Patent Application
20120261409
Packaging for electronic products continues to move away from heavy and bulky metal enclosures for cost and weight-saving purposes. While plastic housings reduce cost and weight, plastic housings can be difficult to mount because plastics that are usable as housings are brittle and have relatively low elastic moduli. Mounting flanges or feet are easily crushed when the plastics they are made from are subjected to c compressive stress. Plastics are therefore somewhat ill-suited for use as housings or enclosures of electronic devices.
Each mounting foot 106 is comprised of a plastic upper, generally cylindrically-shaped lug 108. The lug 108 has a hole or cylinder, which receives a separately-made and separately installed metallic insert support 112. The plastic lug 108 is attached to a second lug 110 that is metallic and which extends' laterally away from the side 109 of a metallic lower portion 104 of the housing 100. The metal insert 112 extends from the top of the plastic lug 108 to the bottom of the second metal lug 110.
The metal insert 112 is installed into the foot 106 to provide a structure that can withstand compressive loads applied to the foot 106 by fasteners, which are not shown. Fasteners extend through the insert 112 and through an attachment surface to which the housing 100 is mounted. The insert 112 thus prevents the plastic lug 108 from being crushed.
Prior art metal inserts 112 that are inserted separately require manual insertion. They are also relatively expensive to manufacture because they are typically formed by rolling a flat metal tab into a cylinder as shown. Reference numeral 114 identifies a seam formed by rolling the insert 112. A housing having a combined metal cover and a crush-resistant or an anti-crush hole would be an improvement an improvement over the prior art.
It is well known that the degree to which structures deform in response to an applied stress depends on the material's modulus of elasticity. When stress and strain are proportional to each other, deformation of a material is considered to be elastic. When a material is stressed to its proportional limit, deformation is plastic, i.e., the material does not return to its original shape. Stated another way, a material fails, when it is subjected to a stress that exceeds its proportional limit or yield strength.
Plastics are generally less dense than metals. Plastics are also generally non-conductive. Another difference between plastics and metals is their elastic modulus. Plastics are not as strong as metals.
Plastics that include low density polyethylene or LDPE, high density polyethylene (HDPE), polypropylene (PP) and polyvinyl chloride (PVC) have a modulus of elasticity of about 0.025×106 psi and about 5.0×106 psi. Light weight aluminum alloys however have elastic moduli of about 10×106 psi. Metals are therefore better able to withstand compressive loads.
The supports 206 are hereinafter referred to as mounting feet. A mounting foot is formed by the joinder or assembly of a top plastic portion 208 of the housing 200 and a metal bottom portion 210 of the housing 200. The metallic bottom portion 210 is formed to provide a metal, load-bearing insert, which when inserted into a plastic sleeve or cylinder resists crushing when a compressive stress is applied to the foot 206.
When viewed from the top, the foot 206 has a form reminiscent of a stilted arch. As used herein, “stilted arch” refers to an arch having a semi-circular rounded portion with straight legs or stilts that extend away from the ends of the semi-circular portion. In
A cylindrical hole 218 is formed in the plastic top portion 208 of the foot 206. The circular-cross section hole 218 formed into the end of the foot 206 imbues the top portion 208 of the foot 206 with a structure that is cylindrical and formed from the plastic material surrounding the cylindrical hole 218. Reference numeral 220 identifies what is considered to be the outer circumference of a “cylinder” of material in the plastic top portion 208 of the foot 206. The plastic top portion 208 is thus considered to have a first cylindrical part 220 of the mounting foot 206.
The bottom portion 210 of the foot 206 is metallic. It therefore has an elastic modulus much greater than the plastic top portion 202.
The bottom portion 210 is comprised of a relatively thin, stilted arch-shaped tab portion 216 that extends laterally away from a side surface 222 of the metallic bottom portion 204.
The bottom portion 204 including the metal tab 216 is formed by stamping. A cylinder 224 extends upwardly from the tab 216 is also formed by a stamping process known as deep drawing. Being formed by stamping, the metal cylinder 224 is seamless. And, unlike prior art inserts that are stamped and rolled and therefore not really circular, the cross sectional shape of the stamped metallic cylinder 224 can be made into a nearly perfect circle.
In addition to being seamless and having nearly perfect circular cross sections, in one embodiment, the stamped metallic cylinder 224 has an outside diameter that tapers, or which has a “draft.” The outside diameter at the top of the cylinder 224 is slightly less than the outside diameter of the cylinder 224 where it meets the tab 216. Providing a draft to the cylinder 224 facilitates assembly of the two pieces 202 and 204 to each other. In other embodiments, the cylinder 224 outside diameter is constant.
The bottom or lower end of the cylinder 224 is surrounded by a relatively flat or planar annulus 225, which meets the plastic “cylinder” 220 portion of the plastic top portion 202. The metallic cylinder 224 has a height that is substantially equal to or slightly greater than the thickness of the plastic first cylindrical part 220 of the plastic top portion 208.
By deep drawing the metal lower portion 204, it is possible to stamp a lower metal panel 204 having a metallic second cylinder 224, the outside diameter of which is just equal to the inside diameter of the hole 218 in the plastic upper portion of the foot 206. The metallic second cylinder 224 also has an inside diameter 226 selected to correspond to the outside diameter of a fastener used to attach the housing 200 to a surface. Fasteners are not shown in
Together,
The thickness 402 of the plastic upper portion 208 of the foot 206 is shown to be substantially equal to the height 404 of the metallic second cylinder 224. Since the height 404 of the inner cylinder 224 is at least equal to and preferably slightly greater than the thickness 402 of the upper portion 208, insertion of the inner cylinder 224 into the cylindrical hole 218 provides a metallic structure inside a plastic structure with the metallic structure bearing load applied to the mounting foot 206 by a fastener 406. Tightening the hex nut 403 on the bolt 401 exerts compressive force on the metallic inner cylinder 224 but not on the plastic outer cylinder. In one embodiment, the thickness 402 is slightly less than the height 404 to enable the metallic second cylinder 224 to engage a compressive load before the plastic.
The metallic inner cylinder 708 has a central hole 712 large enough to receive a fastener, such as a bolt 714. When the plastic top portion 702 is joined to the metallic bottom portion 710, the metallic inner cylinder 708 extends all the way through the plastic outer cylinder 704 as described above with regard to the exterior foot 206.
When the fastener 712 and nut 714 are tightened, compressive stress is applied to the metallic inner cylinder 706. The plastic outer cylinder 704 is thus spared from force that might otherwise permanently deform, i.e., crush, the plastic top portion 702 of the housing 600.
In the embodiments described above and depicted in the figures, the cylinders have circular cross sections. Alternate and equivalent embodiments include “cylinders” that have non-circular cross sections, such as square, triangular and rectangular cross sections.
Those of ordinary skill in the art will recognize that a light-weight housing can be constructed with robust mounting supports by using supports formed from both plastic and metallic components. A metallic insert inside a plastic outer portion is able to withstand compressive loads greater than having a plastic portion.
The foregoing description is for purposes of illustration only. The true scope of the disclosure is set forth in the appurtenant claims.
