Combined axial and lateral rotary cutting mechanism for chopping oil palm frond

The oil palm frond (OPF) is one of the most abundant agricultural by-products in Malaysia and has great potential to be utilized as mulch, fuel, animal feed constituent and fertilizer constituent. Today, it is also an important resource in various modern industries such as pulp and paper, fiberboard and biodegradable film. However, these benefits could not be realized fully due to the absence of a suitable way of reducing the size of the fronds conveniently and economically. Moreover, the high cost of size reduction machines due to high-power requirement, large size and lack of mobility inside the field cause the farmer to bear the transportation costs of moving oil palm fronds outside the field to chop. This necessitated the need to design a new cutting mechanism which commensurate with the physical and mechanical properties of oil palm fronds in order to get the best performance with less energy consumption. Hence, this will reduce the cost of the machine and increase farmer’s income through the sale of the chopped materials. The aim of this research is to develop a cutting mechanism that can chop oil palm fronds completely and efficiently. The specific objectives are 1) to investigate the physical properties and mechanical strength of oil palm fronds 2) to formulate a slicing-chopping mechanism and to investigate the mechanics involved and 3) to evaluate the performance of a physical compound knife employing the formulated mechanism. The properties and strengths of OPF were investigated at two levels of moisture content (72% and 59%) and two levels of maturity (5 and 10 years). A slicing-chopping mechanism consisting of compound lateral and axial blades was then formulated to split the OPF lengthwise to many strips before cutting them one by one to make the cutting process sequentially rather than simultaneously in order to reduce the energy required. The mechanics involved was investigated in detail from which three different sets of compound knives consisting of 4, 5 and 7 axial blades were fabricated. Validation of the models was done by running the knives to chop OPF at the various treatment levels stated above at speeds of 1500 and 1900 rpm and the operating torque, power requirement, throughput capacity and chopping rate measured. Results of strength tests revealed that the stalk is the strongest part of an oil palm frond irrespective of moisture content and maturity. While the lateral shear force is directly proportional to the moisture content, the axial (lengthwise) shear force and the penetration force are inversely proportional to moisture content. Moisture content has a very strong influence on the shear strength of oil palm fronds but not on compressive strength. Maturity consistently has the smallest effect on penetrative, compressive, lateral and axial shear forces. The force required to cut oil palm frond stalks by the lateral blade only (i.e. the conventional way) was about twice more than by the compound knives irrespective of the moisture content and maturity of the fronds. A compound knife with 5 axial blades powered by a petrol engine of 2.8 kW (3.7hp) rated power was able to chop fronds completely right up to the stalk at 1500 rpm. The highest power requirement was obtained when running the 7-axial-blade compound knife at 1900 rpm; being 4.7 kW (6.3 hp). A maximum chopping capacity of 1059 kg/h was obtained using a compound knife with 5 axial blades at 1900 rpm. In conclusion, the slicing-chopping mechanism developed was proven to be able to chop OPF completely up to the stalks and with about 50% less energy, both of which have never been achieved by any commercially available OPF choppers before. This work contributes knowledge on the development of a compound blade that can chop the whole OPF up to the stalk using engine power of less than 3 kW, both of which have never been possible before. Besides it also contributes to the literature in similar works on the development of chopping machine and forage harvesting related machines and expanding the new idea on using new technology and work successfully on the field.

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