81.How to choose interference fit in the actual design?
A: see the picture below.
82.How to label linear dimensional tolerance on part drawing?
A: see the picture below.
83.How are linear dimensional tolerances marked on assembly drawings?
A: see the picture below.
84.How to label the linear dimensional tolerance of standard parts?
A: see the picture below.
85.What are the requirements for linear dimensional tolerance labeling?
A: the tolerance code is the same height as the base size number.When the limit deviation is used to mark the linear dimension tolerance, the upper and lower deviation number is one smaller than the basic size number, and the decimal number of the upper and lower deviations must be aligned, and the positive and negative signs must be marked.One deviation is zero, marked with a "0" and aligned with the units digit of the other deviation.The bottom deviation line is marked on the same line as the basic size.When the upper and lower deviation values are equal, the deviation is only marked once, and the "+/-" sign is marked between the deviation and the basic size, and the font size is the same.
86.What is a conical fit?
Answer: the relation between the inner and outer diameters of the same basic cone, which is formed by different combination.The characteristic of conical fit is to form a gap or interference by combining the specified axial positions of the inner and outer conic.
The gap or interference is in the direction perpendicular to the surface of the cone, but the direction perpendicular to the axis of the cone is given and measured.For a cone with a taper less than or equal to 1:3, the difference between a given value perpendicular to the surface of the cone and perpendicular to the axis of the cone is negligible.
According to the different methods of determining the combined axial position of the inner and outer cone, the cone fit is divided into two types: structural cone fit and displacement cone fit.
87.What is a structural cone fit?
Answer: by the structure itself or the structure size to determine the relative axial position of the inner and outer cone and obtain the match.
88.What is a displacement cone fit?
Answer: specify the axial displacement or the axial force of the axial displacement to determine the relative axial position of the inner and outer cone.
89.What are the three components of the standard tolerance series?
Answer: by tolerance grade, tolerance unit and basic size segment.
90.What is general tolerance?
Answer: it refers to the tolerance that can be achieved by the general processing capacity of the machine tool equipment under the common process conditions of the workshop.
91. What does GB/ t1804-1992 specify for general tolerances for linear dimensions?
Answer: f, m, c and v are four tolerance grades. The letter f means the precision grade, m means the medium grade, c means the rough grade, and v means the roughest grade.The tolerance grades f, m, c and v are equivalent to IT12, IT14, lt16 and IT17, respectively.
92.What is the limit deviation numerical table for general tolerances of linear dimensions?
A: see the picture below.
93.What is the limit deviation table of the radius of the inverted circle and the height of the chamfer?
A: see the picture below.
94.What should I pay attention to during the clearance?
Answer: the reference hole H (or reference shaft H) and the corresponding tolerance grade of the axis a ~ H (or hole a ~ H) to form a gap fit, a total of 11, among which:
H/a (or a/H) has the largest clearance and the smallest fit clearance.
H/a (a/H), H/b (b/H), H/c (c/H) coordination, these three kinds of coordination gap is very large, not often used.Generally used in the working conditions are poor, the requirements of flexible action on the machinery, or for stress deformation, the shaft in high temperature work needs to ensure that there is a large gap.
H/d (d/H), H/e (e/H) fit, these two kinds of fit clearance is large, for the requirements of low easy rotation support.Among them, H/d (d/H) is suitable for loose transmission coordination, such as seal cover, pulley and idling belt wheel, etc. with the shaft.Also suitable for large diameter sliding bearings, such as ball mill, rolling mill and other heavy machinery sliding bearings, suitable for IT7 ~ IT11.For example, the fit of pulley and shaft.
H/f (f/H) fit, this fit clearance is moderate, it is mostly used for IT7 ~ IT9 general transmission fit, such as gearbox, small motor, pump, and other rotating shaft and sliding support.
H/g (g/H) fit, this kind of fit clearance is very small, in addition to the very light load of the precision mechanism, generally do not need to do rotation fit, mostly used for IT5 ~ IT7, suitable for reciprocating swing and sliding precision fit.For example, the matching of drill sleeve and bushing.
H/H fit, the minimum clearance of this fit is zero, it is used for IT4 ~ IT11, it is suitable for positioning fit without relative rotation but with centering and guiding requirements, if there is no temperature and deformation effect, it is also used for sliding fit, it is recommended to match H6 / h5, H7 / H6, H8 / H7, H9 / H9 and H11 / H11.
95.What should be paid attention to during transition?
Answer: the basic deviation code j ~ n of the reference hole H and the corresponding tolerance grade axis forms the transition fit (n forms the interference fit with the high-precision hole).
H/j, H/js fit, these two kinds of transition fit have more chances to obtain clearance, mostly used in IT4 ~ IT7 class, suitable for positioning fit that requires clearance smaller than H and allows slight interference, such as coupling, gear ring and steel hub, as well as rolling bearing and box body.
H/k fit, the average clearance obtained by this fit is close to zero, the centering is good, the parts are subjected to less contact stress after assembly, can be disassembled, suitable for IT4 ~ IT7, such as the rigid coupling.
H/m, H/n coordination, the two kinds of coordination to obtain more chances of interference, good centering, tight assembly, suitable for IT4 ~ IT7.
96.What should be paid attention to when interference fit?
Answer: the basic deviation code p ~ zc of the reference hole H and the corresponding tolerance grade axis forms interference fit (p, r forms transition fit with the H hole with lower accuracy).
H/p, H/r fit, these two kinds of fit in the high tolerance grade for interference fit, can be used to hammer or press assembly, only in the overhaul should be removed.It is mainly used for positioning with high centering accuracy, sufficient rigidity of parts and positioning coordination under impact load. It is mostly used for IT6 ~ IT8.
H/s, H/t fit, these two kinds of fit belong to the medium interference fit, most use IT6, IT7.Used for permanent or semi-permanent bonding of steel parts.No auxiliary parts, relying on the binding force generated by interference, can directly transfer medium load.General with the pressure method of assembly, also useful cold shaft or hot sleeve method of assembly, such as cast iron wheel and shaft assembly, column, pin, shaft, sleeve, etc.
H/u, H/v, H/x, H/y, H/z fit, these are large interference fit, the interference amount increases in turn, the ratio of interference to diameter is above 0.001.They are suitable for the transfer of large torque or bear large impact load, completely rely on the interference generated by the binding force to ensure a strong connection, usually using hot sleeve or cold shaft assembly.The cast steel wheels of the train and high manganese steel hoops should be matched with H7 / u6 or even H6 / u5.Due to the large surplus, the requirements of parts material good, high strength, or will be parts of the extrusion crack, so it is prudent to use, generally after the test to put into production.Selection is often carried out before the assembly, so that a batch of accessories surplus tends to be consistent, more moderate.
97.Why choose base hole system first?
Answer: because the machining of the hole is difficult to the shaft, changing the size of the hole requires changing the number of tools and measuring tools.Changing the size of the shaft will not change the number of tools, measuring tools.
98.How are tolerance levels applied?
A: see the picture below.
99.How do usage requirements determine the type of fit?
Answer: when the hole, shaft has relative move or rotate, must choose clearance to match.Relative movement selects the fit with small clearance, while relative rotation selects the fit with large clearance.
When there are no keys, pins, screws and other connecting parts between the holes and shafts, the interference fit must be selected when the transmission can only be realized by the cooperation between the holes and shafts.
Transition fit is characterized by the possibility of gap or interference, but the amount of gap or interference is relatively small.Therefore, when there is no relative movement between parts, the concentricity requirements are high, and do not transfer power without coordination, often choose transition.
100.What are the selection principles of dimensional tolerance and fit?
Answer: the principle of choice is to be able to obtain optimal technical and economic benefits under the premise of satisfying the use requirements.