Hubbing
Manufacturing Process
New - Better Definition
Rubbing tooling consists of the hub, a
reinforcing ring, a retaining ring, a hardened base and fixing devices. The
fixing devices are for keeping the hub and the retaining ring firmly in place.
Retaining ring (reinforcement. Figure 7.7)
During hubbing, as extreme radial forces
occur in the dies to be hubbed, causing high tangential stresses, the dies
must be reinforced in a retaining ring (shrink fit). The pre-stressing of the
retaining ring counteracts the tangential stresses in the tool. The height h of the retaining rings is equivalent to that of the workpiece. The inner retaining
ring a is hardened, with a
hardness of 58 + 2 HRC. The outer retaining ring is also hardened. Its strength
should be around 1200 N/nim-. Its external diameter D\ should he 2.5 D.
The tool which actually
does the hubbing is the male hub (Figure 7.8):
It should not have any sharp edged ridges.
The head of the hub should
be about 20 mm larger than the shank.
The shank must be finely
ground and polished up to and including the radius of the junction with the
head.
Advantages of cold hubbing
healthy, unbroken grain structure (Figure
7.9)
-
plate-finished smooth surfaces on the hubbed
profile
-
high dimensional accuracy of the hubbed
profile
tolerances: 0.01 - 0.02 mm
- higher tool life due to
optimal grain direction and high surface finish considerably shorter production
times than with production involving chipping.
(
Metal Forming Practise:
Processes - Machines - Tools, 2006, Heinz Tschätsch, P81)
Previous:
Hubbing is a deformation process in which a hardened steel form is pressed into a soft steel (or other soft metal) block. The process is often used to make mold cavities for plastic molding and die casting. The hardened steel form, called the hub, is machined to the geometry of the part to be molded. Substantial pressures are required to force the hub into the soft block, and this is usually accomplished by a hydraulic press. Complete formation of the die cavity in the block often requires several steps- hubbing followed by annealing to recover the work metal from strain hardening. When significant amounts of material are deformed in the block, as shown in our figure, the excess must be machined away. The advantage of hubbing in this application is that it is generally easier to machine the positive form than the mating negative cavity. This advantage is multiplied in cases where more than one cavity are made in the die block.
(Groover, M.P, Fundamentals of Modern Manufacturing: Materials, Processes, and Systems, 4th Edition, pg.419)
Phenolformaldehyde (Bakelite)
Material
New – Better Definition
Phenol-formaldehyde resins were used to make
one of the first syntetic plastic materials, phenol-formaldehyde plastics or bakélite. Since then, the field of
phenol-formaldehyde resins has developed and includes resins and plastics made
from different phenols and aldehydes with varying applications.
Applications
Phenol-formaldehyde and p-tert-butylphenol-formal-dehyde
resins have many industrial applications, although other polymers/plastics have
replaced the use of these resins in many fields. Cilues and glue films based on
phenol-formaldehyde resins are used in the plywood industry. Because of their
moisture resistance, the glues and laminates are used in the building industry
and in boat and aircraft construction. The resins are also good insulators
against electricity; they are thus used in electronic and electric appliances.
In addition, they can be used for the production of decorative laminates and
coatings, and to coat rigid constructions, e.g., pipelines and reaction
vessels, because of their high chemical resistance. They are also used as
binders for glass and mineral fibers in the production of heat-, noise-, and
fire-insulating materials, as well as in foundry molding sand and abrasives,
such as sandpaper, abrasive cloth, and flexible sanding disks. No\olak resins can
be used in the production of grinding wheels, brake linings, and clutch
facings. They are also used as raw materials for polyfunctional epoxy resins
[152-154].
p-tert-Butylphenol-formaldehyde
resin is used in adhesives based on neoprene and other rubbers. These adhesives
can be used in shoes, leather products, automobile interior upholstery,
furniture, adhesive tapes and labels, and in the gluing of certain floor
coverings 1152. 153]. P-tert-Butylphenol-formaldehyde resin is also used as
adhesives for leather, artificial fingernails, and labels.
The third largest group is phenolic resins
modified by natural resins. Rosin-modified phenolic resins are used as binders
for book offset-printing inks [152],
(Contact Dermatitis, 2010, Jeanne Duus Johansen, Peter J. Frosch,
Jean-Pierre Lepoittevin, P 707)
No comments:
Post a Comment