In cro ssbar t ran sfer p resses, flywh eels o f u p t o 2,500 m m in d iam et er an d a weigh t o f 25 t are u sed . Th e m o u n t in g an d lu bricat io n o f t h is
t yp e o f flywh eel in ro ller bearin gs are h igh ly d em an d in g, as a large q u an t it y o f lu brican t an d co n t in u o u s t em p erat u re m o n it o rin g are
req u ired cf. Sect. 3.2.11
. Th e flywh eel is d riven by t h e m ain m o t o r via a flat belt o r h igh -p erform an ce V-belt. W h en t h e m ain d rive system is
swit ch ed o ff, t h e flywh eel is brou gh t to a stan d st ill wit h in a m axim u m o f 30 s by reverse brakin g of th e m otor an d by an ad d it io n al p n eu m atic
brake. In iso lat ed cases, n o rm al car bo d y p resses an d t ri-axis t ran sfer p resses
are eq u ip p ed wit h m ech an ical creep sp eed d rive syst em s o f o n e st ro ke p er m in u t e. In t h is case, t h e d rive is ach ieved by a t h reep h ase m o t o r
act in g o n a wo rm gear wh ich act u at es t h e d rive sh aft via t h e brake flan ge o f t h e m ain brake. Th e t ran sm it t ed t o rq u e gen erally falls sh o rt o f
t h e n o m in al d rive t o rq u e. Ho wever, by m ean s o f a p n eu m at ic o r h yd rau lic servo syst em in t h e brake, t h e n o m in al fo rce m ay be ach ieved
fo r d ist an ces o f u p t o 10 m m . Th is is gen erally su fficien t fo r set -u p o p erat io n .
3.2.4 Clutch and brake
O n e o f t h e ch aract erist ics o f m ech an ical p resses is t h e clutch u sed t o t ran sm it t h e m o t o r an d flywh eel t o rq u e t o t h e gear sh aft an d , aft er
clu t ch release, t h e brake wh ich is u sed t o d ecelerat e t h e slid e, t h e t o p d ie an d t h e gear. Part icu larly wh en wo rkin g in sin gle-st ro ke m o d e, t h e
m asses in tran slation al or rotation al m otion m u st be brou gh t to a stan d - still after every stroke with in an extrem ely sh ort tim e: 200 to 300 m s for
large-p an el p resses an d 100 to 150 m s in u n iversal p resses. Con versely, after en gagin g th e clu tch , th e sam e m asses m u st be accelerated from
zero t o o p erat in g sp eed . Fo r safet y reaso n s, brakin g is gen erat ed m ech an ically by sp rin g p o w-
er. Th e clu t ch t o rq u e is calcu lat ed fro m t h e n o m in al p ress fo rce an d t h e req u ired wo rkin g d ist an ce, gen erally 13 t o 25 m m abo ve bo t t o m d ead
cen t er. Pn eu m atic sin gle-d isk clu tch an d brake com bin ation s with m in im u m
rotatin g m asses h ave been in su ccessfu l u se for d ecad es Fig. 3.2.7
.
61
M echanical presses
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
Pn eu m atic con trol system s with safety valves an d d am p in g d evices are reason able in cost an d gen erally com p ly with req u irem en ts. On e of th e
p roblem s of p n eu m atic system s, h owever, is th e lim ited switch in g fre- q u en cy of sin gle-stroke p resses an d th e en viron m en tal d am age cau sed
by wear to th e clu tch an d brake. In ord er to elim in ate th ese d rawbacks, h yd rau lic system s are bein g u sed in creasin gly in recen t years. With th e
aid of coolin g system s, th ese p erm it far h igh er switch in g load s p er tim e u n it an d are p ractically im m u n e to wear. In sin gle-stroke p resses, sep a-
rate u n its wh ich p erm it switch in g freq u en cies of u p to 30 m in h ave been u sed to p erm it m ore effective con trol an d to avoid oversh ootin g
an d u n d ersh ootin g by th e clu tch an d brake. Large-p an el tran sfer p ress- es u se clu tch -brake com bin ation s based on sin tered d isk sets with u p to
20 friction su rfaces an d tran sm ission torq u e levels of u p to 500,000 Nm . Th e co m p act d rive syst em u sed in sm aller m ech an ical p resses, co n -
sist s o f a flywh eel, clu t ch , brake an d p lan et ary gear in a co m p let e u n it . Su ch a syst em ach ieves a p art icu larly h igh level o f efficien cy wit h an
ext rem ely lo w m o m en t o f in ert ia an d sm all brakin g an gle, co u p led
62
Fundamentals of press design
clutch brake
friction blocks drive shaft
w ear indicator
Fig. 3.2.7
Single-disk clutch and brake in a large-panel press
Metal Forming Handbook Schuler c Springer-Verlag Berlin Heidelberg 1998
wit h a lo n g service life an d lo w m ain t en an ce co st s Fig. 3.2.8
. Th e elec- t ric m o t o r d rives t h e eccen t ric sh aft by m ean s o f a flywh eel, a clu t ch -
brake co m bin at io n t h at can be eit h er h yd rau lically o r p n eu m at ically act u at ed an d a h igh -p erfo rm an ce p lan et ary gear cf.
Fig. 4.4.4 . Th is
elim in at es t h e n eed fo r t h e red u cin g gear gen erally req u ired fo r u n iver- sal p resses. Co m p act d rive syst em s u sin g a h yd rau lic clu t ch -brake co m -
bin at io n are p art icu larly en viro n m en t ally frien d ly, as t h ey p ro d u ce n o abrad ed p art icles an d ru n at an ext rem ely lo w n o ise level.
3.2.5 Longitudinal and transverse shaft drive
