Plastic and nonmetallic article shaping or treating: processes – With measuring – testing – or inspecting – Controlling heat transfer with molding material
Reexamination Certificate
1999-08-20
2001-09-25
Tentoni, Leo B. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
With measuring, testing, or inspecting
Controlling heat transfer with molding material
C156S292000, C264S545000
Reexamination Certificate
active
06294114
ABSTRACT:
TECHNICAL FIELD
The present inventions relate to thermoforming apparatus, methods and articles in general and, in particular, to thermoplastic articles constructed of three thermoplastic sheets formed by triple sheet thermoforming apparatus and methods.
DESCRIPTION OF THE PRIOR ART
The art of twin sheet thermoforming is well known and has been practiced extensively in recent years in the construction of plastic articles. The basic apparatus and principles of twin sheet thermoforming are well known and are provided by way of example in U.S. Pat. Nos. 3,583,036, 3,787,158 and 3,925,140 to Brown. The intended purpose of twin sheet thermoforming is to produce articles having greater strength than similar articles formed from a single sheet of thermoplastic.
Among articles thermoformed using the twin sheet methodology are plastic pallets which are constructed out of two thermoplastic sheets. An early example of a pallet formed in this general character is disclosed in U.S. Pat. No. 4,428,306 to Dresen et al. Twin sheet pallets of the type referenced in U.S. Class 108/53.3 are known in the field as nesting pallets.
The art of twin sheet thermoforming extends to yet another type of plastic pallet referred to as a racking pallet. A racking pallet is designed to support a load between the two parallel beams of warehouse storage racks. Examples of rackable plastic pallets are disclosed in U.S. Pat. Nos. 5,117,762 to Shuert, and 5,197,396 to Breezer et al. As is widely understood in the field, racking pallets formed by thermoforming methods and constructed out of high density polyethylene (HDPE) thermoplastics exhibit a high degree of creep, such that over time and under loaded conditions, the racking pallet deflects and eventually fails. Accordingly, it is common practice to reinforce racking pallets with rigid non-thermoplastic cross-members interposed between the twin sheets forming the structures of the pallet.
Twin sheet thermoplastic pallets of the nesting and racking variety have been employed with some degree of success. The problems associated with traditional pallets formed of wood have been largely overcome with the use of thermoplastic pallets formed by thermoforming methods. There are problems however associated with twin sheet thermoformed plastic pallets. A common problem with twin sheet nesting pallets is that a network of stiffening recesses are molded into the top surface to increase flexural strength as well as to provide fusion points connecting the top sheet to the underlying sheet of the molded plastic pallet. Recesses are disadvantageous because they reduce the surface area available for supporting loads upon the pallet. Recesses also capture debris and liquid that may damage or contaminate goods transported upon the surface of the pallet. Another common problem with many twin sheet pallets is that they are not easily recycled because they contain rigid non-plastic cross-members, or equivalent structures, which are used to add strength. These rigid non-plastic structures have to be removed and separated before the thermoplastic used to construct the pallet can be recycled and reused. Another problem with twin sheet racking pallets of the type disclosed in the prior art is that mechanical fasteners are required in practice to join and maintain an upper load bearing pallet structure to a lower load supporting pallet structure in spaced parallel relation. Mechanical fasteners are costly and require special care and attention to both maintain the working life of the plastic pallet and to provide for the recycling and reuse of the thermoplastic used to form the pallet. The double deck plastic pallet disclosed in U.S. Pat. No. 5,197,396 to Penda Corporation is hereby provided as an example to describe the problems characteristic of twin sheet pallets.
A considerable number of proposals have been offered by Shuert in U.S. Pat. Nos. 5,404,829, 5,391,251, 5,255,613, Continuations-in-part of Ser. No. 993,762, Dec. 18, 1992, U.S Pat. No 5,401,347, and Continuation-in-part of Ser. No. 636,062, Apr. 22, 1996, U.S. Pat. No. 5,676,064, to over come problems associated with twin sheet pallets and in particular with mechanical fasteners. In summary, Shuert proposes “fusion” as a means of joining the various pallet structures referenced in the detailed descriptions of his pallet inventions. However, Shuert does not teach how a plurality of separate thermoplastic pallet structures can be fused together in substitution of mechanical fasteners. Thus, Shuert does not adequately disclose how two or more twin and single sheet components can be fused together to produce a resilient and durable stacking pallet structure.
The traditional 48 inch×40 inch “GMA” wood pallet remains an integral part of America's grocery distribution system today, and is involved in one way or another in the movement of over 90% of all dry goods. It is estimated that the current inventory of wood pallets costs the grocery industry nearly $2 billion annually, almost half of which is determined to be the result of product damage, carrier inefficiencies, productivity losses, and time allocated to sort and repair wood pallets. Although twin sheet thermoformed pallets of the type characteristic in the prior art have been used to some advantage in recent years, they do not yet comply with the set of standard pallet-design specifications that would reduce the costs associated with pallet exchange systems used within the grocery industry. While thermoformed plastic pallets are attractive for durability and ease of sanitation, they still have several shortcomings. Most notably, current thermoformed pallets deform under heavy load and unless reinforced with steel, wood or the like, do not provide acceptable racking strength. Conventionally reinforced thermoformed pallets are therefore costly and less susceptible to recycling. Accordingly, the art must be advanced significantly before thermoformed plastic pallets will enjoy wide acceptance within the many sectors of the material handling industry.
Another application of twin sheet thermoforming is found in the area of thermoplastic dumpster lids. Double walled thermoplastic dumpster lids produced by the twin sheet thermoforming method have been used to replace metal dumpster lids with some success. Thermoplastic dumpster lids have the advantages of being low cost, light weight, quiet, rust proof and relatively dent resistant. Thermoplastic dumpster lids thermoformed of PE materials however have some problems. PE twin sheet dumpster lids undergo significant wear, tear and abuse during regular use. Opening and closing the lid over an extended period of time causes hinge points formed in the dumpster lid to weaken and develop stress cracks which radiate into the main body of the lid, thus causing failure and in some cases danger to children playing upon the dumpster. Therefore, the art still requires further advancement to overcome strength related problems.
Many other small and large articles thermoformed according to the twin sheet methodology are found in a wide variety of primary end markets including recreational and sporting goods, building and construction, automotive and transportation, marine, agricultural, appliance, industrial and consumer products to name a few. Substantially all articles thermoformed according to the twin sheet methodology have either greater strength than similar articles formed from a single sheet of thermoplastic; they provide greater cost efficiencies in the manner in which they are produced and reinforced to replace an existing product of the similar application; or, they offer improved quality as a result of parts consolidation and ease of manufacture.
Although the art of twin sheet thermoforming has resulted in improved products in a wide variety of applications and end markets, a range of needs nonetheless exists to advance thermoforming methods and apparatus to overcome such specific weaknesses as have been mentioned above, or generally, to further increase the strength, lower the costs or improve the quality of articles const
Harness & Dickey & Pierce P.L.C.
Tentoni Leo B.
LandOfFree
Triple sheet thermoforming apparatus, methods and articles does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Triple sheet thermoforming apparatus, methods and articles, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Triple sheet thermoforming apparatus, methods and articles will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2514504