Page 509 - 04. Subyek Engineering Materials - Manufacturing, Engineering and Technology SI 6th Edition - Serope Kalpakjian, Stephen Schmid (2009)

Section 19.2 Extrusion 489

Extruders generally are rated by the diameter, D, of the barrel and the length-
to~diameter (L/D) ratio of the barrel. Machinery costs can be on the order of
$300,000, including the cost for the equipment for downstream cooling and wind-
ing of the extruded product.

I9.2.l Miscellaneous Extrusion Processes
There are several variations of the basic extrusion process for producing a number
of different products.

Plastic Tubes and Pipes. These are produced in an extruder with a spider die, as
shown in Fig. 19.421 (see also Fig. 15.8 for details). Woven fiber or wire reinforce-
ments also may be fed through specially designed dies in this operation for the pro-
duction of reinforced hoses that need to withstand higher pressures. The extrusion
of tubes is also a necessary first step for related processes, such as extrusion blow
molding and blown film.

X

Breaker plate
Polymer melt
Extruder barrel
Section A-A
B Section f
%
Screen pack
_,
Melt flow 5/ Q »:'f Spider |995 (3)
direction V
B
legs (3)

|\/|and,»e| Air channel Air in

(8)

Extruder 1
.EE "
.zjgi
Plastic melt:
‘§f§i
two or more layers

Parison

V Mandrel '~» ~ \;
Extruder 2
(D)

FIGURE l9.4 Extrusion of tubes. (a) Extrusion using a spider die (see also Fig. 15.8) and
pressurized air. (b) Coextrusion for producing a bottle.