An improved corrugator roll for use in an apparatus for making corrugated paperboard wherein the flute tip and a portion flank of the roll base metal are selectively hardened to a predetermined depth by an electro magnetic process. The valleys of the flutes and the remainder of the flank are maintained at the same hardness as the base material.

BACKGROUND OF THE INVENTION 
1. Field of Invention 
The invention relates to an improved corrugator roll for forming a web of 
corrugated paperboard and, more particularly, to an improved corrugator 
roll having a portion of the roll surface selectively hardened to a 
predetermined depth. A corrugator roll hardened in accordance with the 
teachings of the present invention demonstrated superior wear qualities 
while not being susceptible to cracking and chipping. 
2. Description of the Prior Art 
Corrugating rolls are used in machinery such as single-facer corrugators 
which are used in the manufacture of corrugated paperboard. A detailed 
description of a typical single-facer is given in Moser et al., U.S. Pat. 
No. 3,390,040. Since the typical single-facer machine is fully described 
therein, its structure and operation will not be further described herein, 
except where necessary to explain the present invention. 
A typical corrugating roll in use today is 87 inches long, 12 inches in 
diameter and weighs approximately 2100 pounds. Certain prior art rolls are 
forged from alloyed steel and machined to the proper configuration. To use 
ordinary machining techniques, hardness of the base metal of the 
corrugator roll is limited to approximately 40 R.sub.c. Certain other 
prior art rolls are rough machined using ordinary cutting tools and are 
then hardened by conventional heat treatment. The heat treatment distorts 
the machined roll, necessitating the use of grinders and the like to 
regain the desired dimensions. The additional grinding operation requires 
an additional expense in plant equipment and also involves an expense for 
the additional labor. These increased operations necessarily increase the 
cost of a hardened roll. In both types of prior art rolls the entire base 
metal of the roll is of uniform hardness. 
In order to extend roll life, the entire surface of both types of rolls are 
generally chrome plated or coated with metallic oxide. While chrome 
plating and oxide coating do in fact extend the operational life of the 
roll, there are problems with their use. Metallic oxide coatings are 
expensive and it is difficult to get a good finish on this type of 
coating. Both chrome plated and oxide coated rolls are susceptible to 
cracking and chipping. Once they have cracked or chipped, the wear caused 
by the sliding of the paper web over the roll greatly increases. Since the 
cracking or chipping usually occurs at the flute tip, the point of maximum 
sliding friction, the flute tips wear much faster than the rest of the 
roll causing a loss of caliper. When the caliper of the roll is lost, the 
roll must either be replaced or reground. 
The present invention overcomes the foregoing problems of the prior art by 
providing an improved corrugator roll which has superior wear 
characteristics while being economical to both manufacture and use. 
SUMMARY OF THE INVENTION 
The present invention provides an improved corrugator roll wherein the tip 
of the flute and the portion of the tip flank of the base metal are 
selectively hardened either by a laser beam or electron beam process. The 
tip of the flute and portion of the flank are hardened to a predetermined 
depth. The remainder of the tip flank and the valley between the flutes 
remain at the same hardness as the rest of the base metal. The present 
invention provides a new and improved corrugator roll which is a departure 
from past practices in the corrugating art by providing selective 
hardening of the base metal. The foregoing will more fully appear in the 
following detailed description when read in conjunction with the 
accompanying drawing.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring to FIG. 1 which shows a section of a corrugating roll of the "C" 
type, the body of the roll 10 has flutes 12 having tips 14, tip flanks 16 
and 18. The depressions between the flutes 12 are referred to as valleys 
20. FIG. 1, which is not to scale, shows a roll of the "C" type which has 
39 flutes per foot and each flute is 0.142 inch high. The take-up, 1.463, 
is the ratio of the medium to be corrugated to the liner which will be 
glued to the medium. The chordal pitch is 0.304 inch. In the typical "C" 
flute the tip has a radius of curvature of 0.0568 inch, the tip flank 
angle is 56.degree., and the valley has a radius of curvature of 0.0683 
inch. The base metal of the roll is an alloy steel having a hardness of 
approximately 40 R.sub.c. 
In the preferred embodiment of the present invention the tip of the flute 
was hardened by a laser beam process to a depth of 0.031 inch. Hardening 
to this depth resulted in a portion of flanks 16 and 18 being hardened. 
Prior to use of the laser the roll surface 10 was cleaned and coated with 
flat black paint. The power for the hardening is 1150 watts at 21.25 
kilovolts and 188 milliamperes. The transverse speed of the laser beam was 
65 inches per minute. The focal length of the lens was 6 inches and argon 
gas was used to protect the lens. At the flute tip of the roll a beam of 
approximately 0.1 inch was obtained. The hardness achieved was 61 R.sub.c. 
The remainder of the flute and the valleys were not hardened and kept at 
the same hardness as that of the base metal. The present invention is also 
equally applicable to corrugator rolls having different flute 
configurations. An example of such a configuration would be an "A" fluted 
roll having 33 flutes per foot, each flute being 0.1875 inch high. 
The selective hardening of the flute tips and flanks provided by the 
present invention can also be achieved by an electron beam hardening 
process. The electron beam hardening process can be carried out in either 
a partial vacuum or in air. In a partial vacuum, 200 to 1000 torr, the 
accelerating voltage of the electron gun is 25,000 volts. The power of the 
beam is 7.5 kilowatts and beam diameter is 0.002 inch. The beam energy on 
the surface of the roll is twenty kilojoules. The beam is raster scanned 
over the surface to achieve the desired hardening profile. 
In an alternate embodiment the tips 14 of the selectively hardened rolls 10 
of the present invention can also be chrome plated or coated with a 
metallic oxide. The chrome plating can be placed by conventional methods 
to a depth of 0.002 to 0.003 inch. The chrome plating of the flute tip 
will increase its hardness to approximately 70 R.sub.c. 
While we have described certain preferred embodiments of our invention, it 
is understood it may otherwise be embodied within the scope of the 
following claims.