Part 4 of 4
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This information in this article is copyright Texaco Inc., Texaco Magazine
LUBRICATION. This article may not be reproduced, copied, or retransmitted
in any form without express written consent of Texaco Inc.
- ------------------------------------------------------------------------------
ANTIFREEZE AND COOLANT
Courtesy of Texaco Magazine LUBRICATION
Copyright Texaco Inc.
PERFORMANCE EVALUATION
Chemical and Physical Properties
Physical, chemical and performance standards for AF&C concentrates baded on
EG have been established by ASTM (American Society for Testing and
Materials), SAE (Society of Automotive Engineers), government agencies and
various AF&C trade associations. In Europe, standards have been issued by
the different national standard societies, government agencies and various
industrial associations. The Co-ordinating European Council (CEC) has
organized a Special Working Group on engine coolants to come to a common
European standard.
These standards ensure that when AF&C concentrates are used at 40 to 70
percent concentration in water, they will function effectively during both
winter and summer in automotive vehicle cooling systems to provide protection
against freezing, boiling and corrosion.
The most important physical properties are freezing point and boiling point.
Specific gravity and index of refraction are also important because they
relate to the concentration of glycol in the AF&C and, therefore, provide a
means of predicting the freezing protection of AF&C solutions. Determination
of the index of refraction using a refractometer provides a more accurate
assessment of the freezing protection of the AF&C than measurement of the
specific gravity using commercial hydrometers.
The chemical character of an AF&C is represented by pH and reserve
alkalinity. The pH scale indicates the acidity or alkalinity of coolant
solutions (7 is neutral; numbers decreasing below 7 are increasingly acidic,
while numbers increasing above 7 are increasingly alkaline). It is desirable
that the coolant have a neutral or slightly alkaline pH.
The ability of an AF&C solutions to stay alkaline is defined by its reserve
alkalinity, which is a number corresponding to the volume of a standard acid
solution required to neutralize the coolant. The higher the number, the
greater the buffering ability or reserve alkalinity. It is a measure of the
concentration of inhibitors or other chemicals which contribute to the
alkaline character of the coolant. Reserve alkalinity, however, is not an
indication of the quality of corrosion protection; that can only be
determined by actual performance testing.
LABORATORY EVALUATION TESTS
Electromechanical Tests
Due to the increased use of aluminum for engine and cooling system
components, the inhibition of localized forms of corrosion such as pitting
and crevice corrosion has become important. Several engine manufacturers have
introduced test requirements that relate directly to protection against
localized corrosion. More specifically, a galvanic pitting corrosion test
was introduced as a measure of the long-term effectiveness of coolants in
preventing pitting corrosion attack in aluminum heat exchangers. Together
with some conventional tests, cyclic polarization techniques can be used to
determine susceptability to pitting and crevice corrosion of AF&Cs.
Heat Transfer Tests
With the introduction of engines operating at higher temperatures, the
protection of aluminum under heat transfer conditions becomes more important.
Tests have been introduced to evaluate AF&C performance under these
conditions.
HANDLING
Cooling System Preparation
Even the best cooling system will not perform satisfactorily unless the
cooling system is suitably prepared. Before installing any new AF&C, any
necessary service work in the cooling system should be performed. Critical
inspection items are listed below:
1. Check existing coolant concentration - 50% optimum.
2. Check existing coolant level and condition - change if dirty or rusty.
3. Pressure test system for leaks (preferably when cold).
4. Test pressure cap - inspect radiator filler neck.
5. Inspect hoses and tighten connections.
6. Inspect drive belts and check for proper tension.
7. Test thermostat if engine is running too hot or too cold.
The equipment manufacturer's instructions for water flushing and cleaning the
cooling systems prior to installation of the AF&C should be followed
carefully. Opening just the radiator drain cock will remove only about half
of the used solution from the cooling system. Alkaline flush-type cleaners
are often recommended to facilitate removal of sludge and loosely adhering
rust. However, if the system is badly rusted, a heavy-duty acid type cooling
system cleaner will be recommended.
Installation
After inspection and completion of required service, determine the capcity of
the cooling system from the Car Owner's Manual. A 50 percent concentration
[-37C (-35F) freezing protection] is readily determined from the Coolant
Protection Chart on the AF&C container and will provide ample protection in
most cases. Premix the AF&C with water, keeping in mind that an error of 5%
can change the freezing point significantly. Avoid use of water containing
large amounts of minerals and impurities. Close all drain openings and pour
in the AF&C/water mix. With the heater control set on "high", run the engine
until it reaches driving temperature to release trapped air and to thoroughly
mix the solution before driving the car or exposing the cooling system to
freezing temperatures. If the vehicle is equipped with a coolant recovery
system, the plastic reservoir should be filled with the same concentration of
AF&C.
Disposal
Spent AF&C is classified as a hazardous waste if it contains certain metal
ions over specified threshold levels. A concentration of 5ppm of lead is the
most common occurrence that results in a hazardous classification. AF&Cs that
have only seen service in modern automobiles with aluminum heat exchangers
are unlikely to be classified hazardous, but AF&Cs from heavy duty diesel
engines or engines with copper and brass heat exchangers might be.
Regulations by country, state and local governments are changed frequently
and must be followed.
TRENDS
Extended Service
While some car makers still specify an annual coolant inspection, it is
evident that coolant service intervals are being extended. A sealed-for-life
service-free cooling system is an ultimate goal of the auto industry. Driving
factors for these changes include increasing legislation in the area of AF&C
disposal and fluctuations of AF&C prices.
Additive Technology
One can predict that future AF&Cs will be stable and efficient heat exchange
fluids that will provide maintenance-free freezing and corrosion protection
throughout the life of the engine or equipment it is used in, have low
toxicity and be easily disposable or reclaimable.
Future engine coolants will have to contain additive packages that are:
- long lasting,
- stable at high temperature,
- effective under hihg flow conditions,
- compatible with plastics and elastomers and
- ecologically and toxicologically acceptable.
Additive packages based on aliphatic salt technology have arrived. They have
a near neutral pH value and a low reserve alkalinity. Combinations of some
aliphatic monoacids with alkali metal borates provide the required reserve
alkalinity and offer synergistic corrosion protection. However, some engine
manufacturers require coolants that do not contain phosphates, borates or
amines, which has led to identification of alternative organic pH buffers.
A British Military AF&C (AL-39; Specification TS10177) based on organic acid
inhibitors has existed for a long time. It's advantage is that the inhibitors
are not depleted because they prevent corrosion by a different mechanism than
the traditional inhibitors. Theoretically, it could be the basis for an
extended-life AF&C for cars and trucks, but its disadvantage is high cost.
Alternative AF&Cs have been developed that uses similar organic acid
technology with inhibitors that essentially do not deplete and are reasonable
in cost. These coolants are entering the European and United States markets.
Extended life AF&Cs have the tremendous added benifit of reducing AF&C
disposal by reducing the number of AF&C changes over the life of the car.
Propylene Glycol
Toxicological and ecological aspects are considered in the selection of the
chemical to be used as the freezing depressant, as well as in the selection
of additive components. The toxicological and ecological properties of EG and
PG are outlined in Table 3.
EG is more toxic than PG. However, the oxygen demand in the biodegration
process for EG is lower than for PG. Thus, wastewater treatment plants can
handle EG more easily than PG.
Because EG is toxic and under pressure from government agencies and
officials, PG is being considered as a possible substitute. Future
legislation may favor PG AF&C for direct sales to the customer because of its
lower toxicity. There has been some pressure in this regard in the U.S. and
in Europe.
PG has as high a boiling point as EG and the freezing point of a 50% PG AF&C
solution is only 5 degrees higher than EG AF&C.
PG, however, faces many problems. PG is about twice as expensive as EG and
the capacity of PG production could not currently meet the world AF&C demand.
PG AF&Cs do not meet any ASTM or manufacturer specifications, because they
are targeted for solutions containing at least 85% EG (ASTM is working on
developing standards for PG AF&Cs). Since PG does not dissolve silicate and
most AF&C currently sold contains silicate, current AF&Cs cannot be converted
easily to PG (silicate-free organic acid inhibitors work well in PG, however,
so this problem can be overcome). Continued research is required to further
evaluate the corrosion and heat exchange properties of aqueous PG coolants.
Recycling
Recycling has become a solution to environmental concerns for many chemical
products and is consodered to be a postive factor for industries having
recyclable products. Since AF&C is 95% EG and since most of the cost of EG is
the raw material to make it (ethylene), AF&C is an excellent candidate for
recycling. This factor, plus the high cost of AF&C in 1988 and increased
regulation of AF&C disposal, initiated an AF&C recycling movement that
resulted in two acceptable methods of recycling being introduced into the
industry.
Initial approaches to reclaiming AF&C, however, were not true recycling and
are not considered acceptable. Typically, they consist of removing the AF&C
from the engine, filtering it to remove solids, removing heavy metals by
precipitation and adding an addative package to bring the pH and RA back to
normal levels. Extra AF&C concentrate is added, if necessary, to obtain a 50%
AF&C solution. Many original equipment manufacturers have issued policy
statements stating that this approach does not provide acceptable AF&C and
should not be used. Recycling in this way does not insure good quality EG
base or a correct balance of corrosion inhibitors.
One of the acceptable recycling methods involves filtration through 5 and 25
micron filters, followed by passage through dual ion exchange and activated
charcoal systems designed to produce EG/water with all addatives and
contaminants removed. The EG/water is then reinhibited with an additive
concentrate.
the second acceptable method is a distillation process. The water distills off
first, followed by the EF which is collected for reuse. The residual
additives, breakdown products and other contaminants are collected as
distillation bottoms for disposal by appropriate methods. The distilled, pure
EG is then blended into AF&C in the usual manner.
ASTM is currently working on the development of standards for recycled AF&C
to ensure that quality AF&Cs are produced by recycliing processes. In
addition, at least one major automotive manufacturer has undertaken a program
to evaluate recycled AF&C, with the intent of approving individual recycling
companies.
In conclusion, acceptable AF&C recycling processes have been developed; their
acceptance is growing with time.
SUMMARY
The modern AF&C provides year-round freezing, boiling and corrosion
protection to transportation and industrial cooling systems. EG has evolved
as the base fluid of choice, but to ensure that the AF&C is properly
inhibited requires a comprehensive performance evaluation program consisting
of glassware, electromechanical, simulated service, dynamometer and vehicle
testing.
Products related to the conventional automotive AF&C are also used in a
number of other industrial applications where antifreeze, anti-icing, and
corrosion protection are required, such as industrial coolant and heat
transfer, aircraft de-icing, freeze conditioning, recreational vehicle
protection and solar heating systems.
Factors which will influence future AF&C development include increased engine
heat loads, increased service life, increased use of aluminum, equipment
manufacturers recommendations and product safety.
the "sealed radiator" may not be far in the future.
End of part 4 of 4
I hoped you liked it...
Joe Dille
Telford PA USA
(joe@dille.montgomery.pa.us)
Joe Dille
Telford PA USA
(joe@dille.montgomery.pa.us)
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