**3. Object Investigation**

The most important part of a train's moving gear is the bogie, which carries the weight of the body and guides the train to move along the track. A bogie consists of a bogie frame, suspension system, and wheels, as shown in Figure 6. The suspension system is a linking system between the underpinning of the frame and the wheel and has the function of absorbing the kinetic energy of the vibrations, in order that riding comfort is improved [13,14].

**Figure 6.** Composition of train bogie [13].

According to the interviewed workers of the forging workshop, leaf springs and helical springs were commonly used for the trains in early times, as shown in Figures 7 and 8. Initially, leaf springs were used for trains; however, due to the poor comfort they provided, helical springs were used instead. As entire trains had to be disassembled for overhaul, it was necessary to replace the springs if helical springs were worn or their error values exceeded the standard. Taiwan Railways used a lot of helical springs, and the manufacturing technology was not difficult; therefore, there was a series of machines used to produce helical springs at the northeast corner of the forging workshop of the Taipei Railway Workshop. After the Electric Multiple Unit (EMU) series trains were imported from the United Kingdom in 1978, almost all of Taiwan Railways' trains were converted to use air springs. On this basis, it can be inferred that the machines in the Taipei Railway Workshop are the representative

production tools transferred by era and technology. At present, the steel springs seen at the Taipei Railway Workshop are only for the maintenance of early trains; for example, Chu-Kuang Express, freight trains, and Fu-Hsing Express in service now still use helical springs.

**Figure 7.** Helical spring.

**Figure 8.** Leaf spring.

This study numbered and registered 85 objects, including 41 machines, 30 auxiliary vehicles and working platforms, 12 hand tools and parts, and two other cultural relics. The building of the forging workshop is 60 m long and 40.35 m wide. Based on the features of the machines and objects on site, the forging workshop is divided into three parts: "Working area", "material storage area", and "staff rest area", among which the working area is divided into the "shaping area" and "forging area", as shown in Figure 9. The shaping area is a working block where machine parts are heated, shaped, and inspected, and mainly has helical spring and leaf spring production lines according to the configurations of the tools and fields of all production lines. The main machines used in the forging area are forging hammers, which can be divided into steam-driven and electric-driven types based on the engines, including the oldest machine steam hammers used in the Taipei Railway Workshop. In addition, there are two parts in the material storage area, one is for storing the raw wire materials used to make machine parts and the other is for storing finished parts. The staff rest area has many tables, chairs, lockers, and hallstands, as well as a shrine to the patron saint of the workshop. The locations of all areas are shown in Figure 10.

**Figure 9.** Classification of exhibition areas.

**Figure 10.** Locations of working blocks in the forging workshop.

#### *3.1. Shaping Area*

The shaping area is mainly used to manufacture helical springs and leaf springs, which are used for the suspension systems of trains. The manufacturing processes of these two springs, as well as the relevant machines and objects in the forging workshop, are briefly introduced, as follows.

## 1. Helical springs

The raw material of helical springs (Figure 7) is spring steel wire, and the manufacturing process mainly includes six steps. The relevant machines at all steps in the workshop are shown in Figure 11.

The first step is billet shearing, where the shapes of both ends of the wires used as the billets are adjusted with an inclined rolling mill (A27) after being heating in the furnace (A26). The wires are sheared to the appropriate length with a shearing machine (A22). The machines for billet shearing are shown in Figure 12.

**Figure 11.** Flowchart of helical spring production line.

(**a**) (**b**)

**Figure 12.** Billet shearing and heating. (**a**) Inclined rolling mill (A27), (**b**) shearing machine (A22), material rack (A20), large heating furnace.

The second step is heating, where the sheared steel pieces are placed on a material rack (A20), and then, put into a large heating furnace (A14). The full length of the large heating furnace is about 85 m, and the furnace temperature is about 500~800 ◦C. Many motor-driven rollers are equipped in the furnace to convey the billets forward to the outlet to be heated until softened.

The third step is coiling and shaping, where the required spring diameters are selected according to the appropriate spring coiling fixture (A17), in order to wind the softened wires after heating into a spiral shape through a spring coiling machine (A13). If there is any error in the spacing of the shaped springs during manufacturing, hand tools are used to make detailed adjustments. The machines for coiling and shaping are shown in Figure 13.

**Figure 13.** Coiling and shaping. (**a**) Spring coiling machine (A13), (**b**) spring coiling fixtures (A17), (**c**) spring coiling tools (A17).

The fourth step is quenching, where the shaped helical springs are immersed in a quench tank (A11) to rapidly cool the spring steels, in order to change the crystallization mode. According to the oral descriptions of the retired workers, peanut oil was once used as the quenchant for helical spring quenching in the Taipei Railway Workshop. The machines for quenching are shown in Figure 14a,b.

**Figure 14.** Quenching and tempering. (**a**) Quench tank (A15), (**b**) quench hook, (**c**) cooling tank (A11-2).

The fifth step is tempering, where the atoms of iron, carbon, and other alloying elements in steel are quickly diffused, rearranged, and recombined, in order to stabilize the steel structure. Hence, reheating the quenched helical springs in a spring heater (A10) for tempering is intended to bring the springs to an appropriate temperature below the lower critical temperature, and then, the spring ends are trimmed. The cooling tank for tempering is shown in Figure 14c.

The sixth step is post-processing, which includes grinding and rust prevention, and the finished springs are tested. Large springs are polished by an end grinding machine (A06), while small springs are directly hammered by hand, and the finished products are tested by a spring testing machine (A04). A hardness tester (A07) was also found in the field; however, as orally described by the retired workers, while this machine was originally intended for spring testing, it was found to be inapplicable. The machines for this step are shown in Figure 15.

**Figure 15.** Post-processing and testing. (**a**) Grinding machine (A06), (**b**) spring tester (A04), (**c**) Vickers hardness tester.
