This invention relates to a forced draft whitening machine for whitening Rice, Barley, Paper and like grains.
It has been experienced that during whitening, of rice grains using conventional methods, there is a considerable quantity of grains breaking into broken grains and tips. This is mainly because of the heat generated due to abrasive action of the grains against silicon carbide grinding wheels.
There are three types of conventional grain whitening machines in the field.
a) A vertical type conventional machine with suction draft, i.e., the air required for cooling the grains is sucked from atmosphere into the whitening chamber. The same suction draft is also used for collecting the bran generated during whitening. Because of this, the efficiency of the machine is less and also the suction draft is not sufficient enough for cooling of the heat generated during the process and hereby the brokers percentage is high.
b) A vertical cone type polisher is also available in the field. In this, the suction draft is used only for collecting the bran (dust) generated during whitening. The grinding stone is of very heavy construction [M.S. casting coated with abrasive grains] weighing almost 120 Kgs. No mechanism for moving the screens towards or away from the tapered grinding stone [cone type] is provided in this type of machine. When this type of machine is used to whiten the raw rice, the percentage of brokens will be abnormally high, around 50-55%. In general, this type of machine is used only for boiled or parboiled rice only.
c) In the third type, the plurality of grinding wheels are mounted on a shaft horizontally. Because of this arrangement, the whitening process takes place not only on the flakes of rice grain but also on the tips. As a result, the percentage of brokens is very high (=25%). Also this type of whitening machine is not used for Basmati/ boiled/parboiled rice, because the whitening chamber gets clogged with the sticky bran generated. Here also the suction draft used is very low which cannot remove the total bran dust generated.
The present invention provides a forced draft whitening machine for rice, pepper, barley and like grains comprising:

This invention proposes to provide a forced cooling system which carries away the heat generated during whitening. In addition to this another suction fan can be provided for additional suction and carrying away the dust generated called as Bran. By providing this forced draft cooling system the air from the atmosphere is forced into the whitening chamber because of which the rice or the like grains are cooled, thereby reducing broken grains. The air pressure inside the whitening chamber being higher than the air pressure outside the whitening chamber, no clogging of the screens takes place.
A screw-feeder can be provided at the upper end of the housing for uniformly feeding grain from the hopper to the whitening chamber. The screens are preferably mounted on frames which are linked by a lever, so that the screens can be moved towards or away from the grinding wheels. A threaded shaft can be connected to the lever for moving it. The whitened grain exit may comprise a flange fixed to the lower end of the housing, said flange having holes through which whitened grains exit.
The improvement of the present invention is that a whitening machine using forced draft can be used for all varieties of grains i.e., Basmati/boiled/parboiled/steamed/raw rice, barley, pepper and like grains. The draft provided is suitably designed to take care of cooling of the heat generated during whitening. In addition to this, forced draft blows away all the sticky bran generated in the whitening chamber during the process. A suction blower, sucks this dust and blows it into a cyclone and the same can be collected at the bottom of the cyclone. This suction blower and cyclone are optional features of the whitening machine. The suction blower need not be necessarily used.
In a preferred embodiment of this invention, the machine used for whitening the rice grains and other cereals consists of a perforated hollow shaft and a blower is fitted right on top of the hollow shaft. The hollow shaft surrounded by a number of grinding wheels made of silicon carbide is fitted within a housing vertically. The drive for the hollow shaft is transmitted by an electric motor fitted either inside the machine or externally. The machine also consists of a whitening chamber with screening jacket. An additional suction blower is fitted to the whitening chamber so as to maintain the air draft and thereby cooling the product and also carrying away the dust produced during whitening process. A suitable inlet and outlet connection is provided for the machine.

The rotary shaft is hollow inside and also has a number of holes drilled radically on the periphery of the shaft so as to provide passage for the air forced inside the whitening chamber. The hollow shaft is vertically fitted in the housing by means of bearings. A driven taper lock pulley is fitted on to the shaft and made to rotate by means of an electric motor.
The drive arrangement is covered by an M.S Sheet guard over which an air blower is fitted so as to blow air through the hollow shaft into the whitening chamber. This will facilitate cooling of the product being whitened thereby achieving the maximum whiteness of the product with minimum percentage of brokens (for eg. Rice). The air flow also improves the efficiency of dust (bran in case of rice) collection.
The hollow shaft fitted with grinding wheels is surrounded by screens having a number of oblong perforations for retaining the product inside the whitening chamber and allowing only the dust to the outside of the whitening chamber. The air being blown into the whitening chamber blows away the dust from the whitening chamber.
The screens are fitted onto three frames made from circular rings and intermediate ribs cut at 120° and linked together to form a circle. When one of the links is pulled outwards, one end of each screen along its length starts moving towards the grinding wheel. Three vertical brakes are fitted on the screens, and these brakes press the product being whitened along their flanks towards the grinding wheel for achieving whiteness.
The whitening chamber is preferably surrounded by a dust collecting guard, which is in turn connected to a suction blower to carry away the dust generated during whitening process.
The hollow shaft consists of vertical cylindrical shaft which is hollow at its center and number of perforations are provided on the periphery of the shaft. A blower designed for maintaining a differential pressure from inside to outside the whitening chamber is mounted directly above the shaft. Around 4 to 10 numbers of grinding wheels made of silicon carbide material are mounted around the shaft for a length of 250mm to 750mm depending on the requirement.
It has been observed in practice that when the rice grains are allowed to slide around the grinding wheels surrounded by a screening jacket, it starts moving downwards helically at an angle of about 5° to 10°. This path pattern is mainly because of the rotation of the grinding wheels and the pressing of the grains by the brakes. So, a screen is provided around the grinding wheels at a specified distance. The screens can have a number of oblong slots at

specific inclination for effecting the easy passage of "Bran" during Whitening process. The width of said oblong slot should be predetermined so that no rice grains will come out of the slots but only bran dust comes out. These oblong slots will also guide the rice grains in a helical path of predetermined inclination around the grinding wheels. The screen when fitted with brakes, can carryout whitening process by forcing the grains against the grinding wheels.
The whole whitening chamber is preferably surrounded by a guard which is turn is connected to the suction blower for carrying away and collecting the bran through cyclone separators.
In order to achieve maximum degree of whiteness of rice grains with minimum percentage of brokens, it is essential that the whitening chamber is fill of rice grains and all the grains must pass a path of specified degree of inclination around the grinding wheels with the air forced into the chamber for cooling the grains.
To maintain the uniformity of material in the whitening chamber, a screw feeder is preferably fitted in front of the grinding wheels which when they rotate, draws the grains from the hopper and uniformly feeds the grains into the whitening chamber to distribute the grains evenly in the whitening chamber.
The grinding wheels are made to rotate in the whitening chamber by means of a motor and the shaft. The speed of rotation of grinding wheels should be 500-1300 rpm depending on the product being processed. It becomes very much essential that the grinding wheels are dynamically balanced in order to increase the life span of grinding wheels. Inspire of dynamic balancing and forced draft cooling the grinding wheels will have a definite working life after which they must be replaced by new ones.
The hollow vertical shaft has a minimum length of 800mm. The length of the shaft and the number of grinding wheels however depend on the type of grains and the whiteness required.
A preferred embodiment of the present invention will now be described with reference to the accompanying drawings, wherein-
Fig 1. Shows the front elevation in cross section of the machine of the present invention; and
Fig 2. Shows the top view of the whitening chamber along section A-A in fig 1.

The housing (1) of the machine is made of rectangular tube structure covered with M.S Sheets. An inlet hopper (2) supported by two M.S Plates is mounted cantilever to the housing (1). A perforated hollow shaft (3) is vertically placed in the housing and supported by two bearings (4) A screw feeder (5) mounted just above the whitening chamber (1) draws the rice grains from the hopper and distributes them uniformly around silicon carbide grinding wheels (6).
Each grinding wheel is held in between two M.S Flanges (7) and the hollow shaft (3). All the grinding wheels are fixed to the hollow shaft (3). Screens (9) are mounded on to a frame (8). The frame (8) comprises of two circular rings supported by vertical ribs and each ring is slit at 120° to divide it into three pieces which are linked together by lever (11). A wearplate (10) of predetermined thickness is mounted on one end of each of the screens. Each link is connected to a threaded shaft (12). When one of the link is pulled out by rotating the threaded shaft (12), the end of the screen where the wearplate is fixed moves towards the grinding wheels and presses the rice grains against the wheels. Because of the abrasive action, the top layer on the rice grain is removed, which forms a fine dust called Bran
A lot of heat is generated because of the abrasion and the same is carried away by air forced by means of blower (13) into the whitening chamber through the perforation in the hollow shaft. Because of the cooling effect, the rice grains can be pressed more against the grinding wheels which will result in higher degree of whiteness which lesser percentage of brokens the bran generated in the whitening process is sucked outside the whitening chamber from bran exit (18) by suction blower (14). The suction blower (14) can be connected to a cyclone (not shown) for collecting the bran sucked from the bran exit (18). The whitened rice grains will come out of the whitening chamber through holes provided in a flange (15) fixed on the housing (1).
The throughput of the product can be controlled by means of a knob (16) and conical hub (17). When the knob (16) is moved towards the machine, the conical hub (17) blocks the outlet passage and vice versa.
In the operation of the forced draft whitening machine just described, the hollow shaft is driven by an electric motor (not shown) by belts. The forced air draft blower and the suction blower are switched on before the product is fed into the machine, for the product to the cooled and the bran dust to be carried outside the whitening chamber. The product enters

the machine though an inlet chute (19) to the hopper (2). The screw feeder (5) draws the product from the hopper and feeds it into the whitening chamber (1). The three screens (9) with wear plate (10) mounted at one end of each screen are moved towards the grinding wheels by rotating the shaft (12) manually. The rice grains thereby are pressed against grinding wheels which whitens the rice grains by removing the top layer on the flanks of rice grains. During the whitening process the rice grains move helically downwards at a specified angle.
By adjusting the position of the knob (16) it is possible to increase or decrease the output of the machine.
WE CLAIM ;
A FORCED DRAFT WHITENING MACHINE COMPRISING OF:
1. A housing having a whitening chamber in which a perforated hollow shaft extends vertically;
A hopper at the upper end of the housing to feed grain into the whitening chamber;
A plurality of grinding wheels mounted on the shaft for grinding the grain as it moves down from the hopper end of the housing;
A blower connected to said shaft at the upper end of the housing for blowing air into the whitening chamber through the perforation in the shaft;
A plurality of screens mounted inside said housing adjacent to the grinding wheels, said screens being mounted so as to move towards or away from the grinding wheels;
A bran exit provided in the whitening chamber;
An exit for the whitened grain at the bottom end of the housing; and optionally
A suction blower connected to the bran exit for removing bran coming out of said screens.
2. A machine as claimed in claim 1 wherein the shaft is hollow inside and also has a number of holes drilled radically on the periphery of the shaft so as too provide passage for the forced air inside the whitening chamber.
3. A machine as claimed in claims 1 and 2 wherein the hollow shaft is vertically fitted in the housing by means of bearings. A driven taper lock pulley is fitted on to the shaft and made to rotate by means of an electric motor.

The machine though an inlet chute (19) to the hopper (2). The screw feeder (5) draws the product from the hopper and feeds it into the whitening chamber (1). The three screens (9) with wear plate (10) mounted at one end of each screen are moved towards the grinding wheels by rotating the shaft (12) manually. The rice grains thereby are pressed against grinding wheels which whitens the rice grains by removing the top layer on the flanks of rice grains. During the whitening process the rice grains move helically downwards at a specified angle.
By adjusting the position of the knob (16) it is possible to increase or decrease the output of the machine.
WE CLAIM ;
A FORCED DRAFT WHITENING MACHINE COMPRISING OF:
1. A housing having a whitening chamber in which a perforated hollow shaft extends vertically;
A hopper at the upper end of the housing to feed grain into the whitening chamber;
A plurality of grinding wheels mounted on the shaft for grinding the grain as it moves down from the hopper end of the housing;
A blower connected to said shaft at the upper end of the housing for blowing air into the whitening chamber through the perforation in the shaft;
A plurality of screens mounted inside said housing adjacent to the grinding wheels, said screens being mounted so as to move towards or away from the grinding wheels;
A bran exit provided in the whining chamber;
An exit for the whitened grain at the bottom end of the housing; and optionally
A suction blower connected to the bran exit for removing bran coming out of said screens.
2. A machine as claimed in claim 1 wherein the shaft is hollow inside and also has a
number of holes drilled radically on the periphery of the shaft so as too provide passage
for the forced air inside the whitening chamber.
3. A machine as claimed in claims 1 and 2 wherein the hollow shaft is vertically fitted in
the housing by means of bearings. A driven taper lock pulley is fitted on to the shaft
and made to rotate by means of an electric motor.

"4. A machine as claimed in claim 3 wherein the drive arrangement is covered by M.S Sheet guard over which an air blower is fitted so as to blow air through the hollow shaft into the whitening chamber. This will facilitate cooling of the grains being whitened there by achieving the maximum whiteness of the product with minimum percentage of brokens (for eg. Rice). This air flow also improves the efficiency of dust / bran collection.
5. A machine as claimed in claim 1 wherein the grinding wheels are housed on the hollow
shaft is surrounded by screens with number of oblong perforations for retaining the
product inside the whitening chamber and allowing the air blown into the whitening
chamber blows along with the dust to outside the whitening chamber.
6. A machine as claimed in claim 1 and 5 wherein the screens are fitted onto three frames
made from circular rings and intermediate ribs cut at 120° and linked together to form a
circle. When one of the link is pulled outwards, one end each of the screen along the
length starts moving towards the grinding wheel.
7. A machine as claimed in claim 5 wherein the three vertical brakes fitted on the screens
presses the product being whitened along their flanks towards the grinding wheel for
achieving maximum whiteness.
8. A machine as claimed in claims 1 and 5 wherein the screens have a number of
specifically inclined oblong perforations and hence the product in the whitening
chamber starts sinking downwards helically at a path pattern of an angle of specific
degree mainly because of the position and rotation of grinding wheels and the pressing
of the product by the brakes.
9. A machine as claimed in claim 1 wherein the whitening chamber is surrounded by a
dust collecting guard and the said guard in turn is connected to a suction blower to
carry away the dust generated during whitening process.
10. A machine as claimed in a claim 1 wherein the whitening machine in all the claims 1 to
9 shall have suitable inlet and outlet for the product.
11. A machine substantially as herein before described with reference to figures and
illustrated and described in the accompanying drawings.

Although the present invention has been described with reference to a specific embodiment as particularly described and illustrated in the accompanying drawings, it is to be understood that it is not limited to the said specific embodiment but also includes modifications which are clearly within the scope and ambit of the present invention as would be apparent to those in the art.