Patent Publication Number: US-6668460-B2

Title: Corrosion resistant lock blade knife

Description:
FIELD OF INVENTION 
     The present invention relates to a corrosion resistant lock blade knife with a blade made of titanium or titanium alloy and a locking arm (locking lever) made from a corrosion resistant substance that can be used for diving or in any other circumstance where a corrosion resistant knife is required. The locking arm can also be made of titanium or titanium alloy, or any other strong corrosion resistant substance. The invention also has a non-titanium corrosion resistant surface between the locking arm head of the locking arm and the end tang of the blade to prevent the negative effects of titanium/titanium or titanium/other metal rubbing during opening and closing of the knife. 
     PRIOR ART 
     Lock blade knives are relatively common. From the pocketknife to the utility knife there are many different kinds of lock blade knives employing different mechanisms of action. It is prior technology to have a locking arm received into a notch on the blade tang. A spring biases against the locking arm to keep locking arm in place and maintain the locked state of the knife. 
     Heretofore, most lock blade knives were made of stainless steel to take advantage of stainless steel&#39;s generally excellent qualities. With minimal care, stainless steel is generally resistant to tarnish or rust when exposed to normal oxygen and humidity conditions. Stainless steel is easy to clean, and resiliently hard so that it can be honed into a finely sharpened blade. It is very strong and resilient under most circumstances. However, stainless steel is an iron alloy. Because of the iron content, stainless steel is magnetic and highly conductive. Also because of the iron content, the stainless steel is reactive to reduction chemical reactions and is still susceptible to corrosion and rust. It is due to these qualities that stainless steel is a poor material for constructing a diving knife because it is susceptible to the ravages of corrosion by the minerals and pollutants contained in fresh water and salt water. 
     The problem with iron-based metals is that the oxide formed by oxidation does not firmly adhere to the surface of the metal and flakes off easily causing “pitting”. Extensive pitting eventually causes structural weakness and disintegration of the metal. Corrosion occurs in the presence of moisture. For example when iron is exposed to moist air, it reacts with oxygen to form rust. 
     The formation of rust can occur at some distance away from the actual pitting or erosion of iron. This is possible because of iron&#39;s conductive nature and the electrons produced via the initial oxidation of iron can be conducted through the metal and the iron ions can diffuse through the water layer to another point on the metal surface where oxygen is available. This process results in an electrochemical cell in which iron serves as the anode, oxygen gas as the cathode, and the aqueous solution of ions serving as a “salt bridge.” 
     The involvement of water accounts for the fact that rusting occurs much more rapidly in moist conditions as compared to a dry environment such as a desert. Many other factors affect the rate of corrosion. For example the presence of salt greatly enhances the rusting of metals. This is due to the fact that the dissolved salt increases the conductivity of the aqueous solution formed at the surface of the metal and enhances the rate of electrochemical corrosion. This is one reason why iron and steel tend to corrode much more quickly when exposed to salt water or moist salty air near the sea and the ocean. 
     Knife makers have realized this problem and tried to prevent the initial compromise of the metal by applying a protective coating to stainless steel knives, etc. However, if the coating is scraped, the corrosion will have a chance to begin. As explained above, due to the conductive nature of the iron content in steel, once compromised, the integrity of the metal is never the same. Because of the unique uses for which knives are intended, they are inevitably scrapped and scarred during use and thereby compromised. Because of its susceptibility to corrosion, stainless steel is a poor material from which to make a diving knife. 
     Titanium is well known in the metal industry as being very hard and durable. It is an excellent material from which to construct knife blades because of its strength and tendency to retain a very sharp cutting edge. However, titanium metal also has a negative point. When titanium metal comes into contact with and rubs against titanium and other metals including stainless steel, it experiences a galling effect (titanium galling effect) whereby binding and gripping to the other metal. This not only creates a generally unsatisfactory user experience, but it also causes a premature wearing of the contact surface between the titanium contact face and the other metal&#39;s contact face. 
     Knife makers have sought to take advantage of the unique properties of titanium enabling it to be polished into a highly refined cutting edge in both fixed and lock blade knives. However, they only have made fixed blade knives where the blade was made completely of titanium or titanium alloy. Heretofore, knife makers have not been able to take full advantage of the resiliency and strength of titanium in a lock blade knife without suffering the negative effects of the titanium galling effect. Knife makers have created complex dual-metal blades where the majority of the blade is stainless steel but a separate section of the blade that contains the cutting edge joined along a seam and made of titanium or titanium alloy. This involves a highly complex and very expensive manufacturing process and remains undesirable in the field of lock blade knives because the remainder of the knife blade is still made of corrosion susceptible metal. 
     SUMMARY OF INVENTION 
     The present invention relates to a corrosion resistant lock blade knife with a blade made of titanium. The blade is mounted in the handle along with a locking arm made of a substance that is also corrosion resistant. During opening and closing the tang contact edge rubs against the locking arm head. At least one of these surfaces must be composed of a corrosion-resistant non-metal or a corrosion-resistant soft metal substance to prevent the gripping and binding effects that would occur at the contact surface during opening and closing of the knife. The locking arm is biased against the tang of the knife blade by a biasing means. The biasing means pushes against the locking arm, automatically forcing it into the tang notch when the blade is pivoted into its fully open position. This action locks the lock blade knife in the open position. Titanium and titanium alloys are selected for the knife blade because of titanium&#39;s unique properties, including its strength and resistance to corrosion. These same qualities of titanium also make it a good substance from which to make the locking arm. 
     The present invention is a corrosion resistant knife designed for, but not limited to, use in and around salt water. Most lock blade knives are commonly made of stainless steel. With care, stainless steel knives are resistant for most normal uses. However, because of corrosion, these stainless-steel knives fair relatively poorly when exposed to the minerals of fresh water and harsh salt water. Furthermore, stainless steel is relatively heavy. If a common stainless steel lock blade knife is used during diving, it must be cleaned, rinsed, dried and then polished before storage or the stainless steel knife will rapidly show signs of corrosion and wear. If the blade is scraped during diving and corrosion has a chance to begin, the metal will forever be compromised and susceptible to further corrosion. 
     In order to avoid the negative effects of corrosion and rust associated with the wear of mineral and saltwater on stainless steel, it is best to make a knife out of a metal that is strong and resistant to corrosion. Metal alloys such as brass and copper-nickel are more resistant to the corrosion of salt water, but lack the strength, rigidity and resilience necessary to be refined into a fine cutting edge to make the metal alloy useful for knife blades. They also must be polished regularly to retain a pleasant appearance. 
     Titanium is the one metal with all the required properties, but has heretofore been unused in lock blade knives because of its inherent galling effect on other metals. Titanium has excellent resistance to corrosion, erosion, and is relatively lightweight, non-magnetic and very strong. Titanium is immune to corrosive attack by saltwater or marine atmospheres. It also exhibits exceptional resistance to a broad range of acids, alkalis, natural waters, corrosive gases, reducing atmospheres, and organic media. Mere traces of moisture and/or air normally assure the development of a stable protective oxide film that protects titanium. This titanium oxide (TiO2) layer forms easily and readily, thereby preventing the corrosion of titanium. 
     Titanium is fully resistant to natural seawater regardless of chemistry variations and pollution effects. Twenty-year corrosion rates well below 0.003 mm/yr (0.01 mils/yr) have been measured on titanium exposed beneath sea, in marine atmospheres, and in splash or tidal zones. Abrasion and cavitation resistance is outstanding. Titanium develops a thin tenacious and highly protective surface oxide film. The surface of titanium will, if scratched or damaged, immediately re-heal and restore itself in the presence of air or even very small amounts of water. The corrosion resistance of titanium depends on a protective titanium oxide (TiO2) surface oxide film. Titanium is also virtually non-magnetic. These unique molecular properties of titanium allow it to be superiorly resistant to the harsh environment of the ocean without requiring extensive cleaning immediately after usage. 
     Divers and other people can use this corrosion resistant lock blade knife in and around fresh and salt water without being concerned about corrosion. Often, divers will use knives for dislodging items on the ocean floor, or for cutting things while diving in the ocean or sea. The knife must be strong and resistant to breaking. The knife should also be lightweight because the diver will already be loaded with a heavy diving breathing apparatus and wetsuit. Any weight reductions, even to equipment, would prove a great benefit to divers. The titanium alloy in the knife allows for exceptional strength so that the knife will not break or deform during use. The titanium content also enables the knife to retain its superiorly sharp cutting edge. The lightweight feature of titanium will improve the overall use experience by the diver. The corrosion resistant features of titanium will enable the diver to experience the cost saving and time saving benefit of not having to meticulously clean the blade for fear of salt water corrosion even if the surface of the blade is compromised. The TiO2 layer will immediately reform protecting the titanium knife blade from any corrosion. 
     This corrosion resistant knife blade is made of titanium or titanium alloy to take advantage of the unique corrosion resistant and strength properties associated with titanium. The locking arm mechanism must also be made of a corrosion resistant material. Titanium is an excellent material to take advantage of the same superior strength and corrosion resistant properties. The nature and mechanism of the lock blade knife requires that the end tang of the blade rub against locking arm head during opening and closing. The negative property of titanium is that when titanium surfaces rub up against other metal surfaces, including titanium, a galling effect occurs. The unique molecular properties of titanium create a binding effect that results in an unusually high amount of gripping and wear. The gripping also results in an uneven transport during opening and closing of the lock blade knife. 
     To avoid this unusually high amount of wear that leads to a shortened product life, a barrier is placed between the locking arm head contact surface and the knife blade end tang contact edge. A portion of the locking arm head can be replaced with an interlocking divot made of a non-titanium but similarly non-corrodible substance. This divot receptacle region still allows for the knife to take full advantage of the benefits that titanium offers, but avoids the drawbacks of titanium surface/metal surface rubbing. The divot should preferably be composed of a material that contains no titanium. The other requirements for the divot is that it must be strong and resistant to wear and also resistant to corrosion. Reinforced plastic materials such as Dupont&#39;s Delrin® acetal resin or materials such as Teflon® are excellent for use in the divot. Brass may also be used because of its corrosion resistant qualities and nature as a soft metal. If brass is used for the divot, wear will still occur but this will not be detrimental to the knife&#39;s usage experience. The divot may be a separately formed part or it may be injection molded. The benefits of replacing this area with such a corrosion resistant material are that the knife will be easier to open and close and have a longer in service usage life. The smooth opening and closing will also have the side effect of preventing undesirable accidental cuts by the sharp knife blade. 
     By having a strong titanium blade and a strong titanium locking arm, a further benefit of the knife will be its long service life for the user. A further benefit of titanium is that it retains blade sharpness. The ability of titanium to retain superior blade sharpness on the knife&#39;s cutting edge is demanded by users and has long been sought after by lock blade knife makers. 
     The handle parts may be cast or machined metal such as aluminum, or made of a suitable reinforced plastic material such as strong glass fiber-reinforced plastic material, or nylon fiber-reinforced plastic material. The handle can be formed of one piece or composed of multiple parts attached together. The handle should be relatively strong and also resistant to the corrosive qualities of water. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational side view of a lock blade knife made in accordance with the present invention with side cover cutaway and with blade fully extended. 
     FIG. 2 is an exploded and perspective view of FIG. 1 
     FIG. 3 is an exploded detail view of the locking arm. 
     FIG. 4 is an elevational side view with blade half closed to show locking arm tang interaction. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 depicts the titanium lock blade knife  10  in an elevational side view. The blade  20  of the lock blade knife  10  is fully extended and locked into open position. FIG. 1 depicts the blade  20  with a first side  50  and a second side  60  a top edge  30  and a cutting edge  40  and end tang  100  with notch  115 . Locking arm  120  is depicted in locked position with biasing means  170  pushing against locking arm tail  130 . Locking arm head  140  is received in notch  115  thereby locking blade in open position. Both the blade  20  and locking arm  120  are composed of titanium or titanium alloy. This is to take advantage of the corrosion resistant properties of titanium and also take advantage of the metal&#39;s innate strength. Notch  115  is for receiving the locking arm head  140  when the knife blade  20  is extended in open position. Here the locking arm head  140  is seated in notch  115 . The blade axle passage  95  is shown with blade axle  110  piercing the tang  100  of knife blade  20 . 
     FIG. 2 depicts an exploded view of locking arm  120 . This depiction shows the individual components of the locking arm  120 . Locking arm axle  160  is shown extending from a first side plate  90 . The locking arm axle continues through to a second side plate  80 , only shown in cut away. The locking arm axle  160  is stabilized by this configuration. The locking arm  120  is shown with locking arm axle passage  165 . Locking arm  120  pivots about locking arm axle  160  as it passes through locking arm axle passage  165 . Locking arm head  140  is shown with vacant divot receptacle  155 . The divot receptacle  155  may be cast in locking arm  120  or cut away after casting. The interlocking divot  150  is shown isolated from the locking arm head  140  but within context. Divot  150  is comprised of a non-titanium substance. This substance may be a corrosion-resistant reinforced plastic or other substance such as a corrosion-resistant soft metal. 
     FIG. 3 depicts the locking arm  120  with divot  150  exploded from the locking arm head  140 . Also shown is locking arm tail  130  and locking arm axle passage  165 . 
     FIG. 4 depicts the lock blade knife  10  with blade  20  in transition from fully open position to closed position. This depiction shows the tang contact edge  105  in contact with divot  150  of locking arm  120 . To unlock the blade  10  when fully extended into locked position, a user applies pressure against locking arm tail  130 , this forces the spring  170  to give and the locking arm  120  to pivot about locking arm axle  160 . Knife blade  20  is comprised of titanium or titanium alloy. Locking arm  120  is similarly comprised of titanium or titanium alloy. Once the knife blade  20  begins transition, the user will release the locking arm tail  130  allowing the spring to act against the locking arm tail  130 , forcing the locking arm head  140  into contact with the titanium or titanium alloy tang contact edge  105 . Without the divot implanted into the divot receptacle  155  of locking arm head  140 , there would be the galling effect of direct titanium and metal contact. As depicted in FIG. 4., the divot  150  acts as shield allowing for smooth transport without the negative effect of titanium—titanium direct contact grasping and wear. 
     While the description above refers to particular embodiments of the present invention, it will be understood that many modifications may be made without departing from the spirit thereof. The accompanying claims are intended to cover such modifications as would fall within the true scope and spirit of the present invention. 
     The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.