Metal fusion bonding – Process – With clamping or holding
Reexamination Certificate
1999-09-13
2001-12-04
Elve, M. Alexandra (Department: 1725)
Metal fusion bonding
Process
With clamping or holding
C228S029000, C228S044300, C269S043000
Reexamination Certificate
active
06325277
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is generally directed to an apparatus and method for aligning tubing, and more particularly to an apparatus and method for precisely aligning and holding two thin walled stainless steel sanitary tubing segments end-to-end to allow for tack welding of the segments together during a tube assembly process.
It is generally known that thin walled stainless steel tubing is used in a variety of industrial applications. For instance, such tubing is commonly included in the devices used to carry out food and pharmaceutical manufacturing processes. Once a variety of tubing segments are manufactured, segments are typically welded together to form a desired spool of tubing. During this welding process, a joint is formed at each seam positioned between any of the two adjacent tubing segments.
The Food and Drug Administration (FDA) has regulated this welding process of stainless steel sanitary tubing and all joints must pass an inspection under stringent standards. The segments of thin walled stainless steel tubing are ordinarily welded together by a process known as fusion welding. During fusion welding, layers of additional metal (i.e., filler metal) are not added to the joint formed between two abutting tubing segments, as is the case with traditional welding. Rather, during fusion welding, no metal is added and the ends of the tubing segments are fused together to create the welded joint.
Under current FDA standards, an inert gas purge (ordinarily known in the art as a “pure” inert gas purge, must be maintained within the interior (i.e., within the inner wall) of the tubing segments during the entire welding process. This use of an inert gas purge prevents the discoloration and oxidation of the tubing during the tack welding process As used herein, the phrase entire welding process includes both a tack welding process and an orbital welding process, both of which are described below. In those cases wherein the desired spool includes more than two tubing segments so that more than one welded joint is formed, then the entire welding process consists of a tack welding process and an orbital welding process for each welded joint.
Once the entire welding process has been completed, the formed spool, consisting of all the adjacent tubing segments fusion welded together, is ready for installation in the process system. As used herein, the phrase tubing segment shall include not only straight cylindrical tubing, but also any fittings, such as elbows and tees also included within the formed spool. Fittings might be required, for instance, where the desired spool includes a bend at a designated angle. As herein used, a spool is a portion of a process system consisting of a plurality of tubing segments welded together.
During the welding process, the tubing segments are first held in place and tack welded together. Typically, the tack welds formed are no larger than the head of a pin. Their purpose is to hold the tubing segments in alignment during the orbital welding process.
Until now, while performing this tack welding process, a person would typically hold the ends of the tubing segments in alignment while another person tack welded them using a tungsten electrode. The tungsten electrode used typically has an inert gas cap or shield to prevent or at least minimize the exposure of oxygen to the seam between the tubing segment ends. Thus, the tubing segments are held together in a true manual fashion during the tack welding process.
After formation of the tack welds, an orbital welder is used to complete the welding process. During orbital welding, a tungsten electrode traverses about the perimeter of the seam between the tubing segments.
As will be appreciated, until now, this welding process was costly and often ineffective. For instance, those skilled in the art will appreciate the precision with which the ends of the tubing segments must be welded in order to pass FDA inspection. Employing a person to hold the tubing segments in place while tack welding the same rendered it difficult to achieve the necessary precise alignment of the tubing segments. To pass inspection under the FDA standards, several attempts to construct a desired spool were often required, particularly where the desired spool necessitated the formation of a plurality of joints along its length.
Even in those cases where all of the joints formed were able to pass inspection, this practice required the employment of an additional person. As will be appreciated, this increased the costs associated with the welding process.
Furthermore, during tack welding, each joint required its own independent inert gas purge. As will be appreciated, this significantly increased the time necessary to perform the welding process because of the time spent waiting for each purge to be completed. Also, this again increased the costs associated with the welding process. For this reason, costs escalated because of the additional usage of the inert gas, which is relatively expensive.
With the present invention, the previous requirement of using an additional person during the welding process has been eliminated to reduce costs associated therewith. The tubing segments can now be joined together easily in position or on a bench or the like. Additionally, the ends of the tubing segments are now held firmly together in precision alignment to reduce the likelihood of inspection failure and thereby also reduce costs associated with the welding process. Furthermore, in those instances where the desired spool necessitates the formation of a plurality of joints along its length, the present invention permits the adjacent tubing segments to be held firmly in place at each seam during the tack welding process. In other words, the apparatus permits a welder to assemble and tack weld multiple joints on fabricated tubing segments prior to final orbital welding. As a result, only a single inert gas purge is required for both the tack welding and orbital welding processes. Time and money are thereby saved.
The apparatus of the present invention is directed to a unique clamp or jig that permits tubing segments to be held firmly in place while they are tack welded together at their seam. The method of the present invention is directed to employment of an apparatus of this type during the tack welding process of this entire welding process.
Although clamps of many types are generally known, the prior art clamps are not specially designed for precision alignment of two thin walled stainless steel tubing segments while they are tack welded together. In particular, several of the prior art clamps do not come into contact with both tubing segments in a way so that they contact almost an entire circumferential path along the respective outer walls of the adjacent tubing segments. Such contact is required to achieve the requisite precision alignment of the tubing segments in order to increase the likelihood of carrying out the fusion welding process in compliance with FDA standards. One prior art patent disclosing a clamp that would not provide such contact is U.S. Pat. No. 3,400,872, issued to Rogers. In that patent, the disclosed clamp includes four set screws that hold two pipe segments in place, and therefore the clamp does not provide for the precision alignment achieved by the present invention.
Additionally, several of the prior art clamps are designed for pipe, not tubing, and are directed not only to achieving and maintaining alignment between two pipe segments, but also towards reforming the shape of the ends of the adjacent pipe segments when either or both of those segments are out-of-round. Accordingly, these prior art clamps are relatively large and heavy. It will be appreciated that the tubing manufactured for the present process systems is manufactured to more rigid standards than the pipes used in piping systems. Moreover, several of the prior art clamps cannot be clamped in a relatively easy fashion.
An example of a clamp that is useful for certain, limited purposes, but is not useful for present purpos
Collie Gary
Cook, Alex, McFarron, Manzo, Mannings & Mehl Ltd.
Edmondson L.
Elve M. Alexandra
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