Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
  • B29C44/12—Incorporating or moulding on preformed parts, e.g. inserts or reinforcements
  • B29C44/1285—Incorporating or moulding on preformed parts, e.g. inserts or reinforcements the preformed part being foamed
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C44/00—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles
  • B29C44/02—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles
  • B29C44/04—Shaping by internal pressure generated in the material, e.g. swelling or foaming ; Producing porous or cellular expanded plastics articles for articles of definite length, i.e. discrete articles consisting of at least two parts of chemically or physically different materials, e.g. having different densities
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B29—WORKING OF PLASTICS; WORKING OF SUBSTANCES IN A PLASTIC STATE IN GENERAL
  • B29C—SHAPING OR JOINING OF PLASTICS; SHAPING OF MATERIAL IN A PLASTIC STATE, NOT OTHERWISE PROVIDED FOR; AFTER-TREATMENT OF THE SHAPED PRODUCTS, e.g. REPAIRING
  • B29C45/00—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor
  • B29C45/14—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles
  • B29C45/14778—Injection moulding, i.e. forcing the required volume of moulding material through a nozzle into a closed mould; Apparatus therefor incorporating preformed parts or layers, e.g. injection moulding around inserts or for coating articles the article consisting of a material with particular properties, e.g. porous, brittle

Definitions

• THIS * INVENTION relates to the moulding of articles from poiyurethane foam. It is particularly applicable to arti ⁇ cles in which the weight is extremely critical, consistent with an acceptable strength, such as in the surfboard and allied industries. It is equally applicable in other fields demanding similar criteria.
• fibreglass coated poiyurethane The disadvantages of fibreglass coated poiyurethane are that it is extremely labour intensive, it is extremely rigid and hence has less ability to absorb impact. It tends to fracture easily, and separates, and it is a fairly unpleasant and hazardous material to handle.
• the present invention involves the manufacture of the core first, with a very low density, lightweight material, then covering it with a thin medium density poiyurethane skin.
• core material including poiyurethane and styrene.
• the present invention resides in a method of produc ⁇ ing articles from poiyurethane foam which comprises form ⁇ ing «-a core of low density material, placing the core within a mould so that at least part of the core is spaced apart from the wall of the mould and injecting materials to form a skin of poiyurethane foam into the space between the core and the wall of the mould, the skin having a density greater than the density of the core.
• Buoyancy is a major significant factor in that it relates directly to performance. The more buoyant a surfboard is, the less energy that is required to utilize it.
• a surfboard constructed with this method may be significan ⁇ tly reduced in size compared with a similar surfboard constructed with conventional methods, resulting in in ⁇ creased performance, yet carrying the same person.
• a major factor of this invention is the high volume pro ⁇ duction that can be achieved with relatively few rejects, resulting in extremely low cost per unit.
• This invention preferably uses the R.I.M. method (Reaction Injection Moulding) of poiyurethane construction for the formation of both the core and skin.
• Moulds may be constructed from several types of material, however, aluminium moulds were found to be the most suc ⁇ cessful.
• the mould described in this document was highly polished on the surface to be reproduced, with a minimum of 25 mm. aluminium thickness.
• the mould was made in two halves, a top and bottom, joining mid way around the edge, or rail, of the surfboard.
• a skin thickness of between 6mm. and 10 mm. with an average density of between 200-400 kilograms per cubic metre, moulded around a lightweight core of density between 28-50 kilograms per cubic metre gives the most satisfactory balance between weight and strength.
• the density of the skin may be increased to obtain more surface hardness and strength.
• An alternative method is to increase the density of the core, to increase the strength, and corres ⁇ pondingly reduce the skin thickness, thus realising the same overall weight, and strength. With strict control, skin thickness may be reduced to 2 mm., however, at this thickness, a minimum density of 250 kg./c . was most satisfactory.
• OMPI skin thickness is 8 mm. with a density of 250 kg./cm. moulded around a core of density 30 kg./cm.
• Two inserts are constructed, in this case of fibreglass, however any material that can be moulded to the shape of the mould may be used. These inserts are 8 mm. in thick ⁇ ness, and made so that they fit exactly inside both the top and bottom of the mould (halves). When the mould is closed, the void inside with the inserts is 8 mm. thinner all over than the closed mould without the inserts.
• the poiyurethane When the poiyurethane has cured, it may be removed from the mould.
• the core is now 8 mm. thinner all over than the finished article is to be.
• the cores must be stored to minimise distortion and to cure properly.
• another mould may be made up that is exactly 8 mm. thinner all over than the master mould, and the cores may be manufactured separately.
• the demould time of the cores is dependent upon the thick ⁇ ness.
• Moulding a skin around the core may be done by either of two methods?
• Method 1 The aluminium mould is prepared in the usual manner. Spacers are either glued or placed on both sides of the core so that when it is placed inside the mould and it is closed, an even void of 8 mm. exists all around the core. It is into this void that the higher density skin ⁇ ning poiyurethane is to be injected and react. The spacers are positioned so that when the mould is closed, they hold the core tightly and evenly, not allowing any movement of the core when the skin material is reacting. The length of the spacers is 9 mm. so that when the mould is closed, they push into the core slightly, holding it tightly.
• the spacers maybe of any suitable configuration.
• a pre ⁇ ferred form of spacers is formed of nylon or other suit ⁇ able plastic and comprises a disc having a central pig projecting from each face. One peg is pushed into the core until the disc bears against the surface of the core. This leaves the other pig projecting outwardly so that in position the outer end bears against the wall of the mould to hold the core spaced therefrom.
• a predetermined amount of poiyurethane is injected into the void so that the required density is reached.
• the entry gates where the poiyurethane enters the mould must be constructed carefully to enable it to react evenly along both sides of the core. Bad design will result in more material forcing its way to one side of the core, with little or none of the other side.
• Each item to be moulded requires its own gating system. This method becomes extremely difficult where one side of the core is shaped in such a way as to allow for easier flow of the skinning material than the other. In such a case, Method 2 may be used.
• Method 2 The mould is prepared as usual, and the bottom insert is positioned in the bottom of the mould.
• the core is then placed into the insert, fitting exactly as it was moulded in it beforehand. Spacers are then placed on the top of the core, so that when the mould is closed, there will'be a void of exactly 8 mm. around the top of the core only. The closure of the mould will force the spacers into the core, pushing it hard against the bottom insert, so that no material can find its way around the bottom half of the core.
• a predetermined amount of poiyurethane is injected into the mould, which finds its way into the only void i.e. the top of the core.
• the demould time which is rela ⁇ tively short
• the mould is opened.
• the skin around the top of the core adheres to the aluminium, and the whole thing comes away from the bottom of the mould.
• the bottom insert can now be removed.
• Poiyurethane may now be injected into the mould, filling the only void, the bottom half. Adhesion to the top half that has already been skinned is excel ⁇ lent.
• the mould may be opened and the product removed.
• Method 2 involves extra time, for more complicated mouldings, it is preferable to Method 1.
• the amounts of material to be injected into the mould can be calculated from test shots by trial and error.
• Strengthening of the product may be carried out by the insertion of various strengthening rods or by cutting grooves in the core prior to inserting it in the mould, these grooves are filled during the skinning process. These grooves are an ideal method of reinforcing specific sections of the product with little effort. While spacers are specifically mentioned in this description, it was found that plastic straps, equidistant from each other. and fastened each side of the bottom of the mould so that they span the cavity, were satisfactory. When the mould ⁇ was closed the edges of the upper part of the mould bear against the ends of the stoop so that they tightened across the core and hold it sufficiently for the skinning process.

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• Engineering & Computer Science (AREA)
• Manufacturing & Machinery (AREA)
• Mechanical Engineering (AREA)
• Casting Or Compression Moulding Of Plastics Or The Like (AREA)

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• 1984
  • 1984-02-21 EP EP19840900836 patent/EP0138842A4/de not_active Withdrawn
  • 1984-02-21 WO PCT/AU1984/000022 patent/WO1984003251A1/en not_active Application Discontinuation

Patent Citations (9)

Non-Patent Citations (1)

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