CA1072711A - Screw extruder - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
The invention provides a screw extruder for molding plastic materials. The extruder includes a prime mover and an extruding unit, separated from the prime mover. The extruding unit has a screw unit equipped with a screw and a speed reduction unit composed of planetary gears which transmit power to the screw unit. The reduction unit has an input shaft and output shaft aligned with each other and the screw; the output shaft being provided with a hole extending therethrough, and the input shaft being provided with a hole extending therethrough, and communicating with the hole of the output shaft. A transmission assembly transmits power from the prime mover to the reduction unit. The extruder is compact, light in weight and well balanced so that it is well adapted to mounting on a vertical column stand, and the openings through the input and output shafts make it easy to remove the screw from the screw unit in order to clean the inside thereof.

Description

The presen~ invention relates to a novel and improved screw extruder for molding plastic materials, and more particu-larly to a movable extruder having an extruding means mounted on a column standing on a pedestal.

An extruder of the type employing a column needs to be stable, relatively free rom troubles such as tipping over during the operation and transportation thereof, even when the extruding means is located at 2 high position on the column, and it also should be compact, light in weight, and well balanced.
The ability to readily remove the screw from the screw unit in order to clean the inside thereof is another important requir~-ment, in addition to those of economy, operability and the above--- mentioned stability.
Conventional movable extruders, generally provided with multiple stage ordinary reduction gears, are expensive, large in size and heavy since from two to four reduction stages are needed to get a suitable screw speed from the speed of the prime mover owing to the comparatively small reduction ratio per one stage, which results from the fact that the arrangemnt and . 20 dimensions of the parts contained therein are restricted because the peripheries thereof should be spaced from the shaft support-~ ing the screw and/or should not invade the cylindrical space ' ;~ behind the screw so that the shaft can be formed with a hole ''! therethrough into which a bar for removing the screw is insertable from the backside of the gear box. Consequently, in an extruder . ,~
:~: employing such a multiple stage reduction gear, the bending momen~ applied to the column becomes quite large and the ~-stability thereof is affected, since the weight per power ~ capacity is relativei~ heavy and the extruding means must be ;~ 30 considerably spaced from the column owing to the necessary large ;, . . , . . ,, ., .~,, , , - .

volume around the screw.
A worm gear often has been employed in extruders ;
instead of multiple stage ordinary reduction gears. While a comparatively large reduction ratio is obtainable by a single stage worm gear, there still are many troublesome deficiencies ; such as a tendency for the lubricant to become overheated, heavy weight, large size, and short durability due to abrasion of the teeth caused by the friction contact therebetwaen.
On the other hand, although planetary gears are superior to the above-mentioned gears from a viewpoint of effici-ency of power transmission, compactness, lightness in weight, as well as quietness and reduction in v bration, and therefore are quite suitable for an extruder (especially for a movable extruder which is not fixed to a floor), it is difficult to provide a device for r4moving the screw from the screw unit in order to clean the inside thereof, since they generally have output and input shafts which are axially aligned and the input shaft impedes direct contact from the backside of the reduction ~ unit with the end of the screw supported in the screw sleeve.
.~ 20 Therefore, conventional extruders of the column type hereto~or ~ have not adopted planetary gears.
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Conventional extruders often have utilized extruding~

means which are divided into an extruder unit not provided with ,, a speed reduction means and a power source which includes a speed reduction gear and motor, or gearmotor. In that case, the , extruder is apt to become out-oE-balance since the weight of ; the power source is rather heavier than that of the screw unit, and this tendency to instability has been aggravated in recent years by employment of motors of larger ~ower. Additionally, as for the mechanism which transmits power from the power source to , ~ , ~

-the screw unit, or a chain transmission should be employed, since the output shaEt oE the power source is rotated by large torque and at low speed and the center distance is relatively long.
However, chain transmission is not: suitable for an extruder of the column type because of noise and short durability when operated without lubricant.
The screw extruder of this invention has a well bal-anced extruding means consisting of an extruding unit provided with a reduction gear and a prime mover capable of employing a belt transmission, and it therefore it is quite stable and quiet during operation.
In an extruder for molding plastic materials, it is important to be able to readily remove the screw from the screw unit in order to clean the inside thereof. Conventional extru-ders often have employed a mechanism comprising a cap nut which is threaded onto the end of the screw sleeve supporting the screw and formed with a threaded hole at the center portion thereof, and a threaded bar which has enough length to push , the end of the screw and can be threaded into the hole of the cap nut. In a conventional extruder employing multiple stage conventional reduction gears, although there are some of the aforesaid deficiencies, it is not too difficult to provide such a mechanism owing to the comparative free arrangement of parts .i .
` contained therein.

As for an extruder employing planetary gears having an :
output shaft and input shaft aligned on the same axis, it is quite difficult to apply such a mechanism as described above, and therefore planetary gears have never been employed. The screw extruder of the present invention can resolve this diffi-culty by providing a hole extending through both the input shaftand the output shaft.

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A further problem resulting from oil leakage from an oil chamber into the hole in the shaft arises in case of an ex-truder equipped with planetary gears. In an extruder employing multiple stage conventional reduction gears having a wide range of shaft arrangement, it is somewhat easier to reduce or elimi-nate this oil leakage by separation of the output shaft from the input shaft and by providing the output shaft, i.e. the screw sleeve, with a hole extending therethrough to the backside of the gear box. However, in an extruder equipped with a reduction gear having an output shaft and input shaft aligned on one axis, for instance, in planetary gears, it is necessary to provide means to preclude leaks from the oil chamber into the hole com-municating with the oil chamber at the gap between the opposing ends of the input shaft and output shaft which are, of course, r longitudinally separated from each other due to their differences in speed of rotation.
The extruder of this invention employs a sealing mech-anism consisting of a boss extending from the end of the output .. ~
shaft and inserted in an opening formed in the opposing end of the input shaft and an oil seal positioned between the boss and the opposite opening, or alternatively a boss extending from the end of the input shaft and inserted in an opening formed in the opposing end of the output shaft and an oil seal.
Therefore, it is an object of the present invention to provide a novel and improved extruder for molding plastic mate-rials.
In accordance with the present invention, there is ; provided a screw extruder for molding plastic materials which includes a prime moverO an extruding unit, separated from the 30 prime mover, having a screw unit equipped with a screw and a ,~

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speed reduction unit composed of planetary gears which transmits power to the screw unit, the speed reduction unit having an input shaft and output shaft aligned with each other and with the screw in turn, the output shaft being formed with a hole extending therethrough and the input shaft being formed with a hole extend-ing therethrough and communicating with the hole of the output shaft to permit removal of the screw from the extruding unit;
and a transmission assembly for transmitting power from the prime mover to the speed reduction unit.
Other features and advantages of the invention will become apparent from the following description of embodiments of the invention, which makes reference to the accompanying drawings, in which:
Fig. 1 is a partially cutaway side view showing an embodiment of the screw extruder of the present invention;
Fig. 2 is a plan view of the screw extruder of Fig. l;
Fig. 3 is a partial view taken in longitudinal section through tha extruding unit of Fig. l;
Fig. 4 is a longitudinal section view showing another embodiment of a reduction gear in the extruding unit of Fig~ 3;
Fig. 5 is a perspective view showing the reduction gear of Fig.
4;
` Fig. 6 is a longitudinal section view showing another embodiment of a reduction gear in the extruding unit of Fig. 3;
Fig. 7 is a transverse section view showing the reduction gear of Fig. 6; ànd Fig. 8 is a longitudinal section view showing an embodiment of a device for removing the screw from the screw unit in the extruder of Fig. 1.
Referring to Fig. 1, the extruder 100 consists of a ~ - 5 -:~O~Y%~l~

column assembly 101 and an extruding means 102 which includes an extruding unit 80 having a screw unit 104 and speed reduction unit 17, a prime mover 81, and a power transmission assembly 106.
With reference to Fig. 1 and Fig. 2, a pedestal 67 has four legs 68, equipped with wheels 69, which extend radially from the boss 70 which is the central portion of the pedestal 67.
As for the legs, any number more than three may be utilized.
Wheels 69 for transferring may be removed if unnecessary. The lower end 72 of the column 71 is inserted into a hole of the boss i A bracket 73 mounted around the column 71 is slidable therealong up and down with the rotation of a feed screw (not ;~ shown). A rotatable shaft 74 is supported horizontally in a ` hole which passes through an extended portion formed in bracket 73. The rotatable shaft 74 and flanges 75, 76 fixed on each end of the shaft 74 are rotatable as one body.

A lever (not shown) formsd with a longitudinal guide .,~
groove (not shown) projects from the flange 75. A guide member 78 with a threaded hole is inserted slidably in the guide groove of the lever. A threaded bar 77, vertically disposed on bracket 73, is put in the threaded hole of the guide member 78. The threaded bar 77 is formed with a square portion 79 at the lower ~` end thereof and can be readily rotated by means of a spanner ; wrench. The lever rotates rotatable shaft 74 according to the distance moved by guide member 78 transferred up and down with the rotation of threaded bar 77.
An extruding uni-t 80 equipped with feet 82 and fixed on the flange 75 by the feet 82 and a prime mover 81 equipped ; with feet 83 and fixed on the flange 76 by the feet 83 are in-~ 30 clined with rotation of rotatable shaft 74 in accordance with ~ 2~

the revolution of threaded bar 77.
While a DC motor or induction motor with a magnetic coupling is generally utilized for a prime mover, an induction motor with a variable speed changer also is available.
Input shaft 18 of the extruding unit 80 and output shaft 84 of the prime mover are connected by means of a trans-mission assembly 106 consisting of a belt 86 and pulleys 39 and :
Referring to Fig. 3, the extruding unit 80 includes a reduction unit 17 and a screw unit 104. As for the screw unit ; 104, a screw 1 is held in a cylinder 2 which is secured to the hopper mount 3 formed with a feeder hole 4 and equipped with a .;`,3` hopper 5. The screw 1 is inserted into a screw sleeve 6 and is ~`. secured together by means of a key 7. Backpressure due to the .;, reaction of discharge pressure during the extruding operation. is . j ,.
applied to the thrust bearing 8 through the screw 1 and screw 0 sleeve 6.
i,l `~ A connecting bolt 10 is employed to connect the screw : unit 104 and the reduction unit 17 (that is, the hopper mount 3, a casing 9, and a spacer 11 are secured to the gear box 12). :
`~ The screw sleeve 6 is concentrically and longitudinally position~
ed by means of the thrust bearing 8 and a radial bearing 13 which :~
are tightened axially by way of a nut 14. Oil seals 15, 16 are .
used to avoid oil leakage from a chamber containing the above ~.
~ bearings 13 and 8.
,~ The reduction unit 17 consists of a gear box 12 and parts such as an input shaft 18, output shaft 19, solar gear 20 (number of teeth: Sl), planetary gears 21 (number of teeth: P) and internal gear 22 (number of teeth: S2) formed in the gear ;;
box 12. The planetary gears 21 are mounted on shafts 29 and ~ .

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retained by means of collars 30.
In a planetary gear se-t employing a rotatable solar gear 20 mounted fixedly on the iI-pUt shaft 18, stationary in-ternal gear 22 and planetary gears 21 supported rotatably on the shafts 29 which are secured to a flange extending radially from the output shaft l9, the orbital motion of the planetary gears 21 ;;
around the solar gear 20, induced as a result of relative rota-tion of the solar gear 20 and internal gear 22, is employed for the revolution of the output shaft 19. The reduction ratio between the input shaft and output shaft obtained in this gear arrangement is Sl/(Sl + S2), as is well known in the art. On ;..
;~ the other hand, since the reduction ratio derived from an ordi-nary one stage gear arrangement having two gears which possess a number of teeth Sl and S2, respectively, is Sl/S2, it is ob-. .
vious that the reduction ratio achieved by the planetary gear is higher than that by an ordinary gear arrangement. Bearings 25, 26 support the input shaft, and oil seals 32, 33 are employed to preclude oil leaks from the oil chamber 31.
~- The output shaft 19 is supported by bearings 27, 28 and ~` an oil seal 35 is located in the bearing cover 34. A hole 36 formed in the input shaft 18 and a hole 37 formed in the output shaft l9 are substantially isolated from oil chamber 31 by means of the oil seal 32.
In th:is embodiment, a circular space for mounting the oil seal 32 is defined by a gap between a hole formed in the output shaft and a boss projecting from the input shaft. In contrast, however, the gap may be defined by a gap between a -~
hole formed in the input shaft and a boss projecting from the output shaft. Alternatively, without employing an elongated boss inserted into the hole of the opposing shaft, a suitable ~
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sealing device such as a mechanical oil seal which is mount,ed on either the input shaft or the output shaft and can seal a gap between the opposing ends of sha:Ets by face to face sealing con-tact is available for this purpose.
The screw sleeve 6 is fastened to the o~ltput shaft 19 with a key 38. In this way, torque applied to the input shaft 18 is transmitted to the screw 1 through the planetary gears 21, output shaft 19 and screw sleeve 6. - ;
i ! A pulley 39 is fixed on the input shaft 18 by means of ' 10 a key 40. The input shaft 18 is formed with a threaded end 41.

An elongated boss 42 which is insertable into the hole 37 of :

.~ output shaft 19 extends from the end of the screw 1. The pulley . 39 is driven by the prime mover through belt 86. A rear plate ~:
.
23 is fastened to the gear box 12 with bolts 24.
Figures 4 and 5 show another embodiment o~ reduction unit 17, different from the above mentioned one. An eccentric ~-:
ring 43 is mounted on the input shaft 18 and is fixed by a key 44 thereon. The eccentric ring 43 is retained axially by means of snap rings 45, 46. A planetary gear 47 formed peripherally with teeth (number of teeth: P) which are in a s~ape of trochoid curve is mounted slidably on the eccentric ring 43.
An in-ternal gear having rollers 48 (number of the : roller: S) supported slidably on pins 49 which are secured at equal circular pitch to pin holder 50 is in meshing engagement with the planetary gear 47. Inner pins 51 equipped with inner `
rollers 52,~ which are rotatably supported therearound, are fixed to a flange extending radially from the output shaft 190 With the inner rollers 5~ so adapted that they can rotate in holes 53 formed in planetary gear 47 with a small clearance there-between and partially in contact with the inner surface there-;~ _ g _ -lO~

of, the rotation of the planetary gear 47 on its axis is employ-ed for that of output shaft 19. Fig. 5 shows in perspective an arrangement of the input shaft 18, eccentric ring 43, planetary gear 47, inner rollers 52 and output shaft 19.
An end plate 23 and the outer pin holder 50 are secured ; to the gear box 12 by means o extended bolts 24. ~he input ~ shaft 18 is supported by bearings 25, 26. Since other features ;- of the construction, such as the sealing device for preventing . oil;leakage from oil chamber 31 to holes 36, 37 are ~uite similar to those of Fig. 3, the description thereof is omitted. In the planetary gear of this type employing a planetary gear 47 and an . .; .
internal gear with rollers (the planetary gear 47 being revolved around an axis of the input shaft by means of the eccentric ring mounted on the inpuk shaft) the rotation of planetary gear 47 on its axis caused by meshing enyagement with the internal gear or ~ .
the rollers 48 is employed for rotation of the output shaft 19 through the inner rollers 52. The reduction ratio between the ; output shaft and inpu~ shaft obtained in this gear arrangement is (S-P)/P, as is well known in the art. In the case where the difference in the number of teeth between the internal gear and the planetary gear 47 is one, a high reduction ratio of l/P is obtainable.
Figures 6 and 7 show another embodiment of a reduction ~ -unit according to the invention. In this embodiment, an oval cam 54 is mounted fixedly on input shaft 18. With the rotation of the input shaft 18, an outer ring 57 is deformed cyclically and elliptically owing to the rotation of the balls 56 around the inner ring 55 on the oval cam 54. That is, when the outer ring 57 is locked against turning, an oval shape rotates at the same speed as the oval cam 54. A flexible planetary gear 58 (number ~ ,.

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of teeth: P) mounted around the outer ring 57 is also deformed elliptically with the rotation of the oval cam 54.
Since a major axis of a pitch oval di~meter of the flexible planetary gear 58 is so arranged that it is the same as the pitch circular diameter of an internal gear 59 (number of teeth: S) formed in the gear box 12, the flexible planetary gear 58 can be precisely engaged with the internal gear 59 in the neighborhood of the major axis thereof.
On the other hand the portion adjacent to the minor axis is not in meshing engagement with internal gear 59, and therefore the meshing portion between the planetary gear 58 and the internal gear 59 is changeable cyclically with the rotation of the oval cam 54.
Since the internal gear 59 is at rest, the flexible planetary gear 58 ~hich possesses a number of teeth less than that of the internal gear 59 rotates in reverse direction against the rotating direction of the oval cam 54 and revolves the output shaft 19 formed therewith.
~:~ An end plate 23 is fixed on the ~ear box 12 by means of extended bolts 24. The input shaft 18 is rotata~ly supported on the bearings 25, 26. Since other features of the construction such such as the sealing device for preventing oil leakage from oil chamber 31 into holes 36, 37 are quite similar to those of Fig. 3, the description thereof is omitted. In a planetary gear of the : type employing a planetary gear 58 and an internal gear 59, the planetary gear is substantially revolved around the axis of the input shaft 18 by means of the oval cam 54, and the rotation thereof on its axis caused by meshing engagement with the internal gear 59 is employed for the rotation of the output shaft 19 through a flexible cylindrical portion of the planetary gear 58.

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The reduction ratio obtained by t:his mechanism is (S - P)/P, which will be clear to those skilled in the art.
When S - P is two, since S - P (difference in number of teeth between the planetary gear 58 and internal gear 59) should be even-numbered in case of employing an oval cam, a high reduction ratio, that is 2/P, is obtainable. Instead of the oval cam as employed in this embodiment, an eccentric circular cam or polygonal cam (including a trianglar cam), the corners of which are chamfered, is also available. The reduc~ion ratio is . 10 l/P for the eccentric circular cam and is N/P for N-polygonal cam.
Fig. 8 shows in detail the device for removing the screw from the screw unit 104. A cap nut 60 having a threaded hole 66, into which a threaded bar 61 is insertable, is threaded onto the threaded end 41 on input sha~t 18. And end memeber 6Z
provided with a handle 63 is secured to the head of threaded ~ bar 61.
: The threaded bar 61, having enough length to push the end of elongated boss 42 of screw 1, can remove screw 1 from the screw unit 104 as a result of movement o~ the threaded bar 61 along the hole with the rotation of the handle 63. Preferably, the input shaft 18 should be locked against rotation by means of a stopper 64 which extends through a hole 65 formed in pulley 39 and and is threaded into the ~hreaded hole 64a formed at the end plate 23 of gear box 12, and the thus threaded bar 61 can be moved longitudianlly without rotating the input shaft 18.
It has been found that the movable ex~ruder of the invention having an extruding means mounted on a column standing on a pedestal can readily obtain a suitable low speed for operating a screw extruder from a high speed prime mover by means of a reduction gear with a high reduction ratio, for example a ~`
~ ! - 12 planekary gear set.
Further the extruder of this invention is quite stable and relatively free from troubles such as tipping over during the transportation and operation therof, even when the extruding means is located at a high posit:ion on the column, since the extruding means is divided into well-balanced extruding and prime mover units, and the extruding means can be mounted close to the column due to its compactness.
Also, a pumping system for cooling the lubricant is unnecessary for the screw extruder of this invention owing to the high efficiency of the planetary gear set adopted therein. It is difficult to employ such a pumping system in a movable extruder, and particularly for an extruder having an inclinable extruding means.
The extruder of this invention, in spi e of its being a column type, is quite quiet and exhibits little vibration owing to the planetary gears having wel~-balanced transmission elements.
Furthermore, although the extruder of the invention employs a planetary gear set having an output shaft and input shaft aligned on an axis, it is easy to remove the screw from the screw unit due to the presence of the holes through the shafts, and it also is free from oil leakage into those holes from oil chambers owing to the good sealing construction. -.,, , ; . , . ~ ~ ~ ' . , .;., , . 1 ; . ,' !
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Claims (9)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A screw extruder for molding plastic materials, comprising: a prime mover; an extruding unit, separated from the prime mover, having a screw unit with a screw and a speed reduction unit composed of planetary gears which transmits power to the screw unit, the speed reduction unit having an output shaft and an input shaft aligned with each other and with said screw, the output shaft being formed with a hole extending there-through and the input shaft being formed with a hole extending therethrough and aligned with the hole of the output shaft to permit removal of said screw from the extruding unit; and a transmission assembly for transmitting power from the prime mover to the input shaft of said speed reduction unit.

2. A screw extruder as defined in claim 1, wherein the hole in the input shaft and the hole in the output shaft communicate in a space provided with a sealing mechanism to preclude oil leakage from an oil chamber thereinto.

3. A screw extruder as defined in claim 2, wherein said sealing mechanism comprises a boss extending from an end of the output shaft and inserted into an opening formed at the opposing end of the input shaft and an oil seal positioned between said boss and said opening.

4. A screw extruder as defined in claim 2, wherein the sealing mechanism comprises a boss extending from an end of the input shaft and inserted into an opening formed at the opposing end of the output shaft, and an oil seal positioned between said boss and said opposing hole.

5. A screw extruder as defined in claim 2, wherein the sealing mechanism includes an oil seal which is mounted on at least one shaft selected from the group consisting of the input shaft and the output shaft and which is capable of sealing a gap between the opposing ends of said shafts by face to face sealing contact.

6. A screw extruder as defined in claim 1, wherein the transmission assembly is formed by a belt and pulley assembly.

7. A screw extruder as defined in claim 1, 2 or 6, provided with means for removing the screw from the screw unit.

8. A screw extruder as defined in claim 1, 2 or 6, provided with means for removing the screw from the screw unit which comprises a threaded end formed on the end of the input shaft, a cap nut threaded onto the threaded end of the input shaft and having a threaded hole therethrough, and a threaded bar which is insertable into the threaded hole of the cap nut thereby to extend through the holes in said input and output shafts to contact said screw.

9. A screw extruder as defined in claim 1, 2 or 6, mounted on a column standing on a pedestal.