Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Corrugating
Reexamination Certificate
2000-09-07
2004-04-13
Davis, Robert (Department: 1722)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Corrugating
C264S568000, C264S209400, C425S195000, C425S233000, C425S326100, C425S336000, C425S369000, C425S384000, C425S388000, C425S396000
Reexamination Certificate
active
06719942
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to production of thermoplastic tubing and formable plastic products and, more particularly, relates to a method and apparatus for producing small and large diameter thermoplastic tubing and composite tubing structures.
DESCRIPTION OF RELATED ART
One known method for manufacturing corrugated pipes is to extrude a tube of thermoplastic from a head and then conform that tube to the interior of a corrugated mold tunnel formed by mold blocks. Mold blocks typically come in pairs and mate together to form a portion of the mold tunnel, and the thermoplastic is either blown into shape (by pressure created within the plastic tunnel) or vacuumed into shape (where vacuum draws the air from around the mold tunnel). Typically, the mold blocks operate in a clam shell-type fashion such that each of the mold block pairs pivot on an axis into mating engagement with one another. Examples of clam shell type corrugators are shown in U.S. Pat. Nos. 5,645,871; 5,494,430; 4,439,130 and others. The clam shell-type shape of mold blocks are susceptible to “sawtooth” imperfections which can occur throughout the mold tunnel. Sawtoothing occurs when successive mold blocks are tilted slightly rather than perfectly aligned with the axis of the mold tunnel. The hinged mold carrier, when closed, has a tendency to lean back in the opposite direction of travel during the molding process. This “sawtoothing” creates molding lines as well as a potential loss of vacuum.
The clam hell type mold carriers typically require the use of multiple custom-machined components and have a high manufacturing cost. The hinge pin is subject to external forces which results in wear on the hinge pin. A worn hinge pin may not allow the mold to pivot closed properly which could prevent the tubing firm forming properly. Furthermore, wear and misalignment of the pivoting pairs may result in the hinged mold carrier bending or breaking some of the custom-machined components.
At least one prior art device, U.S. Pat. No. 5,510,071 teaches a pair of mold blocks that are operated differently from the clam shell variety. Instead of using a hinged pivot, as is customary in the art, this device allows for transverse linear recipcal travel for closing and opening of the mold block pair. The apparatus taught by the '071 Patent utilizes reciprocal linear travel for the carriage supporting the mold blocks. There is no teaching in the '071 Patent to utilize linearly opening and closing of mold block pairs in a continuous loop corrugator.
Typically mold blocks must be maintained within an acceptable range of temperatures during the molding process. However, during the extrusion press, hot plastic is extruded into the mold blocks which tends to heat the blocks. To maintain acceptable temperatures the blocks must be cooled. Cooling of mold blocks maybe a problem. Inadequate cooling of mold blocks may lead to excessive temperatures for the molding process and result in degradation of the quality of molded tubes. Too much cooling may result in crackling of the exterior surface of molded tubes thereby giving the impression of an alligator-like skin on the pipe surface. Traditionally, mold blocks have been water cooled with internal cooling passages within each blocks. Failure of water lines and water leakage is a problem for many corrugator designs. If significant water leaks into the mold cavity during molding, a defective product may result, requiring the corrugator to be shut down, the leak located and the mold block or other leaking component repaired. Accordingly improved cooling techniques are desired.
In order to keep mold blocks in contact with the product to produce good forming characteristics, prior art corrugators utilize chain driven mold blocks where mold blocks are located substantially around the entire perimeter of a continuous path. At least one improvement is illustrated by U.S. Pat. Nos. 5,494,430 and 5,531,583 where a mold train drive and a shuttle drive are utilized to minimize the number of mold blocks. Nevertheless, this system relies on gearing and at least two separate chain drives: one to shuttle molds from the end of the mold tunnel to the beginning of the mold tunnel and one to drive molds through the mold tunnel.
The mechanical drive system utilized by corrugator designs in the prior art typically have mechanical drives comprised of motors, gear boxes, gear reductions, transmissions, sprockets, chains, idler sprockets, power take off shafts and other mechanical drive systems. These drive methods and systems may require extensive maintenance. Furthermore, these drive methods are subject to wear as many components are in direct contact with one another. There is also the potential problem of backlash in the driving mechanisms, which may be accentuated in the propulsion of the molds.
The corrugators such as taught by U.S. Pat. Nos. 5,494,430; 5,645,871; and others are known as vertical style corrugators. A forming mold tunnel is in line with the extrusion head die. The non-forming (return) of the mold chain is typically overhead or below the product center line. As shown in FIG. 2 of U.S. Pat. No. 5,494,430, the molds which are not in use in the mold process are typically open and cannot be used in the manufacture of product until they return to the forming side of the corrugator. This results in a machine having a greater height in the vertical plane and does not utilize the non-forming molds in production. U.S. Pat. No. 5,257,924 teaches at least one method for using multiple molding sections in a corrugator.
Maintaining a vacuum is another concern in many corrugator and mold designs. U.S. Pat. Nos. 4,718,844 and 5,059,109 teach at least two different vacuum configurations for mold blocks. Thermoexpansion of forming molds can cause vacuum loss through the vacuum interface during production. The vacuum interface is typically a rigidly fixed device that interfaces with the molds. If the interface is not complete, vacuum leakage will occur. Although it appears that improvements have been made to the mold blocks for maintaining vacuum, the interface with the vacuum does not appear to have been thoroughly perfected.
With the clam shell style mold carriers, the mold carriers typically operate on an oval track. The radius on the curved portions of the track typically is relatively large. This causes a need for the extrusion die to be of relatively long length. Longer dies have been found to create problems in the manufacture of double walled tubing such as high head pressures and/or uneven distribution of the extruding plastic. Furthermore, long die lengths reduce the potential selection of materials to be utilized which could otherwise be utilized with shorter die lengths.
A need exists to utilize materials such as polyvinylchloride (PVC). Polyvinylchloride (PVC) requires a shorter die length than is available in many prior art corrugators.
When constructing some prior art corrugators, a mold chain length has been fixed. If a customer has a special product, or wants to increase or decrease the length of the machine, the customer could typically expect extensive modifications to be required and performed upon that particular corrugator. Today, there is a high demand for greater and greater speed which often results in longer and longer forming tunnels. For instance, when a 20-foot mold section was once found adequate, a consumer now may desire a 40-foot mold section. This modification may be extensive and require a lengthy down time for the machine.
SUMMARY OF THE INVENTION
The present invention recognizes and addresses the foregoing disadvantages, and others, of prior art construction and methods. Accordingly, it is an object of the present invention to provide an improved machine, such as a corrugator, for making plastic tubing or other formed plastic product. A trackway defining a continuous path and a plurality of carriages for carrying mold blocks about the continuous path are utilized. Each of the carriages transports at least one pair of mold blocks
Ellis Claude R.
McKeehan Tom
Triplett David A.
Winner Gary
Davis Robert
Del Sole Joseph S.
Miller & Martin LLP
Stark Stephen J.
LandOfFree
Method and apparatus for production of tubing does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and apparatus for production of tubing, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and apparatus for production of tubing will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3197380