WO1990008087A2

WO1990008087A2 - A particle applicator

Info

Publication number: WO1990008087A2
Application number: PCT/GB1990/000091
Authority: WO
Inventors: John Granville Kay
Original assignee: James Halstead Limited
Priority date: 1989-01-20
Filing date: 1990-01-22
Publication date: 1990-07-26
Also published as: AU4843690A; IE900231L; WO1990008087A3; GB8901268D0

Abstract

A particle applicator comprises a holder for the particles having an outlet at a compression zone defined by a roller with axially extending pockets arranged to rotate past a coating pressure surface for pressing the particles into the pockets so as to achieve an accurately metered supply of particles from said applicator.

Description

A PARTICLE APPLICATOR

The invention relates to a particle applicator particularly but not exclusively for use in the manufacture of thermoplastics (preferably polyvinyl chloride - PVC) flooring by a technique involving sprinkling of particles (known as chips) of the thermoplastics material onto a support web to form a layer which is then subjected to heat and pressure so as to weld the particles together into a coherent sheet which is then stripped from the support web.

It is desirable but very difficult to sprinkle the chips onto the support web into a layer of uniform thickness such that the coherent sheet does not require to be subjected to a grinding operation to achieve the requisite uniformity of thickness. Provided that the particles deposition can be accomplished with an accuracy of 2% over the entire layer (i.e. that the variations in level of the upper surface of the layer are no more than 2% of the total thickness of the layer) a finishing grinding operation may be avoided. However it has hitherto proved impossible to achieve such accuracy by conventional techniques.

It is an object of the present invention to provide apparatus whereby such accuracy may be achieved.

A further difficulty with the deposition of particulate material onto a carrier is that the heavier particles will usually be deposited first and the lighter dust particles (if any) will follow to form a surface layer which detracts from the appearance of the final product.

It is a further and independent object of the present invention to obviate or mitigate this disadvantage.

According to a first aspect of the present invention there is provided a particle applicator comprising a holder for the particles having an outlet at a compression zone defined by a roller with axially extending pockets arranged to rotate past a coacting pressure surface for pressing the particles into the pockets so as to achieve an accurately metered supply of particles from said applicator.

According to a second aspect of the present invention there is provided either independently or in conjunction with the aforesaid applicator, a dust separator comprising in combination with means for feeding dust-contaminated particulate material, an inclined perforated surface for receiving said material from said feeding means and directing it onto a conveyor over at least part of the transverse extent thereof, the size of said perforations being selected such that dust can penetrate said surface to fall onto said conveyor in advance of said particles, and the inclined length of said surface being such that the particles fall onto the conveyor after the dust so as to cover the same.

According to a third aspect of the present invention there is provided either independently or in conjunction with the aforesaid applicator, a settling device comprising a plurality of mutually inclined surfaces arranged one above the other so as to enable the particles to cascade from the uppermost surface (receiving the material deposited from the roller) onto the successive lower surfaces, the inclination of said surfaces and their friction coefficient being so selected that dust and other fines slide down successive surfaces at a rate approximating to the rate of decent of the particles thereby encouraging the dust and other fines to settle at the same rate as the particles and avoiding delayed dust settlement.

The invention will now be further described by way of example with reference to the accompanying drawings, in which:-

Fig. 1 is a diagrammatic view from the side of apparatus incorporating both features of the invention, and

Fig. 2 is an alternative design for the lower part of Fig. 1.

Referring now to Fig. 1 of the drawings, a support frame 1 mounts a particle applicator 2 above a dust separator 3 which is in turn located above a conveyor 4 travelling in the direction of Arrow A. A supply 5 of dust contaminated particles is contained in a hopper 6 which provides a gravity feed to a compression zone 7 defined by a rotary roll 8 and a normally stationary roll 9 mounted on respective axes extending transversely of the conveyor 4. The roll 8 has axially extending peripheral grooves or pockets 9 defined by equi-angularly spaced ribs 10. The roll 9 has wear-resistant pressure elements 11, 12 at diametrically opposed locations on its peripheral surface one of which, in this case 11, is positioned at the compression zone 7 for coacting with the pockets 9 as will be described. When the element 11 is worn the roll 9 may be rotated to bring the element 12 into use.

Particulate material delivered by the applicator 2 falls onto the dust separator 3 which has a receiving surface 13 which is downwardly and forwardly inclined as seen in the direction of travel of the conveyor 4. The receiving surface 13 is provided by a perforated metal sheet the size of the perforations being so selected that dust may pass through the surface 13 whereas particles are retained thereon until they fall off the free forward edge. A diffuser mesh 14 permitting the passage of both particles and dust is provided under the surface 13.

In operation, particles 5 from the hopper 6 descend into the compression zone 7 to fill the pockets 9 which are subjected to a uniform filling pressure during their successive rotation past the pressure element 11. On emergence from the pressure zone 7 the filled pockets 9 are inverted to release their contents onto the perforated surface 13 of the dust separator 3 the effect of which is to permit dust to descend through the diffuser mesh 14 and onto the conveyor 4 in advance of the particles which take a longer path to the same destination with the consequence that the particle layer formed on the conveyor 4 comprises an underlying stratum of dust which is therefore concealed in the final product.

An intended application of the apparatus described above is in the production of thermoplastics flooring in which the particles 5 would be chips of thermoplastics, e.g. polyvinyl chloride (PVC) material of irregular flat shape with a maximum dimension of up to about 8mm and a thickness of around 2mm. The flow of such flat chips into the compression zone 7 from the hopper 6 has the effect of orienting the chips with their major surfaces in generally vertical planes for ready reception by empty pockets 9 entering the compression zone 7. In this case the width of the pockets (circumferentially of the roll 8) is about 10mm whereas the depth of the ribs (radially of the roll) is about 3mm. It will be obvious that the perforations in the surface 13 of the dust separator 3 are dimensioned to prevent passage of the chips of the size specified. The diffuser mesh 14, by contrast, has perforations exceeding the size of the chips so as to permit passage both of the chips and the accompanying dust.

A brush (not shown) contacting the lower part of the roll 8 may be provided for the discharge of static electricity so as to ensure complete emptying of the pockets 9.

Referring now to Fig. 2, the apparatus shown therein is illustrated in the same orientation as the dust separator 3 in Fig. 1, i.e. with the conveyor 4 travelling in the direction from right to left as indicated by the arrow A. Whereas the dust separator 3 of Fig. 1 operates by delaying deposition of the particles until the dust has settled, the apparatus of Fig. 2 operates by delaying particle deposition and accelerating dust deposition such that the dust settles no later than the particles and is preferably distributed throughout the thickness of the particle layer without however forming a surface layer which detracts from the appearance of the final product. The apparatus of Fig. 2 comprises an arrangement of slide surfaces that are preferably adjustable transversely of the conveyor 4 so as to accommodate different deposition widths. Particulate material from the pockets 9 falls in a stream indicated by arrow 15 and strikes a surface 16 provided by a blade 17. The velocity of the particles is such that they rebound from the surface 16 onto an opposed surface 18 of a blade 19 as indicated by arrow 20. The blades 17 and 19 are downwardly inclined towards each other with the blade 19 passing beneath the blade 17 with a substantial clearance. The particles travel downwardly on the surface 18 and may rebound onto the opposing surface 21 and back again as indicated by the arrows 22, 23 ultimately passing downwards to a discharge opening 24 as indicated by arrows 25 and 26. The surface 21 is provided on a downwardly inclined blade 27 substantially parallel to the blade 17. The surfaces 16, 18 and 21 are preferably coated with low friction material such as PTFE in order to encourage rapid downward travel thereon of dust and other fines deposited on the surface 16 with the particles 15 from the roll 8. The dust and fines thus slide rapidly down the 4 surfaces 16, 18 and 21 to arrive at the conveyor 4 with the particles and avoid the accumulation of dust on such surfaces which would otherwise tend to deposit as a final layer on the particulate layer so detracting from the appearance of the latter.

Claims

1. A particle applicator comprising a holder for the particles having an outlet at a compression zone defined by a roller with axially extending pockets arranged to rotate past a coating pressure surface for pressing the particles into the pockets so as to achieve an accurately metered supply of particles from said applicator.

2. An applicator as claimed in claim 1, wherein the coacting pressure surface is provided on a cooperating stationary pressure roll.

3. An applicator as claimed in claim 2, wherein the pressure roll has a further pressure surface remote from said compression zone and the pressure roll is rotatable so as to bring said further pressure surface into the compression zone when wear of the first mentioned pressure surface has occurred.

4. An applicator as claimed in any one of the preceding claims, wherein each pocket is approximately 10mm wide and 3mm deep.

5. An applicator as claimed in any one. of the preceding claims further comprising a dust separator arranged below said roller for receiving dust-contaminated particulate material therefrom, said separator including an inclined perforated surface for receiving said material and directing it onto a conveyor over at least part of the transverse extent thereof, the size of said perforations being selected such that dust can penetrate said surface to fall onto said conveyor in advance of said particles, and the inclined length of said surface being such that the particles fall onto the conveyor after the dust so as to cover the same.

6. An applicator as claimed in any one of claims 1 to 4, further comprising a settling device comprising a plurality of mutually inclined surfaces arranged one above the other so as to enable the particles to cascade from the uppermost surface (receiving the material deposited from the roller) onto the successive lower surfaces, the inclination of said surfaces and their friction coefficient being so selected that dust and other fines slide down successive surfaces at a rate approximating to the rate of decent of the particles thereby encouraging the dust and other fines to settle at the same rate as the particles and avoiding delayed dust settlement.

7. A dust separator comprising in combination with means for feeding dust-contaminated particulate material, an inclined perforated surface for receiving said material from said feeding means and directing it onto a conveyor over at least part of the transverse extent thereof, the size of said perforations being selected such that dust can penetrate said surface to all onto said conveyor in advance of said particles, and the inclined length of said surface being such that the particles fall onto the conveyor after the dust so as to cover the same.

8. A settling device comprising in combination with means for feeding dust-contaminated particulate material, a plurality of mutually inclined surfaces arranged one above the other so as to enable the particles to cascade from the uppermost surface onto the successive lower surfaces, the inclination of said surfaces and their friction coefficient being so selected that dust and other fines slide down successive surfaces at a rate approximating to the rate of decent of the particles thereby encouraging the dust and other fines to settle at the same rate as the particles and avoiding delayed dust settlement.