By Nkechi Isaac,
Brake pads are one of the most important safety and performance components in automobiles. They are used in the braking systems of automobiles and other vehicles and machines to control the speed by converting kinetic to heat energy which is dissipated to the atmosphere. The braking system is an indispensable component of an automobile, and is composed of many parts such as brake pads, master cylinder, wheel cylinders, and a hydraulic control system. The brake pad consists of steel braking plates with friction materials bound to the surface facing the brake disc.
The major component in the brake pad is the lining materials, which are categorized as metallic, semi-metallic, organic and carbon-based, depending on the composition of the constituent elements. Typical formulations consist of more than 10 ingredients. These ingredients are classified into four broad groups: binders, reinforcing fibres or structural materials, fillers, and frictional additives/modifiers.
The binder holds the ingredients together to maintain structural integrity of the brake lining under varying mechanical and thermal stresses. The structural materials provide the structural reinforcement to the composite matrix; fillers make up the free volume of the brake lining and friction modifiers stabilize the coefficient of friction and wear rates. These components perform synergistically in controlling friction and wear performance of the brake pad.
The demands on the brake pads are such that they must maintain a sufficiently high friction coefficientwith the disc and should not decompose or break down in such a way that the friction coefficient is compromised at high temperatures. They must also exhibit a stable and constant friction coefficient with the brake disc. For more than 80 years, asbestos has been used as the friction material because of its good physical and chemical properties. However, due to the health hazard associated with its handling, it is no longer popular and several alternative materials are being increasingly used for pads formulation.
Globally now, efforts are being intensified towards developing asbestos free brake pads. Research and development is focusing on ways of utilizing either industrial or agricultural wastes as sources of raw materials in the industry as it is considered that adoption and utilization of wastes will not only be economical, but may also lead to foreign exchange savings and environmental control. In most parts, R@D is focusing on agro wastes that are not only sustainably available, but have properties reminiscent of those of asbestos. One of such wastes produced in Nigeria is palm kernel shell.
Speaking to LEADERSHIP, a professor of mechanical engineering, Prof Olufemi Koya of Obafemi Awolowo University, Ile-Ife, said palm kernel shells (PKS) as by-product of palm oil production are generated in large quantities annually and only some fractions are used for fuel and other applications such as palliative for un-tarred roads and in producing activated carbon.
The expert said the unused PKS are dumped around the processing mills, constituting environmental and economic liability for the mill, pointing out that research and development had shown the coefficient of friction of PKS on metal surfaces to be in the range of 0.37-0.52, adding this is within the friction coefficient of 0.30-0.70 normally desirable for brake lining materials.
“It has been found that incorporation of PKS in the production of structural light weight concretes increased its mechanical strength. Thus, PKS appeared suitable for use as base material in friction composites, because they are unsusceptible to hard and variable braking forces.Studies have also shown that PKS does not change significantly in physical structure and weight, for appreciable time duration, when exposed to organic solvents. Also, PKS does not change when exposed to varying environmental conditions such as wet or dry weather or hydraulic fluid spilling over. These observations stimulated interest in considering PKS for use as friction material in brake lining,” he said.
Koya said the palm oil tree is regarded as an important economic tree because of the value of the palm oil and palm kernel oil produced from it in Nigeria, adding several residues are co-produced, the most important of which is palm kernel shell which is regarded as waste during the production process.
“On annual basis, more than 200,000 tonnes of palm kernel shells are produced and these are either burnt to supply energy to the mills or left in piles to compost. Although the combustion value of palm kernel shell is substantial, the process of burning PKS releases significant volatiles which pose pre- ignition and pollution concerns. This raises the need to find viable, nontoxic industrial use for PKS wastes in Nigeria,” he added.
Speaking on this development, the director-general of the Raw Materials Research and Development Council (RMRDC), Prof. Hussaini Doko Ibrahim, said the council decided to develop brake pad from the available palm kernel shell to combat the problem.
He pointed out that the aim of the council’s intervention is to reduce or completely eliminate the health risks posed by asbestos in friction lining manufacture and to reduce the cost of friction linings, saying this becomes very important as most of the brake pad manufacturing outfits in Nigeria, among which were Feredo, then located in Ibadan, Oyo State; Mintex, then located in Kano, and Fenok, then situated in Onitsha, Anambra State, Apex (Lagos), Edison (Nnewi), Uko (Onitsha), and Nnewi have stopped production as a result of a myriad of problems among which is high dependence on imported raw materials.
“According to industry sources, these firms went under following inconsistent government policies, poor quality control measures and uncontrolled importation of substandard brake pads from Asia. The aim of the project is to develop local content and to save foreign exchange as Nigeria is a large market for automobiles. Though there are few automobile assembly plants in Nigeria, the country remains a net importer of motor vehicles and brake pads, which results in huge foreign exchange losses for the country.
“As a result, the council in collaboration with a professor of mechanical engineering, Prof Olufemi Koya of Obafemi Awolowo University, Ile-Ife and Star Auto Nig. Ltd, Satellite Town Lagos the only surviving brake pad producing outfit in Nigeria, developed a research project that would utilize the abundant palm kernel shells for the production of brake pad and lining.
“The R&D had been successfully completed and patented. The physical, thermal, mechanical and tribological properties of the PKS-based brake pads have been evaluated. The pads produced have been exposed to extensive field tests which were highly successful. The products meet NIS 232 standards as analyzed by the Standards Organization of Nigeria (SON). Also agreement has been signed with Auto Star which has up to date facilities for brake pad production. The council is working assiduously to make the pads available in the Nigerian market. The next steps are to complete trademark registration at the Ministry of Trade and Investment and to commercialize the invention in partnership with prospective investors,” he added.