Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G59/00—Polycondensates containing more than one epoxy group per molecule; Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups
  • C08G59/18—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing
  • C08G59/20—Macromolecules obtained by polymerising compounds containing more than one epoxy group per molecule using curing agents or catalysts which react with the epoxy groups ; e.g. general methods of curing characterised by the epoxy compounds used
  • C08G59/22—Di-epoxy compounds
  • C08G59/30—Di-epoxy compounds containing atoms other than carbon, hydrogen, oxygen and nitrogen

Definitions

• Grinding grade hardness is a measure of the reluctance or the willingness with which a bond gives up an abrasive grain. Grinding grade hardness is an operational grinding parameter. In general, there is a qualitative correlation between physical grade and grinding grade hardness; there is a direct relationship.
• the degree of physical and grinding grade hardness of grinding wheels and abrasive articles is controlled, to a large extent, by the ratios of abrasive grain, bond, and porosity.
• the softest grade of wheels have the greatest amount of abrasive and porosity and the least amount of bond.
• the hardest grade wheels have the least amount of abrasive and porosity and the greatest amount of bond.
• abrasive article in particular should be structurally uniform throughout.
• grinding wheels of a given lot should be all alike.
• grinding wheels from different lots but made to the same manufacturing specification should be virtually identical or at most varied within prescribed tolerances.
• a breakthrough in the development of a soft grade grinding wheel would be to provide soft grinding action with a structural hardness greater than heretofore possible. Additionally, a significant advance would be to pro vide active grinding aids in soft grade grinding wheels without increasing the grade hardness of the basic soft grade grinding wheel.
• an organic resin bond for abrasives comprises an epoxy resin-based system containing frequently-used grinding aids in the molecular structure (substituents) of the resin system.
• an organic bond for abrasives comprises a tetrabromo bisphonol A-based epoxy resin formed by reacting the brominated bisphenol A epoxide with an amine or anhydride curing agent.
• grinding aids in soft grade wheels in such a way that the soft grinding action can be maintained and improved.
• this is done by making the grinding aid a substituent in the molecular structure of the resin bond system. That is to say, the grinding aid substituents, such as sulphur or the halogens, bromine, chrine, iodine, and fluorine, form part of the internal groups of the epoxides or are substituents of the curing agents such as the amines and the anhydrides. It is also possible to provide extenders and additives such as reactive diluents, which have been halogenated or sulphuried.
• halogenated or sulfonated curing agents While it is not necessary to use halogenated or sulfonated curing agents, amongst the curing agents that are suitable are the halogenated anhydrides such as tetrabromo phthalic anhydride, chlorindic anhydride, dichloromaleic hydride, and tetrachloro phthalic anhydride.
• halogenated anhydrides such as tetrabromo phthalic anhydride, chlorindic anhydride, dichloromaleic hydride, and tetrachloro phthalic anhydride.
• curing agents for epoxides which fall within the inventive concept of providing grinding aids in the molecular structure of the resin system are methylene bis 2,6 dichloro dianiline (commonly known as MOCA). Curing agents derived from acyl halides, alkyl halides, silicon tetra halides, carbon disulphide, hydrogen sulphide contain grinding aid substituents.
• MOCA methylene bis 2,6 dichloro dianiline
• Curing agents derived from acyl halides, alkyl halides, silicon tetra halides, carbon disulphide, hydrogen sulphide contain grinding aid substituents.
• the Thiokol Corporation has marketed polysulphides for blending with epoxides in proportions which would tend to contain a great deal of sulphur.
• Grinding efficiency depends, in part, on the ability of a bond to release a wornout or dull abrasive grain in a timely fashion.
• abrasive articles, or grinding wheels are designed to wear.
• a hard grade grinding wheel as a bond which holds onto the abrasive grain very tenaciously and gives up the abrasive with great reluctance.
• a soft grade containing a bond which releases an abrasive grain in a relatively short time. In both cases, the release mechanism is substantially the same.
• the temperatures in the vicinity of an abrasive grain reaches several hundred to over 1000 F. As the grain becomes dull and must work harder to perform a cutting function, the temperature generated in the grain approaches the higher temperatures in the operating range.
• the resin bond undergoes thermal degradation. At some point, it weakens sufficiently to release the gram.
• the structure of the resin breaks down when it thermal- 1y deteriorates when a halogenated or sulphonated epoxy resin system degrades, there are given off hydrogen halides or hydrogen sulphides, in addition to elemental halogen and sulphur.
• the degradation takes place at the interface of the abrasive grain and the workpiece, precisely where the grinding aids function most efliciently.
• the powdered resin/hardener relationship can range from /10 to 60/40 without any significant effect being encountered.
• the dry segment of the resin system is formed by mixing 8085 parts by weight of solid tetrabromo bisphenol A, sold as Epo-Tuf 90-165 with 2015 parts by weight of diamino-diphenyl-sulphone, sold as Eporal.
• the liquid formulation is 65 parts by weight of a lower molecular weight tetrabromo bisphenol A sold as Epi-Rez 5163, mixed with 25 parts by weight of low molecular weight epoxy derivative of bisphenol A sold as Epi-Rez 510 and 10 parts by weight tetra-hydro-furfuryl-alcohol.
• the alcohol acts to reduce the viscosity of the batch. It also acts as a weak solvent to aid in wetting the abrasive grain.
• the abrasive is first weted with the liquid portion of the resin, then the dry resin ingredients are added and mixed until the dry resin has all adhered to the wetted abrasive.
• the resultant mix is loaded into the mold and is cold pressed at a pressure of about two tons/ink
• the wheel is taken from the mold and is then oven-cured in a curing cycle which starts at F., rises to 390 F. in nine hours, and holds at 390 F. for an additional twentyfour hours.
• the grinding wheels will tolerate some variation in curing temperature. For best results, the end curing temperatures should be between 375450 F. Below 375 F., the resin does not cure completely. Above 450 F., the resin system begins to deteriorate.
• a phenolic resin bonded abrasive was used. The phenolic contained 56% abrasive, 8% bond, and 36% pores, all by volume.
• the grinding grades were substantially identical and the cutting action about the same. It is clear from the foregoing that with the added bond, greater uniformity in product is possible, and an increase in mechanical strength is available.
• the average metal removal rate was 224.3 pounds per pair of wheels for the epoxy, as against 179.6 pounds per pair of wheels for the phenolic.
• the penetration into the example wheel was about half of the normal penetration experienced with the phenolic wheel of similar grinding grade.
• the physical grade hardness i.e., the mechanical strength, is inversely related to the depth of penetration.
• the epoxy resin system described is totally reactive. The components become part of the finished bond with little or not volatilization taking place. Previous phenolic resin systems were plagued with considerable volatilization or plasticizers, which tended to disrupt and alter the bonding mechanism of the resin system to the abrasive, producing a nonuniform bond abrasive relationship whenever the bond distribution in the mix was less than perfect.
• bonds will give a softer grinding action than an equivalent phenolic grade.
• tetrabromo bisphenol A is mixed with 5.1 parts by weight of a curing agent, tri-mellitic anhydride, for example, and 69.4 parts of a filler.
• a curing agent tri-mellitic anhydride, for example
• 69.4 parts of a filler Twenty to forty cubic centimeters of tetrahydro furfuryl alcohol is added as a wetting agent per pound resin.
• the mixture is placed in a mold.
• the mold is held under a pressure of about 2-3 tons per square inch and at about 320 F. for 30-45 minutes until the resin is advanced to a non-fusible state, i.e., partially cured.
• This step is followed by an oven cure at 375 F.-450 F. for up to twenty-four hours.
• the specific brominated bisphenol A system has resulted in the bond structure which provides soft grinding action while at the same time providing a more uniform structure having greater strength than prior art grinding wheels which perform similar soft grinding applications.
• a grinding wheel consisting essentially of an epoxybased bond formed by reacting an epoxide with a curing agent, at least one, the epoxide or curing agent, containing a grinding aid in its molecular structure selected from the group consisting of sulphur and the halogens, chlorine, bromine, and fluorine, and abrasive particles distributed in the resin system.
• a grinding wheel as defined in claim 1 which includes, in addition, modifiers of epoxies and extenders of epoxies having said grinding aids in their molecular structure.
• a grinding wheel consisting essentially of an epoxybased resin system formed from the reaction of tetrabromo bisphenol A with a curing agent selected from the group consisting of an amine and an anhydride, and abrasive particles distributed through the resin system.
• a grinding wheel consisting essentially of an epoxybased resin system formed from the reaction of a dry resin segment consisting essentially of tetrabromo bisphenol A and a curing agent with a liquid segment consisting essentially of tetrabromo bisphenol A, bisphenol A, and tetrahydro furfuryl alcohol, and abrasive particles distributed in the resin system.
• a grinding wheel as defined in claim 9 wherein a hot-pressed bond is formed from 25.5 parts of tetrabromo bisphenol A, 5.1 parts trimellitic anhydride, and 69.4 parts filler, all by weight.

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Polishing Bodies And Polishing Tools (AREA)
• Epoxy Resins (AREA)

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• 1968
  • 1968-12-19 US US785400A patent/US3560176A/en not_active Expired - Lifetime
• 1969
  • 1969-11-18 GB GB1290344D patent/GB1290344A/en not_active Expired
  • 1969-12-15 DE DE19691962803 patent/DE1962803A1/de active Pending
  • 1969-12-16 FR FR6943433A patent/FR2026530A1/fr not_active Withdrawn

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