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Guide To Collide - GTC Technology is a size reduction method that manages to guide the fluidized-bed of material to collide with hammers.

GTC Technology Introduction
GTC Technology is a size reduction method that manages to guide the fluidized-bed of material to collide with hammers.
 * It greatly increases the probability of frontal collision between material and hammer under same energy consumption
 * It makes full use of kinetic energy of fluidized-bed of material, succeeds in enlarging impacting capacity 31 times that of single rotor hammer mill, which could dash material into shatters once even eccentric collision
 * It stops the formation of material circulation layer effectively
 * It highly improves the efficiency of screening capacity by enlarging 20% the effective screening area and keeping agitating fluidized-bed of material, reduce the density of material layer against the screen surface
 * It promises to produce more than 40% under same energy consumption; in other words, save more than 30% energy under same production capacity
 * It promises temperature rise less than 15℃ when grinding aquatic and poultry feed

Background
Main reasons for high energy consumption, low throughput, rise in temperature of ground material of hammer mills in feedstuff industry are:

Poor hammer milling capacity. Large amounts of colliding energy wasted as heat due to high rate of eccentric collision which only making materials spinning and bouncing in grinding chamber and cannot size reduction once.

Poor screening capacity. There’s definitely a material circulation layer swept along the inner surface of the screen, hindering correctly sized particles getting through the screen hole in time. As these particles rub against the screen and each other, crushed by hammers, their size is continually reduced by attrition and collision. Energy is wasted in the production of heat, throughput is restricted, and particles become too small.

Poor hammer milling capacity
Materials, such as corn could be broke up by little energy when frontal collision, however large power is needed when eccentric collision. Because when eccentric collision happens, a moment of gyration generated between impact point and corn barycenter. In general, it only makes corn spinning not to break up. That falls into the category of elastic collision, the impact power turns into the form of heat and wasted. However, corn could be broke up along midpoint of its maximum length due to bending moment if the impacting speed is fast enough. During the process of milling in hammer mills, eccentric collision happens mostly, large energy wasted. Therefore, the methods manage to increase the probability of frontal collision between material and hammer and enlarge the impact velocity could improve the efficiency of hammer mills.

Experiment No.1
To see what’s going on in a working hammer mill, researchers designed experiment by using high speed photography technology. High speed photography need specially designed hammer mill like figure 1. Main technical parameter is as below: Diameter of rotor: 400mm Width of grinding chamber: 580mm Quantity of hammer: 4row 8hammers Dimension of hammer: 120X40X5mm Distance from hammer tip to screen is 5mm Shape of grinding chamber: water-drop Feed material through hopper on top of hammer mill

One side of hammer mill was equipped with plexiglass, whole grinding chamber was visible till 10mm outside screen. Camera’s frame rate was 5,000FPS, exposure was 1/25,000s, hammer mill’s rotation speed was 3314RPM, hammer tip speed was 69m/s when photographing. Two videos were captured separately when grinding corn at normal load and below normal load. Videos were analyzed and processed in professional image processing system. Some typical corn particles were tracked and their movements showed like figure 2-3. It could be seen from the video that there’s definitely a material circulation layer formed on the screen surface in chamber. The first tracked corn particle didn’t fall into hammer impacting area, it moved on the hammer impacting area along hammer rotating direction, and it rebounded into hammer impacting area after collided with the screen. Reason for this phenomenon is corn fed into hammer mill with low speed cannot pass through the material circulation layer. The first tracked corn particle was broke up within 0.4ms at a relative speed 57.45m/s when frontal colliding with hammer. The second tracked corn particle rebounded into hammer impacting area after collided with screen as the first one. However, it spun and bounced in the chamber when eccentric colliding with hammer. It needs further impacting to size reduction. Eccentric collision happens mostly in the two videos.

Poor screening capacity
According to traditional size reduction theory, in working hammer mill’s chamber, due to centrifugal force, big particles close to the inner screen surface tightly, the smaller particle the more far from the screen. Big heavy particles are difficult to exit through the screen hole and block the holes, while small light particles are far from the screen hole, also cannot easily exit through, thus form a material circulation layer with outer big particles and inner small ones. In view of the above, various shape of grinding chambers were developed to disrupt material circulation layer, such as hexagonal, elliptical, water-drop etc. However, some researchers did corn grinding experiments to compare every chamber shapes, and they found that when feeding at a low speed, compared with round chamber, hexagonal, elliptical, water-drop shaped chambers’ capacity per kilowatt were higher; but when feeding at a higher speed, capacity per kilowatt of hexagonal, elliptical chambers were lower than round one, while water-drop one was similar to round one. That is because when feeding at a higher speed, stagnated materials appear at hexagon’s every corners, two ends of ellipse and top frontal impacting screen area of water-drop chamber (Figure 4). Stagnated materials reduce real screening area and big particles hard to bounce at those places, so capacity drops. If continue to increase the speed of feeding, stagnated materials will grow to fill the chamber a round one, and the real screening area reduced sharply.

In truth, however, big and small particles are distributed evenly in material circulation layer, the density distribution is the more near inner screen surface the greater density, so material circulation layer is inner loose outer tight. Therefore, reduce the density of material on inner screen surface can largely improve the screening capacity of hammer mills.

Experiment No.2
Researchers designed a special hammer mill (Figure 5) to acquire material circulation layer distribution data directly, which revealed the truth. Materials fed into hammer mill by hopper, correctly sized particles exit through screen and drawn into fan chamber, finally thrown out of hammer mill by air. There’s a fixed partition between grinding chamber and fan chamber. 8 sampling probes (4 as a group) installed along radial direction evenly on fixed partition (Figure 6). Sampling probes connect grinding chamber and fan chamber (negative pressure), high breathability sampling bags covered to end of sampling probes to the fan chamber side. Then distribution data of material circulation layer along radial direction could be aquired.

Main technical parameter of hammer mill is as below: Width of screen: 200mm Diameter of screen hole: Φ2mm Motor power: 5.5kW Hammer tip speed: 60m/s Feeding speed: 700kg/h Corn moisture content: 12.5% Single grinding quantity: 9.5kg

Researchers checked the materials in every sampling probes, found that average particle size was similar along radial direction, all around ensemble average size of sample, 1.12±0.04mm. (Ensemble average size of sample was tested by mixing all samples in probes) Density (definition: material mass per unit volume) distribution of material circulation layer along radial direction was low to high. That is, the bottom of material circulation layer, which close to inner screen surface, density was high; the more near to the center of chamber the lower.

GTC Guide
GTC Guide (fluidized-bed of material diversion plate) ensures high probability of frontal collision between fluidized-bed of material and hammers. GTC Guide is a plate similar to a cuboid, whose section is a parallelogram with two sides bows inward. It is installed between two rotors and through the center of grinding chamber, which separates the whole chamber into chamber 31a and 31b. It blocks the whole chamber’s center space, chamber 31a and 31b could communicate by the tunnel on top and bottom of GTC guide. So GTC guide can guide and divert. Guide: GTC guide guides material into neighboring chamber’s hammer impacting area in suitable angle, making moving direction of fluidized-bed of material is opposite with that of hammer. Divert: GTC guide avoids low efficiency collision between two fluidized-bed of material in two chambers, and ensures high probability of frontal collision between fluidized-bed of material and hammers.

GTC Technology enlarges impacting capacity
Fluidized-bed of material collides with hammers of neighboring chamber in opposite direction, at a speed around 70% of hammer tip speed. Enlarging GTC hammer mills’ impacting capacity 31 times that of single rotor hammer mills. It could dash materials into shatters once even eccentric collision. Hammer milling capacity and efficiency highly improved, temperature rise of ground material obviously lowered.

GTC Technology improves the efficiency of screening capacity
As mentioned above, the density distribution of fluidized-bed of material is the more near inner screen surface the greater density, so fluidized-bed of material is inner loose outer tight. Therefore, reduce the density of material on inner screen surface can largely improve the screening capacity of hammer mills. GTC hammer mill has double grinding chambers and a GTC guide, this unique frame structure keeping agitating fluidized-bed of material, guiding it feed into neighboring chamber and colliding with hammers. Continually disrupt the trend of fluidized-bed of material formed into inner loose outer tight density distribution. Thus reduce the density of material layer against the screen surface, greatly increased the screening capacity. Meanwhile, unique double chamber frame structure enlarged 20% the effective screen area at the bottom, which also contributes much to reduce the density of material layer against the screen surface, and improves efficiency of screening capacity.