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harden off

To systematically expose a young plant to outdoor conditions so that it adapts well when moved outside permanently. A noun or pronoun can be used between "harden" and "off." That delicate plant won't survive outside unless you harden it off first.
See also: harden, off

harden up

1. To cause something to become physically harder or more solid. In this usage, a noun or pronoun is used between "harden" and "up." The tub of ice cream was melting, so I stuck it in the freezer to harden it up.
2. To become physically harder or more solid. If the ice cream is melting, stick it in the freezer for a bit so it hardens up.
See also: harden, up
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.

harden something off

to accustom a young plant to normal weather so it can be moved from a protected environment to the out-of-doors. We put the plants by the open window to harden them off. We hardened off the plants.
See also: harden, off

harden something up

to make something hard or strong. Put the meat in the freezer awhile to harden it up before you try to slice it thin. Harden up the ice cream a little in the freezer.
See also: harden, up
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.
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References in periodicals archive ?
They have rounder corners than the other curves, which indicate the appearance of transient hardening behaviour in the early stage.
Based on the previously mentioned analysis, three kinds of simple harmonic vibrations with different frequency and amplitude are imposed on the concrete specimens at pouring to the initial hardening phase, initial hardening to final hardening phase, and pouring to the final hardening phase, respectively.
To define the "layer hardness" process function, we have determined the specific form of the two process functions given by relations (1) and (2) for the concrete case of electron beam hardening process:
The analytical results, including the effects that material strain hardening, strain rate dependency, and indenter geometry have on the indentation depth, are discussed in Sec.
Since the terrorist attacks, the property/casualty market's rate hardening has accelerated because the insurance capacity in the marketplace has become strained, said Jack Sinnott, chief executive officer and chairman of Marsh inc., one of the largest insurance brokerages.
Diesel engine builders have been induction hardening crankshaft bearing journals since the 1940s, and the process became nearly universal in the '60s with the demand for more power from existing engine designs.
How is a part heated to such temperatures that will allow for work hardening? Metal cutting requires great forces and the action of a tool meeting the material is not always smooth.
So-called hardening of the arteries occurs in part because a key protein called elastin is replaced with a less elastic building material.
There is another concept in ADI which is commonly misinterpreted: hardening the surface of ADI by "work hardening." It is correct that the surface of an ADI part can be hardened by stressing but most of the hardening is done by a mechanism other than work hardening.
One of the most important applications of electron beam processing is surface layer hardening of several steel or alloy steel parts used in modern manufacturing.
The new plant, just commissioned at the Birmingham facility, is designed for vacuum hardening of alloy steels and annealing of stainless steels.
A phosphate containing solution is used as the liquid for a shorter hardening time of 5 min (7).