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History of Metal Stitching
Metal stitching has become a generic phrase that describes methods of repairing cracks in cast metals without welding. Why metal stitching? Well, primarily because of the need for an alternative to the difficulties encountered in welding. Cast iron is the most difficult of all cast metals to weld. All electric welding methods have proven to be less than satisfactory and in many cases can cause even more cracks. Proper cast iron welding techniques require complete disassembly and oven preheat at 900°F to 1500°F. And there is a lot of time and effort involved in the clean-up and machine work of any welded piece.
The main component of the cold, mechanical repair called metal stitching has been many things intended to replace the crack and surrounding material. Some of those items have been: bolts (copper- and zinc-plated); tapered plugs (both threaded and non-threaded); threaded rods; screws; set screws; dowels; and just about anything else that could be stuffed, hammered or screwed into the space. Over time, these items have been called 'plugs', 'pins' and 'stitching pins'. Stitching pins have evolved over the past seventy years from simple threaded bolts through tapered pins to the highly sophisticated threaded fasteners available today.
The other element is locks. They are primarily used in industrial repairs. Locks have also evolved over the years and have been created in many shapes, sizes and strengths. Locks require a flat spot for installation. Two basic types of locks are common. Perhaps the most well-known is a lock that is installed by drilling spaced holes across the crack and chiseling between the holes to connect them. This type of lock is not available as a product but rather as a service only. This type of lock is very crude and offers little strength and a poor finish. The second type is installed by drilling intersecting holes across the crack and driving a similar shaped lock into the hole pattern. This lock also has little strength and a tendency to spread the crack.
Until the innovations of the late 1980’s and early 1990’s, metal stitching had several critical limitations:
• Lack of speed. Installing tapered pins, bolts and sundry other plugs is slow. The tapered taps used to thread the installation holes must be hand-driven. The driving head of a tapered pin or bolt or the remainder of the rod or all-thread must be cut off with a hacksaw or a grinding wheel.
• Difficulty of use. There is a lot of guesswork involved in the installation of these items. The installer has to guess how deeply to run the tap and how tightly to tighten the pin. If the guess is wrong, there are new problems.
• Inconsistent appearance. A tapered pin usually leaves a flawed finish on machined
surfaces. If the pin is overtorqued, it will break off below the surface. And the other items, such
as bolts, rods and set screws, present challenges of their own.
• Unpredictable seal. Because tapered pins rely upon guesswork for tightening, it is
common for them to be installed at different torques. Because bolts, rods, screws and other items
are not precision installed, their pressures also vary. This can result in loosening of previously
installed pins and subsequent leaks.
• Spreading pressure. Tapered stitching pins, bolts, screws, rods, etc. all exert extreme spreading pressure on the crack because they are simply wedges forced into the space. All locks in use until the late 1980’s had the tendency to spread the crack apart when installed and failed to create enough strength to return the casting to its original condition.
• Structural limitations. Repairs attempted on complex contours, such as inside and outside corners, were very difficult at best and impossible at worst. Tapered pins (et. al.) require significant strength in the surrounding material to contain their spreading pressure and locks require a fairly flat spot for installation. Cracks found on or near outside or inside corners or near an edge can’t be repaired with bolts, tapered stitching pins or locks.
To overcome these challenges required innovation–and computer numerically controlled (CNC) machinery. The advent of CNC machine tools has made it possible to design and manufacture thread profiles and lock shapes that can perform in ways that were thought to be impossible. These new thread profiles can literally exert a pulling action instead of a spreading pressure. And the new lock designs have increased drawing capabilites over shorter distances with more strength than ever before. With precision engineering, these new tools have opened the repair world to increasingly complex and challenging opportunities. Craftsmen now have technologically advanced, quality-controlled equipment that gives predicable, consistent and superior performance. Metal stitching was once a guessing game that relied more upon the experience and talent of the practitioner than the level of advancement of the art itself. It has become a true craft that can be learned and performed well by almost anyone with good
eye-hand coordination and common sense.
Here is a glimpse at the advantages of metal stitching now at the fingertips of repair craftsmen:
• Speed. Installing LNS products can be done quickly with pneumatic tools. Up to one inch of repair can be done in 5 minutes in 1/4" thick cast iron.
• Ease of use. The pins are designed with a breakoff groove that causes each pin to break off at the same predetermined torque. All LNS pins have straight shanks, completely eliminating all of the problems associated with tapered pins.
• Flawless finish. All LNS pins have shoulders that set into the casting so the threads aren’t exposed at the surface. Perfect metal-to-metal surface finishes are easy to accomplish.
• High pressure seal. Stress free, uniform repairs seal without the use of epoxies and coatings required by inferior stitching products. Metal-to-metal precision-engineered stitching pins are designed for high pressure applications.
• Holding power. LNS pins and locks create strength and seal over every linear inch of the repair.
• Complex contours. Inside and outside corners are now as easy as flat surfaces. CASTMASTER™ stitching pins don’t spread the crack, in fact they pull the sides of the crack together.
The products developed and patented by LOCK-N-STITCH Inc. have been used for hundreds of thousands of successful repairs in many industries. These repairs have been performed by both LNS repair personnel and LNS product customers to parts used in oil & gas, automotive, power generation, mining, railroad, trucking, metal working, construction, agriculture, shipping, and other industries. These products have been extensively tested, approved, and used by General Motors, Navistar, and Caterpillar. Even the US Air Force uses LNS products.
Possibly the most prestigious repair to date performed using LNS products was done by the developer, Gary Reed. He performed a repair on the US Capitol dome in Washington, DC. The dome itself weighs almost 9 million pounds and is made of cast iron. This is an architectural icon, a monument to freedom and humanity that must stand forever. Repairs done properly with LNS products do, indeed, endure.
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