EP0333034B1 - Flexible grinding tool method of manufacturing the same - Google Patents

Abstract

The finishing (10, 15), filling intermediate spaces, of the textile backing of a flexible grinding tool has a foam structure, as a result of which better filling properties with good adhesion of the fibres are obtained. <IMAGE>

Description

The invention relates to a flexible grinding tool with a flexible base containing a fiber structure, the gaps between which are at least partially filled by equipment which has solidified from the flowable state. The invention further relates to a method for producing such a grinding tool.

Textiles that are used to produce the flexible base for grinding tools, such as fabrics, sewing agents and tiles, need to be solidified before the abrasive grain is applied. The equipment is used for this consolidation. The equipment is understood to mean a mass introduced into the textile material in a flowable state, which solidifies therein and thereby connects and solidifies the fibers of the textile structure. It also has the purpose of filling the interstices of fibers and threads of the underlay, at least in the area near the surface, in order to protect them from the penetration of the grain binder, which is undesirable within the underlay because of its embrittling influence. It also protects against the penetration of other undesirable substances, especially grinding aids such as water, grinding emulsion or oil. Because the equipment is involved in the transfer of forces between the Abrasive grain and the pad as well as within the pad, it must securely anchor on and between the fibers or fiber strands forming the pad. The lower the viscosity in the applied state, the better this is achieved. In other respects, however, low viscosity is undesirable because it is generally synonymous with the presence of significant amounts of solvents or dispersants, which increase the drying effort (energy requirement, dryer length). This can also limit the amount of substance that can be applied. Finally, an excessive depth of penetration caused by low viscosity can bring about disadvantageous changes in the properties of the substrate, for example brittleness of the fibers during finishes based on phenolic resin.

It is known (EP-A 0 104 776) to use a synthetic resin which contains a high percentage of fillers as filling equipment. However, synthetic resins with a high filler content have the disadvantage of low elasticity. The viscosity in the applied state is also increased, and thus the anchoring ability is reduced.

The invention is therefore based on the object of creating a grinding tool of the type mentioned, the equipment of which, with good adhesion to the base, has good filling properties and the ability to form a sufficiently thick layer. The invention is also based on the object of providing a method for incorporating such equipment into the base.

The solution according to the invention is that the equipment is foamed.

The invention is based on the surprising finding that the use of foam reduces the consistency problems explained, because it has two consistencies, so to speak. Even one made of relatively light-bodied material Prepared foam has considerable dimensional stability, which permits the application of a sufficiently thick layer, the mass of the solids remaining after curing and that of the solvent or dispersant to be expelled in the drying process or of the water obtained as a result of chemical reaction being low. The ability of the foam to anchor itself to the fibers and in the interstices of the fibers on the surface of the underlay is, however, influenced by the drainage capacity and by the viscosity of the liquid on which the foam is based, this viscosity being chosen to be comparatively low regardless of the dimensional stability of the foam as a whole can be. The foam structure does not diminish the ability of the liquid forming the foam to penetrate and anchor itself in the interstices of the fibers, especially since it has been shown that the foam tends to increase its density in the lower region bordering the textile surface enlarge because the larger bubbles move away from the base, especially if the application is on the horizontal or inclined path from above. Therefore, the equipment according to the invention is characterized in many cases in that its density at the interface with the base is greater than at a distance from it. At the same time, however, the mass of the liquid freely available in the border area to the textile base is limited. This limits the amount of liquid that can migrate from the foam-filled, larger pores and thread spaces through capillary forces into the fine fiber spaces. This is desirable because only the filling of the larger pores and interstices as well as a good anchoring of the foamed equipment should take place on the fibers delimiting these pores and interstices, while the fine capillary interstices should remain free, particularly in the core of the threads.

A major advantage of the invention is that surface depressions of the base, for example those between fiber strands of textile bases, through Foam equipment can be largely filled. This applies in particular to the gaps between adjacent threads or fiber strands of knitted fabrics. A relatively smooth, flat surface can be achieved even with considerable unevenness of the base.

Furthermore, there is an advantage of the rear side formed by fiber strands and intermediate foam filling in that the fiber strands can take over most of the power transmission as ribs, while the foam filling in between is relieved of the forces. This is achieved in that the foam filling is only arranged between the fiber strands and does not exceed their height. However, the foam filling can also be involved in the power transmission to the desired extent by the height of the rear foam equipment exceeding that of the fiber strands in the unloaded state, without substantial layer thickness on the fiber strands, a foam of such a resilient consistency being chosen that it is operationally suitable occurring forces (primarily the pressure of the drive rollers and / or the pressure of a pressure beam or pressure shoe used to generate the grinding pressure) is compressed as much as the height of the fiber strands allows. In the area of foam equipment, only a force of the size required for this compression is then transmitted. In this embodiment, a substantial layer thickness is avoided on the fiber strands, so that high forces can be transmitted there regardless of the possibly limited strength of the foam equipment.

In another embodiment, the foam equipment can form a layer that completely and essentially covers the back (including the fiber strands). This has the advantage of high smoothness on the back side, which has not previously been achieved by conventional methods with a single application - in particular in the case of inexpensive knitted fabrics with a non-uniform and uneven surface or low fabric density could be. The abrasive effect that some conventional underlays have on the sliding surfaces of pressure beams or pressure shoes on grinding machines can be avoided.

Surprisingly, a pronounced resistance to the walk, tensile and shear loads occurring during the grinding process was also found, so that even at the end of a long-term test with a uniform, smooth back, a correspondingly uniform grinding pattern was obtained on the workpiece surface. Compared to conventionally equipped belts, a particularly quiet, low-vibration running behavior and improved power transmission between the drive elements and the back of the belt were also found.

A foam of medium softness is expediently chosen for the production of a back cover layer and for filling back depressions, namely a foam in which the pressure required for compression to half the thickness is at least 700 kPa and preferably at least 1200 kPa and at most 2500 kPa .

The deep fill, in which the higher fiber strands are not or hardly covered by a foam layer, is expediently knife-coated, so that the excess located above the highest elevations of the base has been removed and these highest elevations themselves have remained essentially free of coatings. In this way, a space filling is formed, the surface of which approximates the height of the fiber strands at the edges of the spaces. The height of the gap filling can be less than the height of the fiber strands if there is a loss of volume after doctoring; it can be as high; however, it can also be bulged higher if the foam rubs after wiping.

If there is a continuous layer of foam on the back, it may be advantageous to calender it after foam formation, i.e. H. to lead by pairs of press rolls. This is expediently done with simultaneous supply of heat. As a result, the density of the layer is greater near its free surface than in its deeper areas. This is due to the fact that the heat from the heated calender roll is more intense near the surface. Thanks to the greater density of the foam layer near the surface, the calender foam layer is characterized by greater mechanical resistance.

If the strength of the foam layer cannot withstand the attack of external forces, for example the frictional force of a drive roller or the force of a surface which acts on the back of the sanding belt and generates the sanding pressure, it may also be expedient to add an additional layer to the foamed equipment on the surface of the underlay Cover layer of greater strength, which can be non-foamed and can consist of the same or a different mass, in particular of synthetic resin.

The density of the foam equipment when ready for use is preferably on average 0.5 to 0.9 b / cm³, preferably about 0.7 g / cm³.

Although the use of the foam equipment on the back of the abrasive belt has particular advantages, it can also be used on the grain side, namely to fill recesses and fiber strand gaps in the grain-side surface of the underlay to form a smooth surface of the finished underlay for receiving the abrasive grain layer. For this, a very firm foam should be chosen that absorbs the grinding pressure practically incompressibly. This means that the flexibility of the foam-filled areas is so low that it does not affect the grinding result. This condition is at least when the compression of the foam-filled areas of the ready-to-use abrasive belt under the grinding pressure is less than a third of the average abrasive grain size.

It is not necessary that the equipment foamed according to the invention is the only equipment of the base. Rather, for example, primary equipment can be applied in front of it, which is perceptibly or preferably imperceptibly between the foam equipment and the fibers forming the base. Furthermore, the invention does not exclude that the foam equipment according to the invention is followed by further equipment with foamed or non-foamed material, for example to form a hard or tough top surface before the abrasive grain layer is applied.

The advantage of the foam equipment that surface depressions of the underlay are filled not only relates to deep recesses in the surface, but also to open ones that pass from one side to the other of the underlay and are only closed by the foam equipment.

It is known (US Pat. No. 4,629,473) to use foam in a flexible grinding tool; however, it is a prefabricated foam layer that is laminated between the backing and the grain layer to give the grain layer compliance. In contrast, the invention does not intend for the grain layer to be compliant.

The process according to the invention is characterized in that the mass to be introduced as equipment into the base contains a foaming agent. It is not necessary but advantageous that the foam formation takes place at least partially after it has been introduced into the base. Common application techniques can be used. For example, if the consistency is very thin, the base to be finished can be used an immersion bath of the equipment mass is performed, after which the excess is squeezed off by a pair of press rolls. In the case of masses of greater toughness and in the case of masses which have already been partially or completely foamed, application by means of a doctor blade is advisable. This applies in particular if the surface of the mass is smoothed out at the same height as the highest elevations of the fiber structure of the base. The smoothing expediently takes place after the completion of the foam formation, if the layer is to have the same height as the fiber structures. If, on the other hand, it is desired that the foamed interstice filling should protrude beyond the height of the fiber structures on the back of the underlay, the smoothing is expediently carried out before the completion of the foam formation. Finally, as already mentioned, calendering can take place. This applies in particular to continuous foam layers on the back of the underlay.

The filling of interstices on the grain side has the advantage that the grain binder cannot penetrate the substrate. It is therefore also possible to use the less expensive open woven and knitted fabrics without the risk of embrittlement.

• Fig. 1 eine perspektivische Schnittansicht einer ersten Ausführungsform
• Fig. 2 eine Schnittansicht einer zweiten Ausführungsform,
• Fig. 3 eine Schnittansicht einer dritten Ausführungsform.

The invention is explained below with reference to the drawing which illustrates advantageous exemplary embodiments. In it show:

• Fig. 1 is a perspective sectional view of a first embodiment
• 2 is a sectional view of a second embodiment,
• Fig. 3 is a sectional view of a third embodiment.

The flexible grinding tool according to FIG. 1, which can be an abrasive belt, comprises a base 1, the textile part of which is a sewing fabric that consists of a fleece or fiber strands 2 with a direction parallel to the plane of the drawing, perpendicular there are threads or fiber strands 3 and sewing threads 4, by means of which the fiber strands 3 and the layer 2 are connected to one another. Such knitted fabrics and their use for flexible grinding tools are known. If fiber structures are generally mentioned above, this preferably means the fiber structures formed by such thread systems.

On the front, a grain layer formed by grains 6 is connected to the base 1 by means of a binder layer 7 and covered by a post-glue layer 8.

Between the fiber strands 3, groove-shaped depressions 9 are formed on the back. The fiber strands 3 and the sewing threads 4 emerge correspondingly more strongly on the back. According to the invention, the depressions 9 are filled with a plastic foam 10, the surface 11 of which reaches approximately the height of the fiber strands 3 and sewing threads 4 and is even curved slightly beyond them. If it is sufficiently soft to be pressed together by rear forces, such as occur when the belt is pressed against a workpiece, such forces are mainly taken up by the fiber strands 3 or sewing threads 4 that appear in the rear surface of the grinding tool. The foam 10 therefore does not have to have a very high strength and only participates in the transmission of the forces running transversely to the band plane in accordance with its bulging and its modulus of elasticity.

The modulus of elasticity to be selected for the foam therefore depends on the forces to be transmitted. It can be very soft if the back pressure forces are to be transmitted mainly through the fiber strands 3, but a high compressive strength can also be selected for the foam if it is to contribute significantly to the transmission of the pressure forces. Its stress can be measured by the degree of its bulge according to its compression up to that of the Fiber strands are limited certain level, which also limits the forces to be transmitted by it in relation to the fiber strands.

Any foamable and then solidifying material that develops sufficient adhesion to the base can be used for the foam finishing. It is preferably synthetic resin, in particular phenols, urea and melamine resins and also plastic dispersions based on polyacrylic acid esters, polyvinyl acetate, polyurethane, polyvinyl chloride, polyvinylidene chloride, polyethylene, polyvinyl ether, acrylonitrile-butadiene-styrene copolymer and polyvinyl propionate, their copolymers, copolymers or terpolymers in each case exclusively or a combination of any proportions of these polymers. Furthermore, the foam formed by the plastic dispersion can contain surfactants, foaming agents, foam stabilizers, dyes and fillers, crosslinking agents, chemical blowing agents and auxiliaries for setting the desired pH. The foam-forming gas can be introduced mechanically as air, nitrogen, carbon dioxide or the like or can be generated by chemical reaction within the liquid on which the foam is based. The designation of the substance on which the foam is based as flowable should not preclude the use of viscous substances, provided that the foam as a whole is at least spreadable. The density of the foam when applied is advantageously between 0.1 and 0.4 g / cm³, preferably between 0.15 and 0.3 g / cm³. The viscosity of the foam is expediently between 3000 and 10000 mPa.s. The viscosity of the liquid forming the foam is advantageously between 50 and 1500 mPa.s. The application weight of the foam (in the dry state) is advantageously between 10 and 300 g / m², preferably between 75 and 150 g / m². The consistency of the ready-to-use foam equipment is best characterized by the compressibility, namely the force required to compress to half its thickness.

This force is expediently between 700 and 2500 kPa with the preferred levels given above.

For the production, the not yet solidified foam is applied to the back of the base and the excess is scraped off by means of a doctor knife in a relative movement running in the direction of the fiber strands 3. The foam mass located on the fiber strands 3 and sewing threads 4 is essentially removed and only the mass 10 remaining in the interstices 9 remains. This can subsequently expand a little as a result of rheological processes during doctoring or due to continuous expansion and - as in 11 - bulge up a little. This is not necessary. In other embodiments, in order to protect the foam against forces acting on the rear, it may also be expedient that the surface 11 is, on the contrary, curved a little concave in order to step behind the surfaces of the comparatively firm ribs formed by the fiber strands 3 and sewing threads 4.

Near the interface to the base, removal of at least the larger bubbles results in a compression of the foam, which is indicated in region 5 and which contributes to the excellent adhesion of the foam to the base.

In the second embodiment according to FIG. 2 one can see the cross section of fiber strands 13, which represent a family of parallel threads forming a conventional fabric, the threads of which run transverse to the threads 13 have been omitted for the sake of simplicity. The threads 13 enclose open spaces 14 with one another. Likewise, the threads running transversely to the threads 13 are spaced apart. The gaps 14 are filled with foam equipment 15 according to the invention. To improve the strength of the base, a firm layer 16 or 17 can then be applied on the front side and, if appropriate, also on the back. Subsequently the binder layer 18, the grain 19 and the post-glue layer 20 are applied.

3 shows an embodiment which differs from that according to FIG. 1 in that a rear foam layer 18 is provided which has a considerable thickness, preferably between 0.2 and 1 mm, more preferably between 0.3 and 0, 6 mm. In a tried and tested example, a knitted fabric with a basis weight of 260 g / m² was first provided with a basic finish and then provided on the back with a foam coating by means of a roller doctor blade with a free gap between the roller doctor blade and the underlay surface of 0.75 mm. The order quantity was 75 g / m². After drying between 85 and 100 ° C, the remaining layer was calendered using a steel paper roll under a line pressure of 50 daN / cm at a roll temperature of 170 ° C. Condensation then took place at 150 ° C. The grain side was treated conventionally.

In comparison to a conventional abrasive belt of the same type, the saving in terms of solid application when finishing was 75 g / m².

The applied foam consisted of a foamed, synthetic resin-containing, aqueous plastic dispersion, namely containing
33.3% by weight of Dicrylan 7326 (Chem. Fabrik Pfersee)
Acrylic ester copolymer self-crosslinking,
50.0% by weight of Dicrylan 7331 (from Chem. Fabrik Pfersee)
Acrylic ester copolymer,
4.2% by weight Knittex CR (Chem. Fabrik Pfersee)
Ethylene urea triazine resin,
4.2% by weight of helizarin white AM (BASF) dye,
8.3% by weight of dicrylan stabilizer 7320 (Chem. Fabrik Pfersee) foam stabilizer.

The foam density was 0.225 g / cm³.

Claims (19)

1. A flexible grinding tool having flexible support (1) containing a fibre structure, the interspaces (9) of which are filled at least partly by a finish (10) hardened from the fluid state, characterised in that the finish is foamed.

2. A grinding tool according to Claim 1, characterised in that the density of the foamed finish is higher at the surface of the support (1) than at a distance therefrom.

3. A grinding tool according to Claim 1 or 2, characterised in that on its surface, between fibre strands (3), the support (1) has cavities (9) which are substantially filled by the foamed finish (10).

4. A grinding tool according to Claim 3, characterised in that the foamed finish is disposed on the back side of the support substantially only between the fibre strands (3), without substantial layer thickness on the fibre strands, and in that the height of the foamed finish (10) between the fibre strands (3) in the unstressed condition is greater than the height of the fibre strands (3).

5. A grinding tool according to Claim 4, characterised in that the foamed finish is compressible under the drive and/or grinding pressures to at least the height of the fibre strands (3).

6. A grinding tool according to any one of Claims 1 to 5, characterised in that the foamed finish forms a layer (18) substantially covering the entire back side.

7. A grinding tool according to any one of Claims 4 to 6, characterised in that the pressure required to compress the foamed finish to half its thickness is at least 700 kPa.

8. A grinding tool according to any one of Claims 1 to 3, characterised in that the foamed finish disposed on the grain side of the support is substantially incompressible under the grinding pressure.

9. A grinding tool according to any one of Claims 1 to 8, characterised in that the foamed finish has a smooth surface.

10. A grinding tool according to Claim 9, characterised in that the density of a layer of the foamed finish on the back side is greater near to its free surface than at a distance therefrom.

11. A grinding tool according to any one of Claims 1 to 10, characterised in that the density of the foamed finish is, on average, more than about 0.5 g/cm³.

12. A grinding tool according to any one of Claims 1 to 11, characterised in that the density of the foamed finish is, on average, less than about 0.9 g/cm³.

13. A grinding tool according to any one of Claims 1 to 12, characterised in that the foamed finish on the surface of the support is covered by a layer (17) of relatively high strength.

14. A method of filling and finishing a flexible abrasive support by introducing a fluid, hardening compound, characterised in that the compound contains a foaming agent.

15. A method according to Claim 14, characterised in that the foam forming is carried out at least partly after the introduction into the support.

16. A method according to Claim 14 or 15, characterised in that the surface of the compound is smoothed to the same height as the highest projections of the fibrous structure of the support.

17. A method according to Claim 16, characterised in that the smoothing is carried out after the termination of the foam forming.

18. A method according to Claim 16, characterised in that the smoothing is carried out before the termination of the foam forming.

19. A method according to Claim 14, characterised in that the foamed layer on the back side is calendered after the foam forming.

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