Разработка ионно-плазменной технологической установки для нанесения функционального покрытия на крышки масляных фильтров, страница 28

Existing methods of measurement and control of cohesive resistance can be classified as follows: quantitative and qualitative methods; destroying and not destroying methods; mechanical and nonmechanical methods; practical methods and the methods representing scientific interest; standard and original methods.

From all these methods most widely apply the mechanical methods based on definition of pryout work (force) of film from the surface. They are divided on two categories depending on the way of film separation: normal and longitudinal (lateral)  film separation from an interface.

Almost all existing methods of adhesion research are destroying. Though it is not absolutely rational, but at the given stage of development effective enough not destroying methods of measurement of cohesive resistance of coverings with a basis are not found yet.

Mechanical methods subdivide on inertial and without inertia methods of cohesive resistance measurement. To inertial methods concern such as "bullet" method, ultracentrifugation and ultrasonic vibration method.

The kernel of "bullet" method consists in that the sample - substrate of the special form with the deposited covering goes-off by the adaptation in direction of a braking target. During the moment of impact of target and covering inertia, normal to interface and proportional to braking acceleration at impact operates. This force on unit of the contact surface area of covering with substrate is equal:

,                                                            (3.24)

where  - covering materials density, g/sm³;

 - covering thickness, sm;

 - braking acceleration, m/s².

The Given method is expedient for using, when functional purpose of  covering for products as a whole provides operation in overload conditions. This way allows to develop braking  acceleration up to 10⁴ m/s².

The ultracentrifugation method is based on a principle of the sample with  covering rotation. The sample from ferromagnetic in the form of the cylinder-rotor, on forming surface of which the covering is deposited, place in the vacuum chamber; here the sample rotates with the big speed around of axis in a rotating magnetic field. The stresses developing under action of centrifugal forces are directed along radius in section of the cylinder and are perpendicular to border of section:

 ,                                         (3.25)

where  - rotation frequency of rotor, s^-1;

 - rotor radius, sm;

 - film thickness, sm;

 - coverings material density, g/sm³.

The cohesive resistance corresponds to the separation stress at frequency of rotation .

At carrying out of tests smoothly increase rotation frequency of rotor and fix value at which the film comes off from the basis. The rotation frequency necessary for separation of continuous film, depends on its tension stress, cohesive resistance. For elimination of hoopential stress the film is cut in parallel with rotor axes so that to divide the layer into a number of strips.

Advantages of the given method are absence of glue, perpendicularity of separation forces to boundary covering-basis. These advantages of the method are really very important; however there are disadvantages which limit its application - the difficult hardware registration, the special form of samples, interrelation of rotation frequency and durability of the rotor-substrate material. Because of small weight of thin films it is difficult to receive big centrifugal forces.

One of inertial methods also is the method of cohesive resistance measurement   using vibrations. The sample together with covering is exposed to ultrasonic fluctuations. Thus on covering operates separation force , reaching maximum  at measurement of the sample with the covering movement direction in an ultrasonic field, and the pressing force operating in the following half-cycle.