CA1294102C

CA1294102C - Method and apparatus for forming an extruded foam product

Info

Publication number: CA1294102C
Application number: CA000564427A
Authority: CA
Inventors: David Hartman; Steven Hartman
Original assignee: Individual
Current assignee: Individual
Priority date: 1988-04-18
Filing date: 1988-04-18
Publication date: 1992-01-14
Anticipated expiration: 2009-01-14

Abstract

ABSTRACT OF THE DISCLOSURE
The synthetic plastic foam products are extruded in a manner to cause a controlled increase in the area of the product after being extruded through a die orifice.
This controlled increase in cross sectional area is limited by a shaping horn which engages the product as it is foaming and limits the cross section of the final product. A lubricant is introduced to reduce friction and avoid adhesion of the product to the shaping horn.

Description

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TITLE: METHOD AND APPARATUS FOR FORMING
AN EXTRUDED FOAM PRODUCT
_ _ _ BACKGRQUND OF THE INVENTION
_ _ The present invention relates to the extrusion of polymer foan product and methods and apparatus for improvîng the production of such product. Apparatus and methods of the present invention provide greater flexibility in the manufacture of different fuam products and greater freedom with respect to the accuracy of the product and the size of the product which are extruded.
The direct or free extrusion of polymer foam product is well known and requires the mixing of a gas in a liquid form with a suitable polymer and forcing the mixture through a controlled orifice which contributes to the final shape of the product. Once this product leaves the orifice, the gas which was previously in a liquid form expands to ~orm the various cells of the foam product and the cross section of the product increases many times until foaming of the product is substantially complete. A
TM
mixture of Freon ' in a liquid form and a hot plastic is passed through a die ori-f'ice and foams at atmospheric pressure beyond the orifice as the FreonTM changes to a gas. The product is typically dischaxged into a llquicJ
filled, llquid sprayed or air cooled trough to ass.lst in ~orming a skin on the product and to cool the product.
In a direct or free extrusion process, the shape of the orifice in -the dle is critical in determinlng the final shape of the product and the density of the product 3û as it is being extruded also contrlbutes to the final size of the product. Because of these factors and others, the tolerance variation of the final cross section of the product varies considerably and changes in density of the product will greatly contribute to even wider tolerance variations.

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The other aspect that is important with free or direct extrusion is the ability to maintain a generally consistent cell structure and this requires -the gas to remain in a liquid form until it is extruded through the die orifice. Thus, there must be a substantial pressure maintained on the mixture of hot plastic and FreonT~
such that the FreonTM on the upstream side of the die orifice is maintained ln a liquid state and evenly distributed. This requirement to maintain a significant pressure is not a problem where the die orifice is small, however7 in the manufacture of larger dia~eter product or larger cross sectional area product, the orifice becomes larger and the ability to continuously maintain this high pressure on the upstream side is much more difficult. In order to accomplish this, for example, in the manu~acture of a five or six inch diameter rod, the initial material is placed in an accummulator and processed on a batch type process. For example, a certain amount of pro~uct, say, sufficient product to produce a ten foot length, would be accummulated in an extruder and then a piston would urge this raw material at the necessary operating pressure through the large orifice and the piston would ensure that the product is maintalned at a suFFiciently high pcessure to avoid th~ FreonTM or other material chan~in~ to a g&l~
state within the extruder. Thus, wi1h such a system, it is possible to produce product o~ larger ccoss sectional area, say, in excess o~ 12 square inches and in length up to about ten feet or more, depending upon the size of the machine on a batch type basis. In order to produce such a large cross sectional area product on a continuous basis, substantial capital costs investment would be required and, to justify this expenditure, the demand for the product woul~ have to be large. Even with such capital expenditure, product variation due to changes in density of the raw material would render the process diFFicult and contribute to substantial tolerance variations.

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According to the present :invention, it is possible to use lower capacity extrusion apparatus for -the manufacture of laryer diameter produc-t and also improving the final tolerance variation on the product.
According to the method and apparatus of the present invertion, it is possible to produce large cross sectional area products using a low capacity extrusion process on a continuous basis.
It is also possible by the present apparatus and method to produce both large and small in cross section products having better accuracy.

SUMMARY OF THE INVENTION
According to the present invention, immediately after the extrusion of a polymer foam product, the progress of the product is impeded to an extent that the product foams to fill a shaping horn of a predetermined cross sectional area, whereby the final cross section of the product is essentially determined by -the shaping horn.

2~ According to an aspect of the inven-tion, a resisting force is applied on the extruded foam as it is foaming which impedes the axial advance of the extruded foam and causes an increase in the cross sectional area of the product as it is Foaming with khe shaping horn lirniting thls lncrease in cross sectional area to -the desired sectlon to be achieved. The shaping horn engages the sides of the procluct and provides a physical restriction to the cross section of the product un-til foaming of the product is at least substantially complete.
According to a further aspect of the invention, a friction reducing lubricant is applied to the exterior of`
the foam as it is extruded to reduce friction between the shaping horn and khe product as the product passes through the shaping horn.
Both a method and apparatus are taught which allow manufacture of foam product of greater cross WH-7289-87 - 4 ~ 08671-1/0057F

sectional area, foam product having more restrictive tolerance variation7 as well as a simplified rnethod for the manufacture of large cross sectional area product.

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Preferred embodiments of the invention are shown in the drawings, wherein:
Figure l is a partial perspective view of the extruding apparatus;
Figure 2 is a sectional view of the shaping horn;
Figure 3 is a partial sectional view of the shaping horn; and Figure 4 is a cross section of a flat sided product more accurately produced by the present method and apparatus~

DETAILED DESCRIPTION OF THE RREFERRED EM~ûDIMENTS
The extruder 2 includes a die 4 having an orifice 6 through which hot plastic is extruded in the forming of a polymer foam product. Immediately acljacent the orifice 6 is a transitional portion 8 having a smooth, curved surface lO associaked wlth the final shaping horn 12. The final shaping horn 12 has a constant cross section generally shown as l4 which limits the extent to which the product can Poam. Thus, the transit.lonal portion 8 and the f`inal shapiny horn 12 make up what can be referred to as the shaping horn o~ the extruder.
As the hot product passes through orifice 6, it starts to foam and a back pressure or retarding force 17 is exerted on the foam to cause the foam to fill the transitional portion and the finaI shaping horn as i-t moves in the axial direction away from the orifice 6. The product takeup or drive 30 beyond the shaping horn is driven at a speed less than but coordinated with khe rate of extrusion to ensure that the shaping horn is full while also removing product at a rate sufficient to avoid WH-728~-87 - 5 - 0~6-/H/0057F

blockage. In this way, -the system can operate on a continuous hasis.
In addition to the resisting -force prcvided by the product drive 30, there is a drag exerted on the product as it passes through the shaping horn. In order to ensure the foam does not become adhered to the shapiny horn as it passes therethrough, a lubricant 7 is introduced through a lubrication system 20 which surrounds the orifice 6. The lubr;cation systern includes a circular port 22 supplied by inlet 23 which surrounds the orifice 6 and applies a thin film of lubricant to the product as it passes through orifice 6. This film of lubricant, generally shown as 26, expands with the ~oam and becomes thinner as the product continues to ~oam in the shaping horn. The film of lubricant remains on the outside and separates the foam from the shaping horn. The product leaving the shaping horn enters a water trough (not shown) where water i5 sprayed on the foam to cool the same and ensure the product does not adhere to the trough.
Lubrication system 22 includes an outer reservoir 20 about orifice 6 which allows the lubricant to pass khrouyh a circular port about the orifice 6. The lubricant can be under pressure to ensu.re a continuous flow to the product as it passes through the die. Othe arrangements for introducing the lubricant a.re possihle and the lubricant is important where the ~oaminy product is likely to adhere to the shaplng horn. This parti.cular arrangement effectively applies the film to the product as it is extruded.
According to the method and apparatus described above, the product 50 may be oversized relative to -the product which would be freely extruded through the orifice 6 and the tolerance variation in the final product are much closer, within 2-3%, as the shaping horn basically determines the final dimensions. Thus, variations in density of the product can be accommodated as the product foams in an area lirnited by the shaping horn. The extruder, generally shown as 2, having a capacity of 200-300 lbs./hour can produce product having a cross sectional area greater than 12 square inches ccntinuously and the accuracy of this product and the ability to forrn desired angles and flat walls on the cross section of the product is much better than with free ex-trusion. The product, when produced, also has a skin thereabout and, as the process is continuous, it can be produced in great lengths. Complicated shapes, such as the flat sided product 52 of Figure 4, are possible by changing of the shaping horn and normally pairing the shape of the orifice with the shape of the shaping horn. Such complicated product shapes were previously difficult to produce and difficult to control the production thereof.
The apparatus and process allow existing apparatus to be modified for production of product having larger cross sectional area and/or improved accuracy. A
free extrusion machine which processes material at 200-300 lbs./hour can produce, for example, cylinder shaped rods up to possibly a 2~1/2 or 3 inch diameter. ~y using the present process and an appropriately shaped shaping horn, the same machine can produce product, for example, rods having a 4, 5 or 6 inch diametsr on a continuous basis.
The same apparatus could also be usecl f`or produclny more compllcated shapes such as those involving fla~ sldes or particular angles betweer1 sides, as bu-t two examples. In addit;on, the accuracy of the die orifice is not as critical as the shaping horn is the dominate factor in determining the final size of the product. In free extrusion, the shaping of the die orifice is critical.
Although various preferred embodiments of the present invention have been described herein in detail, it will be appreciated by those skilled in the art, that variations may be made thereto without departing from the spirit of the invention or the scope of the appended claims.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

l. In a direct or free extrusion of polymer foam product, the improvement comprising:
immediately after extrusion, applying a resisting force, over and above the normal frictional forces with shaping components, on the extruded foam as it is foaming to impede the axial advance of the extruded foam and cause an increase in the cross sectional area of the product and limiting this increase in cross sectional area to a desired section by engaging the sides of the product and physically restricting the cross section of the product until the foaming of the product is at least substantially complete.
2. In a direct or free extrusion of a polymer foam as claimed in claim l including:
applying a friction reducing lubricant to the exterior of the foam as it is freely extruded to reduce friction when the sides of the product are engaged.
3. In a direct or free extrusion of a polymer foam as claimed in claim 1 wherein said lubricant is applied as a film of sufficient thickness to continue to cover the surface of the product as it foams and allow slippage of the product through the physical restriction.
4. In a method as claimed in claim l, 2 or 3 wherein a waker soluble lubricant is applied to the foam product and including cooling of the shaped product in a water bath which additionally serves to strip the foamed product of the lubricant on the exterior thereof.
5. A method of shaping a foam polymer after the polymer has exited along an axial path from a die and during foaming of the polymer comprising:
applying a force slowing the advance of the foam polymer adjacent to such die and to cause a controlled increase of the cross section of the foam polymer, and limiting the cross section to a predetermined section by restricting the thickened foam to this shape during foaming of the polymer and until the foaming is at least substantially complete.
6. A method as claimed in claim 5 including providing a smooth progressively increasing in cross section transition between the die and the thickened cross section which limits the thickening of the product.
7. A method as claimed in claim 6 including withdrawing the formed product at a speed sufficient to ensure the cross section of the product is determined by the step of limiting the cross section to a predetermined section.
8. A method as claimed in claim 7 including introducing a lubricant to the product in a manner to coat the exterior of the foam as it leaves the die and to envelope the cross section of the product up to and during the controlled thickening and limiting of the product cross section.
9. A method as claimed in claim 8 wherein the shape of the die is coordinated with the shape of the predetermined section to complement one another.
10. A method as claimed in claim 9 wherein the predetermined section and the die are selected for forming of extruded foam products having a cross section at least a portion of which is substantially linear.
11. A method as claimed in claim 8 wherein the controlled thickening results in a product of a cross section at least double the area that would occur if the product was freely extruded alone.
12. A method as claimed in claim 11 which is continuous whereby an extruding machine having a capacity of 200 to 300 lbs./hour can continually produce final product having a cross sectional area of over 10 square inches.
13. A method of extruding a foam polymer of greater cross sectional area than is possible if freely extruded through a die of a given capacity machine comprising:
applying a back pressure on the foam product as it leaves such die forcing the foaming product into contact with a shaping horn which restricts the extent to which the cross section of the product is increased to a cross section of the horn as the product is foaming and being removed from such die and such shaping horn.
14. A method as claimed in claim 13 wherein product is removed from such die by positively engaging the product after passage through the shaping horn and moving of the product at a controlled rate coordinated with the rate of extrusion of the product to produce a continuous process.
15. A method as claimed in claim 14 wherein the controlled rate is adjusted to contribute to said back pressure.
16. A method as claimed in claim 13 including applying a film of lubricant to the product in a manner to separate the product from the shaping horn as it passes therethrough.
17. A method as claimed in claim 16 wherein said lubricant is applied to the product as it leaves the die with the lubricant being applied about the orifice of the die.
18. A method as claimed in claim 16 wherein said shaping horn is of a cross section to impart a cross section to a foamed product in excess of 10 square inches and having at least one flat side.
19. In apparatus for the direct or free foaming of a polymer foam product from a first die having a port through which product is extruded 7 comprising a shaping member cooperating and adjacent said first die for receiving extrudate and providing controlled expansion thereof within said shaping member whereby the cross section of the final product is primarily determined by said shaping member and including means for removing product from adjacent the exit of said shaping member, said means for removing product providing sufficient back pressure such that product expands to fill said shaping member prior to removal.
20. In apparatus as claimed in claim 19 wherein said shaping member is of a full cross sectional area at least 5 times greater than the port of said first die and includes a continuous transition region to cause the extrudate to follow the interior wall of said shaping member to the full cross sectional area of said shaping member.
21. In apparatus as claimed in claim 20 wherein said shaping member is of a fixed shape.
22. In apparatus as claimed in claim 21 including lubrication introducing means for introducing a friction reducing lubricant film adjacent or intermediate a junction of said shaping member and said first die such that the film is between the interior walls of said shaping member and the product as it passes through the shaping member.
23. In apparatus as claimed in claim 21 including a lubricant introducing means for creating a lubricant film between the interior surface of said shaping member and the product as it passes therethrough.
24. In apparatus as claimed in claim 23 wherein the apparatus is capable of extruding product at about 200 to 300 lbs./hour and the resulting product is at least 50%
greater in cross sectional area than if extruded in a conventional manner.
25. In apparatus as claimed in claim 24 wherein the apparatus works on a continuous basis to produce a long strip of product.
26. In apparatus as claimed in claim 24 wherein the final dimensions of the extruded product are determined by said shaping member to the extent that minor variations in density of the material being extruded, which in a conventional free extrusion would cause wide variations in the dimensions of the product, do not materially affect the final dimensions of the extruded product.
27. In apparatus as claimed in claim 26 wherein said apparatus is capable of making the product at different densities without replacing the first die and shaping member.
28. In apparatus as claimed in claim 26 wherein said shaping member has a cross sectional area of at least about 10 square inches.
29. An extruded synthetic foam plastic product having a cross sectional area of greater than 12 square inches and of a length greater than fifteen feet, said product having a continuous skin of plastic along the length thereof and to the exterior of the skin a thin film of a lubricant.
30. In extruded synthetic foam plastic product as claimed in claim 29 wherein said lubricant is a water soluble lubricant,
31. An extruded synthetic foam plastic product as claimed in claim 29 wherein said product has a tolerance variation with respect to the dimensions of the cross section of about +3%.
32. An extruded synthetic foam plastic product as claimed in claim 31 wherein said cross sectional area is greater than 20 square inches.
33. An extruded foam product as claimed in claim 29, 31 or 32 wherein said product has at least one flat side.
34. An extruded foam product as claimed in Claim 29, 31 or 32 wherein said product has at least two flat sides cooperating to define a corner having a particular angle between said two flat sides.
35. An extruded synthetic loam plastic product as claimed in claim 29, 31 or 32 wherein all cell structure throughout the product is generally uniform as applied to extruded foam products.
36. An extruded plastic foam product having a non circular or non generally circular cross section and of a cross sectional area greater than 12 square inches and a tolerance variation with respect to cross section of about +3%, said product having a continuous plastic skin along the length thereof.
37. An extruded plastic foam product as claimed in claim 36 wherein said product includes at least one generally flat side.
38. An extruded plastic foam product as claimed in claim 36 or 37 wherein cell structure throughout the product is generally uniform.
39. An extruded foam product as claimed in claim 36 or 37 of a length in excess of fifteen feet.
40. An extruded plastic foam product as claimed in claim 36 or 37 wherein said product has a cross section partially defined by at least two straight sides.
41. An extruded plastic foam product as claimed in claim 36 or 37 wherein said product has a cross section at least substantially defined by generally straight sides.