WINTER 2016

172 THE DISTRIBUTOR’S LINK
CARMEN VERTULLO TO BAKE OR NOT TO BAKE? from page 160
How the processor controls, monitors and reports the
baking time is very important. Time starts when the
fasteners reach the baking temperature, not when they go
into the oven. The processor should be able to report on the
start time, finish time, hours at temperature and baking
temperature, all relatable to the specific lot or lots of
fasteners, in a clear and concise fashion. The baking oven
should have good controls, good instrumentation capable of
measuring the temperature of the fasteners, and a
recording system. It must be in current calibration at all
times. The plater should have adequate oven capacity and
a good understanding of the equipment capability and
characteristics. Baking records with lot traceability should
be easily and quickly retrievable.
When In The Process Sequence Should The
Baking Be Done?
Older specifications usually say that baking should be
done as soon as possible after plating, such as within one
hour or not longer than 4 hours after plating. It has been
shown that this is not critical to removing hydrogen, but it is
a good practice to bake without delay for the sake of
variable control and lead time. It is important that the
product be kept clean and dry between plating and baking.
Baking must be done before any other process such as
chromate conversion coatings or other top coats as they
may be damaged by heat. Some major industrial processors
have in-line baking ovens which accomplish baking with no
delay. In any case, if there are issues with the efficacy of the
baking process, time between plating and baking should not
be considered a factor. Some processors have found that
HE risk can be lowered by baking certain materials prior to
plating, or baking as an intermediate step after a very thin
coating is applied and then completing the process with
additional coating thickness.
Who Decides?
The fastener supplier or user should be making post
plating HE relief baking decisions directly, even if they rely
on specifications, drawings or contract requirements to
make those decisions. Some specifications such as ASTM
F1941/F1941M require the supplier and user to come to an
agreement regarding baking and testing. Too often the
decision is left to the plating vendor who probably looks at
the fastener head mark and makes a judgement based on
the fastener’s specification maximum hardness and ASTM
B850, which can cause confusion when used for fasteners.
Purchase orders to the plater should not say simply “zinc
and bake”. Even being “explicit” by saying “plate and bake
per ASTM F1941” still leaves the plater with an
interpretation decision. Plating Purchase Orders should
clearly state the plating specification, baking temperature
and time, and if baking is not required when it normally
might be.
How Much Does It Cost?
The important thing to know is there is a cost and it is
not only the additional charge but also the lead time and the
certification checking and maintenance, which if done
properly will take someone’s time. The cost for baking will
add at least 10 to 30 percent to the plating cost and could
easily double it depending on the baking time. This can be
a significant part of the cost of the product, especially for
small lots. To remain competitive it is important to not bake
parts that do not need baked. For example, some major
suppliers of zinc plated grade 8 and PC 10.9 bolts bake and
some do not. Those who do not bake have realized the
benefit of controlling hardness in the mid or low range of the
requirements so there is no risk of the odd lot or parts within
a lot being in the susceptible hardness range. These
suppliers obviously enjoy a competitive advantage
compared to those who do bake.
What Specifications Address Baking?
The plating specification and/or the fastener
specification will govern if baking is required or not. For most
fasteners that are zinc plated, cadmium plated or zinc-nickel
plated that specification will be ASTM F1941/F1941M or
ISO 4042. All suppliers and users of plated fasteners
should be thoroughly familiar with the plating specifications
they use; this is especially critical for HE susceptible
fasteners. Often it will be the fastener specification that
requires baking such as ISO 898-1 for metric fasteners, or
ASTM A574 for inch socket head cap screws which refers to
the plating specification for baking requirements.
Beware of inappropriate or obsolete specification callouts.
The most current version of the specification should
be used unless otherwise directed by the contract or order.
ASTM F1941/F1941M has just recently undergone
significant revisions. Be sure you have the 2015 version. A
common zinc plating specification that we see on drawings
for fasteners is ASTM B633. This is not the recommended
specification for fasteners and requires unnecessary baking
of some fasteners. It does refer users to ASTM
F1941/F1941M for fasteners, so when you see ASTM
B633 you should strongly direct your customer to ASTM
F1941/F1941M and tell them not to use ASTM B633 for
fasteners.
CONTINUED ON PAGE 176