Why Blacken?


Corrosion Protection—Adds years of service life to parts and extends the shelf life of stored parts.

Durable—The black chemical conversion finish does not chip, craze or peel.

Anti-Galling—When it is necessary to break-in mating parts, the anti-galling surface sacrifices the lubricating layer of black during initial contact and abrasion while a work-hardened surface is formed.

Lubricity—Oil-based, post treatments not only provide protection against corrosion, but provide for smoother running of mating parts.

Dimensional Stability—Blackening process produces essentially no dimensional change with only 5 to 10 millionths of an inch added to dimension, which means the blackened parts retain their surface properties with polished surfaces retaining their gloss and heat-treated parts retaining their Rockwell hardness. Tool integrity is preserved and critically sized parts can be finished.

Esthetic Appeal—Produces a pleasing, decorative black finish which enhances the perceived quality of the part, which improves the salability of the part.

Reduce Glare—For lessened eye fatigue.

Productivity and Economy—A much faster process which saves time and money versus painting or plating processes. A cost-effective means of providing corrosion protection to iron and steel parts.

Choose The Right Blackening Process For You


In most installations only a simple five-step process is required:

Cleaning—Soils, such as cutting oils, coolants, lubricants and rust inhibitors must be removed. Soils can inhibit or prevent subsequent operations. E-Kleen 105 or E-Kleen 151 aqueous alkaline soak cleaners are most often used, with an immersion of the parts for two to five minutes at 120° to 150°F.

Rinse—Use cold, overflowing rinse water. It is necessary to rinse the parts to remove residual cleaning solution. Immerse for 30 to 60 seconds. A cold-water rinse is sufficient for rinsing light parts. However heavy, thick parts may chill the blackening solution, so a hot-water rinse is preferable , which will preheat the parts, resulting in a faster, more uniform blackening.

Blackening— Parts are immersed in a boiling 285°F solution of UltraBlak until a deep uniform black is developed, usually within 10 to 20 minutes. The bath chemistry is regenerative—the only chemicals being consumed are those physically dragged out on the parts into the rinse water. Since the UltraBlak solution is saturated, it automatically maintains a concentration of 5.75 pounds of salts per gallon of solution when operating at its boiling point. If the solution boils below 285°F, additional salts must be added to raise the temperature to 285°F. If the solution boils above 290°F, water has to be added with an automated water-addition system until the boiling point is reduced to 285°F.

Cold- Water Rinse— To remove residual blackening solution and to ensure the sealant is not contaminated.

Seal—Parts are immersed in one of EPI’s E-Tec brands of corrosion inhibitors to impart corrosion resistance and lubricity to the finish. E-Tec formulations are available to deposit an oily, slightly oily or dry-to-the-touch finish with either water-displacing solvent-based solutions or water-soluble formulations.

Optional: Activation or derusting/descaling for a seven-step process.

UltraBlak will not cover up surface rust or heat-treating scale. These imperfections must be removed in a 50%-by-volume hydrochloric (muriatic) acid solution following Step 2 above. The use of a hydrochloric acid dip will also serve to activate difficult-to-blacken surfaces resulting in a faster blackening reaction and a more uniform finish. The residual acidic solution must be removed with a hot or cold-water rinse prior to the UltraBlak 400. Please see the individual technical data sheets or MSDS sheets for the E-Kleen, UltraBlak 400 and E-Tec products to ensure proper and safe operation.

Benefits of Hot-Temperature Blackening Process

  • Corrosion protection
  • Abrasion Resistance and Durability
  • Surface Preparation
  • Environmentally Friendly
  • Chemical Cost
  • Equipment Cost

Pieces to be blackened may be processed in polypropylene, or stainless steel tumbling barrels, hung on racks or hooks, depending upon the shape, weight and production requirements.

Cleaning - Thoroughly clean and degrease pieces with E-Kleen SR-140-E hot (140°-150°F) soak cleaners. Typical cleaning time is only 5–10 minutes.

Rinse - Rinse pieces in bottom-fed, overflowing cold water rinse for 60 seconds.

Blacken - 50% by volume or E-Pik 215, 2#/gallon for 5-10 minutes.

Rinse - Rinse in bottom-fed, overflowing cold water rinse.

Seal – Immerse in KOOL-BLAK 225 solution (220-255°F) until a deep black color is developed. Immersion time: 15-45 minutes, depending upon the mass of parts, type of steel alloy and condition of surface.

Rinse - Rinse in bottom-fed, overflowing cold water rinse.

Seal - Immerse for 1 minute in one of the following EPi products for your desired finish:

  • Oily Finish: E-Tec 501
  • Soft Dry Film: E-Tec 510
  • Hard, Dry Film: E-LAQ 525

Benefits of Mid-Temperature Blackening Process

  • Corrosion protection
  • Abrasion Resistance and Durability
  • Surface Preparation
  • Environmentally Friendly
  • Chemical Cost

Pieces to be blackened may be processed in polypropylene, or stainless steel tumbling barrels, hung on racks or hooks, depending upon the shape, weight and production requirements.

Cleaning - Thoroughly clean and degrease pieces with E-Kleen SR-140-E hot (140°-150°F) soak cleaners. Typical cleaning time is only 5–10 minutes.

Rinse - Rinse pieces in bottom-fed, overflowing cold water rinse for 60 seconds.

Blacken - 50% by volume or E-Pik 215, 2#/gallon for 5-10 minutes.

Rinse - Rinse in bottom-fed, overflowing cold water rinse.

Seal – Immerse in KOOL-BLAK 225 solution (220-255°F) until a deep black color is developed. Immersion time: 15-45 minutes, depending upon the mass of parts, type of steel alloy and condition of surface.

Rinse - Rinse in bottom-fed, overflowing cold water rinse.

Seal - Immerse for 1 minute in one of the following EPi products for your desired finish:

  • Oily Finish: E-Tec 501
  • Soft Dry Film: E-Tec 510
  • Hard, Dry Film: E-LAQ 525

Benefits of Mid-Temperature Blackening Process

  • Corrosion protection
  • Abrasion Resistance and Durability
  • Surface Preparation
  • Environmentally Friendly
  • Chemical Cost

The most commonly used process in commercial blackening includes seven steps. However, the InstaBlak process in most installations requires only five steps.

Cleaning—Soils such as cutting oils, coolants, lubricants and rust inhibitors must be removed. Soils can inhibit or prevent subsequent operations. They can negatively affect coating adhesion and appearance. E-Kleen 148E, an aqueous alkaline soak cleaner, is most often used with an immersion of the parts for two to five minutes in a 10% solution of E-Kleen 148E at 120˚ to 150˚F.

Rinse In Cold, Overflowing Tap Water—It is necessary to rinse the parts to remove residual cleaning solution. Parts carrying over an unrinsed clinging film of alkaline cleaning solution would quickly contaminate a subsequent step of activation or blackening, resulting in a spotty or nonadherent black finish. Immerse for 30 to 60 seconds.

Blacken—Immerse for two to four minutes at room temperature in a 10% to 15% by volume solution of InstaBlak 333.

Rinse—In cold, overflowing tap water for 30 to 60 seconds to remove residual blackening solution.

Seal—The finish by immersing the parts for one minute in a compatible E-Tec water displacing solution. The E-Tec corrosion inhibitors are formulated to rapidly displace the residual acidic solution from the preceding rinse. The InstaBlak coating is porous and absorbs the E-Tec solution, producing long-term corrosion protection. As the E-Tec is absorbed it enhances the depth of black which may take several hours. E-Tec formulations are available for oily finishes, dry-to-the-touch soft finishes and dry, clear hard finishes.

Activation—In most applications an alkaline cleaning in E-Kleen 148E is sufficient. However, some difficult to blacken steel alloys, will require an activation with E- Prep 258 to make the steel surface receptive to the blackening reaction. E-Prep 258 is used at 5 to 10% by volume in water at room temperature. Immerse for two minutes after step 2. It is followed by another cold-water rinse prior to blackening making the process a seven-step process.

Blackening Process Videos


Troubleshooting for Specific Products


Loose Red Oxide Which Wipes Off

If an Ultra-Blak 400 bath drops below boiling for longer than 2 or 3 minutes when a load of parts is introduced the parts will come out of the bath with a loose red oxide on top of the desired black finish. This red oxide is easily wiped off to reveal the desired black oxide finish. When this happens, more heat must be applied to the bath so that it does not drop below a rolling boil for more than 2 or 3 minutes when a load is introduced or the weight of each load can be reduced. Ideally, a black oxide tank should be sized with 1 gallon of solution for 1 pound of iron or steel parts. The maximum load to go into a hot black oxide tank should be 2 pounds per gallon.

 

Loose Red Oxide Which Wipes Off

A loose red oxide which wipes off easily can also be developed over the desired black oxide finish if the tank is being heated with electric immersion heaters or a hot gas flue. These two types of heating can scorch the solution producing red iron oxide in the solution. This can be overcome by putting a stirrer in the solution to keep it moving during heating, by increasing the number of electric heaters or by increasing the area of the flue running through the solution.

 

Loose Red Oxide Which Wipes Off

A loose red oxide can also develop due to a high level of red iron oxide in the solution. This is seldom a problem with the rectified Ultra-Blak 400 solution but excess iron can be dragged into the bath where it reacts to form red iron oxide. This excess iron can develop from dropping parts into the bath or by carrying finely divided iron into the bath on the surface of steel parts from polishing and buffing operations. In addition, iron can be dragged into the bath from acid pickles high in iron concentration and this iron will readily react to form red oxide. If iron is being dragged into the bath, then the problem can be eliminated by a more thorough cleaning and a more thorough rinsing prior to immersing the parts in the black oxide bath. This is frequently a problem with all other competitive black oxide baths which are not rectified to the extent that Ultra-Blak 400 is. If, by chance, this does happen to an Ultra-Blak 400 bath, then the bath should be desludged and the surface should be periodically skimmed to remove the red iron oxide as it floats to the surface of the bath. Ultra-Blak Rectifier may be added to the bath to clean out the red iron oxide.


A Green Cast To Blacken Parts

A green cast can develop on the parts if the bath temperature is allowed to drop below 275F.

 

A Red Tint to the Black Finish Which Cannot Be Wiped Off

This most often happens when heavy parts are removed from the rinse water following the blackening before they have completely cooled. This can also be caused by too long of a transfer time between the blackening bath and the cold-water rinse. If it is a transfer time problem, the operator should transfer the parts from the blackening solution to the rinse as fast as possible. With automatic blackening machines the time of transfer should also be kept to a minimum. If the problem cannot be eliminated with transfer time, then a fine mist of water spray should be impinged on the parts while they are being lifted out of the blackening solution and being transferred to the cold water rinse.

 

Reddish/Brown Splotchy Oxide Which Can Be Rubbed Off

This discoloration can be caused by too long of a transfer time when the hot parts flash dry leaving solid salts of the solution on the surface prior to the parts being immersed in a cold-water rinse. The dried salts are very corrosive and leave a discolored or thin gray-black oxide underneath. This problem is solved by reducing the transfer time or with the impinging spray rinse.

 

A Red Mahogany Tint Which Cannot Be Wiped Off

This may happen with certain steel alloys and especially with chrome steels when too short of an immersion time is used in the black oxide solution. It also can happen when the steel parts are introduced into a black oxide solution when the temperature is above 290F. The temperature is too high to start the proper reaction and a red oxide results. This problem can be solved by lowering the temperature to 285F or below and immersing the parts for 45 minutes to one hour. This is very seldom a problem with Ultra-Blak 400 which is formulated to blacken a wide range of alloyed steels. Competitors solve this problem by using two black oxide baths with one at 285F and the other one above 290F but this results in an increase in capital cost to install the blackening process.

 

A Red Cast or Other Off Colors Which Cannot Be Wiped Off

Bi-metallic corrosion (galvanic) can happen when common steel alloys are in contact with stainless steel while in the hot black oxide solution. A galvanic cell is created between the steel and stainless steel. It is because of this type of problem that black oxide tanks are constructed of mild steel. However, stainless steel barrels or stainless-steel dip baskets are frequently used in a black oxide line because acid dips are used prior to blackening and stainless steel is used to prolong the life of the baskets and/or barrels. When a stainless-steel barrel is being used with Ultra-Blak 400, it is recommended that the saddles that the barrel rest on be insulated with rubber from the mild steel tank. The rubber and/or wood should be under the mounting bolts as well. If a stainless-steel dipping basket is being used, it is recommended that a wooden bar be used to suspend the basket in the solution rather than a steel or stainless steel bar to avoid the formation of galvanic cells. This off color due to galvanic reaction may show up sporadically, being present with one load and not the next load. It is never recommended that a rotating barrel be constructed of a combination of mild steel and stainless steel and the same goes for dipping baskets.

Problem: Spotty and non-uniform blackening

Reason: Poor cleaning or poor rinsing

Solution:  Increase temperature of E- blackening Kleen 148-E to 150˚F. Increase dwell time. Make sure solution concentration is 10-12% by volume. Rinses must be clean. Residue from cleaner must be removed. Check to see if there is any waterbreak on parts.

 

Problem: Excessive rub-off 

Reason: Improper Blackening

Solution: Blackening solution too strong or excessive time in blackening solution. Check again if parts are clean prior to blackening.

 

Problem: Parts rusting after blackening

Reason: Poor rinsing, insufficient time in sealant or excessive water in sealant

Solution: Rinse must be clean to remove residues of blackening solution. Increase dwell time in sealant making sure water is displaced off parts. Do not let parts dry after rise prior to sealant. Drain water from the bottom of the sealant tank.

 

Problem: Bluish cast on parts or grayish finish 

Reason: insufficient activation

Solution:  Carbon steels, 4130 and heat treated materials may require more time in EPI  E-Prep 258. Longer time in blackening may be helpful.

Parts do not blacken

Check temperature: try running Kool Blak 225 at 240-250°F.

Possible cleaning problem: increase E-Kleen SR 102-E concentration to 20% by volume and increase temperature to 180°F. If using synthetic cutting fluid, it can be very difficult to clean - try switching to another cutting fluid coolant.

Check for water breaks on parts - if you find water breaks, parts are not clean - go back into cleaner. Make new cleaner if needed.

Examine if oil has been dragged down the line or is in the acid tank - this oil will coat the parts and they will not blacken. Improve cleaning – may need to make a new cleaner.

If using Hydrochloric Acid make sure you do not use inhibited Hydrochloric Acid. It will affect the blackening results causing discoloration to no blackening at all.

Silica level has gone over 2000 ppm due to silicate-containing substrates or silicated cleaner. Switch to Kleen SR 102-E non silicated cleaner.

 

Parts turn Brown instead of black

Lag time of parts getting into the rinse tank:  the parts need to be removed from the Kool Blak 225 and into the rinse tanks as quickly as possible. If you have an automated hoist, spray the parts with a hose using fine mist from garden sprayer onto the parts as they are pulled up and out of solution until they are completely immersed in the rinse water.  

Acid dip spent: make a new acid dip.

Kool Blak 225 solution has red/brown sludge in it that drags out with the part and cannot be rinsed off easily: check sludge level (iron hydroxide) - it might be time to desludge the tank (should be done at least once a year).  

 

Slow Blackening

Might be blackening too many parts at one time: process 1 pound of parts per gallon of Kool Blak 225. Typically, temperature drops when you have too many parts.

Make sure all electric heaters are working.

Acid dip spent: make new acid.

Add an electric mixer, such as Lightnin® that is made for high caustic application.

Rinse water is very cold: try using a heated rinse tank at 120-160°F.