Patent Application
20150165594
The present invention relates to a system and process for rapid and uniform curing of green grinding wheels.
The invention particularly relates to a system and process for rapid and uniform curing of resin bonded grinding wheels for obtaining grinding wheels with better durability.
The Invention more particularly relates to curing by accelerated heating of resin bonded grinding wheels embedded with/without fiber reinforcement, with the aid of electromagnetic radiations, such as microwaves.
The invention more particularly relates to rapid and uniform curing of resin bonded grinding wheels with the aid of electromagnetic radiations such as microwaves, specifically in the range of 800 to 5000 MHz, more specifically at 2450±50 MHz using pre-designed, customized sample holders made from microwave susceptor materials.
Grinding wheel is a widely used cutting tool to remove undesired material from work piece by abrasive action. Industrial applications of grinding wheels are: cylindrical grinding, profile grinding, internal grinding, honing and super-finishing, centreless grinding, surface grinding etc. The grinding wheels are typically used in various industries including bearing industries, automobile, defense, foundries, forging industries, steel plants, and machine/cutting tool manufacturing, structural fabrication, etc. Generally, the grinding wheels are used in the entire engineering industry. Efficient grinding wheels should have a high and constant cutting capacity and excellent profile durability.
In the manufacturing of grinding products such as resinoid grinding wheels, which are designed to perform heavy duty tasks such as metal cutting made with an abrasive material which is intimately mixed with the bonding ingredients and temporary binders. The bonding ingredient consists of such compounds as are necessary to combine to form the required resinoid bond during curing. The ingredients are mixed and pressed into the required shape. The green product (green grinding wheel) thus obtained, is then placed in the oven for curing for several hours in order to achieve a slow heating to avoid any damage to the product. Typically in the conventional process, green grinding wheels are cured for several hours ranging from 15-30 hours using radiant heating in electrical or gas fired or oil fired ovens at about 180-220° C. with several intermediate holds at different temperatures, by using radiant heating. During the conventional process of curing, pressure is also employed by inserting metallic plates between the green samples.
The conventional process of curing green grinding wheels requires longer duration heating for achieving desired bond strength between ceramic grains and phenolic resins, as both are bad conductors of heat. This results in spending considerable time and energy to achieve the desired properties.
Thus, there is a need to improve the prior art, by lowering the time and energy required during the conventional process of curing of green grinding wheels.
Prior art teaches various techniques used to lower such time and energy in the process of manufacture of grinding wheels, with the help of use of electromagnetic radiations such as microwave. Examples can be seen as follows:
However, as seen above, these techniques have some limitations in spite of using microwave heating for curing and there is further scope of conserving time and energy.
It is an object of the present invention to carry out the process of curing of green grinding wheels in significantly shortened time period using microwave energy, and consequent reduction in energy consumption.
In the conventional process where curing is done using electrical resistance heating or oil firing or gas firing, a steel plate weighing nearly about 1000 g is used for the curing of single sample each weighing about 90 g to retain the geometry of the samples. This creates nothing but excessive dead load. During the conventional heating process, unnecessary heating of the steel plate and side walls of the furnace/oven also consume disproportionate energy.
The use of such metallic plates during microwave heating may cause reflections of microwaves from the metal plates which may tend to damage the magnetron and there is fear of forming hot spots in the microwave cavity. Therefore, there would be an increased risk of damage to be caused to the magnetron and microwave chamber internally. It would also result in uneven heating of the sample and waste of energy due to reflections.
Thus it is seen that there is a need to improve the prior art by reducing unnecessary and wasteful dead load used in the conventional process of curing and also save the energy wasted in heating the same.
It is clear that a plain substitution of microwave process to the conventional heating process is not the solution to the limitations posed by the prior art.
Further, the sample to be cured needs to be evenly heated with a uniform temperature all over its body for retaining its shape.
The shape of the sample to be cured should not be affected while curing, due to uneven weight load or due to uneven heating.
Thus, there is a need to devise a system for rapid and uniform curing of grinding wheels which steers away from the limitations noted above, and achieves the intended objects.
It is an object of the present invention to provide rapid and uniform curing of resin bonded grinding wheels using microwaves which obviates the drawbacks of the hitherto known prior art as detailed above.
It is another object of the present invention to cure the grinding wheels rapidly and uniformly and produce the finished product with acceptable and desired physical properties, in an energy-efficient, economical and safe way.
It is yet, another object of the present invention to obtain a product that gives better performance in its use and is more durable as compared to products cured using the conventional processes.
The present invention provides a system for rapid and uniform curing of grinding wheels, comprising
The susceptible material used for the sample holders is a carbon bearing material, more preferably graphite.
The present invention also provides a process for rapid and uniform curing of green grinding wheels, comprising
The system and the process are preferably used for curing of resin bonded grinding wheels.
The use of pre-designed, customized sample holders made from microwave susceptor materials in the curing process of grinding wheels with microwave energy, provides the necessary objectives, viz.
The sample holders are preferably made of microwave susceptor material such as graphite, and are predesigned and customized according to the desired shape, geometry and profile of the finished product, whereby rapid and uniform curing of resin bonded grinding wheels is achieved. Use of the microwave energy further saves time and resources. After the curing process, sample holders are separated from the product and used for the next batch. Reuse of the sample holders number of times reduces the cost of the process.
In the system and process of rapid and uniform curing of grinding wheels of the present invention, the sample holders are made from microwave susceptible materials selected from carbon bearing materials such as silicon carbide, zirconia based materials, ferrites or graphite. Graphite is the most preferred material.
In the system and process of rapid and uniform curing of grinding wheels of the present invention, the microwave cavity is arranged to provide microwaves in the frequency range of 800-5000 MHZ, preferably 890-2450 MHz and more preferably at 2450±50 MHz.
Microwave technique is an internal heating process where the heat is generated by interaction of electromagnetic waves with the material at the atomic level. The microwave heating process is also known as dielectric heating. As the microwaves interact with the sample, they cause rapid oscillation of the dipoles of the molecules of the constituents such as ceramic grains and organic binders, causing inter-molecular friction. Due to this inter-molecular friction, heat is generated very rapidly, resulting in heating the sample volumetrically and uniformly. The volumetric heating equilibrates the reaction kinetics and forms bonding rapidly. As a result the intermediate soaking steps of the conventional process are minimized or completely eliminated.
Ceramic grains generally used are made from alumina or silicon carbide having different grit sizes which decides its end application. However, the experiments conducted during this invention use grinding wheels with 24 grit size alumina. Organic binders such as phenolic resins or epoxy resins or urethane resins are used for binding the abrasive ceramic grains.
In the present invention, the microwave heating system installed with infrared temperature sensor and the temperature controller is of prime importance to control the sample temperature.
In the present invention, green resinoid grinding wheels are stacked suitably in the pre-designed and customized sample holders made from machinable susceptor material such as graphite, which is a good absorber of microwaves. These are placed in the microwave cavity in such a way as to get uniform exposure in the microwave field at 2.45 GHz. Another component of our system; an infrared temperature sensor is focused on the sample for monitoring and controlling the temperature, and maintaining a typical heating profile of the grinding wheels during the curing process. The infrared sensors can be replaced by thermocouples with proper design and arrangement. Samples are heated as per heating profile in the microwave cavity. The total time taken for curing is significantly lower as compared to the conventional method, wherein the samples are stacked in the microwave cavity and separated by steel plates.
The sample holders in one embodiment of our invention, for curing green resinoid grinding wheels are pre-designed, customized and made of graphite. They not only aid as the lender of support to the samples, but also play an important role in maintaining the shape and size of the grinding wheel. After considerable experimentation, we have come to the present manner of preparation of snugly fitting sample holders concomitant with the apparatus and the process. The present invention not only leads to significant reduction in the energy consumption by reducing the curing time for grinding wheels, but also retains the desired shape and geometry of the grinding wheels after curing. The present invention also leads to enhancement in the performance of the grinding wheels.
As required, details of one embodiment of the present invention are disclosed herein. However, it is to be understood that disclosed are merely exemplary of the invention which may be embodied in various forms. Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a basis for the claims and as a representative basis for teaching one skilled in the art to variously employ the present invention in virtually any appropriately detailed structure.
In the present invention, green resinoid grinding wheel samples 2 are stacked suitably in the predesigned sample holders 1 made from susceptor material such as graphite as shown in
The invention describes the heating i.e. curing of resin bonded grinding wheels by electromagnetic radiation (EMR) such as microwaves, by using a susceptor 1 material which is a good absorber of microwaves even at room temperature. The susceptor 1 material selected in the invention is graphite, which can be machined in pre-designed shapes and profiles of the grinding wheel samples 2. There are alternatives for graphite, such as silicon carbide, zirconia based materials, and ferrites etc. But, these alternatives have inherent problem as the machining of these ceramic susceptor materials is difficult. They need to be either pressed or casted in the desired shape and then sintered to high temperature to attain the strength and geometry. Therefore, the material used in this invention is graphite which is easily machinable. The multiple roles of graphite in this invention are: a) susceptor for initial heating of grinding wheels, b) sample holder and separator, c) load and pressure provider to maintain the final shape and geometry of the grinding wheels, d) absorber of the reflected microwaves from the metallic ingredients present in the grinding wheels and e) ease of drilling tiny holes in the desired pattern to allow easy escape of volatiles and other gases generated, during the curing.
As mentioned earlier, the selection of graphite of standard quality as the susceptor 1 material for the preparation of sample holders of the present invention makes it easy to machine for arriving at the precise dimensions to tightly cover the entire green sample in its final size and shape. The weight of the sample holder for curing the depressed resinoid grinding wheels is only 10-40% of the weight of the steel sample holders used during the conventional curing processes using electrical or gas fired or oil fired systems. This reduced weight of the sample holder holds true to exert the desired load in the gravitational direction as shown in
It is important to maintain the microwave cavity/sample holder/sample temperature in the range of 150-250° C. The most preferred temperature range is 180-220° C. depending on the shape, size and composition of the grinding wheel sample 2. This helps in uniform curing of the green grinding wheel sample 2.
In the conventional process, a steel plate weighing about 1000 g is used for the curing of single sample weighing about 90 g to retain the geometry of the grinding wheel sample 2. But in the present invention, susceptor plate made of graphite, weighing about 100-400 g was employed thereby reducing the dead load by about 90 to 60%. During the conventional heating process, unnecessary heating of the steel plates consumes disproportionate energy which is reduced drastically by the employment of light weight susceptor which works as an active heater under electromagnetic field. The function of graphite in this invention is also to absorb any reflected microwaves from the metallic components present in the green grinding wheel sample 2 to avoid reflection of microwaves going to the magnetron, for its protection. It also exerts the desired pressure on the green grinding wheel sample 2 that enables the fiber reinforcement to penetrate in the matrix to bond the matrix, thereby achieving the desired strength and geometry. The active participation of the sample holders 1 during microwave curing helps in drastic reduction of total time required for curing of resinoid grinding wheels compared to the conventional processing in an electric or gas or oil fired heating systems with metal separators as shown in
Processing conditions of depressed (DP) and cut-off (C) grinding wheels are given below in Table I
Many modifications in addition to those describes above may be made to the technique described herein without departing from the spirit and scope of the invention. Accordingly, following are examples only and or not limiting of the scope of the invention.
A green compact sample of depressed resinoid grinding wheel (DP1), 100 mm diameter, 5 mm thick and 15 mm hole diameter, weighing 90 g was placed between 12 mm thick graphite susceptors weighing 200 g each. The graphite sample holders were made to hold the samples of green grinding wheels to fit snugly in the sample and with tiny holes in the walls of the susceptors. These green grinding wheels consisting of alumina grains mixed with phenolic resins and fillers were cured at 220° C. in 700 W microwave system within 90 minutes.
The microwave cured sample (MW-DP1) of the grinding wheel thus produced above was evaluated for Metal Removal Rate (MRR) and G-Ratio i.e. durability. For this purpose, cured grinding wheel is mounted on a lathe machine installed with electrical motor that delivers 6200 rpm to the 5 mm thick depressed resinoid grinding wheel of 100 mm diameter. Trial was conducted on 28 mm dia., 338 mm long C22.8 grade carbon steel rod weighing 1.6 kg. The carbon steel rod was mounted on the lathe and by adjusting auto motor travel settings maintained uniform travel speed of the wheel with a constant rate in a forward direction giving a cut of about 1 mm on the rotating carbon steel rod. The duration of cutting was 30 min. for both microwave cured wheel (MW-DP1) and commercial grinding wheel (S1). After completion of 30 min., the rod was removed from the lathe and its final dimensions and weight were noted. Similarly, the change in the diameter and weight of grinding wheel were noted. Simultaneously, a commercial sample (S1) of depressed grinding wheel prepared by the conventional process using steel plate as the sample holder was similarly tested for metal removal rate and G-ratio estimation. Results are listed below in tabular form in the following Table II:
Using the standard formula i & ii mentioned below, the Metal Removal Rate (MRR, mm3/min.) and G-Ratio (durability) i.e. the ratio of metal volume removed to volume of wheel consumed was estimated and the results are given in Table III.
Metal Removal Rate (MRR)=(Vir−Vfr)/T (i)
G-Ratio=(Vir−Vfr)/(Viw−Vfw) (ii)
The results as shown above in Table III demonstrate that MRR and G-Ratio values of MW cured (MW-DP1) grinding wheel are better than the commercial grinding wheels (S1) when they are compared after grinding for 30 min. at 6200 rpm.
Another depressed resinoid grinding wheel (DP2) produced by above invented method as described in example 1 was used for cutting metal and for this purpose was mounted on a lathe machine installed with electrical motor that delivers 11500 rpm to the depressed resinoid grinding wheel of 100 mm diameter. Trial was conducted on 28 mm dia., 338 mm long C22.8 grade carbon steel rod weighing 1.6 kg. The carbon steel rod was mounted on the lathe and by adjusting auto motor travel settings maintained uniform travel speed of the wheel with a constant rate in a forward direction giving a cut of about 1 mm on the rotating carbon steel rod. The duration of cutting was 30 min. for both microwave cured wheel (MW-DP2) and commercial grinding wheel. After completion of 30 min., the rod was removed from lathe and its final dimensions, and weight was noted. Similarly the change in the diameter and weight of grinding wheel was noted. From the data and using the standard formula i & ii mentioned above in example 1, the Metal Removal Rate (MRR, mm3/min.) and G-Ratio i.e. the ratio of metal volume removed to volume of wheel consumed was estimated.
Results are shown below in Table IV
The results as shown above in Table IV demonstrate that MRR and G-Ratio values of MW cured (MW-DP2) grinding wheels are better than those of the commercial grinding wheels (S2) when they are compared after grinding for 30 min. at 11500 rpm.
The results as, shown above in Table III and Table IV show that microwave cured depressed (DP) grinding wheels of this invention perform with better durability (G-ratio) at both high and low cutting rates compared with the conventionally cured commercial grinding wheel with the same composition.
Another depressed resinoid grinding wheel (MW-DP3a) produced by above invented method as described in example 1 was used for cutting metal and for this purpose was mounted on a lathe machine installed with electrical motor that delivers 11500 rpm to the depressed resinoid grinding wheel of 100 mm diameter. Trial was conducted on C22.8 grade carbon steel rod with diameter 25 mm. The carbon steel rod was mounted on the lathe and by adjusting auto motor travel settings maintained uniform travel speed of the wheel with a constant rate in a forward direction giving a cut of about 2 mm on the rotating carbon steel rod. The duration of cutting was 30 min. for both microwave cured wheel (MW-DP3a) and commercial grinding wheel (S3). After completion of 30 min., the rod was removed from lathe and its final dimensions, and weight was noted. Similarly the change in the diameter and weight of grinding wheel was noted. From the data and using the standard formula i & ii mentioned above in example 1, the Metal Removal Rate (MRR, mm3/min.) and G-Ratio i.e. the ratio of metal volume removed to volume of wheel consumed was estimated.
Results are shown below in Table V
The results as shown above in Table V show that by increasing the cut from 1 mm to about 2 mm on the rotating carbon steel rod, G-Ratio value of MW cured (MW-DP3a) grinding wheels is better than that of the commercial grinding wheels (S3) when they are compared after grinding for 30 min. at 11500 rpm.
To check the reproducibility of the batch process for depressed resinoid grinding wheels (DP) using microwave technique, few more batch trials were conducted during which more than one sample was processed by stacking green grinding wheels one over other in nos. 2, 3, 5 per batch (MW-DP3a, MW-DP3b, MW-DP4a, MW-DP4b, MW-DP 5a, MW-DP5b, MW-DP5c, MW-DP5d, MW-DP5e respectively). From these batches, a sample was subjected for performance testing on C22.8 grade carbon steel rod with diameter in the range of 25-32 mm and adjusting cut of about 2 mm and compared with the different commercial resinoid grinding wheels of the same type available in the local market (S3-S10). Data of these testing is given below in Table VI.
For performance checking, microwave cured cut-off resinoid grinding wheel (C1) of 65 mm diameter and thickness of around 10 mm was mounted on a lathe machine and tested for 30 min giving a cut of about 2 mm on a rotating carbon steel rod. The duration of this was 30 min. for both microwave cured (MW-C1) and commercial resinoid cut-off grinding wheel (CS1). After completion of 30 min., the grinding wheel was removed from lathe and its final dimensions, and weight was noted. Results are given in Table VII.
While the invention has been described, disclosed, illustrated and shown in certain terms or embodiments or modifications which has been undertaken practically, the scope of the invention is riot intended to be nor should it be deemed to be limited thereby and such other modifications or embodiments as may be suggested and teachings herein are particularly reserved especially as they fall within the breadth and scope of the claims here appended. The preferred form of this invention has been described above. It is possible that modifications thereof may occur to those skilled in the art which will fall within the scope of the following claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2443/MUM/2011 | Jul 2012 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN2013/000445 | 7/17/2013 | WO | 00 |
