Quality inspection of polyurethane seals

The quality inspection of polyurethane seals mainly includes appearance inspection, size inspection and performance inspection.

1. Appearance quality inspection

1. General principle of appearance quality inspection

(1) The principle of practicality. To do not affect the usability of seals criteria;

(2) The working face is the key point of inspection. Strict specifications are required, and any defects that may affect the performance of the product are not allowed; The requirements for non-working surfaces can be appropriately relaxed;

(3) The number and size of defects in the large diameter series of seals can be appropriately relaxed compared with the small seals, especially for non-working faces, so as not to affect the principle of usability.

2. Requirements for appearance quality inspection

(1) The appearance of the sealing ring requires that the outer shape of the sealing ring should be regular, no deformation, distortion, damage, should be clean, no flash, rough edge, no defect; The color should be bright, not fuzzy, cloudy; Seal ring hand induction smooth, not rough, extrusion seal ring, should feel the obvious elasticity and toughness, hardness should be moderate;

(2) The appearance of the seal working face requires that the surface of the seal working face is round and smooth, and no bubbles, impurities, pores, cracks, scratches and other defects affecting the performance of the seal are allowed, otherwise it is judged as unqualified products;

(3) The appearance of the non-working face of the sealing ring requires the size of the bubbles, impurities, bumps and other defects on the non-working face, the diameter or length cannot exceed 2 mm, the height or depth cannot exceed 0.5mm, and the cumulative number of defects on the same sealing ring cannot exceed 4;

(4) The appearance of the dust ring and the retaining ring must be smooth and smooth, and no pores, impurities, cracks, or burrs are allowed; However, 1 to 2 small bubbles with a diameter <1 mm are allowed.

Second, sealing dimension inspection

(1) Piston drum sealing ring size test index sealing ring diameter and hydraulic cylinder diameter, sealing ring diameter and piston sealing groove bottom diameter, sealing body width and sealing groove width between the degree of coordination;

(2) piston rod seal ring size test index seal ring inner diameter and piston rod diameter, seal ring outer diameter and cylinder head seal groove bottom diameter and seal body width and seal groove width between the degree of coordination. According to the sealing structure, the shape and size of the sealing ring of the corresponding specification and model should be matched with the sealing structure. Dimensional inspection is to detect the seals that can not be well matched, and at the same time, to find the causes, correct the factors that produce unqualified products, increase the amount of qualified products, and improve product quality. The main reasons for unqualified seals are: mold factors, temperature fluctuations in the process of molding, product trimming technology is not skilled, leading to seal size disorders.

Third, seal performance inspection

Generally, 3 ~ 10 samples are taken on the test machine for performance testing. According to the same production process as the production of seals, the smooth and round wafer (film) shaped standard sample is made, and the physical properties are tested, and the test data is taken as the mathematical average value of multiple test values.

(1) Tensile strength

The thin slice sample was formed into a dumbbell standard sample by the sample mechanism, and the sample was held steady on the XL-500 tensile testing machine. The sample was stretched at a fixed tensile speed of 200 mm/min, and the maximum tensile stress was the tensile strength.

(2) Tear strength

Use the slicing machine to cut the sample on the flat, hard surface of the sample, the thickness of 2 mm, cut a cut in the middle of the circular or rectangular sample with a sharp blade, clamp the sample into the fixture, so that its axial alignment with the tensile direction, the testing machine exerts a gradually increasing traction on the sample until the sample breaks. The ratio of z large tearing stress to specimen thickness is the tearing strength.

(3) Hardness

The hardness of polyurethane seals or specimens is tested by A Shaw type A rubber durometer. When testing, place the sample on a solid horizontal surface, hold the hardness meter, and press the pressure needle vertically into the central part of the sample until the pressure foot and the sample are fully in contact with the hardness value within 1 s. In different parts of the sample, test 5 times, and take the average value.

The sealing parts are divided into drum polyurethane rubber sealing ring, bud shaped polyurethane rubber sealing ring and dust ring and stop ring. The surface of polyurethane sealing ring is divided into working face and non-working face. The working face refers to the side that directly seals the contact surface between the cylinder block and the piston and the cylinder head and the piston rod by pressing inside the system; Non-working face refers to other parts other than the working face. The convex lip part in the outer circle direction of the drum polyurethane sealing ring is the main working face, and the convex lip part in the inner circle is the non-working face. The convex lip part in the inner circle direction of the bud shaped polyurethane sealing ring is the main working face, and the convex lip part in the outer circle is the non-working face. The working face and the non-working face are only relatively speaking, when working, the seal ring as a whole is in a working state, playing a sealing role, therefore, the non-working face is also very important.