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American Porcelain Enamel Company
A subsidiary of
Cherokee Porcelain Enamel Corp.
2717 Independence Lane
Knoxville,
TN 37914
Phone 865-637-7833 FAX 865-637-0019
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Information and
Specifications
S-100
MANUAL OF ARCHITECTRUAL
PORCELAIN ENAMEL
Table
of Contents
- Introduction
- Scope
- Definitions
- Detailed
Requirements
- Base Metal
- Processing
- Corrosion Protection
- Porcelain Enamel Finish
- Flatness of Panel
- Clips and Attachments
- Test Methods
- Compliance
and Guarantee
- Supplementary
Considerations
- Introduction
This standard is based on the experiences and recomendations of
architectural porcelain enamel manufacturers and other technical
authorities from the porcelain enameling industry. It has been adopted
as a PEI Tentative Standard by the Standards Committee, specification
authority for the Porcelain Enamel Institute, Inc.
- Scope
The specification applies only to architectural porcelain enamel on
substrates. It does not cover the types of panels, the metal
fabrication, or the assembly of finished units.
- Definitions
- Porcelain Enamel
Porcelain enamel is a substantially vitreous, or glassy, inorganic
coating bonded to metal by fusion at a temperature above 1000 degrees F
(538 degrees C).
- Architectural Porcelain Enamel
An architectural porcelain enamel is one that is used as a facing
material or as a component on any building structure. When signs are an
integral part of the facing material, the finish used on the sign is
considered as an architectural porcelain enamel.
- Steel
For the purposes of this specification, steel is defined to include:
- Special purposed "enameling iron or
steel" of low metalloid and copper content, expecially manufactured and
processed for the production of porcelain enamel units for
architectural purposes. (See PEI-201, Manual for Selection of Porcelain
Enameling Steels.)
- Conventional cold rolled sheets which
can be satisfactorily porcelain enameled and which meet other
requirements of this specification. Note: Warpage may be a significant
factor when using cold rolled steel as it impacts Section IV, E.
- Detailed
Requirements
- Base Metal
Base metal shall be in accordance with the definition under the
definition of steel.
- Processing
A porcelain enamel coating shall be applied to all areas of each unit,
including back and flanges, by methods recognized as good commercial
practice.
At least one additional fired coating shall be applied to the face side
of each unit.
- Corrosion Protection
The back side of non-laminated panels shall be protected with fired
porcelain enamel coating.
The coating requirements for the back side do not apply when adequate
corrosion protection is provided to the panel by the laminated
construction.
Corrosion protection in laminated panels is dependent upon the
durability of the lamination. A test method which has been widely used
for determining the resistance of sandwich panels to severe exposure
conditions is described in ASTM C481-61T.
- Porcelain Enamel Finish
- Weather Resistance
The porcelain enamel finish on all surfaces exposed to weathering shall
pass the acid spot test as given in the Test Methods
section. In addition, all red, yellow and orange porcelain enamels
shall pass the cupric sulfate test as described in the same section.
- Continuity of Coating
Visual inspection of each piece shall reveal no visible breaks or
surface defects in the cover coating that will expose the underlying
coating or the steel on surfaces exposed to weathering, nor the
underlying steel on either the back or flanges. This requirement shall
not apply to sheared edges.
Special metallic coatings are sometimes fired onto porcelain enamel
surfaces to achieve specific textures and finishes. This coating may be
continuous or may have purposely induces breaks and discontinuities.
Such coatings shall qualify under this requirement if the underlying
porcelain enamel satisfies all requirements in this specification.
- Surface Appearance
The porcelain enamel on all surfaces exposed to weathering shall be
free of blemishes in the coating that my impair the serviceability or
detract from the general appearance of the panel when viewed from a
distance of 5 feet or the distance at which the panel will be normally
viewed, whichever is the greater. Orange peel and surface finish should
be reviewed and agreed on before production. Color tolerances should be
agreed on before production. Certain colors are more susceptible to
color stability.
- Flatness of Panel
Finished faces shall have a maximum variation of 3/16" (4.76mm) in a
convex direction when measured perpendicular to the nominal plane of
the panel face. Variation in the concave direction shall be limited to
3/32" (2.38mm) from actual plane of the panel face.
These tolerances are for panels with a face area of 8 sq. ft. (0.86 m2)
or less. Proportionately greater allowance will be permited for panels
of greater areas. Panels are to be measured in the position (usually
vertical) in which the panel will eventually be installed. Note: While
not a part of the specification itself, further data regarding flatness
is set forth in the Section, Supplementary
Considerations.
- Clips and Attachments
All metal lugs, clips and other attachments fastened to the panel, as
well as those furnished unattached by the manufacturer, for the purpose
of attaching the panel to the building structure shall be made of a
recognized corrosion resistant metal such as stainless steel type 302
or equivalent. This requirement specifically excludes stiffener bars or
braces, clips for holding insulation in place, and similar devices not
intended for the purpose of attaching the panel to the building
structure. Also excluded are furring, substructure assemblies, or
braces that may be furnished by the manufacturer.
- Test
Methods
- Acid Spot Test
- Treatment of Specimen
Wash the specimen with soap and water, rinse thoroughly, then dry with
a clean cloth by blotting (not rubbing). Immediately after washing, and
with the specimen at 80 +- 10 degree F (26.6 +- 5 degree C) place
several drops of a 10% citric acid solution (also at 80 +- 10 degree
F). On the specimen to form a pool and immediately cover with a 1"
inverted watch glass. The acid solution shall contain 100 grams of
citric acid per liter of water and shall be prepared not more than 48
hours prior to use. After 15 minutes of treatment, remove the watch
glass and rinse the acid solution from the surface. Dry the specimen
with a clean cloth by blotting (not rubbing).
- Blurring-Highlight Test
This test shall be made in a well-lighted location. Hold the specimen
so that the image of a small light source, such as a frosted lamp bulb,
is observed as a highlight in the untreated area, the line of vision
with 45 degree of the perpendicular to the surface. (A desk lamp is
recommended for this purpose.)
Focus the eyes on the image of the light source, not on the enamel
surface. Then shift the specimen just sufficiently to bring the image
of the light source into the treated area, observing it as it passes
across the boundary line between the two areas. Any color difference in
the enamel due to staining shall be ignored, but if a definite blurring
of the image is observed as it passes from the untreated to the treated
area, the enamel shall fail the acid spot tests.
- Wet-Rubbing Test
If there is no blurring of the highlight, place 4 or 5 marks on the
treated area with a No.1 pencil using a firm pressure. Next, rub these
marks vigorously with a clean cloth that has been dipped in water and
tightly twisted to eliminate the excess. If the marks are removed
completely by this wet-rubbing treatment, the specimen passes the test;
otherwise it fails.
The testing procedures outlined above are the same as those specified
in PEI T-21, "Test for Acid Resistance of Porcelain Enamels (Citric
Acid Spot Test)", a standard of the Porcelain Enamel Institute and ASTM
C282.
Porcelain enamels that pass the tests would be graded wither Class AA
or Class A by the standard test procedure.
- Cupric Sulfate Test for Red, Yellow and
Orange Porcelain Enamels
Place a few drops of a saturated solution of cupric sulfate [prepared
by placing 50 gms. of cupric sulfate (CuSO4.5H2O), reagent grade, in 100 ml. of
distilled water and aging for 16 hours or longer] on the porcelain
enamel surface to be tested. Cover the small pool of solution with a 1"
inverted watch glass and place the specimen in a controlled
illumination environment equivalent to that described below. After 20
hours at room temperature, remove the watch glass, rinse the test area
with water, and dry with a clean cloth. Visually examine the treated
area immediately. If any darkening can be detected visually, the
specimen fails the test. Changes in gloss caused by the treatment shall
not be considered in the grading.
This test is fully described in PEI T-22, "Cupric Sulfate Test for
Color Retention", a tentative standard of the Porcelain Enamel
Institute. The apparatus for control of illumination consists of a
light source and enclosure. The light source shall be a 100-volt, 15
watt white, fluorescent lamp, 1" diameter by 18" long. The enclosure,
made of plywood or other suitable material, shall be 10" long, 6" wide
and 12" high (inside dimensions). It shall be painted white on the
inside and vented for air circulation. Venting is accomplished by 11
1/2" holes, drilled 1" apart on a centerline 1" from the inside top,
and 11 similar holes drilled on a centerline 1" from the bottom on each
of the two long sides. The lamp is centered near the inside top of the
enclosure in such position that the distance between the specimen
surface and the centerline of the lamp is 9".
- Compliance
and Guarantee
- Compliance Statement
Manufacturers shall certify in writing at time of submission of a bid
that the porcelain enameling will be performed in accordance with the
current edition of the Manual for Architectural Porcelain Enamel
(PEI-1001) as issued by the Porcelain Enamel Institute.
- Guarantee
All porcelain enamel for architectural purposes manufactured for
projects giving references to these specifications shall meet these
specifications in every respect except where specifically stated. Any
further guarantee shall be made by the manufacturer in accordance with
his standard practice.
- Supplementary
Considerations
The following, while not a part of the specification, are set forth as
an aid to those specifying architectural porcelain enamel.
- Gloss
The gloss of the porcelain enamel finish, together with permissible
tolerances in gloss, should conform visually with samples selected by
the architect and/or purchaser during negotiation of the contract. When
porcelain enamels of especially low specular gloss are agreed upon,
however, difficulties may be encountered in applying the acid spot
test. An acid resistance test that has been found useful in predicting
the weather resistance of porcelain enamels of this type is the boiling
acit test given in ASTM C283. Experience has shown that if the measured
weight loss is 12 mg./in.2 or
less, the enamel will have good weather resistance.
It is also recommended that the finish be of a type that will not
reflect distinct images. If the reflecting power is high, images seen
in the mounted panels will usually be distorted due to even very small
deviations from flatness. Experience has shown that the overall
appearance of a structure will be considerably improved if the image
reflection (distinctness-of-image gloss) is kept as low as possible. A
qualitative evaluation of this type of gloss can be made by observing
the image of a window mullion in the surface of the panel. If the image
is clear and sharp, the distictness-of-image gloss is normally too high
for architectural purposes. Reproducible, quantitative measurements of
image-gloss can be made using the equipment and procedure described in
PEI T-20, "Image Gloss Test", a standard of the Porcelain Enamel
Institute.
- Color
The color and color tolerance should be specified in the purchase
contract. If possible, this should be based on porcelain enameled
sample color specimens. Compliance with color specification may be
determined by visual matching under viewing conditions mutually agreed
upon by the contracting parties, or may be determined instrumentally.
The color tolerance to be specified should depend upon the color
service requirement and the ease with which particular color or colors
can be controlled in production, and should be clearly specified in the
purchase contract. To be considered also are the type of structure, the
texture of the finish, and the proximity of adjacent panels. Some
colors can be controlled more closely than others.
Decorative colors and coloring processes, such as stenciling, silk
screening and highlighting, may be used to produce designs, letters and
special effects, provided the finish so produced meets all of the
requirements of this specification
- Texture
Unless otherwise specified in the contract, the porcelain enamel will
be furnished in a smooth and non-textured finish. Orange peel tolerance
should be specified with tolerance samples.
Special textures and finishes should be in accordance with samples
agreed upon during contract negotiations. In all other respects,
special finishes shall conform to this specification.
- Thickness of Porcelain Enamel
Various thicknesses are encountered in commercial ware. Thickness
tolerance should be agreed upon in writing before production. Texture,
color and processing techniques influence the amount of porcelain
enamel which is applied.
Thin porcelain enamel coatings are desirable to provide maximum
resistance to damage from flexure. However, processing methods and
desired appearance characteristics may result in variations of
recommended minimum thickness of the coating. A minimum of 0.0035"
(0.089 mm) of cover coat will normally provide acceptable durability.
The total thickness may range from 0.005 to 0.020" ().127-0.508 mm),
depending upon process and appearance.
Total thickness should not exceed 0.020" (0.508 mm), except where
greater thicknesses are necessary to meet specific appearance
requirements.
- Thickness of Metal
Thickness, grade and design tolerance of metal should be agreed upon
during negotiation of the contract. Full consideration should be given
to the size, shape or detail of the unit, and the duty which the unit
is to perform in the building structure. (see PEI-101, Manual of Design
and Fabrication of Metal for Porcelain Enameling.)
- Packaging and Shipping
Packaging, shipping and handling methods should be specified and should
be practical for supplier, shipper, and erector.
- Shop Drawings
Complete drawings should show forming detail, tolerances allowed (both
dimensional and flatness), location in completed structure, and
on-the-job cutting or drilling requirements. The maximum allowable
extent of damage due to drilling and cutting should be agreed upon by
contracting parties.
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Mechanical & Physical
Properties (PEI Bulletin #502)
| Surface Hardness |
3.5 to 6 (Moh's Scale) |
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| Abrasion Resistance |
Excellent |
C448 |
| Compressive Strength |
20,000+ psi |
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| Modulus of Elasticity |
10 x 166 |
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| Ultimate Strength(steel) |
50,000 psi |
A424-62T |
| Yield Strength(of steel) |
35,000 psi |
A424-62T |
| Thermal Expansion |
8-14 x 106 cm/cm/-C |
C359 |
Chemical Properties (PEI
Bulletin #503)
| Salt Spray |
Excellent |
B117-571 |
| Organic Solvents |
Superior |
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| Acids |
Class A |
C282/C283 |
| Alkali |
Max.pH of 12 |
C614 |
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@ 212-F(100-C) psi |
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| Water |
190-(88-C) |
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Continuous service |
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| Oil |
Not affected |
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| Soil Corrosion |
Not affected |
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Appearance Properties
* (PEI Bulletin #501)
Color permanence
Gloss retention
Cleanability |
Superior weatherability as
evidenced by extensive testing by the National Bureau of Standards
(NBS) and the Porcelain Enamel Institute (PEI) at a variety of sites
over a period of 30 or more years |
| * Class A acid resistance
porcelain enamel |
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