Patent Description:
A system of calibration matrices closest to the present invention is known from the European patent <CIT>. This patent describes a system and method for extruding profiles made of reprocessed unidentified mixed plastic waste.

The system of calibration matrices known from this patent comprises four consecutive calibration matrices, whereby each calibration matrix has been formed of a bottom, a cover and the sides between them, which comprise cooling channels and form upon mutual rigid connection the inner chamber running in longitudinal direction of the calibration matrix between the bottom, the cover and the sides, the shape of cross section of which conforms to the extruded plastic profile.

In the direction of movement of the extruded profile, each following calibration matrix has an inner chamber with a cross section, which is <NUM> larger than in the previous one, whereby the cross section of the last calibration matrix in the direction of extrusion (i.e. the size of the profile) has the same dimensions as the extruded final product (profile).

The described solution has several deficiencies. First, each calibration matrix comprises at least four separate details, the precise manufacturing and assembly of which makes the production of the respective calibration matrix expensive and time-consuming. Furthermore, in this solution, the cross section of the inner chamber of every following calibration matrix should be made larger than the previous one, which makes the production of the entire system complicated and expensive, and does not allow mutual exchange of the calibration matrices. In addition, two larger <NUM> calibration matrices are extremely difficult to handle by the operator, requiring lifting mechanisms or at least two persons for installation and opening.

Furthermore, this solution does not provide sufficient surface smoothness to the extruded plastic profile, which is necessary, for example, for its coating with a laminated layer or qualitative differentiation, for example, from similar plastic profiles produced with a die casting method. This is due to the fact that plastics with different melting temperature in the mixture adhere to the surface of the inner chamber of the calibration matrix, causing uneven and rough surface of the extruded profile.

In the case of calibration matrices located continuously without gaps, it is also impossible to control surface quality of the extruded profile, or if the profile fills perfectly the calibration matrix, before exiting from the last calibration matrix. <CIT> discloses a sizing matrix for an extruded product, where said matrix comprises four separate parts, an upper block, a lower block and first and second core blocks. In said matrix a cooling liquid is directed through a plurality of guide holes between the extruded product and surfaces of inner chamber of the matrix and thus the friction between said surfaces and extruded product is decreased. <CIT> discloses a method for producing extruded profiles, where several consecutive calibration matrices are used, each matrix comprising a bottom half and upper half and an inner chamber between them. In order to increase wear resistance and corrosion resistance of the surfaces of the inner chamber, said surfaces are subject to electrochemical treatment to obtain on their surface an oxide anodic coating, known as "hard anodizing". The disadvantage of said solution is that when reprocessed plastic is used, which contains impurities, said impurities would become into direct contact of the surfaces of inner chamber of the matrix, thus damaging said surfaces. A disadvantage of said solution is that said matrices do not contain interchangeable parts, because in this solution individual matrices have different lengths. Also, a common disadvantage of solutions <CIT> and <CIT> is that when reprocessed plastic is used, which usually contains impurities, said impurities would become into direct contact of the surfaces of inner chamber of the matrix, thus damaging said surfaces. Reconditioning said surfaces requires specialized equipment, making said process laborious and expensive.

The present invention is intended for extruding profiles made of raw material (agglomerate, pellets, crushed pieces, etc.) mixed based on a respective recipe, reprocessed from unrefined plastic, such as LDPE, HDPE, PE, PP, PS and ABS. This is not a mixed plastic comprised of unidentified plastic waste, but mixture of reprocessed plastics of relevant type (LDPE, HDPE, PE, PP, PS, ABS), into which colorants, stabilizer/stabilizers (e.g. for protection against UV radiation and thermal decomposition), blowing agent, absorbent or other additives and pure (i.e. fresh) plastic may be added, if necessary.

Although all used abbreviations are standard and have been used in the field for a long time, it should be mentioned for the sake of clarity that the above abbreviations mean the following plastics:.

A typical system for extruding profiles from raw material comprising reprocessed plastic waste comprises a continuously operating extruder, followed by a system of calibration matrices, where solidification of molten plastics takes place, along with the provision of the required cross section to the extruded profile and calibration and the primary cooling of the extruded profile.

The system of calibration matrices is followed by a cooling tank, through which the extruded profile is fed, and where additional cooling of the profile takes place.

The cooling tank is followed by the pull-through device (more specifically a so-called pultrusion device), which feeds the profile through the calibration matrices and cooling tank to the cutting device, where the extruded profile is cut into details with predetermined length.

The deficiencies of prior art are eliminated with the system of calibration matrices for extruding plastic profile comprising several consecutive calibration matrices on a common base, wherein each calibration matrix comprises a bottom half of the calibration matrix and an upper half of the calibration matrix, whereby both upper as well as bottom half comprise cooling channels.

An inner chamber running in longitudinal direction of the calibration matrix is formed between the upper half and bottom half of the calibration matrix in the assembled position of upper half and bottom half, the cross section of which conforms to the extruded profile, the surface of which is coated with anti-adhesive antifriction material.

There is an observation gap between at least some consecutive calibration matrices, whereby the mentioned observation gaps are preferably located between consecutive calibration matrices outside the solidification zone of plastic profile in the direction of extrusion.

The anti-adhesive antifriction material is preferably a glass fibre fabric or tape with a self-adhesive layer coated with polytetrafluoroethylene (PTFE; Teflon®) adhered to the surface of the inner chamber.

The system of calibration matrices preferably comprises at least two calibration matrices.

In the direction of extrusion of the plastic profile, the upper and bottom halves of the first calibration matrix are mutually detachably rigidly connected in the compression and solidification zone of the plastic profile, and outside the solidification zone of the plastic profile, the upper and bottom halves of the remaining calibration matrices are held together during extrusion with the pressure applied to the upper halves by pneumatic or hydraulic cylinders or any other mechanism with a similar purpose.

Cooling and calibration zones with different temperatures are preferably formed in the calibration matrices separated with an observation gap.

The pneumatic or hydraulic cylinders or any other mechanism with a similar purpose are preferably configured to lift the upper halves of the calibration matrices up from the bottom halves to enable quick access to the inner chamber.

In a preferred embodiment, the first cooling and compression zone is located in the first calibration matrix.

In a preferred embodiment, at least some calibration matrices of the system are made as similar exchangeable modules.

The number and length of calibration matrices depends on the complexity and the cross section of the extruded profile. If the required cross section and temperature of the profile are achieved with shorter and fewer calibration matrices, it is possible. Extrusion speed, length and number of calibration matrices, and cross section of extruded profile are also related. Longer cooling process is needed for retaining the speed of production of the profile.

As a technical example, calibration matrices with various lengths have been used, e.g. <NUM>, <NUM> and <NUM>. Combined into a system of matrices with different lengths, they have all provided the required result.

Even more preferably, all calibration matrices of the system have been made as similar exchangeable modules, which would enable fast exchange of module, e.g. in case of damage of the glass fibre fabric or tape with a self-adhesive layer coated with polytetrafluoroethylene (PTFE; Teflon®) adhered to the surface of the inner chamber.

The present invention further provides a calibration matrix for use in the above described system of calibration matrices for extruding a plastic profile, comprising a bottom half of the calibration matrix and an upper half of the calibration matrix, where both upper and bottom halves comprise cooling channels, wherein an inner chamber running in longitudinal direction of the calibration matrix is formed between the upper half and bottom half of the calibration matrix in the assembled position of the upper half and bottom half, the cross section of which conforms to the extruded profile and the surface of which is coated with anti-adhesive antifriction material, which is preferably a glass fibre fabric with a self-adhesive layer coated with polytetrafluoroethylene (PTFE; Teflon®) adhered to the surface of the inner chamber.

The present invention is further described with exemplary embodiments, with references to accompanying schematic figures, where:.

<FIG> is a simplified view, for the sake of clarity (i.e. without connection hoses of coolant connected to the calibration matrices and other equipment), of a possible system for extruding profiles from raw material comprising reprocessed plastic waste. It comprises a continuously operating extruder <NUM> with e.g. one worm, followed by the system of calibration matrices <NUM> where the solidification of molten plastics takes place, along with provision of the required cross section to the extruded profile and calibration and the primary cooling of the extruded profile.

The system of calibration matrices <NUM> is followed by a cooling tank <NUM> with cooling water, through which the extruded profile is fed, ensuring its additional cooling.

The cooling tank <NUM> is followed by the pull-through device <NUM>, which feeds the profile through the calibration matrices <NUM> and cooling tank <NUM> to the cutting device <NUM>, where the extruded profile is cut into details with a predetermined length. Further on, a collection unit of cut details will follow (not depicted).

The system of calibration matrices <NUM> of the invention depicted in <FIG> comprises in the depicted embodiment six calibration matrices <NUM> fixed onto a common base <NUM>. In the depicted embodiment, the leftmost calibration matrix <NUM> is rigidly fixed to the extruder <NUM> nozzle through a seal.

Molten plastic mass is pressed from the extruder <NUM> into the inner chamber <NUM> of the first calibration matrix <NUM>, the cross-section profile of which conforms to the shape of the extruded plastic profile and which is the first cooling zone of the profile. In the depicted embodiment, three first calibration matrices <NUM>, <NUM>, and <NUM> are connected tightly endways together, as the solidification and compression of molten plastic is still taking place inside them. Upper halves <NUM> and bottom halves <NUM> of the mentioned calibration matrices <NUM>, <NUM>, and <NUM> are rigidly mutually connected together, as otherwise the pressure of molten plastic would press the mentioned halves apart. The following calibration matrices <NUM>, <NUM>, and <NUM> are located in relation to the previous matrices in such way that there is an observation gap <NUM> between the calibration matrices <NUM> and <NUM>, <NUM> and <NUM>, and <NUM> and <NUM>.

Calibration matrices <NUM> (<NUM>-<NUM>) consist of a bottom half <NUM> and an upper half <NUM>. In the assembled position (<FIG>), the inner chamber <NUM> is formed between them, the surface of which is coated with anti-adhesive antifriction material <NUM> - the edges of this material <NUM> are turned onto the ends of the calibration matrices <NUM>.

Both halves <NUM> and <NUM> comprise cooling channels <NUM>. In addition, there are alignment pins <NUM> between the halves <NUM> and <NUM>, and for example, the end surface of the bottom half <NUM> has apertures <NUM> for the pins.

<FIG> show a following embodiment of the calibration matrix of the invention, which is intended for extruding a so-called matchboard profile, which is relatively thin - similar details are numbered on these figures as on <FIG>.

<FIG> show a third embodiment of the calibration matrix of the invention, which is intended for extruding a so-called round profile, which is relatively thick - similar details are numbered on these figures as on <FIG>.

Calibration matrix <NUM> is made of steel or aluminium alloy, which efficiently conducts heat away from the surface of the profile, e.g. alloy AA7075.

Antifriction material <NUM> is a glass fibre fabric (tape) with a self-adhesive layer coated with polytetrafluoroethylene (PTFE - Teflon®) adhered to the surface of the inner chamber <NUM>.

If foreign bodies (metal pieces, stones, etc.) present in the reprocessed plastic cause damage to the coating of the mentioned antifriction material <NUM>, the operator can see immediately through the mentioned observation gap <NUM> any traces on the surface of the extruded profile, or if the calibration mould is completely filled by the profile (cavities, etc.), and the extrusion process can be stopped, halves <NUM> and <NUM> of corresponding calibration matrix <NUM> can be detached, and antifriction material <NUM> or corresponding calibration matrix <NUM> can be replaced.

In the system of calibration matrices <NUM> of <FIG>, the upper halves <NUM> of calibration matrices <NUM>-<NUM> are pressed onto the bottom halves <NUM> with pneumatic cylinders <NUM>. The cylinders <NUM> also enable fast lifting of the upper halves <NUM> from the bottom halves <NUM> and thus fast access to the inner chamber <NUM>.

It is clear for a person skilled in the art that instead the mentioned pneumatic cylinders, it is possible to use hydraulic cylinders or any other mechanism with a similar purpose, such as an articulated mechanism with an electric drive.

In a preferred embodiment, in the system of calibration matrices <NUM>, the calibration matrices <NUM>-<NUM> are made as similar exchangeable modules. This simplifies their production and for example, such embodiment also enables keeping one such module in store for the fast replacement of a module with damaged coating of anti-friction material <NUM>. The modular construction consisting of two halves <NUM> and <NUM> also reduces essentially the cost of calibration matrix <NUM>.

Depending on the composition of the used reprocessed plastic, it may expand slightly when passing through the calibration matrices. To minimize this, intermediate sheets (not depicted) with thickness up to <NUM> can be inserted between the upper half <NUM> and the bottom half <NUM> of the calibration matrices <NUM>, <NUM> and <NUM> to decrease the pressure applied by the upper and bottom halves <NUM> and <NUM> of the calibration matrices <NUM>, <NUM> and <NUM> from the side of surfaces of the inner chamber <NUM> to the extruded profile, and to enable the profile to pass through these calibration matrices more easily. In such way, all single calibration matrices can be manufactured with the same dimensions, i.e. mutually exchangeable, and e.g. in the case of a flat matchboard profile, the pressure applied to the extruded profile by rearward calibration matrices in the direction extrusion can be minimized, if necessary.

The calibration matrix of <FIG> is intended for manufacturing an extruded matchboard profile, which is relatively thin (see <FIG>), and therefore it is also suitable for extruding reprocessed plastic, which comprises e.g. following in percentage by weight:.

The calibration matrix of <FIG> is intended for manufacturing an extruded round profile, which is relatively thick (see <FIG>), and therefore, it is also suitable for extruding reprocessed plastic, which comprises e.g. following in percentage by weight:.

Claim 1:
A system (<NUM>) of calibration matrices (<NUM>) for extruding a plastic profile, said system comprising several consecutive calibration matrices (<NUM>),
each calibration matrix (<NUM>) comprises a bottom half of the calibration matrix (<NUM>) and an upper half of the calibration matrix (<NUM>), wherein both upper as well as bottom halves (<NUM>, <NUM>) comprise cooling channels (<NUM>),
wherein an inner chamber (<NUM>) running in the longitudinal direction of the calibration matrix (<NUM>) is formed between the upper half and bottom half (<NUM>, <NUM>) of the calibration matrix in the assembled position of the upper half and bottom half (<NUM>, <NUM>), the cross section of which conforms to the extruded profile and
the surface of which is coated with anti-adhesive antifriction material (<NUM>) wherein there is an observation gap (<NUM>) between at least some consecutive calibration matrices,
characterized in that the anti-adhesive antifriction material (<NUM>) is a glass fibre fabric or tape with a self-adhesive layer coated with polytetrafluoroethylene (PTFE) adhered to the surface of the inner chamber (<NUM>).