CN103048204B - Method for defining allowable stress of gray cast iron centrifugal casting mold material - Google Patents

Abstract

The invention belongs to the technical field of centrifugal casting, and particularly relates to a method for defining the allowable stress of a gray cast iron centrifugal casting mold material. The allowable stress of gray cast iron under a 20 DEG C condition is [Sigma 20] which is equals to Sigma b 20/N, and N is equal to 11 to 13; the allowable stress of gray cast iron under a 400 DEG C condition is [Sigma 400] which is equals to Sigma b 400/N, and N is equals to 20 to 24; the allowable stress [Sigma 1] of gray cast iron under a condition ranging from 20 DEG C to 400 DEG C is obtained according to an interpolation method on the basis of [Sigma 20] and [Sigma 400]; and the allowable stress [Sigma 2] of gray cast iron under a condition higher than 400 DEG C is the product of [Sigma 400], the ratio of the tensile strength of gray cast iron at the temperature T DEG C and the tensile strength of gray cast iron at the temperature 400 DEG C, and the ratio of 400 and T. According to the method, a reliable reference is provided for the design of gray cast iron centrifugal casting molds, and a foundation is laid for quantitative analysis of safety accidents of gray cast iron centrifugal casting mold rupture.

Description

A kind of method of definite casting pig centrifugal casting mould material permissible stress

Technical field

The invention belongs to centrifugal casting technique field, be specifically related to the method for a kind of definite casting pig centrifugal casting mould material permissible stress under hot conditions.

Background technology

The most frequently used centrifugal casting mould material is the gray cast iron material that fragility is larger, and because the mechanical behavior under high temperature test to casting pig is few, basic data is very deficient.In traditional centrifugal casting mould design, people often just using casting pig the ambient temperature mechanical properties under static condition as casting mold design with reference to foundation, and centrifugal casting mould is worked under the operating mode of high temperature, high speed, compared with ambient temperature mechanical properties, the mechanical behavior under high temperature of material can reduce a lot, the fragility of casting pig shows very outstandingly, even if consider the strength of materials by larger remaining, is also often sufficient not.In 6 centrifugal casting accident cases having collected at present, except 1 example is because causing casualty accident for the bolt fracture of locking cover plate in cast steel centrifugal casting mould, remaining 5 example is all due to the casting pig centrifugal casting mould casualty accident causing of breaking.Up to now, not yet have the permissible stress data of casting pig mold material under hot conditions, designer carries out the design of casting pig centrifugal casting mould entirely with personal experience, and this is also the major reason that in centrifugal casting, the accident of causing casualties happens occasionally.

From existing technical information (mechanical engineering society's foundry meeting. cast iron handbook [M]. Beijing: the .1979 of China Machine Press first published, mechanical engineering society's foundry meeting. casting handbook the 1st volume, cast iron [M]. Beijing: the .2011 of the China Machine Press third edition) in, the overview of gray cast iron material mechanical behavior under high temperature is (in bracket, being a routine data): casting pig changes little 20 DEG C to 400 DEG C tensile strength, tensile strength slightly declines at 150～250 DEG C, tensile strength higher (200～350MPa) 400 DEG C time, more than 400 DEG C, tensile strength declines, in the time of 500 DEG C, also has higher tensile strength (160～280MPa), in the time of 600 DEG C, still have certain tensile strength (110～190MPa).So the serviceability temperature of casting pig is controlled in 700 DEG C under normal circumstances.

Because the length growth rate of casting pig is extremely low, from the casting pig of HT150～HT300, elongation after fracture when its tension failure is between 0.3%～0.8%, and the casting mold material overwhelming majority that veining accident occurs in centrifugal casting is casting pig.Casting pig is typical brittle metal material, but its mechanical behavior under high temperature basic data is very deficient, therefore determining of casting pig permissible stress is very difficult.In 6 trades mark that comprise in casting pig national standard, casting pig HT100 and HT150 can not be used for stressed foundry goods because intensity is too low; And casting pig HT300 and HT350 are because fragility is too high also seldom for centrifugal casting mould material; Gray Cast HT200 and HT250 are the conventional trades mark of centrifugal casting mould material.For brittle metal material, permissible stress [σ] is tensile strength sigma _bdivided by safety factor N, i.e. [σ]=σ _b/ N.

Summary of the invention

Technical matters to be solved by this invention is to provide the method for a kind of definite casting pig centrifugal casting mould material permissible stress under hot conditions.

Casting pig is at 20 DEG C within the scope of 400 DEG C, and tensile strength changes little, and temperature is during higher than 400 DEG C, and tensile strength declines very fast.We,, in the time determining the permissible stress of casting pig centrifugal casting mould, are divided into two temperature sections---study within the scope of 20 DEG C to 400 DEG C and 400 DEG C～700 DEG C.

For solving the problems of the technologies described above, technical scheme of the present invention is:

A method for definite casting pig centrifugal casting mould material permissible stress, the permissible stress of casting pig centrifugal casting mould material within the scope of the permissible stress of casting pig centrifugal casting mould material within the scope of 20 DEG C～400 DEG C and 400 DEG C～700 DEG C is determined in segmentation;

Wherein, the determining of casting pig centrifugal casting mould material permissible stress within the scope of 20 DEG C～400 DEG C, comprises the steps:

Permissible stress [the σ of casting pig centrifugal casting mould material while determining 20 DEG C ₂₀] be

$\left[{\mathrm{\σ}}_{20}\right]=\frac{{\mathrm{\σ}}_{b20}}{N}$

In formula, σ _b20the tensile strength of casting pig while being 20 DEG C, N is safety factor, gets N=11～13;

Casting pig centrifugal casting mould material permissible stress [σ while determining 400 DEG C ₄₀₀] be

$\left[{\mathrm{\σ}}_{400}\right]=\frac{{\mathrm{\σ}}_{b400}}{N},$

In formula, σ _b400tensile strength while being 400 DEG C, N is safety factor, gets N=20～24;

Wherein, σ _b400obtain according to following formula:

${\mathrm{\σ}}_{b400}=\frac{{\mathrm{\σ}}_{\mathrm{bn}}}{k}$

σ _bnbe within the scope of 20 DEG C～700 DEG C, tensile strength values when temperature T;

K is within the scope of 20 DEG C～700 DEG C, the ratio of tensile strength values when tensile strength values when temperature T and 400 DEG C;

Permissible stress [the σ of casting pig centrifugal casting mould material in the time of temperature T within the scope of 20 DEG C～400 DEG C ₁] try to achieve according to following formula:

$\left[{\mathrm{\σ}}_1\right]=\frac{\left[{\mathrm{\σ}}_{400}\right]-\left[{\mathrm{\σ}}_{20}\right]}{380}\·(T-400)+\left[{\mathrm{\σ}}_{400}\right];$

Determine casting pig centrifugal casting mould material permissible stress within the scope of 400 DEG C～700 DEG C

$\left[{\mathrm{\σ}}_2\right]=\left[{\mathrm{\σ}}_{400}\right]\·\frac{{\mathrm{\σ}}_{\mathrm{bn}}}{{\mathrm{\σ}}_{b400}}\·\frac{400}{T}=\left[{\mathrm{\σ}}_{400}\right]\·k\·\frac{400}{T}.$

When described temperature T is 20 DEG C～200 DEG C, the ratio k=-0.0002T+0.9604 of tensile strength values when tensile strength values when described temperature T and 400 DEG C.

When described temperature T is 200 DEG C～400 DEG C, the ratio k=0.0004T+0.8225 of tensile strength values when tensile strength values when described temperature T and 400 DEG C.

When described temperature T is 400 DEG C～700 DEG C, ratio k=-6 × 10 of tensile strength values when tensile strength values when described temperature T and 400 DEG C ^-6t ²+ 0.0039T+0.407.

The invention has the beneficial effects as follows: a kind of set up definite casting pig centrifugal casting mould material permissible stress method, the method provides comparatively foundation reliably for the design of casting pig centrifugal casting mould, break away from full Design Mode by rule of thumb, simultaneously also for the quantitative test of casting pig centrifugal casting mould break accident is laid a good foundation.

Embodiment

The mechanical behavior under high temperature of casting pig HT250 is in table 1, and the data of known its tensile strength are extremely incomplete.Casting pig centrifugal casting mould temperature range is set as 20 DEG C～700 DEG C.

The mechanical behavior under high temperature of HT250 example of table 1 casting pig

1, within the scope of 20 DEG C～400 DEG C, centrifugal casting mould casting pig permissible stress determines

(1) 20 DEG C time, centrifugal casting mould casting pig permissible stress determines

Tensile strength sigma 20 DEG C time _b20=219MPa, N is safety factor, gets N=11～13.

$\left[{\mathrm{\σ}}_{20}\right]=\frac{{\mathrm{\σ}}_{b20}}{N}=\frac{219}{N}$

[σ ₂₀]=19.9～16.8 (MPa)

Get the permissible stress [σ of casting pig at 20 DEG C ₂₀]=18MPa, now N=12.2.

(2) 400 DEG C time, centrifugal casting mould casting pig permissible stress determines

${\mathrm{\σ}}_{b400}=\frac{{\mathrm{\σ}}_{\mathrm{bn}}}{k}$

Existing known 425 DEG C time, σ _b425=215MPa, in the time of 400 DEG C～700 DEG C of scopes,

k＝-6×10 ^-6T ²+0.0039T+0.407

＝-6×10 ^-6×425 ²+0.0039×425+0.407

＝0.981

Tensile strength 400 DEG C time is

σ _b400＝σ _bn/k＝σ _b425/k＝215/0.981＝219(MPa)

Permissible stress 400 DEG C time is

$\left[{\mathrm{\σ}}_{400}\right]=\frac{{\mathrm{\σ}}_{b400}}{N}=\frac{219}{N}$

N is safety factor, N=20～24, and 400 DEG C time, the permissible stress of casting pig centrifugal casting mould material is

[σ ₄₀₀]＝(10.95～9.13)(MPa)

Permissible stress [the σ of centrifugal casting mould casting pig while getting 400 DEG C ₄₀₀]=10MPa, now N=21.9.

Within the scope of (3) 20 DEG C～400 DEG C, centrifugal casting mould casting pig permissible stress determines

Due to casting pig at 20 DEG C within the scope of 400 DEG C, the variation of mechanical behavior under high temperature is all little, permissible stress [σ in the time having determined 20 DEG C _{20 DEG C}permissible stress [σ when]=18MPa and 400 DEG C ₄₀₀on]=10MPa basis, remaining permissible stress can calculate by linear distribution within the scope of 20 DEG C～350 DEG C, according to formula

$\left[{\mathrm{\σ}}_1\right]=\frac{\left[{\mathrm{\σ}}_{400}\right]-\left[{\mathrm{\σ}}_{20}\right]}{380}\·(T-400)+\left[{\mathrm{\σ}}_{400}\right]$

Permissible stress can calculate all the other temperature within the scope of 20 DEG C and 400 DEG C time, during as 100 DEG C

$\left[{\mathrm{\σ}}_1\right]=\frac{\left[{\mathrm{\σ}}_{400}\right]-\left[{\mathrm{\σ}}_{20}\right]}{380}\·(T-400)+\left[{\mathrm{\σ}}_{400}\right]=\frac{10-18}{380}\×(100-400)+10=16.3\left(\mathrm{MPa}\right)$

Therefore 100 DEG C time, get 16MPa.

In like manner 200 DEG C time, get 14MPa; 250 DEG C time, get 13MPa; 300 DEG C time, get 12MPa; 350 DEG C time, get 11MPa.

2,400 DEG C～700 DEG C time, centrifugal casting mould casting pig permissible stress determines

K value (1) 450 DEG C time is

k＝σ _b450/σ _b400＝-6×10 ^-6T ²+0.0039T+0.407

＝-6×10 ^-6×450 ²+0.0039×450+0.407

＝0.947

(2) from formula $\left[{\mathrm{\σ}}_2\right]=\left[{\mathrm{\σ}}_{400}\right]\·k\·\frac{400}{T}$

450 DEG C time, the permissible stress of centrifugal casting mould casting pig is

$\left[\mathrm{\σ}\right]=\left[{\mathrm{\σ}}_{400}\right]\·k\·\frac{400}{T}=10\×0.947\×\frac{400}{450}=10\×0.947\×0.89=8.41\left(\mathrm{MPa}\right)$

Just the first calculation value of permissible stress while obtaining 450 DEG C, the determined value 8MPa of permissible stress while just obtaining 450 DEG C after rounding up.

The above embodiments have been set up a kind of method of definite casting pig centrifugal casting mould material permissible stress; For the design of casting pig centrifugal casting mould provides foundation comparatively reliably, break away from full Design Mode by rule of thumb; Simultaneously also for the quantitative test of casting pig centrifugal casting mould break accident is laid a good foundation.

It should be noted last that, above embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is had been described in detail with reference to preferred embodiment, those of ordinary skill in the art is to be understood that, can modify or be equal to replacement technical scheme of the present invention, and not departing from the spirit and scope of technical solution of the present invention, it all should be encompassed in the middle of claim scope of the present invention.

Claims (1)

1. a method for definite casting pig centrifugal casting mould material permissible stress, is characterized in that, the permissible stress of casting pig centrifugal casting mould material within the scope of the permissible stress of casting pig centrifugal casting mould material within the scope of 20 DEG C～400 DEG C and 400 DEG C～700 DEG C is determined in segmentation;

Wherein, the determining of casting pig centrifugal casting mould material permissible stress within the scope of 20 DEG C～400 DEG C, comprises the steps:

Permissible stress [the σ of casting pig centrifugal casting mould material while determining 20 DEG C ₂₀] be

$\left[{\mathrm{\σ}}_{20}\right]=\frac{{\mathrm{\σ}}_{b20}}{N}$

In formula, σ _b20the tensile strength of casting pig while being 20 DEG C, N is safety factor, gets N=11～13;

Casting pig centrifugal casting mould material permissible stress [σ while determining 400 DEG C ₄₀₀] be

$\left[{\mathrm{\σ}}_{400}\right]=\frac{{\mathrm{\σ}}_{b400}}{N},$

In formula, σ _b400tensile strength while being 400 DEG C, N is safety factor, gets N=20～24;

Wherein, σ _b400obtain according to following formula:

${\mathrm{\σ}}_{b400}=\frac{{\mathrm{\σ}}_{\mathrm{bn}}}{k}$

σ _bnbe within the scope of 20 DEG C～700 DEG C, tensile strength values when temperature T;

K is within the scope of 20 DEG C～700 DEG C, the ratio of tensile strength values when tensile strength values when temperature T and 400 DEG C;

Permissible stress [the σ of casting pig centrifugal casting mould material in the time of temperature T within the scope of 20 DEG C～400 DEG C ₁] try to achieve according to following formula:

$\left[{\mathrm{\σ}}_1\right]=\frac{\left[{\mathrm{\σ}}_{400}\right]-\left[{\mathrm{\σ}}_{20}\right]}{380}\·(T-400)+\left[{\mathrm{\σ}}_{400}\right];$

Determine casting pig centrifugal casting mould material permissible stress within the scope of 400 DEG C～700 DEG C

$\left[{\mathrm{\σ}}_2\right]=\left[{\mathrm{\σ}}_{400}\right]\·\frac{{\mathrm{\σ}}_{\mathrm{bn}}}{{\mathrm{\σ}}_{b400}}\·\frac{400}{T}=\left[{\mathrm{\σ}}_{400}\right]\·k\·\frac{400}{T};$

When described temperature T is 20 DEG C～200 DEG C, the ratio k=-0.0002T+0.9604 of tensile strength values when tensile strength values when described temperature T and 400 DEG C;

When described temperature T is 200 DEG C～400 DEG C, the ratio k=0.0004T+0.8225 of tensile strength values when tensile strength values when described temperature T and 400 DEG C;

When described temperature T is 400 DEG C～700 DEG C, ratio k=-6 × 10 of tensile strength values when tensile strength values when described temperature T and 400 DEG C ^-6t ²+ 0.0039T+0.407.