METHOD FOR MAKING A LINEAL MEMBER

Abstract: A method for making a lineal member (14) having a porous core (10) comprises feeding a shaped elongated porous core (10) through a resin-encasing die (24) wherein resin is injected under pressure to encase the core (10), through a curing die (26) having a cross-sectional shape coinciding with and in contact with the resin-encased lineal member (14), with the curing die (26) imparting sufficient heat to the lineal member (14) to initiate cure of the resin, and through a curing chamber (32) which is maintained at a temperature sufficient to complete the cure of the resin without substantial contact with the lineal member (14).

Description: DESCRIPTION METHOD FOR MAKING A LINEAL MEMBER TECHNICAL FIELD This invention pertains to making building components, particularly structural members having relatively low thermal conductivity. BACKGROUND ART Recent advances in the manufacture of structural building components have greatly improved the resistance to thermal conductivity in order to conserve energy. This is particularly evident in the manufacture of lineal members for such uses as window frames and door frames. It is now well known that a composite fiberglass lineal structural member can be used to replace traditional construction materials such as wood and aluminum. These composite lineal members are comprised of a relatively porous core material, generally of glass fibers, and an outer coating of strong, aesthetically pleasing resinous casing material. These lineals can be produced through a pultrusion process in which a porous glass wool core is fed through a coating die which coats the glass wool core with a liquid resinous material. In an ordinary pultrusion process, reinforcement fibers are dipped into a liquid resinous bath and pulled through a die to produce the desired cross-sectional shape. The compressed fibers and resin are then passed through a curing die during which the temperature of the resin is raised to a temperature sufficient to initiate the cure of the resin. Pultrusion of lineal members having a porous glass wool core is different from traditional pultrusion processes. The glass wool core is not dipped into a liquid bath of resin because of the need to limit the resin to the outer edges of the glass wool core. Therefore, the glass wool core is pulled through a die in which resin is injected at a relatively low pressure in order to apply resin only in the outer portion of the glass wool core. After the core is coated, the coated lineal member is passed through a curing die which initiates curing of the resin. Typically, the resin is a polyester resin. One of the problems with the pultrusion of porous- cored structural lineal members is that the curing process is not completed in the curing die. If the curing die were long enough to complete the curing process, it would be of such length that the drag force would be prohibitively high, and the core material would break because of the limitations in its tensile strength. In the traditional pultrusion processes the pultruded material emerges from the curing die with the cure of the resin initiated, and the residual heat of the dense resin and glass composite material is sufficient to continue the curing process even after the pultruded material leaves the curing die. The curing process continues to its completion even in the ambient conditions of the plant facility. In the case of a porous core lineal material, however, the relatively dense resinous area of the lineal is merely in the periphery of the cross-sectional area, and there is not enough residual heat in the pultruded lineal member to continue the curing process to completion in the ambient conditions of the manufacturing facility. Therefore, a problem in the manufacture of porous core, resin coated lineal material is that the materials are not completely cured as they are manufactured. During the curing process, the resin material, which is typically a polyester material, produces styrene gas. The styrene is offgassed during the curing process. The problem with an undercured lineal member is that when it is heated up for subsequent process steps, the styrene will continue to offgas, thereby potentially affecting later processes. This is a particular problem when the lineal is painted, because the painting process includes heating the lineal in the paint curing oven. By heating the lineal member in the oven, styrene bubbles appear on the surface of a lineal member, and these bubbles create surface defects which render the lineal member unacceptable for such visual applications as a window frame for a residential dwelling. Accordingly, it would be desirable to develop a process in which pultruded porous core, resin coated lineal materials can be completely cured during the manufacturing process so that downstream process steps involving raising the temperature of the lineal member do not produce undesirable offgassing of styrene or other materials. DISCLOSURE OF INVENTION According to this invention there is provided a method for making a lineal member having a porous core comprising feeding a shaped, elongated porous core, through a resin-encasing die wherein resin is injected under pressure to encase the core, through a curing die having a cross-sectional shape coinciding with and in contact with the resin-encased lineal member, with the curing die imparting sufficient heat to the lineal member to initiate cure of the resin, and through a curing chamber which is maintained at a temperature sufficient to complete the cure of the resin without substantial contact with the lineal member. The present invention solves the problem of incomplete cure of the pultruded, porous core lineal member by providing a curing chamber which immediately follows the curing die and in which the lineal member is maintained at a temperature sufficient to complete the cure of the resin without substantial contact with the lineal member. The fact that there is no substantial contact with the lineal member means that the curing chamber does not apply significant additional drag force onto the lineal member, thereby subjecting the lineal member to breaking due to forces exceeding the tensile strength of the lineal member. In a specific embodiment of the invention, the porous core has density less than about 320 kg/m 3 (20 lbs./ft 3 ) . Preferably, the porous core has a density within the range of from about 96 kg/m 3 (6 lbs./ft 3 ) to about 192 kg/m 3 (12 lbs./ft 3 ) . In another specific embodiment of the invention, the encased lineal is subjected to an additional coating step, preferably a painting step, which includes heating the encased lineal to temperature of at least 60°C (140°F) after the encased lineal is coated. In another specific embodiment of the invention, the resin is injected under pressure lower than about 207 kPa (30 psi) to encase the core. In yet another embodiment of the invention, the curing chamber applies a drag force of less than about 2.27 kg (5 lbs.) on the lineal member. Preferably, the drag force applied by the curing chamber is less than about 0.91 kg (2 lbs.). The use of the curing chamber with a minimal amount of drag force enables the curing process to be completed before the lineal member cools to the ambient temperature in the manufacturing facility. BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a schematic elevational view showing the coating and curing apparatus used in carrying out the invention. FIG. 2 is a schematic cross-sectional view in elevation of the curing die, taken along line 2-2. FIG. 3 is a schematic cross-sectional view in elevation of the curing chamber taken along lines 3-3. FIG. 4 is a schematic elevational view of the lineal painting process. BEST MODE FOR CARRYING OUT THE INVENTION As shown in FIG. 1, porous core 10 is pulled through various coating and curing equipment by puller 12 to form lineal member 14. The puller can be any mechanical device, commonly known in the art, for pulling materials in a pultrusion process. The porous core is preferably of mineral fibers, and most preferably is comprised of glass wool containing a resinous binder of urea phenol formaldehyde. The porous core is preferably less than about 320 kg/m 3 (20 lbs./ft 3 ) , and more preferably has a density within the range of from about 96 kg/m 3 (6 lbs./ft 3 ) to about 192 kg/m 3 (12 lbs./ft 3 ) . Most preferably, the density of the glass wool porous core is approximately 160 kg/m 3 (10 lbs./ft 3 ) . Preferably the resin coating process is generally carried out as a two stage process. The primer resin coat is applied first to the outer periphery of the porous core. Resin impregnating die 16 connected with primer resin supply 18 can be used to apply a primer coat to the porous core. Primer curing oven 20 can be positioned next in line in order to cure the primer resin. The resin impregnated porous core is then passed through the coating apparatus which is comprised of coating resin supply 22 and resin encasing die 24. In this way, the porous core is first treated with a primer resin and then treated with an outer coating resin. It is to be understood that the invention could be used with a single resin application rather than a double resin application. Immediately following the resin encasing die is the curing die 26. The curing die, as shown in FIG. 2, has an inner surface with a cross-sectional shape coinciding with and in contact with the resin encased lineal member. Curing dies are well known in the art. Typically, they are heated with a heating means, such as electric heaters 30. In a typical use of the invention, the curing die imparts sufficient heat to the lineal member to initiate cure of the resin. Typically, the cure initiation temperature for a polyester resin is approximately 110°C (230 β F) . Since the curing die is in close contact with the lineal member passing through it, a significant amount of drag force is applied to the lineal member. As shown in FIG. 3, after the lineal member is passed through the curing die, it travels through curing chamber 32 which is maintained at a temperature substantially equal to or greater than the temperature of the resin at the exit end of the curing die. The heat applied to the lineal member in the curing chamber is primarily accomplished through hot air convection heat transfer. The hot air is supplied by any suitable heating means, such as heater 34, and driven by fan 36. It is to be understood that any other means for maintaining the temperature of the lineal member at a temperature sufficient to complete the cure can be used. The curing chamber must be long enough and hot enough to enable the resin to be either completely cured or sufficiently advanced in cure so that the cure will be completed in the ambient plant conditions shortly after the lineal member exits the curing chamber. In order to prevent additional drag force on the lineal member, the lineal member is supported in the curing chamber by a series of rollers, such as support rollers 38. It can be seen that the support rollers provide little, if any, substantial contact with the lineal member so that the drag force is not substantially increased. Any other suitable means for supporting the lineal member within the curing chamber can be used. It can be seen in FIG. 3 that the cross-sectional view of the lineal member shows that a substantial portion of the area is the porous core, and only a minor portion of the area is resin coating 40. Preferably, the porous portion of the cross-sectional area is at least 75% of the total cross-sectional area of the lineal member. Most preferably, the porous core portion of the lineal member is at least 85% of the total cross-sectional area of the lineal member. The density of the resin coating is in excess of 800 kg/m 3 (50 lbs./ft 3 ) . In a typical operation, the temperature of the resin will increase while the resin passes through the curing die from a entry temperature of about 93.3 β C (200 β F) to an exit temperature of about 154°C (310°F) . The temperature of the hot gases in the curing chamber is preferably maintained within the range of from about 148.9"C (300 β F) to about 162.78"C (325 β F). Porous-cored, resin-encased lineal members are often subjected to additional process steps which involve heating the lineal to temperatures as high as 60°C (140°F) and possibly as high as 82"C (180"F) or higher. As shown in FIG. 4, a subsequent process step for the lineal member is the painting process. The lineal member is fed through paint die 42 and subsequently passes through paint oven 44 to produce painted lineal 46. These processes are conventional in painting of glass fiber cored window lineals, for example. While in the paint oven, the lineal member will experience temperatures of approximately 93.3°C (200°F). If the lineal member passing through the paint oven has uncured polyester resin in the resin coating, then the resin may offgas styrene, thereby creating bubbles and other surface defects in the surface of the lineal. However, lineal members passing through a curing chamber according to the invention, will have completely cured resin, and will not be subject to offgasing of styrene during a subsequent step, such as a painting process. It will be evident from the foregoing that various modifications can be made to this invention. Such, however, are considered as being within the scope of the invention. INDUSTRIAL APPLICABILITY This invention will be found to be useful in the manufacture of lineal members suitable for such structural components as window frames and door frames.

Claims: CLAIMS 1. The method for making a lineal member having a porous core comprising feeding a shaped, elongated porous core: through a resin-encasing die wherein resin is injected under pressure lower than about 207 kPa (30 psi) to encase the core, the resin being of the type which releases gasses during curing, through a curing die having a cross-sectional shape coinciding with and in contact with the resin- encased lineal member, with the curing die imparting sufficient heat to the lineal member to initiate cure of the resin, and through a curing chamber which is maintained at a temperature sufficient to complete the cure of the resin without substantial contact with the lineal member. 2. The method of claim 1 in which the resin is a polyester resin and curing the resin results in offgasing of styrene from the lineal member. 3. The method of claim 1 in which the porous core has a density less than about 320 kg/m 3 (20 lbs./ft 3 ) . 4. The method of claim 3 in which the porous core has a density within the range of from about 96 kg/m 3 (6 lbs./ft 3 ) to about 192 kg/m 3 (12 lbs./ft 3 ) . 5. The method of claim 1 in which the ratio of the length of the curing chamber to the length of the curing die is within the range of from about 1.5:1 to about 8:1. 6. The method of claim 1 comprising subjecting the encased lineal to an additional coating step including heating the encased lineal to a temperature of at least 60°C (140"F) after the encased lineal is coated. 7. The method of claim 6 in which the additional coating step is a painting process which includes heating the encased lineal to a temperature of at least 60°C (140 β F) after the encased lineal is painted. 8. The method of claim 1 in which the drag force applied by the curing chamber on the lineal member is less than about 0.91 kg (2 lbs.).

Inventors: BEAVER TERRY R, BLINKHORN ARTHUR, SMITH GEORGE R, BEAVER, TERRY, R., BLINKHORN, ARTHUR, SMITH, GEORGE, R.
Applicants: OWENS CORNING FIBERGLASS CORP, OWENS-CORNING FIBERGLAS CORPORATION
Application year: 1993
Main classification: B29C67
IPC codes: B29C35, B29C43, B29C47, B29C70, E06B3