US2117970A - Process for making preformed abrasive articles - Google Patents

Description

May-17, 193s.,

E. s. MERRIAM.

PROCESS FOR MAKlNG PREFORMED ABRASIvE ARTICLE Filed July 21; 1956 m a m V1 resented Mey 17, 193s UNlTED -s'rA'rEs rnocrzss Foa MAKING PnEronMEn massive narrows Edmund amen-1am, Marietta, 01110 Y Application 'July 21, 193s, sei-n1 No. 91,739

4 claim. `(ci. 51-27si o This invention relates to a process and appa' ratus for making preformed abrasive articles. More particularly the invention contemplates the provision of a novel, efficient, and economic process Afor producing abrasive wheels'vof superiorl quality. I

This application is a continuation-impart of my copending application Serial No. 41,003, iiled September 17, 1935.

According to current practice, -abrasive grinding wheels are composedof grains `o1' grit of hard abrasive material,-generally oxide of aluminum or silicon carbide bonded together by a suitable bonding agent. 'I'he nature of the bonding ma,- terial and its quantity determine, to a large extent,- the character of thel wheel and the uses to which it may be put. v

Both organic and inorganic bonding materials are used, the latter, however, being the` most common. 'I'he usual bonding material comprises a. vitried 'substance resembling porcelain produced by a controlled process of heating in some form of kiln.

In the manufacture of vitrif'ied abrasive articles, the abrasive grains or grits are mixed with clays of the desired qualities together with i'eldspar, flint, or like materials and water. The mixture is then formed into the desired shape, such as a wheel, by molding or the like. The wheel is then dried and placed in a kiln. 'Ihe characteristics ofthe wheel areocontrolled to some extent by varying the amount and nature ofthe bond` mature and cool the wheels, ,In the pottery type 40 kilns, it may require as long as three weeksv to produce the finished wheel. The use of any kiln the present invention, the great fuel costs incivdent to the manufacture of vitrined abrasive wheels are reduced to a minimum as are the labor costs and capitalinvestment. Furthermore the production of my improved abrasive wheel Ais reduced. to a one-day operation.

In accordance with' the present invention,'the heat necessary to produce the vitriiled bond in the wheel is generated in immediate juxtaposition to the wheel itself without the application of heat in the manner required in kiln tiring.

. While the invention in its broader aspect vcomprehends any of many modes of generating the necessary heat to form the vitrifled bond in situ in immediate juxtaposition to the wheel, my preferred methodwill be rst described. In thir method the abrasive grains or grits are mixed with the necessary known ingredients yto formV the required bond in the `finished wheel.

In its more specific aspects, the invention contemplates the molding of green abrasive articles, more particularly abrasive wheels, from a vention claimed in my copending application Y Serial No. 41,003, iiled September 17, 1935.

The present invention contemplates placing the green molded abrasive articles in a closed retort wherein each article is completely surrounded by a granular material, for example, abrasive grains similar to those included in the abrasive articles being formed. This material is inert at the temperature necessary to fori'n a vitreous bond between the abrasive grains in the articles being formed. There 'is included in said surrounding granular material a combustible material 'in sume cient amount to generate,'whenburned in the retort, adequate heat to form a vitreous bond between the abrasivev grains in the articles being produced. f

In one/ contemplated procedure, the green abrasive wheels are prepared in the form of two juxtaposed layers, onegsof which is adapted t'o constitute, when the process is completed, the abrasive wheel and the other one of which carries therein combustible material to be burned out during the process for the purpose of generating heat to form a vitreous bond between the abrasive grains in the wheel being produced.

In carrying out my process, it is preferable to employ a combustible material to be burned in the retortwhichwill not react so vigorously as to cause violent escape of volatile products, and it is further preferable to employ a combustible material that will not leavevany objectionablenon-volatile residue lin the granular material after the combustible material has been burned therefrom. I have found petroleum coke or coke produced from coal tar to be very satisfactory for use as the combustible material in the procs of the present inventionqsince such combustible material produces substantially no ash. Y Other. l

combustible materials possessing the above de# nned characteristics are, of course, suitable for I have found it preferable to employ, for forming the vitreous bond between the abrasive grains in the articles produced, a pre-fused or ix'lttedv material since, through the employment of such a bonding agent, only a relatively simple fusion is required to be eiected in the article. It will be appreciated that clays, feldspar, and flint,

formed. This temperature can be produced inA the articles, however, when carrying out my process by employing only a comparatively small amount of -carbon or its equivalent in the granular material surrounding the green molded articles in the retort. By employing, inA carrying out the process, an atmosphere of oxygen, it is possible to even further reduce the amount of con1=l bustible material necessary to generate the requisite heat in the abrasive articles being manufactured. It is to be understood, however, that an atmosphere of oxygen is not essential since the burning may be effected solely through the use of air.

It is to be understood that inthe molding of `the green wheel before heat treatment. any

conventional temporary bonding agent may be employed, such, for example, as dextrine and Bakelite which burn oil completely during the heat treating step.

Where the green wheel is formed in two layers,

one of which contains the vitreousv bonding material and the other of which contains the combustible material, it will be observed that, after the burning out of the combustible material from the layer containing the same, the 'gr-anular material of that layer becomes wholly free and represents loose unbonded grains since the temporary bonding material simply acts to hold the wheel together in its preformed shape during the drying and handling operations preparatory to placing it in the retort. i

'I'he invention will be further described in connection with the accompanying drawing, wherein:

Figure 1 is a vertical cross-sectional view of the retort employed in connection with the invention and illustrating one manner of placing the abrasive wheels therein;

Figure 2 is a crosssectional view o! a temporarily bonded green `wheel formed in layers; and

Figure- 3 is still another view of a special type of green molded Wheel as prepared to be placed in the retort.

Referring to thedrawing and more particularly to Figure 1, the retort embraces the outer cylinder l of thin metal and the somewhat heavier top 2 and bottom 3. The cylinder I carries an-f' nuiar Viianges 4 and 5 at the top and bottom,

respectively,A adapted to cooperate with the pe' ripheral flanges 6 and 1 at the top 2 and bottom 3. A suitable deformable metal washer l is clamped between the anges I and 6 atv the top, and a similar washer s is clamped between the iianges and 'I at the bottom.l V'I'he bottom '3 may, of course, be permanently united to the cylinder I. As illustrated, however, both the top 2 and bottom 3 are removable by simply taking out Y the clamping bolts I0. Y, f 'Ihe top 2 and bottom 3 arelrelnforced by angle iron struts II welded thereto. The top is provided with a central opening I2 and the bottom with an opening I3. An inlet pipe Il has a gastight ilt with the opening I2 and is provided with valve controlled branch line's I5 and II for air and oxygen. There is also mounted on the line Il a suitable pressure gauge I1' for observing the pressure conditions prevailing in the retort. Immediately below the opening I2 in'cqver 2, there is suspended by rods I8 a baille member I9 to prevent channeling of the incoming air or oxygen. `An outlet pipe 2|! for combustion gases and cooling air has a gas-tight ilt in the opening Il in the bottom of the retort. The retort carries trunnions 2| that permit it to be inverted for removal of its charge'of treated wheels.

A free circular space having a diameter somewhat greater than that of the wheels to `be treated is provided at the bottom immediately above the outlet line 20. This space is between thebottom 3 and the perforated plate or screen 22 suitably supported a few inches abovethe bottom.

An open-ended cylinder 23 having a diameter somewhat greater than that of the wheels to be treated is disposed in concentric relation to the outer cylinder I. The annular space vbetween the cylinders I and 23 is packed with vsuitable insulating material. A spark plug 24 is iitted into the cover 2, and a coil of readily ignitable thin ironwire 25 is attached to its terminals. The

lead 26 extends to any suitable source of electric current such as a- 110-volt service line.

In packing a bath of wheels in the retort, a bed of abrasive grains such, for example. as used in the wheels and containing combustible material is filled in at the bottom of the cylinder 23 and supported on the perforated plate 22. baille plate 21 may advantageously be set in the bed. The iirst green wheel is next laid on the bed and, if the wheel is of the type shown in Figure 1, has free abrasive grains filled in around its circumference and in its axial opening. There is then placed over the first wheel a layer of abrasive grains having mixed therewith coke or wheels. The top Wheel is covered with a layerl oi' grains and admixed coke, and there is also advantageously provided a layer of a suitable readily ignitable substance in immediate proximity to said iron wire coil 25.

When the green lwheels are formed in layers, I preferably provide two mixtures for that purpose. The rst mixture comprises suitable abrasive grains, a prefused vitreous bonding material in finely divided form and in .n amount suicient to eiectivelybond, when refused, theabrasive grains in the wheel, and a temporary binder. The second mixture comprises grains that are inert at the temperature necessary to re-fuse the vitreous bonding material in the wheel. Such grains maybe advantageously be additional abrasive grains of the character employed in the wheel.

The second mixture also comprises combustible material,l such, for example, as petroleum coke,v

in suitably weighed proportions to give af controlled degree of heat, and a temperary binder.

Such a green molded wheel is shown in Figure 2 wherein the top layer contains the combustible material and the bottom layer contains the vitreous bonding material. In Figure 3 I have shown still another form of pre-molded green wheel wherein the abrasive wheel containing the vitreous bonding material is surrounded by a molded rim made up of the same .mixture as the tcp layer and, therefore, free from any bonding material.

When pre-molded green wheels of the character shown in Figures 2 and 3 are used in carrying out the process, it will be apparent that they are laid in the retort one directly on top of the other. 'This facilitates the carrying out of the process in that it avoids the necessity for the detailed attention necessary in filling in and leveling off the individual layers of free grains intermediate the respective individual wheels.

When the retort is packed, the cover 2 is affixed in sealed relation thereto, and oxygen is supplied through the line |5. Suitable means such as a iiow meter (not shown) may be provided in the lines Il and 20 for accurately controlling the rate of iiow of air or oxygen through the retort. A switch (not shown) in the spark plug circuit is next closed, which effects ignition in the retort. After ignition has been effected, excess air ymay be vsupplied through line I6 in substitution for all or a part of the oxygen being supplied through :line I5. The burning takes place very rapidly and can be controlled by the pressure at which the air or oxygen is supplied and the rate of. flow thereof through the retort. Ordinarily burning is complete in from twenty yto thirty minutes. During this time no heat leaves the retort, and the outgoing gas remains cool and is largely C02. Heat does not begin to escape through the retort wall until nearly an hour later. If time is not 'a factor, cooling is allowed to occur without acceleration and requires from twenty-four to thirty-six hours. By passing a slow stream of air through the retort, the cooling time can be reduced to around eight hours without deleterious 'eects The current diiilculty of non-uniformity of perature measuring instruments of any kind since, by precise measurement of the fuel introduced to the mix and control of theiiow of the gas. 'a consistently uniform product' necessarily' results.

A further modiiication of the process contemplates adding to the'wheel mixture a substance capable of combining with -various metallic oxides forming a bonding substance and then burning the suitable metal. An illustrative example comprises mixing with the abrasive grains bothl borax and metallic zinc and then burning grains. a previouslyfused vitreous bonding material in finely divided form capable upon being re-fused to effectively bond said abrasive grains, and a temporary binder, molding said mixture into the desired form, placing the resultant green article in a .suitable retort and embedding the same therein in a mass of granular material inert at the temperature required to re-fuse said vitcooling of the articles by circulating a current of a gaseous cooling medium through the retort.

2. A' process for producing abrasive wheelsl comprising preparing two mixtures, a iirst mixture embracing suitable abrasive grains, a vitrifiable bond, and a temporary binder, and a second mixture embracing granular material inert at the temperature required to form a vitreous bond, a combustible material, and a temporary binder, molding a green wheel composed of two layers, one of said layers formed from said first mixture and the other layer from said second 'mixture whereby one of said layers'contains a vitriiiable bond but isfree fromcombustiblematerial and the other of said layers contains combustible material but is free from a vitritlable bond, stacking a plurality of said molded wheels one upon the other in a retort, and igniting and burning the combustible material in the layers containing the same to generate heat for forming a vitreous bond between the abrasive grains in the vjuxtaposed layers.

3.In a process for producing preformed abrasive wheels, the 4steps which comprise preparing a rst mixture embracing suitable abrasive grains, a previously i'used vitreous bonding material in finely divided form capable of being refused to eiectively bond said abrasive grains, and

a temporary binder, preparing a second mixture comprising granular material inert at the tem.- perature required to fuse said vitreous bonding material,` a combustible material, and a tempo-l rary binder, and then molding a green wheel in a plurality of layers in such manner that juxtaposed layers are formed from said first and second mixtures, respectively. f

4. A process for producing preformed abrasive articles comprising molding a mixture comprising suitable abrasive grains, a vitriiiable bond, and a temporary binder, placing the molded articles in a closed retort wherein the articles are separated one from the other by a granular material substantially inert at the temperature required to form a vitreous bond between the abrasive grains in the articles, providing a dispersed comminuted combustible material in such close juxtaposition to the abrasive4 grains of the ar- .ticles that it will, when burned in the retort, gencrate adequate heat in situ to form a vitreous bondv between the abrasive grains of the articles, igniting and burning the combustible material in the closed' retort, and, after the combustible materialhas-been burned and a vitreous 'bond produced between the brasive grains of the articles, circulating a slow current of a gaseous cooling medium through lthe retort to control the cooling of thebonded abrasive articles.

EDMUND s. Miramax.

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