Such machines are disclosed for example in our prior patent application GB9722547.8.

The invention seeks to provide improvements in such moulding, forming or pressing machines or systems and in particular to provide improvements in drying moulded pulp material especially within the press mould.

According to an aspect of the invention there is provided a moulding machine comprising a ultrasonic generator probably located to communicate ultrasonic vibrations to pulp material retained within a press mould in the moulding machine.

Preferably, the moulding machine comprises an upper and lower platen and ultrasonic generator is located in one of these. Preferably the moveable platen which is usually the upper platen.

Preferably, the moulding machine comprises a female press mould which is operably moveable and operably carries the ultrasonic generator. Beneficially the female press mould locates the ultrasonic generator proximal the moulded pulp. Preferably the press mould comprises steam vents and more preferably two or more steam vents are provided in the press mould adjacent the ultrasonic generator.

Beneficially moulds remain relatively cool and be easy to change quickly.

The cool platens and tools do not expand during use thus making tool alignment much simpler.

Beneficially simpler cheaper moulds can be provided. The lack of significant heat required by this process allows non-metallic moulds such as plastic, composites, etc to be utilised.

Beneficially drying time can be significantly reduced depending on the power levels selected for the ultrasonic generator.

Beneficially also, energy requirements can be cut dramatically as almost all of the energy developed can be focused directly into the wet part's water and almost none would be wasted heating platens, heater plates or moulds. This concept takes advantage of, and enhances the vacuum environment within the press mould housing. The vacuum enhances bubble formation due to cavitation, and serves to provide a mechanical exit vehicle for the water vapour formed.

Energising the ultrasonic generator can be done through a closed loop online linear feedback computer control system so that drying and pressing can be tailored to the particular shape and mass being dried. In this way, moisture content can be co-ordinated with drying pressure to effect the optimal surface finish and strength improvement from densification.

Beneficially, there is less stress during drying. This system cavitates both capillary and free water simultaneously, thus eliminating the stress of previous systems which removed free water before the capillary water, thus causing an unnecessary stress on the structure.

Beneficially, smoother, denser surfaces of the moulded material are provided. This system utilises the natural compression by-product of the shock wave formations to compress the pulp fibres confined between the male and female press heads.

Also improvements in safety are achieved. This system utilises much lower electrical power levels, reducing danger from both voltage and amperage, as well as removing the danger of burns from extremely hot parts.

It is believed the system works in that the liquid in moulded pulp parts is converted to vapour via ultrasonically induced cavitation. Water is the primary liquid evacuated although this process may use other fluids with a hydrogen radical. Sound waves in water are mechanical manifestations that can excite water into oscillating movement, independent of the solid pulp in the wet part.

Ultrasonic sound is generated by an oscillating solenoid within a horn structure. This structure can be imbedded in the mould or it may become the mould, or some portion of the mould itself. Alliteratively, the entire platen may become the exciter/transmitter. Ultrasound can be transmitted into water by directing the horn or its vibrating structure into the liquid. If tuned to the correct frequency, the sound resonates with the water molecules but can have no significant effect on the pulp fibres. The ultrasonic vibrations tend to follow the water paths, ignoring the surrounding more rigid mould structure of the press moulds which will act as conduits for the sound waves, and enhance the shock wave effect. As the sound moves or vibrates the water molecules against one another and past the solid"obstacles"presented by the mould and the pulp fibres within the wet part, the water molecules cavitate producing bubbles of water vapour (equivalent to low temperature steam). This cavitation is a result of the water being unable to follow luminar paths as it curves around the"obstacles"at a speed high enough to create the equivalent of a"stall condition". The resulting void is of low enough pressure to form a bubble full of water vapour. In gaseous form, this water vapour is susceptible to the pull of a vacuum and exits the wet part and the press mould cavity (that space formed between the male and female press heads) over similar paths to the present steam evacuation system in both the male and female press heads, thus drying the part without a significant increase in temperature.

An even greater increase in the efficiency of the system is achieved by incorporating an ultrasonic generator in one press mould and ultrasonic receiver (s) in the other press mould. In this way, the energy amplitude waves do not reflect at the end of the mould's press cavity with reversion pulses that could cancel the primary waves. This system preferably incorporates liquid paths (a manifold of small diameter pipes) that are routed back to the sound generator in phase to produce a regeneration effect, thus further reducing the system's energy requirements.

It is believed that 8 to 12 percent moisture of the finished moulded pulp products is sufficient moisture to support the ultrasonic cavitation through the end of the drying process.

The various mould shapes can enhance the cavitation process if complementing fillets are employed where surfaces meet. The sound waves in water cannot smoothly follow the transition from a convex to a concave surface, and tend to lose velocity causing an immediate and tremendous increase in pressure, temperature and enthalpy. This is the proper environment for the creation of shock waves which produce cavitation.

The pressure resulting from the mechanical press increases the viscosity of the water which enhances the cavitation process within the water due to ultrasound excitation, exclusive of its impinging on objects within the liquid body.

Air bubbles formed within the mould's press cavity can densify by a factor of 6, creating natural positive pressure points within the wet part, further pressing and smoothing out the part's surfaces.

It is preferable also to equip the front end transfer head of a moulding system with an ultrasound generator to effect partial drying and reduce cycle times.

The ultrasound generators can be computer controlled in a closed loop linear feedback system by measuring capacitance between the male and female press moulds through the pulp and using this as the factor to automatically control sound generation amplitudes, frequencies and durations (on vs. off).

A preferred embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which:- Figure 1 is a schematic side elevation view of a mould forming part of a moulding machine according to the invention; and Figure 2 is a schematic block diagram of components of a moulding machine according to the invention.

Referring to the drawings there is shown part of a moulding machine (10) according to the invention, comprising an upper platen (12) and lower platen (14). Upper platen (12) carries a female mould part (16) while lower platen (14) carries a male mould part (18). Machine (10) further comprises an ultrasonic generator (20) connected by leads (22) to a controller such as a computer (24) for controlling the frequency, phase and marked spaced ratio of the on and off pulses for the ultrasonic generator (20). As shown in Figure 1, in this embodiment, the ultrasonic generator (20) is partly embedded in platen (12) and also in part of the female mould part (16). The lower horn region (26) is located adjacent the mould cavity (28) such that in use ultrasonic vibrations are communicated via horn (26) into the cavity (28) and hence into the liquid and pulp material contained therein. Female mould part (16) (and part of upper platen (12)) preferably comprise vent holes (30) to allow evacuation of steam from mould cavity (28).

Male parts (18) of the mould can comprise a ultrasonic receiver (32) which can be either passive or active in order to absorb ultrasonic rays emitted from ultrasonic generator (20) thereby to minimise reflections back into cavity (28).

Preferably the system comprises a vacuum pump (34) for evacuating steam from mould cavity (28), for example via venting apertures (30).

In use, a transfer head places pulp into mould cavity (28), for example when upper platen (12) is raised, pulp is placed on top of male part (18) and hence when upper platen (12) is lowered, together with female mould part (16), the pulp material is shaped into the shape of cavity (28) defined by the male and female mould (18) and (16) respectively. Vacuum pump (34) acts to draw off vapour from mould cavity (28) and heating processes can be used in the known manner. However, additionally, computer (24) preferably determines the relative location of mould parts (16) and (18) for example using a capacitive technique communicated via leads (36), and is suitably programmed to drive ultrasonic generator (20). In the event that ultrasonic receiver (32) is an active receiver, computer (24) preferably also drives the receiver to effect the desired ultrasonic wave form within cavity (28).

The sonic horn is shown inserted into the female press mould, but could be inserted anywhere and used to drive the mould's inner surface or mounted in the platen to drive that surface to which the moulds are fastened.

The ultrasonic receiver is preferably positioned at points"32". The receiver (s) are optional and could be either passive or active. A passive receiver would be a material that resonates with the ultrasound. An active receiver would be another exciter horn (s) phased to produce a standing wave within the liquid medium.

According to the present invention there is provided use of ultrasonic sound to dry moulded pulp and/or apparatus and/or method comprising any derivable feature or combination of features as herein described or illustrated.

Further it is to be understood that individual features, method or functions related to the ultrasonic drying method might be individually patentably inventive. In particular, any disclosure in this specification for a range for a variable or parameter shall be taken to include a disclosure of any selectable or derivable sub-range within that range and shall be taken to include a disclosure of any value for the variable or parameter lying within or at an end of the range.

The singular may include the plural or and vice versa.