Lang v. Prescon Corp.

• Decision Date: 13 August 1982
• Docket Number: Civ. A. No. 76-432.
• Citation: 545 F. Supp. 933
• Parties: Frederic A. LANG, Plaintiff and Counterclaim Defendant, v. The PRESCON CORPORATION, Defendant and Counterclaim Plaintiff, v. PIC INCORPORATED, Counterclaim Defendant.
• Court: U.S. District Court — District of Delaware

545 F. Supp. 933

Frederic A. LANG, Plaintiff and Counterclaim Defendant, v. The PRESCON CORPORATION, Defendant and Counterclaim Plaintiff, v. PIC INCORPORATED, Counterclaim Defendant.

Civ. A. No. 76-432.

United States District Court, D. Delaware.

August 13, 1982.

Harold Pezzner, Connolly, Bove & Lodge, Wilmington, Del. (Sidney David, Lerner, David, Littenberg & Samuel, Westfield, N. J., of counsel), for Frederic A. Lang and PIC Inc.

Richard P. Beck, Morris, James, Hitchens & Williams, Wilmington, Del. (Paul Van-Slyke, and Michael O. Sutton, Arnold, White & Durkee, Houston, Tex., of counsel), for The Prescon Corp.

OPINION

MURRAY M. SCHWARTZ, District Judge.

This is an action for patent infringement of United States Letters Patent No. 3,646,748 (the "Lang Patent") brought by Frederic A. Lang against The Prescon Corporation ("Prescon"). Prescon has counterclaimed for a declaratory judgment of patent invalidity, noninfringement, and unenforceability.¹ A bifurcated trial was ordered with the liability phase of the case tried to the Court on March 16-26, 1982. The parties having submitted post-trial briefs, post-trial argument was heard on June 17, 1982. This opinion constitutes the Court's findings of fact and conclusions of law in accordance with Rule 52 of the Federal Rules of Civil Procedure.

The initial application for the Lang patent was filed on March 24, 1970; the patent issued on March 7, 1972 for an invention entitled "TENDONS FOR PRESTRESSED CONCRETE AND PROCESS FOR MAKING SUCH TENDONS." As indicated by its title, the invention disclosed by the Lang patent is a tendon for use in prestressing concrete as well as a method for making such tendons. A certain amount of background information will be required to put the current controversy in perspective.

Concrete is a brittle material which readily develops shrinkage cracks while drying. An untreated, plain concrete beam² is considered unsuitable for many purposes as it will not have the strength to support the required load. One method of reinforcing concrete is to apply force to compress it, thereby overcoming the effects of the cracks formed during the drying process. Concrete which has been compressed is known as prestressed concrete. An example given at trial will serve to illustrate the concept. A series of building blocks placed together can be lifted into the air if they are pressed together from both ends. Although the blocks themselves are not joined, the compressing force allows them to support the load of their own weight. If the force is released, the blocks will fall.

There are two common techniques for prestressing concrete: pretensioning and posttensioning. In pretensioning, a piece of steel is tensioned or stretched between two anchors called "deadmen" and anchored into place. The concrete is then poured around the steel so that the concrete beam is formed with the tensioned steel inside it. As the concrete cures and hardens it mechanically interlocks or bonds with the steel so that the steel cannot move independently of the concrete. The steel is then released from the deadmen and allowed to relax as far as it can. Inasmuch as the steel is bonded to the concrete, it is restrained from relaxing and the pressure it exerts compresses the concrete. This process is known as pretensioned prestressing because the steel is stretched before the concrete is poured.

In posttensioning, the steel is placed in the forms into which the concrete will be poured without being tensioned. The steel is coated with any of a variety of coverings to prevent the concrete from mechanically interlocking with the steel. After the concrete is poured and hardened, jacks are attached to the steel and it is stretched. Permanent anchors are attached to the stretched steel where it exits the concrete; it is these anchors pushing back against the concrete which serve to compress the concrete. This process is known as posttensioned prestressing because the steel is stretched after the concrete is poured.

In the early 1950's, high strength steel bars were used in the posttensioning process. By the late 1950's and early 1960's, some companies were using multiple wire strand instead of steel bars. In some cases, a number of such strands were laid parallel to each other in a large metal duct or plastic tube. Again concrete would be allowed to harden around the ducts before the strands were stretched. After the strands were anchored, the duct would be filled with grout or grease. At least as early as 1965 Prescon manufactured a tendon comprised of four parallel ¼ inch wires wiped with grease and spirally wrapped in brown paper. During the early 1960's, the use of a single 7-wire strand³ was becoming prevalent. It too could be wrapped with grease and covered with spirally wound brown paper. (Tr. 1135-39).

The paper-wrapped, 7-wire strand, grease covered tendons had several problems. The paper tore readily during shipping and handling, necessitating costly and time-consuming repairs. In addition, the tendons had a tendency to leak, causing unsightly grease stains in the concrete. (Tr. at 1140). More fundamentally, paper-wrapped tendons had a serious problem with mechanical interlock (bonding) between the concrete and the steel. The weight of concrete at any particular point in a structure is equal to 150 pounds per cubic foot multiplied by the depth from the top of the pour. Thus, if a tendon were placed ten feet from the top of a form, it would be subjected to 1,500 pounds of force per square foot of its area. That force tended to squeeze the concrete into the interstices of the 7-wire strand and allow it to harden in that position. Once the concrete hardened, the tendon could not be tensioned without shearing the concrete at each of the places it had penetrated. It therefore became difficult to stretch the strand which in turn resulted in a reduced force applied by the anchors against the concrete. (Tr. at 162-64).

A second, although somewhat related problem, which may be referred to as "frictional forces," is best illustrated by reference to a simplified version of example 1 of the Lang patent.⁴ A 200-foot length of tendon is placed in a circular form so as to be embedded circumferentially around one-half of a circular concrete vessel. After the concrete hardens, the tendon is stretched. As it is stretched the tendon will exert a force radially inward toward the center of the tank, pushing the steel against the paper and indirectly the concrete. The friction produced between the concrete, paper and steel strand tends to prevent the steel strand from being stretched, and, as a result, the anchors push against the concrete with less force. (Tr. at 160-62).

In response to these problems, several alternatives to paper-wrapped tendons were developed. One company, Stressteel Corporation, attempted to apply a plastic wrap in the same way as the paper wrap previously described. That method was abandoned because Stressteel discovered that in applying the wrap, it had to tension the plastic to get it to stay in place. In so doing, they caused the plastic strip to conform to the helical shape of the individual strands which resulted in a high degree of mechanical interlock between the concrete and the finished tendon thereby making it difficult to stretch the strand. (Tr. 1142-45). After some further experimentation, Stressteel developed the so-called "push through" or "stuffed" tendon.⁵ The push through tendon was comprised of an extruded tube, a 7-wire strand and grease. As its name implies, the tendon was produced by stuffing or pushing a greased 7-wire strand into a previously extruded plastic tube. (Tr. at 1145-47). In order to prevent damage to the plastic tube, Stressteel covered the end of each new length of strand with a bullet-nosed thimble. The thimbles guided the strand through the tube and were then removed. As a result, the inside of the plastic tube had to be greater than the diameter of the greased strand plus the thimble. (Tr. at 1148).

Another alternative to the paper wrapped tendon was the cigarette wrap or lap seam tendon. The cigarette wrap tendon includes a greased 7-wire strand around which a long plastic strip is curled so that the overlapping edges can be heat or glue sealed. The cigarette wrap tendons have loose jackets with a large air gap between the inside of the plastic jacket and the outside of the greased strand. (Tr. at 319-19A, 660-62).⁶ Although the cigarette wrap was an improvement over the paper wrap, it still had serious drawbacks including a tendency to split at the seam. (Tr. at 828).

In 1965 Mr. Frederic Lang, the plaintiff, first became involved in posttensioning. At that time he developed a plastic coated lubricated wire which became the subject of an India patent. (DX207). The Lang India patent discloses an invention comprised of a smooth single wire coated with an oil lubricant over which was extruded a tightfitting plastic jacket. (Tr. 1984).

The patent in suit discloses yet another tendon for posttensioning and a process for manufacturing it. Specifically, the product invention is described in claim 1 of the Lang patent as:

A tendon suitable for posttensioning concrete and for use in other applications comprising a multiple-wire strand incased in a corrosion inhibitor, having a grease-like consistency relative to worked penetration, in an amount sufficient to provide a circular incasement around the strand of a diameter at least 2 mils⁷ greater than the diameter of the strand, and having a seamless plastic jacket tightly covering said incased strand.

Claim 1, column 4-5, U.S. Patent No. 3,646,748. (DX139).

The process by which that product is to be made is described in claim 6 of the Lang patent which provides:

A process for making a tendon suitable for use in the posttensioning of concrete and for use in other applications which comprises incasing a multiple-wire strand with a corrosion inhibitor having grease-like

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