Patent Background

According to Apple's patent background, stainless steels owe their resistance to corrosion to the presence of chromium. Currently, there is a range of stainless steels from the plain chromium variety to those containing up to six alloying elements in addition to the usual impurities. However, it will be readily appreciated that chromium is the chief alloying element in iron and steel for inhibiting corrosion.

This resistance is not due to the inertness of the chromium, for it combines with oxygen with extreme rapidity, but primarily to the oxide so formed that is very thin and stable, continuous and impervious to further attack. Stainless steel is defined as a steel alloy with a minimum of 10% chromium (Cr) content by mass.

Stainless steel differs from carbon steel by the amount of chromium present. Carbon steel rusts when exposed to air and moisture. This iron oxide film is active and accelerates corrosion by forming more iron oxide. In contrast to ferritic steels, stainless steels have sufficient amount of chromium present so that a passive film of chromium (III) oxide (Cr.sub.2O.sub.3) forms within a surface region. It is this film that prevents further surface corrosion and blocks corrosion spreading in the metal's internal structure. There are different types of stainless steels. Austenitic stainless steel is formed when nickel (Ni) is added to the iron melt. In this way, the austenitic structure of iron is stabilized. This austenitic structure makes austenitic stainless steels non-magnetic and therefore less likely to inhibit electromagnetic (EM) activity which can be a significant consideration when used in the manufacture of consumer electronics such as cell phones that utilize RF, Wi Fi, Bluetooth, or other EM based wireless technologies.

Over the years, stainless steels have become firmly established as materials for cooking utensils, fasteners, cutlery, flatware, decorative architectural hardware, and equipment for use in chemical plants, dairy and food-processing plants, health and sanitation applications, petroleum and petrochemical plants, textile plants, and the pharmaceutical and transportation industries. Some of these applications involve exposure to either elevated or cryogenic temperatures; austenitic stainless steels are well suited to either type of service. However, it has now become desirable to use stainless steel in the manufacture of a variety of portable consumer electronic products particularly for the visual impact and structural integrity provided.

However, in order to maintain the look and feel of the stainless steel used in consumer electronics, it is necessary to protect the stainless steel surface from damage that would adversely affect the outward appearance. Furthermore, the protection provided the stainless steel surface must not adversely affect the look and feel of the component. Therefore, it is desirable to preserve the appearance of consumer electronic products that utilize stainless steel as an aesthetic and structural aspect.

Apple's Patent Summary

First and foremost, Apple's invention facilitates the mass production of consistent and aesthetically pleasing nitrided stainless steel components used in consumer electronic products such as the iPhone 4's stainless steel band. The band adds richness to the aesthetics of the design.

Secondly, beyond the iPhone, such components could be used for a variety of applications, such as to form outer housings for a laptop computer, for a future iPod touch and/or other mobile device designs. In one embodiment, a nitride layer is formed on a stainless steel component used for a consumer electronic product. In the described embodiment, the stainless steel could be austenitic stainless steel where the nitride layer is formed using a salt bath nitride process (See Patent FIG.3 below).

Technically speaking, the initial nitride layer formed could be at least 15-30 microns thick with a Vickers Hardness (HV) value of at least 1000. In the described embodiment, the stainless steel component could be placed in the salt bath at not more than 580 C for a period of time not to exceed approximately 1.5 hours. A finished nitride layer is formed by performing at least one finishing operation on the initial nitride layer. At least one finishing operation removes about 10% of the initial nitride layer.

Apple's patent states that a portable consumer electronic product could include at least a plurality of electronic components and a stainless steel housing having a visible exterior surface so as to provide an aesthetic look and feel to the portable device. In context, Apple's iPhone website page states that they created their own allow, then forged it to be five times stronger than standard steel. The CNC-Machined band is the mounting point for all the components of the iPhone 4. As far as I could tell, Apple's patent has been utilized with the iPhone 4's construction. Meaning, that the patent has been fullfilled.

With that said, it should be noted that while Apple's patent never gets specific about what other device housings it could be applied to in the future, one could at least imagine that the back portions of an iPod touch or iPhone could be considered as candidates should their current materials ever be abandoned. The patent does point to laptops, but I can't see Apple abandoning their current aluminum Unibody. That leaves the MacBook and being that it's an entry unit, I can't see Apple going that route either. Time will tell.    

The bottom line is that Apple could rely on the nitride layer for many things in the future not the least of which includes the aesthetic look and feel of future products in additon to providing scratch and wear resistance, and in some cases, extended corrosion resistance.

Apple's patent FIG. 1 above shows us Table 1 describing various types of austenitic stainless steel. Also noted above in FIG. 2, Apple presents us with a representative cross section of a sample of type SUS 316L stainless steel. Shown below in patent FIG. 3 we see a process suitable for forming a nitride layer on a stainless steel (SUS) component used to form a consumer electronic product.

Apple credits Douglas Weber as the sole inventor of patent application 20100273538, originally filed in April of this year.

Other Noteworthy Patent Applications Published Today

Patent 20100271505 titled "System and Method for RAW Image Processing." Apple's continuation of a 2006 patent covers a technology used in Aperture.

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