, you have to protect the metal surface from rusting.
For that, you can use baking soda mixed with water and apply it to the surface. This will be helpful to neutralize the acid and will prevent it from rusting. In addition, make sure you are using this method in an open place.
All these methods can give you the required result as long as you use them according to the mentioned instructions. If you are being careless, then not only the mill scales will not be removed but also you will compromise your safety. So before choosing any of these methods, make sure you do proper and thorough research.