US3715179A

US3715179A - Moulding apparatus

Info

Publication number: US3715179A
Application number: US00090994A
Authority: US
Inventors: A Westbrook; Thomson I Macknight
Original assignee: Plastic Rotational Mouldings Ltd
Current assignee: Plastic Rotational Mouldings Ltd
Priority date: 1969-11-26
Filing date: 1970-11-19
Publication date: 1973-02-06
Anticipated expiration: 1990-02-06
Also published as: DE2058042A1; GB1325051A; FR2074950A6

Abstract

A rotational moulding apparatus comprises mould-support means, a heating chamber in which the mould-support means may be located, first and second tanks adapted to contain a liquid or liquifiable solid heating medium, first heating means for heating at least the contents of the first tank, a loop path for the heating medium leading from the first tank to a second heating means and back to the second tank, first pump means for causing heating medium to flow along the loop path, supply duct means from the second tank to spray means located in the heating chamber, return duct means leading to the first tank from catchment means in the heating chamber disposed to collect heating medium flowing from the spray means, second pump means to move heating medium from the second tank through the supply duct means to the heating chamber, and overflow means interconnecting the first and second tanks.

Description

United States Patent Westbrook et al. 1 Feb. 6, 1973 [5 1 MOULDING APPARATUS 3,579,738 5 1971 Beattie ..l8/26 RR [75] Inventors: Aubrey Joseph Westbrook, I (1l- Primary Examiner H. A Kflby, Jr

wmmng; Ian David MacKmght Attorne Michael S Striker Thomson, Irvine, both of Scotland y 3] Assignee: Plastic Rotational Moulding Limited, [57] ABSTRACT London, England A t l ]d t 1d rota lona mou mg appara us compnses mou [22] 1970 support means, a heating chamber in which the [21 A N 90,994 mould-support means may be located, first and second tanks adapted to contain a liquid or liquifiable solid heating medium, first heating means for heating at [30] Forelg Apphcat'on Pnomy Data least the contents of the first tank, a loop path for the Nov. 26, 1969 Great Britain ..57,829/69 heating medium leading FY01 the first tank to a second heating means and back to the second tank, 521 US. 01. ..425/86 425/425 164/338 first Pump means for Causing heating medium to flow 511 1111.01. ..B 28b 1/26 the Path Supply duct means fmm the [58] Field of Search l8/26 RR DIG 13 2 V 4 V second tank to spray means located in the heating 18/6 R I7 2 42'5/425 chamber, return duct means leading to the first tank from catchment means in the heating chamber disposed to collect heating medium flowing from the spray means, second pump means to move heating [56] References C'ted medium from the second tank through the supply duct UNITED STATES PATENTS means to the heating chamber, and overflow means interconnecting the first and second tanks. 2,235,906 3/1941 Skoning 2,483,709 10 1949 Paulsen 5 Claims, 2 Drawing Figures 3,369,274 2/1968 Dicks et al 18/26 RR UX I 2a UPS i I1\\\ r A n i/ /;1 i i 012 I I L/1 I :1:

PATENTEDFEB 6 I973 I A llorney MOULDING APPARATUS This invention relates to moulding apparatus of the kind in which a heated hollow mould containing a hardenable liquid composition is rotated by a mould support means about two axes (normally mutually perpendicular axes) until the composition hardens as a coating of substantially uniform thickness on the internal surface of the mould. Throughout this specification such moulding apparatus will be referred to as rotational moulding apparatus. In particular this invention is concerned with an improved design of equipment employed to supply thermal energy to the hollow mould while it is located in a heating chamber.

In the specification of our British Patent Application No. 34309/67 we claim and describe rotational moulding apparatus comprising mould-support means, a heating chamber in which the mould-support means may be located, a tank adapted to contain a liquid or liquefiable solid heating medium, first heating means for heating the contents of the tank, duct means defining a loop path for the heating medium which leads from and returns to the tank, which duct means includes a second heating means and a pump for circulating the heating medium around the loop path, a plurality of spray means for spraying heating medium into the chamber and means for returning heating medium sprayed into the chamber back to the tank.

This invention relates to a modification of, or an improvement in, the apparatus claimed and described in the aforementioned specification and according to the present invention rotational moulding apparatus comprises mould-support means, a heating chamber in which the mould-support means may be located, first and second tanks adapted to contain a liquid or liquefiable solid heating medium, first heating means for heating at least the contents of the first tank, a loop path for the heating medium leading from the first tank to a second heating means and back to the second tank, first pump means for causing heating medium to flow along said loop path, supply duct means from the second tank to spray means located in the heating chamber, return duct means leading to the first tank from catchment means in the heating chamber disposed to collect heating medium flowing from the spray means, second pump means to move heating medium from the second tank through said supply duct means to the heating chamber, and overflow means interconnecting the first and second tanks.

The first and second tanks may be located in one vessel and disposed on opposite sides of a weir which defines the overflow means.

The first heating means may be a combustible fuel furnace supplying heated gas to pipes passing through both tanks below the normal level of heating medium therein, or it may be an immersion heater (fuel-fired or electric) located in the first tank.

The second heating means is conveniently a fuelfired heat exchanger, the loop path including heat exchange pipes in the combustion chamber of the heat exchanger.

The supply duct means is preferably designed so as to slope downwardly from the spray means to the second tank. With this arrangement, when the second pump means is stopped, spraying of heating medium into the heating chamber ceases and the heating medium left in the supply duct means drains back to the second tank.

the same two tanks, each has its own supply and return duct means and its own second pump means, all the supply duct means leading from the second tank and all the return duct means leading to the first tank. Apparatus in accordance with the present invention is particularly suitable for rotational moulding apparatus which embodies two or more heating chambers, since by dividing the heating medium between first and second tanks in the manner described, it is possible to ensure that the supply for any heating chamber of the apparatus is at the correct moulding temperature. To ensure this, we prefer to modulate the output of the second heat exchanger so that under normal operating conditions it discharges heating medium into the second tank at the desired spraying temperature. The first pump means can then operate all the time the apparatus is working, any excess of heating medium transferred from the first tank to the second tank flowing back into the first tank via the overflow means.

One embodiment of rotational moulding apparatus in accordance with the present invention will now be described, by way of example, with reference to the accompanying schematic drawing, in which:

FIG. 1 is a side elevation of the apparatus, and,

FIG. 2 is a sectional end view of the tanks containing heating medium. A

Referring to the drawing, the apparatus comprises a pair of heating chambers (designated A and B) each of which is adapted to contain (during a moulding operation) a mould-support means (designated by A and B). Located in the upper part of each heating chamber is an array of spray nozzles 2a and 2b through which liquid heating medium can be sprayed onto a mould supported in the mould-support means. The nozzles 2a and 2b are fed with heating medium via supply ducts 3a and 3b each of which is fed from an immersed liquid pump 4a and 4b respectively. Catch tanks 5a and 5b are located in the lower part of the heating chambers A and B, respectively, and are positioned to collect heating medium as it is received from the spray nozzles thereabove or such heating medium as drips from the mould. Return ducts 6a and 6b are connected to the catch tanks and serve to return liquid heating medium to a container generally designated 7.

The container 7 is thermally insulated and is divided by a weir 8 into a first tank 9 and a second tank 10. The pumps 40 and 4b are located in the tank 10 while the return ducts 6a and 6b discharge into the tank 9. Also located in the tank 9 is an immersion heater 11. This heater 11 forms the first heating means as referred to above and is normally employed only for initially raising the temperature of the heating medium when the apparatus is started up. In the case of a liquifiable solid heating medium, a prolonged shut-down of the apparatus will result in solidification of the heating medium within the

tanks

9 and 10. The heater 11 will be employed to liquify the heating medium in the tank 9 prior to the apparatus being employed for further moulding operations.

A high efficiency fuel-fired heat exchanger 12 is located in a loop path 13 which is fed from a pump 14 located in the tank 9 and discharges into the tank 10. It is the heat exchanger 12 which is primarily responsible for providing the thermal energy necessary to operate the apparatus. Conveniently the supply of fuel to the heat exchanger 12 is controlled in dependence on the temperature of heating medium flowing into the tank from the loop path 13.

The nozzles 2a (2b) and the supply duct 3a (3b) are disposed so that the supply duct slopes downwardly towards the tank 10. Thus, if the pump 4a (4b) is not operating, the supply duct 3a (3b) and the nozzles 2a (2b) empty of heating medium so that there is no risk of this solidifying in the supply duct or nozzles and interfering with the smooth flow of heating medium when the pump 40 (4b) is restarted. It will be appreciated, therefore, that a spraying operation occurs only when the pump 4a or the pump 4b is operating. When either pump is started, heating medium is drawn from the tank 10, flows through the supply duct 3a (3b) and discharges through the nozzles 20 (2b). Thus shortly after either pump is turned on, spraying will commence in the respective heating chamber, and as soon as the pump is turned off, spraying will cease and the supply duct will begin to empty back into the tank 10.

Heating medium sprayed into a heating chamber is cooled by contact with the mould, the mould-support means or the walls of the chamber and thus returns to the tank 9 at a lower temperature than the optimum spraying temperature. It will be noted, however, that this cooled heating medium cannot be re-used in a heating chamber until it has passed over the weir 8 by being led through the loop path 13 (and thus through the heat exchanger 12). This arrangement ensures that the supply of heating medium to either chamber is always drawn at the operating temperature, since the output from the heat exchanger 12 into the tank 10 is always at this temperature.

Let it be imagined that the apparatus has been shut down for an extended period and that tank 9 is full to the level of the top of the weir 8 and that just sufficient heating medium remains in the tank 10 to cover the inlets of the pumps 4a and 4b. It will be assumed that the heating medium is of the liquefiable solid type and that the shut-down period has been so long that this heating medium has solidified in both

tanks

9 and 10. The sequence of operations to put the apparatus into condition for moulding and the manner in which it will be employed during moulding will now be described.

The heater 11 is activated and this will cause heating medium in the tank 9 to fuse. When the entire contents of the tank 9 are molten, the pump 14 can be actuated to draw heating medium into the loop path l3an'd pass it through the heat exchanger 12. Suitable interlocks are provided to ensure that the pump 14 cannot operate until the contents of the tank 9 have reached a certain minimum temperature (i.e., the contents of the tank 9 are liquid) and that the heat exchanger 12 cannot operate unless the pump 14 is operating.

The heat exchanger 12 raises the temperature of the heating medium to the desired operating temperature and discharges this heating medium into the tank 10 where it falls onto the solidified layer lining the bottom of the tank 10. By normal conduction, the hot heating medium admitted to the tank 10 causes the solidified residue in the tank 10 to fuse. As this initial warm-up procedure continues, it will be appreciated that the level in the tank 9 will drop while the level in the tank 10 will rise. When the level in the tank 10 reaches the top of the weir 8, it will overflow into the tank 9 and will be available for re-circulating through the heat exchanger 12.

The pumps 4a and 4b are provided with temperature sensing cut-out devices which ensure they cannot be operated until the temperature of the heating medium in the tank 10 is at the desired spraying temperature for moulding operations. When this temperature has been reached in the tank 10, operation of either of the pumps 40 or 4b will serve to draw heating medium along the respective supply duct 3a or 3b and discharge it into chamber A or chamber B. The cooled heating medium collected by the catch tanks is fed back into tank 9 via the return ducts 6a and 6b. It will be appreciated that heating medium in the tank 9 cannot be used for spraying into the heating chamber until it has been re-heated by passage through the heat exchanger 12. Conveniently the pumping rate of the pump 14 and the maximum thermal output of the heat exchanger 12 are dimensioned to ensure that even at maximum moulding rate, the tank 10 never empties. However, it is advisable to provide low level cut-outs in the tank 10 to render the pumps 4a and 4b inoperative if .the level of heating medium in the tank 10 falls below a predetermined minimum level.

When it is desired to shut-down the apparatus, it is necessary to transfer heating medium from the tank 10 to the tank 9. This is achieved by turning off the pump 14 and the heat exchanger 12 and then employing one (or both) of the pumps in the tank 10 to pump heating medium via one (or both) heating chamber back into the tank 9. This transfer of heating medium can continue until heating medium flows over the weir 8 from the tank 9 to the tank 10. The pumps can now be turned off and the heating medium left in the ducts will drain down into the respective tanks where it can safely be left to cool (and possibly solidify). Resumption of a moulding operation will then follow according to the proposals given earlier.

If there is a hold-up in moulding operations when the apparatus is operationable, this will merely result in the level of heating medium in the tank 10 rising until it reaches the top of the weir 8. It will then discharge over the weir 8 into the tank 9. If the output of the heat exchanger 12 is modulated in accordance with the temperature of the heating medium in the loop path 13, the heat exchanger 12 will merely maintain the heating medium at a desired operating temperature until spraying in one or other of the chambers recommences.

Although the specific apparatus described employs two heating chambers, it will be appreciated that the in- The weir 8 is conveniently lower at the edges as shown in FIG. 2, so that when the condition arises in which heating medium overflows from the tank 10 to the tank 9, this overflow can be to a part of the tank 9 which is not too close to the inlet of the pump 14.

If it is desired to work with the minimum quantity of heating medium in the

tanks

9 and 10, it may be desirable to arrange that the pumps 4a and 4b cannot be operated simultaneously.

Conveniently the pumps 4a and 4b are interlocked with the pump 14 to ensure that the former cannot (except for filling the tank 9) be operated unless the latter is operating.

Since a certain amount of heating medium is inevitably withdrawn from the heating chambers each time a mould-support means is withdrawn therefrom, there will be a steady loss of heating medium during the course of moulding operations, and it may be desirable to provide means for automatically topping-up the

tanks

9 and 10 to maintain an approximately constant level.

What is claimed is:

l. Rotational moulding apparatus comprising mouldsupport means, at least one heating chamber in which the mould-support means may be located, first and second tanks adapted to contain a liquid or liquifiable solid heating medium, first heating means for heating at least the contents of the first tank, a loop path for the heating medium leading from the first tank to a second heating means and back to the second tank, first pump means for causing heating medium to flow along said loop path, supply duct means from the second tank to spray means located in the heating chamber, return duct means leading to the first tank from catchment means in the heating chamber disposed to collect heating medium flowing from the spray means, second pump means to move heating medium from the second tank through said supply duct means to the heating chamber, and overflow means interconnecting the first and second tanks.

2. Apparatus as claimed in claim 1, in which the first and second tanks are located in one vessel and disposed on opposite sides of a weir which defines the overflow means.

3. Apparatus as claimed in claim 1, in which the first heating means is an immersion heater located in the first tank.

4. Apparatus as claimed in claim 1, in which the second heating means is a fuel-fired heat exchanger, the loop path including heat exchange pipes in the combustion chamber of the heat exchanger.

5. Apparatus as claimed in claim 1, in which two or more heating chambers are fed from the same two tanks, each heating chamber having its own supply and return duct means and its own second pump means, all the supply duct means leading from the second tank and all the return duct means leading to the first tank.

Claims

1. Rotational moulding apparatus comprising mould-support means, at least one heating chamber in which the mould-support means may be located, first and second tanks adapted to contain a liquid or liquifiable solid heating medium, first heating means for heating at least the contents of the first tank, a loop path for the heating medium leading from the first tank to a second heating means and back to the second tank, first pump means for causing heating medium to flow along said loop path, supply duct means from the second tank to spray means located in the heating chamber, return duct means leading to the first tank from catchment means in the heating chamber disposed to collect heating medium flowing from the spray means, second pump means to move heating medium from the second tank through said supply duct means to the heating chamber, and overflow means interconnecting the first and second tanks.