MXPA00010260A - Sheet molding compound manufacturing improvements - Google Patents

Abstract

The present invention provides an apparatus (10) for manufacturing sheet molding compound comprising a fiber processing unit (12) for forming a fiber web. The apparatus also includes a precompaction unit (34) for squeezing air out of the fiber web and a resin mixture paste dispenser (36) for applying paste to the fiber web. The apparatus functions to minimize entrapped air from the resin mixture paste and fiber web.

Description

IMPROVEMENTS FOR THE MANUFACTURE OF LAMINAR MOLDING COMPOUNDS BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates in general to an apparatus and method for manufacturing laminar molding compound, and more particularly to an apparatus for manufacturing laminar molding compound while minimizing trapped air therein. . 2. Discussion of Related Art Compression molding is a technique for forming parts when a load is placed between heated upper and lower die members, which define a mold cavity. The dies are then brought to a closed position where the dies compress the load causing it to flow and fill the mold cavity. After the resin sets, the molds open and the finished part is removed. Compression molding techniques have been employed to produce parts having a relatively flat surface such as exterior automotive body panels. The charges used to produce these parts or pieces, generally consist of a thermophysical ream containing reinforcing fibers and various fillers or fillers. Quite often, fillers are formed in sheets known in the art as compounds lamellar molding (SMC = Sheet Mold g Compounds). The U.S. Patent No. 4,894,292 discloses a method for producing a lamellar molding compound. Briefly, a continuous weft process is employed, wherein a resin is applied by a resin feed tank onto a carrier sheet and in a subsequent processing station, the fibers are distributed over the ream. The sheet is then fed through rollers and curing stages to stage "B" of the compound. The processing steps are carried out under ambient conditions, U.S. Pat. No. 4,288,475, describes the use of a vacuum chamber during a method for impregnating a fibrous web. This reference however is not related to producing or manufacturing the laminar molding compound and simply uses the vacuum to direct the binder material to the weft to impregnate it. It has been difficult to mold pieces of plastic reinforced by fiberglass (FRP = Fiber Glass Remforced Plástic) in such a way that they have an extremely smooth surface. The molded parts sometimes have surfaces that present blisters, are rough or porous that require post-molding processing to smooth the imperfections. It is commonly believed that these imperfections result primarily from air being trapped in the charge during molding. In an effort to To minimize trapped air, one practice is to use a relatively thick load that covers a relatively small area of the molding surface, so that the air in the load is "ejected" when the dies are closed. It has also been recognized that the use of vacuum during the compression molding process is useful to reduce the number of imperfections in the surface of the piece. See, for example, US Patents. Nos. 4,488,862, 4,612,149; 4,551,085; and 5,130,071, which are incorporated herein by reference. These prior patents illustrate the application of a vacuum to the loading of lamellar molding compounds during the compression molding process. Air is also trapped, however, within the reinforcing fibers themselves, while the fibers are mixed with the ream mixture paste during the manufacture of the lamellar molding compound charge. This trapped air can lead to voids, small depressions or micro cavities in the surface of a molded part, requiring additional labor intensive procedures in order to produce a part with an acceptable surface in this way increasing manufacturing costs. Thus, there is a need in the art for providing an improved method and apparatus for removing or Minimizing the trapped air of the resin mixture paste and fiber reinforcement material while the sheet molding compound is formed in order to further reduce the occurrence of surface imperfections in molded articles. COMPENDIUM OF THE INVENTION The present invention provides an apparatus for manufacturing a laminar molding compound, which comprises a fiber processing unit for forming a fiber web. The apparatus also includes a precompaction unit for ejecting by compressing the air from the fiber web and a resin mix slurry jet to apply the pulp to the fiber web. The apparatus works to minimize trapped air from the resin mixture paste and the fiber web. The preferred embodiment of the present invention also provides an apparatus for manufacturing sheet or sheet molding compounds, comprising a water bath of fiber mixture, a conveyor belt receiving the fiber mixture and a soluble binder ream dispensing unit. The apparatus includes a dryer unit and at least two plastic film rollers that release a layer of plastic film on the conveyor belt, wherein the fiber mixture is sandwiched between a first and second plastic layers, to form a web of fibers in plastic layers. The apparatus also includes compression rollers for compressive ejection of the air from the fiber web and a vacuum chamber with a jet mix paste spout and a first mechanism separating the first plastic layer from the second plastic layer. The paste is applied to the fiber web when the plastic layers are separated. Then, the first layer is returned to cover the mixture of pulp and fiber web by a second mechanism. The apparatus further has an outlet unit, wherein the laminar molding compound is rolled or scalloped in a ca. The present invention is further directed to a method for manufacturing laminar molding compound, comprising in the preferred embodiment, the steps of forming a fiber web, compressing the web of fibers between at least two layers of plastic film on a first mechanism of movement and compressively expelling air from the fiber web by moving the web in this pre-compacted manner prior to the addition of a resin blend paste. A first plastic layer is then separated on a second moving mechanism from the fiber web within a vacuum chamber. The present method also includes applying the ream mixture paste on the weft of fibers inside the vacuum chamber and return the first layer of plastic to the fiber web. The compound subsequently leaves the vacuum chamber with the first movement mechanism. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a front perspective view of the preferred embodiment of the lamellar molding compound manufacturing apparatus of the present invention; and Figure 2 is a side perspective view of the apparatus of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT OR METHODS With reference to Figures 1 and 2, a preferred embodiment of an apparatus for manufacturing hobby molding compound is generally illustrated and indicated by the numeral 10. The apparatus of the present invention functions to remove or minimize trapped air from a fiber web, by pre-compacting the web and furthermore it can remove air from both the fiber web and the slurry paste, when manufacturing the sheet molding compound with vacuum reinforcement fibers . Generally speaking, the apparatus 10 comprises a fiber processing unit 12 for forming a fiber web including a fiber mix water bath 1, a movement mechanism or wire mesh conveyor 16, and a fiber dispenser unit. resin soluble binder 18. Water bath 14 also preferably includes a volume adjustable weir 26 to regulate the amount of fiber mixture that is dispensed, as illustrated in Figures 1 and 2. The processing unit may also include a unit dryer 20. The fiber mixture employed in the present invention can be formed into a continuous, wet laid web by suspending the fibers first in a water bath to form a mixture, directing the fiber mixture to the conveyor belt 16, adding a binder of the soluble binder ream-dispensing unit 18 and removing the water and drying the fiber mixture in the dryer unit 20. The conveyor belt 16 is preferably made of wire mesh to allow the bath water to fall through the mesh to a water drain; A web of fibers is formed as the binder dries, causing the fibers to bond together. The fiber web can alternatively be formed from shredded wick or fiber particles. The fiber web preferably comprises glass fibers, but may also be, although not limited to cellulose, cotton and carbon fibers. The fiber web can be made of any composition of material that can be formed into a web. In the preferred embodiment, the apparatus of the present invention also comprises at least two rolls of plastic film or polyho to 22 and 24, respectively. The plastic film is preferably polyethylene, nylon or a mixture thereof, but it can also be any standard plastic film used in the process of manufacturing the lamellar molding compound. Each of the film rolls 22 and 24 releases a layer of plastic film on the conveyor belt 16, which also transports the fiber web from the fiber processing unit, as illustrated in Figures 1 and 2. According to FIG. the conveyor belt continues on the length of the apparatus, the fiber web is sandwiched between a first plastic layer 28 and a second plastic film 30 from the rollers 22 and 24, forming a web of fibers in plastic layers. The apparatus of the present invention may also include a vacuum chamber 32, which encircles a portion of conveyor belt 16 in order to remove or minimize any air trapped from the ream mixture slurry and fiber web. The vacuum chamber 32 houses a ream mixture paste spout 36 and a separation mechanism 38, preferably a second conveyor belt that operates to separate the first plastic layer 28 from the second plastic layer 30. The fiber web in layers of plasticPreference enters the vacuum chamber 32 through a pre-compacting unit, such as compression rollers 34 as illustrated in Figure 1. The compression rollers quickly and efficiently compress air out of the glass fibers in layers in plastic, before the addition of the ream mixture paste. In some applications, the pre-compaction of the fiber web with tightening rollers 34 before the addition of the resin mixture paste, may be sufficient to remove air from the web, and therefore the molding apparatus will not require a vacuum chamber. With reference to Figure 1, the first layer of plastic and roof is removed from the web of fibers in plastic layers, as it travels over the second conveyor belt 38. A sheet or liquid strip of resin mixture paste, then applied to the fiber web as illustrated in Figure 1. The paste nozzle is preferably located within the area or envelope created by separating the first plastic layer on the second conveyor belt from the fiber web. The paste dispenser 36 is also preferably subjected to variable pressure and a vacuum of about 68 to 98 kPa (about 20 to about 29"Hg) is preferably kept in the vacuum chamber.The first plastic layer 28 is then go back to the fiber web by a mechanism for returning the web, more preferably by a second conveyor web 38. In one embodiment, a thermal seal device commonly known in the art such as a rotary strip heat sealer can also be located within the vacuum chamber. The thermal sealant functions to seal the edges of the first and second plastic layers together after the first layer is returned to the fiber web. The web of fibers with plastic layers can then be transported through kneading rolls 40, in order to mix the fiber web in the dough, forming a laminar molding compound. In this way, the apparatus of the present invention functions to minimize entrapped air in both the ream mixture and the fiber chamber while it is under vacuum. Kneading rolls 40 can alternatively be located outside the vacuum chamber and therefore the web of fibers and pulp are mixed together outside the chamber. The apparatus of the present invention further includes an output unit 42 wherein the sheet molding compound with reinforcing fibers is transported, for example through a second set of compression rollers 44 and then laminated to a core or scalloped in a box for additional manufacturing.

By reference to Figure 1, the present apparatus may also include an area densitometer 46, which provides a detection reading of the fiber plot in plastic layer by a light source before the layer enters the vacuum chamber. The sheet molding compound also preferably maintains a constant area weight when it leaves the vacuum chamber 32. The invention has been described in detail with reference to preferred embodiments thereof. It should be understood, however, that variations and modifications may be made within the spirit and scope of the invention. For example, it is envisioned that the roll of polyester film 22 can be located within the vacuum chamber, wherein the fiber web enters the vacuum chamber without first applying plastic roofing layer to the fiber web. A liquid belt or ribbon of the ream mixture paste can then be applied to the fiber web and subsequently, the plastic layer 28 is applied to the top of the fiber web. The web of fibers in plastic layers is then transported through the kneading rolls 40, in order to mix the fiber web in the dough forming a laminar molding compound before leaving the chamber. Still additional alternatives will be apparent to a person with skill in the specialty, after have the benefit of studying the above specification and the following claims.

Claims (3)

1. CLAIMS 1. An apparatus for manufacturing a laminar molding compound that includes a fiber processing unit, for forming a fiber web, means for sandwiching the web between at least two layers, and a vacuum chamber unit having a dispenser of ream mixture pulp, to apply pulp to the fiber web and a mechanism for separating a first layer from the fiber web, such that pulp can be applied to the web within the vacuum chamber unit.
2. 2. The apparatus according to claim 1, characterized in that the pre-compaction unit effects a reduction of approximately 50 to 70% in the thickness of the fiber web.
3. 3. The apparatus according to claim 1, characterized in that it also comprises a binder-based assortment unit, a drying unit and an output unit. 4 - The apparatus according to claim 1 or 3, characterized in that the pasta dispenser is located within a casing created by the separation of the first layer from the fiber web by the mechanism. 5. The apparatus according to claim 4, characterized in that it also comprises a second mechanism for returning the first layer to the fiber web before the fiber web leaves the vacuum chamber. 6. - The apparatus according to claim 1, 3, 4 or 5, characterized in that the vacuum chamber further comprises tapered rollers. 7. The apparatus according to claim 1, 3, 4, 5 or 6, characterized in that the vacuum chamber further includes a thermal sealing device for sealing the first layer to a second layer. 8. - The apparatus according to claim 1, 3, 4, 5, 6 or 7, characterized in that the apparatus further includes a pre-compaction unit having compression rollers for compressively expelling air from the fiber web. 9. The apparatus according to claim 1, characterized in that the plastic film is selected from the group consisting of polyethylene, nylon and their mixtures 10.- Method for manufacturing a laminar molding compound, which includes the steps of forming a fiber web and applying a resin paste on the fiber web, characterized by the steps of: (a) sandwiching the fiber web between at least two plastic films on a first moving conveyor; (b) separate a first plastic layer of the fiber web within a vacuum chamber; (c) applying the paste of beef mixture to the fiber web within the vacuum chamber; (d) returning the first plastic film to the fiber web within the vacuum chamber; and (e) further transporting the web in such a way that it leaves the vacuum chamber. 11.- Method of compliance with the claim 10, characterized in that it also comprises the step of compressively expelling air in the fiber web when moving the web, between two compression rollers on the first movement conveyor where the fiber web is pre-compacted before the addition of a web. Ream mix paste. 12. - Method of compliance with the claim 11, characterized in that the fiber web is pre-compacted to effect an approximate reduction of 50 to 70% in the thickness of the fiber web. 13. Method according to claim 10, 11 or 12, characterized in that it further comprises the step of kneading the pulp and fibers to mix the fiber web and the pulp. 1 . - Method of compliance with the claim 10, 11, 12 or 13, characterized in that it also comprises the step of heat-sealing the first and second layers of plastic in conjunction with the vacuum chamber before leaving the chamber. 15. Method according to claim 8, characterized in that the pre-compaction unit is in an inlet to the vacuum chamber unit. 16. Method according to claim 11, 12, 13 or 14, characterized in that the compression rollers are in an inlet to the vacuum chamber. 17. Method according to claim 11, 12, 13, 14 or 16, characterized in that step (e) further comprises the step of passing the webs through a second pair of compression rollers at the outlet of the vacuum chamber. 18. The apparatus according to claim 1, characterized in that it also comprises at least two rolls of plastic film, which release a layer of plastic film where the fiber web is sandwiched between a first and a second layer of plastic to form a layer of layered fibers.