METALS AND FINISHES

[Metals]  [Finishes]  [Finish Standards]  [Finish Standards Chart]  [Back to Index]


The material from which architectural hardware is made is of fundamental interest. It often affects the ability of the product to maintain appearance and durability and can have an important bearing on the desire to specify as high a quality product as possible under a particular circumstance. Except for the comparatively few instances where plastics, woods and ceramics are used, hardware is made of metal.

Selection of the base metal and finish depend on such factors as use, exposure to elements and appearance desired. Also, hardware in a room should harmonize in design and finish. In discussing metals and finishes, we differentiate between (1) metal material out of which the basic portions of the hardware item are manufactured; and (2) the surface characteristics of the product. This latter may simply be the result of treatment of the basic metal, or it may be applied by the addition of a second metal or other product.


Metals

Basic metals used in architectural hardware are brass, bronze, iron, steel, stainless steel, aluminum and zinc. Competition between producers of the various metals is frequently keen, especially with changes in production capacity and technology. These metals may be cast, extruded, forged or wrought. Pouring molten alloy into pre-molded forms produces cast metal. This method results in a versatile shape that can be machined, etched or carved to yield a great variety of designs. Forcing or drawing semi-molten metal through dies, like a chef uses a pastry bag, produces extruded shapes. Designs having linear characteristics are possible. Forged metal is hammered, pressed or rolled into shape. A smooth, dense product results from this process, the value of which relates to the thickness of the metal. Wrought metal is rolled into flat sheets or strips. The products are formed by punching or die cutting into the desired forms. It may be thick, as in a hinge, or thin, as in a push plate.

Brass and bronze are metal alloys, the greatest portion of which are copper and containing smaller amounts of other metals, notably lead and zinc. Bronze differs in that it contains some tin. Differences in color result from the proportions of the various metals included. Steel is widely used in architectural hardware. It is stronger than iron. Ordinary carbon steel, used in architectural hardware, not only contains iron but portions of other elements such as carbon, manganese, phosphorus and sulfur. Exposed to the weather, carbon steel is likely to rust. It's wide use results largely from its strength and lower cost. Most of the architectural hardware items made of wrought steel are formed from flat sheets by dies in heavy presses.

Stainless steel is an iron product and there are about 40 standard types. Each contains substantial amounts of chromium and small quantities of a number of other elements. A majority of types also contain appreciable percentages of nickel. Because it is highly rust resistant, finishes with a high luster and is easily maintained, stainless steel is prized as architectural hardware material.

Aluminum now is used in many ways in architectural hardware. It is usually alloyed with about 4 percent of other elements. Cast, forged and wrought products are obtained by much the same processes as are other metals. Pressure-cast aluminum frequently is used as a substitute for cast iron in miscellaneous items such as doorstops, handrail brackets and hooks.

Powdered metal is pressed into shape and then sintered in a furnace. For additional strength it may be sintered again. The process is employed to form a range of products from various metals.

Cast iron's characteristics are longwearing qualities, natural lubrication, brittleness, low tensile strength and tendency to rust. Cast iron contains approximately 92 percent iron and small quantities of such other elements as carbon, manganese, silicon, phosphorus and sulfur. As its name implies, pouring into sand molds to achieve the desired shape forms the metal. Malleable iron is cast iron treated by baking or annealing to make it tough and shock resistant. When properly cast and annealed, malleable iron can be bent and even knotted without breaking. Many manufacturers use malleable iron in items like pulls and closer arms, to reduce the possibility of breakage and provide resistance to stress.

Forged iron's greatest use in architectural hardware is in the manufacture of specialized or decorative trim often imitative of early-American hand-forged items. Hammering a red-hot bar of iron into the desired shape produces iron forgings. Forged iron is almost pure iron, with only about 1 percent of other elements. Zinc has long been used in architectural hardware. As a coating over iron and steel, it resists rust. Many products are made using die-cast zinc as a base metal. It is easily cast, machined and plated.


Finishes

Finishes that are natural take the color of the base metal in the product, and may be either high or low luster. A so-called satin finish is one of low luster. Applied finishes result from the addition by plating of a second metal, a synthetic enamel, or other material. Finishes for architectural hardware have undergone tremendous changes in recent years. New techniques and finishes have been introduced, changes in popularity have taken place, and some finishes have been dropped. The preparation given to base metals prior to finishing consists generally of machining, buffing and polishing. Buffing or polishing the metal to a high gloss before applying a synthetic coating produces polished brass and bronze finishes. Satin brass and bronze natural finishes are obtained by dry buffing or scouring, and the resultant finish then is coated. Uncoated finishes of brass or bronze are used where natural oxidation of the entire exposed surface yields the desired result. Oil rubbing of uncoated bronze produces a dark oxidized finish suitable for some decors.

The most popular of the plated finishes are the chromiums, polished and satin. Brass, bronze and nickel plating of architectural hardware has been done for scores of years, usually by means of an electrolytic process, Oxidizing is also used, especially where the designs are ornamental. Coatings are used to prevent tarnishing or oxidation of all natural finishes and plated brass and bronze finishes. The original color and sheen of natural metals can be maintained for a long time with the use of modern synthetic coating treatments. Anodizing forms a protective and uniform oxide on aluminum, giving it a hard, tough skin. A variety of color-anodized finishes, such as black and oxidized bronze, are available.


Finish Standards

The National Bureau of Standards of the U.S. Department of Commerce some years ago prepared product standards for the finishes used with architectural hardware. In recent years a more complete job on these standards, consistent with current practices in the industry, has been done by the Builders Hardware Manufacturers Association, from whom ANSI/BHMA samples of selected standard finishes now may be obtained. Standard Al56.18 gives details of the finishes and the nearest U.S. equivalents. Some representative standard finishes as reported by the BHMA are as follows:

Nearest U.S. Canadian Equivalent BHMA Code Finish Description Base Metal
USP CP 600 Primed for painting Steel
US1B C1B 601 Bright Japanned Steel
US2G C2G 603 Zinc Plated Steel
US3 C3 605 Bright brass, clear coated Brass*
US4 C4 606 Satin brass, clear coated Brass*
US9 C9 611 Bright bronze, clear coated Bronze*
US10 C10 612 satin bronze, clear coated Bronze*
US10B C10B 613 Oxidized satin bronze, oil rubbed Bronze*
US14 C14 618 Bright nickel plated, clear coated Brass, Bronze*
US15 C15 619 Satin nickel plated, clear coated Brass, Bronze*
US19 C19 622 Flat black coated Brass, Bronze
US20A C20A 624 Dark oxidized, statuary bronze, clear coated Bronze*
US26 C26 625 Bright chromium plated Brass, Bronze*
US26D C26D 626 Satin chromium plated Brass, Bronze*
US27 C27 627 Satin aluminum, clear coated Aluminum
US28 C28 628 Satin aluminum, clear anodized Aluminum
US32 C32 629 Bright stainless steel Stainless steel, 300 series
US32D C32D 630 Satin stainless steel Stainless steel, 300 series
* Also applicable to other base metals under a different BHMA code number.



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