"allowable deviation" and "tolerance" is the meaning of unreasonable terms, saying in the daily production and there is often a confusing two terms. Such as the size does not match the objection, often a product of the thickness of "tolerance" ultra-poor, and some production and technical staff would say that the steel plate according to the theory of total delivery, is the rolling of the "negative tolerance" and so on. Here is the meaning of these two terms and use of a brief introduction and description. The size of the steel products manufacturer and user of common concern, the user wants to buy the product size is the size of the orders, but actually processing according to certain production processes, products and order size will always be on a deviates from that is, positive and negative deviations, of course, users always hope that this deviation as small as possible, that the accuracy as high as possible in the actual production, the higher the dimensional accuracy control, the greater the difficulty of production, in order to ensure the interests of both sides in the product standards the size of the deviation has a specified range, ie, the size of the allowable deviation.
Following Baosteel enterprise standard Q/BQB401-1999 cold-rolled steel sheet and strip size, shape, total and allows the thickness of the provisions in the deviation allowable deviation, for example: if the user wants to set the thickness of 1.00mm, width <1200mm strip of ordinary precision supplier, the allowable deviation of ± 0.07mm, ie, thickness 0.93 ~ 1.07mm within the strip is in line with orders thickness requirement that a positive deviation of 0.07 mm and the negative deviation of the strip is qualified 0.07mm. The tolerance is plus or minus deviation is 0.14mm. Of course, the higher the dimensional accuracy and allow the positive and negative deviation is smaller, the smaller the tolerance value, the definition may refer to the relevant information.
Steel plate supplier, according to theoretical weight by weight, the production side of the goal of rolling thickness is set to slightly less than the order thickness, rolling precision control and stricter standard value (not beyond ). Also by the cases of ordering requirements, the steel plate thickness of the order of 1mm, the goal of rolling thickness of 0.97mm, the allowed deviation of ± 0.04mm, so rolling out of the plate not only meet the standard requirements (meet the user requirements), but also save material. This rolling is referred to as "negative and partial rolling, rather than" negative tolerance rolling. Keep this in mind! Deviation is positive or negative, the size of ultra-poor "only" deviation ultra-poor "or" negative deviation ultra-poor ", while the tolerance is not being negative, it is an absolute value.
tolerance
The actual parameter values to allow the amount of change. Parameters, including both the geometric parameters of the machining, but also includes the disciplines of physics, chemistry, electrical and other parameters. So tolerance is the concept of a wide range. For the machinery manufacturing, development of tolerance purpose is to determine the geometric parameters of the product, it changes the amount within a certain range in order to reach the interchange with the requirements.
The geometric parameters of the tolerance of dimensional tolerances, form tolerances, position tolerances.
① dimensional tolerances. Size refers to allow changes in the amount equal to the absolute value of the maximum limit of size and the minimum limit of size algebra.
② shape tolerances. Allowed to refer to the shape of a single practical elements of the full amount of the changes, including straightness, flatness, roundness, cylindricity, of profile and surface profile of six projects.
③ position tolerance. Refers to the changes associated with the actual location of the elements on the base allow the whole amount, it limits the mutual positional relationship between the parts of two or more points, line, surface, including parallelism, perpendicularity, tilt, concentricity , symmetry, location, degree, round beating and the whole run of eight projects. The Tolerances said the manufacture of precision parts, reflecting the processing ease.
Tolerance class is divided into a total of 20 IT01, or IT0 in IT1, ..., IT18, grades were lower, and in turn increases the tolerance value. IT said that the international tolerance. Tolerance level or tolerance values select the basic principle is: should make machine parts manufacturing costs and the economic effects of the use value of the best with the size of IT5 ~ IT13, with special precision parts IT2 ~ IT5, non-tie dimensions with IT12 IT18, raw materials with the IT8 ~ IT14.