Roll Forming Handbook / Edited by George T. Halmos

Подождите немного. Документ загружается.

groove is stretched); e ,starting angle of bend; f ,location of forces on the shaft; g ,width of ﬂat section;

h ,radius/thickness ratio; n ,number of bends formed in the pass.

Table 2.1 shows examples of shaft diameters calculated with Equation 2.1 or Equation 2.2.

The shaft diameter selection chart is based on limited shaft deﬂection. In the case of shortshafts, where

deﬂection maybenegligible, the load carrying capacity of the bearings or shear strength of the shafts

should be checked.

The diagram takesonly the shaft deﬂection into consideration.Shaft deﬂection is only one criterion in

the maximum capacityofamill. Successful roll forming in amill also depends on the construction of the

mill, type of bearings, housing,maximum permitted torque at each pass, drive train, and manyother

factors. Therefore, across-section which can be successfully rollformed with one makeofmill maynot

be formed on another mill with the same shaft diameter and roll space.

2.3.4 Power Train

Rollforming lines are usually powered by electrical motors. In averyfew cases, mills are driven by

hydraulic motors. Most hydraulic motors are powered by hydraulic pumps driven by electrical motors.

Occasionally,the pump is driven by diesel engine, as with the case of truck-mounted lines working at

remote job sites (Figure2.29).

Most of the older type of roll forming mills wereequipped with single speed AC motor.The power

train usually consisted of a“V” belt drivefrom the motor to the mill and individual gear reducers

for each stand. In low-cost models, chains or chain–gear combinations havebeen used for speed

reduction and powertransfer.Occasionally,asingle speed gear-reducerbox was installed between the

electrical motor and the mill.

Eventually,different methods havebeen introduced to change the rpm of the drive shaft of the mill in

ordertomeet with the demand of optimum roll forming speed such as high-speed forming of

long sections and low-speed forming of shortsections. In addition to the one- or two-speed AC motors,

two-, three-, or four-speed gear boxeshavebeen installed in the lines. All of these methods provided a

speciﬁed number of ﬁxed shaft rpm. To further optimize the roll forming speed, variable speed drives

havebeen used in the drivetrains. These speed reducers are either mechanical or occasionally hydraulic

types with manual or electrical means of adjustment.

From the gear reducer or directly from the motor,the power has been transferredtothe shafts at one

location (at the front,atthe end, or around the middle of the mill) or occasionally at twoplaces (at the

two ends, or about one fourth from each end). The transfer in cheaper units is conducted throughchain,

but most of the time, Vortiming belts are used.

2.3.4.1 Chain Drives

Driving each individual top and bottom shaft with acontinuous chain usually provides very little shaft

adjustability, and the speed can be restricted (Figure2.39a). An alternativemethod of chain drive allows

greater vertical adjustabilityofthe top shafts. Chains are considered alow-cost solution and usually they

are not used in better qualitymills.

2.3.4.2 Gear Drives

One possibilityistodrivethe shafts with aspur-gear train (Figure2.38b). The problemwith this gear

arrangement is again the adjustabilityofthe top shafts. Moving the top shafts up asmall amount causes

only the tip of the gears touching each other.This “out-of-pitch diameter” engagement does not provide

asmooth driveand can easily chip or break the teeth of the gears. Moving the top shaft further up will

disengage the top shafts. If the rollsare recut and the shafts havetobemoved closer,then it is possible

that the gear will restrict the downward movement. In some cases, forcing the top shaft gears into the

bottom shaft gears will create acontinuous “chatter,” which can leavemarks on the strip.

Roll Forming Handbook2 -26

Adifferent gear arrangement —installing one idle gear between each top shaft gear as shown in

Figure2.38c —allows to adjust the top shafts 1to2in. (25 to 50 mm) or morewithout disengaging

the gears.

2.3.4.3 Mixed Drives

To reduce the cost of the mill, some companies occasionally combine chain drives with gear drives, or do

not drive certain top shafts.

2.3.4.4 Nondriven TopShafts

In the early mills, following the example of the steel mills, all top and bottom shafts havebeen driven.

Later,custom roll formers and other users found that they could successfully roll form without driving

the top shafts. Custom roll formers often havetouse “nonmatching” roll diameters. The big

circumferential speed difference can create problems if both the top and bottom shafts are driven.

Eventually,some roll forming mills havebeen built without top drive. However,driving the bottom

shafts generates only half the friction between the rolls and the strip.Asaresult, the ﬁrst few passes often:

1. Cannot pull the strip into the mill

2. Generate large ﬂuctuation in the product speed during forming

3. Cannot push the product through the straighteners, curving units, or other equipment

Therefore, in addition to driving the ﬁrst one or twoand the last one or two top shafts, mills are often

supplied with nondriven top shafts, which can be readily equipped with spur-gears when required. It is

usually the roll designer’sfunction, occasionally corrected by the setup technician, to indicate the

intermediate passes that will requiretop drives.

2.3.4.5 Shaft Driven with Individual Motors

Mills havebeen built with aDCmotor attached to each shaft. This method provides the maximum

ﬂexibilitytoany roll formers. However,owing to the relatively highcost, this method is seldom applied.

Single-speed AC drives are inexpensive, but they restrictthe line to one speed and it makes the jog-in

of the leading end difﬁcult. The constant stop-and-go operation during jog-in (feeding the front end of

the coil into each pass) has also some wear and tear effect on the drivetrain.

The introduction of the soft-starter makes the jog-in more operator-friendly.Itispossible to set the

rate of acceleration, which means that during the jog-in operation, the mill starts up slowly and usually

does not exceed acomfortable speed. The variable speed or vector drives developed at alater stage make

the application of most of the soft-starters unnecessary.

DC motors havebeen used for along time to provide variable speed. In the 1950s and 1960s, eddy

current motors were installed in some mills. By the 1990s, all manufacturers offered either DC or variable

speed AC drives. In most cases, the priceand occasionally special requirements such as constant

torque, constant rpm, or high-torque at low-speed requirements are the determining factors in selecting

the motors.

2.3.5 Side-Roll and Cluster-RollStands

In the early applications, roll forming was based on forming by the main passes only.Ifthe result was

unsatisfactory, then side-rollstands havebeen installed retroactively to “cure”the problems. Owing to

time constraints and, frequently,ﬁnancial restrictions, manyofthese side-roll passes consisted of only a

pair of cam rolls fastened to welded angle frames. Frequently,these contraptions did the required job,but

it was difﬁcult to set up and adjust them. Therefore,side-roll stands havebeen looked down at by many

people in the industry.

Side-roll stands, however, are an integral partofthe equipment and tooling.Side rolls haveseveral

advantages. The shafts can be oriented at anyangle instead of just being horizontal, as in the main passes.

This ﬂexibilityallows locating the side rollsatoptimum angles. With the exceptionofafew special cases

Roll Forming Mill 2 -27

(Figure2.42), side rolls are not driven. Therefore, they are less prone to mark or scuffthe surface of the

products.

The shafts of the side-rollstands can either be cantilevered or supported at both ends. There can be

one, two,ormoreshafts with rollsforming or holding one bend line at one point (Figure 5.27, Figure

5.100, Figure5.102a–f). These shafts are fre-

quently not parallel to each other.The designer’s

decision about the type of shafts and their angles

is usually based on local conditions.

Side rollsare excellent for forming the edges of

the strips and are often preferred to the main

forming rolls, especially when the formed “legs”

or strip edges are close to vertical (close to 908 to

the axis of the main shafts). Properly designed

and easily adjustable side-roll stands are the

practical ways to compensate for springback by

overbending angles.

Because side-rollstands are just as important

as the main stands, they should be designed to

similar rigidity, precision, and adjustability.

Side-roll stands are usually fastened to the top

surface of the mill base or raft. They can also

be attached to the operator-side or the drive-side

stands (Figure 2.43). Side rolls can be made

adjustablevertically,horizontally,and in-

between, or can be rotated around abend line.

The type and magnitude of adjustment depends

on the functions of the rolls. To provide extremely

accurate small adjustments, it is recommended

that one adjusting and one “stop”screw for each

direction of adjustment are used (Figure2.44).

To promote ease of installation, the side-roll

stand should be located with keys, after its

alignment is tested. The same type and size of

adjusting and locating screws should be used,

thus allowing the use of aone-size Allen key

wrench or other tool. The stands should have

easily reachable lubricating points.

In certain type of mills, the small horizontal

distancebetween the main rollscan makethe

installation and the adjustment of the side-roll

stands difﬁcult, even impossible.

If the roll designer ﬁnds it advantageous, then

the side rolls can work at the main rolls. In these

cases, the supporting structure must reachin

between the top and bottom shafts (Figure2.45

and Figure5.105). These types of stands are

called “cluster-roll stands.” Onceproperly

installed, cluster rolls seldom require adjustabil-

ityinthe vertical direction, but ﬁne adjustment is

needed in the horizontal direction, usually 908 to

the travelofthe strip (Figure 2.46).

FIGURE 2.42 Driven side-rollstand.

FIGURE 2.43 Side-roll stands attached to main stand.

FIGURE 2.44 “Stop”screws help the ﬁne adjustment of

side-rollstands.

Roll Forming Handbook2 -28

2.3.6 Guides Between Passes

The internal stresses generated in the section by

the forming can frequently result in bow(down-

ward or upwards), camber (sideways), twist, ﬂare,

or springback. These distortions can often be

observedasthe leading end of the strip exits from

the passes. Strips withsubstantial cutouts, such as

holes and notches, can displaysimilar deviation

from straightness and ﬂatness. As an effect of these

deviations, the leading edge of the strip does not

always enter straight into the next roll,but hits the

roll at some other place(Figure2.47). Frequently,

the operator has to manually push the leading

edge into the gap of the next pair of rolls each time

anew coil is fed into the mill. It is accepted by the

industrythat the leading ends are “jogged in”by

the operator at aslow speed, usually in astop-

and-go manner.This method is time consuming

and reduces the efﬁciency of the line. It is also

unsafe because most operators attempt to guide

the leading edge by hand just at the entryside of

the rotating rolls.

Good rolldesign with asufﬁcient number of

passes, large rollentryangles with large radii, and

if required, guides between passes allows “thread-

ing-in”(“jog”) the strip at full speed. Full-speed

forming is always expected when parts are formed

from precut pieces.

To achieve full-speed and safe threading-in

of the leading edge of the coil, large ﬁsh-mouth

openings are required at each restrictedarea such

as straighteners and cutoffdies (Figure 2.48).

Proper guides between passes not only help

to jog in the strip,but also prevent buckling it

between passes. Buckling can happen occasion-

ally when theﬁrstpassesare pushingthe

material, whilesomewhere around thelast

passes, the speed is reduced or the passage is

restrictedinthe straightener or at other

obstacles. To prevent buckling of less rigid

ﬁnished sections in front of the straightener

and the cutoffpress, the partisoften guided at

those locations.

The guides can be made from avarietyof

materials such as cold-rolled steel, heat-treated

steel, bronze, plastic, or combination of the above

materials, and cam or conveyor rolls. Occasion-

ally,toprevent buckling,the operators will use a

temporarysolution of 2 £ 4s, which mayremain

thereasapermanent ﬁxture.

FIGURE 2.46 Fine adjustment of cluster rolls is

required.

FIGURE 2.45 Cluster rolls.

FIGURE 2.47 Internal stresses forces the leading edge of

astrip away from straight line.

FIGURE 2.48 Large “ﬁsh-mouth”opening helps the

entering of the leading edge of the strip.

Roll Forming Mill 2 -29

It has to be noted that guides shall not be used

to form the material. They are in contact with the

strip or section only momentarily during the

feed-in, but not during forming (Figure2.49).

In the case of precut strips, and especially when

the pieces are veryshort, full contact guides are

required at the full length of the parts. Because of

the variations in cross-sections, there are endless

variations in the design of the guides.

2.3.7 Straightener

The internal stresses that are created by the roll

forming process frequently bend or twist the

products after exiting from the last pair of rolls. These deviations can be eliminated by astraightener unit

installed after the last pass.

Wide building panels, with manystraight bent lines, usually remain straight after roll forming,but

most narrow and especially asymmetrically formed products requireastraightener.

Based on the assumption that all problems, including waviness, will be “ironedout” by long

straighteners, some of the early straighteners consisted of long (12 in. or 300 mm) tightly ﬁtted bronze

product

FIGURE 2.49 Guides help entering the leading edge into

the roll are not in touch with the section during the rest of

the forming.

FIGURE 2.50 Straightener.(Courtesy of Metform International Ltd.)

Roll Forming Handbook2 -30

blocks. This assumption is incorrect; the function

of the straightener is to push the bend lines of the

sections at the opposite direction of the deviation

from straightness. Forces applied at the bent lines

in ashortdistance are sufﬁcient in almost all

cases.

Astraightener consists of asupporting struc-

ture andstraightening tool(s) (Figure2.50).

The tool is either a“block”with apassage for

the section or consist of rolls. In both cases, it is

important that the tool reaches into the section

and applies pressureonthe bend lines. To correct

the deviation from straightness of abend line, the

pressure is always applied to one direction at a

time. Therefore, usually,asmall gap can be left

between the outside and inside tool surfaces

(Figure2.51).

The straightener is usually located between the

last pass and the cutoffdie, as close to the last

pass as possible. Wherever feasible, the straigh-

tener stand should movethe blocks in aswinging

motion instead of moving parallel up and down,

or sideways (Figure2.52).

If blocks are used for straightening, then they

should havelong,big ﬁsh-mouth opening to

guide the leading end of the strip into the block

at fullspeed.Ifrequired, additional guides

canbeapplied aheadofthe straightener

(Figure2.53).

It must be remembered that straighteners are

not forming tools. During setup of the tooling,

the forming rollsshould be adjusted to rollthe

sections as straight as possiblewithout a

straightener.Oncethis is achieved, the straigh-

tener can be installed to correct the remaining

deviation from straightness.

If the incomingstrip has extreme camber or

other deviations from straightness and ﬂatness,

then theinternal stresses createdduringroll

formingcan be so high that even thebest

straighteningdevicecannotcorrectthese

imperfections.

2.3.8 Lubrication System

Lubricants areusedtoreducefrictionbetween theformed partsand therolls,toeliminate thepick-up of

zinc, aluminum,orother metalsbythe rolls, and to avoidscratchingormarring theproduct surface.

Lubricants arealsousedtowash away loosesurface particlessuchasscale on hot-rolled steel.Whenthick

materials areformed, lubricants arealsousedascoolanttodissipate theheatcreatedbythe forming. For

details, seeChapter 7.

(a) straightening up (b) straightening down (c) twist

FIGURE 2.51 Straightener tool forcing the bend lines in

one direction. The tool at the opposite end of the bend line

does not havetobeincontact with the material.

cut off die

product exits curved

recommended

product forced in

opposite direction

not recommended

FIGURE 2.52 Moving the straightener blocks parallel up

and down or sidewaysisincorrect. Aswinging motion is

better.

Roll Forming Mill 2 -31

2.3.9 Shaft Shoulder Alignment

During rolldesign and roll manufacturing, it is

assumed that the baseline of all rolls and spacers

are exactly the same. During checking the ﬁnished

rolls, the rolls and spacers are placed on agranite

plate representingthis baseline. The gap between

the rollsiscarefully checked in this position. If one

imagines that this granite plate with the rollsis

rotated to 908 so that the granite plate becomes

vertical and the shafts horizontal, then in this

position, the granite plate represents the location

of the shaft shoulders, against which the rollsare

rested. If in the mill, the shaft shoulders are not

aligned, then the rolls cannot be properly aligned.

Unfortunately,this is the case in alarge pro-

portion of mills currently in operation.

During forming,the shaft bearings wear and the shafts become looser and looser.When the operator

side of ashaft can be moved easily up and down,then the shaft and its shoulder usually can also move in

and out. Loose shoulders cannot be used for accurate rollpositioning.Tocorrect this situation, the tapered

bearings can be tightened by pulling the shafts towards the drive-side direction. This also means that the

shoulder moves towards the driveside. If new bearings are installed, then the shoulders are frequently

moved outwards, towards the operator side. Therefore, amill that was assembled with accurately aligned

shoulders can be out of alignment within afew years. Wear in the bearing blocks and stand interfacecan

also contribute to shaft shoulder misalignment.

Different methods are used to align shoulders. The most frequently used method by the author to align

shoulder is described in Chapter 10 (Section 10.3.9).

2.3.10 Installation of Other Units in the Mill

The roll forming base is frequently the most convenient placetoinstall other units or equipment for the

secondaryoperations. These units can be positioned ahead, in-between, or after the roll forming stands. If

the unit is large, the horizontal center between the stands can be enlarged, or the mill bed can be extended

before the ﬁrst or after the last pass.

It is assumed that all additional operations are continuous (do not require to stop the section).

Such operation can be rotary punching,rotary embossing,welding,curving (sweeping), and others.

Hydraulic presses,which do not generate shocks, can also be mounted on the mill bed. However,

mounting mechanical or pneumatic presses on the mill bed is not recommended.

If the secondaryoperation requires coolant or liquid other than the one used for roll forming,then

aseparate drainage and lubrication system has to be installed. Proper alignment of all additional

equipment and tooling is as crucial as the alignment of the forming rolls.

References

[4] Theis, E. 1995. Handbook of Metalforming Processes.MarcelDekker, NewYork.

[157] Halmos, G.T.1984. Guidelines for purchasing roll forming lines, SME “TechnologyofRoll

Forming”,September 25–27, MF84-954 Toronto,Canada.

[158] Wilson, R.A., Quick change forming cuts inventories, Iron Age ,February3,56–57, 1975.

[160] Wright, J.R., Quick change in roll forming, Prec. Met.,June, 43–45, 1988.

[161] Bradbury, D. 1983. Eliminating roll tooling changeover, FABTECH ’83 Conference,September

26–29, Chicago,IL, MF83-544.

FIGURE 2.53 If required, additional guides can be

applied at the entryside of the straightener and cutoffdie

to help entering the leading edge of the strip.

Roll Forming Handbook2 -32

[162] Jurgenliemk, M., Exploring the double duplex coldroll forming mill, Fabricator,October,18–20,

1996.

[245] Wright, J.R., Fundamentals of roll forming, Prec. Met. ,February, 23–25, 1987.

[248] Jackson, R., Roll forming heavy gauge and highstrength steels. FMA/SME Fabtech East

Proceedings ,April 1992, and Fabricator,October 1992.

[251] Steel Products News Bureau, Roll forming making gains in areas of potential growth, Can. Mach.

Metalwork.,November,58–70, 1977.

[259] Cold forming—practiceinthe United States, Iron Steel Eng.,134–149, November 1959

[262] Weimar,G., ZumGegenwa

rtigen Stand des Walzenproﬁlieren, Ba

nder,Bleche, Rohre,8,5–7,

308–469, 1997.

[269] Winship,J.T., Rollforming: fast and ﬂexible, MetalForming,September,3–15, 1988.

[277] Williamson, H.A., Innovative methods of cold roll forming producecomplex parts more

efﬁciently, Fabricator,January/February, 1984.

[280] Green, R.G., The changing shape of roll forming, Form.Fabricating,January/February,34–41,

1996.

[283] Vandenbroucke, J.,Cardinal, P. ,and Powell, A. 1995. Howtosolvetoday’sproblems with

advanced proventechnology. SME Conference,August 29–30, 1995, Detroit, MI.

[287] Pennington, N., Automated controls operate advanced rollforming lines, Mod. Met.,March,

32–37, 1983.

[312] Arbuckle, H.J., Newroll forming line fulﬁlls 15 year dream of quality, MetalForming,July,29–32,

1995.

[329] Kaiser Aluminum &Chemical Corp., On-site roll forming stops leaks, Prec. Met.,March, 44,

1978.

[365] AerotechInc., Servos do their partmaking rollform mill moreﬂexible, Mod. Appl. News,April,

94, 1999.