Method of manufacturing a moulded pulp product and pulp moulding apparatus

Abstract

Method of manufacturing a moulded pump product. The method includes activating a vacuum source, injecting an amount of pulp into the internal mould chamber through the mould opening, thereby forming a pulp preform on the internal mould surface, injecting a dewatering and heating fluid through the mould opening at gradually increasing pressure until a maximum pressure, thereby performing a dewatering and drying step whereby the pulp preform on the internal mould surface is dewatered and dried, deactivating the injection of dewatering and heating fluid, deactivating the vacuum source, and extracting the moulded pulp product. An option further step includes initiating rotation of the mould about the central axis thereof and increasing rotational speed gradually, maintaining a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step, decreasing rotational speed gradually until standstill of the mould.

1 . A method of manufacturing a moulded pulp product using a pulp moulding apparatus including a mould with an internal mould chamber generally having rotational symmetry about a central axis of the mould and having a closed end and an open end forming a mould opening, the internal mould chamber having an internal mould surface generally provided with a number of evacuation openings connected to a vacuum source, the method including the following steps of:
 activating the vacuum source,   injecting an amount of pulp into the internal mould chamber through the mould opening, thereby forming a pulp preform on the internal mould surface,   injecting a dewatering and heating fluid through the mould opening at gradually increasing pressure until a maximum pressure, thereby performing a dewatering and drying step whereby the pulp preform on the internal mould surface is dewatered and dried,   deactivating the injection of dewatering and heating fluid,   deactivating the vacuum source,   extracting the moulded pulp product,   initiating rotation of the mould about the central axis of the mould and increasing rotational speed gradually,   maintaining a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step,   decreasing rotational speed gradually until standstill of the mould.   
     
     
         2 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the apparatus includes a rotary union having a rotatable fluid port connected to the mould opening, a stationary pulp port and a stationary dewatering and heating fluid port, wherein pulp is injected into the internal mould chamber through the stationary pulp port, and wherein the dewatering and heating fluid is injected into the internal mould chamber through the stationary dewatering and heating fluid port. 
     
     
         3 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the mould is arranged inside a vacuum chamber connected to the vacuum source, and wherein the rotatable fluid port of the rotary union is connected to the mould opening through a tube extending through a wall of the vacuum chamber by a rotary shaft seal. 
     
     
         4 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the relative injection pressure of the dewatering and heating fluid through the mould opening is increased gradually from approximately 0 to minimum 500 kPa, or from approximately 0 to minimum 700 kPa, or from approximately 0 to minimum 1 MPa. 
     
     
         5 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the relative injection pressure of the dewatering and heating fluid through the mould opening is increased gradually with a pressure rate of dp/dt=1 to 20 kPa/s in the range p=0 to 200 kPa and with a pressure rate of dp/dt=1 to 50 kPa/s in the range p=200 to 400 kPa. 
     
     
         6 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the rotational speed of the mould is increased gradually from 0 rpm to at least 5.0005000 rpm, or from 0 rpm to at least 7.0007000 rpm, or and from 0 rpm to about 10.00010000 rpm. 
     
     
         7 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein the rotational speed (r) of the mould is increased gradually with a rotation rate of dr/dt=10 to 1000 rpm/s until a maximum rotational speed. 
     
     
         8 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein simultaneous injection of dewatering and heating fluid and
 mould rotation is maintained for at least 10 seconds, or for at least 20 seconds, or for at least 40 seconds, or for about 1 minute.   
     
     
         9 . A method of manufacturing a moulded pulp product according to  claim 1 , wherein fluid is evacuated to an outer surface of the mould through inner evacuation openings on the internal mould surface, and wherein each inner evacuation opening is connected to an outer evacuation opening on the outer surface of the mould by means of an evacuation channel having a gradually increasing cross-sectional area in the direction from the internal mould surface to the outer surface of the mould. 
     
     
         10 . A pulp moulding apparatus for manufacturing of moulded pulp products including a mould with an internal mould chamber generally having rotational symmetry about a central axis of the mould and having a closed end and an open end forming a mould opening, the internal mould chamber having an internal mould surface generally provided with a number of evacuation openings, a vacuum source connected to said evacuation openings, a pressurised pulp source arranged to inject pressurised pulp into the internal mould chamber through the mould opening, a dewatering and heating fluid source arranged to inject de-watering and heating fluid through the mould opening at gradually increasing pressure in order to perform dewatering and drying of a pulp preform on the internal mould surface, wherein the apparatus includes a rotary union having a rotatable fluid port connected to the mould opening, a stationary pulp port and a stationary dewatering and heating fluid port, in that the pressurised pulp source is connected to the stationary pulp port, in that the dewatering and heating fluid source is connected to the stationary dewatering and heating fluid port, in that a motor is arranged to rotate the mould about the central axis of the mould, and in that the pulp moulding apparatus is adapted to initiate rotation of the mould about the central axis of the mould and increase rotational speed gradually, maintain a maximum rotational speed of the mould at least during a substantial part of the dewatering and drying step, and decrease rotational speed gradually until standstill of the mould. 
     
     
         11 . A pulp moulding apparatus according to  claim 10 , wherein the mould is arranged inside a vacuum chamber connected to the vacuum source, and wherein the rotatable fluid port of the rotary union is connected to the mould opening through a tube extending through a wall of the vacuum chamber by a rotary shaft seal. 
     
     
         12 . A pulp moulding apparatus according to  claim 10 , wherein the mould has inner evacuation openings through which fluid may be evacuated to an outer surface of a mould wall, and wherein each inner evacuation opening is connected to an outer evacuation opening on the outer surface of the mould by means of an evacuation channel having a gradually increasing cross-sectional area in the direction from the internal mould surface to the outer surface of the mould.