Device and method for the injection of atomised fluid in blow air during blow moulding of hollow bodies.

The present invention pertains to a atomiser for the addition of water to blow air, with a main pipe with a main conduit with an inlet for blow air at a first end and an outlet at a second end for blow air for the inflation of a hollow body of molten plastic or the like in a mould.

When blow moulding of plastic, the plastic will undergo three distinct phases:

1. It is heated and becomes mouldable.

2. It is moulded by means of a moulding tool.

3. It is cooled until the plastic consolidates.

The last stage, the cooling stage, is time intensive especially when forming more thick-walled pieces. The external cooling takes place through contact with the water cooled mould tool. Internally the cooling takes place usually by means of a return air system which blows cooling air into the hollow of the piece to bring heat out of the detail. To increase the effectiveness of this internal cooling, one may add water to the blow air in the shape of atomised water. This significantly increases the internal cooling. The use of water as such is known. It is however problematic to find a practical manner in which to rebuild existing blow moulding machines without supplying additional sensors and energy sources for the addition of atomised water to the blow air, and to regulate the initialisation and duration of the atomisation of the water.

Background art

US2004/0156942 describes a system for the cooling of an internal surface in a hollow body wherein a cooling medium such as air or air amixed with water is blown into the hollow body which is being produced. A closed loop system then leads the cooling medium through a series of processes for the extraction of heat, for

compression and the like. US2004/0156942 does not however describe a atomiser in which the opening of the valve for the injection of the cooling media is done by the pressure which is formed in an air outlet within a blow tool after the hollow body completely fills the form in which it is moulded. The abovementioned patent publication solely describes a system which is externally driven and which is not dependent on process parameters such as the internal pressure in the hollow body. Thus the above system is more costly as well as more complicated as it relies on additional sensors and the like for its correct functioning.

Short summary of the invention

A solution to the abovementioned problem is according to the invention a atomiser for the addition of water to blow air with a main pipe with a main conduit with an inlet for blow air at a first end, and an outlet for blow air at a second end for the inflation of a hollow body of molten plastic or the like in a mould, in which said main pipe is furnished with an inlet for water or other cooling liquid to an atomiser with an outlet centrally in said main pipes main conduit. The new and characterizing features of the invention are the following: an air inlet from the main conduit is arranged upstream from said main pipe with respect to said spray diffuser, arranged for directing air out from said main conduit when the inflation of said hollow body has filled said mould, in order for when the pressure in said air outlet rises above a given pressure during the insufflation process, indicating that said hollow body has filled the mould and that the pressure from said air outlet controls the tripping of a valve for injection of water to the inlet for atomisation in said spray diffuser for the cooling of the internal surface of said hollow body.

Short description of the figures.

Figurei is a sketch of the working principle of a preferred embodiment of the invention showing:

1 and 2 : Time regulators with volumetric expansions marked 1' and 2'. 3 : Air cylinder with a shared piston rod with a water cylinder.

4 Deareation valve 5 Reduction valve 6 Valve (normally closed) 8 Water cylinder 7 Dosage valve 9 External pressure source 10 Manual shut off valve

Figure 2 is a cross-section of a spray diffuser according to the invention with the following details:

28 Air outlet

26 water inlet

20 main pipe

21 first end of main pipe 22 inlet for blow air

23 second end of main pipe

24 outlet for blow air

25 atomiser nozzle for water in main conduit

26 inlet for water to atomiser nozzle 27 main conduit in main pipe

28 air outlet from main conduit

Detailed description of a preferred embodiment according to the invention

In the herein described system the water injection into the blow air may take place by means of two energy sources:

1 : Pressurised air: An internal counter pressure is formed by the insufflation, and 2: Pressurised water from the external water grid.

The air from the counter pressure may in one embodiment of the invention be added from the atomiser a distance ahead of the water injection. Other cooling fluids than water may also be used, but water has the advantage of having a large heat capacity

and a large heat of evaporation. The air is distributed to a pressure cylinder (3), to a deareation valve (4) to a reduction valve (5), to two time regulators (1 and 2) with respective volumetric expansions marked 1' and 2' (see Figure 1).

From the time regulators the air passes to a valve (6). This valve (6) is normally closed, but is opened by the action of the manoeuvre air.

When the blow air is turned on, the air piston in the cylinder (3) forces a piston in a water piston (8) towards the right (8), and the pressurised water is lead towards a valve (6). The air piston and the water piston share the same piston rod. When said valve (6) opens upon a signal from said time regulator (1), the water passes through a needle valve (7) that regulates the amount of water to said atomiser.

The first time regulator (1) regulates the moment upon which said valve (6) shall open. The second time regulator (2) regulates the moment upon which said valve (6) shall close.

Cylinder (3 and 8) with respective connected pistons is a pressure riser system that in each end is provided with a check valve.

When the inflow of the blow air ceases, the pressurised water from the water grid pushes the pistons over towards the left of the initial position. Cylinder (3) is deaereated via said deaereation valve (4) that during the insufflation of air is kept shut by the blow air.

The required amount of water varies with the volume and weight and wall thickness of the blown detail. Due to the atomisation of the water it has been demonstrated that the effect is very large. Apart from the installation costs the running costs are almost absent. The system has on an experimental basis been essayed at a Norwegian factory. During trials with atomised water in the blow air, one has used about 13Og of water to cool a blow moulded detail of 7 kg.

Utilising the blow air pressure and counter pressure ensures that the necessary power intake and the necessary control signals for the functioning of the system automatically arrive at the correct time and in the correct order.

In an alternative embodiment of the invention, an external pressure source (9) may provide further pressure support for the injection of water into the atomiser. This may be useful when blow moulding larger pieces. The external pressure source (9) may be shut off manually by the use of a shut off valve (10).