Q: Our company plates hard chrome on hydraulic rods as well as other parts. For many of these parts we apply a flash chrome plate prior to plating with hard chrome. Is there any rule of thumb as to whether we should be using a current density of 2-4 ASI?
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A. No, I do not have a rule of thumb for this particular plating step. If you talk with individuals who are in the hard-chrome-plating business as well as read the printed literature, you soon find out that there are multiple opinions as to whether a flash is required in most situations. When you talk about flash plate, I assume you are thinking in terms of a ramping of the current density for a short period of time until you reach the required current density for doing the chrome plating. Since I don't have a good answer for you, I'll ask our readers if they have any thoughts on this. If you do please respond to me through Products Finishing magazine.
Q. We are a landing gear repair station that hard chrome plates in a standard hexavalent chromium bath. Recently, some of the plated parts have shown rough areas with pits that are teardrop shaped and have a tail that goes up. We have tried a number of different adjustments to our plating bath to no avail. The chemistry has remained the same and within specifications given by our chemical vendor. Do you have any ideas as to what is causing this problem?
A. The two most common causes of pitting and services in a hard chrome plating bath are contaminants on the surface of the part and sticking bubbles. Since you mentioned that the tear-shaped pits have tails that go up, I think that your problem is sticking bubbles that are caused by the evolution of hydrogen gas that is always part of the hard chrome plating process.
You should try increasing the flow of plating solution on the surface of your parts by pumping of the solution. You should also try 'jiggling' on a regular basis to remove the bubbles from the surface. If possible, you might also consider using a modern mist suppressor designed for use in hard chromium plating. You would have to discuss this with your chemical vendor.
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In hard chrome electroplating, detecting defects is critical for addressing them before they cause structural unsoundness or breakdowns in industrial equipment. Poor-quality chrome plating can cause numerous difficulties, so effective hard chrome plating troubleshooting is essential. In the guide below, we'll break down 10 common chrome plating problems and discuss the adverse effects they can have on your operations.
Electroplating is generally an efficient and effective process, but sometimes defects occur either during or after plating. Below are 10 common chrome plating defects you may encounter:
Blistering occurs when gases, generally hydrogen or nitrogen, expand from inside the pores of the plated object. These gases often come from the lubricant applied to the die during manufacturing. When the object becomes heated enough, the gases expand toward its surface and push against the chrome plating, creating a visible bubble or blister. A severe blister can also cause the plating to lift off entirely.
Blistering can also occur if the object's surface was unclean when the plating occurred. In this case, dirt particles may cause blistering because of the plating's poor adherence. Ensuring the cleanliness of the base metal can help avoid this issue.
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Burned deposits typically form in the areas of highest current density, often near endpieces or irregular shapes. Extremely high current density means the chrome plating builds up incredibly quickly. When the chrome builds up under these conditions, the affected areas can burn. Controlling the current density avoids this issue.
Cleavage points typically form during the die-casting process. During die casting, the plating may split in two along its structural planes. Cleavage points can cause structural rigidity issues in finished plated products ' they substantially reduce the product's fracture toughness. Controlling heat during die casting and monitoring the process closely can help reduce cleavage.
Cold shuts are some of the most common problems in chrome electroplating. These defects occur when different parts of the plating material harden at different rates ' typically because the cooler die cools some of the molten metal. When this happens, some of the metal cools before the mold is full. When the next flow of molten metal arrives, it fills in the cracks, and the molten metal bonds with the colder metal.
When a warmer area of metal hardens against a cooler area ' instead of an entire molten section hardening at once ' it interferes with the metal's bonding and creates visible lines or flow marks on the surface of the plating. This cosmetic flaw is also a structural one ' under stress, the product will be more likely to fracture along these lines. Making sure the die is not too cold can prevent the metal from hardening at different rates and causing this flaw.
Chrome plating cracking can take a few different forms:
Dull or milky deposits can result from numerous conditions, including:
Controlling chemical balances, temperature, current density and distribution, along with preheating, submerging and rinsing the metal object effectively, can help the deposits form as they should.
One of the primary reasons to apply chrome plating is to prevent oxidation of the metal beneath ' but what if the metal oxidizes before receiving its plating? If rust forms on the metal before the process is complete, the plating may not adhere to the metal correctly, or it may stick but then lift off. Applying the plating quickly before the metal can react with water or air can help prevent oxidation.
Pitting occurs when small holes form in the chrome plating. It is common under a few different conditions:
These are a few common causes of pitting ' others include reworked metal, stop-off residue, buss arching and bath residues such as oils. Using high-quality base metals, keeping deposits small and taking care with avoiding contaminants and residues can help prevent pitting.
Poor adhesion occurs when the chrome plating fails to stick to the base metal, and it is one of the most common causes of part failure in plated metal components. Poor adhesion can result from a dirty metal surface ' the chrome plating cannot stick to dust or debris. It also occurs when the surface holds oils, dye-releasing substances, alloying agents or oxides ' or when the pretreating agent expires before applying chrome plating. Ensuring the cleanliness of surfaces before plating can help with proper adhesion.
These defects involve the condition of the base metal.
Rough edges often occur because of poor-quality base metal. The reason is that unlike other metals like copper, which tend to fill in cracks, pits and unevenness smoothly, chromium usually follows the form of the metal exactly. If the base metal is rough, the plated metal will be rough as well.
Sharp edges in the base metal present a challenge for electroplating because of how the base metal interacts with the electric current. Some shapes ' including sharp edges ' attract more electric current. Where the current is denser, excessive layers of coating tend to pile up, and they make that section of plating more brittle. Grinding and deburring sharp edges is essential to preventing structural weakness.
To see the benefits of chrome plating or repairs for your industrial components, partner with Hard Chrome Specialists. Family-owned and operated since , we are renowned for our friendly, honest service, industry expertise and quick response times.
At Hard Chrome Specialists, we use conforming anode plating for our hard chrome plating, and we can use electroless nickel plating to give you various choices in bath parameters for corrosion and hardness. We can also address existing chrome plating defects with repairs such as chrome pitting repair for hydraulic cylinders.
Our full warranties certify that our repairs will be free from defects in workmanship and material for one year. When you work with us, you'll gain the peace of mind of knowing your equipment will stand up to corrosion and wear and last for a long time.
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