PROCEEDINGS
OF THE TOMSK POLYTECHNIC INSTITUTE
OF THE ORDER OF THE OCTOBER REVOLUTION AND THE ORDER
OF THE RED BANNER OF LABOR
NAMED AFTER S. M. KIROV

Volume 188　　　　　　　　　　　　　　　　　　　　　　　　　1974

MEASUREMENT OF THE SHAPE OF PISTON RINGS BY MARKING ON TRANSPARENT FILMS

V. D. VARLAKOV, G. S. PUSHKAR

(Presented by the Joint Scientific Seminar of the Departments of Mechanical-Engineering Technology, Machine Tools, and Metal Cutting)

The shape of a piston ring in the free state has a most important influence on the epure of radial pressures and, consequently, on the service life of the piston ring [1]. However, industry lacks methods for both absolute and relative measurement of the shape of piston rings in the free state.

Measurement of the shape of actual rings, carried out on a large toolmaker’s microscope (LTM), did not give satisfactory results.

The following schemes for locating a piston ring were checked:

a) setting by three points, with the following taken as the reference points:
\(x_{\mathrm{t}} x_{\mathrm{t}} o_{\mathrm{t}};\ o_{x} o_{x} o_{\mathrm{t}};\)

b) setting by two planes \((x_{\mathrm{t}} x_{\mathrm{t}}\ \text{and}\ o_{\mathrm{t}} o_{\mathrm{t}};\ \mathrm{km}\ \text{and}\ \mathrm{ln};\ \mathrm{k}'\mathrm{m}'\ \text{and}\ \mathrm{l}'\mathrm{n}');\)

c) setting by three equal radius vectors \((o_{\mathrm{t}};\ o_{\psi};\ o_{\psi'});\)

d) setting by four calculated radius vectors \((o_{\psi};\ o_{\psi'};\ o_{a};\ o_{a'}).\)

\(o_{\mathrm{t}} o_{\mathrm{t}}\) — theoretical plane of symmetry;

\(x_{\mathrm{t}} x_{\mathrm{t}}\) — a plane passing through the center of the ring in the compressed state and perpendicular to the plane of symmetry;

\(\mathrm{km}\) and \(\mathrm{k}'\mathrm{m}'\) — plane of the joint;

\(\mathrm{ln}\) and \(\mathrm{l}'\mathrm{n}'\) — a plane passing through the middle of the joint and perpendicular to it.

A schematic representation of these settings is given in Fig. 1.

In repeated measurements from all these bases of one and the same asymmetrical ring, the difference in the radius vectors determined for one and the same section, on rings with a diameter in the compressed state of 101.60 mm, exceeded 1 mm. It should be noted that measurement of the shape of rings on an LTM requires a very precise setup and is very labor-intensive.

Therefore, a method was proposed and tested for relative measurement of the shape of piston rings in the free state by marking the rings on transparent films.

The essence of the method was as follows. On transparent films, the calculated shape of piston rings was marked for each machining operation and for the finally finished piston ring, in the coordinates and dimensions specified by the working drawing of the piston ring-

Fig. 1. Schematic representation of an actual ring

Labels in the figure: \(O_y\); \(x_t\); \(x_t\); \(O_t\); \(O_3\); \(O\); \(R'_{\max}\); \(R_{\min}\); \(R_p\); \(\psi\); \(a_c/2\); \(a\); \(a'\); \(a_c\); \(O_3\); \(O_t\); \(D_{\max}=R_{\max}+R'_{\max}\); \(H\); \(H'\); \(M\); \(M'\); \(\alpha_k'\); “asymmetrical ring”; “theoretical ring shape.”

Fig. 2. Diagram for marking reference films on a large toolmaker’s microscope

Labels in the figure: \(\beta\); “scriber”; \(t\); \(t'\); “ring (tile)”; “X-ray film”; \(R<0.01\); \(10^\circ\); \(10^\circ\).

of the ring. To eliminate the influence of the width of the scribed line, the dimension was laid off outside the calculated contour of the ring. The layout was carried out on the stage of a large toolmaker’s microscope. The accuracy of laying out one of the calculated contours is characterized by Table 1, where \(R_p\) is the calculated (theoretical) radius vector; \(\psi\) is the angle between the plane of symmetry and the theoretical radius vector;

\(R_n\) is the value of the radius vector obtained on the transparent film.

A special scriber was made for laying out the ring on transparent films (Fig. 2).

On other transparent films the actual shape of the piston rings being measured was laid out. The actual shape of the rings was laid out on a surface plate and on the stage of a large toolmaker’s microscope. Before layout, the ring being measured, together with the film, was fixed on the surface plate or on the stage of the large toolmaker’s microscope with clamps or hold-downs.

Table 1

During fastening, observation was carried out through the microscope eyepiece to check that there were no radial displacements of the entire ring or of its individual sections. The size of the gap at the joint was checked before fastening and after fastening. After fastening, the ring was laid out along the outer and inner contours, with simultaneous observation through the eyepiece of the large toolmaker’s microscope, maintaining the strip width within \(0,02 \div 0,03\) mm. After the sections not covered by the hold-downs had been laid out, the hold-downs were carefully moved to the laid-out sections, and the sections that had been under the hold-downs were laid out.

During layout, the generatrix of the scriber cone touched the generatrix of the ring contour, as shown in Fig. 2. At \(5^\circ < \beta < 5^\circ\) an additional error occurred. The value of the error when tracing gauge blocks is presented in Table 2.

Laying out rings on a surface plate is analogous to laying out on the microscope, but provides lower accuracy and higher productivity.

The transparent films used for laying out the shape of rings must ensure that the dimensions being laid out do not change, that the laid-out lines are clearly visible, that shrinkage during storage is small, and that strength and hardness are sufficient. Diacetate films were adopted for layout.

Table 2

films. The change in the dimensions \(R_x\) during storage of the films for 1 year is presented in Table 1.

After marking the rings on thin films, the following were determined:

1. Deviations of the actual radius vectors from the calculated ones.
2. The marking error of one ring on 10 films.
3. The magnitude and character of the change in the shape of rings during their manufacture under the conditions of UrAZ and ChTZ.

Table 3

The magnitude of the deviation of the actual radius vectors from the calculated ones was determined in the following sequence. The film with the actual shape of the ring being measured was placed over the film with the theoretical shape of the ring for the given operation. The ring contours were aligned along the most similar portions.

The films were fastened together, and the center of the theoretical ring shape was aligned with the center of the microscope stage. The films were secured on the stage with clamps, the stage was set to the calculated radius vectors, and the numerical magnitude of the deviation of the actual radii from the calculated ones was determined. To increase the accuracy of the method, readings were taken along the edge of the line adjacent to the contour of the ring being laid out.

After alignment and fastening of the films, the numerical magnitude of the deviation of the actual radii from the theoretical ones can be determined with an MPB-2 magnifier with a scale division value of 0.1 mm. The error in marking one and the same ring on 10 films was determined, after tracing the ring on 10 films, by successive superposition of the films. The largest absolute value of the difference between the radius vectors was found. For films obtained by marking on a surface plate, the difference between the largest and smallest radius vector did not exceed ±0.1 mm.

For films obtained by marking on the microscope stage, the difference between the largest and smallest radius vector did not exceed ±0.04 mm.

The greatest difference in radius vectors was obtained when comparing film No. 7. The results of the comparison of this film are presented in Table 3.

REFERENCES

1. B. Ya. Ginzburg. Theory and Calculation of Piston Rings. Mashgiz, 1945.

2. G. I. Aksenov, M. S. Morozov. Study of residual stresses in piston rings. In: New Developments in Metallurgy and Heat Treatment. Gorky Book Publishing House, 1954.

3. A. T. Osipov. Study of the influence of nonuniformity of the structure and other properties of cast iron on the quality of a piston ring. MATI. Dissertation, 1952.