Patent Application
20070012399
The present invention relates to methods and devices to make plastic molded articles by a pultrusion process. In particular this invention relates to methods and devices to make dies suitable for use in pultrusion processes.
Pultrusion is a well-established and cost effective manufacturing process for producing continuous runs of molded composite articles of a resin matrix reinforced with a fiber substrate. In this form of plastic molding, the molded article is drawn or pulled through the mold as a continuous article having an engineered profile. The profile is determined by the shape of the mold. At the input end of the mold, the fiber substrate is typically quite loose and flexible. Then a liquid resin is applied in a die and curing occurs as the compound article passes through the mold. The curing has to be sufficiently complete to permit a tractor grip or other type of pulling device to be used to pull the continuous article through the mold from the downstream end. To let the article cure or harden enough for pulling requires a slower feed rate, to permit more curing time in the mold, or longer molds, to permit faster feed rates but longer residence times in the mold for curing.
An expensive element of any pultrusion molding line is the pultrusion die, which is used to form the desired profile in the continuous molded article and is also used to cure the resin impregnated fiber substrate, by subjecting the substrate to a predetermined curing temperature for enough time to permit the article to harden for pulling. A typical pultrusion die is three feet or more in length. Such length imposes certain constraints upon how the die is made which in turn has certain cost consequences for making the die. For example, for a hollow die of this length it is necessary to fabricate the die from two halves, where the join line is along the long axis of the die. Thus, each half or mold part is formed separately from a block of for example steel. By separating the die into two longitudinal halves, each mold part has a face into which a profile is cut transverse to the longitudinal axis. The profile cut into each mold part represents one half of the overall engineered profile desired in the finished article. The two mold parts are then joined together sideways (like a clam shell) with the two grooves carefully axially aligned to match. The result is a pultrusion die with a cavity extending through its full length. The cavity thus formed has a predetermined cross-sectional profile as a result of the combination of the matching transverse-cut shaped grooves.
Forming the shaped grooves is a very expensive, time consuming and unforgiving process, because the profiles have to match exactly when placed together. The typical mode of fabrication is precision grinding, which is possible because the whole side of the mold part is accessible to a precision grinding machine to permit the transverse cut. The grinding process may take weeks to complete and if it turns out that the resulting cavity of the completed pultrusion die does not have the correct cross-sectional profile, then the whole process must be repeated at further cost and with further delay. What is difficult is to get each transversely formed groove to bean exact match to the other so as to produce asymmetrical pultruded article from the mold.
Pultrusion production of articles is a process which is subject to many variables, such as drawing or pulling speed, resin composition, profile shape and size, curing aspects such as temperature control and duration, and die length and shape. The expense of the dies used in pultrusion process limits the producers ability to modify and alter the profile to accommodate one or other of the variables to optimise the molded finished product. The die expense has therefore limited the flexibility of pultrusion equipment to be adjusted to optimise finished articles and the overall quality of pultruded articles is less than is desirable, due to the need to make due with an expensive, but perhaps imperfect, die.
What is desired is a simple, fast, and cost efficient pultrusion die and method of making the same, that can be used to pultrude a fiber-reinforced resin matrix.
One aspect of the present invention is to provide a method of making a segmented pultrusion die, said method comprising the steps of:
selecting a first block having a first length sized to permit end cutting along a longitudinal axis of said first block;
end cutting said first block along said longitudinal axis to form a first die segment having a first cavity extending therethrough, said first cavity having a first cross-sectional profile,
selecting a second block having a second length,
processing said second block to form a second die segment having a second cavity extending therethrough, said second cavity having a second cross-sectional profile which matches said first cross-sectional profile;
aligning said first and said second die segments together to match said first cross-sectional profile together with said second cross sectional profile to form a continuous die having a constant cross-sectional profile; and
securing said aligned first and second die segments together to permit said segmented pultrusion die to be used in place of a single die.
In another aspect, there is provided a segmented pultrusion die made by the method above method.
In yet another aspect, there is provided a segmented pultrusion die comprising:
a first die segment having a first cavity extending therethrough formed by end cutting a first block along an axis thereof; said first block having a first length sized to permit end cutting along said axis of said first block; said first cavity having a first cross-sectional profile;
a second die segment having a second cavity extending therethrough formed from a second block, wherein said second block has a second length, and wherein said second cavity has a second cross-sectional profile which is matches said first cross-sectional profile;
said first die segment being adjoined to said second die segment with said first and second cavities aligned to form a continuous die having a continuous cavity with a constant cross-sectional profile;
a means for securing said first die segment to said second die segment.
Reference will now be made to the preferred embodiments of the present invention with reference, by way of example only, to the following drawings in which:
The present invention is described in more detail with reference to exemplary embodiments thereof as shown in the appended drawings. While the present invention is described below including preferred embodiments, it should be understood that the present invention is not limited thereto. Those of ordinary skill in the art having access to the teachings herein will recognize additional implementations, modifications, and embodiments which are within the scope of the present invention as disclosed and claimed herein. In the figures, like elements are given like reference numbers. For the purposes of clarity, not every component is labelled in every figure, nor is every component of each embodiment of the invention shown where illustration is not necessary to allow those of ordinary skill in the art to understand the invention.
A segmented pultrustion die 10 according to the present invention is disclosed in
As shown in
As shown in
Although, two mechanisms for aligning the first 12 and second 14 die segments are herein describe, many other means for aligning the first 16 and second 20 cavities of the first 12 and second 14 die segments will be known to persons skilled in the art. These alternate means for aligning the first 16 and second 20 cavities are also comprehended by the instant invention.
In this example, the attachment members 32 are L-shaped, permitting one portion of the “L” to be fastened to the outer surface of one die segment, such as with threaded fasteners or the like. The other portion of the “L” is fastened to the matching attachment member 32, which is fastened on the other die segment. As will be appreciated, there are many means for securing the first die segment 12 to the second die segment 14, using various combinations of attachment members 32, threaded fasteners with matching bores, clamps and the like. Furthermore, it is contemplated that the die segments may be welded together, however, care will need to be taken during the welding process to ensure that the heat generated during welding will not warp the cross-sectional profiles 18, 22 of the die cavities 16, 20.
What is important is that the first 12 and second 14 die segments are sufficiently secured together to withstand the pressures and forces to which they will be subjected while in use in a pultrusion process.
Although, the segmented pultrusion die 10 herein described is shown with only two die segments, the instant invention also comprehends a segmented pultrusion die 10 having more than two die segments.
Although, a preferred embodiment of the present invention involves end cutting using wire cutting machines 38, which are known in the art as CNC Wirecut EDMs, other forms of end cutting are also contemplated by the present invention, including for example a hydro cutting machine (not shown). What is important is that the cutting machine 38 chosen is capable of cutting a cavity 16 into a block 34 by cutting from an end 40 of the block 34 and through the block, along an axis of the block.
It can now be understood, that the present invention provides a method of making pultrusion dies quickly and cheaply, as compared to the prior art. The instant invention permits the construction of a full length pultrusion die from a plurality of die segments stacked end to end, where each of the die segments are individually sized to permit end cutting along an axis of the block 34 using wire cutting machines 38 or the like. The die segments 12 formed from the blocks 34 are then aligned and secured to form the segmented pultrusion die 10.
The present invention comprehends being able to from a built up longer die from a plurality of shorter segments. The use of the shorter segments permits end cutting or longitudinal cutting of the individual segments, where the cutting action occurs along the same axis as the molded article is drawn or pulled. Due to the less expensive nature of such cutting than transverse grinding, different shapes and profiles can be tried and tested small changes made to improve the overall appearance of finished pultruded articles.
It is also contemplated that while one die segment is produced using the method of end cutting described above, other embodiments of the present invention may involve adjoining die segments formed using conventional die forming processes. What is important is that time and expense can be saved by forming at least a portion of the pultrusion die with a die segment prepared using an end cutting technique and adjoining it to at least one other die segment.
While reference has been made to various preferred embodiments of the invention other variations are comprehended by the broad scope of the appended claims. Some of these have been discussed in detail in this specification and others will be apparent to those skilled in the art. All such variations and alterations are comprehended by this specification are intended to be covered, without limitation.
| Number | Date | Country | Kind |
|---|---|---|---|
| CA 2,539,465 | Mar 2006 | CA | national |
| Number | Date | Country | |
|---|---|---|---|
| 60699465 | Jul 2005 | US |
