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JOURNAL OF RESEARCH IN NATIONAL DEVELOPMENT VOLUME 8 NO 2, DECEMBER, 2010


 

 

DESIGN, CONSTRUCTION AND EVALUATION OF A STALK CHOPPER

 

I. M. Bashir,    Zubairu Mustafa   and  U. A. Garba

Department of Agricultural Engineering, Kaduna Polytechnic. Kaduna

E-mail: mabash60@yahoo.com

 

Abstract

Proper feeding of animals is very important in any animal husbandry business. Therefore effective utilization of the available food sources is very necessary. It is as a result of this that a stalk chopper was constructed using locally available materials. The major components of the machine are the hopper, the chopping knives, the chopping chamber, the frame and the prime mover which drives the chopping disc carrying the knives.  It has a material capacity of 45.69 kg/hr and cutting efficiency of 91%. Commercialization of this machine will encourage farmers to engage in more animal farming as there will be better usage of crop residue which were hitherto not properly utilized.

 

Keywords: Stalk, chopper, construction, evaluation

 


Introduction

In animal production, proper feeding is very important as the quality and the quantity of the products form them depend on adequate feeding. In the developed countries, the production of animals is so organized that animals are kept in ranches and are fed with enough food such as silage, forage concentrates and so on.

 

However, in the developing countries like Nigeria, there is no organized system of animal husbandry. With   the exception of few large scale farms, most of the animals especially cattle and sheep are reared by the Fulani who move from place to place in search of food and water. As they move about, they eat anything that comes their way ranging from grass to crop residue. If these grass and crop residue were to be gathered and chopped into pieces, they will be better utilized.

 

Analyses have shown that maize residue consists of 54% of stalk, 12% leaves, 21% cobs and 13% husk (Klofentein and Owen 1981). Husk is the most digestible of the maize plant, other parts being lower and more variable. Dry matter digestibility ranges from 40% to 70% and protein content from 2.0% to 7.5% for various parts of maize plant (Kakoh 1992).

Despite the large quantity of maize being produced in Nigeria, the potentials of its residue as feed is yet to be exploited. The residues are either burnt or buried in the soil in the form of manure for the next farming season. It has been discovered that for small scale livestock farmers who practice integrated crop live stock farming, feeding of animals with  chopped forage is more economical than free-grazing.

 

Therefore, a simple design of a stalk chopper like this one will go along way in encouraging the effective use of agricultural residue.

 

 

Material and method

The stalk chopper consists of the following components frame, cutting knives, cutting chamber, and the driving unit. An opening at the cutting chamber is used to feed materials into the cutting chamber when materials are to be cut to a specific length. The cutting unit consists of a round disc with four knives attached at its periphery. As the disc rotates, the rotating knives cut the materials against a stationary blade. The driving unit consists of an electric or internal combustion engine which drives the chopper through a V- belt and pulleys. The entire components are assembled on a frame made up of angle iron. The chopped materials are collected at the base of the machine.


 

Design considerations

The following factors were considered in the design of the machine

i     Properties of the materials dependent on type and moisture content

ii.   Technical condition dependent on knife speed and number of blades.

   

Design calculations

Machine components were designed according to the procedures outlined in Design Data compiled by the Faculty of Mechanical Engineering P.S.G. College of Technology, Coimbatore 641004 India (1982).

i.          Power requirement

            Power required to drive the knives is given by;

                        Pr   =   F.V   =          MV3

                                                            R

Where

            Pr  =  Power required to drive the knives (kW)

            F   =     MV2 centrifugal force

            M  =     Mass  of the  Knives and disc = 4kg (40N)

            R  =      Radius of shaft  = 0.03m.

            V  =     Velocity  = 5.01 m/s

:.          Pr =               

                =      3.77KW

Where Pd = power required to drive the threshing drum (kW).

F=MV2  = centrifugal force,M  = Total mass of the chopping knives

   R

And disc = 4.0kg, R = Radius of shaft 0.03m V = velocity = 5.01m/s.

From available motor standard size, a motor of 5Hp was selected for the design.

Belt design

Angle of contact for pulley is given by the equation

            Q  =  =  π  ±  sim -1 

                                         

Where

            Q  = angle of contact

            D  =  motor pulley

            D  = Diameter of knife disc pulley, calculator

                        From D = 60 x       n = designed rotational speed of disc

                                                 

            C  = centre distance between disc and motor shaft.

                π (radious) 1800   

The conventional negative and positive signs indicating the contacts in the smaller (motor pulley) and the large pulley (knife pulley) respectively.

Centre distance is given by;                Cd = √[b2-32  ]

           

Where

            B  =  ¼   [4L1 – 6.28 (D – d)]

 

Where L = Pitch length of the belt selected from data table (Design data 1982)

Load carrying capacity C is determined for both pulleys and the lowest value is taken to govern the design.

            C =         

For V-belts where        C = load carrying capacity = 3.74

For rubber belts, Q = Contact angle (2.9 rads)

For small angle, x = 40” (groove angle).

 

Power transmitted by belt.            

            P = (T1 – T2)V

Where

            V = belt speed (MĮs)     

            T, = Tension in tight side (547.43N)

            T2 = Tension in slack side (98.68N)

Belt pull factor for V- belts is between 0.7 and 0.9 above which the belt will be unstable and rear at a fast rate. The belt factor calculated is 0.73

Shaft design

The shaft is subjected to vertical and horizontal loadings.

i.          Vertical Loading:- resulting from loads due to weight of pulleys acting downwards. Torque or radial force, load due to weight of disc and knives and reactions at the supports (bearings).

ii.         Horizontal Loading:- Resulting from load due to tangential force, reaction at the supports due to the  tangential force. 

These forces were determined as;

Weight of pulley WP = 5.25N

Radial force   Mt = 25.25N

Weight of disc/Knives (WDK) = 19.75N

Tangential force  = 243.85N

These forces were resolved into resultant forces by the following Equation (Design data calculated from the equation;

 RA = √R2av  +  R2ah,     RB = √ R2bv+R2bh,     TP = √ Tt2 + M2t

Where

RAV and Rbv are reactions at the bearing s due top vertical locating

Rab and Rbh are reactions at the bearings due to horizontal loadings.

Torsional moment in the knives drive shaft is given asTm =   (Ademosun & Olukunle 2003).                                         

                                                                                            = 

                                                                                       Tm  = 30.00Nm.

Bending moment

Bending moment was calculated from a bending moment diagram for the loadings as:         

MBmax = 26.85Nm, with a factor of safety KF  =  1.5

The required shaft diameter is calculated from the maximum  shear Stress and combined stress equation. Thus  = √( )

Where Tmax. = maximum torsional moment  = 30.00Nm

Maximum bending moment = 26.85Nm

Allowable design shear stress = 35.23KPa (3.79 21x10 7N/m2)

Shaft diameter was determined to be 0.018m with a factor of safety of 1.6 assumed for the design, the shaft diameter = 2.9cm (Dobrovolski 1974).

Assure that the torque is constant within limits of torsion is given by the expression below

            θ  = Σi=1M1 x L1 JnxG

Where

            M = Critical torque applied to the shaft

            Jn =        polar moment of inertia of shaft (M4)

                        G  = shear modulus or modulus of rigidity

                                    (8.1x1010 Nm for steel,.

            L1  = shaft length,  Q  = Calculated as 2.50x10- 3radius.

                                    (0.102) this is within acceptable value.

 

Performance evaluation

 The machine was evaluated of the following;

i.          Cutting efficiency

ii.         Throughput Capacity

i) Cutting efficiency:-The machine was set to cut the stalk to a length of between 0 – 10cm length.

It was considered that any piece longer than 10cm of length is to be considered off cut. So the cutting efficiency calculated by talking the weight of cut material over the total weight of machine input into the machine multiplied by 100%.

Cutting efficiency  CE  =  x 100%

Where        

            Wc = weight of cut stalk

            WT = total weight input into machine

Throughput capacity.

Through capacity is the quantity of materials cut per time.

Through put (Kg/hr) =


 

 

 

 

 

 

 

 

 

 

 

 

 

Table 1: Presentation of results 

Sample

 Moisture content (30%)

Weight of

Sample input  (Kg)

Weight of Cut Stalk

     ( Kg)

Weight of off cut stalk

      ( Kg)

Time

  (hr)

Throughput capacity

(Kg/hr)

Cutting Efficiency

    %

Material capacity(kg/hr)

1

56

45.15

4.85

1

50

901

45.15

2

50

46.25

3.75

1

50

92.5

46.25

3

50

46.00

4.00

1

50

92.0

46.00

4

50

45.35

4.65

1

50

90.7

45.35

5

50

95

5.05

1

50

.89.9

44.95

Total

50

45.69

4.46

1

50

91.1

45.69

Moisture content (90%)

 

 

 

 

 

 

 

1

50

30.65

19.35

1

50

61.3

35.13

2

50

30.01

19.99

1

50

60.00

35.01

3

50

31.56

18.44

1

50

63.12

76.56

4

50

29.25

20.25

1

50

58.25

34.25

5

50

30.00

20.00

1

50

60.00

35.00

6

50

30.29

19.91

1

50

60.54

35.29

 

 


Result and discussion

The results of the evaluation of the machine as shown on Table 1 shows that material capacity of 45.1kg/hr was obtained at 30% moisture content and 900 knife angle. This was higher than the 35.29kg/h material capacity at 90% moisture content and 900 knife angle. The higher material capacity at lower moisture content is due to the fact that dry  maize stalk are more brittle and can easily cut than those with higher moisture content which are some what  flexible and no more difficult  to cut. More evaluation is recommended to determine at what knife angle and what modification needs to be done for the machine to be used to cut materials at different moisture content levels.

 

Conclusion

The test result of 45.69kg /hr materials capacity and 91.1% cutting efficiency obtained are very encouraging. It is hoped that with further modification to improve the performance the machine will go along way in encouraging small scale farmers to engage in animal rearing as crop residue will be effectively used when chopped into small pieces.

 

Reference

Ademosun O. C. and Olukunle O. J. (2003): Development of an  Indigenous Combine Harvester NJERD Vol. 2 No 3

Design Data: (1982): Compiled by Faculty of Mechanical Engineering.P,S.G. College of Technology, Coimbotore, India

 

Dobrovolski, V, Zablensky, K, Radchik,A and Erlinch,L  (1974): Design of Machine Elements     2nd Edition, Moscow: Mir Publishers.

   

Kallah,M.S. (1992): Crop Residue Preservation,Treatment and Utilisation.Paper presented to Project Field Staff of the National Livestock held at the Federal Ministry of Agriculture, Water Resources and Rural Development Abuja.

 

Klopfenstein,T and Owen, F.G. (1981): Value and Potential use of Crop Residues and by-product in dairy rations , Journal of Dairy Science 64:1250-1268

Ogunlowo A.S. and Bello, R. (2005): Journal of Agricultural Engineering and Technology Volume13