| Author: IMS Company |
| Mold
Clamps 101 |
How much does your mold clamp really cost?
A mold clamp is a mold clamp... Well no not really! |
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 The
goal of this paper is to not only explain why IMS clamps are the safest
solution for your clamp needs, but also to educate you on the effects of poor
quality clamps and what questions to ask to understand what you are actually
receiving.
Many customers are under the impression that a mold clamp is a mold clamp and
the cheapest one is the best buy. The plain fact is that a failed clamp can
cause a lot of damage, sometimes unseen, to your mold, other clamps, the
surrounding equipment and/or employees. Then the quick savings that you thought
you had is quickly washed away. |
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| A single mold clamp does not do the job by itself; it
works in unison with other clamps to distribute the weight of the mold evenly.
If a clamp begins to fail this puts undue stress on the surrounding clamps
increasing the chances of clamp failure. In addition as a clamp fails the mold
will shift a little causing a “crash”, misalignment of the leader pins. Lastly,
although very rare, it is possible a chain reaction failure leading to the mold
falling completely off the machine altogether. |
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| So what makes a mold clamp a good mold clamp? The
building block - steel, well actually the correct answer is carbon. The amount
of carbon within the steel dictates the strength the steel can obtain. All
steel is not equal and the defining difference starts with the carbon. To have
a quality product one needs to start with a solid base, which leads us into the
next step. |
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| Heat treating is the essential process where the
metal in the clamp is stabilized and hardened to its final quality. Now this is
where carbon plays an important role because any steel can be heat treated, but
hardness is in direct relation to the amount of carbon within. Low grade
steels, used by many competitors and overseas steel, can only be hardened to a
lower level. Why do this? Low carbon steel is cheaper to produce cutting the
cost of the product, but also cutting the quality. IMS clamps are made from
4140 with a carbon rating of .38 to .43 and end with a Rockwell Hardness (RC c)
of 34-36. Watch out, one way inferior clamps vendors hide this quality is to
advertise grade 8 bolts with good hardness and then display mold clamps near
hoping you assume they are the same hardness. If the ad does not state clearly
the clamps hardness, ask and see how they answer. |
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| Another large factor in strength of the clamp is
whether it is machined clamps (made from bar stock steel), cast or forged
(heated steel is forced into a tooling to create the shape desired). By heating
the steel to plastic deformation it ensures a fully densified molecular
structure; a higher strength than machining can offer. Because of this strength
the Forged clamps can hold more weight before failing. In contrast, castings
are pouring steel into a form which could leave voids within the steel from air
pockets from water left in the mold before pouring. These voids can make a
clamp look perfect yet there is a large hole in the steel. This is why the
industry steers clear of cast clamps. The last way to make a clamp is machining
it from bar stock, but the issue here is that they do not reach the same
hardness as the forged versions. This is because the Machined clamps do not
have the additional heating process that forgings do when formed and by cutting
the shape of the clamp out of steel the grain of the steel is cut, further
weakening the metal. |
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| Across the board the plastics industry prefers forged
versions, but there are plenty of machined clamps being used in the industry as
well. IMS carries a line of premium forged clamps and a machined line as well.
Although the sales in this line have dropped over the years and we have elected
to discontinue the line once it has sold out. |
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| Overall carbon makes the steel and steel makes the
clamp, so do not hesitate questioning what you are buying... someone’s life may
depend on it. |
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| FAQ Mold Clamps |
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| What is the difference in closed verses open toed
clamps? Other than the obvious, Open Toe Clamps allow you to work
within a minimal amount of space allowing you to position the leverage closer
to the mold for more holding power. |
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| I need eight Clamps, but I only had seven so that is
all I used. Is this OK? Well, start playing poker….because it is
obvious you like to gamble! It is all in the math (total mold weight/number of
clamps) and less clamps on the mold the more weight each must endure. The more
weight on a clamp increases chance of failure. |
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| I currently need Shims and Makeshifts... can IMS
help? IMS Mold Clamps are designed to fit the most common used molds.
In addition IMS clamps are slotted to allow access to at least two holes on
most die plates. So do it right from the start, buy the correct clamps and toss
the shims and makeshifts. |
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| Is sizing of your clamp important? The
larger the clamp the more weight it is designed to hold in place, using
undersized clamps is a disaster waiting to happen; larger mold... larger clamp! |
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| FAQ’s Bolts |
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| How far should the bolt on the clamp extend into the
platen? The bolt should go (at least) 1.5 times the diameter of the
shaft into the platen and do not forget to allow any spacers/washers you are
using. Formula (Plate thickness + clamp thickness + spacer/washer thickness +
1.5 times bolt Dia= bolt length needed) |
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| How important is it to use the correct length bolt?
I‘ve often heard, “I have 3” bolts and need 3-1/2 can I substitute them?” NO!
Using bolts too short can (and eventually will) cause the threads to strip out
in the platen during standard operation and the clamps will fail. Using to long
a bolt can create a loose clamp that will also fail. Both of these actions are
a disaster waiting to happen, use the right product in the right application. |
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| How much torque should be applied to the bolts on my
mold clamps? This is a wide open question. Because of the amount of
variables included in the formula; materials, heat treating, amount of
lubricant on the threads, etc., and with the liability involved, no one will go
on the official record, including IMS, to state a number to use for any
situation; due to fears of being liable. With that being said IMS can offer
only an estimation of torque. Warning: Over tightening can/will damage the
platen, clamp or the mold. |
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| Thread Size |
Max Torque |
| 1/2”-13 |
125 ft lbs |
| 5/8”-11 |
245 ft lbs |
| 3/4”-10 |
425 ft lbs |
| 1”-8 |
591 ft lbs |
| 1-1/4”-7 |
800 ft lbs |
|
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| WARNING: NEVER use an impact wrench
when tightening mold clamps into place. |
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| You may say, “I can save money by using All-Purpose
bolts and washers!” Right? NO! We all know that failure comes at the
weakest link and remember a clamp only works if it stays attached to the platen
and held securely to the mold! It is not safe, or wise, to use commercial bolts
and/or washers because they are made from softer steel and tend to warp when
used in Injection molding because the surfaces are not flat. Avoid damage and
danger by buying only bolts and washers made for injection molding
specifically. |
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| How is the adjustment bolt used properly and does it
really matter? Correct use of the adjustment bolt is crucial to a safe
stable mold; adjusting to short or to high will cause the clamp toe to not be
in complete contact with the surface of the clamping plate. For maximum holding
power the clamps need to be flush with the plate. Setting these bolts correctly
is very easy. Simply measure the clamp plate thickness and then set your bolt
to this distance. (Here’s a tech tip for you.) For a quick setting, you can
also slide your clamp up to the mold plate and adjust the height from there.
When set correctly you can expect maximum holding power of the clamp. |
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| Products related to this article: |
Forged Steel, Closed Toe Mold Clamps |
|
Forged Steel, Open Toe Mold Clamps |
|
Heavy Duty Mold Clamp Bolts |
|
Heavy Duty Mold Clamp Washers |