Abstract:
A vacuum molding process includes selecting a flexible polymer cover for covering a selected cement container and at least partially filling the container with a cement mixture. The polymer cover is removably attached to the partially filled cement container and a vacuum is applied to the cement mixture in the container. The process may also include connecting a vibrator to the container for simultaneously vibrating the container and the placing of a hollow mold core member having a plurality of apertures therein in the middle of the container for the gas bubbles to escape as a result of the vibration of the cement mixture in a vacuum.

Description:
This is a division of patent application Ser. No. 08/723,183, filed Sep. 27, 1996 now U.S. Pat. No. 5,932,256. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a vacuum molding process and apparatus which utilizes a flexible molding cover or bag to place a vacuum onto a container filled with an uncured cement mixture. 
     In the past, it has been common to mold various types of products out of a cement or concrete which includes the making of a mixture of a predetermined Portland cement which may include the addition of gravel or lightweight components, such as polymer beads or the like. The mixture is typically cured by mixing a predetermined amount of water with the cement mixture and mixed in a mixer which may be a cement truck with a rotating mixer. Typically in a molding operation, the cement is mixed at the location of the molding operation and the mixed cement is placed in the mold and cured to form a predetermined molded product. The product can include sculptures, containers, balustrades, or other building components and can be molded with standard cement or concrete mixture or lightweight concrete having lightweight particles incorporated into the cement to reduce the weight of the molded product. 
     It has been suggested in the past to vibrate the mold once the cement or other molding material has been placed therein to get entrained air or other gases out of the cement material to remove air pockets and bubbles from the molded product. This is commonly done by placing the filled mold with the uncured mixed cement onto a vibrating table in which the vibration causing the bubbles to rise in the cement to suggested to attach a vibrator clamp to a mold and a vibrator to the clamp to vibrate the mold during the molding operation to remove gases and to compact the molded mixture. A centrifugal molding or casting machines have been used which result in the rapid rotation of the mold loaded with a molding material. Another method of removing bubbles is to place the mold on a vacuum chamber or the like and place a vacuum on the area around the mold for withdrawing bubbles from the mold. 
     In contrast to these prior art systems, the present invention uses an ordinary flexible plastic film which may be reinforced with crinkling or with fibers and in which a vacuum pump is connected thereto through a vacuum hose. The plastic sheet material can be rigid or flexible transparent or opaque and formed in such a fashion that would be concave and conform with the flow of vacuum. The plastic film is easily clamped over conventional containers, such as a wheelbarrow or mixing container, with a sealing clamp and may also include a vacuum bag for placing over a mold. The mold can be placed on a vibrating table or having a vibrating clamp attached thereto with a vibrator for vibrating the mold in a partial vacuum for the removal of gas bubbles from the molded material. 
     One prior art U.S. patent can be seen in the Lee U.S. Pat. No. 4,990,082, for a vibrator with suction apparatus which illustrates a vibrator for architectural or civil engineering and uses a reciprocating or rotating vibrator along with a suction system which is integrally formed with the vibrating means and has at least one suction member to be attached to the forming mold. The suction system is such to enable an airtight connection between the vibrator and the forming molds and is substantially in the shape of a disc with an air passage formed therein to operate with an air pump to produce a low pressure area in the disc body. The Gayso U.S. Pat. No. 4,796,686, is a centrifugal casting machine with venturi actuated vacuum venting. A centrifugal force casting machine develops a vacuum as it travels through the air on the spinning arms of a casting machine in order to evacuate unwanted gases from the casting mold. The Abbott U.S. Pat. No. 3,323,188, is an apparatus for molding and compacting hollow concrete products including a pulsating water vibrator. The Emmons U.S. Pat. No. 2,610,040, is an operating mechanism for a vibrating table used in molding a product. The Dubbs et al. U.S. Pat. No. 2,603,850, is a method and apparatus for molding concrete products. The Lake U.S. Pat. No. 2,386,961, is another apparatus for molding tubular concrete products which utilizes both pressure and a vacuum in connection with the molding of the product. 
     The present application includes a suction apparatus which uses a flexible plastic film which may be in the form of a plastic bag or a plastic cover which can be placed over conventional or non-conventional containers, such as placing the mold in a plastic bag and sealing the opening to the bag. A plastic film, such as sold by Film Technology, Inc. under U.S. Pat. No. 5,129,813, can be used in the present invention. A vacuum is then placed in the area under the cover to place a vacuum on the uncured cement mixture in the container or mold which consists in the removal of bubbles and may also include a means for simultaneously vibrating the mold or cement mixture. The system can be made to fit a wide variety of different molds as well as molding operations and unusual containers. 
     SUMMARY OF THE INVENTION 
     A system for placing a vacuum on a container for a cement or molding mixture includes a container for holding the cement which has an opening for adding or removing cement. A flexible polymer film cover is sized to cover at least the open portion of the container and has a vacuum hose coupling attached thereto which connects to a vacuum hose connected to a vacuum pump for drawing a vacuum between the cover and the container. Attaching means, such as a clamping bracket, are provided for removably attaching the flexible polymer cover to the container. A vapor trap is attached in the vacuum line for capturing vapor removed by the vacuum applied to the container. A mold may have a hollow mold core member placed in the center of the mold which has a plurality of apertures therein and which has the uncured cement placed therearound for producing the vacuum in the center of the molded part during the curing of the concrete. The mold may have a vibrator clamp and a vibrator attached thereto for simultaneously vibrating the mold while producing a vacuum to remove gas bubbles from the cement. A method may include selecting a flexible polymer cover for covering a selected cement container and having a vacuum hose coupled thereto and at least partially filling a container with a cement mixture and removably attaching the polymer cover to the partially filled cement container and placing a vacuum on the cement mixture. The process can also include connecting a vibrator to the mold container for simultaneously vibrating the mold and the placing of a hollow mold core member having a plurality of apertures therein in the middle of the mold for the gas bubbles to escape from the vibration and vacuum. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects, features, and advantages of the present invention will be apparent from the written description and the drawings in which: 
     FIG. 1 is a side elevation of a molding apparatus in accordance with the present invention; 
     FIG. 2 is an exploded view of a second embodiment of a molding apparatus of FIG. 1; 
     FIG. 3 is a perspective view of a third embodiment of the apparatus of FIG. 1; 
     FIG. 4 is an exploded view of a vacuum apparatus for a cement mixing drum; 
     FIG. 5 is an exploded view of another vacuum apparatus for FIG. 4; 
     FIG. 6 is an exploded perspective of a vacuum apparatus for a cement hopper; and 
     FIG. 7 is an exploded perspective of a vacuum apparatus for a wheel barrow. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to the drawings and especially to FIG. 1, a vacuum molding apparatus  10  has a mold  11  therein for molding a cement or concrete product, such as a balustrade  12 , therein. The molding apparatus includes a flexible polymer film or a plastic bag  13  for covering the mold  11  and which has an opening  14  so that the mold  11  can be placed inside the bag and then the bag sealed with a tie  15 . The flexible polymer bag  13  is made of a heavy plastic which may be reinforced with reinforcing fibers, or alternatively, may be crinkled to give additional stiffness and strength to the flexible polymer film. The polymer bag  13  has a vacuum hose coupling  16  attached therethrough for attaching a vacuum hose  17  from outside the bag  13  coupled to the inside of the bag  18 . The coupling  16  can be a quick connect type coupling so that the hose  17  can be connected and disconnected rapidly. The vacuum hose  17  has a vapor trap  20  therein for capturing any water or other liquid vapor being drawn from the inside of the bag  18  by the placement of a vacuum on the interior of the bag  13 . A vacuum pump  21  draws a vacuum on the hose  17  to place a predetermined vacuum within the bag  13 . The bag  13  has a mold  11  for molding a cement or concrete type product which may be a mixture of Portland cement mixed with an aggregate material and water to form a concrete baluster  12  or can be filled with a mixture of Portland cement and a lightweight aggregate, such as foamed polymer beads or the like. Additional additives and water are mixed and the mixture poured in the mold  12  where the mixture is cured. In the mold  12 , a hollow central or core tube  22  is placed in the middle of the mold  12  and has a plurality of apertures  23  therein. The core  23  can be made of a metal or polymer material and can be left in the molded product. When a vacuum is placed on the interior of the bag  13 , the vacuum also draws gases that may be escaping from the curing mixture during the curing process. By having the open core  22  with the apertures  23 , the vacuum extends into the center of the curing concrete and assists the escape of bubbles captured in the concrete mix over the entire length of the molded product  12 . The vibrator clamp  24  is attached to the mold  11  and allows a vibrator mechanism to be attached thereto and may extend through an opening in the bag  13  or, alternatively, the vibrator can be clamped onto the vibrator clamp  24  around the plastic bag  13  for vibrating the mold  11 . The vibration of the mold  11  encourages the escape of trapped gas bubbles, which are mostly air from the curing cement mixture, within the mold  11  while placing a vacuum within the bag  13  evacuates the air from tube  22  mounted in the middle of the mold. This substantially increases the escape of trapped air and gases from the cement mixture to enhance the strength of the final molded product, such as the baluster  12 . The use of a flexible plastic covering for enclosing the mold  12  and having a vacuum hose connector  16  therethrough results in the collapsing of the flexible bag  13  onto the mold but does not prevent the vacuum being placed on the curing cement and removes only limited amounts of water and other vapor as the gas escapes from the curing cement. Vapors are trapped in the vapor trap  20 . 
     Turning to FIG. 2, an alternative embodiment utilizes a vibrating table  25  having legs  26  supporting a vibrator table portion  27  under a plurality of springs  28 . The vibrating mechanism vibrates the tabletop portion, which has a plurality of mold pans  30  thereontop. A flexible reinforced polymer cover  31  may have reinforcing fibers therein or be of a wrinkled plastic surface to reduce clinging of the cover once the vacuum is placed on the covered area. The plastic film  31  has a table clamping flange  32  which clamps onto the edges of the plastic film  31  and onto the vibrating table edge  33  to seal the plastic film  31  over the molding vibrating table  25 . The plastic film  31  has a quick connect vacuum hose coupling  34  therethrough connected to a vacuum hose  35  which in turn is connected through a vapor trap  36  and to a vacuum pump  37 . Once an airtight seal is made with the film  31  over the vibrator table  25  tabletop with the raised edges  33 , a vacuum is placed on the area under the plastic film cover  31  and on the tabletop  27  with the pan molds  30  therein. Simultaneously, the vibrator table  25  can be actuated to vibrate the products being molded of a cementuous or other molding material. A vacuum is placed between the cover  31  and table  27  and assists in the removal of air from the molding mixture within the molding pans  30  to enhance the strength of the molded product. 
     FIG. 3 is another embodiment that illustrates a tilt-up wall form  40  for molding a wall section and having flanges  41  therearound with clamp-on vibrators  42  clamped onto the flanges  41 . The flexible polymer cover film  43  is wrapped entirely around the tilt-up wall form  40  where its bonding edge  44  can be used to give a vacuum seal to the folded sheet edge  45  or to the flanges  41  of the container  40 . A quick connect vacuum hose coupling  46  through the polymer material  43  connects a vacuum hose  47  and has a vapor trap  48  along with a vacuum pump  49 . The tilt-up wall form  40  is vibrated with the vibrators  42  while simultaneously placing a vacuum thereon for the removal of air bubbles trapped within the cement mixture forming the wall in the wall form  40 . 
     FIGS. 4-8 illustrate a vacuum system for placing a vacuum onto a container of an uncured cement mixture. In FIG. 4, a mixer drum has an opening  51  thereinto and a flange  52  around the opening  51 . A wrinkled or reinforced flexible polymer or plastic film cover  53  is shaped to cover the opening  51  over the flanges  52 . A clamping ring  54  clamps to the flange  52  over the edges of the flexible plastic cover  53 . A quick connect coupling  55  connects a vacuum hose  56 . The vacuum hose  56  has a vapor trap  57  therein and is connected to the vacuum pump  58 . The mixer drum  50  can have the flexible polymer cover  53  attached to the cover after it is loaded with a cement mixture, such as the mixing of Portland cement, water, aggregate, or lightweight aggregate. The clamp  54  clamps over the flange  52  and onto a sealing O-ring  59 . The O-ring  59  can of course be replaced with a double side sealing tape. The mixer drum  50  can be rolled back and forth for mixing the cement therein while placing a vacuum in the container  50  for the removal of gas bubbles trapped within the cement mixture. 
     FIG. 5 is a similar cement mixing apparatus which has a mixer  60  having an arcuate base and an open top  61  having a flange  62  with a sealing O-ring or the like  63  round the flange  62 . The wrinkled plastic film  64  is cut to the shape of the perimeter flange  62  for fitting thereon and a clamping fixture  65  clamps the cover film  64  over the mixer  60  once the mixer container  60  has been loaded with a cement mixture. The plastic film  64  has a quick connect coupling  66  therethrough connecting a vacuum hose  67  through a vapor trap  68  to a vacuum pump  69 . Once the container  60  is loaded with the desired cement or molding mixture and the plastic film  64  is clamped over the opening  61 , the vacuum is placed on the container  60 , which may be rocked back and forth for mixing the cement. 
     Turning to FIG. 6, a cement hopper  70  has a surrounding flange  71  having a sealing O-ring  72  therearound. A crinkled or reinforced plastic film  73  is shaped to fit onto the flange  71  to cover the opening  74  and a quick connect coupling  75  connects through the flexible plastic cover  73  to a vacuum mold  76  and through a vapor trap  77  to a vacuum pump  78 . A clamping fixture  79  clamps the film  73  onto the flange  71  to give an airtight seal over the cement hopper  70  to assist in removing gases from the cement mixture while in the hopper  70 . The hopper has an opening  80  which allows the removal of the cement mixture within the cement hopper  70 . 
     FIG. 7 shows an additional embodiment where a wheelbarrow  81  has a wheel  82  and handles  83  along with the container portion  84  having a flange  85  therearound. Flange  85  has been fitted with an O-ring or other sealing material  86  and a flexible plastic cover  87  has been shaped to fit over the wheelbarrow flange  85 . A clamping fixture  88  is shaped to fit on top of the flange  81  and onto the perimeter of the polymer cover  87  to seal the cover  87  over the wheelbarrow container  84 . A quick connect vacuum hose  90  connects a vacuum hose  91  through a vapor trap  92  to a vacuum pump  93 . Thus, a cement mixture can be loaded onto the wheelbarrow  81  and the flexible plastic  87  clamped thereover to give an airtight seal and a partial vacuum placed within the sealed container  84 . The wheelbarrow  81  can then be rocked or vibrated to assist in the removal of trapped gas particles within the mixture in the container  84 . 
     It should be clear at this time that a molding apparatus and process has been provided which allows the placement of an inexpensive vapor seal covering a mold to allow a vacuum to be placed on a cementuous or other molded material being curing while simultaneously allowing the mold to be vibrated. It should also be clear that a flexible polymer cover can be designed for easy placement over various types of cement or mixing materials to enhance the removal of gases, such as air, from the materials during the mixing and curing of the materials. However, the present invention is not to be considered as limited to the forms shown which are to be considered illustrative rather than restrictive.