Hammer mills are used to grind the raw materials for animal feed. The raw materials are fed into the hammer mill where the impact of hammers rotating at high speed breaks them down into small particles. The efficiency of the grinding process depends on a number of variables, such as the breaker plate design, the hammer tip speed and the screen perforation.
Van Aarsen designed its first breaker-plate hammer mill more than 65 years ago. The current hammer mill is equipped with a large breaker plate in the upper section of the grinding chamber: this exposes the product in the grinder to multiple impacts. Nowadays, this design is generally considered to be an extremely effective way of achieving high quality and fast grinding results. The right particle size is achieved through the multiple impact action in the top section of the chamber, after which the ground product exits the mill through the screen at the bottom. This design avoids circulation of the ground product in the grinding chamber, which would reduce efficiency and cause an excessive amount of fines. The longer service life of the screens and hammers is an additional benefit.
The screens have a direct effect on end-product quality and the hammer mill's capacity. The combination of the perforation size and open area (the number of holes) in a screen determine the particle size, particle variation and the grinding capacity. How larger the perforation opening, the coarser the ground product. How larger the open screen area, the greater the mills capacity.
In addition to the screen perforation, the hammer tip speed also plays a role in determining the particle size of the ground product. A higher tip speed means a higher impact and will result in a finer grind. A lower hammer tip speed results in a ground material with a coarser structure. At the same time, the capacity of the hammer mill will seriously decrease. There is no such thing as one ideal tip speed; this setting depends on the base ingredients and the desired end-product. The hammer tip speed can be controlled via a frequency controller and this also influences the fineness of the grind.
The desired quality, speed and energy consumption can be accurately managed through consistent use of the right screen. An automatic screen exchange system soon pays for itself when multiple screen perforations are used. Van Aarsen offers an automatic screen exchange system that holds 3 different screen perforations. Depending on the recipe in use, the screen exchange system automatically positions the right screen plates in the hammer mill screen holder, thereby reducing the screen changeover time from 20 minutes to just 1 minute. This results in a much higher capacity and reduced labour. For full flexibility, an automatic screen exchange system can be combined with a frequency controller which regulates the hammer tip speed. By adjusting the hammer tip speed to suit the screen perforation, the ideal setting can be chosen for achieving the right particle size and variation while maintaining capacity at the desired level and keeping the energy consumption per ton of feed as low as possible. Van Aarsen's GD hammer mill with the automatic screen exchange system is characterised by a low energy consumption of approximately 7 kWh/ton.
In addition to the factors mentioned, the quality and position of the hammers, the feeding device and aspiration system also affect hammer mill performance. Thanks to intelligent design, Van Aarsen's GD hammer mill scores well in all these areas.
The feed production process has a significant impact on the nutritional value of animal feed. Grinding the raw materials to the required structure is an essential operation which affects both pellet quality as well as the animals digestibility. Size reduction increases the number of particles and the surface area per unit of volume which results in increased mixing homogeneity. In addition a finer grind has a positive effect on starch gelatinization which leads to improved pellet quality and increased pellet mill capacity.
Van Aarsen is developer, manufacturer and supplier of state of the art machines and complete feed mill solutions for the production of compound feed and premixes worldwide. More information on the GD hammer mill and the automatic screen exchange system is available here: www.aarsen.com/machines/hammer-mills/
The modification in design of the hammer mill focused on the hammer pattern and arrangement; whereas the performance analysis was conducted based on the average particle of bambara nut, cassava, and maizesamples. The average particle sizes of the samples were compared to those produced with standard hammer mill and burr mill. The result shows that although the three grinders had no course (C), few medium (M) and mostly fine (F) particle size particles. The least average particle sizes the modified hammer mill produced were 0.0098mm, 0.0106 mm, and 0.0088mm compared to 0.019 mm, 0.017 mm and 0.03 mm and 0.0066 mm, 0.002 mm and 0.002 mm with the standard hammer mill and standard burr mill (control) for bambara nut, maize, and cassava respectively. Tests of significant mean difference undertaken using Tukeys method (P<0.001) indicated that average particle sizes of bamabara nut and cassava using modified hammer mill and standard burr mill were not significantly different but significantly different with maize, whereas average particle sizes of all the samples produced with thestandard hammer mill were significantly different. In conclusion, the use of the modified hammer mill drastically reduced the non-uniformed particle size associated with most hammer mills as well as eliminates the use of burr mill by farmers in the study area as alternative to produce fine grind. Recommendations for further works were stated.
Nwaigwe KN, Nzediegwu C, Ugwuoke PE (2012) Design, construction and performance evaluation of a modified cassava optimizing hammer mill performance through screen selection and hammer design milling machine. Res J Appl Sci Eng Technol 4(18):33543362
Pujol R, Letang C, Lempereur I, Chaurand M, Mabille F, Abecassis J (2000) Description of a micro-mill with instrumentation for measuring grinding characteristics of wheat grain. Cereal Chem 77(4):421427
Saensukjaroenphon M, Evans CE, Sheldon KH, Jones CK, Paul CB, Stark CR (2017) The effect of hammer mill screen hole diameter and hammer tip speed on particle size and flowability of ground corn. Kansas Agricultural Experiment Station Research Reports 3(7) 52:17
Chukwuezie, O.C., Nwakuba, N.R. & Asoegwu, S.N. Performance Analysis of a Modified Laboratory Hammer Mill: Field Test Results from Different Tropical Crops. Polytechnica 3, 8798 (2020). https://doi.org/10.1007/s41050-020-00025-3
Think Grain Think Feed organized first session of Process Optimization webinar on 28th May with Mr M. Kanagaraj a renowned Feed Milling expert who has trained more than 1,000 feed mill professionals from integrators, commercial feed manufacturers and others in the South Asian sub-continent. Renowned experts including Mr RathanakarShetty(RS), Director, Ace Feeds; Mr Balaji Sundraraman(BS), CEO, RGS Feeds and Mr Rajiv Kr. Taneja(RT), Head of Feed & Oil, Buhler India joined the webinar as speakers. The 90-minute session was attended by 307 attendees from 19 countries. Below is the summary of the discussion. What are the non-value-added activities in a feed mill? RS: Converting raw material to the end product by using resources is value addition but wastage happening during the process also utilizes the same resources which brings no value and is defined as non-value-added activities in the process. Eliminating these non-value additions can bring better efficiency and product quality too. Non-value-additions like labor, complexity in system with too much documentation, space management in the warehouse, material handling system, lack of trained labor, excess or shortage of labor, etc. would lead to poor quality of raw material and end-product and reduce the overall efficiency of the feed mill. This can be avoided with proper planning. Inventory If there is shortage of raw material then production is held up and capacity utilization is not up to the mark due to which all fixed and variable cost multiplies. The thumb rule for the capacity utilization is unloading capacity. It should be higher than intake capacity, which should be higher than batching, it should be higher than the grinding and mixing and that should be more than the pelleting. If the thumb rule is followed properly then the succeeding process wont be held up because of the non-supply of flow of material from the previous system. Over-production in hammer mills If mixer is not able to handle the capacity of the hammer mill, then the hammer mill would run idle which would be a wastage of energy with more wear and tear to the machine, etc. This can be avoided by finetuning the hammer mill capacity. Production scheduling Without proper scheduling, a greater number of changeovers or number of products produced in a day would require more time gap which is again a wastage. There are many benefits of process optimization, one of the most important is consistency. Consistency brings predictability and with predictability, planning can be done with minute details. What are the challenges in managing the inventory in a manner that it should not exceed but also a minimum inventory level is maintained? BS: Each feed mill has its own limitations. The inventory management system is directly proportional to the demand in the market. In case of feed, the end user i.e., the animal is not the decision maker. We have to understand with the psyche of the decision maker then create a forecast and produce the product to match the market. Another difficulty is raw materials which have their own variability in terms of their standards, production, place of production, irrigation standards, water level, temperature, etc. Keeping the inventory to match the production is also challenging. If one can reduce the warehouse space up to 50% then inventory can be automatically managed. For inventory management, data analysis is the key. By data compilation and analysis to understand the movement of raw material in terms of its availability, quantity, and price, etc., one can understand how the market is responding to different seasons which would bring demand versus production season analysis. Availability of raw material and demand in the market cannot be controlled hence it is important to make correct forecast and manage operations accordingly. Inventory management is crucial for any feed miller to control the price and quality of the entire feed mill. Reducing space usage by 50% may result in shortage of raw material. How a feed miller can overcome that? BS: In scarcity, one tends to buy more as observed in the pandemic time. If there is more space, one tends to buy more without proper planning and logistics in place which is a wastage. With more resources people become resourceless while with fewer resources they become resourceful. We follow this in RGS Feeds. Say if per week production is 400 MT with 20% downtime then monthly production would be 10,000 or 11,000 MT. As per planning, the monthly requirement is given and the basis upon which orders are placed on weekly basis to get raw materials at exact time. There is a possibility of keeping the product in the suppliers godown instead of its own space while ensuring to pick it on a particular date. How grain handling solutions can help feed manufacturers to optimize their resources in terms of money and inventory? RT: Grain cleaning is a very important aspect in a feed mill which is accepted worldwide and can soon be adopted in India. The threat of mycotoxin makes it important than ever. A major reason for aflatoxin or other mycotoxins in end product is dust, immature grain, shriveled grain, broken grains etc. which can be removed by the cleaning section. This would further help in better animal performance hence better end-product quality. Grain storage is again a vital aspect of a feed mill. Silos should be planned with complete engineering i.e., proper accessories, aeration, temperature control, fumigation, recleaning of material, recirculation of material etc. It can be a value-added activity for any grain processing industry. Usually, hammer mills overproduce whereas pellet mills remain full, and hence, hammer mill is to be stopped. What is the reason? RS: It can be due to capacity mismatch. Firstly, one produces the mash and keeps it in the pellet mill, shutting the batching system and in the meantime, one may produce mash feed (in case you produce) for capacity utilization. Over-production in a hammer mill can be due to various factors like the kind of material proposition in the formulation when it consists of more grains it would take a longer time for grinding. Also, pushing all powder material through hammer mill increases the grinding time and also power consumption which also results in non-uniform particle size reduction. By using a sieve before the hammer mill, the finer material can bypass the hammer mill and directly come into the mixer. The mixing cycle including wet mixing time, dry mixing time, liquid addition, the sequence of material adding to the mixer is again important. If it is decided properly at the design level itself delay can be avoided. How does the over-production in hammer mill affect the overall efficiency? RT: One should have proper planning in place starting from outlet of batching up to outlet of mixer. In case a feed miller still faces problem, a technique is followed while designing any type of flow diagram is Mixing Cycle Diagram. This diagram considers the conveyor capacity, conveyor discharge time, discharge time from a hopper, various scales, idle time and with detailed planning even the number of batches to be produced on an hourly basis is known. Considering all these factors, if it is a good mixing cycle diagram then the hammer mill will never over-produce or run out of production. How to reduce the idle time in feed milling? BS: To overcome idle time or over-production in hammer mill, firstly one should understand the hammer mill i.e., variance versus the hammer mill behavior. Secondly, people should be completely trained to understand the variation then act accordingly. All machinery should be at the optimum level. One should proportionate sieve versus die, it is important to understand the particle size entering the hammer mill and coming out of the hammer mill. Complete information like mixing time, moisture, mixing cycle, etc. should be collected and then the production should be started. By doing so one would reduce the idle time in production. Otherwise, this idle time can be up to 7% of entire milling operations which is reduced up to 3% in our case. The process standards will vary in a micro level from one feed mill to other due to factors such as change in environment, procurement methodology etc. Would you share your views on grinding process standardization? RS: Standardization is specific to the unit or company or maybe even to the suppliers of the equipment. But from a larger perspective, a hammer mill is used for particle size reduction, one can standardize the speed of the hammer mill like the modern feed plants have 2800-3000 RPM which is standard followed by most of the feed equipment suppliers. Also, selection of the sieve is important, if one is producing a 3mm pellet then one (should use sieve above the hammer mill) or tries to reduce the particle size less than 3mm. It is not a hard and fast rule but basis upon experience one can design the standard. RT: Using sieve above the hammer mill is a very good approach which is used in all feed plants in Europe and recently has been adopted in India. This approach helps to optimize the energy consumption in hammer mill. Different kind of process adoption in a feed mill requires different kinds of hammer mill like vertical, horizontal etc. but the basic principle behind hammer mill optimization is to know particle size distribution range and D50 value. If these two inputs are given while designing the plant then hammer mill would run 100% in an optimum manner. How much is the energy consumption in a hammer mill? RT: In case of vertical hammer mill, coarser grinding is expected hence there is 15-20% less energy consumption is there in the hammer mill not in the whole process. Share your experience on mixing process standardization especially in a country like ours where there is lot of similarity in the process like oil inclusion or using large quantities of molasses? RT: Mixing Cycle Diagram is a very versatile tool to standardize the mixing operation for any particular kind of product which is to be produced. Up to the mixer it is a batch process and after mixer it is a continuous process. If the mixing cycle diagram up to the mixer is followed firmly then one can know the mixing time for different kinds of products and it can be standardized. AUDIENCE QUESTIONS In a humid climate, the moisture content in feed gets above 11% thereby reducing the shelf life. How to manage the moisture above the standard of 11%? RS: The moisture level depends upon the moisture of your input raw material, if it is above 11% then one should make necessary adjustment in the post-pelleting process, particularly in the cooling process. One is adjusting the material at the bed level of the cooler there would be better cooling process. Second is the opening of the damper of the butterfly valve near the blower, by adjusting its airflow can be increased or reduced and excess moisture can be absorbed. Third is bypassing the dry air in the inlet of the cooler which is not common in feed milling but it is practiced in oil milling where hot air is passed through the cooler so that excess moisture can be removed. It can be added to the feed mill also. Your opinion about cost optimization BS: Firstly, a feed miller needs to understand that 85-88% of the output is raw material. The first step for cost optimization is to optimize the purchasing or the formula for the product. Secondly, there are two important factors for process cost reduction are energy and human resources. For energy, you need to look into non-value-added factors like power cost. By controlling idle running of hammer mill, pellet mill, conveyors and other parts, you may reduce the cost of energy. Human resources are most important and after some surveys, we have reduced 20% of our human resources while increasing 40% of our productivity. For costing, one has to go as per batch or formula or product. One should be able to recognize the formula giving the best results and move in that direction. There can be a lot of variability like one formula can give 13 MT per hour while other can give 17 MT per hour. Costing is to be made with every batch. What all seasonal precautions should be taken care by the feed industry? RS: In India, we experience extreme kinds of climate like cold weather to severe-heat condition in summer. We should take few precautions at the time of storage. In an open storage facility, there is a lot of moisture loss happening in peak summer, one should store lesser quantities during that time. Steam is another neglected area in feed milling, in winter the temperature is low and steam gets condensate due to which enough temperature is not maintained for the pelleting process, so to avoid such conditions one should properly insulate the steam line. BS: Feed manufacturing operations and cost optimization does not have any seasonal precaution or activity. Control the efficacy of the system, machine, and manpower within a set means. Improve your production to zero defects and zero downtime. How much losses occur in the feed milling process due to atmospheric conditions? RS: There are two kinds of shortages, one is storage shortage the shortage happening during storage of the raw material like handling shortage, transportation shortage; second is the process loss which starts from intake of material to bagging. If both combined would be less than 1% then it represents an efficient feed mill. Moisture loss is the main factor affecting inventory control and moisture shrinkage results in differences between documented and actual stock especially in terms of grains. How should we control? RS: Moisture loss during the storage is inevitable, especially when material is stored for longer period. Take utmost care while accepting the raw materials particularly high moisture materials. If it is unavoidable, better to consume the grains having high moisture at the earliest, but following FIFO (First In First Out) system is most desirable. What are the process loss and shrinkage loss standard % for the poultry industry? RS: Process loss and Storage loss again depend on the moisture levels of input materials. So always better to have more control on the input materials. In this time of high-cost raw materials, minimization of the loss is paramount importance. For computation of costing, we can keep a provision of maximum 1.0%. Moisture optimization systems available in the industry can minimize the shrinkage or process loss. Factors to be considered to stock ingredients in bulk storage especially in silos with optimum quality for 3-4 months. RS: While storing Grains in the bulk storage system, some points to be taken into consideration to keep the stock in good conditions are:
In the commodity market strategic stocking is required in the feed business? What should be the concept for strategic stocking? BS: Increasing stock level ensures availability of materials and happy customers but holding inventories can be costly and reduces operational fund.
Conclusions Process optimization is one of the key aspects that every feed miller should practice and tune the process as close as possible to the requirement. Below are the take home message from this session:
Hammer mill is the most widely used grinding mill and among the oldest. Hammer mills consist of a series of hammers (usually four or more) hinged on a central shaft and enclosed within a rigid metal case. It produces size reduction by impact.
The materials to be milled are struck by these rectangular pieces of hardened steel (ganged hammer) which rotates at high speed inside the chamber. These radically swinging hammers (from the rotating central shaft) move at a high angular velocity causing brittle fracture of the feed material.
The material is crushed or shattered by the repeated hammer impacts, collisions with the walls of the grinding chamber as well as particle-on-particles impacts. A screen is fitted at the bottom of the mill, which retains coarse materials while allowing the properly sized materials to pass as finished products.
The above subtype is based on the direction of the rotor (clockwise direction, anticlockwise directions or in both directions). Their working and grinding actions remain similar despite the fact that their construction differs in many respects.
Effect of hammer crusher rotor speed was studied during continuous olive oil extraction.Rotor speed increased extraction efficiency, phenolic and triterpenic compounds content in extra virgin olive oil.FFA, PV, UV absorbances, DAGs and PPP were not affected by changes in hammer mill rotor speed.Pungency increased with hammer mill rotor speed.Hammer mill rotor speed may be used to tailor minor components during industrial olive oil extraction.
Crushing is a key step during olive oil extraction. Among commercial crushers, the hammer mill is the most widely used due to its robustness and high throughput. In the present work, the impact of hammer mill rotor speed on extraction yield and overall quality of super-high-density Arbosana olive oils were assessed in an industrial facility. Our results show that increasing the rotor speed from 2400rpm to 3600rpm led to a rise in oil yield of 1.2%, while conserving quality parameters. Sensory analysis showed more pungency with increased rotation speed, while others attributes were unaffected. Volatile compounds showed little variation with the differences in crusher speed; however, total phenols content, two relevant secoiridoids, and triterpenoids levels increased with rotor speed. Hammer mill rotor speed is a processing variable that can be tuned to increase the extraction efficiency and modulate the chemical composition of extra virgin olive oil.Get in Touch with Mechanic