m\


KINDS  OF  CLAYS  231

Dry-press  (PL  XIII)  and  semi-dry-press  process. — This  process  is
commonly  used  for  the  production  of  front  brick,  but  in  some  States  is
extensively  employed  even  for  common-brick  manufacture.  The  clay  is
powdered  and  then  pressed  into  steel  molds  in  a  dry  or  nearly  dry  condi-
tion. In  order  to  prepare  the  clay  for  disintegration,  it  is  usually  stored
in  sheds  for  some  time  before  being  used,  and  is  then  broken  up  either
in  a  disintegrator  or  a  dry  pan  before  passing  to  the  screen,  which  is  com-
monly from  12  to  16  rnesh.  The  molding-machine  consists  of  a  steel
frame  of  varying  height  and  heaviness,  with  a  delivery-table  about  3
feet  above  the  ground,  and  a  press-box  sunk  into  the  rear  of  it.  The
charger  is  connected  with  the  clay-hopper  by  means  of  a  canvas  tube,
and  forms  a  framework  which  slides  back  and  forth  over  the  molds.
It  is  filled  on  the  backward  stroke,  and  on  its  forward  stroke  lets  the
clay  fall  into  the  mold-box.  As  the  charger  recedes  to  be  refilled,  a
plunger  descends,  pressing  the  clay  into  the  mold;  but  at  the  same  time
the  bottom  of  the  mold,  which  is  movable,  rises  slightly,  and  the  clay
is  subjected  to  great  pressure,  which  may  be  repeated  after  a  moment's
interval.  The  plunger  then  rises,  while  the  bottom  of  the  mold  also
ascends,  with  the  freshly  molded  bricks,  to  a  level  with  the  delivery-
table.  These  are  then  pushed  forward  by  the  charger  as  it  advances  to
refill  the  molds.
