DE2130277A1 - Vitrified bonded grinding wheel - Google Patents

Description

Patent attorneys Dr.-Ing. HANS RUSCHtCE Dtpi.-ing. HEINZ AGULAR 8 Munich 80, Pienzenutwrstr. 2

Our Zelohent M. 637

June 18, 1971

Norton Company, 1 New Bond Street, Worchester, Massachusetts, (V.St.A.)

"Vitrified bonded grinding wheel"

Glazed or vitreous (ceramic) bonded grinding wheels consist of particles of an abrasive substance such as Alumina in a vitreous, vitreous or ceramic investment material. Such grinding wheels are very durable, have a: good effect and stand out as a result from that they maintain the shape of the grinding surface. These products are usually to some extent porous, the porosity varies considerably, depending on the grain size, the amount and Type of binding material used and the manufacturing process.

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There have been attempts to increase the strength, toughness and the shock or impact resistance to increase of vitreous bonded grinding wheels, thereby increasing the maximum operating speed at which they can operate, as well as the maximum compressive force and the blow k which they can be exposed by impregnating the pores of the discs with a thermoplastic or thermosetting resin. Various resins and similar substances have been proposed including phenolic resins, waxes, benzofuran resins, shellac, Ψπϊ'ϊ uryl resins, rubber, cellulose-derived resins, asphalt, gum and glue. None of these agents have achieved commercial success. The reasons for this are believed to be as follows

1. It is difficult to put a sufficient amount of the solid resin or other material in the Retaining pores (filling sufficient) to add sufficient strength and impact resistance, to ensure operating costs. The more porous the disk, the softer it is. A adequate filling and retention of resin is im

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particularly difficult with ceramic grinding wheels, which have a relatively high porosity (for example ^{25-50 c} / o volume porosity), relatively large grit sizes (for example 24-GO) and a relatively low ceramic content (for example 3-18 vol. $) . The larger the grain size and the lower the ceramic content, the larger the pore volume and the pore diameter.

2. Such resinous materials, in particular thermoplastics, which may be suitable for sufficiently the Filling pores and being retained there are either too weak or too brittle or too soft to provide sufficient additional strength and shock resistance, or they have pleating properties (too flowable) or melting points (in the pail of thermoplastic materials) which make them unsuitable. If the material tends to flow or break up when operating at high speed and under shock or pressure, it can do more harm than good.

It has now been found that the strength, the impact resistance and resistance to pressure and

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Tensile centrifugal forces largely due to impregnation of the pores of vitrified bonded grinding wheels, in particular of the annular portion next to the disk hole with a thermosetting, unsaturated Polyester resin, i.e. the copolymer of a liquid mixture of an unsaturated polyester prepolymer and an unsaturated extender, for example Co-

) polymerization of the condensation product of an unsaturated dibasic acid and a saturated glycol with an unsaturated vinyl monoeric can be, wherein the copolymerization of the free radical by solo free radical initiators such as organisohe Peroyyde and azo compounds is initiated. As a result, the disks can rotate at extremely high speeds and withstand knocks or impacts, compared to known vitrified bonded grinding

. discs, and they are therefore extremely well suited for grinding at high speed.

According to the invention, there is a ceramic bonded grinding wheel "It has a" hole provided, the pores of at least a predetermined section of the disc next to the hole with a thermosetting cross-linked unsaturated Polyester resin i «are impregnated, with about 95 $ of the pore volume of the impregnated portion bit the cross-linked polymer is filled.

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Copolymers of unsaturated monomers with unsaturated Alcohol esters and polybasic acid prepolymers are used as binders and for impregnating plastic-bound Grinding wheels have been used. However, such disks do not have the looping properties of ceramic discs according to the invention »

The pores are impregnated with a mixture of the prepolymer and the crosslinking composition, and Copolymerization (hardening) occurs in situ within the pores at room temperature, i.e. without the addition of Heat with the exception of the exothermic heat of reaction. Curing at room temperature is preferred to a Reduce foaming or blistering and swelling, although at room temperature after curing is complete to the point where the resin has solidified and hardened, it may be desirable to use a ensure complete hardening by subsequent heat hardening. However, in bestiawten Cases of increased temperature after curing cause uneven expansion and contraction of the resin and the cause glass-grained embedding compound, in particular, when using relatively high temperatures. Hardening temperatures should, if used,

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do not exceed 225 ° O, and preferably should not exceed about 100 ° C.

Surprisingly, the compound with a cure in situ filling and holding it was found that Road network by impregnating the above-mentioned prepolymer and old ^ old resin between 95 and 100 of the pore # k voluaena can be obtained, which is treated, ie between 95 and 100 The treated pore volume can be filled with cross-linked copolymer and the latter holds even with a pore volume between 25 and 52 # of the total disk volume (with the exception of the disk oil), so that the ceramic disk becomes essentially non-porous, ie that it has a pore volume of 0 5 i * . This, combined with the fact that the solid cross-linked copolymer itself is extremely strong, hard, tough, and material-resistant, and nothing noticeably flows even at high wheel speeds and temperatures or when subjected to significant impact forces, that a ceramic grinding wheel can use higher speeds and greater pressure. and can be exposed to impact forces than previously known ceramic grinding wheels. The molecular structure of the cured unsaturated polyester resins is such that they are not brittle, although

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probably they are very resistant to flow and thermal influences. This can be due to the distance of the molecular chains and the relatively low density of crosslinks per surface area of the crosslinked copolymer, i.e. the number of crosslinks per Area of the resin.

Preferably only the separation of the disk next to the disk looh is approximately one third to the Half of the radial distance from the wall of the hole to the disc circumference is impregnated, with the peripheral section remaining untreated. In this way, the grinding properties of the disc remain unchanged. However, the the entire sole or any particular section so treats Min, and in some cases the impregnated unsaturated polyester resin provides sole benefit.

Preferably the liquid mixture is prepolymer and crosslinking compound is applied to one side of the portion of the disc to be treated and is in the pores either by gravity or, preferably, by applying a vacuum on the other side this slice section sucked, with a stopper or a shaft is arranged in the Soheibenlooh. That Vacuum is sufficient to pull only the mixture of prepolymer crosslinking compound into the pores,

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and the amount of vacuum required for this depends on the porosity of the disc and the viscosity of the mixture. In general, the vacuum can be between about 10 and 3.00 or 400 mm Hg with a draft of between 750 mm Hg un ·. 360 or 460 mm Hg vary, which is based on the atmospheric pressure on the side of the disc to which the mixture is applied. V / enn an effective pressure is applied to the mentioned side of the pane, the vacuum can of course can be omitted.

Preferred curing conditions for the impregnated unsaturated polyester resin are those which limit the heat of reaction and eliminate excessive foaming or blistering. This can be done by selecting hardeners which are not
are fast in their action or by using * known polymerization inhibitors, which are mixed with the mixture of prepolymer-crosslinking compound
can be mixed. A high heat of reaction, caused by too rapid polymerization, not only causes foaming, but can also cause non-uniform and harmful expansion and contraction of the impregnation resin and the ceramic

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cause bedding mass. In general, the faster the curing time, the better the results, as long as it is not as fast as it is Difficulty handling the liquid mixture between mixing and application results in the disc or the heat of reaction rises too high or causes excessive foaming.

An inner bearing made of solid, cross-linked], unsaturated polyester resin for the grinding wheel can be combined with radial Penetration can be provided in a substantial portion of the ceramic disc by using a oversized disk hole is started and a shaft is used which has a diameter equal to the one desired for the finished disk hole, but less than the diameter of the hole of the untreated disc. When this is done, mold plates are above and below the ■ disk hole arranged and extending radially along opposite sides of the disc at a distance which is equal to the desired penetration.

Impregnating the pores of the disc portion adjacent to the hole with or without an internal fixed bearing portion can be achieved by using a hollow shaft

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which is arranged in the disk hole and has a plurality of radial holes, which spaced around the perimeter, and with the mentioned plates on each side of the hole, so that the liquid mixture τοη prepolymer / crosslinking compound is introduced into the hollow shaft and radially through the holes in the pores of the wall of the Soheibenloches flows. It has been found that with the aforementioned prepolymer and crosslinking compound a excellent radial penetration can be achieved with or without a fixed internal resin bearing, and although without the use of high pressures such as those used in injection molding.

Ceramic grinding wheels have been provided with a bearing in the past that

(1) Molten lead is poured into the grinding hole around a solid stub shaft and it solidifies can and

(2) by injection molding a hot thermoplastic material into the disk hole around a solid stub shaft and cooling to solidify the plastic let and form a solid plastic bearing,

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The first method is costly, while the second method is inadequate because of the high cost Injection pressures can break the soft grinding structure and because high shrinkage of thermoplastic resins has problems of retention desired hole tolerances caused · By using the mentioned liquid mixture of unsaturated Polyester prepolymer and crosslinking compound according to the invention does not need substantial pressure on the hole of the disk, and the shrinkage of the solid resin material is not sufficient to To cause difficulties in maintaining the hole tolerance · Also according to the invention a harder product can be obtained by controlling the process so that in addition to forming a fixed inner bearing also the pores of a substantial annular portion of the Sehexben structure next to the hole to be filled.

It is actually surprising that when using an unsaturated polyester prepolymer and a crosslinking compound according to the invention, HarBana filling and retention in the pores between $ 95 and $ 100 can be achieved, with pore volumes as high as $ 52, therewith

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other thermosetting resins such as available phenol-formaldehyde systems only part of the pore volume holds back the solid resin. This is undoubtedly one of the reasons that the ceramic impregnated disk According to the invention, a much higher strength than a ceramic disc made with phenolic resins is impregnated, whereby the disc according to the invention also withstands much higher speeds and compressive forces

Another reason for the improved filling and holding of the resin and also for the greater strength of the disc according to the invention is that the unsaturated polyester adheres firmly to the ceramic embedding material because of the highly polar ITature of the crosslinked polymers; the adhesive properties of polyester resins are well known.

Another reason for the improved filling and retention of the resin and also the greater strength of the disk according to the invention is that there are essentially no volatile reaction products during curing be formed in situ so that no volatile material during the curing of the prepolymer with the crosslinking Funds are being developed, whereas phenolic resins

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borrowed volatile agents are developed.

It is also believed that another reason for the higher filling and holding of the resin in the pores, which is achieved apart from the absence of volatiles and adherence to the ceramic by strongly polar groups of the polymer, including the special physical and chemical properties Hardness properties of the prepolymer-crosslinking ingredients

en
composition / are, for example, changing viscosity and exothermic heat acts during curing from the time the prepolymer and crosslinking compound are mixed to the final cured stage on the disc, as well as the cure rate.

The cured unsaturated polyester resin forms an essentially permanent phase in the grinding wheels according to FIG Invention.

Grinding aids can be beneficial to either the resin phase chemically incorporated as part of the adhesive resin or physically as a filler. Polysulfide compounds or elemental sulfur or halogen compounds, such as

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-H-

Cryolite can be incorporated into the mixture of prepolymer and crosslinking compound prior to impregnation such compounds are present as fillers in the hardened resin phase. Iron sulfide, Sodium fluoroborate, vinylidene chloride and other conventional ones Filling materials can be used.

"The invention is described below with reference to the attached Drawings explained in more detail

In the drawing show:

Fig. 1 is a cross section through a device for

Impregnation of a vitrified bonded grinding wheel according to the invention, v / obei impregnated from one side of the wheel and a vacuum is used on the other k side.

Fig. 2 is a partially sectioned view of another device for impregnating a vitrified bond Grinding wheel by impregnating one side of the wheel, with one on the other side Vacuum is used

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Figure 3 is an exploded view of certain parts of the Pig device. 2y

FIG. 4 shows the device according to FIG. 2 in perspective; FIG.

Fig. 5 is a sectional view of another device for impregnating a ceramic grinding wheel according to the invention by radial impregnation;

FIG. 6 shows a plan view of the impregnated grinding wheel according to FIG. 5.

Referring to Figure 1, one is untreated, ceramic bonded grinding wheel 2 is shown, the hole of which is plugged by a rubber stopper or holder 4 and which over a vacuum chamber, 6 by means of an annular rubber mold 7 is held. The TJm & ig of the disc is between the two halves 8 and 10 of the mold 7 and has a 6.5 mm thick, circular rubber washer 12 on the top surface or side. The perimeter sections the rubber washer are clamped on the upper surface of the washer 2 between the two halves of the mold, this disk has a central hole 14, the diameter of which is greater than that of the disk hole 20 and is equal to the impregnation area. Thus the exit

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cut 21 exposed of the top of the disc next to the disc hole A vacuum is created in the vacuum chamber generated with the help of a vacuum hose 16 of a shut-off device 18 and a vacuum pump (not shown)

A mixture of the liquid prepolymer and the crosslinkable composition is applied to the exposed top Area 21 of the grinding wheel is cast and the vacuum in chamber 6 draws the mixture into the pores of the section the grinding wheel next to the wheel hole below the area 21.

In Pig. 2 to 4, 6 * is the vacuum chamber with a cap-shaped section 22 on its upper side for receiving a lower removable molded rubber plate 10 ', the grinding wheel 2 ¹ and an upper removable molded rubber plate ^8f , with a plug 4 * extending through the central hole 14' in the Plate 8, the central hole 23 * in the grinding wheel 2 'and through the central hole 24 ¹ in the lower plate. The hole in the top plate 8 ¹ is larger than the disk hole in order to expose an area of the upper surface of the disk adjacent to the disk hole corresponding to the area to be impregnated. The hole 24 'in the lower plate 10' is much larger than the hole in the upper one

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Plate. The plate 10 'corresponds to the mold half 10 in FIG. 1. The vacuum hose 16 ¹ and the closing element 18 * are connected to a vacuum pump, not shown. In this construction the rubber washer is omitted and the upper mold plate is used to delimit the area of the washer to be impregnated. The mixture of prepolymer and crosslinkable composition is poured into the hole H ^{1 of} the upper mold plate 8 ^f on the exposed area of the pane and drawn into the pores of the pane ^{by the vacuum in the chamber 6 1.}

In Figures 5 and 6, a bolt 26 'having a central axial passage 28 is seated snugly in the hole of the grinding wheel 2 ¹ ' with a pair of mold plates 8 "and 10" on either side of the central portion of the wheel as shown. The assembly is held together by means of an enlarged bolt head 30 and aner nut 32. The lower end of the axial passage 28 communicates with a plurality of radially extending, circumferentially spaced holes or slots 34 in connection. The diameter of the sealing plates 8 ″ and 20 ″ corresponds to the diameter of the one to be impregnated

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Area next to the pane hole · The liquid mixture of prepolymer and crosslinkable curing compound is from a nozzle 33 axially through the passage 28 and then radially through the radial passages 34 into the Pores in the section of the pane next to the pane hole

. imagined radial flow of the mixture into the pores a radial distance equal to the radial distance of the sealing plates · A very small one Pressure, e.g. 0.7 kg / cm, is required to achieve good penetration. Such a Pressure is far below that of injection molding and too low to damage the ceramic investment material to cause »By placing this arrangement in a vacuum chamber, the vacuum becomes the liquid mixture pull into the disc pores with no excess pressure.

"By making the bolt a smaller diameter than the washer hole to allow a clearance between the bolt circumference and the wall of the washer hole create, a solid resin bearing can be obtained along with radial penetration into the disc to eiri To create bearings from an inner resin and an adjacent resin-impregnated disk section.

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Example:

Two ceramic-bonded, aluminum oxide grinding wheel structures in the shape of 4 x 12.7 mm more rectangular Ingots were completely filled with a mixture of 99.5 parts of Marco X 1095 unsaturated polyester resin, containing a styrene thinner sold by from Marco Chemical Company, and 0.5 part of a Cadox HDP, which is a ethyl ethyl ketone peroxide, which is sold by Cadet Chemical Corporation. The impregnation was carried out by the Mixture of unsaturated polyester catalizer was allowed into the ingot under atmospheric pressure The impregnated bars were hardened by standing at room temperature for 48 hours, followed by 96 hours at 50 ° C and 47 hours at 110 ° C. The abrasive structure contained alumina abrasives of 46 grain (girt) and had a volume composition from:

Abrasives 48 56 binder 8.5 Pores 43.5

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These impregnated bars together with five non-impregnated bars were subjected to a bending test, with the following results:

Impregnation agent average !. Fracture improvement

module (Kg / cm)

none 187

Marco X 1095

+ Cadox MDP 305 64 f °

It is where excessive foaming occurs in the initial curing in situ prior to resin curing preferred to use either a slower acting hardener or known inhibitors such as water to to reduce foaming and heat of reaction.

The viscosity of the prepolymer should not be that great be that when it is mixed with the hardener and applied to the disc, the viscosity of the mixture increases large for easy penetration into the pores of the disc.

On the other hand, for the purpose of optimal retention of the resin in the pores, the viscosity of the prepolymer should not be be much less than about 500 centipoise at 25 0 » The minimum and maximum viscosity depends on the size

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Claims (6)

Expectations / 1 ./ Ceramic-bonded grinding wheel with a provided therein Hole, characterized in that the pores of at least a predetermined portion of the disc, which is provided next to the hole, impregnated with a thermosetting crosslinked unsaturated polyester resin being about 95 to 100 # of the pore volume of the impregnated portion with the crosslinked Prepolymer is filled. 2. Grinding wheel according to claim 1, characterized in that the crosslinked unsaturated polyester resin with styrene, Crosslinked vinyl toluene, I-ethyl methacrylate and vinyl acetate is. 3. Grinding wheel according to claim 1, characterized in that only the predetermined section with the crosslinked Polymer is impregnated. 4. Grinding wheel according to claim 1, characterized in that the crosslinked polymer contains a grinding aid. 109852 / U13 5. Grinding wheel according to claim 1, characterized in that the hole contains a bearing of the crosslinked polymer, which extends radially into the impregnated portion > 6. Process aar manufacture of the product according to a of the preceding claims, characterized in that at least the predetermined portion of the disc Impregnated with a liquid mixture of the unsaturated polyester resin and a crosslinkable compound which is then cured in situ. 7. The method according to claim 6, characterized in that that hardening is effected without heat. 109852 / U13 . te · ♦ Blank page