US2280602A - Drying fiber string material - Google Patents

Description

Patented Apr. 21, 1942 I DRYING FIBER STRING MATERIAL Peter D. Pl-ambeck, Chicago, 11]., assignor to Armour and Company, Chicago, 111., a corporation 01' Illinois No Drawing. Application July -19, 1939, Serial No. 285,457

2 Claims.

4 homogeneous and strong by immersing the strand in suitable swelling agents, such as alkaline solutions. After such strings have been swollen they are then deplumped and-finally dried. The drying problem has been a difiicult one to solve. The

wet strings cannot simply be placed in a drying atmosphere. Such strands are of indefinite lengths and in prior practices they-have been supported on pulleys in a'drying room where moisture is removed from the string.

Drying rooms are frequently very long,- as much as 100'feet, and the wet strands are led in parallel rows over a series of pulleys spaced as much as 50 feet apart. Consequently, several hundred feet of strand material will be undergoing drying at any particular time. One of the desired objects in any drying process is to so-dry the strand that no breaks occur in it during the drying stage. Thus, for example, the wet cord is taken directly from treating baths, usually a plain water-wash which follows the deplumping bath, and threaded over pulleys in the drying room as a continuous strand of indefinite length. The drying operation is continuous in the sense that the strand moves continu-. ously through the drying atmosphere. over the pulleys, and the dried strand is collected in coils, or on spools.

In consequence, a drying room will contain several hundred feet of strand material undergoing drying, and under varying degrees of tension. During the drying operation as hitherto practised, any particular desired tension cannot be maintained throughout the entire drying stage .without danger of breakage.

As practised hitherto, the dried strings sufier a loss of tensile strength. This is probably because theouter layer of fibers in the strand dries first, forming a relatively thin, dry outer shell while the core within the string is still-wet. This outer shell tends to fracture and crack as the long strand is guided around pulleys in the drying room. The net result is that the actual cross section of the homogeneous portion of the strin is reduced with resultant reduction in tensile strength. While this explanation may not be correct,-nevertheless, it is an observed fact that strings of this nature. when dried under the usual conditions of temperature and pressure, do frequently break while under tension.

I have, therefore, investigated the drying process, and I have discovered that by observing certain specific values of j temperature and humidity in the drying atmosphere I can obtain a string which is strong and which will not break under the usual drying andfinishing conditions. By finishing conditions I mean those operations usually employed after the string has been dried. Such operations are, for example, sanding and polishing. By maintaining certain temperature and humidity relationships which I- have discovered the outer layer in the strand does not g dry too rapidly, and hence any cracking is avoided. By the process of the present invention the drying takes place more uniformly and the outer layer does not completely dry until the inner core of the strand is substantially dry.

As stated, the present invention is directed primarily to the drying of spun and twisted collagenous-fibrous materials which, in strand form,-

have been subjected to swelling and deplumping agents. I shall, therefore, describe my invention more particularly with reference to such cords.

These cords, which are similar to cat gut' in appearance, and which are used as sutures, tennis strings, musical instrument strings, and the like,'are made from animal tendons or sinews. The dried animal tendon is first hammered to break the outer shell and release the fiber within the shell. These fibers are then carded, formed into a roving, the roving spun into a yarn, and

a plurality of yarn strings twisted to form the final cord or strand. This strand is then immersed in swelling agents, usually dilute solutions of alkalies, such as caustic soda. Such swelling agents cause the fibers in the strand to swell and the entire preassembled cord is thus rendered homogeneous. Before such a swollen strand can be used it must be deplumped in a bath which neutralizes the alkali in the cord and causes the strand to shrink back to normal size. Finally, the deplumped cord is washed in water to remove chemicals used in the swelling and deplumping. The washed cord can then either be directly subjected to the drying conditions f the present process, or it can be first immersed in any suitable binding solution, such as serum albumin or egg albumin, and then subjected to the drying operation.

The present invention is primarily directed to the drying operation and not to the particular been made. is then run Over pulleys in a drying room in the usual way. I depart, however, at this stage from the teachings of the prior art, which have advocated a rather rapid drying. In my drying operation I maintain the atmosphere in the drying room at relatively high humidity.

This distinguishes my process from the customary drying procedure which has hitherto employed atmospheric conditions of low humidity. In my process the drying temperature should range from about 75 F. to 90 F. and the relative humidity should range from about 83% to 89%. More precisely the temperature in the drying room can be 76 F. with a wet bulb reading of 73 F. corresponding to a relative humidity of 84%. Under these condition drying is substantially complete in about three-quarters of an hour, depending largely on the diameter of the cord. The strings, as they come oil the drying .line will ordinarily contain about to of moisture, some of which will be lost during subsequent handling. The strings are' not dried to bone dryness. But they are: dried under such conditions that much less tendency to fracture and break is realized, and the strings retain their original tensile strength.

In another example, the strings, as prepared above, are dried in a drying atmosphere having a temperature of about 90 F. and a relative humidity of 89%.

After drying the strings so prepared can be finished by sanding and polishing, and can be dyed to give the brightly colored tennis strings of commerce. Or they can be polished and finished to give strings for violins, harps, and other washed; and after the tanning treatment the strings are then dried in the manner described above.

The drying processes of the present invention are particularly applicable to the drying of strings made in accordance with my 'co-pending application, -Serial No. 285,458 filed July 19, 1939,

chemical treatments applied to the preassembled iwherein I describe the swelling of the Pr'eassembled sinew fibers in a plurality of alkaline baths of increasing concentrations whereby the fiber angle in the string is maintained throughout the process.

I Although, in the above description, I have re-' ferred to specific temperatures for the drying air, I regard humidity as more important than the temperature of the air. By maintaining the humidity relatively high I'can operate the drying temperaturesconsiderably above those hitherto used without destroying desirable characteristics in the finished string. The temperature and humidity relationships should be such that no apparent swelling of the string, as may be judged by gauging, occurs-during the drying process. That is to say, the diameter of the string should progressively decrease during the drying rather than increase. The present invention deliberately avoids the use of hot, dry air as the drying medium. Such drying conditions are detrimental. But because of the relatively high humidity employed in the present case drying temperatures can exceed those hitherto used.

Although I have more specifically referred to the preparation of the strands prior to drying by chemical treatment involving the use of alkalis, my invention is applicable to strands or strings which have been processed in acid' solutions in accordance with prior art practice.

Having thus described my invention, what I claim is:

1. In the drying of homogeneous strings, while in the form of long, continuously moving lengths,

and which have been prepared from collagenous fibers which have been spun and the string thus formed swollen with alkaline swelling agents and thereafter deplumped and washed, the step which comprises exposing the wet strings, as long, continuously moving lengths, to an atmosphere having a temperature of about 75F. to 90 F. and

' which has a relative humidity from about 83% 2. In the drying of homogenous strings, while in the form of long, continually-moving lengths,

- and which have been prepared from collagenous has a relative humidity from about 83% to 89%.

PETER D. PLAIVLBECK.