ICS 65.060.01  
 
Reference number  
DRS  268-2: 2020  
© RSB2020  
  
 RWANDA 
STANDARD  DRS  
268-2 
 
2nd edition  
2020 -June  
 
Agroprocessing  machine s — Specification  
— 
Part 2 :  
Power operated maize Sheller  
   
DRS  268-2: 2020  
  
I 
 In order to match with technological development and to keep continuous progress in industries, 
standards are subject to periodic review. Users shall ascertain that they are in possession of the latest 
edition  
 
 
 
 
 
 
 
 
© RSB2020  
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 Contents  Page 
Foreword  ................................ ................................ ................................ ................................ .............................. 3 
1 Scope  ................................ ................................ ................................ ................................ ...................... 5 
2 Normative references  ................................ ................................ ................................ ............................ 5 
3 Terms and definitions  ................................ ................................ ................................ ........................... 5 
4 Classification  ................................ ................................ ................................ ................................ ....... 78 
5 Materials of construction  ................................ ................................ ................................ ...................  89 
6 Performance and other requirements ................................ ................................ ...............................  89 
7 Workmanship and finish  ................................ ................................ ................................ ..................  911 
8 Maintenance and operation  ................................ ................................ ................................ .............  911 
9 Sampling and testing  ................................ ................................ ................................ .....................  1011 
10 Marking  ................................ ................................ ................................ ................................ ............  1011 
 DRS  268-2: 2020  
  
III 
 Foreword  
Rwanda Standard s are prepared by Technica l Committees and approved by Rwanda Standards Board (RSB) 
Board of Directors in  accordance with the procedures of RSB,  in compliance with Annex 3 of the WTO/TBT 
agreement on the preparation, adoption and application of standards.  
The main task of technical  committees is to prepare national standards. Final Draft Rwanda Standards 
adopted by Technical committees are ratified by members of RSB Board of Directors for publication and 
gazettment as Rwanda Standards.  
DRS  268-2 was prepared by Technical Committee RSB/TC 023, Mechanical engineering and metallurgy . 
This secondedition cancels and replaces the first  edition (RS  268-2: 2015 ) which has been technically revised.  
DRS  268 consists of the following parts, under the general title Agroprocessing machine — Speci fication : 
 Part 1: Rice thresher  
Part 3: Rice mill  
 Part 4  Heated air mechanical grain dryer  
Part 5: Maize mill  
Committee membership  
The following organizations were represented on the Technical Committee on Mechanical engineering and 
metallurgy (RSB/TC 023) in the preparation of this standard.  
University of Rwanda/college of science and technology  
University of Rwanda/College of agriculture animal science and veterinary medicine  
Kabizu business group  
Rwanda Polytechnic/IPRC Kigali  
Rwanda Polytechnic/IPRC Ngoma  
Rwanda Polytechnic/IPRC Musanze  
RWANTECH Boilers  
Rwanda Inspectorate and competition authority   
 Rwanda Institute for Conservation Agriculture  
ACER Ltd  
Rwanda Standards Board (RSB) – Secretariat  DRS  268-2: 2020  
  
V 
 Agricultural machinery — Spec ification — Part 2: Power operated maize 
sheller  
1 Scope  
This Draft  Rwanda Standard specifies the classification, performance requirements  and methods of test for  
power operated maize sheller.  
2 Normative  references  
The following referenced documents are indispensable for the application of this document. For dated 
references, only the edition cited applies. For undated references, the latest edition of the referenced 
document (including any amendments) applies.  
DRS  269-2,Agroprocessing machines  — Test met hods — Part 2: Power operated maize sheller  
RS 241, Agriculture machine ry  — Methods of sampling  
RS 236, Acoustics — Noise pollution — Tolerance limit  
RS 340,  Food processing machines — Specifications  
3 Terms and definitions  
For the purposes of this standard, the following terms and definitions apply . 
3.1 
blower loss  
ratio of the weight  of maize kennels blown  by the Sheller fan, to the weight of the total maize kernel input of 
the Sheller , expressed  in percent  
3.2 
closed -frame  cylinder  
type of shelling  cylinder  formed by a rolled metal sheet/plate (Figure 1a) or formed by longitudinal bars 
adjacently arranged  forming  a continuous cylinder (Figure 1b)   
  
Figure 1 — Types of cylinders used in maize sheller  
NOTE  The shelling elemen ts are either attached around the periphery of a cylinder or  at the longitudinal bars.  
3.3 
maize husker -sheller  
machine used  to remove  the husk of maize ear, detach, separate and clean the maize kernels from the cobs 
in one operation  
3.4 
maize sheller  
mach ine used  to detach, separate and clean the maize kernels from the cobs  
3.5 
ear maize (Syn .,dehusked maize , maize -in-cob ) 
unshelled  fruit of the maize plant where the husk has been removed mechanically or manually  
3.6 
hopper -fed type 
type of maizesheller  wherein the ear maize are fed into shelling chamber by gravity  
3.7 
kernel -ear maize ratio  
ratio of the weight of the maize kernel present in the ear maize to the weight of the ear maize  
3.8 
mechanically damaged kernels  
kernels  that were  broken and/or scra tched as a result of shelling operation  
DRS  268-2: 2020  
  
VII 
 3.9 
net cracked kernel  
difference  between  the percent cracked  sample taken before and after the shelling operation  
3.10 
open -frame cylinder  
type of shelling  cylinder  where the shelling elements are attached to the equally spaced  longitudinal bars 
arranged cylindrically (Figure 2)  
 
Figure 2 — An open -frame type cylinder  
3.11 
scattering loss  
ratio of the weight  of maize  kernels that fell out from the machine during shelling operation to the weight of the 
total maize kernel input of the sheller, expressed in percent  
3.12 
separation loss  
ratio of the weight  of maize kernels that come out of the shelling chamber with the co bs at the cob outlet, to 
the weight  of the total maize kernel  input of the sheller, expressed in percent  
3.13 
unshelled loss  
ratio of the weight  of maize kernels that remained in the cobs of the maize fed into the shelling chamber, to 
the weight of the tot al maize  kernel input of the sheller, expressed in percent  
4 Classification  
The classification of maize sheller shall be based on the following:  
a) application  
 
 i) maize husker -sheller ; and  
ii) maize sheller  
b) method of feeding  
i) hopper -fed type ; and  
ii) table-fed type  
c) shelling unit ; and  
i) cylinder –type; and  
I) number of cylinder  
1. single  cylinder  
2. multi-cylinder  
II) type of cylinder  
ii) closed -frame cylinder  
I) open-frame cylinder  
II) disc-type 
5 Materials and construction  
5.1 Food zone area shall be made from food grade materials.  
5.2 Non-food zone area may be made from carbon steel that has been rendered corrosion resistant  
5.3 Construction of rice threshing machine shall be done in accordance with RS 340.  
 
 
 
 
6 Performance and other requirements  
6.1 The performance criteria for maize s heller shall be as specified in Table 1.  DRS  268-2: 2020  
  
IX 
 Table 1 — Performance c riteria f or mechanical maize sheller  
S/N Criteria  Performance data  
i.  Shelling recovery, %, min.  97.0 
ii.  Shelling efficiency, %, min.  99.5 
Losses, %, max.  
iii.  a) Blower  
b) Separation  
c) Unshelled  
d) Scattering  1.0 
1.0 
0.5 
0.5 
iv.  Purity, %, min.  98.0 
v.  Mechanically damaged kernel, %, max.  3.0 
vi.  Net cracked kernel, %, max.  5.0 
6.2 Sealed type bearings shall be used as protection against dust.  
6.3 Lubrification shall be provided  for non -sealed type bearings and bushings.  
6.4 Belt guard or cover and provisions for belt tightening and adjustments shall be provided  
6.5    The maximum level for Noise Level, [db ] (A) for threshing machine shall be as specified in RS 236.  
7 Workmanship a nd finish  
7.1 Maize sheller shall be free from manufacturing defects that may be detrimental to its operation. The 
welding shall be satisfactory in all aspects and should not be brittle and porous.  
7.2 Any uncoated metallic surfaces susceptible to corrosion shall be painted properly.  
7.3 Maize sheller shall be free from sharp edges and surfaces that may hurt the operator.  
7.4 Rotating parts should be dynamically balanced.  
7.5 Maize sheller shall be constructed to ease to operat ion and cleaning . 
8 Main tenance and operation  
8.1 Each power operated maize sheller shall be provided with a set of relevant mechanic tool kit.  
8.2 An instruction manual (User’s manual, parts catalogue and service manual) shall be provided . 
8.3 All components that require regular  maintenance, servicing and adjustment should be easily accessible .  
 9 Sampling and testing  
9.1 The power operated maize sheller shall be sampled for testing in accordance with RS 241 . 
9.2 The sampled maize sheller shall be tested in accordance with RS 2 69-2. 
10 Marking  
Each maize sheller shall be marked at prominent place with the following information in one of three official 
languages used in Rwanda:  
a) Name or registered trademark of the manufacturer ; 
b) brand; 
c) model; 
d) serial number ; 
e) country of manufacture ; 
f) rating power , kW; 
g) frequency, Hz;  
h) recommended shelling cylinder speed, rpm ; 
 DRS  268-2: 2020  
 
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