IES59369B2 - A method for producing plastics material - Google Patents

Description

The invention relates to a method for producing pellets of PVC material.

According to the invention there is provided a method for producing pellets of PVC material comprising the steps of activating a mixer at low mixing speed; adding solids into a solids weigher; delivering a desired weight of the solids into the mixer; releasing a bomb containing minor additives from a carousel into a mixer; heating the solids to a temperature of at least 70°C by frictional heat on mixing; delivering liquids including a plasticiser from liquid storage bins into a liquid weigher; delivering a desired weight of liquid into the heated solids in the mixer; S 5936 9 - 2 mixing the liquid and solid ingredients until the temperature of the mixture is increased to from 95 to 105°C to absorb the plasticiser; discharging the mixture from the mixer; cooling the mixture to between 60 and 70°C; delivering the cooled mixture to an intermediate container; delivering the mixture on demand from the intermediate container to a batch hopper; feeding the mixture from the batch storage hopper to a kneader feed hopper; kneading the mixture while removing air; extruding the mixture with an extruder screw; passing the extruded mixture through a die; cutting the die-formed extruded mixture into pellets; cooling the pellets in a fluidised bed cooler; sieving the cooled pellets to remove oversize material; recycling the oversize material to the kneader feed hopper;and packaging the pellets.

In a particularly preferred embodiment of the invention the method includes the step of adding masterbatch material to the recycle line of oversize material.

In a preferred arrangement the method includes the step of adding masterbatch material to the kneader feed hopper.

In a particularly preferred embodiment of the invention a portion of the cooled mixture is delivered into a tote bin for direct delivery to the kneader feed hopper.

In a preferred arrangement after delivery of a bomb of additive materials into the mixer, the carousel automatically indexes to the next position with a further bomb positioned over an inlet to the mixer for delivery of a bomb of additive materials to a following mixer batch.

In one embodiment of the invention solids are added to the solids weigher from a plurality of solids silos.

In another embodiment of the invention liquids are added to the liquid weigher from a plurality of different 5 containers.

In a preferred arrangement the method includes the step of sensing the temperature of the solids mixture and automatically adding the liquids to the mixer when the temperature has reached a preset value, which is typically 10 between 70 and 80°C.

In a preferred embodiment of the invention the method includes the step of sensing the temperature of the mixture in the mixer and heating the mixture if the temperature falls below 10°C to maintain the mixture fluid.

The invention will be more clearly understood from the following description hereof given by way of example only with reference to the accompanying drawing which is a flow chart of a method for producing pellets of PVC material according to the invention.

Referring to the drawings there is illustrated in flow chart form a method for producing pellets of PVC material according to the invention. Solid powder materials used in the method are stored in large silos 1 and solids are delivered on demand by a blower transfer system along feedlines 2 to associated hoppers 3 from which the solids are delivered, as required, along in-feed lines 4 to a solids weigher 5 for delivery to a mixer 6. The mixer 6 includes agitator blades 7 driven by a motor 8. Liquids used in the method of the invention are stored in tanks 10 from which the liquid is delivered on demand along in-feed lines 11 to a liquids weigher 12. Additional liquids are stored in smaller sized barrels 15 from which the liquids are pumped along lines 16 as required into the liquids weigher 12 for delivery into the mixer 6. Minor additives suitable for an individual batch are prepared in individual plastic bags or bombs 17 which are arranged on a carousel 18 for delivery of a bomb 17 into the mixer 6 through an inlet 19.

In the method of the invention the agitator blades 7 of the mixer 6 are first activated and desired weights of solids are delivered along the lines 4 into the solids weigher 5 until a preset weight has been delivered into the weigher 5. The contents of the weigher 5 are then introduced into the mixer 6. A bomb 17 is then automatically released from the carousel 18 and passes into the mixer 6 through the inlet 19. After delivery of a bomb 17 from the carousel 18 the carousel 18 automatically indexes to the next position with a further bomb 17 positioned over the inlet 19 to the mixer 6 for delivery of a bomb 17 of additive materials to a following mixer batch. The solids are mixed by the agitator blades until they have reached a temperature of at least 70°C, the heat being added by frictional heat mixing. When the desired temperature of the solids mixture has been reached desired quantities of desired liquids are delivered from the storage tanks 10 and barrels 15 along lines 11,16 into the liquid weigher 12 until a desired weight of liquids has been reached. The liquids are then automatically introduced into the mixer 6.

Mixing of the liquid and solid ingredients continues until the temperature of the mixture is increased to from 95°C to 105°C to absorb the plasticiser into the mixture. The temperature of the mixture of solids is sensed and a temperature controller 28 is used to automatically introduce from the liquids weigher when a preset temperature of between 7 0 and 80°C has been reached.

The method also includes the step of sensing the temperature of the mixture in the mixer 6 and a temperature controller 29 is used to automatically heat the mixture in the mixer if the temperature falls below 10°C. This is essential to maintain the mixture fluid and avoid blockage of the mixer. When the preset temperature of the mixture has been reached, it is discharged through an outlet 20 into a cooler 21 where the mixture is cooled f to a temperature of between 60°C and 70°C. The cooler 21 may be cooled by cooling water circulated by a pump 23 i from a storage tank 24 along a recirculation cooling line . Cooling water is circulated through a jacket 26 of the cooler 21.

The cooled mixture is delivered along line 30 to an intermediate hopper 31 from which the mixture is delivered on demand along line 32 to a batch storage hopper 35. The mixture is delivered on demand by an auger 36 to a kneader hopper 37 having an agitator 38 for delivering the mixture into a kneading screw 39 which kneads the mixture while removing air from the mixture along a vacuum line 40. The kneaded mixture is then delivered to an extruder screw 42 which extrudes the mixture. The extruded mixture is passed through a die 43 and the die-formed extrudate is cut into pellets of desired size by cutting blades 44.

The pellets are drawn along line 45 to a fluidised bed cooler 50 in which cooling air is drawn as illustrated by the arrows 51 through the pellets as they fall through the fluidised bed cooler 50. Cooled pellets discharged from . the fluidised bed cooler 50 are sieved in a sieve 55, * pellets of a size dictated by the sieve 55 being delivered along line 56 to a diverter valve 57 which directs the pellets either to a first hopper 58 for delivery to a bagging machine 59 or to a second hopper 60 for filling into boxes 61 for transport to a customer. Rework * material may be recycled from a debagging unit 63 either to the solids silos 1 or directly into the solids inlet 5 lines 2.

Oversize material which does not pass through the sieve 55 is delivered along a recycle line 70 to the outlet of the auger feed 36 to the kneader hopper 37. In this way any oversize or waste material is recycled as it is made. It 10 is not stored for future recycling. Thus maximum throughput is achieved and losses are minimised. For improved mixing with the material, masterbatch material is delivered from a first masterbatch hopper 75 by an auger screw feed 76 into the kneader hopper 37. Alternatively, 15 or additionally, masterbatch may be delivered into a hopper 7 8 for direct feed into the inlet of the recycle line 70 for improved mixing with in-feed material and higher quality.

For improved processing flexibility and maximum throughput 20 a portion of the material from the cooler 21 may be > delivered along line 80 to a tote bin 81 from which the material may be delivered directly by an auger feed to a 4’ kneader hopper 37 for further processing. Thus, optimum operating efficiency is attained.

The invention provides a method of preparing high quality PVC pellets in highly efficient manner at maximum throughput with minimum waste.

The invention is not limited to the embodiments hereinbefore described which may be varied in both construction and detail.

Claims (5)

1. A method for producing pellets of PVC material comprising the steps of :activating a mixer at low mixing speed; 5 adding solids into a solids weigher; delivering a desired weight of the solids into the mixer; releasing a bomb containing minor additives from a carousel into a mixer; 10 heating the solids to a temperature of at least 70°C by frictional heat on mixing; delivering liquids including a plasticiser from liquid storage bins into a liquid weigher; delivering a desired weight of liquid into the heated solids in the mixer; mixing the liquid and solid ingredients until the temperature of the mixture is increased to from 95 to 105°C to absorb the plasticiser; discharging the mixture from the mixer; 5 cooling the mixture to between 60 and 70°C; delivering the cooled mixture to an intermediate container; delivering the mixture on demand from the intermediate container to a batch hopper; 10 feeding the mixture from the batch storage hopper to a kneader feed hopper; kneading the mixture while removing air; extruding the mixture with an extruder screw; passing the extruded mixture through a die; 15 cutting the die-formed extruded mixture into pellets; cooling the pellets in a fluidised bed cooler; sieving the cooled pellets to remove oversize material; 5 recycling the oversize material to the kneader feed hopper;and packaging the pellets.

2. A method as claimed in claim 1 including the step of adding masterbatch material to the recycle line 10 of oversize material, preferably the method including the step of adding masterbatch material to the kneader feed hopper.

3. A method as claimed in any preceding claim wherein a portion of the cooled mixture is delivered into 15 a tote bin for direct delivery to the kneader feed hopper, preferably after delivery of a bomb of additive materials into the mixer, the carousel automatically indexes to the next position with a further bomb positioned over an inlet to the mixer for delivery of a bomb of additive materials to a following mixer batch, preferably solids are added to the solids weigher from a plurality of solids silos, preferably the liquids are added to the liquid weigher from a plurality of different containers, preferably the method including the step of sensing the temperature of the solids 5 mixture and automatically adding the liquids to the mixer when the temperature has reached a preset value, preferably between 70 and 80°C, preferably the method including the step of sensing the temperature of the mixture in the 10 mixer and heating the mixture if the temperature falls below 10°C to maintain the mixture fluid.

4. 4 . A method described drawing. as substantially with reference to as the hereinbefore accompanying 15

5. PVC pellets whenever prepared by a method as claimed in any preceding claims CRUICKSHANK & CO.,