US1330661A - Method of casting propeller-wheels - Google Patents

Description

T. 0. THACHER.

METHOD OF CASTING PROPELLE-B WHEELS. APPLICATION- FILEDOCT. 24,1918- RENEWED DEC. 30, 1919.

1,330,661. Patented Feb. 10,1920.

, 3 SHEETSSHEET 1.

.9 v awue mtoz T. 0. THACHER. METHOD OF CASTING PROPELLER WHEELS.

APPLICATION FILED OCT. 24. I918- RENEWED DEC- 30,1919.

Patented Feb. 10,1920.

3 SHEETS-SHEET 2.

T. 0. THACHER.

METHOD OF CASTING PROPELLER WHEELS.

RENEWED DEC. 30,

APPLICATION FILED OCT- 24, l9l8. 1,330,661

Patented Feb. 10, 192.0.

3 SHEETSSHEET 3.

La-:11 F5 UNT STAEg FATENT OFFICE.

THOMASOXENBEIDGE TEACHER, OF ALBANY, NEW YORK, ASSIGNOR T0 TEACHER PROPELLER, AND FOUNDRY COPUPGBATION, OF ALBANY, NEW YORK, A CORPO- RATION 0F NEVT YORK.

METHOD OF CASTING PROPELLER-WHEELS.

issoreei.

Application filed October 24, 1918, Serial No. 259,45 -3.

To all whom it may concern:

Be it known that I, Trro rAs O. THAGT-IER, a citizen of the United States, residing at Albany, in the county of Albany, State of New York, have invented certain new and useful Improvements in Methods of Casting Propeller-Wheels; and I do hereby declare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it appertains to make and use the same.

This invention relates to methods and apparatus for casting propeller wheels, par ticularly large propellers for ocean steamships, and has for its object to produce a cast propeller wheel which will be so ac curately symmetrical in the position, pitch and dimensions of its blades as to require little or no machining to secure a balanced finished propeller.

A further object of the invention is to provide a method and an apparatus for casting propeller wheels whereby the propeller wheels may be properly made by ordinary foundrymen without special care or accurate calibration in the setting of the molds, so that the speed of production is much increased and the cost of manufacture correspondingly reduced.

A further obiect of the invention is to provide a method of casting; propeller wheels which provides a smooth surface for the blades in the original casting so that the blades do not require a surface finishing as is usually necessary to prevent excessive skin friction of the propeller when in use. I Y

My invention also embodies an improved method of pouring the casting whereby the complete filling of the mold with clean metal without contraction is secured even in the large wheels of fifteen feet or greater diameter.

My invention also provements in the whereby the process carried out.

By the method of castingnow practised, large propellers are formed from a pattern consisting of a single blade and hub, the hub being mounted for rotation on a vertical spindle set in the middle of the pit in which the wheel is to be cast. A set of includes certain imapparatus employed may be successfully Specification of Letters Patent.

Patented Feb. 10, 1920.

Renewed. December 30, 1919. Serial No. 348,383.

flasks, one for each blade, is grouped around the spindle in the approximate positions of the blades and filled with green sand. The foundryman then places the pattern over one of the flasks and rams the sand around the pattern to form the impression for that blade. The pattern is then lifted from that flask and turned through the angle required by the number of blades to be formed, to a position over the next flask and the process repeated for each blade. The accuracy of the pitch and balance of the propeller are thus dependent almost wholly on the skill of the workman casting that particular propeller and the wheels cast by inexperienced workmen are frequently so out of true as to be unfit for use.

My improved method of casting consists in employing a separate and identical mold for each blade and locking the blade molds together in accurately radial and properly spaced positions around their common center, the positioning of the blade molds being obtained by means of a bed plate having an accurately machined surface and accurately positioned holes or bearings interlocking with similarv surfaces and holes or projections carried by the separate molds.

In order that the impressions of the blades in the molds may be identical in shape and location the molds are preferably formed in separate flasks from the same pattern or box, the flasks and the pattern box being all divided with each half of the pattern box designed tointer-lock with one half of the flask. The flasks in turn interlock with the holes or projections of the base plate so that if the plate is accurately made and finished the propeller will necessarily be symmetrical if the method has been properly followed.

The flasks containing the blade molds are set up on the bed plate around a bottom core attached to the center of the plate and fixed in position by means of bolts in the registering holes which determine their-accurate positioninpg. The meeting edges of the several molds are then sealed with slurry to avoid fins on the finished casting and the mold is then closed with suitable center cores for forming the hub and is ready for the mold to be poured.

In the accompanying drawings I have illustrated my improved apparatus and also the manner of using the apparatus in carryin out the improved method.

*igure 1 is a plan view of the flask employed for the blade molds;

Fig. 2 is a plan view of the part of the pattern box used with the lower part of the flask;

Fig. 3 is a sectional view showing the arrangement of the lower part of the flask and its pattern box pattern to receive the sand mixture;

Fig. l is a cross section on line H of Fig. 3;

Figs. 5 and 6 are sectional views similar to Fig. 3 showing further steps in the method of forming the molds;

Fig. 7 is a plan view of the other half of the pattern box;

Fig. 8 is a sectional view showing the upper half of the flask and its complementary part of the pattern box ready to receive the sand mixture;

Fig. 9 is a sectional view showing the two parts of the flask assembled;

Fig. 10 is a sectional view on line 1010 of Fig. 9;

Figs. 11 and 12 are, respectively, a central vertical section and a plan view of the assembled molds and cores set up to be poured according to my improved method; and

Fig. 13 is a sectional detail of the trough through which the metal is poured.

The separate flasks for each propeller blade are identical and are made in halves in the usual manner, the line of division between the two halves being near one face as indicated at a Fig. 10. The flanges of the meeting edges of the two halves are of substantial width and are machined off to true horizontal surfaces, and the upper and lower faces of the flask which are also flanged, are machined ofl to true surfaces parallel with the surfaces of the flanges.

At the inner end of the flask, that is. the end of the flask in which the hub end of the blade will be formed, the side walls of the flask are inclined as here shown at an angle of 45 degrees to the middle line of the flask, the angle depending upon the number of blades of the particular propeller to be cast. Each of the inclined faces is provided with sandretaining projections 26, the ends of which are accurately machined off so that their end faces form flat surfaces lying in planes vertical with respect to the machineflnished horizontal faces of the flask and at such angles to the middle line of the flask that the intersections of the two surfaces formed by the ends of the projections accurately coincide at the center of the propeller.

At the outer end of the flask, that is, the end toward which the tip of the blade will extend, each half of the flask has a projecting ear 6 in which is bored a hole 25, the holes being accurately positioned in the middle line of the flask as determined by the inclined end faces and at a predetermined distance from the center as determined by the intersection of the inclined surfaces. Each half of the flask is also provided with holes 30 in its flange for receiving the clamping bolts which hold the two parts of the flask together.

The two halves of the pattern box are shown in Figs. 2 and 7, the part 27 shown in Fig. 2 cooperating with the deeper portion of the flask to form one half of the di vided mold while the other two parts of the pattern box and flask are used together to form the other half of the mold. The part 27 of the pattern box comprises a back plate 28 with the pattern block 29 attached thereto. The face of the plate to which the block is attached is accurately machined to a trxie surface and the pattern block is built up to the desired pitch line from the surface of the plate as a base. Formed in the back plate around its margins are a series of holes corresponding to the holes in the margins of the flask, and there is also provided a middle hole in the end of the plate corresponding with the holes 25 in the ears at the ends of the flasks, the holes being accurately positioned on the center line of the pattern block so that when the portion of the flask and the corresponding half of the pattern box are fastened together by bolts through the registering holes, the pattern will be positioned to form the blade impres- Isgion accurately in the center of the pattern The inner end of the pattern block is shaped to form the impression of the proportional part of the hub for one blade, that is, a sector of 90 degrees amplitude, by means of two upright plates 32 attached to the pattern box with their inner faces ac- .curately finished off and positioned so that when the flask and pattern box are clamped together the ends of all the projections 26 of the flask will abut against the faces of the upright plates and the line of intersection of their faces will correspond with the axis of rotation of the propeller. The pattern box is also provided with a detachable pattern piece 26 for forming a recess in the blade molds to receive the bottom center core which will be later described.

After the parts of the flask and pattern box are clamped together as shown in Figs. 3 and 4 the sand mixture is rammed in through the openings in the top of the flask. A plate 33 having a machine-finished surface is then pressed down on top of the flask and clamped thereto as shown in Fig. 5,

the flask. The connected flask and pattern box parts with the plate clamped to the flask are then inverted and the pattern box part unclamped and withdrawn, the piece 26 being first detached and removed. The flask part containing the molded sand mixture is then placed in an oven and baked in the usual manner, forming a half mold for the propeller blade with true surfaces on its bottom and inner end faces, and its flanged edges, and with the blade impression accurately located in the flask with reference to the surfaces and the bolt holes.

The other half of the mold is formed in the same manner in the upper part of the flask from the half of the pattern box shown in Fig. 7, this half of the pattern box being provided with sidewalls against which the edges of the upper part of the flask are clamped as shown in Fig. 8. The two half molds, when fitted together as shown in Figs. 9 and 10, form a complete mold for a single blade and its proportionate part of the hub.

Identical molds are formed from the same pattern box for each of the blades. The blade molds are then assembled on the base or bed plate 1 which is of greater diameter than the over all dimensions of the propeller and is securely fixed in the ground, preferably in a pit deep enough for the top of the flasks to be flush with the surface. To re duce the weight of the plate without sac rifice of rigidity it may be formed as shown,

' of closely spaced bars 2 with connecting cross bars 3, the upper surface of the bars 2 being machined off to present a true surface.

At the exact center of the plate is provided a bearing or recess 36 to receive a corresponding projection formed on the bottom plate of a bottom center core 37 shown in Fig. 11, the core consisting of a round disk of sand mixture baked to the top of the plate and of a diameter to fit in the recesses formed in the inner ends of the blade molds by the detachable pieces 26 of the pattern blocks when the blade molds are grouped around the center of the plate in the manner shown in Fig. 11.

At equidistant points around the circumference of the plate there is provided a series -of holes 5 corresponding in number to the number of the propeller blades, the holes being spaced from the center of the plate to correspond with the holes in the ends of the flasks so that when the flasks are assembled on the plate in the manner shown and holes in the flasks are accurately registered with those in the plate, the flasks will be properly positioned to produce an accurately symmetrical propeller.

The flasks are positioned around the plate by pins dropped through the holes in the ends of the flasks and may, if desired, be further locked by means of bolts through the flanges of the flasks, but for large propellers the weight of the flasks is so great that there is no danger of any liability of displacement after they have once been set in accurate position.

After the flasks are positioned the joints between the meeting edges of the several blade molds and the bottom core are closed with slurry or other suitable mixture for the purpose, access being had to the interior of the mold through the opening at the top which at this time has not been closed. After the seams have been closed a center core 38 for forming the shaft opening in the hub of the propeller, of the shape shown in Fig. 11, is inserted through the top opening, the tapered bottom end of the center core fitting a corresponding recess in the center of the bottom core. The top opening is then closed with a disk-shaped top core 39 which fits into the recess at the top and the metal is ready for pouring.

The pouring may be effected by any suitable method, but for the best results I prefer to employ my improved method of pouring illustrated in Figs. l1, l2 and 13. To this end the upper halves of the blade molds are provided near the tips of the blades with holes or passages 40 and the top core 39 is also provided with holes, one or more for each blade. Rods (not shown) are set in the holes projecting above the top of the as sembled flasks and green sand is filled in the pit around the mold and piled up on top of the mold as indicated at 41. I then set in the sand two rectangular frames 42 long enough to reach from the end of one blade to the end of the adjacent blade, as indicated in dot and dash lines in Fig. 12, and the sand is then shaped around these frames 42 to form troughs 4a to receive the metal from the ladles. A frame 43 is also set over the center of the mold, and a middle trough 45 is formed with the frame at?) to provide a basin into which the metal can rise. The rods are then Withdrawn, leaving open passages leading from the ends of the troughs 44 into the end of each blade mold and exit passages leading into the middle basin 45.

To skim the metal as it is poured each trough 44: is divided into three compartments by means of transverse partitions 46 indicated in F 13, the partitions being provided with passages 47 leading from the bottom of the middle compartment into the end compartments. The metal is then poured into the middle compartment, the dirt and impurities which are lighter than the molten metal, rising to the top, and the clean metal from the bottom overflowing through the passages 47 into the end compartments when the level in the middle compartment rises above the upper ends of the passages opening into the end compart ments. From the end compartments, the

clean metal flows through the above1nentioned delivery passages into the ends of the blade molds.

It will be noted that the blade molds are set so as to incline downwardly toward the ends so that the mold is filled at the lower ends, the metal "adually rising in the molds so that any loose particles in the mold will rise with the rising level of the metal and fiow to the center. As the mold fills up the level of the metal rises in the hub opening and into the holes in the top core, thence overflowing into the middle basin, so that when the mold is filled there will be a pressure on the metal due to the head provided for by the elevation of the troughs and the receiving basin, thereby avoiding all shrinkage as the metal solidifies in the mold.

I have found in practice that a propeller cast by this method will be so accurately symmetrical in balance and pitch of its blades as to require no finishing after the propellers are removed from the mold. By using baked molds and cores for all parts of the propeller a much smoother surface is obtained than can be had with green sand molds, and by closing the joints in the mold after it is set up the casting is freefrom fins throughout. In recently cast propellers of more than ten thousand pounds weight, the weight of the finished propeller showed a variance of less than one-tenth of one per cent. of the theoretical weight.

It will be observed that with the bed plate and flasks and pattern boxes once accurately constructed, no further calibration or adjustment is required to set up the mold, and any number of propellers, each an exact duplicate of the other, may be successfully cast in the same apparatus.

As pointed out above, the molds are set with the driving face of the propeller downward. This arrangement not only permits the metal to be poured at the ends of the blades in the manner described but also insures a smooth solid surface on the driving face of the blades, for the reason that any dirt in the blade molds which should not be carried out through the risers at the center will of necessity rise to the top of the blade mold which shapes the back of the propeller.

I have shown and described my improved method as used for casting a four-blade propeller, but it will of course be understood that a propeller having any number of blades may be cast in the same manner by employing flasks with their inclined faces at the proper angle for the particular number of blades desired.

I claim:

1. The method of forming molds for east ing propellers which consists in forming separate and identical blade molds for each blade, each mold having a portion of its exterior accurately finished with the impression for the blade accurately positioned with relation to such portion, and then assembling the molds upon a previously prepared bed having a portion accurately finished for cooperation with the accurately finished parts of the blade molds, said finished bed portion being positioned on the bed so that when the blade molds are assembled on the bed with the cooperating parts in registration the impressions for the blades will be symmetrical with relation to a common center.

2. The method of forming molds for easting propellers which consists in forming separate and identical blade molds for each blade, each mold having an accurately finished exterior surface and a fastening part with the impression for the blade accurately positioned with relation to such surface and part, and then assembling the molds upon a previously prepared bed having accurately finished surface portions for cooperation with the accurately finished surfaces and also having fastening parts for cooperation with the fastening parts on said molds, the fastening parts on said bed being symmetrically located on the bed With respect to a common center.

3. The method of forming molds for casting propellers which consists in providing a series of identical flasks, one for each blade, each. flask having an accurately finished surface and a locating part, forming identical blade molds in said flasks with the blade impression in identical and accurate relation to said surface and part, and then assembling said flasks on a bed plate having an accurately finished surface for cooperation with the finished surfaces on the flasks and accurately positioned locating parts for cooperation with the locating parts of the flasks symmetrically arranged with respect to a common center.

14:. The method of forming molds for casting propellers which consists in setting up a bed plate having a machinefinished surface and a series of accurately located holes symmetrically arranged around a com mon center, forming a set of identical blade molds one for each blade, with an accurately finished exterior surface and fastening part accurately located with respect to the blade impression and setting up the blade molds on the bed plate with their position accurately determined by the holes in the bed plate.

The method of forming molds for easting propellers which consists in providing a two-part pattern box, each part having an accurately finished surface surrounding the blade pattern and with the blade pattern accurately positioned with respect to said surface, and a set of identical two-part flasks having accurately finished margins around their open sides and their opposite exterior faces also accurately finished, then forming a series of identical blade molds in said flasks from the same pattern box by positioning the pattern-box parts on the cooperating flask portions with the finished margins of the pattern box parts clamped to the finished margins of the flask parts to accurately and identically locate the blade impression in the flasks, and then assembling said flasks on a bed plate having an accurately finished surface for cooperation with finished surfaces on the flasks in positions determined by previously formed registering holes in the bed plate and flasks.

6. The method of forming molds for casting propellers which consists in setting up on a previously prepared bed plate a series of identical flasks each having a baked blade mold with the impression for the blade accurately positioned in the flasks, and fasten-- ing the flasks to the bed plate by means of previously located holes in the flasks and bed plate, with the ends of the flasks grouped together at a common center and with the blade impressions symmetrical with respect to said center.

7. The method of casting propellers which consists of setting up a series of identical blade molds with the ends of the blade molds grouped together around a common center, said blade molds having their meeting ends formed to provide a central hub opening, then filling the mold with molten metal by simultaneously pouring the metal into the outer ends of all the blade molds from an elevation to maintain a head on the metal and causing the metal to rise through the common central opening into an elevated receptacle, thereby providing a back pressure on the metal to take up the contraction.

8. The method of casting propellers which consists of setting up a series of identical blade molds with the ends of the blade molds grouped together around a common center, said blade molds having their meeting ends formed to provide a central hub opening, then filling the mold with molten metal by means of a trough positioned. above the molds, the trough having a receiving portion and also having a discharge portion communicating with the mold and an upwardly inclined feed orifice within its confines leading from itsreceiving portion to said discharge portion so that the metal Wlll be taken from the bottom of the trough and will flow only when a predetermined level is maintained in the trough.

9. An apparatus for forming molds for casting propellers comprising a bed plate having a finished surface and also having accurately located fastening means symmetrically positioned with respect to a common center, a series of flasks for the blades w th accurately finished surfaces for cooperation with the surface of the plate with their innor ends shaped to engage when the flasks are grouped around the previously determined center of the plate, and'accurately located fastening means on the flasks for cooperation with the fastening means on the plate and positioned to maintain the flasks in position.

10. An apparatus for casting propellers comprising a bed plate having a machinefinished surface, a series of fastening means accurately positioned around a common center on the plate, a series of two-part flasks having their bottom faces and their meeting edges machined to true surfaces, said flasks having their inner ends shaped to fit to gether at the common center when symmetrically arranged on the plate, and fastening means on each flask for cooperation with the fastening means on the plate for maintaining the flasks in position, and a pattern box for forming identical blade cores in each flask, said pattern box consisting of two parts for cooperation respectively with the two parts of the flasks and each part comprising a machine-finished back plate with its pattern block accurately posltloned thereon, said back plate having fastening means cooperating with the fastening means on the flask parts for accurately positioning the blade impression in the mold.

11. In the method of forming molds for casting propellers, the steps of providing a two-part pattern box, each part having a blade pattern accurately positioned upon it, and a set of identical two-part flasks; forming each half of a blade mold by clamping together one part of the pattern box and the corresponding part of the flask, ramming the sand mixture thereinto upon the pattern, then inverting the flask and pattern box parts unclamping the pattern box parts, and baking the flask-part containing the molded sand mixture; and fitting together the two flask parts with their attached half molds to form a flask having within it a complete mold for a single blade.

12. In the method of forming molds for casting propellers, the steps of providing a two-part pattern box, each part having a blade pattern accurately positioned upon it, and a set of identical two-part flasks, forming each half of a blade mold by clamping together one part of the pattern box and the corresponding part of the flask, ramming the sand mixture thereinto upon the pattern, then inverting the flask and pattern box parts, unclamping the pattern box part, and baking the flask part containing the molded sand mixture; fitting together the two flask parts with their attached half molds to form a flask having within it a complete mold for a single blade; repeating the mold-forming operations to obtain from the same pattern box a set of identical blade molds, one for each blade; and assembling the flasks containing the blade molds symmetrically about a common center with the mold cavities accurately positioned with respect to said center.

13. In the method of forming molds for casting propellers, the steps of providing a two-part pattern box, each part having a blade pattern accurately positioned upon it, and a set of identical two-part flasks, each flask having an accurately finished surface and a locating part; forming each half of a blade mold by clamping together one part of the pattern box and the corresponding part of the flask, ramming the sand mixture thereinto upon the pattern, then inverting the flask and pattern box parts, unclamping the pattern box part, and baking the flask part containing the molded sand mixture; fitting together the two-flask parts with their attached half molds to form a flask having within it a complete mold for a single blade; repeating the mold-forming operations to obtain from the same pattern box a set of identical blade molds, one for each blade; and then assembling the flasks containing the blade molds on a bed plate having an accurately finished surface for cooperation with the finished surfaces on the flasks and accurately positioned locating parts for cooperation with the locating parts on the flasks symmetrically arranged with respect to a common center;

14. The method of forming molds for casting propellers which consists in providing a series of flasks, one for each blade, each flask having an accurately finished surface, forming identical blade molds in said flasks with the blade impressions in accurate relation to said surface and then assembling said flasks on a bed having an accurately finished surface for cooperation with the finished surfaces on the flasks, with the flasks symmetrically arranged with respect to a common center.

15. The method of forming molds for casting propellers which consists in attaching a pattern box part to the open side of a flask part in accurately predetermined position, said pattern box part having a partial blade pattern accurately positioned with respect to the portion clamped to the flask part, then filling the flask part with sand mixture, similarly forming in the complementary flask part a mold of the reverse side of the blade with the blade impressions in the flask parts so positioned with respect to each other as to accurately register when the flask parts are connected together, similarly forming a blade mold for each blade of the propeller, then assembling the flasks on a previously prepared bed with the blade impressions symmetrical with respect to a common center.

16. An apparatus for forming molds for casting propellers, comprising a bed having an accurately finished surface and a series of flasks, one for each blade, having accurately finishee exterior surfaces for cooperati on with the surface of the bed whereby the flasks will occupy exact predetermined rela tive positions when assembled around a common center on said plate.

17. An apparatus for forming molds for casting propellers, comprising a bed having an accurately finished surface and a series of flasks, one for each blade, having accurately finished exterior surfaces for cooperation with the surface of the bed whereby the flasks will occupy exact predetermined relative positions when assembled around a common center on said plate, and a sectional pattern box comprising sections having impression forming surfaces and accurately finished locating surfaces, said locating surfaces being accurately positioned with respect to said mold forming faces, said flasks having surfaces finished for cooperation with said locating surfaces on the pattern box section to thereby locate the blade impressions accurately in said flasks.

In testimony whereof I aflix my signature.

THOMAS ()XENBRIDGE THACHER.

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