Tanged screw thread insert with improved removability

A helical-shaped insert to engage a threaded fastener to a receiving member includes a helical coil having a plurality of coil sections having inner and outer surfaces forming a thread shape, and opposing first and second coil end sections. A removable tang extends radially inward from the first coil end section. A continuously curved surface at a finished end of the second coil end section forms a tangent point where the continuously curved surface tangentially meets the second coil end section outer surface. A notch in the first coil end section proximate to the tang and positioned between the inner and outer surfaces permits removal of the tang by mechanical failure at the notch. A second notch in the second coil end section and the continuously curved surface assist coil removal.

FIELD OF THE INVENTION

The present invention relates in general to thread insert members and more specifically to helical coil shaped thread inserts insertable into an aperture of a relatively soft material to provide a female thread for subsequent insertion of a screw or bolt.

BACKGROUND OF THE INVENTION

Thread inserts having a generally helical shape are commonly used to create a receiving thread for subsequent insertion of a screw or bolt into a relatively soft receiving material such as polymeric material or soft metals such as aluminum or magnesium, etc. An aperture is pre-tapped in the receiving material to receive the helical insert. The helical insert or “coil” includes a plurality of both outside and inside surface areas acting as screw threads. A tang which is an extension of the coil extends radially inwardly from a coil section at a leading end of the coil and is provided for grasping by an insertion tool. Using the insertion tool and tang, the coil is threaded into the aperture, the coil outer surfaces engaging the tapped threads of the aperture. The tang can then be broken off by material failure at a notch pre-formed at a junction of the tang and the helical coil. The coil inner surfaces then provide engagement surfaces for receiving the threads of a screw, bolt or other fastener.

Known helical coil designs provide retention strength or resistance to removal by sheared ends provided at both ends of the coil which bite into the softer receiving material when removal of the coil is attempted or a fastener is rotated into the coil. To further improve coil retention, “insert ends” having no chamfers together with the sheared ends are used. Removal of coils is often required, for example to remove and/or replace the fastener during maintenance, or if the coil is damaged or is installed improperly. During coil removal, the softer receiving material is susceptible to damage. When the receiving material is a casting or complex part, the cost to replace the damaged part can be excessive.

Coil designs are known which assist in removal of the coil, for example U.S. Pat. No. 6,171,040 to Sato. Sato discloses a pair of notches10which are formed at a back end portion of the coil and include contact surfaces10bfor engagement by a tool such as a bladed screw driver. At the back end of the coil, Sato also discloses a center flat surface20having chamfered surfaces15,16,17and18. The disadvantage of the Sato and other known designs is that damage to the internal threads of the receiving material aperture can still occur when the coil is backed out, due to the corners of the chamfer geometry at the back end of the coil.

SUMMARY OF THE INVENTION

According to one preferred embodiment, a tanged screw thread insert with improved removability of the present invention includes a helical-shaped insert having a plurality of coil sections, including opposing first and second coil end sections. A continuously curved surface is created at a rounded distal end of the second coil end section. A tangent point is created where the curved surface tangentially meets an outer surface of the second coil end section.

According to another preferred embodiment, a thread insert includes a helical-shaped insert defining a plurality of coil sections including opposing first and second coil end sections. The coil sections each have an inner surface and an outer surface, the inner and outer surfaces each having a thread shape. The outer surface of each of the coil sections are aligned to create a substantially constant diameter coil body. A removable tang extends radially inward from the first coil end section. A continuously curved surface is created at a rounded distal end of the second coil end section. A tangent point is created where the curved surface tangentially meets the outer surface of the second coil end section. A first notch is disposed in the first coil end section proximate to a tang connection and positioned between the inner and outer surfaces. The first notch is operable to create a failure point in the first coil end section for removal of the tang. A second notch is created in the second coil end section proximate to the continuously curved surface, the second notch having a contact surface operable to assist in removal of the insert from an installed position.

According to yet another preferred embodiment, a method for creating a thread insert, the thread insert including a helical-shaped coil defining a plurality of coil sections including opposing first and second coil end sections and an outer coil diameter, includes creating a continuously curved surface at a rounded distal end of the second coil end section. The method further includes blending the continuously curved surface tangentially into an outer surface of the second coil end section to operably create a tangent point.

A tanged screw thread insert with improved removability of the present invention provides several advantages. By retaining a substantially constant outside diameter of the individual coil segments, removal of the coil presents a substantially constant contact diameter against the threads of the receiving member, which reduces the possibility of an out-of-round coil segment causing frictional damage to the threads. By providing a continuously curving end surface at a distal end of the coil second end segment, a smooth surface is presented during removal of the insert which reduces the chance of frictional damage to the threads of the receiving member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to a preferred embodiment of a tanged screw thread insert of the present invention and referring toFIG. 1, an assembly10includes a helical insert12frictionally and rotatably received within a receiving member14. Receiving member14can be a plate or sheet, a casting or molding, etc. Materials for receiving member14which benefit from the use of an insert12are generally materials including polymeric materials or the “soft” metals such as copper, aluminum, magnesium, etc., which do not have a tensile strength sufficient to prevent tear-out of a fastener16if fastener16is engaged only with receiving member14. Insert12is therefore made of a higher tensile strength and harder material than receiving member14, such as a steel, including stainless or spring steel. Fastener16can be any type of threaded fastener such as a screw or bolt, etc. In exemplary use, fastener16can provide hold-down capability to engage another item (not shown) to receiving member14, or can act as an electrical contact post or electrical connection for receiving member14.

Insert12is generally completely received within a thickness “A” of receiving member14in a general direction “B”. Insert12includes a continuous, helical-shaped coil, herein described for simplicity as a plurality of coil sections18. Coil sections18each include an outer surface20having a thread-shape which engage a plurality of receiving threads22pre-tapped or formed in receiving member14. Coil sections18each also include an inner surface24which are thread-shaped and sized to engage a plurality of threads26of fastener16. Insert12, fastener16and receiving threads22are coaxially aligned on a longitudinal axis28. Longitudinal axis28is preferably aligned substantially perpendicular to at least a receiving face29of receiving member14, but can be angled with respect to receiving face29or a central axis through receiving member14if receiving member14is formed in a curved shape. A tang30connects to and extends radially inward from a first coil end section32of coil sections18.

Referring generally toFIGS. 2 through 4, insert12is installed in a clockwise direction “C” and removed in a counterclockwise direction “D”. Directions “C” and “D” can also be reversed if a reverse or left-hand threaded insert12is desired. Each of coil sections18have an outer diameter “E” defined by outer surface20, and an inner diameter “F” defined by inner surface24. Outer diameter “E” is sized to frictionally engage with receiving threads22. Inner diameter “F” is sized to permit inner surfaces24to receive and engage threads26. A finished end34is created at a distal end of a coil second end section36. Coil second end section36is oppositely positioned from coil first end section32. Finished end34is created in a separate operation such as by grinding, lapping, cold-heading, milling, etc. Tang30is preferably created by bending a portion of coil first end section32radially inward and substantially perpendicular to longitudinal axis28until tang30is coaxial to a first radial axis38. First radial axis38is oriented substantially perpendicular to a second radial axis40. Both first and second radial axes38,40intersect at longitudinal axis28. A deformation or notch42is also created in coil first end section32.

As specifically shown in reference toFIGS. 1,3and4, insert12has a total height “G” which is preferably less than thickness “A” of receiving member14. Notch42is provided in coil first end section32to provide a fracture or failure point, allowing removal of tang30by further forcing tang30in direction “B” after insert12is frictionally seated in receiving member14. This permits full insertion of fastener16through height “G” of insert12and thickness “A” of receiving member14. If tang30is removed, a working height “H” of insert12results. Each coil section18is separated from each proximately located coil section18by a pitch “J”, which corresponds to a pitch of receiving threads22.

Referring generally toFIGS. 1 through 4, assembly10is created by grasping tang30with a tool (not shown) inserted within insert12, aligning outer surfaces20with receiving threads22, and rotatably inserting insert12in clockwise direction “C” into receiving member14. Insert12is rotated and thereby translated in direction “B” until insert12is positioned as shown inFIG. 1. Threads26of fastener16are then aligned with inner surfaces24of coil sections18and fastener16is rotatably engaged with insert12in direction “B”. A depth of engagement of fastener16within insert12can vary depending on the materials selected and the holding requirements of assembly10.

With further reference toFIGS. 1 through 4, insert12is removable from receiving member14if no fastener16is present, or after removal of fastener16. A second tool (not shown) is inserted into insert12which frictionally contacts one or more of the inner surfaces24. Insert12is then rotated in the counterclockwise direction “D”. During removal of insert12, finished end34smoothly slides against receiving threads22which prevents galling or damage to receiving threads22.

Referring next toFIG. 5, finished end34of coil second end section36includes a continuously curved surface44having no sharp corners, created by one of the processes previously described herein. In one preferred embodiment, continuously curved surface44tangentially meets outer surface20and inner surface24at a first and second tangent point48and50, respectively. A junction line46is therefore present only where an intersection of continuously curved surface44meets coil second end section36between the first and second tangent points48and50. Tangent point48therefore provides a smooth interface between coil second end section36and receiving threads22.

Referring now toFIG. 6, according to another preferred embodiment of the present invention, a helical insert52includes a plurality of helical coil sections54, similar to coil sections18. A tang56, similar to tang30and a continuously curved surface58, similar to continuously curved surface44are also provided. Insert52also includes a recess60proximate to continuously curved surface58. Recess60includes an inner wall62positioned substantially at a coil centerline64. A contact surface66provides a surface for a tool (not shown) such as a screwdriver blade to engage insert52and rotate insert52in counterclockwise direction “D” for removal of insert52. A radial corner68transitions the inner wall62to the contact surface66. Recess60functions similar to removal notches18disclosed in U.S. Pat. No. 6,726,421 to Giannakakos et al., issued Apr. 27, 2004, and commonly owned by the assignee of the present invention, the disclosure of which is incorporated herein by reference.

A tanged screw thread insert with improved removability of the present invention provides several advantages. By retaining a substantially constant outside diameter of the individual coil segments, removal of the coil presents a substantially constant contact diameter against the threads of the receiving member, which reduces the possibility of an out-of-round coil segment causing frictional damage to the threads. By providing a continuously curving distal end surface at a second end of the last coil segment, a smooth surface is presented during removal of the insert which reduces the chance of frictional damage to the threads of the receiving member.