US2638628A

US2638628A - Apparatus for production of strip stock from polyamides

Info

Publication number: US2638628A
Application number: US106014A
Authority: US
Inventors: Louis L Stott; Paul L Shurr
Original assignee: Polymer Corp
Current assignee: Polymer Corp
Priority date: 1949-07-21
Filing date: 1949-07-21
Publication date: 1953-05-19
Anticipated expiration: 1970-05-19

Description

May 19, 1953 1.. STOTT ET AL APPARATUS FOR PRODUCTION OF STRIP STOCK FROM POLYAMIDES 4 Sheets-Sheet 1 QM hm Filed July 21, 1949 May 19, 1953 L. STOTT ET AL I 2,638,628

APPARATUS FOR PRODUCTION OF STRIP STOCK FROM POLYAMIDES Filed July 21, 1949 4 Sheets-Sheet 2 Iinventor mzw 8g PWMJ/m y 1953 L. STOTT ETAL 2,638,628

APPARATUS FOR PRODUCTION OF STRIP STOCK FROM POLYAMIDES Filed July 21, 1949 4 Sheets-Sheet, 3

Gttomcg May 19, 1953 2,638,628

APPARATUS FdR PRODUCTION OF STRIP STOCK FROM PQLYAMIDES L.-L. STOTT ETAL 4 Sheets-Sheet 4 Filed July 21, 1949 INVENTOR jwafi.

W mfiw Patented May 19, 1953 E'D STATE-S PATENT QFFICE 2,638,628 APPARATUS ort PRo-o cTIoN F STRIP STOCK FROM PO'LYAMTDES' Eouis L. St'ott and Paul L. Sh-urr, Reading; Pa,- assig'nors-to The-Pblymer Corporation, Reading, Pa., a corporation of Pennsylvania Application July 21, 1949; Serial No. 106 014 2' Claims.

This invention relates to" equipment for form-- ing" strip stock from nylon, i. e., from synthetic linear polyamides.

The inventionis concerned with that type of strip forming operation in which the molten nylon' is continuously fed to the entrance nip of a pair of forming rolls; the formed strip being drawn from the rollsunde'r tension. In this general type of operation certain special prob' lems are encountered; particularly when forming' relativelythick strip stock, for example strip stock at least .050 inch in thickness.

The inventionrelates to the establishment of certain operating temperatures for the molten nylon being fed to the roll'sand for the rolls themselves; and also=to*the feeding ofthemolten nylon to the formingrolls in a special manner and" the drawing of" the formed strip from. the rolls at an angle to* the plane of the pass be"- t'ween-the rolls; All of'the'se conditions are conrel'ate'd ancf arrangedto enable production of sound" strip-stock even of substantial thickness; for instance .090 inch in thickness.- 7

Itis' of importance in an operation: of the character referred to above that the roll t'em" perat'ure be quite accurately maintained for a given condition of strip production, for instance with a' given temperature and: rate of feed of the molten nylon to the forming? rolls, and with this in mind; the invention provides: for. accurate maintenanoeof roll temperature; by-the oiroula' tion' ofi a heat transfer medium through the rolls; as will further appear.

.AE further advantage of the capability of accurate regulation of roll te'mp'erature i's thatv some of the properties of-t'he formed strip may'thereby be varied and aoc'urately controlled at will. For instance; the tensile strength, elongation and rigiditymay be controlled by regulation of theroll temperature.

In addition to the more or less general object of ensuring production of sound} stripespecially of relatively heavy gauge stock, the invention further" has as an object avoiding pulling out. of the strip from' the rolls bef'o 're complete solidification of the molten-nylon throughout the thickne'ssof the strip.

Other objects of the invention include arrangement of the equipment to facilitate: ad'- justment-or' regulation thereof so as to accom moda-tethe equipment to the prcductiomofi strip stock of different thicknesses and to accommodate the equipment to the" handling oi?" various different nylon-or'polyamide materials; For example, the equipment may readily be" adjusted to" effectively handle the relatively highi melting point pol yamides as polyhexamethylene adipanii'de' and pbl-yhexamethylene sebacaniide' or the lower melting interpolymers of these two and otherpo-lyai'niiies. The equipment can also te used successfully with the methoxymethyr substituted polyamides. All these materials may or may" not contain plasticizers; fillers", antioxidants or other ingredients.

Still other objects of the invention includeprovision for handling the polyamid'e in such Inanner'as to minimize opportunity oi the poly-"- amide" to" oxidize in the molten condition,-. and to' minimize tendency toward development at gas or air bubbles in the formed strip or development of surf-ace markings thereon.

How the foregoing and other objects and ad'-* vantages are attained will appear more fully hem the following description referring to the accompanying drawings, in which Figure l isa longitudinal vertical sectional view through equipment arranged? according to the present invention;

Figure 2 is a transverse vertical section taken as indicated by' the section" line 2- 2 on: Figure 1";

Figure 3 is a horizontal view of certain por tions of the equipment taken substantially as in cheated by theline 3' 3- on Figure 1, but: with upper portions of the equipment removed;

Figure 4 is a longitudinal sectional view throughthe nozzle for delivering molten nylon to the forming rolls; the arrangement ofthis figure being shown on an enlarged scale Figure- 5 is an enlarged detailed view of a portion of the nozzle; I

Figure 6 is an axial sectionalview through one of the forming rolls this view being taken as indicated by the section line 66' on Figure 1, but beingshown on an enlarged scale and. also further showing connections for the circulation of a heat transfer medium throughthe roll;

Figure? is a plan view of the pair offorming rolls and of the connections for supplying'a heat transfer medium thereto; and

Figure 8 is a sectional View of a detail taken as indicated by the line s -s' on Figure" 6-2 The equipment illustrated in Figures- 1- to' is, inclusive; comprises a vessel 1 adapted to" com tain a liquid cooling bath, the level at which appears at L in Figure'hl- Liquid may he introduced iii-tn the vessel 1' through the inlet con necticn 8, which may advantageously be valven.

A frame l0 is-mounted' at the upper edge of the vessel l and serves-asa support for the pair of. forming rolls l l t'zwhich are fixed on shafts l3-l4. The mounting of the rolls themselves, as

illustrated herein, conforms with that more fully disclosed and claimed in copending application of Robert C. Rahm, Serial No. 39,954, filed July 21, 1948, issued as U. S. Patent No. 2,627,085 on February 3, 1953, which application is assigned to the assignee of the present application. The adjustment and drive mechanism associated with the rolls also conforms with the disclosure of said copending application and since the present invention is not concerned with the arrangement of these parts per se, they need not be described in detail herein. Briefly, however, it is noted that the rolls are adapted to be driven from a power shaft I5 carrying gears I 6l'I which mesh with gears I8I9 fixed on shafts 202l, the latter shafts carrying worms, such as indicated at 22 and 23 which mesh with worm wheels such as shown in Figure 3 at 24 and 25, these worm wheels being fixed to the roll mounting shafts I3 and I4. The roll II is adjustable with relation to the roll I2, so as to vary the spacing between the rolls by means of an adjustable support for shaft I3 including traveling blocks 26 associated with manually adjustable screws 21.

According to the invention, a screw extruder is preferably employed for melting the polyamide being used and for feeding the molten polyamide to the entrance nip of the forming rolls. The details of construction of the extruder device itself need not be considered herein but it may be noted that this device has a hopper 30 adapted to receive the polyamide in granular form. The polyamide is fed from this hopper into the bore of the extruder proper indicated at 3I, in which a screw advances the material (toward the left when viewed as in Figure 1). The material is heated and melted by heater elements indicated in outline at 32 and is delivered in molten condition through the nozzle 33 which has its delivery opening close to the entrance nip between the rolls II-l2.

The formed strip is delivered downwardly from the rolls in an angled run such as shown at S. This initial run of the strip from the forming rolls is defined by placement of a guide element, preferably a flanged roll 34 below and to one side of the plane or axis of the pass between the forming rolls II-I2. After passage around the guide element 34, the strip travels in a run S upwardly at an incline, being drawn by the pairs of

drawing rolls

35 and 36. After delivery from rolls 3B, the strip material may be delivered to a trimmer or it may be wound up or otherwise packaged for shipment or the like.

The guide element 34 is mounted between the lower ends of a pair of generally upright supporting straps 3'I--31, the upper ends of these straps having slots 38 therein cooperating with supporting bolts 39 by means of which the straps are carried by supports 40 secured to the frame Ill. The bolts 39 serve to adjustably fix the guide element 34 in any of a variety of positions including that shown in full lines in Figure 1 and also other positions, for instance as shown in dot-and-dash lines at 34a in Figure 1.

For purposes which will appear more fully hereinafter, a refrigerating coil 4I may be positioned below the surface of the liquid in the cooling bath. This coil may be employed for temperature regulation, advantageously for cooling, the liquid of the bath through which the strip is drawn after it is formed by the form ing rolls.

It is preferred to employ a nozzle for the extruder of the type shown in Figures 4 and 5.

The nozzle member 42 of this arrangement extends beyond the feeding screw of the screw extruder and is provided with a cavity 43 at its entrance end for receiving a screen pack for screening the molten nylon before entrance into the nozzle. The nozzle member 42 is surrounded by heater elements diagrammatically indicated at 44, and the delivery nozzle proper is associated with the delivery end of the member 42. This delivery nozzle comprises a pair of

plates

45 and 46, the former comprising a flat plate and the latter having an aperture 41 for cooperation with the nozzle member 42 and further having a flaring delivery recess 48. As is shown, this recess flares so as to spread the molten nylon along the entrance nip between the rolls. In addition, the recess 48 is tapered transversely of the member 46 so that the delivery passage becomes progressively thinner as it widens toward the delivery port. This configuration is of importance since it maintains the column of material being'fed under pressure all the way to the point of discharge. This aids in minimizing formation of gas bubbles in the material.

1 Indeed, in the construction of the entire nozzle, the several passages thereof are of progressively dimensioned cross-sectional flow area, so that somewhat of a back pressure is imposed on the material all the way back tothe feeding screw in the extruder itself. Thereby the formation of gas or air bubbles within the material delivered from the extruder is greatly diminished.

It is of importance that the nozzle member 42 is maintained at a temperature above the freezing point of the polyamide and attention is also called to the fact that the heater diagrammatically indicated at 44 in Figure 4 extends all the way out to a point adjacent the nozzle tip, and this aids in maintaining even the nozzle tip at the desired high temperature.

The structure and arrangement of the forming rolls themselves is best illustrated in Figures 6, '7 and 8. As seen in Figure 6, roll I I is provided with a. hollow interior, being closed at one end by the closure member 49. At its other end the shaft I3 isalso provided with an interior passage through which a tube 50 projects, with its inner end lying internally of the roll itself. Spaced discs 5| are arranged within the roll, each having an oversized central aperture accommodating the tube 50 and further having additional apertures as indicated at 52 for circulation of a heat transfer medium. Toward its left end when viewed as in Figure 6, the tube 50 is extended for connection with the flexible hose or the like 53. Another flexible hose 54 communicates with the annular passage 55 formed between the tube 50 and the inner wall of roll shaft I3, this latter connection being made through a fitting 56. Suitable internal rotative joints are provided to accommodate rotation of the roll I I and its shafts I3, independently of the fluid supply and

discharge connections

53, 54 and 55. Circulation of heat transfer medium is effected by introducing such medium through the flexible hose 53 from which it is delivered to the tube 50 and thence to the interior of the roll itself. The return circulation is effected through the ports 52 in the discs 5| and also in the annular space surrounding the tube 50, discharge being effected through the annular passage 55 and ultimately through the flexible hose 54.

Similar connections for circulation of heat traisfertmediunxthroueharoll:laarei'providedithef flexible hosereonneetionsa for this r011." beinafindicatediin-Figureflt at'k and-158i.

virtue-oi; the employment; of; the. flexible connectlonsi required adjustments: in relative: positions of: the rollsmay be accommodated;

The heat: transfer?" medium-mas! be" circulated through? the:- rolls? for the purn'oser o-t' heatin'gup" the rolls prior: to feedlot molten nylomth'eretoi' and during: strip formation. thisheat transfer medium is employedi for closer regulation of; the rollwtemperature;.aocordiiigtothe particulamcom ditions'of operatiorrw Such close regulationrisaduantageously achievediby empioymentiof'rtliermo StHtiliOflHtllOt'Gf heat: transfer equipmentthrough: which the medium'zis passedEafter'it-is discharged? from: the? rolls and before? it. is" returned thereto. For mosttoperations, :esp eoial1y= where? substantial quantities offmoltenmai erial are being'fed'litoz the: rolls; the; heat transfen rtredium; serves to heat away from. theuollsr.

The: rolls H and It: should: desirably" haveav nicely polished: or smooth sur-iacelan'di may-be made of aavamiety ofsmetals;inotuding suchmetalm as i-tool steeL-stainless steel; et'oc 'Iihet pairs of drawing rolls a amltflr are ad;- vantag eouslymade off'rulibeitor somasimilar 're silient' compound havi z'i'ga relatively: high: if-tictntciri characteristics to: providev for efiective gripping and drawing: of the: formed strip. The" diawing': rolls should be drivemart Ta -ratesomewhatfi'fastei than; the rate of dtiv-ing of? the forming -rolls 1-4 2, and the pressureof interengagement of thedrawing rolls with the termed strip; andialsw them-fictional charaoteristics ofithe 'di'awingfirolls? sliouli be such" that; some. tension is provided; whileaat the; same tiine permitting 'some' slippage,

sow as to avoidl: pulling out anddeformationn ofi' the-strip as it is being formed by the 1 forming? rel-ls- The" tension applied by the'drawing: rolls should beyariedi atwording to -certain other ope era-"tine conditions and especially atom-ding to the thickness-=01" the. beiiig I forinechv in"- gemera l' the thither the strip the 'lightm themension sliould be;

'I iiepulling out of -the strip-i as it its being? formed, with consequent-tendency toirreeularlit vary the thickness oithe strip is one of;- the special" problems encountered; partieularly when forming" strip" stock of? subst'amtial-"- thiek nesss ibr= instance strip stoolr upwards=- of" .065 inch. in

thickness. We have found." that thistendncy for. the: strip totpull'" out is greatlydiininishedi ifl'the: feed of" the? molten nyloir to the forming? rolls; is effected" in the: marmer show in? Figure 1"; i; e., if the material isd'eliver'ed tooneovtlie other: oi" the forming rolls; partway up; torm stance half'w'ay; from the: ntrancenipto'the" top ofzthelroll'. This apparently aidstin: ensulfiing substantially complete solidifioation of the molten nylon by the time it passes through the pass between tliepair of forming rolls. The feed of the molten nylon at a rate such as to build up a small reservoir of the material in the entrance? nipaisi: also of"v advantage; in; ensuring, uniformity oil strip. produced. Proper. adjustment of the guide rolliW to" a" position somewhat offset from-the plane of therpass between theylfoll'si also"- aids: in avoiding" pu1l-outt of? the strip being formed: A rangeof sueh positions (between position indicated at- 34" and the position indicat'ed at-34mis: shown in Eigure 1 andtfrom inspection of thiafigure it-will he seen that with a that it; may; readily; be handled as it is delivered:

from" the."equipment; Int some :oases the leve'l 1 of? the liquid: cooling: bath may hes-somewhat higher? thaw indicated in: Figure? 1 and" may indeed: be: sufficientl t' hiehwto conta'ct 'thelower portions of the rnlls, although for: accuracy iof temperaturei regulation ofz the rolls; it is preferred to avoid? contautzohtheliquidiwith theirolls;

Water may be employed: as the:- coo'lingzliquid: in: the? bath. and it is contemplated to: employ some rust: preventive" or" inhibitor therein; ewe cially irri the event otf contaotfoff the bath withi the 110115;. a. particularly effective inhibitor: be iIlg potassium bichromate, which serves tliepure pose: but: at the: same time is not subject to. beiIl'g? carried out of theu'bath on the formed strip. In=the event: that the" bath level is kept? highenough:tocontact the rolls it is contemplated thatr-th'eirolls -be equipped with wipers to rem'ove Water therefromiyfor instance wipers of the' cll'ar acten disclosed" in the 'copendih'g'applicatioh of Montross and Shurr Serial No. 3%;966, fil'e'd' July 1 6'; 1948;". issued as P-atent No. 2462439 13 our-Januany 13; 1953'; which application is assigned to the a'ssig-neeofthe*presentzapplicat'ion;

With respect-- to" this matter of temperature" 7 regulationiit must be kept in=mindthat different nylon or" polyamide materials have different"- melting #points; To con'sider' air example oi pre ferred temperature" conditions, reference is first made-to pro'duotion ofi'strip:from polyhexameth 3 cessiv'ely temperatures: interfere. with the the temperature; and rate of: circulation of: the

liquidcirculated through: the rolls but: also on the: volmnev and temperature"of the molten nylon beingdect to. the-rolls. Ditfei'ent pol-yamides also; require: different roll temperatures, although in general with the high melting polyamides it may be said that the roll temperature shouldbe-from about 3759?. below the melting point up to about 209 F1 below-the -temperature at which the polyamide tends;- to: stick to the rolls when making thick strip. Thai conditions should be: adjusted so as t maintain: azrol'latemp'erature below about 395 F: when. usingpol-yhexamethy-leneadipamide. since: this? approximates the temperatureat the guide roll substantially offset from the verwhichcstioking omoursswith:thisaparticular poly-aamide, when making strip upwards of .050 in thickness. The temperature is most desirably kept above about 125 F., a particularly efi'ective range being between 220 F. and 375 F.

When utilizing polyhexamethylene sebacamide (melting point 455 F.) the temperature of feed of the material to the rolls should be between 465 F. and 510 F.; and the roll temperature is preferably kept below 290 F., since this approximates the sticking temperature when making thick strip from this particular polyamide. Most advantageously the temperature should be below 260 R, an effective range being between 75 F. and 225 F. This roll temperature may be maintained even at relatively high rates of operation and even when forming relatively thick and wide stock, by appropriate circulation of cooling liquid in the rolls.

In regulating the feed of the molten material, the screw extruder 3| should be operated at such rate as to maintain a slight excess or reservoir of the molten nylon in the entrance nip of the forming rolls.

With respect to the reference herein to formation of strip stock, it should be understood that the invention is not only applicable to the production of plain flat strip but also to strip of shaped section, for instance beaded material or the like, in which event the forming rolls would be appropriately shaped to give the desired strip section.

In practicing the invention it is of importance that the polyamide used be of very low moisturecontent prior to melting, preferably below 25% water content by weight. to preliminarily and carefully dry the granular or flake material before melting, and this is especially important in the case of polyhexamethylene adipamide and polyhexamethy1 ene sebacamide which must be carefully vacuum dried. In the absence of such drying an excess of bubbles forms in the material and the formed strip has lower elongation and has a tendency to brittleness.

Strip formed in accordance with the present invention is substantially free of bubbles and other defects either within the piece or on the surface thereof. The edges of the strip are frequently somewhat irregular in view of which trimming is contemplated. The formed strip itself has excellent physical characteristics, including toughness, and high tensile strength.

In the case of strip of .060 thickness, madev from polyhexamethylene adipamide, with rolls at 360 F., a tensile strength as high as 12,750 lbs/sq.

in. was achieved, with elongation of25% in a 1 in. gauge length.

After formation of strip according to thisinvention, it is frequently desired to trim the edges of the strip and for this purpose we" prefer to preliminarily treat the stock in boiling water and thereafter feed the material through a slitter. This treatment aids in avoiding chipping or splitting the edges of the strip during the slitting.

I claim:

1. Equipment for forming strip stock from synthetic linear polyamides, comprising a vessel for receiving a liquid coolant, a pair of forming rolls arranged in side-by-side relation with their axes disposed in a common horizontal plane toward the top of said vessel at least in large part above the level of the coolant therein, mechanism above the forming rolls for feeding molten polyamide downwardly into the entrance nip 7,5;

Therefore, we prefer between the forming rolls, means for cooling the forming rolls to a temperature between F. and 375 F. to provide for substantial solidification of the polyamide while passing in contact with the forming rolls, and mechanism for drawing the formed strip downwardly from forming rolls through the coolant in said vessel including a feeding device engaging the formed strip to draw it from the rolls under tension, the feeding device being horizontally offset from the forming rolls and being located above the level of the coolant in'said vessel, and a guide device located between the feeding device and the vertical plane of the pass between the forming rolls but offset downwardly from the forming rolls and feeding device to a position well below the level of the coolant in said vessel and engaging the upper side of the formed strip intermediate the forming rolls and the feeding device to establish a run 'ofthe formed strip extending around an appreciable arc of one of the forming rolls and thence downwardly through the coolant to theguide device.

2. Equipment for forming strip stock from synthetic linear polyamides, comprising a vessel for receiving a liquid coolant, a pair of-forming rolls arranged in side-by-side relation with their axes disposed in a common horizontal plane toward the top of said vessel at least in large part above the level of the coolant therein, mechanism above the forming rolls for feeding molten polyamide downwardly into the entrance nip between the forming rolls, means for cooling the forming rolls to a temperature between 75 F. and 375 F. to provide for substantial solidification-of the polyamide while passing in contact with the forming rolls, mechanism for drawing the formed strip downwardly from the forming rolls through the coolant in said vessel including a feeding device engaging the formed strip to draw it from the rolls under tension, the feeding device being horizontally offset from the forming rolls and being located above the level of the coolant in said vessel, and a guide device located between the feeding device and the vertical plane of the pass between the forming rolls but offset downwardly from the forming rolls and feeding device to a position well below the level of the coolant in said vessel and engaging the upper side of the formed strip intermediate the forming rolls and the feeding device to establish a run of the formed strip extending around an appreciable arc of one of the forming rolls and thence downwardly through the coolant to the guide device, and mechanism for varying the extent of the arc of contact of the formed strip with said one forming roll, including adjustable mounting means for the guide device providing for horizontal shift of the position thereof in a direction toward and away from said vertical plane of the pass between the forming rolls.

LOUIS L. STOTT. PAUL L. SHURR.

References Cited in the file of this patent UNITED STATES PATENTS Martin Jan. 9, 1945

Claims

1. EQUIPMENT FOR FORMING STRIP STOCK FROM SYNTHETIC LINEAR POLYAMIDES, COMPRISING A VESSEL FOR RECEIVING A LIQUID COOLANT, A PAIR OF FORMING ROLLS ARRANGED IN SIDE-BY-SIDE RELATION WITH THEIR AXES DISPOSED IN A COMMON HORIZONTAL PLANE TOWARD THE TOP OF SAID VESSEL AT LEAST IN LARGE PART ABOVE THE LEVEL OF THE COOLANT THEREIN, MECHANISM ABOVE THE FORMING ROLLS FOR FEEDING MOLTEN POLYAMIDE DOWNWARDLY INTO THE ENTRANCE NIP BETWEEN THE FORMING ROLLS, MEANS FOR COOLING THE FORMING ROLLS TO A TEMPERATURE BETWEEN 75* F. AND 375* F. TO PROVIDE FOR SUBSTANTIAL SOLIDIFICATION OF THE POLYAMIDE WHILE PASSING IN CONTACT WITH THE FORMING ROLLS, AND MECHANISM FOR DRAWING THE FORMED STRIP DOWNWARDLY FROM FORMING ROLLS THROUGH THE COOLANT IN SAID VESSEL INCLUDEING A FEEDING DEVICE ENGAGING THE FORMED STRIP TO DRAW IT FROM THE ROLLS UNDER TENSION, THE FEEDING DEVICE BEING HORIZONTALLY OFFSET FROM THE FORMING ROLLS AND BEING LOCATED ABOVE THE LEVEL OF THE COOLANT IN SAID VESSEL, AND A GUIDE LOCATED BETWEEN THE FEEDING DEVICE AND THE VERTICAL PLANE OF THE PASS BETWEEN THE FORMING ROLLS BUT OFFSET DOWNWARDLY FROM THE FORMING ROLLS AND FEEDING DEVICE TO A POSITION WELL BELOW THE LEVEL OF THE COOLANT IN SAID VESSEL AND ENGAGING THE UPPER SIDE OF THE FORMED STRIP INTERMEDIATE THE FORMING ROLLS AND THE FEEDING DEVICE TO ESTABLISH A RUN OF THE FORMED STRIP EXTENDING AROUND AN APPRECIABLE ARC OF ONE OF THE FORMING ROLLS AND THENCE DOWNWARDLY THROUGH THE COOLANT TO THE GUIDE DEVICE.