U.S. patent application number 10/005937 was filed with the patent office on 2002-10-24 for screw bosses for blow-molded structures.
Invention is credited to Haney, Thayne.
Application Number | 20020152934 10/005937 |
Document ID | / |
Family ID | 26674948 |
Filed Date | 2002-10-24 |
United States Patent
Application |
20020152934 |
Kind Code |
A1 |
Haney, Thayne |
October 24, 2002 |
Screw bosses for blow-molded structures
Abstract
A screw boss for blow-molded structures, such as portable tables
and chairs, allows various components to be securely attached to
the blow-molded structure. For example, the screw boss may allow
support legs to be securely fastened to a blow-molded table top.
The screw boss is integrally formed in an outer surface of the
blow-molded structure and it includes a receiving portion that is
sized and configured to receive a fastener such as a screw.
Preferably, the fastener has threads that threadably engage the
inner surface of the receiving portion to provide for secure
attachment of the fastener to the blow-molded structure.
Inventors: |
Haney, Thayne; (Syracuse,
UT) |
Correspondence
Address: |
Richard C. Gilmore
WORKMAN, NYDEGGER & SEELEY
1000 Eagle Gate Tower
60 East South Temple
Salt Lake City
UT
84111
US
|
Family ID: |
26674948 |
Appl. No.: |
10/005937 |
Filed: |
December 5, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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60285305 |
Apr 20, 2001 |
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Current U.S.
Class: |
108/155 ;
108/130; 108/161 |
Current CPC
Class: |
A47B 13/003
20130101 |
Class at
Publication: |
108/155 ;
108/161; 108/130 |
International
Class: |
A47B 003/00 |
Claims
What is claimed is:
1. An apparatus that allows a threaded fastener to be threadably
connected to a blow-molded structure, the apparatus comprising: an
outer surface of the blow-molded structure, the outer surface
having a thickness; and a screw boss integrally formed in the outer
wall surface of the blow-molded structure as part of a unitary
structure, the screw boss comprising: an opening in the outer
surface of the blow-molded structure; and a receiving portion
inwardly extending into the blow-molded structure from the opening,
the receiving portion having an inside diameter that is sized and
configured to threadably receive the fastener, the receiving
portion having a length generally equal to or greater than twice
the thickness of the outer wall of the blow-molded structure.
2. The apparatus as in claim 1, wherein the extended length of the
receiving portion allows one or more threads of the threaded
fastener to engage the screw boss over an extended length to
securely attach the fastener to the blow-molded structure.
3. The apparatus as in claim 1, wherein the blow-molded structure
comprises a table top.
4. The apparatus as in claim 1, further comprising a wall generally
disposed opposite the opening, the wall substantially enclosing the
receiving portion of the screw boss.
5. The apparatus as in claim 4, wherein the wall engages another
surface of the blow-molded structure.
6. The apparatus as in claim 5, wherein the blow-molded structure
is a table top and the opening to the receiving portion of the
screw boss is disposed in a lower surface of the table top and the
wall engages an upper surface of the table top.
7. The apparatus as in claim 1, further comprising a second opening
generally disposed opposite the opening in the outer surface of the
blow-molded structure.
8. The apparatus as in claim 1, wherein the screw boss is generally
disposed in a stretch region in the blow-molded structure.
9. The apparatus as in claim 8, wherein the stretch region is
generally located to minimize or eliminate interference of the
screw boss with other features of the blow-molded structure.
10. The apparatus as in claim 1, further comprising an inner
diameter of the receiving portion, the inner diameter being
generally equal to or slightly greater than a minor diameter of the
threaded fastener to allow the threaded fastener to be readily
received within the receiving portion of the screw boss.
11. The apparatus as in claim 1, further comprising an inner
diameter of the receiving portion, the inner diameter being
generally smaller than a major diameter of the threaded fastener to
allow the threaded fastener to be securely received within the
receiving portion of the screw boss.
12. A method of manufacturing an apparatus that allows a threaded
fastener to be threadably connected to a blow-molded structure, the
method comprising the steps of: forming an outer surface of the
blow-molded structure, the outer surface having a thickness; and
forming an integral screw boss in the outer wall surface of the
blow-molded structure as part of a unitary structure, the screw
boss comprising: an opening in the outer surface of the blow-molded
structure; and a receiving portion inwardly extending into the
blow-molded structure from the opening, the receiving portion
having an inside diameter that is sized and configured to
threadably receive the fastener, the receiving portion having a
length generally equal to or great than twice the thickness of the
outer wall of the blow-molded structure.
13. The method as in claim 12, wherein the extended length of the
receiving portion allows one or more threads of the threaded
fastener to engage the screw boss over an extended length to
securely attach the fastener to the blow-molded structure.
14. The method as in claim 12, wherein the blow-molded structure
comprises a table top.
15. The method as in claim 12, further comprising forming a wall
generally disposed opposite the opening, the wall substantially
enclosing the receiving portion of the screw boss.
16. The method as in claim 15, wherein the wall engages another
surface of the blow-molded structure.
17. The method as in claim 16, wherein the blow-molded structure is
a table top and the opening to the receiving portion of the screw
boss is disposed in a lower surface of the table top and the wall
engages an upper surface of the table top.
18. The method as in claim 12, further comprising forming a second
opening generally disposed opposite the opening in the outer
surface of the blow-molded structure.
19. The method as in claim 12, wherein the screw boss is generally
disposed in a stretch region in the blow-molded structure.
20. The method as in claim 19, wherein the stretch region is
generally located to minimize or eliminate interference of the
screw boss with other features of the blow-molded structure.
21. The method as in claim 12, further comprising forming the
receiving portion of the screw boss with an inner diameter that is
generally equal to or slightly greater than a minor diameter of the
threaded fastener to allow the threaded fastener to be readily
received within the receiving portion of the screw boss.
22. The method as in claim 12, further comprising forming the
receiving portion of the screw boss with an inner diameter that is
generally smaller than a major diameter of the threaded fastener to
allow the threaded fastener to be securely received within the
receiving portion of the screw boss.
23. An attachment system for use in securing one or more components
to a blow-molded structure, the attachment system comprising: a
fastener; a surface of the blow-molded structure having a
thickness; and a screw boss integrally formed in the blow-molded
structure as part of a unitary structure, the screw boss
comprising: an opening in the surface of the blow-molded structure;
and a receiving portion aligned with the opening in the surface of
the blow-molded structure, the receiving portion having an inside
diameter that is sized and configured to receive the fastener, the
receiving portion having a length generally equal to or great than
twice the thickness of the surface of the blow-molded
structure.
24. The attachment system as in claim 23, wherein the fastener is a
threaded fastener with one or more threads disposed on an outer
surface of the fastener.
25. The attachment system as in claim 24, wherein the length of the
receiving portion allows the one or more threads of the threaded
fastener to engage the screw boss over an extended length to
securely attach the fastener to the blow-molded structure.
26. The attachment system as in claim 23, wherein the blow-molded
structure comprises a table top.
27. The attachment system as in claim 23, further comprising a wall
generally disposed opposite the opening in the surface of the
blow-molded structure, the wall substantially enclosing the
receiving portion of the screw boss.
28. The attachment system as in claim 27, wherein the wall engages
another surface of the blow-molded structure.
29. The attachment system as in claim 28, wherein the blow-molded
structure is a table top and the opening in the surface of the
blow-molded structure is disposed in a lower surface of the table
top and the wall engages an upper surface of the table top.
30. The attachment system as in claim 23, further comprising a
second opening generally disposed opposite the opening in the
surface of the blow-molded structure.
31. The attachment system as in claim 23, wherein the screw boss is
generally disposed in a stretch region in the blow-molded
structure.
32. The attachment system as in claim 31, wherein the stretch
region is generally located to minimize or eliminate interference
of the screw boss with other features of the blow-molded
structure.
33. The attachment system as in claim 23, further comprising an
inner diameter of the receiving portion, the inner diameter being
generally equal to or slightly greater than a minor diameter of the
fastener to allow the fastener to be readily received within the
receiving portion of the screw boss.
34. The attachment system as in claim 23, further comprising one or
more threads on an outer surface of the fastener and an inner
diameter of the receiving portion, the inner diameter being
generally smaller than a major diameter of the threaded fastener to
allow the threaded fastener to be securely received within the
receiving portion of the screw boss.
35. The attachment system as in claim 23, wherein no portion of the
fastener extends through the receiving portion of the screw
boss.
36. The attachment system as in claim 23, further comprising a wall
generally disposed opposite the opening in the surface of the
blow-molded structure, the wall engaging another surface of the
blow-molded structure, the wall substantially enclosing the
receiving portion of the screw boss.
37. The attachment system as in claim 36, wherein the opening is
formed in a lower surface of a table top and the wall engages an
upper surface of the table top.
38. A method of attaching a component to a blow-molded structure,
the method comprising the steps of: forming an integral screw boss
in an outer surface of the blow-molded structure, the screw boss
including an opening in the outer surface of the blow-molded
structure, the screw boss including a receiving portion aligned
with the opening and having an inner diameter that is sized and
configured to receive a threaded fastener; threadingly engaging the
receiving portion of the screw boss with the threaded fastener, the
threaded fastener having a minor diameter that is generally equal
to or larger than the inner diameter of the receiving portion, the
threaded fastener having a major diameter that is generally greater
than the inner diameter of the receiving portion; and attaching the
component to the blow-molded structure by the threaded fastener and
the screw boss.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present application claims priority to and the benefit
of U.S. provisional patent application serial No. 60/285,305,
entitled "Method and Apparatus for Creating Screw Bosses in a
Blow-Molded Workpiece," filed on Apr. 20, 2001, which is hereby
incorporated by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention generally relates to blow-molded
structures. In particular, the present invention relates to screw
bosses that can be used to attach and secure a variety of
components to blow-molded structures.
[0004] 2. Description of Related Art
[0005] The use of plastic today reaches into nearly every facet of
everyday living. Ease of manufacturing, strength, and durability
are qualities that make plastic a popular choice for manufacturing
a wide variety of products. For example, products such as table
tops, park benches, chair backs and seats, and basketball
backboards may be constructed from plastic.
[0006] Blow-molding is one of many methods for producing plastic
products. Structures produced by blow-molding are substantially
hollow, which makes this process a preferred method for
manufacturing products that are lightweight yet durable. Blow
molding is also a relatively simple process, which further
increases its popularity.
[0007] In order to construct conventional blow-molded plastic
structures, an extruded parison, comprising a hollow tube of heated
plastic, is positioned between two opposing sides of a blow-molding
press. The inner sides of the blow-molding press serve as the mold
against which the blow-molded structure is formed. Once the parison
is positioned inside the press, the two opposing sides of the press
are closed. This closure clamps either or both ends of the parison
to create an air-tight chamber or inner volume. A needle or air
inlet is then inserted through the plastic parison wall and
pressurized air or other gas is injected into the air-tight
chamber. The air or gas causes the plastic parison to deform and
engage the sides of the blow-molding press, which causes the
plastic to take the shape of the mold. Once the plastic has been
molded into the desired shape, the press is cooled and the
structure, now substantially rigid, is removed from the press. The
process may then be repeated using a new parison.
[0008] While blow-molding is an effective process for manufacturing
plastic structures, it has several limitations and disadvantages.
For instance, because blow-molded structures are hollow,
thin-walled structures, it is difficult to use standard mechanical
fasteners to attach components to blow-molded structures. In
particular, the thin outer walls of blow-molded structures
typically have a thickness of about {fraction (1/16)} inch to about
1/4 inch and standard mechanical fasteners, such as screws, require
a greater thickness for secure attachment. Specifically, because
the threads of the screw only engage the thin outer wall, there is
very little engagement between the screw threads and the
blow-molded structure. As a result, there is not a secure
engagement of the screw to the blow-molded structure and the screw
can be easily loosened or torn out of the structure altogether.
Accordingly, components attached to blow-molded structures by
screws or other mechanical fasteners are prone to wobbling or
complete separation from the structure. In the case of components
serving as a support for the blow-molded structure, such as legs
for a plastic blow-molded table top, the screws may not securely
attach the legs to the table top and the table may collapse or
fail.
[0009] In order to strengthen the engagement of screws to
blow-molded structures, it is known to increase the outer wall
thickness. Disadvantageously, it is very difficult to control the
wall thickness in blow-molded structures. Thus, increasing the
outer wall thickness may still not provide secure engagement of
standard mechanical fasteners to blow-molded structures because
sometimes the outer wall may have sufficient thickness while other
times it may not. Additionally, the increased wall thickness
increases costs, manufacturing time and weight of the structure.
Further complicating this situation is the fact that some regions
of the blow-molded product are thicker than others. Thus, a
fastener that may engage the structure with sufficient strength in
one region may not adequately hold in another region.
[0010] It is also known to construct blow-molded structures with
outer walls that are substantially parallel and adjacent to one
another. In this way, a fastener such as a bolt or a screw may pass
through both walls of the blow-molded structure to more securely
attach components to the structure. A nut is typically placed on
the end of the bolt to tighten the connection. This approach,
however, suffers from several drawbacks, including increased time
and parts required to assemble the product, and the unsightly
presence of the fastener on multiple surfaces of the blow-molded
structure. Further, this type of fastening system may still be
unable to prevent undesired loosening or removal of the bolt or
screw because of the limited engagement of the threads with the
thin outer walls and the bolt or screw can still be torn out of the
thin outer walls.
[0011] Another known way to fasten components to blow-molded
structures involves the use of hollow wall fasteners commonly used
in dry wall anchoring. An enlarged hole is made in the wall of the
blow-molded structure and a bolt with an attached anchoring device
is inserted into the hollow interior of the blow-molded structure.
Once inside the structure, the anchoring device, which may have
toggle wings or an expandable collar, expands and engages the inner
surface of the wall. The bolt is then tightened to securely attach
the component to the structure. Disadvantageously, this known type
of fastener requires a large hole be formed in the blow-molded
structure, which increases costs and labor, and requires additional
parts, which further increases costs and labor.
[0012] It is further known to attach a separate part to the
blow-molded structure and a fastener is then threadably connected
to that part to allow components to be attached to the blow-molded
structure. For example, a hole could be formed in the blow-molded
structure and an insert could then be inserted into the hole and
attached to the structure. The insert includes a receptable that is
sized and configured to receive the fastener. Disadvantageously, a
hole must be formed or made in the blow-molded structure and the
insert must be inserted and attached to the hole. This increases
both costs and manufacturing time.
[0013] Additionally, it is known that an insert may be attached to
the blow-molded structure during the manufacturing process. In
particular, the insert is positioned on or proximate an inner mold
surface of the blow-molding press and the plastic parison deforms
around the insert during the blow-molding process. Protrusions
disposed on the outer surface of the insert may help secure it to
the blow-molded structure. The insert includes an opening with
threads that are sized and configured to receive the fastener.
Unfortunately, attaching the insert to the structure during the
blow-molding process is very time consuming because an insert must
be positioned proximate the inner surface of the mold before each
blow-molding cycle. Additionally, this known fastening scheme
requires multiple parts, which increases costs, and often requires
specially manufactured inserts. Disadvantageously, the strength of
the connection is dependent upon the engagement of the insert and
the blow-molded structure. Thus, if the blow-molded plastic does
not completely deform about the insert, then the insert may not be
securely attached to the blow-molded structure. Further, because
the protrusions of the insert may easily become disengaged from the
blow-molded structure, the insert may not provide a secure
engagement of the fastener to the structure.
SUMMARY OF THE INVENTION
[0014] A need therefore exists for an apparatus that allows
fasteners to be securely attached to blow-molded structures, while
eliminating the above described problems and disadvantages.
[0015] One aspect of the present invention is a screw boss that
allows components to be securely attached to blow-molded
structures. Advantageously, the screw boss is integrally formed in
the blow-molded structure and it requires no additional parts or
components to be attached to or formed in the structure. Thus, no
inserts or other parts have to be attached to or formed in the
blow-molded structure.
[0016] Another aspect is a screw boss that is formed in an outer
surface of a blow-molded structure during the manufacturing
process. The screw boss includes an opening and a receiving portion
with an elongated cavity. The receiving portion extends inwardly
into the blow-molded structure and it includes inner and outer
surfaces. The receiving portion is sized and configured to receive
a fastener such as a bolt or screw. Preferably, the receiving
portion is sized and configured to threadably receive a fastener
such as a screw wherein the inner diameter of the receiving portion
is generally equal to or greater than the minor diameter of the
screw and smaller than the major diameter of the screw.
[0017] A further aspect is integrally forming the screw boss in the
plastic structure during the blow-molding process. Preferably, the
blow-molding process includes a blow-molding press having two
halves with molds disposed on their respective inner sides. The two
mold halves cooperatively mate to form a mold cavity therein. An
inwardly extending pin or projection is disposed on an inner
surface of the mold where a screw boss is desired to be formed. A
heated plastic parison is then placed in the mold cavity, the mold
halves are mated, and the blow molding process is begun. During the
process, the heated plastic is filled with gas such that the
parison engages the inner sides of the mold cavity and it conforms
to the shape of the mold halves. The heated plastic parison also
deforms about and conforms to the shape of the projection disposed
on the inner surface of the mold to form the screw boss. Once the
blow-molded structure is cooled and removed from the press, the
screw boss is integrally formed in the structure.
[0018] A still further aspect of the screw boss is it can have any
suitable size and configuration depending, for example, upon the
desired type of fastener to be connected to the structure.
Advantageously, the projection attached to the mold press can be
used to form screw bosses with different sizes and configurations.
For example, the length, thickness and shape of the projection may
vary according to the type of the screw boss to be formed.
[0019] A further aspect is the size and shape of the screw boss is
preferably dependent upon the desired type of fastener to be
connected to the blow-molded structure. For example, the screw boss
can have an elongated receiving portion to receive an elongated
fastener or a shorter receiving portion to receive a shorter
fastener. Preferably, the length and inside diameter of the
receiving portion are sized and configured such that the inner
surface of the receiving portion engages at least a portion of the
fastener. More preferably, the receiving portion has a length and
inside diameter that is sized and configured to engage the threads
of the fastener along all or a substantial length of the fastener.
For example, the length of the receiving portion is preferably
greater than twice the thickness of the outer wall of the
blow-molded structure to allow the fastener to be securely attached
to the structure. Advantageously, the engagement of the threads of
the fastener with the receiving portion of the screw boss over an
extended length greatly increases the strength of the connection
between the fastener and the blow-molded structure.
[0020] Still another aspect is the thickness of the wall of the
inwardly extending receiving portion of the screw boss is
preferably sufficient to allow the threads of the fastener to bite
into the wall without puncturing the wall. This provides for secure
engagement of the fastener to the screw boss.
[0021] Another aspect is the screw bosses can be located in
virtually any desired portion of the blow-molded structure. This
allows fasteners and other components to be attached to virtually
any desired portion of the blow-molded structure. The screw bosses,
however, are preferably located a suitable distance away from
structural support members such as support bars or reinforcing bars
such that the structural support members do not lose any of their
strength or rigidity.
[0022] A further aspect is the screw bosses are preferably formed
in portions of the blow-molded structure that have a relatively
thick outer surface. This allows the screw bosses to be formed in
the blow-molded structure without creating an opening or stress
point in the outer wall of the blow-molded structure.
[0023] Yet another aspect is the screw bosses are preferably
located in portions of the blow-molded structure that have a
stretch region sufficient to accommodate the forming of the screw
boss during the manufacturing process. The stretch region allows
the plastic to stretch while the screw boss is being formed without
creating holes, unnecessary stress points or weaknesses in the
outer surface of the structure. The proper stretch region is
significant because the plastic in the stretch region deforms or
stretches about the protrusion, which causes the thickness of the
plastic outer wall to decrease. The site of the stretch region may
vary according to the size of protrusion used to form the screw
boss. Advantageously, forming the screw boss in an area that has a
sufficient stretch region prevents the outer wall of the
blow-molded structure and the wall forming the receiving portion of
the screw boss from being insufficiently thick or from rupturing
during the blow-molding process. Also, the placement of a screw
boss too close to another structure feature, such as a structural
rib or tack-off, may cause improper formation of the boss.
[0024] These and other aspects, features and advantages of the
present invention will become more apparent from the following
detailed description of preferred embodiments and appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] The appended drawings contain figures of preferred
embodiments to further clarify the above and other aspects,
advantages and features of the present invention. It will be
appreciated that these drawings depict only preferred embodiments
of the invention and are not intended to limits its scope. The
invention will be described and explained with additional
specificity and detail through the use of the accompanying drawings
in which:
[0026] FIG. 1A is a perspective view of an exemplary table with a
table top constructed from blow-molded plastic and a pair of table
legs attached to the table top, the table top includes screw bosses
in accordance with a preferred embodiment of the present invention
to allow the table legs to be securely attached to the table
top;
[0027] FIG. 1B is a perspective view of a portion of the table
shown in FIG. 1A, illustrating the underside of the table and the
table legs attached to the table top by a plurality of screw
bosses;
[0028] FIG. 2A is an enlarged perspective view of a screw boss in
accordance with another preferred embodiment of the present
invention;
[0029] FIG. 2B is a cross sectional side view of the screw boss
shown in FIG. 2A taken along the line 2B-2B;
[0030] FIG. 3A is an enlarged perspective view of a screw boss in
accordance with yet another preferred embodiment of the present
invention;
[0031] FIG. 3B is a cross sectional side view of the screw boss
shown in FIG. 3A taken along the line 3B-3B;
[0032] FIG. 4A is an enlarged side view of an exemplary fastener in
the form of a screw that may be used in connection with the screw
boss;
[0033] FIG. 4B is an enlarged perspective view of a screw boss in
accordance with still another preferred embodiment of the present
invention, illustrating the screw boss formed in an outer surface
of a blow-molded structure and the screw shown in FIG. 4A attaching
a component to the blow-molded structure via the screw boss;
[0034] FIG. 4C is a cross sectional side view of the screw boss
shown in FIG. 4B taken along the line 4C-4C;
[0035] FIG. 5A is an enlarged side view on an exemplary projection
attached to a blow-molding press and an exemplary plastic surface,
illustrating the plastic surface before engagement with the
projection during the blow-molding process;
[0036] FIG. 5B is a side view of the projection and plastic surface
shown in FIG. 5A, illustrating the plastic surface initialing
contacting the projection of the blow-molding press;
[0037] FIG. 5C is a side view of the projection and plastic surface
shown in FIG. 5B, illustrating the plastic deforming about the
projection of the blow-molding press;
[0038] FIG. 5D is a side view of the plastic surface shown in FIG.
5C, illustrating a preferred embodiment of the screw boss formed in
the plastic surface with a closed end;
[0039] FIG. 5E is a side view of the plastic surface shown in FIG.
5C, illustrating another preferred embodiment of the screw boss
formed in the plastic surface with an open end;
[0040] FIG. 6A is an enlarged side view of a preferred embodiment
of a projection that may be used to form a screw boss;
[0041] FIG. 6B is an enlarged side view of another preferred
embodiment of a projection that may be used to form a screw
boss;
[0042] FIG. 6C is an enlarged side view of a yet another preferred
embodiment of a projection that may be used to form a screw
boss;
[0043] FIG. 6D is an enlarged side view of still another preferred
embodiment of a projection that may be used to form a screw
boss;
[0044] FIG. 7A is a top view of an exemplary fastener that may be
used in connection with the screw boss;
[0045] FIG. 7B is a side view of the exemplary fastener shown in
FIG. 7A;
[0046] FIG. 8A is a top view of another exemplary fastener that may
be used in connection with the screw boss;
[0047] FIG. 8B is a side view of the exemplary fastener shown in
FIG. 8A;
[0048] FIG. 9A is a top view of still another exemplary fastener
than may be used in connection with the screw boss; and
[0049] FIG. 9B is a side view of the exemplary fastener shown in
FIG. 9A.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0050] The present invention is directed towards screw bosses
formed in blow-molded structures such as tables and chairs. The
principles of the present invention, however, are not limited to
screw bosses for tables or chairs. It will be understood that, in
light of the present disclosure, the screw bosses disclosed herein
can be successfully used in connection with other types of
furniture and other suitable structures.
[0051] Additionally, to assist in the description of the screw
bosses, words such as top, bottom, front, rear, right and left are
used to describe the accompanying figures. It will be appreciated,
however, that the present invention can be located in a variety of
desired positions--including various angles, sideways and even
upside down. A detailed description of preferred embodiments of the
screw boss now follows.
[0052] As shown in FIGS. 1A and 1B, a portable table 10 includes a
plastic, blow-molded table top 12 and metal support legs 14. The
table top 12 has a top surface 16, a bottom surface 18, and side
surfaces 20. In general, blow molded tables are a popular choice
because of their portability, low weight, and durability. These
characteristics are possible in part because of the blow-molded
nature of the table top 12.
[0053] As best seen in FIG. 1B, the support legs 14 are attached to
the bottom surface 18 of the table top 12 via a plurality of
brackets 22 and fasteners such as screws 24. Though obscured by the
brackets 22, the screws 24 are securely attached to the table top
12 via screw bosses 30. Advantageously, the screw bosses 30 enable
the table support legs 14 to be securely attached to the bottom
surface 18 of the table top 12.
[0054] Note that for clarity the screw bosses 30 are shown in the
accompanying figures and described in the accompanying text as
being used to connect support legs 14 to the table top 12. It will
be appreciated, however, that the screw bosses 30 can be used in
connection with a variety of blow-molded structures and components,
as may be required for a particular application. Additionally, the
screw bosses 30 can be used with a wide variety of fasteners such
as screw and bolts, and the screw bosses allow a wide variety of
components and objects to be connected to blow-molded structures.
Significantly, the screw bosses 30 described herein can be used in
connection with any suitable type of blow-molded structures.
[0055] FIGS. 2A and 2B depict an embodiment of the screw boss 30
with an opening 32 and a receiving portion 34. The receiving
portion 34 includes an end 36 disposed opposite the opening 32 and
the receiving portion is generally defined by a wall 38 with an
inner surface 40 and an outer surface 42. The screw boss 30 is
preferably formed in the bottom surface 18 of the table top 12, but
the screw boss could be located in any suitable location. The
opening 32 of the screw boss 30 is desirably generally flush with
the bottom surface 18 of the table top 12 and the receiving portion
34 extends generally inwardly into the hollow center section of the
table top.
[0056] The opening 32 and the receiving portion 34 of the screw
boss 30 are sized and configured to threadingly receive a fastener,
such as the screw 24, in order to secure the attachment of the
support legs 14 to the bottom surface 18 of the table top 12. One
skilled in the art will appreciate that the opening 32 and the
receiving portion 34 of the screw boss 30 may have any one of a
variety of shapes according to the physical characteristics of the
fastener that is to be received therein. In one aspect, and as best
seen in FIG. 2B, the receiving portion 34 has a generally bullet
shaped central cavity with a tapered end 36. Alternatively, the
receiving portion 34 could have cylindrically or conically shape,
for instance. A detailed discussion concerning the
inter-relationship between the receiving portion 34 and the
fastener, as well as the mating thereof, is given further
below.
[0057] Reference is now made to FIGS. 3A and 3B, illustrating
another embodiment of the screw boss 30. In this embodiment, the
receiving portion 34 is disposed in the bottom surface 18 of the
table top 12 and the receiving portion has a generally conical
shaped configuration with a rounded end 36. In contrast to the
screw boss shown in FIG. 2B, the end 36 of the receiving portion 34
engages another wall of the blow-molded structure. In particular,
the end 36 of the receiving portion 34 preferably engages the top
surface 16 of the blow-molded table top 12. The screw boss 30 of
the type shown in FIG. 3B may be referred to as a "tacked" boss.
The screw boss 30 of FIG. 2B, on the other hand, may be referred to
as a "blind" boss in that it makes no contact with any other
surface. This contact between the end 36 of the receiving portion
34 of the screw boss 30 and a surface such as the top surface 16 of
the table top 12 may be incorporated into the design of the
blow-molded structure to provide the screw boss and/or blow-molded
structure with increased strength.
[0058] Reference is now made to FIGS. 4A, 4B, and 4C, which
illustrate further details of the screw boss 30. FIG. 4A depicts
various details of an exemplary fastener, such as a screw 50, which
threadably engages the screw boss 30. It should be understood that
the screw 50 of FIG. 4A is but one example of a threaded fastener
that may be employed to engage the screw boss 30. Accordingly, it
will be appreciated that other types and configurations of suitable
fasteners may be used in connection with the screw boss 30
depending, for example, upon the type, size and intended use of the
blow-molded structure. The screw 50 generally includes a head 52, a
shaft 54, one or more threads 56, a minor diameter d.sub.1, and a
major diameter d.sub.2. The head 52 of the screw 50 may include a
washer-like extension 58 to facilitate engagement of the screw with
another surface. It will be appreciated, for example, that the
screw 50 may have a tapered shaft 54 and/or the threads 56 may have
variable sizes and spacing. The shaft 54 and/or threads 56 may also
have different diameters and thicknesses that vary, for example,
along the length of the shaft. The size and configuration of the
screw 50, however, is preferably complementary to the screw boss 30
to allow the screw to be securely attached to the blow-molded
structure.
[0059] FIGS. 4B and 4C illustrate an embodiment of the screw boss
30 that may be used to secure the support legs 14 to the bottom
surface 18 of the blow-molded table top 12. One skilled in the art
will appreciate that this may be accomplished a variety of ways;
thus the particular configuration shown in FIGS. 4B and 4C should
be considered exemplary and not limiting of the present invention.
In these figures, the screw boss 30, which is similar to that shown
in FIG. 3B, is shown threadingly receiving the screw 50 in the
receiving portion 34. A portion of the bracket 22 is interposed
between the washer-like extension 58 of the screw 50 and the screw
boss 30. The bracket 22, in turn, securely holds the support legs
14 in the desired position. In this way, the support legs 14 are
securely attached to the table top 12, thereby enabling the
combination to function as a table 10.
[0060] As best seen in FIG. 4C, the screw 50 is received within the
screw boss 30 such that the threads 56 engage the inner surface 40
of the receiving portion 34. In particular, the screw 50 is
inserted it a short distance into the receiving portion 34 and then
it is rotated with a tool such as a screwdriver while applying a
predetermined amount of downward force, as is well known in the
art. In comparing FIG. 4B with FIG. 3B, note that the inner surface
40 of the receiving portion 34 is preferably not pre-threaded.
Thus, the screw threads 56 bite into the inner surface 40 of the
receiving portion 34 as the screw 50 is inserted into the screw
boss 30 and the thread paths 59 are "cold formed" by the screw upon
its insertion into the screw boss. It will be appreciated, however,
that the receiving portion 34 of the screw boss 30 may be
pre-threaded if so desired.
[0061] Advantageously, the size and configuration of the screw boss
30 and screw 50 are preferably correlated or matched to maximize
the engagement between the two. Specifically, the length, thickness
and diameter of the receiving portion 34 are preferably sized and
configured to receive a particular type of fastener or screw. In
particular, the screw preferably has a specified length, minor
diameter d.sub.1, and major diameter d.sub.2 to be generally
received within the receiving portion 34 of the screw boss 30 and
to securely engage the inner surface 40 of the receiving
portion.
[0062] Desirably, the length of the receiving portion 34 is
generally equal to or greater than the length of the screw shaft 54
such that the threads 56 of the screw 50 engage the inner surface
40 of the screw boss 30. Significantly, because the threads 56
engage the inner surface 40 of the receiving portion 34 over an
extended length, this allows secure engagement of the screw 50 to
the screw boss 30. For example, the length of the receiving portion
34 may be at least twice the thickness of the out wall or twice the
diameter of the screw 50 to allow for secure engagement of the
screw to the screw boss 50. Preferably, the length of the receiving
portion 34 is sufficient to receive the screw shaft 54 without
having the tip of the screw puncture the end 36 of the receiving
portion in a blind boss, as shown in FIG. 2A and 2B, or without
having the screw tip puncture the second end of the receiving
portion in a tacked boss, as shown in FIG. 4C. It will be
appreciated, however, that the screw 50 and receiving portion 34
can have any suitable lengths depending upon, for example, the type
of fastener or intended use of the blow-molded structure and the
screw may protrude through one or more surfaces.
[0063] The inner diameter of the receiving portion 34 of the screw
boss 30 is preferably slightly larger than or generally equal to
the minor diameter d.sub.1, of the screw, yet smaller than the
major diameter d.sub.2 of the screw. Such an arrangement is seen in
FIG. 4C. This enables at least a portion of the threads 56 to bite
into the inner wall 40 of the receiving portion 34 when the screw
50 is threadably engaged with the screw boss 30. At the same time,
the thickness of the wall 38 of the receiving portion 34 should be
sufficient to prevent the threads 56 from puncturing and extending
through the outer surface 42 of the receiving portion because that
may reduce the strength of the attachment between the screw 50 and
the screw boss 30. It will be understood that when the screw boss
30 is tacked to another surface of the blow-molded structure, such
as a table top 12, the tip of the screw 50 may protrude through the
end 36 of the receiving portion and it may engage or protrude
through the other surface.
[0064] During the manufacturing process of the screw boss 30, which
is more fully described below, the thickness of the receiving
portion 34 typically varies along the length of the receiving
portion. In general, the thickest portion of the receiving portion
34 resides near the opening 32 and the thinnest portion is located
at the end 36. Factors that may affect the wall thickness of the
receiving portion 34 include the length of the receiving portion,
the location of the screw boss 30 in the blow-molded structure, and
the thickness of the outer walls of the blow-molded structure.
Because the wall thickness of the screw boss 30 typically varies
along the length of the receiving portion 34, this may impact
whether a portion of the screw 50 extends through the screw
boss.
[0065] As best seen in FIG. 4C, it is preferable that the receiving
portion 34 engage the threads 56 of the screw 50 along
substantially all or the entire length of the screw shaft 54 to
maximize the engagement of the threads with the screw boss 30. Of
course, engagement of the receiving portion 34 with the threads 56
along less than the entire length of the screw shaft 54 is also
possible. Generally, however, it is desired that the threads 56
engage a length of the receiving portion 34 that is approximately
equal to at least twice the average outer wall thickness of the
blow-molded structure. This helps ensure sufficient screw thread 56
to screw boss 30 engagement to create a secure attachment of the
screw 50 to the blow-molded structure.
[0066] Reference is now made to FIGS. 5A-5E, which depict a
preferred method for integrally forming the screw boss 30 in the
blow-molded structure, such as the table top 12. This method
generally includes molten or heated thermoplastic material being
fed into an extrusion die from a suitable supply source (not
shown). The thermoplastic material is extruded from the extruder or
die in the form of a hollow cylinder or parison 60 (a portion of
which is shown in the accompanying figures) between a pair of mold
sections 62 (only one of which is shown in the accompanying
figures). The mold sections 62 are preferably movable into and out
of engagement with the parison 60. In particular, the parison 60 is
positioned between the mold sections 62 and the mold sections are
then moved into engagement with the parison such that at least a
portion of the parison is trapped between the mold sections. The
mold sections 62 also pinch or close the parison 60 along one or
more mold lines to form a generally sealed enclosure. Air or other
suitable gases are introduced into the sealed enclosure to expand
the thermoplastic material against the mold surfaces to form the
molded structure. As known to those skilled in the art, the mold
surfaces and molded plastic structures can be vented and cooling
water can be circultated through the mold sections. This method
forms a hollow, thin-walled structure such as a table top.
[0067] Advantageously, the screw boss 30 is formed directly in the
blow-molded structure and the screw boss is formed entirely during
the blow-molding process. This saves valuable manufacturing time
because the screw boss 30 is integrally formed in the blow-molded
structure and no additional parts or components have to be
inserted, connected or attached to the blow-molded structure to
form the screw boss. Again, while this method focuses on the
formation of a screw boss 30 in a blow-molded table top 12, one
skilled in the art will appreciate that the screw boss can be
formed in any suitable structure and a variety of suitable methods
to form the screw boss may be used.
[0068] The screw boss 30 is formed by a pin or projection 70 that
is disposed on an inner surface 64 of the mold 62. The projection
70 is preferably disposed in a fixed or stationary position on the
inner surface 64 of the mold 62, and the projection is preferably
removably attached in order to allow projections with different
sizes and configurations to be attached to the mold. This allows
screw bosses 30 of different sizes and configurations to be formed.
The projection 70 can also be retractable from the inner surface of
the mold 62, if desired.
[0069] The shape and size of the projection 70 is preferably
dependent upon the size and characteristics of the screw 50 that is
intended to be connected to the screw boss 30. Additionally, the
particular placement of the projection 70 on the inner surface of
the mold is dependent upon the desired location of the screw boss
30 in the blow-molded structure. Preferably, the screw boss 30 is
located a predetermined distant away from other features or
components of the blow-molded structure, such as structural ribs or
surface indentations, so that the screw boss does not interfere
with these features. In addition, this distance separating the
screw boss 30 from the other features or components avoids
stretching of the plastic near these features and components, which
may impact their strength and/or appearance.
[0070] As seen in FIGS. 6A-6D, the projection 70 includes a base 72
that is attached to the inner surface 64 of the mold 62, a main
body portion 74 and a tip 76, and the projection can have a variety
of different configurations to form various types of screw bosses
30 during the blow-molding process. These figures are
representative of the variety of shapes that may comprise the
projection 70, but one skilled in the art will understand that the
projection can have any suitable configuration depending upon the
intended configuration of the screw boss 30. For example, FIG. 6A
shows a generally bullet-shaped projection 70 having a generally
cylindrical body 74 and a smoothly pointed tip 76. The projection
70 of the type shown in FIG. 6A may be used to form the screw boss
30 shown in FIGS. 2A and 2B. FIG. 6B shows a projection 70 having a
substantially cylindrical body 74 and a rounded tip 76 which may be
used to form the screw boss 30 shown in FIGS. 3A-4B.
[0071] FIGS. 6C and 6D show other exemplary configurations of the
projection 70. FIG. 6C shows a projection 70 comprising a
substantially cylindrical body 74 and a frustoconical tip 76. FIG.
6D shows a projection 70 including a tapered body 74 and tip 76.
Such a projection 70 may be used to form a screw boss 30 having a
tapered receiving section 34 that is sized and configured to
receive a screw 50 having a tapered shaft 54 and threads 56.
[0072] The projections 70 shown in FIGS. 6A-6D preferably have
generally smooth outer surfaces to allow the projections to be
easily removed from the molded structure and to prevent the plastic
from snagging on a sharp edge during the blow-molding process. The
generally smooth outer surfaces may also help prevent damage to the
screw boss or molded structure when the structure is removed from
the mold. It will be appreciated, however, that the projections may
have one or more pointed surfaces or sharp edges depending, for
example, upon desired configuration of the screw boss 30 to be
formed in the blow-molded structure.
[0073] As seen in FIGS. 5A-5E, the process for making screw bosses
30 in a blow-molded structure begins by placing the heated plastic
parison 60 in the mold cavity and the mating of the mold sections
62 causes the parison to be either positioned near the tip 76 of
the projection 70, as shown in FIG. 5A, or the parison contacts the
tip of the projection as shown in FIG. 5B. The parison 60 is then
filled with air or gas which causes it to conform to the shape of
the mold 62. In particular, the parison 60 engages and begins to
deform about the projection 70 as shown in FIG. 5C. Once the
parison 60 has been fully expanded against the inner surfaces of
the mold, and formed about the projection 70, the mold is cooled
and the blow-molded structure, such as the table top 12, is removed
from the mold press. As shown in FIG. 5D, once the heated plastic
parison is deformed about the projection 70 and the blow-molded
structure is removed from the mold, the screw boss 30 is integrally
formed in the blow-molded structure. As seen in the figure, the
receiving portion 34 of the screw boss 30 is thicker near the
opening 32 and thinner near the end 36. This thinning is due to the
stretching of the heated plastic around the projection 70 during
the manufacturing process. It is also evident from FIG. 5D that the
portion of the outer wall of the blow-molded structure is thinner
proximate the screw boss 30. This thinner area proximate the screw
boss 30 is generally referred to as the stretch region.
Significantly, the stretching and deforming of the plastic about
the projection 70 causes both the thinning of the plastic near the
end 36 of the screw boss and the thinning of the outer wall of the
structure near the screw boss. For this reason it is desirable to
choose a location for the such as structural ribs and tack offs, in
order to protect the plastic surface of the blow-molded structure
from excessive stretching or weakening.
[0074] FIG. 5E illustrates that the end 36 of the screw boss 30 can
include an opening 78. The opening 78 is generally undesirable
because it may allow foreign objects into the hollow center portion
of the blow-molded structure and it may provide less surface area
for the threads 56 of the screw 50 to engage. The opening 78 is
typically the result of excessive stretching of the heated plastic
caused either by an excessively large projection 70, or by the
selection of a screw boss location that is either too close to
other blow-molded features or the outer wall of the structure was
too thin. The screw boss 30 with the opening 78 may still be
utilized to threadingly receive a fastener in secure engagement
with the blow-molded structure and it may be preferred in some
instances.
[0075] Reference is now made to FIGS. 7A-8B, wherein various
possible configurations of fasteners that my be used with suitable
screw bosses 30 are shown. As mentioned above, the size and shape
of a particular screw boss preferably corresponds to the size and
shape of the fastener that is received by it such that a secure
connection between the two is achieved. To the extent that a
variety of screw shapes and sizes may be used to secure components
to blow-molded structures, the particular size configurations of
the screw bosses 30 are equally as diverse. It should be
understood, therefore, that the types of fasteners that may be used
with the screw bosses 30 are in no way limited to those shown in
these figures.
[0076] FIGS. 7A and 7B show top and side views, respectively, of a
screw 80 having a tapered shaft 82 and threads 84. A screw 80 of
this type would be complementarily received by a screw boss 30
formed by the tapered projection 70 shown in FIG. 6D, for
example.
[0077] FIGS. 8A and 8B show top and side views, respectively, of a
screw 90 including a head 92, a tapered shaft 94 and threads 96.
The head 92 includes a washer-like extension 98, a raised key
portion 100, and a torx-type inset 102. The raised key portion 100
allows the head 92 of the screw 90 to be received into a key
hole-type fitting (not shown) disposed in a component to be
attached to the blow-molded structure. In the table top 12, for
example, the shaft 94 and threads 96 of the screw 90 shown in FIGS.
8A and 8B could threadingly engage the screw boss 30 disposed in
the table top 12, while the raised key portion 100 could engage a
key-hole fitting disposed in the support legs 14. Because the
key/keyhole engagement is typically hidden from view once engaged,
it is often used where it is desirable to hide the screw 90.
[0078] One skilled in the art will appreciate that other threaded
fasteners may be alternatively used with the screw boss 30 while
preserving its functionality. For instance, FIGS. 9A and 9B are top
and side views, respectively, of an insert 110 that may be
threadingly connected to the screw boss 30. The insert 110 includes
a head 112 that is integrated into the top of the shaft 114. The
integrated head 112 includes a female engagement 116 that accepts a
tool such as an Allen wrench, and a threaded interior core 118 that
may receive a screw therein. The insert further includes a tapered
body 120 and segmented threads 122 that allow the insert 110 to
threadingly engage the screw boss 30. In use, the insert 110, being
threadingly engaged with the screw boss 30, includes a screw
disposed within the threaded interior core 118. The screw may be
used to connect a component to the blow-molded structure.
Accordingly, the above discussion makes clear that a variety of
threaded fasteners may be adapted for use with the present screw
boss 30.
[0079] Although the invention has been described in connection with
certain preferred embodiments, other embodiments apparent to those
of ordinary skill in the art are also within the scope of the
invention. Accordingly, the described embodiments are to be
considered in all respects only as illustrative and not
restrictive, and the scope of the invention is intended to be
defined only by the appended claims. It will also be understood
that the principles of the present invention can be applied to
other types of structures and not only blow-molded tables and
chairs.
* * * * *