US2074856A - Lead extrusion apparatus - Google Patents

Description

March 23, 1937.

Filed May `16, 1955 1 -l sn mw .4 @v wl u n I n v n u n ww n m m N PF1; unw- \-r.l ..l lmm. Nw

HH- :lll il--- IIIIIV@ u WU t... .W... h. O AA.. 1 .Q M o Nnv m N s i s wm. o o S Inventors: Carl A.Fier`cy, Eugene: I... Crandall by ThenA AttoPney.

Patentes Mar. 23, 1937 PATENT oFFicE LEAD EXTRJSION APPARATUS Carl A. Piercy, lallston Lake, and Eugene L. Crandall, Scotia, N. Y., assignors to General Electric Company, a corporation of New York Appiiauon May 1c, i935, serian No. 21,818

8 Claims.

In the manufacture of electric cables of certain kinds, it is the practice to enclose the insulated conductors in a lead sheath. In some instances, only a single insulated conductor is provided and in other instances, a greater number. As the requirements of such a cable inservice become more and more exacting-the importance of having a good sheath becomes outstanding. This is particularly true where the paper or equivalent lo insulation on the conductors is impregnated with a liquid dielectric, as thin oil for example. 'Ihe principal defects found in cable sheaths made of lead are due to'occluded gas or air holes, laminations in the lead due to oxides or sub-oxides of l5 lead, oxidized tallow or grease used as lubricants in the lead press, and other impurities in the lead. One of the principal reasons why these impurities are present in the sheath as ordinarily made is due to the fact that the cylinder of the without protection for the lead from the effects of air. Other reasons are that adequate means are not provided for removing foreign matter from the lead while it is being melted and for preventing access of atmospheric air to the parts of the lead press and especially to the exposed surface of the residual charge in the press when it is opened to receive the new charge.

lI'he object of our invention is to improve the manufacture of lead sheaths to the end that they will be free of the defects or impurities 'above noted.

For a consideration of what we believe to be novel andy our invention, vattention is directed to the Vaccompanying description and the claimsaptrative of our invention, in Fig. 1 is shown partlyV in section a so-called straight-through lead press;. Fig. 2 is a cross section taken on line v2--2 of Fig. 1, and Fig. 3 `is a detail view of an electric heater. y l

The lead press illustrated in the drawing is of a' known type but has been modied in certain 35 respects and parts added wherever necessary to conform to the requirements of our invention.

In the drawing, 3 indicates the cylinder of a so-called straight-through lead press and t the ram for extruding lead therefrom after its temperature has been suitably reduced. The lead is extruded through a space between a so-called point, nozzle or die 5 and a matrix or outer die 6 to form a sheath 'l around the cable 8, the cable moving through the press from right to left. The extruding ram is moved into the cylinder by an press is iilled from the top with molten leadA hydraulically actuated piston 9. Water is admitted to and released from the cylinder il) con-i taining the piston by valve controlled pipe li, and l2 indicates a pipe by means of which any trapped air may be discharged after the press has been shut down. The ram` and piston are withdrawn by a second piston i3 located in a separate cylinder It. Water is employed for actuating the second piston and is admitted and removed through a pipe |15l subject to suitable control valves.

The ram is hollow and inside of it is a tubular guide member lli which also supports the point or inner die 5. To theright hand end of the member I6 is secured a thin walled guide tube il which extends through the ram and also the piston i3 and is supported at its outer end by a head lll.-` Since this tube is fixedly supported at its outer end, it also serves as a means to deflnitely position the inner die or point 5 with respect to its surrounding and cooperating die 6. In order to prevent the admission of air into the press through the member it and tube il as the unleaded cable moves, a packing is provided. In this case, it comprises a chambered vcasing l@ supported by the head i8. Inside the casing is a flexible packing element through which the cable passes, the packing being caused to engage the outer surface of thecable by a garter spring 2l. The chamber is maintained under a vacuum as will appear later on. A generally similar packing 22 isprovided for the leaded cable as it leaves the press. The chamber of this packing is also maintained under a vacuum, as will appear later. The packing of the cable both at the point of entrance and its exit from the press has an important part in preventing oxidation of lea'd within the press. Without the entrance packing, atmospheric air would pass. through the tubular parts il and I6 and thence between the outer. surface of the point or die 5 and the residual charge into the cylinder of the ram when the latter is withdrawn preparatory to the introduction of a new charge. Without the left hand packing, 'air would enter between the matrix 6 and a surface of the residual charge when the. ram is withdrawn. Any air acting on the residual charge causes oxidation andl any oxidesso formed would onthe next inward movement or Working stroke of the ram be forced with the lead of the new charge into the sheath and appear as defects therein. The importance of keeping all air out of the cylinder of the ram during the idle stroke 4of the ram is thus made apparent.

One oi the diflculties incident to the operation 2. of a press of this character is the removal of the thin shim which isv formed around the ram on each of its working strokes. This is due to the fact that the ram has to be slightly smaller in diameter than its cylinder to compensate for unequal expansions. These -shims have to be removed from ltime to time and on occasions after each working stroke of theram. To facilitate this removal, the ram 4 is made as follows: The head 24 or left hand end is annular and makes a good working ilt with the inner wall of the cylinder 3. The wall of its bore makes a good working t with the peripheral surface of the central guide member I6. Formed integral with the head are three segmental bars or members 25, Fig. 2, spaced 120 apart and acting as guides therefor. The right hand ends of these guides are secured to the piston 9 and hence the piston and ram move back and forth with the unit. `As shown in Fig. 1, the ram is in its fullyretracted position where it is possible to vremove the shim. Openings 26 are provided in the right hand end of the cylinder 3 as indicated in dotted lines in Fig. 2, throughwhich access may behad to the ram /for removing the shims. The openings are normally tightly closed and sealed by removable covers 21. The dotted lines at theleft of the ram indicate its position at the time of illling or charging of the cylinder 3 with molten lead takes place. It will be noted that inthis position, the ram has closed the right hand end of the cylinder so that the charge is confined to the cylinder. f A Molten lead is introduced into the cylinder which is under high vacuum due to a vacuum pump as will appear later, from the under or botvtom side by the pipe 30, the port- 3|!a in the cylinder wall through which the pipe discharges being covered and uncovered by the ram as it moves. Diametrically opposite the pipe and its port is an overflow port or opening 3| in the cylinderwall, shown also in Fig. 2; In charging the press, molten leadis admitted to the cylinder 3 and when filled. the lead rises to a lpoint Where it is visible at or near the flat and substantially horizontal wall adjacent the port 3|, after which the supply is shut off as by the valve 32, The

lchamber 3|'a communicating with the port 3| Vacts as al receiver for excess metal discharged from the cylinder during the early portion of the working stroke of the ram. In this connection,

it will be noted that the ram has to move some distance on its inward stroke before it covers the lead admitting port 30B and the overflow port 3|.

In the interest of clarity, the lead supply valve-A 32 is shownsome distance away from the' cylinder but in practice it is desirable to have the valve as close as possible to the cylinder. Until these ports are sealed by the head of the ram, a certain amount of -lead will of necessity be forced outwardly into the chamber 3P. The dotted lines near the front end of the ram 'indicate its position after thelshirxrhasj been removed if such action' is necessary, and in any event its position during the lling of the cylinder. Before the interior parts of the press arerf open to remove 1. F\shims, also referred to as cleaning the ram, a supply of neutral gas under positive 'pressure is admitted in such manner as to prevent access of air to said parts.

In this type of press, as heretofore made, only one port-was provided and that at the top for nlling and through it air was lfree to enter the cylinder of the press and act directly on the'exposed face of the residual charge and thus oxidize which desirably may be heavier than air.

it. We accomplish the desired result by filling from the bottom and providing a completely enclosing overflow port at the top. The Ienclosure for the port has a cover 33 made in one or more parts which is firmly clamped to the cylinder wall in such a way as to form an air tight chamber 3|. A portion of the cover maybe made movable so that access may be had to the interior of the chamber and a portion may also have a glass covered sight opening through which the molten charge can be observed as it rises from the cylinder. The top part'may be taken as illustrating the sight opening. Entering the chamber is a pipe 34 which is connected to a vacuum system or pump which evacuates not only the chamber 3|* but also theA entire cylinder space when the ram is in the outermost or retracted position. The pipe is also used to supply a non-oxidizing gas The cylinder of the press and that of the ram actuating piston are in spaced relation which provides` the necessary space for the travel of the parts and affords access to the ram. The cylinders ar united by a series of longitudinal bolts having peripheral surface of the ram and'its enclosure opens into the chamber, air would leak from the chamber in the cylinder space of the press when the ram is moving on its idle stroke and when it is stationary during the press filling operation. To prevent this, the space between the `parts is entirely boxed in with covers 31 having sealed joints, and connected to the chamber 36 thus formed is a pipe 38 which is connected to a vacuum system or pump. The pipes 34 and 38 leading to chambers 3|a and 36 are also lused to supply COror other non-oxidizing or neutral gas under certain conditions kas will appear later.

' As previously stated, molten lead from which air is excluded is admitted to the cylinder of the press from which air is likewise excluded at the bottom as distinguished from the prior practice of admitting it at the top. This distinction is important because impurities which may exist in the lead have a tendency to/float to the top ofthe `charge and in so doing will flow outwardly through the overflow port 3|. To facilitate this action, the press cylinder is downwardly inclined Vso that the overflow port is located at or about the highest point therein. This is particularly l noticeable when the ram has been advanced from its fully retracted position to a. position where it is just about to close the overflow port, under which conditions there is a forced discharge of molten lead-through the overflow'port and with it any impuritiesfwhich may have collected near the outlet port. By using the ram to close both the admission and overflow ports, the substantial advantage is obtained that the valves and piping in the lead supply portion of they system are not subjected to the very high pressures incident to the extrusion of `plastic lead from the cylinder but only to such low pressures as' are necessary to move the molten lead from its` source into the cylinder. As will be noted, the inlet port is closed cylinderl on its idle or return stroke, a vacuum would be created within the cylinder, and unless means are provided to prevent' it, air will be sucked in through the clearances both inside and outside of the ram. To prevent the entrance of air in the manner stated, non-oxidizing gas is admitted to the chamber 33 into which the overow port opens and also into the chamber 36 so that the atmosphere within the cylinder at this of molten metal begins its entry into the cylinder,

the non-oxidizing gas is removed and a vacuum Brieily stated, the cylinder when the ram is withdrawn is alternately lledwith non-oxidizing gas and then evacuated. g

` 1W indicates an open melting or mixing pot for the lead and may be of usual construction. After the lead is melted and its temperature raised to a suitable degree, it is conveyed by a pump 4l to a suitably placed sealed Vtank orpot d2 desirably above the press so that the hot lead will flow by gravity thereto. The pump may advantageously be located within the pot, it being located outside in the present case to simplify the illustration. It is preferable to pump lead from the bottom of the pot since foreign matter has atendency to rise to the top from which 'region it can readily be skimmed. The elevated tank or pot 42 is main-l tained under vacuum for the purpose of removing air and other gases from the lead as completely as possible and at the same time prevent the formation of oxides. Inside of the tank is a heated baiiler 43 against which the hot lead is discharged by a spray nozzle 43e. The baiiier may advantageously be heated by a suitable' electric heater, the purpose being to prevent the lead from being chilled. The tank is also heated for the same reason. This may be done by electric heaters of known construction or by any other.

Fig. 3, having terminals dll, Fig. 1, for connection tor a suitable source of electric supply. Such heating units may be taken as illustrating suitable heaters for the other parts of the apparatus such as the pots which are required to be heated in order to. maintain the lead at the proper temperature.

du? indicates a vacuum tank and desirably it is of large size so as quickly to effect a vacuum when the parts of the system are to be subjected thereto. 49 indicates a vacuum pump which may operate continuously or intermittently as desired, providing of course that a proper, degree of vacuum in the system is maintained. The vacuum tank is connected to the lead pot or tank 42 by a pipe 50 containing a shut-olf or controlling valve 50a. The vacuum tank is also connected to chambers 3l and 36 of the lead press around a part of the ram by the pipes I, 34 4and 38 so that the clearance between the ram and the wall of the bore of the lead cylinder and also other parts are under vacuum during the extrusion part of the cycle. In this connection. it should again be noted that in all lead presses a certain although small clearance is required between the ram and the'cylinf der wall due to the unequal expansion and contraction of the parts during each cycle of operation. By maintaining a vacuum around the ram 5 ywhich in the present illustration does not leave the cylinder at any time, it will be seen that no air can get into the-cylinder. The vacuum tank is also connected to the chambers of the end sealing'means by the pipes 5|, 52, 53 and 54, pipe 10 52 having a valve 55 for shutting oi the seals when the press is not in use. During operation. the seals are always under vacuum.

56 indicates a source of gas supply, in the present instance a tank containing gas under relal5- tively high pressure and connected to the piping l system previously described by a pipe lcontain- Vingv a combined regulating and shut-olf valve 58.

The gas which is used during the ram cleaning operation may be a neutral or non-oxidizing gas such as CO2.` and one desirably heavier than air, or it may be an active oxide reducing gas such as hydrogen, for example. Assuming that all of the parts surrounding the ram are maintained tight and that air and objectionable gases have been removed from the molten lead, there should be no oxides in the lead to be reduced but such gas being under positive pressure will act eectively to prevent air from'leaking into the system when the covers 2l and 3l are open to permit cleaningl 30 of the ram. It is to be understood that during the cleaning operation a continuous iiow of gas is maintained.

lin the operation of our improvedapparatus, the pig lead is melted in the pot M and then elevated to the heated supply pot or tank d2 by the pump di. The lead is kept hot in this transfer and is discharged by the spray nozzle d3 against the hot bafiler d3 which has the effect of liberating air and other gases in a rapid manner and said gases are removed by the action of the vacuum pump t9. Molten lead is delivered b'y the heated pipes d5 and 3U to the cylinder of the press subject to the control of the valve 32 while the ram is in its rearward position as shown by the dotted Li5 line in the drawing. The filling continues until lead iiows out of the overflow port 3l into the receiver tia, the latter being under vacuum as well as the cylinder of the press. Filling from the bottom permits any impurities in the lead to rise v to the top and when the cylinder is iilled said impurities will ow outward through-the overflow port, and since the cylinder is under vacuum the formation of oxides therein `is prevented. vThe supply valve 32 is then shut andthe ram moved 55 forward by admitting water by the pipe lll to the cylinder of the ram until the ram completely covers the inlet and overflow ports 30B and 3l at which point it is stopped until the lead is cooled to the proper degree to form'the sheath by ex 60 trusion. Until the ram closes the overllow port 3l, a limited amount of hot lead will be forced by the ram therethrough, the inlet valve 32 being closed at this stage of the cycle. 'During the cooling period, the charge of lead is maintained under pressure by the ram. After the temperature .iss

pressure into the chambers Ill and 36, after which either or both chambers may be opened and a constant outward iiow of gas maintained. The reason for introducing a neutral or an oxide reducing gas into the chambers 3i'L and 36 is to prevent air from coming into contact with the residual charge of lead in the press cylinder through the clearances between relatively moving parts which clearances are necessary on account of 'unequal expansions of the parts. In this particular, our invention further dierentiates from the standard practice which permits air freely to contact with residual charge when the ram'is moved to the filling position. vAfter the ram is cleaned, if that be necessary, the covers of the chambers are replaced and gasv from `the tank 58 shut olf by valve 58 and that contained in chambers 3i*L and 36 is then removed by the vacuum system by opening valve 59 and establishing communication with the tank 48 and vacuum pump 49.

It. will be noted from the foregoing description that our improved arrangement has among others the following advantages:

1. The nozzle or die parts through which the lead is extruded is maintained under vacuum by the end seals, thereby preventing air from working back into the press cylinder where it would oxidize the charge.`

2. The filling of the lead cylinder takes place from the bottom and asthe cylinder is slightly inclined downwardly with' the overflow port 3i at the highest point and any foreign matter' which tends to collect on the surface of the incoming charge will pass out through the port into chamber Il.

3. During the melting and filling operations, any gases which existed or are formed in the molten ie'ad will be removed bythe vacuum pump.

4'. Dueto the fact that the pot 42 is heated as are also the pipes leading to and from it, the lead is kept hot during the entire period that the press-is in operation, and since the 'heating is done electrically, .the temperature can be accurately controlled.

- 5. summarizing the` advantages of our improved construction, it will be seen that from the time the llead is melted in the melting or mixing pot Illuntil it is applied to the cable and issues as a sheath on the cable, no airis permitted to come into contactwith the lead and thus the ladvantage of a sheath which is free of oxides, gas holes and laminations is obtained. What I claim as new and desire to secure by Letters Patent of the United States is:l

.1. In an apparatus of the character described, the combination of a downwardly inclined press cylinder having a filling port in its under side and an overflow port in its upper side at the highest part thereof so that foreign matter floating on the incoming charge will freely pass outwardly therethrough, said overflow port being diametrically opposite the fillingl port, a sealed chamber `in free communication withthe overflow port', a ccmduit for supplying a charge of molten metal to the cylinder through the filling port, extruding dies communicating with the cylinder, a ram in the cylinder which on .its working stroke first closes the ports and thereafter forces the metal through the dies, means for evacuating the cylinder and chamber subsequent to the withdrawal l of the-ram and while the charge is being admitted y to the cylinder, and means for .actuatingthe ram.

2. In 4an apparatus of the character described, combinbtion of an. inclined press cylinder having a filling port in its under side and an overflow port in its upper side at the highest part thereof so that foreign matter floating on the incoming charge will freely pass outwardly therethrough, said overflow port beingdiametrically opposite the filling port, a closed chamber into which the overflow port opens, extruding dies communicating with the cylinder, tubular means aligned with the dies through which the article to be covered moves longitudinally, said means supporting one of the dies, a hollow ram which surrounds the means and makes a. sliding flt therewith and with the cylinder of the press, said ram on its working stroke rstfclosing the filling port and then the overflow port, thereby causing a limited amount of the charge to iiow into said chamber, means for actuating the ram, means for admitting a supply of non-oxidizing gas to the chamber and cylinder on the return stroke of the ram. and means for removing the gas from the cylinder and chamber prior to the introduction of the charge through the filling port.

3. In an apparatus of,4 the character described. the combination of a downwardly inclined cylinder with its head at the lower end, extruding dies at the head end of the cylinder, a filling port formed in the cylinder in its under side and an overfiow port formed in its upper side at the highest part thereof so that foreign matter floating on the incoming charge will freely pass outwardly therethrough, said ports being located diametrically opposite each other, a closed chamber located above the cylinder into which molten 4metal and impurities therein-- are free to flow from the overflow port 'when the latter is open during the charging operation, a conduit for supplying charges of molten metal to the filling port, means for removing air and other gases from the metal prior to its passage through the filling port, a'ram in the press cylinder which on its working stroke first closes the filling port and then the -bverflow port, thereby permitting a limited amount of each charge to escape from the cylin' der, a means for actuating the ram, means for filling the cylinder and chamber upon the return stroke of the ram with non-oxidizing 4gas to prevent the entrance of air thereto, and means for removing thegas and evacuating the cylinder and chamber prior to the introduction of the charge.

4. In an apparatus of the character described, the combination of a downwardly inclined 'press cylinder having a lling portin its under side and an overflow port in its upper side at the highest part thereof so that foreign matter floating on the incoming charge will pass outwardly therethrough, said port being diametrically opposite the iilling'port, a first closed chamber into which the overflow port opens, extruding dies commu- `nicating with the cylinder, tubular means aligned with the dies through which the article to be `covered moves longitudinally, said means supporting one of the dies, a hollow ram which surrounds the means and makes a sliding fit therewith and with Athe cylinder of the press,- said ram on its working stroke first closing the filling port andl then the overfiow port, thereby causing a limited amount of each charge positively to be forced out of the cylinder, means for actuating the ram, a second closed chamber which is in communication with the clearance between the tracted to prevent entrance of air into the'cylin- 75 der, and means for evacuating the cylinder and both chambers and thereby removing the gas immediately prior to introducing the charge into the cylinder.

5. In an apparatus of the character described,

the combination of a downwardly inclined press cylinder having a lling port in its under side and an overiiow port in its upper side, said ports being located near the elevated outer end of the cylinder and diametrically opposed to each other, extruding dies communicating with the cylinder, means for supporting the dies'in co-operative positions, a conduit supplying molten metal to the iilling port so that any impurities iloating therein will rise and freely escape through the overflow port, a closed chamber formed in the upper wall of the cylinder and receiving molten metal from the overllow port, a means for maintaining said receiving chamber under a vacuum during the period that the overow port is open, and a ram in the press cylinder which closes the iilling and overflow ports successively as it moves inwardly,

the relation of the inner end of the ram to the ports being such that a limited quantity of molten metal is forced by the ram through the overflow port at the beginning of its working stroke.

6. In an apparatus of the character described, the combination of a press cylinder having a lling and an overow port, the lling port being in the lower side of the cylinder and the overflow port diametrically opposite it in the upper side of said cylinder, extrusion dies communicating with the cylinder, a ram in the cylinder which as it moves inwardly on its working stroke iirst discharges a limited amount of the charge through the overflow port and then closes both ports and forces metal from the cylinder through the dies and uncovers both ports on its return stroke, al means for actuating the ram, a chambered enclosure with which the clearance between theram and the cylinder is in communication, a heated receptacle containing molten metal, a conduit for conveying metal from the receptacle to the illing port of the press cylinder, and a pump means for maintaining a vacuum in said chambered enclosure during the charging operation and also` in the heated' receptacle.

7. lIn an apparatus of the character described,

lthe combination of a downwardly inclined press cylinder having a filling and an overflow port, the filling port being in the lower side of the cylinder and the overilow port diametrically opposite it at the highest part of the cylinder, extrusion dies communicating with the cylinder, a ram in the cylinder which as it moves inwardly on its working stroke first discharges a limited amount of the charge through the overilow port and then closes both ports and forces metal from the cylinder through the dies and uncovers the ports on its return stroke, a means for actuating the ram, a chambered enclosure with which the clearances between the ram and its cooperating parts are in communication, a heated receptacle containing molten metal, a conduit for conveyingmetal fromV the receptacle to the illling port` of the press cylinder, a pump means for maintaining a vacuum in` the chambered enclosure during the charging of the cylinder with metal and also in the heated receptacle to remove gas from the hot metal, and means for supplying a non-oxidizing gas to the chambered enclosure when it is opened to clean the ram.

8. In an apparatus'of the character described, the combination of a downwardly inclined press cylinder having diametrically opposed filling and overflow ports, the latter being located at ,the highest part of the cylinder to permit impurities oatingon the charge to escape, a ram which is permanently within the press cylinder which covers both ports onlts Working stroke and uncovers them on its return stroke, the inner end of the ram being so related to the overflow port that a small portion of each charge is discharged through the port at the beginning of each working stroke, an hydraulic motor for actuating the ram, a chambered enclosure with which the clearance between the ram and the enclosing wall of the press cylinder are in free communication at all times, a heated receptacle containing molten metal and supplying it to the filling port, a vacuum pump for evacuating the cylinder prior to receiving the charge, for evacuating the receptacle to remove gases from the molten metal and.' for evacuating the chambered enclosure to prevent the entrance of air through the ram clearance into contact with the metal in the press cylinder, a source of gas supply, conduit means for admitting gas from the supply into the chambered enclosure and the cylinder when` the ram is retracted preparatory to lling the press cylinder with molten metal from the receptacle.

CARL A. PIERCY. EUGENE L. CRANDALL.

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