Method of manufacturing a decorative cover for a lamp post

A decorative cover for a post having a hollow body. The hollow body includes a continuous wall having a substantially uniform thickness, and a cavity having at least one undercut that would prevent a core from being pulled from the cavity. The decorative post can be manufactured by providing a mold, introducing a liquid thermosetting resin within the mold, rotating the mold about first and second axes, curing the liquid thermosetting resin as the mold is rotated to form a body with a substantially uniform wall thickness, and removing the cured liquid thermosetting resin from the mold.

FIELD OF THE INVENTION

The invention relates to composite covers, and, more particularly, to composite covers for light poles.

BACKGROUND OF THE INVENTION

Covers for light poles, traffic signal poles, street sign poles, bollards, or utility poles have been used for many decades to add a decorative base to a light pole, or to hide and protect an access hole to wiring splices or fuses in the pole. Traditionally, these covers were made of cast iron and formed by statically pouring molten iron into sand molds. This process includes breaking out sand molds, finishing and painting the covers, and installing the covers onto the poles.

The cast iron covers are disadvantageous because they are heavy, expensive, brittle, corrosive in urban environments, and electrically conductive. More specifically, the cast iron covers present a shock hazard and are subject to galvanic corrosion. In addition, many of the foundries are no longer in business, and the original patterns for production have been lost. Other alternative covers are made of cast aluminum and cast concrete, both of which have several of the same drawbacks of the original cast iron covers.

In recent years, covers duplicating the old cast iron covers have been manufactured from fiberglass and polyester resin using traditional techniques such as hand lay-up or spray-chopped. These covers are light, non-corrosive, aesthetically pleasing, and inexpensive. In addition, they are less likely to cause damage or injury when hit by vehicles compared to the traditional covers.

Even more recently, covers have been manufactured by pouring a urethane into a mold, allowing it to cure, and removing the part. These covers possess the advantages associated with the fiberglass covers, and the urethane covers are more impact resistant and less expensive to produce.

To form a poured urethane (or resin injection molded) cover, a core is placed into a mold, and the urethane is poured or injected into the cavity formed by the outer mold and the core. After the urethane is polymerized, the core is extracted and the mold opened to remove the cover.

The disadvantage of the poured urethane method is that many of the more decorative covers have large undercuts, which prevent a core from being removed after molding. As a result, the wall thickness is much thicker than necessary in the undercut areas. These large variations in wall thickness increases the production cost and reduces the structural integrity of the cover. Since the cost of urethane is higher than the material cost of fiberglass, the cost advantages of lower labor costs for urethane covers is largely offset by the higher material costs. It would be commercially important if a urethane cover could be molded with a relatively constant wall thickness, thus minimizing both the material and labor costs. The described invention produces a uniform and stable wall section, with low labor cost.

SUMMARY OF THE INVENTION

One embodiment of the present invention is directed to a method of manufacturing a decorative cover for a post. The method including providing a mold, introducing a liquid thermosetting resin within the mold, rotating the mold about first and second axes, curing the liquid thermosetting resin as the mold is rotated to form a body with a substantially uniform wall thickness, and removing the cured liquid thermosetting resin from the mold.

Another embodiment of the invention is directed to a decorative cover for a post having a hollow body. The hollow body includes a continuous wall having a substantially uniform thickness, and a cavity having at least one undercut that would prevent a core from being pulled from the cavity.

DETAILED DESCRIPTION

FIG. 1illustrates a decorative cover10according to one embodiment of the present invention covering a light pole14. The method of manufacturing the cover10is described in more detail below.

A female mold is formed by conventional means, such as from composite materials or metals. In the case of composites, a pattern of the desired base cover may be made from materials such as clay, wood, plaster and the like (or from an antique cast iron base cover). The pattern is then overlaid with composite materials such as a gel coat and fiber reinforced resin such as epoxy or polyester. Alternatively, the pattern may be overlaid with silicone rubber reinforced with composite materials. This forms an impression of the outside of the desired cover.

In the disclosed invention, the mold is made in two halves which are registered together so that seams and mold mismatch are minimized. After joining the halves together, caps are fitted on both ends, thus forming a closed mold without any core. One of the closed ends has a removable stopper with a vent tube in it, through which a thermosetting liquid monomer such as urethane or unsaturated polyester may be introduced. More specifically, the liquid monomer can be dicyclopentadiene. The liquid monomer can additionally have reinforcement such as short chopped fiberglass, or other property improving materials for specific applications such as static reduction and electrostatic finish application, or fillers such as calcium carbonate or glass micro balloons. The liquid may also be pigmented to match the desired final color. In this case, paint damage to the exterior paint would tend to be hidden by the color of the molded part, which may be pigmented all the way through the wall of the cover10.

To produce the cover10, the joined mold is placed into a rotational molding machine, which is designed to rotate about two axes simultaneously. The liquid material is poured into the mold through the hole in one end, the stopper is inserted, and the machine is rotated. After the material has at least partially polymerized, the mold may be opened, and the cover10removed. The process maybe done at room temperature, since the resins are liquid, or may be done at elevated temperature to speed up the polymerization.

Additionally, the cover10may be built up in stages with polymerizing between stages. For example, the first layer may be a different material than subsequent materials. The first layer may be a material with excellent weathering properties, while the next layer may have improved structural properties, such as obtained with fiber reinforcement. In this case, the first layer would be allowed to at least partially solidify, then a second layer would be added and rotated again with the rotational molding machine.

After removal from the mold, the top and bottom of the cover10is cut out to accept the diameter of the pole14for which it is made. The cover10can be optionally painted through conventional means.

Through this means, a one-piece cover10is produced which slips over a light pole14before the lighting fixture is attached. This prevents the cover10from being stolen or otherwise removed without removing the light fixture. Since there is also a demand for two-piece covers for replacement purposes, the cover10may also be made in halves either by splitting the one-piece cover10and attaching fasteners, or rotational molding it in separate halves.