NBSIR 74-443

Weight Cleaning Procedures

H. E. Aimer

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1973

Final

Prepared for Optical Physics Division

Institute for Basic Standards

Washington, D. C. 20234

NBSIR 74-443

WEIGHT CLEANING PROCEDURES

H. E. Aimer

Institute for Basic Standards

National Bureau of Standards

Washington, D. C. 20234

November 1973

Final

Prepared for Optical Physics Division

Institute for Basic Standards

Washington, D. C. 20234

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Weight Cleaning Procedures

by

H. E. Aimer

It is essential that weights being calibrated as well as the

standards used be clean if the calibration is to be accurate

and meaningful. Therefore, a cleaning procedure should be a part of every calibration.

A. Categories of Weights

For cleaning purposes, weights may be divided into

four categories.

1. One-piece weights.

This category will include all one-piece weights

except lacquered weights, sheet metal weights and

small wire weights.

2. Screw-knob weights.

This category will include all weights with

adjusting cavities except lacquered weights.

3. Lacquered weights.

This category includes all lacquered or painted

weights.

4. Sheet metal weights and wire weights.

B. Cleaning Procedures

1. One-piece weights.

One-piece weights, one gram and larger, are steam

cleaned. The v/eights are either held or placed

in a jet of steam and manipulated so that the

entire surface of the v/eight is subjected to the

cleaning action of the steam long enough to clean

it. A superficial steaming is not enough. The
weight is then dried, either by evaporation or

careful wiping with a soft non-abrasive material

free from oil and other substances that will

leave a residue on the weights, such as high

grade cheesecloth. Care must be exercised that

no water spots are left on the weights as they

dry. Visible particles on the weights should be

brushed or wiped off before steam cleaning them.

If a steam generator is not available, one-piece

weights may be cleaned either by immersing them

in a hot or boiling distilled water bath in a non-metallic container or according to the

procedures for screw-knob weights.

Occasionally, a weight will have foreign material

adhering to it that requires the use of solvents.

Ethyl alcohol is a good general solvent.* If

alcohol does not remove the material, other solvents may be used, such as benzene, trichloroethane 111, etc. Alcohol is then used to remove

any film left by the other solvents. The weights

are then steam cleaned as outlined above.

Screw-knob weights.

Weights in this category are usually cleaned by

wiping with a soft non-abrasive material free

from oils or other substances that will leave a residue of any kind on the weights, such as high

grade cheesecloth. Occasionally, a weight will

have foreign matter adhering to it that requires

the use of solvents, applied with a cloth. Ethyl

alcohol is a good general solvent. If alcohol

does not remove the foreign material, other

solvents may be used. Alcohol is then used to

remove any film left by the other solvents.

To prevent spctting the weights when using

solvents, the weights should be wiped dry. Care

must be taken that no liquid gets under the knobs

or especially into the adjusting cavity.

A modified steam cleaning procedure may be used

on screw- knob weights. The bottoms and sides are

steam cleaned, care being taken that no liquid or

vapor gets under the knob or into the adjusting

cavity.

* Some solvents are health hazards and should be used in an approved safe manner.

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3. Laquered weights.

The cleaning of lacquered weights requires

special care because their protective lacquer

coating is soluble in most solvents. Lacquered

weights are cleaned by wiping with a soft nonabrasive material free from oils and other

substances that will contaminate the v/eights, or

by brushing with a soft brush such as a camel

hair brush or both. A rubber bulb type syringe

may be used to blow off lint or other small

particles, however, be careful not to touch the

weights with the nozzle. An electro-static

charge may be placed on the surfaces of the

weights during the cleaning process or while

handling them. This will be especially

troublesome in a very dry atmosphere. If

reliable mass values are to be obtained, the

charge must be bled off of the weights before

calibration

4. Sheet metal weights.

Either of the following two procedures may be

used in cleaning sheet metal and other small onepiece weights.

a. Two step method.

First, the weights are placed in an acetone

bath agitated to help loosen any foreign

material. A soft brush, such as a camel hair

brush, may be used to agitate the weights.

The weights are removed from the acetone,

allowed to dry and then steam cleaned. For

steam cleaning, the weights are held in front

of a jet of steam with forceps until the

entire surface has been covered with steam.

(See Note on next page) . In order that the

portion of the surface under the forceps may

be steamed, the weight is set down and picked

up again with the forceps holding the weight

at a different spot than the first time; the

weight is again steamed. Do not allow the

weights to touch the steam, nozzle. Only a low ash filter paper is used for drying the

sheet metal weights. A circular disk is

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folded unsyininetr ically (see figure 1) . The

main body of the weight is placed between the

folds of the paper with the turned up edge of

the weight protruding. The main body of the

weight is dried by pressing lightly on the

top of the paper. The turned up edge is

brushed lightly with a piece of filter paper.

In some cases, it may be necessary to brush

the body of the weight with filter paper to

remove drops of water. Care must be

exercised that no water spots are left on the

weights as they dry.

b. Three step method.

First, the weights are placed in an ether

bath and agitated with a soft brush to help

loosen any foreign material adhering to the

weights. The weights are removed from, the

ether, allowed to dry, then placed in an

ethyl alcoiiol bath and agitated. The weights

are removed from the alcohol bath, allowed to

dry, and then steam cleaned and dried as

outlined in the two step procedure.

Note ; The smaller fractional weights, say smaller than

5mg, may be placed in a hot or boiling distilled

water bath for the final cleaning instead of

steam cleaning them. A hot or boiling distilled

water bath

cleaning of

generator is

m^ay also be used for the final

all sheet metal weights when a steam

not available.

FIGURE 1

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C. Cleaning Interval

1. Weights under test.

The weights under test are cleaned before calibration.

2. Standards.

Standards need not be cleaned every time they are

used. If the standards are handled carefully,

and kept under a reasonably dust tight cover,

when not in use, in a clean atmosphere, the

interval between cleanings may be several months,

or until the calibration procedure checks

indicate that the standards are changing and may

need cleaning. Under less favorable conditions

the interval may be only a few weeks.

D. Temperature Equilibrium

Newly cleaned weights should be allowed to come to

temperature equilibrium before they are calibrated.

This may take several hours for the larger v/eights

that have been steam cleaned.

Generally, laboratory weights will come to temperature equilibrium over night.

E. Storage

Usually, weights are not placed in the balance

immediately after cleaning, but are stored for

varying periods. The weights should be stored

under cover so that they will stay clean. Weights,

one gram and larger, may be stored on a tray lined

with filter paper and covered with an inverted

glass dish. The smaller weights may be stored in a small glass dish covered with a watch glass. In

both cases, the container should be labeled with

the weight identification. When the weights are to

be moved, carry the tray or dish in a level

position so that the weights do not slide around.

When the weights are placed in the balance, they

should be carefully brushed to remove any particles

that may be on them. A small bulb type rubber

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syringe is useful in removing lint and other small

particles from weights. The particles are blown

off the weights. Therefore, neither the nozzle nor

any other part of the syringe need touch the

weights, and care must be taken that they do not.

F. Brushes

All of the equipment used in cleaning and handling

weights should, of course, be clean. But, brushes

require special attention because they are easily

contaminated and often are the last cleaning

instrument used before the weights are calibrated.

Only soft brushes, such as camel hair brushes

should be used on weights.

The brushes are cleaned by washing with soap and

water, then rinsing in ethyl alcohol and allowed to

dry in air. When drying the brushes, place them so

that the bristles do not touch anything. New

brushes are cleaned before using to remove any oil

or other matter that might contaminate the weights.

Used brushes are cleaned as often as necessary to

be sure that the brushes themselves do not

contaminate the weights. Store cleaned brushes in

containers that will keep them clean until needed.

V When handling the brushes do not touch the

bristles, as oil from the skin will contaminate

them. When the brushes are laid down, place them

so that tlie bristles do not touch anything.

G. Steam Generator

The steam generator may be purchased from a laboratory supply house or one can be constructed.

A simple steam generator may be constructed from a 500ml wash-flask, a two hole stopper, some glass

tubing, hot plate for the heat source, a large

graduate, and some flexible tubing.

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i
STEAM GENERATOR

Hot

FIGURE 2

J

II

Graduate

XT i 1 I i_-

A piece of glass tubing is bent, as shown in the illustration, with one end drawn to form a nozzle and the other end

is inserted in one of the holes in the stopper. Another

piece of glass tubing with a piece of flexible tubing

attached to it is inserted in tn^ other hole of the stopper.

The other end of this flexible tube is placed in water in

the large graduate. This acts to provide some pressure

inside the wash-flask and also acts as a safety valve. The

wash-flask is partially filled with distilled water, about

two-thirds full, then the stopper is put in place and the

flask placed on the hot plate. It may be necessary to

insulate Lhe neck and the tube with the nozzle.

USCOMM-NBS-DC

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NBS-114A (REV. 7-73)

U .S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. I^UHLK AriON OK Rl'I^OR T NO. NBSIR 74-4432, Cjov't Accession

No.

3 » R c c 1 p I c n t

* s Accession No

4 TITI AND SlilVl ITI I- 5. Publication Date November 1973

6. Performing Organization Oodc

7. AUTH0R(S1

H. E. Aimer

8. Performing Organ. Report No. NBSIR 74-443

7. riir\r(^r\Mli>ILj L'rxvjAlNlZ-AilUlN INnMil AINU AUUK too NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

10. Project/Task/Work Unit No.

11. Contract/Grant No.

12. Sponsoring Organization Name and Complete Address (Street, City, State, ZIP)

SAME

13, Type of Report & Period Covered

Pinal

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

This report supercedes NBS Report 9683

16. ABSTRACT (A 200-word or less factual summary ol most significant information. If document includes a significant

bibliography or literature survey, mention it here.)

Accurate, and meaningful results In the calibration of weights

depend on clean weights. This paper describes a method of

cleaning weights.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Cleaning; standards; steam generator; storage; terrperature

equilibrium; weights.

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