In giving the processes of the methods used in the conversion of the
corkwood waste and virgin corkwood, which is classed as waste, it will
not be possible to go too far into the details, as most of them are
secret, and in justice to those who use them a résumé is all that will
be incorporated in this monograph. But this will give a good idea and
understanding of the utilization, which is all that is intended. As in
the first processes of corkwood manipulation the best is taken first;
so, in the department of waste utilization, a process is now used
whereby the best scrap is made into cork disks for the Crown seal as
described, and serves its purpose well.
This scrap is taken and granulated in an iron rotary cutter mill, to a
degree of fineness that will pass a 1/8″ mesh, it is then screened and
mixed with a secret binder that has a wonderful holding quality; it is
then dried by steam and pressed into sheets by hydraulic presses, dried
again, and then stamped out in the usual manner. There is no waste to
this process as the unused portions go back to the grinders again and
through the usual process.
Granulated cork is made by grinding the waste in ordinary metal roller,
cage or bur mills, and then screening same for the various degrees of
fineness; if cork-flour is desired, a tube mill may be used.
These two uses are generally confined to the best scrap, but there still
remains a large quantity which has a great value. A portion of this is
made into Spanish black by carbonizing same in a closed iron kettle, or
retort, and then grinding same in a regulation ball mill, until the
desired fineness is obtained; this process producing a very fine black.
The above uses in no degree exhaust the amount of scrap corkwood that
leaves the various factories here and abroad, nor is its usefulness
expended, for there is one use to which cork scrap is being put that
bids fair to rival the stopper industry in importance, and that is in
the form of cork-board for insulating purposes.
The processes for the making of cork-board differ in many ways, widely
divergent in principle. The corkwood waste and virgin cork are broken up
and chipped in an ordinary iron mill as a preliminary to all processes;
in one, claimed to be the best, this chipped material is poured into
iron molds the desired shape of the slab, subjected to heavy pressure
and run into an oven kept at about 800 to 900 degrees Fahrenheit. This
oven, being a low brick type, resembling a lear and heated by coal
fires, the slab molds being drawn through on an endless chain, which
runs at a speed to keep the cork in just long enough, for the resin in
same to exude and bind the little particles together; the cork is also
charred in this process, thereby converting it into a carbonized
cellulose which makes it an excellent material for insulation.
Steam-heated hydraulic presses are also used for making small tile,
etc., being the same principle as above, without the charring.
The other process involves the use of tar, pitch or asphaltum, as a
binder for the cork particles, and in one, the cork is mixed with a clay
before being mixed with the asphaltum. The binder being heated in steam
jacketed kettles, and in one it is mixed in the proportion of one to
four, while in the other it is forced into the mass under pressure and
then drawn out again by vacuum, both mixtures being poured into molds of
the desired shape of the slab or in large molds, to be cut up after, and
subjected to heavy pressure, the sawing being done by an ordinary
rip-saw, cutting the block into any desired thickness of slab.
The above described processes do not include all of the various
manipulations of corkwood, for there are innumerable things as stated
under the “Uses” for which there is a necessity of mechanical operation,
in their making; but the general processes are as stated and will cover
most all.