Bülent Öztürk

Effects of Different Kinds of Fibers on Mechanical and Tribological Properties of Brake Friction Materials

The purpose of the present study is to compare the effects of different kinds of fibers on the mechanical and tribological properties (in dry conditions) of a phenolic resin–based friction material. The series of fibers used in the study include rockwool, ceramic, E-glass, and steel wool fibers. The fiber volume fraction in all composites was kept constant at 30%. Tribological studies were performed on a pin-on-disc apparatus at sliding speeds of 3.2–12.8 m/s, disc temperatures of 100–350°C, and applied loads of 312.5–625 N. Experiments showed that the friction coefficient in general decreased with increasing sliding speed and applied load but increased with increasing disc temperature up to 300°C and then decreased above this temperature. The specific wear rate was found to increase with increasing sliding speed and disc temperature. The highest friction coefficient and specific wear rate were obtained with E-glass and steel wool fiber–reinforced composites, respectively. The wear mechanism was also analyzed by observing the worn surface morphology using a scanning electron microscope (SEM).

Effect of Type and Relative Amount of Solid Lubricants and Abrasives on the Tribological Properties of Brake Friction Materials

The effects of graphite and hexagonal boron nitride (h-BN) as solid lubricants and aluminum oxide (Al2O3) and boron carbide (B4C) as abrasives on brake friction performance were evaluated. Friction material samples were produced based on an experimental formulation, and the lubricants and abrasives were added to the raw materials mixture at a total volume fraction of 10.5%. The composites had a fixed composition of 25% resin, 22% fibers, and 42.5% fillers. The friction tests were performed on a Chase friction material testing machine according to the brake lining quality test procedure as per SAE J661. The friction materials containing h-BN–B4C and h-BN–Al2O3 showed better friction stability and improved fade resistance compared to those containing graphite–Al2O3 and graphite–B4C. The results also indicated that the friction coefficient and specific wear rate of the composites increased with decreasing solid lubricant and increasing abrasive content. The worn surfaces and wear debris of the composites were examined using a scanning electron microscope (SEM) coupled with an energy-dispersive X-ray spectrometer (EDS). The atomic fraction of Fe on the worn surfaces and wear debris of the composites increased with decreasing solid lubricant and increasing abrasive content.

Effect of process parameters on production of metal powders by water jet cooled rotating disc atomisation

Abstract An experimental centrifugal atomiser was designed and constructed. The apparatus operates on the principle of atomising molten metal by pouring it onto a water jet cooled rotating disc. The disc was of a cylindrical reversed cup shape and the disc was cooled on the reverse side. The cooling water did not come into contact with the liquid metal and powders produced. Liquid metal did not stick on the disc because of effective cooling. Pure tin was used as the raw material to investigate the effects of production parameters, such as disc geometry, disc diameter, rotating speed, fin number, fin type, superheat and flowrate, of the liquid metal on the mean powder size and yield rate. Pure lead, zinc, aluminium and AA2014 alloy were also atomised to investigate the effects on metal types. The mean particle size of powders produced were in the range of 100–150 μm for tin and lead, 170–220 μm for zinc and 350–400 μm for aluminium and AA2014 alloy depending on the process parameters. The shapes of the powders were generally irregular, flaky, teardroplike and ligamental. The amount of spherical and rounded powders increased with decreasing mean particle size. A flat disc geometry with inverted triangle shaped fins gave a finer mean particle size and higher yield rate than other designs. Increasing disc rotation speed, disc diameter, superheat of liquid metal (up to 218°C) and decreasing liquid metal flowrate resulted in a finer mean particle size and a higher yield rate for tin. Discs with two fins gave a finer mean particle size and a higher yield rate.

Effects of Zinc Borate and Fly Ash on the Mechanical and Tribological Characteristics of Brake Friction Materials

ABSTRACT Friction materials based on several combinations of zinc borate (ZB) and fly ash (FA) were fabricated and characterized for their mechanical and tribological performance. The triboperformance of the friction materials was evaluated on a Chase friction testing machine according to the brake lining quality test procedure as per SAE J661. The composites were manufactured based on a nonasbestos organic-based friction material for an automotive brake system and contained typical ingredients for commercial brake friction materials. The composites had a fixed composition of 15 wt% resin, 15 wt% fibers, and 5 wt% friction additives. ZB and FA as fillers were added to the the raw materials mixture at a total fraction of 65 wt%. The results showed that ZB and FA contents have a significant influence on the mechanical and tribological properties of the friction composites. In particular, the composites containing 0–5 wt% ZB and 65–60 wt% FA showed better friction stability and improved fade resistance compared to those containing 10–35 wt% ZB and 55–30 wt% FA, whereas the composite with 5 wt% ZB and 60 wt% FA showed a maximum friction coefficient. On the other hand, the specific wear rate of the composites decreased with increasing ZB and decreasing FA contents. The morphologies of the worn surfaces as well as wear debris were analyzed by means of scanning electron microscopy.

Effect of production parameters on cooling rates of AA2014 alloy powders produced by water jet cooled, rotating disc atomisation

Abstract In this study, a novel type of rotating disc unit was designed and constructed and was used to produce rapidly solidified AA2014 alloy powders. Copper and stainless steel were used as the disc material and the temperature of the cooling water was selected as 0°C and 18°C. Effects of the production parameters, such as disc material, cooling water temperature, superheat of liquid metal and disc speed on the microstructure and the cooling rate of the powders, have been investigated. The microstructure of the produced powders was cellular and changed to cellular-dendritic with increasing powder size. It was found that cooling rates were relatively higher using a copper disc and 0°C cooling water temperature. The results indicated that cooling rates of 25 μm powders produced with a copper disc were estimated as 1·01×106 K s-1 and 9·02×105 K s-1 for 0°C and 18°C cooling water temperatures respectively. Decreasing the superheat of the liquid metal and increasing disc rotating speed also increased the cooling rates. PM/1050

Effect of Chill Wheel Cooling on Magnetic Properties of Nd 15 Fe 77 B 8 Alloy Powders Produced by Melt Spinning Method

In this study, effect of wheel cooling on magnetic properties of Nd 15 Fe 77 B 8 alloy powders produced by melt spinning method has been investigated. The present method includes the cooling of the copper wheel by externally contacting a coolant block which is cooled by internally circulating freon gas. Within this framework, the effect of wheel temperature on the microstructure and magnetic properties of Nd 15 Fe 77 B 8 powders have been investigated. The temperatures of cooling block and melt spinning wheel were measured as -15°C and -5°C, before experimental run, separately. Produced powders exhibited different morphologies depending on the powder sizes. The smallest size of powders was formed as spherical, ligamental and fiber-like morphologies. As powders get larger, the amount of spherical, ligamental and fiber-like shaped powders decreased and the length of the fibers declined. The microstructural cell sizes for 5 µm and 48 µm size powders were measured as 0.22 µm and 1.23 µm, respectively. The cooling rates of 4 µm, 28 µm and 52 µm sized powders were measured as 5.95 x 10 6 K/s, 0.85 x 10 6 K/s and 0.45 x 10 6 K/s, respectively. The Curie temperature of produced powders was 321.5°C. The coercivity value of melt-spun powders was obtained as 2.842 kOe.

Production of bronze powders by water jet cooled rotating disc atomisation

Abstract New type of water jet cooled rotating disc atomisation unit was designed and constructed. The raw material was melted in graphite crucible with high frequency induction heating, and atomisation was performed in high purity argon gas atmosphere. Cu–10Sn alloy was atomised to investigate the effect of production parameters, such as disc speed, disc surface condition, liquid metal flowrate, disc fin number and superheat of liquid metal with respect to mean particle size and powder yield rate. The produced powders appeared spherical, rounded, ligamentous, irregular and flaky, depending on particle size. The mean particle size of produced powders was in the range of 100–250 μm with 65–85% powder yield rate depending of atomisation parameters. The ZrO2 material coated disc with four fins gave the finer mean particle size and higher powder yield rate in comparison with uncoated disc with two fins.

Characteristics of rapidly solidified Cu–10%Sn alloy powders produced by water jet cooled rotating disc atomisation

Abstract In the present work, an experimental water jet cooled rotating disc centrifugal atomiser was designed and constructed and used to produce rapidly solidified Cu–10%Sn alloy powders. The characteristics of rapidly solidified Cu–10%Sn alloy powders have been investigated with respect to powder size and disc surface condition. Uncoated and ZrO2 coated copper discs were used to investigate the effect of disc surface conditions on the microstructure and cooling rate of the powders. The produced powders appeared in the shape of sphere, rounded, ligament, irregular and flaky, depending on the particle size. The powders exhibited fine grained microstructure, cell size increased with increasing powder size and higher cooling rates were obtained using uncoated disc. The results indicated that cooling rates of 20 μm powder produced with uncoated and ZrO2 material coated discs were estimated as 5·82×105 and 1·44×105 K s−1 respectively.