METHOD OF FORMING A HIGH PRECISION FLEXIBLE ABRASIVE MEMBER

Abstract: A method of manufacturing a flexible abrasive member, comprises the steps of: providing a porous substrate, impregnating the substrate with an electrically isolating material, treating a side of the impregnated substrate so as to provide areas with different properties as to water or solvent resistance, washing the impregnated substrate with water or a solvent so as to wash away the areas with a relatively low water or solvent resistance for obtaining a prepared substrate with discrete areas, placing the prepared substrate in a metal deposition bath, and depositing metal in said discrete areas in the presence of abrasive particles so as to form abrasive metal deposits.

Description: Method of forming a high precision flexible abrasive member The invention is related to the field of forming flexible abrasive members. Such members, which may take the form of circular pads for grinding discs , or of loop shaped bands , are generally manufactured by depositing metal on a substrate, in the presence of abrasive particles . These abrasive particles become embedded in the metal deposits, and provide the abrasive action of the abrasive member. The metal deposits , which support the abrasive particles , are usually adhered to a substrate in order to provide a strong bond. This bond should be strong enough to withstand the high wear and tear which occurs during grinding. From the state of the art, several methods are known for manufacturing such abrasive members. According to GB-A-1375571ι a sheet is embedded in a backing material, leaving only isolated areas exposed on one side of the sheet. Subsequently, a metal together with embedded abrasive particles is deposited on these isolated areas by means of a plating process. This prior art method has the disadvantage that, due to the fact that the isolated areas are only on one side of the sheet, the process of depositing the metal is rather slow. The isolated areas should be activated by a metal activation bath, then be cleaned in a separate cleaning bath and be plated by electroplating. Apart from the slow progress of this method, it is environmentally unfriendly having regard to the chemicals used in the activating and cleaning baths. Furthermore, the quality of the adhesion between metal deposits and the sheet is relatively poor. GB-A-15 ^48 teaches a method for manufacturing an abrasive member by masking off a backing sheet with a mask such as a perforated tape, plastic, paint, photoresist rubber or the like, and by subsequently depositing a metal with abrasive particles on isolated exposed portions of the backing sheet. Also from EP-B-263785 a method of this kind is known. Both prior art methods suffer from the problem that the metal deposits cannot be formed within a well defined boundary, in case the mask is applied on one side of a porous substrate. In those cases, the non covered side of the substrate will be plated together with the isolated, exposed areas on the other side. This results in a long production time, and also in a less flexible product. The object of the invention is to provide a method for manufacturing a precision flexible abrasive member which is both cheap and quick, and which provides a better adherence of the metal deposits onto the substrate. This object is achieved by a method of manufacturing a flexible abrasive member, comprising the steps of: -providing a porous substrate, -impregnating the substrate with an electrically isolating material, -treating a side of the impregnated substrate so as to provide areas with different properties as to water or solvent resistance, -washing the impregnated substrate with water or a solvent so as to wash away the areas with a relatively low water or solvent resistance for obtaining a prepared substrate with discrete areas, -placing the prepared substrate in a metal deposition bath, and -depositing metal in said discrete areas in the presence of abrasive particles so as to form abrasive metal deposits. By impregnating the substrate, it is fully and reliably covered on both sides. This means that only in discrete areas from which subsequently the impregnating material is removed, the porous substrate is accessible. The rest of the substrate is fully inaccessible, which ensures that metal deposition only takes place in very well defined, discrete areas. As before, it is still possible to create open, discrete areas only on one side of the substrate. However, for obtaining a good adherence, it is preferred to create open areas on both sides of the substrate. In case the discrete areas thus obtained on both sides of the substrate are congruent, the substrate is embedded fully in the metal deposits, thus providing a strong bond. Alternatively, it is possible to treat the other side of the substrate fully. In that case, said side is completely covered by the electrically isolating material. The treatment referred to before, by means of which discrete areas are obtained, can take several forms. Preferably, said treatment comprises the steps of: -impregnating the substrate with a resin, and -exposing the discrete areas to UV-light so as to render them water or solvent resistant for forming a prepared substrate. The discrete areas may be defined by the openings of a film placed between a source of UV-light and the side in question of the substrate. The step of impregnating the substrate may be carried out in several ways as well. According to a first possibility, the substrate is impregnated by dip coating. Separate pieces of substrate material are dipped in a container comprising a fluid coating material . After removing and drying the coating, the substrate can be processed further. This method is in particular suitable for small batches, According to a second embodiment, the method comprises the steps of: -unreeling the substrate from a reel, -guiding the substrate through a resin bath so as to impregnate the substrate, -guiding the impregnated substrate along a heating device so as to dry the resin, -exposing discrete areas of the impregnated substrate to UV-light so as to render those areas water or solvent resistant, -guiding the impregnated substrate through a wash tank so as to wash away the non-exposed areas for obtaining a prepared substrate, -drying the prepared substrate, -reeling the prepared substrate onto a reel. In this process, the substrate is moving at a continuous speed, and is exposed by means of a source of UV-light which travels along with the substrate. In the alternative, the source of UV-light is stationary, and the part of the substrate opposite said source of UV- light is moving in a step-wise manner along said source. Preferably, the porous substrate is electrically conductive, and the metal deposits are electro-formed. Figure 1 shows a step of dipcoating a substrate. Figure 2 shows the step of drying the impregnated substrates. Figure 3 shows the step of treating the substrate. Figure shows the step of washing the substrate. Figure 5 shows the step of treating a substrate from both sides. Figure 6 shows a step of washing said substrate of figure 5> Figure 7 shows a first flexible abrasive member. Figure 8 shows a second flexible abrasive member. Figure 9 shows the process of manufacturing a web-shaped, prepared substrate. Figure 10 shows a second process of continuously manufacturing a flexible abrasive member. According to the method of figure 1, porous substrate 1 is dipcoated in a resin bath 3- The thickness and the precision of the thickness of the resin coating 2 is controlled by precision doctor blades or squeegees 4. The product 5 thus obtained, comprising the porous substrate 1 once filled with the precise and controlled amount of resin 2 is ovendried, as shown in figure 2. The next step is to expose discrete portions 9 of product through a film 6 with a specific pattern 7. of the ovendried resin to UV-light 8 to render those exposed portions 9 water and solvent resistant: see figure 3- The non exposed areas 10 will not become water-resistant and will be washed away (figure 4) in a water stripping tank 11 which is moved by pressing air through a perforated tube 12 to accelerate the washing process. This method is working and is valid as long as very thin substrates are being used between 25 and 100 micron with at least 25% open areas. Thus, a prepared substrate 14 comprising open areas 13 is obtained. Another aspect of the invention is to also be able to make an abrasive according to the invention on substrates which are thicker than 100 micron or less open than 25%. As explained before, any exposed parts of the substrate will plate independently from being masked or not as long as they are not fully covered by electrically isolating material as a resin for example. This means that in the case the porous substrate used is thicker than 100 micron or less open than 25%, the UV-light will not be able to fully penetrate the resin and to make it water and solvent resistant. The result would be that the resin would be washed away at the backside of the substrate and this uncovered area would be filled with metal bond in the deposition process . To avoid this problem the fully in resin imbedded porous substrate 5 will be exposed (see figure 5) to UV-light 15 from both sides. On both sides a film 16 with the desired pattern can be applied but at least to one side. This substrate is than freed (figure 6) from the areas of not water-resistant resin in a water stripping tank and providing a prepared substrate 17 having open areas 18 on one side only. Thanks to this process , a precision is achieved which was unknown in flexible super abrasive members using an open porous substrate. The size and quantities of the strands, parts or openings are not relevant anymore. The resin hardened with UV-light will stay exactly in the desired place with the desired thickness as wanted. Once the so prepared flexible porous substrate is dried, the metal bond is being electroformed within the discrete openings. An electroforming process has been elected instead of a classical electroplating technique used in the filled because it avoids the activating and cleaning process as mentioned in the state of the art. The metal bond is formed directly in an on the strands, parts and openings of the flexible, porous substrate in the presence of abrasive in an electrodeposition bath. As a result, an abrasive member 20 or 23 is obtained with metal deposits 21 respectively 24, carrying abrasive particles 22. The abrasive member 20 with throughgoing deposits 21 of figure 7 is obtained by carrying out the deposition process on the prepared substrate 14 according to figure 4. The abrasive member 23 of figure 8 is obtained by carrying out the deposition process on the prepared substrate 17 according to figure 6. Even though the here described method is quite expensive when applied with small quantities the cost of manufacturing is unbeaten when a mass production process is applied. The dipcoating of the porous substrate with a resin can be done reel 26 to reel 27: see figure 9- n the continuous process once the web-shaped substrate 29 has been dipcoated as at 29, it will pass through a sandwich of ventilated heat elements 30 which will dry the resin. Once dried the substrate moves onto a UV-light bench on wheels 31 where a film with the desired pattern has been applied. The exposure is relatively short in comparison to the movement of the substrate. The bench will move along with the substrate at the speed of the substrate. Once the exposure process is terminated for a specific length of the substrate the table moves back to its original place and will start the exposure process with a new section of the substrate. Another solution could be to move the roll 32 up and down, having a fix bench which then will be applying the substrate exposure in a static mode. The roll 3 moves up and down to allow the continuous process to continue also during UV-light exposure time. If two sided exposure is needed a second UV-light will be applied. After exposure to the UV-light the unexposed areas are being washed away by passing through a water powerwashing tank 33 where the resin is being removed under pressure. The substrate 28 moves on through ventilated heaters 34 which will dry the substrate before it being rolled up. The so prepared substrate can now be cut to sheetform and electroforming can take place in and on the discrete areas by applying the sheet on a cylinder, in a flat gig or reel to reel. In all cases however the laws of electrodeposition have to be respected. The deposition goes through several stages in which the situation in the bath is very different. There is a form in and on stage, an abrasive sprinkle stage (with a subsequent diamond reclaim stage within the same tank), a form up stage and a rinsing stage. During the first stage, which is also the longest one, extensive solution movement is required to avoid the adherence of hydrogen bubbles , to allow for an acceptable deposition time and also to ensure an even deposition of metal across the sheet width and length. During that stage the current density is very high. The second stage, the abrasive sprinkling stage, is preferably done in a static mode for the crystals to be tacked or adhered to the metal bond. Any movement will reduce adhesion or even avoid it Static means no moving of the substrate, no moving of the solution and very low current density. The third stage is again comparable with the first stage with the difference to be shorter in time. A normal time ratio between stage 1, 2 and 3 would be 6:1:3- This only shows that the drawings and explanations in the Diabrasive patent do not achieve the set goal because all stages take place in the same bath at the same time. To guarantee a simple and efficient production of a precision flexible abrasive in a reel to reel mode one aspect of the invention is to harmonise the working times within the separate stages in separate tanks. The example shown in figure 10 is based on that concept and on a flexible substrate 35 with 310 mm width and a tank length of 1200 mm per tank 36. The flexible substrate will initially be pulled into tank No. I of 1200 mm length. In this tank 3 the first stage of forming on and in will last 20 minutes at 300 - 450 Amps, and under very high solution movement. Inside each tank, there is an agitating tube 44 emitting a gas fed by pump 46; furthermore, there is an anode 4 . After this operation the first length of 1200 mm of substrate will be pulled into tank 37 and therefore a yet uncoated 1200 mm length of substrate will be pulled into tank 36. In tank 3 the operation at 300 - 450 Amps, is repeated, and tank 37 will first go through a diamond sprinkling phase of about 5 minutes from a diamond hopper (not shown) above tank 37. then during a period of 10 minutes it will go through a diamond hold phase at 15 - 30 Amps, and at last the unnecessary diamond crystals are being blown of the substrate surface for another five minutes and reclaimed through the diamond recovery system 38, comprising a funnel 4l, pipe section 42, and recovery unit 42. The diamond particles thus recovered are to be fed back into the diamond hopper above tank 37- The diamond sprinkling phase as well as the diamond hold phase have to happen under absence of movement of the solution or the substrate. After this second stage the diamond covered substrate is then pulled into tank 39. the substrate in tank 36 is automatically pulled in tank 38 and a yet uncoated piece of substrate is automatically pulled into tank 36. In tank 39 the substrate will go through a form up stage where the diamond crystals will get increased hold in the metal bond during again 20 minutes at 100 to 450 Amps. Once this third 20 minutes cycle is done the basically finished piece of substrate is pulled into the water rinsing tank 40 and is being rinsed and cleaned. The reason for the possible difference in Amps . used is that depending on the gritsize used, different power per tank is used to harmonise the working times in the different tanks. This means that the whole process is a reel to reel process with short movements of the substrate when moving from one tank to the other but with static electroforming stages in all tanks.

Claims: C l a i m s 1. Method of manufacturing a flexible abrasive member, comprising the steps of: -providing a porous substrate, -impregnating the substrate with an electrically isolating material , -treating a side of the impregnated substrate so as to provide areas with different properties as to water or solvent resistance, -washing the impregnated substrate with water or a solvent so as to wash away the areas with a relatively low water or solvent resistance for obtaining a prepared substrate with discrete areas, -placing the prepared substrate in a metal deposition bath, and -depositing metal in said discrete areas in the presence of abrasive particles so as to form abrasive metal deposits. 2. Method according to claim 1, wherein both sides of the substrate are treated. 3- Method according to claim 2, wherein the discrete areas of both sides are congruent. 4. Method according to claim 1 , wherein the other side of the substrate is fully treated. 5- Method according to any of the preceding claims, comprising the steps of: -impregnating the substrate with a resin, and -exposing the discrete areas to UV-light so as to render them water or solvent resistant for forming a prepared substrate. 6. Method according to claim 5. wherein the discrete areas are defined by the openings of a film placed between a source of UV-light and the side in question of the substrate. 7. Method according to any of the preceding claims , wherein the substrate is impregnated by dip coating. 8. Method for manufacturing a prepared substrate for use in the method according to any of claims 1-6, comprising the steps of: - unreeling the substrate from a reel, - guiding the substrate through a resin bath so as to impregnate the substrate, - guiding the impregnated substrate along a heating device so as to dry the resin, - exposing discrete areas of the impregnated substrate to UV- light so as to render those areas water or solvent resistant, - guiding the impregnated substrate through a wash tank so as to wash away the non-exposed areas for obtaining a prepared substrate, - drying the prepared substrate, - reeling the prepared substrate onto a reel. 9> Method according to claim 8, wherein the substrate is moving at a continuous speed, and is exposed by means of a source of UV-light which travels along with the substrate. 10. Method according to claim 8, wherein the source of UV-light is stationary, and the part of the substrate opposite said source of UV-light is moving in a step-wise manner along said source. 11. Method according to any of claims 1-6, wherein the porous substrate is electrically conductive, and the metal deposits are electro-formed. 12. Method for manufacturing a flexible abrasive member from a prepared substrate manufactured according to any of claims 8-10, comprising the steps of: - unreeling the prepared substrate from a reel, - guiding the prepared substrate through a first plating solution, - guiding the prepared substrate through a second plating solution while adding abrasive particles to said solution, - guiding the prepared substrate through a third plating solution, - guiding the prepared substrate through a rinsing liquid, - guiding the rinsed prepared substrate through a drying station, - reeling the dried prepared substrate onto a reel. 13. Method according to claim 12, wherein the prepared substrate is moving stepwise from the one reel towards the other. 14. Method according to claim 13, wherein the rest time between consecutive movements of the prepared substrate is about 20 minutes. 15- Method according to claim 14, wherein the plating processes are carried out electrically, the plating current in the first plating solution being 300 - 450 Amp. 16. Method according to claim 15, wherein the plating current in the second plating solution is 15-20 Amp. 17. Method according to claim 16, wherein the plating current in the third plating solution is 300 - 450 Amp.

Inventors: FERRONATO SANDRO GIOVANNI GUIS, FERRONATO, SANDRO, GIOVANNI, GUISEPPE
Applicants: FERRONATO SANDRO GIOVANNI GUIS, FERRONATO, SANDRO, GIOVANNI, GUISEPPE
Application year: 1997
Main classification: B24D18
IPC codes: B24D3, B24D11, B24D18