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Cleaning Steel

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Cleaning Steel

Cleaning Steel Before Brazing

There are many differing opinions in this area. I recommend Easy Off Oven Cleaner for cleanliness test because it is easy, cheap, effective and everyone knows it is dangerous. Freud says that caustic solutions can damage the carbide. I think the difference here is the amount of exposure. I do not think the amount of damage done by oven cleaner in a minute or so is significant.

Pretty well all the methods recommended here can be dangerous. I don’t like some of them for safety reason and others are just too flammable.

There are two areas here:

  1. Cleaning saw plate, just the steel part before the tips are put on.
  2. Cleaning a saw blade after use.

There are two differences. When cleaning saw plate for brazing you have to have the plate scrupulously clean so that the braze alloy will chemically bond with the carbide. However, when cleaning saw blades you are simply removing the resin, pitch, etc. Saw blades do not have to be clean enough for chemical bonding. For more information on chemically bonding tips to a saw blade take a look at some of the articles in our Brazing Section.

Cleaning saw plate, just the steel, before the tips are put on

Cleanliness - Testing Saw Plate for Cleanliness

Clean saw plate is essential for welding or brazed tips. New saw plate comes with a protective coating. Used saw plate has its own set of contaminants from use. You must remove this to get the best braze or weld.

Following is a test on a saw plate that was sent to me for analysis. They had tip loss and wanted to know what to do about it.

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I took an eye dropper and put three drops of water on the saw plate and it formed a nice, round bubble (left picture.) For comparison I took a piece of steel and ground it with a very rough wheel. You can see the bar on the right of the far left picture and how the water spread out more. The technical term is “contact angle” (see drawing above)

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The next step was to take cleaner and clean the saw plate. Then I put three drops of water in the clean area (above left) You can see how the 3 drops of water on the left spread out much more than the three drops of water on the right. You can also see how the clean area around the big spread has a different reflectivity than the uncleaned area.

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Left aboveis what it looks like when it is brazing alloy on a saw plate.You can see the distinct, steep ridge along the edge of the brazing alloy. Another sign is the feathering out from the brazing alloy ridge. When the brazing alloy doesn’t flow well the constituents tend to separate out and you get some bleed out from the main mass of alloy.

Center and Right are tests of brazing alloy in the same areas where I ran the water drop test. (Clean area centerand uncleaned far right.) I measured the areas of the flow as rough rectangles. Clean was .63” x .41” for .25 sq. in. Uncleaned was .52” x .31” for .16 sq. in. The clean area wet 60% better.

The real difference is that there is an edge on the uncleaned area where it didn’t wet at all. Uncleaned plate wets poorly and parts of it may not wet at all.

Cleaning Saw Blades For Brazing

Saw blades need to be clean before brazing so that you can form a chemical bond between the saw steel and the carbide or other tipping material. You have an advantage with brazing in that the flux and the heat of brazing do perform some cleaning function. However this is not be relied on. Flux is primarily a protectant to keep air from the braze area. A torch or other heat source can change any oils and greases on the steel into free carbon or other unbrazeable compounds.

Cleanliness of all the parts is an essential step to successful brazing. Clean parts braze well. Dirty parts cause trouble. Oil on steel or carbide causes problems a couple ways.

  1. It contaminates the braze alloy and makes it less effective.
  2. It forms gasses and causes bubbles in the braze alloy.
  3. It burns and creates free carbon and carbon compounds. Carbon is terrible for brazing. That’s why so many people use graphite blocks for brazing fixtures.

Saw plate is supplied with a protective coating to prevent rusting. This coating also allows handling. Some saw plate is supplied coated and hermetically sealed in plastic as well.

Three Case Studies

It is very easy to accidentally get parts dirty.

  1. One involved parts that were covered with oil. It seems the customer received the parts and then stored them in a chest. The chest was in an area where they were grinding using oil and other fluids. The mist from the grinding eventually worked its way onto the parts. You could actually feel the oil on the carbide.
  2. In another case the brazer was using a torch to burn the oil out of the notches on the plate. When you burn carbide or steel with a torch to clean it you do two things. You burn the steel and create metal oxides. This is like painting over rust. You also burn the oil and create ash and other compounds from the burnt oil. This is like painting over rust that is also dirty.
  3. There was a third case where the customer was sandblasting to get oil out of the notch. Sandblasting does not generally remove oil very well. It tends to contaminate the sand and make oily sand, which spreads the oil over everything.

Much of the following comes out of our work in electroplating. Fortunately it is easy to apply this technology to saw blades.

Cleaning has two parts:

The first one is physical removal like blowing leaves off a sidewalk. The second one is a chemical reaction such as using hand cleaner to get grease off. Water is a solvent and will dissolve many things such as sugar and salt but it will not dissolve oil and grease. The same thing is true with any solvent you use. Whatever cleaner you use it will almost certainly work better with some physical removal such as brushing, wiping, high pressure spray or similar.

There are basically three kinds of materials to be cleaned off saw steel.

  1. Organic soils (A chemical term meaning carbon based) such as lubricants, oils, greases, polymers and similar, which are usually spread in thin films and may not be visible.
  2. Inorganic soils (not carbon based) including heat and weld scales, carbon, dust, rust, oxides and similar on surfaces exposed to air and can be worse at elevated temperatures.
  3. A mix of 1 and 2. this can include buffing compounds, fingerprints, shop soils, marking compounds. These can be the most difficult to remove.

Selecting the proper cleaner is necessary to remove specific soils efficiently and effectively. Carefully consider the following factors:

Considerations in cleaning

  1. What do you want to remove
  2. Underlying metal – you can use caustic cleaners in steel but they will react aggressively
  3. What are you truing to achieve – how clean, how rough, etc.
  4. What has been done before – have the grease been heated and baked on
  5. How big and what shape is the area – Do you need a can of spray cleaner or a dip tank.
  6. Cost – equipment, processing and disposal
  7. Health and safety

Cleaning Steel for Brazing

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Tools

Spray on left and wipe on right

After rinsing

 

This is an old saw plate sprayed with WD 40. A thick, water based ink solution was poured over it to show the underlying grease. The left side was sprayed with Easy Off oven cleaner and the right side was wiped three times using a paper towel soaked in acetone. In the middle picture you can see the oven cleaner bubbling up on the left and the streak marks on the right from the acetone wipe. Finally the plate was rinsed under running water. The oven cleaner side rinsed clean and the acetone left side has streaks.Solvents are not cleaners. They can be used to clean but that is not their intended use.

 

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This is a picture (left) of the braze joint where carbide (top) is attached to the steel (bottom). The braze alloy balled up between the steel and the carbide. Both sides were dirty so the braze alloy did not stick well to either side. You can also have steel or carbide that is not completely clean and it won’t show up on the sides. It will create pockets inside where the alloy doesn’t stick and that means weak joints. Carbide that came off showing pockets in the braze alloy (right.)

Solvents

Solvents used to be great cleaners. Now most of the really effective solvents are illegal.

Solvent cleaning is a process of dissolving the materials covering the steel. The more often you repeat the process, the better it works. If you get 90% the first time then you will get 90% of the remaining 10% the second time for a total of 99% removal. You never get it all but you can get it clean.

Solvent comes from dissolve which means to merge with a liquid. The idea is that you dilute the oil and make it easier to wipe away. However, you are only dissolving the oil so there will always be a little remaining even if it is in a much smaller concentration. Also, the oil sticks to the saw plate and a solvent dissolves from the top down so it does not get under the oil and remove it.

You have to know which solvent to use. Water is an excellent solvent but it won’t touch oils and greases. Acetone, alcohols and other common solvents do not dissolve everything no matter which one you use. The old solvents that used to be very effective are now largely illegal. Vapor degreasing has often been replaced by wiping with methanol or a similar process with a great reduction in both quality and reliability.

There are also modern protectants, many plastic based, that are much more solvent resistant than the older, traditional petroleum and animal based protectants.

Easy Off makes soap

The sodium hydroxide (caustic soda) in Easy Off mixes with the oil or grease to make soap. Dishwashing detergent and laundry soap use the same process but they use milder chemicals than oven cleaner does. Another example of this process is the old-fashioned method of making lye soap. It called for mixing lard with lye and cooling the mixture to form soap.

Soaps and detergents

Molecules of detergents are long and thin, like a match. The head end dissolves in water and the tail

dissolves in grease. When something greasy is washed in detergent, the grease-soluble tails plug themselves into globules of grease. They surround it and form ball-shaped micelles, which float the grease, into the water.

Ultrasonics

Ultrasonics can be extremely effective. However ultrasonics just apply energy to help the chemicals work. How you load the machine is very important because these are sound waves and can be blocked by corners and walls just as voices are. In addition the ultrasonic echoing effect in the tank can be either good or bad. Also thick grease probably attenuates the sound, causing it to deaden and decreasing its effectiveness.

Vapor degreasing

Chemicals used in vapor degreasing are most effective when they go through the evaporation and condensation cycle. When used merely as solvents they lose a great deal of their effectiveness.

Cleaning the Saw Notch Before Brazing

The best way we have of explaining cleanliness to brazers came from a customer. He said just tell them it’s like painting a car. You have to get to clean, bare metal. Nobody who was serious about doing a good paint job would just go out and start spraying. You make sure all the old paint is off. You make sure the surface is really clean. You make sure that the surface stays clean while you are painting.

In brazing you have to have clean carbide and clean steel and keep them clean.

How to braze good saws

  1. Clean steel and clean carbide
  2. Rough steel and rough carbide
  3. Good solder and keep it good. No contamination
  4. Enough heat but not too much - see fillets
  5. Not too thick a joint
  6. But thick enough
  7. Good fillets

A lot of times the saw tip will come lose from the saw body because the notch was not properly prepared. A dirty notch can leave oil and grease as well as grinding dust and general dirt. Anything (repeat anything) left in the notch will cause a weaker braze joint. It dilutes and contaminates the braze alloy. It prevents chemical and physical bonding between the braze alloy and the steel or carbide.

The most thorough method I have heard of was given to me by a customer who never has a tip loss problem.

  1. Grind the notch smooth, flat and square. You can buy sandblasted plate but sandblasting rarely removes the full amount necessary for good joining. When the plate is laser cut there is a heat affected zone about .003” to 0.004” deep that has to be entirely removed.
  2. Wipe the notch with a clean cloth. Clean means no oil, no dirt, no greases, no dust and no fabric softener or sizing.
  3. Remove all oils and greases with a caustic solution or something with an equally good affect. Solvents are not recommended.

The essential thing is to provide a clean flat, smooth, surface so that the braze alloy can chemically and physically bond to the steel. Grinding the notch will remove heat scale. Wiping with a clean cloth will remove a lot of the film and oil. The final dip will clean the surface.

There have been questions about whether the notch should be “rough” or “polished” since I use both terms above. A common braze joint thickness for saws is about .003” (3/1,000). With this in mind then anything under .0005” (5/10,000) ought to be good. If the final joint is .003” then you do not want anything over .001”.

You must remove all oil and grease. It is essential to remove oil and grease for a lot of reasons. An oily base metal will repel the flux. This will leave bare spots that will oxidize under heat and create voids. Oil and grease will also carbonize when heated and form a film that prevents solder from flowing over the carbonized areas. The carbon will contaminate and weaken the braze alloy. The oils and grease can vaporize and cause bubbles in the braze joint.

Summary

Cleanliness of all the parts is an essential step to successful brazing. Clean parts braze well. Dirty parts cause trouble. Oil on steel or carbide causes problems a couple ways. 1. It contaminates the braze alloy and makes it less effective. 2. It forms gasses and causes bubbles in the braze alloy. 3. It burns and creates free carbon and carbon compounds. Carbon is terrible for brazing. That’s why so many people use graphite blocks for brazing fixtures.

More Information:

http://www.cleanersolutions.org/ - Cleaning solutions and solvent substitutes
http://www.mntap.umn.edu/ - University of Minnesota, Minnesota Technical Assistance Program


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