GOST 25282-93

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  ГОСТ 25282-93

GOST 25282−93 (ISO 3995−85) Powder metal. A method of determining the strength of pressovac

GOST 25282−93
(ISO 3995−85)

Group B59

INTERSTATE STANDARD

POWDER METAL

A method of determining the strength of pressovac

Metallic powders. Method for determination of pressings strength

OKS 77.160*
AXTU 1790
____________________
* In the index «National standards», 2008
OKS 77.040.10 and 77.160. — Note the manufacturer’s database.

Date of introduction 1997−01−01

Preface

1 DEVELOPED by the Russian Federation, Technical Committee TC 150 «Powder metallurgy"

INTRODUCED by Gosstandart of Russia

2 ADOPTED by the Interstate Council for standardization, Metrology and certification (Protocol No. 3−93 from 17.02.93)

The adoption voted:

The standard contains the full authentic text of international standard ISO 3995−85 «Powder metal. Determination of ultimate strength in lateral bending respecing of pressovac rectangular shape» and additional requirements that reflect the needs of the economy

3 Decree of the Russian Federation Committee on standardization, Metrology and certification dated June 19, 1996 N 383 inter-state standard GOST 25282−93 (ISO 3995−85) introduced directly as a state standard of the Russian Federation from January 1, 1997

4 REPLACE GOST 25282−82

1 SCOPE

This standard specifies a method for determining the tensile strength in bending of pressovac made from metal powders, powders of alloys and powder mixtures.

The method consists in the manufacture of compression with a given density at a given pressing pressure and the test of lateral bending with uniformly increasing, concentrated load with subsequent calculation of the ultimate strength.

You can define a limit of bending strength of pressovac according to the international standard ISO 3995−85 given in Appendix A.

2 NORMATIVE REFERENCES

The present standard features references to the following standards:

GOST 2768−84 Acetone. Specifications

GOST 6507−90 Micrometers. Specifications

GOST 12026−76 laboratory filter Paper. Specifications

GOST 23148−78* Powder metal. Methods of sampling and sample preparation
________________
* On the territory of the Russian Federation GOST 23148−98. Here and further. — Note the manufacturer’s database.

3 SAMPLING METHOD

3.1 sampling Method — according to GOST 23148.

3.2 Density or pressing pressure of the pressing choose, based on the density or pressure of pressing the pressed parts.

3.3 the Pressing needs to have a length of 30 mm, width 10−13 mm and a height of 5.5 to 6.5 mm. Height made pressing on the length of at least 25 mm should not differ by more than 0.1 mm.

3.4 Mass of hinge-plate , g, for the manufacture of compression is calculated by the formula

, (1)

where is the specified compaction, g/cm;

 — the amount of compression, cm.

3.5 Weight of sample for test shall be not less than four times the mass of the compact.

4 APPARATUS, MATERIALS, REAGENTS

Press, providing the force of 300 kN and the measurement error not more than 2%. The press should ensure the application of the pressing force with a constant speed of no more than 50 kN/s.

The mold shown in figure 1, with the matrix, made of hard metal or tool steel with a hardness of at least 750 N. The height of the punches (): top 25 mm, bottom 70 mm.

Figure 1 — mold with the matrix, made of hard metal or tool steel with a hardness of at least 750 N

1 — ferrule; 2 — matrix; 3 — punch; 4 — support

Figure 1

Steel supports — 2 PCs (figure 1). The poles height (in): 36 and 40 mm. allowed the use of press equipment of a different design, allowing manufacturing of pressing the same dimensions as the principle of bilateral pressing.

Scales with a weighing error of no more than 0.01 g.

MICS MK MK 25−1 and 50−1 GOST 6507 or other devices with a measuring error of not more than 0.01 mm.

Testing machine, providing the force to 1000 N with a measuring error of not more than 1%.

Device for testing pressovac bending diagram is shown in figure 2, consists of two rigidly connected with the support roller located parallel to each other at a distance of (25,0±0,2) mm and a load roller mounted on a movable punch. All three rollers should have a diameter (3,0±0,1) mm and be made of hardened steel with a hardness of at least HV 700 or from a firm alloy. The length of the rollers must be greater than the width of pressing. Load roller is located exactly in the middle of the distance between the support rollers. The distance is measured with an error of not more than 0.1 mm Misalignment of the load and support rollers must not be more than 0,1 mm over a length equal to the distance between the support rollers.

Figure 2 — Device for testing pressovac bending

and — filling powder in a mold; b — installation of the upper punch; in — pre-compressor; g — replacement of the supports and final pressing; d — pushing

Figure 2

Zinc stearinovokisly in the normative documentation.

Acetone GOST 2768.

Filter paper according to GOST 12026.

5 PREPARING FOR THE TEST

Powder pressing get double-sided pressing in the mold with a clean surface of the die cavity and punches, or covered with a layer of grease. To clean the dirt from the cavity of the die and punches is wiped with filter paper soaked in acetone, which should be dry. For applying the grease cavity of the die and punches lubricated with a solution stearinovokisly zinc (100 g stearinovokisly of zinc per 1000 cmof acetone) and allow it to dry.

In the thus prepared mold pressed powder without grease or after it is added. Powder with added solid lubricant (for example, stearinovokisly zinc or stearic acid) with a mass fraction of from 0.5 to 1.5% are thoroughly mixed prior to compression.

The sequence of operations of the pressing and ejection are shown in figure 2.

First, the lower punch is introduced into the matrix and mounted on the support for pressing. Poured a charge of powder into the cavity of the matrix and aligning. Enter into the matrix of the upper punch to the powder surface. Pre-pressed to the efforts of 20 kN. Replace support for pre-pressing for support for the final pressing and pressed to the stop that provides the pressing of a given height. In the final pressing force is applied at a constant rate, which must be not more than 50 kN/s. Remove prop 2 from the bottom of the mold, install support 1 on top of the mold and push pressing. This way you get three of the compact. Pressing weighed, measured the length, width, and height accuracy up to 0.01 mm and calculate their density. The divergence of the parallel measurements of the density of pressovac should be no more than 0.1 g/cm. For compaction taking the arithmetic average of the densities rounded to the second decimal place.

Allowed to receive pressovac at a given pressing pressure. Recommended pressing pressure of 400 MPa, other pressure agree and specify in the normative-technical documentation for the particular powder. Upon receipt of pressovac at a given pressing pressure of the final pressing operation (figure 3) runs without stops.

Figure 3 — Operation final pressing with a predetermined pressing pressure

1 — load roller; 2 — support roller

Figure 3

6 TESTING

The pressing is placed in a device for testing the bending so that she was lying on the supporting rollers with a surface perpendicular to the direction of pressing, and was located in relation to them perpendicularly and symmetrically. Device for testing pressovac bending set in the Central part of the pressure plate of the testing machine. Loading is carried out at a constant speed. Time from start of loading to failure of compression should not be less than 10 s. Determine the force of destruction pressing with an error less than 1%. The test is carried out at three pressovyj.

Requirements for the use of various devices for loading pressovac when the bending test is given in the Appendix.

7 PROCESSING OF RESULTS

7.1 tensile strength of pressovac on a bend , MPa, calculated by the formula

, (2)

where  — the force of destruction, N;  — distance between supports, mm;  — height of compact, mm; width of roll, mm.

7.2 tensile strength in bending be the arithmetic mean of results of three tests, rounded to the first decimal place.

7.3 test Results recorded in a Protocol containing:

— the name (brand) of powder or the composition of the mixture;

— the structure and content of the lubricant introduced into the powder;

— information on the lubrication of the cavities of the matrix mold and the punch;

— compaction or pressure its pressing;

— the tensile strength of the pressing;

— the designation of this standard;

— the date of the test.

Annex a (mandatory). THE METAL POWDERS. DETERMINATION OF ULTIMATE STRENGTH IN LATERAL BENDING RESPECING OF PRESSOVAC RECTANGULAR SHAPE (ISO 3995−85)

APPENDIX A
(required)

A. 1 Purpose and scope

This international standard specifies a method for determining the tensile strength of respecing pressovac rectangular cross section by measuring the strength at a bending.

A. 2 the essence of the method

Obtained by pressing from metal powder pressing are destroying ever-increasing under controlled conditions of force transverse bending. Determine the tensile strength (tensile strength in bending) respecing of pressovac by calculating according to the formula of bending stress required to fracture the rectangular pressing (block), supported at the ends, and to which is fixed midway between the centers of the support device applied force.

The tensile strength of respecing pressovac determine pressovyj with a certain density or pressed at a given pressing pressure.

A. 3 Apparatus

A. 3.1 Matrix, made of hard alloy or tool steel, and two of the punch for producing rectangular samples for testing, the size of which is given in A. 4. A sample of the mold shown in figure A. 1.

Figure A. 1 — the mold for pressing the rectangular samples

1 — ferrule; 2 — matrix; 3 — punch the upper (=25 mm) and lower (=70 mm)

Figure A. 1 — the mold for pressing the rectangular samples

Note — Mated parts should be fitted and lapped.

A. 3.2 Press, providing the force to 300 kN with an accuracy of ±2% and to increase the force at a speed of not more than 50 kN/s.

A. 3.3 Micrometer or other measuring device to measure sizes of pressovac with an accuracy of ±0,01 mm.

A. 3.4 test Device (figure A. 2) with two support cylinders (rollers) and a fixed distance between them and a load cylinder (roller). All three cylinders should have a diameter of (3±0,1) mm and shall be made of hardened steel with a hardness according to Vickers of at least 700 HV or from a firm alloy. Cylinders must be installed in parallel and the distance between the centers of the support cylinders is measured with an accuracy of ±0.1 mm, should be (25±0,2) mm. Load the cylinder must be located in the middle of the supporting cylinders.

Figure A. 2 — Scheme of device for testing

Figure A. 2 — Scheme of device for testing

The cylinders must be installed so as to provide a permissible deviation from the parallel arrangement of the upper and lower surfaces of the test sample.

A. 3.5 Load device

A. 3.5.1 Machine for compression testing, which provides the definition of breaking stress with a minimum accuracy of ±2 N.

A. 3.5.2 Device with a yoke to loading for proper installation of the test sample and ensure the efforts of destruction on the same level. The applied force can be obtained in different ways (figure A. 3). Stress is applied to the subject sample is determined with an accuracy of ±2 N.

Figure A. 3 — Device for loading

1 — opposed; 2 — installation of sample; 3 — load

Figure A. 3 — Device for loading

A. 4 Sampling

The sample quantity for test choose is sufficient for obtaining the three samples sizes: width — from 10 to 13 mm, length not less than 30 mm, thickness from 5.5 to 6.5 mm. the thickness of the test sample on the distance between supports should not differ by more than 0.1 mm. If necessary, carry out preliminary tests to determine the amount of powder that enforces these requirements.

A. 5 test Procedure

A. 5.1 cleaning matrix and punches

Wipe the cavity of the die and punches soft and clean paper soaked in a suitable solvent, for example acetone. The solvent needs to evaporate.

A. 5.2 conditions of test powder

A. 5.2.1 Powder, not containing grease, pressed:

a) in the matrix without lubrication (at high pressing pressures possible die wear);

b) in the matrix, the walls of which are lubricated by A. 5.3.1;

C) in the matrix without lubrication and after adding a lubricant to the powder by A. 5.3.2.

A. 5.2.2 Powder containing a lubricant, is pressed:

a) in the matrix without lubrication;

b) in the matrix without lubrication and after adding extra lubrication by A. 5.3.2.

A. 5.3 grease

A. 5.3.1 apply grease to the die wall

On the walls of the matrix cause the mixture or solution of lubricant in a volatile organic liquid, for example, 100 g of zinc stearate per 1000 cmof acetone. When excess fluid has drained, allow the solution adhering to the walls, to evaporate, leaving on them a thin layer of grease.

A. 5.3.2 adding a lubricant to the powder

Powder for testing mixed thoroughly after adding a certain amount (e.g., 0.5 to 1.5%) of a suitable solid lubricant (e.g. zinc stearate or stearic acid).

A. 5.4 Pressing and vypressovyvaniem

Enter the lower punch into the cavity of the matrix. A matrix on the height of the filling using support constraints between the matrix and the base of the lower punch. Pour the powder into the cavity of the matrix, ensuring uniform distribution. Install the upper punch and placed the die punches between the plates of the press. Pre-load force of approximately 20 kN. Removed the limiters that support the matrix. If the matrix is supported by springs or other comparable method, the pre-stress loading is not used.

The final force applied at a constant rate, which must be not more than 50 kN/s.

The pressing from the die is extruded through the bottom of the punch.

The sequence of pressing and vypressovyvaniem shown in figure A. 4.

Figure A. 4 — the Process of pressing and vypressovyvaniem

1 — fill; 2 — pre pressing; 3 — compression; 4 — vypressovyvaniem

Figure A. 4 — the Process of pressing and vypressovyvaniem

A. 5.5 pressing Pressure of

The tensile strength of respecing pressovac determined on samples obtained at a given pressure or density, in agreement with the consumer. In the first case, the recommended pressure of 400 N/mm. In the second case, samples for test is compressed to a predetermined density, the maximum deviation from which three test specimens shall be not more than 0.1 g/cm.

A. 5.6 density Determination

Given the effort measure the length, width and thickness of the test sample with an accuracy of 0.01 mm. Determine the mass and volume (calculated by the average value of the sizes).

A. 5.7 the definition of the effort of the breaking load

Destroy the test sample under controlled conditions using a testing machine, compression or device with a yoke for loading.

A. 5.7.1 Method 1. The use of the machine for compression testing

In the device for testing lateral bending (figure 2) install the sample, ensuring its alignment and perpendicular to the axes of the support cylinders. The device is placed between the plates of the testing machine and a constant speed is applied a compressive force so that the test sample is destroyed not earlier than after 10 s. Record the force of destruction with an accuracy of 2 N.

A. 5.7.2 Method 2. The use of the device with the rocker for loading

The rocker arm using the balancer lead in a horizontal position. The test specimen is installed in the center in the device with the rocker for loading, ensuring that it is perpendicular to the axes of the support cylinders. Increase the load with the same speed so that the test sample is destroyed not earlier than 10 p.

Determine the force of destruction with an accuracy of 2 N.

Note — In the case of the container with pellets rocker and the container needs to be balanced. The applied load is only calculated when the mass fraction.

A. 6 processing of the results

A. 6.1 Calculate the density of the test sample by its weight and volume. Calculate the arithmetic mean of the definition of the three different samples with an accuracy of 0.05 g/cm.

A. 6.2 tensile strength respecing of pressovac , N/mm, calculated by the formula

, (A. 1)

where is the bending force, N; is the distance between supports fastening, mm;  — the thickness of test sample, mm;  — the width of the test specimen, mm.

A. 6.3 Calculate the arithmetic average of the three definitions, rounding it with the accuracy of 0.2 N/mmfor values up to 10 N/mm, inclusive, with an accuracy of 0.5 N/mmfor values greater than 10 N/mm.

A. 7 test report

The test report must include:

a) reference to this international standard;

b) all information required to identify the test sample;

C) the type, the type and amount of lubricant if it was added to the powder; in some cases, indicate the method of introducing lubricant to the powder;

d) the density of the test sample or the pressing pressure;

d) the matrix material (tool steel or hard alloy);

e) the result obtained;

g) all operations not specified in this international standard or regarded as optional;

h) the exact details of any event that may affect the result.



The electronic text of the document
prepared by JSC «Code» and checked by:
the official publication of the
M.: IPK Publishing house of standards, 1996