Drawings of standard products
The drawings of a number of parts, the shape and dimensions of which are standardized, are carried out according to special rules. If the product has several designs, then above their images do the inscriptions: Execution 1, Execution 2 , etc. (Figure 8.2).
Fig. 8.2. Nut
GOST 1759-87 establishes the technical requirements for bolts, screws, pins and nuts, in particular their mechanical properties, the types and symbols of coatings for them, the maximum deviations in the shape and arrangement of surfaces, etc. To characterize the mechanical properties of bolts, screws, studs made of carbon and alloy steels have 12 strength classes. The strength class is indicated by two numbers: 3.6: 4.6; 4.8; 5.6; 5.8; 6.6; 6.8; 6.9; 8.8; 10.9; 12 .9; 14.9.
The first number, multiplied by 100, determines the value of the minimum time resistance (in MPa), the second number, multiplied by 100, determines the ratio of the yield stress to the time resistance (in%); the product of numbers determines the yield strength (in MPa).
For the nuts of the same steels, there are seven classes of strength, each of which is denoted by one number: 4; 5; 6; 8; 10; 12 and 14.
To protect the fasteners from corrosion, suitable protective coatings are used. There are 14 kinds of coatings and 12 kinds of their symbols.
Coatings of standard fasteners are indicated by the numbers: 01 - zinc with chromatin; 02 - cadmium with chromatin; 03 - multilayer - copper - nickel; 04 - multi-layer - copper - nickel - chromium; 05 - oxide; 06 - phosphate with oiling; 07 - tin; 08 - copper; 09 - zinc; 10 - oxide anodization with chromatin; 11 - passive; 12 - silver.
Index 00 characterizes details that are performed without coverage (this is not indicated in the symbol).
According to GOST 1759-87, the designations for standard fasteners with metric thread are recorded in this order: the first place is the name of the product; next to the name put a figure indicating the order number of the performance; in third place - the designation of the thread and its diameter; on the fourth, the step size (if the thread is shallow); on the fifth - the field of admission; on the sixth - the length (bolt, screw), in the designation of the nuts this place is not filled; on the seventh - a class (or group) of strength; on the eighth - a brand of material or an indication of the use of calm steel; on the ninth - the type and thickness of the coating layer and, lastly, the reference to the number of the dimensional standard.
Do not include the most common data in the notation: Execution 1, large thread pitch, tolerance range 8g and 7H
For example, consider the notation, which includes the largest number of data: Nut 2M20 × 1.5-6Н.8.029 GOST 5915-70. The number of the dimensional standard makes it possible to find out the design of the product - in this case we are talking about a hexagonal nut of normal accuracy. According to Execution 2 we determine that the nut must be with one chamfer. The portion M20 × 1.5-6N the designation is read as follows: thread metric, outer diameter 20 mm, step small 1.5 mm, tolerance range 6 N. Digit 8 indicates the strength class characterizing the mechanical properties the material from which the nut must be made: 029 must be divided by reading on 02 and 9, the first two digits are the designation of the type of coating, in this case the cadmium with chromate, and the number 9 is the thickness of the coating layer in micrometers.
Two images define the shape of the nut (see figure 8.2).
Similarly, the notation Bolt 2 M20 x 1.5-6dx 60.56.019 GOST 7798-70 stands for: a bolt with a hexagon head of normal accuracy (this we learn from the standard number), version 2, i.e. with a hole for the cotter pin in the rod of the bolt, thread diameter 20 mm, thread pitch small 1.5 mm, thread tolerance 6 g, bolt length 60 mm, strength class 5.6, zinc coating with chromating (01 ), coating thickness 9 microns, GOST 7798-70.
The shape of the bolt is transmitted by two kinds (Figure 8.3).
Fig. 8.3. Bolt
Let's consider an example of a symbol of a hairpin (in accordance with GOST 1759-87): Hairpin M 16-6 dx * x & gt; 120.58.029 GOST 22032-76 (Figure 8.4). From the standard number we learn that the stud with the screwed end l 1 equal to d, of normal accuracy, thread diameter d = 16 mm, l = 120 mm, with a large thread pitch (not specified), with a tolerance range 6g, cadmium coating with chromating (02), thickness 9 μm. The stud is made of material of strength class 5.8 (the point in the designation is not indicated).
Fig. 8.4. Hairpin
Drawings and symbols for other standard products (washers, keys, pins, pins, rivets, etc.) can be found in the manuals.
The designations of the standard products, the content of which was shown above, include their complete description, which is necessary for the execution of design documents for assembly units of products. These designations are entered in the Name column of the assembly drawing specification. In the training practice, you can use abbreviated symbols.
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