Illustrated Sourcebook of Mechanical Components Part 4 pptx

T h e torque transmitting capacity of the clutch, or the torque resisting capacity of the detent wheel, is then obtained by assigning suitable values ro the engaging force, tooth angle

5-16

slipping rpm, a n d the horscpowcr pcr 5hoc

curve for hp vs p to determine the best value Foi p

Plot the (12)

A centrifugal clutch shoe has a radius of 5.25 in and

a width of lining of 2.50 in Lining pressurc is not to

cxcccd 100 psi Angulai- length of lining is 4 = 108

cleg, and the link is at a n angle of a = 48 des T h e

shoe is pivoted at a distance h of 4 in from the center

BY Eq (73

tall 8 = p [(4)(5.25) (0.80902) - -4(1.88496+0.95l0G)T _-

4 (1.88496-0.95106)

= l S l l p Total inward sprinq force of both springs is 15 Ib BY Eq (2)

Weight of shoc-is 7 Ib with its center- of -gravity al a AT,,= -($)(2 5)(5.25)(100)(2.8.3602) C O S Q

= - 1861 ('08 B

radius of 4.6 in

As there are linings on the market with a diRerent

coefficient of friction for values of II of 0.1 0.2 0.3, BY Eq (3)

0.4 and 0.5 find the corresponding v'alues o t ' forccs Q ,

R , :ind F,-F, Find the torque T , the corrcsponding N,,= -(i12.0 sin 0

2 Floating-link design

%he calculations are bcst carried out in tabular form

(see table) Thus, for the case of p = 0.1

is obtained with shoe-linings having a coefficient of about 0.35%

Calculations for various iinings

5-18

Small Mec

for Precise

Marvin taylor

PAWL AND RATCHET SISGLE CYCLE CLUTCH (Fig 1 ) K n o w n as Dennis Clutch, parts B, C and D , aro primary components, R , heing the driving ratchet,

C, t h e driven cam platc and, I ) , tho connecting pawl c a r r y i d by t h e cam plate

Normally t h e pawl is held disengaged by the l o w e r portion of clutch arm A When activated, arm A rocks counter-clockwise until it is o u t of tho path of rim

F on cam plate C a n d permits pawl D under tho effect of spring E t o engage

with ratchet B Cam plate C then turns clockwise until, near the end o f one

cyde, pin G on t h e plate strikes t h e upper part of a r m A camming it clockwise

back to its normal position T h e lower part of A then performs two functions:

(1) cams pawl D out of engagement with the d r i + i n g ratchet B and ( 2 ) hlocks fnrther motion of rim f and the cam plate

Fig I

PAWL AND RATCHET SINGLE CYCLE DUAL CONTROL CLUTCH-(Fig 2) Principal

parts are: driving rztohet, B, directly connected t o the motor and rotating frccly

on rod A ; driven crank, C, directly connected t o t h e main shaft of the machine and

also free on A ; and spring loaded ratchet pawl, D, which is carried by crank, C,

and is normally held disengaged by latch E T o activate t h e elutch, a r m F is raiscd,

permitting latch E to t r i p and pawl D t o engage with ratchet E The left arm of

clutch latch 6 , which is i n tho path of the lug on pawl D, is normally permitted t o

m o v e out of interferrnre by t h e rotation of t h e camming edge of era& C For certain

operations block W is temporarily lowered, preventing niotion of latch C , resulting i n

dismgagement o f thc clutch after part of the cycle until subsequent raising o f block H

pcrmits motioii of latch C and resumption o f the cyele

PLANETARY TRANSWISSION CLUTCH (Fig 3) A positive clutch with external

control, two gear trains to provide hi-directional drive to a calculator for q c l i n g t h e

machine and shifting t h e carriage Gear A is t h e driver, gear I t h e driven member

is directly corxneeted to planet carrier F T h e planet consists of integral gears B and

C ; E3 meshing with sun gear d and free-wheeling rtng gear 6 , and C meshing wirh

free-whceling gear D Gears D a n d C carry projecting lugs, E and H respectively,

which can contact formings on arms J and K of the control yoke When the machine

is a t r e s t , the yoke is centrally positioned 50 that the a r m s J and K are out of t h e

path of the projecting lugs permitting both D and G t o free-wheel T o engage the

drive, t h e yoke rocks elockwise as shown, until t h e forming on a r m K engages lug H

blocking further motion of r i n g gear C A solid gear train is thereby established driv-

ing F and L in t h e same direction as t h e drive A and a t t h e same time altering t h e

speed of D as it continues counter-clockwise A reversing signal rotates the yoke coun-

ter-clockwise until arm J encounters lug E blocking f u r t h e r motion of D This actuates

the other gear train of the Same ratio

FlQ 2

3

L

Clutches 5-19

€ 'E! Shift clutch F

I

OVERLOAD RELIEF CLUTCH (Fig 6 ) This is a simply constroered, double-

plate, spring loaded, friction coupling Shaft G drives collar E which drives

slotted plates C and D and formica disk B Spring H is forced hy the adjusting

nuts, which a r e serewed on t o collar E, to maintain t h e nnit under axial pressure

against the shoulder a t t h e left end of t h e collar This enables t h e formica disks

B t o drive through friction against both faces of the gear whieh is f r e e t o t u r n on

t h e collar, eausing output pinion J t o rotate If t h e machine should jam a n d pin-

ion J prevented from turning, t h e motor can continue rnnning without overloading

while alippage takes place between formica plates B a n d t h e gear

MULTIPLE DISK FRICTION CLUTCH (Fig 4)

T w o multiple disk friction clutches a r e combined in

a single two-position unit which is shown shifted

to the left A stepped cylindrical housing C enelos-

ing both clutches is carried hy solf-lubricated h r a r - ing E o n shaft J a n d is driven by the transmission gear W meshing with the housing gear teeth K At

either end, the housing carries multiple metal disks

Q that engage keyways Y and can make frictional

contact with formica disks N which, in turn, can

contact a set of metal Jisks P which have d o t t e d openings f o r coupling with flats o n sleeves B and W In the position hhown, pressure is exerted

&rough rollers L forcing t h e housing to t h e l e f t

making t h e left clutch compact against adjusting

nuts R, thereby driving gear A via sleeve B which

is connected t o jack shaft J by pin U When t h e carriage is t o he shifted, rollers L force t h e hous- ing t o rhe right, first relieving t h e pressure between

t h e adjoining disks o n t h e left clutch then passing

through a neutral position in which both clutches

are disengaged a n d finally making t h e right clutch compact against t h r u s t bearing F, thereby driving

gear G through sleeve W which rotates freely o n

the jack shaft

SINGLE PLATE FRICTION CLUTCH (Fig 5 )

The hasic clutch elements formica disk A , stcel

plate B a n d drum 6 , a r e normally kept separated

by spring washer G To engage the drive, the l e f t

end o f a control a r m i s raised, causing ears F,

which sit in slots in plates H, t o rock clockwise

spreading t h e plates axially along sleeve F Sleeves

E a n d P a n d plate B a r e keyed to t h e d r i v e s h a f t ; all other members c a n rotate freely The axial m o -

tion loads t h e assembly t o t h e right through t h e

t h r u s t ball bearings K against plate L and adjust- ins n u t M, a n d t o the l e f t through friction surfaces

on A, B a n d C t o t h r u s t washer S, sleeve E a n d against a shoulder o n Ehaft D, thus enabling plate

A t o drive %he d r u m C

IN THE DESIGN OF straight toothed components such as

serrated clutches, Fig 1 ( A ) , and detent wheels, Fig 1 ( B ) ,

the effective pitch radius is usually set by size considera-

tions T h e torque transmitting capacity of the clutch, or

the torque resisting capacity of the detent wheel, is then

obtained by assigning suitable values ro the engaging force,

tooth angle, and coefficient of friction

T h e nomogram, Fig 2, is designed to be a convenient

means for considering the effect of variations in the values

of tooth angle and coefficient of friction For a given coeff-

cient of friction, there is a tooth angle below which t h e

clutch or detent is self-locking and will transmit torque

limited only by its structural strength Where

T = torque transmitted without clutch slip, or torque resisted

R = edective clutch, or detent wheel, radius, in

F = axial, or radial, force, lb

.f = tangential force acting at radius R, lh

N = reaction force of driven tooth, or detent :irtiiiq norm:il t o

by detent wheel, lb in

From Eqs ( 1 ) and ( 2 ) , when all other rerins hnve cow stant values, it is obvious that the required axial force, cr the radial fo:ce, diminishes as the value of K increases Dependent upon the values of 0 and p , the value of K can vary from zero to infinity

T h e circular nomogram shown in Fig 2 relates the values

of the parameters I( 0, rind that satisfy the basic equation

Ir' 11,

l(c~rs w' '%I - air1 \ -

Clutches 5-2 1

R = (1 + p tan @)/(tan e - p)

lodting clutch, or for which K is infinity, taking the coeffi-

cient of friction as 0.4 minimum

the nomogram gives a maximum tooth angle slightly less

than 22 deg for the self-locking condition

EXAMPLE 11 Find the minimum value of K to be expected

for a clutch having a tooth angle of 30 deg and a coefficient

of friction of 0.2 minimum

the nomogram gives a value for K of 3 approximately

EXAMPLE 111 Find the value of K for a flat-face ( 8 equals

90 deg) friction clutch, the face material of which has a coefficient of friction of 0.2 Compare its torque transmit- ting capacity with that of the toothed clutch of Example 11

SOLUTION 111 Line 111 through these values for 0 and p on

the nomogram gives a value for K of 0.2

Torque transmitting capacity of flat-face clutch :

Torque transmitting capacity of toothed-clutch :

T = 3 R P

Thus for equal effective radii and engaging forces, the torque capacity of the toothed-clutch is 3/02, or 15, times greater than that of the flat face clutch

T = 0 2 R F

40

Fig 2

5-22

Spring Bands Grip Tightly

actuates clutch

Spiral-band assembly releases clutch

Contact area with pulley (typical each clutch band)

Spiral bands direct force inward as outer ring drives counterclockwise Roller and sprag types direct force outward

A new type of overrunning clutch

that takes up only half the usual

space employs a series of spiral-

wound bands instead of the conven-

tional rollers or sprags to transmit

high torques The new dcsign (draw-

ings, above) also simplifies the as-

sembly, cutting costs as much as

40% by eliminating more than half

the parts in conventional clutches

The key to the savings in cost and

bulk is the new design’s freedom

from the need for a hardened outer

race Roller and sprag types must

have hardened races because they

transmit power by a wcdging action

between the inner and outer races

Role of spring bands Overrun-

ning clutches, including the spiral-

band type, slip and overrun when

reversed-in drawing above, when

outer member is rotated clockwise

and inner ring is the driven member

The new clutch, developed by Na-

tional Standard Co., Niles, Mich.,

contains a set of high-carbon spring-

steel bands (six in the design illus-

trated) that grip the inner mcmbcr

when the clutch is driving The

outer member merely serves to rc-

tain the sorine anchors and to Dlav

a part in actuating the clutch Since

it isn’t subject to wedging action,

it can be made of almost any mate- rial, and this accounts for much of the cost saving For example, in the automotive torque converter in the drawing at right, the bands fit into the aluminum die-cast reactor

Reduced wear The bands are spring-loaded over the inner mem- ber of the clutch, but they are held and rotated by the outer member

Thc centrifugal force on the bands thus releases much of the force o n the inner member and considerably dccreases the overrunning torque

Wear is, therefore, greatly reduced

The inncr portion of the bands fits into a V-groove in the inner member Whcn the outer member is reversed, the bands wrap, creating

a wedging action in this V-groove

This action is similar to that of a spring clutch with a helical-coil spring, but the spiral-band type has very little unwind before it over- runs, compared with the coil type

Thus it responds faster

Edges of the clutch bands carry the entire load, and there is also

a conmound action of one band uDon

National Standard plans to sell the bands as separate components, without the inner and outer clutch members (which the user customar- ily builds as part of his product)

The bands are rated for torque ca- pacities from 85 to 400 ft.-lb Ap- plications includc auto transmissions and starters and industrial machin- ery 0

Clutches 5-23

Accurate Solution for

Nils M Sverdrup

the mean radius R of the clutch disks

is often used The torque equation

then assumes the following form:

R = mcan radius of disks, in

n = no of friction surfaces

This formula, however, is not math-

ematically correct and should be used

cautiously The formula’s accuracy

varies with the ratio D,/D, When

DJD, approaches unity, the error is

negligible; but as the value of this

ratio decreases, the induced error will

increase to a maximum of 33 percent

By introducing a correction factor,

9, Eq (1) can be written

The value of the correction factor can

be derived by the calculus derivation

of Eq ( 2 ) ’

Sketch above represents a disk

clutch with n friction surfaces, pres-

sure between plates being p psi In-

side and outside diameters of effective

friction areas are D, and DO in., re-

spectively Since the magnitude of

pressure on an element of area, dA,

at distance x from center is pdA, the

friction force is pdAp and the moment

of this force around the center is Integrating within limits D,/2 and

DO/2 and multiplying by 12 friction surfaces, the expression for total torque

or T = 0.262 p p n (Dos - D?) ( 5 )

If the total pressure acting on clutch

disks be P lb, the expression for pres-

sure per unit area is

(8) Similarly, by substituting value of

Dl from Eq ( 7 ) in Eq ( 2 ) , and hav- ing

I of torque can be easily determined

I L LU S T RAT E D S O U R C E B 0 0 K of ME C H A N I CAL C 0 M P 0 N E N T S

S E C T I O N 6

EALS

Rubber Seals for Oil Retention

Non-Rubbing Seals for Oil Retention

How to Seal Air Ducts that Separate

More Seals for Ducting that Separate

Window Awning Unit Sealing

Window Casement Unit Seals

Multiple Seals & Bonding for Dam Retrofitting

6-2 6-4 6-6 6-8 6-10 6-1 1 6-12

Seals & Packings 6-3

abrasive surroundings Types that are held against the rotating member by spring pressure can

be used where there is a pressure head of fluids within the assembly or on the exterior For

high pressure stuffing box and O-ring type seals are used O-rings are also used for zero leakage

and sealing ring material may be varied so that a variety of

applieations can be handled Small units can be had where the 0 D is the same as the 0 D of the sleeve bearing, (B), thus eliminating the counterboring operation on the housing

The seal may be reversed and used t o keep foreign matter out of the assembly A drain hole may be provided to earry away surplus lubricant Retention is by press fit on the outside diameter

FIG 5-Rubbing seals of the stuffing box type ( A ) , are used where high pressure are encountered It can be used for all types of motion and the packing material can be varied de- pending upon the fluid to be sealed and the application For rotating motion some leakage is necessary so it cannot be used when permissible leakage is zero O-rings can also be used for rotary motion if the speed is slow Special designs use O-ring seals (B), when zero leakage is demanded for either stationary or reciprocating motion

This ring is made of natural rubber or synthetic rubber de- pending on the type of solution resistance required Synthetic rubber, such as buna or neoprene, is resistant to aromatic hydrocarbons, while natural rubber resists the action of alco- hol and glycerine

0-rings ean be located either in the shaft or in the housing and any movement or pressure forces the ring to one side, thereby forming a tight seal

$!-Seals 8t Packings 6-5

friction is negligible They are, however, often more expensive than rubbing seals since the shaft, bearing, or housing must be grooved to distribute the lubricant Distribution over the bearing area is, however, better Lubricants may be forced-fed or gravity-fed

Fig 5-Labyrinth seals offer good protection espe- cially at high speeds where the narrow zigzag passage

is used in conjunction with centrifugal force Oil and foreign matter are separated by slinger which limits

oil flow past rotating member (A) Inner member (B) throws oil back to sump Member ( C ) throws

out foreign matter

Fig 6-Non-rubbing seal for oil lubrication Shaft rotation throws lubricant into the inboard groove ( B )

in the housing and is returned to the oil sump First slinger ( D ) throws foreign material out of the assem- bly Secnnd slinger (0) feeds foreign material out through groove (A) and hole at (C) Lubricant feeds between shaft and bearing to housing grooves

Fig ?'-Reservoir type feed for grease lubrication Grease is distributed in annular groove and feeds through holes in bearing to lubricate the shaft Foreign matter can be excluded if clean grease is used Grease will be lost through open bearing ends and assembly must be repacked periodically

Fig 8-Reservoir type feed for oil lubrication Two bearings are used forming an oil reservoir between them If porous wall type bearings are used oil will saturate and feed through bearings to the shaft Outward flow of oil prevents entry of foreign mate- rial Reservoir must be periodically refilled with new oil Bearings are a press fit i n the housing

Seals & Packings 6-7

[ - I FLAT RUBBER AND GUIDE BRACKETS FOR CENTERING

7 ? CONFINED RUBBER STRIP

Seals & Packings 6-9

Different Mechanical Methods for Attaching Tubing

Multiple Piping Arrangements in a Wastewater Treatment Facility

Design Hints for Pipe Connections

Pumphouse Piping System for Fire Protection Facility

3 Bolted connection is used for racks and frames Requires

a threaded insert and notching the end of joining tube

I

Section A-A

Tubing 8t Pipe Connections 7-3

Tubes of different sizes can be more rigidly connected by

4 inserting the smaller tube inside the larger one

"7

Reinforced connection can be made by attaching pads to outside or inside surface Flattened tubing simplifies the connection

7 for brazing or projection welding Pads may be threaded either for pipe or screw fitting

Flattened tubing makes joint when tubes intersect in same

5 plane Connection is welded, riveted or bolted together 6 Welded connection can be made between tubes in contact

m Tubes may cross at any angle

Tubing & Pipe Connections 7-5

END FITTINGS

Fig 1&-End plug may be threaded or

press-fitted on the OD or ID of tubing

Fig 12-Detachable cap uses bayonet- type connection for convenient removal

Fig 11-Ornamental cap may be used to give tubing finished appearance

Fig 14-Spring-steel nut is used for attaching objects to the ends of tubing Nut requires two slots in the tubing and i s held in position by screw

Fig 13-Threaded insert, welded inside,

facilitates the assembly of plates

Fig 6-Rolled-end of tubing simplifies attachment of end fitting

Fig 15-Arched-nut attachment requires no machining Nut is first rammed into tube;

tightening of screw forces barbs into metal for positive anchorage

Fig 18-Formed plate facilitates attach- ment of tubing by welding or brazing

Fig 19-Flange fitting for piping is made

by welding flange to tubing

Fig 17-Roil and press operation can be

used to firmly hold tubing in plate

Click for high-quality image

Click for high-quality image

Click for high-quality image

I L L U S T R A T E D S O U R C E B O O K of M E C H A N I C A L C O M P O N E N T S

S E C T I O N 8

Seven Creative Ideas for Flanged Rubber Bushings

Go Creative with Flanged Bushings

How to Calculate Stress in Press-Fit Bushings

When Expandable Bushings are the Answer

Sleeve Bearing Alignment

Getting Better Performance from Instrument Bearings

Which Bearing and Why?

Formula Found for Predicting the Reliable life of Bearings

Rotary-linear Bearing

a-2 a-4 a-7 a-9 8-13

8-14

8-17 8-23 8-24

Bushings 8t Bearings 8-3

I ”

‘ : I

: \ Ffonged rubber bushing

Bushings & Bearings 8-5

Slot

n

Post or location-pin holder

Journolbushing/ %Seat plate

8-6

ddiusf spring fension -use long phnger

f o set bushing (press fit

Checkvalve

nch

Holding fixture, complete with feet

Cornerinq pia

( Press fit in base only 1