An apparatus for extracting screw elements from a screw shaft comprises a frame, a stationary clamp mounted on the frame and disposable between open and closed positions, a carriage mounted on the frame for motion toward and away from the stationary clamp, a movable clamp mounted on the carriage for motion therewith and disposable between open and closed positions, a first drive coupled to the stationary clamp for opening and closing the stationary clamp, a second drive coupled to the movable clamp for opening and closing the movable clamp, and a third drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a downstream screw element by the stationary clamp, clamping of an upstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element held in place by the stationary clamp from the screw shaft. The procedure is repeated until all the remaining screw elements are removed.
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0. 25. An apparatus for extracting a plurality of screw elements from a screw shaft comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a first screw element, the stationary clamp being movable between an open position permitting reception of a first screw element and a closed position clamping the first screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, and d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a second screw element, the movable clamp being movable between an open position permitting reception of a second screw element and a closed position clamping the second screw element, wherein clamping of a first screw element by the stationary clamp, clamping of a second screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of one of the first and second screw elements from the screw shaft.
0. 24. An apparatus for extracting a plurality of screw elements from a screw shaft comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a first screw element, the stationary clamp being movable between an open position permitting reception of a first screw element and a closed position clamping the first screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a second screw element, the movable clamp being movable between an open position permitting reception of a second screw element and a closed position clamping the second screw element, and e) a drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a first screw element by the stationary clamp, clamping of a second screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of one of the first and second screw elements from the screw shaft.
0. 11. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a stop provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a downstream screw element, the stationary clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, and d) a movable clamp mounted on the carriage for motion therewith and configured to clamp an upstream screw element, the movable clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, wherein clamping of a downstream screw element by the stationary clamp, clamping of an upstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
0. 22. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a stop provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp an upstream screw element, the stationary clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, and d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a downstream screw element, the movable clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, and wherein clamping of an upstream screw element by the stationary clamp, clamping of a downstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
0. 21. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a stop provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp an upstream screw element, the stationary clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a downstream screw element, the movable clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, and e) a drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of an upstream screw element by the stationary clamp, clamping of a downstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
0. 10. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a stop provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a downstream screw element, the stationary clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp an upstream screw element, the movable clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, and e) a drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a downstream screw element by the stationary clamp, clamping of an upstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
0. 23. An apparatus for extracting a plurality of screw elements from a screw shaft comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a first screw element, the stationary clamp being movable between an open position permitting reception of a first screw element and a closed position clamping the first screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a second screw element, the movable clamp being movable between an open position permitting reception of a second screw element and a closed position clamping the second screw element, e) a first drive coupled to the stationary clamp for opening and closing the stationary clamp, f) a second drive coupled to the movable clamp for opening and closing the movable clamp, and g) a third drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a first screw element by the stationary clamp, clamping of a second screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of one of the first and second screw elements from the screw shaft.
1. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a collar provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp a downstream screw element, the stationary clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp an upstream screw element, the movable clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, e) a first drive coupled to the stationary clamp for opening and closing the stationary clamp, f) a second drive coupled to the movable clamp for opening and closing the movable clamp, and g) a third drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a downstream screw element by the stationary clamp, clamping of an upstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
0. 12. An apparatus for extracting a plurality of screw elements from a screw shaft, the screw elements being slid over the screw shaft from a downstream end thereof and held in place against a stop provided at an upstream end thereof, the apparatus comprising:
a) a frame, b) a stationary clamp mounted on the frame and configured to clamp an upstream screw element, the stationary clamp being movable between an open position permitting reception of an upstream screw element and a closed position clamping the upstream screw element, c) a carriage mounted on the frame for motion toward and away from the stationary clamp, d) a movable clamp mounted on the carriage for motion therewith and configured to clamp a downstream screw element, the movable clamp being movable between an open position permitting reception of a downstream screw element and a closed position clamping the downstream screw element, e) a first drive coupled to the stationary clamp for opening and closing the stationary clamp, f) a second drive coupled to the movable clamp for opening and closing the movable clamp, and g) a third drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of an upstream screw element by the stationary clamp, clamping of a downstream screw element by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft.
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This application is a continuation of U.S. patent application Ser. No. 09/174,644, filed on Oct. 19, 1998 now U.S. Pat. No. 6,081,983, and claims the benefit of U.S. provisional patent application Serial No. 60/085,536, filed May 15, 1998.
The present invention generally relates to plastic forming processes (casting, molding, etc.) and, particularly, to extruders used in such processes. More particularly, the present invention relates to an apparatus for removing screw elements from an extruder screw shaft for cleaning, inspection, repairs or replacement.
Extruders are used extensively in the plastics industry. For example, extruders are typically employed in the plastics industry for producing plastic pellets from raw materials. These extruders comprise of two basic sections: the process section (extruder screw and barrel) and the forming section (head and die).
Raw material is loaded into a hopper which gravity feeds to an extruder screw rotatably mounted in a heated barrel. The screw is the heart of the extruder and consists of feed, transition and metering zones. The feed zone conveys the solid or sometimes half-molten or molten raw material out of the feed throat area to the transition zone, which starts compressing the preheated material. This zone forces the plastic against the heated barrel and continues the melting process, which is completed at the beginning of the metering zone. The metering zone conveys the molten plastic to the head and die section at uniform rates and under high pressure. The molten plastic passes through the die, where it is continuously formed into round strands or filaments (or other geometrical shapes). The round strands are then carried through a water cooling bath. When sufficiently cooled, the strands are fed to a chopper to be cut into pellets.
These pellets are produced in many different colors depending upon the application. Typically, injection molding process is used to transform these plastic pellets into molded products at high production rates and with good dimensional accuracy. For example, injection molding machines are used for molding television cabinets in assorted colors in the consumer electronics industry.
A conventional extruder screw comprises a rotatable shaft carrying a plurality of screw elements, which are configured to form a continuous helical spiral or thread on the outer surface thereof. Each of these screw elements have a central opening therein for receiving the shaft. The outer diameter of the shaft is slightly smaller than the inside diameter of the opening in the screw elements to provide a slip fit. The screw elements are slid over the shaft from one end ("the downstream end") and securely held in place against a collar or a flange either secured or integrally formed at the other end ("the upstream end"). The inner surfaces of the opening in the screw elements and the outer surfaces of the shaft are splined or serrated to ensure a good coupling between the screw elements and the shaft.
Normal extrusion operations at high temperatures and pressures force molten plastic between the screw elements and the shaft and into the splines meshing the screw elements to the shaft. Often the screw elements bond to the shaft due to close tolerances, high temperatures and use of highly filled plastics.
It is desirable to remove the screw elements from the screw shaft every time there is change in the pellet color to avoid cross contamination (which can be often depending on the batch size). The screw elements can then be thoroughly cleaned to remove the plastic from the previous batch and re-installed on the screw shaft. The need for frequent removal of the screw elements from the shaft is a problem that has plagued the extruder industry for a long time.
Screw elements may be heated to very high temperatures (for example, 900 degrees Fahrenheit) and forced out by using a sledge hammer and a brass bar (so-called "heat and beat" technique). This method of removing the screw elements from the shaft is undesirable due to the damage it can cause to the microstructure and the dimensional accuracy of the screw elements and the shaft. The hardened and wear resistant screw shaft and elements are particularly susceptible to cracking. Local overheating can cause deformation of the screw elements. The screw element extractor in accordance with the present invention allows removal of the screw elements from the screw shaft while reducing the risk of element damage, reducing the time for element removal and improving the safety of the personnel.
According to a first aspect of the present invention, an apparatus for extracting screw elements from a screw shaft comprises a frame, a stationary clamp mounted on the frame and disposable between open and closed positions, a carriage mounted on the frame for motion toward and away from the stationary clamp, a movable clamp mounted on the carriage for rectilinear motion therewith and disposable between open and closed positions, a first drive coupled to the stationary clamp for opening and closing the stationary clamp, a second drive coupled to the movable clamp for opening and closing the movable clamp, and a third drive coupled to the carriage for causing motion of the carriage toward and away from the stationary clamp, wherein clamping of a downstream screw element by the stationary clamp, clamping of an upstream screw element (or an upstream section of the screw shaft) by the movable clamp and one or more strokes of the carriage away from the stationary clamp result in removal of the downstream screw element from the screw shaft. The procedure can be repeated to remove all the remaining screw elements.
In accordance with another aspect of the present invention, a screw element extractor and a method of operating a screw element extractor comprise an apparatus for, and the steps of, mounting a stationary clamp on a frame, reciprocally mounting a carriage on the frame for motion toward and away from the stationary clamp, mounting a movable clamp on the carriage for motion therewith, opening the stationary clamp, opening the movable clamp, positioning the carriage adjacent the stationary clamp, supporting a screw shaft along an axis defined by the stationary and movable clamps such that its downstream end is disposed toward the stationary clamp and its upstream end is disposed toward the movable clamp, positioning a downstream screw element into the stationary clamp, closing the stationary clamp to hold the downstream screw element in place, closing the movable clamp to clamp an upstream screw element (or an upstream section of the screw shaft), moving the carriage away from the stationary clamp to extract the downstream screw element held in place by the stationary clamp, and opening the stationary clamp to release the downstream screw element.
Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiments exemplifying the best mode of carrying out the invention are presently perceived and the accompanying drawings which illustrate the invention.
In the drawings:
FIGS. 8(a) and (d) are schematic views of a screw shaft carrying one or more screw elements.
Referring now to the drawings, a screw element extractor 10 constructed according to the present invention includes a base frame 12 having downstream and upstream ends 14 and 16 respectively. A stationary clamp 18 is mounted on the frame 12 adjacent to the downstream end 14 thereof. As shown in
As shown in
As shown in
A set of three (3) operator controls 86, 88 and 90 are mounted on the frame 12 and coupled to the first set of hydraulic motors 28, 30, the second set of hydraulic motors 48, 50 and the hydraulic motor 52 for respectively controlling the operation of the stationary clamp 18, the movable clamp 38 and the carriage 32. An emergency stop 92 is mounted next to the operator controls 86-90 to allow the operator to shut down all operations instantaneously should an emergency occur. An electrical control panel and a motor starter box, identified by the numeral 94, is conveniently located on the front side of the frame to increase the safety of operations and to protect the electrical system from spikes in the power line.
The extruder screw 100 comprises a rotatable shaft 106 carrying a plurality of screw elements 108, which are configured to form a continuous helical spiral or thread on the outer surface thereof. Each of these screw elements 108 have a central opening 110 therein for receiving the shaft 106. The outer diameter of the shaft 106 is slightly smaller than the inside diameter of the opening 110 in the screw elements to provide a slip fit. The inner surfaces of the opening 110 in the screw elements 108 and the outer surfaces of the shaft 106 are splined or serrated to ensure a good coupling between the screw elements and the shaft. The screw elements 108 are slid over the shaft from the downstream end 102 and securely held in place against a collar 114 formed at the upstream end 104. A drive pinion 116 is provided for driving the shaft 106 during the operation of the extruder.
The operation of the screw element extractor 10 of the present invention will be now described in conjunction with four (4) illustrative examples diagrammatically shown in FIGS. 8(a) to (d). Referring to FIG. 8(a), the method of removing a single screw element 108 from the screw shaft 106 comprises the steps of: opening the stationary clamp 18, opening the movable clamp 38, positioning the carriage 32 adjacent the stationary clamp, supporting the screw shaft 106 on the outriggers 54 and 56 along the generally horizontal axis 58 defined by the stationary and movable clamps such that its downstream end 102 is disposed toward the stationary clamp and its upstream end 104 is disposed toward the movable clamp, positioning the screw element 108 to be extracted into the stationary clamp, closing the stationary clamp to hold the screw element in place, closing the movable clamp to clamp the screw shaft 106, moving the carriage away from the stationary clamp to extract the shaft from the screw element held in place by the stationary clamp, opening the stationary clamp to release the screw element and opening the movable clamp to release the screw shaft.
Referring to FIG. 8(b), the method of removing a single screw element 108 from the screw shaft 106 comprises the steps of: opening the stationary clamp 18, opening the movable clamp 38, positioning the carriage 32 adjacent the stationary clamp, supporting the screw shaft 106 on the outriggers 54 and 56 along the generally horizontal axis 58 defined by the stationary and movable clamps such that its downstream end 102 is disposed toward the stationary clamp and its upstream end 104 is disposed toward the movable clamp, positioning the screw element 108 to be extracted into the stationary clamp, closing the stationary clamp to hold the screw element in place, closing the movable clamp to clamp the screw shaft 106, moving the carriage away from the stationary clamp to displace the screw element held in place by the stationary clamp toward the downstream end 102 of the screw shaft, performing the following steps one or more times until the screw shaft is completely extracted from the screw element: (opening the movable clamp, moving the carriage toward the stationary clamp, closing the movable clamp to clamp the screw shaft and moving the carriage away from the stationary clamp to further displace the screw element held in place by the stationary clamp toward the downstream end of the screw shaft), opening the stationary clamp to release the screw element and opening the movable clamp to release the screw shaft.
Referring to FIG. 8(c), the method of removing a pair of screw elements 108 and 108' from the screw shaft 106 comprises the steps of: opening the stationary clamp 18, opening the movable clamp 38, positioning the carriage 32 adjacent the stationary clamp, supporting the screw shaft 106 on the outriggers 54 and 56 along the generally horizontal axis 58 defined by the stationary and movable clamps such that its downstream end 102 is disposed toward the stationary clamp and its upstream end 104 is disposed toward the movable clamp, positioning the downstream screw element 108 to be extracted into the stationary clamp, closing the stationary clamp to hold the downstream screw element in place, closing the movable clamp to clamp the screw shaft 106, moving the carriage away from the stationary clamp to extract the shaft from the downstream screw element held in place by the stationary clamp, opening the stationary clamp to release the downstream screw element, moving the carriage toward the stationary clamp to return the screw shaft to its original position, closing the stationary clamp to hold the screw shaft in place, opening the movable clamp, moving the carriage away from the stationary clamp, closing the movable clamp to clamp the screw shaft, opening the stationary clamp, moving the carriage toward the stationary clamp to position the upstream screw element 108' into the stationary clamp, closing the stationary clamp to hold the upstream screw element in place, moving the carriage away from the stationary clamp to extract the screw shaft from the upstream screw element, opening the stationary clamp to release the upstream screw element and opening the movable clamp to release the screw shaft.
Referring to FIG. 8(d), the method of removing a plurality of elements 108, 108', 108" from a screw shaft 106 comprises the steps of: (a) opening the stationary clamp 18, (b) opening the movable clamp, (c) positioning the carriage 32 adjacent the stationary clamp, (d) supporting the screw shaft 106 on the outriggers 54 and 56 along the generally horizontal axis 58 defined by the stationary and movable clamps such that its downstream end 102 is disposed toward the stationary clamp and its upstream end 104 is disposed toward the movable clamp, (e) positioning the downstream screw element 108 to be extracted into the stationary clamp, (f) closing the stationary clamp to hold the downstream screw element 108 in place, (g) closing the movable clamp 38 to clamp an upstream screw element (for example, 108"), (h) moving the carriage away from the stationary clamp to displace the downstream screw element 108 held in place by the stationary clamp toward the downstream end of the shaft, (i) performing the following steps one or more times until the screw shaft is completely extracted the downstream screw element 108: (opening the movable clamp, moving the carriage toward the stationary clamp, closing the movable clamp to clamp an upstream screw element and moving the carriage away from the stationary clamp to further displace the downstream screw element 108 toward the downstream end of the clamp shaft), (j) opening the stationary clamp to release the downstream screw element 108, (k) opening the movable clamp to release the upstream screw element 108, (1) moving the carriage toward the stationary clamp, (m) positioning the second downstream screw element 108' to be extracted into the stationary clamp, (n) closing the stationary clamp to hold the second downstream screw element 108' in place, (o) closing the movable clamp to clamp an upstream screw element, (p) moving the carriage away from the stationary clamp to displace the second downstream screw element 108' held in place by the stationary clamp toward the downstream end of the shaft, (q) performing the following steps one or more times until the screw shaft is completely extracted the second downstream screw element 108': (opening the movable clamp, moving the carriage toward the stationary clamp, closing the movable clamp to clamp an upstream screw element and moving the carriage away from the stationary clamp to further displace the second downstream screw element 108' toward the downstream end of the screw shaft), (r) opening the stationary clamp to release the second downstream screw element 108', and (s) repeating the steps "k" to "r" to extract all the remaining elements from the screw shaft.
Illustratively, the hydraulic motors 28, 30, 48 and 50 for actuating the stationary clamp 18 and the movable clamp 38 are manufactured by Parker Hannifin Corporation, Model No. 2.50J2HU14AX3.00. The hydraulic motor 52 for driving the carriage is manufactured by Parker Hannifin Corporation, Model No. 5.00CP2HU24AX12.00. The hydraulic motors 54", 56" for driving the outrigger supports 54', 56' are manufactured by Parker Hannifin Corporation, Model No. 1.50J2HU18AX4.00. The hydraulic motor and pump used for supplying pressurized fluid to various hydraulic motors is manufactured by Fenner Stone, Model No. KMC17, KP16, KN12, KC08, KR46, KH, AA-1.
In the embodiments shown and described in
Alternately, one may reverse the configuration by clamping a downstream screw element to be extracted by the movable clamp 38, clamping an upstream screw element by the stationary clamp 18 and displacing the carriage 32 one or more times to extract the downstream screw element held in place by the movable clamp from the screw shaft. The procedure can be repeated until all the remaining elements are removed.
Although the present invention has been described in detail with reference to certain preferred embodiments, variations and modifications exist within the scope and spirit of the present invention as described and as defined in the following claims.
Hodgson, Robert S., Mattingly, Michael J.
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