Development and performance evaluation of a rubber tapping machine

Abstract

Hevea brasiliensis, the common rubber tree, is the most important species which is the commercial source of natural rubber. The natural rubber is harvested in the form of latex, a sticky, milky colloid through the tapping process. The Hevea latex obtained from the bark of rubber tree contains natural rubber particles that can be harvested and utilised for various industrial applications. Tapping is the process of making a controlled wound in the bark of rubber tree to cut open the latex vessels, which cause the flow of latex for capturing the latex. The process of rubber tapping poses potential risk of various health problems among rubber workers. Scarcity of skilled labours for rubber tapping is one of the main challenges in the rubber industry. Mechanization of the tapping process can reduce the effort of the labour and reduces the human drudgery. Hence, the present study was undertaken to develop a rubber tapping machine and to evaluate the performance of the machine. The developed rubber tapping machine consists of a cutting blade, shaft, connecting rod, crank, gear assembly, bearing, coupling, frame, casing, motor and a battery. The rubber tapping machine is connected to a 12 V, 5 Ah battery. The battery powers the motor. 0.25 hp wiper motor was used and it delivers a rotational speed of 72 rpm. The rotary motion of the motor is transmitted to the gear assembly using a gear shaft. The gear of 48 teeth which is connected with the motor rotates at 72 rpm. The speed is increased to 288 rpm by meshing gear of 48 teeth with 12 teeth gear to obtain a speed ratio of 4. A crank is attached to the gear of 12 teeth and rotates at 288 rpm. A connecting rod linking the shaft and the crank converts this rotary motion into reciprocating motion of the shaft. The required stroke is achieved by an eccentricity of 15 mm in the connecting rod. The blade is reciprocated along with the shaft with a stroke length of 30 mm and 144 strokes per minute. The reciprocating motion of the cutting blade helps to cut the bark of the rubber tree while tapping.The field evaluation of the developed machine was conducted in two farmer’s field by three tappers and the performance of the was evaluated in terms of its capacity, depth of cut of bark, bark consumption or thickness of cut of bark, time for tapping operations and weight of the machine and compared with manual tapping. The developed machine has an average capacity of about 157 trees per hour. The machine cuts the bark with an average depth of cut of 7.2 mm and a thickness of cut of 1.8 mm. The developed machine weighs 1.6 kg without the power source and 3.6 kg with power source. The cost of operation of rubber tapping machine is estimated as Rs.1.16/tree whereas the manual tapping charges are Rs. 2/tree. The developed rubber tapping machine is more advantageous for tapping the rubber trees with less effort and human drudgery compared with the traditionally using tapping knives.