Roll Forming Handbook / Edited by George T. Halmos
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Occasionally,overhead crane supporting structureand rails are extended from the plant into the yard,
allowing unloading outside the plant and moving coils, in one handling,toinside storage. This method is
less frequently used in harsher climates, because the large opening needed for the crane to enter the plant
can create problems in winter or on rainy, humid days.
8.12 Material Handling Accessories
8.12.1 Crane Attachments
Auxiliaryequipment attached to cranes is used
to lift, move, rotate, weigh, and load coils or
bundles of sheets. Equipment cost, available
headroom,storage space, isle width, coil orien-
tation, type of storage, method of line loading,
limitationinequipment,and structurecan
determine the type of crane attachment to be
used.
Well-selected lifting attachments will reduce
handlingtimeand can reduce thematerial
handling crew to one person.
If the crane handles only one type of product,
then the attachment can be permanently left on
the crane hook. If the axes of the coils are rotated
from vertical to horizontal, coils, sheets, and
finished products are handled by the same crane,
then several below-hook attachments will be
required.
8.12.2 “C” Hook
The “C”hook is one of the most frequently used
attachments to handle coils with ahorizontal
axis (see Figure8.52). It is simple, has no moving
parts, and is inexpensive.The disadvantage of
the “C”hook is the isle space required to insert
and remove hook from coils (Table 8.1).
FIGURE 8.52 “C” hook coil lifter.
TABLE 8.1 "C" Hook and Coil Grab
“C” Hook Coil Grab
Advantage Disadvantage Advantage Disadvantage
Simple Increased coil storage space
required
Requires less coil storage
space
More expensive
No moving parts Cannot load coil on
uncoiler
Mayload on uncoiler
directly
Higher headroom required
Less expensiveUsable only for coils
with horizontalaxis
Coil widths must be
within specific range
Can handle wide range
of coil widths
Applicable only for coils
with horizontal axis
Roll Forming Handbook8 -38
8.12.3 Coil Grabs
The twovertical, moveable arms of the telescopic
or parallelogram coil grab,shown in Figure8.51
and Figure8.53,can reach into the inside coreof
the coil. The small horizontal, grabbing move-
ment allows for leaving only aminimal, approxi-
mately 12 to 18 in. (300 to 450 mm) of space
betweenrowsofcoils.However,itusually
requires morehead room than the “C” hooks.
This either restricts the number of coils piled on
top of each other or increases the crane hook and
plant ceiling height.
The telescoping type of coil grab needs less
headroom but more space between the rows. The
gain in additional storage spacedue to the small
isle requirements usually far outweighs the small
purchase price difference with respect to “C”
frame and the extra cost attributed to ahigher
building.
Figure8.53 provides agraphic illustration of
the isle space requirementwhen coils are handled
with forklift truck or crane with “C” hook or coil
grab attachment.
8.12.4 Fork Attachment
As mentioned earlier,the “C”hooks are limited
to handling only coils with horizontal axes. To lift
coils on pallets, or bundles of sheets, crane
attachments with forks are available. Forks may
be directly attached to the stackercranes or
supplied as underhook “C”units.
8.12.5 Below the Hook Coil
Upenders
There are below-hookattachmentsavailable,
which lift the coils with vertical axes and rotate
them into horizontal position in one handling.
Atypical attachment (shown in Figure8.54)
provides asimple, timesaving method for lifting
and upending narrow coils.
8.12.6 Slings and Chains
Metalorfiberslings goingthroughthe coil core can
be usedtohandlecoils if loading/unloadingisat
floor,oreasily accessible,level.Fiber(nylonor
other) slings should be frequentlychecked for
damage. Metalslings maydamagethe insideedges
FIGURE 8.53 Coil storage isle width depends on the
type of handling equipment.
FIGURE 8.54 Combined coil lifting and upending of
narrowcoils.
Coil Processing, Material Handling, and Plant Layout 8 -39
of thecoil. Slings or chains aresometimesappliedtonarrow coilswith vertical axes,and they canbeusedto
rotate into horizontal positionduringlifting.
Chains and ropesmay damage the edges of thinner or softer metal coils and thereforetheir usage
should be restricted.
8.12.7 Other Crane Attachments
Coil orientation, receiving and inventorypolicy,weighing,orother requirements may requirethe
application of additional attachments separately or in conjunction with the previously described below-
hook attachments.
8.12.7.1 Rotating Crane Hook
If possible, the direction of the horizontal coil axis on the incoming transportvehicle, in storage, and on the
uncoiler,should be the same. Unavoidable conditions, however,may make it necessarytochange the
direction of the horizontal axis of the coils or rotate it, for example, from north/south to east/west
direction.
Coils hanging on the swivel hook of the crane can be rotated by hand after lowering the load to near-
floor level. Motorized rotation is preferred,however,toincrease efficiency and reducematerial handling
time. Amotorized rotating hook can be ordered with the crane, while coil grabs and some other units
may be purchased separately with rotating attachment.
8.12.7.2 Crane Scales
If the weight of the incoming,stored, or outgoing material has to be checked, then using acrane
scale can save time and floor space. Alarge varietyofmechanical, hydraulic,and electroniccrane
scales are available with different accuracy. Crane scales are available with optional features such as
printout and direct or radio data transmission to production/inventorycontrol depar tments or
computers.
8.13 Crane Controls
Most crane controls are located either hanging on pendulum, or in acab or crane, and attachments may
be controlled by radio.
8.13.1 Pendulum Control
Pendulum hanging from the crane is the lowest cost and simplest method of operating crane. As the
operator walks with the crane, the crane speed and the distance covered is restricted. Aclear walkway
through the plant for the operator and for the load is required.
8.13.2 Control in Cab
The controls and the operator can be located in the cab traveling with the crane. The cab is either located
underneath one end of the crane bridge or,inthe case of the stackercrane, maybeattached to the stacker
unit. This provides greater comfort when operating the crane, but the operator is confined to the cab all
day.Inmost cases, an additional “ground” crew is required, increasing material handling costs.
8.13.3 Radio Control
Aradio transmitter unit with all control functions hanging on straps from the operator’sneck allows the
remote operation of the crane from asafe but desireddistance. The operator can perform additional
functions such as inventorycontrol, load manipulation, and so on. One operator can easily unload coils
from transportvehicle or storage space, and then weigh, mark, and load roll forming lines.
Roll Forming Handbook8 -40
8.14 Plant Layout
Moving the material through the plant is anecessarypartofthe manufacturing process. The labor
involved in moving the products does not increase the value of the product, only its cost. In most
manufacturing plant, the actual time spent on moving the material in the plant is more than the time
required to form the product. Therefore, aproper plant layout and an efficient method of handling and
storing both the starting and finished products haveasignificant effect on product cost and profit.
The volume of the finished products after roll forming can be 2to50times the volume of the coil. The
expansions of afew typical products are shown in Figure8.48.
Owing to the “expanded” volume, both the storage spaceand the number of “lifts” to movethe
finished products is multiple of those required for coils. Layout of the plant has to take this fact into
consideration.
Plants with several roll forming lines usually haveone high-capacitycrane dedicated to unload the
incoming coils, transfer them into the storage area, and from storage to the uncoilers. More equipment
and aconsiderably larger storage area is required for the finished products removal, storage, and loading
of outgoing trucks.
8.14.1 Flow of Material
To reduce the material traveltime and expenses, it is importanttoprovide as shortand smooth flow
as possible (see Figure 8.55). Excessive crane or other equipment travel, even if it is only 10 to 20 ft
(3 to 6m)atatime, can be aconsiderable expense when the total number of lifts is considered during the
life time of the equipment working in the plant.
FIGURE 8.55 Flowofmaterial throughthe plant.
Coil Processing, Material Handling, and Plant Layout 8 -41
The following should be considered when plant layout is prepared and equipment selected:
Material Flow:“IN”
*
Yearly quantity(weight and number of lifts)
*
Peak quantity(number of lifts per shift)
*
Transportation method of incoming material (railway: gondola or boxcars; truck: open bed or
closed vans)
*
Material handling equipment and unloading at receiving point
*
Method of weighing (if required)
*
Method of coil or strip storage (pile, rack etc.)
*
Weight and size of coils
*
Orientation of coils (center line or eyeofcoils —horizontal or vertical)
*
Coil packaging (band, skid, with or without core, etc.)
*
Susceptibility of material to environment (warehouse conditions)
*
Snow, water,dirtremoval at receiving
*
Inventoryadministration (coil identification and necessaryadministration)
*
Number of mills to be served(present and estimated future equipment)
*
Auxiliaryequipment (upender,turnstile, storage rack, coil car,etc.)
*
Frequency of returning par tially used coils to storage
*
Special care in handling and storage (protecting surface, edges, highvalue of material, etc.,
if required)
*
Separate storage spacefor rejected or damaged coils
Material Flow:“OUT”
*
Material handling equipment at the product unloading and shipping point
*
Type of transportation equipment (truck, railway)
*
Auxiliaryequipment at the exit of the lines (conveyor,power conveyor,droptable, drag chain
etc.)
*
Bundle or package size (weight, width and length)
*
Packaging,strapping,orcrating requirements
*
Feasibilit yofloading directly from line on to transportation equipment
*
Indoor or outdoor storage requirements
*
Method of weighing outgoing shipment (if required)
*
Storage method (stacking,storage racks, crates, tote boxes, etc.)
*
Stackability of products (bundles, boxes, crates, etc.)
*
Storage space requirements for subsequent operation (if any)
*
Shortduration or seasonal, long duration storage requirements
*
Capabilitytoship anyofthe stored packages or bundles (opposite to “first in, first out” or “first
in, last out”method)
*
Sensitivity of material to storage conditions (humidity, temperature, dust)
*
Necessitytohandle certain products with special caretoavoid scratching,bending,and so
on
*
Orientation of products (direction of long pieces in relation to material handling and
transportation equipment)
*
Shipping or production priorities (e.g., prioritytoload customer’struck versus unloading
rollforming mill)
*
Availabilityofequipment, labor and other services (such as lights at outdoor storage)
if afternoon and night shift work is required
*
Lifting height restrictions (e.g., lifting crates over the side supportofrailwaygondola cars).
Roll Forming Handbook8 -42
References
[45] Theis, H.E., Correctivesheet metal leveling —science, artorblack magic? FABTECH Conference,
September 16–19, 1985, Chicago,IL, Technical Paper MF85-857, and Fabricator,April 1987.
[47] Theis, E. 1995. Strip shape control for roll formers (levelers are not for leveling). SME Roll
Forming Conference,August 29–30, Detroit, MI.
[48] Kaufmann,H., Developments in sheetmetal straightening, MetalForming ,November ,45–49,1990.
[50] Scheider,A.F.1988. Edge cleaning,deburring,and surface conditioning —anupdate. FABTECH
EAST ’88,April 5–8, Baltimore, MD,Technical Paper MR88-156.
[52] Steinmeyer,L., Accumulate uptime by joining coils, MetalForming,January, 30–36, 1999.
[140] Costello,T.1977. Elimination of downtime between coils. FMA TechnologyofRoll Forming
Proceedings ,February8–10.
[141] Shaffer,S., End joining on rollforming lines, Met. Build. Rev.,September,1982.
[142] Costello,T., What is the cost of coil change downtime? Stamp.Quart.,42.
[143] Accra-WireControls, Inc., Pallet decoilers come of age, MetalForming,January, 1996.
[144] Editorial, Free loop accumulator boosts roll forming productivity, Prec. Met.,May,33–34, 1976.
[145] Halmos, G.T., Efficient material handling for roll forming mills, Mater.Manage. Distrib.,
December,28–31, 1978.
[146] Halmos, G.T., Designing aplant layout for efficient roll forming operations, Fabricator,
November/December, 21–25, 1981.
[147] Costello,T., Newsystem provides continuous coil without accumulators, Fabricator,May/June,
1986.
[148] Users feed coil strip with atwist (horizontal uncoiler), MetalForming,July,23–28, 1992.
[149] Heuring,J., Applying pallet decoilerstorollforming applications, Fabricator,September,26–28,
1997.
[150] Hydrostatic speed variator delivers constant flowindynamic decoilers, MetalForming,32–33,
July 1997.
[152] Urbas, E., Forbetter feeding,look at the loop, Met. Stamp. ,July,18–19, 1978.
[154] Kotynski, R., Installing and maintaining coil cradles and reels, Fabricator,April, 56–58, 1999.
[155] Cary, A., Applied loop control, MetalForming,January, 19 –24, 1997.
[156] Carey,A., Loop control for stable stamping, Form.Fabricating,May,26–30, 1995.
[399] Remirez, F.,Leveling defects —causes and cures, MetalForming,July,32–34, 2000.
[400] Theis, E., When to level, MetalForming,July,36–40, 2000.
Coil Processing, Material Handling, and Plant Layout 8 -43
9
Designing Products for
Roll Forming
GeorgeT.Halmos
Delta Engineering Inc.
9.1 Developing Light Gage Products ...................................... 9 -1
9.2 Design Considerations ...................................................... 9 -2
Influence of the Forming Procedures on Design
†
Selecting
Bending Radius
†
Designing aProduct with aLarge Radius
†
Minimum Bending Radius of Coated Products
†
Minimum
Bending Radius of Presheared/Prenotched Metals
†
Minimum Radius of Embossed Metals
†
Discontinued
Bend Lines
†
Width of Flat Elements
†
Stiffener Ribs
9.3 SecondaryOperations ....................................................... 9 -10
Operations in the Line
†
Punching
†
Rotary Punching
†
Notching
†
Lancing, Partial Punching, Louvering, and
Embossing
†
Mitering
†
Slitting
†
Cut-to-Length
†
Joining
Different Materials
†
Bending across the Rolling Direction
†
Roll Forming Nonparallel or Nonstraight Bend Lines
†
Curving and Sweeping
†
Coining
†
Marking
†
Welding,
Brazing, and Soldering
†
Coating
†
Adhesive Bonding,
Caulking, and Foaming
9.4 Profiles Manufactured in Different Sizes ......................... 9 -20
Spiral Pipes, Panels, and “U” Channels
†
“C” Channels
and “Z” Sections
†
Building Panels
9.5 Design of Specific Products .............................................. 9 -22
9.6 Dimensioning and To lerancing ........................................ 9 -22
Dimensioning
†
Tolerancing
†
Length and Cutting
Tolerances
†
Section Dimension Tolerances
†
Deviation
from Straightnessand Flatness
†
Tolerances Applied to Other
Features (Curvatures, Holes, Notches, Embossments,etc.)
†
Other Tolerances Such as Burr and Appearance
†
Influence
of the Applied TolerancesonCost
References ....................................................................................... 9 -29
9.1 Developing Light Gage Products
The forerunners of the presently used light gage metal building,drainage, grain storage, appliance,
automotive,and other products were developed decades ago by trial and error.Tinkerers and designers
recognized that the principles of strength calculations developed for thick materials, plates, and structural
components havelimited or no applicabilitytolight gage materials.
9 -1
It was only in the early 1940s that significant
research commenced on cold formed, light gage,
steel structures, spearheaded by Dr.George Winter
at Cornell University and followed by along line of
other researchers in NorthAmerica, Europe, and
other parts of the world. Sincethen, the behavior
of thin, light gage, metals under strain havebeen
thoroughly studied. The result of these works
became the foundation of the present specification
for the Design of Cold-Formed Steel Structural
Members by AISI[382] andother design
guidelines.
Theloadcarryingcapacityoflight gage
components is frequently restricted by thebuckling
of compressed,flat elements.Therefore,the present
codesallow forconsideration of thecross sections
of allbentelements, butonlythose flatelements,
whichdonot exceed aspecifiedwidth:thickness
ratiolimit.Inseveral codes, thewidth:thickness
ratioislimited to approximately w : t ¼ 60:
To utilize all or most of the compressed elements, edge stiffeners and simple or multiple stiffener
elements can be added to the sections. Figure9.1 shows some typical stiffened sections.
This chapter provides practical guidelines for the application of design principles to rollformed
products without repeating the information and equations provided in the specifications and books.
Designers haveasignificant influenceonthe qualityofthe product, as well as on the tooling,
equipment, and production cost by selecting the best bending radii, choosing the best shape of stiffeners
at the practical locations, and keepingholes, notches, and embossments at the practical distancefrom
bend lines and other variables. Frequently,the success or failure of the products as well as the profit of
the companyisheavily dependent on the judgment and expertise of the product designers.
9.2 Design Considerations
The product design is influenced by manyrequirements such as:
*
Function of the parts or assembly
*
Strength requirements; static and dynamic loads, fatigue, impact resistance,and others
*
Assembly or erection requirements
*
Appearance, styling,and customer’srequirement
*
Repair or interchangeability, replacement methods
*
Safetystandards or common sense safetyconsiderations
*
Welding,painting,plating,packaging,and other requirements
*
Corrosion, erosion, friction, wear,heat, or other exposures
*
Vibration, noise, or heat transfer
*
Availabilityofmaterial (including company’sown inventory)
*
Special requirements such as crash energy, military, and so on
*
Quantityper production run and total quantityper year or tool life
Awell-designed product, which meets all the aboveconditions, still cannot succeed unless it meets with
the following twoadditional requirements:
*
Manufacturability
*
Competitivecost per pieceand total equipment and tooling cost
Wr
Wo
t
Wo
Wr
FIGURE 9.1 Different stiffener ribs and heads.
Roll Forming Handbook9 -2
9.2.1 Influence of the Forming Procedures on Design
Both brake forming and roll forming provide straight bend lines. During brake forming, the cross section
is uniformly changed along the full length of the product. Majorstresses are restricted to the bent
elements and their nearby vicinity.
Roll forming,however,isaprogressive process. While one end of the strip is flat, the other end is
completely formed (Figure 5.1 and Figure 5.11). Stretching and compressing elements of the strip,with
or without prepierced holes, notches or embossments, leavesresidual stresses in the product. Excessive
residual stresses result in camber,twist, cross-bow,edge or center waviness, herringbone effect or other
deviations from straightness and flatness shown in Figure4.1 and Figure10.38d–l.
Product design has asignificant influence on both the residual stresses developed during forming, and
the achievable tolerances.
9.2.2 Selecting Bending Radius
To form aflat strip to the specified shape, the stresses in the bent elements must exceed the yield point. It
is generally accepted that the stresses exceeding the yield point and resulting in apermanent deformation
develop over 0.2% permanent elongation. In cases involving mild steel, the total strain at this point will
be in the magnitude of 0.6 to 0.8%, or amultiple of that when higher strength steel or aluminum are
formed. To achieve apermanent deformation, or “set”asfrequently described in roll design terminology,
the outside fiber of the bend line should be stretched from aminimum of approximately lto2%tothe
maximum strain attainable without material failure (Figure 6.9).
Forthe abovereason, roll designers prefer to form the bend lines with arelatively small radius. The
large elongation at the outside fiber of the bend line creates stresses well over the yield point and “sets”
the shape withminimum springback. When bending to alarge radius, the stress will be barely abovethe
yield point and the elastic strain/permanent strain ratio will be high, resulting in alarge springback.
The percentage of elongation over the outside fiber (Figure9.2) can be calculated as
e
e
þ e
p
¼ e ¼
a
o
2 r
n
£ 100%
where
e
e
¼ elastic strain
e
p
¼ permanent strain
e ¼ total strain in percentage
t ¼ thickness of material
r
n
¼ bending radius at actual neutral axis of
strip
r
i
¼ inside bending radius
k ¼ bending factor
a
o
¼ distanceofthe outside fiber from the
actual neutral axis or a
o
¼ð1 2 k Þ t
Example
if r
i
¼ 2 t and k ¼ 0 : 33
then r
n
¼ 2 t þ 0 : 33t ¼ 2 : 33t
and
e ¼
ð 1 2 0 : 33Þ t £ 100
ð 2 þ 0 : 33Þ t
¼
0 : 67 £ 100
2 : 33
¼ 28: 75%
whereas
if r
i
¼ 80t ; then e ¼
0 : 67 £ 100
80: 33
¼ 0 : 83%
r
i
r
n
α
t
a
o
FIGURE 9.2 Theoretical approach to calculate the
elongation of the outside fiber.
Designing Products for Roll Forming 9 -3