Glossary

We provide the following definitions in the hope that they may be helpful in explaining words, terms, and processes used within the text of our web site. Please contact us if you need further clarification or require additional information about these particular words or about any aspect of Roll Technology services or procedures.

Chromium Plated and Belt Polished
Roll to be received ready to plate with a fine ground, defect free finish. Roll Technology would belt polish, hard chromium plate, and belt polish the roll face. No precision grinding is involved.

Cylindrical Roll Grinding
Cylindrical, precision roll grinding involves supporting the roll, shaft, or drum either between machined centers or directly on the roll's bearing surfaces. The outside diameter of the roll is then precision ground using appropriate grinding wheels. Critical to the roll grinding operation is basic knowledge such as the construction of the roll, wall thickness, deflection characteristics, and the base metal material.

Decorative Chrome Plating
Decorative chrome plating such as that used on furniture, motorcycles, hubcaps, etc. is a completely different process from hard chromium plating. It involves electroplating a thin layer of chromium onto a metal object. Roll Technology does not do decorative plating.

Fine Precision Ground and Belt Polished Finish
Roll to be precision ground after chromium plating to a fine ground finish and then belt polished smooth.

Fine Precision Ground Finish
Roll to be precision ground after chromium plating and shipped with a fine ground (not polished) finish. Typical of high precision coating rolls.

Finish Grinding in Precision Bearings
When it is necessary to produce an industrial roll that has the lowest possible operating T.I.R. (precision roll coating, precision calendering, etc.), it is possible to cylindrically grind the roll with its precision bearings in place on the journals.

When a roll is ground in its bearings, the resulting T.I.R. is typically lower than the specified accuracy of the bearings. Finishing in bearings also significantly simplifies the installation of the roll into a production line. The cost of finishing in bearings is usually offset by the savings in installation costs.

Finishing in bearings creates a dedicated assembly of the roll, bearings, seals, housing caps, locknuts, and other related hardware. All items mounted on the journals located between the bearings need to be supplied by the customer for mounting in place by Roll Technology technicians.

Hard Chromium
Hard chromium plating, as the name implies, is extremely hard (68-70 Rc as deposited) and, as such, is suitable for a wide variety of industrial applications that require resistance to wear. It is also the finest metal deposition to utilize when specifications call for very low smoothness characteristics on the roll face.

Hard chromium plated rolls must be precision ground after plating to obtain exacting tolerances for accuracy and surface finish.

Hydrogen Entrapment
In its as-plated condition, hard chromium has entrapped hydrogen within its structure. This hydrogen can be removed by baking the chromium plated roll at 350°F for 8 hours after plating. During the baking process, the hydrogen is driven from the micro pores of the plated deposit, and the chromium becomes denser.

In heating applications, it is critical to ramp the temperature at controlled intervals, and not cause a "thermal shock" to the chromium deposit. A roll that is heated too quickly will expand at a faster rate than the chromium, and could cause cracking of the plating. We recommend 1 degree F per minute starting at ambient, with the roll rotating.

Baking of a chromium plated deposit is also recommended for producers of plastic sheeting to eliminate the dissipation of hydrogen bubbles onto a sheet, when initially started. Even though the hydrogen will eventually be driven from the roll during operation in a sheet line under heated conditions, it does not yield immediate production.

Matte Finish
A matte finish is created by grit blasting into a ground and polished chromium plated surface. The resulting finish is comprised of a field of sharp, jagged peaks to a roughness specification as called out by the customer. The finish is dull and gray in appearance, and is utilized when a dull or printable product is required.

Mirror Finish
The term "mirror finish" can be, and has been, used to define almost any smooth reflective finish. It is important to define the Ra or RMS of the required finish in order to avoid conflict in interpretation.

In some industries, the term "mirror finish" can be used to define a smooth, reflective finish ranging from 4-8 Ra, as generated by commercial belt polishing techniques. Generally speaking, 4 Ra and under refers to surface finishes with higher degrees of luster and reflection generated by precision belt and stone polishing operations.

Roll Technology's standard mirror finish classifications range from 2-4 Ra and extend to optical mirror finishes measured to 1 Ra and less.

Optical Mirror Finish
When calendering, heating, or cooling a web such as magnetic tape, clear plastic sheeting, or film, where perfection of the chromium plated surface is imperative, Roll Technology offers an optical mirror finish. In the most critical of applications, we generate an optical mirror finish measured between .1-.2 Ra in surface smoothness (one tenth of one millionth).

Ra / RMS
Chromium plated roll surfaces are typically defined in terms of Ra or RMS. The RMS (root mean square) of a given surface typically runs about 10% higher than it equivalent Ra (average roughness) value. In English units, 10 Ra is equal to 11 RMS, and for many applications the two units of measure are used interchangeably. Either of these terms can also be expressed in metric units. For example, 10 Ra in inches is equal to .25 Ra micrometers or .27 RMS in micrometers.

The lower the Ra or RMS, the smoother the finish.

Satin Finish
A chromium plated satin finish is created by grit blasting a ground and polished base metal, followed by a thin layer of chromium in the range of .001"-.002" thick. The resulting surface finish reproduces the hills and valleys of the blast, yet is somewhat slick to the feel. The surface is considerably brighter when compared to a "matte" finish, and can be mechanically buffed to increase luster. Satin finishes are often specified for textured snag-free applications in textile, packaging and casting.

Taper
Taper is the measurement of the variance of the roll's diameter over the width of the roll face. A perfect cone shaped roll would have virtually undetectable T.I.R. (total indicator reading), but may vary in diameter (taper) significantly from one side of the roll face to the other. Specifying the exact tolerance for allowable taper in refinishing an industrial roll is just as critical as specifying its T.I.R.

At Roll Technology, electronic instrumentation is used to accurately measure and record taper on a roll face. These precise instruments measure a single plane passing through the roll's centerline, and are then recorded to compare to customer specifications. Machine adjustments are made to correct any irregularity to taper measurements that fall outside acceptable limits.

Roll Technology regularly works on coating, metering and applicator rolls that require tolerances to be within millionths of an inch.

TIR
T.I.R. is a measurement of how round a roll face is at a given single plane, perpendicular to the roll's centerline and in relation to the accuracy of the bearing surfaces. T.I.R. is established using both dial indicators and electronic probes to record specific roundness values.