Roll Forming Handbook / Edited by George T. Halmos
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Paint cracking may occur if less ductile paint or plastic and smaller than the required bending radius
are used. Larger bending radius can overcome this problem. If the bending radius must remain small,
then preheating of the bend lines in front of the forming rolls can makethe paint flexible and elastic
enoughtobeformed without cracking.Depending on the type of paint or laminate, the surface
temperature mayberaised to 130 to 2308 F(55 to 1108 C). Coils can be preheated with electricity, gas, or
by just passing it through ahot water bath.
On the other hand, paint can be less flexible at low temperatures. Painted coils transported or stored
below the freezing point may develop paint cracks if they are roll formed without first warming them to
room temperature.
Possible paint cracks on the exposed surfacesmust be carefully checked. Almost invisible small cracks
at the bend lines will pass water and corrosiveatmosphere through and corrosion (white rust or brown
rust or other corrosion on metals other than steel) may startduring storage or after installation.
Correcting problems caused by paint cracking is extremely expensive.
In the case of laminated material, the thickness of lamination should be added to the thickness of
material when rolls are designed and installed. For example, rolls designed for 0.036 in. thick material will
not be able to process the 0.034 in. thick steel coatedwith 0.010 in. thick laminate.
Longitudinal scratches caused by the entryguides, straighteners, cutoffdies, or other componentscan
be avoided by making the above items from the right material, providing agood, smooth entry, and
avoidingsharp edges.
6.14 Joining Different Materials in the Roll Forming Process
Metals can be combined withother metallic or with nonmetallic materials during the roll forming
process. The other material can be adhesive bonded, mechanically joined (folded, pinched, lock seamed),
soldered,brazed, welded to (or extruded on) the metal strip.Roll forming of these composites can
be successfully accomplished if proper conditions are provided.
6.15 Aluminum
To specify the material just as “aluminum”isone of the most common mistakes made by designers not
familiar with metals. There are manydifferent aluminum alloys (as with steels), with vastly different
properties. Therefore, it is essential to use the proper designation for aluminum used in roll forming.
6.15.1 Wrought Aluminum Alloy Designations
The mechanical and other properties of the wrought aluminum used for roll forming are influenced by
the alloying elements, heat-treatment, and cold work.
The numbering system used by the Aluminum Association standards [381] classifies the commonly
used aluminum alloys by their major alloying elements in the following groups:
1xxx Aluminum min. 99% Low strength, elastic, good corrosion,and electrical properties
2xxx Copper High strength, heat treatable, reduced corrosion resistance
3xxx Manganese Medium strength, relatively good corrosion resistance
4xxx Silicon Mainly used for castings
5xxx Magnesium Good corrosion resistance, reasonable strength
6xxx Magnesium and Silicon Good corrosion resistance, moderate strength, excellent weldability
7xxx Zinc High strength, lowcorrosion resistance
8xxx Other Elements
The 3000 series alloys, such as 3003, 3004, and 3105 (designating different alloys), are the most
frequently used alloys by roll formers. Aluminum alloys called “Building Sheets”and other trade names
usually belong to this group of alloys.
Roll Forming Handbook6 -18
6.15.2 Basic Temper Designations
F as fabricated, no mechanical limits specified
O annealed to achievethe lowest strength, highest ductility, and formability
H strain (work)hardened by rolling (with or without additional heat treatment)
W can be formed right after heat treatment, age hardened at room temperature
6.15.3 Temper Designations
T heat treated, aged at hightemperature(with or without strain hardening)
H 1Strain Hardened only
H 2Strain Hardened and Partially Annealed
H 3Strain Hardened and Stabilized by low temperatureheat treatment.
Asecond digit after the abovedesignations indicates avariation of the temper.
Forthreedigit designations, such as H112, H364, and others, see the reference literature[381].
Numbers T1 to T10 refers to the combinations of hot and cold working, heat treatments, cooling,and
aging.The basic treatmentdepends on the type of alloy and on the properties to be achieved.
Twodigits tempers such as TX51 and others mayrefer to the stress relieving by stretching (or
compressing) process.
The 1000, 2000, 3000, and 5000 series of alloys cannot be strengthened by heat treatment.
6.15.4 Cladding
The good corrosion resistance of the 1000 or other series of alloys can be combined by the highstrength of
other alloys. Thin layer of the low strength, highcorrosion, resistancealloyismetallurgically bonded (hot
rolled) on one or both sides of the higher strength but low corrosion resistance alloy.During roll forming,
additional care has to be taken not to scratch or damage the soft protective surface of the clad alloys.
6.15.5 Bimetals
Aluminum can also be bonded to other metals
such as stainless steel. The combination pro-
vides arelatively light weight product with the
stainless steel (or other metal) properties. It is
not too difficult to roll form these types of
bimetals, but more attention must be paid to
the forces applied by the rolls. The larger force
required to form the stainless steel reduces the
thickness of the aluminum. Uneventhickness
reduction can create an unacceptable camber,
twist, or other imperfections in the product.
6.15.6 Roll Forming of Aluminum
Roll forming of aluminum is not as difficult as
forming steel, but more attention has to be
- H 12 one-quarter hard-H 32 one-quarter hard(and stabilized)
- H 14 one-half hard-H 34 one-half hard(and stabilized)
- H 16 three-quarters hard-H 36 three-quarters hard(and stabilized)
- H 18 full hard-H 38 full hard(and stabilized)
Work roll
Work roll
Back up roll
Back up roll
FIGURE 6.17 Reducing metal thickness during hot and
cold rolling.
Materials 6 -19
paid to:
1. Careful setting and adjustment of roll gaps
2. Application of the right lubricant to prevent pick up of aluminum on rolls
3. The use of well-designed and finished rolls to prevent surface marks.
The recommended minimum bending radii for aluminum alloysare shown in Table 6.2.
6.16 Other Metals and Materials
Practically all metals that can be formed by other processes can be rollformed. Typical roll formed
metals are copper,brass, tin, zinc, titanium, zirconium, and nickel alloys(such as Monel, Hastelloy,
Inconel, Invar,etc.) and manyother metals and alloys. Owing to space limitations, other metals
cannot be listed in this book. However,other referencebooks and sales information will provide
most of the required data to rollformers. Many of these alloys work harden quickly.This increases
the springback and can limit the formability. Occasionally stress relieving or annealing is required
after or in between rollforming.
Nonmetallic materials can be roll formed too.Thick rubber or plastic coating extruded on thin
metalcarrier is occasionally“roll formed”after theextrusionprocess. Certain plastics
(e.g., thermoplastics) can also be roll formed.
6.17 Influence of PrimaryMetal Processes on Roll Forming
Forsimplicity, the following processes, applied
before roll formingand influencing roll
forming,are grouped together in this section.
1. Metallurgical Processes to make the
metals
2. Hot and Cold Rolling
3. Coating
4. Embossing
5. Slitting.
6.17.1 Metallurgical Process
It is not within the scope of this book to discuss
the processes involved in producing the starting
material for coils, strips, and sheets. However,
these processes havesignificant influence on the
formabilityofthe metals.
6.17.2 Hot and Cold Rolling
The cast metal slabs are usually hot rolled to a
minimum practical limit then coldrolled further
to reducetheir thickness.
Both hot and coldrolling are accomplished
by reducing thethickness between pairs
FIGURE 6.18 Rolling load deflects rolls.
FIGURE 6.19 Thinner and longer edges will be wavy.
Roll Forming Handbook6 -20
of smallerdiameterworkrolls,supported
against deflection by larger back-up rolls(see
Figure6.17)
Regardless of their diameter,the rollswill be
deflected by the large forces required to reduce
material thickness. The forces can be in the
magnitude of amillion pounds (500 tons).
If the straight rollsdeflect, then the edges will
be thinner than the metal at the longitudinal
center of the coil (Figure6.18). The thinner the
material gets during rolling,the longer it will be.
The thinner and thereforelonger edges of the coil
cannot “run away” from the center part; there-
fore,itwill take awavy shape (Figure 6.19). To
counteract the deflection, the center of the rollsis
grounded to larger diameters, creating a“crown”
on the barrel-shaped rolls. If the increase in
diameter at the center of the rollistwice the
anticipated deflection, then the working side of
the roll will become straight under the load (see
Figure6.20). Coil rolled under this condition will
havethe same thickness at anypoint.
Theactualdeflection,however,deviates
from the theoretical one. Rolling temperature,
uniformityofthe starting size, the amount of
alloying elements, and the thickness reduction
schedulewillchange theforcerequired for
rolling,and thus the deflection. With changing
forces, the deflection will fluctuate. If the forceis
higher than the crown prepared for,then the
center of the coil will be thicker.Ifthe actual
forceisless than the anticipated one, then the
center of the sheet will be thinner and the edges
will be thicker (Figure6.21). In the case of thin
edges, visible edge waviness, and in the case of
thin center,visible center waviness (oil canning)
candevelop (Figure6.22).The mills can
influence the deflection and produce coils with
longer center or longer edges. In most cases, the
latter type of coils (thinner at edges than at the
center) are produced.
If an “oil canny” sheet is cut in half in a
longitudinal direction, then the long center part
will create an outward camber in the strip (sheet)
as shown in Figure6.23.Ifthe edges are longer,as
is usually the case, the camber will be in the
opposite direction (Figure 6.24).
The coil can also be rolled with acamber if,
during rolling,one end of the rollgap is larger
than the other end (Figure6.25). Slitting will not
remove the camber from the coil.
No
material
between
rolls
Material between rolls
FIGURE 6.20 Deflection compensated by crown on the
rolls will result in uniform strip thickness.
Increased load Decreased load
FIGURE 6.21 Roll gap variations caused by increased or
decreasedload.
FIGURE 6.22 Thinner and longer center results in center
waviness.
Materials 6 -21
6.17.3 Tension Leveled Metal
To provide aflat surface and to eliminate the
waviness,the material canbecontinuously
stretched.Duringthisprocess,the tension
(pulling) rolls are running faster than the pay-
offrolls. Because this continuous leveling is an
additional process, often extra priceischarged for
this type of product. In most cases, it is not
required to tension level the coils for roll forming.
In the case of wide, flat products, the usual
tension leveling can be detrimental. However,
sophisticated leveling (shape control) equipment
can induceapredetermined amount of edge or
center waviness which is sometimes needed to
manufacturestraight, flat end products.
6.17.4 Slitting
High speed slitting is the most economical way
to cut the wide mill coils into narrower strips. If
there is anoticeable difference in thickness within
the width of the coil, then during rewinding,the
thinner and thereforelonger strips will startto
sag.The thicker,shorter length, coil segments
will remaintight while the thin ones will hang in
aloop.Insome older slitter installations, 20 to
40 ft deep pits havebeen built to accommodate
these loops. To keep atension on all recoiled
narrow strips and to eliminate the loop,card-
boardpieces were placed between the wraps to
increase the rewound coil diameter.Newer,better
slitting equipment can rewind all the strips under
tension and eliminate the dangerous practiceof
inserting cardboard pieces.
As mentioned earlier,slitting willnot elimin-
ate camber in the strip.Actually,dull slitting
knives, applying more forcethan required or
creating burr,may inducecamber in the formerly
straight material.
FIGURE 6.23 Slitting straight center wavy (oil canny)
coil can result in cambered strips, curving away from the
center line.
FIGURE 6.24 Slitting straight edge wavy coil can result
in strips having camber towards the center.
FIGURE 6.25 Nonparallel rolls will producecoils with one edge thickerthan the other one. Uneven thickness
(length) causes camberinthe coil.
Roll Forming Handbook6 -22
TABLE 6.5 Guideline Prices of Different Carbon Steel Strips Compared with the Base Price of HRS
1. HRS (Hot Rolled Steel)Base Price
Thickness0.180 to 0.229 in. (4.6 to 5.8 mm) HRS Base 5 1
Width 24 to 48 in.(610 to 1220 mm)
Type Grade 1(CS)and Structural
2. HRS(HotRolled Steel) Extras (Typical)
HRS Extras Over HRS Base Price
Grade 2or3(DS, DDS) 2.5%
30, 33,36, 40 ksi min. yield 1.8%
45 ksi min. yield 3.5%
50 ksi min. yield 4.4%
HSLA 40 4.4%
HSLA 65 20.0%
HSLA 80 22.0%
H.R. Pickled and Oiled 8.0%
Width and Thickness Extras 0to15.0%
3. CRS (Cold-Rolled Steel)
Over HRS Base Price
Thickness0.028 to 0.063 in. (0.7 to 1.6 mm) Base Price 20.3%
Width 45 to 60 in.(1145 to 1525 mm)
Type ASTM A366
CRS Extras (Typical) Over CRS Base PriceOver HRS Base Price
0.15 in. thick (base width) 3.6% 23.0%
36 in. wide (base thickness) 15.2% 36.0%
0.015 in.thick, 36 in. wide 16.8% 38.0%
StructuralASTM 61 Grade A2.9% 23.8%
StructuralASTM 61 Grade B2.9% 23.8%
StructuralASTM 61 Grade C2.9% 23.8%
StructuralASTM 61 Grade D6.6% 28.2%
StructuralASTM 61 Grade E1.6% 22.2%
ThicknessTolerance: Tighter 5.1% 26.4%
Width &Thickness To lerance: Tighter 0to28.6% 20.3 to 54.7%
HSLA 45 to 50 min yield 10.3 to 13.9% 33.6 to 37.0%
Electrical0to 93.0% 40.0 to 130.0%
4. Galvanized Extras on Cold Rolled Steel (Typical)
a
Increase over HR Coil
Base Price
Thickness0.023 to 0026 in. (0.59 to 0.66 mm) Base Price Add55.7%
Width 40 to 55 in.(610 to 1220 mm)
Type Grade 1(CS)orGrade A
Galvanized Steel Extras Over Galvanized Base Price Over HRS Base Price
Grade 2and 3(DS) 4.53% 62%
Grade 4(DDS) 6.79% 66%
Grade 5(EDDS) 9.05% 70%
Grade B(37 ksi) 0.79% 57%
Grade C(40 ksi) 2.26% 59%
Grade D(50 ksi) 5.66% 65%
Grade E(80 ksi) 2.26% 59%
Grade F(50 ksi) 6.23% 66%
HSLA 40 to 120ksi 6.79 to 19.24% 66 to 86%
Lighter Coatings: Deduct 0.22 to 7.0% 55 to 45%
Heavier Coatings:ADD $0.30 to $7.47 Add0.68 to 16.91% 57 to 82%
Thicker Products: Deduct 2.45 to 22.5% 52 to 23%
Thinner Products: Add2.4 to 28.0% 60 to 99%
This guideline is based on steel prices from different mills. Other producers may have different ranges and extras.
a
Galvanized on hot rolled steel base is available at alowerpricethan shown in this table.
Materials 6 -23
6.18 Guideline to Steel Prices
Basic steel price is usually based on aminimum 20 ton purchased quantity. To comparethe prices of
different types of steels, the base price of HRS (hot rolled steel) was chosen as priceunit 1(one).
Table 6.5 shows the average prices of different types of strip steels in percentage relative to the base
hot rolled steel (HRS) price. The percentages shown in this table varyfrom time-to-time and depend
on the pricing policy of different steel mills. However,itprovides reasonably good guidelines to the
product designers.
Reference
[381] The Aluminum Association. Aluminum Standardsand Data,latest edition.
Further Reading
[99] Glance, P.M., Howtochoose the right material, Des. Eng.,September,29–31, 1976.
[100] Wright, J.R., Sorting out steel terminology, Prec. Met.,December,18, 1986.
[101] Guide to Engineered Materials, Selecting materials for temperatureresistance, Adv. Mater.
Process,33–49, 1988.
[102] Guide to EngineeredMaterials, Selecting materials for fatigue resistance, Adv. Mater.Process,
51–63, 1988.
[103] Guide to Engineered Materials, Selecting materials for toughness, Adv. Mater.Process,65–74,
1988.
[104] Guide to EngineeredMaterials, Selecting materials for wear resistance, Adv. Mater.Process,
75–90, 1988.
[105] Guide to EngineeredMaterials, Selecting materials for corrosion resistance, Adv. Mater.Process,
93–104, 1988.
[106] LaBoube, R.A. 1989. Mechanical properties of steel and effect of cold-work of forming. Short
Course on “ColdRolled Steel Standard” ,November,St. Louis, MO.
[107] Halmos, G.T., Selecting the right material for roll forming and brake forming, MetalForming
1991, and Fabricator,September 34, 1999.
[108] Shapiro, J.,Bhat, S.P., and Borchelt, J.E., Proper Steel Selection for Roll Forming.Inland Steel Flat
Products, unpublished presentation.
[109] Hand, E.W., Howtosavemoney when specifying sheet steel, Mach. Des.,July,70–73, 1975.
[110] Comparing HighStrength Steels and Aluminum for Automotive Weight Reduction Programs,AISI,
Committee of Sheet Steel Producers an AISI Publication, SG-834-279-25M-DJ.
[111] Decker, R.F., Maraging Steels: Getting Better with Age. Advanced Materials &Processes Inc.
Metal Progress, 6/88, pp.45–50
[112] Porter,L.F.and Repas, P. E., The evolution of HSLA steels, J. Met.,April, 14–21, 1982.
[113] Halmos, G.T., 1983. Roll forming HSLA steels. ASM Metal Congress,October,Philadelphia, PA.
[114] Halmos, G.T., Roll forming —use of HSLA steels increase, Fabricator,July/August, 12–15, 1984.
[115] Editorial on presentation by Beecher,D.J., Roll forming systems for heavy gauge, hightensile
steels, Prec. Met.,October,31–36, 1977.
[116] Peterson, P. T.,Steel, not plastic, reduces auto weight —amyth dispelled, MetalForming,
November,43–47, 1991.
[117] Leslie, B.,Cutting and bending stainless steel sheet metal, Fabricator,April, 38–43, 1997.
[118] Matanle, I., Roll-forming colour-coated aluminum, Sheet Met. Ind. ,October,882–884, 1980.
[119] Davies, R.G., Edge cracking in highstrength steels, J. Appl. Metalwork.,2,4,293–299, 1983.
[120] Foster,G., Hotroll-forming shapes titanium for airframes, Metalworking,June, 38–42, 1971.
Roll Forming Handbook6 -24
[121] Takechi, H. 1980. The present state of high-strength steel sheets for automobiles and their
application in the Japanese Automotive Industry. Sheet Metal Forming Seminar,Adelaide,
August.
[122] Balliger,N., Nayor, D.,Dasarathy, C., Hudd, R., Jones, A., and Hessey,J.1981. Developments
in dual phase steel by the British Steel Corporation. The Metal Society Conference Proceeding,
September.
[123] Demeri, M.Y., Formability guidelines for aluminum alloys, J. Appl. Met. Work.,2,4,288–292,
1983.
[124] Conrad, R.O., Roll forming aluminum, Fabricator,July/August, 22–27, 1977.
[125] Kindelvich, F.T. 1981. Roll forming aluminum. SME “Technolog yofRoll Forming Clinic”,
January27–29, Clearwater Beach, FL.
[126] Editorial, The rolled zinc alternative for architectural designs and more, Prec. Met.,July,15–21,
1978.
[127] Remich, N.C. Jr., To prepaint from postpaint: guide to cost justification, Appliance Manuf.,July,
3132, 1992.
[128] Gibbons, J.,Smith, D.,Hicks, R.E., Lezzi, B., Wafler,V., Swaney,L., Boone, B., Simonseu, R.,
and Keeling,T., Coated coil comments, Natl Coil Coaters Assoc. Cooperation Met. Build. Rev.,
1980.
[129] Graziano,F.D.Coil coating: the better way, October 1996, unpublished.
[130]Simonsen,R., Howtoget themostout of roll formingcoatedcoil, Fa br icator ,
November/December,21–23, 1979.
[131] National Coil Coaters Association, Howtofabricate prepainted materials, Fabricator,April,
34–35, 1997.
[132] Hipchen, J.,Protecting surface-sensitive materials in coil processing, Fabricator,September,
p.22–25, 1997.
[264] Altenpohl, D.A., Aluminum: Technology, Applications, andEnvironment ,The Aluminum
Association and TMS, 1998.
[379] ASTM (American Societyfor Testing and Materials), Appropriate Standards.
[380] ASM (American Societyfor Metals), Metals Handbook –Properties &Selection,Vols. 1–3, latest
edition.
[382] AISI (American Ironand Steel Institute). Appropriate Standardsand Guides.
[383] ASM, Worldwide Guide to Equivalent Irons and Steels,latest edition.
[398] SAE (Society of Automobile Engineers). Appropriate Standardsand Guides .
[582] The Aluminum Association, The Aluminum Design Manual,latest edition.
Materials 6 -25
7
Lubrication
Joseph Ivaska
Tower Oil&Technology Co., IL
7.1 TribologyofLubrication ................................................... 7 -1
Friction
†
Wear
†
Lubricating Mechanisms
†
Role
of Surface Tension and Wetting
7.2 Selection of Lubricants ...................................................... 7 -5
Evaporative Compounds
†
Chemical Solutions
(Synthetics)
†
Microemulsions(Semisynthetics)
†
Macroemulsions
†
Petroleum-BasedRoll Forming
Lubricants
†
Additives
7.3 SurfaceProperties of Formed Material ............................ 7 -8
Steel
†
Galvanized Steel
†
Nonmetallic Coated Metals
†
Stainless Steel
†
Aluminum
†
Copper, Bronze, and Brass
7.4 Lubricants for the SecondaryOperations ....................... 7 -10
Pre- or Postnotching and Punching
†
Cutoff
†
Other
Postforming Operations and End Use
7.5 Application Te chniques ..................................................... 7 -11
Drip
†
Roller Coat
†
RecirculatingSystems
†
Airless
Sprayers
7.6 Preparation and MaintenanceofLubricants ................... 7 -12
Preparation of the Lubricant
†
Maintenance and Control of
Lubricant
†
Lubrication for Total Productive Maintenance
7.7 Operating Problems during Production .......................... 7 -18
Accelerated Tool Wear
†
“Metal Pickup” on the Rolls
(Its Causes and Cures)
†
Hard-to-Lubricate Surfaces
†
Coated Stock
†
Bimetals
†
Long-TermStorage of Formed
Products
†
White Rust
7.1 Tribology of Lubrication
Boundaryfriction, which is associated with almost all metal forming operations, is caused by the relative
movement of twoadjacent surfacesunder pressure.Inthe case of rollforming, the relativemovement
between rolls and workpiece is enhanced by the surface speed differential of the rolls.
7.1.1 Friction
Friction may be defined as the resistance to relative motion between twobodies in contact. Friction is an
energydissipating process, causing the temperatureatthe interface to rise and, if excessive, can result in
surface damage. It will also influencethe deformation taking placeinthe roll forming operation.
The earliest theories suggested that friction was the result of interlocking tworough surfacessliding
along each other.Friction is actually brought on by alarge number of variables, such as load, speed,
7 -1