Juicer, Mixer, Grinder Testing Methodology
The Consumer Voice team checks out various brands of food juicers/mixers/grinders to assess how equal they are to various operational, efficiency and safety parameters. The comparative testing carried out in an NABL-accredited laboratory is mainly based on Indian Standard IS 4250: 1980, covering rated input not exceeding 600 watts. Relevant provisions of IS: 302-1: 2008 are also referred to. While electric JMGs/grinders are manufactured in both the organized and unorganized sectors, we focus on the former for the comparative testing.
This test has a total weightage of 30%. The brands are tested for their performance on these tasks: grinding coffee, whisking egg whites, making idli batter, grinding rice and juice extraction. The material retained on each of the first two sieves shall not be more than 20 per cent of the weight obtained at the end of the test.
a) Grinding coffee: As per IS, the recommended quantity of roasted coffee beans is taken for grinding and filtered in the three sieves of different microns. The material passing through the third sieve shall not be less than 30 per cent of the same weight.
b) Whisking egg whites: In this test, the material shall remain in the bowl when inverted for five seconds.
c) Making idli batter: This test indicates uniform performance in making a batter of rice and black gram. This requires grinding and mixing of the material in water to make a uniform, smooth and homogeneous batter for further cooking. The mixture shall be smooth and frothy, and no lumps shall be detected.
d) Grinding rice: The material retained on 1.4 mm sieve shall be 10 per cent maximum; on 1.0 mm sieve, 15 per cent maximum; and on 0.5 mm sieve, 70 per cent maximum.
e) Juice extraction: Carrots are chosen and operated as per the guidelines of the manual. The observation is mainly for smooth and uniform/ homogeneous juice. Juice pouring out of the vent should have an even flow. The rate of juice extraction shall not be less than 500 gm/minute and the amount of juice extracted shall not be less than 65 per cent. Finally, the juicer shall be dismantled, cleaned and inspected. There shall be no spillage/leakage.
This test has a total weightage of 15%. This test consists of following sub-tests:
a) Construction: It shall satisfy the requirements of Indian standard.
b) Internal wiring: Wireways shall be smooth and free of sharp edges. Wire shall be protected from coming in contact with burrs, cooling fins or similar edges. Holes in metal through which insulated wires pass shall have a smooth, well-rounded surface or be provided with bushings. Wiring shall be effectively prevented from coming into contact with moving parts. Internal wiring and electrical connections between different parts shall be adequately protected or enclosed.
Beads and similar ceramic insulators on live wires shall be fixed or located so that they cannot change their position or rest on sharp edges. Compliance is checked by inspection and by manual test.
c) Components: Components complied with the safety requirements specified in the relevant Indian standard.
d) Supply connections and external flexible cables and cords
- Cross-sectional area of conductors of supply cords: Conductors of supply cords shall have nominal cross-sectional area of not less than 0.50 mm2.
- Conductor’s resistance for supply cord: Conductor resistance for the supply cord shall be 39.0 Ω/km maximum.
e) Resistance to heat and fire: External parts of non-metallic material, parts of insulating material supporting live parts including connections, and parts of thermoplastic material providing supplementary or reinforced insulation shall be sufficiently resistant to heat. Parts of non- metallic material shall be resistant to ignition and spread of fire.
f) Screws and connections
g) Creepage distance and clearance
h) Resistance to rusting
Electrical and Mechanical Safety Test
a) Protection against electric shock: Appliances shall be so constructed and enclosed that there is adequate protection against accidental contact with live parts.
b) Electric insulation and leakage current at operating temperature: Leakage current in appliance shall be within the required limit of the standard. The appliance shall withstand 1,000 volts for one minute and no breakdown shall occur during the test.
c) Moisture resistance: The enclosure of appliance shall provide the necessary degree of protection against moisture. The test is carried out for 48 hours in humidity not less than 90 per cent. The appliance shall withstand the humidity treatment.
d) Insulation resistance and electric strength: This covers two aspects:
- Leakage current and electric strength at operating temperature
- High voltage: Appliance shall withstand 1,250 volts for one minute. No breakdown shall occur during the test.
e) Stability and mechanical hazards: Appliances intended to be used on a surface such as the floor or a table shall have adequate stability.
f) Mechanical strength: The appliance shall have adequate mechanical strength and be constructed to withstand such rough handling that may be expected in normal use. Accessible parts of solid insulation shall have sufficient strength to prevent penetration by sharp implements.
The test is carried out as per Indian standard. After the test the appliance shall show no damage that can impair compliance with this standard.
g) Temperature withstand test for bowl: Boiling water shall be poured into the bowl at room temperature, rapidly enough to fill it to its capacity. After the test, the bowl shall be emptied and brought back to room temperature. The test shall be repeated five times.
The bowl shall not show any sign of cracks and deformation, and shall properly fit into the holder after the test.
h) Strength of assembly: Food mixer shall be so constructed that in course of normal use there will be no electrical or mechanical failure. The insulation shall not be damaged and contacts and connections shall not work loose as a result of heating, vibration, etc. After the test, there shall be no chipping, cracking or visible denting on the mating surface.
Other Operational Test
a) Abnormal operation: In order to find out how well a JMG machine would stand the risk of fire or mechanical damage, the motor of each brand is stalled by locking its moving parts. Safety devices like OLP, fuses, thermal cutouts, or any other motor-protection device must operate and the temperature of the windings should not go beyond the specified limit. During the tests, appliances shall not emit flames or molten metal; enclosures shall not deform to such an extent as would impair compliance with this specification. After the tests, the appliance shall withstand electric strength test.
b) Temperature rise
- The temperature rise of rubber or polyvinyl chloride insulation of internal wiring can be 50K maximum, and that of external wiring 35K maximum.
- For surfaces of handles, knobs, grips and similar parts of metal, the limit is 35K maximum.
- For external enclosure of motor-operated appliances (except handles held in normal use), the limit is 60K maximum.
- For winding of Class B insulation, the limit is 95K maximum.
c) Controls: Controlling switches shall be capable of breaking the stalled motor current at the maximum rated voltage six times without failure
Packing and Marking
Marking is checked on appliance as well as on control switch.
Input (power consumption)
The appliance shall not deviate from the rated power input by +15 per cent or 60 W, whichever is greater.
Noise-Level Measurement during Operation Noise (dB) is measured in normal loading condition with paper pulp load at rated voltage.
Workmanship and finish
The appliance and accessories shall have no rugged and sharp edges. Different position of controls shall be indicated on the appliance.
The instruction manual is expected to contain the following information:
a) Precautions while positioning appliance and before switching on appliance
b) Warning about parts not to be brought into contact with liquids, keeping away from moving parts, and running empty, if necessary
c) Instructions for
i) assembling and dismantling the bowl for cleaning and servicing,
ii) electrical connection and type of supply,
iii) pouring of a little amount of hot water into bowl to remove leftovers after every use, and
iv) overhauling at least once a year to increase its useful life, if required
d) Directions to switch off when motor stalls or smoke emanates
e) Guidance for operation giving maximum quantity per loading