PDF Technical Aspects

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TECHNICAL AS PECTS O F S HOT

PEENING MACHINERY AND MEDIA

H

1

Plaster

When He rb er t exper imente d i n 1926 by pourin g 3

mm

d i a . s t e e l b a l l s down a

s p e a ki n g tu b e on t o a s t e e l sp ec im en c o n ta i n ed i n a m e t al b i s c u i t t i n , h e c ou ld

no t have fo res een how f a r r each i ng h i s work wou ld be . Th i s ide a o f mechan ica l

hammering was b as i c a l l y co r r e c t .

From th es e ea r l y exper imen t s o f peen ing ha s grown a who le va s t a r e a o f an

i n d u s t r y t h a t h a s w a rr an t ed o v er t h e y e a r s t h e a t t e n t i o n o f s c i e n t i s t s and a c a -

d em ic s on t h e on e h an d and s p e c i a l i s t e n g i n e e r s o n t h e o t h e r .

The f i r s t e s s e n t i a l f o r s h ot -p e en i ng t o e x a c ti n g s t a n d a rd s a r e a c c ep t a b le

media of which today th e r e i s a wide cho i ce .

C h i l l e d I r o n S ho t C h i l l e d i r o n s h o t i s a c a s t m a t e r i a l . t

i s

manufactured by

m e l t i n g s u i t a b l y g ra de d i r o n i n a c up o l a, and a t a c r i t i c a l t e m p e ra t u re , p ou ri ng

o r p r o j e c t i n g

i t

i n t o a quench t ank . By the se means the met a l i s b roken up i n

f l i g h t a nd sh oc ke d by t h e w a t er a s s p h e r i c a l s h a pe s .

The l a r g es t pe r cen t age a r e round ; many a r e pea r shaped , e lon ga te d and worm-

l i k e .

As would be a n t i c i p a t e d many p a r t i c l e s c o n t a i n i n c i p i e n t s t r e s s c r a c k s .

S c r e e n i ng an d g r a d i n g e l i m i n a t e a g r e a t d e a l o f t h e un wan ted m i ss - sh a p es a nd t a i l -

i n g s . D e s p it e any s h o rt c o mi n g s, c h i l l e d i r o n s h o t h a s two v a l u a b l e a s s e t s , i t i s

cheap and r emarkab ly ha rd ; us ua l ly i n t he o r der o f 700-1000 V P N

C h i l l e d i r o n s h o t f a i l e d a s a p e en in g medium b e c au s e of i t s v i r t u e , t h e v e r y

h a r d n e s s , r e s u l t e d i n r a p i d f r a c t u r e and b ro ke n s h o t c an no t be t o l e r a t e d i n a s h o t

p e e n i n g o p e r a t i o n .

S t e e l Sh ot Made by a s i m i l a r t ec h n iq u e a s c h i l l e d i r o n s h o t , e x c e p t t h a t i t i s

m e lt e d e l e c t r i c a l l y , s t e e l s h o t was i nt ro d uc e d c om m er ci al ly i n t h e l a t e 1 9 5 0 ' s .

The raw m at er ia l i s s t e e l s c r a p , b u t t o p ro du ce a h ig h s t a n d a rd pr od u ct t h i s i s

v e ry c a r e f u l l y s e l e c t e d f o r g e n e ra l u s e b u t p e en in g q u a l i t y i s u s u a l l y d o ub le a nd

c l a s s i f i e d t o e n s ur e a b e t t e r s i z i n g s t a n da r d and t h e re mo va l of s u r f a c e s c a l e .

A l l s t e e l s h o t i s pro du ce d t o a r a ng e of s i z e s a nd s u b j e c t t o a cc e pt ed g ra d in g

s t a n d a r d s .

The h a r d n e s s f i g u r e s o f s t a n d a r d s t e e l s h o t i n E u ro pe ,a nd t h e U n it ed S t a t e s

a r e between 350-500 V P N b u t s h o t f o r p e en in g pu rp os es h a s be en s a t i s f a c t o r i l y

p roduced a s h igh a s 665 V P N

Cut W ire Sh o t C ut w i r e i s , a s i t s name i m p l i e s , w i r e c u t i n t o t h e f or m of p e l l e t s

Each p e l l e t i s c u t w it h t h e l e n g t h e q u a l t o t h e d i a m e te r . The s i n g l e m os t im p o rt -

a n t p o i n t i s t h a t t h e w i re f ro m which t h e p e l l e t s a r e c u t s ho ul d b e of t h e r ec o g-

n i s e d s t a n d a r d .

With s p e c i f i c a l l y drawn s t e e l w i r e, b e ca u se o f i t s manufac tu r ing methods th e

Cha irman Br i t i s h Impac t Treatmen t As soc ia t io n .



p ro du ct i s f r e e of l a t e n t i m p e rf e c ti o n s su ch a s i n c i p i e n t c r a c k s , b low h o l e s e t c .

I n a d d i t i o n , e a c h p e l l e t may b e s a i d t o b e i d e n t i c a l a nd u n if o rm . Drawn v i r g i n

w i re i s a c o s t l y m a t e r i a l a nd most w i re used f o r c u t t i n g p e l l e t s i s u s u a l l y t h a t

which may h a ve b ee n r e j e c t e d f o r m in or s u p e r f i c i a l d e f e c t s o n t h e s u r f a c e o r

s l i g h t i n c o n s is t e n cy i n t h e d i a m et e r . The w i r e i s o f h i g h q u a l i t y an d w h i l s t t h e

q u a l i t y may f a i l on t h e s e p o i n t s a s w i r e f o r t h e o r i g i n a l p u rp o se s ,

i t

a d e q u a t e l y

m ee ts t h e s t a nda r d f o r s ho t - pe e n ing .

O bviously i n p e l l e t f or m, c u t w i r e i s uns u i t a b l e a s a pe en ing medium and

r e q u i r e s t o b e c o n d i t i o n e d . T h i s e n t a i l s p r o c e s s i n g t h e medium i n a s u i t a b l e s h o t

b l a s t m ac hine when g r a du a l l y t h e e dge s a r e r ounde d o f f t o f or m a s p he r i c a l s ha pe .

Gla ss Beads From t h e po in t of view of a man-made mass produced o b j e ct t h e g l a s s

bead i s n e a r e r t o p e r f e c t i o n t h a n an y o t h e r a b r a s i v e . U n li k e m e t al s h o t which

o f t e n i n c l u d e s p e a r s h ap ed an d o t h e r m i ss ha pe ne d p a r t i c l e s , g l a s s s h o t k ee p s c l o s e

-1y t o a s p he r i c a l f or m. Even t h e f i n e s t s i z e m a in t a in s a de g r e e o f un i f o r m i ty o f

shape .

The s p e c i f i c g r a v i t y o f g l a s s i s o ne t h i r d of t h a t o f c a s t i r o n . I n e f f e c t

t h i s im p l i e s t h a t t he medium may be p i c ked up qu i c k ly i n to a n a i r s t r e a m a nd

r a p i d l y a c c e l e r a t e . The al m o s t p e r f e c t s p h e r i c a l sh ap e a s s i s t s i n r a p i d movement

thou gh t h e f e e d pi p e and t h e p a r t i c l e s t h e o r e t i c a l l y ke ep c l o s e r t o t h e a i r s pee d

t ha n h e a v i e r m e t a l l i c p a r t i c l e s .

T h i s i s o ne o f t h e p ro bl em s wi t h a i r o p e r a t e d

b l a s t p l a n t s i n t h a t t h e f r i c t i o n a l l o s s e s a r e h ig h due l a r g e l y t o t h e p u l s a t i o n s

o f t he a i r and t he e r r a t i c movement t h r ough t he s upp ly t ub e s .

The problem with

g l a s s bea ds i s t h e l o s s o f e ner gy im m e dia te ly the y e merge fr om the noz z l e a nd h i t

t he a i r b a r r i e r . T his w l l have a n im me diat e and d r a m a t i c e f f e c t up t he s ho t

s t rea m and the speed i s r educed cons i de ra bly i n consequence . When us in g beads

i t

i s n e ce s s ar y t o r ed u ce t h e n o zz le d i s t a n c e t o 5 0 t o 9 0

mm

i n or d er t o l e s s e n t h e

l o s s o f k i n e t i c en e rg y .

I n s h o t p e e ni ng o p e r a t i o n s a s s i s t a n c e c a n b e g a i n ed by

an i n c r e a s e i n bead s i z e a nd i n c r e a s i n g t h e a i r p r e s s u r e .

Ceramic Beads Of rec en t in t r od uc t i on and produced to a ve ry h ig h s tan da rd and

wi th a good re s i s t an ce t o breakdown, ce ramic beads may f i nd a ready accept anc e in

shot -peenin g . Made i n s i ze s f rom 0 .20

mm

t o 0.60 mm. Niku ~ a r i z i n v e s t i ~ a t e dh e

medium a nd h i s c on c lus ion s s ugge s t t h a t c e ra m ic be a ds a r e com pa ra bl e t o s t e e l s ho t

i n p e en i ng o p e r a t i o n s .

S t a i n l e s s S t e e l S ho t Made by te c h n iq u e s s i m i l a r t o c a s t s t e e l s h o t . A more

e x p e ns i v e medium and g r e a t c a r e mu st b e e x e r c i s e d t o e n s u r e t h a t a l l t h e f a b r i c

l i n i n g o f a b l a s t mach in e

i s f u l l y p ro t ec te d t o p r o h i b i t t h e s t a i n l e s s q u a l i t y of

the sh ot be impa ired by fe r ro us contam ina t ion .

ERVIN SHOT TESTING MACHINE

T hi s machin e i s mo de ll ed s i m i l a r l y t o a n a i r l e s s b l a s t m ac hi ne, h a vi n g a

th r ow ing w he el , a t a r g e t a nd a r e c i r c u l a t i n g d e v i c e wh ic h r o t a t e s a round a common

c e n t r e l i n e .

S h o t d u r a b i l i t y i s determined by th e number of impacts ag ai n s t

t h e

a n v i l t h a t a r e r e q u i r ed t o b re ak

i t

i n t o a n un us ab le s t a t e .

PNEUMATIC SHOT PEENING SYSTEMS

Ther e a r e t h r e e s ys te m s o f u s ing c ompre ss ed a i r f o r s h o t pee n ing pu r pos e s , i n

which t h e s h o t i s p r o j e c t e d f ro m a b l a s t n o z zl e .

1 ) . I n d u c t i o n

-

syphon method.

2 .

I nduc t i on g r a v i t y m ethod.

3 .

D i r e c t p r e s s u r e .

1 ) . Syphon I n d u c t i o n m ethod i s o ne i n which t h e s h o t i s a s p i r a t e d t o t h e n o z z l e .

The m ethod i s u n co m pl ic at ed a nd l e n d s i t s e l f r e a d i l y f o r u s e i n h an d c a b i n e t s .

F ig . 1 ) .

The on ly c l a im tha t may be made i s t h e s im p l i c i t y o f t h e s ys t em th a t pe r m i t s

c ons t a n t un i n t e r r u p t e d w ork ing .

The on e r e a l o b j e c t i o n

i s

t h a t most i n s t a l l a t i o n s do n o t i n c o r p o r a t e s h o t

c l e a n ing a nd s ho t g r a d ing w hich i n t h e c a s e o f s h o t pe en ing w ou ld no t be t o l e r a b l e .

t i s

t r u e t h a t many p a r t s r e q u i r i n g p e e ni n g a r e gr ou nd an d h a rd en e d an d a r e i n

t h e f i n i s h e d s t a t e . I n co nsequ en ce th ey a r e c l a s s e d a s c l e a n , s o t h e r e i s l i t t l e



p o s s i b i l i t y of c on ta mi na ti on of t he s h o t , b u t a l l ab r a s i v e s b re ak d o ~ n , ~ a r t i c u l a r -

l y g l a s s b e a d s , w h ich i s a popu l a r m edium f o r u s e i n t h i s t y pe o f m a c h ine ) and

t h i s f a c t which h a s be en e m ph as is ed c o n t i n u a l l y i s n o t t o l e r a b l e i n s h o t - p ee n i n g .

S ho t c le a n i n g an d s e p a r a t i o n i s j u s t a s i m po r ta n t i n s h ot - pe e ni n g a s

i t i s

man-

d a t o ry i n s p e c i f i c b l a s t c le an in g i n t h e

U. K.

2 . The G r a v i t y I n d u c t i o n T h i s s y s te m o f f e r s im pr ov ed e f f i c i e n c y , w i t h t h e s h o t

b e i n g e l e v a t e d a bo ve t h e p o i n t o f u s a ge , f ro m t h e r e b e i n g p e r m i tt e d t o f r e e f a l l

t o t h e n o z z l e w h e r e

i t

i s e n e r g i s e d by t h e co mp re ss ed a i r . T h i s i s a n e a t method

o f p r o v id i ng c o n ti nu ou s o p e r a t i o n by e l e v a t i n g t h e s h o t i n t h e r e c i r c u l a t i o n

s y st em . The e s s e n t i a l meth od o f i n c o r p o r a t i n g s c r e e n i n g , g r a d i n g and c l e a n i n g may

be i nc l ude d .

3 .

D i r e c t P r e s s u r e T h is s y st em i s t h e mo st u n i v e r s a l l y u s ed .

t

i s b a se d upo n

t h e us e o f a p r e s s u r e v e s s e l F i g . 2 ) i n w hic h t h e s h o t i s f e d u nd er p r e s s u r e t o

t h e n o z zl e . A m e t e ri n g v a l v e i s i n c o r p or a t e d i n t h e s y s t em t o a d j u s t t h e volume

of a b r a s iv e i n t o t h e a i r s t re a m. T he re i s a p r e c i s e b a l a n c e b e t we e n t h e v olu me o f

s h o t an d t h e b o r e s i z e o f t h e n o z z l e. The v a l u e of t h i s s y s t em i s i n t h e a d j u s t -

m en ts t h a t may b e made p o s i t i v e l y t o t h e a i r p r e s s u r e . The p r e s s u r e v e s s e l a s a

u n i t may b e i n c o r p o r a t e d i n t o h an d c a b i n e t s a nd b l a s t c h am be rs .

Fo r f l e x i b i l i t y , t h e d i r e c t p r e s s u r e method i s s u p e r i o r t o o t h e r m eth od s.

E ve ry t y p e of s h o t may b e u se d w i t h e q u a l e a s e . P r e s s u r e s a r e e a s i l y a d j u s t e d ,

c o n t r o l l e d . They s h o u l d

b e l o c a t e d a t t h e c o r r e c t d i s t a n c e , w it h t h e p r e c i s e a n g l e and w it h e x a c t s pe ed

o f movement. The m ac hi ne s h o ul d a l s o b e f i t t e d w i t h a t i m e r s o t h a t t h e d u r a t i o n

of e a ch pe en in g o p e r a t i o n i s c a r r i e d o u t w i th p r e c i s i o n . T hi s do es n o t e l i m i n a t e

t h e n e c e s s i t y t o i n c o r p o r a t e means of k e ep i n g a c o n s t a n t s h o t c o n d i t i o n . A l l s h o t

p e en i ng m ac hi ne ry s h ou l d b e f i t t e d w it h g r a d e r s t o e n s u r e a c o n s i s t e n t s t a n d a r d

o f s ho t . B roke n s ho t m us t be re move d, s o t oo s hou l d s ho t w hi ch i s und e r s i z e . W it h

s m al l a i r o p e ra te d p l a n t s i t i s d i f f i c u l t t o f i t s h ot r ep l e n i s h e r s , b u t where t h e

consumption i s s u f f i c i e n t l y h ig h t he y a r e e s s e n t i a l .

FIG.

FIG.

2

Syphon Type Hand Cabinet

D i r e c t P r e s s u r e Type S hot

B l a s t U n it



TARGETING

The co mp re ss ed a i r method o f s h o t- p e en i n g h a s a s i t s main a t t r i b u t e t h a t o f

f l e x i b i l i t y . N oz zl es may b e p o s i t i o n e d p r e c i s e l y , a nd d i r e c t e d on t o a n a r e a w i t h

t h e n e c e ss a r y a cc u ra c y. A reas of s t r e s s c o n c e n t r a t i o n s uc h a s f i l l e t s , g ro o ve s ,

s hou ld e r s e t c . a r e t y p i c a l of where t h e noz z l e may be t a r ge t e d1 ' w i th p r e c i s e

a c c u r a c y . Mask ing by means of r ubbe r i s e d t a pe over t he non- s t r e s s e d a r e a i s o f t e n

a s a t i s f a c t o r y way of l i m i t i n g t h e e f f e c t of t h e b l a s t .

B e fo re a ny s h o t -p e e n in g o p e r a t i o n i s c a r r i e d o u t t h e w o rk pi ec e s h o u ld be

c r i t i c a l l y e xam in ed a s t o how

i t

should be proc essed . The an gl e of

t h e no z zl e t o

t h e a r e a r e q u i r i n g t r e a t m en t ; t h e p r e s s u r e r e q u i r e d ; t h e s i z e and t y p e of s h o t

a nd t he d i s t a n c e of t he noz z l e . Sho t e me rg ing fr om a noz z l e opens ou t a nd r a d i -

a t e s f ro m t h e t i p and t h e c o n c e n t r a t i o n of s h o t

w i l l

be t h e h i g h e s t i n t h e c e n t r e

o r c o re of t h e j e t o f s h o t . T h is i s t h e h o t- sp o t1 ' .

Whenever a c y l i n d r i c a l component i s r e q u i r e d t o b e s h o t- p e en e d , c a r e s h o u l d

b e t ak e n t o r e l a t e t h e h o t - sp o t t o t h e p o i n t o f im pa ct a nd n o t t o o v e r va l u e t h e

pe r ip he ra l b l a s t . For example a 50 .00 wide b l a s t when measured re ve a l s a core

c on c e n t r a t i on o f 15 .875 mm The t r a v e r s e o r h e l i x s h o u ld be b a se d u pon t h i s

CENTRIFRUGAL SHOT PEENING

PRINCIPLES OF WHEEL DESIGN

As w i t h o t h e r f orm s of s h o t b l a s t i n g t h e o r i g i n a l i d e a s o f p r o j e c t i n g

ab ras iv es by means of c en t r i f r u g a l ac t io n were those of T ilghman*, who took ou t

pa te n t s in 1870. The pa te n t s cove red two d i s t i n c t me thods, one of which was to

f e e d t h e a b r a s i ve by g r a v i t y on t o t he w hee l b l a de s w her e i t was ene rg i sed by th e

f o r c e o f im pa ct . Th i s was r e f e r r e d t o a s t h e B a t t e r w hee l . The s ec ond pa t e n t

was a method o f f e e d ing t he a b r a s i ve t o t h e c e n t r e o f t he w he el and

i t

could be

s a i d t h a t

i t

i s fr om t h i s t h a t t h e p r e s e n t t yp e s o f s l i d e r w h ee ls h av e b e en

de veloped . T i l ghm a n l s w hee l was de s igne d t o p r o j e c t t he a b r a s i ve ove r 360 de g r e e s

and some time was t o e lap se be f or e a wheel was evolved t h a t had d i r e c t io n a l

c o n t r o l o f t h e a b r a s i v e . T h is c h a r a c t e r i s t i c was t o p ro ve i n v a l u a b l e i n a p p l i -

c a t i o n s o f h i g h l y t e c h n i c a l m e r i t . An e a r l y form o f t h i s was f i t t e d w i th e i g h t

f l a t b la d e s s i t u a t e d betw een two s i d e p l a t e s .

t

i s no rm al w it h t h i s t y p e of

w he el t o f e ed t h e s h o t by g r a v i t y t hr ou g h a t u be t o t h e c o r e of a s t a t i o n a r y

c on t r o l c age on to t he b l a de s o f t h e w he el ( F i g . 4 ) .

t

i s t h e c o n t r o l cag e, a s i t s

name i m p l i e s t h a t d e t er m i n es t h e d i r e c t i o n i n w hich t h e s h o t i s t h ro wn .

Tilghman. B C F i r s t B r i t i s h P a t e n t No. 2900 - 1876

FIG.

B l a s t P a t t e r n I n c o r r e c t C o r r e ct



As th e sh ot l e ave s t he whee l i t f or ms a c o n f i gu r a t i o n w he re in t h e h igh ly c onc en-

t r a t e d ar e a i s a g a i n r e f e r r e d t o a s t h e h ot -s po t ( F ig . 5 ) t i s i n t h i s a r e a

t h a t t h e s h o t -p e en i ng w ork i s p er fo rm ed , a s t h e c o n c e n t r a t i o n i s h i g h e s t and t h e

a n g l e of i m p ac t a t

the optimum.

The c o n t r o l c a ge may b e a d j u s t e d t o s u i t i n d i -

v id ua l componen ts s o t h a t t he ho t - s po t ' '

i s

a t t h e p r e c i s e p ee ni ng p o i n t . The

c o n t r o l c a g e

w i l l

i n t ime wear and i n consequence th e hot - spot

w i l l

move off the

w o rk p ie ce . I mm ed ia te ly t h i s o c c u r s t h e s h o t p ee n in g o p e r a t i o n i s s u s p e c t .

These

a r e t h e p r i n c i p l e s which c o n t r o l a c e n t r i f r u g a l s h ot -p e en i ng o p e r a t i o n .

The o r i g i n a l d o u b le si d e d wh ee l p e r m i t s t h e g r e a t e s t c o n t r o l o v e r t h e s h o t

s t ream. The method of b lade f ix in g however l im i t s such a wheel t o a s i n g le

d i r e c t i o n o f r o t a t i o n . Th i s was overcome by t he i n t r od uc t i on o f a w hee l w hich

d i s p en s e d w i t h b l ad e s a nd us ed i n s t e a d a s e t o f s p e c i a l l y de si g ne d t u b e s .

B l a s t

w h ee ls ha ve b ee n g e n e r a l l y d e s ig n e d f o r b l a s t c l e a n i n g p u r po s e s an d n o t f o r s h o t -

peening.

They a r e d e si g n e d f o r g e n e r a l p ur p os e u s e , n o t w i t h a ny s p e c i a l a p p l i -

c a t i on i n mind. The re may w e l l be room f o r more r e s e a r c h i n to t h e de s ign of b l a s t

whee ls , e s pe c i a l ly wi th th e growing demands fo r sho t -pe eni ng . Whatever th e d i a -

m e te r of t h e b l a s t w he el t h e volum e o f s h o t t hro wn i s d i r e c t l y r e l a t e d t o t h e

energy consumed.

An in cr ea se i n wheel speed

w i l l

p r od u ce an i n c r e a s e i n s h o t

ve lo c i t y , bu t w i th a de c r e a s e i n volum e. S lowing down the b l a s t whee l w i l l have

t h e r e v e r s e e f f e c t ( i n c r e a s i n g t h e volume o f s h o t a t t h e e xp en se of v e l o c i t y )

( F i g . 6 . )

The ge n e r a l l y a c c e p t e d s pe e d f o r a b l a s t w hee l 508 .00

mm

i n d i a m et e r i s 2250

r .p .m . Wheels va r y i n d i a m et e r a nd sp ee d an d t h e c r i t e r i o n i s t h e r e l a t i o n s h i p

betwe en t h e s e f a c to r s and a p ropos ed a p p l i c a t i o n .

BLAST WHEEL DESIGN Ob ser vat ion s sug ge st th a t b l a s t whee ls a r e a r b i t r a r i l y

d e s ig n e d w i t h t h e co mm er ci al a s p e c t a s t h e d om in an t f a c t o r . V a r i a t i o n s a r e i n t r o -

du ced t o be d i s t i n c t and t e c h n i c a l c o n s i d e r a t i o n s a r e o f t e n n o t t h e p rim e m ot iv -

a t i o n . The s t a n d a r d w h ee l, b a s i c a l l y t h e o r i g i n a l d e s i g n , h a s be en pr od uc ed w o rl d

w id e, w it h s l i g h t v a r i a t i o n s i n o u t l i n e . T h is i s a w e l l b a l a n ce d d e s i g n and

f i t t e d i n t o a s u i t a b l e h o u s in g , r o t a t e s w i t h t h e minimum o f t u r b u l e n c e . The

e f f i c i e n c y o f t h i s w hee l i s re v e a le d by i n s p e c t i o n o f t h e b l a d e s a f t e r a p e ri o d o f

time when i t h a s b een t hr ow in g c h i l l e d i r o n g r i t . B ecause g r i t h ug s t h e s u r f a c e

of t h e b l a d e , a t r a c e r y i s l e f t wh ich r e v e a l s t h a t t h e movement down t h e b l a d e i s

e x a c t ly c e n t r a l .

Open s i de d w hee l s a r e de signe d w ith a s i de p l a t e w h ich r e q u i r e s

t h e b l a d es t o be h e l d i n p o s i t i o n b y t h e o ne ed ge ( F i g . 7 ) .

Most whee ls of t h i s

type

a r e de s igne d t o a ccommodate e i gh t b l a d e s , ye t t h e r e a r e s i m i l a r w hee l s w hich

a r e f i t t e d w i t h f o u r b l a d e s . W heth er e i g h t o r f o u r b l a d e s a r e u s ed , t h e movement

of th e wheel th rough t he whee l hous ing mus t s e t up a more d i s r up t i ve f low than a

d ou bl e s id e d w h ee l. The t r a c e r y of t h e a b r a s i v e i n t h i s c a s e w i l l h av e a n o f f s e t

fa n p a t te rn sug ges t ing some movement toward th e unshrouded s id e of th e b l ad es .

FIG.

Ea r ly de s ign o f

d i r e c t i o n a l l y c o n t r o l l ed

B l a s t Wheel i l l u s t r a t i n g

Im pe l le r and Con trol Cage



Thi s may be due t o t h e whee l c r e a t i ng more a i r t u r bu l e nc e a s

i t

moves through f ree

a i r . T h is d oe s n o t s u g g e st t h a t t h i s t yp e of wh eel i s i n e f f e c t i v e , f o r i t h a s a

p ro ve n r e c o r d i n g e n e r a l a p p l i c a t i o n s of c l e a n i n g and s u r f a c e p r e p a r a t i o n , b u t

i t

d oes s u g g e s t t h a t i n c r i t i c a l p e e ni n g o p e r a t i o n s t h e r e may be room f o r more

i n v e s t i g a t i o n on t h e q u e s t i o n o f e f f e c t i v e n e s s .

t

c a nno t be cl a im e d t h a t b l a s t w hee l s a r e a e r odyna m ic a ll y de s igne d . One

wheel which may be s o des cr i be d however , i s o f a more r e c e n t i n t r o d u c t i o n i n which

t u b e s r e p l a c e c o n v e n t i o n a l b l a d e s . I n o p e r a t i o n t h e a i r movement ar ou nd t h i s

w he el i s s mooth and ve r y l i t t l e d i s t u r be d . W hether t h i s i s a n im provem en t upon

the b a s i c doub le s i de d w he el i s ope n t o i nv e s t i ga t i on . The re i s how ever , a funda -

m e nt al d i f f e r e n c e i n t h e f lo w of s h o t t hr o ug h t h e t u b u l a r b l a d e s e s p e c i a l l y when

compared w it h t h e t r a d i t i o n a l f l a t b l a d e .

When t he sh ot ha s passed f rom th e imp e l lo r th rough t he c o nt ro l cage and

e n t e r s t h e t u b u l a r b l a d e , t h e p as s ag e i s smooth a nd u n r e s t r i c t e d . The s h o t f lo ws

down the t ube i n a c onc e n t r a t e d f or m i n a na rr ow pa th wh ich r e s u l t s i n a l e n g th -

e ne d , b u t n ar ro w b l a s t p a t t e r n . The a v e ra g e b l a s t p a t t e r n l e n g t h when th ro wn

f rom the optimum f rom t h i s w hee l i s 1600 w her ea s t h e b l a s t p a t t e r n l e ng th f rom

a f l a t b l a d ed w h eel i s a p p r o x i m at e ly 1 066 mm Thi s w i l l i nd i c a t e s om e a ppr e c i a -

b l e d i f f e r e n c e i n t h e two fo rm s o f b l a s t w h ee ls . O bv io us ly i n t h e c a s e o f t h e

t u b u l a r wh eel t h e s h o t i n i t s i n i t i a l t r a v e l down t h e tu be i s c o n ce n tr a te d i n a

f i n e s t r e a m i n t h e r a d i u s a nd o pen s o u t upon b e i n g r e l e a s e d i n t o f r e e a i r . W ith

a l e ng th en ed b l a s t p a t t e r n t h e r e

w i l l

b e s h ot - p ee n i n g a p p l i c a t i o n s w he re t h e r e

i s

some d i s t i n c t a dvan t a ge and on t he o th e r ha nd , i n s t a n c e s where t h e a p p l i c a t i o n

may be s u pe r i o r w i th t he u s e o f a f l a t b l a de d w he el .

Some ye ar s ago Campbell* in t ro du ced a sm al l wheel i n which th e de s ig n

p e rm i tt e d t h e b l a d e s t o e x te n d beyond t h e p e ri p he r y of t h e s i d e p l a t e s ( ~ i g . 8 ) .

Th i s was i n t r oduc e d w i th t he o b j e c t of c ons e r v ing e ne r gy by e l im ina t i n g t h e vee

b e l t d r i v e an d d i r e c t c o u p li n g t h e w he el t o t h e e l e c t r i c m ot or . B ecause o f t h e

l o a d on t h e b e a r i n g s o f t h e m ot o r, t h e s i z e o f b l a s t w h ee l was l i m i t e d , e s p ec -

i a l l y a s a r o t a t i o n a l s pe ed of t h e b l a s t wh ee l t o b e e f f e c t i v e must b e ov er 2 600

r .p .m. There fore an e l e c t r i c motor wi th a speed of 2800 r .p .m. was an obvious

c ho i c e , t og e th e r w i th hea vy du ty be a r in gs t o t a ke t he l oa d ing . C am pbell

abandoned th e des i gn a f t e r some extended pe r io d of use a s t he method was not

c ons ide r e d t o be a s uc c e s s . t a pp e ar ed t h a t t h e e xt en d ed t i p s of t h e b l a d e s

c r e a te d t u rb u le n ce r e s u l t i n g i n a s i m i l a r e f f e c t t o b l a d e s of t h e s i n g l e s i d ed

w he el , e x c e p t t h a t t h e t r a c e r y o f t h e a b r a s i v e ap pe ar ed t o f a n i n bo t h d i r e c t i o n s .

B la s t w hee l s ope r a t e i n a f o rm s i m i l a r t o l i q u i d pumps a nd ye t pe r fo r m w i th

t h e f u n c t i o n o f a f a n .

A i r

i s e s s e n t i a l t o t h e f r e e f lo w o f t h e a b r as i v e t hro ug h

t h e w he el u n i t . W it ho ut a i r t h e a b r a s i v e w i l l ch ok e a nd f a i r t o f l o w e x c ep t i n a

minute q u an t i ty . The volume of sho t thrown

i s

d i r e c t l y r e l a t e d t o h or sep ow er

( F i g . 9 ) . B l a s t w h ee ls a r e u s u a l l y d r i v e n b y e l e c t r i c m o to r s by means of m u l t i p l e

* Campbell

J A

l a t e o f

St.Georgels En gin eer s Lt d. of C en tr al Gauge Tool Co.

FIG. 5

I l l u s t r a t i n g t h e Hot-Spot

of a Bl as t S t ream.



r o p e d r i v e s w hic h h a ve t h e a d va n ta g e i n t h a t t h e

f i n a l w h ee l s p eed may b e ad j u s t -

ed when n eces s a r y by v a r i a t i o n o f t h e p u l l ey s i z e s . Wheel sp eed d i c t a t e s s h o t

v e l o c i t y , a v e r y i m p a r t a n t a s p e c t o f s ho t - pe e n in g . T h i s i s a n o p p o s i t e v ie w t o a

f i x e d s i n g l e s p eed u n i t , w i t h a d i r e c t co u p l ed wh ee l w he re o f t e n when s p eed v a r i -

a t i o n i s r e q ui re d ,

t s

i m p o ss i bl e t o a c h i e v e . Sometim es t h i s i s n e c e s s a r y

b ecau s e t h e m achi ne h a s b een b u i l t down t o s i z e ,

and t h e a b i l i t y t o i n t ro d u c e a

v e e r o p e d r i v e i s p r o h i b i t e d . C e n t r i f r u g a l m ac hin es l a c k t h e f l e x i b i l i t y o f th o s e

of compres sed a i r typ e , where f o r example the op er a t i ng p r es sur e may be as low a s

0.070 3 k g. /s q. cm t o as hi gh a s 7.03 KG./sq. cm. Any and every means which

i mp ro ve t h e v e r s a t i l i t y o f m achi ne s

i n c o r p o r a t i n g b l a s t w h ee ls mu st b e c o n s i d e r e d

Wheel Blade s The ran ge of bl ad e de si gn s s l e g i o n , a l l may ha ve s p e c i f i c

f e a t u r e s w hich a r e p u rp o rt ed t o be e s s e n t i a l .

They a r e t h e p a r t of a b l a s t

machine which i s su b j ec t t o the mos t s ev ere wear and because o f t h i s a r e made o f

c a se h a r d i r o n a l l o y u s u a l l y c o n t a i n i n g

28

chr om e. Each s e t o f b l ad es i s

b a la n ce d t o f i n e l i m i t s , b u t b e in g o f c a s t c o n s t r u c t i o n may c o n t a i n v e ry s l i g h t

i m p e r f e c t i o n s .

These a r e o f t e n n o t d i s c e r n a b l e o n v i s u a l i n s p e c t i o n ,

b u t w i l l be

very e v ide n t i n us e , when the whee l u n i t may become ou t o f ba la nce .

The o r i g i n a l d e s i g n of a b la d e was f l a t w i th s l i g h t l y l i p pe d s i d e s t o

p r o t e c t t h e s i d e p l a t e s o f t h e w he el f ro m w e ar .

B lades o f forms o t he r tha n f l a t have been in t ro duc ed , somewith convex and

o t h e r s w i t h co ncav e f ac e s . A f or m o f t h e l a t t e r was p a t en t ed * i n t h e p r e- w ar

y ea r s , a l t h o u g h no p a r t i c u l a r c l a i m was made f o r t hem ex cep t t h a t t h e d e s i g n

p e r m i t t e d a t h i c k e n i n g of t h e b l a d e t i p w hich h e l p e d t o r e s i s t wear a nd i n c r e a s e

t h e l i f e of t h e b l ad e . More r e ce n t l y a b l a s t w heel was i n t r o d u ced f o r w hich t

i s cl ai me d t h a t a s i m i l a r co nc av e b l a d e a s s i s t s s h o t v e l o c i t y I ?i g .l O ).

By

c o i nc i d e nc e a w he el i n t r o d u c e d c o n c u r r e n t l y c a r r i e d a s i m i l a r c l a i m f o r a b l a d e

w i t h a n i n i t i a l c u r ve i n t h e o p p o s i t d i r e c t i o n . The h ea vy wear e x h i b i t e d u pon

the wheel b lad es when compared wi th o t he r e l ements o f th e wheel u n i t sug ges t s

th a t th e b la de s do mos t o f th e work and t h e i r des i gn may i n consequence be mos t

c r i t i c a l t o wheel e f f i c i e n c y . Th ere i s l i t t l e doubt t h a t t h e le ng th of t he

b l a d e s a r e a n e f f e c t i v e p a r t o f w he el d e s i gn ,

b u t t i s q u e s t i o n a b l e w h et he r a ny

c u r v a t u r e i s s i g n i f i c a n t l y e f f e c t i v e i n sh o t v e l o c i t i e s . T hi s i s e s p e c i a l l y so

when c o n s i d e r a t i o n i s g i v e n t o t h e p e c u l i a r b ou nc e of t h e s h o t d u r i n g

t s

passage

down th e bl ad e .

The b l a s t wheel in t rodu ced wi th b lade s o f tu bu la r fo rm F ig .11) may be

f i t t e d w i th b la d e s of v a r i o u s l e n g t h s a c co rd i ng t o t h e a p p l i c a t i o n . T ub ul ar

b la des have been made of hard chrome a l l o y ; o f ce ramic and o f p l a s t i c . A l l t h e

b l a d e s , i n c l u d i n g t h o s e of c e r am i c , which ha d b o r e s of s u p e r f i n e f i n i s h , d i s p l a y e d

the same undul a t io ns upon the su r fa ce caused by t he bounce o f the sho t a s found

on a l l o t h e r t y p es of b l a d e s . T h i s b ou nc e

s

very pronounced and

s

o f t e n

m e a s ur a b le , th e i n i t i a l bounce b e i n g t h e l a r g e s t w i t h p r o g r e s s i v e l y s m a l l

u n d u l a t i o n s on t h e s u r f a c e t o t h e p o i n t w here t h e s h o t l e a v e s t h e b l a d e t i p .

Spencer Ka ls t ea d Ltd. Pa te nt No. 1003441



A

w hee l o f more r e c e n t i n t r od uc t i on * ha s b l a de s o f a c om ple t e ly i nd iv idu a l

de s ign . They a r e de s igne d i n a

V

shape and a r e a l s o wi de r a t t h e t i p t h an a t

t h e r o o t . T h i s h a s t h e e f f e c t of t hr ow in g a wide b l a s t p a t t e r n .

The

normal speed of a

300 mm

d i a . wh eel i s

3 0 0 0

r .p .m. and when used fo r sho t-pee nin g

t h e s pe ed i s i n c r e a s e d t o

4 5 0 0

r .p .m.

To i l l u s t r a t e t h e e f f e c t i v e n e s s o f t h e b l a s t w hee l f o r s ho t -p e en i ng a n

example may be ta ken from an ai r c r a f t component. Th is was sho t-peen ed

t o Almen g auge

A

t o a n a r c h e i g h t a v er ag e o f

0 2 8 3 mrn

w it h s t e e l s h o t

5 2 3 0

The

time taken was

9

minutes on a ro ta ry t ab le type machine. The b l a s t was powered

by a 15

H . P .

motor.

CONTROL

CAGE - A s

h a s bee n d es c r ib e d p r e v i o u s l y , b l a s t p a t t e r n s v a r y w i th t h e t y pe s

of throwing whee ls . The p a t te rn s may a l so be a f fe c t ed by the shape and s i z e of

t h e a p e r t u r e i n t h e c o n t r o l c a g e. G e n e r a l l y o p en i ng s of s q u a re an d r e c t a n g u l a r

f or m a r e f a vour e d , t hough t r i a n gu l a r open ings and o f f s e t ope n ings ha ve be en us e d ,

and i n t h e c a s e o f t h e t u b u l a r b l ad e d wh ee l h a l f r ou nd o pe n in g s a r e e f f e c t i v e .

The op en i ng , o r a p e r t u r e , o f t h e c o n t r o l c ag e d e t er m i ne s t h e l e n g t h o f t h e

b l a s t p a t t e r n an d t o some d e g re e t h e s i z e o f t h e h o t -s p o t . ( T h i s t er m i s u se d

b ec au se when t e s t i n g a b l a s t p a t t e r n w i th a s h e e t o f m il d s t e e l , t h i s a r e a w i l l be

f ound t o be s l i g h t l y warmer t o t he t ouc h ) .

Bl as t wheels do not have the same f l e x i b i l i t y a s compressed a i r methods and

t hey c a n b e w as t e f u l i n s p e c i f i c a p p l i c a t i o n s u n l e s s e v er y c ar e i s t a ke n i n

r e l a t i n g t h e b l a s t z one t o t h e w or kp ie ce .

The c o n t r o l c ag e i s a d j u s t a b l e t o e n a b l e t h e s h o t s t r ea m t o b e p r o j e c t e d a t

any p o i n t i n

3 6 0

d e g r e es . Fo r example i f t h e c o n t r o l c ag e a p e r t u r e i s s e t a s on

a c l o c k f ac e a t 1 2 o ' c l o c k t h e s h o t w i l l b e d i sc h a rg e d a t a p o i n t fro m

3

o ' c l o c k

o nw ards. The i l l u s t r a t i o n i n d i c a t e s t h e whole b l a s t p a t t e r n , n o t t h e h o t- s po t ,

f o r t h i s must be c he cke d and a s c e r t a i ne d p r e c i s e l y by means o f u s ing a p i e c e o f

m il d s t e e l s h e e t p la ce d i n a s t a t i o n a r y p o s i t i o n u nd er t h e wh ee l.

FEED IMPELLERS

-

This component

i s

o f t e n d is r e ga r d e d a s o ne o f no r e a l s i g n i f i -

a n ce . I m p e l l e r s v a r y s l i g h t l y i n d e s ig n b u t a r e b a s i c a l l y t h e same. Two

c om pan ies i n t h e U n it ed S t a t e s i n c o r p o r a t e c on ed i n l e t s i n t h e d e s i g n s an d t h i s

seems t o have th e e f f e c t of s t i mu la t in g t he movement of a g re a t e r volume of sho t

t h ro u gh t h e wh ee l u n i t .

Sampoh Co .L td ., Tokyo

HP

- 15 HP

1

4 5 9 5 9071

13608

181.4422 8 272 317.5 36 8

WHEEL SPEED vs. ABRASIVE FLOW.

1

2 0 0 3 0 0 4 0 0 5 0 0 6 7 0 0 € br.

per

mln.

FIG.

FIG.

7

S i n g l e S i de d

Blas t Wheel .



The i m p e ll e r i s c l o s e l y r e l a t e d t o t h e b l a s t wheel i n t h a t

i t i s

made i n a

s eg men ted f orm a nd t h e se gm en ts r e l a t e t o t h e b l a d e s . I n o p e r a t i o n t h e s h o t i s

p i c ke d up by t he im p e l l e r and pa s s e d t h r ough t h e c on t r o l c a ge a p e r tu r e on to t h e

b l a d es . T hi s d i s t a n c e i s s m a ll b u t t h e s pe ed i s s o g r e a t a nd eac h seg ment i s s e t

s l i g h t l y i n ad van ce of t h e w he el b l a d e s i n o r d er f o r t h e s h o t t o a l i g h t o n t o t h e

f a c e o f t he b l a de .

I n t im e t h e i m p e l l e r w i l l w ea r t o a po in t w her e t he s h o t w i l l b e i n e f f e c t -

i v e l y s t r i k i n g t h e i n n e r l e a d i n g ed ge of t h e b l a d e. t i s r ecommended t h a t t h i s

c r i t i c a l component s hou ld be r e p l a c e d when a ny p a r t o f i t s s e gme nt s i s worn more

than 3.175

mm

The w ear r a t e i s h i g h ; o ne i m p e l l e r

w i l l

usual ly outwear two

cont ro l cages* .

SHOT SEPARATION

AND

GRADING With th e ad ve nt of peen ing q u a l i t y s h o t which h as

b ee n s e l e c t i v e l y p r od uc ed t h e p r ob le ms i n v o lv e d w it h m a i n t a i n i n g a h i g h e r q u a l i t y

p e en i ng o p e r a t i o n h a ve b ee n co n s i d e r a b l y l e s s e n e d . W ith a l l w e l l d e s ig n e d b l a s t

p l a n t s t h e s e p a r a t i o n s ys te m r e c e i v e s a s much c o n s i d e r a t i o n a s t h e r e s t o f t h e

machine.

T hi s s e c t i o n i s s i t u a t e d a t t h e h ea d of t h e e l e v a t o r , which r a i s e s t h e s h o t

f rom th e ba s e o f t h e m ac hine f o r r e - u s e . As t he s ho t pa s s e s t h r ough t he s e p a r a t o r

i t

i s s u bj e c t t o t he

a i r drawn by t h e v e n t i l a t i o n f a n w hich p u l l s o u t

t h e d u s t ,

s c a l e and f r agm e n ts o f b roken s h o t , a nd l e a ve s t he good s ho t f o r r e - us e . w e l l

d e si g ne d s e p a r a t o r p r o v id e s a c u r t a i n o f s h o t e v e n l y d i s t r i b u t e d i n s uc h a manner

tha t good s ho t

i s

no t l o s t by be ing drawn ou t .

This oc cas io na l ly happens when

t h e r e i s a b re ak i n t h e c u r t a i n which d i s t u r b s t h e b a l an c e and p er m it s a t t h a t

p o i n t

t h e v e n t i l a t i n g a i r t o p u l l good s p o t i n t o th e d u s t a r r e s t e r .

t i s p r e - r eq u i s i t e o f good s h o t -p e e n in g t h a t t h e s h o t s ho u ld b e k e p t a t a l l

t i m es a s n e a r t o t h e recommended s i z e s t a n d a r d s e l e c t e d f o r t h e p a r t i c u l a r

o p e r a t i o n . T h i s r e q u i r e s t h e i n c o r p o r a t i o n of a s h o t g r a d e r which

i s

d e s i g n e d t o

s e l e c t o u t t h e s i n g l e s i z e r e q u i re d . s h o t g r ad e r i s a s i e v i n g d e vi c e i n which

t h e r e a r e t i e r s o f s e l e c t e d wi r e s c r ee n s .

SHOT REPLENISHING Sh ot of co ur se , i s an expen dabl e pr od uc t, and i t s l i f e i n

known c o n d i t i o n s i s p r e d i c t a b l e .

t

f ol lo w s t h e r e f o r e t h a t a s t h e s h o t l o s e s t h e

op t im um s i z e f o r t he pe e n ing ope r a t i on ,

i t i s

drawn from th e machine and re q u ir es

r ep la ce me nt . r e p l e n i s h e r l o c a t ed a t t h e b oo t o f t h e e l e v a t o r o r o t h e r s u i t a b l e

p o i n t

w i l l

ke e p t he volume o f s ho t i n t he m ac hine i n a ba l anc e d c on d i t i on .

S i g n a ls from t h e s h o t h o pp e r, s i t u a t e d below t h e s e p a r a t o r , i n d i c a t i n g t h e s h o t

l e v e l , e n e r g is e t h e s h o t r e p l e n i s h e r and s u f f i c i e n t s h ot i s ad ded t o m a i n t a i n t h e

n e c e s s a r y b a l a n c e .

Tilghman-Wheelabrator Ltd.

Book of Running Ins truc t ions .

FIG

9

FIG

8



THE ENERGY FACTOR The c e n t r i f u g a l method of sh ot -p ee ni ng i s of h i g h e r

e f f i c i e n c y th a n th a t of t h e pn eu ma ti c s ys t em . I t l a c k s t he f l e x i b i l i t y of t h e

compressed a i r me thod bu t has th e a b i l i t y t o make much more e f f i c i e n t use o f

energ y. The power used fo r a purpose b u i l t shot-p eenin g machine

w i l l

be r e l a t i v e

t o t h e demand and u s u a ll y t h i s i s i n t h e a r e a of

20

t o 5 H.P. The r e g i s t e r o f

e f f i c i en cy i s i n the ammeter which in d i ca te s t he volume of sho t th rown by t he

whee 1

A cco rd in g t o s i z e s t e e l s h o t w i l l l o s e v e l o c i t y i n c om p ar at i ve ly s h o r t

d i s t a n c e s .

Th i s sh o u ld g iv e some in d i c a t io n o f t h e c u b ic c a p a c i ty of a b l a s t

c a b in e t

With a c o r r e c t l y e n gi n ee re d b l a s t ma ch in e t h e n e x t e s s e n t i a l i s f o r

s u f f i c i e n t a i r movement t o e n s u r e t h e c l e a n e s t a t mo sp he re i n s i d e t h e c a b i n e t

d u r in g th e s h o t -p e e n in g o p e ra t i o n . Many co mp on en ts an d wo rkp iec e s a r e i n t h e i r

f i n a l s t ag es and may be themse lves sc rupu lous ly c le an and the se

w i l l

n o t p r e s e n t

a p ro bl em . I n t h e c a s e o f h e a v i l y s c a l e d w o r kp i ec e s s uc h a s l e a f s p r i n g s t h e a i r

volumes must be adequate fo r t he co nt inu ous removal of a l l du st and impedimenta .

INSTRUMENTATION

AMMETER This ins tru me nt r e f e r r e d t o pre vio usl y in di ca te s th e volume of sho t

be in g th rown. The mete r shou ld a lways show a t the co r r ec t read i ng dur ing

proce ss in g and must be f req ue n t l y moni to red .

PROCESS TIMER A v i t a l i ns t ru m en t f o r i n sh ot -p ee ni ng o p e r at i o ns t im e i s an

i m p o r t a n t f a c t o r .

CONVEYOR SPEED INDICATOR An e s s e n t i a l ins tr um en t f o r th e p ro c es s pe ri o d i s t h e

s pe ed a t which th e wo rkp iec e p a s s e s t h ro u gh th e b l a s t s t r e a m .

WHEEL HOUR METER A va l ua b l e a d d i t i o n t o a l l pee nin g machines . The met er re co rd s

th e a c tu a l p e r io d o f t im e i n which t h e whe el

i s

t h ro win g s h o t .

SHOT REPLENISHER CONTROL Methods of m a in t a i n i n g th e amount of s h o t i n a ma ch ine

may be e i t h e r e l e c t r i c a l o r pneumatic . In each cas e methods may be incor pora t ed

t o i n d i c a t e a s h o r t a g e o f s h o t i n t h e s y s t em a nd th e r e p l e n i s h e r . The se may b e

v i s u a l o r a u d i b l e o r a c om b in at io n of b o t h .

MANOMETER Inco rpor a ted i n a dus t a r r e s t e r t h i s ins t rume nt in d i ca te s th e

p r e s s u r e d ro p i n t h e s y st e m and i n s o do in g a s s i s t s i n ma i n ta i n in g a c o n s t a n t

a i r movement th rough th e s ep ar a t o r .

The se a r e t h e m ain i n s t ru m e n t s . M a n ufa ctu re r s a r e c o n s t a n t ly im p ro ving

machine d e s i g n an d i n s t r u m e n t a t i o n i s a n a r e a w hich i s r e c e i v i n g a t t e n t i o n .

Compute ri sed c on t r o l s have a l r ea dy been inc orpor a ted i n sp ec ia l pu rpose mach ines .

FIG

10

Curved Bladed Si ng le Sid e

Wheel Co urt es y Pangborn

Corpora t ion .



Fo r c i r c u l a r o b j e c t s , a s i mp le r o t a t i o n a l method i s o f t e n

. Fig . 12) . w ide v a r i e ty o f mach ines o f t h i s type a r e made

W h i ls t s i n g l e i n d i v i d u a l t a b l e m ac hi ne s a r e u s e d , many a r e m u l t i t a b l e d e s i g n .

The

ta b l es va ry c ons ide ra b ly i n s i z e and a mach ine may have a s many a s 20 t ab le s

a c h i n e b e i n g p ur p o se l y d e s i g ne d f o r a s p e c i f i c p r o d u c t .

M ac hi ne s of t h i s d e s i g n i n w hi ch a n e n d l e s s r u b b e r

work ~ i g . 1 3 ) ave a good de al t o commend them,

e s p e c i a l l y i t e ms s uc h a s l e a f s p r i n g s . The b e l t s a r e h ea vy r e i n fo r c e d w it h c o t t o n

p l y t o w i t h s t a n d t h e a r du o us c o n d i t i o n s a nd a r e f r e q u e n t l y pe gg ed t o l o c a t e t h e

i n d i v i d u a l w o r k pi e c es .

S t e e l ba r s o f s u f f i c i e n t l eng th may be conveyed upon a

F i g . 1 4 ) . T h i s p r e su p p os e s t h e b a r s o r s h a f t s a r e of c l e a n

and have no upse t a r ea s .

S h a f t s wh ich ha v e an u p s et l i n e , s uc h a s h a l f - s h a f t s w hic h

d may b e s a t i s f a c t o r i l y s h ot -p e en e d i n a mac hin e of t h i s t y p e

Due t o t h e e x p os u r e t o t h e b l a s t s t r e a m t h e s c r o l l r e q u i r e s t o be made of a

s i m i l a r a b r a s iv e r e s i s t a n t m e ta l .

Th i s i s a method o f convey ing gea r s and c r an ks ha f t s . The

s t e m i s t h a t t h e c om po ne nts may b e r o t a t e d a s t h e c a r r i a g e

proceeds under th e b l a s t . The same sys tem has been used fo r heavy locomot ive l e a f

s p r i n g s F i g . 1 5 ) .

S t Both l e a f and c o i l sp r i ng s may be s t r e s s peened upon

su i t a b l y d e s i g n e d m a c h i n e s .

M ach in es of t h i s t y p e a r e t h e r e s u l t o f c o n s i d e r a b l e

e x p e r t i s e a nd d e s i g n e x p e r i e n c e .

F or t h i s p u r p o se , t h e ma ch in es g e n e r a l l y u se d a r e of w id e

b e l t d e s i g n w i t h u s u a l l y t wo o r t h r e e down f i r i n g b l a s t w h ee l s, s o t h a t t h e s p e c i a l

a i r c r a f t s e c t i o n i s c a r r i e d i n t h e h o r i z on t a l p o s i t io n . I t would be remiss t o

over l ook th e many peen-forming machines of the compressed a i r type i n which ca se

t h e w or kp ie ce s a r e p ro c es s ed i n t h e v e r t i c a l p o s i t i o n .

F IG

Tubular Bladed Blast Wheel

Courtesy of Vacu Blast Co. Ltd.



FIG. 2

FIG. 13

FIG. 14

FIG. 15

REFRENCES

1. Herbert E .G. Work Hardening of Steel by Abrasion

Journal of Iron Steel Institute 1927 pp 265

-

282

Cloudburst Process for Hardness Testing Hardening

Trans. A.S.S.T. 1929

pp

77 92

2. Niku-Lari Sechaud R. Grenaillage d1Eprouvettes Almen

Mesures et Calcul de la Repartition des Contraintes Residuelles

Minibilles S.E.P.R. pour Traitment de Surface.

The Author gratefully acknowledges the

following Companies for their valuable assistance

Barton Abrasives Ltd.

Cleveland Metal Abrasives

Irvin Industries Inc.

Lockers Ltd.

Metabrasives Ltd.

Pangborn Corporation

Potters Industries Inc.

Sampoh Co.

Societe Europeene des Produits

Refractaires

Tilghman Wheelabrator Ltd.

Vacu Blast Ltd.

Vogel Schemann A.G.

Wheelabrator-Alevaid

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