A METHOD FOR PRODUCING A DOOR BY PLASTIC MOULDING AND A DOOR PRODUCED BY THIS METHOD

Abstract: Polyurethane is formed in a mould on a tiltable carrier. The mould is lined at least on two faces to give a moulding of a door. A welded steel reinforcement frame is fixed on pins extending to edges of the moulding so that the frame becomes encapsulated in the moulding. The frame may suspend a sheet of fire resistant or anti-ballistic material. After an interval, the mould is tilted to an upright position. After moulding, the door is removed from the mould, stripped of flash and release agent, and finished like wood. The door may be of security and/or external quality, and included as part of a door set.

Description: A METHOD FOR PRODUCING A DOOR BY PLASTIC MOULDING AND A DOOR PRODUCED BY THIS METHOD DESCRIPTION Technical Field The invention relates to a plastics moulding process whereby a door of reinforced polyurethane is produced. Background Art Polyurethanes are moulded by feeding polyol (containing additives) and isocyanate separately to a mixer head which meters them in a fixed ratio into a mould. The difference in temperature between the expanding polyurethane and the mould surface causes a self-skin to form on the cellular product obtained. A mould lining taken, for example, from a hardwood original can give a moulding fine detail of surface texture relief closely simulating the original, but such high definition reproduction has generally been required on one face only. The products are of structural foam and do not hold screws or other fittings securely. A door presents a special problem in that it requires at least two faces of good reproduction quality, and must hold screws. A security door also needs reinforcement and weight. The Invention The invention provides a plastics moulding process in which polyol (containing additives) and isocyanate are fed separately to a high pressure mixer head which meters them into a mould in a generally horizontal position on a tiltable mould carrier characterised in that the mould is lined at least on two faces to give a moulding of a door, a welded steel reinforcement frame is fixed on pins extending to edges of the moulding so that the frame becomes encapsulated in the moulding, and after an interval the mould is tilted to an upright position. The mould is preferably lined on four or all six faces to give a moulding with good reproduction quality on the side, and optionally the top edges too. The nature and quantities of the polyols and isocyanate, and the pressure of the mixer head are selected in relation to each other and the time periods allowed for initial mixing and reaction so as to yield a self-skinned high density- structural foam. The feeding of the polyols and isocyanate into the mould initially wets a lower face of the door and the reinforcement frame. The tilting combines with the foaming of the polyurethane to fill the mould and give a second face of reproduction quality to the door. After moulding, the door is removed from the mould, stripped of flash and mould release agent, and finished like wood with stain and varnish or painted. Recesses in the edges of the door for locks and hinges are generally provided in the moulding, or may be cut out later. Locks and hinges are preferably bolted directly onto the steel frame encapsulated in the moulding. A grille and other accessories such as a knocker, may be provided for. The reinforcement frame may suspend by means of lugs and/or have mounted centrally therein a sheet of material which, like the frame itself, becomes encapsulated in the moulding. Suitable sheet materials include 10 mm thick melamine-faced chipboard or glass fibre reinforced gypsum (GYPROC TM) which improve fire resistance or steel or KEVLAR (TM) which are anti-ballistic or ball resistant. The sheet may have holes of 8 mm diameter formed at random therein to receive the polyurethane and add strength. The polyol may incorporate a fire-retardant additive, and any door frame an intumescent sealing strip. In a further modification, the reinforcement frame may be moulded into a part-formed core in a preliminary stage. The frame itself and any sheet mounted therein may be encapsulated in an intermediate density (perhaps about 200 kg per cubic metre) foam by moulding at low pressure. This preliminary stage can quickly and easily be effected, and the whole resulting moulding fixed as a core in the mould in which the main moulding process is performed. This modification speeds the process overall, because the lower bulk of material in the main moulding process means that less heat is generated and has to be dispersed, and yields a door with a harder surface and better thermal insulating properties. The door is usually sold with a matching door frame as part of a door set for ease of fitting into an appropriate space in a wall of masonry. Matching door frame members can be made by a process similar to that for the door. In this process, mould parts are lined on at least three faces to give a moulding simulating a door frame, a steel reinforcement is mounted therein, the mould is closed, polyurethane plastics components are injected, the polyurethane is allowed to foam and set, and the frame member is removed from the mould. The three faces preferably of reproduction quality are those on the inside and outside of the frame in a use position in a building, and the one facing inward against which the door abuts, but at least the edge facing the door is preferably also of this quality. The member is finished in the same way as the door itself, and four such members are bolted together with an aluminium threshold to make a frame. Hinges and locks are screwed into the reinforcements of the frame, which is itself secured to the wall of masonry through the same reinforcement. Drawings Figure 1 is a schematic side view of a tiltable mould carrier suitable for use in the process of the invention; Figure 2 is an end view of the mould carrier of Figure 1; Figure 3 is a perspective view of a door mould bottom half for use in the process of the invention in an open position, the top half of the mould (not shown) being a mirror image of the bottom half; Figure 3a is the same as Figure 3, but omits a mould lining to reveal a heater/cooler tube; Figure 4 is a section through a door frame mould; Figure 4a shows a corner of a door frame comprising members produced in the mould of Figure 4; Figure 5 is a component circuit for the chemical ingredients to be introduced into the moulds of Figures 3 and 4; and Figure 6 is an elevation of a door set comprising a security door and door frame according to the invention secured in a wall. Best Mode In Figure l the mould carrier comprises a baseframe weldment 20 having a lower platen/cylinder support weldment 21 pivotally mounted thereon, an upstroking lower platen 22 mounted on the support weldment 21, and an upper platen support weldment 23 pivoted (see Figure 2) with respect to the support weldment 21. These weldments are of stable, robust fabrication from mild steel profile plate. The baseframe weldment 20 comprises pillars 25 at opposite ends, each having a fabricated pivot point assembly 26 at the top supporting the lower platen/cylinder support weldment 21. The top of the pillar 25 to the right in Figure 1 is provided with a trunion-mounted hydraulic motor 27 for tilting the lower platen/cylinder support weldment 21 with respect to the baseframe weldment 20. The lower platen/cylinder support weldment 21 is provided with a central column 28 supporting a frame 29 machined to accept six flange-mounted cylinders 30 and three sliding location guide bush assemblies (not shown) . The guide bush assemblies are of large diameter and maximum length for accurate location of the lower platen 22 with an upper platen 32. The column 28 comprises a multi-axis swivel and lock arrangement located on substantial machined face plates beneath the frame 29. Each axis support arrangement is machined from the solid, and rotation to any predetermined position is achieved through a large diameter lead screw. Pneumatically actuated interlock pins are provided to ensure safety. The lower platen 22 is of lattice construction. Surface ground on both sides, drilled and tapped on a predetermined grid to ensure fast and accurate location of a mould tool. Flange mounted guide bars are located on the lower platen surface. The upper platen support weldment 23 is hinged to the lower platen/cylinder support weldment 21 at 33, and lockable thereto in a book-closed position at 34 by cylinders 35. A separate pair of pneumatic cylinders 37 is attached to the lower platen/cylinder support weldment 21 and the upper platen/support weldment 23 adjacent the hinges 33 for locking the platens when in a book-opened position. Figure 2 shows in feint lines the lower and upper platen support weldments 21,23 tilted to the left, and in broken lines the book-opened position with the upper platen support weldment 23 distanced at the left-hand end from the lower platen support weldment 21. Figure 3 shows a mould tool which is bolted for use to the lower platen 22. The top half of the mould (not shown) is similarly secured to the upper platen 32 with inserts 41 for hinges and 42 for a 3-point lock common to both. The mould lining is not illustrated, but is an epoxy pull-cast moulding made in a manner known in itself so as to give moulded products a surface texture relief and appearance closely simulating an original door which may be made of hardwood. To the left there are shown two of twelve pins 44 mounted in the mould to support a welded steel reinforcement frame (see Figure 6) . In opposite sides of the mould tool, a total of four holes 45 are provided for the introduction of thermocouples for use in the control of mould temperature. To the right a feeder duct 47 is provided for the introduction of polyurethane plastics components into the mould. Figure 3a shows the mould tool half of Figure 3 with its epoxy lining removed so that heating/cooling tubes 50 are visible. In Figure 4, a door frame member 54 appears in cross-section with a steel reinforcement member 52 embedded therein. Welded to the reinforcement member 52 is a threaded sleeve 53 by which the door frame members are held together at the door corners by means of cap-head screws 53a as shown in Figure 4a. The hand operated mould in Figure 4 comprises top and bottom parts 61,62 with heating/cooling tubes 50 running therethrough as in Figure 3a. The mould parts 61,62 are each secured between a pair of hollow-section steel supports 64, with angle brackets 65 all round, and similar supports (not shown) at the ends. The lower supports 64 have a number of pads 66 welded thereto for clamping. Figure 5 shows the circuit through which the chemical components of the polyurethane plastics material are introduced into a high pressure mixer head (not shown) and thence to the feeder duct 47 of the mould. The component circuit of Figure 5 is essentially duplicated to left and right for each component. In each half, there is a tank 1, a check valve 2 with a common low pressure pump unit 3, a self-cleaning filter 4, a feed pressure gauge 5, a high pressure pump 6, a pour pressure gauge 7, a calibration head 8, a heat exchanger 9, and a water electrovalve 10 for one of the components. The circuit is thermostatically controlled by a unit (not shown) , in conjunction with the flow of water (heat exchange medium) through the tubes 50, and a controlled flow of air for the nucleation of the polyurethane, according to a pre-set temperature level and the heat generated in the mould during the process. The door set shown in Figure 6 comprises a door 51 produced* according to the invention having a steel reinforcement frame 52 moulded integrally and encapsulated therein. Hinges 41* and a 3-point lock 42' are shown in the spaces left by the inserts 41,42 respectively in Figure 3, and are secured by screws directly into the reinforcement frame 52, although this is not actually shown. The door 51 is mounted in the frame 54 which itself is fabricated from steel-reinforced polyurethane members made in a manner similar to the door 51 itself, but without tilting, cut to size and bolted into the masonry as indicated at 55. To the left of the door, a sidelight 56 is similarly secured in the door frame 54. Example A polyurethane system is used which consists of the following two chemical components fed through the circuit shown in Figure 5: A: polyol, catalyst, stabilizer, blowing agent, pigment, and flame retardant; and B: 4,4 '-diphenylmethane-diisocyanate (MDI) containing isomers and oligomers having a functionality of about 2.7, and free from solvent. The components circuit is fitted with an automatic system for monitoring and adjusting the amount of air introduced, and comprises an emulsifying unit for mixing air with the chemical components, and a dispensing unit leading to a high pressure mixer head. The components are injected into the mould in a thoroughly mixed condition. The injection cycle, and hence the volume of material injected is controlled by preset timers in the dispensing unit. The ratio of air to polyol is 25% by volume, and the ratio of isocyanate to polyol is from 1.06 to 1 by volume. The water content in the air is kept to a minimum by an air dryer and filter between the compressor and the point where the air is mixed with the polyol. The mould temperature is controlled at 45° plus or minus 4 degrees C by thermocouple sensors introduced through the holes 45 shown in Figure 3 which provide signals to the system controlling the flow of water to the heating/cooling tubes 50. This ensures that the heat generated by the chemical reaction which forms the polyurethane plastics material does not cause the mould temperature to rise and affect the product quality. The moulding sequence is as follows: With the mould open and horizontal, the mould lining is sprayed with a mould release agent. The steel reinforcement frame 52 is inserted into the mould, and suspended on the pins 44 which project inward from the mould perimeter. The mould is closed, and the chemical components of the polyurethane system are injected for 16.4 seconds at a rate of 1.83 kg per second. This gives an excess of 2.5 kg based on the door size illustrated and a door material density of 350 kg per cubic metre. The venting of this excess ensures a high quality defect-free surface on both sides of the product. The mould is kept in the horizontal position for 30 seconds from the start of the injection cycle, and then rotated through 90° to a vertical position during a period of 25 seconds. The mould is held in the vertical position for 20 minutes, then returned to the horizontal and unloaded. The product is a rigid foam with an integral skin suitable for an external security door. It is stripped of flash, and vapour blasted to remove mould release agent. The fixing holes for the hinges and lock are cut or drilled out. The product is spray coated with a sealant, two coats of stain, and a final coat of clear lacquer. The hinges and lock are screwed directly into the steel reinforcement frame 52, and the hinges are similarly screwed to a steel reinforcement in the door frame. The door frame can relatively easily be trimmed to fit in an aperture in a wall, and secured to the masonry by means of bolts seated in the metal frame.

Claims: CLAIMS 1. A plastics moulding process in which polyol (containing additives) and isocyanate are fed separately to a high pressure mixer head which meters them into a mould in a generally horizontal position on a tiltable mould carrier characterised in that the mould is lined at least on two faces to give a moulding of a door, a welded steel reinforcement frame is fixed on pins extending to edges of the moulding so that the frame becomes encapsulated in the moulding, and after an interval the mould is tilted to an upright position. 2. A process according to claim 1 in which the mould is lined on four or all six faces to give a moulding with good reproduction quality on the side, and optionally the top edges too. 3. A process according to claim 1 or claim 2 in which, after moulding, the door is removed from the mould, stripped of flash and mould release agent, and finished like wood with stain and varnish or painted. 4. A process according to any preceding claim in which recesses in the edges of the door for locks and hinges are provided in the moulding. 5. A process according to any preceding claim in which the reinforcement frame suspends or has mounted centrally therein a sheet of fire resistant or anti-ballistic material. 6. A process according to claim 5 in which the sheet has holes formed therein to receive the polyurethane and add strength. 7. A process according to any preceding claim in which the reinforcement frame is encapsulated in an intermediate density foam by moulding at low pressure in a preliminary stage before fixing as a core in the mould in which the main moulding process is performed. 8. A door produced by a process according to any preceding claim. 9. A door set comprising a door according to claim 8 with a matching door frame.

Inventors: FAIRFAX COLIN JAMES, GODDARD MICHAEL HOLLAND, FAIRFAX, COLIN, JAMES, GODDARD, MICHAEL, HOLLAND
Applicants: ARTWOOD DOORS LTD, ARTWOOD DOORS LIMITED
Application year: 1992
Main classification: B29C39
IPC codes: B29C33, B29C44, B29C70, E06B3, E06B5