A MATERIAL, METHOD AND APPARATUS FOR POLISHING PARTS

Abstract: The invention relates to a method and apparatus for polishing parts which have at least one cavity (14) to be polished, said parts (12) being in the form of moulds for the production of plastic items, and the cavity (14) to be polished being the shaped mould for the item. The method envisages the preparation of a polishing mixture (13), which is then brought into contact with the surface of the cavity (14) to be polished, the polishing mixture (13) being moved, for a preset time, relative to the surface to be polished. The polishing mixture (13) is advantageously inserted in the cavity (14) in the part (12), which is an element for containing the polishing mixture (13). The present invention also relates to a composition of the present polishing mixture (13).

Description: Description A material, method and apparatus for polishing parts Technical Field The present invention relates to a mixture, a method and an apparats for polishing parts which have at least one cavity to be polished The present invention is preferably applied to parts m the form of moulds or portions of moulds for the production of plastic items, where the cavity to be polished is the shaped mould for the item. Background Art Metal parts are currently polished by barrel cleaning. A tumbling barrel or container is filled with disassembled parts and a cleaning mixture or material designed to abrade the surface of the corresponding wall of the parts, polishing its surface The relative movement of the surfaces to be polished and the cleaning mixture is obtained by causing the hermetically sealed container to keep rotating for a given time. Barrel cleaning carried out m accordance with the prior art is not only expensive due to the fact that it requires the use of a special machine with a large container for the parts and the use of a large amount of polishing material, but m addition does not allow selective polishing of the various areas of the part This is a problem, for example, for portions of moulds in which there are reference surfaces which guide the various mould parts and hold them in their reciprocal positions, and whose abrasion following repeated barrel cleaning operations leads to the production of defective plastic items Such types of moulds are used, for example, for the production of PET bottles Disclosure of the Invention The aim of the present invention is, therefore, to overcome the above-mentioned disadvantages individually or as a whole The technical features of the present invention, in accordance with the above-mentioned aims, are set out m the claims herein and the advantages more clearly illustrated in the detailed description which follows, with reference to the accompanying drawing, which illustrates a preferred embodiment, without limiting the scope of its application. In accordance with the present method for polishing parts which have at least one cavity to be polished, in particular parts in the form of moulds or portions of moulds for the production of plastic items m which the cavity to be polished is the shaped mould for the item, the method envisages the preparation of a polishing mixture, which is then brought into contact with the surface of the cavity to be polished and the movement of the polishing mixture relative to the surface to be polished for a preset time. The method advantageously envisages the insertion of the polishing mixture in the cavity in the part, which is specially designed to define an element for containing the polishing mixture. This avoids the use of excessive amounts of polishing material. The quantity which can be inserted m the cavity whose surfaces are to be polished is sufficient. As is explained below, the cavity has an upper lip. In accordance with another advantageous feature of the method, the polishing mixture is inserted up to a level which is above the upper lip of the cavity. In accordance with another characteristic of the present invention, when the polishing mixture has been inserted in the cavity, the part is subjected to vibration. According to the method, an advantageous polishing result is obtained by using a dry polishing mixture consisting of a percentage weight varying between 50 and 80% of metal pellets, or abrasive ceramic elements, or abrasive plastic elements, and a percentage weight of from 20 to 50 of an abrasive which is normally in powder form. The use of such a dry mixture, suitably moved within the non- linear path of the cavity, allows noticeable polishing of all points of the item moulding cavity. Moreover, it has be observed that the addition of a given percentage of water improves the amalgamation of the abrasive on the metal pellets and facilitates the action which brings it into contact with the surfaces to be polished. The wet polishing mixture preferably consists of a 70 to 90% percentage weight of metal pellets, or abrasive ceramic elements, or abrasive plastic elements, between 5 and 20% abrasive and from 3 to 10% water. The addition of between 3 and 10% of polish is also possible. For example, a liquid detergent, which increases material detachment and gives the cavity a more glossy finish after polishing. Tests have revealed that an optimum composition of the polishing mixture which allows the most remarkable polishing result to be obtained consists of an 80% percentage weight of metal pellets, 10% abrasive, 5% polish and 5% water. The metal pellets advantageously consist of copper pellets with various shapes, for example, rhomboid, triangular and cylindrical, with a larger dimension of between 3 and 6 mm The abrasive ceramic elements or bodies, or the abrasive plastic elements or bodies may have similar or greater dimensions. The length of the polishing treatment is preferably between 6 and 20 hours. With reference to the accompanying drawing, a preferred embodiment 10 of an apparatus made according to the present invention comprises a base or support table 16 for a plurality of parts to be polished 12. As illustrated, the table is mounted on springs 17 on a fixed base 15. Advantageously, use of the present apparatus envisages the insertion of the polishing mixture in the cavity 14 of the parts 12 m such a way that the latter define container elements for the polishing mixture 13. Means which are able to cause the parts 12 to vibrate are envisaged m order to move the polishing mixture relative to the surface to be polished. In particular, as shown in the only illustration, the vibrating means consist of a vibrator 22, applied to the table 16, which is switched on m order to make the table 16 vibrate. A vibration is transmitted to the part, causing the polishing material to rotate m a direction of circulation which results m direct contact between the effective side of the abrasive current and a first face of the cavity in the part (indicated by the arrows m the illustration) . This is due to the fact that the vibration on the table has a horizontal vibration parallel with the table and a jerking vibration perpendicular to tne table. In order to evenly polish the entire circumferential surface of the cavity, the table vibration s interrupted, at preset intervals, and the part turns through a preset angle until the surface is completely polished. Alternatively, the polarity of rotation of the vibration motor may be inverted, m order to invert the direction of rotation of the polishing material circulating in the cavity. This allows polishing of all circumferential walls, particularly those of small parts. This operating solution can be obtained thanks to the fact that, in the present apparatus, the device which imparts the vibration to the table comprises a rotary vibrating shaft, with weights which are offset relative to the axis of the shaft, positioned so that the axis is parallel with the table. The present apparatus avoids the use of the expensive and bulky tumbling barrels referred to in the prior art. For each part 12, there are special means for hermetically sealing the cavity 14, consisting of an upper lid 18 shaped m such a way that it extends upwards, defining an upper expansion chamber 20 for the polishing mixture 13 inserted m the cavity 14 This shape advantageously allows the insertion of the polishing mixture up to a level which is above the upper lip of the cavity 14, allowing complete polishing of all surfaces of the cavity 14 to be polished. The upper lid comprises a first ring-shaped element 18' and an upper disc-shaped sealing element 18'' The polishing material 13 is inserted m the part before the upper disc-shaped element 18'' is put m place. The sealing means are hermetically sealed and the part is fixed to the table using a single plate 21 for each part, positioned above the part and lid, and held on the table 16 by extended legs 23, threaded at the ends on which locknuts 25 are screwed. As shown in the illustration, the ring-shaped portion 18' of the means 18 for sealing the cavity 14 forms means or portions 22 which extend to cover and protect those areas of the part 12 located m the cavity 14 which must not be polished. In this way, the polishing operation is prevented from causing unwanted wear on positioning or contact areas required for the good operation of the mould. The present method is clearer with reference to the following examples . Example 1 A wet polishing mixture is used, consisting of a percentage weight of 80% copper pellets with a length of 4 mm, 10% powder abrasive, such as Rollwash Dialbπl (brand name) , 5% liquid polish, such as Rosier CL30 (brand name) and 5% water. The part is subjected to vibration. The treatment time is 12 hours. Example 2 A dry polishing mixture is used, consisting of a percentage weight of 50% copper pellets with a length of 6 mm and 50% powder abrasive, such as Rollwash Dialbril (brand name) . The part is subjected to vibration. The treatment time is 6 hours . Example 3 A wet polishing mixture is used, consisting of a percentage weight of 90% copper pellets with a length of 3 mm, 5% powder abrasive, such as Rollwash Dialbril (brand name) , 3% water, 2% polish, such as the detergent Rosier CL30 (brand name) . The part is subjected to vibration. The treatment time is 20 hours . After the first polishing stage, the cavity is subjected to an identical second, final polishing stage. A second polishing mixture is used for the latter, consisting of a percentage weight of from 70 to 95% metal pellets, or abrasive ceramic elements, or abrasive plastic elements, preferably 90%, from 3 to 20% water, preferably 5%, and from 3 to 20% polish, preferably 5%. The length of the second polishing stage is between 2 and 3 hours. The invention described can be subject to modifications and variations without thereby departing from the scope of the inventive concept. Moreover, all the details of the invention may be substituted by technically equivalent elements.

Claims: Claims 1. A method for polishing parts which have at least one cavity to be polished, in particular parts in the form of moulds or mould components for the production of plastic items, in which the cavity to be polished is the shaped mould for the item, the method envisaging the preparation of a polishing mixture, the latter being brought into contact with the surface of the cavity to be polished and the polishing mixture being moved relative to the surface to be polished for a preset time, the method being characterised m that the polishing mixture is inserted directly in the cavity in the part, the part therefore defining a container element for the polishing mixture 2. The method according to claim 1, characterised m that the cavity has an upper lip, and also characterised m that the polishing mixture is inserted up to a level which is above that of the upper lip of the cavity. 3. The method according to either of the foregoing claims, characterised in that when the polishing mixture has been inserted m the cavity, the part is subjected to vibration. 4. The method according to any of the foregoing claims, characterised m that the polishing mixture consists of a percentage weight of from 50 to 80% metal pellets, or abrasive ceramic elements, or abrasive plastic elements and from 20 to 50% abrasive. 5. The method according to any of the foregoing claims from 1 to 3, characterised m that the polishing mixture consists of a percentage weight of from 70 to 90% metal pellets, or abrasive ceramic elements, or abrasive plastic elements, from 5 to 20% abrasive and from 3 to 10% water. 6. The method according to claim 5, characterised in that the polishing mixture comprises a percentage weight of from 3 to 10% polish. 7. The method according to any of the foregoing claims from 3 to 6, characterised in that the optimum polishing mixture consists of a percentage weight of 80% metal pellets, 10% abrasive, 5% polish and 5% water. 8. The method according to any of the foregoing claims from 4 to 7, characterised in that the metal pellets are made of copper. 9. The method according to any of the foregoing claims from 4 to 8, characterised m that the larger dimension of the metal pellets is between 3 and 6 mm. 10. The method according to any of the foregoing claims from 3 to 9, characterised m that the length of the polishing treatment is between 6 and 20 hours. 11. The method according to any of the foregoing claims from 3 to 10, characterised m that, in order to evenly polish the entire circumferential surface of the cavity, the vibration is interrupted and the part turns through a preset angle, once or more, until the surface is completely polished. 12. The method according to any of the foregoing claims from 3 to 11, characterised in that the vibration imparted to the part has a component parallel with the table and a jerking component perpendicular to the table. 13. The method according to any of the foregoing claims from 3 to 12, characterised in that, following the first polishing stage, the cavity is subjected to a second, final polishing stage, using a second polishing mixture, consisting of a percentage weight of from 70 to 95% metal pellets, or abrasive ceramic elements, or abrasive plastic elements, preferably 90%, from 3 to 20% water, preferably 5%, and from 3 to 20% polish, preferably 5%, the length of the second polishing stage being between 2 and 3 hours. 14. An apparatus (10) for polishing parts (12) which have at least one cavity (14) to be polished, m particular parts (12) m the form of moulds or mould components for the production of plastic items, m which the cavity (14) to be polished is the shaped mould for the item, the apparatus being characterised in that it comprises a support base (16) for at least one part (12) to be polished, and, following the insertion of a polishing mixture (13) m the cavity (14) m the part (12), means for moving the polishing mixture (13) relative to the surface to be polished, for a preset time, where the means for moving the polishing mixture (13) relative to the surface to be polished in the cavity (14) comprise means (22) which cause the part (12) to vibrate. 15. The apparatus according to claim 14, characterised in that the means which cause the part (12) to vibrate comprise means which vibrate the mobile support base (16) for the part (12) to be polished. 16. The apparatus according to either of the foregoing claims 14 or 15, characterised in that it comprises means for sealing the cavity (14) m the part (12) . 17. The apparatus according to claim 16, characterised in that the means for sealing the cavity (14) m the part (12) define an upper expansion chamber (20) for the polishing mixture (13) inserted m the cavity (14) . 18. The apparatus according to claim 17, characterised in that the means for sealing the cavity (14) m the part (12) define means or portions (22) for covering and protecting those areas located in the cavity (14) which must not be subjected to polishing of the part (12) . 19. The apparatus according to claim 17 or 18, characterised in that, in order to hermetically seal the sealing means and fix the part to the table in such a way that it may subsequently be removed, a plate (21) is used, being positioned above the part and the sealing means and held on the table (16) by extended legs (23), the latter having threaded ends onto which locknuts (25) are screwed. 20. The apparatus according to any of the foregoing claims from 14 to 19, characterised in that the vibrating means (22) impart to the part a vibration which has a component parallel with the table (16) and a jerking component which is perpendicular to the table. 21. The apparatus according to claim 20, characterised in that the vibrating means (22) comprise a rotary shaft fitted with offset vibrating weights (22'), the shaft being positioned parallel with the part (12) support table (16) . 22. A mixture or material for polishing parts, characterised in that it consists of a percentage weight of from 50 to 80% metal pellets, or abrasive ceramic elements, or abrasive plastic elements and from 20 to 50% abrasive. 23. A mixture or material for polishing parts, characterised in that it consists of a percentage weight of from 70 to 90% metal pellets, or abrasive ceramic elements, or abrasive plastic elements, from 5 to 20% abrasive and from 3 to 10% water. 24. The mixture according to claim 23, characterised in that the polishing mixture comprises a percentage weight of from 3 to 10% polish. 25. A mixture or material for polishing parts, characterised in that it consists of a percentage weight of 80% metal pellets, 10% abrasive, 5% polish and 5% water. 26. The mixture according to any of the foregoing claims from 22 to 25, characterised in that the metal pellets are made of copper. 27. The mixture according to any of the foregoing claims from 22 to 26, characterised in that the metal pellets have a larger dimension of between 3 and 6 mm.

Inventors: MINGOT CLAUDIO, MINGOT, CLAUDIO
Applicants: MINGOT CLAUDIO, MINGOT ROBERTO, MINGOT, CLAUDIO, MINGOT, ROBERTO
Application year: 1999
Main classification: B24B
IPC codes: B24B31