As is well known to the people of this industry, raw materials can be used to make feed have tens of thousands of species, of these several hundred can get into feed processing plant, but specific to a feed processing plant it also have thousands of raw materials. Species of end products various, they can be divided into the following kinds according to the raw materials and processing characteristics.

1. Components to be crushed, mainly including grain, oil plant seed, cake meal and so on. Most are pellets, accounting for about 70% -80% of the total.

2. All kinds of grain and animal processing by-products, such as rice bran, wheat bran, protein powder, bean powder, blood powder and so on, accounting for about 20%-30% of the total, the state is generally powder.

3. Large unit weight inorganic salt, such as sulfate, phosphate, mountain flour, salt and so on. These kind of materials are mainly packaged. Salt can corrosive metal, absorb moisture and caking, pay attention to the character while storing.

4. Liquid raw materials, such as molasses, oils, and certain liquid amino acids, vitamins and so on.

5. Medicine and micro component, mainly consist of antibiotic, antimicrobial, vitamins, fragrances and so on. Characters of the kind of material are various in species, less amount, high price, some of the species is harmful to people, should be stored in a special place and managed by specially-assigned person, cannot be mixed with other materials.

6. End products are powder or pellet, packaged or bulk.

According to the raw material and end product species, in the feed processing, except for a small quantity of liquid, most of the products are pellet and powder, which are called granular mixtures. In the storage and production process of granular mixtures, we should research the characteristics of granular mixtures below.

I. Physical Characteristics of Material

1. Scattering

Scattering is the reaction of ability of the material to diffuse around under the free state, which is a characteristic of the material flow. Granularity of powder and pellet material can be divided into:

Powder: 10μm-2.0mm

Pellet: 1.0mm-5.0cm

Larger than 5.0mm are called block, less than 10μm belong to the colloid.

Granular mixtures have similar fluidity as liquid, the fluidity shows as scattering. Shear stress between pellets making the fluidity limited. Shear stress of granular mixtures consists of friction and adsorption, shear stress is proportional to the vertical pressure to which the granular mixtures are subjected. When the vertical pressure is zero, the shear stress is also called original shear stress (τ0)，granular mixtures of τ0 is well fluidity granular mixtures, also called ideal granular mixtures. Powder and flake materials are of poor fluidity. Moisture content, granularity and compaction degree will affect the fluidity of materials.

Fluidity of granular mixtures is generally expressed by its angle of repose (the angle of repose or angle of accumulation), that is the maximum inclination angle formed by the free surface and the horizontal plane of granular mixtures. The angle of repose of the ideal granular mixtures is equal to the internal friction angle, independent of the manner in which the angle of inclination is formed. Granular grain used its angle of repose to express its angle of friction, for poor fluidity granular mixtures, the angle of repose greater than the internal friction angle.

2. Friction coefficient

Friction between granular mixtures is called internal friction, the size of the internal friction generally represented by internal friction angle. The tangent of the internal friction angle is the internal friction coefficient. The friction between the granular mixtures and the surface of a variety of solid materials is called external friction. Corresponding to the external friction, there is an external friction angle, also known as gravity angle, that is, the minimum angle formed by the horizontal plane and the solid material surface which bulk material slip along.

3. Automatically Classification

In the process of transport, flow and vibration, the phenomenon of the accumulation and re-classification of the granular mixtures according to their density, granularity and surface characteristics is called automatic grading. In general, large and light granular mixtures floating at the top of the pile or floating to the edge of the pile, small and heavy materials easy to accumulate in the lower part. When the transmission distance is far, vibration is large, automatic classification is serious. Automatic classification is benefit for raw materials to clean up and grading, because the accumulation of impurities easy to be cleaned-up, and for the mixing of feed is a reaction, is the main factor affecting for mixing uniformity. So, while designing the feed processing technology, minimize the classification of mixture, take pelleting, add liquid feed and reduce the transmission section can effectively ensure the product quality.

4. Density

Density is the unit volume mass of the granular mixtures when it is naturally piled. The volume mass of the granular mixtures is related to granular mixtures size, surface smoothness and water content. The density is a significant index in the calculation of storage capacity.

II. Physical Characteristics and Chemical Characteristic of Material

1. Adsorbability

Adsorbability is the ability of a substance atom or molecule to adsorb on another substance. For the feed industry, adsorbability is the character for a certain kind of feed raw material to adsorb other material on its own surface. Adsorbability is one of the basis to select the carrier for feed trace additives thinner. In order to make the trace additive mixed evenly in the feed, you need to select a material with good adsorbability as the carrier, mixed with a small amount of materials, and then evenly mixed into large quantities of feed to ensure that the feed price and safety. Adsorbability of feed is often related to the shape of the material (pellet, piece), surface properties (smooth, rough) and the water content.

2. Hygroscopicity

Hygroscopicity refers to the capacity for feed material to absorb and release the moisture that contains in surrounding air. Some feed raw materials have strong hygroscopicity, such as salt, sulfate, choline chloride and fish meal with higher saltness.

For high hygroscopic feed, the stability is not good, easy to failure, mildew, agglomeration or automatically decomposition. In addition, the material in the mixed feed will also affect others’ quality in the storage.

3. Thermostability

Thermostability refers to the ability of some certain chemical ingredients in the feed to resist thermal damage under thermal processing conditions. Vitamins (such as VC, VA, etc.), amino acids contains in feed are easily to oxidized failure at high temperatures. The biological potency of certain minerals at high temperatures is also reduced. In addition, some harmful ingredients in raw materials, such as soybean anti-trypsin, rapeseed meal sinensis enzymes and some harmful microorganisms and bacteria will also be lost or killed at high temperatures.

4. Chemical Stability

Chemical stability refers to the ability to resist destruction of a certain feed bio-active substances under the effect of foreign chemicals. Chemical stability is the main requirement to choose vitamins, trace salts and other certain additives such as antioxidants, mildew and so on.

5. Poisonousness

For some feed raw materials, mainly trace mineral additives and some drugs contain heavy metals and other toxic components that are harmful to human body and carcasses, such as copper sulfate, zinc sulfate, etc. contain heavy metals like lead, arsenic, cadmium, etc., harmful to humans and livestock. So the selection of trace mineral additives must meet the national quality standards. Another example is a trace amount of additives such as sodium sulfite is necessary for animal growth, but overuse of it will be easy to cause toxic. And these substances has a certain harmful effect to the processing environment and the operator, the finished product content too much or unevenness mixed can cause poisoning or death to livestock and poultry after eating.

6. Electrostatic Ability

Electrostatic phenomena are generally associated with active ingredients. Dry and high fineness materials are often with electrostatic charge, resulting in the adsorption of active ingredients adsorbed in the mixer or conveyor equipment, end up with unevenness mix. Pre-mixed feed plants usually install grounding device on main equipment to overcome the electrostatic phenomenon.