Roll Forming Handbook / Edited by George T. Halmos

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Thicker materials, such as 0.060 to 0.100 in. (1.5 to 2.5 mm), require morepulling force. Pairs of driving

rolls located between each idle forming roll passes can producestructural “U,” “C,” “Z,”and other sections.

Proﬁles within the limits can be changed quickly by exchanging the idle proﬁle forming rollsonly.

2.2.9 Spiral-Tube Mills

Corrugated spiral tubeswithlock-seamed,

welded, or other joints are used for rigid culvert

pipes, ﬂexible water/electrical hoses, and other

applications.

The corrugated section is formed in amill

(Figure2.27)and curvedwith aspecial curving

head (Figure2.28). Most frequently,the edges are

lock-seam joined continuously in the curving

head (mechanical joint) or they are welded.

The diameter of the ﬁnished tubes/pipes is

changed by altering the “helix angle” (the angle

between the entering proﬁle and the exiting

tubular product), without changing the width of

the roll formed section. Usually,the curving head

and the run-out table remaininaﬁxed position,

and the helix angle is changed by “swinging”the

mill bed around apivot point, which is located at

the curving head.

The same principle is used in the manufactur-

ing of smooth wall lock-formed (or welded)

ventilationpipes. For lightgauge ventilation

pipes, the spiral tube curving is often accom-

plished with “bronze shoes.”Inthis case, each

diameter (and helix angle) must haveits own

shoes.

FIGURE 2.26 Nondriven, pull-through mill.

FIGURE 2.27 Corrugated spiral-tube (culvert) mill.

Roll Forming Handbook2 -16

2.2.10 Truck-Mounted Mills

Installers of construction products occasionally ﬁnd it necessaryand often moreeconomical to form the

products at the job site.

Forexample, to reroof an existing building,the architect mayspecify over 100-ft (33-m) long sheets.

Because transporting and handling these sheets from the plant to the job site is not practical, it is easier to

move the complete line to the job site.

Most special, trailer-mounted lines havetheir own diesel generator,hydraulic or other drive, cutoff

press, and an uncoiler that can be loaded fromground level(Figure2.29).

These self-contained units are also used in less developed countries or at anyplacewhere, owing to the

lack of proper infrastructure, it is easier to transport the equipment in one truck and the coils in another

one than to ship manytruckloads of ﬁnished products.

FIGURE 2.28 Curving head of aspiral mill.

FIGURE 2.29 Trailer-mounted roll forming line.

Roll Forming Mill 2 -17

Several types of truck-mounted units are used by contractors for job site manufacturing of

eavestrough, sidings, sofﬁts, and similar products. These units usually havea“plug-in”electrical motor

drive. Small items such as eavestroughare often manufactured in a“stop-and-go”operation, and the

products are cut by amanual shear mounted at the end of the mill.

2.2.11 Special Mills

Avarietyofspecial application or “homemade”mills are in use by the industry. Many of them do not ﬁt

into the previously mentioned groups, but they work satisfactorily.Several of these homemade units are

eventually replaced with better qualityorhigher output, standard,commercially available lines. However,

the lack of experience eliminates manypreconceived ideas and homemade roll forming lines often

incorporate ingenious methods of roll forming.

2.3 Mill Components

2.3.1 Mill Bed

The mill base, sometimes called “bed,”supports the stands, shafts, rolls, drivetrain, and the components

needed to form the sections. The most important requirements for the base are:

Rigidityduring operation, transportation, and installation

Smooth, leveled top surface for installation of the components

Akeyway or other component to be used for aligning the stands

Drainage for the rollforming lubricant

Long mill bases may havetobesplit into twoormoresections to accommodatemachining,handling

(lifting), and transportation. If the base is split, if extension is anticipated, or other units are to be

attached to it at alater date, then additional plates and joining ﬁxtures have to be mounted to the joining

end(s) of the mill bases.

Mill bases must be capable of accommodating recirculated lubricant used during forming. In the case

of split bases, attention has to be paid to providing recirculation to each base section and to making a

watertight joint between the bases.

In most cases, the base also supports the drivetrain. The gear boxesthat drive the stands are very

seldom mounted on aseparate base.

Standardmill base design does not exist, but most beds are similarly constructed either from plates or

from tubular sections. Atypical bed made from plates is shown in Figure2.30.The upper surfaceofthe

top plate is either fully machined or is machined only along the longitudinal edges where the stands and

gear boxesare mounted. An alignment keyway is machined in the full length of the top plate. The keyway

(or other components) should be straight within 0.001 to 0.002 in. (0.025 to 0.050 mm) along the full

length of the mill even if it is assembled from sections. Holes are drilled and threaded for mounting the

stands and other components. The upper edges of the base sides are welded to the top plate, and the lower

edges are attached to aframe structure.Leveling and foundation plates are attached to the frame. Cross-

plates and other members welded into the cavity of the base provide additional rigidityand support.

FIGURE 2.30 Roll forming mill bed.

Roll Forming Handbook2 -18

To provide areturn ﬂow to the lubricant, most mills haveachannel around their top perimeter.

Frequently,the channels are made from structural angles welded to the bed with asufﬁcient gap for the

lubricant and access for cleaning. It is useful if the bottom of the channel is slanted towards the liquid

discharge opening.During construction, the top of the outside vertical leg of the angle should be above

the mill bed. The protrudingleg machined to level with the mill bed provides an additional supportto

the outboard stands during tool change and installation.

The basic requirements for structural or tubular frame construction are the same as for plates. If the

bed does not haveacontinuous top plate, then athinner lubricant collector-plate can be utilized.

Special consideration should be given to the motor/gear/drivetrain supports. If the top plate is cut out

around the center of the mill to provide space for the drive belt or chain, then the rigidityofthe base

should be rechecked. The cutout mayhavetobereinforced.

In mills traveling sideways on rails, proper supportshould be provided for the casters (or slides) and

the forces exerted during the sideways movement should be checked.

In most cases, the height of the mill base is calculated to provide comfortable pass line height for the

product. Usually,the pass line height is set at 36 to 40 in. (900 to 1025 mm) abovethe ﬂoor.However,the

size of the stands, the type of presses, other secondaryoperations in the line, and the method of material

handling may determine the actual pass line height. If the pass line height is too high, then a

walking/working platform must be provided along the operator side of the mill. However,safetyand

fatigue (the frequency the operator must step on and offthe platform) are additional factors to be

considered. Therefore,occasionally,the cutoffpress or other equipment is installed in apit to create a

comfortable pass line height for the operators.

2.3.2 Stands

In most cases, the drive-side stands are exposed to considerable forces and bending moments.

The operator-side (outboard) stands are exposed to lesser forces. They usually supportthe shafts

through needle bearings and long bearing sleeves. As aresult, there are no forces acting on the stand in

the axial direction of the shaft. The outboard stands are fastened withone or twobolts to the mill base

(Figure2.31a –d). The latter two(Figure2.31c,d)take the shortest time to remove and install the stands.

The vertical forces are contained by the vertical legs of the stands. The forming resistance, the uncoiler

brake,the changing roll perimeter speeds, and occasionally the jamming of the strip create horizontal

forces in the direction of strip travel. These forces are accentuated by torque of the drivetrain. To

withstand the resulting stresses, the drive-side stands must be sturdy and well anchoredtothe mill base.

Both side stands havetobesturdy enoughtowithstand the shafts separating forces. These forces are

occasionally multiplied by incorrect setup (too much pressureapplied by the operator) or mishaps such

as double or triple strip thickness, or foreign materials forced through the rolls.

Large forces bending the shafts increase the shaft deﬂection (the shaft’scenter-to-center distanceat

the middle of the shaft). Excessiveshaft bending can change the cross-section of the product, especially

in the case of long roll spaces (shaft lengths). Excessively highforces can bend the shafts permanently.

Permanently bent shafts will change the product dimensions at everyrevolution of the shafts.

To avoid costly downtime and repair of bent shafts, some suppliers provide limited strength crossbars

at the top of the stands. These crossbars havebeen designed to break beforethe shafts permanently bend.

However,changing the crossbars is also time consuming.Analternative method is to use calibrated

ab cd

FIGURE 2.31 Different methods to fasten the outboard stands to the mill base.

Roll Forming Mill 2 -19

strength screws to fasten the crossbars to the stand. These screws act as “shear pins” (Figure2.32).

However,the simplest solution to avoid shaft bending is to use an elastic top shaft (bearing block) hold-

down mechanism such as preloadedsprings, or pneumatic or hydraulic cylinders (see also Section 15.2.6).

Adrawingofatypical stand is shown in Figure2.17.Most rollforming mills made in NorthAmerica

havethe bottom shafts in aﬁxedposition above the mill bed. The top shafts can be adjusted up and down

with screws. To allow easy and accurate adjustabilityofthe top shaft, the lifting/pushing screws above the

bearing blocks, and their attachments to the bearing blocks and to the cross bars, must be free of play,

with gaps not exceeding 0.0005 in. (0.015 mm).

The bearing blocks should movefreely up and down, but the gap should be sufﬁciently small, especially

at the driveside, that when the operator-side stands are removed, the end of the shafts cannot be moved

up or down by hand (Figure2.33).

The approximate position of the upper shafts is shown on avertical scale fastened to the side of the

stand (Figure2.18b). Amoreaccurate up and down adjustment can be observedonthe micrometer scale

attached to the adjusting screws (Figure2.2 and Figure 2.18b). The micrometer scales at both the drive

and the operator side shall show the same number when the shafts are exactly parallel.

It is essential that all shafts should be set exactly at 908 to the direction of the strip travelduring

installation of the drive-side stands. The smallest angular deviation can create serious rollforming

problems.

(a) (b) (c)

Detail A

FIGURE 2.32 Using calibrated strength screws or springs or pneumatic/hydraulic cylinders can prevent permanent

shaft bending.

gap

FIGURE 2.33 Gap between the bearing block and the stand should be small in order to keep the end of the shafts

rigidly in position.

Roll Forming Handbook2 -20

The drive-side stands are usually equipped with

tapered bearings. The tapered bearings are taking

both the vertical (shaft separating), and the axial

loads. Wear in these bearings result in loosely held

shafts. Looseshaftsmakeitdifﬁcult, if not

impossible, to set up the rolls accurately.There-

fore,once the shafts become loose, tightening or

replacing the bearings will be required, followed

by shoulder realignment (see Section 2.3.9).

The operator side of the shafts is supported by

needle bearings. The nut at the end of each shaft

is pushing the needle bearing sleeve against the

spacers and rolls which, in turn, are pushed

against the shaft shoulder (Figure2.34).

When the operator-side stands are removed,

retaining clips at both ends of the long bearing

sleevesare preventing the sleevesfrom falling out

from the bearing blocks. When the stands are installed on the mill, the bearing blocks should be about at

the center of the long sleeves, leaving moreorless identical size gaps between the bearing blocks and the

retaining springs (Figure2.35).

2.3.3 Shafts

The construction of the cantilevered shafts and

theoperatorsideofthe two-end-supported

shafts are similar.However,tosavespace, the

rollsonthe cantilever shafts are frequently held

by the countersunk screws, threaded into the

center of the shafts (Figure2.36).

Atypical linkage type gear-boxstand is shown

in Figure2.37.Shafts can be driven by spur gears

(Figure2.38a–c), chain (Figure2.39a), or

universal joint (Figure2.39b). In these cases,

the top and bottom shafts can be identical except

the operator-side threads at the end of the shafts.

Experienceshows that if all threads are right-

handed (RH), then the nuts either at the top or at

bearing

nut

spacer

roll

spacer

shaft shoulder

shoulder alignment spacer

sleeve

FIGURE 2.34 The nut at the end of the shafts pushes the bearing sleeve, rolls, and spacers against the shaft shoulder.

stand

retaining ring

equal gap

shaft

sleeve

FIGURE 2.35 The bearing sleeves should be about at the

center of the bearing block.

shoulder

shaft

bolt

roll

washer

FIGURE 2.36 In cantilever mills, the rolls are often

secured by bolts screwed into the shafts.

Roll Forming Mill 2 -21

the bottom level shafts will become loose. To avoid this problem, all the shafts at one levelhaveright-handed

and at the other levelleft-handed (LH) threads and nuts as shown in Figure2.40.The direction of thread is

always opposite to the direction of shaft rotation; that is, if during rollforming, the shaft rotates

counterclockwise, then RH nuts are required (tightened clockwise). If the shaft rotates clockwise, then the

nuts must be tightened counterclockwise (LH thread). This requirement makes the mill unidirectional. In

(a)

(c)

gears on

shafts

gears on

shafts

limited

adjustability

bigger

adjustability

idle gear

(b)

FIGURE 2.38 Typical gear driven stand (a); gear train with limited (b) and bigger adjustability(c).

FIGURE 2.37 Typical linkage-typedrive-side stand.

Roll Forming Handbook2 -22

other words, the mill (observing from the operator side) can run only from left to right, or from right to left.

Lock nuts, hydraulic nuts, and other devices do not solve the problem if the mill is operating in the wrong

direction.

The shafts can have ﬁxed or variable rollspace. The operator side of the ﬁxed roll space shaft has a

smaller diameter partthat ﬁts into the bearing (Figure 2.17). On variable roll space shafts, the ID of the

needle bearings ﬁt the shafts at anyposition (Figure2.18). This allows moving the stand to different

location along the shafts. Moving the operator-side stand closer to the drive-side stand reduces the shaft

deﬂection, permitting to roll form narrower but thicker/higher strength materials.

The stresses generated by the axial forces and by the torque on the shafts are usually negligible. In very

shortshafts, the forces required to form the material, which separate the shafts, maycreate substantial

FIGURE 2.39 Chain (a) and universal joint (b) driven shafts.

Roll Forming Mill 2 -23

shear stresses, but in most cases, these stresses are secondarytothe stresses created by the bending

moments deﬂecting the shafts. Therefore, practically all shafts are designed for limited bending

(deﬂection). Bending above the permitted limit creates dimensional problems in the products. Normal

use will not permanently deform the shafts, but abuse can cause problems.

The shaft diameters, selected for the speciﬁed applications, are afunction of the thickness and

mechanical properties of the material to be formed, the rollspace (shaft length between supports), and by

the type and number of bends made at each pass.

The selections of shaft diameters havebeen almost exclusively based on past experience. Equation 2.1 is

the ﬁrst attempt made by the author to calculate proper shaft diameters:

DIA ¼ 1 : 46 0 : 173

ﬃﬃ

þ 0 : 47 þ 0 : 7

ﬃﬃ

ﬃﬃﬃﬃﬃ

ð 2 : 1 Þ

whereDIA is shaft diameter; L ,length of the shaft (roll space); t ,material (metal) thickness; Y ,yield

strength on the material (DIA, L , t , Y are in imperial units).

Figure2.41 shows agraph based on Equation 2.1. It is applicable to calculate shaft diameters for

mills that roll form mild steel, withapproximate 40,000 psi yield strength (275 MPa).

Equation 2.2 is an extended version of Equation 2.1. Additional factors such as the actual yield

strength of the formed material, different types of forming, and others are included into the equation.

These factors, to be used in borderline cases, are shown in the lower half of Figure2.41.

DIA ¼ 1 : 46 0 : 173

ﬃﬃ

þ 0 : 47 þ 0 : 7 £ a £ b £ c £ d £ e £ f £ g £ h £ n

ﬃﬃ

ﬃﬃﬃﬃﬃ

ð 2 : 2 Þ

whereDIA is shaft diameter (DIA, L , t ,and Y are in imperial units); L ,length of the shaft (roll space);

T ,material (metal) thickness; Y ,actual yield strength on the material the following factors are relative

numbers, deviating from 1depending on the severityofforming (see Figure2.41); a ,length of the bent

leg; b ,typeofbend; c ,formed groove (enter 1ifnogroove is formed); d ,stretched groove (enter 1ifno

NUT

SHAFT

ROTATION

TOP

NUT

SHAFT

ROTATION

BOTTOM

STRIP

TRAVEL

SHAFT

ROTATION

TOP

BOTTOM

NUT

STRIP

TRAVEL

SHAFT

ROTATION

SHAFT

ROTATION

RIGHT TO LEFT DIRECTION

LEFT TO RIGHT DIRECTION

FIGURE 2.40 The thread at the end of the shaft is opposite to the direction of the shaft rotation.

Roll Forming Handbook2 -24

.074

CHECK

FOR

BEARING LOAD

SHAFT DIAMETER

1.5"

2.5"

3.5"

4.5"

.010

.018

.027

.036

30"

18"

12"10"

16"

24"

72"

ROLL SPACE

48"

36" 60"

54"

.438

.500

.550

.750

.225

.275

.085

.104

.150

.164

.188

.250

.060

.125

.110

.096

.048

.200

.066

.012

.030

.024

.033

.015

.040

.054

.021

.135

.312

.350

.400

.438

.500

.550

.375

.625

.700

.750

.625

.700

.150

.125

.015

.010

.021

.012

.036

.048

.074

.027

.040

.054

.030

.018

.033

.024

.104

.085

.110

.060

.066

.096

.135

.225

.312

.375

.350

.275

.400

.188

.164

.200

.250

(a) (b) (c) (d) (e)

(f) (g) (h)

(n)

Starting angle

of bend

Stretched

groove

Formed

groove

Type

of bend

Length of

bent leg

Location of forces

on the shaft

Thickness used in the diagram=metal thickness (t) ×a×b×c×d×e×f×g×h×n

Width of flat R/t Ratio Number of bends

made in the pass

R/t=4

R/t=1 or

smaller

Factor

Factor Bends

Ratio

1.0

0.8

1.0

1.1

1.2

0.8

1.2

0.6

0.8

1.1

1.2 2.0

0.6

0.8

1.0

0.6

1.0

1.2

0.8

0.6

FIGURE 2.41 Roll forming mill shaft diameter selector (in inches).

Roll Forming Mill 2 -25