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FAQ and Answers

Q.What kind of a surface treatment does CROMAX provide?
A.CROMAX is a plating process originally developed by Chunichi that is an advanced version of hard chrome plating with superior hardness and abrasion resistance.
When compared to normal hard chrome plating, CROMAX is 20% harder and has 2-3 times more wear resistance.
Q.It seems hard chromium plating contains hexavalent chromium. Does the actual plated surface also contain hexavalent chromium?
A.The chromium plating processed surface does not contain hexavalent chromium because hexavalent chromium in the plating solution is reduced to zero valent chromium (metallic chromium) by electrolysis. After this reduction the chrome plating is deposited on to the product surface.
Q.What is the expansion coefficient of chrome plating?
A.The expansion coefficient of various metals is listed below. Chromium has the lowest rate. Please slide sideways.

スライドしてください。

Material Expansion coefficient(α・108)
Cast iron 1,144
Wrought iron 1,200~1,300
Hardened steel 1,000
Nickel 1,300
Copper 1,650
Brass 1,905
Chromium 840
Q.Why is the bolt attached to the product sometimes broken after the hard chromium plating process?
A.It is caused by delayed fracturing due to hydrogen embrittlement.
A steel with high tensile strength (150 kg / mm² or higher) such as spring material, tempered carbon steel products, and high tension bolts are easily embrittled either during the pretreatment of plating (acid treatment) or the actual plating process. Therefore, the following measures are necessary.
  1. Baking treatment is required at 191°C for 3 hours to remove hydrogen after the plating process.
  2. Avoid plating on objects with high tensile strength (for example, remove the bolts before the process).
Q.What is the heat resistance of electroless nickel plating?
A.The hardness of electroless nickel plating is approximately Hv550 at the time of precipitation. However, the hardness and the abrasion resistance are improved by heat treatment.
A hardness of around Hv900 can be attained by heat treatment at 400°C, but the hardness decreases if the temperatures becomes higher than 400°C.
The melting point is about 890°C.
Q.What is the electrical resistance of electroless nickel plating?
A.Normally, the resistivity of nickel is 6.84µΩ/cm, but because the electroless nickel plating contains 8 to 10% phosphorus, the specific resistance increases up to 80 to 100µΩ/cm
Q.What kind of surface treatment is strike plating?
A.Stainless steel and hardened steel are difficult to obtain adequate adhesion strength without extra treatment. To obtain adequate adhesion strength, the products are first treated with strongly activated nickel electroplating for a very short time (a few seconds) before the main electroless nickel plating process. This quick process is called "strike plating".
Q.Please tell me the amount of hexavalent chromium contained in a hexavalent chromium chromate treated surface and zinc plated surface?
A.See the below listing comparison. Please slide sideways.

Please slide sideways.

Coating type Total chrome amount(mg/m²) Hexavalent chromium amount(mg/m²)
Shiny chromate 40~80 ~10
Color chromate 100~200 20~40
Black chromate 300~500 40~70
Green chromate 500~700 50~120

Please note, recently chromate treatment using trivalent chromium is becoming more popular as an alternative option to hexavalent chromium, and this trivalent chromium does not contain hexavalent chromium on treated surfaces.

Q.Please tell me about corrosion resistance of black dye?
A.Black dye is basically an "iron" or "iron compound". Therefore, the corrosion resistance is not very good.
However, applying a black dye treatment produces fine micro pores on the surface allowing higher retention of oil for corrosion resistance compared to surfaces without black dye treatment.
Therefore, it is common to add anti-rust oils after black dye treatment.
Q.Please tell me about dimensional change of aluminum products after alumite treatment?
A.Alumite is an anodizing treatment which does not create a new coating, but a process of changing the aluminum itself.
Normally, the film thickness increases by about 33% - 50%. For example, an alumite 10µm indication will increase by 3µm to 5µm to become 13µm to 15µm.
Q.Can nitrided steel be plated?
A.There is a strong nitride layer on the surface of nitrided steel which hinders the adhesion of the plating. Plating is possible by removing the nitrided layer by a physical method, but if the nitride layer is removed, the hard characteristic of the nitride layer is also lost.
Q.Is it possible to chrome plate aluminum?
A.Yes, it is possible. At Chunichi, chromium plating is done directly without electroless nickel plating on the base materials.
However, special preprocessing is needed, and auxiliary poles cannot be used.
Products that require auxiliary poles during chromium plating will require consultation before processing.
Q.What material is unsuitable for laser welding?
A.[1] SUS 303, [2] Nitrided products, [3] Plated products, [4] Cast iron with extremely large pin holes, etc. We will work with you in detail to come up with the best possible solution for your requirement(s).
Q.What is the lead-time for Laser Welding?
A.The time needed depends on: [1] weight, shape of the product and its loading/unloading difficulties. [2] the workability of the welding area, etc.
For example, for a welding area the size of an A4 piece of paper that is 2mm thick, about 3 working days are required.
Q.Is it possible to harden (temper) cast iron FC200 and FC250 by Laser Hardening?
A.You cannot temper cast iron with normal hardening or frame hardening, but it is possible with Laser Hardening.
It is possible because Laser Hardening reaches the required high temperature to temper cast iron rapidly as well as self-cooling down very quickly.
Q.What is the minimum thickness of a product needed for Laser Hardening?
A.In Laser Hardening, "self-cooling" requires "a thickness of more than 10 times the standard depth of hardening".
Since the standard hardening depth is 0.5mm, a plate thickness of at least 0.5mm×10 = 5mm is required. For a stable performance, at least 10mm thickness is needed at the working area.

Chunichi Craft Co., Ltd.