Part 8

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 classification of necessity applies to the trade and gives a size for almost any character of work there is, though another general classification that is used principally abroad, is as follows:—

Thick corks having more than 31 millimeters in diameter. Ordinary or commercial, from 25 to 31 millimeters. Bastard corks, from 23 to 25 millimeters. Thin corks, having less than 23 millimeters.

Millimeter = .0394 inch.

These classes of sizes are of course divided again and again by the manufacturers. To this size classification 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-class 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 accumulates, 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 shipped 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 ship 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 washing 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 washing 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 pass 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 principal 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 washing 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 retards 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 principal 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 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.