Reinforced cap head screws

A self-tapping screw for use in securing at least two materials together. The self-tapping screw may include a screw cap that receives a screw body to reinforce the strength of the screw head. The screw cap is composed of a zinc-aluminum alloy that may be die casted and provides additional strength and hardness to the attached screw body. The screw cap has a rolled flange that helps to securely retain the flat rim of the attached screw body.

BACKGROUND OF THE INVENTION

The present invention relates generally to screws and bolts, and in particular, to screws and bolts with a reinforced cap that provides a strengthened screw head resisting breakage.

Screws and bolts are common fasteners used in construction and machine assembly to secure materials together. For example, self-tapping screws are commonly used to secure sheet metal together with another material, for example, metal-to-metal and metal-to-wood applications. Self-tapping screws “tap” or cut mating threads in the hole into which they are driven. Self-tapping screws tap into the material by turning the head of the screw to advance the screw into the hole. Other types of screws may require a pre-drilled hole.

Self-tapping screws usually require a pilot hole to be pre-drilled before use while self-drilling screws do not require a pilot hole because of the addition of a drill point. Self-drilling screws are also self-tapping so both self-drilling and self-tapping screws will be referred to as “self-tapping” screws herein.

The head of a self-tapping screw is typically larger than the body of the screw and may include an “external drive” designed to fit a ratchet or spanner torque wrench so that the screw can be tightened into the hole. For example, a hex-head screw may include a head with a six-sided bolt driven by a torque wrench or torque drill. Alternatively, the head of the screw may include an “internal drive” such as slots or sockets allowing a screwdriver to be inserted into the slots or sockets of the head so that the screw can be tightened into the hole. For example, a slot screw may include a single horizontal indentation driven by a flat-bladed screwdriver (handheld or electric).

The cylindrical body portion of the screw, on the underside of the screw head, provides a shank which may be partially or fully threaded with helical threads that are inserted into the material to form a thread in the hole around the screw and drive the screw into the hole. The tip of the shank may contain a chamfer to allow the end of the screw shank to progressively make wider cuts reducing the amount of force required in order to tighten the screw. The tip may also include a drill flute allowing the drilled material to exit the hole. The tip may also include a drill point, in the case of a self-drilling screw, allowing the screw to drill its own hole instead of the screw being driven into a pre-drilled pilot hole.

Metal screws will typically have a flat face on the underside of the head so that the screw lies flush on top of the bearing surface. In some instances, the flat face is formed by a flanged head where the head is flanged to provide a broader contact surface. The metal screw may support an additional flat washer, on the underside of the screw head, that is broader than the screw head and provides a smooth, flat bearing surface abutting the upper surface of the bearing surface. The flat washer distributes pressure over a wider area preventing damage to the bearing surface and provides more clamping torque to the bearing surface. The flat washer may be attached to the screw head or be freely removable.

One of the common problems encountered when using self-tapping screws is failure of the screw as it is being driven into the hardened material. The high forces used when driving in the screw into the hardened material causes damage to the tip or shank threads, chipping or melting the flutes of the tip or the shank threads, thus, stripping the screw. Another area of the screw susceptible to damage is the head of the screw where the high forces strip the external or internal drive of the screw head. These screw failures result in a slower cutting speed or screw failure.

SUMMARY OF THE INVENTION

The present invention provides a self-tapping screw with a screw cap suitable for securing sheet metal for metal-to-metal and metal-to wood applications. In one embodiment, a screw cap of the screw is firmly attached to a screw body and provides a zinc alloy cap composition with higher copper content that withstands the high forces placed on the screw cap during drilling and adds corrosion protection against red rust.

Specifically, one embodiment of the present invention provides a screw comprising a screw body having an elongate shaft extending along a central linear axis and supporting threads extending about the linear axis in a helical path. At a lower end, the elongate shaft provides a screw tip and, at an upper end, provides an outwardly extending rim extending perpendicular to the linear axis. A screw cap has an inner bore receiving the outwardly extending rim therein and supporting a rolled flange extending inwardly from an inner surface of the screw cap and having an innermost end that is angled upwardly from horizontal to retain the outwardly extending rim.

It is thus a feature of one embodiment of the invention to provide a substantially new form of cap screw with a reinforced cap head installed over a standard screw body with an improved attachment method.

The inner bore of the screw cap may be a non-circular bore. The inner bore may be a hexagonal bore with six sides.

It is thus a feature of one embodiment of the invention to provide a screw cap that resists rotation of the screw body so that the screw cap and screw body rotate together.

An exterior surface of the screw cap may provide a hex head.

It is thus a feature of one embodiment of the invention to provide standard hex head bolts that can be used with an electric drill and is strong enough to endure maximum drill speeds.

The innermost end of the rolled flange may be angled upwardly from horizontal toward the linear axis. The innermost end of the rolled flange may be angled upwardly at least 20 degrees from horizontal. The innermost end of the rolled flange may be angled upwardly at least 30 degrees from horizontal.

It is thus a feature of one embodiment of the invention to provide a flange that tends to retain the screw head and to counter separation due to heavy clamping loads.

The rolled flange may extend approximately 0.5 to 1.5 mm from the inner surface inwardly to the linear axis.

It is thus a feature of one embodiment of the invention to provide improved retainment of the screw cap to the screw body about a circumference of the outwardly extending rim.

A cross section of the rolled flange may be hook shaped. The innermost end of the rolled flange may contact a lower surface of the outwardly extending rim.

It is thus a feature of one embodiment of the invention to secure the screw body to the screw cap that is naturally reinforced when the screw is screwed into the material by upward forces of the bearing surface against the upwardly rolled flange.

The screw cap and the elongate shaft may be made of different materials wherein the screw cap has a higher micro hardness than the elongate shaft.

It is thus a feature of one embodiment of the invention to provide a strong screw cap having a harder material composition than the screw body.

The screw cap may be a zinc-aluminum alloy. The screw cap may have at least 95 weight percent zinc. The screw cap may have at least 3 weight percent aluminum.

It is thus a feature of one embodiment of the invention to provide a screw cap with a harder composition and higher density to withstand installation conditions.

The screw body may further comprise a screw head providing a non-circular end attached to the shaft at the upper end.

It is thus a feature of one embodiment of the invention to provide a screw body that includes a screw head that can be tightly retained within the screw cap bore, and rotates with rotation of the screw cap to prevent sliding of the screw head within the screw cap bore. It is also a feature to use the screw cap with commonly used hex head screws.

The shaft may taper inwards toward the axis to a pointed tip at the lower end.

It is thus a feature of one embodiment of the invention to provide a self-drilling screw that can be used to drill its own hole.

The lower end may include a flute and a cutting edge.

It is thus a feature of one embodiment of the invention to allow the screw to provide self-tapping that can be used to tap its own hole.

It is thus a feature of one embodiment of the invention to provide improved strength to screws commonly used for securing hard materials together and thus more susceptible to breakage.

The self-tapping screw may further include a rubber washer positioned partially within the inner bore of the screw cap to abut the rolled flange.

It is thus a feature of one embodiment of the invention to provide additional upward forces against the upwardly extending rolled flange in order to retain the screw body within the screw cap and to seal the cap bore from moisture.

In one embodiment of the present invention, a self-tapping screw provides a screw body wherein the screw body comprises an elongate shaft extending along a linear axis and supporting threads extending about the axis in a helical path and, at a lower end, providing a pointed tip; a non-circular head supported at an upper end of the elongate shaft; and an outwardly extending rim supported below the screw head and extending perpendicular to the linear axis. A screw cap has an exterior providing a hex head and a non-circular inner bore receiving the non-circular head and outwardly extending rim therein and supporting a rolled flange extending inwardly from an inner surface of the screw cap and having an innermost end that is angled upwardly to retain the outwardly extending rim.

One embodiment of the present invention provides a method of manufacturing a screw wherein the screw comprises an elongate shaft extending along a linear axis and supporting threads extending about the axis in a helical path and, at a lower end, providing an insertion tip and, at an upper end, providing an outwardly extending rim extending perpendicular to the linear axis; and a screw cap having an inner bore receiving the outwardly extending rim therein and supporting a rolled flange extending inwardly from an inner surface of the screw cap and having an innermost end that is angled upwardly to retain the outwardly extending rim. The method comprises the steps of attaching the screw cap and the elongate shaft to retain the outwardly extending rim within the rolled flange of the screw cap.

It is thus a feature of one embodiment of the invention to provide a strong cap that is attached to standard screws in a reinforced manner preventing breakage.

DETAILED DESCRIPTION OF THE INVENTION

Referring now toFIGS.1and2, a self-tapping screw10for use with the present invention may be used to assist with the attachment of hard and soft materials, such as sheet metal, plastic, fiberglass, wood and the like.

The self-tapping screw10provides a cylindrical shaft12extending along a central, linear shaft axis13and having a circular cross-section, for example, having an approximately 5 to 6 mm diameter. The shaft12may extend a length approximately 18 to 30 mm along the shaft axis13. A lower end of the shaft12may terminate at a tip14of the shaft12with a drill point16allowing the screw itself to drill a hole into the bearing surface18. The bearing surface18may be an upper surface of sheet metal20where the self-tapping screw10is used to attach the sheet metal20to another metal, plastic or wood substrate22by tapping a hole into the substrate22.

Referring briefly toFIG.3, an upper end of the shaft12may support a screw head26attachable to a screw cap28by being received within a bore socket30at a lower open end of the screw cap28. The screw head26may be held within the bore socket30by an inwardly extending rolled flange32of the bore socket30as further described below.

The screw head26at the top of the shaft12may be an outwardly extending “external drive”, for example, a non-circular head or hex head bolt having six sides. The screw head26extends upwardly a height of approximately 3.5 to 4.5 mm and has a width across the flats of approximately 7.5 to 8 mm and a point to point width of approximately 8.5 to 9 mm. A center of an upper surface of the screw head26may contain a circular dimple33.

The screw head26may include an outwardly protruding circular flat rim or circular flange34projecting circumferentially outwardly from underneath the screw head26and which typically acts like a washer to distribute the load on the screw head26but in this case also assists with the attachment of the screw head26to the screw cap28. The circular flange34may have an approximately 8 to 9.5 mm diameter. In this respect, the circular flange34may extend approximately 0.5 to 1.5 mm outwardly from the screw head26and may be integral with the screw head26.

Referring again toFIGS.1and2, extending downwardly from the screw head26and circular flange34is the shaft12. An upper end35of the shaft12, positioned below the screw head26and circular flange34, may provide for helical threads36covering a majority of the length of the shaft12and extending between the circular flange34and the tip14of the shaft12. The threads36form ridges wrapped around the shaft12in the form of a helix and may have a major diameter of approximately 5 to 6.5 mm and a pitch of approximately 1 to 2 mm. It is understood that the major diameter and the pitch of the threads36may vary depending on the length of the shaft12, or alternatively, the major diameter and the pitch of the threads36may be constant regardless of length of the shaft12. The threads36may be standard right-hand threads allowing the shaft12to drill downward into the hole with clockwise rotation of the screw10as viewed from the screw head26.

A lower end37of the shaft12may narrow toward the shaft axis13to form a chamfer and terminating at the tip14of the shaft12extending along a tip axis40common to the shaft axis13. The tip14is unthreaded and includes helical flutes42allowing the drilled material to exit the drilled hole and forming cutting edges. The tip14may converge to a sharpened drill point16that is able to drill its own hole. The tip14is generally long enough to completely drill through the sheet metal material20to be fastened before the threads36of the shaft12engage the sheet metal material20, for example, extending approximately 5 to 8 mm in length. In this respect, the thickness of the sheet metal material20to be attached to the substrate22is less than the length of the tip14to allow the tip14to drill through the material to be fastened before the threads36are engaged.

The shaft12and screw head26may be fabricated of a hardened metal, such as plain steel, plain steel with a weather-resistant coating such as zinc, aluminum, stainless steel and the like. It is understood that the shaft12and screw head26may by an integral or unitarily constructed by being machined from a single cylinder of metal or wire.

The screw head26may be strengthened by the addition of the screw cap as further described below.

Referring now also toFIG.3, the self-tapping screw10provides a screw cap28attachable to the screw head26and may provide a cover50placed over the screw head26of the screw10and providing an inner bore socket51accessible at the lower open end of the screw cap28receiving the screw head26of the screw10therein. The inner bore socket51may be sized and shaped to receive the screw head26of the screw10therein, and therefore, has an inner diameter that matches the outer diameter of the screw head26and has a geometry that matches the geometry of the screw head26. In one embodiment, the inner bore socket51may have a diameter that is slightly greater than approximately 8.5 to 9 mm and may be approximately 8.5 to 9.5 mm.

The inner bore socket51may have a geometry that is non-circular. In one embodiment, the inner bore socket51is a hexagonal bore that matches the hex head of the screw head26. In this respect, the screw head26is tightly fitted within the inner bore socket51so that rotation of the cover50also rotates the screw head26. It is understood that the geometry of the inner bore socket51and the screw head26may vary, for example, square, pentagon, etc. but generally the inner bore socket51has non-circular sides that resist rotation of the screw head26within the cover50. Generally, the inner bore socket51and screw head26provide a keyed alignment so as to lock the rotational alignment therebetween.

An exterior surface of the cover50may provide an outwardly extending hexagonal shaped head with six sides that may be rotated with a wrench or socket. The cover50has a height of approximately 3.5 to 4.5 mm and a width across the flats of approximately 7.5 to 8 mm and a point to point width of approximately 8.5 to 9 mm. A center of an upper surface of the cover50may contain a circular dimple53.

A lower end of the cover50provides a downwardly extending rounded flange52, resembling an umbrella, projecting circumferentially from the cover50and having a horizontal portion54extending outwardly and generally perpendicular to the shaft axis13, and a vertical portion56extending downwardly along the shaft axis13, to accommodate therein the extension of the circular flange34of the screw head26of the shaft12that is too wide to fit within the inner bore socket51of the cover50. The rounded flange52has an approximately 16 to 17 mm diameter.

An inner flange bore58of the rounded flange52supports an upwardly rolled flange32projecting circumferentially from an inner surface59of the rounded flange52and forming a generally J-shape or hook shape in cross section (as seen inFIG.3). The rolled flange32has an attachment end62extending downwardly from an inner surface of the horizontal portion54and a distal, innermost end63extending inwardly toward the shaft axis13. The innermost end63may provide a smooth, blunt edge. The rolled flange32may extend approximately 0.5 to 1.5 mm from the inner surface59.

A distal end64of the innermost end63is angled upwardly or “rolled” upwardly to contact a lower surface66of the circular flange34of the screw head26. The distal end64may contact the lower surface66of the circular flange34approximately 0.5 to 1.5 mm inwardly from the outer end of the flange34, therefore, gripping 0.5 to 1.5 mm of a perimeter of the circular flange34.

The distal end64may be angled upwardly from horizontal, i.e., an angle of elevation θ, that is approximately 20 to 60 degrees, approximately 30 to 50 degrees, approximately 40 to 50 degrees, at least 20 degrees, at least 30 degrees, at least 40 degrees, approximately 30 degrees, approximately 35 degrees, approximately 40 degrees, and approximately 45 degrees, and angled toward the shaft axis13to help retain the circular flange34of the screw head26. In this respect, the distal end64of the rolled flange32improves the attachment of the screw cap28to the screw head26. Also, the upward forces of the bearing surface18against the rolled flange32further reinforce the retention of the screw cap28to the screw head26.

The screw cap28may be manufactured of a zinc-aluminum alloy. In this respect, the screw cap28is manufactured of a different material than the shaft12and screw head26. The cover50and rounded flange52may be integrally formed for example, by die casting. The screw cap28may have a micro hardness of approximately 95 to 115 HV 0.5 via 500 g Vickers, may have a uniform microstructure. The screw cap28may have a higher micro hardness compared to the shaft12and screw head26and may have a higher density compared to the shaft12and screw head26. The screw cap28may contain the following chemical composition:

Referring toFIG.2, a rubber washer70may provide a ring of rubber or neoprene that is installed underneath the screw head26and provides a smooth, flat bearing surface abutting the bearing surface18of the sheet metal20. The rubber washer70may has a diameter that is less than the diameter of the rounded flange52and therefore fits partially within the inner flange bore58positioned beneath and abutting the rolled flange32. In this respect, the rubber washer70provides upward support against the rolled flange32and promoting the upward angle of the distal end64. The rubber washer70also provides a moisture seal to prevent moisture from entering the bore socket30when the self-tapping screw10is used for exterior or outside use.

The rubber washer70distributes pressure preventing damage to the bearing surface and provides more clamping torque to the bearing surface keeping the screw head26from loosening. The rubber washer70may be fixedly attached to the screw head26or may be removably attached to the shaft12.

Referring now toFIG.4, the shaft12and screw head26may be manufactured by cold forging the wire into the desired length and head shape as illustrated in step100. Threads are formed by rolling or cutting the wire as illustrated in step102and then the screw is heat treated and surface treated to improve strength and durability, respectively, as illustrated in step104.

The screw cap28may be integrally formed for example, by die casting, as illustrated in step106. Next, the screw head26may be strengthened by the addition of the screw cap28as illustrated in step108. In one embodiment, the screw head26is inserted into the bore socket30of the screw cap28to lock the rotational alignment therebetween. Then the rolled flange32is rolled upward, in a configuration as described above, to retain the circular flange of the screw head26within the inner flange core59. The rolled flange32may be bent using annealing or hot forming methods to prevent cracking. Finally, the rubber washer70may be installed onto the shaft12as illustrated by step110.