Cork: Its Origin and Industrial Uses Part 4

In taking up the processes of manipulation we naturally start from the beginning, but the beginning in this case has a peculiar significance as relating to the whole, for it is apparent to utilize corkwood to the fullest extent its qualities must be studied and the best, used first, so that the beginning of the corkwood industry is peculiar in this fact, that it takes the best part and leaves but sc.r.a.p, which must be studied carefully to realize the value lost in the first process; therefore, in the manufacture of one article of corkwood it is necessary to make provision for the sc.r.a.p created, and this is a characteristic of all such establishments.

RAW STOCK

The baled cork, as received, is our first consideration, for its bulk, being out of all proportion to its value, attracts the attention at once.

As in all business where the raw stock is conveyed from a distance and there is a possibility of delay in s.h.i.+pments, a large stock must necessarily be kept on hand, and this feature is very p.r.o.nounced in and about a "cork factory." Great piles appear in the open or within large sheds, covering much s.p.a.ce, and sometimes in the factory itself.

This stock is carefully watched and care taken to keep it large enough to supply all needs for a long time as a shortage in raw material would not only mean no work, but the loss of business, due to the inability to supply first-grade material, for this is the prime factor, the various other grades being compelled to await a favorable market. Appended is a diagram that will give some idea of the utilization of corkwood.

The corkwood bale as received, measures as a general rule 2' 2'7? 4'

and is securely strapped with iron bands about one inch in width and a thickness of 1/16? to 1/32?, and the weight depending upon the quality of corkwood ranging from 150 pounds to 200 pounds per bale.

SORTING

The first operation, that is, the first thing done with the corkwood, is the sorting. This is becoming more important as the uses of cork increase, as various grades can be used for so many particular things now, without the necessity of being called a by-product; but the princ.i.p.al divisions are: superfine, fine, common and coa.r.s.e.

These of course are now extended to many cla.s.ses, and is resulting in careful scrutiny of the s.h.i.+pments and stock, the sorter becoming an expert, and an increasing factor in the business. His knowledge not only including the grades of corkwood, but the uses to which the various grades may be put so that waste is avoided and the full value gotten out of all.

CORK STOPPER MAKING

After the sorting, the slabs are placed in steam boxes and subjected to a steam bath, which it is claimed softens the material and also prepares it for the sc.r.a.per, who cleans and removes the dirt and callous or "raspa" acc.u.mulated in its mountain home. This sc.r.a.ping is done either by hand or machine, the handwork being done with a short handle, curved bladed knife called a "doladera," raspador or raspeta: a workman being able to sc.r.a.pe from two to three metric quintals of cork in a day, or ten hours. The sc.r.a.per machine being a vertical steel shaft carrying several knives placed at a very slight helix and making about 1400 revolutions per minute and will sc.r.a.pe from ten to twelve metric quintals[35] per day or ten hours. Cutting the slabs into strips or fillets (tiras o'rebanadas) is the next step. These strips, the width of which is equal to the length of the cork to be cut, as the cutting is done across and not with the grain, were formerly cut by hand with a knife having a flat surface and curved edge called "cuchilla de rebanar," but now replaced by the circular knife, which operates the same as a rip-saw. From here the strips go to the stopper-makers'

punches or blocking machines. This machine has a rotating tubular die with sharpened edges of the diameter of the cork to be cut, made to revolve about two thousand revolutions per minute, the operator having a foot lever attachment which permits him to thrust the die through the strips of cork as he holds it against a resisting piece parallel with the operating plane of the die. Thus, he can punch out many thousands of corks a day, the noise of the punches being a very characteristic sound in all such establishments. The operator, of course, must use care to avoid defective spots in the bark, and also to cut the corks out as closely together as possible so as to reduce waste to a minimum. For it is here that the cork manufacturer seems to lay his particular lament.

If he could but make his corks the sizes most in demand, s.h.i.+p them and thereby do a business that would clearly figure up the year's work, and perhaps keep a surplus on hand for unexpected orders. But this he cannot do, for almost every cork he cuts there is enough waste material to make three or four smaller sizes, and this he fain would discard if it were not for the possible profit there is in it; and consequently in almost every cork factory will be found a large surplus stock of all sizes, and the owner anxiously hoping that some one will take them off his hands.

[35] The metric quintal is used officially in Spain, which is equal to 220.36 pounds, the Catalon quintal equaling 91.71 pounds.

The stoppers which come from these machines are round with parallel sides. If tapered corks are desired, larger at the upper end than at the lower, the cylindrical or straight pieces must be pa.s.sed through another machine which handles them deftly, holding them against the edge of another circular knife; seemingly motionless, the only outward indication of the speed with which the keen blade is revolving being a delicate shaving which curls upward for an instant, and then is drawn away by air suction to the waste bin, where this material is all collected and used in various, useful ways as will be shown later. In cutting the corks, although care is exercised, many will be imperfect and defective, and in order to utilize them they are cut into smaller sizes by men who sit at low tables and deftly handle the sharp-edged knife, which with one stroke reduces the cork to the size that it can fill, using a scale which is apparently standard with all cork dealers.

The general standard of corks or stoppers, known as the United States standard, is as follows:

SCALE OF DIAMETER OF STOPPERS

_United States Standard, showing Diameter at Large End_

No. 0 3/8 inch No. 1 7/8 inch.

" 2 1/2 " " 3 9/16 "

" 4 5/8 " " 5 11/16 "

" 6 3/4 " " 7 13/16 "

" 8 7/8 " " 9 15/16 "

" 10 1 " " 11 1-1/16 "

" 12 1-1/8 " " 13 1-3/16 "

" 14 1-1/4 " " 15 1-5/16 "

" 16 1-3/8 " " 17 1-7/16 "

" 18 1-1/2 " " 19 1-9/16 "

" 20 1-5/8 " " 24 1-7/8 "

" 22 1-3/4 " " 26 2 "

Length is generally designated as short, regular, extra long, and the shape as tapered, or straight.

This cla.s.sification of necessity applies to the trade and gives a size for almost any character of work there is, though another general cla.s.sification that is used princ.i.p.ally abroad, is as follows:-

Thick corks having more than 31 millimeters[36] in diameter.

Ordinary or commercial, from 25 to 31 millimeters.

b.a.s.t.a.r.d corks, from 23 to 25 millimeters.

Thin corks, having less than 23 millimeters.

[36] Millimeter = .0394 inch.

These cla.s.ses of sizes are of course divided again and again by the manufacturers. To this size cla.s.sification must be added a quality distinction, and this generally takes the same as before described, in sorting the cork-board, grading down from the best which is tawny or pink in color, with a fine texture, free from cracks, stone cells, or other blemishes.

As has been stated, the punch is now employed in most corkwood establishments, but there are still a few who do the work by hand and maintain that the best results are obtained in this manner.

Hand-cut corks or stoppers are used mostly for the high-cla.s.s wine trade and are a little more expensive than machine cut. There is also a hand machine for shaping corks, which consists of a knife, the blade of which is placed horizontally, joined generally to a piece of wood, to which a back and forward movement is given similar to that of a carpenter's plane. In moving, the knife turns the square cork, or whatever shape it may be, by a series of belt attachments, and takes off a strip of cork (palilla) more or less thick, according to the distance from the axis of the cork and the edge of the blade; the principle being the same in the power machine, if these are parallel the resulting cork will be cylindrical, and if not, it becomes conical.

The standard size stopper is the prime use to which corkwood has been put, and in the making of it the best material is used; this material coming in varying thicknesses, it sometimes is difficult to secure enough for making "champagnes," so some manufacturers produce a stopper that answers the requirements by fastening two pieces of thin superfine corkwood together with a rubber cement made by dissolving pure Para rubber in disulphide of carbon, which makes a very good binder and not lessening the quality service to any appreciable degree.

After the corks are cut, the ends are not always as even and as smooth as desired, so they are taken to a sandpaper wheel which revolves very rapidly in an upright position, and against this the corks are held for a few seconds until the surface becomes smooth and straight, the dust created being collected and used in various ways. (See "Waste Utilization.")

CORK-DISK MAKING

(See "Waste Utilization")

Since the Crown Seal stopper, for beer bottles particularly, has come into vogue, there has been a great demand for cork disks which form the medium for air tightness and this has given the cork-worker an opportunity to utilize a grade of corkwood that usually had but little commercial value, that is, a thin bark.

It may be well to state here for the uninitiated that the Crown Seal is made up of a tin cap, corrugated on the lapped edge, for gripping the top of the bottle, a corkwood disk and a water-proof paper between the disk and cap, a very ingenious device.

As you have already read in a previous chapter that corks are cut vertical parallel, or, to state more clearly, the axis of the stopper must be parallel with the axis of the tree that furnished the bark; and the desired direction is easily recognizable by the colored striae due to the annual layers of suberous substance that are observed in the direction of its axis, this rule being followed because cork is found to be more impervious to liquids if cut in this manner. It will be readily seen that if disks are cut horizontally parallel, that is, the annual layers running at right angles to the axis of the disk, this grade of cork can be utilized to great advantage. The mode of cutting is by a horizontal revolving blade, which slices the cork to the desired thickness, usually a quarter of an inch, and then it follows the usual course of punching, etc. From these operations a great deal of waste acc.u.mulates, and this would be a great loss if methods were not devised for its utilization. Many firms work up this waste on the premises, but most of it is s.h.i.+pped out and its conversion forms a separate part of the corkwood industry, which will be described later. We might say now that the cork is made, for it has been cut and shaped into the desired commercial size; and all that remains is to sort them and s.h.i.+p them away. But if commerce desires sizes and quality, it has also exacted many other requirements of a cork before it is acceptable and we will now take up the further manipulation of cork before it leaves the factory. Naturally, this corkwood, coming such a distance and being handled by so many in the general processes just described, gets more or less dirty, and aside from that perhaps in the growing the tissue has not remained as white as is desired, so before the cork can leave the factory it has to be washed or cleaned. And in this was.h.i.+ng I will not say that there is not an attempt to improve the looks of the corks in order to get a better price. Now this was.h.i.+ng or bleaching is carried on in the simplest manner and is just soaking the corks in water and a chemical and then placing them in a centrifugal spinner, which is nothing more than a perforated receptacle made to revolve within an iron jacket, which is connected to a drain, naturally forcing the material against the periphery and thereby causing the excess water and acid to pa.s.s out through the perforations, this system becoming quite common in cork factories to-day, greatly facilitating the drying, which is done mostly by the atmosphere. This is all there is to the mechanical part, but curiosity prompts us to inquire what chemicals are used to clean the corks, so I have ascertained the princ.i.p.al ones, but of course every manufacturer will have his own way of doing this part of the work, although the principle remains the same. An old way was to wash them in water containing chloride of tin or oxalic acid and then subjecting them to the fumes of burning sulphur, but the sulphur bleach has been discontinued. Bioxalate of potash has also been used in solution, as also chloride of lime, ammonia and sulphuric acid. Another way is to wash in a 10 per cent solution of hydrochloric acid and then immerse in a solution of sodium hyposulphate and hydrochloric acid, finally was.h.i.+ng with a solution of soda and water. All of these produce the desired effect when mere cleaning and bleaching is all that is required: but in the poorer grade of cork, mostly a thick cork that has been jaspered or contains micro-organisms, a system of treatment with formol or methylal, ethyl alcohol or spirit wine and formaldehyde and impregnating with casein has been used. These bleaches are applied to regular stoppers and disks alike, but in addition to this the disks are given a bath of hot paraffin, or glycerine and paraffin, which improves their resistance and r.e.t.a.r.ds discoloration. This generally being done in a steam-jacketed kettle, or tumbling barrel, and then placed in a centrifugal to remove the excess of water and paraffin.

In some factories, and when the customer requests it, the name is branded upon the stopper by irons heated by gas, gasolene or in a coal fire, automatic gas heated machines being most general.

In the foregoing it has been shown how the stopper and disk are made, and although there are many different manufacturers of corkwood stoppers, it will be found that the _modus operandi_ just described is followed generally, with perhaps a variation in the details. The waste material, "recortes" as stated is collected and used in various ways, but either in conjunction with other materials or alone in a granulated or powdered state.

The following chapter will enumerate the three princ.i.p.al uses of waste corkwood, and as these cover the fundamentals of the other uses it will not be necessary to describe them, e.g., linoleum, made by mixing cork-flour and linseed oil.

WASTE UTILIZATION

In giving the processes of the methods used in the conversion of the corkwood waste and virgin corkwood, which is cla.s.sed 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 resume 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 sc.r.a.p is made into cork disks for the Crown seal as described, and serves its purpose well.

This sc.r.a.p is taken and granulated in an iron rotary cutter mill, to a degree of fineness that will pa.s.s 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.