Mold assembly for making an expanded polystyrene article

Abstract

A mold assembly and method for molding a substantially hemispherical construct from pre-expanded polystyrene beads. The mold assembly includes a female half mold; a mating male half mold; a first male mold insert mountable on the male half mold and having a continuous, peripheral, beveled edge; and a second male mold insert mountable on the first male mold insert. For forming a construct having an impact-resistant exterior layer and an energy-absorbing interior layer, such as a motorcyclist safety helmet, the beads are initially molded under heat and compression between the female half mold and the first insert to form a first intermediate product of a first volume having a continuous, peripheral, beveled edge; said product is thereafter molded under heat and compression between the female half mold and the second insert to a second, reduced volume to form a compressed, second intermediate product, the beveled edge of the first intermediate product serving to uniformly distribute the force applied thereto. The second intermediate product is then remolded to the same volume to improve volume stability, and thereafter backfilled between the male half mold and the female half mold with additional pre-expanded polystyrene beads to form an energy-absorbing inner layer.

I claim:  
     
         1 . A process for molding an expanded polystyrene bead construct within a mold assembly, said mold assembly including a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct, a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis, a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold, and a second male mold insert mountable on the first male mold insert, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold, the process comprising: 
 (a) filling the female half mold with pre-expanded polystyrene beads of a predetermined density;    (b) mounting the first male mold insert on the male half mold;    (c) molding the beads under applied heat and pressure by forcing the first male mold insert against the beads to fuse the beads together to form a first intermediate product of a first volume having a continuous, beveled edge surface formed between the beveled edge surface of the first male mold insert and the peripheral edge surface of the female half mold;    (d) rapidly cooling the fused first intermediate product to within a subplasticizing temperature range to cause lower than atmospheric pressure within the beads of the first intermediate product;    (e) mounting the second male mold insert on the first male mold insert; and    (f) compressing the cooled first intermediate product between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads.    
     
     
         2 . A process for molding an expanded polystyrene bead construct within a mold assembly, said mold assembly including a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct, a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis, a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold, and a second male mold insert mountable on the first male mold insert, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold, the process comprising: 
 (a) filling the female half mold with pre-expanded polystyrene beads of a predetermined density;    (b) mounting the first male mold insert on the male half mold;    (c) molding the beads under applied heat and pressure by forcing the first male mold insert against the beads to fuse the beads together to form a first intermediate product of a first volume having a continuous, beveled edge surface formed between the beveled edge surface of the first male mold insert and the peripheral surface of the female half mold;    (d) rapidly cooling the fused first intermediate product to within a subplasticizing temperature range to cause lower than atmospheric conditions within the beads of the first intermediate product;    (e) mounting the second male mold insert on the first male mold insert;    (f) compressing the cooled first intermediate product between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads; and    (g) remolding the cooled intermediate product under heat and compression between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads.    
     
     
         3 . A process for molding a layered, expanded polystyrene bead construct within a mold assembly, said mold assembly including a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct, a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis, the male half mold having an exterior surface configured to impart a desired interior surface to the construct, a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold, and a second male mold insert mountable on the male half mold, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold, the process comprising: 
 (a) filling the female half mold with pre-expanded polystyrene beads of a predetermined density;  
 (b) mounting the first male mold insert on the male half mold;  
 (c) molding the beads under applied heat and pressure by forcing the first male mold insert against the beads to fuse the beads together to form a first intermediate product of a first volume having a continuous, beveled edge surface formed between the beveled edge surface of the first male mold insert and the peripheral surface of the female half mold;  
 (d) rapidly cooling the fused first intermediate product to within a subplastizigin temperature range to cause lower than atmospheric conditions within the beads of the first intermediate product;  
 (e) mounting the second male mold insert on the first male mold insert;  
 (f) compressing the cooled first intermediate product between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads;  
 (g) removing the second male mold insert and the first male mold insert from the male half mold; and  
 (h) adding pre-expanded polystyrene beads to the mold assembly and remolding the added beads between the female half mold and the male half mold under heat and compression to cause fusion of the added beads at an interface to the expanded bead body to form a layered construct comprising at least two layers of beads wherein the layers have different densities.  
 
     
     
         4 . A process for molding a layered expanded polystyrene bead construct within a mold assembly, said mold assembly including a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct, a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis, the male half mold having an exterior surface configured to impart a desired interior surface to the construct, a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold, and a second male mold insert mountable on the male half mold, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold, the process comprising: 
 (a) filling the female half mold with pre-expanded polystyrene beads of a predetermined density;    (b) mounting the first male mold insert on the male half mold;    (c) molding the beads under applied heat and pressure by forcing the first male mold insert against the beads to fuse the beads together to form a first intermediate product of a first volume having a continuous, beveled edge surface formed between the beveled edge surface of the first male mold insert and the peripheral surface of the female half mold;    (d) rapidly cooling the fused first intermediate product to within a subplasticizing temperature range to cause lower than atmospheric conditions within the beads of the first intermediate product;    (e) mounting the second male mold insert on the first male mold insert;    (f) compressing the cooled first intermediate product between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads;    (g) remolding the cooled intermediate product under heat and compression between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads;    (h) removing the second male mold insert from the first male mold insert; and    (i) adding pre-expanded polystyrene beads to the mold assembly and remolding the added beads between the female half mold and the male half mold under heat and compression to cause fusion of the added beads at an interface to the expanded bead body to form a layered construct comprising at least two layers of beads wherein the layers have different densities.    
     
     
         5 . The process of  claim 1 ,  2 ,  3 , or  4 , wherein the beveled edge surface of the first male mold insert is deviated at least 45 degrees, but not more than 60 degrees, from a mold parting line normal to the alignment axis.  
     
     
         6 . A mold assembly for molding an expanded polystyrene bead construct, comprising: 
 (a) a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct;    (b) a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis;    (c) a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold; and    (d) a second male mold insert mountable on the first male mold insert, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold.    
     
     
         7 . The mold assembly of  claim 5 , wherein the first male mold insert has a plurality of upstanding alignment pins and the female half mold has a plurality of first apertures in mating alignment with said pins, whereby said first apertures receive said pins when the first male mold insert is mounted on the male half mold and is inserted into the female half mold.  
     
     
         8 . The mold assembly of  claim 6 , wherein the second male mold insert has a plurality of second apertures in mating alignment with said pins, whereby said second apertures receive said pins when the second male mold insert is mounted on the first male mold insert.  
     
     
         9 . The mold assembly of  claim 7 , wherein an exterior surface of the male half mold is configured to impart a desired interior surface to a construct molded within said mold assembly.  
     
     
         10 . A layered volume-stable expanded polystyrene bead construct, the construct produced by a molding process within a mold assembly, said mold assembly including a female half mold having a first, continuous, peripheral edge surface and an interior surface configured to impart a desired exterior surface to the construct, a male half mold having a second, peripheral edge surface in mating alignment with the first peripheral edge surface when the female half mold and the male half mold are aligned on an alignment axis, the male half mold having an exterior surface configured to impart a desired interior surface to the construct, a first male mold insert mountable on the male half mold and having a third, beveled, continuous peripheral edge surface, the female half mold and the first male mold defining a first volume therebetween when the first male mold is inserted into the female half mold, and a second male mold insert mountable on the male half mold, the female half mold and the second male mold insert defining a second, reduced volume therebetween when the second male mold insert is inserted into the female half mold, and said process comprising: 
 (a) filling the female half mold with pre-expanded polystyrene beads of a predetermined density;    (b) mounting the first male mold insert on the male half mold;    (c) molding the beads under applied heat and pressure by forcing the first male mold insert against the beads to fuse the beads together to form a first intermediate product of a first volume having a continuous, beveled edge surface formed between the beveled edge surface of the first male mold insert and the peripheral surface of the female half mold;    (d) rapidly cooling the fused first intermediate product to within a subplasticizing temperature range to cause lower than atmospheric conditions within the beads of the first intermediate product;    (e) mounting the second male mold insert on the first male mold insert;    (f) compressing the cooled first intermediate product between the second male mold insert and the female half mold to a second, reduced volume before the low pressure conditions within the beads equilibrate to ambient conditions to produce a fused expanded bead body of at least 200 percent higher density than the predetermined density of the pre-expanded beads;    (g) removing the second male mold insert from the first male mold insert; and    (h) adding pre-expanded polystyrene beads to the mold assembly and remolding the added beads between the female half mold and the male half mold under heat and compression to cause fusion of the added beads at an interface to the expanded bead body to form a layered construct comprising at least two layers of beads wherein the layers have different densities.    
     
     
         11 . The construct of  claim 10 , wherein the construct is a safety helmet.  
     
     
         12 . The construct of  claim 10 , wherein the construct is an edge protector.  
     
     
         13 . The construct of  claim 10 , wherein the construct is a corner protector.  
     
     
         14 . The construct of  claim 10 , wherein the construct is a packing crate.