EMBOSSING EQUIPMENT

Most embossed metal is produced in coil form. Ideally, the embossing machine is situated directly after an uncoiler in the processing line and may be followed by a number of different operations. Typcially, these operations include recoiling, sheeting or cutting-to-length, roll forming, stamping, or any combination thereof.

The embossing machine can either be a stationary fixture in the metal processing line, or it can be made movable with wheels, rails, or a crane and lifting bolt assembly. While most machines are driven with an integral motor and drive package, embossing can also be performed using the power of a recoiler or other device and an unpowered pull-through embossing stand. Horsepower requirements depend on line speed and, to a lesser degree, material thickness, pattern, and roll size.

Located within the embossing stand itself are two engraved and mated hardened steel rolls, geared together to maintain top-to-bottom pattern registration. The width and diameter of these rolls depends on the strip width, material thickness, pattern depth, and material tensile strength and hardness.

The engraved roll journals are housed in a bearing and block assembly. In most machines, the upper roll blocks are stationary, while the bottom roll blocks are movable. The pressure with which the bottom roll is raised is referred to as the tonnage capacity. This figure also depends on the aforementioned parameters.

Embossing machines are generally sized to give 2" of strip clearance on each side of an engraved embossing roll. However, each unit is custom-manufactured, so there are no standard widths. In fact, machines less than 6 " wide and more than 76" wide are currently in operation.

WHY IS EMBOSSED METAL USED?

The reasons for employing embossed metal can be divided into two distinct categories: aesthetic and functional. Many applications serve both purposes.

Aesthetic uses- those to enhance the appearance of a product, make up the majority of embossed metal applications. Within this category, one of the most visible uses is in the appliance industry. More than 30 years ago, appliance manufacturers discovered that a flat, glossy painted steel panel highlighted fingerprints scratches and mars so they instituted the leather grain surfaces common today.

Aesthetic applications also include elevator panels, garage door panels, building products, automotive trim, small appliances, office furniture, etc.

Functional applications-those in which a performance characteristic is enhanced-can involve liquid dispersion, friction and static reduction, stiffness and rigidity increase, surface area increase for acoustic or heat transfer applications, and traction improvement.

While most of the functional applications are not visible to the average person, school bus and subway interiors, gasoline pump sides, light reflectors, copier guides and absorption tubes have all been manufactured and improved with the use of textured metal.

Many embossed metal applications that begin as aesthetic, such as building panels, end up with functional improvements. One common benefit is reduced weight and material relating to embossed metal’s increased stiffness. Reduction of "oil canning", diffusion of light, and decreased in-house manufacturing rejects are other common side benefits.

THE ENGRAVING PROCESS

The most popular embossed metal patterns include leather grains, wood grains, and stuccos, although almost any pattern can be engraved on a mated set of hardened rolls. Creating a new pattern and engraving the rolls are complex and highly skilled tasks. Engravers can take an idea, prototype, or artwork and develop original tooling by methods including electroforming, etching, punching, routing, laser, or computer generated graphic enhancement.

Once tooling has been manufactured, a mill is produced specific to the work roll that will be engraved. This mill displaces an acid-resist coating on the rolls and exposes metal, which is subsequently etched with acid and removed. The entire process is repeated again and again until the full depth and finish are obtained.

Thus, the pattern on the small mill is transferred to a large hardened work roll. This hardened top roll is then mated with and geared with a bottom roll in the embossing machine. Rolls can be re-engraved on- site as long as the pattern fidelity of the top roll and gear clearance and roll diameter parameters remain adequate.

USING EMBOSSED METAL

The three methods for obtaining embossed metal are:

1.  Purchase pre-embossed material from a service center, coil coater, or custom embosser

2.  Obtain a set of embossing rolls to be run in a third-party’s embossing machine for toll embossing applications

3.  Procure an embossing machine and roll set for in-house production.

In any of these cases, you can compare the additional cost of outside embossing with the equipment and labor costs associated with inside embossing.

With a pertinent cost model, a make or buy decision can be made. Usually, for a coil processing piece of equipment to be purchased, material throughput volumes need to be reasonably steady.

Once a metal embosser is installed, it requires little labor beyond the initial feed through, roll closure, and speed settings. As a material history is developed, predetermined wedge, pressure, and speed setpoints further simplify the process.

While embossed metal is handled and formed in exactly the same way as its flat counterpart, keep the following in mind:

Bending radii and die clearances must take into account the material’s actual cross-section thickness versus material thickness only. Some deep draws or severe bends may distort, wash out, or even split open sharp patterns and should, therefore, be avoided (or tested on a small scale before production).

Shallower embossed patterns, such as the leather grain family, may affect material flatness and, therefore, need corrective leveling. This is especially true as the product increases in width.

A matched set of embossing rolls will deflect during the embossing process. While this deflection can be compensated for by adding crown to the rolls, this crown is pertinent to one particular gauge (usually the most commonly run). Embossing above or below the target thickness may result in sheet shape and/or pattern appearance anomalies. Again, this is more pronounced with shallower patterns.

While materials more than .040 inch thick can be textured, the result is usually a coined/embossed hybrid. Manufacturers recommend staying in the .005-.040 inch range.

Uniform in-feed tension is a must, while material can exit with or without the same.

CONCLUSION

Metal embossing is a value-added operation. A metal embossing machine can be easily integrated into any coil processing line. Embossing can help open new markets, solidify existing business relationships, and enhance almost any flat-rolled product.