Method for defrosting a laboratory freezer door

The disclosure involves a method for defrosting an inner door of a laboratory freezer having (a) a plurality of inner doors, each closing a separate compartment, and (b) an outer door covering the inner doors. The method includes the steps of opening the outer door, removing at least one inner door, closing the outer door and defrosting the removed inner door. In that way, an inner door is defrosted without disturbing the contents of the freezer and, particularly, the contents of the compartment from which the door is removed. Optionally, the freezer user may keep a spare inner compartment door on hand and use it to immediately replace the removed door before closing the outer door. Door defrosting steps and a new hinge mechanism facilitating quick door removal are also disclosed.

FIELD OF THE INVENTION 
This invention relates generally to refrigeration and, more particularly, 
to cold-storage freezers. 
BACKGROUND OF THE INVENTION 
Freezers are used for a wide variety of purposes including for storage of 
food products, of materials being tested and for long-term storage of 
animal and human tissue and fluids. The precautions taken for each type of 
storage vary with the criticality of the integrity of the freezer 
contents. 
An aspect of freezer operation with which the user must sooner or later 
contend involves the formation of frost. Frost impairs the ability of the 
freezer to retain an optimum cold temperature and, with sufficient frost 
buildup, can prevent tight door closure. An ill-fitting door permits warm 
air to migrate into the cold compartment and impair the quality of the 
stored contents. 
At or near one end of the criticality "spectrum" are food freezers, both 
residential and commercial. Unless special equipment configurations are 
employed, the usual procedure for remedying an "over-frosted" freezer is 
to remove the freezer contents to other cold storage, shut down the 
freezer and either scrape away frost or simply let it melt as the freezer 
warms to room temperature. 
The prior art includes some of the special equipment configurations used to 
help avoid total freezer shutdown. For example, U.S. Pat. No. 3,858,408 
(Kenyon) relates to detachable frost shields mounted tightly against the 
surface of the permanent liner of a food cooler, e.g., a refrigerated ice 
cream cabinet. 
U.S. Pat. No. 4,603,558 (McAdams) relates to a chest-type food freezer and 
is directed to a separate, conformably-shaped container placed into the 
freezer. During defrosting, the container contents are removed. 
But with a food freezer, the worst that can occur in the event of heavy 
frost buildup is that a batch of food is ruined. However, such ruined food 
is replaceable at fairly nominal expense. 
Laboratory freezers are at the other end of the spectrum in terms of 
criticality of the integrity of the freezer contents. This is so because 
of the types of items required to be stored without significant 
deterioration. Consider, for example, that laboratory freezers contain 
specimens of human tissue and fluids which may be vital for diagnosis, for 
long-term patient treatment strategies or as evidence in a legal 
proceeding. Such specimens may be irreplaceable, either per se or as 
reflective of a condition of the person at the time the specimen was 
taken. 
For some time, companies have manufactured and sold freezers for ultra-low 
temperature storage of laboratory specimens. Such freezers are available 
in chest and upright type and Thermotron Industries of Holland, Mich., is 
the leading manufacturer of such freezers. 
Upright freezers have a single outer door covering several inner 
compartment doors, each of which can be separately opened without 
disturbing the door of any other compartment. While the inner doors are 
typically made of metal, the compartment liner is sheet steel and the 
"rim" around each compartment opening is of plastic. And until the advent 
of the Thermotron invention, the inner doors were permanently attached to 
the freezer and could not be removed except, presumably, by using tools. 
When an inner compartment door is opened, ambient air (with its "entrained" 
water vapor) migrates toward and around such door and the compartment 
opening. Because the door is extremely cold and because it is made of 
metal, moisture tends to condense and freeze on such door, especially the 
door edges. Over a short time, the inevitable frost buildup makes the door 
difficult to close and seal properly against the compartment rim. 
When that occurs, it has been necessary to either scrape or melt away the 
frost. This often necessitates moving the compartment contents to another 
freezer or to an alternate storage area cooled by, say, liquid nitrogen. 
The invention addresses this problem in a unique way. 
OBJECTS OF THE INVENTION 
It is an object of the invention to provide an improved method for 
defrosting a laboratory freezer door which overcomes some of the problems 
and shortcomings of the prior art. 
Another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which obviates the need for 
"sacrificial" components or air "curtains" or the like. 
Another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which minimizes the time the 
compartment contents are exposed to ambient air. 
Yet another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which, in some variations, eliminates 
the need for additional freezer components. 
Still another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which avoids having to move 
compartment contents to other cold storage facilities. 
Another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which helps maintain the integrity of 
the freezer contents. 
Another object of the invention to provide an improved method for 
defrosting a laboratory freezer door which can be carried out without the 
use of tools. How these and other objects are accomplished will become 
apparent from the following descriptions and the drawing. 
SUMMARY OF THE INVENTION 
The invention involves a method for defrosting an inner door of a 
laboratory freezer of the type having (a) a plurality of inner doors, each 
closing a separate compartment, and (b) an outer door covering the inner 
doors. The method includes the steps of opening the outer door, removing 
at least one inner door, closing the outer door and defrosting the removed 
inner door. In this way, an inner door is defrosted without disturbing the 
contents of the freezer and, particularly, without disturbing the contents 
of the compartment from which the door is removed. 
Defrosting of the removed door(s) is in any of a variety of preferred ways. 
In one aspect of the novel method, the defrosting step includes retaining 
the removed inner door in a space, the ambient temperature of which is 
above the freezing point of water. Such space may be the room in which the 
freezer is located or may be another room. 
Defrosting may also be by rinsing the removed inner door in a liquid, e.g., 
tap water, the temperature of which is above the freezing point of water. 
Or defrosting may be by applying a gas, e.g, air, to the removed inner 
door. The temperature of such gas is above the freezing point of water 
and, most preferably, the gas is heated for expeditious defrosting. 
The new method contemplates a number of variations. In the method outlined 
above, the inner compartment from which the door is removed is devoid of a 
door while such door is being defrosted. This variation is quite 
satisfactory if the freezer is entered only occasionally. There is then 
little or no risk of the contents of the compartment "sans door" becoming 
impaired by exposure to ambient air. 
On the other hand, if there is a reasonable possibility that the outer door 
may be opened (especially, opened frequently) before the removed door is 
defrosted and replaced, the user may wish to stock one or more spare 
doors. In that event, the inner door removing step is followed by the step 
of replacing the removed inner door with a spare frost-free door. 
The user may find that more than one inner door needs defrosting at a 
particular time. In a variation of the method, the door removing step 
includes removing a first inner door and further includes the steps of 
removing a second inner door and in either order, replacing the removed 
inner doors with frost-free doors. The defrosting step includes defrosting 
both removed inner doors. 
In another variant of the method (and irrespective of whether there are 
several inner doors to remove and defrost), the door removing step 
includes removing a first inner door and further includes the steps of 
replacing the removed first inner door with a frost-free door, then 
removing a second inner door and replacing the removed second inner door 
with a frost-free door. The defrosting step includes defrosting both 
removed inner doors. In this variant, the contents of each inner 
compartment from which doors are removed are exposed to ambient air for a 
minimum time since a removed inner door is immediately replaced with a 
frost-free door before proceeding to remove the next inner door. 
In a highly preferred method, the door removing step includes detaching the 
inner door from the freezer without the use of tools. In a freezer well 
suited for carrying out the new method, at least one of the inner doors 
has a hinge mechanism including a first hinge component attached to the 
freezer and a second hinge component attached to the inner door. The door 
removing step includes the step of grasping the inner door and urging the 
second hinge component away from the first hinge component, thereby 
detaching the inner door. 
An arrangement facilitating speedy inner door removal without tools, one of 
the hinge components (e.g., that attached to the freezer) includes a 
pin-like projection and the other hinge component (e.g., that attached to 
an edge of the inner door) includes a ferrule-like tube for receiving the 
projection. The inner door (with its attached hinge component) is lifted 
slightly upward to "clear" the projection and the tube from one another. 
Detachment is in seconds and without the use of tools. 
Other aspects of the invention will become apparent from the following 
detailed description and from the drawing.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
The invention involves a method for defrosting an inner door of a 
laboratory freezer 11 like that shown in FIG. 1. Such exemplary freezer 11 
includes an upright, box-like cabinet 13 having an interior cavity 15. 
While the invention is described in connection with an upright freezer 11, 
those of ordinary skill will, after appreciating the specification, 
understand how to adapt the invention to chest and other types of 
freezers. 
Referring also to FIG. 2, the freezer cavity 15 has a freezer liner 17, 
preferably made of painted cold rolled sheet steel or stainless sheet 
steel. The cavity 15 is divided into several separate storage compartments 
19 and while there are five such compartments 19 in the illustrated 
exemplary freezer 11, a fewer or greater number of compartments 19 can be 
used. 
The freezer 11 has a plurality of inner doors 10, each closing a separate 
compartment 19. A "master" outer door 21 covers all of the inner doors 10 
and must be opened to gain access to any inner door 10. Each compartment 
19 has one or more edge strips 23 known as "thermal breaks" which define a 
"line of demarcation" between the interior of the compartment 19 and that 
portion 25 of the freezer 11 on which the first hinge components 27 are 
mounted- The forward edge(s) of such strip(s) 23 abut and seal against the 
interior surface 29 of the compartment door 10. 
In the exemplary freezer 11, each compartment door 10 is generally 
rectangular but other door and compartment opening shapes are contemplated 
by the invention. Such door 10 is preferably fabricated of stainless sheet 
steel, painted cold rolled sheet steel or plastic. 
When the outer door 21 is closed, its interior perimeter edge 31 abuts and 
seals against the cabinet 13. Similarly, the interior perimeter 33 of each 
inner compartment door 10 seals against edge strips 23 and the result is a 
"double barrier" to help prevent migration of ambient air into the freezer 
11 and into each inner compartment 19. 
Notwithstanding such precautions, a small amount of such ambient air (and 
vaporized water entrained therein) migrates into each compartment 19 even 
if the outer door 21 and the inner doors 10 are kept tightly closed for 
extended periods. Frost forms as a result. If left to accumulate, such 
frost impairs the ability of the freezer 11 to retain optimum compartment 
temperature and temperatures in the range of about -55.degree. F. to 
-300.degree. F. (about -50.degree. C. to -150.degree. C.) are commonly 
used in laboratory freezers. 
Equally notable is the fact that such accumulated frost "packs" between the 
edges of each inner compartment door 10 and the strips 23. Compartment 
doors 10 accumulate frost around their perimeters 33 and literally freeze 
shut with consequent difficulty in opening. And in any event, such frost 
impairs the air-excluding capability of the inner door-to-cabinet seal so 
that, when re-closed, the inner compartment door 10 does not seal as well 
as it might. The invention resolves this difficulty in a unique way. 
Referring also to the diagram of FIG. 3, a method for defrosting a 
laboratory freezer door 10 includes the steps of opening the outer door 
21, removing at least one inner door 10, closing the outer door and 
defrosting the removed inner door. These steps are represented by the 
symbols 35, 37, 39 and 41, respectively. In this way, an inner door 10 is 
defrosted without disturbing the contents of the freezer 11 and, 
particularly, without disturbing the contents of the compartment 19 from 
which the door 10 is removed. This is a very important result for at least 
two reasons. 
One is that the compartment contents need not be removed to other cold 
storage facilities. Necessarily, removal of such contents results in at 
least a brief exposure (and, perhaps, a prolonged exposure) to warmer 
ambient air and its possibly-deleterious effects on such contents. Another 
reason why the new method is advantageous is that it avoids the necessity 
of retaining or providing "spare" temporary cold storage facilities. Such 
facilities inevitably add cost to the operation of a laboratory and are 
inconvenient to use--and, with the invention, are unnecessary. 
Defrosting of the removed door(s) 10 is in any of a variety of preferred 
ways. In one aspect of the novel method, the defrosting step includes 
retaining the removed inner door 10 in a space, e.g., the laboratory room 
itself, the ambient temperature of which is above the freezing point of 
water. In due course, the frost melts, the inner door 10 dries and is 
ready for re-use. 
Defrosting may also be by rinsing the removed inner door 10 in a liquid, 
e.g., tap water, the temperature of which is above the freezing point of 
water. Or defrosting may be by applying a gas, e.g, air, to the removed 
inner door 10. The temperature of such gas is above the freezing point of 
water and, most preferably, the gas is heated by a hot air blower for 
expeditious defrosting. 
The new method contemplates a number of variations. In the variation 
outlined above, the inner compartment 19 from which the door is removed is 
devoid of a door 10 while such door 10 is defrosted. This variation is 
quite satisfactory if the freezer 11 is entered only occasionally and if 
the inner compartment door 10 is rather quickly defrosted and 
re-installed. There is then little or no risk of the contents of the 
compartment 19 "sans door 10" becoming impaired by exposure to ambient 
air. 
On the other hand, if there is a reasonable possibility that the outer door 
21 may be opened (especially, opened repeatedly) before the removed door 
10 is defrosted for replacement, the user may wish to stock one or more 
spare doors 10. In that event, the inner door removing step is followed by 
the step of replacing the removed inner door 10 with a frost-free door 10. 
The user may find that more than one inner door 10 needs defrosting at a 
particular time. In a variation of the method, the door removing step 
includes removing a first inner door, e.g., door 10a, and further includes 
the steps of removing a second inner door, e.g., door 10b, and in either 
order, replacing the removed inner doors 10a, 10b with frost-free doors 
10. The defrosting step includes defrosting both removed inner doors 10. 
In another variant of the method (and irrespective of whether there is one 
or more inner doors 10 to remove and defrost), the door removing step 
includes removing a first inner door 10a and further includes the steps of 
replacing the removed first inner door 10a with a frost-free door 10, then 
removing a second inner door 10b and replacing the removed second inner 
door 10b with a frost-free door 10. The defrosting step includes 
defrosting both removed inner doors 10. In this variant, the contents of 
each inner compartment 19 from which doors 10 are removed are exposed to 
ambient air for a minimum time since a removed inner door 10 is 
immediately replaced with a frost-free door 10 before proceeding to remove 
the next inner door 10. 
In a highly preferred method, the door removing step includes detaching the 
inner door 10 from the freezer 11 without the use of tools. In a freezer 
well suited for carrying out the new method, at least one of the inner 
doors 10 has a hinge mechanism 43 including a first hinge component 27 
attached to the freezer 11 and a second hinge component 45 attached to the 
inner door 10. The door removing step includes the step of grasping the 
inner door 10 and urging the second hinge component 45 away from the first 
hinge component 27, thereby detaching the inner door 10. 
An arrangement facilitating speedy inner door removal without tools, one of 
the hinge components 27, 45 (e.g., the first component 27 attached to the 
freezer 11) includes a pin-like projection 47 and the other hinge 
component 45, 27 (e.g., the second component 45 attached to an edge 49 of 
the inner door 10) includes a ferrule-like tube 51 for receiving the 
projection 47. The inner door 10 (with its attached hinge component 45) is 
lifted slightly upward to "clear" the projection 47 and the tube 51 from 
one another. Detachment is in seconds and without the use of tools. 
While the inventive method has been described in connection with a few 
preferred variations, it should be understood clearly that such variations 
are by way of example and are not limiting.